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Nondestructive evaluation of demineralized enamel in human incisor and molar using laser ultrasonics

Kaihua Sun, Ling Yuan, Shen Zhong-Hua, and Qingping Zhu

Doc ID: 308825 Received 23 Oct 2017; Accepted 12 Jan 2018; Posted 12 Jan 2018  View: PDF

Abstract: This study aims to evaluate early caries in human teeth with different geometry structures by using the dispersion curves of surface acoustic wave (SAW) generated by a pulsed laser. Through the finite element method (FEM), SAWs propagating on teeth models with different enamel thickness and curvature radius were simulated, and the influence of the geometry difference on the dispersion curves of SAWs was discussed. Laser ultrasonic experiments were performed on extracted human incisor and molar with different demineralization conditions. The received dispersive surface wave signals were processed via the spectral analysis method to obtain the dispersion curves, and the difference of the dispersion spectra between the incisor and the molar were analyzed and discussed. The result demonstrates that the laser generating SAW has the ability to evaluate the elastic properties of early caries with different geometry nondestructively.

Diverse mode of operation of an ANDi mode-locked fiber laser employing two nonlinear loop mirrors

Sourav Das Chowdhury, ATASI PAL, SAYAN CHATTERJEE, Ranjan Sen, and Mrinmay Pal

Doc ID: 312484 Received 07 Nov 2017; Accepted 12 Jan 2018; Posted 12 Jan 2018  View: PDF

Abstract: In this paper, we propose an all-normal-dispersion (ANDi) ytterbium-fiber laser with a novel ring cavity architecture having two nonlinear amplifying loop mirrors (NALM) as saturable absorbers, capable of delivering distinctly different pulses with adjustable features. By optimizing the loop lengths of the individual NALMs, the cavity can be operated to deliver Q-switched mode-locked (Q-ML) like pulse bunches with adjustable repetition rates or mode-locked pulses in dissipative soliton resonance (DSR) regime or noise-like pulses (NLP) regime with tunable pulse width. The DSR pulses exhibit characteristic narrowband spectrum while the noise-like pulses exhibit large broadband spectrum. The operation regime of the laser can be controlled by adjusting the amplifier pump powers and the polarization controllers. To the best of authors’ knowledge, this is the first demonstration of a single mode-locked cavity where narrowband DSR pulses and broadband NLPs alongside Q-ML pulse bunches can be selectively generated by employing two NALMs.

Cost-effective plane-grating monochromator designfor extreme-ultraviolet application

Luca Poletto and Fabio Frassetto

Doc ID: 314059 Received 22 Nov 2017; Accepted 12 Jan 2018; Posted 12 Jan 2018  View: PDF

Abstract: The optical design of a plane-grating monochromator mainly intended for high resolution in the extremeultraviolet and soft-X-ray is presented. The configuration has three optical elements. It uses an uniform-line-spacedplane grating illuminated in the converging light coming from a focusing concave mirror and an additional planemirror that is needed to change the grating subtended angle to keep the system in focus on a fixed slit. Theparameters of the focusing mirror are determined to introduce a coma that compensates for the coma given by thegrating. A monochromator for the 12-50 eV region is designed for application to high-order laser harmonics.

Comparison and evaluation of geometric calibrationmethods for infrared cameras to perform metricmeasurements on a plane

Ruben Usamentiaga, Clemente Ibarra-Castanedo, and Xavier Maldague

Doc ID: 315336 Received 11 Dec 2017; Accepted 12 Jan 2018; Posted 12 Jan 2018  View: PDF

Abstract: Geometric information from infrared images can complement the information about the measured infraredradiation. However, this requires geometric camera calibration. In this work, three calibrationmethods for infrared cameras are compared: a direct and an iterative estimation of the transformationbetween image and world coordinates, and a complete camera calibration method using a specificallydesigned calibration target. The three methods are compared and the obtained performance for metricmeasurements on a plane is evaluated. The results indicate acceptable performance in the three cases,with the complete method clearly outperforming the two others with an average error of only 0.060mm,which represents 0.08% error of the measured distance.

Computer-generated hologram marked by correlatedphoton imaging

Wen Chen

Doc ID: 311243 Received 30 Oct 2017; Accepted 11 Jan 2018; Posted 11 Jan 2018  View: PDF

Abstract: Computer-generated hologram (CGH) has been studied for many applications. In this paper, CGH is watermarkedby correlated photon imaging. An input image is encoded into two cascaded phase-only masks by using CGHprinciple. Subsequently, two different marks are independently encoded into one-dimensional (1D) intensitypoints by using correlated photon imaging (or ghost imaging), and the recorded 1D intensity points are embeddedinto the extracted phase masks for optical watermarking. During the decoding, the input is recovered by using twowatermarked phase masks. To verify copyright of the recovered input image, information embedded in two phaseonlymasks is retrieved, and is used to decode the hidden marks. The decoded marks do not visually render clearinformation due to only a few measurements, and instead are authenticated. It is illustrated that quality of therecovered input image is high, and a different imaging approach can be applied in CGH system for opticalwatermarking. The proposed approach provides a promising strategy for optical information security.

Tunable spectral and spatial filters for mid-infraredbased on hyperbolic metamaterials

Marcin Kieliszczyk, Bartosz Janaszek, Anna Tyszka-Zawadzka, and Pawel Szczepanski

Doc ID: 308872 Received 10 Oct 2017; Accepted 10 Jan 2018; Posted 10 Jan 2018  View: PDF

Abstract: In this paper we present the possibility of shaping reflectivity characteristics of tunable hyperbolic metamaterials(THMMs). By example of voltage-sensitive graphene-based structures, we indicate the existence of spectral andspatial functionalities of edge and narrowband filters, controlled dynamically over 3-5 μm spectral range,important for both civilian and military applications. We also demonstrate that adoption of apodization techniquesto THMM design leads to reduction of side lobe’s parasitic effect in edge filters, as well as provides the means toreshape the overall reflectivity characteristics, which not only unveiled the tunable angle aperture functionality,but significantly extended the potential for tailoring optical properties of THMM nanostructures in general.

Design of an optical trap for storing femtosecond laser pulses

Abdalla Shehata, Vladimir Chvykov, Reinhold Schuch, and Tarek Hassan

Doc ID: 314245 Received 27 Nov 2017; Accepted 10 Jan 2018; Posted 10 Jan 2018  View: PDF

Abstract: An optical trap for storing femtosecond laser pulses to enhance the interaction effectiveness with optically thin targets is being proposed and investigated. Presently we studied the trapping of 10-100 fs laser pulses of wavelength 800 nm, 1μJ energy per pulse, and 10 Hz repetition rate. To compensate the optical losses in the trap, a Ti: Sapphire crystal as an amplifying medium is been considered that should be synchronously pumped by the 2nd harmonic of the Nd: YAG laser. Due to the propagation of the short pulses through optical trap components, group velocity dispersion introduces a significant broadening in pulse duration. To compensate for this broadening, chirped mirror with suitable parameters is being proposed. An increase of the average power of the laser pulse in the optical trap that includes an amplifying medium (Ti: Sapphire crystal) by a factor of 805 compared to a single passage of the laser pulse was derived. It should be possible to store the laser pulse in the optical trap for  4 μs with constant power and with a repetition rate up to 250 MHz.

Heterodyne detection of scattered light: Application tomapping and tomography of optically inhomogeneousmedia

G. Kozlov, Valerii Zapasskii, and Pavel Shapochkin

Doc ID: 307686 Received 28 Sep 2017; Accepted 10 Jan 2018; Posted 11 Jan 2018  View: PDF

Abstract: The signal registered by a plane photodetector placed behind an optically inhomogeneous object irradiatedby two coherent Gaussian beams intersecting inside the object at small angle to each other iscalculated in the single-scattering approximation. In the considered arrangement, only one of the beamshits the detector and serves as local oscillator for heterodyning the field scattered by the other beam (nothitting the detector). The results of analytical calculation show that the signal detected in this way iscontributed only by the region of the inhomogeneous object where the two beams overlap. By movingthe scatterer with respect to the overlap region and monitoring the heterodyned signal, with the aid of thederived expression, one can reconstruct the refractive-index relief of the scatterer. We also propose a simplemethod of spatial mapping of the sample that allows one to estimate the magnitude and characteristicdimensions of the inhomogeneities.

Scattering characteristics of a cylindrical reflectorcovered with a general bi-isotropic layer

zeeshan awan

Doc ID: 308421 Received 03 Oct 2017; Accepted 10 Jan 2018; Posted 11 Jan 2018  View: PDF

Abstract: The scattering characteristics of an electric line source radiating in the presence of a bi-isotropic coated circularcylindrical reflector have been investigated using numerical calculations. The analytic expressionsof the electric and magnetic fields in the bi-isotropic coating and the background medium have beenfound using the wave-field decomposition approach. It is studied that a bi-isotropic coating enhancesthe gain in the forward direction as compared to chiral, Tellegen and dielectric coatings. It is found thatfor a thin coating layer, the scattering gains in the forward direction for chiral and bi-isotropic coatingsare almost same. It is investigated that a specific type of bi-isotropic coating can be used to significantlyenhance the scattering gain in the forward direction. This type of enhanced forward direction scatteringgains are preferred in point to point communications. On the other hand, it is found that a specific typeof Tellegen coating significantly reduces the scattering gain in the backward direction. This phenomenonof reduced gain can be used to hide a cylindrical reflector in the backward direction. A comparative studyof the scattering gains for realistic bi-isotropic and low loss dielectric coatings have also been discussed.

Freeform lens design to eliminate retro-reflection for optical system

Sifeng He, Yuan Meng, and Mali Gong

Doc ID: 314104 Received 23 Nov 2017; Accepted 10 Jan 2018; Posted 11 Jan 2018  View: PDF

Abstract: This paper presents an effective approach to alleviate cat-eye effect by inserting a freeform single lens into original optical system. By shifting the image of the given optical system transversely on the original image plane, the reflected beams originated from the sensor are subsequently blocked by the optical aperture, substantially eliminating retro-reflections from the system. The influence of incident angel on retro-reflected beams is analyzed in detail and the optimal image translation distance for completely eliminating cat-eye effect is also proposed via numerical simulations. According to the translation requirement, a freeform single lens comprised of two different freeform surfaces is designed for the given system as the only translation element. The design recipe is elaborated on the basis of phase pupil function. Furthermore, a design example is demonstrated to verify the feasibility of our proposal. After optimization with optical design software, the MTF of modified system after translation is close to diffraction limit and the cat-eye reflected beam could be eliminated thoroughly.

Comb referenced frequency-sweeping interferometry for precisely measuring large stepped structures

Weipeng Zhang, Haoyun Wei, Honglei Yang, Xuejian Wu, and Yan Li

Doc ID: 314338 Received 28 Nov 2017; Accepted 10 Jan 2018; Posted 11 Jan 2018  View: PDF

Abstract: A precise 3D surface measurement method for large stepped structures without height ambiguity is proposed based on optical frequency comb referenced frequency-sweeping interferometry and Fourier transformed fractional phase retrieval. Unlike other interferometry that depending on the absolute phase value for several certain wavelengths, this method obtains results by the phase change during frequency-sweeping and thus suffers free from the confined non-ambiguity range. By referencing to an optical frequency comb, the relative uncertainty from the tunable laser frequency was reduced by three orders of magnitude and the sweeping frequency range can be precisely determined. Besides, the fractional phase can be rapidly retrieved in only one-step using a Fourier-transform method, with advantages of high accuracy and immunity to light intensity fluctuation and mechanical vibration noise. Samples of step heights from one micron to one millimeter were measured, and the standard uncertainty was 45 nm. This permits applications such as quality assurance in microelectronics production and MEMS manufacture.

Principal frequency component analysis based onmodulate chopper technique used in diffusereflectance spectroscopy measurement

Shaoxiu Song, Gang Li, Xingwei Hou, Shengzhao Zhang, Yue Yu, and Ling Lin

Doc ID: 312353 Received 31 Oct 2017; Accepted 09 Jan 2018; Posted 09 Jan 2018  View: PDF

Abstract: Diffuse reflectance spectroscopy (DRS) is significantly affected from the interference of the ambient light anddark current of the instrument. Optical choppers, together with lock-in/synchronous amplification, can overcomethese interferences. However, in spectral measurement, the sampling rate of spectrometer is different from the Δ-pulse sampling, which is not high enough because of the integration time. In addition, the energy distribution is notperfectly concentrated as expected in modulate chopper technology. Therefore, in this study, based on themodulate chopper technique, we proposed a principal frequency component analysis (PFCA) method for DRS. Thistechnique not only effectively eliminated the interference and dark current of the instrument, but also improvedthe measurement precision using the energy of different frequency. First, experiments were designed tosuccessfully verify the function of optical choppers, eliminating the interference of the ambient light. Second, a setof 64 mixture solutions was designed and measured by DRS using the PFCA method to prove the feasibility of theproposed method. The solution was mixed with intralipid-20% suspension, India ink and Rhodamine B. Thesesamples were analyzed by DRS under different conditions: no-chopper with overlapping and averaging, chopperdemodulated by Fourier transform, and chopper demodulated by PFCA. The Partial Least Square regressionanalysis was implemented to predict the concentration. Compared to the result of three methods, DRS equippedwith chopper using the PFCA method showed the best results. The results of this study showed that the PFCAmethod not only satisfactorily eliminated the interference signals, but also extracted useful information as much aspossible, improving the analysis accuracy.

Five-step phase-shifting white-light interferometryfor the measurement of fiber optic extrinsicFabry-Perot interferometers

Hongchun Gao, Yi Jiang, Liuchao Zhang, and Lan Jiang

Doc ID: 312592 Received 15 Nov 2017; Accepted 08 Jan 2018; Posted 09 Jan 2018  View: PDF

Abstract: Five-step phase-shifting white-light interferometry (PSWLI) is presented for interrogating the absolute cavitylength of the fiber optic extrinsic Fabry–Perot interferometer (EFPI). It combines ideas of phase-shiftinginterferometry (PSI) and white-light interferometry (WLI) to extend the measurement range of fiber optic WLI.Five sub-interferograms intercepted from the white-light optical spectrum are used to recover the optical pathdifference (OPD) of the EFPI. This method is demonstrated to interrogate wider range of OPD. The experimentalresults show that the measurement resolution ranges from 0.5 μm to 5 μm with the cavity length ranges from 16μm to 12402 μm, and it has a great advantage in measuring EFPIs with short cavity length.

Compact optical fiber temperature sensor with highsensitivity based on liquid-filled silica capillary tube

Yu Mao, Yuxi Zhang, Ruikai Xue, Yi Liu, KunJian Cao, and ShiLiang Qu

Doc ID: 312799 Received 07 Nov 2017; Accepted 08 Jan 2018; Posted 09 Jan 2018  View: PDF

Abstract: We proposed a highly sensitive fiber temperature sensor based on a section of liquid-sealed silica capillary tubeinserted in the single-multi-single mode fiber structure. The liquid polymer was filled into the silica capillary tubethrough two micro-holes drilled by femtosecond laser. Then the micro-holes were blocked by UV curable adhesivewith ultra-small volume. Obvious Mach-Zehnder interference peaks were shown in its transmission spectrum. Theproposed fiber temperature sensor can be reliably used for actual point detection owing to its high sensitivity (8.09nm/°C), good linearity (99.93%), compact size, good mechanical property, high fabrication efficiency, and goodrepeatability and stability..

Wavefront reconstruction of non-coaxial diffractionmodel in a lens system

Xin Jin, Xuemei Ding, Jiubin Tan, Cheng Shen, Shutian Liu, and Zhengjun Liu

Doc ID: 312829 Received 07 Nov 2017; Accepted 08 Jan 2018; Posted 09 Jan 2018  View: PDF

Abstract: To reconstruct wavefront in a non-coaxial lens system, we propose a diffraction model using Fresnel integral.Inclination angle is the newly included parameter in the mathematical formula describing beam propagation. It isdetermined through two ways in this paper, which are correlation operation and optical flow method. Furthermore,the multi-image phase retrieval is incorporated to reconstruct the complex optical field of sample from anoverdetermined dataset. The combination is much closer to the actual situation, thus more practical. The proposeddiffraction model is validated by numerical analysis and experiment. The work will further benefit the applicationof multi-image phase retrieval, like biomedical imaging and optical metrology.

Weighted Spline based Integration for Reconstructionof Freeform Wavefront

kamal pant, Daliramu Burada, Mohamed Bichra, Amitava Ghosh, Gufran Khan, Stefan Sinzinger, and Chandra Shakher

Doc ID: 313794 Received 17 Nov 2017; Accepted 08 Jan 2018; Posted 09 Jan 2018  View: PDF

Abstract: In the present work, a spline based integration technique for the reconstruction of a freeform wavefront from the slopedata has been implemented. The slope data of a freeform surface contains noise due to its machining process and thatintroduces reconstruction error. We have proposed a weighted cubic spline based least square integration method(WCSLI) for the faithful reconstruction of a wavefront from noisy slope data. In the proposed method, the measuredslope data are fitted into piecewise polynomial. The fitted coefficients are determined by using a smoothing cubic splinefitting method. The smoothing parameter locally assigns relative weight to the fitted slope data. The fitted slope data arethen integrated using the standard least square technique to reconstruct the freeform wavefront. Simulation studiesshow the improved result using the proposed technique as compared to the existing cubic spline based integration(CSLI) and Southwell method. The proposed reconstruction method has been experimentally implemented to asubaperture stitching based measurement of a freeform wavefront using a scanning Shack-Hartman sensor. Theboundary artifacts are minimal in WCSLI which improves the subaperture stitching accuracy and demonstrates animproved Shack-Hartman Sensor for freeform metrology application.

Temperature-insensitive sum frequency generation of355-nm UV laser radiation in LiB3O5 by compensatingthermally-induced phase mismatch

Xun LIU, xue shen, Dongmei Diao, and Long Wang

Doc ID: 314115 Received 22 Nov 2017; Accepted 08 Jan 2018; Posted 09 Jan 2018  View: PDF

Abstract: A temperature-insensitive sum frequency generation method based on thermally-induced phase mismatchcompensation is proposed to enhance the thermal stability and scale up the output power of UV laser. In themethod, three LiB3O5 crystals are cascaded for sum frequency generation of 355-nm UV laser, the two crystals atthe ends are employed for frequency conversion, the middle one, which is not required to be phase matched andhas an opposite sign of first temperature derivative of phase mismatch, compensates the thermally induced phasemismatch generated in the first crystal. The temperature acceptance bandwidth of frequency conversion in thethree cascaded crystals is about double that in a single long crystal with the same interaction length.

Effect of angle-of-arrival fluctuation on heterodyne detection in slant atmospheric turbulence

Xizheng Ke and Zhen Tan

Doc ID: 304680 Received 15 Aug 2017; Accepted 08 Jan 2018; Posted 09 Jan 2018  View: PDF

Abstract: A mathematical model of the effect of random pointing errors on the mixing efficiency of heterodyne detection is established and the effect of angle-of-arrival fluctuation on the mixing efficiency of heterodyne detection is investigated. The results show that the average mixing efficiency is significantly affected by the angle-of-arrival fluctuation in the outer scale. The larger the obscuration ratio and the receiving aperture of the optical system, the lower the average mixing efficiency. The receiving aperture should satisfy D/r0 < 0.9. Based on the turbulence intensity, the error rate of heterodyne detection can be lower than 10−9.

A radiometric model for coaxial single- and multi-mode optical emission from double-clad fiber

Kathy Beaudette, Mathias Strupler, Jian Ren, Brett Bouma, and Caroline Boudoux

Doc ID: 305280 Received 17 Oct 2017; Accepted 08 Jan 2018; Posted 09 Jan 2018  View: PDF

Abstract: Double-clad fibers (DCFs) are versatile waveguides supporting a single-mode core surrounded by a multimode inner cladding. DCFs are increasingly used for multimodal biomedical applications, such as imaging or therapy, for which the core is typically used for coherent illumination and the inner cladding, to support a concurrent modality. A proper optimization is, however, critical to ensure high optical performance and requires accurate modeling of coaxial single- and multi-mode output beams. In this paper, we present an approach based on geometrical optics and radiometry, which provides a simple and efficient modeling tool for designing and optimizing DCF-based systems. A radiometric definition of single- and multi-mode output beams in terms of irradiance and radiant intensity allows for the modeling of the energy distribution along the beams' propagation. We confirmed the validity of the model through comparison with experimental measurements and demonstrate the use of the model for optimizing a catheter for concurrent OCT and laser coagulation.

Temporal coherence study of four wave mixingproducts with and without the laser cavity effect

Suchita Yadav and R. Vijaya

Doc ID: 308929 Received 10 Oct 2017; Accepted 08 Jan 2018; Posted 09 Jan 2018  View: PDF

Abstract: In this work, we have studied the temporal coherence property of a four wave mixing (FWM)-assisted CW erbium-dopedfiber ring laser source. To understand the temporal coherence characteristics of FWM, we have analyzed the visibility oftheir interference pattern with the help of a Mach-Zehnder based fiber interferometer. The visibility of FWM sidebandsis compared with respect to the input pumps, with and without the cavity effect. The stand-alone FWM without anycavity effect has a visibility comparable to its input coherent pumps, while the FWM in the presence of the cavity effecthas a poorer visibility due to the intra-cavity noise arising from the amplified spontaneous emission which is notentirely annulled in broadband lasers. The study also confirms that the visibility/temporal coherence property of FWMsidebands does not depend on efficiency of their generation.

Distribution of Splice Loss in Single Mode Optical Fiber

Jonathan Nichols, Joseph Michalowicz, and Frank Bucholtz

Doc ID: 309962 Received 25 Oct 2017; Accepted 08 Jan 2018; Posted 09 Jan 2018  View: PDF

Abstract: This work investigates a probabilistic model for splice loss in singlemode optical fibers. We derive the probability density function for loss values as a function of lateral and angular misalignment. We then use observed data to estimate these model parameters; both Bayesian and maximum likelihood estimation procedures are described. These estimates can then be used to provide an indication of the relative importance of various loss mechanisms. Alternatively, if one is given values for maximum lateral and angular misalignment, our results allow for predictions of expected distribution of loss values. An overall goal of this paper is to demonstrate that, beyond the mean and variance of splice loss, there is significant information in the shape of the distribution of values. A second goal is to understand the trade-off between the number of splice loss measurements and the confidence in estimates of parameters in the splice loss model.

VIIRS reflective solar bands on-orbit calibration using solar diffuser illuminated by scattered light through the nadir-port

Junqiang Sun, Mike Chu, and Menghua Wang

Doc ID: 312702 Received 03 Nov 2017; Accepted 08 Jan 2018; Posted 11 Jan 2018  View: PDF

Abstract: A new variant to the standard on-orbit calibration of the reflective solar bands (RSBs) using a solar diffuser (SD) is formulated. Instead of direct solar exposure through the SD port in the front of instrument as originally designed, the variant method uses light reflecting off Earth’s surface coming through the nadir port as the light source to illuminate the built-in onboard SD. The methodology is applied to the Visible Infrared Imaging Radiometer Suite (VIIRS) on board the Suomi National Polar-orbiting Partnership (SNPP) satellite, and is shown to be viable. This approach effectively preserves the same calibration pipeline other than using a different set of illumination data, corresponding to a different illumination source, for computing the luminosity emanating from the SD. It has the added advantages of not dealing with operational needs for the standard calibration activities and completely bypassing the characterization of the transmission function of the attenuation screen in the front of the SD port. The RSB calibration coefficients are computed from the data of scattered light from the SD sector per each orbit and a sixteen-day average is taken. The variant calibration coefficients are shown to well match the standard solar-based RSB calibration coefficients for all RSBs studied. The result also shows a consistent 2% variation mission-long for all RSBs, showing the overall consistency of this first analysis of the new method but also the level of the uncertainty. The result and the implication of this study are discussed.

High-efficiency polarization-independent widebandmultilayer dielectric reflective bullet-alike crosssectionfused-silica beam combining grating

Hongchao Cao, Jun Wu, Junjie Yu, and Jianyong Ma

Doc ID: 312835 Received 07 Nov 2017; Accepted 08 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: A high-efficiency polarization-independent wideband multilayer dielectric reflective bullet-alike cross-section(combination of trapezoidal-rectangular grating profile) fused-silica beam combining grating (BCG) used in the -1storder for spectral beam combining (SBC) is designed and fabricated. Exact grating profile parameters areoptimized by using the rigorous coupled-wave analysis (RCWA) and simulated annealing algorithm (SA). Thesimplified modal method is introduced to analyze the designed grating. As a comparison, traditional puretrapezoidal and pure rectangular grating are also designed. Numerical results show that such bullet-alike crosssectionBCG exhibits wide bandwidth with the lowest maximum electric field enhancement (MEFE) in the gratingmaterial, which is greatly beneficial for the promotion of the power scaling level of the grating based SBC system. Atwo-step dry-etching procedure is developed to fabricate such a grating. The averaged diffraction efficiency ofgreater than 91% was experimentally demonstrated.

Symmetric decomposition of experimentaldepolarizing Mueller matrices in the degenerate case

Jérémy Vizet and Razvigor Ossikovski

Doc ID: 307938 Received 27 Sep 2017; Accepted 07 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: We propose a detailed procedure for determining the two retardance matrix factors entering the symmetricdecomposition of Mueller matrices in the case where the depolarizer matrix is partially degenerate (i.e., two out ofthree of its depolarization coefficients are equal), this case being widely met in practice. Thanks to a relativelysimple algebraic method, we show that linear retardance, as well as its eigenaxes orientation can be determinedunambiguously from each retardance matrix factor. The method, applied on both experimental Mueller matrices ofan ad hoc sample, as well as on that of a biological tissue, shows its efficiency for decoupling the differentpolarimetric effects of retardance that occur during the propagation of light throughout a complex medium.

Calculation model of scattering polarization coherencymatrix for detection system of oil spill on sea

jiang xu, weixian qian, Qian Chen, and yang zhou

Doc ID: 308234 Received 03 Oct 2017; Accepted 07 Jan 2018; Posted 10 Jan 2018  View: PDF

Abstract: As a new analytical method to identify oil spill on sea, the main effect of polarization measurement system is thescattering polarization information of different measured parts. To improve measurement accuracy, the scatteringpolarization characteristic of oil film and seawater had been observed in this paper. And a useful computationalmodel, scattering polarization coherency matrix (SPCM) had been derived, which is a probabilistic mixture ofpolarization coherency matrix. Combined with Fresnel formula, the amplitude ratio and phase retardation hadbeen extracted to verify the scientific nature of the physical model. Experiments were performed, and the SPCM ofoil film and seawater had been measured. In order to test the practicability of the model, we derived the degree ofpolarization (DOP) from the SPCM, and used it as the basis for identification of the actual oil spill on sea in the caseof sunlight. Research indicated that the path of multiple scattering was in connection with the molecular structureand interactions of medium. Under the different measuring angles, the SPCM of oil film and seawater have bothdifference and regularities, the experimental results indicated that it can be used for rapid detection of oil spill onsea, and the data is accurate and reliable.

Calibration of the degree of linear polarizationmeasurements of the polarized Sun-sky radiometerbased on the POLBOX system

Zhengqiang Li, Kaitao LI, Li Li, Hua XU, Yisong Xie, Yan Ma, Donghui LI, Philippe Goloub, Yinlin Yuan, and Xiaobing Zheng

Doc ID: 308704 Received 06 Oct 2017; Accepted 07 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: Polarization observation of sky radiation is the frontier approach to improve the remote sensing of atmosphericcomponents, e.g. aerosol and clouds. The polarization calibration of ground-based Sun-sky radiometer is the basisfor obtaining accurate degree of linear polarization (DOLP) measurement. In this paper, a DOLP calibrationmethod based on laboratory polarized light source (POLBOX) is introduced in detail. Combined with CE318-DPSun-sky polarized radiometer, a calibration scheme for DOLP measurement is established for the spectral range of440-1640nm. Based on the calibration results of Sun-sky radiometer observation network (SONET), thepolarization calibration coefficient and the DOLP calibration residual are analyzed statistically. The results showthat the DOLP residual of the calibration scheme is about 0.0012, and thus it can be estimated that the final DOLPcalibration accuracy of this method is about 0.005. Finally, it is verified that the accuracy of the calibration resultsis in accordance with the expected results by comparing the simulated DOLP with the vector radiative transfercalculations.

Polarimetric Infrared Imaging Simulation of a Synthetic Sea Surface with Atmospheric Scattering

Si He, Xia Wang, Runqiu Xia, Weiqi Jin, and Jian an Liang

Doc ID: 308412 Received 12 Oct 2017; Accepted 06 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: A novel approach to simulate the polarimetric infrared imaging of a synthetic sea surfaces with atmospheric scattering effects is presented. The infrared emission, multiple reflections and infrared polarization of the sea surface and the atmospheric scattering are all included for the first time. A new method to retrieve the radiative characteristics of a wind-roughened sea surface is introduced. The sea surface realization and the light transfer calculation are carried out at the same time thus the consumption of time and memory is decreased obviously. Then the polarimetric infrared images of the sea surface are generated by the inverse ray tracing based on the radiative characteristics. The influence of the atmospheric scattering is added by a polarized light Monte Carlo model. Polarimetric and unpolarized infrared images of the synthetic sea surface of different environment and observation conditions are generated and compared. The results show that this simulation can be well utilized to predict the infrared polarization characteristics of the sea surface and the quality of the polarimetric infrared images in the oceanic environment.

Orbital angular momentum channel monitoring of coaxially multiplexed vortices by diffraction pattern analysis

Shiyao Fu, Wang Zhai, Tonglu Wang, Ci Yin, and Chunqing Gao

Doc ID: 313009 Received 08 Nov 2017; Accepted 06 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: We theoretically and experimentally demonstrate a scheme to monitor the weight of single orbital angular momentum (OAM) channel for coaxial multiplexed optical vortices with large mode-spacing. A special designed holographic grating is illuminated by the incident multiplexed vortices firstly. Then the weight of each single OAM channel is obtained after analyzing the captured diffraction patterns. The response time is measured as about 0.1 s for patterns analysis, indicating the feasibility of the real-time monitoring. This work will find applications in domains where multiplexed optical vortices are of interest, such as the OAM based data-transmission system, and so on.

Q-plates with nonlinear azimuthal distribution of the principal axis: Application to encode binary data

Joseph Holland, Ignacio Moreno, Jeffrey Davis, Maria del Mar Sanchez-Lopez, and Don Cottrell

Doc ID: 307527 Received 20 Sep 2017; Accepted 06 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: We encode q-plates where the angular orientation of the principal axes is varied spatially with non-standard distribution. In the usual q-plate design, the orientation of the optical axes depends linearly on the azimuthal angle. In this work, we examine cases where this azimuthal dependence is nonlinear. We consider two cases – first, where the principal axis distribution is like an inverse-tangent function of the azimuth; and second, where it displays linear and flat segments. This last case is proposed as a new method to encode binary data into the azimuthal lobes of the vector beam. We encode these patterns using a spatial light modulator system that allows new and exotic q-plate designs without the difficulty of fabricating individual plates. Experimental results are presented.

Optimized star sensors laboratory calibration methodusing regularization neural network

Chengfen Zhang, Yanxiong Niu, Zhang Hao, and Lu Jiazhen

Doc ID: 306499 Received 06 Sep 2017; Accepted 05 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: High precision ground calibration is essential to ensure the performance of star sensors. However, the complexdistortion and multi-error coupling have brought great difficulties to traditional calibration methods, especially forlarge Field of View (FOV) star sensors. Although increasing the complexity of models is an effective way to improvethe calibration accuracy, it significantly increases the demand for calibration data. In order to achieve highprecision calibration of star sensors with large FOV, a novel laboratory calibration method based on aregularization neural network is proposed. A multi-layer structure neural network is designed to represent themapping of the star vector and the corresponding star point coordinate directly. To ensure the generalizationperformance of the network, regularization strategies are incorporated into the net structure and the trainingalgorithm. Simulation and experiment results demonstrate that the proposed method can achieve high precisionwith less calibration data and without any other priori information. Compared with traditional methods, thecalibration error of the star sensor decreased by about 30%. The proposed method can satisfy the precisionrequirement for large FOV star sensors.

Ultrathin endoscopic lens design for high optical performance over a wide range of working distance

YuShan Chang, Long Hsu, and Kuang-Lung Huang

Doc ID: 313490 Received 21 Nov 2017; Accepted 05 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: An internally focusing design is developed for an endoscopic lens to have optical performance close to the diffraction limit. When changing the working distance from infinity to a predetermined short distance, the overall system length remains constant and compact, with high optical performance over a wide range of object distances. It is shown that diffraction-limit-like performance is maintained in the whole range, which indicates a novel long depth of field. It is also shown that a lens system with a total track length of 1.04 mm is possible. The design concept is thus proven to be feasible and can enable very high-resolution examination for doctors checking the position of biological entities through the immediate capture of clear images at different working distances. The corresponding lens configuration, PNN, is shown to be useful in achieving the high-resolution performance once the number of lens elements is four, where P and N are used to denote positive and negative optical power respectively for the lens groups. A corresponding tolerance analysis is also presented.

Compact optical multipass matrix system design basedon slicer mirrors

Yin Guo and Liqun Sun

Doc ID: 315603 Received 12 Dec 2017; Accepted 05 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: High path-to-volume ratio (PVR) and low aberration output beam are the two main criteria to assess theperformance of multipass absorption cells. However, no substantial progress has been reported for largenumerical-aperture-coupled multipass cells, which is due to the accumulated aberrations caused by a largenumber of off-axis reflections. Based on Chernin’s design, in this study, we modified Chernin’s four-objectivemultipass matrix cell by using slicer mirrors to eliminate alignment difficulty and decrease the system volume. Ageneralized design routine based on user requirements is also proposed. Based on the automatic modeling toolpackage (Pyzdde) connected with Zemax and boundary conditions of the parameters selection proposed, a lowaberration output beam and a high PVR are easily obtained compared with other multipass cells schemes. In onedemo design, 108 passes (5×7 matrix spots) in a base length of 300 mm are presented. The PVR and peak-to-valley(PV) value wavefront error are 67.5 and 0.92 , respectively. Finally, a tolerance analysis of this opticalmultipass system is also presented. This work may provide better broadband optical absorption cells in terms ofresponse time, and a better detection sensitivity in versatile applications.

First Decadal Lunar Results from the Moon and EarthRadiation Budget Experiment (MERBE)

Grant Matthews

Doc ID: 301994 Received 10 Jul 2017; Accepted 05 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: A need to gain more confidence in computer model predictions of coming climate change has resulted ingreater analysis of the quality of orbital Earth Radiation Budget (ERB) measurements, being used todayto constrain, validate and hence improve such simulations. These studies conclude from time series analysisthat for around a quarter of a century, no existing satellite ERB climate data record is of a sufficientstandard to partition changes to the Earth from those of un-tracked and changing artificial instrumentationeffects. This led to the creation of the Moon and Earth Radiation Budget Experiment (MERBE),which instead takes existing decades old climate data to a higher calibration standard using thousands ofscans of Earth’s Moon. The Terra and Aqua satellite ERB climate records have been completely regeneratedusing signal processing improvements, combined with a substantial increase in precision from morecomprehensive in-flight spectral characterization techniques. This study now builds on previous OSAwork by describing new Moon measurements derived using accurate analytical mapping of telescopespatial response. That then allows a factor of three reduction in measurement noise along with an orderof magnitude increase in the number of retrieved independent lunar results. Given decadal length devicelongevity and the use of solar and thermal lunar radiance models to normalize the improved ERB resultsto the SI traceable radiance scale of the ‘MERBE Watt’, the same established environmental time seriesanalysis techniques are applied to MERBE data. They evaluate it to perhaps be of sufficient quality toimmediately begin narrowing the largest of climate prediction uncertainties. It also shows that if suchTerra/Aqua ERB devices can operate into the 2020’s it could become possible to halve these same uncertainties,decades sooner than would be possible with existing or even planned new observing systems.

Design and analysis of a triple reflection grazingincidence X-ray telescope

Yunhan Huang, ZhiYing Liu, yuegang fu, and jia ke wang

Doc ID: 312884 Received 07 Nov 2017; Accepted 04 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: A triple reflection grazing incidence X-ray telescope is proposed and evaluated. This form of an optical system candetect X-ray energy that is close to the optical axis, which solves the problems encountered by traditionalWolter-type systems. In this paper, we also propose a new design method to ensure that the entire telescopestructure is compact and integrated. Finally, a proof-of-concept design with an acceptable image quality isproposed.

Light-absorbing aerosol properties retrieved from the sunphotometer observation over the Yangtze River Delta, China

Jing Wang, Shengjie Niu, and Dan Xu

Doc ID: 312441 Received 09 Nov 2017; Accepted 04 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: In this study, aerosol optical depth (AOD) and extinction Ångström exponent (EAE) are derived from ground-based sunphotometer observationsbetween 2007-2014 at urban sites of Nanjing over the Yangtze River Delta (YRD). In addition, the present study aims to investigate aerosol lightabsorbingproperties such as single scattering albedo (SSA), absorption Ångström exponent (AAE) and the aerosol absorbing optical depth (AAOD).The retrieval of aerosol properties is compared with AERONET inversion products. The results demonstrate that the retrieved AOD have a goodagreement with the AERONET Level 1.5 data, with the root mean square error (RMSE) being 0.068, 0.065 and 0.026 for total, fine mode and coarsemode at 440nm, respectively. The SSA values indicates similar accuracies in the results, which are about 0.003, -0.009,-0.008 and 0.010 differentfrom AERONET at 440,670,870 and 1020nm, respectively. The occurrence frequency of background level AOD (AOD < 0.10) at 440 nm in this regionis limited (1%). Monthly mean AOD, SSA, the effective radius (Reff) and the volume concentration at 440 nm were 0.6-1.3, 0.85-0.92, 0.24-0.40 μmand 0.18-0.28 μm3μm-2, respectively. The mean value of AAOD at 440 nm (AAOD440) was the highest in both summer (0.095 ± 0.041) and autumn(0.094±0.042), but was the lowest in winter (0.079 ± 0.036). It was also noted that SSA was found to be higher during summer (0.89±0.05). Thespectral variation of SSA was observed to be strongly wavelength dependent during all seasons. The seasonal mean AAE440-870 is the highest inwinter (0.86 ± 0.41) and lowest in spring (0.49 ±0.29). In winter, the cumulative frequency for AAE between 1.0-1.2 was about 87% .The peak in theAAE distribution was close to 1.0, indicating that the aerosol column was dominated by urban-industrial aerosols and absorption species other thanblack carbon (BC). Analysis of the relationship between EAE and SSA showed that the aerosol populations could be classified as “mixed” aerosolincluding a mixture of both anthropogenic particles and secondary organic aerosol with highly variable sphericity fraction.

Target recognition method on retina-like LADAR range images

Hongsheng Wang, Qun Hao, jie CAO, Chongdao Wang, HENG ZHANG, Zigu Zhou, and Sihui Li

Doc ID: 305354 Received 31 Aug 2017; Accepted 04 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: A target recognition method on retina-like LADAR range images is proposed in this study. The method does not require complicated image preprocessing due to speeded-up robust features (SURF) combined with retina-like sampling as feature match descriptors. Subpixel resampling achieves optimization and avoids affecting the accuracy and precision of target recognition. Several experiments are conducted to analyze the validity of SURF directly. The separate exploration of SURF with Cartesian, log-polar (LP), and inverse LP images are discussed. Furthermore, examples are used to demonstrate the capability of the proposed method. Finally, important conclusions are drawn as follows. (I) SURF extraction becomes difficult when it is directly used in LP images as expected. (II) Applying SURF with inverse LP process is valid. (III) SURF key match points in inverse LP images are less than those in Cartesian images. (IV) The accuracy of the proposed solution agrees well with that of Cartesian solution when angle and scale variants are used. The present recognition solution may be used in various applications involving space-variant image processing.

Use of a broadband monitoring system for the determination of the optical constants of a dielectric bilayer

Severin NADJI, Michel Lequime, Thomas Begou, Cihan Koc, Catherine GREZES-BESSET, and Julien Lumeau

Doc ID: 308842 Received 09 Oct 2017; Accepted 04 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: This paper extends a method previously applied to the determination of the optical constants of a high index thin film to a dielectric bilayer. This method is based on the time recording of the spectral transmittance of the stack during its deposition with the help of an in situ broadband monitoring system.

Study on the inversion of doped concentration induced by millisecond pulsed laser irradiation Si-APD

Yuan Dong, Wang Di, Zhi Wei, and Tairan Fu

Doc ID: 308962 Received 10 Oct 2017; Accepted 04 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: In this paper, an experimental study of Si-APD with millisecond pulse laser irradiation was carried out, and the C-V curve of Si-APD was obtained by using a semiconductor analyzer. Based on the single-side abrupt junction character of n+p, combined with the corresponding theoretical derivation, the doping concentration varying with the axial depth of damaged Si-APD was obtained by inverse computation. The lattice dislocation and junction reduction were the fundamental causes of the reduced doping concentration. The research results provide a new method for the study of the internal doping concentration for detectors with millisecond pulse laser damage.

Exact surface profile measurement without subtracting dispersion phase through Fourier transform in a white–light scanning interferometer

Songjie Luo, Osami Sasaki, Ziyang chen, Samuel Choi, and Jixiong Pu

Doc ID: 309104 Received 19 Oct 2017; Accepted 03 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: A new signal processing is proposed where the dispersion phase is not subtracted from the detected spectral phase distribution. The linear and bias components in the spectral phase distribution are used to calculate the complex-valued interference signal (CVIS). The simulations verify that the dispersion phase generates an inclination in the measured surface profile along one direction in which the magnitude of the dispersion phase changes linearly. The simulations also show that the position of zero phase nearest to the position of amplitude maximum in the CVSI almost does not change due to the bias component although the random phase noise contained in the interference signal changes the slope of the linear component. Measured surface profiles show that the new signal processing achieves a high accurate measurement by the CVIS.

Tracking moving targets behind a scattering mediumvia speckle-correlation

Chengfei Guo, jietao liu, Tengfei Wu, Lei Zhu, and Xiaopeng Shao

Doc ID: 309839 Received 02 Nov 2017; Accepted 03 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: Tracking moving targets behind a scattering medium is a challenge and it has many important applications invarious fields. Due to the multiple scattering, instead of the object image, only a random speckle pattern can bereceived on the camera, when light passing through highly scattering layers. Significantly, an important featureof speckle pattern has been found and it showed the target information can be derived from the specklecorrelation.In this work, inspired by the notions used in computer vision and deformation detection, by specificsimulations and experiments, we demonstrate a simple object tracking method, in which by using the specklecorrelation,the movement of a hidden object can be tracked in the lateral direction and axial direction. Inaddition, the rotation state of the moving target can also be recognized by utilizing the autocorrelation ofspeckle. This work will be beneficial for biomedical applications in the fields of quantitative analysis of theworking mechanisms of micro-object and the acquisition of dynamical information of the micro-object motion.

Spectral optimization of phosphor-coated white LEDfor road lighting based on the mesopic limitedluminous efficacy and IES color fidelity index

LICAI XIAO,, CHUANWEN ZHANG, ping zhong, and Guoxing He

Doc ID: 312471 Received 31 Oct 2017; Accepted 02 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: The spectral optimization of phosphor-coated white LED (pc-W LED) with green and orange phosphors excited byblue chip for road lighting was investigated based on the mesopic limited luminous efficacy (LLEm) and colorfidelity index (Rf). The average LLEm of four road lighting standards of the USA and the UK decreases as Rf increases,but the optimal S/P ratio increases slightly with Rf increases for given correlated color temperature (CCT). Theaverage LLEm could reach the highest of 339 lm/W for Rf = 70, 326 lm/W for Rf = 80, and 309 lm/W for Rf = 90 atCCT = 5000 K. Six real pc-W LEDs with different Rf at CCT ≈ 5000 K and with Rf ≈ 70 at different CCT weredemonstrated. Comparing with current pc-W LEDs with YAG:Ce3+ phosphors, the average LLEm of six demonstratedpc-W LEDs will be over 5.0 % and above. So It is suggested that the road lighting should choose pc-W LEDs with highefficiency green phosphors (520-530 nm) instead of YAG:Ce3+ phosphors.

Multispectral phase imaging based on acousto-opticfiltration of interfering light beams

Alexander Machikhin, Ludmila Burmak, Olga Polschikova, Alina Ramazanova, Vitold Pozhar, and Sergei Boritko

Doc ID: 312593 Received 02 Nov 2017; Accepted 02 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: Acousto-optic spectral selection of light is an effective technique for interference imaging at multiple wavelengths.In this paper, we show that depending on the location of acousto-optical tunable filter relative to theinterferometer, it is possible to enhance important characteristics of the whole system: spectral contrast,insensitivity to ambient light, performance stability, measurement accuracy. We analyze theoretically and compareexperimentally quantitative phase imaging system based on Mach-Zehnder interferometer with one and twoacousto-optical filters located in the illumination or/and in the output channels. Visibility of the interferencepatterns and noise RMS in the calculated phase maps are estimated for all cases at room temperature. It is shownthat acousto-optic filtration of interfering light beams in the output channel ensures better contrast of theinterference pattern and, therefore, provides better stability and higher precision of the phase measurements.

Full-field fabric stress mapping by micro Ramanspectroscopy in yarn push-out test

Zhenkun Lei, Fuyong QIn, QC Fang, RX Bai, Wei Qiu, and XG Chen

Doc ID: 314250 Received 29 Nov 2017; Accepted 02 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: The full-field stress distribution of a two-dimensional plain fabric was mapped using micro Raman spectroscopy(MRS) through a novel yarn push-out test, simulating a quasi-static projectile impact on the fabric. The stress–strain relationship for a single yarn was established using a digital image correlation method in a single-yarntensile test. The relationship between Raman peak shift and aramid kevlar 49 yarn stress was established usingMRS in a single-yarn tensile test. An out-of-plane loading test was conducted on an aramid Kevlar 49 plain fabric,and the yarn stress was measured using MRS. From the full-field fabric stress distribution, it can be observed thatthere is a cross-shaped distribution of high yarn stress; this result would be helpful in further studies on loadtransfer on a fabric during a projectile impact.

“Achromatic Limits” of Pancharatnam Phase lenses

Comrun Yousefzadeh, Afsoon Jamali, COLIN MCGINTY, and Philip Bos

Doc ID: 303695 Received 02 Aug 2017; Accepted 02 Jan 2018; Posted 08 Jan 2018  View: PDF

Abstract: Lenses based on Pancharatnam phase have the advantages of being thin and inexpensive. Unfortunately theiroptical effect is strongly wavelength dependent, and in general their applications are limited by the requirement ofa monochromatic source. However low power lenses based on Pancharatnam phase can be considered forapplications over the visible range. In this paper, we provide intuitive “limits” for the lens power below whichthese devices can be considered for use with the eye and visible light imaging applications.

Volumetric calibration of a plenoptic camera

Elise Hall, Timothy Fahringer, Daniel Guildenbecher, and Brian Thurow

Doc ID: 310132 Received 27 Oct 2017; Accepted 02 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: The volumetric calibration of a plenoptic camera is explored to correct for inaccuracies due to real world lens distortions and thin lens assumptions in current processing methods. Two methods of volumetric calibration basedon a polynomial mapping function which does not require knowledge of specific lens parameters, are presented and compared to a calibration based on thin lens assumptions. The first method, volumetric dewarping, is executed by creation of a volumetric representation of a scene using the thin lens assumptions, which is then corrected in post processing using a polynomial mapping function. The second method, direct light field calibration, uses the polynomial mapping in creation of the initial volumetric representation to relate locations in object space directly to image sensor locations. The accuracy and feasibility of these methods is examined experimentally by capturing images of a known dot card at a variety of depths. Results suggest that use of a 3D polynomial mapping function provides a significant increase in reconstruction accuracy, and that the achievable accuracy is similar using either polynomial mapping based method. Additionally, direct light field calibration provides significant computational benefits by eliminating some intermediate processing steps found in other methods. Finally, the flexibility of this method is shown for a non‐planar calibration.

Acousto-optic visualization of optical wavefronts

Vladimir Balakshy

Doc ID: 312376 Received 31 Oct 2017; Accepted 02 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: The paper presents a short survey on theoretical and experimental investigations of an acousto-optic method of optical wavefront visualization proposed and developed in Moscow State University. The method is based on angular selectivity of Bragg diffraction. It is shown that distribution of light intensity in the visualized image is proportional to the phase gradient in the acousto-optic interaction plane. Spatial resolution and contrast of the visualized image are determined primarily by the divergence angle of the acoustic beam. Most attention in the paper is concentrated on the problem of AO visualization of two-dimensional phase objects. The important advantage of the AO method consists in possibility of optical field phase structure registration in the presence of amplitude modulation of the initial optical field. Examples of computer simulation as well as some experimental results are presented for illustration of potentialities of this method.

Microlens array expander with improved lightintensity distribution through periodic submicro scalefilling for near-eye display

Li Min, wang lu, wenjiang shen, Dongmin Wu, and Yu Bai

Doc ID: 302980 Received 24 Jul 2017; Accepted 02 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: A type of microlens array(MLA)expander with an improved light intensity distribution(LID) is designed andfabricated through submicro scale filling, which could be applied to near-eye displays. Through the reflection of a0.8-μm-wide metal-filling, the light field is only split and superimposed through the microlens. The bright spot atthe center of the LID is effectively eliminated. The results demonstrate that the expanded numerical aperture(NA)and focal length are about 0.38 and 19μm, respectively, and the error in theradius of curvature is within 5%between the experimental and designed values. An improved image quality with an 80% brightness uniformity foran area of 22 × 22 mm2 is realized through the MLA. Compared with the MLA based on thermal reflow, the largestNA is obtained with the smallest focal length and gap. The experimental LID is consistent with that obtained by atheoretical simulation.

Multilevel data writing in nanoporous glass by fewfemtosecond laser pulses

Alexey Lipatiev, Sergey Fedotov, Andrey Okhrimchuk, Sergey Lotarev, Alexey Vasetsky, Alexander Stepko, Georgiy Shakhgildyan, Kseniya Piyanzina, Ivan Glebov, and Vladimir N Sigaev

Doc ID: 303022 Received 26 Jul 2017; Accepted 02 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: Multidimensional data recording inside nanoporous high-silica glass by a femtosecond laser beam has been investigated. It is shown thatthree femtosecond laser pulses at pulse repetition rate up to 1 MHz are sufficient for recording 3 bits of information inside thenanoporous glass, which is an order of magnitude lower than the number of pulses required for data writing in silica glass and provides acorresponding gain in data writing speed. Multilayer data recording and reading were demonstrated providing the storage densitycorresponding to the capacity of 25 GB in the optical compact disc form factor. Outstanding thermal stability of proposed optical datastorage is confirmed by the 24 h long heat treatment at 700 °C which couldn’t damage the recorded data.

Dual-view Table-top 3D Display System Based on Integral Imaging

MIN-YANG HE, Han-Le Zhang, Huan Deng, Xiao-Wei Li, Dahai Li, and Qiong-Hua Wang

Doc ID: 302966 Received 21 Jul 2017; Accepted 02 Jan 2018; Posted 02 Jan 2018  View: PDF

Abstract: In this paper, we propose a dual-view-zone table-top 3D display system based on integral imaging by using amultiplexed holographic optical element (MHOE) which has the optical properties of two sets of microlens arrays.The MHOE is recorded by a reference beam using the single-exposure method. The reference beam records thewavefronts of a microlens array from two different directions. Thus, when the display beam is projected on theMHOE, two wavefronts with the different directions will be rebuilt and the 3D virtual images can be reconstructedin two viewing-zones. The MHOE has the angle and wavelength selectivity. Under the conditions of the matchedwavelength and the angle of the display beam, the diffraction efficiency of the MHOE is largest. Because theunmatched light just passes through the MHOE, so the MHOE has the advantages for see-through display. Theexperimental results confirm the feasibility of the dual-view-zone table-top 3D display system.

Conventional soliton or stretched pulse delivered bynanotube-mode-locked fiber laser

Xiaoxiang Han

Doc ID: 309860 Received 24 Oct 2017; Accepted 01 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: We propose a nanotube-mode-locked erbium-doped fiber laser that can deliver conventional solitons (CSs) orstretched pulses (SPs) based on D-shaped fiber saturable absorber (DF-SA) where evanescent-field interactionworks. The net cavity dispersion of laser is slightly negative. In our experiment, by optimizing the polarizationcontroller (PC) in the cavity, CS and SP can be obtained at the central wavelengths of 1530.6 nm and 1530.3 nm dueto on carbon nanotubes and the spectral filtering effect induced by nonlinear polarization rotation. Although theacquired CS and SP nearly have the same central wavelengths, they show distinct optical spectra, 3-dB bandwidths.The proposed fiber laser is attractive for practical applications.

Designing and experimental verification of aphotoacoustic flow sensor using computational fluiddynamics

Mikael Lassen, David Balslev-Harder, Anders Brusch, nikola Pelevic, Stefan Persijn, and Jan Petersen

Doc ID: 309903 Received 26 Oct 2017; Accepted 01 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: A photoacoustic (PA) sensor for fast and real-time gassensing is demonstrated. The PA sensor is a standalonesystem controlled by a Field-Programmable Gate Array(FPGA). The PA cell has been designed for flow noiseimmunity using computational fluid dynamics (CFD)analysis. The aim of the CFD analysis was to investigateand minimize the influence of the gas distributionand the flow noise on the PA signal. PA measurementswere conducted at different flow rates by excitingmolecular C-H stretch vibrational bands of hexane(C6H14) and decane (C10H22) molecules in clean air at2950 cm􀀀1 (3.38 mm) with a custom made mid-infraredinterband cascade laser (ICL). We observe a (1s, standarddeviation) sensitivity of 0.4 0.1 ppb (nmol/mol)for hexane in clean air at flow rates up to 1.7 L/min, correspondingto a normalized noise equivalent absorption(NNEA) coefficient of 2.510􀀀9 W cm􀀀1 Hz􀀀1/2,demonstrating high sensitivity and fast real-time gasanalysis. An Allan deviation analysis for decane showsthat the detection limit at optimum integration time is0.25 ppbV (nmol/mol).

Dynamic analysis and rotation experiment of an optical-trapped microsphere in air

Wenqiang Li, Nan Li, Yu Shen, Zhenhai Fu, heming Su, and Huizhu HU

Doc ID: 308197 Received 09 Oct 2017; Accepted 01 Jan 2018; Posted 05 Jan 2018  View: PDF

Abstract: A dual-fiber optical trap system to trap and rotate a borosilicate microsphere has been proposed and experimentally demonstrated. The trapping system can be used as a probe to measure environmental parameters, such as torque, force and viscosity of surrounding medium. Under various conditions with different fiber misalignments, optical power and fiber separation, the trapped sphere will exhibit three motion types including random oscillation, round rotation and abnormal rotation. Power spectrum analysis method is used to measure rotation rates up to 385 Hz, which can be further increased by increasing laser power. Besides, simulation and experiment show consistent results in rotation rates and motion trajectory, which verifies the validity and accuracy of dynamic analysis.

Accurate estimation of the illumination pattern’sorientation and wavelength in sinusoidal structuredillumination microscopy

Marcel Lahrberg, Mandeep Singh, Kedar Khare, and Balpreet Ahluwalia

Doc ID: 305681 Received 06 Sep 2017; Accepted 31 Dec 2017; Posted 05 Jan 2018  View: PDF

Abstract: Structured illumination microscopy is able to improve the spatial resolution of wide-field fluorescence imaging by applying sinusoidal stripe pattern illumination to the sample. The corresponding computational image reconstruction requires precise knowledge of the pattern's parameters, that are its phase phi and wave vector p. Here, a computationally inexpensive method for estimation of p from the raw data is proposed and illustrated with simulations. The method estimates p through a selective discrete Fourier transform at tunable sub-pixel precision. This results in an accurate p estimation for all the illumination patterns and subsequently improves the super-resolution image recovery by a factor of 10 around sharp edges as compared to an integer pixel approach. The technique as presented here is of major interest to the large variety of custom-build systems that are used. The feasibility of the presented method is proven in comparison with published data.


Alexei Kolgotin, Detlef Mueller, Eduard Chemyakin, Anton Romanov, and Valentin Alehnovich

Doc ID: 312384 Received 09 Nov 2017; Accepted 31 Dec 2017; Posted 05 Jan 2018  View: PDF

Abstract: We conclude our series of publications on the development of thegradient correlation method (GCM) which can be used for an improvedstabilization of the solution space of particle microphysical parametersderived from measurements with multiwavelength Raman and High-Spectral-Resolution Lidar (3 backscatter + 2 extinction coefficients).We show results of three cases studies. The data were taken with aground-based multiwavelength Raman lidar during the Saharan MineralDust Experiment (SAMUM) in the Cape Verde Islands (North Atlantic).These cases describe mixtures of dust with smoke. For our dataanalysis we separated the contribution of smoke to the total signal andonly used these optical profiles for the test of GCM. The results show asignificant stabilization of the solution space of the particle microphysicalparameter retrieval on the particle radius domain from 0.03 μm to10 μm, the real part of the complex refractive index domain from 1.3 to1.8 and the imaginary part from 0 to 0.1. This new method will be includedin TiARA (Tikhonov Advanced Regularization Algorithm)which is a fully automated, unsupervised algorithm that is used for theanalysis of the world-wide first airborne 3 backscatter + 2 extinctionhigh-spectral-resolution lidar developed by NASA Langley ResearchCenter.

Measuring optical activity with the internalreflection in a glass prism

Anderson de Oliveira, José Domenegueti, and Sergio Zilio

Doc ID: 312421 Received 02 Nov 2017; Accepted 30 Dec 2017; Posted 05 Jan 2018  View: PDF

Abstract: A novel internal reflection-based polarimeter and measurement method to characterize optically activesubstances is presented. The working principle relies on the phase difference acquired by s- and p-polarizedlight undergoing internal reflection: they interfere after passing through an analyzer and produce a minimumnear the critical angle, whose position depends on the rotation angle imposed by the optically active sample.Since the location of the minimum does not depend on the laser power, the measurement is nearly insensitive toany power fluctuation. Furthermore, this low cost device is rugged, very compact and stable, practically immuneto mechanical vibrations. It was used to measure concentrations of sucrose and fructose dissolved in distilledwater and presented a resolution better than 0.04º.

Decomposition of group-velocity-locked-vector-dissipative-soliton and the recombination

Xuan Wang, Lei Li, YING GENG, hanxiao wang, Lei Su, and Luming Zhao

Doc ID: 310005 Received 26 Oct 2017; Accepted 30 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: By using a polarization manipulation and projection system, we numerically decomposed the group-velocity-locked-vector-dissipative-solitons (GVLVDSs) from a normal dispersion fiber laser and studied the combination of the projections of the phase-modulated components of the GVLVDS through a polarization beam splitter. Pulses with structure similar to a high-order vector soliton could be obtained, which could be considered as a pseudo-high-order GVLVDS. It is found that, although GVLVDSs are intrinsically different from group-velocity-locked-vector-solitons (GVLVSs) generated in fiber lasers operated in the anomalous dispersion regime, similar characteristics for the generation of pseudo-high-order GVLVDS are obtained. However, pulse chirp plays a significant role on the generation of pseudo-high-order GVLVDS.

A novel orthogonal vector algorithm to obtain thesolar vector using the single-scattering Rayleigh model

Yinlong Wang, Jinkui Chu, Ran Zhang, and Chao Shi

Doc ID: 312481 Received 03 Nov 2017; Accepted 30 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: Information obtained from a polarization pattern in the sky provides many animals like insects and birds with vitallong-distance navigation cues. The solar vector can be derived from the polarization pattern using the singlescatteringRayleigh model. In this paper, an orthogonal vector algorithm, which utilizes the redundancy of thesingle-scattering Rayleigh model, is proposed. We use the intersection angles between the polarization vectors asthe main criteria in our algorithm. The assumption that all polarization vectors can be considered coplanar is usedto simplify the three dimensional (3D) problem with respect to the polarization vectors in our simulation. Thesurface-normal vector of the plane, which is determined by the polarization vectors after translation, representsthe solar vector. Unfortunately, the two-directionality of the polarization vectors makes the resulting solar-vectorambiguous. One important result of this study is, however, that this apparent disadvantage has no effect on thecomplexity of the algorithm. Furthermore, two other universal least-squares algorithms were investigated andcompared. A device was then constructed, which consists of five polarized light sensors as well as a 3D attitudesensor. Both the simulation and experimental data indicate that the orthogonal vector algorithms if used with asuitable threshold perform equally well or better than the other two algorithms. Our experimental data reveal thatif the intersection angles between the polarization vectors are close to 90°, the solar-vector angle deviations aresmall. The data also support the assumption of coplanarity. During the 51 min experiment, the mean of themeasured solar-vector angle deviations was about 0.242°, as predicted by our theoretical model.

Lumen degradation analysis of LED lamps based onsubsystem isolation method

Hong-Liang Ke, Hao Jian, Jian-hui Tu, Pei-Xian Miao, Chao-Quan Wang, Jing-Zhong Cui, Qiang Sun, and Ren-Tao Sun

Doc ID: 306558 Received 07 Sep 2017; Accepted 30 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: The lumen degradation of LED lamp undergoing accelerated aging test is investigated. The entire LED lamp is dividedinto three subsystems, namely, driver, lampshade and LED light source. The Parameters of output power (Watt),transmittance (%) and lumen flux (lm) are adopted in the analysis of the degradation of drive, lampshade and LED lightsource, respectively. Two groups of LED lamps are respectively aged under the ambient temperature of 25°C and 85°C,with the aging time of 2000 hours. The lumen degradation of the lamps is from 3.8% to 4.9% for the group undertemperature of 25°C and it is from 10.6% to 12.7% for the group under temperature of 85°C. LED light source is themost aggressive part of the three subsystems, which accounts for 70.5% of lumen degradation of LED lamp in average.Lampshade is the second degradation source which causes 21.5% of the total amount in average. Driver is the thirddegradation source which respectively causes 6.5% under 25°C and 2.8% under 85°C of the total amount in average.

Phase unwrapping algorithm using polynomial phaseapproximation and linear Kalman filter

Rishikesh Kulkarni and Pramod Rastogi

Doc ID: 309312 Received 17 Oct 2017; Accepted 29 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: A noise robust phase unwrapping algorithm is proposed based on state space analysis and polynomial phaseapproximation using wrapped phase measurement. The true phase is approximated as a two-dimensional firstorder polynomial function within a small sized window around each pixel. The estimates of polynomial coefficientsprovide the measurement of phase and local fringe frequencies. A state space representation of spatialphase evolution and the wrapped phase measurement is considered with the state vector consisting of polynomialcoefficients as its elements. Instead of using the traditional nonlinear Kalman filter for the purpose of stateestimation, we propose to use the linear Kalman filter operating directly with the wrapped phase measurement.Adaptive window width is selected at each pixel based on the local fringe density to strike a balance betweenthe computation time and noise robustness. In order to retrieve the unwrapped phase, either a line scanningapproach or quality guided strategy of pixel selection is used depending on the underlying continuous or discontinuousphase distribution, respectively. Simulation and experimental results are provided to demonstrate theapplicability of the proposed method.

An image decomposition model Shearlet-Hilbert-L2 with better performance for denoising in ESPI fringe patterns

wenjun xu, Chen Tang, yonggang su, Biyuan Li, and Zhenkun Lei

Doc ID: 309442 Received 18 Oct 2017; Accepted 28 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: In this paper, we propose an image decomposition model Shearlet-Hilbert-L2 with better performance for denoising in electronic speckle pattern interferometry (ESPI) fringe patterns. In our model, the low-density fringes, high-density fringes and noise are respectively described by Shearlet smoothness spaces, adaptive Hilbert space and L2 space and processed individually. Since shearlet transform has superior directional sensitivity, our proposed Shearlet-Hilbert-L2 model achieves commendable filtering results for various types of ESPI fringe patterns, including uniform density fringe patterns, moderately variable density fringe patterns and greatly variable density fringe patterns. We evaluate the performance of our proposed Shearlet-Hilbert-L2 model via application to one computer simulated and ten experimentally obtained ESPI fringe patterns with various densities and poor quality. Furthermore, we compare our proposed model with windowed Fourier filtering (WFF) and coherence-enhancing diffusion (CED), both of which are the state-of-the-art methods for ESPI fringe patterns denoising in transform domain and spatial domain, respectively. We also compare our proposed model with the previous image decomposition model BL-Hilbert-L2.

Slowing down light using THz semiconductor MM for Dual-Band thermally tunable modulator applications

Zohreh Vafapour

Doc ID: 309509 Received 18 Oct 2017; Accepted 28 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: Compared to the neighboring infrared and microwaveregions, the terahertz regime is still in need of fundamentaltechnological advances. We have designed a terahertz(THz) semiconductor metamaterial (MM) waveguidesystem, which exhibits a significant slow-light effect,based on a classical electromagnetically inducedtransparency (Cl-EIT) phenomenon. The potential ofmetamaterials for THz radiation originates from a resonantelectromagnetic response which can be tailoredfor specific applications. By appropriately adjustingthe distance between the two radiative and nonradiativemodes, a flat band corresponding to nearly constantgroup index (of order of 4924) in THz regime canbe achieved. Finite-Difference Time-Domain (FDTD)simulations show that the incident pulse can be sloweddown. The proposed device, in part, from a paucity ofnaturally occurring materials with useful electronic orphotonic properties at terahertz frequencies. This proposedcompact configuration may find potential applicationsin plasmonic slow-light systems, optical buffersand thermal and electromagnetic modulating applicationsand temperature sensors.

Fiber-based simultaneous mode- and wavelength demultiplexer

Amr Mahros and Islam Ashry

Doc ID: 312943 Received 07 Nov 2017; Accepted 28 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: We theoretically design and analyze the performance of a fiber-based linearly polarized (LP) mode-demultiplexer using Fabry-Perot interferometer. The all-fiber geometry of the reported demultiplexer is obtained by writing fiber Bragg gratings (FBGs) in a few-mode-fiber (FMF), such that the FBGs act as partial reflecting mirrors for the LP modes. We also demonstrate the ability to decompose a received optical signal into its individual LP components in wavelength-division-multiplexing (WDM) networks.

Highly Amplified Light Transmission in Parity-TimeSymmetric Multilayered Structure

Jyoti Prasad Deka and Amarendra Sarma

Doc ID: 307750 Received 22 Sep 2017; Accepted 28 Dec 2017; Posted 05 Jan 2018  View: PDF

Abstract: We propose a parity-time symmetric dielectric-nanofilm-dielectric multilayered structure that couldfacilitate highly amplified transmission of optical power in the infrared spectrum. We havetheoretically studied our model using the transfer matrix formalism. The reflection and thetransmission coefficients of the S-matrix are evaluated. The theoretical results are validated by FDTDnumerical simulation. We have shown how the thickness of the layers and the gain/loss coefficient ofthe active layers could generate spectral singularities in the S-matrix and how these singularitiescould be exploited to achieve amplified transmission of a single wavelength through the structure.

Research on the compensation of laser launch opticsto improve the performance of the LGS spot

Jie Liu, Jianli Wang, wang yuning, D T, Quan Zheng, Xudong Lin, liang wang, and Qingyun Yang

Doc ID: 313275 Received 13 Nov 2017; Accepted 28 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: To improve the beam quality of the uplink laser, a 37-channel piezo-ceramic deformable mirror was inserted intothe laser launch optics to compensate the static aberrations. An interferometer was used as the calibration lightsource as well as the wavefront sensor to perform closed-loop correction for the moment. About 0.38 λ rms (rootmean square) aberrations including the deformable mirror’s initial figure error were compensated and theresidual error was less than 0.07 λ rms. Field observations with a 2-meter optical telescope demonstrated that thepeak intensity value of the LGS spot increased from 5650 to 7658 and the FWHM (Full Width at Half Maximum) sizereduced from 4.07" to 3.52". With the compensation, an improved guide star spot can be obtained which is crucialfor the adaptive optics systems of ground-based large telescopes.

Spatial characterization of light beams analyzed by cylindrical-grating slit-less spectrometers

Balazs Major, Zoltan Horvath, and Katalin Varjú

Doc ID: 308230 Received 03 Oct 2017; Accepted 28 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: In this work we theoretically analyze the spatial information provided by cylindrical-grating slit-less spectrometers. We show that the spatial features measured with them are different from what can be obtained using a spectrometer with an entrance slit, and that they do not provide information directly on the real spatial beam profile. It is important to consider this fact in spatio-spectral analysis of extreme ultraviolet radiation often carried out using cylindrical-grating slit-less spectrometers. Since the models used are based on the Fresnel diffraction integral and ideal optical systems, the results are valid also for other spectral regions.

Sensitivity of Diffraction Efficiency to Period Width Errors for Multilayer Diffractive Optical Elements

yang hongfang and Changxi Xue

Doc ID: 308433 Received 03 Oct 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: Multilayer diffractive optical elements (MLDOEs) can achieve broadband high efficiency in the hybrid refractivediffractiveoptical systems. The reliable performance of MLDOEs requires high precision during manufacture. Themicrostructure period width errors should be well defined. In this work, the relationship between diffractionefficiency and different period width errors was analyzed with the rigorous electromagnetic method. Compared toresults predicted by the most used scalar diffraction method, the effect of period width errors on diffractionefficiency is underrated. The simulation results showed that diffraction efficiency is sensitive to the period widtherrors. This research provides a reliable method to control the fabrication errors for fabricating MLDOEs.

Practical Splicing of Poly-Methyl-Methacrylate Plastic Optical Fibres

Michele Zanon, Vinicius Silva, Andres Barbero, and Ricardo Ribeiro

Doc ID: 302855 Received 25 Sep 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: These Engineering Laboratory Notes describe a simple, fast, cost-effective and practical splicing technique for Poly- Methyl-Methacrylate (PMMA) plastic optical fibres. We believe it can be useful for home networks and with laboratory developments. It uses a widely available, low-cost transparent adhesive and does not require cleaning or polishing of the fibre tips, nor does the polyethylene jacket have to be removed. Low insertion losses were measured for the main PMMA-based fibre types.

Characterization of the pinhole diffraction based onwaveguide effect in point diffraction interferometer

Chen Wang, Yongying Yang, Li Yao, Yuankai Chen, and Jian Bai

Doc ID: 308098 Received 28 Sep 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: The nearly ideal spherical wavefront generated by pinhole diffraction is the key factor determining the achievableaccuracy in point diffraction interferometer (PDI) as it is employed as the reference wavefront. A comprehensivecharacterization of the diffraction of a pinhole at the operating-wavelength scale which is normally adopted in PDIis given. The incident light is coupled into the pinhole which functions as a cylindrical waveguide, and diffracted inthe end. The field in the pinhole is analyzed based on mode theory and the diffraction wave in farfield is derivedfrom the field equivalence principle. The diffraction wave is characterized on the light transmittance, thepolarization and the wavefront aberration, which are all determined by the properties of the mode in the pinhole.The diameter of pinhole should not be smaller than 0.6λ to make the transmittance sufficient. With a linearlypolarized incident light, the diffraction wave is elliptically polarized and the wavefront aberration is dominated bythe astigmatic component. The method explicitly reveals the physical mechanism of pinhole diffraction. Theanalytic solutions are fast to compute, easy to analyze and intuitive to show the diffractive properties of pinhole.The conclusions are significant for insight into the nature of pinhole diffraction and provide theoretical referencefor analysis of numerical results and design of PDI system.


Sumit Kumar and Anant Singh

Doc ID: 303404 Received 28 Jul 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: Surface finishing is a promising method to improve the opticalcharacteristics of crown glass. BK7 finds its applications intransmissive optics i.e. lens of binocular, lens of microscope, lens oftelescope and light emitting diodes. The magnetorheologicalnanofinishing of optical glasses using solid rotating core tool is foundmore advantageous than the other advanced finishing processes inaspects like precision and accuracy. In present research, themagnetorheological (MR) nanofinishing with solid rotating core tool iscarried on the BK7 glass of size 10×10×3 mm. Response surfacemethodology is conducted in order to find the optimum processparameters. The effects of process parameters on the percentagechange in surface roughness are analyzed. The best surface roughnessRa and Rq values are achieved as 22 nm and 32 nm from the initial of 41nm and 57 nm in 30 minutes of finishing time cycle. To study thesurface morphology of nanofinished BK7 glass, scanning electronmicroscopy (SEM) is performed with sputter coating of gold on glassspecimen.

Investigation of focusing and correcting aberrations with binary amplitude and polarization modulation

Peter fiala, Yunqi Li, and Christophe Dorrer

Doc ID: 305457 Received 23 Aug 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: We investigate the focusing and correcting wavefront aberration of an optical wave using binary amplitude and polarization modulation. Focusing is performed by selectively modulating the field in different zones of the pupil to obtain on-axis constructive interference at a given distance. The conventional Soret zone plate (binary amplitude profile) is expanded to a polarization Soret zone plate with twice the focusing efficiency. Binary pixelated devices that approximate the sinusoidal transmission profile of a Gabor zone plate by spatial dithering are also investigated with amplitude and polarization modulation. Wavefront aberrations are corrected by modulation of the field in the pupil plane to prevent destructive interference in the focal plane of an ideal focusing element. Polarization modulation improves the efficiency obtained by amplitude-only modulation, with a gain that depends on the aberration. Experimental results obtained with Cr-on-glass devices for amplitude modulation and liquid crystal devices operating in the Mauguin condition for polarization modulation are in very good agreement with simulations.

Acceleration of diffraction calculations in cylindricallysymmetrical optics

Jeremy Rubin, Eric Shirley, and Zachary Levine

Doc ID: 305855 Received 29 Aug 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: We have significantly accelerated diffraction calculations using three independent acceleration devices. Theseinnovations are restricted to cylindrically symmetrical systems. In the first case, we consider Wolf’s formula forintegrated flux in a circular region following diffraction of light from a point source by a circular aperture or acircular lens. Although the formula involves a double sum, we evaluate it with the effort of a single sum by use offast Fourier transforms (FFTs) to perform convolutions. In the second case, we exploit properties of the Fresnel-Kirchhoff propagator in the Gaussian, paraxial optics approximation to achieve the propagation of a partial wavefrom one optical element to the next. Ordinarily, this would involve a double loop over the radial variables on eachelement, but we have reduced the computational cost by a factor approximately equal to the smaller number ofradius values. In the third case, we reduce the number of partial waves, for which the propagation needs to becalculated, in order to determine the throughput of an optical system of interest in radiometry when at least oneelement is very small, such as a pinhole aperture. As a demonstration of the benefits of the second case, we analyzeintricate diffraction effects that occur in a satellite-based solar radiometry instrument.

Scattering phase function depolarization parameter model and its application to water droplets sizing using off-axis lidar measurements at multiple angles

Gilles Roy, Grégoire Tremblay, and Xiaoying Cao

Doc ID: 305547 Received 24 Aug 2017; Accepted 27 Dec 2017; Posted 05 Jan 2018  View: PDF

Abstract: The backscattering lidar depolarization parameter D of water droplets contains information on their size that can be directly modelled as a function of the forward scattering diffraction peak. Using a polarimetric Monte Carlo simulator, water clouds having different extinctions and droplet size distributions are analyzed to estimate their depolarization parameter at various backscattering off-axis angles. It is shown that depolarization parameter of the polarimetric phase function can be found using off-axis lidar measurements at multiple angles, and that it could be used to estimate the water cloud droplets size.

Ultra-widely tunable mid-infrared (6–18 μm) optical vortex source

Shungo Araki, Kana Ando, Katsuhiko Miyamoto, and Takashige Omatsu

Doc ID: 313427 Received 14 Nov 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: We demonstrate the generation of an ultra-widely tunable mid-infrared (6–18 μm) optical vortex output with amoderate pulse energy from a AgGaSe2 difference frequency generator pumped by an optical vortex parametricoscillator. The handedness of the vortex output can be controlled/selected by swapping the lasing frequencies ofthe signal and idler outputs and rotating the AgGaSe2 crystal by 90 degrees.

A high-sensitivity optical fiber relative humidity probe with the temperature calibration ability

Lei Liang, Hao Sun, nan liu, Hao Luo, Tingting Gang, Qiangzhou Rong, Xue-Guang Qiao, and Manli Hu

Doc ID: 309360 Received 18 Oct 2017; Accepted 27 Dec 2017; Posted 05 Jan 2018  View: PDF

Abstract: A high-sensitivity optical fiber relative humidity (RH)sensing probe with the ability of temperature calibration isproposed and experimentally demonstrated, which consists of a simple Fabry-Perot interferometer (FPI)constructed by coating a layer of thin polyimide (PI) film on the end face of single-mode fiber (SMF) and anupstream fiber Bragg grating (FBG). The polyimide is one of organic polymer humidity-sensitive materials with thegood comprehensive properties. The cascaded FBG is used for temperature calibration and eliminate thetemperature cross-sensitivity in the process of measuring RH. Experimental results show that this sensing probecan realize simultaneous measurement of temperature and RH. The RH response sensitivity reaches up to 986.25pm/%RH. This sensing probe with the advantages of simple structure, compact size, high sensitivity, easy topackaging and dual-parameter measurement has an extensive application prospect.

Theoretical and experimental evaluation of piezo-opticparameters and photoelastic constant in TetragonalPWO

Pier Paolo Natali, Luigi Montalto, Fabrizio Davi, Paolo Mengucci, Andrea Ciriaco, Nicola Paone, and Daniele Rinaldi

Doc ID: 312267 Received 30 Oct 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: The tetragonal PbWO4 (PWO) is one of the most important scintillating crystals, being used both intoCMS at CERN and in the PANDA project at FAIR. Light yield and other relevant scintillation propertiesdepend, among many factors, also on the crystal mechanical quality. Accordingly, a detailed knowledgeof crystal piezo-optic properties is a mandatory step towards understanding its the elasto-optic behaviourand to perform crystal quality control. In this paper we evaluatefor the first time, by means of both fromphotoelastic and X-ray measurements, some components of the piezo-optic tensor; moreover, when thecrystal is acted upon by an uniaxial stress, we obtain an evaluation for angle of rotation angle of the opticplane under stress as well as the photoelastic constant. These parameters are necessary in order to detectthe residual stresses within the crystal, if any, and to give an overall quality measure. Such a methodologyis in general suitable for any tetragonal crystals.

Polarization independent directional coupler and polarization beam splitter based on asymmetric cross slot waveguides

limin chang, Lei Liu, Yuanhao Gong, Manqing Tan, yude yu, and Zhi-Yong Li

Doc ID: 309826 Received 25 Oct 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: The polarization dependence of directional coupler (DC) based on asymmetric cross slot waveguides isinvestigated. Due to structural birefringence, the coupling behaviors of the quasi-TE and quasi-TM mode in the DCvary with the waveguide geometry. A polarization independent directional coupler (PIDC) and a polarization beamsplitter (PBS) are proposed by tailoring the ratio of the coupling length for quasi-TE and quasi-TM mode. Thesimulated results show that the coupling lengths of the designed PIDC and PBS are 8 μm and 28.25 μm,respectively. Both the PIDC and PBS show an insertion loss (IL) < 0.7 dB on a bandwidth over 100 nm. Theextinction ratios (ER) are ~20 dB for PIDC and ~14 dB for PBS. The fabrication-error tolerance of the practicaldevices is also discussed. In this study we employ a commercial software tool for Finite Difference Eigenmodemethod (FDE) and three-dimensional Finite Difference Time Domain method (FDTD) to perform the numericalsimulations.

A Python-Based Dynamic Scheduling Assistant forAtmospheric Measurements by Bruker InstrumentsUsing OPUS

Alexander Geddes, John Robinson, and Dan Smale

Doc ID: 308633 Received 05 Oct 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: Atmospheric remote sensing by instruments suchas spectrometers and interferometers often requiresscheduling that is dependent on external factors, forexample; time and solar (or lunar) zenith angle. Suchinstruments manufactured by Bruker often use thesoftware package OPUS, which, while useful, is notflexible enough for automatic, repeated, atmosphericmeasurements of this nature. In this brief articlewe describe ASAP, a Python tool developed to runour network of Fourier Transform Interferometers inNew Zealand and Antarctica. It allows the automatedscheduling of measurements by time, lunar or solarzenith angle while accounting for weather or other externalparameters. There is a wide range of useful functions,all packaged in a simple graphical user interfaceand is available on request.

A geometric approach to the alignment of sensor arrays in optical instruments

Travis Sawyer

Doc ID: 308902 Received 16 Oct 2017; Accepted 27 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: Alignment of sensor arrays in optical instruments is critical to maximize the instrument's performance. While many commercial systems use standardized mounting threads for alignment, custom systems require specialized equipment and alignment procedures. These alignment procedures can be time-consuming, dependent on operator experience, and have low repeatability. Furthermore, each alignment solution must be considered on a case-by-case basis, leading to additional time and resource cost. Here I present a method to align a sensor array using geometric analysis. By imaging a grid pattern of dots, I show that it is possible to calculate the misalignment for a sensor in five degrees of freedom simultaneously. I first test the approach by simulating different cases of misalignment using Zemax before applying the method to experimentally acquired data of sensor misalignment for an echelle spectrograph. The results show that the algorithm effectively quantifies misalignment in five degrees of freedom for an imaging system, accurate to within ± 0.871 deg in rotation and ± 0.857 μm in translation. Furthermore, the results suggest that the method can also be applied to non-imaging systems with a small penalty to precision. This general approach can potentially improve the alignment of sensor arrays in custom instruments by offering an accurate, quantitative approach to calculating misalignment in five degrees of freedom simultaneously.

Plasmonic enhancement of mid- and far-infraredacousto-optic interaction [invited]


Doc ID: 312500 Received 02 Nov 2017; Accepted 26 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: We present a concept of acousto-optical device with plasmonic efficiency enhancement at 10.6 μm wavelength.Interaction of light, Rayleigh surface acoustic wave and surface plasmon-polariton excited via prism coupling usingOtto geometry enhances the diffraction efficiency. In the case of Otto geometry the surface acoustic wave affectsboth refraction index of the optical medium and the air gap thickness between the prism and the metal.Dependencies of reflective coefficient of prism-air-metal system on gap thickness and dielectric permittivitymodulation were analyzed. The analytical results were confirmed by experimental measurements of angularspectrum of the reflected beam.

Finding trap stiffness of optical tweezers using digital filters

Pedro Almendarez-Rangel, Beatriz Morales-Cruzado, Erick Sarmiento-Gomez, and Francisco Pérez Gutiérrez

Doc ID: 313305 Received 28 Nov 2017; Accepted 26 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: Obtaining trap stiffness and calibration of the position detection system is the basis of a force measurement using optical tweezers. Both calibration quantities can be calculated using several experimental methods available in the literature. In most cases, stiffness determination and detection system calibration are performed separately, often requiring procedures in very different conditions, and thus confidence of calibration methods is not assured due to possible changes in the environment. In this work, a new method to simultaneously obtain both the detection system calibration and trap stiffness is presented. The method is based on the calculation of the Power Spectral Density of positions through digital filters to obtain the harmonic contributions of the position signal. This method has the advantage of calculating both trap stiffness and photo detector calibration factor from the same dataset in situ. It also provides a direct method to avoid unwanted frequencies that could greatly affect calibration procedure, such as electric noise, for example.

2D Mono detection spatially super-resolvedmicrowave imaging for Radar applications

Isahar Gabay, Amir Shemer, Ariel Schwartz, and Zeev Zalevsky

Doc ID: 306384 Received 06 Sep 2017; Accepted 26 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: In this paper we present an advanced 2D novel microwave photonic approach to super resolved Radar imaging.Unlike synthetic aperture Radar that require movement to improve resolution by synthetically increasing theantennas dimensions, our super resolved imaging solution not only does not require movement to syntheticallyincrease the antennas dimensions but it also allows this super resolved sensing with only a single (mono) detector.The operation principle is based upon phased array antennas which consist of four radiating horn antennas whichgenerate a projected plane at the far field zone. Setting an appropriate phase to each one of the antennas inputs,causes scanning of projected structured electromagnetic beam over the imaged object. Summing each azimuth cutof the reflections, received from the object at different frequencies can spatially reconstruct high resolution imageof the object despite the fact that the receiving was done with small size antenna and only with a mono detector.Following several CST simulations, experiments and Matlab code based simulations, we are able to demonstratereconstruction results having satisfying resolution enhancement factor.

Dynamic microscopic 3D shape measurement based on marker embedded Fourier transform profilometry

Yan Hu, Qian Chen, Yuzhen Zhang, Shijie Feng, Tianyang Tao, Hui Li, Yin Wei, and Chao Zuo

Doc ID: 300792 Received 23 Jun 2017; Accepted 26 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: In recent years, fringe projection profilometry (FPP) has become an established and increasingly efficient method for dynamic microscopic three dimensional (3D) measurement in many fields, such as on-line inspection and quality control, etc. When applying FPP in high speed 3D measurement, the number of projected patterns should be as few as possible to minimize the sensitivity to motion. The commonly used phase-shifting method needs at least three images to acquire the wrapped phase, which is very dependent on a fast hardware to decrease the sensitivity to motion. Fourier transform profilometry (FTP) can retrieve 3D information using only one fringe image, which is very suitable for dynamic 3D measurement. In this paper, a marker embedded Fourier transform method is proposed to realize dynamic microscopic 3D shape measurement based on a stereomicroscope. We embed two specially designed markers in the projected patterns at different positions to help calculate the fringe orders. The inter-frame phase deviation is also referred to improve the accuracy rate of absolute phase retrieval. Experiments on both static and dynamic scenes are performed, verifying that our method can achieve a robust measurement of a vibrating diaphragm at the speed of 200 frames per second.

The giant Goos–Hӓnchen shift in two different enantiomers chiral molecules via quantum coherence

Rajab Nasehi and Mohammad Mahmoudi

Doc ID: 302077 Received 18 Jul 2017; Accepted 25 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: The GH shifts in the reflected and transmitted probe light through a cavity mixture of left-handed and right-handedchiral molecules into two enantiomer states are investigated. Due to broken mirror symmetric of the left- andright- handed chiral molecules in presence of cyclic population transfer, such the quantum systems can beselectively excited because of the coexistence of one- and two-photon transitions. With the help of coupling Rabifrequencyand damping effects due to scattering processes, the generated GH shifts accompany by simultaneouslynegative and positive lateral shift in reflected and transmitted probe lights are realized to be greatly enhanced. It isfound that the large negative and positive GH shifts are available in the presence of multi-photon resonance andoff-resonance conditions for two different enantiomers chiral molecules. Moreover, the switching betweensuperluminal and subluminal light propagation are extremely dependence to choose the left- and right-handedchiral molecules. Furthermore, the effects of pulse shape and mode of Laguerre-Gaussian probe light on the GHshifts leads to switch between negative and positive shift are also studied. The negative and positive GH shifts inreflected and transmitted probe beam for an incident Gaussian and different mode of Laguerre-Gaussian shapedbeam are also discussed with various widths by use of two different enantiomer chiral molecules.

Time-domain fluorescence lifetime imaging bynonlinear fluorescence microscopy constructed ofpump-probe setup with two-wavelength laser pulses

Fumihiro Dake and Yusuke Taki

Doc ID: 306993 Received 10 Oct 2017; Accepted 25 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: We propose a time-domain approach for fluorescence lifetime measurements using nonlinear fluorescencemicroscopy constructed of a pump-probe setup with two-wavelength laser pulses. Nonlinear fluorescence signalsgenerated by fluorescence reduction due to stimulated emission were detectable through a lock-in technique.Changing the time delay between the two-wavelength pulses enables acquisition of a time-resolved nonlinearfluorescence signal, which directly reflects the fluorescence lifetime of the sample and is thus applicable tofluorescence lifetime imaging. We also quantitatively demonstrate that nonlinear fluorescence microscopypossesses better optical resolution than conventional laser-scanning fluorescence microscopy. Experimental trialsindicate that straightforward fluorescence lifetime imaging with high optical resolution is readily available.

Broadband self-collimating phenomenon in low losshybrid plasmonic photonic crystal

Lingxuan Zhang, Wenfu Zhang, Guoxi Wang, zhongyu li, Shujian Du, Weiqiang Wang, Leiran Wang, Qibing Sun, and Wei Zhao

Doc ID: 307307 Received 18 Sep 2017; Accepted 25 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: A 2D planar self-collimating photonic crystal, based on dielectric square lattice and hexagonal lattice, isproposed. We demonstrate that the proposed structure can support the propagation of hybrid surface plasmonpolarition (SPP) mode with the loss of -0.017 dB/μm, and the mode size is only 0.33μm. The defined FOM is oneorder of magnitude higher than that of the dielectric-metal structure. In addition, the self-collimating angle of morethan 10° can be tuned with the silica index change of 0.08. The proposed structure possesses broad operationbandwidth of 88nm and 58nm for dielectric square lattice and hexagonal lattice, respectively. These two kinds ofPhCs promise potential applications in photonic modulator and SPP photonic device.

Closed-loop laser polishing using in-process surface finish metrology

Oliver Faehnle, rolf rascher, Christian Vogt, and Dae Wook Kim

Doc ID: 308466 Received 03 Oct 2017; Accepted 25 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: This paper lays out the trail onto a closed-loop polishing process of optical elements enabling the application of the optimum polishing time needed. To that aim, an in-process testing method for monitoring an inclusive micro surface quality (e.g., comprising surface roughness and scratch-and-dig) within the polishing spot is analyzed and its applicability to closed-loop polishing for classical loose-abrasive full-aperture polishing as well as for computer controlled laser polishing is experimentally tested and verified. This enables the determination of the optimum local dwell time resulting in a stable and cost optimized polishing.

Focus detection by shearing interference of vortexbeams for non-imaging systemssystems

Xiongfeng Li, Shichao Zhan, and Yiyong Liang

Doc ID: 306905 Received 15 Sep 2017; Accepted 25 Dec 2017; Posted 05 Jan 2018  View: PDF

Abstract: In focus detection of non-imaging systems, the common image-based methods are not available. Also, interferencetechniques are seldom used because only the degree but hardly the direction of defocus can be derived from thefringe spacing. In this paper, we propose a vortex-beam-based shearing interference system to do focus detectionfor a focused laser direct-writing system where a vortex beam is already involved. Both simulated andexperimental results show that fork-like features are added in the interference patterns due to the existence of anoptical vortex, which makes it possible to distinguish the degree and direction of defocus simultaneously. Thetheoretical fringe spacing and resolution of this method are derived. A resolution of 0.79 μm can be achieved underthe experimental combination of parameters and it can be further improved with the help of image processingalgorithm and closed-loop controlling in the future. Finally, the influence of incomplete collimation and wedgeangle of the shear plate is discussed. This focus detection approach is extremely appropriate for those non-imagingsystems containing one or more focused vortex beams.

Tunable plasmon-induced transparency in H-shaped Dirac semimetalmetamaterial

Huan Chen, huiyun zhang, XiaoHan Guo, shande Liu, and Yuping Zhang

Doc ID: 309317 Received 18 Oct 2017; Accepted 25 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: We present a numerical and theoretical study on the realization of tunable plasmon-induced transparency (PIT) effect at terahertz frequencies inDirac semimetal (known as “three-dimensional graphene”) metamaterials. Simulations reveal that the PIT effect is generated by electric fieldtransferred from the central strip to side strips due to the structural symmetry breaking. The most prominent feature is that the plasmonic resonancein Dirac semimetals can be actively tuned by changing the Fermi energy and an ultrahigh group delay of about 6.81ps is obtained in our proposeddesign. Our study can provide guidance for various THz devices in practical applications.

A Zeonex based asymmetrical terahertz photoniccrystal fiber for multichannel communication andpolarization maintaining applications

Mr. Islam, Jakeya Sultana, Alex Dinovitser, BRIAN W.-H. NG, and Derek Abbott

Doc ID: 313178 Received 10 Nov 2017; Accepted 24 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: We report on the design, in-depth analysis and characterization of a novel elliptical array shaped corerectangular shaped cladded photonic crystal fiber (PCF) for multichannel communication and polarizationmaintaining applications of terahertz waves. The asymmetrical structure of air holes both in coreand cladding results in increased birefringence, a compact geometry and different cladding air hole sizemakes the dispersion characteristic flat. The modal characteristics of the PCF are calculated using a FiniteElement Method (FEM). The simulated results show a near-zero dispersion flattened property of0.02 ps/THz/cm, high birefringence of 0.063, low effective material loss (EML) of 0.06 cm􀀀1, and negligibleconfinement loss of 5.45 10􀀀13 cm􀀀1 in the terahertz frequency range. Additionally, the core powerfraction, effective area, physical attributes and potential fabrication possibilities of the fiber is discussed.

A hybrid quantum receiver for QAM coherent-state discrimination beating the classical limit

Tian Chen, Ke Li, Yuan Zuo, and Bing Zhu

Doc ID: 308246 Received 03 Oct 2017; Accepted 24 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: We present a quantum receiver for quadrature amplitude modulation (QAM) coherent-state discrimination with the homodyne-displacement hybrid structure. Our strategy is to carry out two successive measurements on parts of the quantum states. The homodyne result of the first measurement reveals partial information about the state and is forward to a displacement receiver, which finally identifies the input state by using feedback to adjust a reference field. Theoretical analysis and numerical simulation results show that for 16-QAM, the hybrid receiver could outperform the standard quantum limit (SQL) only using on-off single photon detectors with a reduced number of code-word interval partitions, which shows great potential toward implementing the receiver practically.

A kinematic model for material removal distribution and surface figure in the full-aperture polishing

defeng liao, Lele Ren, Feihu Zhang, jian wang, and Qiao Xu

Doc ID: 306798 Received 11 Sep 2017; Accepted 23 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: Full-aperture polishing is a significant process for fabricating large ultra-precision optic flats. Surface figure is one of the key specifications required of the optic flats, which is determined by the material removal distribution during polishing. To date, the most frequently referred Preston Equation only provides a solution for qualitative calculation of material removal of a single point on the optic surface. In this study, we present a kinematic model for deterministic calculation of the removal amount at every local optic position. The model is based on the sliding track of each local optic position on the lap, and it incorporates local pressure and most key kinematic parameters and considers the effect of the lap grooves. With the model, we analyzed the impacts of various kinematic parameters and grooves features on the distribution of the removal amount in terms of sliding distance, assuming a uniform pressure distribution at the lap/optic interface. Several polishing experiments have been carried out, in which the model is validated.

Light propagation in ordered and disordered opticalwaveguide arrays with a transverse loss gradient

Abbas Ghasempour Ardakani

Doc ID: 312623 Received 03 Nov 2017; Accepted 23 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: We first investigate the propagation of an initially localized optical beam trough an ordered waveguide array inwhich the real part of refractive index of all waveguides is the same while there is a linear gradient loss along thetransverse direction x. When the optical loss is an increasing function of x, the beam injected into every point of thearray propagates to the left edge of the array. But for the case at which optical loss is a decreasing function of x, theoptical beam propagates to the right edge of array. In both cases, as the beam reaches the array edge, it is firstreflected by the edge due to the presence of a repulsive potential near the array boundary and then its widthremains constant. We next study the wave propagation through a disordered array of waveguides in which the realparts of refractive indices of waveguides are random numbers and there exists a transverse loss gradient. Fordifferent random realizations with the same disorder level, when the beam is injected into the central waveguide,the beam becomes localized near the array edge with the lower loss.

Investigation of pressure-dependent refractive index ofgermanium film with an optical fiber-film sensor

Dongxu Yuan, Yun Gao, Hao Chen, and Min Li

Doc ID: 312448 Received 31 Oct 2017; Accepted 23 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: The refractive index of Ge is found decline with the applied pressure at a specific wavelength in the absorptionregion below 1900nm, where the absorption coefficient rises dramatically with decreased wavelength. Wedemonstrate quantitatively using a Ge-coated fiber optic probe in this paper that the downward trend in therefractive index to increasing pressure matches the theoretically simulated optical properties of Ge with ameasurement error of 1.03×10-3 in refractive index, which further calculated within the framework of densityfunctional theory with local density approximation (DFT-LDA). For the first time, both theoretical and experimentresults prove that the refractive index reduces linearly with a gradient of -3.30×10-4/MPa as the pressure increasesfrom 0 to 20MPa.

Telescope based cavity for negative ion beam neutralization in future fusion reactors

Donatella Fiorucci, ALI HREIBI, and Walid Chaibi

Doc ID: 309146 Received 17 Oct 2017; Accepted 22 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: In future fusion reactors, heating systems efficiency is of the utmost importance. Photo-neutralizationsubstantially increases the Neutral Beam Injector (NBI) efficiency with respect to the foreseen system inthe International Thermonuclear Experimental Reactor (ITER) based on gaseous target .In this paper, wepropose a telescope based configuration to be used in the NBI photo-neutralizer cavity of the DEMOnstrationPower Plant (DEMO) project. This configuration greatly reduces the total length of the cavity whichlikely solves overcrowding issues in a fusion reactor environment. Brought to a tabletop experiment, thiscavity configuration is tested : a 4 mm beam width is obtained within a ' 1.5m length cavity. The equivalentcavity g factor is measured to be 0.038(3) thus confirming the cavity stability

High accuracy vibration sensor based on a Fabry-Perotinterferometer with active phase tracking technology

Wei Xia, Chuncheng Li, Hui Hao, Yiping Wang, Xiaoqi Ni, Dongmei Guo, and Ming Wang

Doc ID: 313153 Received 09 Nov 2017; Accepted 22 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: A novel position sensitive Fabry-Perot interferometer was constructed with direct phase modulation by a built-inelectro-optic modulator. Pure sinusoidal phase modulation of the light was produced and the first harmonic of theinterference signal was extracted to dynamically maintain the interferometer phase to the most sensitive point ofthe interferogram. Therefore, the minute vibration of the object was coded on the variation of the interferencesignal and could be directly retrieved by the output voltage of a photo-detector. The operating principle and thesignal processing method for active feedback control of the interference phase have been demonstrated in detail.The developed vibration sensor was calibrated through a high precision piezo-electric transducer and tested by anano-positioning stage under vibration magnitude of 60 nm and frequency of 300 Hz. The active phase trackingmethod of the system provides high immunity against environmental disturbances. Experimental results show thatthe proposed interferometer can effectively reconstruct tiny vibration waveform with sub-nanometer resolution,paving the way for high accuracy vibration sensing especially for MEMS/NEMS and ultrasonic devices.

Study of the spectral bandwidth of a double-pass acousto-optic system [Invited]

Justine Champagne, Jean-Claude Kastelik, Samuel Dupont, and Joseph Gazalet

Doc ID: 309899 Received 27 Oct 2017; Accepted 22 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: Acousto-optic tunable filters are known as efficient instruments for spectral and spatial filtering of light. In this paper, we analyze the bandwidth dependence of a double pass filter. The interaction geometry chosen allows the simultaneous diffraction of the ordinary and the extraordinary optical modes by a single ultrasonic frequency. We present the main parameters of a custom device (design, optical range, driving frequency) and experimental results concerning the angular deviation of the beams including the effect of optical birefringence. The spectral resolution and the side lobes significance are discussed. Spectral bandwidth of such a system is analyzed.

Optimized digital speckle patterns for digital imagecorrelation by consideration of both accuracy andefficiency

Zhenning Chen, Xinxing Shao, Xiaoyuan He, and xiangyang Xu

Doc ID: 309050 Received 19 Oct 2017; Accepted 21 Dec 2017; Posted 02 Jan 2018  View: PDF

Abstract: The technique of digital image correlation (DIC), which has been widely used for non-contact deformationmeasurement in both the scientific and engineering fields, is greatly affected by the quality of speckle patterns interms of its performance. This study was concerned with the optimization of the digital speckle pattern (DSP) forDIC in consideration of both the accuracy and efficiency. The root-mean-square error (RMSE) of the inversecompositional Gauss-Newton (IC-GN) algorithm and the average number of iterations were used as quality metrics.Moreover, the influence of subset sizes and the noise level of images, which are the basic parameters in the qualityassessment formulations, were also considered. The simulated binary speckle patterns were first compared withthe Gaussian speckle patterns and captured DSPs. Both the single-radius (1-R) and multi-radius (multi-R) DSPswere optimized. Experimental tests and analyses were conducted to obtain the optimized and recommended DSP.The vector diagram of the optimized speckle pattern was also uploaded as reference.

Fiber-coupled ultrashort-pulse-laser-based electronic-excitation tagging velocimetry

Paul Hsu, Naibo Jiang, Paul Danehy, James Gord, and Sukesh Roy

Doc ID: 309694 Received 23 Oct 2017; Accepted 21 Dec 2017; Posted 21 Dec 2017  View: PDF

Abstract: Transmission of intense ultrashort laser pulses through hollow-core fibers (HCFs) is investigated for molecular-tagging velocimetry. A low-vacuumed HCF beam-delivery system is developed to transmit high-peak-power pulses. Vacuum pressure effects on transmission efficiency and nonlinear effects at the fiber output are studied for 100-ps and 100-fs laser beams. With a 0.1 bar vacuum in the fiber, transmission efficiency increases by ~30%, while spectral broadening is reduced. A 1-m-long, 1-mm-core metal-dielectric-coated HCF can transmit ~45 mJ/pulse and ~2.9 mJ/pulse for 100-ps laser pulses (at 532 nm) and 100-fs laser pulses (at 810 nm), respectively. Proof-of-principle, single-laser-shot, fiber-coupled, ps- and fs-laser-based, nitrogen electronic-excitation tagging velocimetry is demonstrated in a free jet. Flow velocities are measured at 200 kHz to capture high-frequency flow events.

Backscatter signal in underwater lidars: temporal and frequency features

Alexander Luchinin, Mikhail Kirillin, and Lev Dolin

Doc ID: 314293 Received 24 Nov 2017; Accepted 21 Dec 2017; Posted 22 Dec 2017  View: PDF

Abstract: Formation of backscatter signal in underwater lidar systems is studied and its temporal and frequency characteristics are analyzed using Monte Carlo technique. Both frequency and phase response of the backscattered signal demonstrate similar dependencies showing stronger frequency dependence in high-frequency range. The beats of the frequency response due to dephasing of corresponding spectral harmonics are shown in the high-frequency range. Results of Monte Carlo simulations of the backscattered signal are in good agreement with the approximate analytical expression derived in the small-angle approximation, however, frequency responses calculated by Monte Carlo technique and by small-angle approximation demonstrate difference in the high-frequency range due to interference effects while phase response demonstrated good agreement in the entire frequency range.

A multi-aperture laser transmissometer system for long-path aerosol extinction rate measurement

Chensheng Wu, John Rzasa, Jonathan Ko, Daniel Paulson, JOSEPH COFFARO, Jonathan Spychalsky, ROBERT CRABBS, and Christopher Davis

Doc ID: 312728 Received 03 Nov 2017; Accepted 20 Dec 2017; Posted 21 Dec 2017  View: PDF

Abstract: We present the theory, design, simulation and experimental evaluations of a new laser transmissometer system for aerosol extinction rate measurement over long paths. The transmitter emits an ON/OFF modulated Gaussian beam that doesn’t require strict collimation. The receiver uses multiple point detectors to sample the sub-aperture irradiance of the arriving beam. The sparse detector arrangement makes our transmissometer system immune to turbulence induced beam distortion and beam wander caused by the atmospheric channel. Turbulence effects often cause spatial discrepancies in beam propagation and lead to miscalculation of true power loss when using the conventional approach of measuring the total beam power directly with a large aperture optical concentrator. Our transmissometer system, on the other hand, combines the readouts from distributed detectors to rule out turbulence induced temporal power fluctuations. As a result, we show through both simulation and field experiments that our transmissometer systems works accurately with turbulence strength C_n^2 up to 10-12 m-2/3 over a typical 1.0 km atmospheric channel. In application, our turbulence and weather resistant laser transmissometer system has significant advantages for the measurement and study of aerosol concentration, absorption and scattering properties, which are crucial for directed energy (DE) systems, ground level free space optical (FSO) communication systems, environmental monitoring, and weather forecasting.

Slow light propagation in an Er3+-doped optical fiber with dual - frequency laser pumping

Wei Qiu, jianjun liu, Yuda Wang, yujing yang, and Yuan Gao

Doc ID: 309007 Received 13 Oct 2017; Accepted 20 Dec 2017; Posted 21 Dec 2017  View: PDF

Abstract: In this paper, a general theory of coherent population oscillation effect in an Er3+ -doped fiber under the dual - frequency pumping laser with the two directions and the same direction at room temperature is presented. Using the numerical simulation, in case of dual frequency light waves (1480nm and 980nm) with the same direction and the opposite directions, we analyze the effect of the pump optical power ratio (M) on the group speed of light. The group velocity of light can be varied with the change of M. We research the time delay and fractional delay in an Er3+ -doped fiber under the dual - frequency pumping laser with the two-directions and the same directions. Moreover, we compare slow light propagation with the single-pumping light and the slow light propagation with dual pump light in the same direction or the two directions at room temperature. We conclude that the larger time delay can be got by using the technique of dual - frequency laser pumped fiber with the opposite directions.

Coherent Anti-Stokes Raman Scattering (CARS) under frequency comb excitation

Alexey Shchekin, Sergey Koptyaev, Maxim Ryabko, Anton Medvedev, Alexey Lantsov, Hong-Seok Lee, and Young-Geun Roh

Doc ID: 312668 Received 07 Nov 2017; Accepted 19 Dec 2017; Posted 21 Dec 2017  View: PDF

Abstract: We study the efficiency of Coherent Anti-Stokes Raman scattering (CARS) under frequency comb excitation.We calculate the power density of anti-Stokes signal for two major cases: 1) molecular excitationby frequency comb and cw probe, 2) both excitation and probing by frequency combs. In the first caseaverage CARS power varies as an inverse third degree of frequency combs free spectral range (FSR􀀀3),in the second case it varies as FSR􀀀5. These results were applied to CARS on blood glucose under frequencycomb excitation. It was found that the resulting glucose CARS signal could approach nano-watt(nW) level at FSR = 10 GHz.

Passively Q-switched Yb:YAG laser base on MoSe2 saturable absorber

Jiasai Ma, wenguagn jiang, chuanhe shen, and shanfu yuan

Doc ID: 313803 Received 17 Nov 2017; Accepted 19 Dec 2017; Posted 19 Dec 2017  View: PDF

Abstract: MoSe2 nanosheets based saturable absorber (SA) was fabricated successfully by liquid-phase exfoliation (LPE) method. A passively Q-switched crystalline Yb:YAG laser was realized with the MoSe2-SA inserted inside the cavity. The shortest pulses at a wavelength of 1049 nm with a duration of 250 ns, maximum repetition rate of 181 kHz and an average output power of 158 mW were emitted, corresponding to a maximum pulse energy of 0.87 μJ. To the best of our knowledge, this is the first experimental demonstration of nonlinear absorption property of MoSe2 nanoplatlets in a crystalline Yb-doped solid-state laser, which also proves the great potential of MoSe2-SA as optical modulator in 1 μm spectral region.

Statistical and temporal irradiance fluctuations modeling for ground to geostationary satellite optical link

Adrien-Richard Camboulives, Marie-Thérèse Velluet, Sylvain Poulenard, Laurent Saint-Antonin, and Vincent Michau

Doc ID: 305508 Received 18 Sep 2017; Accepted 19 Dec 2017; Posted 20 Dec 2017  View: PDF

Abstract: An optical communication link performance between the ground and a geostationary satellite can be impaired by scintillation, beam wandering and beam spreading due to its propagation through atmospheric turbulence. These effects on the link performance can be mitigated by tracking and error correction codes coupled with interleaving. Precise numerical tools capable of describing the irradiance fluctuations statistically and of creating irradiance time series are needed to characterize the benefits of these techniques and optimize them. The wave optics propagation method have proven their capability of modeling the effects of atmospheric turbulence on a beam but it is known to be computationally intensive. We present an analytical-numerical model that provides good results on the probability density functions of irradiance fluctuations as well as time series with an important saving of time and computational resources.

No-Reference HDR Image Quality Assessment based on Tensor Decomposition and Manifold Learning

Feifan Guan, Gangyi Jiang, Yang Song, Mei Yu, Zongju Peng, and Fen Chen

Doc ID: 306237 Received 18 Sep 2017; Accepted 19 Dec 2017; Posted 20 Dec 2017  View: PDF

Abstract: The practical applications of the full-reference image quality assessment (IQA) method are limited. Here we propose a new no-reference quality assessment method for high-dynamic-range (HDR) images. First, the tensor decomposition is used to generate three feature maps of a HDR image, considering color and structure information of the HDR image. Second, for a given HDR image, its first feature map contains its main energy and important structural feature information; thus, manifold learning can be used in the first feature map to find the inherent geometric structure of high-dimensional data in a low-dimensional manifold. In addition, the corresponding multi-scale manifold structure features are extracted from the first feature map. For the second and third feature maps of the HDR image, multi-scale contrast features are extracted as they reflect the perceived detail contrast information of the HDR image. Finally, the extracted features are aggregated by support vector regression to obtain the objective quality prediction score of the HDR image. Experimental results show that the proposed method is superior to some representative full and no-reference methods, and even superior to the full-reference HDR IQA method, HDR-VDP-2.2, on the Nantes database. The proposed method has a higher consistency with human visual perception.

Analytical approach of Brillouin Amplification over threshold

Fikri Gokhan, Hasan GÖKTAŞ, and Volker Sorger

Doc ID: 308231 Received 29 Sep 2017; Accepted 19 Dec 2017; Posted 20 Dec 2017  View: PDF

Abstract: We report on an accurate closed-form analytical model for the gain of a Brillouin fiber amplifier that accounts for material loss in the depleted pump regime. We determined the operational model limits with respect to its relevant parameters and pump regimes through both numerical and experimental validation. As such, our results enable accurate performance prediction of Brillouin fiber amplifiers operating in the weak pump, high–gain, and saturation regimes alike.

Influence of absorption on the refractive index determination accuracy by minimum deviation method

Victor Plotnichenko and Vyacheslav Sokolov

Doc ID: 312851 Received 07 Nov 2017; Accepted 19 Dec 2017; Posted 20 Dec 2017  View: PDF

Abstract: By means of computer simulation, the influence of absorption index, κ, on accuracy of determining the refractive index, n, of optical materials by minimum deviation method (prism method) is studied at different measuring angular accuracy from 5" to 0.1". The n values within 1.0-4.0 and κ values within 0-0.1 are considered.It is shown that 1) except for the far IR region, the error in determining n by formula (1) commonly used in minimum deviation method, i.e. neglecting absorption, is less than the error due to the accuracy of measuring the prism and minimum deviation angles; 2) the difference between n values calculated with and without absorption taken into consideration is, in most cases, negligible throughout the optical range; 3) however, the total error in determination of n is higher when absorption is taken into account than that in the case when absorption is neglected. The further increase in accuracy of measuring the angles and sensitivity of radiation detectors, the proposed calculation technique will allow to optimize the prism angle value and to calculate more correctly the values of n and error in its determination.

Quantitative detection of oxygen in reduced graphene oxide by femtosecond laser-induced breakdown spectroscopy

Bo Yang, Lan Jiang, Sumei Wang, Peng Wang, Fan Yang, and Yongfeng Lu

Doc ID: 308640 Received 05 Oct 2017; Accepted 19 Dec 2017; Posted 17 Jan 2018  View: PDF

Abstract: This paper proposes a simple, visual, and instant method for the quantitative detection of oxygen in reduced graphene oxide (r-GO) by femtosecond laser-induced breakdown spectroscopy (fs-LIBS). Firstly, graphene oxide was reduced by continuous wave (CW) laser beams with different powers; subsequently, the oxygen content in the r-GO was detected through intensity of oxygen obtained by fs-LIBS. The fit of the observed data and errors by LIBS were compared with the results of X-ray photoelectron spectroscopy and the curves were almost anastomotic; it was evident that fs-LIBS realized online testing and quantitative analysis of the reduction degree. The method provides a convenient and time-efficient way for detecting the reduction degree of r-GO and can extend the applications of r-GO with different reduction degrees.

Evaluation on the communication quality of free-space laser communication based on the power-in-the-bucket method

Xianghui Yin, Rui Wang, shaoxin wang, Yukun Wang, Chengbin Jin, Zhaoliang Cao, and Xuan Li

Doc ID: 308712 Received 06 Oct 2017; Accepted 18 Dec 2017; Posted 19 Dec 2017  View: PDF

Abstract: Atmospheric turbulence seriously affects the quality of free-space laser communication. The Strehl ratio (SR) is used to evaluate the effect of atmospheric turbulence on the receiving energy of free-space laser communication systems. However, the SR method does not consider the area of the laser-receiving end face. In this study, the power-in-the-bucket (PIB) method is demonstrated to accurately evaluate the effect of turbulence on the receiving energy. A theoretical equation is first obtained to calculate PIB. Simulated and experimental validations are then performed to verify the effectiveness of the theoretical equation. This work may provide effective guidance for the design and evaluation of free-space laser communication systems.

Multiple scattering of polarized light inbirefringent slab media: experimentalverifications and simulations

Soichi Otsuki

Doc ID: 309421 Received 24 Oct 2017; Accepted 18 Dec 2017; Posted 19 Dec 2017  View: PDF

Abstract: The effective scattering Mueller matrices were measured for backward and forward scattering by shedding anarrow polarized light on a polyacrylamide slab gel, which was strained vertically to generate birefringence inside.Monte Carlo simulations were performed in the conditions as same as possible. The measured and simulatedmatrices were simplified to the reduced ones. They agreed well in both original and reduced forms. While theyapproximately take reciprocal forms for backward scattering, they approximately satisfy matrix forms thatcorrespond to a reciprocal position of the mirror image for forward scattering. The reduced matrices werefactorized by the Lu-Chipman polar decomposition to obtain the polarization parameters. The polarizationparameters were in good agreement between measurement and simulation and showed characteristic features ofanisotropic slab media with birefringence axis parallel to the slab surface.

Tunable mechanisms of quantum efficiencies in CdSe and TiO2 quantum dot solar cells

Tahseen Dakhil, Samir Abdulalmuhsin, and Amin Al-Khursan

Doc ID: 305495 Received 28 Aug 2017; Accepted 17 Dec 2017; Posted 21 Dec 2017  View: PDF

Abstract: The absorption spectra of CdSe/ZnO and TiO2/MgZnO quantum dot (QD) solar cells were calculated, then their quantum efficiency (QE) are studied at different QD sizes and junction depths. It is shown that doping the QD layer only gives high QE, as in the case of CdSe while doping bulk layer in addition to QDs gives low QE but at wide bandwidth, as in TiO2/MgZnO QD solar cells. The structures studied covers the range 120-370nm which is important in solar cell applications.

Polarizer-free two-pixel polarimetric camera by compressive sensing

Julien FADE, Estéban Perrotin, and Jerome Bobin

Doc ID: 307683 Received 27 Sep 2017; Accepted 16 Dec 2017; Posted 18 Dec 2017  View: PDF

Abstract: We propose an original concept of compressive sensing (CS) polarimetric imaging based on a digital micro-mirror (DMD) array and two single-pixel detectors and without using any polarizer. The polarimetric sensitivity of the proposed setup is due to the tiny difference in Fresnel's coefficients of reflecting mirrors which is exploited here to form an original reconstruction problem, including a CS problem and a source separation task. We show that a two-step approach tackling each problem successively is outperformed by a dedicated combined reconstruction method, which is explicited in this article and preferably implemented through a reweighted FISTA algorithm. The combined reconstruction approach is then further improved by including physical constraints specific to the polarimetric imaging context considered, which are implemented in an original constrained GFB algorithm. Numerical simulations demonstrate the efficiency of the 2-pixel CS polarimetric imaging setup to retrieve polarimetric contrast data with significant compression rate and good reconstruction quality. The influence of experimental imperfections of the DMD are also analyzed through numerical simulations, and 2D polarimetric imaging reconstruction results are finally presented.

Phase control of high efficient four-wave mixing in a six-level tripod atomic system

Hongjun Zhang, Ximei Li, Dong Sun, Huijing Li, and Sun Hui

Doc ID: 313542 Received 15 Nov 2017; Accepted 16 Dec 2017; Posted 21 Dec 2017  View: PDF

Abstract: We investigate theoretically an enhancement of four-wave mixing (FWM) process in a phase-dependent double electromagnetically induced transparency (EIT) six-level atomic media. It is shown, owing to the multiphoton destructive interference, that the conversion efficiency of FWM can be enhanced by manipulating the relative phase of the applied fields in this ultraslow propagation regime. Moreover, we also find that the conversion efficiency is amplified with the presence of the microwave field in comparison with the previous six-level scheme [Phys. Rev. A 76, 043809 (2007)].

Non-Line-of-Sight 2 x N Indoor Optical CameraCommunications

Navid Bani Hassan, Zabih Ghassemlooy, Stanislav Zvanovec, Pengfei Luo, and Hoa Le Minh

Doc ID: 306843 Received 12 Sep 2017; Accepted 10 Dec 2017; Posted 12 Dec 2017  View: PDF

Abstract: We propose, for the first time, a novel non-line-of-sight 2 N indoor optical camera communication system,where N is the number of pixels in the camera with a unique packet structure and a detection methodologyfor extracting the data from the recorded video streams. A comprehensive theoretical model for theproposed system is presented. The proposed system is experimentally investigated and the measuredresults show that higher ISO levels and exposure times led to reduced transmit power level by 3 dB forevery doubling of the exposure time and ISO at a bit error rate of 10􀀀3. It is also shown that when theoverlapping area of two interfering transmitters is larger than approximately 30% of the footprints, thedata cannot be recovered.

Multi-aperture stereo reconstruction for artificial compound eye with cross image belief propagation

Sidong Wu, Gexiang Zhang, Tao Jiang, Ming Zhu, Kechang Fu, Haina Rong, Kaiyi Xian, Hui Song, and Klaus-Dieter Kuhnert

Doc ID: 308404 Received 03 Oct 2017; Accepted 05 Dec 2017; Posted 17 Jan 2018  View: PDF

Abstract: Artificial compound eye is a new type of cameras which has miniature volume and large field-of-view (FOV). While the captured image is an array of sub-images, and each sub-image captures a part of the full FOV. To obtain a complete image with a full FOV, the reconstruction is needed. Due to the parallax between adjacent sub-images, the reconstruction of image is depth related. In this paper, to address the image reconstruction of a specific artificial compound eye - eCley, a cross image belief propagation method is proposed to estimate the depth map. Since the small size and small FOV of the sub-image lead to little contextual information for pairwise matching, the information of neighboring sub-images is integrated into the belief propagation step to propagate the message across images. Therefore, the belief propagation step is able to gather as much as information from all the sub-images to obtain an accurate depth result. As a consequence, a stereo image with the full FOV and corresponding depth map can be obtained based on the estimated depth of sub-images. Experimental results on real data show the effectiveness of the proposed method.

Real-time identifying the singleness of a trapped bead in optical tweezers

Chunguang Hu, Chen Su, Zelin Yun, Si Wang, Chingzhi He, Xiaoqing Gao, Shuai Li, Li Hongbin, Xiaodong Hu, and Xiaotang Hu

Doc ID: 304858 Received 18 Aug 2017; Accepted 01 Dec 2017; Posted 17 Jan 2018  View: PDF

Abstract: Beads trapped in optical tweezers are aligned along the optical propagation direction so that it is difficult to determine the number of beads with bright-field microscopy. This problem also dramatically influences the measurement of the optical trapping based single molecule force spectroscopy. Here, we propose a video processing approach to account the number of the trapped micro-objects in real time. It utilizes a normalized cross-correlation algorithm and image enhancement techniques to amplify a slight change of the image induced by an entry of an exotic object. As tested, this method introduces ~10% change per bead to the image similarity and up to four beads one-by-one falling into the trap are identified. Moreover, the feasibility of the above analysis in a moving trap is investigated. A movement of the trap just leads to a fluctuation of the similarity signal less than 2% and can be ignored in most cases. The experimental results prove well that image similarity measurement is a sensitive way to monitor the interruption, which is very useful especially during experiments. In addition, the approach is easy to be applied to an existing optical tweezers system.

Multilayer graphene-based metasurfaces: Robust design method for extremely broadband, wide-angle and polarization-insensitive terahertz absorbers

Mahdi Rahmanzadeh, Hamid Rajabalipanah, and Ali Abdolali

Doc ID: 297272 Received 05 Jun 2017; Accepted 28 Nov 2017; Posted 02 Jan 2018  View: PDF

Abstract: In this study, by utilizing an equivalent circuit method, a novel polarization-insensitive terahertz (THz) absorber based on multilayer graphene-based metasurfaces (MGBMs) is systematically designed, providing an extremely broad absorption bandwidth (BW). The proposed absorber is a compact-size three-layered structure, comprising square-, cross-, and circular-shaped graphene metasurfaces embedded between three separator dielectrics. The equivalent-conductivity method serves as a parameter retrieval technique to characterize the graphene metasurfaces as the components of proposed circuit model. Good agreement is observed between the full-wave simulations and the equivalent-circuit predictions. The optimum MGBM absorber exhibits >90% absorbance in an extremely broad frequency band of 0.55 to 3.12 THz (BW = 140%). The results indicate a significant BW enhancement compared with both the previous metal- and graphene-based THz absorbers, highlighting the capability of the designed MGBM absorber. To clarify the physical mechanism of absorption, the surface current and the electric-field distributions, as well as the power loss density of each graphene metasurface, are monitored and discussed. The MGBM functionality is evaluated under a wide range of incident wave angles to prove that the proposed absorber is omnidirectional and polarization-insensitive. These superior performances guarantee the applicability of the MGBM structure as an ultra-broadband absorber for various THz applications.

Single-Pulse Ablation of Multi-Depth Structures via Spatially Filtered Binary Intensity Masks

Daniel Heath, James Grant-Jacob, Robert Eason, and Benjamin Mills

Doc ID: 307609 Received 21 Sep 2017; Accepted 31 Oct 2017; Posted 12 Jan 2018  View: PDF

Abstract: Digital Micromirror Devices (DMDs) show great promise for use as intensity spatial light modulators. When used in conjunction with pulsed lasers of a timescale below the DMD pixel switching time, DMDs are generally only used as binary intensity masks (i.e. ‘on’ or ‘off’ intensity for each mask pixel). In this work, we show that by exploiting the numerical aperture of an optical system during the design of binary masks, near-continuous intensity control can be accessed, whilst still maintaining high-precision laser machining resolution. Complex features with ablation depths up to ~60 nm, corresponding to grayscale values in bitmap images, are produced in single pulses via ablation with 150 fs laser pulses on nickel substrates, with lateral resolutions of ~2.5 µm.

Dependence of depth of focus on spherical aberration of optical systems

Antonin Miks and Jiri Novak

Doc ID: 267338 Received 31 May 2016; Accepted 05 Jul 2016; Posted 06 Jul 2016  View: PDF

Abstract: This paper presents a theoretical analysis and computation of aberration coefficients of the third and fifth order of transverse spherical aberration of an optical system, which generates a ray bundle with a diameter of a geometric-optical circle of confusion smaller than a predetermined limit value. Equations were derived for the calculation of aberration coefficients of an optical system, which satisfy given conditions, and for the determination of the maximum possible depth of focus for given conditions.

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