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Accepted papers to appear in an upcoming issue

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Measurement of the vortex and orbital angularmomentum spectra with a single cylindrical lens

Alexander Volyar, BRETSKO Mihail, Akimova Yana, and Egorov Yuriy

Doc ID: 364031 Received 01 Apr 2019; Accepted 21 Jun 2019; Posted 21 Jun 2019  View: PDF

Abstract: A new technique for measuring the degenerate spectra of optical vortices and orbital angular momentum (OAM) ofsingular beams is theoretically studied and experimentally verified. The technique is based on measuring theintensity moments of higher orders of a beam containing vortices with both positive and negative topologicalcharges. The appropriate choice of the vortex mode amplitudes of the combined beam forms anomalous regions inthe form of resonant dips and bursts in the OAM spectrum. Since the intensity moments for vortices with positiveand negative topological charges are the same (degenerate) for an axially symmetric beam, it was necessary tobreak the symmetry of the beam, so measurements were taken at the plane of the double focus of a cylindrical lens.The calibration measurements showed that the experimental error is not higher than 3.5%. The technique wasimplemented for measuring and analyzing combined beams with OAM anomalies. It was found that the dips andbursts in the OAM spectrum are caused by the vortex avalanche induced by weak perturbations of the holographicgrating responsible for shaping the beam. The OAM dips or bursts are controlled by the ratio between the energyfluxes of the vortex avalanche with positive or negative topological charges.

A High-dynamic Wavelength Tracking and Millimeter-level Ranging Inter-satellite Laser Communication Link with Feedback-Homodyne Detection

Eve Tian, Jie Zhong, Xiaoxiang Lin, Pei Xiao, Haifeng Yang, Yu Zhong, and Dongpeng Kang

Doc ID: 366193 Received 30 Apr 2019; Accepted 20 Jun 2019; Posted 20 Jun 2019  View: PDF

Abstract: The Integrated Laser Communication/Ranging System, which uses coded signal as the ranging informationcarrier, is of great importance to the next large-capacity inter-satellite information network. In this paper,a system design with high-sensitivity feedback-homodyne detection scheme and asynchronous rangingalgorithm is demonstrated with real-time FPGA implementation. The parallel FFT estimation is appliedto improve the speed and range of wavelength drift tracking, which can handle dynamic wavelengthdrift up to 2.4 pm/s (300 MHz/s). Meanwhile, for clock sources with subtle dynamic frequency offset andsufficient stability, the proposed fractional symbol ranging method is proven to achieve millimeter-levelmeasurement accuracy. The designed system is shown to perform well in terms of both laser linewidthtolerance and noise resistance.

Selection of the optimal bands of first-derivativefluorescence characteristics for leaf nitrogenconcentration estimation

jian Yang, Yinjia Cheng, Lin Du, Wei Gong, Shuo Shi, Jia Sun, and Biwu Chen

Doc ID: 366683 Received 03 May 2019; Accepted 20 Jun 2019; Posted 20 Jun 2019  View: PDF

Abstract: Laser-induced fluorescence technology provides a nondestructive and rapid method for monitoring leaf nitrogenconcentration (LNC) based on its optical characteristics. Crop growth status can be efficiently diagnosed andquality evaluated by monitoring LNC. In this study, the first-derivative fluorescence spectrum (FDFS) was proposedand calculated based on the fluorescence spectra excited by 355, 460, and 556nm excitation lights for rice LNCestimation. Then, the performance of each band FDFS characteristics and the FDFS ratio for LNC estimation werecomprehensively discussed using the principal component analysis and back propagation neural network (BPNN).And, we analyzed the number of FDFS characteristics influence on the accuracy of LNC monitoring. Results showedthat R2 does not clearly improve for the LNC monitoring based on BPNN model when the number of extracted FDFSfeatures exceed 4 or 5. Therefore, the FDFS optimal band combination of different excitation light wavelengthsmentioned was selected for LNC monitoring. The selected band combinations contained the majority of FDFScharacteristics and could effectively be applied in monitoring LNC (for 355, 460, and 556nm excitation lights, withR2 of 0.764, 0.625, and 0.738, respectively) based on BPNN model.

Highly Sensitive Fiber-Optic Accelerometer Using aMicro Suspended-Core Fiber

Wen Wang, Yedi Shen, teng guo, Xueguang Qiao, and Qiangzhou Rong

Doc ID: 361011 Received 19 Mar 2019; Accepted 20 Jun 2019; Posted 21 Jun 2019  View: PDF

Abstract: A compact fiber-optic accelerometer was proposed and demonstrated experimentally based on Fabry-Perotinterference (FPI). The device consists of a suspended core fiber embedded in a hollow core fiber, forming anenclosed cavity structure. A short section of multi-mode fiber (MMF) was spliced on the leading-in single-modefiber (SMF), which worked as a micro lens to focus the light to decrease the transmission loss. A well-definedinterference spectrum was achieved by a low-fitness FP interferometer formed by both the end-face of lead-in fiberand the end-face of suspended core fiber. Thanks to the outstretched FP cavity by suspended core fiber, the sensoris highly sensitive to vibration along the fiber axis. Moreover, one-dimensional mechanical transducer was used toimprove the frequency band of the sensor. By the side-band filtering technology, the vibration was detected andanalyzed by a simple intensity interrogation technology.

Radiometric calibration methods for Day/NightWhole Sky Imagers and Extinction Imagers

Janet Shields and Monette Karr

Doc ID: 361939 Received 08 Mar 2019; Accepted 20 Jun 2019; Posted 21 Jun 2019  View: PDF

Abstract: This article discusses the new radiometric calibration methods and results that wehave developed to apply to Day/Night Whole Sky Imager data and Extinction Imager data.Day/Night Whole Sky Imagers detect the presence and location of clouds, and categorizethem by opacity. The new day and night cloud algorithms for these instruments aredocumented elsewhere and these algorithms depend on the use of the new calibrations wehave developed. In this article, we document our calibration methods for determining theabsolute radiance of the Whole Sky Imager scene at each pixel in the images, as well as theresults of the calibrations. The Extinction Imagers are new systems we developed thatdetermine beam transmittance and path extinction for horizontal paths through theatmosphere. These instruments and their algorithms are documented elsewhere, and they alsodepend on the new calibration results. The Extinction Imager algorithms only require relativeradiances, as opposed to absolute radiances. The calibration steps for the two instruments arequite similar, and include dark correction; linearity calibration, which corrects for nonlinearitiesin the signal vs. flux relationship; absolute calibration (for the Whole Sky Imager);and uniformity calibration, which corrects for pixel-to-pixel non-uniformities. Thesedevelopments include methods for handling uniformity calibrations in a system using afisheye lens, and the calibration of both visible and Short Wave IR systems. This articlepresents both the new methods and results, in support of the articles documenting thealgorithms.

Development of space active optics for a whiffletreesupported mirror

Pingwei Zhou, DongXu Zhang, Guang Liu, and Changxiang Yan

Doc ID: 366125 Received 26 Apr 2019; Accepted 19 Jun 2019; Posted 20 Jun 2019  View: PDF

Abstract: The requirements of lightweight primary mirror for large-aperture space telescopes include precise mirror figureand high reliability. However, lightweight mirrors are easy to be affected by environmental disturbances, as they lackstructural stability and rigidity. Active optics can be used to compensate the gravity induced deformation and correct loworderaberrations due to thermal changes and gravity relief during observing periods. Due to its complexity, the activeoptics has been rarely used in space. To validate the technology of space active optics, an active optics system based on thepassive, whiffletree supported mirror is developed. During integration and testing on ground and under normal conditionsin space, the surface accuracy is guaranteed by passive support. Within this hybrid support, the active optics system onlyserves to assist support. This paper focuses on the compatibility between passive multi-supporting system and active optics.We present the prototype of a 0.676 m diameter passive supported lightweight mirror and active support with 9 axial forceactuators. The passive support includes a 9-point axial support and 3 A-frame lateral support. The active actuatordistribution has been optimized with Finite Element Analysis and its experimental performance characterized inrepresentative conditions. The effectiveness of the hybrid passive-active support developed has been verified.

AdaBoost-SCN algorithm for optical fiber vibrationsignal recognition

Hongquan Qu, Tingliang Feng, Yanping Wang, and Yuan Zhang

Doc ID: 359557 Received 04 Feb 2019; Accepted 19 Jun 2019; Posted 20 Jun 2019  View: PDF

Abstract: Recognition of different types of fiber vibration signals is important for the optical fiber pre-warning system(OFPS). Nowadays, the recognition of fiber vibration signals with neural networks is one of common methods inthis field. As a small, well-trained network, stochastic configuration networks (SCN) can achieve good results whenapplied to fiber vibration signal recognition. However, in the case of a limited number of vibration signals, therecognition rate of SCN is also limited. In order to improve the recognition rate of vibration signals, this paperproposes AdaBoost-SCN algorithm. It integrates different SCNs as base classifiers in AdaBoost. The experimentsshow that the testing accuracy of AdaBoost-SCN algorithm is 12.1% higher than that of original SCN when trainingwith a small vibration signal set. The algorithm proposed in this paper not only increases the recognition rate offiber vibration signals, but also improves the generalization ability of original SCN in the case of a limited numberof vibration signal samples.

Tunable triangular frequency modulatedmicrowave waveform generation with improvedlinearity using an optically injected semiconductorlaser

Bowen Zhang, Dan Zhu, Pei Zhou, Chenxu Xie, and Shilong Pan

Doc ID: 365790 Received 23 Apr 2019; Accepted 17 Jun 2019; Posted 17 Jun 2019  View: PDF

Abstract: A photonic approach to generating a triangular frequency modulated microwavewaveform with improved linearity using an optically injected semiconductor laser is proposedand demonstrated. By controlling the optical injection strength to the semiconductor laser atthe period-one (P1) oscillation state to have a triangular shape, a triangular frequencymodulated microwave waveform is generated after the optical-electrical conversion. Amethod based on a generalized regression neural network is proposed to improve the linearityof the generated waveform. By adjusting the parameters of the low-frequency electricaltriangular control signal, the tunability of the center frequency, bandwidth, and time durationof the generated waveform can be realized. In the proof-of-concept experiment, a triangularfrequency modulated microwave waveform with a frequency range from 14 to 24 GHz and atime duration of 2 μs has been successfully generated. The improvement of the linearity of thewaveform is experimentally verified. The performance of the generated triangular frequencymodulated microwave waveforms for reducing the range-Doppler coupling is verified throughthe analyses of the ambiguity function. The tunability of the center frequency, bandwidth, andtime duration is also experimentally demonstrated.

Vibration displacement immunization modelfor measuring the Free Spectral Range bymeans of Laser Self-mixing Velocimeter

Yunkun Zhao, Guanting Xu, Chen Zhang, Keyan Liu, and Liang Lu

Doc ID: 366433 Received 30 Apr 2019; Accepted 17 Jun 2019; Posted 17 Jun 2019  View: PDF

Abstract: In this paper, a vibration displacement immunization model is proposed to measurethe free spectral range of the resonant cavity by using the laser self-mixing velocimeter. Thevalidity of this method is demonstrated by the experimental results that can effectively get ridof the low measurement accuracy related to the self-mixing vibration system due to thevibratory displacement. According to the waveform separation periodic characteristic of theself-mixing velocity signal, of which the free spectral range of a multi-longitudinal modediode laser is calculated to be 88.24 GHz. Moreover, the influences of different targetvelocities and signal sampling frequencies on the free spectral range have been analyzed indetail from the theoretical analysis. In the case of high signal sampling rate and low velocity,which the undistorted velocity signal waveform where at the integral order external cavitymode keeps stable so that it is possible to obtain relatively accurate measured results.

Optical current sensing mechanism undernon-uniform magnetic field

yansong li, Weiwei Zhang, Minhao Wang, and Jun Liu

Doc ID: 366886 Received 07 May 2019; Accepted 17 Jun 2019; Posted 17 Jun 2019  View: PDF

Abstract: The effect of the inhomogeneous magnetic field on the Faraday rotation angleand output light intensity was analyzed using finite element simulation, at different distancesbetween the conductor and the magneto-optical glass. The results show that under aninhomogeneous magnetic field, the magnetic birefringence effect due to the Cotton–Moutoneffect decreases the output light intensity of the straight-through optical path. The Faradayrotation angle is nonlinearly inversely proportional to the distance. Based on these results,which were verified by the theoretical model, a reasonable geometric arrangement of thesensing component of a straight-through optical current sensor is proposed.

An asymmetric multiple-image encryption systembased on chirp z-transform

Edward Fabian Mosso Solano, Omar Suarez, and Nestor Bolognini

Doc ID: 363088 Received 01 Apr 2019; Accepted 17 Jun 2019; Posted 18 Jun 2019  View: PDF

Abstract: An asymmetric multi-image encryption system basedon the chirp z-transform (CZT) is demonstrated. Thesetup is a hybrid architecture that combines a doublerandom-phase encryption scheme in 4 f configuration(DRPE-4f), and a multiplexing procedure based on theCZT. The setup allows to encode multiple images andtransmit them in a single multiplexed element. The decryptionstage has a compact design which allows retrievingseveral data without crosstalk noise. Since thesystem is asymmetric, the users’ decryption keys aredifferent from those used in the encryption process. Itwas demonstrated that the system is resistant to cryptanalysisattacks. The viability of this proposal is verifiedusing virtual optical systems (VOS).

Polarization simulation and analysis of residualbirefringence in optical materials for hyper-NAlithography illumination system

Ruyi Zhou, Linglin Zhu, Chong Zhang, Tiecheng Liu, Aijun Zeng, SERGEY AVAKAW, and Huijie Huang

Doc ID: 363663 Received 01 Apr 2019; Accepted 17 Jun 2019; Posted 18 Jun 2019  View: PDF

Abstract: A polarization simulation and analysis method was carried out for a hyper numerical apertures (NA) lithographyillumination system which is affected by residual birefringence in optical materials. The lens is divided intomultiple small annuli according to finite element method (FEM), and retardation distribution is obtained by settingresidual birefringence of each annulus. Finally, the polarized ray tracing is cleverly changed to geometric raytracing. A hyper-NA lithography illumination system is modeled, and the residual birefringence is set between0.1nm/cm and 1nm/cm. The simulation result shows that the degree of polarization performance degradation isproportional to the magnitude of residual birefringence, and the tolerance of residual birefringence in lensmaterials is below 1nm/cm for the system. The polarization simulation and analysis method provides a powerfultool to calculate the polarized parameters of the system, which is helpful for selecting lens material of the hyper-NAillumination system.

Error diffusion method with optimized weightingcoefficients for binary hologram generation

Yang Gao, Shuming Jiao, Jung-Ping Liu, Ting Lei, and Xiaocong Yuan

Doc ID: 364402 Received 08 Apr 2019; Accepted 17 Jun 2019; Posted 18 Jun 2019  View: PDF

Abstract: Error diffusion method can effectively reduce the quality degradation bypropagating thresholding errors to neighboring pixels in the conversion of a grayscalehologram to a binary hologram. In previous works, the four weighting coefficients in errordiffusion are mostly set as the Floyd-Steinberg coefficient, which was determined empiricallyand originally proposed for photograph processing. In this work, we point out that the Floyd-Steinberg coefficients can be sub-optimal for hologram error-diffusion binarization.Furthermore, the weighting coefficients are optimized for each different hologram adaptively.Compared with conventional coefficients, our optimized coefficients can better preserve thefidelity of reconstructed image after a hologram is binarized.

Development and application of an airbornedifferential absorption lidar for the simultaneousmeasurement of ozone and water vapor profiles inthe tropopause region

Andreas Fix, Felix Steinebach, Martin Wirth, Andreas Schäfler, and Gerhard Ehret

Doc ID: 366225 Received 29 Apr 2019; Accepted 17 Jun 2019; Posted 18 Jun 2019  View: PDF

Abstract: A new, combined, lidar system has been developed which is able to simultaneously measure profiles of ozone andwater vapor onboard of aircraft. The concurrent measurement of these complementary trace species in the uppertroposphere and lower stratosphere allows inferring exchange processes in the tropopause region. Whereas anadvanced H2O differential absorption lidar at 935 nm has successfully been developed and extensively tested at DLR inthe past, we describe here an amendment of this lidar by the addition of a UV channel to measure ozone. Thetransmitter of the ozone DIAL is based on a near-IR optical parametric oscillator that is frequency-converted into theUV spectral range by intracavity sum frequency mixing. Hereby, a continuous UV tuning range of ~ 297-317 nm hasbeen achieved. The average output power in this range is higher than 1 W corresponding to more than 10 mJ perpulse at a repetition rate of 100 Hz. The ozone DIAL system has been carefully characterized both on the ground andin flight. The first simultaneously measured 2-dimensional cross-sections of ozone and water vapor in the uppertroposphere and lower stratosphere have been recorded during the WISE field campaign in 2017 demonstrating thehigh potential of this system for studying exchange processes in this region of the atmosphere.

Fast copolymer network liquid crystals fortunable birefringence colors

Fatemeh Jahanbakhsh and Alexander Lorenz

Doc ID: 366945 Received 07 May 2019; Accepted 17 Jun 2019; Posted 18 Jun 2019  View: PDF

Abstract: A fast switching, tunable color filter was found in a copolymer network liquidcrystal (LC), which was in-situ generated in a conventional LC test cell with parallel alignedglass plates and investigated with polarized light. Polarization filters were used to convert thetunable optical phase retardance of the test cells to birefringence colors as is always possiblein a LC test cell with carefully adjusted cell gap and effective birefringence. The cell gap ofthe samples could be adjusted to a value of 9 μm, which is not easily possible in a polymerLC composite without creating defects. In these samples, the typical pastel colors seenfrequently in birefringent samples could be avoided. The transmittance spectra were recordedand converted to CIE 1931 color coordinates, which showed that the colors seen had areasonable distance to the white point. The electro-optic switching times of the samples wereinvestigated: Fast responses of ton + toff < 5 ms were found, which is an impressive speed fortunable birefringence colors in LCs and LC composites. Upon increasing addressing voltages,a blue-shift of the peak seen in the transmittance spectra was observed. The samples consistedof copolymer network LC, generated from a reactive mixture with mesogenic monomer andnon-mesogenic comonomer. The tunable color was seen selectively in samples with dodecylacrylate as comonomer. The experiments show how even a straight-forward electro-opticexperiment still can result in unexpended findings, which may expand the use of LCcomposites in non-display applications. The polymer morphology in samples with a largercell gap was investigated with scanning electron microscopy and inter-defect distances of ≈40 μm were found. The appearance of defects in test cells with a cell gap of 9 μm could beavoided because the cell gap was much smaller than the measured inter-defect distances intest cells with a larger cell gap.

Surface Emitting Distributed Feedback Laserbased on High-order Gratings

Yingquan Ao, Jinghao Wong, Deming Liu, and Minming Zhang

Doc ID: 365939 Received 24 Apr 2019; Accepted 16 Jun 2019; Posted 17 Jun 2019  View: PDF

Abstract: This paper reports a surface emitting distributed feedback laser based on highordersurface gratings. The proposed device not only retains the advantages of edge emittinglasers such as excellent single-mode property, high internal quantum efficiency and highoutput power, but also obtains other appealing characteristics, such as easy realization of thehybrid integration, simple fabrication process etc. The surface emitting distributed feedbacklaser is analyzed and optimized for better performances using an improved traveling wavemodel.

Correction of keystone distortion in tilted imagingsystems using a digital micro-mirror

Zhiying Liu, Wenbo Li, Yan Li, and Yueqi Wang

Doc ID: 361793 Received 12 Mar 2019; Accepted 16 Jun 2019; Posted 17 Jun 2019  View: PDF

Abstract: To reduce keystone distortion in tilted imaging systems when the object area is much larger than the lensdiameter, an optical system design using a digital micro-mirror device (DMD) is proposed. Keystone distortion isanalyzed, establishing the relationships between keystone distortion and object height, tilt angle of the objectplane, focal length, and object distance. A design with a DMD in a reimaging setup is analyzed, providing a solutionthat eliminates keystone distortion in tilted imaging systems. The method is validated by simulation andexperiment; it provides an innovative method to correct keystone distortion without digital signal processing.

Extinction Imagers for measurements ofatmospheric beam transmittance

Janet Shields and Monette Karr

Doc ID: 361937 Received 07 Mar 2019; Accepted 16 Jun 2019; Posted 17 Jun 2019  View: PDF

Abstract: Optical beam transmittance for a horizontal path of sight through the atmospheremay be measured with transmissometers, which typically are double-ended, with source and areceiver at opposite ends of the path. Determination of the beam transmittance for longerpaths is more challenging in some applications such as monitoring the surround of a ship atsea or an urban environment. Extinction Imaging is a new method we have developed fordetermining the beam transmittance and effective path extinction coefficient over extendedatmospheric paths in multiple directions with a single-ended system. Our new advances to theclassical theory are enabled by use of calibrated imagers operating in visible, near infrared, orshort-wave infrared wavebands. This article presents the theory, hardware, and tests withsupporting instrumentation including transmissometers and point scatter meters.

Mole Fraction Measurement Through a TransparentQuarl Burner Using Filtered Rayleigh Scattering

Yedhu Krishna, Ayman Elbaz, Yuanfu Yue, and Gaetano Magnotti

Doc ID: 362718 Received 19 Mar 2019; Accepted 16 Jun 2019; Posted 17 Jun 2019  View: PDF

Abstract: A filtered Rayleigh scattering system is developed and applied to measure the mole fraction of methane in amethane-air swirl flow through a transparent conical quartz quarl. Light scattering from the location where thelaser beam is incident on the surface of the quarl is orders of magnitudes larger than Rayleigh scattering from thegas mixture of interest. This diffusive scattering is suppressed using molecular absorption by an iodine cell andusing spatial filtering by an optical aperture. Residual stray light accounted for up to 5% of the total signal and hadto be removed for accurate measurements. The flow consisted of a non-premixed mixture of methane and air in thecentral jet surrounded by a strong swirling air flow. Measurements were conducted at a height of 4 mm from thefuel tube’s exit for six different conditions of the swirl flow to demonstrate the ability of the instrument to study theeffects of swirl strength and fuel flow rate on the mixing process. By using a 4-leg pulse stretcher to allow higherlaser energies in the probe volume, large collection optics and a reference iodine cell to monitor laser wavelengthvariations, standard deviations of ~ 0.006 in air and ~ 0.012 in a laminar methane flow were achieved for molefraction measurements.

Analytic model for optimizing a long-range, pulsedLiDAR scanner for small object detection

Alain Quentel, Olivier Maurice, and Xavier Savatier

Doc ID: 363793 Received 29 Mar 2019; Accepted 15 Jun 2019; Posted 17 Jun 2019  View: PDF

Abstract: This paper presents an analytic expression for optimizing a monostatic, incoherent pulsed LiDAR scannerfor small object detection. Using an hexagonal raster-scan pattern, we constrained the link budgetby the need of detecting a distant object at a defined refresh rate with a 100% probability of detection,independently of its position on the scene. From the obtained expression, we minimized the needed lasermean power by playing on the beam divergence and collection efficiency via a drilled hole mirror diameter.An expression for the probability of detection of said object was also deduced. The impact of boththe refresh rate and the distance on the probability of detection was then studied, defining an expressionfor the cutoff distance and giving a complete overview of the system capabilities.

Application of Wiener filter for intensity noisereduction in fiber optic gyroscopes

Chao Zhang, Yao Mao, Xi Zhou, and ren ge

Doc ID: 364682 Received 09 Apr 2019; Accepted 15 Jun 2019; Posted 17 Jun 2019  View: PDF

Abstract: An essential issue for low-noise system application of fiber optic gyroscope (FOG) is to reduce its noiselevel. The relative intensity noise (RIN) of light source is the dominant noise of the FOG when the lightpower on the detector reaches certain level. Noise subtraction method is effective for RIN reduction andeasy to implement in a FOG. This paper theoretically analyzed the factors that influence the result of themethod and deduced the function to calculate the noise suppression ratio that can be achieved. A methodthat uses optimum filter designed based on Wiener filter in the reference detector signal is proposedto improve the subtraction result. A FOG system is set up to test the feasibility of the method. Theexperiment results meet with the theoretical analyze and by using the Wiener filter the achieved noisesubtraction factor reached the limitation that restrained by the optical system and detection circuit.

Novel slot-slot waveguide with negative largeand flat dispersion covering C+L+U wavebandfor on-chip photonic networks

Zhanqiang Hui, min yang, Deng Pan, Tiantian Zhang, jiamin gong, Meizhi Zhang, and Zeng Mei

Doc ID: 361044 Received 25 Feb 2019; Accepted 14 Jun 2019; Posted 19 Jun 2019  View: PDF

Abstract: A novel dual-core slot-slot waveguide with extreme high dispersion is proposed.The high dispersion value at the desired wavelength is obtained based on strong resonancecoupling between two slot-waveguide modes. The properties of dispersion magnitude andbandwidth are numerically analyzed by using the finite difference time domain (FDTD)method with perfectly matched layer (PML) boundary. All numerical simulation resultsreveal that for the optimized geometrical parameters of H1=350nm, L1=565nm, S1=29.3nm,La=1062.39nm, H2=427nm, L2=137.4nm, S2=63.5nm, the maximum dispersion of negative3.645×105 ps·nm-1·km-1 and dispersion full width at half maximum (FWHM) of 6.3nm at1550nm have been obtained. By cascading the slot-slot waveguides with varying width andheight, a large and flattened dispersion of -3.5×105 ps·nm-1·km-1 covering C+L+U wavebandis obtained. Dispersion compensation of 100 Gbit/s return-to-zero-on-off keying (RZ-OOK)optical time division multiplexing (OTDM) signal after 50-km full spectrum single-modeoptical fiber transmission with five different central wavelengths is demonstrated throughsimulation for the first time. In addition, fabrication tolerance of the proposed slot-slotwaveguide is analyzed. Such a waveguide is compatible with complementary-metal-oxidesemiconductor(CMOS) technology and has potential applications in next-generation largescale photonic integrated circuit.

Measurement of propagation of ultrafast surfaceplasmon-polariton pulses using dual-probe scanningnear-field optical microscopy (DSNOM)

Yuta Masaki, Keita Tomita, Yasuhiro Kojima, and Fumihiko Kannari

Doc ID: 365807 Received 26 Apr 2019; Accepted 14 Jun 2019; Posted 20 Jun 2019  View: PDF

Abstract: We report the construction of a diagnostics for ultrafast surface plasmon polariton (SPP) pulses that evolvespatiotemporally in femtosecond and nanometer scales. We constructed two types of scanning near-fieldoptical microscopes (SNOMs) and verified that the temporal waveform of ultrafast SPP pulses can bemeasured by combining spectral interferometry (SI). In the illumination-collection (I-C) mode SNOM, whichuses a single fiber probe to excite samples and collect optical responses, a lock-in detection scheme using alock-in camera detects SI fringes even for extremely weak signal light pulses. With this I-C SI-SNOM scheme,we measured the complex plasmon response functions of gold (Au) nanorods on Ge2Sb2Te5 thin film, both inthe crystal and amorphous phases. For a dual-probe SNOM (DSNOM), a dual-band modulation techniquewas introduced to independently control the probe-sample and probe-probe distances. With the DSNOMand by employing femtosecond SPP pulse excitation, we successfully measured the temporal waveform ofan ultrafast SPP pulse that is propagating on Au thin layer.

Three-Dimensional Confocal Raman TemperatureCharacterization of Electrokinetically PumpedMicrochannels

Guillermo Brinatti Vazquez, Oscar Martinez, and Juan Martín Cabaleiro

Doc ID: 364250 Received 04 Apr 2019; Accepted 14 Jun 2019; Posted 14 Jun 2019  View: PDF

Abstract: A novel method for non invasive, three dimensional temperature characterization in microfluidic devicesis presented. A specially designed confocal microscope was built and used to measure water temperatureby sensing the Raman spectrum variations of the liquid. This is achieved by splitting the spectrum inthe isosbestic point and detecting with two photon counters. The difference between the signals of eachdetector divided by their sum shows a linear dependence with temperature. A fiber coupled laser beamis used to pump the sample with 25 mW of optical power at 405 nm. This allows a 0.8 K temperatureprecision and a 9 mm axial resolution using a 1 second integration time. These features make temperatureprofiling in all dimensions possible, in contrast with previous methods where the information presentin the height of the channel is lost and the whole spectrum needs to be recovered before computing thesample temperature. Using this technique, different geometries of PDMS microchannels sealed with a150 mm thick glass coverslip were studied, showing that heat flow through the glass is the dominatingdissipation mechanism and defines the maximum temperature in the channel. The results show goodagreement with previous work found in literature.

Generation of stable clean ultrashort pulses in asimple all-fiber, all-normal dispersion Yb-dopedmode-locked laser

Pradeep Gupta, Chandra Singh, Pranab Mukhopadhyay, and kushvinder Bindra

Doc ID: 367895 Received 22 May 2019; Accepted 14 Jun 2019; Posted 14 Jun 2019  View: PDF

Abstract: We report an all-fiber, all-normal dispersion Ytterbium (Yb) doped fiber oscillator mode locked by nonlinearpolarization evolution. The mode locking is realized in different pump power regimes by adjusting the polarizationcontrollers. The average output power, pulse energy and compressed pulse duration varies from 60 – 150 mW, 1.4- 3.5 nJ and 350 - 146 fs respectively, when the pump power to the oscillator is varied from 250 to 500 mW.Particularly at 500 mW pump power, the oscillator generates highly chirped 5 ps duration pulses at 42 MHz whichare compressed to 146 fs duration with clean temporal profile. The signal to noise ratio of train of mode lockedpulses is 85 dB, indicating stable mode locking operation. The generalized nonlinear Schrödinger equation issolved numerically to model the passive mode locking in Yb-oscillator which support the experimental results. In achirped pulse Yb-amplifier, the signal power is scaled to 10 W level and the amplified pulse is compressed to 355 fsduration.

Theoretical and experimental study on thermallydependent transient response of the high power CWYb-doped fiber laser

mingjian yan, Siyu Li, Zhigang Han, Hua Shen, and Rihong Zhu

Doc ID: 366120 Received 26 Apr 2019; Accepted 13 Jun 2019; Posted 13 Jun 2019  View: PDF

Abstract: In this paper, transient thermal effects of the Yb-doped fiber and the laser diode (LD) in high power Yb-doped fiberlasers (YDFLs) are studied theoretically to analyze the transient response of the fiber laser. Based on the transientheat conduction equation, we simulated temperature variation of the YDF and LD. It is found that transientresponse of the laser is mainly affected by the thermally induced wavelength shifting of LDs. We modified the rateequations of the fiber laser according to the temperature variation of the LD. To improve the transient responsespeed of the fiber laser, we present three methods: (a) Raising the cooling temperature, (b) increasing the length ofgain fiber, and (c) using YDF with high doping. Finally, experiments were carried out to verify the theory and theresults are in good agreement.

Investigation of Roughness Evolution of Ion SputteredFused Silica Surface

Jianwei Ji, Wei Fan, Wei Gao, chao wang, Yunfei Zhang, Min Xu, and Fang Ji

Doc ID: 361518 Received 04 Mar 2019; Accepted 13 Jun 2019; Posted 13 Jun 2019  View: PDF

Abstract: Ion beam polishing (IBP) has been widely used in smooth surface manufacturing. Nevertheless, the evolution of theprocess and mechanisms of the change in surface roughness have not yet been fully clarified. In this paper, theevolution of surface morphology at the micrometer scale under IBP is studied. First, a series of experimentalresults indicate that the results at the nanometer and micrometer scales are not consistent. Second, a two-steppositioning method that can accurately acquire a contour location before and after polishing is proposed toimprove the reliability of the experimental results at the micrometer scale. This method can help analyze the effectof surface morphology on the amount of material removal, and can eliminate errors introduced by the method ofaveraging measurements at different positions selected randomly. Furthermore, a correlation analysis isconducted, between the profiles of the amount of material removal, and the initial contours, at the micrometerscale. A similarity is revealed, between the removal amount and the initial morphology. Finally, a simulation of theevolution process of morphology is performed, based on the dominant smoothing mechanism. It is consistent withthe experimental results. The simulation reveals that the mass redistribution of surface atoms, induced by the ionbeam, plays an important role in the evolution of the micro-morphology of the surface. The analysis helps tofurther research on roughness optimization at the micrometer scale.

Compact and robust diode laser system technology fordual-species ultracold atom experiments with rubidiumand potassium in microgravity

Julia Pahl, Aline Dinkelaker, Christoph Grzeschik, Julien Kluge, Max Schiemangk, Andreas Wicht, Achim Peters, and Markus Krutzik

Doc ID: 364405 Received 11 Apr 2019; Accepted 12 Jun 2019; Posted 13 Jun 2019  View: PDF

Abstract: We present a compact and robust distributed feedback diode laser system architecture for ultracold atomexperiments with 41K and 87Rb in a mobile setup operating at the ZARM drop tower in Bremen. Oursystem withstands DC accelerations of up to 43 g in operation with only minor adjustments over severaldrop campaigns. Micro-integrated master-oscillator-power-amplifier modules in conjunction with miniaturized, free space opto-mechanics are integrated on a platform with a volume of 43 L. With compact control and driver electronics, this laser system features output power and spectral characteristics suitable for2D+ and 3D-MOT operation, atomic state preparation, Bragg-diffraction based atom interferometry, anddetection

Sensitivity study on the contribution ofscattering by randomly oriented non-sphericalhydrosols to linear polarization in clear tosemi-turbid shallow waters

Masada Tzabari, Wushao Lin, Amit Lerner, David Iluz, and Carynelisa Haspel

Doc ID: 366339 Received 30 Apr 2019; Accepted 12 Jun 2019; Posted 13 Jun 2019  View: PDF

Abstract: The influence of hydrosol non-sphericity on the polarization characteristics of lightunder water is investigated by combining accurate single-scattering models for randomlyoriented spheroidal scatterers with a radiative transfer model that employs Stokes formalismand considers refraction of direct unpolarized solar radiation and 100% linearly polarizedradiation at the air-water interface followed by single scattering. Variations in what we callthe “linear polarization phase function” (the degree of linear polarization (DoLP) as a functionof scattering angle and the angle of linear polarization (AoLP) as a function of scatteringangle) are examined for a wide range of spheroid aspect ratios and complex refractive indicesof hydrosols. Implications for polarization-sensitive marine organisms and for remote sensingof the marine environment are discussed.

The SLS-based Compact Thermal Imager for theInternational Space Station

murzy Jhabvala, Donald E. Jennings, Compton Tucker, anh la, Beth Keer, Elizabeth Timmons, Robert Stone, Thomas Flatley, frank cepollina, sachidananda babu, allen lunsford, Justin Cassidy, David Parker, Mani Sundaram, Jason Bundas, William Squicciarini, Paul Finneran, Ireneusz Orlowski, Chris Fetter, and Markus Loose

Doc ID: 365944 Received 26 Apr 2019; Accepted 12 Jun 2019; Posted 13 Jun 2019  View: PDF

Abstract: The Compact Thermal Imager (CTI) is a dual-band, strained-layer superlattice (SLS) detector-basedinstrument that was installed on the exterior of the International Space Station (ISS) in conjunction withthe third Robotic Refueling Mission 3 (RRM3) in 2018. The CTI serves as a pathfinder for futurethermal infrared capability on Landsat. The CTI incorporates an SLS hybrid, a dual-band 3-5 and 8-10μm, electrically switchable, 320 x 256 array with 30 μm2 pixels, bonded to an Indigo ISC0903 ReadoutIntegrated Circuit (ROIC). The telescope was built around an integrated detector cryocooler assemblydeveloped under a NASA Small Business Innovative Research (SBIR) award with QmagiQ, LLC. Thecooler is a Ricor K508 and the front-end optics is a custom designed, doublet lens telescope with a 150mm focal length. The ground resolution is 80 meters/pixel from the ISS altitude of 400 km. A filtercreates two spectral channels from the dual-bands, 3.3-5.4 and 7.8-10.2 microns. The detector hybridcontrol electronics is a custom developed system based on the Teledyne Imaging Systems SIDECARApplication Specific Integrated Circuit (ASIC). This module provides the electronic interface from theRRM3 SpaceCube on-board processor to the detector/ROIC assembly. The primary goal of thismission was to perform a technology demonstration of the SLS technology and the commercial coolertechnology elevating the Technology Readiness Level (TRL) to TRL 9 on a bare-bones budget andrelatively fast development cycle. Some science objectives include locating fires, approximate landsurface temperatures, monitor evapotranspiration, sea ice and glacier dynamics. In this paper, we willpresent the design of the focal plane, optics, electronics and mechanical structure of the CTI. We willalso describe the operation and qualification tests that were performed to bring the CTI to the NASATRL 6 in preparation for the launch on a SpaceX Dragon from the Kennedy Space Center.

Modeling and analysis of high sensitivity refractiveindex sensors based on plasmonic absorbers withFano response in the near-infrared spectral region

Fatemeh Tavakoli, ferdows Zarrabi, and Hamed Saghaei

Doc ID: 365104 Received 15 Apr 2019; Accepted 11 Jun 2019; Posted 12 Jun 2019  View: PDF

Abstract: In this paper, we present various optical metamaterial nano-absorbers with the aim of improving the refractiveindex sensitivity using Fano response. The proposed absorbers consist of various parasitic elements such as singlecross, broken cross, Jerusalem cross, and also single L and double L models. We numerically study their absorptionand reflection using three-dimensional finite-difference time-domain method and calculate the sensitivity andfigure of merit (FOM) in every absorption peak (reflection dip). Our simulations reveal that the Fano resonance atlonger wavelength can be used for increasing the sensitivity and FOM. The proposed absorbers have been coatedwith an external material with a maximum thickness of 100 nm and refractive indices in the range of 1.05 to 1.2.We also study and compare the FOM for these structures. They are modified for 900 nm and 1200 nm to 1300 nm.The maximum FOM is achieved around 2400 RIU-1 for the double L nano-absorber coated with 1.05 indexedmaterial while its sensitivity is 473 nm/RIU. This absorber is an appropriate component for the design of highlysensitive optical sensors.

Deep Iterative Reconstruction for Phase Retrieval

Cagatay Isil, Figen Oktem, and AYKUT KOC

Doc ID: 365141 Received 25 Apr 2019; Accepted 11 Jun 2019; Posted 12 Jun 2019  View: PDF

Abstract: Classical phase retrieval problem is the recovery of aconstrained image from the magnitude of its Fouriertransform. Although there are several well-knownphase retrieval algorithms including the hybrid inputoutput(HIO) method, the reconstruction performanceis generally sensitive to initialization and measurementnoise. Recently, deep neural networks (DNNs) havebeen shown to provide state-of-the-art performance insolving several inverse problems such as denoising, deconvolution,and superresolution. In this work, wedevelop a phase retrieval algorithm that utilizes twoDNNs together with the model-based HIO method. First,a DNN is trained to remove the HIO artifacts, and isused iteratively with the HIO method to improve thereconstructions. After this iterative phase, a secondDNN is trained to remove the remaining artifacts. Numericalresults demonstrate the effectiveness of ourapproach, which has little additional computationalcost compared to the HIO method. Our approachnot only achieves state-of-the-art reconstruction performancebut also is more robust to different initializationand noise levels.

Dual-focal-plane augmented reality head-updisplay using a single picture generation unitand a single freeform mirror

Zong Qin, Shih-Ming Lin, Kuang-Tso Luo, Cheng-Huan Chen, and Yi-Pai Huang

Doc ID: 362210 Received 15 Mar 2019; Accepted 11 Jun 2019; Posted 11 Jun 2019  View: PDF

Abstract: Two or more focal planes are required in augmented reality head-up displays (ARHUDs) to respectively present basic and interactive driving information to car drivers;whereas, solutions using two separated picture generate units (PGUs) with two sets of opticsincur increased cost, reduced reliability, and expanded volume. To develop an AR HUD usinga single PGU and a single curved mirror, we propose to set two logically separated regions ona single PGU and optically relay one of them to a new position to create two focal planes. Asingle freeform mirror acquired through careful optical and mechanical design optimizationproduces high image quality in an eyebox of 120 mm by 60 mm, simultaneously for a farimage (9 m, 10° by 3°) and a near image (2.5 m, 6° by 2°). Finally, an AR HUD product witha compact volume of 8.5 L is fabricated to experimentally verify the design.

Development of an all-sky imaging system forcloud cover assessment

Fa Tao, Wanyi Xie, Yiren Wang, and Yingwei Xia

Doc ID: 363528 Received 27 Mar 2019; Accepted 11 Jun 2019; Posted 11 Jun 2019  View: PDF

Abstract: This study develops a novel automatic all-sky imaging system, namely, all-skycamera (ASC) system, for cloud cover assessment. The proposed system does not requireconventional solar occulting devices and can capture complete hemispheric sky images.Cloud detection is performed innovatively using convolutional neural network model (i.e., theoptimized U-Net model). Experiments demonstrate that the optimized U-Net model caneffectively detect clouds from sky images. In terms of cloud cover, the estimation results ofthe ASC system exhibit a high correlation with those obtained via manual observation,thereby indicating the applicability of the ASC system in ground-based cloud observation andanalysis.

A novel calibration method for hand-eye system withrotation and translation couplings

Yuan Zhang, Zhicheng Qiu, and Xianmin Zhang

Doc ID: 363653 Received 28 Mar 2019; Accepted 11 Jun 2019; Posted 11 Jun 2019  View: PDF

Abstract: This paper develops a novel hand-eye calibration method for hand-eye system with rotation and translationcoupling terms. First, a nonlinear camera model with distortion terms and a model of hand-eye system withrotation and translation coupling terms are established. Based on non-linear optimization method and reverseprojection method, a decoupling calibration method for lower degree of freedom hand-eye system is proposed.Then the path planning for the calibration process is carried out. Based on the analysis of coupling constraint andhand-eye system motion constraints, three types of hand-eye calibration paths with high efficiency and easyoperation are developed. In addition, the influence of key parameters on hand-eye calibration accuracy is analyzed.Finally, calibration experiments and parametric influence experiments are carried out. The results demonstratethat the proposed method is effective and practical for calibrating the hand-eye system.

Compact General Interference Hybrid-PlasmonicMultimode Interferometers used for Optical Hybrid

Jin Wang, Nannan Ning, Zhen Wang, Guoning Li, Ji Xu, and Yuqing Lu

Doc ID: 363868 Received 02 Apr 2019; Accepted 11 Jun 2019; Posted 11 Jun 2019  View: PDF

Abstract: We propose three general interference multimode interferometers (MMIs) based on hybrid plasmonic waveguides(HPW). Among them, the general 2×2 and 4×4 MMI are designed for 90° optical hybrid, while the 3×3 MMI is for120° optical hybrid. First, by considering the mode interference characteristics inside the multimode HPWs, acompromise between the number of guided modes and the device length is obtained at a determined height of theSiO2 interlayer of HPW. Also, by analyzing the characteristics of multimode propagation in the HPW-MMI, it is foundthat the optimal positions of self-images would shift from their theoretical ones. In addition, tapered HPW sectionsare implemented to improve the coupling efficiencies for lights coupled into/out of the multimode section.Therefore, by optimizing the width and length of the multimode section, and especially the position of the inputand output single-mode waveguides, the appropriate structure parameters of three HPW-MMIs are obtained,where the footprints of the 2×2, 3×3, and 4×4 HPW-MMIs are only 1.96×5.4 μm2, 2.18×12.0 μm2, and 2.52×11.5 μm2,respectively. The simulation results show that, at the wavelength of 1550 nm, the 2×2 HPW-MMI exhibits atransmission of 75.6%, a maximum transmissions imbalance of 0.55 dB, and a phase error of 3.68°; the 3×3 HPWMMIexhibits a transmission of 69.2%, a maximum transmissions imbalance of 0.43 dB, and a phase error of 4.66°,the 4×4 HPW-MMI exhibits a transmission of 68.5%, a maximum transmissions imbalance of 0.91 dB, and a phaseerror of 4.81°. All these performances meet the standard industry requirements.

Effects of multiplication layer on dark currentcomponents of InGaAs/InP avalanchephotodiodes

Aofei Liu, Junqin Zhang, Hailong Xing, and yintang yang

Doc ID: 365549 Received 19 Apr 2019; Accepted 10 Jun 2019; Posted 11 Jun 2019  View: PDF

Abstract: Based on results from the Silvaco Atlas device simulation software, a separateabsorption grading charge multiplication (SAGCM) InGaAs/InP avalanche photodiode hasbeen modeled. The Shockley-Reed-Hall (SRH) current, avalanche amplification current, TATand BBT current are combined and considered as the dark current. Individual component ofthe dark current has been obtained separately through numerical simulation. Due to themultiplication effect, the influence of the multiplication layer on the dark current componentshas been studied. The simulation results are analyzed based on semiconductor physicsknowledge. The conclusions presented provide some theoretical guidance for the optimumdesign of avalanche photodiodes.

High speed polarized low coherence scanninginterferometry based on spatial phase shifting

Jeon woo, Hee Won Jung, Hyo Bin Jeong, and Ki-Nam Joo

Doc ID: 368061 Received 21 May 2019; Accepted 10 Jun 2019; Posted 10 Jun 2019  View: PDF

Abstract: In this investigation, we describe the polarized low coherence scanning interferometry (PLCSI) to enhance themeasurement speed based on the spatial phase shifting technique by using a polarized CMOS camera. In everyscanning step, the visibility of the correlogram can be directly extracted by the spatial phase shifting. PLCSI doesnot need any scanning conditions such as smaller scanning step size than that determined by the Nyquist samplinglimit and equidistant scanning step, which restrict the measurement speed of the typical low coherence scanninginterferometry (LCSI). Even, the measurement data can also be significantly reduced due to the larger scanningstep size. PLCSI can be comparable to confocal scanning microscopy in the view of monitoring visibilities. In theexperiments, three types of specimens such as a plane mirror, a concave mirror and a step height specimen weremeasured by PLCSI with various scanning step size and it was confirmed that the surface profiles were successfullyreconstructed. Moreover, the compensation technique of the surface profile, precisely determined by the phaseinformation, was also discussed.

Spatial light modulator phase calibration basedon spatial mode projection

Katherine Isabel Remulla and Nathaniel Hermosa

Doc ID: 360200 Received 14 Feb 2019; Accepted 10 Jun 2019; Posted 11 Jun 2019  View: PDF

Abstract: Spatial light modulators (SLMs), which are devices used to manipulate the phase ofan incident wavefront, are prolific in fields such as optical trapping, dynamic diffractive opticalelements, and display technology. Of the many challenges inherent to using SLM, one of themost ubiquotous is the calibration of the device’s phase shifting mechanism. In this article, wepresent a new SLM calibration method based on spatial mode projection. We also implement adata processing technique to our data to generate accurate look-up tables from our calibrationcurves. We then evaluate the success of our method by propagating Laguerre-Gauss beamswith computer generated holograms. Our results show that the qualitative analysis of modespropagated using the spatial light modulator is a viable method of assessing performance. On awhole, we show that spatial mode projection provides clear performance improvements in theSLM’s phase-modulating capabilities.

Hierarchical quality-guided phase unwrappingalgorithm

Heping Zhong, Jinsong Tang, Zhen Tian, and Haoran Wu

Doc ID: 362784 Received 18 Mar 2019; Accepted 10 Jun 2019; Posted 10 Jun 2019  View: PDF

Abstract: A hierarchical quality-guided phase unwrapping algorithm in shared memory environment is proposed. Firstly,wrapped phase is divided into regular blocks, and local wrap counts of every block are obtained by quality-guidedstrategy. Then, the gradient of block wrap counts of adjacent blocks and the quality of every block are defined bythe boundary local wrap counts of every block. Each block data can be regarded as an abstract phase point, and thequality-guided strategy can be used again to solve the block wrap counts of each block. Finally, the absolute wrapcounts of each phase point are obtained by adding local wrap counts and corresponding block wrap counts, andthen the final unwrapped phase is obtained. The performance of the proposed algorithm is verified throughunwrapping experiment performed on simulated data and real interferometric synthetic aperture sonar (InSAS)wrapped phase in shared memory environment. The results show that the proposed method greatly improvesphase unwrapping efficiency while maintaining the correctness of unwrapped results.

Super-wavelength, Wavelength and Sub-wavelengthLaser Induced Periodic Surface Structures on Zn andTheir Energy Dispersive X-ray Analysis

Atal Mundamajhi, P. Chandrakanta Singh, and Susanta Das

Doc ID: 364665 Received 10 Apr 2019; Accepted 10 Jun 2019; Posted 13 Jun 2019  View: PDF

Abstract: In this work we demonstrated simultaneous generation of three types of Laser Induced Periodic Surface Structures (LIPSS) on the metalsurface by processing Zn with a linearly polarized femtosecond (fs) laser pulses of 100 fs duration at wavelength 800 nm. In the centre of the laserprocessed region (a line), the period was found to be as high as 1470 nm (super-wavelength LIPSS) where as at the outer region the LIPSS periodwas found to be as small as 200 nm (sub-wavelength LIPSS). In between these two regions, the LIPSS were found to have period of 800 nm(wavelength LIPSS). In the Energy Dispersive X-ray (EDX) study, the Zn : O atomic ratio is found to be 70% : 30% in LIPSS containing region. Incontrast to this in region containing no LIPSS, the Zn : O atomic ratio is found to be 90% : 10%. Discussion is given on the significance of the observedLIPSS, in terms of their possible growth mechanism and comparison with previously published results.

Demonstration of a cost-effective single-pixel UVcamera for flame chemiluminescence imaging

Jiaqi Zhang, Qian Wang, Jinghang Dai, and Weiwei Cai

Doc ID: 362645 Received 21 Mar 2019; Accepted 09 Jun 2019; Posted 10 Jun 2019  View: PDF

Abstract: Combustion is the dominant form of energy conversion for a span of power systems such as engines and powerplant boilers. It is an extremely complicated process which produces a huge number of intermediate products thatusually feature non-uniform spatial distributions. Among those intermediate products, free radicals emitting in theUV band are of special interest because they contain abundant useful information of the target flame. Imagingmethods such as planar laser-induced fluorescence or chemiluminescence imaging with UV cameras are ofparamount importance to resolve the non-uniformities for a better understanding of combustion. However, amajor limitation of UV cameras is that they are usually expensive, especially when multiple cameras are needed,such as in a tomographic system. In this work, we report the attempt of flame imaging with a cost-effective singlepixelUV camera which enables 2-D spatial resolution of a single-pixel detector through light modulation toovercome this limitation. Meanwhile, numerical studies were conducted to systematically assess the performanceof a few representative reconstruction algorithms. The impact of important factors such as sampling ratio andmeasurement matrix were also investigated. A validation as well as a demonstrative experiment was alsoconducted to reconstruct a laminar diffusion flame. The high similarity between the reconstruction and the imagetaken by a CMOS camera proves the feasibility of flame imaging with a single-pixel camera.

Tunable Tm/Ho-codoped fiber lasers based onextensible liquid core between a pair of fusedmultimode-single mode fibers

Hajime Sakata, Fuma Kosaka, Masanari Kubota, Ryota Kimbara, and Kengo Okada

Doc ID: 363763 Received 29 Mar 2019; Accepted 09 Jun 2019; Posted 10 Jun 2019  View: PDF

Abstract: We present mechanically-tunable Tm/Ho-codoped fiber lasers based on multimode interference in single modemultimode-single mode structures. The intermediate multimode fiber (MMF) is separated into two segments witha liquid core in-between. The mode field diameter of the single-mode fiber is designed to 13 μm for the MMF havinga core diameter of 105 μm. Tunable range is attained to 64 nm by extending the effective length of the MMF. Thelaser wavelength is tuned over the ranges of 1809–1866 nm and 1866–1930 nm for the initial MMF lengths of 35.3mm and 34.5 mm, respectively.

Temperature dependence of energy transfer betweenNd3+ and Yb3+ ions in phosphate glass

LISI XIA, Zhiquan Lin, Shiyu Sun, Qiang He, Fan Wang, Chunlei Yu, Lili Hu, and Qiuhong Yang

Doc ID: 364075 Received 02 Apr 2019; Accepted 09 Jun 2019; Posted 10 Jun 2019  View: PDF

Abstract: The temperature dependence of energy transfer between Nd3+ and Yb3+ ions in phosphate glass were investigatedwith emission spectra, time-resolved spectroscopy and luminescence lifetimes. The time-resolved spectrogramsvividly displayed processes of both Nd3+→Yb3+energy transfer and Yb3+→Nd3+energy transfer. The impact oftemperature on energy transfer rate has been studied by analyzing the cumulative rise times and decay times ofYb3+ upon excitation of Nd3+ and the cumulative rise times and decay times of Nd3+ upon excitation of Yb3+ atdifferent temperatures, respectively. It has been found that both Nd3+→Yb3+ energy transfer and Yb3+→Nd3+ energytransfer get accelerated along with increasing temperatures in a certain temperature range.

Proof of concept for adaptive sequential optimizationof free-space communication receivers

Carlos Carrizo, Ramon Mata Calvo, and Aniceto Belmonte

Doc ID: 363611 Received 27 Mar 2019; Accepted 08 Jun 2019; Posted 10 Jun 2019  View: PDF

Abstract: In a downlink scenario, the performance of laser satellite communications is limited due to atmosphericturbulence, which causes fluctuations in the intensity and the phase of the received signal leading to anincrease in bit error probability. In principle, a single-aperture phase-compensated receiver, based onadaptive optics, can overcome atmospheric limitations by adaptive tracking and correction of atmosphericallyinduced aberrations. However, under strong-turbulence situations, the effectiveness of traditionaladaptive optics systems is severely compromised. We have developed an alternative intensity-based techniquethat corrects the wave-front by iteratively updating the phases of individual focal-plane speckles,maximizing the power coupled into a single-mode fiber. Here, we present the proof of concept for thismethod. We show how this technique offers around 4 dB power gain with less than 60 power measurementsunder strong turbulence conditions. It delivers a good performance in different turbulent regimes,and it shows robustness against severe deterioration of the signal to noise ratio.

HIRAS noise performance improvement based onprinciple component analysis

Lu Lee, Peng Zhang, Chengli Qi, XIUQING HU, and Mingjian Gu

Doc ID: 362838 Received 19 Mar 2019; Accepted 08 Jun 2019; Posted 10 Jun 2019  View: PDF

Abstract: Mirror jitters around a bias tilt angle can make noise performance degradation for a space-borne Michelsoninterferometer. A numerical model simulates the Hyperspectral Infrared Atmospheric Sounder (HIRAS) spectraaffected by the mirror jitters. According to the simulation, mirror jitters mainly generate spectrally correlatednoise, which can be estimated by subtracting the random noise component from the total noise. The random noiseis estimated through a Principle Component Analysis (PCA) technique. Applying the PCA noise estimator as adiagnostic tool to monitor the noise level in the process of the bias tilt angle tuning, an optimized HIRAS noiseperformance is achieved with the correlated noise component minimized.

A Phase Unwrapping Method Based on ImprovedQuadratic Pseudo Boolean Optimization

Hao Hongxing, Lingda Wu, and Yu Ronghuan

Doc ID: 364818 Received 19 Apr 2019; Accepted 08 Jun 2019; Posted 12 Jun 2019  View: PDF

Abstract: Maximum a posteriori estimation of a Markov RandomFields(MRFs) is a popular research in the area of computervision, and many algorithms are proposed to deal with thistype of problems. Phase unwrapping problem is modelledas the optimization of MRFs in this research, and the binaryalgorithm, Improved Quadratic Pseudo Boolean Optimization(QPBOI), is utilized to solve the phase unwrappingproblem. Both the interferometric phases generatedfrom the commonly used computer simulated surfaces andalso real terrains are researched in the experimental section,and the unwrapping results are compared. The proposedalgorithm gets comparable unwrapping results as thestate of the art unwrapping method but costs less time forthe large scale phase images.

Pre-distortion and Pre-equalization for Non-Linearitiesand Low-Pass Effect Mitigation in OFDM-VLC Systems

Luis Carlos Mathias, José Carlos Marinello, and Taufik Abrao

Doc ID: 363228 Received 25 Mar 2019; Accepted 07 Jun 2019; Posted 10 Jun 2019  View: PDF

Abstract: The orthogonal frequency division multiplexing(OFDM) transmission is a promising candidate forvisible light communication (VLC) applications. However,the nonlinearity in the optical power emittedby the high-power light emitting diode (HPLED) as afunction of current and temperature implies in drasticOFDM-VLC performance degradation. The first partof this work experimentally confirms and models thisdegradation due to temperature in a white HPLED.The higher attenuation at high frequencies, which isinherent to the HPLED and which is accentuated bythe effect of the intrinsic capacitance of the photodiode,is another factor of degradation due to the reductionin the signal-to-noise ratio (SNR) at the receiver forsuch frequencies. For the mitigation of these combinedeffects, we propose a pre-distortion and a digitalpre-equalization scheme using a luminous feedbacksignal at the transmitter side. The VLC system ismodeled so that the operating points are mathematicallydeduced and evaluated by simulations and byan experimental setup. By allowing the linearizationof the transmitted light signal and the maintenanceof a uniform SNR among all OFDM subcarriers, theperformance improvement is confirmed in comparisonwith other schemes, such as a VLC system withoutpre-distortion, pre-distortion with fixed parameters, aswell as a simple post-equalization.

Tunable optical delay with low intensity loss in a cascade structureEr3+-doped optical fiber amplifier

Yuan Gao, Wei Qiu, yuqi wu, xian zhang, zhi li, pin lv, and Qiuli Jiang

Doc ID: 367384 Received 13 May 2019; Accepted 07 Jun 2019; Posted 10 Jun 2019  View: PDF

Abstract: In this paper, we propose a new pumping scheme—dual-frequency laser-pumped cascadestructure of Er3+-doped optical fiber based on the theory of coherent population oscillation. Whilerealizing slow light transmission, the loss of output signal light power is reduced. Using thenumerical simulation, we compare the effects of single fiber without pumping, 980nm singlepumping single fiber and dual-frequency laser-pumped cascade structure of Er3+-doped opticalfiber on signal light intensity loss coefficient τ and maximum time delay with the increase of inputsignal light power. The results show that the signal light intensity loss coefficient τ of the threestructures decrease gradually with the increase of input signal light power. However, thetransmission of lower signal light intensity loss coefficient τ =0.08 and a larger time delay of0.15 ms can be obtained under the dual-frequency laser-pumped cascade structure of Er3+-dopedoptical fiber. On the basis of dual-frequency laser-pumped cascade structure of Er3+-doped opticalfiber, the signal light intensity loss coefficient τ decreases gradually with the increase of pumpratio M (M=P1480:P980) and the decrease of length ratio N (N=L2:L1,L1 and L2 represent the lengthof the first and second cascaded optical fibers,respectively).Moreover, we compare the effects ofion density of the Er3+-doped optical fiber on the time delay of three structures. Dual-frequencylaser-pumped cascade structure of Er3+-doped optical fiber can provide larger time delay andsmaller signal light intensity loss coefficient τ at low ion density of the Er3+-doped optical fiber.

Engineering the structural, plasmonic and opticalproperties of multilayered aluminum-doped zincoxide metamaterial grown by pulsed layer deposition

Priscilla Kelly, Wenrui Zhang, Mingzhao Liu, and Lyuba Kuznetsova

Doc ID: 364151 Received 03 Apr 2019; Accepted 07 Jun 2019; Posted 07 Jun 2019  View: PDF

Abstract: We engineer a tunable multilayered aluminum-doped zinc oxide metamaterial with low-loss and high-carrierconcentration using the pulsed laser deposition. The results of the scanning probe microscopy study showexcellent surface quality with a root mean square roughness value of 1.88 ± 0.07 nm. The transmission electronmicroscopy measurements indicate a clear layer-by-layer structure of the multilayered samples. The opticalpermittivity results, obtained using the ellipsometry approach, show that the hyperbolic dispersion of thedielectric constant (Re (ε∥) > 0, Re (ε⊥) < 0) is achieved in the near IR spectral range. The low imaginary part of theoptical permittivity Im (ε⊥) = 0.003 and Im (ε||) = 0.011 is achieved for the optimized sample at the epsilon-nearzerospectral point (Re (ε⊥) = 0 at 1885 nm). The results of the ellipsometry analysis show that the systematicvariation of different fabrication conditions, such as AZO/ZnO ratio, the thickness of an individual layer, total film’sthickness, and deposition temperatures allows for tuning the plasma frequency ωp and damping frequency γp of theinvestigated samples which is a promising approach for the future precise engineering of linear and nonlinearoptical properties of the multilayered aluminum-doped zinc oxide metamaterial.

1550-nm external cavity diode laser withenhanced SMSR based on polarizationmismatch by grating rotation

Yan Wang, Hao Wu, Xing Zhang, Jianguo Liu, Chao Chen, Yubing Wang, Zhou yinli, Lei Liang, jun zhang, Qin li, and Lijun Wang

Doc ID: 366164 Received 26 Apr 2019; Accepted 07 Jun 2019; Posted 07 Jun 2019  View: PDF

Abstract: A tunable external cavity diode laser (ECDL) with high side mode suppressionratio (SMSR) is demonstrated. The ECDL is operated at both strong and weak feedbacksteady-states with single longitudinal mode. Compared with the strong feedback mode, theSMSR of the weak feedback mode is significantly enhanced by rotating the grating along theaxis of incident beam which changes the polarization orientation versus the grating grooves.The highest SMSR of the weak feedback mode is 54 dB at the injection current of 300 mA.The tunable range of the ECDL with weak feedback mode reaches 130.9 nm.

Grinding and chemical mechanical polishingprocess for micropore X-ray optics fabricatedwith deep reactive ion etching

Aoto Fukushima, Maiko Fujitani, Kumi Ishikawa, Masaki Numazawa, Daiki Ishi, Ryota Otsubo, Hikaru Nagatoshi, Hikaru Suzuki, Tatsuya Yuasa, Takaya Ohashi, Kazuhisa Mitsuda, and Yuichiro Ezoe

Doc ID: 361489 Received 04 Mar 2019; Accepted 07 Jun 2019; Posted 10 Jun 2019  View: PDF

Abstract: Silicon micropore optics using deep reactive ion etching of silicon wafers have beenbeing developed for future X-ray astronomy missions. Sidewalls of the micropores through athin wafer with a typical thickness of hundreds m and a pore width of 20 m are used forX-ray mirrors. However, burr structures observed after etching with a typical height of a fewm at the micropore edges are known to significantly reduce X-ray reflectivity. A new grindingand chemical mechanical polishing process is introduced to remove the burr structures. Bothsides of the silicon wafer was ground and precisely polished after etching. X-ray reflectivitymeasurements confirmed an increase of reflectivity by 2–15 times at incident angle 0.8–0.2 deg.The surface microroughness worsened from 2:0 0:2 nm rms to 7:8+0:6􀀀0:8 nm rms; however, anadditional annealing recovered the smooth surface and the estimated surface microroughness was<1.4 nm rms. This new process enables not only removing the burr structures but also choosinga flat part of the sidewalls for better angular resolution.

Design of simple fisheye lens

Lirong Fan and Lijun Lu

Doc ID: 367152 Received 08 May 2019; Accepted 06 Jun 2019; Posted 06 Jun 2019  View: PDF

Abstract: We present a simple design of fisheye lens which consists of a pre-group optics, two negative meniscus lenses, anda post-group optics, three singlet lenses. The pre-group optics is first designed according to the requirements forthe compression ratio of field angle and the transverse dimension of the lens. The balance conditions of the fieldcurvature, longitudinal and transverse chromatic aberrations between the pre-group and post-group optics andthe requirement of the total optical power of the system are used to determine the optical powers and the spacingof the lens of the post-group optics in the thin-lens model; the initial curvature radii of the three lenses are thendetermined according to the resultant optical powers of lenses, and their thicknesses are determined to the exactbalance of field curvature, longitudinal and transverse chromatic aberrations. Finally, we apply self-adaptive andnormalized real-coded genetic algorithm to optimize the starting design of the fisheye lens obtained above.

A silicon nitride/titanium oxide hybrid waveguide design enablingbroadband athermal operation

Jianbin Ma, Yu Sun, and Shaowu Chen

Doc ID: 363506 Received 10 Apr 2019; Accepted 05 Jun 2019; Posted 11 Jun 2019  View: PDF

Abstract: This paper presents a special design of a new kind of silicon nitride/titanium oxide hybrid waveguide withmulti-layer materials laminate structure aiming at broadband athermal operation. By incorporating three layers of titaniumoxide whose thermo-optic coefficient (TOC) is negative in the waveguide core and upper cladding regions, the thermal drift ofthe conventional strip waveguide induced by the positive TOC of silicon nitride is fully compensated, with the effective TOC ofthe hybrid waveguide achieving zero at 1550 nm and only varying extreme slightly within ±6 × 10-7 /K in the wavelength bandfrom 1350 nm to 1850 nm. In addition, due to the inherent alternate growth manner of titanium dioxide and silicon nitride thinlayers, this new kind of multi-layer materials laminate structure waveguide holds the potential of avoiding the challenginggrowth of low stress crack-free single layer silicon nitride film thick enough for realizing anomalous dispersion waveguide.What’s more, we numerically demonstrate the different influence of the temperature change on optical frequency combgeneration between the traditional waveguide and the hybrid waveguide, the athermal hybrid waveguide is much moretemperature insensitive than the strip waveguide.

Reconfigurable Characteristic of Graphene Plate

khatereh moradi, Ali Pourziad, and Saeid Nikmehr

Doc ID: 365469 Received 18 Apr 2019; Accepted 05 Jun 2019; Posted 05 Jun 2019  View: PDF

Abstract: In this paper, the potential of graphene in designing of the reconfigurable nano-antennas is investigated basedon the Characteristic Modes Analysis (CMA) approach. The Characteristic Modes (CMs) of a graphene plate arecalculated by Electrical Field Integral Equation (EFIE) technique. The effects of the dimension and chemicalpotential of the graphene plate are investigated on the CMs. For achieving CMs, a novel formulation isintroduced. The results of this analysis can be useful in designing of efficient nano-antennas for wirelesscommunications in the THz band.

Cryptographic key distribution over a public network via variance-based watermarking in compressivemeasurements

Wen-Kai Yu

Doc ID: 363275 Received 25 Mar 2019; Accepted 05 Jun 2019; Posted 06 Jun 2019  View: PDF

Abstract: The optical communication has an increasing need for security in public transmission scenarios. Herewe present a protocol for cryptographic key distribution over a public network via photon-counting compressiveimaging system with watermarking, which utilizes watermarking technique to distribute securekeys, and uses reconstructed images for simultaneous identity authentication and tampering identification.The watermark is embedded in the rearranged compressed measurements of the object, and thenthe signal is transmitted through a public network. At the receiving terminal, the legitimate users caneasily extract the watermark as the cryptographic key by using initial keys and the variance characteristicof random measurements. Artificial tampering and attacks can be detected by the accurately retrievedimages. The realization of this protocol is a step forward toward the practical applications, and will bebeneficial for the broader fields of optical security in many ways.

High-Performance position-sensitive detectorbased on the lateral photovoltaic effect inMoSe2/p-Si junctions

Xiaofeng Zhao, Lingrui Zhang, Qiying Gai, Chang Hu, and Xianjie Wang

Doc ID: 365742 Received 22 Apr 2019; Accepted 05 Jun 2019; Posted 06 Jun 2019  View: PDF

Abstract: Optoelectronic position-sensitive detectors (PSDs) based on the lateral photovoltaic effect(LPE) have been a focus of research due to their ability to detect very small displacements. In thispaper, we investigate the LPE properties of MoSe2/p-Si junctions prepared using pulsed laserdeposition. The LPE shows a good linear dependence with the position of the laser spot. A largepositional sensitivity and a fast optical relaxation time of 563 mV mm-1 and 2 μs, respectively, wereobserved in the MoSe2 (10 nm)/p-Si junction. The influence of the laser power and the wavelength onthe LPE suggests that the observed response originates from the photoelectric effect. The largepositional sensitivity and fast relaxation time of the LPE make the MoSe2/p-Si junction a promisingcandidate for position–sensitive detectors.

Polymer multimode waveguide bend based onmultilayered Eaton lens

Seyed Hadi Badri, Hassan Rasooli Saghai, and Hadi Soofi

Doc ID: 366443 Received 30 Apr 2019; Accepted 05 Jun 2019; Posted 06 Jun 2019  View: PDF

Abstract: Reducing the bending radius of low-index contrast waveguides is essential in reducing the size of the integratedoptical components. A polymeric multimode waveguide bend is presented based on the Eaton lens. The ray-tracingcalculations are utilized to truncate the Eaton lens in order to improve the performance of the bend. The truncationof the lens decreases the footprint of the bend as well. The designed waveguide bend with a radius of 18.4 μm isimplemented by concentric cylindrical multilayer structure. The average bend losses of 0.69 and 0.87 dB areachieved for the TM0 and TM1 modes in the C-band of optical communication, respectively. The bend loss is lowerthan 1 dB in a bandwidth of 1520-1675 nm for both modes.

Mid-infrared optical characterization of thin SiNxmembranes

Matteo Stocchi, Davide Mencarelli, Luca Pierantoni, Dawid Kot, Marco lisker, Alexander Goeritz, Canan Baristiran Kaynak, Matthias Wietstruck, and Mehmet Kaynak

Doc ID: 363056 Received 25 Mar 2019; Accepted 05 Jun 2019; Posted 05 Jun 2019  View: PDF

Abstract: The investigation of the optical constants (e.g. the refractive index n and theextinction coefficient ) has been performed in the Mid-InfraRed (MIR) spectrum for variousSilicon Nitride (SiNx) configurations. By exploiting the Transfer Matrix Method (TMM)formulation, photometric measurements of transmission and reflection have been used foriteratively calculating the optical parameters of interest. For ensuring the reliability of the n and, the same material from which such parameters were extracted from was deposited for threedifferent thicknesses, e.g. 600, 200 and 100 nm. While the former is optically characterized, theremaining two are used for validation purposes. For each experimental/calculated comparison,the average (made over the whole considered spectrum interval) of the relative error never exceeds1:5%, which ensures the correctness of the given n and . For the sake of completeness, adetailed analysis of the intrinsic limitations arising from the very nature of the method will alsobe conducted.

High x-ray resolving power utilizing asymmetricdiffraction from a quartz transmission crystalmeasured in the 6 keV to 22 keV energy range

John Seely, Eric Galtier, Larry Hudson, Albert Henins, and Uri Feldman

Doc ID: 363886 Received 03 Apr 2019; Accepted 04 Jun 2019; Posted 05 Jun 2019  View: PDF

Abstract: A Cauchois type spectrometer utilizing the (203) lattice planes at an oblique angle of 11.53o to the normal to thesurface of a quartz transmission crystal recorded the Kα and Kβ spectral lines of six elements from Fe to Ag in the 6keV to 22 keV energy range from a laboratory x-ray source. After deconvolving the natural lifetime widths and theimage-plate detector broadening from the observed spectral line widths, the intrinsic crystal resolving power wasdetermined to be 4000 at the lower energies and decreasing to 1000 at the higher energies. Previously, a Si wafercrystal exhibited twice this resolving power when the (331) planes had been used in asymmetric geometry. Theinvestigation of diffraction with this quartz crystal, with a very similar lattice spacing and therefore spectralcoverage, was motivated by the larger integrated reflectivity of quartz due to its well-known quasimosaicity uponelastic bending. The measured spectral line widths were in good agreement with the widths calculated byaccounting for various broadening mechanisms including source size, crystal thickness, crystal height, crystalrocking curve width, geometrical aberrations, and possible spectrometer configuration errors. This is the firstdemonstration of high resolving power achieved by asymmetric diffraction over a wide energy range (6 keV to 22keV) and with detailed comparisons with theoretical broadenings. Based on these results, Cauchois spectrometersemploying asymmetric planes of perfect quartz and silicon crystals can be reliably designed and optimized for highresolution spectroscopy in the > 6 keV energy range.

Determination of spectral line profile using a phasegradient step and stationary Fourier transformspectroscopy

Ameneh Jabbai, Khosrow Hassani, and Mohammad Tavassoli

Doc ID: 362641 Received 18 Mar 2019; Accepted 03 Jun 2019; Posted 04 Jun 2019  View: PDF

Abstract: This paper introduces a new, simple, fast and affordable spectroscopy technique, in which Fresnel diffraction caused by a phase gradient step is used to determine the spectral profile of light sources by Fourier transformation of the interferogram data. To realize the phase gradient step, a Fresnel biprism or double mirror can be used. In principle, a single interferogram is sufficient to obtain the line profile. To demonstrate the technique, four Light Emitting Diode (LED) sources have been investigated using a Fresnel biprism with 0. 52° apex angle and a Fresnel double mirror with adjustable angle. The obtained results are confirmed by a commercial spectrometer showingrelative uncertainties in the order of 10-2 for the linewidth.

SPEX airborne spectro-polarimetercalibration and performance

Job Smit, Jeroen Rietjens, Gerard van Harten, Antonio Di Noia, Wouter Laauwen, Brian Rheingans, David Diner, Brian Cairns, Andrzej Wasilewski, Kirk Knobelspiesse, Richard Ferrare, and Otto Hasekamp

Doc ID: 360591 Received 26 Feb 2019; Accepted 03 Jun 2019; Posted 19 Jun 2019  View: PDF

Abstract: To improve our understanding of the complex role of aerosols in the climate system and onair quality, measurements are needed of aerosol optical and microphysical. From manystudies it has become evident that a satellite-based multi-angle, multi-wavelengthpolarimeter will be essential to provide such measurements. Here, high accuracy (~0.003)on the degree of linear polarization (DoLP) measurements is important to retrieve aerosolproperties with an accuracy needed to advance our understanding of the aerosol effect onclimate. SPEX airborne, a multi-angle hyper-spectral polarimeter, has been developed forobserving and characterizing aerosols from NASA’s high-altitude research aircraft ER-2. Itdelivers measurements of radiance and DoLP at visual wavelengths with a spectralresolution of 3 nm and 7-30 nm respectively for radiance and polarization, at nine fixedequidistant viewing angles from -56° to +56° oriented along the ground track, and a swathof 7° oriented across-track. SPEX airborne an airborne polarimeter to use spectralpolarization modulation to determine the state of linear polarization of scattered sunlight.This technique has been developed in the Netherlands and has been demonstrated withground-based instruments. SPEX airborne serves as a demonstrator for a family of spacebasedSPEX instruments that have the ability to measure and characterize atmosphericaerosol by multi-angle hyper-spectral polarimetric imaging remotely from a satelliteplatform. SPEX airborne was calibrated radiometrically an polarimetrically using JetPropulsion Laboratory (JPL) facilities including the Polarization Stage Generator-2(PSG-2) which is designed for polarimetric calibration and validation of the AirborneMultiangle SpectroPolarimetric Imager (AirMSPI). Using the PSG-2, the accuracy of theSPEX airborne DoLP measurements in the laboratory setup is found to be 0.002-0.004.2Radiometric calibration is realized with an estimated accuracy of 4%. In 2017, SPEXairborne took part in the “Aerosol Characterization from Polarimeters and Lidar”(ACEPOL) campaign on the ER-2 that included four polarimeters and two lidars.Polarization measurements of SPEX airborne and the co-flying Research ScanningPolarimeter (RSP), recorded during the campaign, were compared and display root-meansquare(RMS) differences ranging from 0.004 (at 555nm) up to 0.02 (at 410nm). Forradiance measurements excellent agreement between SPEX airborne and RSP isobtained with an RMS difference of ~4%. The lab- and flight-performance values forpolarization are similar to those recently published for AirMSPI, where also an intercomparisonwith RSP was made using data from field campaigns in 2013. The intercomparisonof radiometric and polarimetric data both display negligible bias. The inflightcomparison results provide verification of SPEX airborne’s capability to deliverhigh-quality data.

In-situ characterization of thermal cleaned surface forpreparing superior transmission-mode GaAsphotocathode

Chengwei Fang, Yijun Zhang, Zhang min, Feng Shi, Gangcheng Jiao, Hongchang Cheng, Qingxin Dai, and Jingzhi Zhang

Doc ID: 361825 Received 07 Mar 2019; Accepted 30 May 2019; Posted 31 May 2019  View: PDF

Abstract: Considering that it is impractical to utilize in-situ surface diagnostic means to determine the surface cleanliness oftransmission-mode GaAs photocathodes in the vacuum device manufacturing process, the thermal desorptiontechnique with the aid of the quadrupole mass spectrometer during thermal cleaning process was employed to insitucharacterize the thermal cleaned surface. The desorption behaviors for various impurity gases during thethermal cleaning process are analyzed. The experimental results show that the amount of desorbed impurity gasesvaries due to the different heat treatment temperature. Through the verification of Cs/O activation and quantumefficiency measurement, it is found that the desorption behaviors of the specific impurity gases including AsH3 andAs2 are crucial to surface cleanliness of transmission-mode GaAs photocathodes, which relate to the finalphotoemission capability. This simple and reliable criterion would provide an effective way to guide the thermalcleaning process of transmission-mode GaAs photocathodes, and the desorption behaviors would assist in in-situevaluating the surface cleanliness.

Innovative integrated numerical-experimental methodfor high performance multispectral Muellerpolarimeters based on ferroelectric liquid crystals

Arvid Lindberg, Jérémy Vizet, Jean Rehbinder, Camille Gennet, Jean-Charles Vanel, and Angelo Pierangelo

Doc ID: 363012 Received 22 Mar 2019; Accepted 29 May 2019; Posted 29 May 2019  View: PDF

Abstract: In this work, an original and effective integrated numerical-experimental approach is proposed for buildinga high-performance multispectral Ferroelectric Liquid Crystals (FLCs)-based Mueller polarimeter.This method relies on an accurate experimental characterization of the optical components specificallyselected to construct such a system, combined with a numerical procedure used to optimize it, in thespectral range of interest, by means of a global optimization function. Proposed strategy enabled theconstruction of a FLCs-based Mueller polarimeter in transmission configuration operating between 450and 700 nm. The robustness of this system for various optical components misalignments as well as theconditions to keep the measurement error at less than 1% over the whole spectral range of interest havebeen experimentally determined. The proposed strategy is very well suited to build optimized multispectralMueller polarimetric systems for biomedical applications, for which variations on the elements ofmeasured Mueller matrices in the order of few percent need to be appreciated.

Fabrication of hierarchical moth-eyestructures with durable surperhydrophobicproperty for ultra-broadband visual andmid-infrared applications

Litong Dong, Ziang Zhang, Lu Wang, Zhankun Weng, Mingzhao Ouyang, Yuegang Fu, Jiake Wang, Dayou Li, and Zuobin Wang

Doc ID: 363419 Received 26 Mar 2019; Accepted 27 May 2019; Posted 28 May 2019  View: PDF

Abstract: Multifunctional antireflective coatings have practical applications as importantoptical components in many fields, especially for optical devices and imaging systems.However, a good antireflection application in the visible region is often unsatisfactory formid-infrared devices, and difficulty obtaining multiple capabilities simultaneously is one ofthe main factors limiting their applications. In this work, the hierarchical moth-eyestructures with superhydrophobicity were fabricated via inductively coupledplasma-reactive ion etching (ICP-RIE) using nanodisc-array masks, which were formed bythree-beam laser interference lithography (LIL), for improving the ultra-broadband opticalproperties. The uniform antireflection efficiency, which was close to 1%-reflectivitycovering over the visual and mid-infrared wavelength range, was exhibited by the moth-eyestructures with high-quality pillar arrays. Additionally, irregular nanostructures weretailored onto the top of the pillars to generate the hierarchical moth-eye structures forsimultaneously obtaining both the superhydrophobic and anticorrosive properties. Thefabricated antireflective structures with the features of self-cleaning and durability have theadvantage of being for long-term use in harsh environments.

Study of Optical Rotation Generated by theTwisted Nematic Liquid Crystal Film: Based onCircular Birefringence Effect

xiangshen meng, Xiaoyan Qiu, Guoqing Li, Wenjiang Ye, Yueqiang Lin, Xiaodong Liiu, Minglei Cai, xiaoyan wang, Jian Li, and Zhenghong He

Doc ID: 361805 Received 07 Mar 2019; Accepted 22 May 2019; Posted 10 Jun 2019  View: PDF

Abstract: The optical behavior of the twisted nematic liquid crystals (TNLCs) is revealed throughangular scanning technique. Experimental results show that the optical rotation and the degreeof polarization of transmitted light are dependent on the polarization direction of incidentlight. The optical rotation is reciprocal, i.e. the polarization direction of incident andtransmitted light can reciprocate when optical rotation is π/2. In some case, the opticalrotation is zero. The orientation of alignment layers in the TN cell can be determined from thebehavior of optical rotation, which is agreed with the measurement by the atomic forcemicroscope (AFM). The experimental results are explained with the model of circularlypolarized light based on circular birefringence effect. The linearly polarized incident light isthe superposition of right- and left-handed circularly polarized light. The propagation velocityof circularly polarized light in the liquid crystal is relevant to the polarization direction ofincident light, so that the refractive indexes of left- and right-hand circularly polarized light,n- and n+, or the circular birefringence n( n n ) − + Δ = − are not constants. As a result, when alinearly polarized light with the wavelength λ propagates through a TN cell with the cell gap l,the polarization direction of transmitted light is rotated to an angle Δθ. The optical rotationθ ( π (n n )l λ ) − + Δ = − is dependent on the polarization direction of incident light whereas theaveraged refractive index ( ( ) 2) − + n = n + n could be independent of that. The incident lightis partially linearly polarized light in our experiments, so that the degree of polarization oftransmitted light varies with the polarization direction of incident light because the opticalrotatory rates for the primary and secondary light beams are different.

A multi-wavelength multi-focus Fresnel solarconcentrator with square uniform irradiance:design and analysis

Yanru Jiang, Qingkun Xie, EnShi Qu, Liyong Ren, Jian Liang, and Jing Wang

Doc ID: 363655 Received 28 Mar 2019; Accepted 21 May 2019; Posted 07 Jun 2019  View: PDF

Abstract: In this paper, a two-step optical design method is proposed to build a superiorFresnel-based photovoltaic concentrator for enhancing the light conversion efficiency withthe multi-junction solar cell. In the first step, we orthogonally segment a traditional Fresnelconcentrator and remove the two normal stripe bands around the horizontal and vertical axes,as well as recombine the resultant four quadrants again. By using such a specific Fresnelconcentrator designed, a square light pattern could be constructed owing to the off-axis nonrotationallysymmetric superposition of light; In the second step, as for the responsewavelengths of a specific triple-junction solar cell, we further carry out a triple-wavelengthand multi-focus design to the above Fresnel concentrator for improving the uniformity oflight distribution on the solar cell. To show the validity of this novel design method, a solarconcentrator, with typical design parameters including the geometrical concentration ratio of800× and the F-number of 0.775, is designed and simulated. As a result, a theoreticalirradiance uniformity up to 87% is obtained. In addition, considering the fact that no secondoptical element is involved in the concentrator system, our design method inherently has theadvantageous of good compactness, high efficiency, low cost and easy to massive production.We believe that such a concentrator is of great significance to solar cells for high conversionefficiency of light in the concentrator photovoltaic system.

996 nm high-power single-longitudinal-modetapered gain-coupled distributed feedbacklaser diodes

Yuxin Lei, Yongyi Chen, Feng Gao, Dezheng Ma, peng jia, Hao Wu, Chunkao Ruan, Lei Liang, Chao Chen, jun zhang, Qin li, Yongqiang Ning, and Lijun Wang

Doc ID: 356135 Received 27 Dec 2018; Accepted 08 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: High-power single-longitudinal-mode regrowth-free tapered gain-coupleddistributed feedback laser diode based on periodic current injection is achieved at 996 nm. Itenhances the output power without beam quality degrading. A continuous-wave output powerof over 1.12 W is achieved at 3 A. The maximum output power in single-longitudinal-modeoperation is up to 0.56 W at 1.4 A. The power conversion efficiency is over 24 % and theslope efficiency is 0.58 W/A. The side mode suppression ratio is over 38 dB, the 3 dBspectral linewidth is less than 2.4 pm. The lateral far field divergence angle is only 14.98 °,the beam quality factor M2 is 1.64, achieving a near-diffraction-limit emission. Our devicehas great potential in commercial applications and experimental study of high-powernear-diffraction-limit laser diode for its low-cost fabrication technique and narrowbandsingle-longitudinal-mode emission at high power.

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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