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Accepted papers to appear in an upcoming issue

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Impact of the scattering phase function on the bulk reflectance of a turbid medium with large-scale inhomogeneities.

Vitaliy Marinyuk and Sergey Sheberstov

Doc ID: 294770 Received 28 Apr 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We study the total bulk reflectance of a turbid medium with large (as compared to the light wavelength)inhomogeneities at grazing angles of light incidence. To model highly forward scattering in the medium,we take advantage of the Reynolds-McCormick scattering phase function. Using the scaling analysis forthe small-angle radiative transfer equation, we derive simple analytical formulae for the total reflectance.For grazing incidence angles, we find a range of values of the medium transport coefficients where thetotal reflectance proves to be a universal function of a single parameter which is expressed in terms ofthe incidence angle, the absorption coefficient and the transport scattering one. The explicit form of thisfunction is governed by the specific angular profile of the scattering phase function. The results obtainedare verified by comparison with results of a direct numerical integration of the radiative transfer equation.

Elimination of self-mode-locking pulses in high powerCW Yb-doped Fiber Lasers with external feedback

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

Doc ID: 298293 Received 16 Jun 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: Sustained self-pulsing and self-mode-locking (SML) are detrimental to the performance of CW fiber lasers.We demonstrated an all-fiber method to eliminate the SML pulsing by employing a low reflectivity fiber Bragggrating (FBG) outside of laser cavity to provide feedback. A narrow bandwidth FBG is used to form an externalcavity with the output coupler FBG which suppresses the SML, up to a certain output power level, at which, the laseremission linewidth is still within the bandwidth of the FBG. On the other hand a broad bandwidth FBG forms achirped cavity with the output coupler FBG which can suppress the SML at a much higher power level, tested up to50W. This method provides a simple effective all-fiber solution for suppressing self-pulsing in CW fiber lasers athigh pump levels with no need to change the laser configuration.

A positive dwell time algorithm with minimum equal extra material removal in deterministic optical surfacing technology

Longxiang Li, Xue Donglin, Weijie Deng, Xu Wang, Yang Bai, Feng Zhang, and Xuejun Zhang

Doc ID: 301538 Received 05 Jul 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: In deterministic computer-controlled optical surfacing, accurate dwell time execution by CNC machines is crucial in guaranteeing a high convergence ratio for optical surface error. However, machine dynamics limitations are always ignored by numerical dwell time algorithms. In this paper, these constraints on dwell time distribution are analyzed and a model of the equal extra material removal is established. A positive dwell time algorithm with minimum equal extra material removal is developed. Results of simulations based on deterministic Magnetorheological Finishing demonstrate the necessity of considering machine dynamics performance and the validity of the proposed algorithm. Indeed, the algorithm effectively facilitates the determinacy of sub-aperture optical surfacing processes.

Fiber-integrated refractive index sensor based on a diced Fabry-Perot micro-resonator

Sergiy Suntsov, Christian Rüter, Tom Schipkowski, and Detlef Kip

Doc ID: 302519 Received 14 Jul 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We report on a fiber-integrated refractive index sensor based on a Fabry-Perot micro-resonator fabricated using simple diamond blade dicing of a single-mode step-index fiber. The performance of the device has been tested for the refractive index measurements of sucrose solutions as well as in air. The device shows a sensitivity of 1160 nm/RIU at a wavelength 1.55 µm and a temperature cross-sensitivity of less than 10-7 RIU/K. Based on evaluation of the broadband reflection spectra, refractive index steps of 10-5 of the solutions were accurately measured. The conducted coating of the resonator sidewalls with layers of a high-index material with real-time reflection spectrum monitoring could help to significantly improve the sensor performance.

Astigmatism-free Czerny-Turner compactspectrometer with cylindrical mirrors

Guo Xia, Su Wu, guodong wang, Mingyong Hu, and Jinyu Xing

Doc ID: 303082 Received 21 Jul 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: A modified optical design for broadband, high resolution, astigmatism-free Czerny-Turnerspectrometer is proposed. Astigmatism is corrected by using cylindrical mirrors over a broad spectralrange. The theory and method for astigmatism-correction are thoroughly analyzed. The comparisonbetween the modified Czerny-Turner spectrometer and the traditional Czerny-Turner spectrometer isalso described in detail. The ray-tracing results show that RMS spot radius has decreased to 4.2 μm atthe central wavelength and 17μm at the wedge wavelength.

Frequency and timing stability of an airborneinjection-seeded Nd:YAG laser system for directdetectionwind lidar

Christian Lemmerz, Oliver Lux, Oliver Reitebuch, Benjamin Witschas, and Christian Wuehrer

Doc ID: 303491 Received 26 Jul 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We report on the design and the performance of the laser deployed in the airborne demonstrator Doppler windlidar for the Aeolus mission of the European Space Agency (ESA). The all-solid-state, diode-pumped and frequencytripledNd:YAG laser is realized as a master oscillator power amplifier (MOPA) system, generating 60 mJ of singlefrequencypulses at 355 nm wavelength, 50 Hz repetition rate and 20 ns pulse duration. For the measurement ofthe Doppler frequency shift over several accumulated laser shots, the frequency stability of the laser is of crucialimportance. Injection-seeding in combination with an active cavity control based on the Ramp-Delay-Firetechnique provides a pulse-to-pulse frequency stability of 0.25 MHz measured at 1064 nm under laboratoryconditions. This value increases to 0.31 MHz for airborne operation in a vibration environment that has beencharacterized by multiple acceleration sensors during different flight conditions. In addition, a pure Ramp-Firesetting was tested for comparison leading to a frequency stability of 0.16 MHz both in airborne operation and onground. The laser cavity control electronics have to provide a trigger signal also for the lidar detection electronics,but about 60 μs prior to the expected laser pulse emission and with high timing stability. An in-flight timingstability of below 100 ns was measured decreasing to 20 ns for a shorter pre-trigger time of 10 μs.

A Hybrid Artificial Bee Colony Algorithm for Parameter Optimization of Five-parameter BRDF Model

Qianqian Wang, Jing Zhao, Yong Gong, Qun Hao, and Zhong Peng

Doc ID: 303914 Received 02 Aug 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: A hybrid artificial bee colony (ABC) algorithm inspired by the best-so-far solution and bacterial chemotaxis was introduced to optimize the parameters of the five-parameter bidirectional reflectance distribution function (BRDF) model. To verify the performance of the hybrid ABC algorithm, we measured BRDF of three kinds of materials and simulated the undetermined parameters of the five-parameter BRDF model using the hybrid ABC algorithm and the genetic algorithm, respectively. The experimental results demonstrate that the hybrid ABC algorithm outperforms the genetic algorithm in convergence speed, accuracy and time-efficiency under the same conditions.

A compact single-shot d-scan setup for the characterization of few-cycle laser pulses

Maité Louisy, Chen Guo, Lana Neoričić, Shiyang Zhong, Anne L'Huillier, Cord Arnold, and Miguel Miranda

Doc ID: 305207 Received 29 Aug 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We present a compact implementation of the ultrashort pulse measurement technique based on dispersion scans (d-scan), allowing single-shot measurement of few-cycle pulses.The main novelty in our design, making our setup extremely compact and simple, is the use, after a prism, of a spherical mirror in an off-axis geometry. The intentionally introduced strong astigmatism makes it possible to image the output of the crystal in one direction while focusing it in the other direction, resulting in the output face of the prism being imaged into a line in the second harmonic crystal. The technique is validated by comparing measured dispersion scans, retrieved spectral phases and temporal profiles of this single-shot system with standard d-scan results.

Microwave Photonic Filter-Based Interrogation Systemfor Multiple Fiber Bragg Grating Sensors

Maria Iulia Comanici, Lawrence Chen, and Peter Kung

Doc ID: 305632 Received 25 Aug 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: Fiber optic sensors based on fiber Bragg gratings (FBGs) find potential use in condition monitoring because theirspectral properties change according to external environmental and/or physical factors. We propose and demonstratea technique for interrogating multiple FBG-based sensors based on microwave photonic (MWP) filtering. In particular,we exploit the spectrum slicing properties of two different FBG Fabry-Pérot cavities to implement a double passbandMWP filter. Each sensor spectrum results in a unique MWP filter passband. As temperature is applied to a sensor, thecorresponding MWP filter passband will shift in frequency; we track such shifts by monitoring the detected power at afixed RF frequency. We discuss the use of a ratiometric approach for enhancing the sensitivity and the impact of crosstalkfrom the MWP filter responses in terms of simultaneous multi-sensor operation. Results show that we canmonitor local temperatures at two (or multiple) different locations simultaneously and independently using a singlemeasurement system.

Watt-level tunable 1.5 μm narrow linewidth fiber ring laser based on a temperature tuning π-phase shifted fiber Bragg grating

junjie sun, Zefeng Wang, meng wang, Zhiyue Zhou, Ni Tang, Jinbao Chen, and Xijia Gu

Doc ID: 306437 Received 06 Sep 2017; Accepted 16 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: A watt-level tunable 1.5 μm narrow linewidth fiber ring laser using a temperature tuning π-phase shifted fiber Bragg grating (π-PSFBG) is demonstrated here, to the best of our knowledge, for the first time. The π-PSFBG is employed as both a narrow band filter and a wavelength tuning component, and its central wavelength is thermally tuned by a thermo-electric cooler. The maximum laser power is about 1.1 W with a linewidth of ~318 MHz (~2.57 pm) and a power fluctuation of less than 3%. The wavelength tuning range of the laser is about 1.29 nm with a sensitivity of ~14.33 pm/˚C, and the wavelength fluctuation is about 0.2 pm. This work provides important reference for tunable fiber lasers with both high power and narrow linewidth.

Reduction of the effects of angle errors for achanneled spectropolarimeter

Xue Ping Ju, Bin Yang, Junqiang Zhang, and Changxiang Yan

Doc ID: 306147 Received 31 Aug 2017; Accepted 15 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: Angle errors of high-order retarders will decrease the accuracy of a channeled spectropolarimeter. This paperpresents an easily-implemented and widely-applicable method for reducing the effects of the angle errors. Firstly,we theoretically derive a modified reconstruction model to express and analyze the effects of the angle errors.Based on the modified reconstruction model and current reference beam calibration technique, we put forwardthe modified reference beam calibration technique to reduce the effects of the angle errors. This method cancalculate the angle errors by employing the amplitude terms, which have been ignored in the results of the currentreference beam calibration. The effectiveness of the presented method is verified by numerical simulations, whichshow that the demodulated deviations of polarization parameters have been reduced by one order of magnitude.Experiments are further implemented to validate the proposed method. The convenience and wide applicability ofthe presented method make it suitable for regular correction of the instrument, especially for the case on track.

Manipulating and detecting the chirpyness of spatialchirp signals via fractional Fourier lenses designed bytransformation optics

JING CHEN, Jin Hu, XIAO-BO YANG, and Xiangyang Lu

Doc ID: 302277 Received 17 Jul 2017; Accepted 15 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: Estimating the chirpyness of a spatial chirp signal is important in many optical engineering applications. With thehelp of transformation optics, a new kind of fractional Fourier transform lens is designed by deforming theconventional graded index lens through a conformal mapping, which can manipulate the chirpyness of the inputchirp signal. The low-input chirpyness is magnified by the transformation material, and the error of the detection iskept approximately the same; thus, the designed lens has enhanced chirpyness detection precision anddistinguishability for the low chirpyness. The design is validated by numerical simulations.

Modeling near-null testing method of freeform surface with deformable mirror compensator

He Yiwei, Lei Huang, Xi Hou, wu fan, and Rongguang Liang

Doc ID: 303021 Received 21 Jul 2017; Accepted 14 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: We present and analyze a new measurement method of freeform surfaces with a deformable mirror (DM), which functionsas a wavefront compensator. We discuss the maximum slope compensation of DM in the first order approximation andderive how to calculate the ideal DM form. A constrained optimization procedure is conducted to ensure the actual DM formfit the ideal DM form as close as possible. To demonstrate the feasibility and understand the measurable range of ourmethod, we evaluate freeform surfaces with a single Zernike term, the first 36 random Zernike terms, and 0 randomZernike terms, respectively. A tolerance analysis of the DM position is carried out to show the effect of the tilt and decenterof DM on the measurement accuracy. Our studies show that the proposed system is very flexible for freeform surfacemetrology.

Multi-element direct design using a freeform surface for a compact illumination system

Zhenfeng Zhuang, philip Surman, and Simon Thibault

Doc ID: 304790 Received 14 Aug 2017; Accepted 14 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: An iterative optimization algorithm is introduced to address the surface iterative errors as well as source extension issues in freeform illumination system for producing satisfactory illumination distribution. A unique two-parameter coordinate system is utilized to represent the emitted ray directions. Then, the direction vector for the incident rays, which propagate through several surfaces, is obtained using ray-tracing techniques. Based on the mapping between the incoming rays and a target grid, a freeform surface is generated as a good starting design. An iterative optimization strategy is further employed to alleviate the deterioration of illumination distribution on the target region, and the uniformity of the illumination system is evaluated during optimization. Very few variables are demanded and more flexibility in the design of the freeform surface is offered. Successive iterations can be performed until the desired result is attained. An optical system is used as an example to demonstrate the validity of this method, and numerical simulations are carried out to evaluate the optical performance. The simulation results show that a small angular intensity distribution and prescribed rectangular illumination pattern can be achieved simultaneously.

Theoretical investigation on mid-infrared cascaded Raman fiber laser based on tellurite fiber

Chenquan Ni, Weiqing Gao, Xiangcai Chen, Li Chen, Zhou Yong, Zhang Wei, Jigang Hu, Meisong Liao, Takenobu Suzuki, and Yasutake Ohishi

Doc ID: 306677 Received 07 Sep 2017; Accepted 13 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: A numerical simulation of 3rd-order cascaded Raman fiber laser based on tellurite fiber at 2-5 μm waveband is presented. The Raman fiber laser can be optimized with the most suitable tellurite fiber length of 0.5-1.0 m and the most reasonable reflectivity of the 3rd-order Stokes output FBG32 of 10%-20%. We demonstrate numerically that the 3rd-order Stokes wave can reach the maximum average power of 44 W and the maximum optical conversion efficiency of 44% corresponding to the FBG32 reflectivity of 10% and the tellurite fiber length of 0.5 m with the attenuation of 0.85 dB/m, when pumped by 2 μm light with the average power of 100 W. Our simulated results provide a valuable theoretical guidance for the design and experiment of tellurite Raman fiber laser at mid-infrared waveband.

Refractive index measurement of suspended cells using opposed-view digital holographic microscopy

Juanjuan Zheng, Peng Gao, Xiaopeng Shao, and Gerd Nienhaus

Doc ID: 306258 Received 06 Sep 2017; Accepted 13 Oct 2017; Posted 13 Oct 2017  View: PDF

Abstract: Opposed-view digital holographic microscopy (OV-DHM) with autofocusing and out-of-focus background suppression was demonstrated and applied to measure the refractive index (RI) of suspended HeLa cells. In OV-DHM, a specimen is illuminated from two sides in a 4π-like configuration. The generated two opposite-view object waves, which have orthogonal polarization orientations, interfere with a common reference wave, and the generated holograms are recorded by a CMOS camera. The image plane of the sample was determined by finding the minimal variation between the two object waves. The out-of-focus background was suppressed by averaging the two object waves. Simultaneous determination of both the cell thickness and the phase retardation is avoided by using a spheroidal model for the detached cell obtained from confocal microscopy. Thus, the RI of suspended HeLa cells was measured from phase images of OV-DHM, with the thickness of the cells estimated by using a constant axial-to-lateral ratio. This stand-alone measurement strategy reveals the RI with an accuracy of ~10% of the RI difference between cell and surrounding medium.

Tailoring lens functionality by 3D-laser printing

Shlomi Lightman, Gilad Hurvitz, Raz Gvishi, and Ady Arie

Doc ID: 304299 Received 07 Aug 2017; Accepted 13 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: Conversion of a Gaussian beam into a top-hat beam or to an annular beam is demonstrated using 3D direct laser printing. Micron-scale refractive phase elements were designed and printed directly on standard commercially available lenses. These structures modify the phase of the incoming beam into either three intensity-flattened profiles, having line, square or circular shapes, or to an annular beam profile. This method to functionalize lenses opens new and exciting opportunities for compact and robust beam shaping, as well as to reduce the aberrations of the lens itself.

On-stream analysis of iron ore slurry using laser-induced breakdown spectroscopy

Xiao Cheng, xinyan yang, Zhihao Zhu, Lianbo Guo, Xiangyou Li, Yongfeng Lu, and Xiaoyan zeng

Doc ID: 306054 Received 31 Aug 2017; Accepted 12 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: On-stream analysis of the elements content in ore slurry has important significance in the control of flotation process and full use of raw materials. Therefore, techniques that can monitor the chemistry in slurries online are required. Laser-induced breakdown spectroscopy (LIBS) is one of the potential approaches to online measurements due to its capability of in situ and real-time analysis. However, using LIBS for on-stream analysis of slurries is challenging due to the issues such as surface ripples, sample splashing, sedimentation, etc. To address these problems, we developed a slurry circulation system. The effects of slurry flow rate on LIBS spectra were investigated to achieve the optimal detecting surface for better repeatability of LIBS. The coefficient of determination R² of the calibration curve for Fe element is 0.982, and the limit of detection of Fe element was estimated to be 0.075 wt.% under the optimized experimental parameters. The results show that this slurry circulation system is applicable to the on-stream slurry analysis.

Automatic obscuration elimination for off-axis mirror systems

Chen Xu, Dewen Cheng, and Yongtian Wang

Doc ID: 306431 Received 06 Sep 2017; Accepted 11 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: The degree of automation in optical design has always been improving, and several human-competitive automatic lens design programs have been developed. However, no such works on off-axis systems have been reported, which we think is largely due to the complicated unfeasible conditions caused by obscuration. Here, we propose a model to detect and evaluate the degree of obscuration for off-axis mirror systems and also a method to automatically eliminate the obscuration by structural optimization. This effect of obscuration elimination is demonstrated by several examples. It can greatly facilitate the design of off-axis mirror systems. Particularly, the method can be applied in the search for feasible off-axis structures from on-axis ones. This work may provide insight for further study of human-competitive automatic design of off-axis systems.

Improved back-projection method for circular scanning based photoacoustic tomography with improved tangential resolution

Jiaying Xiao, Xiaofei Luo, Kuan Peng, and Bo Wang

Doc ID: 303726 Received 31 Jul 2017; Accepted 11 Oct 2017; Posted 13 Oct 2017  View: PDF

Abstract: While photoacoustic computed tomography (PACT) are generally built with planer transducers of finite size, most current reconstruction algorithms assume the transducer to be an ideal point, which leads to a spinning blur in the consequent obtained PACT images due to the model mismatch. To overcome this problem, here we put forward a new method that can factor in the geometry of the transducers to improve the tangential resolution. Compared with the model-based algorithms or other proposed methods, our proposed method inherits the robustness and minor calculation from the conventional back-projection algorithm, allows the fast reconstruction of the PACT images, and can greatly improve the fidelity of the reconstructed image. This method is evaluated in 2D circular scanning configurations with both simulated and experimental data. Results show that this method can effectively restore the tangential distortion of the PACT image with both simulated and experimental data, lower the background noise, and bring no other artifacts. The stability of this method was tested by changing the transducer size in the reconstruction parameter around the true value. Results also indicated that the improvement of the tangential resolution is more obvious for transducers with larger size. This method can also be extended to transducers with other geometrical surface other than planer ones. This method may help to guide the selection of transducer and design of scanning strategy in PACT.

Laser Display System for Multi-Depth Screen Projection Scenarios

Juan Pablo La Torre, Nathan Mayes, and Nabeel Riza

Doc ID: 302453 Received 18 Jul 2017; Accepted 11 Oct 2017; Posted 16 Oct 2017  View: PDF

Abstract: Proposed is a laser projection display system that uses an Electronically Controlled Variable Focus Lens (ECVFL) to achieve sharp and in-focus image projection over multi-distance Three Dimensional (3-D) conformal screens. The system also functions as an embedded distance sensor that enables 3-D mapping of the multi-level screen platform before the desired laser scanned beam focussed/defocused projected spot sizes are matched to the different localized screen distances on the 3-D screen. Compared to conventional laser scanning and Spatial Light Modulator (SLM) based projection systems, the proposed design offers in-focus non-distorted projection over a multi-distance screen zone with varying depths. An experimental projection system for a screen depth variation of 65 cm is demonstrated using a 633 nm laser beam, a 3 KHz scan speed galvo-scanning mirrors and a liquid-based ECVFL. As a basic demonstration, an in-house developed Matlab based Graphic User Interface (GUI) is deployed to work along with the laser projection display enabling user inputs such as text strings or predefined images projection. The user can specify projection screen distance, scanned laser line width, projected text font size, projected image dimensions and laser scanning rate. Projected images are shown highlighting the 3-D control capabilities of the display including the production of a non-distorted image onto two-depths versus a distorted image via dominant prior-art projection methods.

Carrier frequency tuning of few-cycle light pulses by Broadband Attenuating Mirror (BAM)

Olga Razskazovskaya, Marcus Ossiander, Florian Siegrist, Vladimir Pervak, and Martin Schultze

Doc ID: 303373 Received 26 Jul 2017; Accepted 11 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: We demonstrate the performance of a novel multilayer dielectric reflective thin-film attenuator capable of reshaping the super-octave spectrum of near-single-cycle visible laser pulses without deteriorating thephase properties of the reflected light. These novel Broadband Attenuating Mirrors (BAM) redistribute in a virtually dispersion free manner the spectral weight of the incident spectrum such, that the carrier wavelength of the reflected few-cycle pulses shifts from approx. 700 nm (Eg =1.77 eV) to approx. 540 nm (Eg =2.25 eV) or beyond while maintaining their initial pulse duration. This constitutes an elegant approach to convert conventional few-cycle ultrafast laser system into a source with an excitation wavelength broadly tunable to meet the requirements of single-/multi-color high-resolution spectroscopic experiments.

Refractive index profilometry using Total InternallyReflected light field

Tania Das and Kallol Bhattacharya

Doc ID: 304690 Received 11 Aug 2017; Accepted 11 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: A full field polarization-based technique is presented for quantitative evaluation of the spatial distribution ofrefractive index in macro and micro samples. The sample is mounted on a glass-air interface of a prism, illuminatedby a linearly polarized collimated light beam and two intensity frames are digitally recorded with specificorientations of an analyzer. The pair of intensity data frames captured with this simple setup is combined throughan algorithm specially developed for the purpose, to yield the phase difference between the transverse electric andtransverse magnetic components of the total internally reflected light field. The phase difference is then related tothe refractive index of the sample. Experimental results for refractive index variations in a laser etched glass plateand red blood corpuscles are presented. One of the salient features of the proposed technique is that the depth ofmeasurement is dependent on the penetration depth of the evanescent field in the sample, which is typically of theorder of a few hundred nanometers, thereby facilitating refractive index measurements along a thin section of thesample.

Comparison of photoemission characteristics between square and circular wire array GaAs photocathodes

Wenjuan Deng, xincun peng, Jijun Zou, Weilu Wang, yun Liu, tao Zhang, Yijun Zhang, and Daoli Zhang

Doc ID: 304272 Received 07 Aug 2017; Accepted 10 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: Two types of negative electron affinity gallium arsenide (GaAs) wire array photocathodes were fabricated by reactive ion etching and inductively coupled plasma etching of bulk GaAs material. High density GaAs wire arrays with high periodicity and good morphology were verified using scanning electron microscopy, and photoluminescence spectra confirmed the wire arrays had good crystalline quality. Reflection spectra showed that circular GaAs wire arrays had superior light trapping compared with square ones. However, after Cs/O activation, the square GaAs wire array photocathodes showed enhanced spectral response. The integral sensitivity of the square wire array photocathodes was as approximately 1.6 times as that of the circular arrays.

A Hybrid GWO-ANN Classification Approach for MR Brain Images

Heba Ahmed, Bayumy Youssef, Ahmed Elkorany, Adel Saleeb, and Fathi Abd El-Samie

Doc ID: 305109 Received 18 Aug 2017; Accepted 10 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: Automated and accurate classification of magnetic resonance images (MRI) of brain has great importance for medical analysis and interpretation. This paper presents a hybrid optimized classification method to classify the brain tumor by classifying the given MR brain image as normal or abnormal. The proposed system implements grey wolf optimizer (GWO) combined with supervised classifier Artificial Neural Network (ANN) so as to achieve enhanced MRI classification accuracy via selecting the optimal parameters of ANN. The introduced GWO-ANNs classification system performance is compared with the traditional NN classifier using receiver operating characteristic (ROC) analysis. Experimental results obviously indicate that the presented system achieves high classification rate and perform much better than the traditional NN classifier.

Edge effect correction using ion beam figuring

Bing Yang, Xuhui Xie, Li furen, and Lin Zhou

Doc ID: 297413 Received 05 Jun 2017; Accepted 10 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: Edge effect is regarded as one of the most difficult technical issues for fabricating large primary mirrors, which can greatly reduce the key performances of the optical system. Ion beam figuring (IBF) has the advantage of no edge effect, so we can use it to remove edge up-stand and improve the surface accuracy. The edge local correction method (ELCM) of IBF only processes the surface edge-zone, and is very different from the current full caliber figuring method (FCFM). Therefore, it is necessary to study the ELCM of IBF. In this paper, the key factors of ELCM are analyzed, such as dwell time algorithm, edge data extension methods and the outward dimension of starting figuring point. At the same time, the distinctions between the ELCM and FCFM are compared. Finally, a 142mm diameter fused silica mirror is fabricated to verify the validity of the theoretical of ELCM. The experimental results indicate that the figuring precision and efficiency can be obviously improved by ELCM.

A low cost three-dimensional millimeter-wave holographic imaging system based on frequency scanning antenna

Ehsan Mansouri, Vahid Amin Nili, Zahra Kavehvash, mohammad fakharzadeh, Mahdi Shabany, and Amin Khavasi

Doc ID: 302225 Received 17 Jul 2017; Accepted 10 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: In this paper, a closed-form two-dimensional (2D) reconstruction technique for hybrid frequency and mechanical scanning millimeter-wave (MMW) imaging systems is proposed. Although being commercially implemented in many imaging systems as a low-cost real-time solution, the result of frequency scanning systems have been reconstructed numerically or have been reported as the captured raw data with no clear details. Furthermore, this paper proposes a new framework to utilize the captured data of different frequencies for three-dimensional (3D) reconstruction based on novel proposed closed-form relations. The hybrid frequency and mechanical scanning structure together with the proposed reconstruction method, yields a low-cost MMW imaging system with a satisfying performance. The extracted reconstruction formulations are validated through numerical simulations, which shows comparable image quality with conventional MMW imaging systems, i.e. switched-array (SA) and phased-array (PA) structures. Extensive simulations are also performed in presence of additive noise demonstrating the acceptable robustness of the system against system noise compared to SA and comparable performance with PA. Finally, 3D reconstruction of the simulated data shows a depth resolution of better than 10 cm with minimum degradation of lateral resolution in 10 GHz frequency bandwidth.

Generation of long-range curved-surface plasmonicmode and their propagation through thin metal filmsin a tandem array.

Gabriel Martinez-Niconoff, Marco Antonio Rodriguez, Mayra Morales, Saul Garcia, Patricia Martinez Vara, and Adrian Carbajal-Dominguez

Doc ID: 302849 Received 19 Jul 2017; Accepted 09 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: We describe the generation of plasmonic modes that propagate in a curved trajectory. This is performed bymasking a metal surface with two screens containing a randomly distributed set of holes that follow aGaussian statistic. The diameter of the holes is less than the wavelength of the illuminating plane wave. Byimplementing scaling and rotations on each screen, we control the correlation trajectory and generate longrangecurved plasmonic modes. The study is generalized for the transmission of a plasmonic modepropagating in a tandem array of thin metal films using the evanescent character of the electric field.

Co-phasing experiment of segmented mirror using acombined broadband and two-wavelength algorithm

Li Bin, Wenhao yu, Chen Mo, tang long, and Hao Xian

Doc ID: 304264 Received 07 Aug 2017; Accepted 09 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: In this paper, a broadband phasing algorithm is combined with a two-wavelength phasing algorithm todetect the piston error of a segmented mirror with the advantages of long range, high precision, and fast detection.Moreover, an active optics co-phasing experimental system of the segmented mirror is built to verify thealgorithm’s effectiveness. The segmented mirror consists of four hexagonal segments, with flat-to-flat lengths of100 mm and radii of curvature of 2000 mm. First, a Shack-Hartmann sensor and piezoelectric actuators are used tofinely co-focus the segmented mirror. Then, the broadband phasing algorithm is used to reduce the piston error ofthe segmented mirror to several microns. Finally, the two-wavelength phasing algorithm is used to reduce thepiston error of the segmented mirror to zero. The experimental results show that the measurement accuracy isbetter than 26 nm, and the adjustment accuracy is approximately 55 nm, which demonstrates that the combinedalgorithm is valuable for segmented-mirror co-phasing measurement and adjustment.

Analysis of Illumination Uniformity Affected by SmallscaleSelf-focusing of Pump Beam in Radial SmoothingScheme

Xiaofeng Weng, Tengfei Li, Zheqiang Zhong, and Bin Zhang

Doc ID: 304522 Received 10 Aug 2017; Accepted 09 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: In the radial smoothing scheme, the small-scale self-focusing (SSSF) can degrade beam quality of the pump beamwith Gaussian pulse train, resulting in the degradation of the smoothing performance of the radial smoothingscheme. Considering small-scale self-focusing of the pump beam in optical Kerr medium, the propagation model ofthe laser beam in the radial smoothing scheme has been built up, and the effects of the characteristics of the pumpbeam and the thickness of the optical Kerr medium on the radial smoothing performance have further beennumerically simulated and analyzed. The results show that the small-scale self-focusing decreases the illuminationuniformity in the radial smoothing scheme by inducing distorted wavefront modulation of the pump beam.Consequently, the beam quality of the pump beam should be controlled for avoiding the degradation of the radialsmoothing performance affected by SSSF. In addition, the peak intensity of the pump beam and the thickness ofoptical Kerr medium should be reasonable to ensure the radial smoothing performance while mitigate the impactof small-scale self-focusing.

Wet etching technique for fabrication of high-qualityplastic optical fiber sensor

M Zhao, LANG DAI, Nianbing Zhong, ZHENGKUN WANG, MING CHEN, BINGXIN LI, Bin-bin Luo, Bing Tang, Shenghui Shi, Tao Song, and Xue Zou

Doc ID: 305008 Received 16 Aug 2017; Accepted 09 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: IN THIS STUDY, A SIMPLE WET ETCHING TECHNIQUE IS DEVELOPED BY EMPLOYING AQUEOUS SOLUTIONS OF ACETIC ACID AND ULTRASONICIRRADIATION FOR THE FABRICATION OF A HIGH-QUALITY, PLASTIC OPTICAL FIBER (POF) SENSOR. THE EFFECTS OF THE ACETIC ACIDCONCENTRATION AND TEMPERATURE AND THE ULTRASONIC POWER ON THE ETCHING RATE AND SURFACE MORPHOLOGY OF THE ETCHED POFS AREINVESTIGATED. THE TRANSMISSION SPECTRUM AND SENSITIVITY OF THE ETCHED POF SENSORS ARE EVALUATED USING GLUCOSE SOLUTIONS. WEDISCOVERED THAT THE POF SENSORS, WHICH ARE FABRICATED USING THE AQUEOUS SOLUTION OF ACETIC ACID WITH A CONCENTRATION OF 80%(V/V) UNDER AN ULTRASONIC POWER OF 130 W AND TEMPERATURE OF 25 °C, EXHIBITS GOOD LIGHT TRANSMISSION AND A HIGH SENSITIVITY OF9.10 [(RIU)(G/L)]–1 IN THE GLUCOSE SOLUTIONS.

Reduction of the defocusing effect in lensless ghost imaging and ghost diffraction with the cosh-Gaussian modulated incoherent sources

Chao Duan, Yanfeng Bai, Ling Tang, Suqin Nan, Qian Shen, and Xiquan Fu

Doc ID: 304033 Received 03 Aug 2017; Accepted 09 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: The inhibition effect from the cosh-Gaussian modulated incoherent sourceon the defocusing effect is investigated theoretically in lensless ghost imaging (LGI) and ghost diffraction (LGD) systems. The corresponding numerical simulations are presented to show the influence of the cosh-Gaussian incoherent source on the defocusing effect in LGI and LGD. Compared with the widely used Gaussian incoherent source, it is shown that the defocusing effect in LGI and LGD can be greatly weakened by properly adjusting the modulation parameter ! of the cosh-Gaussian source. To explain this phenomenon, the analytical expression for point-spread function (PSF) of lensless ghost imaging system with the cosh-Gaussian source is derived.

Fine-filter method for Raman lidar based onwavelength division multiplexing and fiber Bragggrating

Jun Wang, Jiao Zheng, Hong Lu, Qing Yan, Wang Li, Jingjing Liu, and hua Dengxin

Doc ID: 297202 Received 01 Jun 2017; Accepted 09 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: Atmospheric temperature is one of important parameters for the description of atmospheric state. Most of thedetection approaches to atmospheric temperature monitoring are based on rotational Raman scattering for betterunderstanding atmospheric dynamics, thermodynamics, atmospheric transmission and radiation. In this paper, wepresent a fine-filter method based on wavelength division multiplexing incorporating fiber Bragg grating in visiblespectrum for rotational Raman scattering spectrum. To achieve the high-precision remote sensing, the strongbackground noise is filtered out by using the secondary cascaded light paths. Detection intensity and signal-tonoiseratio are improved by increasing the utilization rate of return signal form atmosphere. Passive temperaturecompensation is employed to reduce the temperature sensitivity of fiber Bragg grating. In addition, the proposedmethod provides a feasible solution for the filter system with the merits of miniaturization, high anti-interferenceand high stability in the space-based platform.

Wide area mapping of liquid crystal devices withpassive and active command layers

Thomas Bennett, Matthew Proctor, Jon Forster, Elena Perivolari, Nina Podoliak, Matthew Sugden, Roger Kirke, Thomas Regrettier, Thomas Heiser, Malgosia Kaczmarek, and Giampaolo D'Alessandro

Doc ID: 298352 Received 21 Jun 2017; Accepted 09 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: We track the non-uniformity of a wide area liquid crystal device using multiple cross-polarised intensitymeasurements. They give us not only accurate estimates of the core physical liquid crystal parameters,such as elastic constants, but also spatial maps of the device properties, including the liquid crystal thicknessand pretilt angle. A bootstrapping statistical analysis coupled with the multiple measurements givesus reliable error bars on all the measured parameters.

Dielectric metalenses with engineered point spreadfunction

mohammad mahdi shanei, Mahdieh Hashemi, Davood Fathi, and Carlos Zapata-Rodriguez

Doc ID: 302630 Received 18 Jul 2017; Accepted 09 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: High-index silicon nanoblocks support excitation of both electric and magnetic resonance modes attelecommunication wavelengths. At the frequencies which both electric and magnetic resonance modes are excited simultaneously, changing the geometrical dimensions of the silicon cubes creates a 2π full span over the phase of the transmitted light in different amplitude ranges. We take advantage of the ad- ditional power-flux modulation of the scattered signal, to focus the incident light with desired full width at half maximum (FWHM) and side lobe levels (SLLs) both in the lateral and axial directions. By imple- menting proper amplitude filters within the telecommunication working wavelength (1.55 µm), FWHM less than half of the wavelength (0.42λe f f ) and apodization with nearly faded SLLs are achievable. Our approach which is introduced in this article pave a new way to design high efficiency metalenses withdesired FWHM and SLL of focal spot.

Accuracy evaluation of demodulation results of fiber Bragg grating sensors

Wei Zhang, Weimin Chen, Xiaohua Lei, and Chuhong Wang

Doc ID: 307011 Received 20 Sep 2017; Accepted 08 Oct 2017; Posted 10 Oct 2017  View: PDF

Abstract: Fiber Bragg grating (FBG) sensors are prone to spectral distortions in practical applications, which may cause large demodulation errors. There are many algorithms demodulating FBG spectra, but no approach is able to evaluate demodulation results under spectral distortions. To address this problem, four spectral indices are comparatively utilized to quantify distortions of spectra. Seven representative demodulation algorithms are adopted to analyze impacts of various simulated distorted spectra. Simulation results show that the side-mode suppression ratio (SMSR) of the spectrum is the most suitable spectral index for accuracy evaluation of demodulation results. In particular, when SMSR is larger than 6.3dB, demodulation results will be accurate, and inaccurate when SMSR is smaller than 2.1dB. The effectiveness of proposed evaluation approach is validated with fatigue experiments of 9 FBG sensors.

An Efficient Signal Design and Optimal Power Allocation for VLC Attocell Systems

Zheng-Guo Sun, Hong-Yi Yu, and zhu yi-jun

Doc ID: 300989 Received 26 Jun 2017; Accepted 07 Oct 2017; Posted 12 Oct 2017  View: PDF

Abstract: In this paper, we investigate visible light communication (VLC) attocell systems in which any two neighbor attocells have overlapping. An efficient signal design for VLC named time superposition reuse (TSR) is proposed to mitigate interference and improve spectral efficiency. In the scheme, two neighbor cells are allocated with two time slots that have superposition in time domain. By adjusting superposition between time slots, the system can achieve a flexible spectral efficiency and system performance. Further,we develop an optimal power allocation strategy for TSR in the system. The strategy is given according to the position of user and the level of superposition, then the corresponding optimal Euclidean distance isderived. In addition, we analyze the system performance and get that the optimal Euclidean distance is a decreasing function on the level of superposition. Simulation results demonstrate that the optimal powerallocation has a better performance than uniform power allocation and TSR outperforms time division multiple access (TDMA) significantly for the user in VLC attocell systems.

Self-recalibration of a robot-assisted structured-light-based measurement system

Jing Xu, Rui Chen, shuntao liu, and Yong Guan

Doc ID: 304848 Received 14 Aug 2017; Accepted 07 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: The structured-light-based measurement method is widely employed in numerous fields. However, for industrial inspection, to achieve complete scanning of a work piece and overcome the occlusion problem, the measurement system needs to be moved to different viewpoints. Moreover, frequent reconfiguration of the measurement system may be needed based on the size of the measured object, which makes the self-recalibration of extrinsic parameters indispensable. To this end, this paper proposes an automatic self-recalibration and reconstruction method, wherein a robot arm is employed to move the measurement system for complete scanning; the self-recalibration is achieved using fundamental matrix calculationsand point cloud registration without the need for an accurate calibration gauge. Experimental results demonstrate the feasibility and accuracy of our method.

Complex object wave reconstruction utilizing spatial multiplexing in off-axis digital holography

Erkhembaatar Dashdavaa, Munkh-Uchral Erdenebat, Chang-Won Shin, and Nam Kim

Doc ID: 303896 Received 02 Aug 2017; Accepted 07 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: In this paper, we present an algorithm for complex object wave extraction in off-axis digital holography using spatial multiplexing and frequency spectrum shifting technique. First, the proposed approach utilizes spatial multiplexing (SM) technique, in which 90 degree rotated two off-axis holograms are recorded in sequence and corresponding spectrums are subtracted in the computed Fourier domain to eliminate the DC term. Then two subtracted holograms are digitally multiplexed into one complex hologram in the same plane and by shifting the spatial frequency spectrums of the subtracted hologram in the spatial frequency domain, one of the two cross-correlations can be obtained in the center. And also, it simply extracts the spectrum of the real image in the frequency domain than the spatial filtering method

Performance analysis of UV multiple-scatter communication system with height difference

peng song, Xianli Zhou, Fei Song, Caixia Su, and Anxiang Wang

Doc ID: 303055 Received 01 Aug 2017; Accepted 07 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: Based on the Monte Carlo (MC) method, a non-coplanar ultraviolet (UV) multiple-scatter propagation model with a height difference between transmitter (Tx) and receiver (Rx) was presented. We focused on the relationship between bit error rate (BER) and the height difference between Tx and Rx. We also studied the impact of the elevation angle and the off-axis angle of Tx and Rx on BER under the condition that the height difference is not zero. In addition, an outdoor UV communication testbed was set up to provide support for the validity of the MC model. The simulation results show that with the height difference h between Tx and Rx increases, the BER first decreases and then increases, the BER can be reduced by adjusting the transceiver elevation angle, and the bigger off-axis angle is, the bigger BER is. The experimental results are in good agreement with the simulation results.

Phase-locked optical metrology I: identification of intrinsic camera parameters from multiple grid views

Yves Surrel

Doc ID: 303640 Received 02 Aug 2017; Accepted 06 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: Camera-based optical metrology crucially relies on a proper identification of intrinsic (optical center po- sition) and extrinsic (camera position) parameters of the used camera. A novel approach for processing phase data from multiple views of a target grid is presented, allowing these identifications within a pin- hole camera model. First, the homography associated with the perspective distortion of each grid image is accurately identified using a phase-locking loop. Then, the affine transform for each view is determined, with the constraint of an identical set of intrinsic camera parameters. This requires to slightly adjust each homography. As there are highly redundant data, a criterion has to be chosen to optimize the result. The chosen criterion is the simultaneous minimization of the standard deviation between in-plane grid line displacements between the acquired grid images and the reconstructed ones. Experimental results demonstrate the efficiency of the method

High-power continuous-wave narrow-linewidth 253.7 nm deep-ultraviolet laser

Ruchen Zhao, Xiaohu Fu, Lei Zhang, su fang, Jianfang Sun, Yan Feng, Zhen Xu, and Yu-zhu Wang

Doc ID: 302934 Received 25 Jul 2017; Accepted 06 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: A 760 mW stable continuous-wave narrow-linewidth 253.7 nm deep-ultraviolet laser is developed for laser cooling of mercury atoms. It is based on a high-power 1014.8 nm room-temperature fiber laser amplifier and two cascaded efficient frequency-doubling stages. The saturated absorption spectrum of 202Hg on the 61S0 - 63P1 transition is demonstrated with a high signal to noise ratio. This deep-ultraviolet laser has significant applications in quantum optics and laser cooling of mercury atoms in 2D and 3D magneto-optical traps.

Achieving electric field focusing using annular metal-dielectric multilayers

WU FENG

Doc ID: 304084 Received 04 Aug 2017; Accepted 06 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: We present studies on an electric field focuser composed of annular epsilon-near-zero metamaterials (ENZMs) and inner free space. According to effective medium theory, annular ENZMs can be realized via annular metal-dielectric multilayers. In practice, we choose silver and air to design the focuser. Our numerical simulations demonstrate that the electric field can be focused on a fixed point regardless of the number and location of electromagnetic sources in annular multilayers, which might be helpful for laser ignition.

A Tunable Graphene Plasmonic Y-Branch Switch inTerahertz Region Using Hexagonal Boron Nitride withElectric and Magnetic Biasing

ali farmani, Mahdi Yavarian, Abbas Alighanbari, Mehdi Miri, and Mohammad Hossein Sheikhi

Doc ID: 304093 Received 03 Aug 2017; Accepted 06 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: A tunable graphene plasmonic Y-branch switch at THz wavelengths is proposed. In the structure, hexagonal boron nitride is utilized as a substrate for graphene. Also, the effects of the magnetic and electric biasing are studied to harness the transmission of the transverse electric and magnetic guided mode resonances. The application of the hexagonal boron nitride with the advantage of high mobility and ultra-low ohmic loss, introduces a promising alternative substrate for graphene. Analytical and numerical results show that, by a slight variation of the doping level in graphene through the magnetic and electric biasing, the characteristics of the propagation of the guided mode resonances can be manipulated. A large extinction ratio of 40 dB at the wavelength of 60 µm is obtained. Besides, the proposed switch exhibits a low insertion loss of about 1 dB, and relatively large optical bandwidth of 1 µm. The electric biasing is in the order of 0.1 mV. Additionally, with the presence of the magnetic biasing, a compact switch with the size of 25 µm is achieved. Exhibiting a high extinction ratio, low insertion loss, and compact size, the proposed switch can find potential applications in graphene plasmonics integrated devices.

Quality of reconstruction of compressed off-axisdigital holograms by frequency filtering and wavelets

Pavel Cheremkhin and Ekaterina Kurbatova

Doc ID: 303949 Received 02 Aug 2017; Accepted 06 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: Compression of digital holograms can significantly help with storage of objects and data in 2D- and 3D-form, itstransmission and reconstruction. Compression of standard images by methods based on wavelets allows to reachhigh compression ratios (up to 20-50 times) with minimum losses of quality. In the case of digital hologramsapplication of wavelets directly not allow to obtain high values of compression. However additional preprocessingand post-processing are able to afford to significantly compress holograms and to achieve the acceptable quality ofreconstructed images. In this paper features of application of wavelet transforms for compression of off-axis digitalholograms are considered. The combined technique based on zero and twin orders elimination, waveletcompression of the amplitude and phase components of obtained Fourier spectrum and further additionalcompression of wavelet coefficients by thresholding and quantization is considered. Numerical experiments onreconstruction of images from the compressed holograms are performed. The comparative analysis of applicabilityof various wavelets and methods of additional compression of wavelet coefficients is performed. Optimumparameters of compression of holograms by the methods can be estimated. Sizes of holographic information weredecreased up to 190 times.

Two-dimensional coherent random laser in photonic crystal fiber with dye-doped nematic liquid crystal

Yusuke Nagai, Shao-Chieh Chen, and Kotaro Kajikawa

Doc ID: 306763 Received 08 Sep 2017; Accepted 05 Oct 2017; Posted 09 Oct 2017  View: PDF

Abstract: A random laser of a photonic crystal fiber (PCF) with holes filled with laser-dye doped nematic liquid crystal (NLC) is reported. When the excitation polarization was along the PCF axis, the measured laser threshold was 80μJ/mm² per pulse, which is much lower than that the previously reported random laser of PCF filled with laser-dye-doped organic solvent. This low threshold is due to the high refractive index of the NLC, which produces a greater scattering efficiency. In contrast, when the excitation polarization is perpendicular to the PCF axis, the threshold was much higher or the laser oscillation was absent. This is because of the lower refractive index of the NLC for the perpendicular polarization. The laser oscillation was absent in the isotropic phase because of a low fluorescence efficiency at high temperatures.

Learning-based single-shot superresolution in diffractive imaging

Ryoichi Horisaki, Takagi Ryosuke, and Jun Tanida

Doc ID: 304129 Received 04 Aug 2017; Accepted 05 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: We present a method of retrieving a superresolved object field from a single captured intensity image in diffraction-limited diffractive imaging based on machine learning. In this method, the inverse process of diffractive imaging is regressed by using a number of pairs each consisting of object and captured images. The proposed method is experimentally demonstrated by using a lensless imaging setup with or without scattering media.

High Power Diode-Pumped Kerr-Lens Mode-Locked Bulk Yb:KGW Laser

Reza Akbari and Arkady Major

Doc ID: 304282 Received 07 Aug 2017; Accepted 05 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: A high power (>1 W) pure Kerr-lens mode-locked bulk Yb:KGW laser with multimode fiber-coupled diode pumping was demonstrated. The laser delivered 240 fs pulse with 2.3 W of average output power at 86.8 MHz, corresponding to 97 kW of peak power and 26 nJ of pulse energy. The shortest generated pulse duration was 120 fs with 1.2 W of output power. The self-starting regime was also observed with a background CW component. The laser exhibited more than an order of magnitude higher output power when compared to the previously reported bulk Yb-ion doped lasers with multimode laser diode pumping systems.

Application of spatially modulated NIR structured lightto study changes in optical properties of mouse braintissue during heatstress

OREN SHAUL, Michal Fanrazi-Kahana, OMRI MEITAV, Gadi Pinchasi, and David Abookasis

Doc ID: 302358 Received 18 Jul 2017; Accepted 05 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: Heatstress (HS) is a medical emergency defined by abnormally elevated body temperature that causes biochemical,physiological and hematological changes. The goal of the present research was to detect variations in opticalproperties (absorption, reduced scattering, and refractive index coefficients) of mouse brain tissue during HS byusing near-infrared (NIR) spatial light modulation. NIR spatial patterns with different spatial phases were used todifferentiate the effects of tissue scattering from those of absorption. Decoupling optical scattering from absorptionenabled the quantification of tissue’s chemical constituents (related to light absorption) and structural properties(related to light scattering). Technically, structured light patterns at low and high spatial frequencies of sixwavelengths ranging between 690 to 970nm were projected onto the mouse scalp surface while diffuse reflectedlight was recorded by a CCD camera positioned perpendicular to the mouse scalp. Concurrently to patternprojection, brain temperature was measured with a thermal camera positioned slightly off angle from the mousehead while core body temperature was monitored by thermocouple probe. Data analysis demonstrated variationsfrom baseline measurements in a battery of intrinsic brain properties following HS.

An automatic, high-accuracy image registration in confocal microscopy

Jian Liu, Yong Li, Weibo Wang, Yuhang Wang, He Zhang, and Jiubin Tan

Doc ID: 302557 Received 18 Jul 2017; Accepted 05 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: We proposed a high-accuracy image registration method of confocal microscopy for large field of view and high-resolution. The spatialinformation (edge information) and the entropy correlation coefficient have been both taken into account for higher accuracy ofregistration. The edge information is introduced to calculate the normalization correlation coefficient of the image. Then the normalizationcorrelation coefficient and the entropy correlation coefficient of the original image have been used to improve the proposed similaritymeasures, the normalized mutual information with edge information (called EMI). Meanwhile, a parallel particle swarm optimization (pa-PSO) with the idea of conditional initialization and parallel cooperation is developed to speed up the convergence rate and further reducethe mismatch. Experiments verified that the registration accuracy can be up to 0.2 pixels and has better robustness to the noise.

Illumination-related errors in limited-angle optical diffraction tomography

Arkadiusz Kuś

Doc ID: 302947 Received 20 Jul 2017; Accepted 05 Oct 2017; Posted 06 Oct 2017  View: PDF

Abstract: In the paper the design and tolerances of optical systems and scanning components used in limited-angle optical diffraction tomography (LAT) are analyzed in order to improve the performance of the systems and to encourage the application of tomography as a standard method for quantitative analysis of 3D refractive index distribution in biological microstructures. The first part of the presented analysis consists of component selection for scanning device and optical system in the illumination part of the setup and the influence of illumination wavefront on the reconstruction quality. In the second part, the sensitivity of the tomographic reconstruction quality to three representative measurement-related errors is demonstrated. Finally, a configuration of the system, selected to minimize reconstruction errors, is proposed and alignment tolerances, calculated using Monte Carlo method, are provided.

Silicon ring resonator-coupled Mach-Zehnderinterferometers for the Fano resonance in the mid-IR

Benedetto Troia, Jordi Soler Penades, Zhibo Qu, Ali Khokhar, Ahmed Osman, Yangbo Wu, CALLUM STIRLING, Milos Nedeljkovic, Vittorio Passaro, and Goran Mashanovich

Doc ID: 303221 Received 24 Jul 2017; Accepted 04 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: We present ring resonator-coupled Mach-Zehnder interferometers (MZI) based on silicon-on-insulator (SOI) ribwaveguides, operating around the mid-IR wavelength of 3.8 μm. A number of different photonic integrated deviceshave been designed and fabricated experimentally to obtain the asymmetric Fano resonances in the mid-IR. Wehave investigated the influence of the coupling efficiency between the ring resonator (RR) and the MZI as well asthe phase shift between the two arms of the MZI on the Fano-type resonance spectral features in agreement withtheoretical predictions. Finally, wavelength-dependent Fano transmittances have been successfully measured withinsertion losses up to ~1 dB and extinction ratios of ~20 dB. A slope of sharp Fano resonances as high as -547.6/μmhas been achieved and estimated to be 35.5 % higher than the slope of single ring resonator Lorentzian-typeresonances.

Characterization of the reference wave in a compact digital holographic camera

Ian Park, Robert Middleton, Russell Coggrave, Pablo Ruiz, and Jeremy Coupland

Doc ID: 303484 Received 31 Jul 2017; Accepted 04 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: A hologram is a recording of the interference between an unknown object wave and a coherent reference wave. Providing the object and reference waves are sufficiently separated in some region of space and the reference beam is known, a high-fidelity reconstruction of the object wave is possible. In traditional optical holography, high-quality reconstruction is achieved by careful re-illumination of the holographic plate with the exact same reference wave that was used at the recording stage. To reconstruct high-quality digital holograms the exact parameters of the reference wave must be known mathematically. This paper discusses a technique that obtains the mathematical parameters that characterize a strongly divergent reference wave that originates from a fiber source in a new compact digital holographic camera. This is a lens-less design that is similar in principle to a Fourier hologram, but because of the large numerical aperture, the usual paraxial approximations cannot be applied and the Fourier relationship is inexact. To characterize the reference wave, recordings of quasi-planar object waves are made at various angles of incidence using a Dammann grating. An optimization process is then used to find the reference wave that reconstructs a stigmatic image of the object wave regardless of the angle of incidence.

Dual use architecture for innovative Lidar and Free Space Optical Communications

Filippo Scotti, Daniel Onori, Claudio Porzi, Fabio Falconi, Vito Sorianello, Andreia Aparecida Alves, Muhammad Imran, Sergio Pinna, Arismar Cerqueira Sodre Junior, Marco Romagnoli, and Antonella Bogoni

Doc ID: 300683 Received 23 Jun 2017; Accepted 04 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: An innovative and effective architecture for lidar system is presented and experimentally demonstrated. The proposed scheme can be easily exploited also for optical communications. In particular, the system includes an innovative lidar software-defined architecture based on optically coherent detection, overcoming current drawbacks of ToF incoherent systems. The experiments demonstrate the ability to perform long range detection resorting to the waveform compression on CW approach, obtaining a range resolution of 15cm with a sensitivity of -95dBm. Beside the bulk implementation, the system has been also implemented in a photonic integrated circuit using CMOS-compatible silicon on insulator technology with extremely reduced footprint of 1.5x3.5 mm². The testing of the integrated device confirms the effectiveness of this proof-of-concept realization.

Graphene oxide coated interferometric opticalmicrofiber ethanol vapor sensor

jing zhang, Fu Wei, ji ding, Min Zhang, and Yi Zhu

Doc ID: 302758 Received 18 Jul 2017; Accepted 04 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: A graphene oxide coated interferometric microfiber sensor based polarization-maintaining optical fiber (PMF) wasproposed for high sensitive detecting for ethanol vapor concentration at room temperature in this paper. Thestrong sensing capability of the sensor to detect the concentration of ethanol vapor was demonstrated, takingadvantage of the evanescent field enhancement and gas absorption of a graphene oxide coated microfiber. Thetransmission spectrum of the sensor varies with concentrations of ethanol vapor, and the red-shift of transmissionspectrum has been analyzed for the concentrations range from 0 to 80ppm with sensitivity as high as of0.138nm/ppm. The coated graphene oxide layer induces the evanescent field enhancement and gas selectiveadsorption, which improves sensitivity and selectivity of the microfiber gas sensor for ethanol vapor detection.

Analysis and Elimination of Bias Error in Fiber-Optic Current Sensor

Xiaxiao Wang, Zijie Zhao, Chuansheng Li, Jia Yu, and zhenjie wang

Doc ID: 304389 Received 08 Aug 2017; Accepted 04 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: Bias error is another key factor that affects the measurement accuracy of the fiber-optic current sensor (FOCS) besides the scale factor error. Because of the polarization crosstalk, the coherence of parasitic interference signals could be rebuilt and form an output independent of the current to be measured. The bias error is a variable of the birefringence optical path difference. Hence, when the temperature change, the bias error shows a quasi-periodical tendency whose envelop curve reflect the coherence function of SLD. With the key factors of bias error identified and the propagation directions of SLD, PM coupler and polarizer all set to fast axis, the coherence of parasitic interference signals will be eliminated. Experiments show that the maximum bias error decreases by one order of magnitude at the temperature -40℃ to 60℃.

The speckle pattern sequential extraction metric forestimating the focus spot size on a remote diffusetarget

zhan yu, Yuanyang Li, Lisheng Liu, Jin Guo, Tingfeng Wang, and Guoqing Yang

Doc ID: 302778 Received 20 Jul 2017; Accepted 03 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: The speckle pattern (line by line) sequential extraction (SPSE) metric is proposed by the one-dimensional speckleintensity level crossing theory. Through the sequential extraction of received speckle information, the specklemetrics for estimating the variation of focusing spot size on a remote diffuse target are obtained. Based on thesimulation, we will give some discussions about the SPSE metric range of application under the theoreticalconditions and the aperture size will affect the metric performance of the observation system. The results of theanalyses are verified by experiment. This method is applied to the detection of relative static target (speckled jitterfrequency is less than the CCD sampling frequency). The SPSE metric can determine the variation of the focusingspot size over a long distance, moreover the metric will estimate the spot size under some conditions, therefore themonitoring and the feedback of far-field spot will be implemented in the applications of laser focusing system andhelp system to optimize the focusing performance.

Measurement of the absolute velocity of blood flow in early-stage chick embryos using spectral domain Optical Coherence Tomography

Zenhe Ma, Yushu Ma, Yuqian Zhao, Jian Liu, Jianghong Liu, Jiangtao Lv, and Yi Wang

Doc ID: 300797 Received 30 Jun 2017; Accepted 03 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: Doppler optical coherence tomography (OCT) is a noninvasive imaging modality that provides quantitative flow information with high spatial and temporal resolution. However, it is only sensitive to the flow velocity vector parallel to the incident beam. To calculate the absolute velocity, it is necessary to obtain the angle between the incident beam and flow field. In this paper, we describe a practical method to measure the Doppler angle based on the structural information of blood vessels extracted from spectral domain OCT images. In this method, a normal sectional scan of the vessel is performed where the probe beam is perpendicular to the vessel. Next, the axial diameter (Z direction) of the vessel (DA) was measured in the acquired image. For a certain scan in which the probe beam is oblique to the blood vessel, the axial diameter of the vessel (DA’) can be measured. Thus, the Doppler angle can be calculated depending on the ratio of DA and DA’, and absolute blood flow was determined. We validate this method in a capillary tube as well as in large blood vessels of early-stage chick embryos. This technique is suitable for early-stage embryo blood flow measurement because most of the blood vessels are easily differentiated from the transparent surrounding structures during that time.

Three Dimensional Imaging of Trapped Cold Atoms with a Light Field Microscope

Gordon Lott, Michael Marciniak, and John Burke

Doc ID: 295938 Received 22 May 2017; Accepted 03 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: This research images trapped atoms in three dimensions, utilizing light field imaging. Such a system is of interest in the development of atom interferometer accelerometers in dynamic systems where strictly defined focal planes may be impractical. In this research a light field microscope was constructed utilizing a Lytro® Development Kit micro-lens array and sensor. It was used to image fluorescing rubidium atoms in a magneto optical trap. The three dimensional (3D) volume of the atoms is reconstructed using a modeled point spread function (PSF), taking into consideration that the low magnification (1.25) of the system changed typical assumptions used in the optics model for the PSF. The 3D reconstruction is analyzed with respect to a standard off-axis fluorescence image. Optical axis separation between two atom clouds is measured to a 100µm accuracy in a 3mm deep volume, with a 16μm in focus standard resolution with a 3.9mm by 3.9mm field of view. Optical axis spreading is observed in the reconstruction and discussed. This 3D information be used to determine properties of the atom cloud with a single camera and single image, and can be applied anywhere 3D information is needed but optical access may be limited.

Multiple-band directional excitation of surface plasmons based on electromagnetically induced transparency

yueke wang, Xin Yan, and xiaorong hong

Doc ID: 304388 Received 07 Aug 2017; Accepted 02 Oct 2017; Posted 02 Oct 2017  View: PDF

Abstract: We propose a structure of two metallic slits, one of which is accompanied by two non-equal length cavities. Our simulation results, conducted by finite difference time-domain method, show that there are four bands which achieve launching surface plasmons (SPs) unidirectionally at communication region, and each band is very narrow(between 10nm and 30nm). Our design method is based on SPs interference, and originates from the phase shift variation of SPs in electromagnetically induced transparency (EIT) wavelength region. This method provides a new way to manipulate SPs and control SPs’ propagating direction in photonic circuits.

Design of wedge structure with non-dispersive wedge wave propagation

Jing Jia, Shen Zhong-Hua, Qingbang Han, and Xueping Jiang

Doc ID: 298224 Received 16 Jun 2017; Accepted 02 Oct 2017; Posted 02 Oct 2017  View: PDF

Abstract: This paper focuses on designing a structure by using laser ultrasound technique, wherein wedge waves can propagate without dispersion. First, the impact of curvature radius and truncations on the wedge waves were investigated using finite element method and the dispersion curves were obtained by using 2D Fourier transformation method. Subsequently, the propagation of non-dispersive wedge waves was realized via a special wedge shape, which was designed with a unique relationship between the curvature radius and truncation, and its correctness was validated using numerical simulation. Finally, experiments were performed to detect the wedge waves, wherein a pulsed laser was coupled with optical fiber excitation, and the waves were detected using an optical vibrometer.

Weighted iterative algorithm for beam alignment in scanning beam interference lithography

ying song, wang wei, Shan Jiang, heshig bayan, and Ning Zhang

Doc ID: 298043 Received 16 Jun 2017; Accepted 02 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: To obtain low phase errors and good interference fringe contrast, an automated beam alignment system is used in scanning beam interference lithography (SBIL). In the original iterative algorithm, if the initial beam deviation is large or the optical parameters are inappropriate, the beam angle (or position) overshoot may exceed the detector’s range. To solve this problem, a weighted iterative algorithm is proposed in which the beam angle and position overshoots can be suppressed by adjusting the weighting coefficients. The original iterative algorithm is introduced. The weighted iterative algorithm is then presented, and its convergence is analyzed. The simulation and experimental results show that the proposed weighted iterative algorithm can reduce the beam angle and position overshoots by sacrificing convergence speed, avoiding the alignment failure caused by exceeding the detector’s range. Besides, the original and weighted iterative algorithms can be combined to optimize the iteration.

Design of diffractive optical elements for subdiffractionspot arrays with high light efficiency

Chen Wu, Huarong Gu, Zhou Zhehai, and Qiaofeng Tan

Doc ID: 301171 Received 27 Jun 2017; Accepted 02 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: The spot arrays beyond the diffraction limit are required in many optical applications. And the shaping of a lightbeam into sub-diffraction spot arrays can be implemented by the diffractive optical elements(DOEs). However, thelow light efficiency of spot arrays is undesired in many applications. In this paper, a modified GS algorithm is presentedfor generating the DOEs to realize sub-diffraction spot arrays with higher light efficiency. In the simulation,the spot size is reduced to approximately 70%-90% of the diffraction limited spot, and the corresponding light efficiencyis within the range from 20% to 50%. The experimental results are also performed to demonstrate the effectivenessof the proposed algorithm.

Flat metaform near-eye visor

Arka Majumdar, Shane Colburn, and Chuchuan Hong

Doc ID: 302185 Received 11 Jul 2017; Accepted 02 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: A near-eye visor is one of the most vital components in a head-mounted display. Currently, freeform optics and waveguides are used to design a near-eye visor, but their structures are complex and their field of view is limited when the visor is placed near the eye. In this paper, we propose a flat, freeform near-eye visor which uses a sub-wavelength patterned metasurface reflector. The visor design imparts a spatial phase profile on a projected display pattern and can be implemented using a micron-thick metasurface. As the resulting metaform visor relies on diffraction, it can preserve a large field of view (77.3° both horizontally and vertically) when placed only 2.5 cm away from the eye. We simulate the metasurface visor to estimate the modulation transfer function, and find that the projected image quality is sufficiently high for human vision. While the design of the metasurface is initially performed via ray optics, using full-wave finite-difference time-domain simulation we validate a scaled version of our metasurface visor design.

Propagation of partially coherent Lorentz-Gauss vortex beam through oceanic turbulence

Dajun Liu, Hongming Yin, guiqiu wang, and Yaochuan Wang

Doc ID: 302642 Received 19 Jul 2017; Accepted 02 Oct 2017; Posted 03 Oct 2017  View: PDF

Abstract: The partially coherent Lorentz-Gauss vortex beam generated by a Schell-model source has been introduced. Based on the extended Huygens-Fresnel principle, the cross-spectral density function of partially coherent Lorentz-Gauss vortex beam propagating in oceanic turbulence is derived. The influences of coherence length, topological charge M and oceanic turbulence on the spreading properties and position of coherence vortex for partially coherent Lorentz-Gauss vortex beam are analyzed in detail. The results show that partially coherent Lorentz-Gauss vortex beam propagating in stronger oceanic turbulence will evolve into Gaussian-like beam more rapidly as the propagation distance increases, and the number of coherent vortices will change.

Planar broad-band and wide-angle hybridplasmonic IMI filters with induced transmissionfor visible light applications

Noha Anous, Tarek Ramadan, Mohamed Abdallah, Khalid Qaraqe, and Diaa Khalil

Doc ID: 303772 Received 01 Aug 2017; Accepted 02 Oct 2017; Posted 05 Oct 2017  View: PDF

Abstract: This work presents a technique for the design of visibleoptical filters using a hybrid plasmonic insulator-metal- insulator (IMI) structure. The proposed IMI visible light filter exhibits high transmission (~91%) and an insertion loss of ~0.4 dB with almost an omnidirectional field-of-view (FOV) (0o~70o), a feature that is important for light collection in miniaturized devices. The proposed design also has a minimal polarization dependent loss (PDL) of 0.2 dB at AOI of 60o. The effects of design parameters on the filter’s performance are studied. Design rules of the filter are ced along with physical justifications of the obtainedresults.

Absolute three-dimensional shape measurement with two-frequency square binary patterns

Chufan Jiang and Song Zhang

Doc ID: 303418 Received 26 Jul 2017; Accepted 01 Oct 2017; Posted 02 Oct 2017  View: PDF

Abstract: This paper presents a novel method to achieve absolute three-dimensional (3D) shape measurement solely using square binary patterns. This method uses six patterns: three low-frequency phase-shifted patterns and three phase-shifted high-frequency patterns. The phase obtained from low-frequency phase temporally unwraps the phase obtained from high-frequency patterns. The projector is defocused such that the high-frequency patterns produce high-quality phase, but the phase retrieved from low-frequency patterns has large harmonic error that fails two-frequency temporal phase unwrapping process. In this paper, we develop a computational framework to address the challenge. The proposed computational framework includes three major approaches to alleviate the harmonic error problem: i) use more than one period of low-frequency patterns enabled by geometric constraint-based phase unwrapping method; ii) artificially apply a large Gaussian filter to low frequency patterns before phase computation; iii) create an error look-up table (LUT) to compensate for harmonic error; and iv) develop a boundary error correction problem to alleviate problems associated with filtering. Both simulation and experimental results demonstrated the success of the proposed method.

Femtosecond versus picosecond laser pulses for filmfreelaser bioprinting

Stephane Petit, olivia kerouredan, Raphael DEVILLARD, and Eric Cormier

Doc ID: 303692 Received 31 Jul 2017; Accepted 01 Oct 2017; Posted 02 Oct 2017  View: PDF

Abstract: We investigate the properties of microjets in the context of film-free Laser Induced Forward Transfer in the femtosecondand picosecond regimes. The influence of the pulse duration (ranging from 0.4 to 12 ps) and the energy (ranging from 6 to12 μJ) is systematically studied on the height, diameter, speed, volume and shape of the jets. 400 fs pulses generate thinand stable jets compatible with bioprinting while 14 ps pulses generate more unstable jets. Pulse duration around 8 psseems therefore to be an interesting trade-off to cover many bio-applications of microjets generated by lasers.

Extending the applicability of the four-flux radiativetransfer method

Marc Gali, Angus Gentle, Matthew Arnold, and Geoff Smith

Doc ID: 303900 Received 02 Aug 2017; Accepted 29 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: A generalized four-flux method which is capable of modeling and tuning the spectral reflectance of diverserange of complex composite coatings is presented. An example application is exploring and maximisingthe visible and near infrared (IR) spectral reflectance available from the diverse structures arisingfrom combinations of the many practical paint ingredients which are available or can be made when appliedto different substrates. This requires consideration of scatterers which can differ in composition,particle size, size distribution, fill factor, and are held in place by a variety of organic binders (whichtypically partially absorb in the near IR). This extended model is further enhanced by an explicit matrixalgorithm which allows analysis of diverse multilayer stacks. This is applied to a multilayer and is designedto model useful changes that result from varying pigment fill factor as a function of depth withina layer. A novel feature is the way the scattering impacts on matrix absorptance. The model includescontributions to total absorptance from the scattering pigments and from paint binder which can arise indifferent bands or simultaneously at the same wavelengths. Model accuracy is demonstrated by exampleresults when compared to experimental data on dried single layer paint profiles using imaged crosssections. The model input covering actual pigment and binder properties used are; material, shape, size,and size distributions, mass added, and the measured optical constants from 400nm to 2,500nm of theun-doped binder resin layer. One interesting novel result is the comparison of a two-layered stack, withbigger particles in the first layer and smaller in the second, to one with the opposite depth profile.

3D Shape, Deformation and Vibration Measurements Using Infrared Kinect Sensors and Digital Image Correlation

Hieu Nguyen, Zhaoyang Wang, Patrick Jones, and Bing Zhao

Doc ID: 297593 Received 06 Jun 2017; Accepted 29 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: Consumer-grade RGB-D (red-green-blue and depth) sensors such as the Microsoft Kinect and the Asus Xtion are attractive devices due to their low cost and robustness for real-time sensing of depth information. These devices provide the depth information by detecting the correspondences between the captured infrared (IR) image and the initial image sent to the IR projector, and their essential limitation is the low accuracy of 3D shape reconstruction. In this paper, an effective technique that employs the Kinect sensors for accurate 3D shape, deformation, and vibration measurements is introduced. The technique involves using the RGB-D sensors, accurate camera calibration scheme, and area- and feature-based image matching algorithms. The IR speckle pattern projected from the Kinect projector considerably facilitates the digital image correlation analysis in the regions of interest with enhanced accuracy. A number of experiments have been carried out to demonstrate the validity and effectiveness of the proposed technique and approach. It is shown that the technique can yield measurement accuracy at 10 micron level for a typical field of view. The real-time capturing speed of 30 frames per second makes the proposed technique suitable for certain motion and vibration measurements such as non-contact monitoring of respiration and heartbeat rates.

Technique developments and performance analysis of chirped-probe-pulse femtosecond coherent anti-Stokes Raman scattering combustion thermometry

Levi Thomas, Aman Satija, and Robert Lucht

Doc ID: 301488 Received 03 Jul 2017; Accepted 29 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: This work characterizes the state-of-the-art in the analysis of high-repetition-rate, ultrafast combustion thermometry using chirped-probe pulse femtosecond coherent anti-Stokes Raman Scattering (CPP fs CARS). Several key aspects of the CARS spectroscopy system are described including: (1) the ultrafast laser source, (2) use of the frequency-doubled idler vs signal from the optical parametric amplifier, (3) the geometry constraints for phase matching, and (4) spectral fitting for single-shot temperature measurements. A frequency-dependent instrument response function (IRF) for the detection system was modeled as a variable-width Gaussian, and implemented through a frequency convolution of synthetic spectra. Proper accounting of the IRF increased spectral fitting performance in the high-frequency region where signal oscillations are weaker and narrower. Aggregated data from 25 system performance assessments taken over four months yielded accuracy and precision of 2.7% and ±3.5% for flame temperatures, and 9.9% and ±6.1% at room temperature, using the commonly-reported method. A new processing technique, based on the statistical method of maximum likelihood, was implemented for turbulent flames where strong fluctuations in expected temperatures necessitate use of multiple temperature calibrations. Results from multiple sets of laser parameters are combined, to generate an error-weighted temperature from the top-performing calibrations. A testing procedure was designed to characterize system performance when the range of expected temperatures is unknown, simulating the random temperature field of a highly-turbulent flame. Accuracy error of the CPP fs CARS system increased in this more-stressing test at all temperatures, but precision was significantly affected only at room temperature. System stability is characterized and the contribution from shot-to-shot laser fluctuations on measurement precision is quantified. Finally, the near-adiabatic and steady assumptions for the Hencken Burner calibration flame are examined in an axial scan; significant deviations from ideal behavior were observed only at heights of more than four diameters above the burner surface.

Design and Analysis of a Polarization Modulator Based on Surface Plasmons

Ramin Djabery, Mohammad Naser-Moghadasi, and Alireza Andalib

Doc ID: 301847 Received 10 Jul 2017; Accepted 29 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: In this paper, a polarization modulator is proposed, based on surface plasmons in telecommunication wavelength. Following the generalized Snell’s law, the meta-surface for converting an incident propagating wave to a surface wave is carefully designed with nearly 84% efficiency. Moreover, the coupling ratio for TE and TM polarization of the incident wave is calculated. Furthermore, the LiNbO3 structure is used as a polarizer. Finally, the calculations are verified by employing the rigorous numerical finite-difference time-domain (FDTD) simulation method, and the results are found to be in excellent agreement. Our findings may help in the realization of compact plasmonic circuits.

Tunable angular shearing interferometer based on wedged liquid crystal cells

Romain Laberdesque, Aurelie Jullien, Umberto Bortolozzo, Nicolas Forget, and Stefania Residori

Doc ID: 302694 Received 18 Jul 2017; Accepted 29 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: The concept of Liquid Crystal Wedge as tunable angular shearing interferometer is introduced and demonstrated to ally both high stability and high tunability. Different wedges are fabricated from planar aligned nematic liquid crystal cells with thickness gradient. These wedges are shown to produce stable interferograms from the polarization interference between the ordinary and extraordinary waves propagating at different directions at the output of the cell. The fringe periods, ranging from 70 μm to 1.25 mm, can be precisely controlled by a low-voltage. Despite the wedge-shaped structure, no inhomogeneity has been detected when the wedge is driven adiabatically and the interferograms are uniform over regions as large as 5x5 mm. Moreover, dynamical measurements show that the wedges behave as a succession of multiple cells with different thickness, giving rise to a moving front of stabilizing fringes when driven dynamically. All the observations show that the device is suitable for large beam size and tunable shearing interferometry, with attractive features for applications, such as phase-sensing, photo-alignment or photolithography.

Experimental investigation of thermal effects in Laser-nanofluid interaction By Moiré Technique

shahrzad Shahrabi Farahani, Khosro Madanipour, and ata allah koohian

Doc ID: 303267 Received 25 Jul 2017; Accepted 29 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: Interaction of a CW laser with a nonlinear medium leads to some thermal phenomena. Thermal lensing is the most important phenomenon among them that changes the distribution of refractive index of the medium in the interacting area. Moiré deflectometry is a known technique for measuring the profile of refractive index. In this work by using non-scanning Moiré deflectometry, refractive index profile in interaction region of a graphene oxide (GO) nanofluid sample and a green CW laser is measured. By using the thermal diffusion equation, the thermo-optical coefficient is calculated. The obtained thermo-optical coefficient value, is in good agreement with value from other method. Having the thermo-optical coefficient and three dimensional profile of refractive index, the three dimensional distribution of temperature is obtained. Although this method is inexpensive and simple, it is applicable for liquid, solid and gas samples.

Freeform-objective Chernin multipass cell: Application of freeform surface on assembly simplification

Yingmo Wang, Zexiao Li, Xianlei Liu, Fengzhou Fang, and Xiaodong Zhang

Doc ID: 304777 Received 15 Aug 2017; Accepted 28 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: This paper aims at decreasing the assembly difficulty and reducing the cost of optical systems using multiplecomponents. A strategy is proposed to substitute one freeform surface for multi separated surfaces. A freeformobjectiveChernin multipass cell is implemented as a typical instance for assembly simplification. The applicationof freeform surface helps in decreasing the degree of objective assembly tolerances from 24 to 4, by representingthe original four objectives by a linear combination of 2D Gaussian RBF, which is analytical, global C∞ smooth, andlocally influencing. Simulation result verifies the feasibility and performance of the designed freeform-objectiveChernin multipass cell, whose base length is 0.2 m, volume is less than 0.8 L, and an adjustable optical length of 0.4–34 m. Results prove that by using a proper approach to approximate the origin surfaces as an integrated freeform,one can simultaneously reduce the assembly cost and the assembly difficulty.

Virtual view PSNR prediction based on depth distortion tolerance model and support vector machine

Fen Chen, Jiali Chen, Zongju Peng, Gangyi Jiang, Mei Yu, Hua Chen, and Renzhi Jiao

Doc ID: 304982 Received 16 Aug 2017; Accepted 28 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: Quality prediction of virtual view is important for free viewpoint video system, and can be used as feedback to improve the performance of depth video coding and virtual view rendering. In this paper, an efficient virtual view PSNR prediction method is proposed. First, the effect of depth distortion on virtual view quality is analyzed in detail and depth distortion tolerance (DDT) model which determines the depth distortion tolerance range is presented. Next, the DDT model is used to predict the virtual view quality. Finally, the support vector machine (SVM) is utilized to train and obtain the virtual view quality prediction model. Experimental results show that the spearman's rank correlation coefficient and root mean squared error between the actual PSNR and the predicted PSNR by DDT model are 0.8750 and 0.6137 on average, and by SVM prediction model are 0.9109 and 0.5831. The computational complexity of the SVM method is lower than the DDT model and the state-of-the-art methods.

A New Approach for the Production Chain of Printed Polymer Optical Waveguides (POWs) - An Overview

Florian Loosen, Carsten Backhaus, Jochen Zeitler, Gerd-Albert Hoffmann, Thomas Reitberger, Lukas Lorenz, Norbert Lindlein, Jörg Franke, Ludger Overmeyer, Oliver Suttmann, Klaus-Jürgen Wolter, and Karlheinz Bock

Doc ID: 300494 Received 07 Jul 2017; Accepted 28 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: The research for new production chains in the field of waveguide fabrication is a challenging task. Realizing a cost efficient manufacturing process allows integrating optical data communication in arbitrary structures as for example the wing of an airplane or the car body. The production chain described in this paper contains the design, simulation, and fabrication process of printed Polymer Optical Waveguides (POWs).

An efficient method for fabricating a directional volumetric display using strings displaying multiple images

Atsushi Shiraki, Masataka Ikeda, Hirotaka Nakayama, Ryuji Hirayama, Takashi Kakue, Tomoyoshi Shimobaba, and Tomoyoshi Ito

Doc ID: 303481 Received 31 Jul 2017; Accepted 28 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: In this study, we describe the fabrication of a high-resolution directional volumetric display that can display multiple images in different directions. The display designs can be used to show animations using strings; however, improving the resolution of such displays is difficult. Previously, the arrangement of strings has only been determined experimentally, making fabrication of volumetric displays a challenge. The goal of the present study is to improve resolution using simulations and to determine the arrangement of strings under three constraints. This simplified the fabrication of a directional volumetric display with 345 strings, which can display two different 20 × 20 pixel images in two different directions. A large high-resolution directional volumetric display can be fabricated using the proposed method. The string-type display has high artistic potential and is expected to find applications in the amusement and entertainment fields.

Universal phase-depth mapping in structured light field

Zewei Cai, Xiaoli Liu, Xiang Peng, and Bruce Gao

Doc ID: 303796 Received 31 Jul 2017; Accepted 28 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: Technologies and devices of light field imaging have been recently developed for both industrial applications and scientific research to achieve excellent imaging properties. In the previous work, we combined light field imaging with structured illumination to propose a structured light field method in which multidirectional depth estimation can be performed for high-quality 3D imaging. However, the projection axis was implicitly assumed to be perpendicular to the reference plane, which is hard to meet in practice. In this paper, we derived a universal phase-depth mapping in the structured light field by relaxing this implicit condition. Both nonlinear and linear models were proposed based on this universal relationship. To test the model’s practical performance, we simulated experiments by adding errors to the real measured values to evaluate the deviation in depth estimation. By comparing the root-mean-square distributions of the depth deviations with respect to the depth positions, we demonstrated that the nonlinear model was precise and consistent in a wide range of depth, which was finally employed to realize high-quality multidirectional scene reconstruction.

Spatial Intensity Profiling of Elastic and InelasticScattering in Isotropic and Anisotropic Liquids byImmersion of a Spherical Silicon Photocell

Muhammad Hamza Humayun, Syed Sultan Shah Bukhari, Muhammad Zakwan, Mustafa Bayer, Ulas Gokay, Ali Serpenguzel, Kenichi Taira, Etsuji Omura, and Josuke Nakata

Doc ID: 301899 Received 14 Jul 2017; Accepted 28 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: The transverse spatial intensity distribution of elastic and inelastic light scattering in passive and active, as well asweak and strong scattering liquid media has been studied by using Sphelar® One p-n junction silicon sphericalphotocells. We immersed a Sphelar® One in these scattering solutions, and measured the photoconductiveresponse in reverse biased photodiode (PD) configuration. The passive weak scattering medium was pure ethanol(EtOH), whereas the passive strong scattering medium 5CB nematic liquid crystal (NLC). Solutions of 0.1 mMRhodamine 640 perchlorate laser dye in EtOH and in 5CB NLC were used as active scattering media. The responseof Sphelar® One was strongly enhanced in 5CB NLC compared to EtOH, as well as in active solutions compared topassive solutions. The morphology of the Sphelar® One is already advantageous over conventional one-sidedplanar PDs inside liquid solutions. This omnidirectional response of the Sphelar® One can further be enhanced byoptimizing the properties of the surrounding passive elastic and active inelastic scatterers.

A simplified model of pinhole imaging for quantifying systematic errors in image shape

Laura Robin Benedetti, Nobuhiko Izumi, Shahab Khan, George Kyrala, Otto Landen, Tammy Ma, S.R. Nagel, and Arthur Pak

Doc ID: 305230 Received 21 Aug 2017; Accepted 28 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: We examine systematic errors in x-ray imaging by pinhole optics for the purpose of quantifying uncertainties in the measurement of convergence and asymmetry in inertial confinement fusion implosions. We present a quantitative model for the total resolution of a pinhole optic with an imaging detector that can be used to predict loss of shape detail due to imaging; we find that fractional error in observable shapes (FME) is proportional both to the relative resolution element we define, r, and to the mode of asymmetry observed, N: FME = -0.2r N. We have experimentally validated our results by imaging a single object with differently-sized pinholes and with different magnifications.

FLEET Velocimetry for Combustion and FlowDiagnostics

Nicholas DeLuca, Richard Miles, Naibo Jiang, Waruna Kulatilaka, Anil Patnaik, and James Gord

Doc ID: 301999 Received 10 Jul 2017; Accepted 27 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: We report the use of femtosecond-laser electronic-excitation tagging (FLEET) for velocimetry at 100-kHzimaging rate. Sequential, single-shot, quantitative velocity profiles of an under-expanded supersonicnitrogen jet were captured at 100-kHz rate. The signal and lifetime characteristics of the FLEET emissionwere investigated in a methane flame above a Hencken burner at varying equivalence ratios, and roomtemperature gas mixtures involving air, methane, and nitrogen. In the post-flame region of the Henckenburner, the emission lifetime was measured as two orders of magnitude lower than lab air conditions.Increasing the equivalence ratio above 1.1 leads to a change in behavior, with doubled lifetime. Bymeasuring the emission in a cold methane flow, a short-lived signal was measured that decayed after thefirst microsecond. As a proof of concept for velocimetry in a reacting environment, the exhaust of a pulseddetonator was measured by FLEET. Quantitative velocity information was obtained, corresponding to amaximum centerline velocity of 1,800 meters per second for the detonation wave. Extension of FLEET tolarger scale, complex flow environments is now a viable option.

Self-training based spectral image reconstruction forart painting with multispectral imaging

Peng Xu, Haisong Xu, Changyu Diao, and Zhengnan Ye

Doc ID: 295661 Received 10 May 2017; Accepted 27 Sep 2017; Posted 27 Sep 2017  View: PDF

Abstract: A self-training based spectral reflectance recovery method was developed to accurately reconstruct the spectralimages of art paintings with multispectral imaging. By partitioning the multispectral images with k-meansclustering algorithm, the training samples are directly extracted from the art painting itself to restrain thedeterioration of spectral estimation caused by the material inconsistence between the training samples and artpainting. The coordinate paper is used to locate the extracted training samples. The spectral reflectances of theextracted training samples are acquired indirectly with the spectroradiometer, and the circle Hough transform isadopted to detect the circle measuring area of the spectroradiometer. Through simulation and practicalexperiment, the implementation of the proposed method was explained in detail, and it is verified to have betterreflectance recovery performance than that using the commercial target and to be comparable to the approachusing painted color target.

Ray tracing in ellipsoidal reflectors for optical biometry of media

Mikhail Bezuglyi, Natalia Bezuglaya, and Ivan Helich

Doc ID: 303934 Received 02 Aug 2017; Accepted 27 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: In this paper, an analytical basis of ray tracing for optical biometry of media by ellipsoidal reflectors was developed. A ray-tracing algorithm was created, which involves determining the point of interaction of the incident beam with the ellipsoidal reflector, calculating the direction of the reflected beam, and determining the intersection point of the reflected ray with the second ellipsoid focal plane, taking into account the statistical weight of photons. For imaging in the optical biometry of media by ellipsoidal reflectors, the results of a real experiment and a Monte Carlo simulation for chicken muscle tissue samples of different thickness on the wavelength of 632.8 nm are used.

Infrared target detection method based on thereceptive field and lateral inhibition of HVS

Shangnan Zhao, Yong Song, Yufei Zhao, Yun Li, lin li, Qun Hao, and Maoyuan Li

Doc ID: 303535 Received 28 Jul 2017; Accepted 27 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: In this paper, an infrared (IR) target adaptive detection method based on the receptive field (RF) and lateralinhibition (LI) of human visual system (HVS) is proposed. In the proposed method, the direction parameters ofGabor filter is adaptively determined according to the gradient direction, so that edges in image can be detectedwithout manual intervention. Meanwhile, background prediction based on LI is used for regulating the gray valuein image so as to achieve background suppression and target enhancement. Experimental results indicate that theproposed method can extract both small target and area target from complex background, and has satisfactorytarget detection ability.

Design of Large Aperture Tunable Fresnel Liquid Crystal Lens

Afsoon Jamali, Doug Bryant, Yanli Zhang, Anders Grunnet-Jepsen, Achintya Bhowmik, and Philip Bos

Doc ID: 304213 Received 07 Aug 2017; Accepted 27 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: A large aperture tunable lens, based on liquid crystals, considered for near-to-eye applications, is designed, built and characterized. Large liquid crystal lenses with high quality are limited by very slow switching speed due to the large Optical Path Difference (OPD) required. In order to reduce the switching time of the lens, the thickness is controlled through the application of several phase resets, similar to the design of a Fresnel lens. A main point of the paper is the design of the Fresnel structure to have a minimal effect on the image quality. Our modeling and experimental results demonstrate that minimal image degradation due to the phase resets is observable when the segment spacing is chosen by taking into account the human eye resolution. Such lenses have applications related to presbyopia, and in Virtual Reality systems to solve the well-known issue of accommodation-convergence mismatch.

Multispectral metasurface hologram at millimeter wavelengths

Nicholas Caira and David Smith

Doc ID: 303962 Received 02 Aug 2017; Accepted 26 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: We demonstrate a computer-generated metasurface hologram in which four distinct images are encoded at four different W-band (75-110 GHz) frequencies. The metasurface hologram consists of a planar array of resonant metamaterial elements excited by a collimated reference beam incident on the hologram at an oblique angle. Each of the images is encoded by a subset of metamaterial elements that are resonant at the specific excitation frequency, and are spatially positioned to achieve a desired phase distribution in the plane in conjunction with the reference wave. The phase-only hologram is optimized using the Gerschberg-Saxton algorithm. The four, well-defined images are produced at specific distances within the Fresnel zone of the aperture.

Raman Scattering in Single-Crystal Sapphire at Elevated Temperatures

Juddha Thapa, Bo Liu, Steven Woodruff, Benjamin Chorpening, and Michael Buric

Doc ID: 303867 Received 02 Aug 2017; Accepted 26 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: Sapphire is a widely used high-temperature material and this work presents thorough characterization of all the measurable Raman scattering modes in sapphire and their temperature dependencies. Here, Raman scattering in bulk sapphire rods is measured from room temperature to 1081 °C and is illustrated as a method of noncontact temperature measurement. A single-line argon ion laser at 488 nm was used to excite the sapphire rods inside a cylindrical furnace. All the anti-Stokes peaks (or lines) were observable through the entire temperature range of interest, while Stokes peaks were observable until they were obscured by background thermal emission. Temperature measurements were found to be most reliable for A1g and Eg modes using the peaks at ±418, ±379, +578, +645, and, +750 cm-1 (+ and – are designated for Stokes and anti-Stokes peaks respectively). The 418 cm-1 peak was found to be the most intense peak. The temperature dependence of peak position, peak width, and peak area of the ±418 and ±379 peaks is presented. For +578, +645 and +750, the temperature dependence of peak position is presented. The peaks’ spectral positions provide the most precise temperature information within the experimental temperature range. The resultant temperature calibration curves are given, which indicate that sapphire can be used in high-temperature Raman thermometry with an accuracy of about 1.38°C average standard deviation over the entire >1000°C temperature range.

Sixth-order wave aberration theory of ultra-wideangleoptical systems

Lijun Lu and Yiqing Cao

Doc ID: 302235 Received 11 Jul 2017; Accepted 26 Sep 2017; Posted 27 Sep 2017  View: PDF

Abstract: In this paper, we develop the sixth-order wave aberration theory of ultra-wide-angle optical systems like fisheyelens. Based on the concept and approach to develop wave aberration theory of plane-symmetric optical systems,we first derive the sixth-order intrinsic wave aberrations and the fifth-order ray aberrations; second, we present amethod to calculate the pupil aberration of such kind of optical systems to develop the extrinsic aberrations; third,the relation of aperture-ray coordinates between the adjacent optical surfaces is fitted with the second-orderpolynomial to improve the calculation accuracy of the wave aberrations of a fisheye lens with large acceptanceaperture. Finally, the resultant aberration expressions are applied to calculate the aberrations of two designexamples of fisheye lenses; the calculation results are compared to the ray-tracing ones with Zemax software tovalidate the aberration expressions.

Field Imaging Near to the Surface of THz ReflectiveOptics using a Vector Network Analyzer

Maryam Hajji, Jonathan Hammler, Dagou Zeze, Claudio Balocco, and Andrew Gallant

Doc ID: 302128 Received 03 Aug 2017; Accepted 26 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: A Vector Network Analyzer based quasi-optical measurement system, which is suitable for mapping electric fieldintensity and phase near to the surface of terahertz reflective optics, is presented. The system uses a fixed five parabolicmirror and transmitter/receiver head arrangement which has the benefit of requiring only the sample to be sweptduring measurement. The system has been tested with a micromilled aluminum zone plate reflector used as anexemplar structure. The measured focal point of the zone plate reflector, at its designed frequency of 1 THz, is shown tocorrespond well to both Finite Difference Time Domain simulations and analytical theory.

A fast, wide-field and distortion-free telescope withcurved detectors for surveys at ultra-low surfacebrightness

Eduard Muslimov, David Valls-Gabaud, Gerard LEMAITRE, Emmanuel Hugot, Wilfried Jahn, Simona Lombardo, Xing Wang, Pascal Vola, and Marc FERRARI

Doc ID: 302824 Received 18 Jul 2017; Accepted 26 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: We present the design of an all-reflective, bi-folded Schmidt telescope aimed at surveys of extended astronomicalobjects with extremely-low surface brightness. The design leads to a high image quality withoutany diffracting spider, along with a large aperture and field of view, with a small central obstructionwhich barely alters the PSF. As an example, we present the design of a high-quality, 36 cm diameter, fast( f /2.5) telescope working in the visible with a large field of view (1.6°× 2.6°). The telescope can operatewith a curved detector (or with a flat detector with a field flattener) and a set of filters. The entrance mirroris anamorphic and replaces the classical Schmidt entrance corrector plate. We show that this anamorphicprimary mirror can be manufactured through stress polishing, avoiding high spatial frequency errors, andtested with a simple interferometer scheme. This prototype is intended to serve as a fast-track scientificand technological pathfinder for the future space-based MESSIER mission.

Direction-dependent waist-shift-difference ofGaussian beam in a multiple-pass zigzag slab amplifierand geometrical optics compensation method

Zhaoyang Li, Takashi Kurita, and Noriaki Miyanaga

Doc ID: 303342 Received 25 Jul 2017; Accepted 26 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: Zigzag and non-zigzag beam waist shifts in a multiple-pass zigzag slab amplifier are investigated based on thepropagation of Gaussian beam. Different incident angles in the zigzag and non-zigzag planes would introduce adirection-dependent waist-shift-difference, which distorts the beam quality in both the near- and far-fields.Theoretical model and analytical expressions of this phenomenon are presented, and intensity distributions in thetwo orthogonal planes are simulated and compared. A geometrical optics compensation method by beam 90°rotation is proposed, which could not only correct the direction-dependent waist-shift-difference but also possiblyaverage the traditional thermally induced wavefront-distortion-difference between the horizontal and verticalbeam directions.

High speed combined NIR low coherenceinterferometry for wafer metrology

Hyo Mi Park and Ki-Nam Joo

Doc ID: 303346 Received 25 Jul 2017; Accepted 26 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: In this investigation, we describe a combined low coherence interferometric technique to measure the surface andthickness profiles of wafers at once with high speed. The measurement system consists of a spectrally-resolvedinterferometer to provide and monitor optical path difference between two incident beams of the optical sourcepart and a low coherence scanning interferometer to measure the dimensions of wafers with significantlyshortened scanning length. In the experiments, a silicon wafer and a sapphire wafer, of which both sides arepolished, were used as targets of the measurement system for verification of the proposed system. As the result, thescanning length of the low coherence scanning interferometer was reduced from a few millimeters to a fewhundreds of micrometers as approximately 10 times. In addition, surface profiles of both sides and thicknessprofiles were simultaneously measured to reconstruct 3D shape of wafers.

Suppression of Interference Noise Caused byFresnel Reflection in all-Fiber White LightInterferometer

Yonggui Yuan, Yongqing Cheng, Jun Yang, Haoliang Zhang, Dongchuan Lu, Yan Lv, Feng Peng, Hanyang Li, and Libo Yuan

Doc ID: 300992 Received 26 Jun 2017; Accepted 26 Sep 2017; Posted 02 Oct 2017  View: PDF

Abstract: We propose the methods to suppress the interference noise of all-fiber white light interferometer (WLI),which is caused by the residual Fresnel reflective beam. The methods are proposed to ensure the widedynamic range and enhance the high accuracy measurement. The INs can cause the misjudgment of therealistic optical characteristic parameters, such as the fault diagnosis and polarization coupling of the opticaldevices under test. In addition, the INs can reduce the dynamic range of the WLI. The optical path mismatch(OPM) method and the intensity suppression (IS) method by changing the positions and intensity of the INsare presented. The two suppression methods can successfully restrain the INs caused by the Fresnel reflectionbeams. The experimental results show that the INs are successfully suppressed by the OPM method orrestrained by IN method in the interferograms, and the dynamic range can achieve 85 dB without INs.

A digital demodulation algorithm based on frequency correction for the near-infrared spectrometer

Jingru Wang, Zhihong Wang, Yuzhe Wang, Jie Liu, and Xufei Ji

Doc ID: 304083 Received 03 Aug 2017; Accepted 26 Sep 2017; Posted 05 Oct 2017  View: PDF

Abstract: For the scanning near-infrared (NIR) spectrometer, the employments of traditional digital demodulation algorithms require that the sampling frequency is an integral multiple of the measured signal frequency. However, the measured signal frequency is unstable and the sampling frequency is a fixed value in the spectrometer, which affects the accuracy of amplitude demodulation results. To improve the signal-to-noise ratio of spectra, this paper proposes an improved digital demodulation algorithm based on frequency correction. Through theoretical analysis, simulations and experiments, the improved digital demodulation algorithm based on frequency correction was compared with a digital demodulation algorithm based on the average of the absolute value in a complete period. The results showed that the former algorithm decreased the noise caused by the fluctuation of the measured signal frequency. The signal-to-noise ratio of spectra increased from 628 to 1124, and the measurement time only increased 0.73%.

Spectral and Far-Field Broadening due to Stimulated Rotational Raman Scattering Driven by the Nike Krypton Fluoride Laser

James Weaver, Robert Lehmberg, Stephen Obenschain, David Kehne, and Matthew Wolford

Doc ID: 296855 Received 11 Jul 2017; Accepted 25 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: Stimulated rotational Raman scattering (SRRS) in the ultraviolet region (λ=248 nm) has been observed at the Nike laser over extended propagation paths in air during high power operation. Although this phenomenon is not significant for standard operating configurations at Nike, broadening of the laser spectrum and far field focal profiles has been observed once the intensity-path length product exceeds a threshold of approximately 1 TW/cm. This paper presents experimental results and a new theoretical evaluation of these effects. The observations suggest that significantly broader spectra can be achieved with modest degradation of the final focal distribution. These results point to a possible path for enhanced laser-target coupling with the reduction of laser-plasma instabilities due to broad laser bandwidth produced by the SRRS.

ASimulations of a multi-wavelength differentialabsorption LIDAR method for CO2 measurement

Ge Han, Hao Xu, Wei Gong, Xin Ma, and Ailin Liang

Doc ID: 303040 Received 25 Jul 2017; Accepted 24 Sep 2017; Posted 25 Sep 2017  View: PDF

Abstract: The increase of greenhouse gas is one of the most important factors leading to global climate change. Differential absorptionlight detection and ranging (LIDAR) (DIAL) is considered to be the most potential tool to measure CO2 remotely. However, it isdifficult to obtain accurate CO2 retrievals and determine carbon fluxes with the traditional dual-wavelength differentialabsorption inversion method, which is characterized by a low signal-to-noise ratio (SNR). Therefore, a multi-wavelengthdifferential absorption inversion framework is proposed in this work. Based on the measurement of the absorption opticaldepths of a single line at 30 different wavelengths, we tried to minimize the differences between the simulated and measuredabsorption optical depths through an iterative process, which consisted of forward simulation and reverse inversionprocesses. The retrievals are determined when an optimal solution is obtained. The simulation experiments show that theprecision of the nonuniform sampling wavelength method is better than that of the dual-wavelength method. The precision ofthe proposed method was improved by more than 60% for an SNR of 30–40 dB compared to the traditional method.Furthermore, the average error of this method is about 1/9 of the traditional method.

Single-shot 3D–topography of reflective samples withdigital holographic microscopy

Raul Castañeda and Jorge Garcia-Sucerquia

Doc ID: 303990 Received 02 Aug 2017; Accepted 24 Sep 2017; Posted 25 Sep 2017  View: PDF

Abstract: In this work, an off-axis digital holographic microscope operating in reflection mode and telecentric regimen toproduce 3D-topography of microscopy sample is shown. The main characteristics of the proposed method thatmake it different from the previous works in the field are the possibility of producing the 3D-topography by asingle-shot, over the complete field of view, with sensitivity of λ 100 , without phase perturbations introduced bythe illuminating-imaging system and with no further numerical processing beyond the required for recovering thephase map of the sample. A complete analysis of the illuminating-imaging system of the digital holographicmicroscope is presented. The proposed digital holographic microscope is tested on imaging an USAF resolution testtarget and some MEMs.

A Constrained Solver for Optical Absorption Tomography

Nick Polydorides, Alex Tsekenis, Edward Fisher, Andrea Chighine, Hugh McCann, Luca Dimiccoli, Paul Wright, Michael Lengden, Thomas Benoy, David Wilson, Gordon Humphries, and Walter Johnstone

Doc ID: 304564 Received 10 Aug 2017; Accepted 23 Sep 2017; Posted 25 Sep 2017  View: PDF

Abstract: We consider the inverse problem of concentration imaging in optical absorption tomography with limited data sets. The measurement setup involves simultaneous acquisition of near infrared wavelength-modulated spectroscopic measurements from a small number of pencil beams equally distributed among six projection angles surrounding the plume. We develop an approach for image reconstruction that involves constraining the value of the image to the conventional concentration bounds and a projection into low-dimensional subspaces to reduce the degrees of freedom in the inverse problem. Effectively, by re-parameterising the forward model we impose simultaneously spatial smoothness and a choice between three types of inequality constraints, namely positivity, boundedness and logarithmic boundedness in a simple way that yields an unconstrained optimisation problem in a new set of surrogate parameters. Testing this numerical scheme with simulated and experimental phantom data indicates that the combination of affine inequality constraints and subspace projection leads to images that are qualitatively and quantitatively superior to unconstrained regularised reconstructions. This improvement is more profound in targeting concentration profiles of small spatial variation. We present images and convergence graphs from solving these inverse problems using Gauss-Newton's algorithm to demonstrate the performance and convergence of our method.

Equivalent wavelength self-mixing interferencevibration measurement based on envelope extractionFourier transform algorithm

Dongyu Li, Huang zan, Mo Brus, Ling Yan, zhang Zhenghe, and Zhen Huang

Doc ID: 300789 Received 06 Jul 2017; Accepted 23 Sep 2017; Posted 29 Sep 2017  View: PDF

Abstract: In order to improve measurement precision and facilitate the instrument installation of the equivalent wavelength selfmixinginterferometer, an envelope extraction Fourier transform algorithm is presented for microscopic vibrationmeasurement. In theory the precision is about 21 nm without modulation and the minimum measurable vibrationamplitude is about 87 nm. The validity of the proposed method was demonstrated by means of simulated signals andconfirmed by several experimental measurements.

Polar decompositions of negative-determinant Mueller matrices featuring non-diagonal depolarizers

Razvigor Ossikovski and Jérémy Vizet

Doc ID: 302331 Received 12 Jul 2017; Accepted 23 Sep 2017; Posted 25 Sep 2017  View: PDF

Abstract: We generalize an existing algebraic procedure for the polar decomposition of Mueller matrices with negative determinants (R. Ossikovski, M. Anastasiadou, A. De Martino, Opt. Commun. 281, 2406 (2007)) to the case of non-diagonal depolarizer matrix factors. The generalized procedure is applied to experimental Mueller matrices illustrating its potential for the phenomenological interpretation of complex polarimetric data.

Dynamic projection theory for fringe projection profilometry

hong sheng, Jing Xu, and Song Zhang

Doc ID: 302562 Received 17 Jul 2017; Accepted 21 Sep 2017; Posted 21 Sep 2017  View: PDF

Abstract: Fringe projection profilometry (FPP) has been widely used for 3D reconstruction, surface measurementand reverse engineering. However, fringe projection profilometry is prone to overexposure if objectshave a wide range of reflectance. In this paper, we propose a dynamic projection theory based onfringe projection profilometry to rapidly measure the overexposed region with an attempt to conquerthis challenge. This theory modifies the projected fringe image to the next better measurement basedon the feedback provided by the previously captured image intensity. Experiments demonstrated thatthe number of overexposed points can be drastically reduced after one or two iterations. Compared withthe state-of-the-art methods, our proposed dynamic projection theory measures the overexposed regionquickly and effectively, and thus broadens the applications of fringe projection profilometry.

Temperature characterization of a radiating gas layer using DSLR camera-based two-color ratio pyrometry

Sneh Deep, Yedhu Krishna, and Gopalan Jagadeesh

Doc ID: 303862 Received 02 Aug 2017; Accepted 21 Sep 2017; Posted 22 Sep 2017  View: PDF

Abstract: Two-color ratio pyrometry (TCRP) technique using a digital single-lens reflex (DSLR) camera has been used to measure the time-averaged and line of sight integrated temperature distribution in the radiating shock layer in a high-enthalpy flow. A 70 mm diameter cylindrical body with a 70 mm long spike was placed in a hypersonic shock tunnel and the region behind the shock layer was investigated. Systematic error due to contribution from line emissions were corrected by monitoring the emission spectrum from this region using a spectrometer. The relative contribution due to line emission on R, G, and B channels of the camera were 7.4 %, 2.2 % and 0.4 % respectively. The temperature contours obtained clearly distinguished regions of highest temperature. The maximum absolute temperature obtained in the experiment was ~2920 K ±55, which was 20% lower than the stagnation temperature. This lower value is expected due to line-of-sight integration, time-averaging and losses in the flow. Strategies to overcome these limitations are also suggested in the paper.

A polarization study about telescope-basedtransmitter for quantum communication

Jincai Wu, Zhiping He, Liang Zhang, Liyin Yuan, TianHong Wang, Jianjun Jia, Shu Rong, and Jianyu Wang

Doc ID: 304814 Received 14 Aug 2017; Accepted 20 Sep 2017; Posted 22 Sep 2017  View: PDF

Abstract: We studied the polarization evolution of a reflective telescope designed for quantum satellite, Micius. The changein polarization extinction ratio (PER) of quantum light was derived and calculated. The PER deterioration causedby the increase of incidence angle was calculated to determine the boundary conditions for the system design. Theperformances of the Micius prototype were evaluated both theoretically and experimentally to verify thevalidation of our optical design. Minimum and maximum PERs of 38 and 55dB were recorded, respectively,which were mostly in good agreement with the numerical calculations. Our investigations have contributed to thesuccess of Micius, which is a significant milestone for building a global security network.

Matrix multi-pass scheme disk amplifier

Evgeny Perevezentsev, Ivan Kuznetsov, Ivan Mukhin, and Oleg Palashov

Doc ID: 302364 Received 13 Jul 2017; Accepted 20 Sep 2017; Posted 21 Sep 2017  View: PDF

Abstract: Two multi-pass optical schemes of a disk laser amplifier have been proposed. Different variants of both the schemes with the smallest amount of optical elements and with lens in the active element taken into account have been calculated. For 32 V-passes of radiation through the active element, the average power of ~50 W with ~10% optical to optical efficiency in a pulse-periodic regime with a repetition rate of 10 kHz and a pulse duration of 2 ns was obtained at the amplifier output. The small signal gain amounted to 200.

Effect of graded band-gap structure on photoelectric performance of transmission-mode AlxGa1-xAs/GaAs photocathode modules

Cheng Feng, Yijun Zhang, Jian Liu, Yunsheng Qian, Xinxin Liu, Feng Shi, and Hongchang Cheng

Doc ID: 302644 Received 18 Jul 2017; Accepted 20 Sep 2017; Posted 16 Oct 2017  View: PDF

Abstract: The graded band-gap AlxGa1-xAs/GaAs photocathode with graded composition and exponential doping structure has shown great potential for improving the photoemission capability. In order to better study the performance of transmission-mode AlxGa1-xAs/GaAs photocathode with the complex graded band-gap structure, the experimental optical properties and quantum efficiency are measured by comparison with uniform composition and exponential doping Al0.7Ga0.3As/GaAs photocathode. The theoretical optical properties of the multi-layer AlxGa1-xAs/GaAs photocathode modules are calculated by matrix formula in the basis of thin film optical principles. The effect of cathode thickness and Al proportion on optical properties are analyzed by simulation. The results show that these parameters have complicated effects on the optical properties. Different parameters are presented as the changes of peak and valley of the optical property curves. Meanwhile, the emission layer has a significant effect on the absorptivity values of the photocathode modules, which will obviously influence the photoemission performance. By using the optical properties via calculation, a better fit of the experimental data with the theoretical model can be achieved, which would make reasonable guidance for further investigation of this complex graded bandgap photoemitters.

Laterally coupled distributed feedback type-I quantum well cascade diode lasers emitting near 3.22 µm

Tao Feng, Takashi Hosoda, Leon Shterengas, GELA KIPSHIDZE, Aaron Stein, Ming Lu, and Gregory Belenky

Doc ID: 300735 Received 23 Jun 2017; Accepted 19 Sep 2017; Posted 19 Sep 2017  View: PDF

Abstract: The laterally coupled distributed feedback (LC-DFB) GaSb-based type-I quantum well cascade diode lasers using the 2nd and the 6th order gratings to stabilize the output spectrum near 3.22 µm were designed and fabricated. The laser heterostructure contained three cascades. The devices were manufactured using single dry etching step defining the ~5- µm-wide ridge with ~5-µm-wide gratings sections adjacent to the ridge sides. The grating coupling coefficients were estimated to be about 1 cm 1. The stability of the single frequency operation was ensured by alignment of the DFB mode to the relatively wide gain peak. The 2-mm-long 2nd order LC-DFB lasers generated above 10 mW of continuous wave (CW) output power at 20 °C in epi-side-up configuration and demonstrated power conversion efficiency above 2%. The 6th order LC-DFB lasers showed lower efficiency but still generated several milliwatts of CW output power. The devices demonstrated CW current tuning range of about 3.5 nm at the temperature of 20 °C.

Automatic and Rapid Whole-body 3D Shape Measurement Based on Multi-Node 3D Sensing Speckle Projection

Jiping Guo, Xiang Peng, Ameng Li, Xiaoli Liu, and Jiping Yu

Doc ID: 304142 Received 07 Aug 2017; Accepted 19 Sep 2017; Posted 19 Sep 2017  View: PDF

Abstract: Automatic and rapid whole-body 3D shape measurement has attracted extensive attentions in recent years, and been widely used in many fields. Rapid 3D reconstruction, automatic 3D registration and dedicated system layout are critical factors to enable an excellent 3D measurement system. In this paper, we present an automatic and rapid whole body 3D measurement system that is based on multi-node 3D sensors using speckle projection. A rapid algorithm for searching homologous point pairs is suggested, which takes advantage of the optimized projective rectification and simplified sub-pixel matching techniques, leading to an improved time efficiency of 3D reconstruction. Meanwhile, a low cost automatic system with a flexible setup and an improved calibration strategy are proposed, where system parameters of each node sensor can be simultaneously estimated with the assistant of a cubic and a planar target. Furthermore, an automatic range data registration strategy by employing two aided-cameras is investigated. Experiment results show that the presented approach can realize automatic whole body 3D shape measurement with high efficiency and accuracy.

Methods of polarimetric calibration and reconstruction for a fieldable channeled dispersive imaging spectropolarimeter

Bin Yang, Jq zhang, cx yan, and Xping Ju

Doc ID: 301649 Received 05 Jul 2017; Accepted 19 Sep 2017; Posted 20 Sep 2017  View: PDF

Abstract: Polarimetric calibration and reconstruction methods for a fieldable channeled dispersive imaging spectropolarimeter (CDISP) are presented. A theoretical model for the polarimetric calibration is derived firstly. In the polarimetric calibration for the CDISP, the alignment errors of the polarimetric spectral intensity modulation (PSIM) module, and the polarization effects of the optical system and phase factors of the high-order retarders at different viewing angles, are considered and determined independently. Based on the results of the polarimetric calibration, the Stokes vector of the target is reconstructed through the derived reconstruction model. By using the presented polarimetric calibration and reconstruction methods, the measurement accuracy at each viewing angle of the fieldable CDISP can be improved effectively. Results of simulation experiments with a fieldable CDISP designed for airborne remote sensing are summarized and analyzed to demonstrate the effectiveness of the presented methods.

Laser absorption precursor research: microstructuresin the subsurface of mono-crystalline silicon substrate

Ye Tian, Shi Feng, Yifan Dai, Xiaoqiang Peng, and Yaoyu Zhong

Doc ID: 297846 Received 09 Jun 2017; Accepted 01 Sep 2017; Posted 06 Sep 2017  View: PDF

Abstract: In high-energy laser systems, the energy absorption coefficient of silicon optical elements is one of the most criticalserve indicators. The absorption coefficient of substrate limits the absorption of the overall elements. Since monocrystallinesilicon is transparent in working wavelength range, the subsurface absorption precursors also influencethe entire absorption dramatically. In this paper, the subsurface of a super-polished silicon substrate is exposed byion beam etching (IBE) as deep as 4.6μm. In different depth layers, morphology and energy absorption aremeasured with atom force microscope and photothermal instrument, respectively. In 100nm layer,microstructures are found and their heights decrease while widths increase with IBE. Finally, structures arediminished below the 1.12μm layer. Absorption increases with structures appearance. When the structures arefully exposed, absorption reaches the peak value, 327.5% of the unremoved surface. Once structures are removed,the absorption value falls down to the lowest point, 67.5%, which verifies that structures influence the absorptionsignificantly. According to the structure depth and Energy Dispersive Spectrometer (EDS) results, the structuresare most likely the densificated micro zones, generated by fabrication processes. In practical fabrication,subsurface layer of 1.12μm thick needs to be removed by stress-less processes, to obtain a low-absorption element.

Suomi NPP VIIRS solar diffuser screen transmittance model and its applications

Ning Lei, Xiaoxiong Xiong, and Jeff McIntire

Doc ID: 296116 Received 16 May 2017; Accepted 17 Aug 2017; Posted 17 Aug 2017  View: PDF

Abstract: The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership satellitecalibrates its reflective solar bands through observations of a sunlit solar diffuser (SD) panel. Sunlight passesthrough a perforated plate, referred to as the SD screen, before reaching the SD. It is critical to know whether theSD screen transmittance measured prelaunch is accurate. Several factors such as misalignments of the SD paneland the measurement apparatus could lead to errors in the measured transmittance and thus adversely impact onorbitcalibration quality through the SD. We develop a mathematical model to describe the transmittance as afunction of the angles that incident light makes with the SD screen, and apply the model to fit the prelaunchmeasured transmittance. The results reveal that the model does not reproduce the measured transmittance unlessthe size of the apertures in the SD screen is quite different from the design value. We attribute the difference to theorientation alignment errors for the SD panel and the measurement apparatus. We model the alignment errors andapply our transmittance model to fit the prelaunch transmittance to retrieve the “true” transmittance. To use thismodel correctly, we also examine the finite source size effect on the transmittance. Furthermore, we compare theproduct of the retrieved “true” transmittance and the prelaunch SD BRDF value to the value derived from on-orbitdata to determine whether the prelaunch SD BRDF value is relatively accurate. The model is significant in that itcan evaluate whether the SD screen transmittance measured prelaunch is accurate and help retrieve the truetransmittance from the transmittance with measurement errors, consequently resulting a more accurate sensordata product by the same amount.

Dependence of depth of focus on spherical aberration of optical systems

Antonin Miks and Jiri Novak

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

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

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