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Accepted papers to appear in an upcoming issue

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Calibration of an array projector used for high speed 3-D shape measurements using a single camera

Eugene Wong, Stefan Heist, Christian Braeuer-burchardt, Holger Babovsky, and Richard Kowarschik

Doc ID: 333011 Received 31 May 2018; Accepted 16 Aug 2018; Posted 16 Aug 2018  View: PDF

Abstract: Geometric calibration of Digital Light Processing (DLP) projectors in single camera, fringe projecting, 3-D measurement systems have been studied assuming the projector is inverse pinhole modelled. Conversely, a high-speed Multi-Aperture Array Projector (MAAP) projecting aperiodic fringes is not dependent on a Digital Mirror Device (DMD) and cannot be pinhole modelled. With MAAP projection, a stereo camera setup is required. This paper presents a model-less method to calibrate a MAAP by direct measurement of its illumination field and re-enables 3-D measurements with a single camera even with surface discontinuities present. Experimental proof of principle and preliminary measurement performance is shown.

Realizing terahertz far-field sub-diffractionoptical needle with sub-wavelength concentricring structure array

Desheng Ruan, Zeyu Li, Liang-Hui Du, Xun Zhou, Li-Guo Zhu, Cuiping Lin, Mengyu Yang, Gang Chen, Weiqing Yuan, Gaofeng Liang, and Zhongquan Wen

Doc ID: 335367 Received 25 Jun 2018; Accepted 16 Aug 2018; Posted 16 Aug 2018  View: PDF

Abstract: The terahertz (THz) lens is an essential and strategic element of THz opticalsystems, while a conventional THz lens cannot even reach high resolution due to thediffraction limit. Optical super-oscillation paves a way to generate sub-diffraction hotspots inthe far field, and demonstrates the capacity for resolution improvement of microscopicimaging in the visible range. However, there are few demonstrations of THz lenses forfocusing hotspots or needles based on super-oscillation. We propose and experimentallydemonstrate a far-field sub-diffraction focusing planar lens, consisting of a sub-wavelengthconcentric ring structure array, for a wavelength of 118.8 μm with focal length 420 λ andradius 160 λ. Utilizing the silicon etching process, a sub-diffraction focusing lens isfabricated. The experimental results show that the planar lens can generate a sub-diffractionneedle with length 19.7 λ in the focal region along the optic axis. Moreover, the smallest focalspot, with a transverse size of 1.212 λ, is smaller than the diffraction limit of 1.476 λ. Theproposed sub-diffraction optical needle planar lens can substitute for its traditionalcounterpart, and it has great potential in super-resolution tomography THz imaging systems.

Thermal conductivity determination of Erbium-dopedcrystals measured by spatially resolved confocalluminescence

Adamo Monte, Guilherme Alves, and Flavio Marques

Doc ID: 335436 Received 18 Jun 2018; Accepted 16 Aug 2018; Posted 16 Aug 2018  View: PDF

Abstract: Thermal conductivity of Er3+-doped Yttrium Aluminum Perovskite has been obtained by the use of laser inducedtemperature distribution and time-independent heat propagation equations. By using the spatially resolvedmicroluminescence technique, the fluorescence spectra on the sample surface were mapped during the laser focusedheating process, and the local temperature was measured at different spots on the sample surface with micrometricresolution. Significant information about the temperature profile was obtained following the maximum temperature ofthe laser spot and the behavior of the heat diffusion on the surface of the irradiation side. This data were finally used tofeed the heat propagation equations from where the thermal conductivity was evaluated.

Optimization of a quantum weak measurement system with digital filtering technology

Yang Xu, Lixuan Shi, Tian Guan, Dongmei Li, Yuxuan Yang, Xiangnan Wang, Zhangyan Li, Luyuan XIE, Xuesi Zhou, Yonghong He, and WenYue Xie

Doc ID: 336044 Received 26 Jun 2018; Accepted 16 Aug 2018; Posted 16 Aug 2018  View: PDF

Abstract: In this paper, we propose a post-Gaussian filtering theory for weak measurement in the frequency domain, and propose a highly-deformed digital filtering technique that can be used to optimize sensors based on weak-frequency measurement techniques. And we completed the experimental verification based on the weak measurement total internal reflection sensor. The experimental results show that the digital filtering technology can optimize the system in the range of working range, sensitivity and resolution of the frequency domain weak measurement system, so that it can reach the 0.210 rad, 3210.9 nm/RIU, 7.12×10-7 RIU respectively.

Optical differential temperature measurement withbeat frequency phase-fluorometry

Dmitri Lanevski, Koit Mauring, Eric Tkaczyk, and Raivo Jaaniso

Doc ID: 334914 Received 11 Jun 2018; Accepted 15 Aug 2018; Posted 16 Aug 2018  View: PDF

Abstract: We present a new method for differential temperature measurement based on thermal sensitivity of the fluorescencelifetime of thermographic phosphors (TP). Pairs of thermographic phosphors are excited with intensity modulated lightat frequencies 􀣓 and 􀣓 + 􀢤􀣓. The phase shift 􀢤􀣂 of the summary fluorescence intensity beat signal envelope ismeasured. A prototype of fluorometric differential temperature sensor is developed and feasibility of the method isexperimentally demonstrated with a Sm2+:SrFCl crystal and the 5D1->7F0 transition for high thermal sensitivity. Theobserved linear dependence between envelope phase shift Δθ and temperature difference ΔT agrees with thetheoretical prediction. Sensitivity of 􀡿 = −􀫙. 􀫢􀫠 °/℃ was achieved. This method could also be applied to differentialmeasurements of any parameter affecting fluorescence lifetime.

A Double D-shaped Hole Optical Fiber Coated withGraphene for Polarizer

shanshan chen, Li Li, Qu Hongkun, ZhenLan SU, Jianzhong Zhang, and Fengjun Tian

Doc ID: 328058 Received 10 Apr 2018; Accepted 15 Aug 2018; Posted 16 Aug 2018  View: PDF

Abstract: A double D-shaped hole optical fiber coated with graphene is proposed for polarizer at wavelength 1.55 μm. As theplanar surfaces of D-shaped holes are both coated with graphene, the interaction between core and graphene canbe doubled. Moreover, the interaction can be further improved by introducing functional materials into the holes.The proposed fiber provides high extinction ratio, low insertion loss and operates in single polarization mode. Theextinction ratio (ER) of 42.5 dB with 2.5 mm length optical fiber can be achieved for TE-pass polarizer, and theinsertion loss is about 1.08 dB. Specially the proposed fiber can achieve simultaneously dual-band polarizer at1.55 μm and 1.31 μm. The proposed fiber is feasible for seamless integration in existing fiber systems. We hope ourworks could be helpful to a high efficient polarizer, and expect the proposed fiber has some potential applicationsin photonic integrated circuits.

Determination of the optical turbulence parameters from the adaptive optics telemetry : critical analysis and on-sky validation

Laurent Jolissaint, Sam Ragland, Julian Christou, and Peter Wizinowich

Doc ID: 332679 Received 29 May 2018; Accepted 15 Aug 2018; Posted 16 Aug 2018  View: PDF

Abstract: It has been demonstrated by several authors that the optical turbulence parameters associated with a given adaptive optics (AO) run - the seeing angle and the outer scale - can be determined from a statisti- cal analysis of the commands of the system’s deformable mirror (DM). The higher the accuracy on these parameters, the more we can make use of them, allowing for instance a better estimation of the seeing statistics at the telescope location, or a more accurate assessment of the performance of the adaptive op- tics system. In the context of a point spread function reconstruction project (PSF-R) for the W. M. Keck observatory AO system, we decided to identify, in the most exhaustive way, all the sources of system- atic and random errors (most but not all of them are found in the literature) affecting the accuracy of the determination of the seeing and outer scale of optical turbulence, and find ways to compensate or miti- gate these errors, with the objective to determine these parameters to an error of no more than 10%. The seeing estimated using our method has been compared with more than 70 nearly simultaneous seeing measurements from open loop PSF, on the same optical axis, and with independent seeing monitors mea- surements acquired at the same time but far from the telescope (DIMM/MASS): the correlation with the open loop PSF is very good (the error is about 10%) validating the whole procedure for accurate seeing determination, while it is weak and sometimes completely uncorrelated with the DIMM/MASS seeing monitors data. We concluded that the DM based seeing can be very accurate if all the errors terms are considered in the DM data processing, but seeing taken from non-collocated seeing monitors is of no use even when moderate accuracy is required.

Experimental Characterization and Physics-BasedModeling of the Temperature-Dependent, DiffuseReflectance of Plasma-Sprayed Nd2Zr2O7 in the Nearto Short-Wave Infrared

Michael Brupbacher, Dajie Zhang, William Buchta, Timothy Montalbano, Keith Caruso, Marc Airola, David Brown, Michael Thomas, and James Spicer

Doc ID: 327583 Received 05 Apr 2018; Accepted 15 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: Supercontinuum-laser illumination in conjunction with CO2-laser heating has been implemented to measurethe near to short-wave infrared (970-1660 nm) diffuse reflectance of plasma-sprayed Nd2Zr2O7 as a function oftemperature. Owing to the broadband nature of this experimental technique, the diffuse reflectance of plasmasprayedNd2Zr2O7 has been measured at many wavelengths and has been shown to decrease with increasingtemperature. A physics-based model for diffuse reflectance predicated on the crystal/electronic band structureof highly-scattering semiconductor materials has been constructed to interpret the results of thesemeasurements. Baseline materials characterization has also been performed to assist in the development ofcrystal/electronic band structure-optical property relationships that could be useful for the design of nextgenerationenvironmental barrier coatings. This characterization has included ambient and non-ambient X-raydiffraction, as well as room-temperature, integrating-sphere, diffuse reflectance spectroscopy.

Adaptive Turbulence Compensation with a HybridInput-Output Algorithm in Orbital AngularMomentum-based Free-Space Optical Communication

Xiaoli Yin, huan chang, xiaozhou Cui, Jianxin Ma, Yongjun Wang, Guohua Wu, Lijia Zhang, and Xiangjun Xin

Doc ID: 331890 Received 16 May 2018; Accepted 15 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: Atmospheric turbulence is a major challenge for practical orbital angular momentum (OAM)-based free-spaceoptical (FSO) communication systems that causes intermodal crosstalk and degrades the performance of thesystem. Herein, we propose a hybrid input-output algorithm (HIOA)-based adaptive optics (AO) system tocompensate for distorted OAM beams. The principle and parameters of the HIOA-based AO system in an OAMbasedFSO system are analyzed, and the performance is discussed. The simulation results indicate that the HIOAbasedAO system can effectively correct distorted OAM beams and that the HIOA improves the compensationperformance and convergence speed compared to the traditional Gerchberg-Saxton algorithm. Moreover, weanalyze the compensation performance based on different probe beams. Using an OAM beam with state l=1 as aprobe beam can yield better correction effects than a Gaussian beam. This work verifies the feasibility of using anHIOA for adaptive turbulence compensation and provides new insights into OAM communication systems.

Polarization-modulated 3D imaging using largeaperture electro-optic modulator

Zhen Chen, Bo Liu, Shengjie Wang, and Enhai Liu

Doc ID: 334802 Received 11 Jun 2018; Accepted 15 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: To implement high-resolution and low-light sensitive 3D imaging for long-range applications while simplify datacollection and reduce collection time, a polarization-modulated 3D imaging structure, using large aperture electroopticmodulator (EOM) and electron multiplying CCD (EMCCD), is proposed in this paper. As the EMCCD cameraitself has no ability of time resolution and high-speed gating due to the time integration mechanism, large apertureelectro-optic modulators are used to provide time resolution and high-speed shutter simultaneously for the EMCCDcameras to obtain the polarization-modulated images, from which a 3D image can be reconstructed. A narrow fieldof-view was designed to match the divergence of laser beam for long-range imaging, and therefore through thereceiver, the incident angle on the electro-optic modulator would still be limited to within a small angle, whichwould not degrade the modulation performance significantly during electro-optic modulation. Ultimately, wefound that the polarization-modulated 3D imaging lidar showed very promising performance on time-resolvedimaging in a field-of-view of 0.9mrad.

Analyzing the performance of pseudo-random singlephoton counting ranging Lidar

Yang Yu, Bo Liu, and Zhen Chen

Doc ID: 335643 Received 21 Jun 2018; Accepted 14 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: The detection principle and performance of the pseudo-random single photon counting ranging (PSPCR) Lidarsystem are investigated. The detection probability and single photon detection efficiency (SPDE) of the macro codefor the PSPCR Lidar system are derived based on statistical theory. The effects of the echo primary electronsnumber and the dead time on the detection probability and SPDE are analyzed. The detection probability increaseswith the increase of the primary electrons number and tends to saturation. The change of dead time length haslittle effect on the detection probability of macro code, especially when the number of echo primary electrons islarge. However, the length of dead time is inversely proportional to the number of detected codes. The longer thedead time, the fewer the number of detected codes, and the worse the ranging performance. The Signal-to-NoiseRatio (SNR) of the PSPCR Lidar is analyzed based on the cross-correlation function. The Monte Carlo simulationresults show that the PSPCR Lidar has a satisfactory SNR even in a high noise level. As the number of signal primaryelectrons increases, the SNR gradually increases and tends to be saturated. As the noise increases, the SNRgradually decreases, and the greater the noise, the more severe the SNR decreases. At the same time, based on theassumption that the power of the single code in Gaussian distribution and the time resolution of the photoncounting module is less than the code width, the theoretical formula of the range error is deduced. The effects ofecho signal primary electrons number and code width on range error are analyzed. The results shows that thefewer the primary electrons number or the narrower the code width, the smaller the range error of the PSPCRLidar system. The ranging error of the PSPCR Lidar system is verified by Monte Carlo simulation. The simulationresults are in good agreement with the theoretical analysis.

Broadband Infrared Müller-Matrix Ellipsometry for Studies of Structured Surfaces and Thin Films

Andreas Furchner, Cordula Walder, Matthias Zellmeier, Jörg Rappich, and Karsten Hinrichs

Doc ID: 335648 Received 21 Jun 2018; Accepted 14 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: We present a high-optical-throughput infrared Müller-matrix (MM) ellipsometer for the characterization of structured surfaces and ultrathin films. Its unprecedented sensitivity of about 10¨⁴ in the normalized MM elements enables studies of the complex vibrational fingerprint of thin organic films under different ambient conditions. The ellipsometer acquires quadruples of MM elements within a few 10 s to min, rendering it interesting for process and in-line monitoring. It uses retractable achromatic retarders for increased signal to noise, and tandem wire-grid polarizers for improved polarization control. We demonstrate several scientific and industry-related applications. First, we determine the 3D profile of μm-sized trapezoidal SiO₂ gratings on Si from azimuth-dependent MM measurements. Data modeling based on rigorous coupled-wave analysis is employed to quantify grating structure and orientation. We then monitor polymer relaxation processes with a time resolution of 47 s. Measurements of polymer films as thin as 7.7 nm illustrate the sensitivity of the device. We finally couple a liquid flow cell to the ellipsometer, highlighting for the first time the prospects for in situ infrared MM studies of thin films at solid–liquid interfaces.

Multi-depth three-dimensional image encryptionbased on the phase retrieval algorithm in the Fresneland fractional Fourier transform domains

Mei-Lan Piao, Zi-Xiong Liu, Yan-Ling Piao, Huying Wu, Yu Zhao, and Nam Kim

Doc ID: 338567 Received 11 Jul 2018; Accepted 14 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: We propose a multi-depth three-dimensional (3D) image cryptosystem by employing the phase retrieval algorithmin the Fresnel and fractional Fourier (Fr-FrF) domains. Encryption was realized by applying the phase retrievalalgorithm based on the double-random-phase-encoding architecture in which two encryption keys will beincessantly updated in each iteration loop. The phase-only functions (POFs) are generated in two cascaded Fr-FrFtransforms (Fr-FrFT), serving as decryption keys efficiently reduced the speckle noise and crosstalk betweenencrypted 3D image depths. The use of Fr-FrFT position parameters and fractional order as decryption keysfurther extended the key space, enhancing the cryptosystem level. Numerical simulations demonstrated thefeasibility and robustness of our proposed scheme.

Parametric Study on Photoluminescence Enhancement of High-Quality ZnO Single Crystal Capping with Dielectric Microsphere Array

Yinzhou Yan, Jinwen Liu, Cheng Xing, Qiang Wang, Yong Zeng, Yan Zhao, and Yijian Jiang

Doc ID: 332529 Received 25 May 2018; Accepted 14 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: Dielectric microsphere is a multifunctional platform to manipulate light in microscale by nano-focusing, optical whispering-gallery resonance and unidirectional antenna. Dielectric microsphere array (MSA) have demonstrated the capability for photoluminescence (PL) and Raman enhancement without plasmonics. In this work, we investigate the effects of excitation power, tilting angle and temperature on PL enhancement of high-quality ZnO single crystal capping with fused silica MSAs. The microsphere diameter is optimized to 3.5-5.5 μm achieving the maximum UV-PL enhancement ratio of intensity (ERI) up to 10 folds by strong focusing and unidirectional antenna effects. Under the excitation power <0.2 mW, the incident light focused by the MSA increases the localized exciton state density for a higher ERI of ~15-fold. The angle-sensitive PL intensity from the MSA enhancer provides a simple approach achieving unidirectional UV emission from planar ZnO. The 16-fold enhancement for UV-PL near 130oC is also demonstrated, for the first time, owing to thermal ionization of H-related donor that increases free-exciton concentration. The high temperature stability and reproducibility of PL enhancement up to 400oC promote the non-plasmonic MSAs superior to SP-related metal nanostructures for ZnO-based high-efficient luminescence and high-sensitive photon detection above room temperature.

A method to reduce motion artefacts of sequentialimaging polarimetry: Long enough exposuresminimize polarization blurs of wavy water surfaces

Adam Egri, Gyorgy Kriska, and Gabor Horvath

Doc ID: 334425 Received 04 Jun 2018; Accepted 14 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: Researchers studying the polarization characteristics of the optical environment prefer to use sequential imaging polarimetry (SeqIP) due to itscheapness and simpleness. This technique takes the polarization pictures through polarizers in succession. Its main drawback is, however, thatduring sequential exposure of the polarization pictures the target must not move, otherwise so-called motion artefacts are caused after evaluationof the polarization pictures. How these disturbing motion artefacts could be minimized? Taking inspiration from photography, our idea was to takethe polarization pictures with a long enough exposure during which the changes of the moving/changing target are averaged and thus motionartefacts are reduced, at least in a special case, when the motion has a stable mean. In laboratory, we demonstrated the performance of thismethod when the target was a wavy water surface. We found that the errors of the measured degree and angle of polarization of light reflectedfrom the undulating water surface decreased with increasing exposure time (shutter speed) and converged to very low values. Although varioussimultaneous polarimeters (taking the polarization pictures at once) are available which do not suffer from motion artefacts, our method is muchcheaper and performs very well, at least when the target is a wavy water surface.

Lidar algorithms in 3D scanning for atmosphericlayering and planetary boundary layer heightretrieval. Comparison with other techniques

Alexandros Pantazis, Alexandros Papayannis, and Georgios Georgoussis

Doc ID: 334549 Received 08 Jun 2018; Accepted 14 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: The Planetary Boundary Layer Height (PBLH), of great importance in meteorology andatmospheric physics, is strongly correlated with the geographical location, the solar irradiance, theseasonal variations and the variability of the weather phenomena. So far, several lidar techniqueshave been developed to detect the PBLH, beside the radiosoundings, sodars or other techniques. Inthis work we propose new algorithms to provide PBLH in near real time using a 3 dimensional (3D)lidar in vertical or slant pointing. We show that the proposed Variable SPAce Time (VASPAT) andVERtical DEcision (VERDE) algorithms are able to estimate the PBLH under various meteorologicalconditions of more than 80% of the cases studied. Furthermore, these algorithms are user friendly(user adjustable), they work automatically at any location and period of the year for any vertically/slant pointing lidar system. These algorithms are extremely helpful for meteorologists, airporttower controllers, atmospheric scientists and in general for the remote sensing community.

Passive Q-switching of Yb:CNGS lasers by Cr4+:YAGand V3+:YAG saturable absorbers

Xuzhao Zhang, Pavel Loiko, Josep Maria Serres, Venkatesan Jambunathan, zhengping wang, Yi Guo, Anatol Yasukevich, Antonio Lucianetti, Tomas Mocek, Uwe Griebner, Valentin Petrov, Xin-guang Xu, Magdalena Aguilo, Francesc Diaz, and Xavier Mateos

Doc ID: 334212 Received 07 Jun 2018; Accepted 13 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: Trigonal langasite-type ordered silicate crystal Yb:Ca3NbGa3Si2O14 (Yb:CNGS) is a promising material for efficient~1 μm lasers. We report on the first passively Q-switched Yb:CNGS laser using Cr4+:YAG and V3+:YAG saturableabsorbers (SAs) with a 976 nm Volume Bragg Grating (VBG)-stabilized diode as a pump source. The laser crystalwas a c-cut 3 at.% Yb:CNGS grown by the Czochralski method. It was placed in a compact microchip-type lasercavity. With a Cr4+:YAG SA, very stable 62.2 μJ / 4.4 ns pulses were achieved at a repetition rate of 22.5 kHz. Theaverage output power was 1.40 W at 1015.3 nm corresponding to a Q-switching conversion efficiency of 90%. Withthe V3+:YAG SA, the pulse characteristics were 13.3 μJ / 11.1 ns at a higher repetition rate of 68.4 kHz. Theperformance of the Yb:CNGS/Cr4+:YAG was numerically modelled showing a good agreement with the experiment.

Reseach on degradation of lightweight mirror surfaceaccuracy

Pingwei Zhou, Kenjun Wang, Changxiang Yan, and Xiaohui Zhang

Doc ID: 334881 Received 11 Jun 2018; Accepted 13 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: The vibration test is one of the many tests that space telescopes endure to ensure that functionality is notimpaired by severe launch. Then the telescopes will undergo detailed measurements including mirror surface accuracymeasurements. Due to the design shortcoming, the degradation of lightweight mirror surface accuracy may exceed thedesign error budget at times. In this paper, we demonstrate a method to determine the cause of the degradation. By usinginertia relief, the influence functions were obtained and structural deformation was derived from the FEA. Based on thestructural deformation, we found that the back frame of telescope had insufficient torsional and bending stiffness. With theindicated need for higher stiffness, the rigidity of the back frame was improved. In addition, the high and low temperaturecycling was used to reduce residual stresses which caused the high frequency distortion. The new vibration test verified themechanical safety and optical stability of the improved structure. The measured surface accuracy by optical interferometerwas maintained at 0.015 wave within the design error budget.

Design of Plasmonic Sensor Based on Square Array ofNanorods and Two Slot Cavities with High Figure of Merit forGlucose Concentration Monitoring

Mohammad Reza Rakhshani, Alireza Tavousi, and Mohammad Ali Mansouri-Birjandi

Doc ID: 334868 Received 11 Jun 2018; Accepted 13 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: In this article, a plasmonic nano-sensor by using the nanorods array in square resonator coupled with twoslot cavities with properties for the detection of glucose concentration in water is proposed and analyzed. We haveinvestigated the sensing feature by changing the concentration of the glucose from 0~60%. Obtained results showthat by placing different water samples in square resonator and two cavities, resonance wavelengths can be changed.These resonances demonstrate different dependence on the glucose concentration of water samples. Also, varyingthe physical parameters of the configuration can also change the resonance wavelength and can be simply tuned.These features recommend flexibility to propose the structure. Simulation results show that the values of sensitivityand FOM (figure of merit) can be obtained as 892 nm/RIU and 3.5×106 RIU-1, respectively, which can discovergreatly applications in the plasmonic sensor domain.

A Method to Determine the Anisotropy Parameter g of a Turbid Medium

Kalpak Gupta and M. shenoy

Doc ID: 336033 Received 25 Jun 2018; Accepted 13 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: We present a method to determine the anisotropy parameter g of a scattering liquid medium. A simple experimental setup is used to measure the scattered light from turbid samples, and a calibration curve is used to determine g. The interaction coefficient of the medium is experimentally determined, and the calibration curve is obtained through Monte-Carlo simulations. The method is tested for non-absorbing solutions of polystyrene spheres, and the simulation results are found to agree with the experiments. Possible improvements to increase the range and accuracy of the calibration curves are also discussed.

Research on TunableDistributed SPR SensorBased on Bimetal Film

chen qiang chen, 刘瑾 刘, Haima Yang, Hai-shan LIU, Yu WEI, Jun LI, Bao-long YUAN, and Kai Zhao

Doc ID: 336347 Received 02 Jul 2018; Accepted 12 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: In order to overcome the limitations in range oftraditional prism structure SPR single-point sensormeasurement, a symmetric bimetallic film SPR multi-sensorstructure is proposed. Based on this, the dual-channel sensingattenuation mechanism of SPR in gold and silver compositefilm and the improvement of sensing characteristics wasstudied. By optimizing the characteristics such as material andthickness, a wider range of dual-channel distributed sensing isrealized. Using a He-Ne laser (632.8nm) as the refenence lightsource, prism-excited symmetric SPR sensing was studiedtheoretically for a symmetrical metal-clad dielectric waveguideusing thin-film optics theory. The influence of the angle ofincidence of the light source and the thickness of the dielectriclayer on the performance of SPR dual formant sensing isexplained. The finite-difference time-domain (FDTD) methodwas used for the simulation calculation for various thicknessand compositions of the symmetric combined layer, resultingin the choice of silver (30nm) gold (10nm). When the incidentangle was 78 deg, the quality factor reached 5960, showingexcellent resonance sensing effect. The sensitivity reached amaximum of 5.25×10􀬿􀬹RIU when testing the water content ofan aqueous solution of honey, which proves the feasibility andpracticality of the structure design. The structure improves thetheoretical basis for designing an SPR multi-channeldistributed sensing system, which can greatly reduce the costof biochemical detection and significantly increase thedetection efficiency.

Low Voltage Defect Quantum Cascade LasersBased on Excited-States Injection at λ ~ 8.5μm

yue zhao, jinchuan zhang, Ning Zhuo, fengmin cheng, Dongbo Wang, Shenqiang Zhai, lijun wang, Junqi Liu, Shuman Liu, Liu Fengqi, and Zhanguo Wang

Doc ID: 338167 Received 09 Jul 2018; Accepted 12 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: Quantum cascade laser (QCL) emitting at λ ~ 8.5 μm based on the excited-stateinjection is presented. The operating voltage is reduced for a low voltage defect in theexcited-state design, compared with the conventional ground state injection design. Thethreshold voltage and voltage defect is as low as 6.3 V and 54 mV for 30-stage active regionrespectively. Devices were fabricated through standard buried-heterostructure processing todecrease the heat accumulation. A continuous-wave (CW) optical power of 340 mW isobtained at 283 K with a threshold current density of 2.7 kA/cm2. Such a design has apotential to further improve the wall plug efficiency (WPE) for the increased voltageefficiency.

Continuous wavelet transform based automatic curve fitting method for laser-induced breakdown spectroscopy

Wenbin Yang, Bincheng Li, Jiangning Zhou, Yanling Han, and Qiang Wang

Doc ID: 332790 Received 29 May 2018; Accepted 12 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: In this work, an automatic curve fitting method based on continuous wavelet transform (CWT) is proposed to resolve overlapped peaks and to adaptively extract the major peaks in laser induced breakdown spectroscopy (LIBS). From the local minimum of the second derivative of the LIBS spectrum calculated with CWT, the number of individual peaks is determined and corresponding peak positions are estimated. FWHMs (full width half maximum) of individual peaks are estimated from the separation of two maxima siding the minimum. A threshold is introduced to eliminate the small peaks therefore to reduce the number of fitting parameters and adaptively extract the major peaks with different spectral intensities. The Trust-Region algorithm is used for parameter optimization. The proposed method is used to analyze both simulated LIBS spectra and experimental overlapped peaks. Both simulated and experimental results show that the proposed method can resolve overlapped peaks even with a low separation degree, though the minimum resolvable separation degree depends on the FWHM ratio and strength ratio of individual peaks and wavelet scale. In a calibration experiment of N2/SF6 gases mixture, after resolving the overlapped peaks, good linear correlations between concentration and intensity of F (with an adjusted R-squared 0.9972), as well as between the concentration ratio and intensity ratio of nitrogen to fluorine (with adjusted R-squared values > 0.95) are obtained.

Single shot large field of view imaging with scatteringmedia by spatial demultiplexing

Dongliang Tang, Sujit Sahoo, Vinh Tran, and Cuong Dang

Doc ID: 330871 Received 03 May 2018; Accepted 12 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: Benefiting from the memory effect (ME) for speckle intensity correlations, only one single-shot specklepattern can be used for high quality recovery of the objects. However, ME gives a restriction to the fieldof view (FOV) for imaging with scattering media. Objects beyond the ME region cannot be recovered andproduce unwanted speckle patterns, which causes reduction in the speckle contrast and recovery quality.Nevertheless, all the spatial information from a large object is embedded in a single speckle image. Here,we extract the spatial information from these unavoidable speckle patterns, and enlarge the FOV of theimaging system with scattering media. Regional point spreading functions (PSFs), which are fixed andonly need to be recorded once for all time use, are employed to recover corresponding spatial regions ofan object by deconvolution. Then an automatic weighted averaging in an iterative process is performedto obtain the object with significantly enlarged FOV. Our results present an important advancement ofimaging technique with strongly scattering media.

Error performance of underwater wireless opticalcommunications with spatial diversity underturbulence channels

Aiping HUANG, Linwei TAO, Cheng Wang, and Lichen Zhang

Doc ID: 332135 Received 18 May 2018; Accepted 12 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: In underwater optical wireless communications(UOWC), absorption, scattering and turbulenceseverely degrade the reliability and transmissionrate of the UOWC link. In this paper, spatial diversity(SD) is exploited to improve the error performanceof UOWC links, which involves the deployment ofmultiple transmit/receive apertures. Channel impulseresponses for various configurations in coastal oceanwater link are obtained by Monte Carlo (MC) simulation.By using maximum-likelihood sequencedetection depending on the Euclidean distance, theerror probability of the SD UOWC is derived. Wefurther present efficient approximated closed-formwith one-dimensional integral for the error probabilityof single-input multiple-output (SIMO) and multipleinputsingle-output (MISO) systems. Our analyticalderivations build upon an approximation to the sumof correlated log-normal random variables. Both thederived bit error probability (BEP) expressions andsimulations are used to quantify the effect of SDand the performance of SD UOWC is compared withsingle-input single-output (SISO) link. Our numericalresults indicate that SD combats with impairing effectsof fading and considerably improve the UOWC systemperformance.

Terahertz communication windows and their point-topointtransmission verification

Zhenyang Xiao, Qiujie Yang, jingguo huang, Zhiming Huang, wei zhou, Yanqing Gao, Shu Rong, and Zhiping He

Doc ID: 332355 Received 25 May 2018; Accepted 11 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: Terahertz communication is recognized as a transformational technology that can meet the futuredemands of point-to-point communication. The study of terahertz atmospheric transmission characteristics isimportant for guiding the terahertz communication window selection process. In this report, based on the modifiedITU-R P.676-10 model, we determined that the terahertz communication windows above 100 GHz were located atthe bands at approximately 140 GHz, 220 GHz, 340 GHz, 410 GHz and 460 GHz, which is verified by recentexperiments. We also verified the feasibility of indoor point-to-point communication by the 110 m transmissionexperiment through the communication window around 460 GHz.

A high resolution ex vacuo objective for coldatom experiments

Xiao Li, Feng Zhou, Min Ke, Peng XU, Xiaodong He, Jin Wang, and Mingsheng Zhan

Doc ID: 334397 Received 05 Jun 2018; Accepted 11 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: We present a versatile and cost-efficient objective with a five-lens configuration,which consists of commercial singlets completely. The home-built objective has a numericalaperture (NA) of 0.44 and a long working distance of 35.9 mm, making it suitable for ex vacuoutilization. A diffraction-limited resolution of 1.08 m and a field of view (FOV) of about 210 mare achieved when a 780 nm light passes through a 5 mm thick vacuum window. Moreover, suchdesign can be well adopted to a broad range of laser wavelengths (560 1000 nm) and vacuumwindow thicknesses (0 6 mm) by simply modifying one lens spacing, while maintaining a NAof above 0.43. The characteristics of the objective are evaluated experimentally, which are ingood agreement with the simulations. Also, the objective has been successfully used for singleatom trapping and detecting in experiment. And we believe it will find more applications invarious cold atom experiments.

UAV-based hyperspectral analysis and spectral indices constructing for quantitatively monitoring leaf nitrogen content of winter wheat

hongchun zhu, Haiying LIU, Yuexue Xu, and Guijun YANG

Doc ID: 335632 Received 21 Jun 2018; Accepted 10 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: In flag leaf and flowing stages of winter wheat, unmanned aerial vehicle (UAV)-based- and ground-measured hyperspectral data were conducted simultaneously, and leaf nitrogen content (LNC) data were then measured in a laboratory. First, the accuracy of UAV-based hyperspectral data was analyzed using ground-measured hyperspectral data, and the analysis showed that the effectiveness and spectrum sampling precision of the UAV-based hyperspectral data are reliable. Hyperspectral characteristic analysis of winter wheat canopies of different LNCs was also conducted. Second, representative spectrum bands that are sensitive to the LNC of winter wheat were extracted through first-order differential spectral, continuum-removed reflectance, and band correlation prediction threshold methods. The optimal band combination that is sensitive to the LNC of winter wheat was obtained by comparing and analyzing the representative spectrum band results. Thus, several LNC spectral indices (LNCSI) were established through ratio, difference, and normalization methods, and linear regression statistical models for quantitatively simulating LNCs were established using the LNCSIs. Finally, comprehensive and comparative analyses of the LNCSIs and the inversion values of the LNC using the LNCSIs confirmed that the LNCSIs are effective in quantitatively inversing the LNC of winter wheat.

A Simple Method for Volumetric Thickness Measurement using a color camera

GARAM CHOI, Yoonhyuk Lee, Seung Woo Lee, Yeongchan Cho, and Heui Jae Pahk

Doc ID: 334200 Received 01 Jun 2018; Accepted 10 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: A simple volumetric thickness measurement method for in-line high–speed inspection is proposed. Witha color camera alone, spectrally resolved reflectance in a spatial domain is obtained: A Bayer filter spectrallyresolves the reflected signal, and a CMOS sensor acquires three multi-spectral reflectance from RGBdata at a single shot. In order to determine an accurate thickness, a modified reflectance is derived to converta conventional spectral reflectance throughout a wavelength domain into an adequate form in anRGB domain by considering the characteristics of wide-band multi-spectral acquisition. The proposedmethod is validated by the measurement of a uniformly deposited SiO2 film and a tapered SiNx film.

Adaptive Beam Control Techniques for Airborne Free-Space Optical Communication Systems

Vuong Mai and Hoon Kim

Doc ID: 332295 Received 25 May 2018; Accepted 10 Aug 2018; Posted 10 Aug 2018  View: PDF

Abstract: In this paper, we study two adaptive beam control techniques, where the beam divergence angle is adjusted at the transmitter to (i) maximize the link availability or (ii) minimize the transmitter power while maintaining a target link availability. For this purpose, we provide closed-form expressions about the link availability and optimum beam divergence angle under the effect of generalized two-dimensional Gaussian distribution of alignment error between the transmitter and receiver. These simple and closed-form expressions reduce the computational complexity for the performance optimization. Thus, they can be used to (i) reduce the power consumption required for the adaptive beam control and (ii) facilitate the fast operation of the control techniques. The results show that the adaptive beam control techniques can improve the system performance under various scenarios.

Full-color holographic 3D display with horizontal full viewing-zone by spatiotemporal division multiplexing

Yusuke Sando, Daisuke Barada, and Toyohiko Yatagai

Doc ID: 336066 Received 26 Jun 2018; Accepted 10 Aug 2018; Posted 10 Aug 2018  View: PDF

Abstract: A technical full-color reconstruction method is presented to develop our previous monochromatic holographic three-dimensional (3D) display with a horizontal full viewing-zone. A digital micromirror device (DMD) is used as a high-speed spatial light modulator, and its modulation area is divided into three parts which independently handle three sub-holograms corresponding to red, green, and blue components. The reconstructed images from a single frame of the DMD never form full-color images. However, given that this spatial division is combined with the time division method for the full viewing-zone, each monochromatic image is temporally mixed, and practically full-color images are reconstructed. After monochromatic reconstruction from a single frame was confirmed, full-color reconstruction with a horizontal full viewing-zone was demonstrated.

Optimizing the Approach of Obtaining Cirrus OpticalDepth over the Ocean from Collocated CALIPSO andAMSR-E Observations

Qiang Tang, Yongxiang Hu, Wei Li, Jian Huang, and Knut Stamnes

Doc ID: 334557 Received 06 Jun 2018; Accepted 09 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: Retrievals of particulate optical depths and extinction coefficients from the Cloud-Aerosol Lidar withOrthogonal Polarization (CALIOP) instrument deployed on the CALIPSO satellite mainly rely on a singleglobal mean extinction-to-backscatter ratio, also known as the lidar ratio. However the lidar ratio dependson the microphysical properties of particulates. An alternative approach is adopted to infer single-layersemi-transparent cirrus optical depths (CODs) over the open ocean that does not rely on an assumed lidarratio. Instead the COD is inferred directly from backscatter measurements obtained from the CALIOPlidar in conjunction with collocated sea surface wind speed data obtained from AMSR-E. This method isbased on a Gram-Charlier ocean surface reflectance model relating wind-driven wave slope variances tosea surface wind speeds. To properly apply this method, the impact ofmultiple scattering between the seasurface and ice clouds should be taken into account. We take advantage of the 532 nm cross polarizationfeature of CALIOP and introduce an empirical method based on the depolarization change at the seasurface to correct for potential bias in sea surface backscatter caused by white-caps, bubbles, foam, andmultiple scattering. After the correction, the COD can be derived for individual CALIOP retrievals in asingle cloud layer over the ocean with this method. The global mean COD was found to be roughly 14%higher than the current values determined by the CALIOP extinction retrieval algorithm in their version4 products. This study is relevant to future improvements of the CALIOP operational products and isexpected to lead to more accurate COD retrievals.

Characterization and optimization of a tapered amplifier by its spectra through a long multi-pass Rb absorption cell

Chao Zhou, Sachin Barthwal, Wendong zhang, chuan he, biao tang, Lin Zhou, Jin Wang, and Mingsheng Zhan

Doc ID: 336373 Received 27 Jun 2018; Accepted 09 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: We present a method to characterize and optimize a tapered amplifier laser system (TALS) by its spectral quality through a long multi-pass rubidium absorption cell. Thermal vapor cell is used to measure the non-resonant spectrum of TALS including the broadband amplified spontaneous emission (ASE) which is it’s main spectral noise. This method gives a simple quantified measurement to optimize various working parameters of a tapered amplifier including current and temperature online. It can as well be used to compare various tapered amplifier chips based on their usage time during our precision measurement experiments. The results of this method are compared and are found in sync with traditional methods of Fabry-Parot cavity and beat measurements. Such characterization and optimization is important for noise control in atom interferometers, atomic clocks and other atomic manipulations. It can very well be used for investigating non-linearity and ASE inside amplifying chips and can be utilized in other applications of ASE using bioimaging.

Speckle noise reduction in digital speckle patterninterferometric fringes by nonlocal means and itsrelated adaptive kernel-based methods

Yassine Tounsi, Manoj Kumar, ABDELKRIM NASSIM, and Fernando Mendoza-Santoyo

Doc ID: 334071 Received 01 Jun 2018; Accepted 09 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: Digital speckle pattern interferometry (DSPI) has been widely used in many scientific and industrial applications.Besides its several advantages, one of the basic problems encountered in DSPI is the undesired speckle noiseexisting in the fringe pattern. In this paper, we demonstrate the performance of nonlocal means (NLM) and itsrelated adaptive kernel-based filtering methods for speckle noise reduction in DSPI fringes. The NLM filter and itsrelated kernel-based filters such as NLM-average (NLM-av), NLM-local polynomial regression (NLM-LPR), and NLMshapeadaptive patches (NLM-SAP), are implemented first on simulated DSPI fringes and their performances arequantified on the basis of peak signal-to-noise ratio (PSNR), mean square error (MSE), and quality index (Q) andtheir effectiveness and abilities in reducing the speckle noise are compared with other speckle denoising methods.These filtering methods are then employed on experimental DSPI fringes. The obtained results reveal that thesefiltering methods have the ability to improve the PSNR and Q of the DSPI fringes and provide better visual andquantitative results. It is also observed that the proposed filtering methods preserve the edge information of theDSPI fringes which is evaluated on the basis of edge preservation index (EPI) of the resultant filtered images.

Dynamic compensation of gradient index rod lens’ aberrations by using liquid crystals

Louis Begel and Tigran Galstian

Doc ID: 340576 Received 24 Jul 2018; Accepted 09 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: An electrically variable liquid crystal lens is used to compensate the aberrations of commercial gradient index rod lenses used for deep brain endoscopy. This is achieved by the use of a weakly conductive layer in the so called “modal control” lens approach with a segmented peripheral electrode. The root mean square aberrations of the system are reduced by a factor of 4.3. The proposed solution can be used in many photonic applications using fixed optical components with high aberrations that have significant sample to sample variability.

Interconnecting data based on vortex beams byadjusting the ellipticity of a ring-core fiber

Xiaohui Wang, Yingxiong Song, Qianwu Zhang, fufei pang, yingchun li, and bingyao cao

Doc ID: 332087 Received 18 May 2018; Accepted 08 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: In order to exchange data in a space division multiplexing (SDM) system, a novel data interconnection conceptbased on the vortex beams is proposed by adjusting the ellipticity of a ring-core fiber. A new ring-core fiber is alsodesigned and fabricated for exchanging and propagating the data carried by the first or second order vortex (OAM)beams. The proposed scheme isn’t only analyzed and simulated in principle but also be verified by experiments.The numerical results demonstrate that the vortex beams can be exchanged by appropriately adjusting the phasedifference (with respect to the ellipticity of a ring-core fiber) between the even and odd vector modes. For the sakeof investigating the feasibility of the proposed scheme, a new experimental platform is designed and established.The experimental results are consistent with the simulation, and demonstrate that the data carried by the first orsecond order vortex beams can be successfully switched with the acceptable BERs between the first order vortexbeams (L=1 OR -1), or between the second order vortex beam (L=2 OR -2, left or right circular polarization) ,respectively. The measured BERs and constellation diagrams of 16-QAM are employed to evaluate the dataexchanging performance in terms of the different cases (i.e., exchanging data once or twice, and exchanging datawith or without crosstalk). The measured BERs and constellation diagrams also demonstrate that theperformances degrade with the increase of topological charge or crosstalk. The proposed scheme is flexible, simple,and reliable for data exchange in a SDM system.

Finite aperture correction for spectral cameras with integrated thin-film Fabry-Pérot filters

Thomas Goossens, Bert Geelen, Julien Pichette, Andy Lambrechts, and Chris Van Hoof

Doc ID: 328596 Received 08 Jun 2018; Accepted 08 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: Spectral cameras with integrated thin-film Fabry-Pérotfilters enable a wide variety of applications.Some applications require the detection of spectral features that are only visible atspecific wavelengths and some need to quantify small spectral differences that are undetectablewith RGB color cameras.One factor that influences the central wavelength of thin-film filters is the angle ofincidence. Therefore, when light is focused from an imaging lensonto the filter array, undesirable shifts in the measuredspectra are observed. These shifts limit the use of the sensor in applications that require fast lenses or lenses with large chief ray angles.To increase flexibility and enable new applications we derive an analytical model that explains andcan correct the observed shifts in measured spectra. The model includes the size of the aperture and physical position of each filter on the sensor. We experimentally validate the model with two spectral cameras: one in the visible andnear-infrared (VNIR) region and one in the short-wave infrared (SWIR) region.

Phase-dependent Fano-shape optomechanically induced transparency

Ye Qu, Shuting Sheng, and Jiahua Li

Doc ID: 334761 Received 08 Jun 2018; Accepted 08 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: We present a detailed study of a three-mode-coupling cavity optomechanical system where one mechanical mode and two optical whispering-gallery modes are coupled together. We extend the earlier investigation of regular optomechanically induced transparency (OMIT) [S. Weis et al., Science 330, 1520 (2010)] in a more general case. A complete analytical description of the present system is obtained, and quantitative analyses of the Fano-shape OMIT spectrum are provided. It is clearly shown that sharp and asymmetric Fano-shape OMIT lineshape, which is decided by the phase difference between the probe field and the mechanical driving, can be observed from the probe output.

Scanning Diffracted-Light Microscopy

Hira Farooq, Sueli Skinner Ramos, HAWRA ALGHASHAM, Ayrton Bernussi, and Luis Grave de Peralta

Doc ID: 335905 Received 22 Jun 2018; Accepted 07 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: Scanning the direction of the light that is diffracted by a sample permits achieving the image diversity, which is necessary for implementing the Fourier ptychographic microscopy technique (FPM) using only perpendicular illumination. We also demonstrated that the same method allows for implementation of the illumination-direction-multiplexing FPM technique when the sample is illuminated using a ring-shaped condenser.

Energy Calibration of Integrated Path Differential Absorption Lidars

Andreas Fix, Mathieu Quatrevalet, Axel Amediek, and Martin Wirth

Doc ID: 336162 Received 26 Jun 2018; Accepted 07 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: The stringent requirements for the energy reference measurement represent a challenging task for Integrated Path Differential Absorption Lidars (IPDA) to measure greenhouse gas columns from satellite or aircraft. The coherence of the lidar transmitter gives rise to speckle effects which have to be considered for the accurate monitoring of the energy ratio of outgoing on- and off-line pulses. Detailed investigations have been performed on various measurement concepts potentially suited for deployment within future satellite missions. © 2018 Optical Society of America

Fast and Precise 6D Pose Estimation of Texture-lessObjects Using the Point Cloud and Gray Image

Wang Pan, Feng Zhu, Yingming Hao, and Limin Zhang

Doc ID: 328945 Received 20 Apr 2018; Accepted 07 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: Pose estimation for texture-less objects is a challenging task in robotics, due to the scanty information of surfaces.In this paper, we design a vision system for fast and precise position and orientation measurement of texture-lessobjects with a depth camera and a CCD camera. The corresponding process includes two parts: object segmentationin the point cloud and pose measurement in the gray image. Considering the relation between the object and itsfixed panel, we first extract the panel in the point cloud by combining the RANSAC algorithm with local surfacenormal. And then coarsely segment the possible area of the object based on oriented bounding box. Finally,transform the point cloud coordinates into the image coordinate system, and measure the precise pose of theobject with a view-based matching method. Two types of cameras are brought together to make their respectiveadvantages play well. Downscale method and coarse to fine strategy are utilized sufficiently to increase efficiency.Experiments show that our vision system achieves high pose measurement precision and enough efficiency. Theaverage error is less than 2 mm for x, y, less than 4 mm for z and 1° in orientation, meeting the requirements forour robotic grasping task.

Enhanced light extraction of deep ultraviolet lightemittingdiodes by using optimized aluminumreflector

Xingxing Liu, Yun Mou, Hao Wang, Renli Liang, xinzhong wang, Yang Peng, and Mingxiang Chen

Doc ID: 334569 Received 06 Jun 2018; Accepted 07 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: Deep ultraviolet light-emitting diodes (DUV-LEDs) have become a promising UV light source for sterilization,disinfection, and purification. However, the challenge in practical application of DUV-LEDs still remain in their lowlight efficiency. In this paper, we proposed an optimized aluminum (Al) reflector for the light extractionenhancement of DUV-LEDs. The optical model of DUV-LEDs was established and the optical simulations wereperformed to achieve the optimized reflector. The DUV-LEDs exhibit a highest light efficiency when the reflectorhas the optimized feature sizes with an angle of 60°, a height of 2.0 mm, and an internal radius of 2.5 mm.Furthermore, the optimized reflector with different reflectance were fabricated and applied for the packaging ofDUV-LEDs. Consequently, the light output powers of DUV-LEDs are enhanced by 28.8%, 37.0%, and 43.8%,respectively, by using the different reflectors at the driving current of 100 mA. It is attributed to the remarkablereflection effect of the Al reflector, which increases the light extraction of the sidewall emission from DUV-LED chip.

Determining the colorimetric attributes of multicoloredmaterials based on a global correction and unsupervisedimage segmentation method

Zhongjian Li, Nian Xiong, JIAJUN LIU, Weidong Gao, and Renzo Shamey

Doc ID: 334658 Received 07 Jun 2018; Accepted 07 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: Fast and accurate measurement of colors in multicolored prints using commercial instruments or existing computervision systems remains a challenge due to limitations in image segmentation methods and the size and complexity ofthe colored patterns. To determine the colorimetric attributes (L*a*b*) of multicolored material, an approach based on aglobal color correction and an effective unsupervised image segmentation is presented. The colorimetric attributes ofall patches in a ColorChecker chart were measured spectrophotometrically and an image of the chart was alsocaptured. Images were segmented using a modified Chan-Vese method and the sRGB values of each patch wereextracted and then transformed into L*a*b* values. In order to obtain an optimum transformation model theperformance of ten models was examined by minimizing the average color differences between measured andcalculated colorimetric values. To assess the performance of the model a set of printed samples was employed and thecolor differences between the predicted and measured L*a*b* values of samples were compared. The results show thatthe modified Chan-Vese method, with suitable settings, generates satisfactory segmentation of the printed images withmean and maximum ΔE00 values of 2.43 and 4.28 between measured and calculated values.

Phase-matching properties of BaGa₂GeSe₆ for three-wave interactions in the 0.778-10.5910 μm spectral range

Kiyoshi Kato, Kentaro Miyata, Valeriy Badikov, and Valentin Petrov

Doc ID: 332918 Received 30 May 2018; Accepted 07 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: We present new experimental results for the phase-matching properties of the recently discovered BaGa₂GeSe₆ crystal for harmonic generation of a Nd:YAG laser-pumped KTP OPO and a CO₂ laser in the 0.778-10.5910 μm spectral range. In addition, we present new Sellmeier equations that provide a good reproduction of the present experimental results as well as the published data points for SHG of a CO₂ laser at 10.5910 μm and a 1.85 μm-pumped OPO in the 2.156-3.220 μm and 4.348-13.035 μm spectral ranges.

Structural changes and electrical properties of nano-weldedmulti-walled carbon nanotubes junctions

Zhi Liu, Yanping Yuan, Yitong Shang, and Weina Han

Doc ID: 334118 Received 04 Jun 2018; Accepted 07 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: This study proposes an efficient approach which uses 1064 nm continuous fiber laserto achieve nanoscale welding of crossed multi-walled carbon nanotubes (MWCNTs).We investigate the effects of laser irradiation time (from 1 second to 6 seconds) on thestructure changes and welding quality of crossed MWCNTs by scanning electronmicroscope (SEM), transmission electron microscope (TEM) and Raman spectroscopy.The experiments results demonstrate that: 1) after 2 or 3 seconds laser irradiation,moderate temperature of MWCNTs can be formed, and cause higher degree ofgraphitization; 2) degree of graphitization and effective contact of nano-weldedMWCNTs junctions strongly affects its electrical properties.

Deformations of Circularly Polarized Bessel vortexbeam reflected and transmitted by a uniaxialanisotropic slab

Haiying Li, Jiawei Liu, Lu Bai, and Zhen-Sen Wu

Doc ID: 334848 Received 11 Jun 2018; Accepted 07 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: Bessel vortex beams are widely studied since their intensity is independent of the propagation distance, and alsotheir original field intensity distribution can be reconstructed after passing through an obstacle. Therefore, suchbeams are more advantageous for long-distance communication, optical imaging and other potential applications.Based on the expansion of electromagnetic fields in terms of vector wave functions, in this investigation, a methodhas been proposed to study the reflection and transmission of an incident circularly polarized Bessel vortex beamby a uniaxial anisotropic slab. The expansion coefficients of a circularly polarized Bessel vortex beam are derivedby use of the cylindrical vector wave functions. The magnitude profiles of the electric field amplitude and phase, aswell as the distribution of orbital angular momentum (OAM) states for both the reflected and transmitted beams,are numerically simulated and discussed. The effects of dielectric tensor and incident angle on the propagationcharacteristics of circularly polarized Bessel vortex beam are analyzed. The observed results indicate that thecontours of the electric field components cannot retain circularly symmetric structures; the distortion of phasedistribution is obvious, and except for the predominant OAM state, other OAM states are derived, particularly forthe reflected beam. Although few OAM states emerge in the transmitted beam, the predominant OAM state is stillthe same as that of the incident Bessel vortex beam.

Suppression of backscattering-induced noise bysideband locking based on high and low modulationfrequencies in ROG

Ning Liu, Yanxiong Niu, Li Shuang Feng, Hongchen Jiao, and Xiao Wang

Doc ID: 334905 Received 12 Jun 2018; Accepted 07 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: The backscattering-induced noise is a dominant noise in the resonant optic gyroscope. This paper proposes amethod to suppress the carrier and the backscattering-induced noise by sideband locking technique. The resonantcavity can be taken as a band-pass filter, and the carrier frequency component locates at the stop-band while onesideband is locked to the cavity resonance. Then, the carrier will be suppressed by the cavity itself, which willreduce the interference with carrier backscattering. For the adoption of different modulation frequencies inclockwise (CW) and counter-clockwise (CCW) directions, the first-order sidebands of CW and CCW have afrequency offset to each other. Therefore, the first-order sideband backscattering can be eliminated when thesideband is locked to the cavity resonance. And both high and low modulation frequencies are applied to the phasemodulator, which will further suppress the carrier and the demodulation of low frequency will reduce thesensitivity to phase fluctuation noise in the system. The method has low requirements for parameter accuracy ordevice performance.

Review and Accuracy-Comparison of VariousPermittivity-Averaging Schemes for MaterialDiscontinuities in the 2-Dimensional FDFD Method:Implementation Using Efficient Computer GraphicsTechniques

Elias Glytsis, Aristeides Papadopoulos, and Theodoros Koutserimpas

Doc ID: 336445 Received 28 Jun 2018; Accepted 06 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: Several known and widely used averaging techniques aiming to improve the accuracy of the 2D Finite-Difference Frequency-Domain (FDFD) method, in the presence of material discontinuities, are reviewed,numerically tested, and compared with respect to their accuracy. Furthermore, all averaging techniquesare rigorously and efficiently implemented using the supercover Digital-Differential-Analyzer and a modifiedLiang-Barsky algorithms suitably adapted from computer graphics applications. The FDFD withGaussian blurring [FDFD (GB)], the FDFD with volume-polarized effective-permittivity [FDFD (VP-EP)],the FDFD with volume-polarized effective-permittivity on shifted cells [FDFD (VP-EPs)], and the FDFDwith anisotropic smoothing [FDFD (AS)] are compared with respect to their accuracy (for both TE and TMpolarization), in the case of scattering by an infinite homogeneous cylinder (for which analytical solutionexists) comprised of either a lossless dielectric, or of a high-index low-loss dielectric, or of a metal. Sampleplots of the relative errors are presented for various field components. Absolute error norms (L2 andL¥) are also presented for both polarizations and for two grid-cell sizes for quantitative comparisons. Theresults show that FDFD (AS) prevails in accuracy mainly due to the better satisfaction of the boundaryconditions at the cylinder’s boundary. However, for high-index dielectrics and metals, even the FDFDwithout any averaging gives very good results for the field components parallel to the uniformity direction.However, the FDFD (AS) is always more accurate when the in-plane field components are sought.

All-PM Wavelength-Tunable and harmonically modelockingYb-doped Fiber Laser

Lin Shangjing, Yu Jianguo, Wuyi Li, and Jinlong Ke

Doc ID: 338021 Received 11 Jul 2018; Accepted 06 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: We report a wavelength-tunable harmonically mode-locking (HML) dissipative soliton fiber laser based on highspeedintensity modulator with a simply all-polarization-maintaining (all-PM) cavity. The center wavelength can beprecisely tuned from 1029.35 nm to 1079.25 nm by only tuning the frequency of the pulse pattern generator (PPG),and the linearly tuning accuracy of the wavelength can reach 0.0093 nm/kHz. The degree of polarization (DOP) canreach 98.969%.The full width at half maximum (FWHM) of the pulse is measured to be 30.1 ps and the intracavitypulse energy after the gain fiber can reach 5.41 nJ. All orders of HML repetition rate is turned from ~33.346 MHz to~366.806 MHz through adjustment of the data length and frequency of PPG.

High performance sensor achieved by hybrid GMR/SPR platform

La Wang, Tian Sang, Jian Gao, Xin Yin, and Honglong Qi

Doc ID: 336226 Received 26 Jun 2018; Accepted 06 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: We perform a comprehensive analysis of multi-band absorption properties in a metal-dielectric-metal-dielectric (MDMD) nanostructure under TM wave illumination. The multi-band absorption can be attributed to the hybridization of the surface plasmon resonance (SPR) and the guide-mode resonance (GMR), and we identify the hybrid GMR/SPR by the dispersion relation equations of the SPR and GMR, respectively. More importantly, the MDMD nanostructure is very sensitive to the change of the dielectric environment for the special hybrid structure, thus, it can be functioned as a good candidate for the ultra-sensitive biochemical sensing. The highest sensitivity of the MDMD nanostructure reaches 1087nm/RIU with the figure of merit (FoM) of and the new figure of merit (FoM*) of 483, it is performed by the absorption peak at 1796.1 nm of the double SPP with the strongest field enhancement at the surface.

Fabrication of Laser Cavity Mirror in Large Mode Area Fiber by Ultra-short Pulse Laser

Kazuo Hasegawa, Satoru Kato, Tomoya Okazaki, Hiroshi Murotani, and K. Saito

Doc ID: 332140 Received 18 May 2018; Accepted 06 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: We present herein a method to fabricate a higher-order fiber grating (HOFG) for use as a fiber-cavity mirror in a fiber laser. The HOFG was fabricated by irradiating the Yb-doped large core of a double-clad fiber by a femtosecond pulsed laser. The HOFG served as a laser cavity mirror with a reflectance of 13.2% and yielded a laser line with a spectral full width at half maximum of 0.56 nm.

Photonic Generation of Microwave Waveforms Based on a DP-QPSK Modulator

Xiangrui Li, Aijun Wen, Zhaoyang Tu, and zhongguo xiu

Doc ID: 332634 Received 29 May 2018; Accepted 06 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: A novel microwave waveforms generator based on a dual-polarization quadrature phase shift keying modulator (DP-QPSK) is proposed and experimentally demonstrated in this paper. The X-QPSK modulator is modulated by a local oscillator (LO) signal, for XI-MZM, odd sidebands are eliminated, for XQ-MZM, even sidebands are eliminated, while the Y-QPSK modulator is not modulated. Triangular or square waveform can be generated by biasing the X-QPSK and adjusting the polarization controller (PC) properly. 3 GHz and 6 GHz triangular and square waveforms are successfully generated by experiment. The scheme does not need high modulation index (m=1.25 in this paper). In addition, it features easy adjustment, low cost, and simple structure without filter and phase shifter.

Research on the optimal optical attenuation in laserradar using a Geiger-mode APD

Zhijian Li, Jiancheng Lai, Chungyong Wang, Yan Wei, and Zhen-hua Li

Doc ID: 332833 Received 04 Jun 2018; Accepted 06 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: For a laser radar (LADAR) system using a Geiger-mode avalanche photodiode (GmAPD), attenuating echo andbackground noise simultaneously affects the original data output from the GmAPD and eventually affects thedetection performance. In this study, we established a model that applies to the GmAPD-based LADAR with opticalattenuation and also applies to any typical single photon detector which has a dead-time (e.g. the photomultipliertube); thus, a comprehensive and fundamental study is performed for the mathematical expectation of the numberof signal detections (ES), the mathematical expectation of the number of noise detections (EN), the signal-to-noiseratio (SNR), and the range bias (absolute error, Rb) and precision (standard deviation, Rp) under variousattenuation levels with different dead-times and signal-noise conditions. We observed the following: on one hand,there exists an optimum attenuation level at which ES and SNR are maximized; on the other hand, there existsanother optimum attenuation level for shorter dead-times, at which Rp is minimised. The phenomenon of themaximum ES, SNR or minimum Rp disappears gradually as the echo or noise decreases from high levels (e.g., 10photoelectrons/echo or an equivalent background noise of 10 photoelectrons/range-gate). Further, higherattenuation, which shows advantages under strong echo or noise conditions, yields a larger improvement in ES forlonger dead-times; and with the reduction of the dead-time or the noise, the maximum ES gradually increases, andthe corresponding optimum attenuation level becomes slighter. Additionally, we found that as the opticalattenuation increases, EN decreases to 0, Rb changes from a negative value to 0, and Rp is minimised, becomesslightly worse, and reaches a constant. Moreover, the shorter dead-times, which show advantages when they areshorter than the end time of the echo, lead to a larger ES, better Rb, and slightly worse Rp than the longer ones.

M2-factor of controllable dark-hollow beams through a multi-apertured ABCD optical system

Zeng Mei, Zhanqiang Hui, and Meizhi Zhang

Doc ID: 332341 Received 25 May 2018; Accepted 06 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: Under an optical system with multiple hard-edged apertures in cylindrical coordinate system, therecurrence propagation expression is derived for the controllable dark-hollow beams (CDHBs) by expanding thehard-aperture function into a finite sum of complex-Gaussian functions. Given the recurrence propagation expression,we deduce the approximate analytical expressions of the beam propagation factors M2 in terms of the generalizedtruncated second-order moments. This provide a fast algorithm for the evaluation of the beam propagation quality forCDHBs through complicated optical trains with a series of apertures. The propagation of CDHBs through twoaperture-lens ABCD optical system serves as the special case of multi-apertured ABCD optical system. Our numericalresults suggest that one aperture-lens optical system reduces the beam propagation quality of CDHBs, and twoaperture-lens optical system improves the beam propagation quality of CDHBs by selecting appropriate beam parametersand aperture parameters.

Direct inscription and evaluation of fiber Bragggratings in carbon-coated optical sensor glass fibersfor harsh environment oil and gas applications

Antonio Nedjalkov, Jan Meyer, Christian Waltermann, Maximilian Reimer, Andrew Gillooly, Martin Angelmahr, and Wolfgang Schade

Doc ID: 332643 Received 29 May 2018; Accepted 05 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: In this research work, we show the successful inscription of fiber Bragg gratings into carbon-coated pure silica aswell as germanium-doped glass fibers by applying the pulsed laser point-by-point manufacturing technique. First,the utilized parameters for the Ti:Sapphire femtosecond laser process are demonstrated. Without removing thepolymeric carbon coating, destruction free formation of high reflective Bragg gratings is performed with selectedtypes of hermetically enclosed fibers. We demonstrate the advantage of the carbon coating by long-term exposureto a pure hydrogen atmosphere at an elevated temperature. Compared to the also examined standard glass fiberswith a distinct signal attenuation, carbon-coated fibers show no significant degradation. Additionally, we analyzethe mechanical stability of the processed fibers by standardized tensile tests. No substantial decrease in strengthoccurs among the sensor-integrated samples. Finally, usage scenarios in the gas and oil industry are illustrated.

In-flight characterization of the Lunar Orbiter Laser Altimeter instrument pointing and far-field pattern

Michael Barker, Xiaoli Sun, Dandan Mao, Erwan Mazarico, Gregory Neumann, Maria Zuber, David Smith, Jan McGarry, and Evan Hoffman

Doc ID: 336291 Received 27 Jun 2018; Accepted 05 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: The Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO) has collected nearly 7 billion measurements of surface height on the Moon with an absolute accuracy of ~1 m and a precision of ~10 cm. Converting time-of-flight laser altimeter measurements to topographic elevations requires accurate knowledge of the laser pointing with respect to the spacecraft body-fixed coordinate system. To that end, we have utilized altimetric crossovers from LOLA, as well as bidirectional observations of the LOLA laser and receiver boresight via an Earth-based laser tracking ground station. Based on a sample of ~780,000 globally-distributed crossovers from the circular-orbit phase of LRO's mission (~27 months), we derive corrections to the LOLA laser boresight. These corrections improve the cross-track and along-track agreement of the crossovers by 24% and 33%, respectively, yielding RMS residuals of ~10 m. From early in the LRO mission, the bidirectional laser tracking experiments have confirmed a pointing anomaly when the LOLA instrument is facing towards deep space or the night side of the Moon, and have allowed the reconstruction of the laser far-field pattern and receiver telescope pointing. By conducting such experiments shortly after launch and nearly 8 years later, we have directly measured changes in the laser characteristics and obtained critical data to understand the laser behavior and refine the instrument pointing model. The methods and results presented here are also relevant to the design, fabrication, and operation of future planetary laser altimeters, and their long-term behavior in the space environment.

Performance Investigation of the Polar Coded FSO Communication System Over Turbulence Channel

Jiafei Fang, Meihua Bi, shilin xiao, Guowei Yang, Changying Li, Ling Liu, Yunhao Zhang, Tiancheng Huang, and Weisheng Hu

Doc ID: 334855 Received 11 Jun 2018; Accepted 05 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: In this paper, for the first time, the polar codes are introduced and experimental implemented in free space optical (FSO) communication system to combat the atmospheric turbulence induced fading. By analyzing the characteristics of turbulence channel, a method of evaluating the channel state information (CSI) for polar decoding is proposed, which can achieve good trade-off between the performance and computational complexity of this polar coded system. To verify our scheme, an intensity modulation direct detection (IM/DD) FSO communication experimental platform with a turbulence chamber is established. For the weak turbulence condition, comparing with the low-density parity check (LDPC) codes, the experimental results show that our proposed scheme has stronger error correcting capacity and lower computational complexity in combating the turbulence induced fading. Moreover, for moderate and strong turbulence conditions, the Gamma-Gamma turbulence model is adopted for constructing the Monte Carlo simulation. The results of experiment and simulation both show that our proposed scheme can effectively combat the atmospheric turbulence induced fading with a relatively low computational complexity in a wide range of turbulence conditions.

Astigmatism-reduced spherical concave grating holographically recorded by a cylindrical wave and a plane wave for Rowland circle mounting

Lijiang Zeng and Xinwei Chen

Doc ID: 334909 Received 11 Jun 2018; Accepted 05 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: We propose a new recording system that employs a cylindrical wave and a plane wave to holographically record astigmatism-reduced Rowland-circle spherical gratings. We find that the astigmatism of the grating can be sharply reduced, so that the spectral intensity is improved. Meanwhile, its defocus aberration and meridional coma remain zero throughout the working spectrum, meaning the spectral resolution is similar to that of a conventional grating recorded by symmetric dual plane waves. We designed and made one astigmatism-reduced grating and one conventional grating for an actual Rowland-circle spherical-grating spectrometer. Our experimental results showed that the spectral intensity of the astigmatism-reduced grating is about five times that of the conventional grating, while the resolution of the astigmatism-reduced grating is close to that of the conventional grating.

Ultrasound vibration measurements based on LaserOptical Feedback Imaging (LOFI)

Vadim GIRARDEAU, Olivier Jacquin, olivier HUGON, and eric lacot

Doc ID: 335865 Received 22 Jun 2018; Accepted 04 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: This paper is devoted to the detection of ultrasound vibrations with nanometric amplitude by using a LOFI (LaserOptical Feedback Imaging) setup. By means of numerical simulations, we show typical examples of ultrasoundvibrations having different temporal shapes (harmonic and transient) extracted from the laser output powermodulation induced by the frequency shifted optical feedback. Considering the laser quantum noise dynamic andthe detection noise separately, we show that the simulated vibration noise is in good agreement with thetheoretical prediction. Also, we demonstrate that Ultra High Frequencies (in the GHz range) can be detected byusing a usual LOFI setup with a low power laser (few mW) and a conventional detection with a usual white noiselevel. Then we show how the noise of a short transient vibration can be reduced by the reconstruction of its widevibration spectrum by concatenation. Finally, the experimental detection of transient-harmonics ultrasoundvibrations propagating in water and detected at the air/water interface is presented.

Blood vessel segmentation of fundus images via cross-modality dictionary learning

Yan Yang, Feng Shao, Zhenqi Fu, and Randi Fu

Doc ID: 332882 Received 29 May 2018; Accepted 04 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: Fundus vessel is the only vascular structure in human body that can be observed noninvasively, which are significant for early computer-aided diagnosis of blood vessel related clinical disorders. Traditional supervised vessel segmentation methods are usually based on classification which classify all pixels into vessel pixels and non-vessel pixels. In this paper, we proposed a new fundus vessel segmentation method with the motivation to extract vessels via cross-modality dictionary learning. In this method, we first enhance the structural information of vessels using a multi-scale filtering model. Then, cross-modality description and segmentation dictionaries are trained to build the intrinsic relationship between the enhanced vessel blocks and label blocks for the block-based vessel segmentation. Also, effective pre-processing and post-processing are adopted to promote the performance. Experimental results on three benchmark datasets demonstrate that the proposed method can achieve good segmentation results.

Flame temperature estimation from light field image processing

Tian-Jiao Li, Chuan-Xin Zhang, Yuan Yuan, Yong Shuai, and ping Tan

Doc ID: 334447 Received 15 Jun 2018; Accepted 04 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: We propose a novel flame temperature estimation method based on a flame light field sectioned imaging model of complex temperature distribution in different media. The proposed method relies on multipixel reconstruction to improve the resolution of sub-aperture images. In addition, the wavelet transform denoises the flame refocused image, and the Lucy–Richardson algorithm deconvolves the image. The temperature estimation accuracy using the proposed method is higher than that reported in a previous work, with a larger temperature estimation range from 1250K to 1800K. Moreover, we found that deconvolution plays an important role to determine the temperature estimation accuracy.

Analysis of interference fringes formed by three circularly polarized beams targeted for birefringence distribution measurements

Akito Shimomura, Takashi Fukuda, and Akira Emoto

Doc ID: 332185 Received 11 Jun 2018; Accepted 03 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: As a potential means of measuring birefringence distribution, we analyzed the interference fringes formed by three circularly polarized beams: a right-handed signal beam, a left-handed reference beam, and a right-handed reference beam. All beams were crossed at the same angle on the interfering plane, creating a two-dimensional interference fringe with three grating vectors. We proposed that by analyzing the interference fringes, we can measure the anisotropic phase shift in the signal beam. The obtained features of the anisotropic phase shift can be extended to the measurement of two-dimensional birefringence distributions without rotational manipulations of the objectives or polarizers. The fringes were generated by monolithic gratings, which can generate three-beam interfering fields precisely and easily. Finally, we confirmed the feasibility of a birefringence measurement system without any rotational manipulations of optics.

Fiber optic gyroscope noise reduction with fiber ringresonator

Haisheng Zhang, Xingfan Chen, xiaowu shu, and Cheng Liu

Doc ID: 328630 Received 17 Apr 2018; Accepted 03 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: A method of improving the angular random walk (ARW) of a fiber optic gyroscope (FOG) using a fiber ringresonator (FRR) to reduce the relative intensity noise (RIN) is demonstrated. In a FOG adopting square-wavebiasing modulation technology, only the RIN near the proper frequency limits the ARW when the detected powerreaches tens of microwatts. An FRR reduces the RIN near the proper frequency and hence improves the ARW. Whenthe resonator length of the FRR is shorter than the length of the FOG coil, the ARW improvement is furtherenhanced by adjusting the window length of the averaging process in FOG demodulation. An experimentdemonstrated a 7-dB decrease in the RIN, which reduces the standard deviation by 3.5-dB. The ARW was reducedfrom 970 to 570 μdeg/h1/2, which amounts to a 2.3-dB reduction.

Propagation and asymmetric behavior of optical pulsesthrough time-dynamic loss-gain assisted media

Piyali Biswas, Harsh K. Gandhi, Vaibhab Mishra, and Somnath Ghosh

Doc ID: 335160 Received 13 Jun 2018; Accepted 03 Aug 2018; Posted 03 Aug 2018  View: PDF

Abstract: We report an asymmetric behavior of optical pulses during their propagation through a time-varyinglinear optical medium. The refractive index of the medium is considered to be varying with time andcomplex such that a sufficient amount of gain and loss is present to realize their effect on pulse propagation.We have exploited the universal formula for optical fields in time-varying media. Numericallysimulated results reveal that pulses undergo opposite temporal shifts around their initial center positionduring their bi-directional propagation through the medium along with corresponding spectral shifts.Moreover, the peak power and accumulated chirp (time derivative of accumulated phase) of the outputpulse in both propagation directions are also opposite in nature irrespective of their initial state. Numericallysimulated behavior of the pulses agrees well with the analytical solutions.

Spectral characteristics of Guided mode resonantfilter with plane of incidence

Danyan Wang, Qingkang WANG, and Mengtian Wu

Doc ID: 330930 Received 03 May 2018; Accepted 02 Aug 2018; Posted 02 Aug 2018  View: PDF

Abstract: Spectral responses of the guided mode resonant filter (GMRF) under different planes of incidence (POI) arecomprehensively investigated in this paper. Commercially available software based on rigorous coupled waveanalysis (RCWA) method is used to perform the reflectance spectra. For normal incidence, there exists a pair ofresonance bands, whose diffraction efficiencies can be tuned from 3.5% to 100% and 3.2% to 100% withoutshifting the resonant location as POI angle ranging from 0° to 90°. Whereas, the resonances split into two branchesas POI angle decreasing from 90° to 0° for oblique incidence, and there exists a crossing point between the splitbands which is proved to be polarization independent. Moreover, the physical mechanism of the above spectralcharacteristics is analyzed in detail by means of the wave vectors. The intensity-tunable feature under normalincidence can be used in the field of bioactive fluorescent protein dyes, displays, and signal processing. And thesplit characteristic under oblique incidence is applied to seek the polarization-independent wavelength, which haspotential applications in the field of dense wavelength division multiplexing (DWDM) and laser devices.

Investigation of an apodized imaged Hartmann wavefront sensor

Christophe Dorrer, Adam Kalb, Peter fiala, Seung-Whan Bahk, Archana Sharma, and Kyle Gibney

Doc ID: 332328 Received 25 May 2018; Accepted 02 Aug 2018; Posted 02 Aug 2018  View: PDF

Abstract: Quantitative wavefront measurements are demonstrated using a Hartmann mask re imaged onto a camera. The wavefront is reconstructed using standard algorithms applied to the difference of beamlet centroids determined from fluence distributions obtained for two different longitudinal locations of the mask. The wavefront of the optical wave in the object plane is measured independently of imaging-system collimation. Apodization obtained with spatially dithered distributions of small transparent or opaque pixels improves the measurement accuracy by reducing the spatial-frequency content of the mask holes. Simulations and experiments demonstrate the excellent accuracy of this diagnostic over a wide range of parameters, making it suitable, for example, to characterize laser systems.

Single-transverse-mode waveguide-coupled deformed hexagonal resonator microlasers

Fu-Li Wang, Yue-De Yang, Yong-Zhen Huang, Zhi-Xiong Xiao, and Jin-Long Xiao

Doc ID: 334964 Received 12 Jun 2018; Accepted 02 Aug 2018; Posted 02 Aug 2018  View: PDF

Abstract: AlGaInAs/InP waveguide-coupled deformed hexagonal resonator microlasers with enhanced mode quality (Q) factors are demonstrated for realizing single-transverse-mode operation. A circular hole is introduced to the center of the hexagonal resonators with rounded corners to enhance the mode Q factors and suppress high-order transverse modes simultaneously. Single-mode lasing with side-mode suppression ratios up to 40dB is obtained for the 10μm-sidelength hexagonal microlasers with a center hole. All the lasing spectra demonstrate pure single-transverse-mode properties within the whole tuning range of injection current, and mode-hopping with one, two and three longitudinal-mode intervals is observed due to the mode Q factor modification by the center holes. To further reduce the device size and threshold current, the deformed hexagonal resonator microlasers with the flat sides replace by circular arcs are analyzed and demonstrated experimentally. The Q factors of the fundamental transverse modes can be enhanced by two orders of magnitude due to the convergence effect of the circular-sides by optimizing the deformation amplitude, while the single-transverse-mode property is still maintained. A threshold current of 2.4 mA is realized for circular-side hexagonal microlaser with the side-length of 8.5 μm and the deformation amplitude of 0.55 μm.

Active optical modulator based on metasurface interahertz region

Yue Tian, Jie Ji, Siyan Zhou, Hu Wang, Zhichao Ma, furi ling, and Jian-Quan Yao

Doc ID: 332536 Received 25 May 2018; Accepted 02 Aug 2018; Posted 17 Aug 2018  View: PDF

Abstract: The characteristics of EIT analogue exposed under different illumination powers have been investigatedtheoretically and experimentally. The EIT analogue is composed of a fixed aluminum structure fabricated on thesilicon substrate. It was found that the resonance degree of the transparent window displayed a decrease trend,and a blue-shift phenomenon emerged by increasing the powers of laser. Similarly, the properties of the time delayunder different illumination powers have also been researched. The realization of the tuning effect may provide apossible choice for the modulation of the slow light devices.

How light absorption modifies the radiative force on a microparticle in optical tweezers

Warlley Campos, Jakson Fonseca, joaquim Mendes, Marcio Rocha, and Winder Moura-Melo

Doc ID: 334164 Received 04 Jun 2018; Accepted 01 Aug 2018; Posted 02 Aug 2018  View: PDF

Abstract: Reflection and refraction of light can be used to trap small dielectric particles in the geometrical optics regime. Absorption of light is usually neglected in theoretical calculations, but it is known that it occurs in the optical trapping of semi-transparent particles. Here, we propose a generalization of Ashkin’s model for the radiative force exerted on a spherical bead, including the contribution due to attenuation/absorption of light in the bulk of the particle. We discuss in detail the balance between refraction, reflection and absorption for different optical parameters andparticle sizes. Our findings contribute to the understanding of optical trapping of light-absorbing particles, and may be used to predict whenever absorption is important in real experiments.

An analytical method for the transformation ofZernike polynomial coefficients for scaled, rotated andtranslated pupils

Lei Li, Zhang Bao, yongsen xu, and dejiang wang

Doc ID: 334414 Received 04 Jun 2018; Accepted 01 Aug 2018; Posted 02 Aug 2018  View: PDF

Abstract: Zernike polynomials provide an excellent metric basis for characterizing the wavefront aberrations of human eyesand optical systems. Since the Zernike expansion is dependent on the size, position and orientation of the pupil inwhich the function is defined, it is often necessary to transform the Zernike coefficients between different pupils.An analytic method of transforming the Zernike coefficients for scaled, rotated and translated pupils is proposed inthis paper. The normalized coordinate transformation functions between the polar coordinates of the transformedpupil and the Cartesian coordinates of the original pupil are given. Based on the Cartesian and polarrepresentations of Zernike polynomials, the coefficients transformation matrix can be derived directly andconveniently. The first 36 terms Standard Zernike polynomials are used to validate the proposed method. Fordifferent types of transformation, transformation rules of individual Zernike terms are systematically analyzed,revealing how individual terms of the original pupil transform into terms of the transformed pupil. Numericalexamples are presented to demonstrate the validity of the proposed method. Further application of the proposedmethod to the alignment of pupil-decentered off-axis optical systems is discussed.

Bidirectional mode-locked thulium-doped fiber laser

Nurmemet Abdukerim, Md Imrul Kayes, Alexandre Rekik, and Martin Rochette

Doc ID: 335101 Received 13 Jun 2018; Accepted 01 Aug 2018; Posted 01 Aug 2018  View: PDF

Abstract: We report a bidirectional mode-locked thulium-doped fiber laser. Mode-locking is enabled by the combination of semiconductor saturable absorption and nonlinear polarization rotation. Two stable mode-locked picosecond pulse trains in opposite directions are generated with a fundamental repetition rate of ~16.57 MHz. Output wavelengths are tunable over 35 nm.

First industrial-grade coherent fiber link for optical frequency standard dissemination

Fabiola Camargo, Vincent Ménoret, Etienne Cantin, Olivier Lopez, Nicolas Quintin, Emilie Camisard, Vincent Salmon, Jean-Marc Le Merdy, GIORGIO SANTARELLI, Anne Amy-Klein, Paul-Eric Pottie, Bruno Desruelles, and Christian Chardonnet

Doc ID: 335171 Received 15 Jun 2018; Accepted 31 Jul 2018; Posted 01 Aug 2018  View: PDF

Abstract: We report on a fully bi-directional 680 km link connecting two cities for which the equipments, the set up and the characterization are managed for the first time by an industrial consortium. The link uses an active telecommunication fiber network with parallel data traffic and is equipped with three repeater laser stations and four remote double bi-directional Erbium-doped fiber amplifiers. We report a short term stability at 1-s integration time of 5.4E-16 in 0.5 Hz bandwidth and a long term stability of 1.7E-20 at 65000 s of integration time. The accuracy of the frequency transfer is evaluated as 3E-20. No shift is observed within the statistical uncertainty. We show a continuous operation over 5 days with an uptime of 99.93%. These performances are comparable with the state of the art coherent links established between National Metrology Institutes in Europe. It is a first step towards building an optical fiber network for metrology in France which will give access to an ultra-high performance frequency standard to a wide community of scientific users.

Adaptive Dual-Exposure Fusion based Transport ofIntensity Phase Microscopy

Junbao Hu, Yan Kong, Zhilong Jiang, Liang Xue, Fei Liu, Liu Cheng, and Shouyu Wang

Doc ID: 332610 Received 29 May 2018; Accepted 31 Jul 2018; Posted 01 Aug 2018  View: PDF

Abstract: Via the transport of intensity phase microscopy, quantitative phase can be retrieved directly from captured multifocalintensities, the accuracy of the retrieved phases highly depends on the quality of the recorded images,therefore, the exposure time should be carefully chosen for high-quality intensity captures. However, it is difficultto record well-exposure intensities to maintain rather high signal to noise ratio and to avoid over-exposure due tothe complex samples. In order to simplify the exposure determination, here the adaptive dual-exposure fusionbased transport of intensity phase microscopy is proposed: with captured short- and long-exposure images, thewell-exposure multi-focal images can be numerically reconstructed and then high-accurate phase can be computedfrom these reconstructed intensities. With both simulations and experiments provided in this paper, it is provedthat the adaptive dual-exposure fusion based transport of intensity phase microscopy not only providesnumerically reconstructed well-exposure image with simple operation and fast speed, but also extracts highaccurateretrieved phase. Moreover, the exposure time selection scope of the proposed method is much wider thanthat based on single exposure, and even there is over-exposure region in the long-exposure image, well-exposureimage can still be reconstructed in high precision. Considering its advantages as high accuracy, fast speed, simpleoperation and wide application scope, the proposed technique can be future adopted as quantitative phasemicroscopy for high-quality observations and measurements.

Iterative phase retrieval in coherent diffractive imaging: practical issues

Tatiana Latychevskaia

Doc ID: 332776 Received 31 May 2018; Accepted 31 Jul 2018; Posted 01 Aug 2018  View: PDF

Abstract: In this work issues in phase retrieval in of coherent diffractive imaging (CDI) technique, from discussion on parameters to set up a CDI experiment to evaluation of the goodness of the final reconstruction, are discussed. It is often that distribution of object under study by CDI cannot be cross-validated by another imaging technique. It is therefore important to make sure that developed CDI procedure delivers artifact-free object reconstruction. Critical issues that can lead to artifacts are presented and recipes on how to avoid them are provided.

Astigmatism and deformation correction for aholographic head-mounted display with wedgeshapedholographic waveguide

Wen-Kai Lin, Osamu Matoba, Bor-Shyh Lin, and Wei-Chia Su

Doc ID: 327703 Received 10 Apr 2018; Accepted 30 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: In this study, a head-mounted display (HMD) system based on a wedge-shaped holographic waveguide which canpresent holographic virtual images with tunable distance is achieved. The compact computer-generated-hologram(CGH) system using a spatial-light-modulator (SLM) was employed to offer the dynamic image, where the probebeam for the hologram reconstruction is a convergent wave and the DC term of the diffraction wave can be blockedby a barrier. The wedge-shaped holographic waveguide element was used as the combiner of the HMD system inorder to generate a compact structure. The wedge with the polished surface was designed for the image in-couplinginto the waveguide, and a reflection-type HOE was used for the image out-coupling from the waveguide. Theastigmatism aberration and deformation of the diffraction images locating at various distances are analyzed andthen are compensated. Finally, the virtual image can be obtained without aberration with experimentalverification.

Probing multi-pulse laser ablation by means of self-mixing interferometry

Simone Donadello, Ali Gokhan Demir, and Barbara Previtali

Doc ID: 330869 Received 03 May 2018; Accepted 30 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: In this work self-mixing interferometry (SMI) is implemented inline to a laser microdrilling system in order to monitor the machining process by probing the ablation-induced plume. An analytical model based on the Sedov–Taylor blast wave equation is developed for the expansion of the process plume under multiple-pulse laser percussion drilling conditions. Signals were acquired during laser microdrilling of blind holes on stainless steel, copper alloy, pure titanium, and titanium nitride ceramic coating. The maximum optical path difference was measured from the signals to estimate the refractive index changes. An amplitude coefficient was derived by fitting the analytical model to the measured optical path differences. The morphology of the drilled holes was investigated in terms of maximum hole depth anddross height. The results indicate that the SMI signal rises when the ablation process is dominated by vaporization, changing the refractive index of the processing zone significantly. Such ablation conditions correspond to limited formation of dross. The results imply that SMI can be used as a non-intrusive tool in laser micromachining applications for monitoring the process quality in an indirect way.

Quantum laser radar based on wavelength-time-quantum states random interleaved optical pulse sequence

Dongsong Shi, Li Ming, Genghua Huang, and Shu Rong

Doc ID: 332265 Received 25 May 2018; Accepted 30 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: Based on the wavelength-time-quantum states random interleaved optical pulse sequence, we have established a quantum laser radar model. The multi-quantum state is used as a detection tool for the interception and interference of the target, and the multi-wavelength covering the ultraviolet to near-infrared waveband is used to avoid interference and improve detection efficiency. We elaborate the working principle of the whole quantum radar detection system model and demonstrate its feasibility through simulation design. It lays a foundation for the application of quantum radar in the long distance and high precision detection of satellite platform.

Improved analysis model for material removal mechanisms of bonnet polishing incorporating pad wear effect

chenchun shi, Yunfeng Peng, Liang Hou, Zhenzhong Wang, and Yinbiao Guo

Doc ID: 333059 Received 05 Jun 2018; Accepted 30 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: The bonnet polishing technology has been widely applied in the precision optical machining. Till now most of the researches concerning the modeling for material removal mechanisms of bonnet polishing are presented based on the well-known Preston model. However, those various parameters involved in the bonnet polishing process are not formulated into that model, such as slurry characteristics, pad properties, bonnet sizes, processing conditions, etc. Recently, several analysis models capturing those various parameters are developed and even capable of interpreting Non-Prestonian behaviors, but the pad wear effect is still not taken into account. Hence, the purpose of this paper is to establish an improved analysis model by incorporating the pad wear effect with the cumulative polishing time. Compared with the previous analysis model and Preston model, the predicted results of the improved analysis model are much closer to the experimental data and become more acceptable. According to the analysis of key parameters, the understanding of material removal mechanisms in bonnet polishing is further completed, and the time-dependent pad wear effect should not be neglected any more.

CIOMP-Near-diffraction-limited Bragg Reflection Waveguide Lasers

Lijie Wang, Zhen Li, Cunzhu Tong, Shili Shu, Sicong Tian, jun zhang, Xin Zhang, and Lijun Wang

Doc ID: 334374 Received 05 Jun 2018; Accepted 30 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: We report a near-diffraction-limited tapered Bragg reflection waveguide laser (BRL) with a 10-μm ridge width,which is significantly larger than the conventional design. The large mode expansion in the vertical waveguideenables a scalable increase in the ridge width for single lateral mode operation. The role of the taper angle in theperformance of tapered BRLs with the intrinsic characteristics of thick vertical waveguide was investigated. Theresults indicate that the BRL with a taper angle of 3° shows the best far-field performance. An extremely lowvertical divergence angle of 14.5° and a lateral divergence of as low as 2.8° for 95% power inclusion were realized.A continuous-wave power of exceeding 1 W was demonstrated. Over the entire operating current range, thevertical beam is almost unchanged with an excellent beam quality (M2) of about 1.3. Lateral beam width increasesslightly at higher currents due to the increasing contribution of side lobes, but it still remains nearly diffractionlimitedwith a lateral M2 of less than 2. Narrow beam divergence and high beam quality of the lasers allow simpleand inexpensive collimation and coupling.

Distinctive roles of elevated absorbing aerosol layers on Free-Space Optical Communication systems

Anand Sarma, SUNILKUMAR K, S Satheesh, and Krishnamoorthy K

Doc ID: 334589 Received 06 Jun 2018; Accepted 30 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: The impact of enhanced local heating due to absorption of solar radiation by elevated layers of aerosol Black Carbon (BC) in the lower troposphere in the performance of Free-Space Optical (FSO) communication links is investigated. It is seen that a strong elevated BC layer at an altitude around 4.5 km enhances the atmospheric stability locally and leads to large reduction in the atmospheric refractive index structure parameter (Cn2), leading to improved performance of the FSO communication links. For layers in the tropical atmosphere with sufficiently high BC concentration, the signal attenuation due to BC absorption is alleviated by the large reduction in Cn2 due to BC-induced warming and brings down the link outage probability. Synergy between reduction in Cn2 and long wavelength transmission improves the link budget significantly by reducing the beam wander and number of adaptive optics units required.

Preliminary measurements of fluorescent aerosolnumber concentrations using a laser-inducedfluorescence lidar

Zhimin Rao, tingyao he, hua Dengxin, Yunlong Wang, Xusheng Wang, Yinyin Chen, and JING LE

Doc ID: 335387 Received 15 Jun 2018; Accepted 30 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: A laser-induced fluorescence lidar has been developed for detecting number concentration of fluorescent aerosolsin the air. The fluorescence lidar was constructed with a pulsed fourth-harmonic Nd:YAG laser at the ultravioletwavelength of 266 nm, with a repetition rate of 10 Hz. A 250 mm diameter custom telescope was used to collectoptical spectra ranging from 260∼560 nm. Fluorescence signals with the wavelength ranging 310∼440 nm wasextracted exploring a filter with a bandwidth of 130 nm. The preliminary experiments were conducted at thecampus of Xi’an University of Technology, in which the fluorescence signals of atmospheric fluorescent aerosolswere continuously collected from 20:00 to :00 CST on 13 December 2017. Based on fluorescence lidar equation,the density of fluorescence signals was calibrated using Rayleigh-Mie scattering signals and ozone (O3)concentration data at the ground level. Measured ranges show a strong dependent with the O3 concentrations due toits absorption characteristics at ultraviolet 266 nm. Moreover, number concentration of the biogenic particles wasalso calculated based on the raw data of the fluorescence channel. Obtained results show that the numberconcentration of biogenic particles in Xi’an area varied greatly ranging from 3456 particlesm-3 to 8835 particlesm-3during Winter.

Slowing designer surface plasmons in asurface-wave photonic crystal

Wang Zhuoyuan, Zhen Gao, Yongping Zhang, Jianming Lou, Peihong Cheng, and Hongxia Zhao

Doc ID: 336354 Received 27 Jun 2018; Accepted 30 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: We propose and experimentally demonstrate a broadband slow-wave system in asurface-wave photonic crystal based on a non-uniform line-defect waveguide with gradedmetallic pillars, whose dispersions and cutoff frequencies vary gradually along thewaveguide. Since the group velocity of designer surface plasmons at the cutoff frequencies iszero, we show that surface waves can be slowed and stopped at different positions underdifferent frequencies. Experimental evidences including transmission measurements anddirect near-field profiles imaging performed in the microwave frequencies validate thestopping of surface waves in a broadband range within the forbidden bandgap of the surfacewavephotonic crystal. This proposal is a promising candidate for the slow-wave devicesimplemented on a single metal surface in both microwave and terahertz frequency ranges.

Multicore optical fiber based vibration sensors for biomedical applications

Md Rejvi Kaysir and Md Jahirul Islam

Doc ID: 331662 Received 16 May 2018; Accepted 28 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: Vibration is one of the key parameters for extracting information from surrounding environments, and optical fiber-based sensors show great promise for achieving such information. In this work, an intensity-based multicore fiber (MCF) based vibration sensor is designed, fabricated and characterized for biomedical applications. The fabricated MCF has seven cores, in which the middle core is used for launching light and the surrounding cores are used for collecting lights from any reflective substances. The working principle of the MCF sensor is based on the intensity modulation of reflected light from vibrating substances that is coupled to the collecting cores (i.e. side cores) of the MCF. Here, light from a 532 nm laser was launched into the middle core of the MCF and the reflected light from a mirror, situated at the output face of MCF, was collected from a single side core. To characterize the sensor and demonstrate the sensing activities of MCF, two experimental approaches were taken: (i) static sensitivity and (ii) dynamic measurements. The static measurement demonstrated the region of maximum sensitivity and helped to find out the optimal design parameters of MCF for any desired applications. A simple ray tracing model also included getting the maximum sensitive regions of the designed sensor that verifies our experimental results. Dynamic measurement demonstrates the vibration sensing activities of the sensor. This information provides pathways to design MCF based vibration sensors for the specific applications.

Measured performance of shadow-cast coated gratings for spectro-polarimetric applications

Roberto Casini, Dennis Gallagher, Anthony Cordova, and Matt Morgan

Doc ID: 330748 Received 08 May 2018; Accepted 28 Jul 2018; Posted 02 Aug 2018  View: PDF

Abstract: We measured the efficiency of a reflective echelle grating that was specially coatedin order to reduce the polarization of the diffracted light. The standard coatedgrating can be used between approximately 350 nm and 1200 nm, for diffraction ordersbetween 14 and 5. In these orders, the standard grating can be strongly polarized(up to ${\sim}80$\%), which impacts its usability in spectro-polarimetric instruments.The adoption of the shadow-cast coating technique, which implies selectivelydepositing the reflective coating exclusively onto the blazed facets, cansignificantly reduce the polarization of the grating, while preserving its averageefficiency.

Effect of sensor SNR and extinction ratio onpolarimetric imaging error for nanowire-based system

sun he, dejiang wang, Cheng Chen, Kehui Long, and Sun XueQian

Doc ID: 332998 Received 04 Jun 2018; Accepted 27 Jul 2018; Posted 27 Jul 2018  View: PDF

Abstract: High sensor SNR and high extinction ratio (ER), often contradictory requirements for nanowire-filter-basedpolarimetric imaging systems, aid in attenuating polarimetric imaging system errors. Expressions were derived toanalyze their attenuation effects and simplified using photoelectronic numbers received by super pixels (PNRS).First derivative ratios of PNRS and ER were calculated to compare their attenuation effects. Mathematical modelsand experiments conducted using polarimetric imaging systems with various ERs and PNRSs indicate that systemswith low PNRS and high ER exhibit a polarization error affected more by the attenuation effect of PNRS than that ofER. When system ER is higher than 28, the attenuation effect of PNRS is higher than that of ER. Thus, system errorattenuation is a trade-off between sensor SNR and ER.

CIOMP-Study of influence of the removal depth of silicon modification layer on grating structures in reaction-sintered silicon carbide substrate and improvement method

Chen Shen, xin tan, Qingbing Jiao, Wei Zhang, Tongtong Wang, wenhao li, na wu, Xiangdong Qi, and heshig bayan

Doc ID: 334625 Received 13 Jun 2018; Accepted 27 Jul 2018; Posted 27 Jul 2018  View: PDF

Abstract: The influence of the removal depth of silicon modification layer on grating structures and mirrors is studied. The removal depth 6μm-14μm is the optimization result for Si modified RS-SiC used as mirror substrates, but the removal depth 9μm-12μm is the optimization result for Si modified RS-SiC used as grating substrates. The diffraction efficiency and stray light of the gratings fabricated in the Si modified RS-SiC substrates with removal depth 9μm-12μm is 90.5%-94% and 5.30×10-7-5.45×10-7 respectively. Additionally, the number and scale of high reflection points can be used as the basis for judging the removal depth of the Si modified RS-SiC used as grating substrates. These results and the regularity have guiding significance for the application of Si modified RS-SiC as a microstructural substrate.

Analytical-performance improvement of aqueous solution by chemical replacement combined with surface-enhanced laser-induced breakdown spectroscopy

Xinyan Yang, Xiangyou LI, zhifeng cui, Zhong Qi Hao, Yongfeng Lu, jingchun huang, Guanxin Yao, and Xiaoli Wang

Doc ID: 332412 Received 25 May 2018; Accepted 27 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: In this study, chemical replacement combined with surface-enhanced laser-induced breakdown spectroscopy (CR-SENLIBS) was introduced for detecting the trace chromium (Cr) element in an aqueous solution, which could use chemical replacement to change the sample from the liquid to the solid. In order to illustrate the analytical-performance of the CR-SENLIBS, the direct analysis of the liquid surface by LIBS (LSLIBS) was investigated for comparion. The results shown that the spectral intensity of Cr I 357.86 nm, plasma lifetime, and spectral stability were improved. Moreover, the limit of detection (LoD) of Cr I 357.86 nm was 0.018 μg/mL, which was lower than 1.814 μg/mL for LSLIBS. Furthermore, the accuracy and precision were improved more than 60% and 80%, respectively, such as the root-mean-square error of cross-validation (RMSECV) was improved from 1.09 to 0.75 μg/mL, the average RSD (ARSD) of predicted concentration of Cr was reduced from 22.89% to 4.53% by using CR-SENLIBS. These results suggest that CR-SENLIBS has a good analytical-performance, which exhibits great potential in water quality monitoring.

Optical design of short-wave infrared prism-gating imaging spectrometer

JIANJUN CHEN, yang jin, jianan liu, Jianli Liu, ci sun, xiaotian li, heshig bayan, and Jicheng Cui

Doc ID: 334314 Received 05 Jun 2018; Accepted 27 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: A miniaturized portable short-wave infrared imaging spectroscopy optical system is designed based on a prism-grating dispersion module. We established a prism-grating model to calculate the optimal combination of prism and grating parameters to balance spectral line curvature over the entire band. The design method for the telescopic system and spectroscopic system combines independent design with integrated optimization. The system's spectral line curvature and spectral keystone are less than 15 µm and less than one half pixel in size, respectively. The total optical system length is 0 mm, which meets the miniaturization requirements for airborne systems. The system’s spatial resolution is 1 mrad, and its average spectral resolution is 6.2 nm. The system offers the advantages of large relative aperture, excellent imaging quality, reduced spectral line curvature and spectral keystone, miniaturization and portability.

Transformation algorithm and analysis of Fourier-transform spectrometer based on cascaded Fabry-Perot interferometers

Islam El-Sayed, Yasser Sabry, Waleed ElZeiny, Niveen Badra, and Diaa Khalil

Doc ID: 334961 Received 12 Jun 2018; Accepted 27 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: The Fourier transform spectrometer based on cascaded Fabry-Perot interferometers is analyzed, where one of the interferometers has a fixed length while the other is scanning. We propose a method to reconstruct the spectrum correctly based on solving the integral equation of the overall response of the cascaded interferometers. The method is tested for different design parameters and noise conditions. Low reconstruction error below -80 dB is found to be achievable.

Advances and Challenges of Intraocular Lens Design

Lan Zeng and Fengzhou Fang

Doc ID: 325338 Received 05 Mar 2018; Accepted 27 Jul 2018; Posted 27 Jul 2018  View: PDF

Abstract: Phacoemulsification technique with intraocular lens implantation has been a common treatment for cataract patients. With the rising demand of the public, new technologies on lens design have come around to minimizing intraocular aberrations, improving visual quality to the largest extent. This paper systematically review the development of the materials applied in the lens manufacturing, the different categories of intraocular lenses and the principle of design respectively. The advantages and potential drawbacks of intraocular lenses are illustrated in the paper and the prospective research to improve the design are presented in the end

Bidirectional reflectance characteristics of the seasurface based on mid-infrared measured data

Hang YUAN, Xiao-rui Wang, BingTao Guo, weiguo zhang, Ke LI, Jia-chen Mao, and Xiongxiong Wu

Doc ID: 332098 Received 21 May 2018; Accepted 26 Jul 2018; Posted 07 Aug 2018  View: PDF

Abstract: In order to establish a more realistic radiation model of sea surface, the effects of solar radiation, sky radiation, andatmospheric thermal radiation on the sea surface radiation are taken into consideration, on the basis of which theinfrared radiative transfer equation of sea surface is deduced in this paper. A method for calculating thebidirectional reflection characteristics of sea surface based on measured data is proposed according to theprojection imaging of beam propagation. Based on the measurements of the sea surface temperature, incident skyradiation, incident solar radiation, and radiance of sea crests at different times, the radiative transfer equation isused to retrieve the bidirectional reflectance of mid-wave infrared sea surface. Meanwhile, the results of themethod mentioned-above are compared with the calculated results of Cox–Munk, Mermelstein, Wu, and Beckmannbidirectional reflection characteristics models. Research shows that the bidirectional reflectance at the wave crestof sea surface increases gradually, when the solar incident zenith angle changes from 56.39 ̊ to 76.02 ̊ as well as thedirection of observation remains constant (θr=80.0°, φr=73.0°). The reflection ability at the wave crest of the seasurface is the strongest when the incident direction of the sun is close to the observation direction, which is inaccordance with the law of reflection. The Cox-Munk model and Wu model are closer to our values when the solarincidence zenith angle is small (θi ≤65.93 ̊). On the other hand, the calculated values of the Mermelstein and Wumodels are closer to the values in this paper when the solar incidence zenith angle is large (θi >65.93 ̊). In general,the error of the Beckmann model is a little greater than other three models.

Design of ultra-compact tunable fractional-ordertemporal differentiators based on hybrid-plasmonicphase-shifted Bragg gratings

Azadeh Karimi, Abbas Zarifkar, and Mehdi Miri

Doc ID: 332683 Received 29 May 2018; Accepted 25 Jul 2018; Posted 07 Aug 2018  View: PDF

Abstract: The design and simulation of tunable fractional order temporal differentiators based on Si-hybrid plasmonicphase-shifted Bragg grating (SHP-PSBG) are proposed in this manuscript where the strong light confinement in thehybrid plasmonic waveguide is employed to significantly reduce the overall length of the differentiator. Accordingto 2D- and 3D-FDTD simulation results, the proposed structures with the overall lengths less than 8 μm can providearbitrary differentiation order and differentiation bandwidths as high as 1.6 THz. The differentiation order and thebandwidth of the proposed structures can be tuned in relatively wide ranges by changing the geometricalparameters of the structure. For example, the differentiation order can be changed from 0.57 to 0.97 by changingthe number of the Bragg grating periods in 3D differentiator structure. Furthermore, it is shown that using anelectro-optical polymer as the low index material of the hybrid plasmonic waveguide, the differentiation order andthe central frequency of the proposed differentiator can be actively tuned through applying a proper actuatingelectrical field (voltage) to the structure. This property along with the ultra-compact footprint and wide bandwidthof the proposed differentiator suggest its application in ultrafast all-optical signal processing systems.

Improvement of printing efficiency in holographic stereogram printing with the combination of field lens and holographic diffuser

Jian Su, Xingpeng Yan, Yingqing Huang, Xiaoyu Jiang, Yibei Chen, and Teng Zhang

Doc ID: 328417 Received 16 Apr 2018; Accepted 25 Jul 2018; Posted 26 Jul 2018  View: PDF

Abstract: In this paper, we use a field lens and a holographic diffuser together to improve the printing efficiency of holographic stereogram printing system based on effective perspective images’ segmentation and mosaicking(EPISM) method. The light rays’ regulation function of field lens and the modulation function of holographic diffuser are analyzed. Holographic diffusers with different expanding angles are optimized by numerical simulations and verified by optical experiments. We can achieve a better holographic stereogram reconstruction effect as well as a better printing efficiency when adopting a field lens and a 10°holographic diffuser together. With the proposed method, the energy efficiency can be improved and the printing time can be reduced greatly.

An efficient hybrid method for electromagnetic scattering from a coated object above a two-layered rough surface

Hong-Jie He and Lixin Guo

Doc ID: 330949 Received 04 May 2018; Accepted 25 Jul 2018; Posted 26 Jul 2018  View: PDF

Abstract: A powerful and efficient hybrid method combining finite-element boundary-integral method with fast multipole method (FE-BI-FMM) is proposed in this paper to study the electromagnetic scattering characteristics from a coated object above a two-layered dielectric rough surface. Finite element method (FEM) is applied to model the scattering from the coated object, and multiple interactions between the object and layered rough surface are handled by FMM-enhanced boundary integral method (BIM). A hybrid solver is adopted to efficiently solve the FEM-BIM matrix equation. Several numerical results are presented, and the influence of several parameters of the composite model on the scattering characteristics is analysed in detail. Both vertical and horizontal polarizations for the incident waves are considered.

Compact Echelle Spektrometer Employing a Cross-Grating

Daniel Thomae, Tobias Hönle, Matthias Kraus, Verena Bagusat, Arnaud Depernay, Robert Brüning, and Robert Brunner

Doc ID: 332019 Received 18 May 2018; Accepted 25 Jul 2018; Posted 26 Jul 2018  View: PDF

Abstract: The concept and the implementation of a compact and simplified Echelle Spectrometer are presented, and the working principle is demonstrated by first experimental measurements. The crucial element of the setup is a cross-grating, combining an Echelle grating utilizing several higher diffraction orders (5th up to 11th) and a superposed perpendicular oriented cross-dispersing grating. Two alternative manufacturing methods for the cross-grating are presented and discussed. The first approach combines Talbot lithography for the deep Echelle grating and interference lithography for the cross-dispersing structure. As a second technique, direct laser beam writing was applied. The compact Echelle Spectrometer covers a spectral range from 380 nm to 700 nm and offers a spectral resolution of ~2 nm.

Wavefront prediction with reservoir computing for minimizing the effects of angular anisoplanatism

Stephen Weddell and Philip Bones

Doc ID: 327459 Received 03 Apr 2018; Accepted 24 Jul 2018; Posted 24 Jul 2018  View: PDF

Abstract: Supervised learning with recurrent neural networks has been used to estimate perturbations that adversely affect image quality of natural guide stars due to atmospheric turbulence. While this method has been shown to be effective for generating spatially variant point spread functions (PSFs) for image reconstruction using low turbulence models, recent extensions to these methods, facilitated by enhancements to optimise network parameters, show potential to extend this method to moderate turbulence, multilayer models. In this article, spatio-temporal learning using reservoir-computing tomographic imaging, a discriminative learning method known as an echo state network, is proposed to estimate the spatially variant PSF, allowing for improved image restoration of point-source exo-atmospheric objects outside the isoplanatic patch. The forward problem is modelled by training an echo state network with time-series perturbations from three or more natural guide stars. Known site profile data is incorporated to optimise the model for training, where perturbations under similar conditions are used to test estimated aberrations over a wide, anisoplanatic field.

Signal detection algorithms for interferometric sensors with harmonic phase modulation: miscalibration of modulation parameters

Leonid Liokumovich, Konstantin Muravyov, Philipp Skliarov, and Nikolai Ushakov

Doc ID: 332251 Received 21 May 2018; Accepted 24 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: In the current paper, we have developed an analytical apparatus, allowing to calculate the phase error, produced by miscalibration of modulation parameters. The case of harmonic modulation is considered, the analysis is performed for cases of two parameters miscalibration: amplitude and start phase. Two demodulation algorithms are considered: conventional 4-point algorithm, based on ordinary least squares approach and previously developed 4+1 algorithm with high immunity to phase error, induced by change of target phase on demodulation interval. Predictions, given by developed analytical equations are verified by means of numeric modeling.

Fabrication of high fill-factor cylindrical microlens array with isolated thermal reflow

Jinfeng Qiu, Mujun Li, Huichun Ye, Chen Yang, and CUICUI SHI

Doc ID: 330657 Received 08 May 2018; Accepted 23 Jul 2018; Posted 07 Aug 2018  View: PDF

Abstract: We demonstrate a simple, controllable and stable method for fabricating high fill-factor cylindrical microlens array with a novel isolated thermal reflow process. In this method, micro stripes with very small gap were obtained via DMD-based lithography. Then covered with polydimethylsiloxane (PDMS) solution, the prepared micro stripes were isolated, and were heated and reflowed to cylindrical microlens array. During the reflow process, the semi-crosslinked PDMS can serve as a barrier to prevent the diameter change and the bonding of adjacent microlenses. By this special treatment, the fill factor of cylindrical microlens array can be significantly improved. Moreover, the reflow time and temperature have very little effect on the microlens shape due to the surrounded semi-crosslinked PDMS. This will make our process more stable compared with traditional methods. The measured 3D profile are good and satisfactory, and excellent optical performance are demonstrated with the fabricated cylindrical microlens arrays. The proposed method may offer a viable route for fabrication of high fill-factor microlens arrays in a very simple and stable way.

Influence of self- and cross-phase modulations on optical frequency doubling process for metamaterials

Rena Kasumova, Gulnara Safarova, Asmar Ahmadova, and Nazaket Kerimova

Doc ID: 328000 Received 18 Jul 2018; Accepted 20 Jul 2018; Posted 06 Aug 2018  View: PDF

Abstract: In the process of doubling the frequency of high-power laser radiation in metamaterials, the self- and cross-phase modulations associated with the cubic nonlinearity of the medium are studied in the constant-intensity approximation. It is assumed that the pump wave propagates in a region with negative refraction. It is shown that in the case of a nonlinear-optical process of the frequency doubling of an intense light wave in a metamaterial, it is important to take into account the self-action and cross-interaction effects that directly affect the optimal phase relationship between the interacting waves. It is received, that as a result of counter interaction of waves the period of spatial beats changes. According to the analytic expressions obtained in the work, the choice of optimal parameters of the problem makes it possible to realize the regime of the effective frequency doubling. By varying the intensity of the pump, it is possible to control and manipulate the intensity of the output coherent radiation from the minimum to the maximum value. A numerical evaluation of the efficiency of the doubling process in a metamaterial is given and a comparison is made with similar results in LiNbO3 and KDP crystals. It is demonstrated that the effects of self- and cross-modulation in media with negative refraction can be used as a powerful tool for developing effective frequency doublers in such materials.

A compact, fiber-coupled, single-ended laserabsorption-spectroscopy sensor for high-temperatureenvironments

Yuzhe Zhou, Garrett Mathews, and Christopher Goldenstein

Doc ID: 330795 Received 09 May 2018; Accepted 19 Jul 2018; Posted 20 Jul 2018  View: PDF

Abstract: The design and demonstration of a compact single-ended laser-absorption-spectroscopy (SE-LAS) sensor formeasuring temperature and H2O in high-temperature combustion gases is presented. The primary novelty ofthis work lies in the design, demonstration, and evaluation of a sensor architecture which uses a single lensto provide single-ended, alignment-free (after initial assembly) measurements of gas properties in acombustor without windows. We demonstrate that the sensor is capable of sustained operation attemperatures up to at least 625 K and is capable of withstanding direct exposure to high-temperature (≈1000K) flame gases for long durations (at least 30 min) without compromising measurement quality. The sensoremploys a fiber bundle and a 6-mm diameter AR-coated lens mounted in a 1/8’’ NPT-threaded stainless-steelbody to collect laser light that is backscattered off native surfaces. Distributed-feedback (DFB) tunable diodelasers (TDLs) with a wavelength near 1392 nm and 1343 nm were used to interrogate well characterized H2Oabsorption transitions using wavelength-modulation spectroscopy (WMS) techniques. The sensor wasdemonstrated with measurements of gas temperature and H2O mole fraction in a propane-air burner with ameasurement bandwidth up to 25 kHz. In addition, this work presents an improved wavelength-modulationspectroscopyspectral-fitting technique which reduces computational time by a factor of 100 compared topreviously developed techniques.

A hyperspectral imaging system based on a single-pixelcamera design for detecting differences in tissueproperties

Joseph Peller, Faramarz Farahi, and Susan Trammell

Doc ID: 324964 Received 27 Feb 2018; Accepted 29 May 2018; Posted 20 Jul 2018  View: PDF

Abstract: Optical spectroscopy can be used to distinguish between healthy and diseased tissue. In this study, the design andtesting of a single-pixel hyperspectral imaging system that uses autofluorescence emission from collagen (400 nm)and NAD(P)H (475 nm) along with differences in the optical reflectance spectra to differentiate between healthyand thermally damaged tissue is discussed. The changes in protein autofluorescence and reflectance due tothermal damage are studied in ex vivo porcine tissue models. Thermal lesions were created in porcine skin (n =12) and liver (n=15) samples using an IR laser. The damaged regions were clearly visible in the hyperspectralimages. Sizes of the thermally damaged regions as measured via hyperspectral imaging are compared to sizes ofthese regions as measured in white light images and via physical measurement. Good agreement between the sizesmeasured in the hyperspectral images, white light imaging and physical measurements were found. Thehyperspectral imaging system can differentiate between healthy and damaged tissue. Possible applications of thisimaging system include determination of tumor margins during surgery/biopsy and cancer diagnosis and staging.

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

Rajab Nasehi and Mohammad Mahmoudi

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

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

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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