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Accepted papers to appear in an upcoming issue

OSA now posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Fusion of infrared and visible images for night-vision context enhancement

Zhi Zhou, Ming Dong, Xiao Xie, and Zhi Gao

Doc ID: 263009 Received 11 Apr 2016; Accepted 22 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: Because of the poor lighting conditions at night time, visible images are often fused with corresponding infrared (IR) images for context enhancement of the scenes in night vision. In this paper, we present a novel context enhancement technique through visible and infrared image fusion for night vision applications with the guided filter. Firstly, to enhance the visibility of poorly illuminated details in the visible image before the fusion, an adaptive enhancement method is developed by incorporating the processes of dynamic range compression and contrast restoration based on the guided filter. Then, the important IR spectral information from the infrared image is injected into the visible image, while simultaneously the details and background scenery of the visible image are persevered by using a novel fusion method based on a multi-scale decomposition with the guided filter. Moreover, in order to obtain the fused image more suitable for human perception, an automatic parameter selection method based on the human vision system (HVS) is proposed to determine a proper amount of the IR spectral information injected into the visible image, for which a new metric of perceptual saliency is created to compare the saliency of perceptual information contained in the infrared and visible images. Experimental results show that the proposed technique is able to achieve better context enhancement in night vision.

Electrically controlled spatial-polarization switch based on patterned photoalignment of nematic liquid crystals

Elena Melnikova, Alexei Tolstik, Irina Rushnova, OLGA KABANOVA, and Alexander Muravsky

Doc ID: 263520 Received 20 Apr 2016; Accepted 22 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: A switching scheme for two orthogonal modes of laser radiation that is based on the total internal reflection effect realized at the interface of two liquid crystal regions with the orthogonal director orientations is proposed. To create the photorefractive interface within the bulk of a liquid crystal, an original technique based on self-alignment of azo dye photoalignment and absorbing electrode patterns has been developed. Spatial separation of the orthogonally polarized light beams and their switching (when the positions of reflected and transmitted light beams are switched) due to the voltage applied has been experimentally realized.

Optical Turbulence in Confined media: Part I, TheINdoor TurbulENce SEnsor (INTENSE) instrument

Julien Chabé, Flavien Blary, Aziz Ziad, Julien Borgnino, Yan FANTEI-CAUJOLLE, Arnaud Liotard, and Frederic Falzon

Doc ID: 263541 Received 19 May 2016; Accepted 22 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: Optical system performances can be affected by local optical turbulence created by its surroundingenvironment (telescope dome, clean room, atmospheric surface layer). We present our newinstrument INTENSE (INdoor TurbulENce SEnsor) dedicated to this local optical turbulence characterization.INTENSE consists of using several parallel laser beams separated by non redundant baselinesbetween 0.05 and 2.5 m and measuring Angle-of-Arrival fluctuations from spots displacements on a CCD.After introducing the theoretical background, we give a description of the instrument including a detailedcharacterization of instrumental noise and finally give the first results for the characterization ofthe turbulence inside clean rooms for optical systems studies.

Terahertz ultrathin film thickness sensor below λ/90 based on metamaterial

Meng Chen, Fei Fan, Si Shen, Xianghui Wang, and Shengjiang Chang

Doc ID: 267917 Received 07 Jun 2016; Accepted 22 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: The film thickness sensing based on metamaterial is investigated in the terahertz (THz) region. We fabricated the metamaterial sensor, and demonstrated its resonance by using the THz time-domain spectroscopy system. According to the corresponding moving of the resonance dependent on the different thickness of the film on the sensor, the thickness sensing can be achieved. Its sensitivity is up to 13.5GHz/μm with the applicable film thinner than λ/90. Meanwhile, the limitation of the sensor is also explained with the electric dipole resonant field distribution, which leads to the nonlinear sensing property. This simple and flexible method can realize the thickness sensing of ultrathin film in THz region, and has the applied potential in the real-time monitoring of sample quality.

Remote picometer FBG demodulation using a dual-wavelength source

Carlos Fernandez-Pousa, Germán Torregrosa, Haroldo Maestre Vicente, and Juan Clement Bellido

Doc ID: 268084 Received 15 Jun 2016; Accepted 22 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: We report on the self-referenced, intensity-based, remote and passive interrogation of a fiber Bragg grating (FBG) for point sensing, by use of a reconfigurable dual-wavelength source composed of a tunable wavelength and subsequent suppressed-carrier, electro-optic amplitude modulation. The demodulation procedure is based on the measurement of the reflected power at two different wavelengths within the FBG spectral response. The grating was interrogated by use of conventional spectral analysis, and also after 32.9 km of single-mode fiber using a dispersive incoherent OFDR technique. Both procedures provide picometer resolution in the determination of Bragg wavelength shifts at a comparatively similar scan time (~1 s) and received power (-16 dBm). The main limitations in each interrogation scheme have been identified. These results show the feasibility of interrogation systems incorporating relatively simple frequency combs at a calibrated, and eventually reconfigurable, wavelength grid with an, at least, similar performance to that of commercial FBG interrogators.

Simulation of optical caustics associated with the tertiary rainbow of oblate droplets

guan lu, Haitao Yu, Jianqi Shen, and Cameron Tropea

Doc ID: 268085 Received 10 Jun 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: In the present paper, vector-ray tracing (VRT) model is used to simulate optical caustic structures, including rainbow and hyperbolic umbilic (HU) fringes, in the tertiary rainbow region of light scattering from oblate spheroidal droplets. In order to apply the optical caustic structures to particle diagnostics, the evolutions of rainbow fringe and HU fringe with the increase of aspect ratio of oblate spheroidal droplets are investigated in detail and the curvature of rainbow fringe is also calculated. Then, on the basis of VRT model, the location of cusp caustics is calculated and compared with theoretical prediction.

Effect of codoped interface layer on passively Q-switched laser performance of composite crystals

Jun Dong and Jie Xu

Doc ID: 265490 Received 17 May 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: By using combinations of appropriate laser crystals, we simulated Yb:YAG/Cr4+:YAG composite crystal with Cr,Yb:YAG interface layer. The effect of Cr,Yb:YAG interface layer on laser performance of Yb:YAG/Cr4+:YAG composite crystal has been investigated for the first time to our best knowledge. The formation of Cr,Yb:YAG interface layer in Yb:YAG/Cr4+:YAG composite crystal has a negative impact on average output power, optical efficiency as well as single pulse energy and peak power. In addition, Cr,Yb:YAG interface layer also leads to a strong mode competition, resulting in the decrease of the longitudinal mode number, the widening of the longitudinal mode separations and the poor stability of laser pulse trains. The results of this study are of theoretical and practical importance to develop novel types of Yb:YAG/Cr4+:YAG composite crystals which could be used to obtain laser pulses with high peak power and high optical efficiency.

Frequency spacing switchable multi-wavelengthBrillouin Erbium fiber laser utilizing cascaded Brillouingain fibers

Wang Xiaorui, Yanfu Yang, Meng Liu, yijun yuan, Yunxu Sun, Yinglong Gu, and Yong Yao

Doc ID: 267077 Received 25 May 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: A new hybrid Brillouin Erbium fiber laser scheme that employing cascaded multiple Brillouin gain fibers in a ringcavity to realize multi-wavelength laser output with switchable frequency spacing is proposed and experimentallyinvestigated. The multiple frequency down-shifting processes introduced by multiple stimulated Brillouinscattering (SBS) effects in one round trip of the cavity make it possible to realize multi-wavelength output withfrequency spacing which is an integer multiple of SBS frequency shifting. With two cascaded SBS fibers, thefrequency spacing can be switched between single and double SBS frequency shifting by properly adjustingBrillouin pump power. Multi-wavelength outputs with triple or quadruple SBS frequency spacing are alsodemonstrated by employing three or four SBS gain fibers, respectively.

Compact KGd(WO₄)₂ picosecond pulse-train synchronously pumped broad-band Raman Laser

Xiaoqiang Gao, meng chen, and Mingliang Long

Doc ID: 267215 Received 27 May 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: We demonstrated an efficient approach realizing extra-cavity synchronously pumped stimulated Raman cascaded process under low repetition frequency (1 kHz) pump condition. We also constructed compact KGd(WO₄)₂ (also KGW) crystal picosecond Raman laser which has been configured as the developed method. Pulse-train green laser pumped the corresponding 120mm long KGW crystal Raman cavity, in which the pulse-train contains 6 pulses for every millisecond with about 800ps distance separated thus it can realize synchronously pumping between pump pulse and the pumped Raman cavity. The investigated system produced collinear Raman laser output which includes 6 laser lines covering 532nm to 800nm spectra and it’s the first report on the high-average-power picosecond collinear multi-wavelength (more than three laser components) generation to our knowledge. The method has never been reported before wherein synchronously-pumped stimulated Raman scattering (SRS) realm.

Application of Gaussian beam ray-equivalent modeland back-propagation artificial neural network in laserdiode fast axis collimator assembly

Guido Perrone, HAO YU, Andrea Braglia, and Giammarco Rossi

Doc ID: 267394 Received 31 May 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: The paper presents the development of a tool based on a back-propagation artificial neural network to assistin the accurate positioning of the lenses used to collimate the beam from semiconductor laser diodesalong the so-called fast axis. After training using a Gaussian beam ray-equivalent model, the network iscapable of indicating the tilt, decenter and defocus of such lenses from the measured field distribution,so the operator can determine the errors with respect to the actual lens position and optimize the diodeassembly procedure. An experimental validation using a typical configuration exploited in multi-emitterdiode module assembly and fast axis collimating lenses with different focal lengths and numerical aperturesis reported.

Study of a micro-CPV system based on Cu(In,Ga)Se2 microcells array

Sebastien Jutteau, Jean-Francois Guillemoles, and Myriam Paire

Doc ID: 263185 Received 02 Jun 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: We study a micro-CPV system based on micro solar cells made from a thin film technology, Cu(In,Ga)Se2. Wedesigned, using the ray-tracing software Zemax OpticStudio 14, an optical system adapted and integrated to themicrocells, with only spherical lenses. The designed architecture has a magnification factor of 100x for an opticalefficiency of 85% and an acceptance angle of +/- 3.5°, without antireflective coating. An experimental study isrealized to fabricate the first generation prototype on a 5x5cm² substrate. A mini-module achieved a concentrationratio of 72x under AM1.5G, and an absolute efficiency gain of 1.8% for a final aperture area efficiency of 12.6%.

GRASSP: A Spectrograph for the Study of Transient Luminous Events

María Passas Varo, Justo Sanchez, Ernesto Sanchez-Blanco, Alejandro Luque, and F Gordillo-Vazquez

Doc ID: 262890 Received 08 Apr 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: We present the main parameters, design features and optical characterization of GRASSP, a ground-based spectrographic system intended for the analysis of the spectroscopic signature of transient luminous events (TLEs) occurring in the mesosphere of the Earth. It has been designed to measure the spectra of the light emitted from TLEs with a mean spectral resolution of 0. 5 nm and 0.07 nm/px dispersion in the wavelength range between 700 and 800 nm.

Extrinsic Calibration of Non-overlapping Camera Network Based on Close-range Photogrammetry

Shuai Dong, Xinxing Shao, Xin Kang, Fujun Yang, and Xiaoyuan He

Doc ID: 264697 Received 06 May 2016; Accepted 21 Jul 2016; Posted 21 Jul 2016  View: PDF

Abstract: In this paper, an extrinsic calibration method for a non-overlapping camera network is presented based on close-range photogrammetry. The method does not require calibration targets or the cameras to be moved. The visual sensors are relatively motionless and do not see the same area at the same time. The proposed method combines the multiple cameras using some arbitrarily distributed encoded targets. The calibration procedure consists of three steps: reconstructing the three-dimensional (3D) coordinates of the encoded targets using a hand-held digital camera, performing the intrinsic calibration of the camera network and calibrating the extrinsic parameters of each camera with only one image. A series of experiments, including 3D reconstruction, rotation and translation, are employed to validate the proposed approach. The results show that the relative error for the 3D reconstruction is smaller than 0.003%, the relative errors of both rotation and translation are less than 0.066%, and the re-projection error is only 0.09 pixels.

Diffractive fan-out elements for wavelength-multiplexing subdiffraction-limit spot generation in three dimensions

Yusuke Ogura, Masahiko Aino, and Jun Tanida

Doc ID: 264748 Received 11 May 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016  View: PDF

Abstract: Wavelength-multiplexing generation of subdiffraction-limit spots in three dimensions using propagating light was demonstrated and evaluated. Our previous design algorithm [Y. Ogura et al., Opt. Exp. 22, 25196 (2014)] was extended to consider multiple output planes and multiple wavelengths by integrating modulation distributions for individual wavelengths. A diffractive fan-out element that generates subdiffraction limit spot arrays with two wavelengths on two planes was demonstrated. Spot sizes were reduced to 79% of that of the diffraction limit spot on average. Numerical calculations showed that seven-wavelength multiplexing is achievable, and the crosstalk suppression conditions are effective for crosstalk suppression between wavelengths.

Transmittance properties in a magnetized cold plasma-superconductor periodic multilayer

Alireza Aghajamali

Doc ID: 265256 Received 16 May 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016  View: PDF

Abstract: This study theoretically investigates the transmittance properties in a one-dimensional photonic crystal containing magnetized cold plasma and high temperature superconductor materials. The cutoff frequency as a function of the magnetic field and the electron density of the plasma layer and the temperature will be investigated. The results illustrate that the temperature, the electron density, and the variations of the magnetic field affect the cutoff frequency. In addition, the shift trend in the cutoff frequency proves to be dependent on the polarization due to the presence of polarization-dependent magnetized cold plasma. Moreover, in temperature-dependent transmittance, weak oscillation and intensity can be seen at higher temperatures, which is in sharp contrast with low temperature superconductor-dielectric structure. The proposed structure could certainly provide helpful information for designing new types of antennas, reflectors, and high pass filters at microwave frequency.

Cavity-dumped Yb:YAG ceramic in the 20 W, 12 mJ range at 6.7 ns operating from 20 Hz - 5 kHz with fluorescence feedback control

Christian Fries, Marco Weitz, Christian Theobald, Patric v. Loewis of Menar, Jürgen Bartschke, and Johannes Lhuillier

Doc ID: 266868 Received 24 May 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016  View: PDF

Abstract: Increasing data acquisition rates in metrology applications based on optical parametric oscillators (OPOs) can accelerate measurement processes. To achieve this, flash-lamp systems with low pulse repetition frequency of 10-100 Hz used as pump source for the OPOs could be replaced by diode-pumped solid state lasers in the kHz range. We demonstrate a 969 nm pumped Yb:YAG ceramic laser, yielding 21.6 W output power, 12.5 mJ pulse energy and excellent beam quality. A fluorescence feedback control, developed from gain dynamics simulations in two operating regimes, allows stable operation at 6.7 ns from 20-5000 Hz. Third harmonic generation to 343 nm yields 3.24 W at 2 kHz. The system provides constant pulse duration in a huge repetition rate interval, which is beneficial for a pump source for future metrology devices.

Transmission characteristics and transmission line model of metal-insulator-metal waveguide with a stub modified by cuts

yueke wang, Xinru shen, Xin Yan, lin yuan, and Tian Sang

Doc ID: 267038 Received 25 May 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016  View: PDF

Abstract: We propose a structure of Metal-Insulator-Metal (MIM) waveguide with a stub modified by cuts. Our simulation results, conductedby finite element method, show that the wavelengths of transmission dip vary with the position of the cuts and form the zigzag lines.A transmission line model is also presented, and it agrees with simulation results well. It is believed that our findings provide a smartway to design plasmonic waveguide filter at communication region based on MIM structures.

Half-Disordered Photonic Crystal Slabs

Jacob Keilman, David Citrin, and Vincent Beque

Doc ID: 254326 Received 29 Feb 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016  View: PDF

Abstract: Optical transmission spectra of finite-thickness slabs of two-dimensional triangular-lattice photonic crystals of air holes in a dielectric matrix with various concentrations of randomly located vacancies (absent air holes) are studied. We focus on structures in which only one half of the structure—the incidence or transmission side—is disordered. We find vacancy-induced scattering gives rise to a strong difference in the two cases; for light incident on the disordered side, high transmission within the photonic pseudogap at normal incidence is predicted, in strong contrast to the opposite case, where low transmission is predicted throughout the pseudogap, as is observed in the case of an ideal structure with no defects.

An ultra-broadband polarization splitter based on three-core photonic crystal fiber with a modulation core

Tongtong Zhao, shuqin lou, Zhenggang Lian, Xin Wang, and Min Zhou

Doc ID: 262920 Received 11 Apr 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016  View: PDF

Abstract: We design an ultra-broadband polarization splitter based on three-core photonic crystal fiber. A modulation core and two fluorine-doped cores are introduced to achieve an ultra-wide bandwidth. The properties of three-core photonic crystal fiber are modeled by using the full-vector finite element method along with full-vector beam propagation method. Numerical results demonstrate that an ultra-broadband splitter with 320 nm bandwidth with an extinction ratio as low as -20 dB can be achieved by using 52.8 mm long three-core photonic crystal fiber. This splitter also has high compatibility with standard single-mode fibers as the input and output ports due to low splicing loss of 0.02 dB. All the air holes in the proposed structure are circular holes and arranged in a triangular lattice that makes it easy to fabricate.

Flexible Calibration of Phase-to-Height Conversion in Fringe Projection Profilometry

Jin Lu, Rong Mo, Huibin Sun, and Chang Zhiyong

Doc ID: 267039 Received 27 May 2016; Accepted 19 Jul 2016; Posted 21 Jul 2016  View: PDF

Abstract: A flexible new technique is presented to calibrate the monocular system of phase-based fringe projectionprofilometry, which is made of a camera, a projector and a computer. The proposed algorithm mainly consists of amore flexible phase-to-height conversion (PHC) model and a minimum norm solution, followed by a nonlinearoptimization based on the maximum likelihood criterion. In the whole calibration procedure, this method onlyrequires the camera to capture a few two-dimensional (2D) checkerboard target images and several deformedfringe images at least three different orientations. And the proposed technique neither subjects to certainlimitations nor measures additional geometry parameters in advance. Also, no high precise gage blocks or no extrareference phases are involved. In contrast with the existing methods, the proposed technique is easier to use andmore flexible. Experiments have been performed to validate the performance of this technique.

Canceling the momentum in a phase-shifting algorithm to eliminate spatially uniform errors

Kenichi Hibino and Yangjin Kim

Doc ID: 267604 Received 02 Jun 2016; Accepted 19 Jul 2016; Posted 21 Jul 2016  View: PDF

Abstract: In phase-shifting interferometry, phase modulation nonlinearity causes both spatially uniform and non-uniform errors in the measured phase. Conventional error-compensating algorithms only eliminate the spatially variable error component. The uniform error is proportional to the inertial momentum of the data-sampling weight of a phase-shifting algorithm. This paper proposes a design approach to cancel the momentum by using characteristic polynomials in the Z-transform space, and shows that an arbitrary M-frame algorithm can be modified to a new (M + 2)-frame algorithm that acquires new symmetry to eliminate the uniform error.

Strain and high temperature discrimination using a type II fiber Bragg grating and a miniature fiber Fabry-Pérot interferometer

Yajun Jiang, Dexing Yang, Yuan Yuan, Jian Xu, Dong Li, and Jianlin Zhao

Doc ID: 269328 Received 27 Jun 2016; Accepted 19 Jul 2016; Posted 21 Jul 2016  View: PDF

Abstract: A novel method for simultaneous measurement of strain and high temperature using a type II fiber Bragg grating (FBG) and a miniature fiber Fabry-Pérot interferometer (MFFPI) is proposed. The MFFPI is produced by fusion splicing a short section of quartz capillary tube with two single mode fibers, and then it is exposed by focused femtosecond laser and a phase mask to inscribe a type II FBG nearby. The reflection spectrum of this sensor is the superposition of reflection spectrum of the FBG and interference fringe of the MFFPI. This sensor shows perfect high temperature and strain responses. Due to the different responses to the uniform variations of strain and temperature, by measuring the reflection peak of FBG and one of the interference dips of MFFPI, strain and temperature can be determined simultaneously. The resolutions of this particular sensor in measuring strain and temperature are estimated to be ±8.4 με and ±3.3 °C in the range from 0 με to 1122 με and from °C to 600 °C.

Preparation and transmission characteristics of mid-infrared ATR hollow waveguide based on stainless steel capillary tube

Xu Wang, Hong Guo, Lin Wang, Fangyu Yue, Chengbin Jing, and Junhao Chu

Doc ID: 265443 Received 17 May 2016; Accepted 19 Jul 2016; Posted 19 Jul 2016  View: PDF

Abstract: Stainless steel (SUS) capillary tubes were examined as a category of structural tube for establishing a metallic ATR GeO2 hollow waveguide. GeO2 films were grown on the inner wall of SUS tubes by different liquid phase deposition (LPD) cycles. FTIR spectra, SEM and transmission loss for CO2 laser were measured to investigate the effects of the LPD cycles on the transmission behavior of the hollow waveguide samples. The film thickness and surface roughness increase with every LPD cycle. The 2 LPD cycled sample has a film thickness equivalent to the CO2 laser wavelength while the surface roughness is acceptable. This sample has the lowest transmission loss (0.27dB/m) among these samples. The bending loss, output beam profile and full divergence angle (FDA) were further studied. Higher-order modes are excited by bending the sample, inducing additional loss, decentralized beam profile and larger FDA.

Metal powder absorptivity: modeling and experiment

Charles Boley, Scott Mitchell, Alexander Rubenchik, and Sheldon Wu

Doc ID: 265226 Received 16 May 2016; Accepted 19 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: We present results of numerical modeling and direct calorimetric measurements of the powder absorptivity for a number of metals. The modeling results generally correlate well with experiment. We show that the powder absorptivity is determined, to a great extent, by the flat-surface absorptivity. Our results allow the prediction of the powder absorptivity from normal flat-surface absorptivity measurements.

Effects of small misalignments on the intensity and Strehl ratio for a laser beam focused by an Off-Axis Parabola

Luca Labate, Paolo Ferrara, Leonida Gizzi, and Lorenzo Fulgentini

Doc ID: 263874 Received 06 May 2016; Accepted 18 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: A general procedure is described to calculate the intensity and Strehl ratio, at a generic plane in the focalregion, of a beam focused by an off-axis parabolic mirror in the presence of small misalignments. Thegeneral theoretical framework is first developed, which allows a full vector diffraction treatment in thecase of general misalignments. Then, a parametric numerical study is reported, aimed at highlighting thetolerances of both the intensity and Strehl ratio for small misalignments, for different focusing and offaxisparabola parameters. A set of experimental measurements aimed at validating the theoretical modelis also discussed.

Novel integral imaging system using an adaptive lens array

Kwan-Hee Yoo, minho song, Ji-Seong Jeong, Munkh-Uchral Erdenebat, Ki-Chul Kwon, and Nam Kim

Doc ID: 263978 Received 26 Apr 2016; Accepted 18 Jul 2016; Posted 19 Jul 2016  View: PDF

Abstract: We produced an adaptive lens array composed of multiple flat lens arrays arranged in a curved shape with an adjustable radius of curvature, in order to overcome the hardware problem of the conventional flat or curved lens array-based systems. The manufactured adaptive lens array is applied to an integral imaging system. The gap mismatch that occurs when using a curved lens array is resolved by computing the exact display mapping position of element images through each lens. The results of the experiment demonstrate that the adaptive lens array-based integral imaging system successfully generated elemental images according to the curvature transformation of the adaptive lens array and they were reconstructed as 3D images.

Mid-infrared supercontinuum generation in silica photonic crystal fibers

Meisong Liao, wanjun bi, Juanjuan Gao, Xia Li, and Liangming Xiong

Doc ID: 264532 Received 04 May 2016; Accepted 18 Jul 2016; Posted 19 Jul 2016  View: PDF

Abstract: Mid-infrared supercontinuum (SC) light source, which has important applications in many fields, is extensivelyinvestigated in soft glass fibers. However, the poor instinct properties of soft glass fibers and the development ofultra-short pulse lasers left an opportunity to the mid-infrared SC generation in silica fiber. Until now, silica fiber isthe commonly used medium for SC generation due to its outstanding properties. In this paper, mid-infrared SCgeneration in short silica photonic crystal fibers (PCFs) is investigated theoretically and systematically. In case of1550 nm pump, the soliton self-frequency shift effect is utilized to extend the long wavelength edge of SC. Adoptinga fiber which has a zero dispersion wavelength away from the pump pulse is benefit for the suppression of bluespectral component and the energy distribution in the long wavelength band. In case of 1950 nm pump, thegeneration of red-shifted dispersive wave (DW) is an efficient way to extend the long wavelength edge of SC.Additionally, the coherence for femtosecond pulse pumping is discussed in this paper. Finally, the long wavelengthedge of SC is beyond 3000 nm when 1950 nm femtosecond pump pulse propagates in a PCF with negativedispersive slope around the pump pulse.

Experimental demonstration of optical stealth transmission over WDM network

Tao Pu, Huatao Zhu, Rong Wang, Tao Fang, Peng Xiang, Jilin Zheng, Yeteng Tang, and Dalei Chen

Doc ID: 267516 Received 01 Jun 2016; Accepted 18 Jul 2016; Posted 19 Jul 2016  View: PDF

Abstract: We propose and experimentally demonstrate an optical stealth transmission system over 200 GHz-grid WDM network. The stealth signal is processed by spectral broadening, temporal spreading and power equalizing. The public signal is suppressed by multi-band-notch filtering at the stealth channel receiver. The interaction between the public and stealth channel is investigated in terms of public signal to stealth signal ratio, data rate, notch filter bandwidth and public channel number. The stealth signal can transmit over 80 km single mode fiber with error free. Our experimental results verifies the feasibility of optical steganography used over the existing WDM based optical network.

Analyzing the propagation behavior of coherence and polarization degrees of a phase-locked partially coherent radial flat-topped array laser beam in underwater turbulence

F Kashani and Masoud Yousefi

Doc ID: 265035 Received 11 May 2016; Accepted 17 Jul 2016; Posted 19 Jul 2016  View: PDF

Abstract: In this research, based on an analytical expression for Cross- Spectral Density (CSD) matrix elements, coherence and polarization properties of phase-locked partially coherent flat-topped (PCFT) radial array laser beams propagating through weak oceanic turbulence are analyzed. Spectral degrees of coherence and polarization are analytically calculated using CSD matrix elements. Also, the effective width of spatial degree of coherence (EWSDC) is calculated numerically. The simulation is done by considering the effects of source parameters (such as radius of array setup’s circle, effective width of the spectral degree of coherence and wavelength) and turbulent ocean factors (such as the rate of dissipation of the turbulent kinetic energy per unit mass of fluid and relative strength of temperature and salinity fluctuations, Kolmogorov micro-scale, and rate of dissipation of the mean squared temperature) in detail. Results indicate that, any change in the amount of turbulence factors that increase the turbulence power, reduces the EWSDC significantly and causes the reduction in the degree of polarization occurs at shorter propagation distances but with smaller magnitudes. In addition, being valid for all conditions, the degradation rate of the EWSDC of Gaussian array beams are more in comparison with the PCFT ones. The simulation and calculation results are shown by graphs.

Design and fabrication of a tunable wavelength-selective polarization grating

Kotaro Kawai, Moritsugu Sakamoto, Kohei Noda, Tomoyuki Sasaki, Nobuhiro Kawatsuki, and Hiroshi Ono

Doc ID: 265347 Received 16 May 2016; Accepted 17 Jul 2016; Posted 19 Jul 2016  View: PDF

Abstract: Tunable wavelength-selective diffraction with polarization conversion is realized by the design of a liquid crystal (LC) grating containing a twisted nematic alignment structure that is fabricated by an efficient one-step photoalignment method. The diffraction efficiency strongly depends on the wavelength of the incident beam, and this property can be controlled by adjusting the birefringence of the nematic LC using a thermal control. These properties are well described by a theoretical analysis based on the Jones calculus and are experimentally demonstrated using 488-, 532-, and 633-nm wavelength incident polarized laser beams. The resultant LC grating has potential application as diffractive optical elements that can simultaneously control the parameters of light such as amplitude, wavelength, and polarization.

Fourier ptychographic microscopy using an infrared-emitting hemispherical digital condenser

Sanchari Sen, Ishtiaque Ahmed, Batool Aljubran, Ayrton Bernussi, and Luis Grave de Peralta

Doc ID: 264781 Received 16 May 2016; Accepted 16 Jul 2016; Posted 19 Jul 2016  View: PDF

Abstract: Fourier ptychographic microscopy is demonstrated in the near-infrared spectral range using a computer-controlled hemispherical digital condenser comprising multiple 940 nm wavelength light emitting diodes. This technique was used to image periodic patterned samples (photonic crystals). Experimental and simulated results using a phase retrieval algorithm were found to be in excellent correspondence. We show that for samples with a single period in each direction, the resolution of the obtained high-resolution near-infrared images is limited by the Rayleigh criteria.

Fabrication of Phase Transmission Holographic Optical Element in Polycarbonate and its Characterization

Vadivelan. V Varadarajan and Chander Bellan

Doc ID: 264226 Received 28 Apr 2016; Accepted 16 Jul 2016; Posted 19 Jul 2016  View: PDF

Abstract: The phase transmission holographic optical element in silver halide holographic emulsion especially for holographic weapon sight is fabricated and obtained desired diffraction efficiency with very high transmission. One of a main drawback of these holograms are become dark by exposed under Sun light, it is drastically reduce the visible transmission and diffraction efficiency of a holographic optical element, hence it is not suitable for weapon sight application. To overcome this problem, we transferred holographic optical element with reticle image from silver halide into polycarbonate by using electroforming and recombination techniques. The holographic optical element in polycarbonate have many advantages, the details method of fabrication, transfer and its characterization are presented. The very interesting result of diffraction efficiency variation with angle obtained in polycarbonate is discussed.

Visual and instrumental correlation of sparkle by themagnitude estimation method

Omar Gomez, Esther Perales, Elisabet Chorro, Valentin Viqueira, and Francisco Martínez-Verdú

Doc ID: 267073 Received 25 May 2016; Accepted 15 Jul 2016; Posted 19 Jul 2016  View: PDF

Abstract: Most real surfaces and objects show variation in appearance with viewing and illumination directions. Besidesangular dependency, they also show spatial variation in color; i.e. they exhibit some sort of texture. Of the surfaceswe see, surfaces colored by special-effect pigments produce several complex visual effects, like change in color andlightness with viewing and illumination angles, and effects like sparkle and gloss on other textures.In the last two decades, different commercial devices have appeared to help ensure the proper characterization ofmaterials with special-effect pigments. However, the instrumental characterization of sparkle is currently availableonly by a commercial device integrated into a multi-angle spectrophotometer. As it is difficult to find completeopen original studies about the sparkle effect for designing and calibrating this commercial instrument, the mainobjective of this work was to check whether a good visual and instrumental correlation exists between the sparklethat the observer perceives and the sparkle value provided by the device using some subsets of goniochromaticsamples with different types of special-effect pigments and colors. Visual assessments were made by aconventional magnitude estimation method in a directional lighting booth, which belonged to the same companyowner of the sparkle instrument, in different geometries and at distinct illuminance levels.The results revealed that there was a good visual correlation of the sparkle-grade value. By separately analyzingthe factors used in its instrument algorithm, such as sparkle intensity and sparkle-area values, it was clearly shownthat the correlation was not good or simply did not exist. Consequently, and perhaps as regards choice of newspecial-effect pigments, such as synthetic mica and other future ones, we generated herein even more questionsabout current mathematical algorithms, and only recognized calculating this texture effect at the industrial level.

Eye-Safe Transmitter for Ground-Based, Integrated Path Differential Absorption LIDAR Measurement of CO₂, CH₄, and H₂O near 1.6 μm

David Plusquellic and Gerd Wagner

Doc ID: 262752 Received 07 Apr 2016; Accepted 15 Jul 2016; Posted 15 Jul 2016  View: PDF

Abstract: The eye-safe transmitter of a ground-based, integrated path, differential absorption light detection and ranging (IPDA LIDAR) system is described and specified in detail. The transmitter is based on an actively stabilized, continuous-wave, single-frequency external-cavity diode laser (ECDL) operating from 1.60 μm to 1.65 μm. The ECDL is microwave (MW) sideband tuned using an electro-optical phase modulator (EOM) driven by an arbitrary waveform generator (AWG) and filtered using a confocal cavity to generate a sequence of 1 frequencies separated by 300 MHz. The scan sequence of single sideband frequencies of 600 ns duration covers a 37 GHz region across absorption lines of CO₂, CH₄, and H₂O at a spectral scan rate of 10 kHz (100 μs per scan). Simultaneously, an eye-safe backscatter LIDAR system at 1.064 μm is used to monitor the atmospheric boundary layer. IPDA measurements of the CO₂ and CH₄ dry air mixing ratios are presented in comparison with those from a commercial cavity ring-down (CRD) instrument. Differences between the IPDA and CRD concentrations in several cases are well correlated with the atmospheric aerosol structure from the LIDAR measurements. IPDA dry air mixing ratios of CO₂ and CH₄ are determined with fit uncertainties of 2.7 μmol/mol (ppm) for CO₂ and 0.025 μmol/mol (ppm) for CH₄ over 30 s measurement periods. For longer averaging times (up to 1200 s), improvements in these detection limits by up to 3-fold are estimated from Allan variance analyses. Two sources of systematic error are identified and methods to remove them are discussed, including speckle interference from wavelength decorrelation and the seed power dependence of amplified spontaneous emission. Absolute accuracies of CO₂ and CH₄ are estimated at 1.6 μmol/mol (0.4 % of ambient levels) and 0.042 μmol/mol (2 %), respectively.

Multispecies Absorption Spectroscopy of Detonation Events at 100 kHz using a Fiber-Coupled, Time-Division-Multiplexed Quantum-Cascade-Laser System

Keith Rein, Sukesh Roy, Scott Sanders, Andrew Caswell, Frederick Schauer, and James Gord

Doc ID: 263202 Received 26 Apr 2016; Accepted 15 Jul 2016; Posted 15 Jul 2016  View: PDF

Abstract: A mid-infrared fiber-coupled laser system constructed around three time-division-multiplexed quantum-cascade lasers capable of measuring the absorption spectra of CO, CO2, and N2O at 100 kHz over a wide range of operating pressures and temperatures is demonstrated. This system is first demonstrated in a laboratory burner and then used to measure temperature, pressure, and concentrations of CO, CO2, and N2O as a function of time in a detonated mixture of N2O and C3H8. Both fuel-rich and fuel-lean detonation cases are outlined. High-temperature fluctuations during the blowdown are observed. Concentrations of CO are shown to decrease with time for fuel-lean conditions and increase for fuel-rich conditions.

Temperature drift Modeling and compensation of Fiber Optical Gyroscope Based on improved support vector machine and particle swarm optimization algorithms

Wei Wang and xiyuan chen

Doc ID: 264686 Received 06 May 2016; Accepted 15 Jul 2016; Posted 15 Jul 2016  View: PDF

Abstract: Temperature drift is one of the main error sources of fiber optic gyroscope (FOG). Modeling and compensation of temperature drift is an important method to improve the precision of FOG. In this paper, a new method of modeling and compensation for FOG based on improved particle swarm optimization (PSO) and support vector machine (SVM) algorithms is proposed, which is called PSO-RBFP, and the experiment results show the validity and practicability of the method. The convergence speed and reliability of PSO are improved by introducing dynamic inertia factor. The regression accuracy of SVM is improved by introducing the combined kernel function with parameters. The regression accuracy of PSO-RBFP is further improved by introducing the algorithm of piecewise regression, and the algorithm is called PSO-RBFP-P. The steps to model and compensate the temperature drift of FOG are as follows. Firstly, the parameters of the combined kernel function are optimized by the improved PSO algorithm. Secondly, the new kernel function of SVM is used to carry out piecewise regression of temperature drift, and the regression model is also obtained. Thirdly, the temperature drift is compensated by the regression model and regression data. The experimental results show that the method proposed in this paper can effectively compensate the temperature drift of FOG. The regression accuracy of temperature drift (in the case of MAPE indicators) increased by 89% compared to the traditional SVM.

Performance estimation of dual-comb spectroscopy in different frequency-control schemes

Honglei YANG, Haoyun Wei, Hongyuan Zhang, Kun Chen, Li Yan, Viktor Smolski, and Konstantin Vodopyanov

Doc ID: 267714 Received 03 Jun 2016; Accepted 15 Jul 2016; Posted 19 Jul 2016  View: PDF

Abstract: Dual-comb spectroscopy (DCS) has shown unparalleled advantages but at the cost of highly mutual coherence between comb lasers. Here, we investigate spectral degradation induced by the laser frequency instability and improvement benefited from active laser stabilization. Mathematical models of DCS in the cases of direct radio-frequency (RF) locking and optical phase-stabilization were separately established first. Numerical simulations are utilized to study the impact of laser intrinsic stability and the improvement by different locking strategies on spectral performance in the following. Finally, both simulations are proven by corresponding experiments. It shows that optical phase-stabilized system owns a better immunity of laser frequency perturbation than direct RF-stabilized one. And the performance improvement by the feedback servos is also more effective in the optical phase-stabilized system. In addition, the simulations could instruct optimal design and system improvement.

Analysis of autostereoscopic three-dimensionalimages with horizontal parallax using multiviewwavelets

Vladimir Saveljev and Irina Palchikova

Doc ID: 267162 Received 27 May 2016; Accepted 13 Jul 2016; Posted 15 Jul 2016  View: PDF

Abstract: We propose the multiview wavelets which can be used in the real-time processing of the multiview images. The reference functions for the synthesis/analysis of multiview images are described. The synthesized binary image was observed experimentally as a three-dimensional visual image. The wavelets are built basing on the reference functions as scaling functions of the wavelet analysis. The locations recognized in the continuous wavelet transform correspond to the layout of the testing object. The proposed wavelets can be applied to the multiview images with the horizontal parallax, and in a generalized two-dimensional form, to the integral and plenoptic images.

Terahertz polarization splitter based on a dual-elliptical-core polymer fiber

Guofeng Yan, Erik Forsberg, Sailing He, and Hongzhi Chen

Doc ID: 264517 Received 03 May 2016; Accepted 13 Jul 2016; Posted 15 Jul 2016  View: PDF

Abstract: A terahertz (THz) polarization splitter based on a dual-elliptical-core polymer fiber is proposed and theoretically optimized. Dual-elliptical cores of subwavelength-scale diameters are independently suspended within the fiber, which not only support two orthogonal polarization modes being single-mode guided with low absorption losses, but also allow them to switch from one core to the other, with different coupling lengths. As a consequence, the two polarizations can be easily separated by choosing a suitable transmission length at a desired operation frequency. Here, the transmission modes, coupling lengths for x- and y-polarization, as well as the performance of the proposed polarization splitter at a center-frequency of 0.6 THz are investigated and numerically analyzed. A 1.43 cm long splitter with an ultra-low loss of 0.4 dB, a high extinction ratio (ER) better than -10 dB and a bandwidth of 0.02 THz is achieved.

Demonstration of a Homogeneous Yb-Doped Core Fully-Aperiodic Large-Pitch-Fiber Laser

Romain Dauliat, Aurélien Benoit, dia darwich, Raphael Jamier, Jens Kobelke, Stephan Grimm, Kay Schuster, and Philippe Roy

Doc ID: 264579 Received 11 May 2016; Accepted 12 Jul 2016; Posted 13 Jul 2016  View: PDF

Abstract: The first demonstration of a 40 µm core homogeneously ytterbium-doped fully-aperiodic large-pitch-fiber (FA-LPF) laser is reported on here. In this concept, the amplification of unwanted high-order modes is prevented by means of an aperiodic inner cladding structure, while the core and inner cladding material has a higher refractive index than pure silica. In a laser configuration, up to 252 W of extracted power, together with an optical-to-optical efficiency of 63 % with respect to the incident pump power, have been achieved. While an average M² of 1.4 was measured, the emitted power becomes temporally unstable when exceeding 95 W, owing to the occurrence of modal instabilities.

Phase control of optical bistability and multistability in tripod four-level atomic medium

Xionghui Hu, Hongjun Zhang, Sun Hui, Yaohua Lei, Wei Liu, and Huijing Li

Doc ID: 265288 Received 16 May 2016; Accepted 12 Jul 2016; Posted 13 Jul 2016  View: PDF

Abstract: Optical bistability and multistability behaviors are investigated in a tripod four-level atomic configuration including a unidirectional ring cavity. We find that optical bistability and multistability can be obtained by changing the relative phase of the driven fields and the intensity of the microwave filed. In addition, we can switch optical bistability to optical multistability by adjusting the relative phase of the driven fields or vice versa and the threshold can be controlled via changing the parameters of the scheme.

Large Range Manipulation of Exciton Species in Monolayer WS2

Tian Jiang, Ke We, Yu Liu, Hang Yang, and Xiang'ai Cheng

Doc ID: 267100 Received 26 May 2016; Accepted 12 Jul 2016; Posted 13 Jul 2016  View: PDF

Abstract: Unconventional emissions from exciton and trion in monolayer WS2 are studied by photoexcitation. Excited by 532nm laser beam, the carrier species in the monolayer WS2 is affected by the excess electrons escaping from photoionization of donor impurity, the concentration of which varies with the location of the sample. Simply increasing the excitation power at room temperature, the excess electron and thus the intensity ratio of excited trion and exciton can be continuously tuned over a large range from 0.1 to 7.7. Furthermore, this intensity ratio can also be manipulated by varying temperature. However, in this way the resonance energy of the exciton and trion show red-shifts with increasing temperature due to electron−phonon coupling. The binding energy of the trion is determined to be ~ meV and independent to temperature, indicating strong Coulomb interaction of carriers in such 2D materials.

Two-way shift of wavelength in holographic sensing of organic vapor in nano-zeolites dispersed acrylamide photopolymer

Yu Dan, Mao Dongyao, Geng yaohui, Hongpeng Liu, Zhou ke, and Xian Lihong

Doc ID: 266658 Received 20 May 2016; Accepted 12 Jul 2016; Posted 12 Jul 2016  View: PDF

Abstract: Holographic sensing of alcohol organic vapor is characterized in detailed at transmission and reflection geometries in Y nanozeolites dispersed acrylamide photopolymer. Two-way shift of diffraction spectrum and its temporal evolution with various vapor concentrations are measured. Obvious blue shifts of diffraction spectrum peaks are observed and analyzed in transmission recording geometry. The competition mechanism between decreasing of average refractive index and swelling of grating space are proposed for exploring the wavelength shift mechanism. In reflection grating, as organic vapor increases, the red shift after blue shift of wavelength peaks are observed clearly. It is further demonstrated the significance of this competition mechanism. In low concentration region, at transmission <700ppm and reflection <200pmm, the blue shift of wavelength is a significant factor for identify organic vapor with low refractive index. These experimental results provide a probability for improving the applicability of holographic sensor. This work can accelerates the development of holographic sensing strategy and provide a novel identification method for organic vapor.

Passive vibration compensation in scanning white-light interferometry

Stanislav Tereschenko, Peter Lehmann, Angelika Bruecker-Foit, and Lisa Zellmer

Doc ID: 267390 Received 31 May 2016; Accepted 11 Jul 2016; Posted 12 Jul 2016  View: PDF

Abstract: We present a passive vibration compensation approach in scanning white-light interferometry (SWLI). A pointwise distance measuring interferometer (DMI) obtains fast temporal distance changes during the white-light depth-scan of an areal measuring Michelson white-light interferometer for topography measurement. Both interferometers share a part of the optical path so that the measurement spot of the DMI is within the field of view of SWLI. With the real positions of the interferometer with respect to the measuring object during the depth scan known from DMI measurements we can compensate for the influence of unintentional distance changes caused by environmental vibrations or scanner nonlinearities. By reordering of the captured image frames and improved correlogram interpolation, we are able to reconstruct correct signals from completely distorted (and unusable) SWLI signals. Although the basic idea of the system already has been published, we improved the signal reconstruction technique, so that the specimen’s topography measurement can be obtained with the same accuracy as without any vibrations or scan distortions influece. In addition we demonstrate the feasibility of the approach by different practical measurements with and without vibrations.

Measurement of refractive index dispersion of a fused silica plate using Fabry-Perot interference

Myoungsik Cha, Choonghwan Lee, Heejoo Choi, and Jonghan Jin

Doc ID: 262857 Received 11 Apr 2016; Accepted 11 Jul 2016; Posted 12 Jul 2016  View: PDF

Abstract: We used Fabry-Perot interferometry to measure the refractive indices of a fused silica plate at four different wavelengths ranging from 544 nm to 1550 nm, giving a detailed analysis on the uncertainty of this experimental method. Because of a small expanded uncertainty of 2.7 × 10^−5 (k = 1.96) obtained using the experimental method, it was possible to make corrections to the existing Sellmeier formula [I. H. Malitson, J. Opt. Soc. Am., 55, 1205 (1965)] for our fused silica sample. The corrected Sellmeier formula resulted in a group index value larger than that evaluated using the Malitson's Sellmeier formula by 3 × 10^−4. We verified this by comparing it with the group index measured with spectral domain interferometry at 1530 nm.

Temperature dependence of Birefringence in ethanol-filled suspended core fibre

Jose Luis Vilas, Jose Sanchez-Martin, and Eusebio Bernabeu Martinez

Doc ID: 264511 Received 04 May 2016; Accepted 11 Jul 2016; Posted 12 Jul 2016  View: PDF

Abstract: The temperature dependence of the birefringence in a Suspended Core Fibre (SCFs) has beenexperimentally analyzed by using a polarimetric setup. The used configuration consists on two linearpolarizers and the SCF as birefringent medium. A theoretical study based on Jones matrices has been carriedout to analyze the experimental observed behavior. For this, it was used a polarimetric all-fibre configurationwhose sensitivity depends on the wavelength variation with temperature. Results obtained show that it isstrongly affected when the air-holes of SCF are partially-filled with ethanol.

Modified Iterative Vector Similarity Measure for Particle Size Analysis Based on Forward Light Scattering

Tian‘en Wang, Jianqi Shen, and Chengjun Lin

Doc ID: 264664 Received 05 May 2016; Accepted 11 Jul 2016; Posted 12 Jul 2016  View: PDF

Abstract: The vector similarity measure (VSM), originally applied to information retrieval, has been recently introduced to analyze particle size distribution (PSD) based on forward light scattering. The VSM technique can predict the PSD with low sensitivity to the experimental errors. However, the simulations and experiments of multimodal distributed particle system were not satisfying. In this paper, a modified inverse algorithm is presented to improve the VSM technique. Simulated results and experimental evidence show that, with this modification, the VSM technique can re-construct the PSD more efficiently.

Surface deformation and friction characteristic of nano scratch at ductile-removal regime for optical glass BK7

Chen Li, Feihu Zhang, Ye Ding, and Lifei Liu

Doc ID: 265472 Received 20 May 2016; Accepted 11 Jul 2016; Posted 12 Jul 2016  View: PDF

Abstract: Nano scratch for optical glass BK7 based on ductile-removal regime was carried out and the influence rule of scratch parameters on surface deformation and friction characteristic were analyzed. Experimental results showed that with increase of the normal force the deformation of burrs in the edge of the scratch was more obvious, and with increase of the scratch velocity the deformation of micro-fracture and burrs in the edge of the scratch was more obvious similarly. The residual depth of the scratch was measured by the atomic force microscope. The experimental results also showed that with the increase of the normal force, the residual depth of the scratch increased linearly while the elastic recovery rate decreased. Furthermore, with the increase of the scratch velocity, the residual depth of the scratch decreased while the elastic recovery rate increased. The scratch process of the Berkovich indenter was divided into the cutting process of many large negative rake faces based on the improving cutting model, and the friction characteristic of the Berkovich indenter and the workpiece was analyzed. The analysis showed that the coefficient of friction increased and then tended to be stable with the increase of normal force. Meanwhile, the coefficient of friction decreased with the increase of scratch velocity and the coefficients, kln(v) and μ0, were introduced to improve the original formula of friction coefficient.

Real-Time Two-Dimensional Beam Steering with Gate-Tunable Materials: A Theory Design Investigation

Jierong Cheng, Samad Jafar-Zanjani, and Hossein Mosallaei

Doc ID: 264690 Received 06 May 2016; Accepted 10 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: A leaky wave antenna is proposed that furnishes two-dimensional beam scanning in both elevation and azimuth planes via electrical control in real-time, and at a single frequency. The structure consists of a graphene sheet on a metal-backed substrate. The two-dimensional beam scanning performance is achieved through proper biasing configuration of graphene. Traditional pixel-by-pixel electrical control makes the biasing network a huge challenge for chip-scale designs in the terahertz regime and beyond. The method presented here enables dynamic control by applying two groups of one-dimensional biasing on the sides of the sheet. They are orthogonal and decoupled, with one group offering monotone impedance variation along one direction, and the other sinusoidal impedance modulation along the other direction. The conductivity profile of the graphene sheet for certain radiation angle, realized by applying proper voltage to each pad underneath the sheet, is determined by holographic technique, and can be reconfigured electronically and desirably. Such innovative biasing design makes the real-time control of the beam direction and beamwidth simple and highly integrated. The concept is not limited to graphene-based structures, and can be generalized to any available gate-tunable material system.

Single-shot dual-wavelength phase reconstruction in off-axis digital holography with polarization-multiplexing transmission

Zhe Wang, Zhuqing Jiang, and Yifei Chen

Doc ID: 265497 Received 17 May 2016; Accepted 10 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: A new system for single-shot dual-wavelength digital holographic microscopy with polarization-multiplexing path-shared transmission is presented. The key feature of the optical configuration is that the interference waves of two wavelengths having orthogonal polarization can transmit in the same interferometer paths at the same time, and two polarizers orthogonal to each other are placed in front of the CCD to realized single-shot recording of two holograms. The correlative filtering algorithm of spatial frequency spectrum for dual-wavelength digital holograms is reliable and efficient in the dual-wavelength path-shared configuration. The phase reconstruction in dual-wavelength digital holographic imaging is achieved by using this filtering algorithm. The experiment results of phase reconstruction of a groove grating demonstrate the reliability and validity of this optical configuration and the correlative filtering algorithm. This polarization-multiplexing configuration for dual-wavelength digital holography is compact and has more flexibility for the replacement of different wavelength lasers.

Scintillation analysis of multiple-input single-output underwater optical links

Muhsin Gökçe and Yahya Baykal

Doc ID: 267016 Received 25 May 2016; Accepted 10 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: Multiple-input single-output (MISO) techniques are employed in underwater wireless optical communication(UWOC) links to mitigate the degrading effects of oceanic turbulence. In this paper, we consider a MISO UWOC system which consists of a laser beam array as transmitter and a point detector as receiver. Our aim is to find the scintillation index at the detector in order to quantify the system performance. For this purpose, the average intensity and the average of the square of the intensity are derived in underwater turbulence by using the extendedHuygens - Fresnel principle. The scintillation index and the average bit-error-rate ( BER ) formulas presented inthis paper depend on the oceanic turbulence parameters such as the rate of dissipation of mean-squared temperature, rate of dissipation of kinetic energy per unit mass of fluid, Kolmogorov microscale, and the ratio of temperature to salinity contributions to the refractive index spectrum, the link length and the wavelength. Recently, we have derived an equivalent structure constant of atmospheric turbulence and expressed it in terms ofin this paper, this equivalent structure constant isutilized which enables us to employ the existing similar formulation valid in atmospheric turbulence.

All-fiber, narrow linewidth and linearly-polarized fiber laser in a single-mode-multimode-single-mode cavity

Xijia Gu, Man Jiang, Haiyang Xu, Pu Zhou, and Guomin Zhao

Doc ID: 267308 Received 30 May 2016; Accepted 10 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: We report the design of an all-fiber, linearly-polarized Yb-doped fiber laser at 1064 nm with a narrow linewidth and high output power required by the master oscillator of the amplifier for high power spectral beam combining. The laser has achieved linearly-polarized output with a polarization extinction ration of dB, a narrow linewidth of ≤ 52 pm and an output power of 32.7W. Such a performance was obtained by the cavity design that incorporated a wavelength shifted PM fiber Bragg grating pair and single-mode-multimode-single-mode structure

Defects evaluation system for spherical optical surfaces based on microscopic scattering dark-field imaging method

Yongying Yang, Yihui Zhang, Chen Li, Fan Wu, Huiting Chai, Kai Yan, Lin Zhou, Yang Li, Dong Liu, Jian Bai, and Yibing Shen

Doc ID: 264561 Received 04 May 2016; Accepted 09 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: In the field of the automatic optical inspection (AOI), it is imperative to measure the defects on the spherical optical surfaces. So a novel spherical surface defect evaluation system (SSDES) is established in this paper to evaluate defects on optical spheres. In order to ensure the microscopic scattering dark-field imaging of optical spheres with different surface shape and radius of curvature, the illumination with variable aperture angle is employed. Besides the scanning path of sub-apertures along the parallels and meridians is planned to detect the large optical spheres. Since analysis shows that the spherical defect information could be lost in the optical imaging, the three-dimensional correction based on pin-hole model is proposed to recover the actual spherical defects from the captured two-dimensional images. Given the difficulty of sub-apertures stitching and defects features extracting in the three-dimensional space after the correction, the 3D sub-apertures are transformed into a plane to be spliced through geometric projection. And then methods of the surface integral and the calibration are applied to quantitatively evaluate the spherical defects. Furthermore, the 3D panorama of defect distribution on the spherical optical components can be displayed through the inverse projective reconstruction. Finally, the evaluation results are compared with the OLYMPUS microscope, testifying the micron resolution and the detection error is less than 5%.

Field experiment and image reconstruction using aFourier Telescopy imaging system over a 600-m-longhorizontal path

Yu Shuhai, Lei Dong, Xinyue Liu, lin xudong, Haoran Meng, and Xing Zhong

Doc ID: 259940 Received 26 Feb 2016; Accepted 09 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: To confirm the effect of uplink atmospheric turbulence on FourierTelescopy (FT), we designed a system for far-field imaging, utilizing aT-type laser transmitting configuration with commercially availablehardware, except for a green imaging laser. The horizontal lighttransmission distance for both uplink and downlink was ~300 m. Forboth the transmitting and received beams, the height upon the groundwas below 1 m. The imaging laser’s pointing accuracy was ~9.3 μrad. Anovel image reconstruction approach was proposed, yieldingsignificantly improved quality and Strehl ratio of reconstructed images.From the reconstruction result, we observed that the tip/tilt aberrationis tolerated by the FT system even for Changchun’s atmosphericcoherence length parameter (r0) below 3 cm. The resolution of thereconstructed images was ~0.615 μrad.

Annealing effects on microstructure and laser induced damage threshold of HfO₂/SiO₂ multilayer mirror

Shuvendu Jena, Raj Tokas, Divakar Kompalli, Sudhakar Thakur, and Naba Sahoo

Doc ID: 264069 Received 27 Apr 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: HfO₂/SiO₂ periodic multilayer high reflection mirrors have been prepared by reactive electron-beam evaporation technique. The deposited mirrors were annealed in the temperature range from 300ºC to 500ºC. The effects of annealing on optical, microstructural and laser induced damage characteristics of the mirrors have been investigated. The high reflection band of the mirror shifts towards shorter wavelength with increasing annealing temperature. As-deposited and annealed mirrors show polycrystalline structure with monoclinic phase of HfO₂. Crystalinity and grain size increase upon annealing. The roughness of the mirror increases with annealing up to 400ºC and decreases at 500ºC. The laser induced damage threshold (LIDT) has been assessed using 532 nm pulsed laser at a pulse width of 7 ns. The LIDT value of the multilayer mirror increases from 44.1 J/cm² to 77.6 J/cm² with annealing up to 400ºC. The improvement of LIDT with annealing is explained through oxygen vacancy as well as grain size dependent thermal conductivity. Finally the observed laser damage morphology such as circular scalds and ablated multilayer stacks with terrace structure are analyzed.

CW and QCW Thulium-doped all-fiber laser: implementation on kidney stone fragmentation

ATASI PAL, DEBASIS PAL, Aditi Ghosh, and Ranjan Sen

Doc ID: 264584 Received 04 May 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: A continuous-wave (CW) as well as quasi continuous wave (QCW) thulium-doped all-fiber laser at 1.94 µm has been designed targeting application in Urology. The thulium-doped active fiber with octagonal-shaped inner cladding is pumped at 793 nm to achieve a stable CW laser power of 10 W with 32% lasing efficiency (against launched pump power).The linear variation of laser power with pump offers scope of further power scaling. A QCW operation with variation of duty cycle from 0.5% to 90%; repetition rate from 0.1 Hz to 1 KHz and pulse width from 40 µs to 2s has been presented. Laser power of 9.5 W in CW mode of operation and average power of 5.2 W with energy range of 10.4 to 104 mJ in QCW mode of operation has been employed to fragment COM kidney stones (size of 1.5-4 cm) having different color and composition. Dependence of ablation threshold, ablation rate and average fragmented particle size on the average power and energy has been studied. 1 min of laser exposure results fragmentation of stone surface with ablation rate of 8 mg/min having minimum particle size of 6.54 µm with an average size of 20-100 µm ensuring the natural removal of fragmented parts through the urethra.

Study of Evaluating Beam Quality of double-cladding fiber laser in application

Qirong Xiao, Xuejiao Wang, Ping Yan, and Mali Gong

Doc ID: 264599 Received 04 May 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: We put forward a new βFL factor which is used exclusively in fiber laser to assess beam quality and choose LP01 mode as the new suitable ideal beam. We present a new simple measurement method and verify the reasonability of βFL factor in experiment in 20/400 μm fiber laser. Furthermore, we use the new βFL factor to evaluate the beam quality of the 3 kW level fiber laser. It can be concluded that βFL is a key factor not only for assessing the performances of the high power fiber laser that we mainly concern, but also for the simple measurement.

50-kHz, 50-ns UV pulse generation by diode-pumped frequency doubling Pr3+:YLF Q-switch laser with a Cr4+:YAG saturable absorber

Fumihiko Kannari, Hiroki Tanaka, Ryosuke Kariyama, and Kodai Iijima

Doc ID: 264644 Received 05 May 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: We demonstrate intracavity second harmonic generation at 320 nm of a diode-pumped praseodymium-doped YLF laser Q-switched by a Cr4+:YAG crystal. By employing two 3.5-W high power blue InGaN diode lasers as the pump source, we obtained 50-ns Q-switched pulses with a pulse energy of 1.54 μJ at a repetition rate of 50 kHz. A rate equation analysis shows good agreement with the experimental results.

Climatology of aerosol optical properties over four locations in the Indo-Gangetic plains

Humera Bibi, Khan Alam, Thomas Blaschke, Samina Bibi, and Muhammad Jawed Iqbal

Doc ID: 268103 Received 13 Jun 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: The emphasis of the present work lies on the examination of the distribution and spectral behavior of the optical properties of atmospheric aerosols in the Indo-Gangetic Plains (IGP). Measurements were performed using an AErosol RObotic NETwork (AERONET) Sun photometer at four sites (Karachi, Lahore, Jaipur and Kanpur) with different aerosol environments during the period 2007-2013. The Aerosol Optical Depth (AOD) and angstrom exponent (α) were measured, and the results revealed a high AOD with a low α value over Karachi and Jaipur in July, while a high AOD with a high α value was reported over Lahore and Kanpur during October and December. The pattern of the aerosol Volume Size Distribution (VSD) was similar across all four sites, with a prominent peak in coarse mode at a radius of 4.0-5.0 um, and in fine mode at a radius of 0.1-4.0 um, for all seasons. On the other hand, during the winter months, the fine-mode peaks were comparable to the coarse mode, which was not the case during the other seasons. The Single Scattering Albedo (SSA) was found to be strongly wavelength-dependent during all seasons and for all sites, with the exception of Kanpur, where the SSA decreases with increasing wavelength during winter and post-monsoon. It was found that the phase function of the atmospheric aerosol was high at a small angle and stable around a scattering angle of 90-180º at all sites and during all seasons. Spectral variation of the ASYmmetry parameter (ASY) revealed a decreasing trend with increasing wavelength, and this decreasing trend was more pronounced during summer, winter and post-monsoon as compared to pre-monsoon. Furthermore, extensive measurements suggest that both real (RRI) and imaginary (IRI) parts of the Refractive Index (RI) show contrasting spectral behavior during all seasons. Finally, the analysis of the NOAA HYSPLIT back trajectory revealed that the seasonal variation in aerosol types was influenced by contribution of air masses from multiple source locations.

The effects of femtosecond laser pulse width on the formation of micro-structured silicon

Yiming Zhu, Kun Luo, Xiangqian Chen, and Yan Peng

Doc ID: 263960 Received 25 Apr 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: We experimentally investigated the properties of the surface micro-structured silicon fabricated by 15 and 130 fs laser pulses. By changing parameters of femtosecond laser pulses, including laser flux, actual pulse acting time and laser peak intensity we found that the average height of spikes on the surface of micro-structured silicon are only determined by the laser peak intensity. These results are important for the preparation and structure control of micro-structured silicon.

Performance of low-cost few-mode FBG sensor systems: polarization sensitivity and linearity of temperature and strain response

Denis Ganziy, Bjarke Rose, and Ole Bang

Doc ID: 264060 Received 26 Apr 2016; Accepted 07 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: We evaluate whether 850nm FBG sensor systems can use low-cost 1550 nm telecom fibers, in other words, how detrimental the influence of higher-order modes is to the polarization stability and the linearity of the strain and temperature response. We do this by comparing polarization sensitivity of a few-mode 850nm FBG sensor to a strictly single-mode 850nm FBG sensor system using 850 nm single-mode fibers. We also compare the performance of the FBGs in strain and temperature tests. Our results show that the polarization stability and the linearity of the response degrade due to the presence of the higher-order modes. We demonstrate that using simple coiling of the 1550 nm fiber one can regain the performance of the few-mode system and make it usable for high precision measurements.

Creating Airy beams employing a transmissive spatial light modulator

Tatiana Latychevskaia, daniel schachtler, and Hans-Werner Fink

Doc ID: 262560 Received 05 Apr 2016; Accepted 07 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: We present a detailed study of two novel methods for shaping the light optical wavefront by employing a transmissive spatial light modulator (SLM). Conventionally, optical Airy beams are created by employing SLMs in the so-called all phase mode. In the first method, a numerically simulated lens phase distribution is loaded directly onto the SLM, together with the cubic phase distribution. An Airy beam is generated at the focal plane of the numerical lens. We provide for the first time a quantitative properties of the formed Airy beam. We derive the formula for deflection of the intensity maximum of the so formed Airy beam, which is different to the quadratic deflection typical of Airy beams. We cross-validate the derived formula by both simulations and experiment. The second method is based on the fact that a system consisting of a transmissive SLM sandwiched between two polarisers can create a transmission function with negative values. This observation alone has the potential for various other wavefront modulations where the transmission function requires negative values. As an example for this method, we demonstrate that a wavefront can be modulated by passing SLM system with transmission function with negative values by loading Airy function distribution directly onto SLM. Since the Airy function is a real-valued function but with negative values, an Airy beam can be generated by direct transfer of the Airy function distribution onto such an SLM system. In this way, an Airy beam is generated immediately behind the SLM. As both new methods do not employ a physical lens, the two setups are more compact than conventional setups for creating Airy beams. We compare the performance of the two novel methods and the properties of the created Airy beams.

Linearity enhancement of scale factor in optical interrogated micromechanical accelerometer

Li Shuang Feng, Yu Zhang, Xiao Wang, and yang wang

Doc ID: 265388 Received 16 May 2016; Accepted 07 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: A method to reduce the residual stress of support arms in optical interrogated micromechanical accelerometer is proposed in order to enhance the linearity of scale factor of accelerometer. Firstly, the behavior of residual stress in support arms is analyzed in detail, and the simulation of shape curvature caused by residual stress in aluminum-made support arms is completed using finite element analysis (FEA). Then, by comparing two different materials of support arms (aluminum-made and silicon-made support arms), a modified fabrication is introduced in order to reduce the unexpected residual stress in support arms. Finally, based on contrast experiments, the linearity of scale factor of accelerometers with aluminum-made and silicon-made support arms are measured using force feedback test system, respectively. Results show that the linearity of scale factor of accelerometer with silicon-made support arms is 0.85%, which is reduced about an order of magnitude than that of accelerometer with aluminum-made support arms with the linearity of scale factor of 7.48%, linearity enhancement of scale factor is validated in optical interrogated micromechanical accelerometer. This allows accuracy improvement of accelerometer in the application of inertial navigation and positioning.

A Comparison of Three Dimensional Particle Tracking and Sizing using Plenoptic Imaging and Digital In-line Holography

Daniel Guildenbecher, Brian Thurow, and Elise Hall

Doc ID: 264468 Received 03 May 2016; Accepted 07 Jul 2016; Posted 14 Jul 2016  View: PDF

Abstract: Digital in-line holography and plenoptic photography are two techniques for single-shot, volumetric measurement of 3D particle fields. Here we present a comparison of the two methods by applying plenoptic imaging to experimental configurations that have been previously investigated with digital in-line holography. These experiments include the tracking of secondary droplets from the impact of a water drop on a thin film of water and tracking of pellets from a shotgun. Both plenoptic imaging and digital in-line holography successfully quantify the 3D nature of these particle fields. This includes measurement of the 3D particle position, individual particle sizes, and three-component velocity vectors. For the initial processing methods presented here, both techniques give out-of-plane positional accuracy of approximately 1-2 particle diameters. For a fixed image sensor, digital holography achieves higher effective in-plane spatial resolutions. However, collimated and coherent illumination makes holography susceptible to image distortion through index of refraction gradients, as demonstrated in the shotgun experiments. On the other hand, plenoptic imaging allows for a simpler experimental configuration and, due to the use of diffuse, white-light illumination, plenoptic imaging is less susceptible to image distortion in the shotgun experiments.

Optical reflectance of pyrheliometer absorption cavities: progress towards SI-traceable measurements of solar irradiance

Heather Patrick, Thomas Germer, Clarence Zarobila, Catherine Cooksey, and Howard Yoon

Doc ID: 263998 Received 20 May 2016; Accepted 06 Jul 2016; Posted 20 Jul 2016  View: PDF

Abstract: We have accurately determined the absorptance of three pyrheliometer cavities at 532 nm by measuring the residual reflectance using an angle-resolved bidirectional reflectometer. Measurements were performed at normal incidence as a function of viewing angle and position on the cavity cone. By numerically integrating the measured angle resolved scatter (ARS) over both direction and position and accounting for an obstructed view of the cavity, we determined that the effective cavity reflectance was between 8 × 10-4 and 9 × 10-4. Thus, the absorptance of the three cavities ranged from 0.99909 (0.00014) to 0.99922 (0.00012) where the values in parentheses indicate the k = 2 expanded uncertainties. These measurements, when extended over the spectral range of operation of the pyrheliometer, are required to establish SI traceability for absolute solar irradiance measurements.

Diffraction-based Sensitivity Analysis for an External Occulter Laboratory Demonstration

Dan Sirbu, Yunjong Kim, N Kasdin, and Robert Vanderbei

Doc ID: 260850 Received 14 Mar 2016; Accepted 06 Jul 2016; Posted 06 Jul 2016  View: PDF

Abstract: An external flower-shaped occulter flying in formation with a space telescope can theoretically provide sufficient starlight suppression to enable direct imaging of an Earth-like planet. Occulter shapes are scaled to enable experimental validation of their performance at laboratory dimensions. Previous experimental results have shown promising performance but have not realized the full theoretical potential of occulter designs. Here, we develop a two-dimensional diffraction model for optical propagations for occulters incorporating experimental errors. We perform a sensitivity analysis, and comparison with experimental results from a scaled-occulter testbed validates the optical model to the $10^{-10}$ contrast level. The manufacturing accuracy along the edge of the occulter shape is identified as the limiting factor to achieving the theoretical potential of the occulter design. This hypothesis is experimentally validated using a second occulter mask manufactured with increased edge feature accuracy and resulting in a measured contrast level approaching the $10^{-12}$ level -- a better than one order of magnitude improvement in performance.

Degradation non-uniformity in the solar diffuser bidirectional reflectance distribution function

Junqiang Sun, Mike Chu, and Menghua Wang

Doc ID: 261672 Received 22 Mar 2016; Accepted 04 Jul 2016; Posted 06 Jul 2016  View: PDF

Abstract: The assumption of angular dependence stability of the solar diffuser (SD) through out degradation is critical to the on-orbit calibration of the reflective solar bands (RSB) in many satellite sensors. Recent evidence has pointed to the contrary, and in this work we present a thorough investigative effort into the angular dependence of the SD degradation for the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard Suomi National Polar-orbiting Partnership (SNPP) satellite and for the twin Moderate-resolution Imaging Spectroradiometer (MODIS) onboard Terra and Aqua spacecrafts. One common key step in the RSB calibration is the use of the SD degradation performance measured by an accompanying solar diffuser stability monitor (SDSM) as a valid substitute for the SD degradation factor in the direction of the RSB view. If SD degradations between these two respective directions do not maintain the same relationship then the unmitigated use of the SDSM-measured SD degradation factor in the RSB calibration calculation will generate bias and consequently long-term drift in derived science products. We exploit the available history of the on-orbit calibration events to examine the response of the SDSM and the RSB detectors to the incident illumination reflecting off SD versus solar declination angle and show that the angular dependency, in particular at short wavelengths, evolves with respect to time. The decisive conclusion is that the bidirectional reflectance distribution function (BRDF) of the SD degrades non-uniformly with respect to both incident and outgoing directions. The analysis also reveals additional interesting phenomena, for example the abrupt behavioral change in the evolving angular dependence observed in Terra MODIS. For SNPP VIIRS the mitigation for this “SD degradation non-uniformity effect” with respect to angles relies on a “Hybrid Methodology” using lunar-based calibration to set the reliable long-term baseline. For MODIS, the use of earth targets in the major release Collection 6 to improve calibration coefficients and time-dependent response-versus-scan-angle (RVS) characterization inherently averts the use of SD and its associated issues. The work further supports that having an open-close operational capability for the space view door can minimize SD degradation and its associated effects due to solar exposure, and thus provide long-term benefits for maintaining calibration and science data accuracy.

Ground-based detection of nighttime clouds aboveManila Observatory (14.64N, 121.07E) using a digitalcamera

Glenn Franco Gacal, Nofel Lagrosas, and Carlo Antioquia

Doc ID: 260064 Received 25 Feb 2016; Accepted 04 Jul 2016; Posted 06 Jul 2016  View: PDF

Abstract: Ground-based cloud detection at nighttime is achieved by using cameras, lidars, and ceilometers. Despite thesenumerous instruments gathering cloud data, there is still an acknowledged scarcity of information on quantifiedlocal cloud cover, especially at nighttime. In this study, a digital camera is used to continuously collect imagesnear the sky zenith at nighttime in an urban environment. An algorithm is developed to analyze pixel values ofimages of nighttime clouds. A minimum threshold pixel value of 17 is assigned to determine cloud occurrence.The algorithm uses temporal averaging to estimate the cloud fraction based on the results within the limitedfield of view. The analysis of the data from the months of January, February, and March 2015 shows that cloudoccurrence is low during the months with relatively lower minimum temperature (January and February) whilecloud occurrence during the warmer month (March) increases.

Compensation of fringe distortion for phase-shifting 3D shape measurement by inverse map estimation

Kohei Yatabe, Kenji Ishikawa, and Yasuhiro Oikawa

Doc ID: 265480 Received 17 May 2016; Accepted 03 Jul 2016; Posted 06 Jul 2016  View: PDF

Abstract: For three-dimensional shape measurement, phase-shifting techniques are widely used to recover objective phase containing height information from images of projected fringes. Although such techniques can provide an accurate result in theory, there might be huge error in practice. One main cause of such error is distortion of fringes owing to non-linearity of a measurement system. In this paper, a post-processing method for compensating distortion is proposed. Comparing to other compensation methods, the proposed method is flexible in two senses: (1) no specific model of non-linearity (such as gamma model) is needed; and (2) no special calibration data is needed (only observed image of fringe is required). Experiments using simulated and real data confirmed that the proposed method can compensate multiple types of non-linearity without concerning its model.

High Raman-to-fluorescence ratio of Rhodamine6G excited with 532nm laser wavelength Using a closely-packed, self-assembled monolayer of silver nanoparticles.

Seyed Hassan Tavassoli, Najmeh Sadegh, and Hossein Khadem

Doc ID: 260435 Received 10 Mar 2016; Accepted 03 Jul 2016; Posted 11 Jul 2016  View: PDF

Abstract: Highly efficient Raman to fluorescence ratio of Rhodamine6G obtained by means of 532nm laser wavelength which is in close proximity of the dye's absorption maximum. Closely-packed, gap-filled self-assembled monolayers of silver nanoparticles were produced to observe the Raman signals of rhodamine 6G. Two mechanisms contribute to detect the Raman signals of the fluorescent sample: Surface Enhanced Raman Scattering (SERS) and Nanomaterial Surface Energy Transfer (NSET). Self-assembled monolayers of silver nanoparticles with different coverage densities and also those filled with probe molecules were prepared through variation of substrate's immersion time in nanoparticle solution and drying the substrate, respectively. Examination of the effects of these two factors on the plasmonic response and SERS efficiency of substrate revealed that in a gap-filled dense coverage, near-field interactions dominate, which remarkably increase the Raman-to-fluorescence ratio (RFR). To have a perfect dense coverage, the efficient immersion time was obtained about 48 hours. Drying the substrates also caused further enhancement in RFR through filling inter-particle spaces with dye molecules and, accordingly, an increase in NSET efficiency.

Characterization of optical polarization properties forliquid-crystal based retarders

Juan López-Téllez, Neil Bruce, and Oscar Rodriguez Herrera

Doc ID: 259239 Received 10 Feb 2016; Accepted 01 Jul 2016; Posted 06 Jul 2016  View: PDF

Abstract: We present the analysis and implementation of a set of experimental procedures to characterize opticalpolarization properties as a function of the applied voltage for liquid-crystal variable retarders (LCVRs), intransmission mode. The studied properties are those involved in the operation of the LCVRs and, generally, are themost significant for optical applications: retardance, diattenuation, optical axes position, and output depolarizationeffects. The correct characterization of these polarization properties can be useful to improve results, or estimateerrors, in applications using these devices. The results obtained show good accuracy and good agreement with theexpected results.

Volume holographic printing using unconventional angular multiplexing for three-dimensional display

Liangcai Cao, Zheng Wang, Hao Zhang, Guofan Jin, and Claire Gu

Doc ID: 262268 Received 07 Apr 2016; Accepted 01 Jul 2016; Posted 06 Jul 2016  View: PDF

Abstract: We propose and demonstrate a volume holographic printing method for dynamic three-dimensional (3-D) display with expanded space-bandwidth product (SBP) using unconventional angular multiplexing techniques. By wavefront encoding of the 3-D scene, with the help of computer-generated holography, the object beam is loaded onto a 2-D phase spatial light modulator (SLM) with a limited SBP. The printing method then writes a single hologram through the interference of the object beam with a reference beam as a holographic element (hogel) in the volume holographic polymer. In addition, multiple 3-D scenes can be recorded and dynamically reconstructed by angular multiplexing in the same hogel location. The SBP can be increased by two orders of magnitude compared to the conventional holographic printing method, showing the potential to realize a dynamic and high-resolution 3-D display.

Smart electro-optical iris diaphragm based on liquid crystal films coating with photoconductive polymer of poly(N-vinyl carbazole)

Shing Trong Wu, Andy Y.-G. Fuh, and chen Konan

Doc ID: 263245 Received 14 Apr 2016; Accepted 01 Jul 2016; Posted 06 Jul 2016  View: PDF

Abstract: This study develops an electro-optical light shutter that adjusts the transmittance upon the intensities of the exposed UV lights. The LC film applies the photoconductive material of poly(N-vinyl carbazole) (PVK) based on twist nematic (TN) liquid crystals (LCs). The device becomes optical sensitive to UV light from the hole-transport layer of PVK. Further, it could be operated under a parallel/cross-polarizer to change the light beam/ring in optic integrated system.

Automated alignment of a reconfigurable optical system using focal-plane sensing and Kalman filtering

Joyce Fang and Dmitry Savransky

Doc ID: 261436 Received 18 Mar 2016; Accepted 30 Jun 2016; Posted 01 Jul 2016  View: PDF

Abstract: Automation of alignment tasks can provide improved efficiency and greatly increase the flexibility of an optical system. Current optical systems with automated alignment capabilities are typically designed to include a dedicated wavefront sensor. Here, we demonstrate a self-aligning method for a reconfigurable system using only focal plane images. We define a two lens optical system with eight degrees of freedom. Images are simulated given misalignment parameters using ZEMAX software. We perform a principal component analysis (PCA) on the simulated dataset to obtain Karhunen-Loève (KL) modes, which form the basis set whose weights are the system measurements. A model function which maps the state to the measurement is learned using multivariate regression and serves as the measurement function for the optimal estimator (Extended and Unscented Kalman filters) used to calculate control inputs to align the system. We present and discuss both simulated and experimental results of the full system in operation.

Surface-enhanced coherent anti-Stokes Raman imaging of lipids

Eric Potma, Alexander Fast, John Kenison, and Christopher Syme

Doc ID: 265073 Received 13 May 2016; Accepted 30 Jun 2016; Posted 01 Jul 2016  View: PDF

Abstract: A wide-field surface-enhanced coherent anti-Stokes Raman scattering (CARS) microscope, which enables enhanced detection of sample structures in close proximity (~100 nm) of the substrate interface, is described in detail. Unlike in conventional CARS microscopy, where the sample is illuminated with freely propagating light, the current implementation utilizes evanescent fields to drive Raman coherences across the entire object plane. By coupling the pump and Stokes excitation beams to the surface plasmon polariton mode at the interface of a 30 nm thick gold film, strong CARS signals from cholesteryl oleate droplets adhered to the surface are obtained. It is shown that the surface-enhanced CARS imaging system visualizes lipid structures with vibrational selectiviyty using illumination doses per unit area that are more than three orders of magnitide lower than in point-scanning CARS microscopy.

Improved quantitative visualization of hyper-velocity flow through wavefront estimation based on shadow-casting of sinusoidal gratings

R. Vasu, Biswajit Medhi, Gopalkrishna Hegde, Sai Gorthi, Kalidevapura Polareddy Reddy, and Debasish Roy

Doc ID: 263736 Received 21 Apr 2016; Accepted 29 Jun 2016; Posted 06 Jul 2016  View: PDF

Abstract: A simple non-interferometric optical probe is developed to estimate wavefront distortion suffered bya plane wave, in its passage through density variations in a hypersonic flow obstructed by a testmodel in a typical shock tunnel. The probe has a plane light wave trans-illuminating the flow andcasting a shadow of a continuous tone sinusoidal grating. Through a geometrical optics, eikonalapproximation to the distorted wavefront, a bilinear approximation to it is related to the locationdependentshift (distortion) suffered by the grating, which can be read out space-continuously fromthe projected grating image. The processing of the grating shadow is done through an efficientFourier fringe analysis scheme, either with a windowed or global Fourier transform (WFT and FT ).For comparison, wavefront slopes are also estimated from shadows of random-dot patterns, processedthrough cross-correlation. The measured slopes are suitably unwrapped by using a discrete cosinetransform ( DCT )-based phase unwrapping procedure, and also through iterative procedures. Theunwrapped phase information is used in an iterative scheme, for a full quantitative recovery of densitydistribution in the shock around the model, through refraction tomographic inversion. Hypersonicflow field parameters around a missile shaped body at a free-stream Mach number of ~8 measuredusing this technique are compared with the numerically estimated values. It is shown that, whilstprocessing a wavefront with small space-bandwidth product ( SBP ) the FT inversion gave accurateresults with computational efficiency; computation-intensive WFT was needed for similar resultswhen dealing with larger SBP wavefronts.

A new least-squares method for data reconstruction from gradient data in deflectometry

Xiangqian Jiang, Feng Gao, and hongyu ren

Doc ID: 261344 Received 18 Apr 2016; Accepted 28 Jun 2016; Posted 30 Jun 2016  View: PDF

Abstract: Least-squares integration (LSI) and radial basis function integration (RBFI) methods are widely used to reconstruct specular surface shape from gradient data in a deflectometry measurement. The traditional LSI method requires gradient data having a rectangular grid, and RBFI method is effective at handling small size measurement data set. Practically, the amount of gradient data is rather large and data grids are in quadrilateral shapes. With this in mind, a new LSI method is proposed to integrate gradient data, which is based on an approximation that normal vector of one point is perpendicular to the vectors connecting points at either side. A small measurement data set integrated by RBFI method is employed as a supplementary constraint of the proposed method. Simulation and experimental results show that this proposed method is effective and accurate at handling deflectometry measurement.

Oversaturated part-based visual tracking via Spatio-temporal Context learning

liu wei, Jicheng Li, Zhiguang Shi, Xiaotian Chen, and Xiao Chen

Doc ID: 263446 Received 18 Apr 2016; Accepted 27 Jun 2016; Posted 29 Jun 2016  View: PDF

Abstract: Partial occlusion is one of the key challenging factors in a robust visual tracking method. To solve this issure, part-based trackers are widely explored, while most of which are computationally expensive and therefore infeasible for real-time applications. Context information around the target has been used in tracking, which is renewed by spatio-temporal context (STC) tracker recently, the Fast Fourier Transform adopted in STC equips it with high efficiency. However, the global context used in STC alleviates the performance when dealing with occlusion. In this paper, we propose an oversaturated part-based tracker based on spatio-temporal context learning (OPSTC), which tracks objects based on selected parts with spatio-temporal context learning respectively. Furthermore, a structural layout constraint and a novel model update strategy are utilized to enhance the tracker’s anti-occlusion ability and deal with other appearance changes effectively. Extensive experimental results demonstrate our tracker’s superior robustness against the original STC and other state-of-art methods.

Development of an optical microscopy system for automated bubble cloud analysis.

Daniel Wesley, Stuart Brittle, and Daniel Toolan

Doc ID: 260966 Received 11 Mar 2016; Accepted 22 Jun 2016; Posted 08 Jul 2016  View: PDF

Abstract: Recently, the number of uses of bubbles has begun to increase dramatically, with medicine, biofuel production and wastewater treatment just some of the industries taking advantage of bubble properties, such as high mass transfer. As a result, more and more focus is being placed on the understanding and control of bubble formation processes and there are currently numerous techniques utilised to facilitate this understanding. Acoustic bubble sizing (ABS) and laser scattering have long held the advantage over photographic methods due to the high levels of automation. This paper demonstrates how photographic methods can be improved upon utilising machine vision to yield high levels of automation, comparable to the other techniques outlined. We also discuss the added benefits of the photographic system and how it is possible to obtain considerable additional information above and beyond that which ABS and laser scattering can supply. This work could easily be exploited by both industrial scale operations and small scale laboratory studies, as the simplistic and cost effective approach is highly transferrable and intuitive to use.

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