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Accepted papers to appear in an upcoming issue

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Odd excitation of symmetric MultiMode Interference (MMI) structures

Salwa El-Sabban and Diaa Khalil

Doc ID: 354893 Received 10 Dec 2018; Accepted 17 Apr 2019; Posted 17 Apr 2019  View: PDF

Abstract: In this work, we study the odd excitation of symmetric Multi-Mode Interference MMI integrated optical structures. We develop a simple formula for the imaging length in the guide under odd excitation in the MMI structures using the symmetry of the structure. The obtained analytical results are verified by numerical calculations using the Beam Propagation Method BPM. The developed model is applied for both 2D and 3D MMI structures successfully. It also allows building functional devices like power splitters or mode converters for the odd (asymmetric) modes of the waveguide

Compact polarization splitter based upon a silicon angled-multi-mode interferometer structure

Haibo Liang, Richard Soref, and Jianwei Mu

Doc ID: 359654 Received 05 Feb 2019; Accepted 17 Apr 2019; Posted 17 Apr 2019  View: PDF

Abstract: The difference between TE and TM mode effective indices in a waveguided angled multi-mode interferometer (a-MMI) structure is found to produce practical polarization-splitting (PS) in the silicon-on-insulator platform at 1550 nm. Simulations show that this PS offers competitive performance in low insertion loss (0.4dB for TE and 0.8dB for TM), high extinction ratio (27.6dB for TE and 26.5dB for TM), low crosstalk (-27.3dB for TE and -28.0 dB for TM), and a 53-nm bandwidth for ER > 20 dB. The compact footprint (~25 µm²), the identical single-mode input/output waveguides for integration without altering the cross-section and the simplicity in implementation are prominent advantages compared with prior-art designs.

Study on Auto Bias Control of Silicon Optical Modulator in PAM-4 Modulation Format

honggang chen, Bo Zhang, weidong ma, Hu Yi, Xi Xiao, xuerui liang, leilei hu, feng li, and lan ding

Doc ID: 360148 Received 14 Feb 2019; Accepted 17 Apr 2019; Posted 17 Apr 2019  View: PDF

Abstract: Recently, the high-speed silicon optical modulator plays more and more role in optic fiber communication. Due to silicon material nonlinear electro-optic effect, quadrature bias point of modulator is difficult to be locked precisely. In this paper, a novel automatic bias control (ABC) method for four-level pulse amplitude modulation(PAM-4) format silicon modulator is presented. Firstly, a sinusoidal dither signal is applied to the modulator DC bias and the normalized output optical signal function which is modulated by the dither signal is obtained. Then a pair of orthogonal reference functions are created, whose numerical size is equal to the absolute value of sinusoidal and cosine functions that the frequency is the same as the dither signal. Through the cross-correlation integral operation between the normalized and reference functions above, we find that the zero point of the above integral operation is the best quadrature bias point through numerical simulation and experiment. The phase accuracy error of ABC is lower than 2 degrees and it satisfies the business specification of high-speed silicon optical modulator.

Baseline correction method based on doubly reweighted penalized least squares

Song Liu, Degang Xu, Yaoyi Cai, and Chuanhua Yang

Doc ID: 356175 Received 02 Jan 2019; Accepted 16 Apr 2019; Posted 17 Apr 2019  View: PDF

Abstract: The acquired spectrum from optical instruments usually contains the pure spectrum as well as undesirable components such as baseline and random noise. According to previous research, the primary limitation of spectral applications is that the intensity of the baseline can be much stronger than the signal spectrum, which can seriously submerge the spectrum; therefore, baseline correction is one of the most important challenges for the qualitative and quantitative analysis of spectra in many fields. In recent years, baseline correction methods based on penalized least squares have been widely applied to spectral preprocessing. Those methods typically contain two items: the sum of the penalized least squares between the analytical spectrum and established baseline, and the second-order derivative of baseline multiplied by penalties, which is expressed as the constraints of baseline smoothness. In this paper, we present a doubly reweighted penalized least squares (drPLS) method to estimate the baseline. It takes full account of the first-order derivative of the established spectrum at each iteration that is closest to the original spectrum, while the doubly reweighted strategy makes the cost function act in accordance with the characteristics of the local baseline. Considering the drawbacks of the weighting rules for previous methods, we adapt a boosted weighting rule based on the softsign function that provides the continuous weights and steeper weighting curves as the iteration increases, which can perform well when the spectrum contains high noise. The simulated results confirm that the proposed method yields better outcomes than the previous methods. This proposed method was also successfully applied to Raman and near-infrared spectra, and the results show that it can effectively estimate various kinds of baselines, significantly improving the performance of the classification and prediction models after baseline correction.

Designing a Nearly Perfect Infrared Absorber inMonolayer Black Phosphorous

Daxing Dong, Youwen Liu, Yue Fei, Yongqing Fan, jun li, Yuncai Feng, and Yangyang Fu

Doc ID: 361299 Received 07 Mar 2019; Accepted 16 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: Black phosphorous (BP) is a type of 2D layered material with a direct band gap that displays high carrier mobilityand strong in-plane anisotropy, and exhibits potential as a promising optoelectronic material for IR applications. Inthis paper, we propose a nearly perfect IR absorber comprised of a metal film, a spacer with a monolayer BP inside,and a distributed Bragg reflector (DBR). The electric field is confined inside the resonator generated by the metalfilm and DBR, and the absorption can be enhanced up to nearly 100% owing to the strong interaction of BP with theconfined field. Our results show that the absorption performance of the proposed structure is not only criticallydependent on the electron density, but also relies on the position of the BP within the spacer. This dependence canbe mitigated because the absorption peak wavelength can be tuned by adjusting the angle of the light and theparameters of the DBR. Moreover, the absorber can be served as a reflective linear polarizer based on theanisotropic absorption properties. Our work can be helpful to design a narrow perfect absorber and polarizationsensitivedevices for IR waves.

Comparing the performance of a femto fiber-basedlaser and a Ti:sapphire used for multiphotonmicroscopy applications

Juan Bueno, Francisco Avila, and Pablo Artal

Doc ID: 361635 Received 04 Mar 2019; Accepted 16 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: Ti:sapphire laser systems are the more extended excitation sources in multiphoton (MP) microscopy. Althoughtunable, the cost, size and lack of portability often limit their use in some research fields. Femtosecond fiber-basedlasers represent an attractive alternative since they are portable, compact and at an affordable price. Most MPapplications using these devices employ wavelengths beyond 1000 nm. This work evaluates the performance of amode-locked fiber-based laser emitting at 780 nm (within the spectral region often used with Ti:sapphire devices)for use in MP imaging microscopy. MP images acquired with this laser system have been compared with thoseobtained with a “regular” solid-state source. Results herein show that the images recorded with both laser sourceswere similar, independently of the depth location of imaged plane. The structural information contained in theimages hardly differed. Moreover, the images of deeper layers improved by means of adaptive optics were alsosimilar. These ultrafast laser sources are expected to enhance the impact of MP microscopy in basic research, aswell as in biomedical environments.

Comparison of existing laser-inducedbreakdown thermometry techniques alongwith a time-resolved breakdown approach

Andrew Pressley Williamson, Ulrich Thiele, and Johannes Kiefer

Doc ID: 348842 Received 22 Oct 2018; Accepted 16 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: Temperature is an important parameter for characterizing chemical, physical, andflow processes occurring in combustion environments. Laser-induced breakdown is a processwidely used for determining a material's elemental components and its composition, known aslaser-induced breakdown spectroscopy (LIBS). The breakdown event, or more specificallythe breakdown threshold, for a low-pressure gas strongly depends on density effectsemanating in the likelihood for multi-photon and avalanche ionization. In this work, acomparison of thermometry techniques utilizing laser-induced breakdown is made and anovel approach to perform simultaneous gas-phase thermometry on a shot-to-shot basis andspectroscopy is demonstrated by monitoring the moment in time the thermal plasma developsalong the intensity gradient of a laser pulse. Breakdown thresholds are profiled along theheight of a lean methane-air and partially combusting rich propane-air McKenna flame, andcorrelated to radiation and convection corrected thermocouple readings.

Salinity effects on elemental analysis in bulk water bylaser-induced breakdown spectroscopy

Nan Li, Jinjia Guo, Chao Zhang, Yongquan Zhang, Qingyang Li, Ye Tian, and Ronger Zheng

Doc ID: 357735 Received 16 Jan 2019; Accepted 16 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: The effects of salinity on underwater LIBS were investigated with the salinities rangingfrom 2‰ to 50‰. Both the spectroscopic and fast imaging techniques were used to observe theplasma emission. It was shown that as the salinity increases, emission intensities of the atomiclines increase, while the intensities of the ionic lines are suppressed. The signal-to-backgroundratios of the spectral lines decrease as a function of salinity, but the signal-to-noise ratios changeirregularly with salinity. Image results demonstrated that brighter and longer plasma can beproduced at higher salinity with higher plasma temperature and electron density. The calibrationcurves at different salinities indicated the high salinity environment does not limit the detectioncapability of LIBS. The obtained results reveal the significant influences of salinity on underwaterLIBS detection, which plays an important role in promoting the applications of LIBS in the ocean.

3D Push-pull heterodyne interferometer for SPMmetrology

Tatiana Kazieva, Konstantin Gubskiy, Andrey Kuznetsov, and Vladimir Reshetov

Doc ID: 359583 Received 04 Feb 2019; Accepted 16 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: Three-coordinate heterodyne laser interferometer has been developed to measure the displacement of the probemicroscope scanner with subnanometer resolution that provides traceability of measurements to the standard ofmeter through the wavelength of a stabilized He-Ne laser. Main sources of errors are investigated and theirinfluence is minimized so that the resulting measurement uncertainty of the system does not exceed 0.2 nm, andthe resolution is 0.01 nm. The investigation of metrological characteristics of the three-coordinate interferometerwas carried out with SPM NanoScan-3D using TGZ-type calibration gratings. The values measured with SPM fellwithin the 95% confidence interval given by PTB. SPM equipped with laser interferometer was used to measure thecharacteristics of dynamic etalons of geometric dimensions.

Off-Resonant Photoacoustic Spectroscopy forAnalysis of Multi-component Gas Mixtures atHigh Concentrations using BroadbandVibrational Overtones of Individual GasSpecies

Ramya Selvaraj, Nilesh Vasa, and Shiva S M

Doc ID: 360633 Received 20 Feb 2019; Accepted 16 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: Broadband photoacoustic spectroscopy (PAS) technique is proposed anddemonstrated for measurement of CH4, CO2 and H2O vapor in 1.6 to 2.0 μm wavelengthregion. The wide spectrum of super continuum light source is used to cover broadbandabsorption bands of multiple gas species. This sensor works in the off-resonant frequency ofthe designed photoacoustic cell and exhibits a wide concentration measurement range of partsper billion by volume (ppb-v) to 100%. The PAS sensor is further tested in real time bymeasuring the concentration of CO2, CH4 and H2O vapor in biogas plants.

Optical design of the High Resolution Imaging Channelof SIMBIO-SYS

Michele Zusi, Riccardo Paolinetti, Vincenzo Della Corte, Gabriella Marra, Marco Baroni, Pasquale Palumbo, and Gabriele Cremonese

Doc ID: 361157 Received 27 Feb 2019; Accepted 15 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: This paper describes the optical design of the High Resolution Imaging Channel (HRIC), which is part of theSpectrometers and Imagers for Mercury Planetary Orbiter (MPO) BepiColombo Integrated Observatory SYStem(SIMBIO-SYS) suite, for imaging and spectroscopic investigation of Mercury. The optical design has been optimizedto achieve the stringent scientific requirement of 5 m ground sampling at 400 km from the planet surface in theharsh Mercury environment.

High-power supercontinuum generation by noise-likepulse amplification in Yb-doped fiber amplifieroperating in nonlinear regime

Ebrahim Aghayari and Kazem Jamshidi-Ghaleh

Doc ID: 359521 Received 04 Feb 2019; Accepted 15 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: In this paper, we report on a supercontinuum generation by amplifying noise-like pulses (NLPs) in a nonlinear Yb-dopedfiber amplifier. The NLP source is a homemade Yb-doped all-fiber ring oscillator based on nonlinear polarizationrotation mode-locking method. Noise like pulses possess repetition rate of 11.57 MHz, energy of 16.5 nJ and 3 dBspectral bandwidth of 42 nm. Intensity autocorrelation function of NLPs has a broad pedestal and a narrow centralspike. The pedestal and the spike have temporal widths of 63 ps and 92 fs, respectively. The NLPs are amplified by a Ybdopedfiber nonlinear power amplifier to achieve output power of 7.5 W. Nonlinear effects in amplifier drasticallybroaden the spectrum of NLPs and generate high power supercontinuum light with 10 dB spectral bandwidth of 1130nm (from 1037 nm to 2167 nm). The presented supercontinuum generation system is an all-fiber compact structure andhas an advantage that does not require long single-mode, nonlinear or photonic crystal fibers.

Real-time acceleration sensing with an arctanalgorithm based on modal interferometer

Gang Zhang, Xuqiang Wu, Qiang Ge, Shili Li, Jinhui Shi, Wei Liu, Cheng Zuo, and Benli Yu

Doc ID: 361529 Received 04 Mar 2019; Accepted 15 Apr 2019; Posted 17 Apr 2019  View: PDF

Abstract: This study proposes a fiber-optic accelerometer (FOA) for low frequency vibrationsignals detection. The phase velocities of the polarization eigenmodes are affected differentlyby signals, leading to a polarization rotation of the transmitted lights. The orthogonal squareroots of the photovoltages are utilized for arctan demodulation scheme. Experimental resultsshow that it provides a flat response of 75.04 mrad/g, an average resolution of 13.44 μg/√Hzand a dynamic range of 111.62 dB below 180 Hz. The environmental instability and sensorcomplexity are significantly reduced so that the sensor can be further used in the warning ofcoal and gas outburst.

Three-dimensional thermal model of high-power semiconductor lasers

Di-Hai Wu, Chung-en Zah, and Xingsheng Liu

Doc ID: 358077 Received 17 Jan 2019; Accepted 14 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: In this paper, three-dimensional, steady-state, analytical thermal models of highpowersingle-emitter semiconductor lasers (SEs) and laser diode array (LDAs) are presented.Heat flow in the laser chips for an epi-down bonded SE and LDA is described using thismodel, and it is observed that the laser chips contributes to 8% and 6% of the total heatdissipation for the SE and LDA, respectively. The submount size requirement for this modelis discussed by revealing the heat flow in the submount. Through finite element simulations,the solution accuracy for the lasers with a non-ideal submount is confirmed. Finally, theperformance of our proposed analytical models is verified by finite element simulations andexperimental measurements based on the wavelength shift method.

Spectroscopic setup for submicrometerresolutionmapping of low-signal absorptionand luminescence using photothermalheterodyne imaging and photoncountingtechniques

Semyon Papernov

Doc ID: 358904 Received 28 Jan 2019; Accepted 13 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: A spectroscopic setup that enables one to map the absorption andphotoluminescence with submicrometer spatial resolution and high sensitivity is described. Aphotothermal heterodyne imaging pump/probe technique is employed for absorptionmapping, and low-signal, spatially resolved photoluminescence is recorded using photoncounting. High-spatial-resolution mapping is accomplished by using high-numerical-aperturemicroscope objective focusing laser beams (pump and probe) into a submicrometer spot andraster-scanning sample mounted on the nanopositioning translation stage. Performance of thesetup is illustrated by mapping absorption and luminescence of the hafnium oxide film withembedded hafnium nanoparticles and multilayer dielectric grating. In both casessubmicrometer spatial resolution is demonstrated and possible physical mechanisms leadingto image contrast on a submicrometer scale is discussed.

Influence of astigmatism and field curvatureon the correction zones of an optical imagingsystem

Antonin Miks and Jiri Novak

Doc ID: 361553 Received 04 Mar 2019; Accepted 13 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: By a detailed analysis of the dependence of aberrations on the numerical apertureand the field of view of the optical system it is possible to find such values of the numericalaperture and the field of view, where the residual wave aberration is zero. These values can becalled correction zones. Our work presents a theoretical analysis of the described problem andgeneral formulas are derived for the expression of wave aberration coefficients usingcorrection zones for astigmatism and field curvature of the third and fifth order. Finally, ananalysis of optimum values of correction zones and the optimum position of the image planehas been performed using derived equations with respect to maximization of the Strehldefinition. The analysis of the correction zone and the position of the image plane is presentedon two examples of the same optical system, where the image plane is located either in theparaxial image plane or in the optimum image plane.

Three-component zoom lens with fixedposition of optical center

Antonin Miks and Jiri Novak

Doc ID: 362119 Received 11 Mar 2019; Accepted 13 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: A method is proposed for a calculation of initial parameters of three-element zoomlens with an identical position of object and image principal planes of the optical system andapproximately zero Petzval sum. Such an optical system has a fixed position of its opticalcenter, which does not depend on the object distance. The proposed method makes possible todetermine focal length values of individual elements and trajectories of their movementsduring zooming. The analysis was presented on examples of the calculation of parameters ofsuch optical systems. Such systems could be useful in optical measuring methods,photogrammetry, and machine vision techniques.

Design of secondary light source forreflectors with axisymmetric light guide

Hiroshi Ohno, Katsutoshi Nakagawa, and Takahiro Kamikawa

Doc ID: 362154 Received 11 Mar 2019; Accepted 13 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: A reflector lamp is a type of electric lamp that is widely used in commercial,residential, and transportation illumination. A typical reflector surface, namely, one that isparaboloid, has a focus on which a light source of the reflector lamp should be placed. Thelight source approximates a point source, which enables light rays reflected by the reflector toform a parallel beam with a narrow light distribution angle. However, it is difficult to place alight-emitting diode (LED) at the focal point of the reflector because a heat dissipater attachedthermally to the LED prevents the reflected light rays from emitting out. Thus, anaxisymmetric light guide to produce a secondary light source that can be placed on a focus ofa reflector is proposed here. The lighting efficiency of the light guide is about 83% with wideangledistribution toward the reflector. A spotlight consisting of the light guide and aparabolic reflector is fabricated, and shows that a parallel beam with a half-intensity angle of9.0 degrees can be realized with the reflector opening diameter of 69.0 mm using a secondarylight source produced by the axisymmetric light guide.

Paraxial design of four-component zoom lens with zero separation of principal planes and fixed position of image focal point composed of members with constant focal length

Antonin Miks and Pavel Novak

Doc ID: 362507 Received 14 Mar 2019; Accepted 12 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: Our paper presents a detailed theoretical analysis of a four-component zoom lens with coincident principal planes, fixed position of image focal point and approximately corrected Petzval sum. New formulas enabling calculation of paraxial parameters of such optical systems are derived and the practical application of these formulas is shown on an example. The position of optical center of these optical systems does not depend on the object distance (for a given value of focal length of the zoom) and the position of the image focal point (with respect to the last element of the system) is fixed during the operation of the zoom. Such optical systems could be used in various measuring systems in photogrammetry, computer vision, triangulation sensors, fringe projection techniques, surveying, machine vision, etc.

Three-element optical system with a given fixed position of optical center

Antonin Miks and Pavel Novak

Doc ID: 363092 Received 22 Mar 2019; Accepted 12 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: Our paper presents a detailed theoretical analysis of the three element optical system with the zero separation of principal planes and approximately corrected Petzval sum, which has the required value of axial position of its optical center for a given value of focal length and a given value of axial distance of image focal point from the last element of the system. Formulas that makes possible to calculate paraxial parameters of such types of optical systems are derived and the application of the derived formulas is presented on several examples. Such optical systems represent a subset of the new family of optical systems with the constant position of the optical center. The optical center of such optical system is at given required axial position and this position does not change with the object distance, which could be advantageous for certain applications.

Suspended graphene double-layer modulatorwith ultrahigh figure of merit and subwavelengththickness modulator with leakymode

Jiamin Liu, Zia Khan, and Siamak Sarjoghian

Doc ID: 361815 Received 07 Mar 2019; Accepted 12 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: A comparison between graphene suspended double-layer modulator (SDM) andsub-wavelength thickness modulator (STM) is presented. The physics of both are analyzed indetail which show confined mode in suspended modulator but a leaky mode in subwavelengthmodulator. The leaky mode shows zero light-matter interaction and zeromodulation depth which should be avoided in designing. The suspended modulator canachieve much lower insertion loss and extraordinary higher figure of merit (FOM) (~ 2480)than sub-wavelength modulator. Both are with high modulation efficiency and comparablemodulation speed. We believe these designs will pave the way to realize high-efficiency, nearfundamental limits graphene modulators.

Enhanced direct binary search algorithm forbinary computer-generated Fresnel holograms

Jung-Ping Liu, Chu-qiao Yu, and Peter Tsang

Doc ID: 361298 Received 28 Feb 2019; Accepted 12 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: Direct binary search (DBS) algorithm was originally invented for the synthesis ofbinary Fourier hologram, and was applied for the generation of binary Fresnel hologramrecently. DBS performs quality evaluation on every pixel. Therefore, both the quality anddiffraction efficiency of the generated binary hologram are better among various algorithmsof binary hologram. However, DBS is a time-consuming algorithm and thus is impractical forthe generation of high-definition computer-generated hologram. In this paper, we proposedenhanced direct binary search (E-DBS) method to speed up the hologram computation. EDBSis based on the same pixelwise evaluation strategy of DBS, but the diffraction field of asingle pixel is precomputed as a look-up table. In evaluating any pixel value, only a smallarea in the region of interest affected by the diffraction field of single pixel is calculated. Inaddition, it is also found that qualified results can be obtained by using only 4% of the area ofthe diffraction field. As a result, the computing complexity of E-DBS can be reduced by atleast two orders of magnitude in contrast to conventional DBS.

Experimental investigation of quantum key distributionover water channel

shi-cheng zhao, Wen-dong Li, Yuan Shen, YongHe Yu, Xin-Hong Han, hao zeng, Maoqi cai, Tian Qian, shuo wang, zhaoming Wang, Ya Xiao, and Yong-jian Gu

Doc ID: 361391 Received 01 Mar 2019; Accepted 11 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: Quantum key distribution (QKD) has undergone significant development in recent decades, particularlywith respect to free-space (air) and optical fiber channels. Here, we report a proof-of-principle experimentfor the BB84 protocol QKD over a water channel. Firstly, we demonstrate again the polarizationpreservation properties of the water channel in optical transmission according to the measured Muellermatrix, which is close to the unit matrix. The reason for the polarization preservation, revealed by MonteCarlo simulation, is that almost all the received photons are unscattered. Then, we performed the firstpolarization encoding BB84 protocol QKD over a 2.37m water channel. The results show that QKD canbe performed with a low quantum bit error rate (QBER), less than 3.5%, with different attenuation coefficients.

Automated tree detection from 3D lidar imagesusing image processing and machine learning

Kenta Itakura and Fumiki Hosoi

Doc ID: 360695 Received 06 Mar 2019; Accepted 11 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: The trees in three-dimensional (3D) images obtained from lidar were automaticallyextracted in the presence of other objects that were not trees. We proposed a methodcombining 3D image processing and machine learning techniques for this automatic detection.Consequently, tree detection could be done with a high accuracy of 95%. First, the objects inthe 3D images were segmented one by one; then, each of the segmented objects was projectedonto 2D images. Finally, the 2D image was classified into “tree” and “not tree” using oneclassSVM (support vector machine), and trees in the 3D image were successfully extracted.

Digital image correlation with reduced bias errorbased on digital signal upsampling theory

Wei Heng, Buwei Huo, Xinxing Shao, and Xiaoyuan He

Doc ID: 359523 Received 04 Feb 2019; Accepted 11 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: Based on digital signal upsampling theory, a new computing strategy has been proposed to reduce the bias error indigital image correlation (DIC) caused by intensity interpolation. For each subset, before sub-pixel image matching,the sub-image around the target subset was processed by increasing the sampling rate with an integer factor. Theincrease of sampling rate is realized by resampling in the digital domain. The combination of digital signalupsampling processing with DIC can greatly reduce the interpolation bias error. The measurement accuracy of theproposed computing strategy was investigated in this study. Both numerical experiments and real-worldexperiments have been conducted in order to verify the effectiveness of the proposed computing strategy. Theresults indicate that the bias error can be significantly reduced without sacrificing the standard deviation error.With the proposed computing strategy, high-accuracy DIC measurement with near negligible bias error is expected.

Micro particle velocity sensing using a conicallens fiber array

XIN MA, SHUNGE DENG, and Xinwan Li

Doc ID: 354785 Received 10 Dec 2018; Accepted 11 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: We report a micro particle velocity sensor with a conical lens fiber array. Theconical lens fibers are linearly arrayed at same interval to behave as a spatial filter. Thecharacteristics of the sensor in terms of cone angle, divergence angle, aperture angle, blindarea, and detection area are investigated. Compared with sensor using a normal flat end fiberarray, our sensor has a high signal/noise ratio with smaller blind area and wider detection areato avoid the signal deterioration caused by movement deviation of the particle from fiberarray. Taking advantage of not only compact and tiny structure but also better ability of highelectromagnetic noise tolerance, corrosion resistance and temperature resistance, the sensormay have the potential for velocity sensing in harsh environment and micro particle sensing,such as sand movement monitoring in sandstorm, particle state monitoring in combustion, etc.

Optimized single-shot laser ablation of concave mirror templates on optical fibers

Thibaud Ruelle, Martino Poggio, and Floris Braakman

Doc ID: 355207 Received 28 Jan 2019; Accepted 11 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: We realize mirror templates on the tips of optical fibers using a single-shot CO₂ laser ablation procedure and perform a systematic study of the influence of the pulse power, pulse duration, and laser spot size on their geometry. This investigation provides new insights into CO₂ laser ablation of optical fibers and should help improve current models. We notably find that the radius of curvature, depth, and diameter of the templates exhibit extrema as a function of the power and duration of the ablation pulse, and observe that compound convex-concave shapes can be obtained. We additionally identify regimes of ablation parameters that lead to mirror templates with favorable geometries for use in cavity quantum electrodynamics and optomechanics.

Imaging Processing for GEO Object with 3D Rotationbased on Ground-based InISAL with OrthogonalBaselines

Xuan Hu, Daojing Li, and Jianbo Du

Doc ID: 356530 Received 02 Jan 2019; Accepted 11 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: While imaging geosynchronously orbiting objects with ground-based inverse synthetic aperture LADAR (ISAL),target rotation and vibration will introduce phase errors in the echo and cause the two-dimensional imaging resultto be defocused. To solve this problem, one layout of the ISAL receiving channels is designed, combining theorthogonal short baselines in the inner field with the orthogonal long baselines in the external field. On this basis,an imaging method based on orthogonal interferometry processing is proposed. The proposed method estimatesand compensates for the phase errors introduced by the rotation and vibration of the target so that the focus of thetwo-dimensional image is improved and three-dimensional imaging results with high accuracy are obtained. Theeffectiveness of the proposed method is verified by simulation data.

Image deconvolution for confocal laser scanning microscopy usingconstrained total variation with gradient field

Tao He, yasheng sun, Jin Qi, Jie Hu, and Haiqing Huang

Doc ID: 358831 Received 28 Jan 2019; Accepted 11 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: As for confocal laser scanning microscope(CLSM) imaging system, the collected weak fluorescence signals arealways distorted by optics blur and severe photon-counting noise, and the deconvolution for CLSM images is atypical ill-posed inverse problem which is highly sensitive to the measurement noise. To promote thereconstruction quality for characteristics of low intensity and strong noise, we employed the prominent totalvariation regularization(TV) to enforce the sparsity of fluorescent images gradient with rich details. However, thewell-known reconstruction artifacts (e.g., artificial staircase) emerge with TV prior. To settle this issue, we utilizeda robust first order discretization yielding near-isotropy with gradient field to depress the reconstruction artifacts.Furthermore, the bound constraint was suited to restrain final reconstruction results from appearingunreasonably explosive. For the proposed optimization minimizer with linear constraint, we take one proximalgradient for approximate estimation of each subproblem under the framework of inexact alternating directionmethod of multipliers (I-ADMM). Moreover, we incorporated a Nesterov’s scheme into the numerical method foracceleration of iteration updating. Compared with other competing methods, both the simulation and practicalresults demonstrate the effectiveness of our proposed model for CLSM image deconvolution.

ALL-CIRCULAR HOLE MICROSTRUCTURED FIBER WITH HIGHBIREFRINGENCE AND LOW CONFINEMENT LOSS

Sneha Verma

Doc ID: 359035 Received 30 Jan 2019; Accepted 11 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: An air-silica microstructure optical fiber of ultra-highbirefringence of the order ~10-2 and low confinement lossis proposed. The birefringence is achieved by axialanisotropy introduced in the fiber geometry by thepreferred arrangement of circular air holes of differentsize in the cladding structure. Vital properties of themicrostructure fiber like birefringence, confinement loss,dispersion and walk-off has been studied by employingnumerical solution through finite element method. Thesefinding should be useful for the fabrication of theproposed microstructure optical fiber.

3D mapping of droplet Sauter mean diameter insprays

Yogeshwar Nath Mishra, Matthias Koegl, Kevin Baderschneider, Bernhard Hofbeck, Edouard Berrocal, CHRIS CONRAD, Stefan Will, and Lars Zigan

Doc ID: 359857 Received 27 Feb 2019; Accepted 11 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: In this study, we report on the 3D (three-dimensional) characterization of a spray in terms of its droplet SMD (SauterMean Diameter) using the LIF (Laser-Induced Fluorescence)/Mie ratio technique. The spray structure is analyzed for amulti-hole DISI (Direct-Injection Spark Ignition) injector. A calibration curve to convert LIF/Mie ratio to dropletdiameter is deduced using LIF/Mie imaging and analysis of single droplets generated by a droplet generator. The DISIspray investigated here is optically sectioned by means of two-phase SLIPI (Structured Laser Illumination PlanarImaging) to suppress the intensity of multiple light scattering from LIF and Mie images prior to their ratio. A series ofcalibrated LIF/Mie ratio images of spray is then recorded at several depths along the Z-direction following the lightsheet scanning of the spray. The droplet SMD is ranging from less than 5 μm up to a maximum of 50 μm in single-shotimages. The averaged SMD results (1-30 μm) obtained by using the calibration curve from the droplet generator arecompared with measurement results from Phase-Doppler Anemometry (PDA). Finally, a 3D map is reconstructed fromthe successive 2D layers generated from spray scanning. The resulting 3D representation of the droplet SMD shows anon-symmetric spray structure produced by the studied multi-hole injector, which cannot be resolved by analyzing onlyone central plane.

All-fiberized transverse mode switching method basedon temperature control

Jiaxin Song, Haiyang Xu, Hanshuo Wu, Jun Ye, Xu Jiangming, Liangjin Huang, Jinyong Leng, and Pu Zhou

Doc ID: 359899 Received 11 Feb 2019; Accepted 11 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: In this paper, an all-fiberized transverse mode switching method was proposed based on temperature control offew-mode (FM) fiber Bragg gratings (FBGs). Two types of fibers were selected to fabricate the FBG pair in order tomatch the reflection peaks of the desired mode. The temperature-dependence property of the FM FBGs has beenutilized to tune the reflection spectra. Through temperature control, 20 W level output power was obtained whenthe output laser was switched between LP11 mode and LP01 mode in both an all-fiberized ytterbium-doped laserand a Raman laser, which is increased by ~2 orders of magnitude compared with previous demonstrations (almostless than 100 mW).

Real-time assessment of catheter contact andorientation using an optical coherencetomography integrated cardiac ablation catheter

Xin Yu, Rajinder Singh-Moon, and Christine Hendon

Doc ID: 359247 Received 31 Jan 2019; Accepted 10 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: The efficacy of catheter ablation treatment for atrial fibrillation is directly impactedby the quality of lesion formation. Two parameters which are critical for maximizing energydelivery are sustained catheter contact and orientation. Currently, these parameters must beinferred indirectly through tactile feedback or measurements of bioelectrical impedance and tipforce. In this work, we propose a method for discerning contact and orientation based on directendomyocardial imaging mediated by optical coherence tomography (OCT)-integrated ablationcatheters. A two-stage classifier was developed to deduce contact parameters from M-modeimages. Experimental validation within swine left atrial specimens demonstrate accuracies of99.96% and 92.88% for contact and orientation stages, respectively. These results highlight thepotential of OCT M-mode imaging for guiding catheter placement during RFA interventions.

Improved Vector Extrapolation Based Richardson-LucyAlgorithm Used for Wave-front Coded Imaging

Hui Zhao, Jingjing Xia, Ling Zhang, and Xuewu Fan

Doc ID: 359939 Received 11 Feb 2019; Accepted 10 Apr 2019; Posted 10 Apr 2019  View: PDF

Abstract: Richardson-Lucy (RL) algorithm is a well known nonlinear restoration method and has been widely applied in thefields of astronomical image restoration, microscopic image restoration and so on because of its capability ingenerating high-quality restoration results and potentials in realizing super-resolution. However, when beingapplied to restore the wave-front coded blurry images, classical RL algorithm converges very slowly and it has to beiterated many times before obtaining a satisfactory result, which severely prohibits its real-time application.Vector extrapolation based RL algorithm is invented to solve this problem but the noise amplification increases fastand additional post-processing is needed to further improve the signal to noise ratio. Therefore in this manuscript,an improved RL algorithm is proposed by introducing an exponential modified correction term into the frameworkof the original vector extrapolation based RL algorithm. Not only a bigger iteration step which ensures a fasterconvergence can be obtained, but also the noise amplification is effectively prohibited. Besides that, we design astructure similarity index metric (SSIM) based stopping criterion, based on which the optimum number ofiterations for each color channel is obtained. Experimental results reveal that the total iterations decreasesapproximately 78.9% and the restored images demonstrate a superior visual quality without denoisingadditionally.

U-Net Based Blocked Artefacts Removal Method forDynamic Computed Tomography

Bo Wang, Zhiqiang Chen, Wim Dewulf, Ruben Pauwels, Zhiyang Yao, Qinhan Hou, and Yongshun Xiao

Doc ID: 356518 Received 04 Jan 2019; Accepted 10 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: Airplane engines are vital aircraft components, so regular inspections of the engines are required to ensure theirstable operation. A dynamic computed tomography (CT) system has been proposed by our group for in-situ nondestructivetesting of airplane engines, which takes advantage of the rotor’s self-rotation. However, static parts ofthe engines cause blocked artefacts in the reconstructed image, leading to misinterpretations of the condition ofengines. In this paper, in order to remove the artefacts produced by the projection of the static parts in CTreconstruction, two deep-learning-based methods are proposed, which use U-Net to perform correction in theprojection domain. The projection of static parts can be estimated by the well-trained U-Net and subsequently besubtracted from the projections of the engine. Finally, the rotor can be reconstructed from the correctedprojections. The results shown in this paper indicate that the proposed methods are practical and effective forremoving those blocked artefacts and recovering the details of rotating parts, which will, in turn, maximize theutilization of the dynamic CT system for in-situ engine tests.

Fundus-simulating Phantom for Calibration of RetinalVessel Oximetry Devices

Hongyu Chen, Guangli Liu, Shulin Zhang, Shuwei Shen, Yuhao Luo, Jialuo Li, Cynthia Roberts, Mingzhai Sun, and Ronald Xu

Doc ID: 358569 Received 23 Jan 2019; Accepted 10 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: Retinal vessel oxygen supply is important for the retinal tissue metabolism. Commonly used retinalvessel oximetry devices are based on dual-wavelength spectral measurement of oxyhemoglobin and deoxyhemoglobin.However, there is no traceable standard for reliable calibration of these devices. Inthis study, we developed a fundus-simulating phantom that closely mimicked the optical properties ofhuman fundus tissues. Microchannels of precisely controlled topological structures were produced bysoft lithography to simulate the retinal vasculature. Optical properties of the phantom were adjusted byadding scattering and absorption agents to simulate different concentrations of fundus pigments. The developedphantom was used to calibrate the linear correlation between oxygen saturation (SO2) level andoptical density ratio in a dual-wavelength oximetry device. The obtained calibration factors were used tocalculate the retinal vessel SO2 in both eyes of 5 volunteers aged between 24 and 27 years old. The test resultsshowed that the mean arterial and venous SO2 levels after phantom calibration are coincident withthose after empirical value calibration, indicating the potential clinical utility of the produced phantomas a calibration standard.

Co-optimization method to reduce the patterndistortion caused by polarization aberration inanamorphic EUV lithography

Naiyuan Sheng, Yiyu Sun, Enze Li, Tie Li, Yanqiu Li, Pengzhi Wei, and lihui liu

Doc ID: 361058 Received 27 Feb 2019; Accepted 10 Apr 2019; Posted 10 Apr 2019  View: PDF

Abstract: Extreme ultraviolet (EUV) lithography is regarded as the most attractivetechnology to achieve 7 nm node and below. A new high numerical aperture (NA)anamorphic objective lens is designed to extend the single exposure resolution limit.However, the polarization aberrations (PAs) induced by the multilayer coatings on mirrorscause pattern distortions that cannot be neglected. In this paper, a source, mask, and processparameters co-optimization (SMPCO) method is developed to compensate for the patterndistortions caused by PAs and increase the process window. We first present an asymmetricsource represented by the superposition of Zernike polynomials to reduce the patternplacement error (PPE). Then a weighted cost function that incorporates the influences of PAsis innovated. Finally, a gradient-based statistical optimization method is adopted to minimizethe cost function by optimizing the lithography system parameters alternately. Simulations at7 nm node of 1D mask pattern indicate that for the system with PA of marginal field,compared with our earlier work, the critical dimension error (CDE) and PPE of the proposedmethod are reduced by 75.0% and 82.4%, respectively, and the PW is increased by 97.4%.

The structure design of conic lens pair forimproving the transmission efficiency ofCassegrain antenna

miaofang zhou, Yang Huajun, Ping Jiang, Yan Qin, Wei Caiyang, Shengqian Mao, and Biao Cao

Doc ID: 361223 Received 08 Mar 2019; Accepted 09 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: The central energy loss is a critical factor decreasing the transmission efficiency ofCassegrain antenna. In this paper, a pair of conic lens are designed and set in front of Cassegrainantenna to improve the transmission efficiency of the antenna instead of designing complicated antennastructure. On the basis of the analysis, the optimized conic lens pair can theoretically improve thetransmission efficiency up to 100% at the wavelength of 1550 nm under ideal condition. After severalpractical factors such as the dispersion of the material, the transmissivity and chamfering of the coniclens and the reflectivity of the mirror composing Cassegrain antenna are considered, the conic lens paircan still increase the transmission efficiency of Cassegrain antenna up to 92.37% at the wavelength of1550 nm. Compared with designing complicated antenna, the method proposed here provides a morepractical approach to improve the transmission efficiency of Cassegrain antenna.

Analysis and correction of stray thermalradiation in infrared optical systems includingan experimental case study

zhihui yang, yonghui Ma, juguang Guo, weiwei Jiang, and aihui Geng

Doc ID: 358007 Received 17 Jan 2019; Accepted 09 Apr 2019; Posted 10 Apr 2019  View: PDF

Abstract: In infrared systems, the stray radiation from optical elements and mechanicalstructures is an important factor affecting quantitative measurements because the irradianceon detectors due to stray radiation depends on the operating temperature of the optical system.Without correcting for this effect, the accuracy of quantitative measurements made with suchsystems is degraded. To better understand this phenomenon, we derive herein a mathematicalmodel that describes stray radiation as a function of temperature and use the model to analyzequantitatively the stray radiation of an infrared system at different operating temperatures. Totest the theory, we use it to calculate the stray radiation from an experimental infrared systemcomprising a Cassegrain reflector in the first stage, and a transmission mirror in the secondstage. The maximum relative error between theory and experiment was 8.72%. At the sametime, a corrective measure of stray radiation is provided to account for the effect of strayradiation on quantitative measurements. The relative error of quantitative measurementsdecreases from 2.16% to 0.31%. The measurement accuracy of infrared system has beenimproved effectively.

Terahertz beam focusing through designed obliquemetal-slit array

Takehito Suzuki, Masashi Sekiya, and Hideaki Kitahara

Doc ID: 356571 Received 02 Jan 2019; Accepted 09 Apr 2019; Posted 10 Apr 2019  View: PDF

Abstract: Manipulation of propagating beams is essential in applications, and the potentially arising phenomena offerattractive optical components. However, the design of optical components using only naturally occurring materialshas approached physical limits, and artificial materials such as metamaterials and meta-surfaces are a wayforward to open the door to sophisticated optical components. This report shows manipulation of terahertz beamsthrough designed oblique metal-slit arrays where a common metal-slit array does not perform as a lens. Theoblique metal-slit array has a refractive index determined as a function of a steep angle. The lens consists ofmultiple metal plates with a designed oblique angle, and a convex output structure produces a focusing effect. Wealso suggest that the Brewster phenomenon in the lens can simply enhance the electric field intensity at the focalpoint. The Brewster condition of the lens is correlated with a jagged edged face on the input side with anappropriate metal-slit spacing and thickness. The phenomenon would be applicable to numerous promisingcomponents and applications such as gain-enhancement optical components and perfect impedance-matchingpolarizers.

Terahertz Refractive Index Sensor Based on Tamm Plasmon-Polaritons With Graphene

Mohammad-Mehdi Keshavarz and Abbas Alighanbari

Doc ID: 360140 Received 14 Feb 2019; Accepted 09 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: A novel terahertz (THz) refractive index sensor based on Tamm plasmon-polaritons (TPPs), comprising a Bragg reflector and a graphene layer, is proposed. A semi-analytical transfer matrix method (TMM) is used to study the proposed structure and its sensing performance. The sensor demonstrates a sensitivity of 0.744 THz per refractive index unit (THz/RIU), equivalently 175.5 μm/RIU, and a figure of merit (FoM) of 10.33 RIU−1 at the operating frequency of 1.132 THz. The effects of structural parameters on the sensing performance are studied, offering new methods for improving TPP-based sensors. The proposed approach is a simple and practical alternative to traditional, and often more complex, THz sensing approaches, due to the ease of excitation which lifts the requirement of phase and polarization matching devices, such as polarizers, prisms, and gratings. The proposed structure is studied for gas sensing, and its performance is compared with previous THz refractive index sensing structures.

Ultra-smooth beryllium substrates for solar astronomyin extreme ultraviolet wavelengths

Nikolay Chkhalo, Mikhail Mikhailenko, Alexey Pestov, Vladimir Polkovnikov, Mariya Zorina, Sergey Zuev, Dmitry Kazakov, Aleksandr Milkov, Igor Stroulea, Vera Filichkina, and Aleksandr Kozlov

Doc ID: 360573 Received 19 Feb 2019; Accepted 09 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: The paper describes a multistage method of forming ultra-smooth substrates based on bulk beryllium. Such substrates aresuggested to be used for multilayer EUV mirrors of spacecraft missions on solar corona investigations in the spectral range17.1 - 58.4 nm. The technique for chemical nickel plating of the sample surface is described. The process parameters thatprovide the formation of an amorphous film with a thickness of about 100 microns are presented. The results of mechanicalpolishing are shown. The effective roughness of 1.3 nm is obtained, which is twice lower than one achievable for nickel-freeberyllium surface. The applicability of the ion beam figuring technique is demonstrated: the initial surface roughness of anickel film after etching with Ar ions (Eion=200–800 eV) to a depth of 250 nm does not deteriorate. The amorphous siliconfilm deposition followed by ion polishing made it possible to reduce the microroughness (AFM frame 2x2 μm) to σ2х2=0.15nm from the initial σ2х2=0.46 nm. The reflectivity of multilayer mirrors deposited on these substrates turned out to be closeto the values obtained on “witnesses” (supersmooth silicon substrates). Moreover, for the Mg/MoSi2 mirror optimized forthe wavelength λ = 58.4 nm the values of the reflection coefficients of structures on the beryllium substrate and on the silicon“witness” were identical (about 28%).

Method to define non-diffracting optical beamsmimicking the shape of simple plane curves

João Paulo de Amaral, José Carlos Rocha, Eduardo Fonseca, and Alcenisio Silva

Doc ID: 351284 Received 07 Nov 2018; Accepted 09 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: We theoretically and experimentally demonstrated a method to define non-diffracting beams with differentgeometries. Our findings constitute an alternative way to current methods of finding non-diffracting beams, whichrely on the solution of the wave equation in a given coordinate system, which has a limited number of possibilities,or uses a complicated and time-consuming optimization algorithm. Therefore, the method is easier to follow,because does not require an optimization, and allows one to obtain non-diffracting beams mimicking the geometryof simple plane curves. The method could find applications in manipulation of matter with optical waves, such ascolloidal and living particles, and in quantum, nonlinear and atom optics.

Effect of strong atmospheric non-Kolmogorovturbulence on the M-ary PSK subcarrier intensitymodulated free space optical communications systemperformance

Yalçın Ata, Yahya Baykal, and Muhsin Gökçe

Doc ID: 359923 Received 11 Feb 2019; Accepted 08 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: Atmospheric turbulence is one of the significant phenomena which degrades the free space optical (FSO)communications system performance, and thus designers need to define the requirements related to turbulenceand optimize the system design to ensure optimum performance. The subcarrier intensity modulation (SIM) showssuperiority in terms of bandwidth usage over the other modulation techniques. Performance of FSOcommunication system exercising M-ary phase-shift-keying (PSK) SIM with the PIN photodiode receiver isevaluated in non-Kolmogorov strong atmospheric turbulence when Gaussian beam is used as the excitation. Biterror-rate (BER) of PSK SIM FSO communications system is examined and the results are presented versus the non-Kolmogorov atmospheric turbulence and positive-intrinsic-negative (PIN) photodetector parameters such as, PINphotodetector responsivity, equivalent load resistor, modulation order, noise factor, bandwidth, propagationdistance and beam source size.

Notes on lateral and axial resolution criteria inincoherent and coherent optics and holography, nearand far-field regimes

Tatiana Latychevskaia

Doc ID: 357317 Received 09 Jan 2019; Accepted 08 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: This work presents an overview of spatial resolutioncriteria in classical optics, digital optics and holography.Although the classical Abbe and Rayleigh resolutioncriteria have been thoroughly discussed in theliterature, there are a few issues which still need to beaddressed, for example: the axial resolution criteria forcoherent and incoherent radiation - a crucial parameterthree-dimensional (3D) imaging, the resolution criteriain the Fresnel regime, the lateral and the axial resolutioncriteria in digital optics and holography. This workdiscusses these issues and provides a simple guide onwhich resolution criteria should be applied for particularimaging scheme: coherent/incoherent, far- and nearfield,lateral and axial resolution. Different resolutioncriteria such as as two-points resolution and the resolutionobtained from the image spectrum (diffractionpattern) are compared and demonstrated with simulatedexamples. Resolution criteria for spatial lateraland axial resolution are derived and their applicationwhen imaging with coherent and incoherent (noncoherent)waves is considered. It is shown that for coherentlight, the classical Abbe and Rayleigh resolution criteriado not provide accurate estimation of the lateraland axial resolution. The lateral and axial resolutioncriteria based on the evaluation of the spectrum of thediffracted wave provide more precise estimation of theresolution for coherent and incoherent light. It is alsoshown that the resolution criteria derived in approximationof the far-field can be applied for the near-field(Fresnel) imaging regime.

Efficient Simulation of Autofluorescence Effects inMicroscope lenses

Xiang Lu, Olga Rodenko, Yueqian Zhang, and Herbert Gross

Doc ID: 352446 Received 20 Nov 2018; Accepted 08 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: The use of fluorescence in microscopy is a well-known technology. Due to autofluorescence in the materials of theoptical components, the contrast of the image is degraded. The calculation of autofluorescence is usuallyperformed by brute-force methods such as the Monte-Carlo-based volume scattering. The efficiency of calculationsin this case is extremely low and a huge number of rays must be calculated. In stray light calculations the concept ofimportant sampling is used to reduce computational effort. The idea is to calculate only rays, which have thechance to reach the target surface. The fluorescence conversion can be considered to be a scatter process andtherefore a modification of this idea is used here. The reduction factor is calculated by comparing the size of theilluminated phase space domain with the corresponding acceptance domain in every z-plane of the lenses. Theboundaries of the domains are determined by tracing the limiting rays of the light cone of the source as well as thepixel area under consideration. The small overlap of both domains can be estimated by geometrical considerations.The correct photometric scaling and the discretization of the volumes must be performed. The errors resultingfrom necessary approximations can be corrected without greatly increasing computational effort. The run time isreduced by a factor of 104. It is shown with some practical examples of microscope lenses, that the results arecomparable with conventional methods. Additionally, a quasi-analytical model that describes the dependence ofautofluorescence on various lens parameters is derived.

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.

Unwrapped phase correction for robust 3Dscanning

Donguk Kam, Jeong Hee Kim, and Kunwoo Lee

Doc ID: 358552 Received 23 Jan 2019; Accepted 08 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: A temporal phase unwrapping method is proposed to generate an unwrapped phasemap for a robust three-dimensional (3D) scan. The proposed algorithm seeks to improve theaccuracy of the 3D data points obtained through the phase unwrapping process. By applyingthe k-nearest neighbor search method, the error bound of the wrapped phase is controlled withimproved flexibility. To achieve the desired scanning quality, a series of fringe patterns isgenerated with multiple phases at three different frequencies. For this method, the pattern isshifted by utilizing a six-step temporal phase unwrapping process. In this unwrapping process,the error bound is controlled by employing the k-nearest neighbor search method and spatialcomparison method to obtain an accurate fringe order. Through our correction method, thewrapped phases can be unwrapped more accurately, thus enhancing the robustness of the scanningsystem compared to the previous phase unwrapping methods.

Bending effect on the circular polarizer oforganic light emitting diode display

Jimin Park and Ji-Hoon Lee

Doc ID: 361083 Received 26 Feb 2019; Accepted 08 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: We investigated the retardation change of a reactive mesogen (RM)-type quarterwave plate (QWP) by bending. We measured the retardation of the QWP when the slow axisof the QWP was perpendicular or parallel to the bending axis. We simulated the effect of theretardation change on the anti-reflection property of a quasi-circular polarizer used for theorganic light emitting diode (OLED) display. The light leakage was diminished with bendingin the vertical viewing direction, while it was increased in the horizontal viewing directionregardless of the orientation of the slow axis.

Ptychographic Imaging of IncoherentlyIlluminated Extended Objects using SpeckleCorrelations

Dennis Gardner, Shawn Divitt, and Abbie Watnik

Doc ID: 361652 Received 21 Mar 2019; Accepted 08 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: A scattering layer is usually considered an obstacle to imaging. However, usingspeckle correlation imaging techniques, the scattering layer effectively acts as a lens. To date,the speckle correlation imaging method has been limited to imaging sparse samples. Here wedemonstrate imaging of incoherently illuminated extended objects in transmission and aroundthe-corner geometries. We are able to image extended objects by constraining the illuminationspot on the object and then scanning the object. A ptychography algorithm is used to reconstructthe extended object. This work demonstrates the applicability of ptychography to spatiallyincoherent light, and enables a new method of imaging in spectral regions where there is limitedchoice in optics, such as the terahertz, extreme ultraviolet, and x-ray regions.

On the uncertainties in determining fringephase in Doppler Asymmetric SpatialHeterodyne Spectroscopy (DASH)

John Harlander, Christoph Englert, Kenneth Marr, BRIAN HARDING, and Kristina Chu

Doc ID: 362221 Received 11 Mar 2019; Accepted 08 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: The mean fringe phase measured by Doppler Asymmetric Spatial Heterodyne(DASH) spectroscopy is a direct measure of atmospheric wind. The uncertainty in measuringthe mean phase is investigated and found to be accurately predicted by an analytic formula formoderate and high signal to noise ratios. At lower signal to noise ratios, numeric issues in thephase calculation result in non-Gaussian distributions of mean phase. Analysis techniques aredescribed to mitigate these numeric issues to the extent possible.

Magnetoplasmon excitation and hybridization ingyroelectric cylinders

Yudong Chen, Wen Xiao, Kui Han, Xiaopeng Shen, and Weihua Wang

Doc ID: 362935 Received 21 Mar 2019; Accepted 08 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: We investigate magnetoplasmon resonances and their coupling effcts in gyroelectriccylinders. In individual cylinders, the dipole plasmon can be excited by plane wave illumination,and the dipole plasmon splits into lower energy and higher energy rotational magnetoplasmonsin presence of an external magnetic field. With respect to the external magnetic field, the twomagnetoplasmons carry either right-handed chirality or left-handed chirality. Besides, originallydark plasmons can also be excited as increasing the magnetic field. They are lower order bulkplasmons (such as the radial breathing mode). In cylindrical dimers, the optically bright modes arecombinations of magnetoplasmons with the same chirality. If the magnetic fields are antiparallel,the absorption spectra will be different for light incident from two opposite directions. Thisasymmetry can be well understood by carrying out the eigenstate analysis, where the eigenstatedoes not possess mirror symmetry respecting to the dimer axis. The dark modes engineering andasymmetrical optical behavior could have potential for THz device applications.

Histograms of oriented gradients for automaticdetection of defective regions in thermograms

Jorge Erazo Aux, Humberto Loaiza-Correa, and Andrés Restrepo-Girón

Doc ID: 357887 Received 15 Jan 2019; Accepted 07 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: This paper presents a new methodology for the automatic detection of defective regions of interest (d-ROI) in thermal images of composite materials acquired with pulsed thermography based on obtaininglocal histograms of oriented gradients (HOGs) that are analyzed using a simple strategy to differentiatethe material background from the defective areas. The procedure is independent of image contrast orenhancement; it does not require analysis of a complete sequence of images, nor does it involve heattransfer models or the extraction of nonuniform heating information. The methodology is tested withsynthetic images of a carbon fiber-reinforced plastic (CFRP) sample, containing diameter/depth ratio defectswith different values (between 150 and 0.56). The performance of the d-ROI detection method isvalidated using the area under the ROC curve (AUC) measure, generally obtaining a maximum averagevalue of 0.949 with variations between 0.891 and 0.993 for all the defective depth and size conditions studied.In addition, the method is highly robust when detecting defects in 48.84% of the total number ofimages, as determined by the sequences analyzed with AUC values higher than 0.95. Outside the highdetectability index range, the AUC performance increases abruptly and decays gradually. The recentliterature proposes automatic detection of defects in thermograms with performances similar to those obtainedwith the proposed method; however, they require preprocessing of all the thermograms to improveimage contrast and visibility and to attenuate the adverse effect of nonuniform heating, which affects theimplementation complexity and the computational cost.

Laser frequency noise characterization by selfheterodynewith both long and short delay

Weichao Ma, Bing Xiong, Changzheng Sun, Xu Ke, zhibiao hao, Wang Lai, Jian Wang, yanjun han, Hongtao Li, and YI LUO

Doc ID: 356134 Received 27 Dec 2018; Accepted 07 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: We propose a novel approach to laser frequency noise characterization by delayed self-heterodyne. Compared withtraditional treatment, our method applies to both long and short delay, corresponding to uncorrelated andcorrelated self-heterodyne. In the case of long delay, it overcomes the influence of 1/f noise on intrinsic linewidthextraction from broadened spectrum and the results are more accurate than Voigt profile fitting. For short delayedcorrelated heterodyne, it eliminates artifact peaks at multiples of reciprocal of delay time introduced bytransferring measured RF phase noise to laser phase noise, thus extending the measurement range. In addition, itcalibrates the frequency noise overestimation caused by finite noise floor. This method remains valid when thedelay and the coherence time are comparable. Experimental results are presented to demonstrate the effectivenessof the proposed approach in characterizing lasers with intrinsic linewidth ranging from sub-100Hz to MHz.

Signal correction by detection of scanning position ina white-light interferometer for exact surface profilemeasurement

Songjie Luo, Takamasa Suzuki, Osami Sasaki, Samuel Choi, Ziyang Chen, and Jixiong Pu

Doc ID: 358951 Received 30 Jan 2019; Accepted 07 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: In order to perform an exact surface profile measurement with a white-light scanning interferometer (WLSI), anactual optical path difference (OPD) changing with time is detected with an additional interferometer in which thelight source of the WLSI and an optical band-pass filter are used. This interferometer is simply equipped in theWLSI and does not give bad influences to the WLSI. The real OPD is easily calculated from an interference signalwith the same signal processing as that in the WLSI. The interference signal of the WLSI is corrected with the realOPD values or the real scanning position values. The corrected interference signal with a constant samplinginterval is obtained with an interpolation method. By this correction method a surface profile with a step shape of3μm-height is measured accurately with an error less than 2 nm.

Wavefront sensing applied to determine the temperature dependence of liquids

rohan radhakrishnan, Laurent Gallais, and Serge Monneret

Doc ID: 360685 Received 21 Feb 2019; Accepted 07 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: A method based on wavefront sensing is described to determine thetemperature dependence of refractive index of liquids. The technique only implies to measure the wavefront of a light beam passing through a micro-vessel containing the liquid. Here, this vessel is a crater made by CO2 laser processing in a fused silica plate. From the wavefront analysis, the optical path that is related to the refractive index of the liquid can be determined.This measurement can be done at different temperatures to obtain the temperature dependence of the refractive index. This method is applied to three liquids : water, ethanol and cyclohexane at λ=630 nm. The results show a linear dependence in the range 17◦C−50◦C and give coefficientsdn/dT that are in good agreement with values from the literature.

Linear multimode interference fiber temperaturesensor using the liquid in glass thermometer principle

Daniel May-Arrioja, Victor Ruiz-Perez, Daniel Lopez-Cortes, and Nestor Lozano-Crisostomo

Doc ID: 352032 Received 21 Nov 2018; Accepted 07 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: A temperature sensor based on a Multimode Interference (MMI) thermometer is designed and fabricated. The operationmechanism is based on the thermal expansion of a specific volume of ethylene glycol contained into a glass bulb which isconnected to a capillary of the same material, with a No-Core fiber (NCF) inserted and centered into the capillary tube. Asthe temperature is increased, the liquid is expanded and the NCF is gradually covered by the liquid, resulting in a peakwavelength shift which is correlated to the temperature variations. A sensitivity of 0.4447 nm/°C and highly linear responsewith a R2 of 0.99962 is obtained. The advantage of this configuration is that the sensing temperature range can be adjustedby changing either the inner diameter of the capillary tube or the bulb volume. We can also measure negative temperaturesby just modifying the freezing point of the liquid, which demonstrates the viability of the sensor for many applications.

Measurement of atmospheric neutral wind andtemperature from Fabry-Perot interferometer datausing piloted deconvolution

Matthew Grawe, Kristina Chu, and Jonathan Makela

Doc ID: 354911 Received 10 Dec 2018; Accepted 06 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: Nonlinear regression techniques, when applied to sky exposures obtained using a Fabry-Perot interferometer(FPI), are able to recover atmospheric neutral wind and temperature through inversion of theresulting fringe pattern. Current inversion methods often account for temporal fluctuation of the etalon’soptical path length (caused by temperature variation in the instrument housing, for example) by characterizingthe system function using isolated exposures of a frequency stabilized laser. Because thesepath length changes correspond directly to shifts in the fringe pattern, they can significantly increase thetotal wind velocity uncertainty between laser exposures. We propose an extension to current regressiontechniques allowing for characterization of the optical path length and measurement of neutral wind andtemperature simultaneously, reducing the need for frequent isolated laser exposures. This is achievedby using the laser as a pilot signal that enters the aperture of the instrument during sky exposures. Weshow that the extension can lead to a lower variance estimator for velocity when the optical path lengthhas a significant time varying component. Additionally, several pragmatic physical configurations thatwould allow for construction of a piloted signal in a real system are tested and compared using an FPIinstallation at the Urbana Atmospheric Observatory.

Precision Optical Path Alignment System forPoint Diffraction Interferometer Based onImage Information

Zhuo zhao, Bing Li, Xiaoqin Kang, Lei Chen, and Xiang Wei

Doc ID: 360441 Received 19 Feb 2019; Accepted 06 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: In point diffraction interferometer, the existence of alignment error betweenobjective convergent spot and diffraction pinhole can lead to wavefront error and diffractionintensity reduction. Meanwhile, the contrast of the point diffraction interferograms probablydecreases in this procedure. These changes will have much influence on its inspectionprecision. A precise alignment system of optical path for point diffraction interferometer isproposed in this paper. Firstly, diffraction theory is used to analyze the mathematicalrelationships of alignment error to diffraction wavefront error and numerical aperture,wavefront error to pinhole size. Then according to the requirement, scheme of optical pathalignment system is designed. In this stage, alignment images as well as intensities ofreflected and diffracted beam from point diffraction plate will be acquired. In addition, animage processing algorithm for measuring alignment error is designed and mathematicalmodel between quantities of measurement and control is constructed. Finally, implementationand experiment of this method are also introduced. Misalignment situations including lateraltranslation, longitudinal defocus and tilt error are well eliminated and the quality ofinterferograms is also improved. From the results, it can be concluded that the system is ofdesirable precision and efficiency.

A model for separating the contributions ofnon-algal particles and colored dissolvedorganic matter to light absorption by seawater

Dariusz Stramski, Linhai Li, and Rick Reynolds

Doc ID: 359706 Received 06 Feb 2019; Accepted 05 Apr 2019; Posted 05 Apr 2019  View: PDF

Abstract: We evaluated the performance of a recently developed absorption partitioningmodel [J. Geophys. Res. Oceans 120, 2601 (2015)] which derives the spectral absorptioncoefficients of non-algal particles, aNAP(λ), and colored dissolved organic matter, ag(λ), fromthe total absorption coefficient of seawater. The performance was found unsatisfactory whenthe model was tested with a large dataset of absorption measurements from diverse openoceanand coastal aquatic environments. To address these limitations we developed a newmodel based on a different approach for estimating aNAP(λ) and ag(λ) from the sum of thesetwo coefficients, adg(λ), within the visible spectral region. A very good overall performanceof the model is demonstrated with no tendency for bias and relatively small absolutedifferences (the median ≤ 20%) between the model-derived and measured values of aNAP(λ)and ag(λ) over a wide range of aquatic environments.

Design and engineering verification of ultrashortthrow ratio projection system with a freeform mirror

Baihua Yu, Zhihui Tian, Dongqi Su, Yongxin Sui, and Huaijiang Yang

Doc ID: 358588 Received 23 Jan 2019; Accepted 05 Apr 2019; Posted 05 Apr 2019  View: PDF

Abstract: A refractive-reflective combined ultrashort throw ratio projection optical system is designed. We use afreeform mirror to shorten the projection distance and correct distortion, and a plane mirror to turn back theoptical path and reduce system volume. The projection system design method combines refractive lens groupdesign and freeform surface mirror design with integrated optimization. The system’s throw ratio is 0.11 with aprojection distance of 320 mm and a 130 in. (1 in. = 2.54 cm) screen size, which illustrates the advantages of thelow throw ratio. The system’s maximum distortion is 0.07%. To demonstrate the proposed system’sperformance, a prototype is developed. Experimental results confirm that the system performs excellentlywhile meeting the design requirements. The system’s advantages include low throw ratio, excellent imagingquality, miniaturization and engineering feasibility.

Tunable multi-functional reflection polarizer based ongraphene metasurface

zhifei yao, tongtong wei, yueke wang, mengjia lu, Chunyang Zhang, and lulu zhang

Doc ID: 359628 Received 04 Feb 2019; Accepted 04 Apr 2019; Posted 04 Apr 2019  View: PDF

Abstract: Herein, we present a tunable multi-functional reflection polarizer based on graphene metasurface, which iscomposed of an array of cross double-ellipse graphene patches. Dual-band of linear-to-linear polarizationconversion is achieved due to the superimposition of the two reflection components with a near 0° or 180° phasedifference, in the mid-infrared region. By carefully choosing the parameters, linear-to-circular polarizationconversion and broadband of linear-to-linear polarization conversion (about 0.7THz) are also realized. Besides,the tunable responses of the proposed reflection polarizer are discussed under different Fermi energy and electronscattering time. It is believed that our proposed polarizer can be widely used for multi-functional and tunablepolarization conversion.

Dual-Rod Pumping Concept for TEM00-Mode Solar Lasers

Bruno Tibúrcio, Dawei Liang, Joana Almeida, Dário Garcia, and Cláudia Vistas

Doc ID: 359683 Received 06 Feb 2019; Accepted 04 Apr 2019; Posted 05 Apr 2019  View: PDF

Abstract: We propose here a novel concept to a large improvement in TEM00-mode side-pumped solar laser collection,conversion efficiencies and brightness figure of merit by pumping two thin laser rods simultaneously, each rodbeing pumped by half of solar collector area instead of today’s one thick rod scheme pumped by full solar collectorarea. A semicylindrical fused silica lens allows an efficient focusing of the concentrated solar power from the focalzone of the parabolic mirror into the two thin laser rods mounted within two compound parabolic concentratorsemicylindricalpump cavities within the same laser head. 17.2 W continuous-wave TEM00-mode solar laser powerwas numerically calculated, corresponding to 11.0 W/m2 solar laser collection efficiency, 1.31%incoming solar power-to-TEM00-mode laser power conversion efficiency and 14.3 W brightness figure of merit,being 1.39, 1. and 2.21 times, respectively, higher than the previous state-of-the-art experimental records.

Mach-Zehnder fiber sensing and positioning systembased on common optical path technology

Ailing Zhang, Dan Li, HongGang Pan, and Bin Hao

Doc ID: 358181 Received 18 Jan 2019; Accepted 03 Apr 2019; Posted 03 Apr 2019  View: PDF

Abstract: A Mach-Zehnder interferometer (MZI) fiber sensing and positioning system based on common optical pathtechnology that combine the advantages of the positioning method of conventional MZI and the common opticalpath technology is proposed to improve the performance of the system in this paper. The feasibility of theinterferometer has been proved by simulation and experiment. In conventional MZI, the temperature andenvironment have effect on the system performance due to the interference light transmit through different opticalfibers. The system proposed in this paper overcomes the disadvantages of the conventional MZI.

Solar energy-actuated back and forth opticalmechanism

Lihui Wang, Hongjin Xu, and Masatoshi Ishikawa

Doc ID: 356837 Received 03 Jan 2019; Accepted 03 Apr 2019; Posted 04 Apr 2019  View: PDF

Abstract: A self-active back and forth motion mechanism for optical systems was designedand realized without electrical power consumption. The system utilized the beam convergingfeature and thermal heating performance of lenses in combination with the thermal-basedphase-changing feature of a shape memory alloy (SMA) actuator. Prototype 1 was designedand fabricated with a fixed lens group and a moveable lens group, and its feasibility wasconfirmed through experiments. An optimized focusing pattern suitable for the SMA actuatorwas realized by employing a cylindrical Fresnel lens, and prototype 2 was built using asimplified fabrication method. We believe that our design is economical and environmentfriendly. A few potential applications can be optical/mechanical switches for solar energypanels, control units for outdoor equipment, and solar power chargers.

IR camera based measurements of 2D/3Dcognitive fatigue in 2D/3D display systemusing task-evoked pupillary response

Sangin Park, Sungchul Mun, Dong Won Lee, and Mincheol Whang

Doc ID: 356131 Received 24 Jan 2019; Accepted 02 Apr 2019; Posted 02 Apr 2019  View: PDF

Abstract: This study was carried out to evaluate a method used to measure three-dimensional(3D) cognitive fatigue based on the pupillary response. This technique was designed toovercome measurement burdens by using non-contact methods. The pupillary response isrelated to cognitive function by a neural pathway, and may be an indicator of 3D cognitivefatigue. Twenty-six undergraduate students (including 14 women) watched both 2D and 3Dversions of a video for 70 minutes. The participants experienced visual fatigue after viewingthe 3D content. Measures such as subjective rating, response time, event-related potentiallatency, heartbeat-evoked potential (HEP) alpha power, and task-evoked pupillary response(TEPR) latency were significantly different. Multitrait-multimethod matrix analysis indicatedthat HEP and TEPR latency measures had stronger reliability and higher correlations with 3Dcognitive fatigue than other measures. TEPR latency may be useful for quantitativelydetermining 3D visual fatigue, as it can be easily used to evaluate 3D visual fatigue using anon-contact method without measuring burden.

Micro-optical vibrometer/accelerometer usingdielectric microspheres

Amir Ali

Doc ID: 348924 Received 23 Oct 2018; Accepted 02 Apr 2019; Posted 02 Apr 2019  View: PDF

Abstract: In this paper, an optical vibrometer/accelerometer is designed using microopticaldielectric sensors based on whispering gallery modes (WGM) phenomena. Theproposed design is created as a sphere made from polydimethylsiloxane (PDMS). Thedielectric sensor would be laying between piezo stack and a proof mass of 10-4 kg(implemented as body force to the sensor) in a vertical position. Once, the piezo start toimpose a vibration in the vertical direction, the proof mass start to vibrate leading to a changein the morphology of the sensor. In turn, the WGM shifts would be seen on the transmissionspectrum and would be related to the vibration / acceleration of the piezo. An analysis basedon the force transmissibility from the piezo to the optical sensor and calibrations are carriedout along with preliminary designs and experiments. Results showed that the proposed sensorcould reach a very high resolution up to 8 nano-g with sensitivity dλ/da ≈ 2.33 pm/μg.

Laser varifocal system synthesis forlongitudinal Gaussian beam shifting

Pavel Nosov, Dmitry Piskunov, and Alexander Shirankov

Doc ID: 355506 Received 21 Dec 2018; Accepted 01 Apr 2019; Posted 01 Apr 2019  View: PDF

Abstract: This article presents modeling approach of laser varifocal system for longitudinalGaussian beam waist shifting. Developed approach is based on laser optics theory, which isconsidered to be classical optics generalized for coherent radiation. A basic optical system,consisting of two components, was developed using this theory. Components have fixed focallengths and specific movements. Automated modeling algorithm was proposed, and anexample was provided in text. Various systems shown in this paper forms a Gaussian beamwith required waist parameters and provide its longitudinal shifts, which exceeds the length ofthe near-zone of a focused Gaussian beam. Such systems can be used in laser technologies,including micro- and nanosized objects manipulation.

Quantitative phase imaging based on simpleMichelson-type lateral shearing interferometry withrotational right-angle prisms

Tengfei Sun, Zhuang ZHUO, Wenhao Zhang, Peng Lu, and Jianren Lu

Doc ID: 357522 Received 11 Jan 2019; Accepted 01 Apr 2019; Posted 02 Apr 2019  View: PDF

Abstract: By using a kind of simple Michelson-type lateral shearing interferometry, in this paper, the precise quantitativephase measurement of the transparent microscopic objects is realized successfully. For this interferometry, on thebasis of the fundamental structure of the traditional Michelson interferometer, the two plane mirrors are replacedwith two very ordinary right-angle prisms. In the beginning, the ridges of the two right-angle prisms both are set toalign with the optical axis and be in the vertical direction. Subsequently, to achieve the lateral shear, one of thesetwo right-angle prisms is rotated around its ridge. Furthermore, the goal that gets more lateral shear can beperformed by introducing a bigger rotating angle or rotating another prism simultaneously. In addition, owing tothe simple structure of the Michelson interferometer and the inexpensive optical components used, the system iscompact, portable, easy to operate and low cost. The experimental results show the practicability of this system.

Compact fiber-optics ultrasonic sensor usingencapsulated micro-cantilever interferometer

Teng Guo, Peilong Li, Tianxi Zhang, and Xue-Guang Qiao

Doc ID: 359143 Received 04 Feb 2019; Accepted 01 Apr 2019; Posted 02 Apr 2019  View: PDF

Abstract: A compact optical fiber Fabry-Perot interferometer was proposed and demonstrated forultrasound wave (UW) measurement. The sensor consists of a suspended cantilever in a sealedhollow-core fiber (HCF), while end-face of leading-in fiber together with end-face of suspendedfiber act as two reflection mirrors and form an air cavity. A short section of graded index fiber(GIF) was also employed as micro-lens to improve the fringe contrast of interference spectralpattern. Thanks to the suspended fiber structure, the sensor presents high sensitivity to UWloading that allows the free suspended fiber to be stretched and compressed easily. By spectralside-band filtering technology, a simple intensity interrogation technology is used for UWdemonstration. Moreover, the sealed sensor structure avoids the disturbance from otherenvironment parameters, thus, presents good stability for UW detection.

Diffraction properties of liquid crystal cellwith beat structure formed by photoalignmentsubstrates

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

Doc ID: 360254 Received 15 Feb 2019; Accepted 01 Apr 2019; Posted 02 Apr 2019  View: PDF

Abstract: The diffraction properties of the liquid crystal (LC) cells fabricated byphotoalignment substrates with differently-periodic optical anisotropic distributions havebeen demonstrated. The twist angle distribution structure inside the LC cells formed by thegrating period difference between photoalignment substrates, has been named “beatstructure.” In addition to diffraction corresponding to the grating periods of photoalignmentsubstrates, beat structure itself also functions as a diffraction grating. The diffractionproperties can be controlled by varying the retardation. The fabrication method anddiffraction properties of the LC cells with beat structure have been explained by bothexperiment and theoretical analysis.

Divided-aperture subtraction-differentialconfocal method with nanoscale axialresolution

Rongjun Shao, Weiqian Zhao, Lirong Qiu, Yun Wang, Hanxu Wu, and Zhang rui

Doc ID: 359941 Received 11 Feb 2019; Accepted 31 Mar 2019; Posted 01 Apr 2019  View: PDF

Abstract: In this paper, a divided-aperture subtraction-differential confocal method(DASDCM) is proposed to meet the requirements of nanoscale non-contact heightmeasurements for precision machining, materials science, and biology. The DASDCMdivides the spot on the detection focal plane into two groups of circular detection areas, whichare symmetrical to the optical axis and consist of two concentric detection pinholes withdifferent sizes in each group. Then, the DASDCM uses a subtraction of the intensity signalsreceived from the two detection pinholes in each group to suppress the interference of thenon-conjugated information on the intensity signal, and uses the differential subtraction oftwo obtained circular detection signal to obtain a very sensitive axial response curve. Andthereby, the DASDCM greatly improves the axial resolution while considering the signal-tonoiseratio and axial dynamic range of the system, and can realize surface heightmeasurement without axial scanning by using the linear range of the axial response curve.Theoretical analysis and preliminary experiments show that DASDCM has an axial resolutionof 2 nm with a laser wavelength of λ = 632.8 nm and numerical aperture of NA = 0.8. Itprovides an effective technique for nanoscale height detection with high axial resolution.

Mueller matrix imaging of electrospun ultrafine fibers for morphology detection

Jun Wang, Xiaopeng Li, Yuanwen Zou, and Yong Sheng

Doc ID: 358452 Received 22 Jan 2019; Accepted 30 Mar 2019; Posted 01 Apr 2019  View: PDF

Abstract: In the fields of tissue engineering, drug delivery, and filtering material, the electrospun ultrafine fibers with micropores have important applications. The scanning electron microscope (SEM) is usually used to observe the microstructure of ultrafine fibers, but SEM has the disadvantages, such as small field of vision, high cost, and ionization damage. Given this, 16 (4×4) full transmission Mueller matrices of electrospun fibers with three different morphologies: smooth surface, microporous, and beaded microspheres were obtained. We find that the Mueller matrix element M44 is most sensitive to the micropores on fibers. In the M44 transformed image proposed in this paper, the different morphologies and contours of fibers can be clearly shown, providing a low-cost method for mass, nondestructive, rapid morphology detection of fibers

High efficiency tunable plasmonically-inducedtransparency-like in metasurface composed ofgraphene nano-ring and ribbon arrays and itsapplication

Somayyeh Asgari, Elnaz Shokati, and Nosrat Granpayeh

Doc ID: 349616 Received 29 Oct 2018; Accepted 30 Mar 2019; Posted 01 Apr 2019  View: PDF

Abstract: In this paper, plasmonically-induced transparency (PIT)-like phenomenon in the metasurface composed of theperiodic graphene ring and ribbon arrays are studied in THz region. We used the Lorentz oscillator model to analyze themetasurface physically and theoretically. PIT-like effect can be tuned by alternation of the chemical potential anddimension of the nano-graphene ring and ribbon. Resonance frequency of PIT-like phenomenon is not sensitive to theincident lightwave angle. As an application of the structure, a refractive index sensor is proposed and simulated.Furthermore, we propose the metasurface composed of double ring and graphene ribbon to realize the PIT-like effectwith three dips. Our results express an appropriate accost for the expansion of mid-infrared (MIR) absorbers andsensors.

Effects of forward models on thesemi-analytical retrieval of inherent opticalproperties from remote sensing reflectance

Wen Zhou, Jungfang Lin, and Ronghua Ma

Doc ID: 351405 Received 13 Nov 2018; Accepted 29 Mar 2019; Posted 29 Mar 2019  View: PDF

Abstract: Inherent optical properties (IOPs) play a key role in modulating the aquatic light field, and they are the core link to remotely sensing water constituents based on ocean color. Many semi-analytical algorithms (SAAs) have been developed to obtain IOPs from remote sensing reflectance (Rrs) data, and these algorithms require a forward model (FM) to link IOPs to Rrs. Most currently available SAAs use the FM presented in Gordon et al. [J. Geophys. Res. 93, 10909 (1988)](G88 hereafter) without knowledge of how other models would impact the retrieval of IOPs from R_rs. In this study, the effects of two popular SAAs, namely the Quasi-Analytical Algorithm (QAA) and the Generalized IOP Algorithm (GIOP-DC), combined with six different FMs on retrieval of IOPs from a synthetic dataset generated by Hydrolight software were evaluated. The results indicated that different FMs can have quite different effects on the computed Rrs (λ), and the effects are not uniform across the Rrs spectra. Of the six FMs tested, G88 and P05 [Appl. Opt. 44, 1 6 (2005)] produced the best estimates of Rrs (λ), and they also were less impacted by changes in particle phase function and different ranges of Rrs. When the two SAAs were combined with the six FMs, the SAAs combined with FMs G88 and P05 had slightly better quality in the retrieval of IOPs and were less impacted by changes in particle phase function and different ranges of Rrs compared to the other combinations.

An ultra-long-distance (>160km) distributedoptic fiber vibration sensing system withoutin-line repeater

Zi Ye, Churui Li, and Chao Wang

Doc ID: 358867 Received 28 Jan 2019; Accepted 29 Mar 2019; Posted 29 Mar 2019  View: PDF

Abstract: We proposed a distributed optic fiber vibration sensing system which can realize asensing distance more than 160km without any repeater. The system’s optical structure isbased on the Mach-Zehnder and Sagnac hybrid interference technique. To increase themonitoring distance, we used reflective Erbium Doped Fiber Amplifier (EDFA) instead oftraditional reflector at the end of sensing system. Besides, the phase generated carrier (PGC)was applied to eliminate the parasitic interferometric effects of Rayleigh scattering.

Estimation of colouration and luminous transmittanceof eyewear filters using a digital camera and whitepaper

Craig Williamson and Wesley Kinerk

Doc ID: 359191 Received 01 Feb 2019; Accepted 28 Mar 2019; Posted 29 Mar 2019  View: PDF

Abstract: Quantifying the colouration and luminous transmittance of eyewear filters is essential to understand their impacton human visual performance. Accurate measurements require the use of a spectrophotometer, with suchequipment often being prohibitively expensive for wide-scale use. This note details a new technique tocharacterise eyewear filters using only a digital camera and a sheet of white paper. Images of the paper arecaptured with and without the filter in front of the camera lens, and then subsequent analysis of pixel intensitiesallows the filter colouration and luminous transmittance to be determined. The technique has been applied to sixdifferent eyewear filters using three different camera and illumination configurations, demonstrating a reasonablematch to the spectrophotometer data. This technique is suited to implementation in a smartphone app, in order toprovide a low-cost and widely-deployable solution to monitor the ageing of eyewear inventory.

Impact of background and modulation on parameterestimation using fractional Fourier transform and itssolutions

jinmin wu, Ming-Feng Lu, Zhen Guo, and Ran Tao

Doc ID: 358187 Received 21 Jan 2019; Accepted 28 Mar 2019; Posted 29 Mar 2019  View: PDF

Abstract: Analysis of closed fringe patterns with quadratic phase that are often encountered plays an important rolein optical interferometry. But because the frequency spectra of the two exponential signals that composeclosed fringe patterns overlap in the Fourier domain while the one is clearly distinct from the other in thefractional Fourier domain, Fractional Fourier transform (FRFT) is hence a useful method for analyzingthe images to provide parameter estimation. However, when the fringe pattern has varying backgroundand/or modulation due to non-uniform illumination, parameter estimation accuracy based on FRFT is affected,which lacks a theoretical justification. Thus, the impact of varying background and/or modulationon the FRFT is studied with the theoretic analysis and presented in this paper. And the key factors thatcontribute to the optimal results are discussed when employing three kinds of fringe normalization methodsto eliminate the impact. Here, the fringe pattern is firstly processed by the normalization technique.Then the cosine-only term is used to estimate parameter by use of FRFT-based method. The physicalquantities can then be obtained by the parameter estimation. In comparison with our previous methodbased on FRFT, more accurate results are achieved. The feasibility and applicability of the proposedapproach are demonstrated using simulation and experimental results.

Broadband Static Fourier Transform Mid-Infrared Spectrometer

Michael Koehler, Stefan Naßl, Patrick Kienle, Xingchen Dong, and Alexander Koch

Doc ID: 357143 Received 08 Jan 2019; Accepted 28 Mar 2019; Posted 28 Mar 2019  View: PDF

Abstract: For applications where only moderate spectral resolution is required, static Fourier transform infrared spectrometers (sFTS) offer a comparatively cost-effective alternative to classical scanning instruments. In this paper we present a sFTS based on a single-mirror interferometer using only standard optical components and an uncooled microbolometer array.Since the instrument does not contain any lenses, broadband operation in the mid-infrared range from 2800 cm-1 to 600 cm-1 at a spectral resolution of 12 cm-1 is possible. In addition, the design guarantees comparatively high light throughput and can potentially be designed for high temperature stability. Alongside a simulation of the temperature and wavenumber dependent behaviour of the system, we provide a proof of principle of the proposed design by means of experimental results.

Batch denoising of ESPI fringe patterns based onconvolutional neural network

Fugui Hao, Chen Tang, Min Xu, and Zhenkun Lei

Doc ID: 358666 Received 25 Jan 2019; Accepted 28 Mar 2019; Posted 28 Mar 2019  View: PDF

Abstract: The denoising of electronic speckle pattern interferometry (ESPI) fringe patterns is a key step in the application ofESPI. In this paper, we propose a method for batch denoising of ESPI fringe patterns based on convolution neuralnetwork (CNN). In the proposed method, the network is firstly trained by our training dataset that consists of thenoisy ESPI fringe patterns and the corresponding noise-free images. And we propose a new computer-simulatedmethod of ESPI fringe patterns to create our training dataset. After training, the other multi-frame ESPI fringepatterns to be processed are fed to the trained network simultaneously, the corresponding denoising images canbe obtained in batches. We demonstrate the performance of the proposed method via application to 50 computersimulatedESPI fringe patterns and three groups of experimentally obtained ESPI fringe patterns. The experimentalresults show that our method can obtain desired results even when the quality of ESPI fringe images isconsiderably low because of variable density, high noise and low contrast. And our method can denoise multiframefringe patterns simultaneously. Moreover, we use the computer-simulated ESPI fringe patterns to train thenetwork, after training, the trained network can be used to denoise either computer-simulated ESPI fringe patternsor the experimentally obtained ESPI fringe patterns. The proposed method is especially suitable for processing alarge number of ESPI fringe patterns.

Multidimensional vector quantization-based faststatistical estimation in compressed digitalized RoFsystems

Hongliang Ren, Yu Pu, Jin Lu, Mingyi Gao, Zichun Le, Yali Qin, Shuqin Guo, and Weisheng Hu

Doc ID: 359765 Received 07 Feb 2019; Accepted 27 Mar 2019; Posted 28 Mar 2019  View: PDF

Abstract: A multi-dimensional vector quantization-based fast statistical-estimation algorithm (VQ-FSE) has been proposed toenhance data compression performance in digitalized radio over fiber (D-RoF) systems. The original samples withGaussian distribution are firstly transformed into these with uniform distribution via companding transformation.After companding transformation operation, the signal vector is constructed by grouping multiple samples in acertain way so that there is little correlation between each other for these samples. The constructed signal vectormay follow approximately multi-dimensional uniform distribution, and then multi-dimensional uniformquantization can be easily carried out, where the complex optimized process in nonuniform quantization is notrequired. For the proposed two-dimensional (2D) VQ-FSE algorithm, the proposed scheme is numerically verifiedin a 20km digitized RoF system with 2Gbit/s RF wireless signal. Compared with the scalar quantization (SQ)-basedFSE algorithm, its compression ratio is significantly enhanced. In comparison to 2D k-means clustering based VQalgorithm, the proposed scheme shares similar compression ratio and offers a lower computational complexity.Therefore, the proposed algorithm has the ability to provide better compression and a lower complexity for thedigitized radio over fiber (D-RoF) system when the original sample follows Gaussian distribution.

Novel metalens based on constructive interference

Lixia Liu, Han Wang, Yuansheng Han, Xiaoqing Lu, HaoRan Lü, and Shuyun Teng

Doc ID: 357196 Received 15 Jan 2019; Accepted 27 Mar 2019; Posted 28 Mar 2019  View: PDF

Abstract: A kind of metalens consisting of nanometer rectangular holes etched on silver film is proposed and the focusingeffect is actualized in the visible region. These rectangular holes are arranged on the concentric circles and thefields excited by these holes constructively interfere because of the same propagation phase. The propagation phaseis obtained through optimizing the sizes of rectangular holes and the radii of the circles. This metalens can focusthe linearly or circularly polarized light. Numerical simulations and experiment measurement confirm the focusingperformance of our proposed metalens. Our proposed metalens has advantages of flexible design, loose constraintto incident polarization, low-cost equipment and simpler experiment operation. We think it is helpful for theapplications of metalenses in optical integration and visible light imaging.

Cryptoanalysis on optical image encryption systemsusing vector decomposition technique in Fourierdomain

YI XIONG, Aohan He, and Chenggen Quan

Doc ID: 361088 Received 26 Feb 2019; Accepted 27 Mar 2019; Posted 27 Mar 2019  View: PDF

Abstract: In this paper, the security of optical cryptosystems based on vector decomposition technique in Fourier domain isanalyzed. Compared to the conventional cryptosystem based on equal modulus decomposition (EMD) technique,an additional EMD structure is introduced in the cascaded EMD-based cryptosystem; hence, the mask including thephase information of the Fourier spectrum is further encoded in the second EMD structure to enhance the securitylevel. However, it is shown that the number of the private keys has not been increased in the cascaded EMD-basedcryptosystem, which makes possible to crack the cascaded EMD-based cryptosystem. Therefore, a chosen plaintextattack (CPA) and a special attack with an arbitrarily given private key are proposed to retrieve information fromencoded images obtained by the cascaded EMD-based cryptosystem. In addition, the security of the cryptosystembased on random modulus decomposition (RMD) technique is also analyzed. Compared to the EMD-basedcryptosystem in which the Fourier spectrum is decomposed into two vectors with equal moduli, the security levelof the cryptosystem has been improved by using RMD technique to decompose the spectrum into vectors withunequal moduli to decrease the number of the amplitude constraints. However, it is found that the arbitrarily givenciphertext provides the attackers enough information to retrieve the precise information of the plaintext withoutany knowledge of the private keys. A special attack is proposed to crack the RMD-based cryptosystem. This is thefirst time to report that these two cryptosystems based on vector decomposition technique are attackedsuccessfully. Numerical simulation is conducted to validate the feasibility and effectiveness of the proposed attacks.

Predictive models for the Strehl ratio of diamond-machined optics

Hamidreza Aryan, Kevin Liang, Miguel Alonso, and Thomas Suleski

Doc ID: 352179 Received 16 Nov 2018; Accepted 26 Mar 2019; Posted 26 Mar 2019  View: PDF

Abstract: This paper provides a practical connection between the Strehl ratio as an optical performance metric and manufacturing parameters for diamond machined optics. The choice of fabrication parameters impacts residual mid-spatial frequency groove structures over the part’s surface, which reduce optical performance. Connections between the Strehl ratio and the fabrication parameters are studied using rigorous Rayleigh-Sommerfeld simulations for a sample optical system. The connections are generalized by incorporating the shape of diamond-machined groove structures and the effects of optical path differences for both transmissive and reflective optics. This work validates the analytical representation of the Strehl ratio as a Fourier transform of a probability density that relates to surface errors. The result is a practical tool that can be used to guide the choice of machining parameters to achieve a targeted optical performance.

Characteristics of Laser-induced Damage in K9 Glass Based on ANSYS

Fei Wang, Gao Fan, Zhang Xiang, and Xiao Yuan

Doc ID: 357827 Received 15 Jan 2019; Accepted 26 Mar 2019; Posted 26 Mar 2019  View: PDF

Abstract: Characteristics of damage in K9 glass irradiated by pulsed laser were analyzed, based on the three-dimensional model of transient heat conduction and the FEM software ANSYS. Simulation results show that, the thermal stress damage in K9 glass is mainly determined by the hoop stress, and the bulk damage occurs earlier than surface damage below the melting temperature. The tensile stress damage caused by the Gaussian beam is slightly higher than that caused by the flattop beam at the same irradiation energy. Besides, the inclusion has strong absorption to the laser energy due to electric field modulation and the stress on the rear surface is higher than that on the front surface.

A Comparative Study of Calibration-free Laser Induced Breakdown Spectroscopy (CF-LIBS)Methods for Quantitative Elemental Analysis of Quartz-bearing Limestone

Muhammad Fahad, Zahid Farooq, and Muhammad Abrar

Doc ID: 358643 Received 24 Jan 2019; Accepted 26 Mar 2019; Posted 26 Mar 2019  View: PDF

Abstract: Laser-induced breakdown spectroscopy (LIBS) has been employed for thequalitative and quantitative analysis of quartz-bearing limestone using two different calibrationfree LIBS methods, that is, one line calibration-free LIBS (OLCF-LIBS) and self-calibrationLIBS (SC-LIBS) methods in conjunction with energy dispersive X-ray spectroscopy (EDS) andX-ray fluorescence spectroscopy (XRF). The plasma is generated by focusing a Q-switchedNd:YAG laser (1064 nm, 134 mJ pulse energy, 9 ns pulse duration) in air under the atmosphericpressure. Spectral analysis revealed the presence of Ca, Si and Mg. Plasma temperature isdeduced using the neutral spectral lines of pertinent elements using Boltzmann plot method andan average value of 3462 K is used for the quantitative analysis. An average value for electronnumber density is calculated as (1.3 ± 0.3) × 1017 cm-3 from the Stark broadening of isolatedneutral Ca, Si and Mg lines and a singly ionized Ca line. The elemental composition determinedby different LIBS methods and other traditional analytical techniques are: OLCF-LIBS (Ca:71.82%, Si: 28.12%, Mg: 0.048%), SC-LIBS (Ca: 69.19%, Si: 28.92%, Mg: 1.87%), EDS (Ca:68.86%, Si: 30.12%, Mg: 0.32%), and XRF (Ca: 68.62%, Si: 27.18%, Mg: 1.56%). Bycomparing the results of both CF-LIBS methods along with EDS and XRF, it is demonstratedthat SC-LIBS method is appropriate than the OLCF-LIBS and gives compositions comparable2with that determined by EDS and XRF and hence, displays its ability as a powerful tool for thecompositional analysis of complex minerals.

Annular Subaperture Interferometry for High-Departure Aspheres Using Paraboloidal Parameterization

Keith Nowicki and Kelvin Wagner

Doc ID: 359690 Received 06 Feb 2019; Accepted 25 Mar 2019; Posted 26 Mar 2019  View: PDF

Abstract: A low-cost technique is presented for constructing stitched Fizeau interferometric measurements of high-spherical-departure concave aspheres of arbitrary conic constant without the use of null optics. The optical test configuration assembles the surface figure of the asphere using subapertures parameterized as variances from best-fit paraboloids. Subtracting the optical path difference between each idealized paraboloid and the corresponding annulus of measured data removes the annular wavefront aberrations without the need to fit Zernike polynomials. The proof-of-concept measurement and reconstruction of a 250 mm diameter diamond-turned ellipsoidal mirror with more than 3000 waves of spherical departure is reported. The presented technique is an inexpensive addition to the array of tools used to measure large aperture aspheres and high-departure freeform optics.

Differential phase standard deviation basedoptical coherence tomographic angiographyfor human retinal imaging in vivo

weisong shi, Chen Chaoliang, CHRISTOPHER PASARIKOVSKI, Wanrong Gao, and Victor Yang

Doc ID: 355915 Received 20 Dec 2018; Accepted 25 Mar 2019; Posted 26 Mar 2019  View: PDF

Abstract: We present a differential phase standard deviation (DPSD) based optical coherencetomographic angiography (OCTA) technique to calculate images of human retinalmicrovasculature. Standard deviation (STD) was calculated along depth direction on thedifferential phase image of two B-scans (same position at different times) to contrast dynamicvascular signals. The performance of DPSD was verified by both phantom and in vivoexperiments. When comparing to other OCTA algorithms such as phase variance OCT(PVOCT), speckle variance OCT (SVOCT) and optical micro-angiography (OMAG) on thesame data set, we showed that DPSD achieved improved image contrast and highersensitivity. Furthermore, we also found improved signal-to-noise-ratio (SNR) and contrast-tonoise-ratio (CNR) of 1.6 dB and 0.5 respectively in large scanning range images.

System for simultaneous sensing of sulfur dioxide andcarbon disulfide based on deep ultraviolet absorptionspectroscopy

Lin Wang, Yungang Zhang, Xue Zhou, and Zhiguo Zhang

Doc ID: 357514 Received 11 Jan 2019; Accepted 25 Mar 2019; Posted 25 Mar 2019  View: PDF

Abstract: In this study, a sensitive system for simultaneous sensing of sulfur dioxide and carbon disulfide was developedbased on absorption spectroscopy in the deep ultraviolet. An effective spectrum-unfolding approach is proposed toexamine the overlapping spectral characteristics. Direct proportional relations with determination coefficients of0.999 were obtained. The detection limit of sulfur dioxide was determined to be 42 ppb and a detection limit of 5ppb for carbon disulfide was achieved with an optical length of 20 cm. The interplay between the measurementresults of the two components was investigated. Interference close to the detection limits has been confirmed forboth sulfur dioxide and carbon disulfide measurements. An automatic and reliable simultaneous sensing systemfor sulfur dioxide and carbon disulfide was constructed.

A filter-free image-reject microwave photonic downconverterbased on cascaded modulators

Dongjuan Shan, Aijun Wen, Weile Zhai, Xiangrui Li, Wu Zhang, and Zhaoyang Tu

Doc ID: 358428 Received 24 Jan 2019; Accepted 25 Mar 2019; Posted 25 Mar 2019  View: PDF

Abstract: As an essential equipment of the receiver, a novel filter-free image-reject mixer based on a Mach–Zehndermodulator (MZM) and a polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) is proposed andexperimentally demonstrated in this paper. The received radio frequency (RF) signal is applied to the MZM andquadrature local oscillator (LO) signals are sent to the PDM-MZM which includes two sub-modulators in parallel.After a polarization controller and a polarization beam splitter, quadrature intermediate frequency (IF) signals areobtained by two photodetectors. Image rejection is implemented by combining quadrature IF signals via anelectrical 90° hybrid coupler. The scheme uses no filter, so the working frequency can be widely tuned andeffective spectrum utilization is achieved. Experimental results verify that image rejection ratios can reach 50 dB.Moreover, the variation of the conversion gain is lower than 2 dB.

A progressive scheme for blending empiricalocean color retrievals of absorption coefficientand chlorophyll concentration from open oceansto highly turbid waters

Shaoling Shang, Zhongping Lee, Gong Lin, Yonghong Li, and Xue Li

Doc ID: 351652 Received 14 Nov 2018; Accepted 25 Mar 2019; Posted 26 Mar 2019  View: PDF

Abstract: To achieve a smooth transition between algorithms for “clear” water and for“turbid” water, we propose a single formula to calculate the input parameter (ip) used forempirical retrieval of absorption coefficients (a) or chlorophyll concentration ([Chl]) fromremote-sensing reflectance (Rrs). This formula for ip takes the ratio of the maximum Rrs in theblue-green bands to the sum of Rrs(green) and the scaled Rrs in the red and infrared bands(termed as ipMax-Sum). We found that, compared to the widely used OC4-type formula for ip,ipMax-Sum can improve the coefficient of determination from ~0.88 to 0.99 for absorptioncoefficient at 440 nm (a(440)) in ~0.01 – 20.0 m-1 ([Chl] ~0.01 – 500 mg m-3). Especially, thesensitivity of ipMax-Sum to the change of a(440) is about five times greater than that of OC4-type for a(440) > ~1.0 m-1 ([Chl] > ~10 mg m-3). These results indicate an advantage of ipMax-Sum for generating robust and seamless a(440) or [Chl] from clear to highly turbid waters. Theinclusion of such a scheme in a quasi-analytical algorithm is also presented.

Titanium dioxide fiber saturable absorber for Q-switchedfiber laser generation in the 1-micron region

MOHD F. A. RAHMAN, P. H. Reddy, MUKUL PAUL, DAS SHYAMAL, Anirban Dhar, M. F. Baharom, Anas Abdul Latiff, Muhammad Farid Mohd Rusdi, Pengfei Wang, Kaharudin Dimyati, and Sulaiman Wadi Harun

Doc ID: 356100 Received 24 Jan 2019; Accepted 24 Mar 2019; Posted 27 Mar 2019  View: PDF

Abstract: A passively Q-switched Ytterbium-doped fiber laser (YDFL) operating at 1062 nm wasdemonstrated by using a segment of 20 cm Titanium dioxide-doped fiber saturable absorber(TiO2DF SA). The Q-switched YDFL emerged stably with tunable repetition rates, rangingfrom 32 kHz to 53 kHz as the pump power raised from 109 mW to 3 mW. Within thisrange of pump power, a maximum output power of 10.1 mW, a maximum peak power of 75mW and a maximum pulse energy of 191 nJ were obtained. The narrowest pulse width of2.55 μs was attained at the maximum pump power of 3 mW, while the signal to noise ratio(SNR) of the fundamental frequency was 47 dB. This demonstration reveals that the proposedTiO2DF SA is feasible for constructing a flexible and reliably stable Q-switched pulsed fiberlaser in the 1-micron region.

STATISTICAL PROPERTIES OF DYNAMIC SPECKLES IN APPLICATIONTO LASER FOCUSING SYSTEM

Zhan Yu, Jin Guo, Lisheng Liu, Tingfeng Wang, and Yuanyang Li

Doc ID: 355093 Received 11 Dec 2018; Accepted 22 Mar 2019; Posted 22 Mar 2019  View: PDF

Abstract: The dynamic speckles which carry the information about the beam parameters of the diffuse object is produced bya moving diffuse object under illumination of a Gaussian beam. In this paper, we consider that the diffuse objectmoves in a plane with constant velocity and discusses the statistical properties of dynamic speckles for estimatingthe variation of focusing spot size. The space-time statistical properties of dynamic speckle have been revealed byanalyzing the space-time cross-correlation function of speckle intensity fluctuations detected at the two points inthe receiving plane. We will discuss the influence of the distance between two point detectors on the detectionresults by simulation analyses, and the theoretical analysis results are verified by experiment. This method whichapplys feed-back dynamic speckles field for estimating the variation of focusing spot size will help the laserfocusing system to optimize the focusing performance.

Method for designing Phase RetrievalAlgorithms for Ronchi Phase-Shifting LateralShearing Interferometry

Feibin Wu, Jun Han, and Feng Tang

Doc ID: 356721 Received 04 Jan 2019; Accepted 22 Mar 2019; Posted 22 Mar 2019  View: PDF

Abstract: We propose a general method of designing phase-analysis algorithms for Ronchiphase-shifting lateral shearing interferometry. Based on the expression and method, three newphase-shifting algorithms are designed to eliminate negative error effects of interference fromunwanted diffraction orders, which limits the accuracy of wavefront aberration measurement.The proposed eight-, ten-, thirteen- frame algorithms can eliminate the effects of the first ±5,±9, and ±15 multi-diffraction orders, respectively. Simulation works and experimental resultsverify the general expression and the corresponding designed method.

Research on calculation method of multi-anglepolarization measurement of oil spill detection

Kan Ren, Yanyao Lv, Guohua Gu, and Qian Chen

Doc ID: 357474 Received 11 Jan 2019; Accepted 21 Mar 2019; Posted 22 Mar 2019  View: PDF

Abstract: This paper takes the thin oil film on the sea surface in oil spill pollution as the research object. Combining with thephysical characteristics of the target, the Mueller matrix of the target is analyzed by polarization technique. Thepaper use Mueller matrix derived the Mueller-Jones matrix. Based on the Mueller-Jones matrix, the opticalrecognition model of oil film on the sea surface is established. This paper designs a multi-angle polarizationmeasurement technology for oil spill pollution on the sea surface, and proposes a new data processing method. Bycalculating the corresponding amplitude ratio, phase retardation, refractive index and degree of polarization ofeach pixel, the optical properties of the oil film on the sea surface are analyzed, the surface characteristics of oilfilm on the sea surface are extracted, the calculation accuracy is improved and the ocean oil spill opticalrecognition is developed.

Research on scattering models of air particleswith variable size distribution and shapedistribution

zhirui cao and Hanbing Jiang

Doc ID: 357273 Received 11 Jan 2019; Accepted 19 Mar 2019; Posted 25 Mar 2019  View: PDF

Abstract: This paper proposes a new method for solving an average scattering model of airparticles with variable size distribution and shape distribution, analyzes the effects of sizedistribution and shape distribution of particles on the new scattering model, and compares thedifference of scattering models simulated by different shapes. The results indicate that theaccuracy of the new model is much better than that of Mie model and the previous averagescattering model, and the maximum relative errors of the new model for calculating theintensity distribution and polarization are 12% and 13%, respectively. The maximum relativedeviation between Mueller matrix phase functions is less than 7% when the effective radiusand variance of air particles are the same, the maximum relative deviation between Muellermatrix phase functions reaches more than 700% when the shape distribution of air particleschanges, and the maximum relative deviation between Mueller matrix phase functions is lessthan 18% when the shapes used to simulate the scattering model is changed.

Nano-finishing of the monocrystalline silicon waferusing magnetic abrasive finishing process

mohammad mosavat, Abdolreza rahimi, and Saeideh Karami

Doc ID: 358640 Received 25 Jan 2019; Accepted 18 Mar 2019; Posted 04 Apr 2019  View: PDF

Abstract: Monocrystalline silicon wafer is the key material for micro-electro-mechanical-systems. The performance of these wafers depends on their surface and subsurface quality. This research aims to study the effect of process parameters to the reduction ratio rate in surface roughness (%∆R· ) of monocrystalline silicon wafer during the Magnetic Abrasive finishing (MAF) process using Response Surface Methodology (RSM). The parameters studied were machining gap, rotational speed, abrasive size, and MAP size. Quadratic models were developed by applying Box-Behnken Design (BBD). Also, experiments were carried out on the silicon wafer and the results of surface roughness data were analyzed by using analysis of variance (ANOVA) and the most significant factor on each experimental design response was identified. According to our findings, the maximum %∆R· value and the best surface roughness of silicon wafer achieved 3.70 and 31nm respectively. Furthermore, the material removal mechanism in wafers was investigated by using AFM. Our observations showed that both micro-fracture and micro-cutting mechanisms might happen and it highly depends on polishing parameters.

Photonic-assisted wideband frequency downconverterwith self-interference cancellation and imagerejection

Beiyue Weng, Yu Chen, and Yang Chen

Doc ID: 357389 Received 11 Jan 2019; Accepted 12 Mar 2019; Posted 05 Apr 2019  View: PDF

Abstract: A photonic-assisted wideband frequency downconverter with self-interference cancellation and image rejectionfor in-band full-duplex radio-over-fiber (ROF) systems based on a dual-polarization quadrature phase-shift keying(DP-QPSK) modulator is proposed. The upper dual-parallel Mach–Zehnder modulator (DP-MZM) of the DP-QPSKmodulator is used to cancel the self-interference directly in the optical domain and generate two first-order opticalsidebands of the desired received radio-frequency (RF) signal. The lower DP-MZM generates two optical sidebandsof the local oscillator (LO) signal with optical carrier suppressed via properly biasing the modulator. The opticalsignals generated from the two DP-MZMs are combined, and then the upper and lower optical sidebands of thecombined signal are separated by a wavelength division multiplexer (WDM). The two outputs from the WDM aredetected by two photodetectors (PDs) and then combined at a 90° hybrid coupler to achieve frequency downconversionand image rejection. A simulation is performed. A quadrature phase-shift keying (QPSK) modulated RFsignal is successfully down-converted to 1-GHz intermediate-frequency signal with self-interference and imagefrequency cancelled. The performance of the frequency downconverter is also evaluated.

High-resolution terahertz coded-aperture imagingfor near-field three-dimensional target

Cheng-Gao Luo, Bin Deng, Hongqiang Wang, and Yuliang Qin

Doc ID: 351718 Received 13 Nov 2018; Accepted 08 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: In this paper, we propose a high-resolution terahertz coded-aperture imagingmethod with fast beam scanning for near-field three-dimensional target. This method utilizes acoded aperture to modulate incident terahertz wave randomly and to drive the terahertz beamto scan the entire imaging space step by step. Theoretical analyses based on physical opticsare performed and simulation experiments are implemented to demonstrate the feasibility ofthe proposed method.

Automated, Unsupervised Inversion of MultiwavelengthLidar Data With TiARA: Assessment of RetrievalPerformance of Microphysical Parameters UsingSimulated Data

Detlef Mueller, Eduard Chemyakin, Alexei Kolgotin, Richard Ferrare, Chris Hostetler, and Anton Romanov

Doc ID: 346995 Received 28 Sep 2018; Accepted 02 Jan 2019; Posted 04 Jan 2019  View: PDF

Abstract: We evaluate the retrieval performance of the automated, unsupervised inversion algorithm TiARA(Tikhonov Advanced Regularization Algorithm) which is used for the autonomous retrieval of microphysicalparameters of anthropogenic and natural pollution particles. TiARA (version 1.0) has been developedin the past 10 years and builds on the legacy of a data-operator controlled inversion algorithm that is usedsince 1998 for the analysis of data from multiwavelength Raman lidar. The development of TiARA hasbeen driven by the need to analyze in (near) real-time large volumes of data collected with NASA LangleyResearch Center’s HSRL-2 (High-Spectral-REsolution Lidar). HSRL-2 was envisioned as part of theNASA ACE (Aerosols-Clouds-Ecosystems) mission in response to the NAS Decadal Study (DS) missionrecommendations 2007. TiARA could thus also serve as inversion algorithm in the context of a futurespace-borne lidar. We summarize key properties of TiARA on the basis of simulations with monomodallogarithmic-normal particle size distributions which cover particle radii from approximately 0.05 – 10 mm.The real and imaginary parts cover the range from non-absorbing to highly light-absorbing pollutants.Our simulations included up to 25% measurement uncertainty. The goal of our study is to provide guidancewith respect to technical features of future space-borne lidars if such lidars will be used for retrievalsof microphysical data products, absorption coefficients, and single-scattering albedo. We investigated theimpact of two different measurement-error models on the quality of the data products. We also obtainedfor the first time a statistical view on systematic and statistical uncertainties if a large volume of data isprocessed. Effective radius is retrieved to 50% accuracy for 58% of cases with an imaginary part up to 0.01iand up to 100% of cases with an imaginary part of 0.05i. Similarly, volume concentration, surface-areaconcentration and number concentrations are retrieved to 50% accuracy in 56-100% of cases, 99-100% ofcases, and 54-87% of cases, respectively, depending on the imaginary refractive index. The numbers representmeasurement uncertainties of up to 15%. If we target 20% retrieval accuracy, the number of casesthat fall within that threshold are 36-76% for effective radius, 36-73% for volume concentration, 98-100%for surface-area concentration, and 37-61% for number concentration. That range of numbers again representsa spread in results for different values of the imaginary part. The real part should be retrieved toapproximately 0.075 or better. At present we obtain an accuracy of (on average) 0.1 for the real part. A casestudy from ORACLES is used to illustrate data products obtained with TiARA.

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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