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Doping concentration distribution in 2-signal LP modering-core erbium-doped fiber

Makoto Yamada, Daiki Nobuhira, Shota Miyagawa, Osanori Koyama, and Hirotaka Ono

Doc ID: 308964 Received 10 Oct 2017; Accepted 22 Nov 2017; Posted 22 Nov 2017  View: PDF

Abstract: We simulated an improvement in fiber characteristics, specifically the differential modal gain (DMG) and the LP11mode wavelength dependent gain (WDG) characteristics. We defined the DMG as the gain difference between the CbandWDM signal channels of the LP01 and LP11 modes at the shortest wavelength, and WDG was the gain differencebetween the signal gain of the LP11 mode at the shortest and longest wavelengths, when the DMG of the LP01 modewas zero. We achieved this improvement by changing the erbium doping distribution in ring-core erbium-dopedfiber (RC-EDF), which has been attracting attention as an amplification medium for a 2-mode (LP01 and LP11 modes)erbium-doped fiber amplifier for mode-division multiplexed transmission. We applied an α-th power profile,trapezoid profile, and right and left triangular profiles to the RC-EDF. We found that the DMG value changed fromnegative to positive despite the value of the LP11 mode WDG being positive, and confirmed that the DMG could beadjusted by changing the distribution. We show level curve maps of the DMG, LP11 mode WDG, pump power andEDF length on the allowable 2-signal-mode area map for inner and outer radius combinations of the RC-EDF, andclarify that it is possible to realize a region that provides high efficiency amplification with a low DMG of < |0.1| dBand a low WDG of < 0.1 dB. Furthermore, we show that by varying the distribution of the erbium dopingconcentration we can greatly change the position of the region on the map of the allowable 2-signal-mode area.

Spectral characteristics of coralline algae: a multi-instrumental approach, with emphasis on underwater hyperspectral imaging

Aksel Mogstad and Geir Johnsen

Doc ID: 307047 Received 13 Sep 2017; Accepted 21 Nov 2017; Posted 22 Nov 2017  View: PDF

Abstract: Coralline algae constitute a cosmopolitan group of calcifying rhodophytes (red algae) that display characteristic optical fingerprints due to light absorption by specific light-harvesting pigments. The spectrally conspicuous nature of coralline algae makes them potential candidates for optical remote sensing surveys, and recently, a novel optical remote sensing technique has entered the scene of marine research: underwater hyperspectral imaging (UHI). The aim of the study was to characterize the spectral properties of different coralline algal species, and to assess the potential of UHI as a coralline algal identification and mapping tool. Four species of coralline algae were investigated: Corallina officinalis, Lithothamnion glaciale, Phymatolithon lenormandii, and Phymatolithon tenue. Important coralline algal pigments were identified using spectrophotometry and high-performance liquid chromatography (HPLC). Reflectance spectra of all species were obtained using both a spectrometer and UHI. Multivariate statistical analyses were performed on the reflectance data to identify spectral differences between species and instruments. In addition, supervised classification of coralline algae in UHI transects recorded both in vivo and in situ was carried out. R-phycoerythrin and chlorophyll a were found to be the most dominant coralline algal pigments. The analyzed species of coralline algae displayed highly similar reflectance spectra, and dips in reflectance corresponding to the absorbance peaks of R-phycoerythrin and chlorophyll a were identified in all spectra. Wavelengths corresponding to R-phycoerythrin light absorbance were the greatest contributors to interspecific spectral differences, but the investigated coralline algal species could not be spectrally distinguished with great accuracy. Optical signatures recorded using different instruments were comparable, but inter-instrumental spectral differences were found to be greater than interspecific differences. Supervised UHI classification was unable to accurately map different coralline algal species due to the similarity of the optical fingerprints, but as a group, coralline algae could easily be identified. In the future, large-scale UHI surveys of coralline algal habitats should be carried out using platforms such as remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) to enhance our understanding of this widespread and ecologically important organism group.

Distribution law of dust concentration by imagetransmission in cement workshop

Jieping Wu, Guohui Li, Zhiwen Luo, Ming Zhu, and Xin Wu

Doc ID: 308040 Received 28 Sep 2017; Accepted 20 Nov 2017; Posted 22 Nov 2017  View: PDF

Abstract: The traditional experimental method has a common disadvantage that it only can measure the dust concentrationof a few sampling points, resulting in a limitation of the further research about distribution law of dustconcentration in cement workshop. Aiming at revealing more visually and accurately the distribution law of dustconcentration, a Vision Based Measurement (VBM) system for dust concentration based on the image transmissionis constructed by utilizing an established dust simulation device in cement workshop. The measurement systemmeasured the dust concentration in the X-direction and Z-direction with a line-scanning-measuring mode and that ofend face XOZ in a face-scanning-measuring mode. Experimental results show that the distribution law of dustconcentration can be regarded as a first exponential function and then oscillating function relationship between thedust concentration and the distance from the dust source in X-direction, a parabolic function between the dustconcentration and the distance from the dust source in Z-direction, and a type of laminar or turbulence distribution inthe end face XOZ. The proposed VBM and the revealed law can provide a reference for the study of dust concentrationdistribution and dust control.

Gallium and polydimethylsiloxane molding for self-organized spherical lens surface fabrication

Keisuke Nakakubo, Hiroaki Nomada, Hiroaki Yoshioka, Kinichi Morita, and Yuji Oki

Doc ID: 307913 Received 27 Sep 2017; Accepted 20 Nov 2017; Posted 21 Nov 2017  View: PDF

Abstract: We present a new fabrication method for optical surfaces using liquid metal molding. Common optical surfaces are fabricated by the polishing of glasses or plastics. By contrast, the fabrication method we propose involves the transfer of a spherical surface of liquid molded metal with silicone rubber. The concept presented in this paper is of a new molding method in which a mold is placed inside. The curvature can be controlled from ~ 0.37 to -0.37 by wetting the liquid metal. An application of this method is to produce on-demand optical elements (e.g., lenses and mirrors).

A hollow fiber based surface plasmon resonance sensor with large RI detection range and high linearity

Liangcheng Duan, Xianchao Yang, ying lu, and Jianquan Yao

Doc ID: 308134 Received 28 Sep 2017; Accepted 20 Nov 2017; Posted 21 Nov 2017  View: PDF

Abstract: A surface plasmon resonance (SPR) sensor based on the gold coated hollow fiber (HF) is proposed to realize the detection of refractive index (RI). The large hollow core (HC) of the HF is utilized as the microfluidic channel of the analyte and gold is coated inside the air holes surrounding the core to generate surface plasmons (SPs). Benefitting from the unique structure of HF and liquid filling into the core, the sensor can work in a large RI range from 1.27 to 1.45 at the near-infrared (NIR) region, overcoming the limitation of 1.42 as other side-hole-filled photonic crystal fiber (PCF) based SPR sensors reported. Moreover, the relations between the resonance wavelength and RI are highly linear, more suitable for the standardization while almost all of similar works show higher sensitivity for the high RI change than for the low. The average spectral sensitivity 5653.57 nm/RIU is obtained. Other structure parameters like gold coated air hole numbers and gold layer thickness are also investigated.

Tunable single-longitudinal-mode Ho:YAG laser pumped by 1.13 μm diode laser

Wenjing Li, Qing Wang, Yalong Wang, Yalan Wang, and Chunqing Gao

Doc ID: 305932 Received 30 Aug 2017; Accepted 20 Nov 2017; Posted 21 Nov 2017  View: PDF

Abstract: We demonstrated a 1.13 μm diode-pumped tunable single-longitudinal-mode Ho:YAG laser. With double intracavity Fabry-Perot etalons, the maximum single-longitudinal-mode output power of 102 mW at 2129.6 nm was obtained. The tuning range was from 2119.7 to 2131.5 nm by precisely rotating two etalons. The beam quality factors M² were 1.29 and 1.28 in x and y directions, respectively.

Digital synthesis of optical interleaver based on solidmulti-mirror Fabry-Perot interferometer

Juan Zhang, Dong Hua, Yipeng Ding, and Yang Wang

Doc ID: 306435 Received 11 Sep 2017; Accepted 19 Nov 2017; Posted 21 Nov 2017  View: PDF

Abstract: Starting from the matrix method introduced by Stadt, Muller and Bae, digital signal processing (DSP) techniquesare used to design multi-mirror Fabry-Perot (MMFP) interferometers. Solid MMFP interleavers with different filterorders and duty cycles are synthesized and optimized with this DSP method to achieve high isolation, wide flat-top,and large passband bandwidth ratio. Tolerance analysis of a typical structure is presented as well. This method isused to explain an interferometric measurement to show its utility in experimental practice. This method can alsobe applied to the design and analysis of other interference devices based on Fabry-Perot etalons.

Deformation of a spherical lens caused by its own weight

Petr Pokorny, Filip Smejkal, and Antonin Miks

Doc ID: 305910 Received 29 Aug 2017; Accepted 19 Nov 2017; Posted 21 Nov 2017  View: PDF

Abstract: The paper presents method for calculation of a surface deformation of a spherical lens or a plane-parallel plate caused by their own weight. Formulas for the case of support at the edge or for the inner radius support are presented. Since it is not possible to find an analytical solution with appropriate boundary conditions, the paper presents numerical methods enabling us to calculate an approximate solution. The mentioned deflection has enormous impact in the field of optical metrology of large lenses where it has to be taken into account during precise measurements.

Performance Improvement of GSSM prototype:Calibration, Added-on Damping Treatment andWarping Harness

qichang an, zhang jingxu, Fei Yang, Hongchao Zhao, and liang wang

Doc ID: 307736 Received 22 Sep 2017; Accepted 19 Nov 2017; Posted 21 Nov 2017  View: PDF

Abstract: Giant Steerable Science Mirror (GSSM), the tertiary mirror of Thirty Meter Telescope (TMT), is designed to meet complicatedrequirements. Calibration, added-on Damping Treatment and Warping Harness will lower the cost to meet thosestrictrequirements. Laser Tracker and Sphere Mounted Retro-reflector (SMRs) were used to calibrate the GSSM prototype. Usingof un-uniform distribution SMRs will lower the systematic metrology error. Frequency Response Function (FRF) between inputsexcitation and dummy mirror responses is investigated to realize the design of Tuned Mass Damping (TMD), which will be addedon GSSMP as a damping treatment to improve settling time and tracing performance.Finally, we utilized the Warping Harness,combining Zernike mode and Bending mode, to relax the requirements of GSSM for low order mirror figure aberrations.

Closed-form Harmonic Contrast Control with Surface Impedance Coatings for Conductive Objects

Giuseppe Labate, Symon Podilchak, and Ladislau Matekovits

Doc ID: 310188 Received 03 Nov 2017; Accepted 18 Nov 2017; Posted 22 Nov 2017  View: PDF

Abstract: The problem of suppressing the scattering from conductive objects is addressed in terms of harmonic contrast reduction. A unique compact closed-form solution for a surface impedance Zs(m,kr) is found in a straightforward manner and without any approximation as a function of the harmonic index m (scattering mode to suppress) and of the frequency regime kr (product of wavenumber k and radius r of the cloaked system) at any frequency regime.In the quasi-static limit, mantle cloaking is obtained as a particular case for kr << 1 and m=0. In addition, beyond quasi-static regime, impedance coatings for a selected dominant harmonic wave can be build with their proper dispersive behaviour, resulting in improved reduction levels and harmonic filtering capability.

Improvement of high-power laser performance for super-smooth optical surfaces using electrorheological finishing technology

Hao Yang, Haobo cheng, and Yunpeng Feng

Doc ID: 307367 Received 18 Sep 2017; Accepted 18 Nov 2017; Posted 21 Nov 2017  View: PDF

Abstract: Laser induced damage threshold (LIDT) is a key parameter for optical components heavily influenced by the surface roughness in high-power laser uses. Present polishing technologies often bring about directional micro waviness to the optical surfaces due to path effect. Roughness features of a K9 glass surface were studied in this paper. A new evaluating restriction for power spectral density (PSD) specification was established and the off-specification frequency contents were found out. Then the electromagnetic simulation of light field modulation was carried out and the field enhancement factor (FEF) reached 12.04, verifying the impact of these contents on the laser damage performance of optical components. To restrain the modulation effect by the textures, electrorheological finishing (ERF) technology was proposed and the processing was undertaken on the K9 surface. Roughness data converged to minimal Ra 1.00 nm and the angular spectrum decreased in expected ranges. ERF proved to be effective in eliminating the directional textures and restraining the light intensity modulation of the textures. As a result, the LIDTs of optical components can be improved by ERF processing.

Advanced Environmentally Resistant Lithium Fluoride Mirror Coatings for the Next-Generation of Broadband Space Observatories

Brian Fleming, Manuel Quijada, John Hennessy, Arika Egan, Javier Del Hoyo, Brian Hicks, James Wiley, Nicholas Kruczek, Nicholas Erickson, and Kevin France

Doc ID: 306985 Received 12 Sep 2017; Accepted 17 Nov 2017; Posted 17 Nov 2017  View: PDF

Abstract: Recent advances in the physical vapor deposition (PVD) of protective fluoride films have raised the far ultraviolet (FUV: 912 – 1600 Å) reflectivity of aluminum-based mirrors closer to the theoretical limit. The greatest gains, at more than 20%, have come for lithium fluoride protected aluminum (LiF+Al), which has the shortest wavelength cutoff of any conventional overcoat. Despite the success of the NASA FUSE mission, the use of LiF-based optics is rare as LiF is hygroscopic and requires handling procedures that can drive risk. With NASA now studying two large mission concepts for astronomy (LUVOIR and HabEx) that mandate throughput down to 1000 Å, the development of LiF-based coatings becomes crucial. This paper discusses steps that are being taken to qualify these new enhanced LiF protected aluminum (eLiF) mirror coatings for flight. In addition to quantifying the hygroscopic degradation, we have developed a new method of protecting eLiF with an ultrathin (10 – 20 Å) layer of a non-hygroscopic material to increase durability. We report on the performance of eLiF-based optics and assess the steps that need to be taken to qualify such coatings for LUVOIR, HabEx, and other FUV-sensitive space missions.

An empirical extension to the multi-oscillator model: The beta distributed oscillator (β_do) model

Steffen Wilbrandt and Olaf Stenzel

Doc ID: 307620 Received 20 Sep 2017; Accepted 17 Nov 2017; Posted 17 Nov 2017  View: PDF

Abstract: An empirical extension to the multi-oscillator model has been deducted. In order to comply with inhomogeneous line broadening, we have developed a novel approach based on the application of the beta distribution of single oscillators. The new model has been successfully applied in the course of optical constants determination from photometric measurements of single dielectric, amorphous semiconductor, metal and organic layers. Thereby, the number of required model parameter can be significantly reduced when comparing with the multi-oscillator model, while the Kramers-Kronig consistency remains guaranteed.

Discrete plasmonic Talbot effect in single mode graphene ribbon arrays

Lei Wang, yonglei jia, and Zhichao Ji

Doc ID: 308179 Received 28 Sep 2017; Accepted 16 Nov 2017; Posted 17 Nov 2017  View: PDF

Abstract: Controllable manipulation of surface plasmon polaritons in discrete waveguide arrays is critical in plasmonic applications. In this paper, exploiting the coupled-mode theory with the tight-binding approximation, discrete plasmonic Talbot effect in the weak coupled single mode graphene ribbon arrays is investigated. The Talbot distance can be flexible modulated by changing parameters (i.e. the carrier doping or array periods) of the graphene ribbon arrays, and the significantly subwavelength Talbot distances (λ/13) are obtained. In the configuration, the coupled-mode theory with the tight-binding approximation is proved intensely efficient to describe the propagation of surface plasmon supermodes. Our analysis can thus open a new avenue for developing graphene-based imaging devices and pave a way for their potential applications.

Optical multi-beam forming method based on a liquid crystal optical phased array

Feng Xiao and Lingjiang Kong

Doc ID: 309804 Received 23 Oct 2017; Accepted 16 Nov 2017; Posted 17 Nov 2017  View: PDF

Abstract: Three multi-beam forming methods based on the optical phased array technology are presented in this paper. These methods can achieve simultaneous multiple-beam pointing in the optical band. The principles of these methods are introduced, the far-field pattern calculation formulas of the sub-aperture method and the array division multiplexing method are derived, and the algorithm flow of the iterative Fourier transform method is described in detail. Simulations and experiment have been conducted to verify the validity of these methods.

Accurate shape measurement of focusing microstructures in Fourier Digital Holographic Microscopy

Marta Mikula, Tomasz Kozacki, Michal Jozwik, and Julianna Kostencka

Doc ID: 303086 Received 31 Jul 2017; Accepted 16 Nov 2017; Posted 16 Nov 2017  View: PDF

Abstract: This paper proposes a measurement method of focusing objects with high gradient shape of small and large radius of curvature. The measurements are carried out on a Fourier Digital Holographic Microscope with optimized illumination conditions maximizing the usage of the system numerical aperture. The obtained fringe patterns are the result of interference of deformed spherical object and spherical reference waves. The key elements of the method are the aberration compensation and calibration procedures. They provide accurate reconstruction of the object wave and determination of the focus position of the sample. The shape is calculated in two steps. First, the object wave is reconstructed at the plane of the object focus using single or multi-frame phase extraction algorithm and the specialized propagation method. The step includes also compensation of spherical aberration. In the second step, the sample shape is computed with Local Ray Approximation approach. The proposed method is experimentally validated with measurements of challenging, high gradient shapes (convex, concave) of different radiuses of curvature.

Small-mode-volume, channel-connected Fabry-Perotmicrocavities on a chip

Mohammad Bitarafan and Ray DeCorby

Doc ID: 304748 Received 14 Aug 2017; Accepted 15 Nov 2017; Posted 17 Nov 2017  View: PDF

Abstract: A monolithic thin-film buckling process was used to fabricate arrays of high-finesse ( 2 103) curvedmirrorFabry-Perot cavities on a silicon chip, with areal density 104 per square centimeter. The cavityshape matches the predictions of elastic buckling theory, with maximum curvature at the center where thefundamental mode resides. We describe cavities with mode volume < 1.5l3 for the fundamental spatialresonance. We also describe cavities connected to air-core channels. Preliminary light-coupling resultssuggest that these structures have potential to enable the side-coupling of gases, liquids, and pump, probeor trapping beams.

Noise suppression of micro-grating accelerometerbased on dual modulation method

Tianhang Zhang, huilan liu, Li Shuang Feng, Xiao Wang, and Yu Zhang

Doc ID: 297044 Received 30 May 2017; Accepted 15 Nov 2017; Posted 15 Nov 2017  View: PDF

Abstract: The micro-grating accelerometer, as a representative Micro-optical Eletromechanical Systerm (MOEMS) accelerometer,is studied widely on account of the advantages of small size and high resolution performance. The extremeaccuracy of the micro-grating accelerometer is mainly restricted by the noise floor. In order to improve theperformance of the micro-grating accelerometer, a dual modulation method is proposed which combined withintensity modulation and phase modulation. The intensity modulation can move the signal to a high frequency, andthe light source noise is suppressed perfectly by combining phase modulation. The dual modulation method isverified by constructing the micro-grating accelerometer prototype. Based on the two conditions above, the impactof 1/f noise is diminished. By comparison, the fluctuation of the system at 0.01g (1g=9.8 m/s2) is reduced about 3 dBwhich is in line with expectations. The power spectral density image shows that the system noise floor reaches -50dB with a decrease of about 10 dB. We hope that the low noise micro-grating accelerometer will be used generally inthe future.

Ultra-compact beam splitter and filter based ongraphene plasmon waveguide

Yang Junbo, XIN HE, YUNXIN HAN, DINGBO CHEN, JINGJING ZHANG, JIE HUANG, and ZHAOJIAN ZHANG

Doc ID: 302616 Received 18 Jul 2017; Accepted 15 Nov 2017; Posted 15 Nov 2017  View: PDF

Abstract: This paper presents a sheet of graphene ribbon waveguide as a simple and ultra-compact splitter and filter in midinfraredwaveband. The central wavelength of the graphene surface plasmons (GSPs) and the coupling intensity ofthis splitter can be tuned by changing the physical parameters, such as the chemical potential, the width ofwaveguide, the gap between neighbor graphene ribbons, the refractive index of the substrate, and the carrierrelaxation time and so on. The effects of these parameters on GSPs waves and beam splitter specifications arenumerically depicted based on the finite-difference time-domain (FDTD) method. This proposed structure can beused to construct an ultra-compact fast-tunable beam splitter, filter, modulator, switch in the mid-infrared range.

Direct Evidence of Laser-Induced Shock Wave Plasma from Organic Targets inLow Pressure He Ambient Gas Showing the Effect of Target Hardness on ItsPropagation Speed and the Resulted Spectral Performance

Kurnia Lahna, Marincan Pardede, Koo Hendrik Kurniawan, Kiichiro Kagawa, and May-On Tjia

Doc ID: 306310 Received 07 Sep 2017; Accepted 15 Nov 2017; Posted 15 Nov 2017  View: PDF

Abstract: We report the experimental evidence of shock wave plasma generation by directobservation of the plasma propagation using 68 mJ 1064 nm Nd:YAG laser irradiation on arelatively soft organic sample in He ambient gas at 2 kPa. The density jump associated withthe arrival of plasma front at a certain position is detected by means of the highly sensitiveinterferometric technique in conjuction with the observation of the first apperance of theplasma emission at the same position and time of the plasma front arrival. The result showsthat the plasma front moves at the Sedov speed typical of shock wave propagation yieldingexcellent emission spectrum for the harder sample. The shock front speed is further found todecrease in the case of softer sample resulting in lesser spectroscopic performance asdemonstrated by the emission spectra measured from mochi samples of different hardnesses.The result of this study is promising for paving the way of extending the LIBS application tothe much needed spectrochemical analysis of agricultural and food products.

Optical diffraction tomography with fully and partiallycoherent illumination in high numerical aperturelabel-free microscopy

Juan Soto, Jose A. Rodrigo, and Tatiana Alieva

Doc ID: 307386 Received 18 Sep 2017; Accepted 15 Nov 2017; Posted 15 Nov 2017  View: PDF

Abstract: Quantitative label-free imaging is an important tool for the study of living micro organisms which duringthe last decade has attracted wide attention from the optical community. Optical diffraction tomography(ODT) is probably the most relevant technique for quantitative label-free 3D imaging applied in widefieldmicroscopy in the visible range. The ODT is usually performed using spatially coherent light illuminationand specially designed holographic microscopes. Nevertheless, the ODT is also compatible withpartially coherent illumination and can be realized in conventional wide-field microscopes by applyingrefocusing techniques as it has been recently demonstrated. Here we compare these two ODT modalitiesunderlining their pros and cons and discussing the optical setups for their implementation. In particular,we pay special attention to a system which is compatible with conventional wide-field microscope andcan be used for both ODT modalities. It consists of two easily attachable modules: the first one for sampleillumination engineering based on DLP technology and another one for focus scanning by using anelectrically-driven tunable lens. This hardware allows for a programmable selection of the wavelengthand the illumination design, as well as it provides fast data acquisition. Its performance is experimentallydemonstrated in the case of ODT with partially coherent illumination providing speckle-free 3Dquantitative imaging.

The alignment error analysis of detector array forspatial heterodyne spectrometer

wei jin, dihu chen, Zhiwei Li, luo yan, and Hong Jin

Doc ID: 308111 Received 29 Sep 2017; Accepted 14 Nov 2017; Posted 15 Nov 2017  View: PDF

Abstract: Spatial heterodyne spectroscopy(SHS) is a new spatial interference spectroscopy which can achieve high spectralresolution. The alignment error of the detector array can lead to a significant influence with the spectral resolutionof SHS system. Theoretical models for analyzing the alignment errors which are divided into three kinds arepresented in this paper. Based on these models, the tolerance angle of these errors has been given respectively.The result of simulation experiments shows that when the angle of slope error, tilt error, and rotation error areless than 1.21 °, 1.21 °, 0.066 ° respectively, the alignment reachs an acceptable level.

Long Period Fiber Grating: A Specific Design forBiosensing Applications

Sankhyabrata Bandyopadhyay, Palas Biswas, Francesco Chiavaioli, TANOY DEY, Nandini Basumallick, Cosimo Trono, Ambra Giannetti, Sara Tomelli, Francesco Baldini, and Somnath Bandyopadhyay

Doc ID: 307343 Received 18 Sep 2017; Accepted 14 Nov 2017; Posted 14 Nov 2017  View: PDF

Abstract: In this paper, a detailed investigation on the modeling of long period fiber grating (LPFG) sensors is discussed withthe aim to provide a more realistic solution for their use in biosensing. Add-layer sensitivity, i.e. sensitivity of thesensor to an additional layer adhered on the fiber surface, has been quantified. A clear and complete analysisabout the influence of the average thickness of the deposited biological sensing layers, as well as the change inrefractive index (RI) of these layers, on the resonant wavelength of the cladding modes of an LPFG has beenprovided. Add-layer sensitivity of LPFG sensors close to mode transition (MT) and also at turn-around point (TAP)has been taken into account. Adsorbed layer thicknesses as estimated from measured wavelength shifts of LPFGwere found to have good match with the values obtained through other measurement techniques.

Spectral response characteristics of the transmission-mode AlGaNphotocathode with varying Al composition

Guanghui Hao, Junle Liu, and Senlin Ke

Doc ID: 310231 Received 30 Oct 2017; Accepted 13 Nov 2017; Posted 14 Nov 2017  View: PDF

Abstract: In order to research spectral response characteristics of transmission-modenanostructure AlGaN photocathode, the AlGaN photocathodes materials with variedAl composition were grown by MOCVD and measured its optical properties. The Alcompositions of each AlGaN film of the photocathodes were analyzed from itsadsorption properties curves, also the thickness of them were calculated by the matrixformula of thin film optics. The nanostructure AlGaN photocathodes were activatedwith the Cs-O alternation, and after the photocathode was packaged in vacuum, thespectrum responses of them were measured. The experimental results showing thatthe changes trend of spectrum response curves were first increased and then decreasedalong with the increasing of the incident light wavelength. The peak spectrumresponse value was 17.5 mA/W at 255nm, and its quantum efficiency was 8.5%. Thelattice defects near the interface of AlGaN heterostructure could impede the electronsmotion that crossing this region and moving toward the photocathode surface, thiswas a factor that reduces the electron emission performance of the photocathodes.Also the experimental result showing that the thickness of each AlGaN layer wasaffecting the electron diffusion characteristic, this was a key factor that influenced thespectrum response performance.

Novel green optical dissolved oxygen sensor onbased chlorophyll-zinc complex extracted from theplant Brassica Oleracea L

Erandir Silva, Paulo Pinto, Jécol Chretien, João Miranda, Hilton Pinho, Átila Timbó, Wilton Fraga, José Menezes, Marcos Silva, and Glendo Guimarães

Doc ID: 302820 Received 21 Jul 2017; Accepted 13 Nov 2017; Posted 14 Nov 2017  View: PDF

Abstract: In this study we present the development of a novel green and highsensitivity optical dissolved oxygen sensor for measuring dissolvedoxygen in water using spectrofluorimetry. For the development of thesensor element, an organometallic complex was synthesized from the‘chlorophyll A’ molecule, extracted from the plant Brassica OleraceaL.with zinc insertion (Zn+2) replacing the magnesium (Mg+2). In theinvestigation, we evaluated the fluorescence suppression of theorganometallic zinc complex for samples with different concentrationsof dissolved oxygen. The complex has shown two absorption regions,350-475 nm and 600-700 nm. We observed the fluorescencesuppression of the complex, when excited at 440 nm and analyzed at635 nm, using spinning oxygenation and air pump flow methods,respectively. The fluorescence suppression curves presented firstorder decay with good correlation, resulting in R2 = 0.98282 and R2 =0.83849 for the spinning and air pump flow methods, respectively. Inorder to validate the methodology, we developed a prototype of abench sensor. For the relation between the fluorescence intensity andoxygenation time, we obtained a ratio curve with R2 = 0.9809. Themethodology and prototype sensor developed in this work arepresented as a new optical method for the measurement of dissolvedoxygen.

Accurate calibration of multi-camera system based onflat refractive geometry

Mingchi Feng, Shuai Huang, Jingshu Wang, Bin Yang, and Taixiong Zheng

Doc ID: 307007 Received 13 Sep 2017; Accepted 13 Nov 2017; Posted 14 Nov 2017  View: PDF

Abstract: Multi-camera system is widely applied in many fields, but the camera calibration is particularly important anddifficult. In the application of multi-camera system, it is very common for multiple cameras distributed on bothsides of the measured object with overlapping FOV. In this paper, we present a novel calibration method for multicamerasystem based on flat refractive geometry. All cameras in the system can acquire calibration images oftransparent glass calibration board (TGCB) at the same time. The application of TGCB leads to refractivephenomenon which can generate calibration error. The theory of flat refractive geometry is employed to eliminatethe error. The proposed method combines the camera projection model with the flat refractive geometry todetermine the intrinsic and extrinsic camera parameters. The bundle adjustment method is employed to minimizethe reprojection error and obtain optimized calibration results. The simulation is performed with zero-meanGaussian noise of the standard deviation changes from 0 to 0.4 pixels, the results show that the error of rotationangle is less than 5.6e-3 degree, and the error of translation is less than 4.6e-3 mm. The four-cameras calibrationresults of real data show that the mean value and standard deviation of the reprojection error of our method are4.3411e-05 and 0.4553 pixels, respectively. Both the simulative and real experiments show that the proposedmethod is accurate and feasible.

Laser induced breakdown spectroscopy for threedimensionalelemental mapping of compositematerials synthesized by additive technologies

Vasily Lednev, Pavel Sdvizhenskii, Mikhail Grishin, Cheverikin Vladimir, Anton Stavertiy, Roman Tretyakov, M Taksanc, and Sergey Pershin

Doc ID: 308999 Received 13 Oct 2017; Accepted 13 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: Three-dimensional multielemental mapping of composite wear resistant coatings by laser induced breakdownspectroscopy has been demonstrated for the first time. Individual clads of 1560 nickel alloy reinforced withtungsten carbide were synthesized by co-axial laser cladding technique. Electron energy dispersive X-rayspectroscopy revealed elemental maps for major elements (W, Ni, Co, Cr, Fe) but failed to measure silicon andcarbon. Laser induced breakdown spectroscopy was utilized for elemental mapping of carbon and all otherelements of interest. It was demonstrated that three-dimensional elemental profiling for few tens of micronsrequires substantial laser spot overlapping during scanning procedure in order to achieve good accuracy of depthmeasurements. Elemental maps for nickel, iron, chromium, silicon, tungsten and carbon were quantified for900x900x45 μm3 volume with 30 μm lateral and 4 μm depth resolution in case of tungsten carbide particles innickel alloy.

A homogeneous material based calibration methodfor correcting laser induced breakdown spectroscopymeasurement-error bias in the case of dust pollution

Yang Zhao, Lei Zhang, Wangbao Yin, Jiajia Hou, Zhe Wang, Zongyu Hou, Weiguang Ma, Lei Dong, Guangye Yang, Liantuan Xiao, and Suotang Jia

Doc ID: 304604 Received 10 Aug 2017; Accepted 13 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: A calibration method based on homogeneous material for correcting laser induced breakdown spectroscopy (LIBS)measurement-error bias in the case of dust pollution under laboratory conditions is proposed. The measuredplasma spectra of the sample can be corrected by measuring spectral integral of the homogeneous material. Thuswe can effectively minimize the dust pollution effect on LIBS and guarantee the precision. Results show that themean absolute errors (MAE) of CaO, MgO, Fe2O3, Al2O3 and SiO2 in cement sample are decreased notably from1.02%, 0.06%, 0.15%, 0.57% and 0.80% to 0.41%, 0.02%, 0.04%, 0.35% and 0.39%, respectively. Combination ofthis calibration method with the traditional optical dust proof methods will significantly extend the LIBSequipment maintenance cycle and make preliminary preparations for the next practical industrial application.

Wide-angle absorption of visible light from simplebilayers

Athanasios Papadimopoulos, Nikolaos Kantartzis, Nikolaos Tsitsas, and Constantinos Valagiannopoulos

Doc ID: 304219 Received 08 Aug 2017; Accepted 12 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: Color-selective absorption of light is a very significant operation used in numerous applications fromphotonic sensing and switching to optical signal modulation and energy harnessing . We demonstrateangle-insensitive and polarization-independent absorption by thin bilayers comprising ordinary bulkmedia: dielectrics, semiconductors, and metals. Several highly efficient designs for each color of the visiblespectrum are reported and their internal fields’ distributions reveal the resonance mechanism of absorption.The proposed bilayer components are realizable, since various physical or chemical depositionmethods can be used for their effective fabrication. The absorption process is found to exhibit endurancewith respect to the longitudinal dimension of the planar structure, which means that the same designscould be successfully utilized in non-planar structures composed of arbitrary shapes.

Integrated Lloyd's mirror on planar waveguide facet as a spectrometer

alain morand, Pierre Benech, and martine gri

Doc ID: 307204 Received 15 Sep 2017; Accepted 12 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: A low cost and simple Fourier Transform Spectrometer based on the Lloyd's mirror configuration is proposed in order to have a very stable interferogram. A planar waveguide coupled to a fiber injection is used to disperse spatially the optical beam. A second beam superposed to the previous one is obtained by a total reflection of the incident beam on a vertical glass face integrated in the chip by dicing with a specific circular precision saw. The interferogram at the waveguide output is imaged on a NIR camera with an objective lens. The contrast and the fringe period are thus depending on the type and the fiber position and can be optimized to the pixel size and the length of the camera. Spectral resolution close to λ / Δλ = 80 is reached with a camera with 320pixels of 25µm width in a wavelength range from O to L bands.

Exposure fusion based dot-grid image acquisition andrecognition for sheet metal strain analysis

Bao-Quan Shi, Li-Kun Zhang, Chen-Song Yao, Shu-Xing Du, and JunJie Ye

Doc ID: 306276 Received 06 Sep 2017; Accepted 10 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: Dot-grid images are usually captured for grid strain analysis during sheet metal forming. Due to the strongreflective characteristic of the metallic surfaces, the recorded dot-grid images often have poor quality, lowpositioning accuracy and low recognition rate. Therefore, an exposure fusion based dot-grid image acquisition andrecognition approach is proposed. Firstly, Multiple dot-grid images are captured at different exposure levels.Subsequently, the recorded multi-exposure dot-grid images are fused into a new high quality dot-grid image basedon exposure fusion technology. Finally, a dot-grid image recognition procedure is developed to detect the dot-gridsin the new dot-grid image. Both synthetic and real dot-grid images were tested to verify the performance of thenovel approach. When synthetic dot-grid images were tested, the maximum positioning error is up to 6.044 pixelsif they were recognized in traditional way. Whereas, the maximum positioning error is reduced to 0.132 pixels ifthe novel approach was adopted. When real dot-grid images were tested, the lowest recognition rate is only50.52% if they were recognized in traditional way. Nevertheless, the recognition rate can reach about 91% if thenovel approach was employed. These experimental results show the superiorities of the novel approach.

Scanning Resonator Microscopy Integrating Phase Sensitive Detection

Robert Dunn

Doc ID: 307796 Received 25 Sep 2017; Accepted 10 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: Scanning resonator microscopy (SRM) is a scanning probe technique that uses a small, optical resonator attached to the end of a conventional atomic force microscopy (AFM) cantilever to simultaneously measure optical and topography properties of sample surfaces. In SRM, whispering gallery mode (WGM) resonances excited in the attached optical resonator shift in response to changes in surface refractive index (RI), providing a mechanism for mapping RI with high spatial resolution. In our initial report, the SRM tip was excited with a fixed excitation wavelength during sample scanning, which limits the approach. An improved method based on a wavelength modulation coupled with phase sensitive detection is reported here. This results in real-time characterization of WGM spectral shifts while eliminating complications arising from measurements based solely on signal intensity. This improved approach, combined with a modified tip design enabling integration of smaller resonators, is shown to enhance signal-to-noise and lead to sub-100 nm spatial resolution in the SRM optical image. The improved capabilities are demonstrated through measurements on thin dielectric and polymer films.

A robust method to probe the topological charge of a Bessel beam by dynamic angular double slits

Jing Zhu, Pei Zhang, Dongxu Chen, Ruifeng Liu, Yingnan Zhou, Jinwen Wang, Hong Gao, and fuli li

Doc ID: 305839 Received 28 Aug 2017; Accepted 10 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: Precisely determining the topological charge (TC) of both integral Bessel beams(IBB) and fractional Besselbeams (FBB) is a key issue for their applications. However, most of the common methods could not probeboth the IBB and FBB precisely and robustly. In this paper we give a robust method to probe the topologicalcharge of a Bessel beam by dynamic angular double slits (ADS). We find that when a Bessel beam verticallyilluminates on a dynamic ADS, the information of the TC can be retrieved from its Fourier transform patternsnear the optical axis. Even though there is a small misalignment between the center of the beams and the ADS,the global variation tendency is still good enough to obtain the TC. Based on these properties, the dynamicADS device combining the method of fitting the experimental data can be used to measure the TC of any Bessellight beam precisely and robustly. The error is less than 2% without the misalign and is less than 6% with asmall misalign for our experimental data. This method paves a new way to measure the TC of vortex beams.

Optimizing alignment and growth of low-loss YAGsingle crystal fibers using laser heated pedestal growthtechnique

Subhabrata Bera, Craig Nie, Michael Soskind, and James Harrington

Doc ID: 305864 Received 31 Aug 2017; Accepted 09 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: Effect of misalignments of different optical components in the laser heated pedestal growth apparatushave been modeled using Zemax optical design software. By isolating the misalignments causing thenon-uniformity in the melt zone, the alignment of the components was fine-tuned. Using this optimizedalignment, low-loss YAG single crystal fibers of 120 mm diameter were grown, with total attenuation lossas low as 0.5 dB/m at 1064 nm.

Dynamic modulation of wideband slow-light with continuous group index in polymer-filled phtonic crystal waveguide

Changhong Li, Chongqing Yan, and yong wan

Doc ID: 304863 Received 14 Aug 2017; Accepted 09 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: The dynamic modulation of wide bandwidth and low dispersion slow light with continuous variation of group index ng is realized in polymer-filled photonic crystal waveguide (PF-PCW) with optimal structure. By adjusting the unified radius of air holes under different refractive index of polymer in the first two rows of holes adjacent to the defect, firstly, the structure optimization of PF-PCW is studied and obtain the fixed optimal structure. In the optimal PCW with hole radius r0=0.328a, fixed refractive index n1=1.74 of polymer in the first row holes, by adjusting refractive index n2, the flatten wide band slow light with large normalized delay bandwidth product of group index from 17.15 to 55.65 has been demonstrated. Then, by filling polymer with electro-optic effect into the second row holes, the dynamic modulation of the optimized slow light in PF-PCW is investigated. The simulation shows that the center operating frequency linearly slightly shifts to higher one, and the group index increase exponentially, as the applied voltage increases. And the average sensitivity of group index is about 0.3467/V, when applied voltage vary from 0V to 120V. These results opened the possibility for the dynamic control of slow light according to the practical requirements of flexibility and tunability.

Mueller Matrix Polarimetry on Plasma SprayedThermal Barrier Coatings for Porosity Measurement

David Luo, Enrique Barraza, and Michael Kudenov

Doc ID: 305270 Received 21 Aug 2017; Accepted 09 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: Yttria-Stablizied Zirconia (YSZ) is the most widely used material for thermal plasma sprayed thermal barriercoatings (TBCs) used to protect gas turbine engine parts in demanding operation environments. The superiormaterial properties of YSZ coatings are related to their internal porosity level. By quantifying the porositylevel, tighter control on the spraying process can be achieved to produce reliable coatings. Currently,destructive measurement methods are widely used to measure the porosity level. In this paper, we describe anovel nondestructive approach that is applicable to classify the porosity level of plasma sprayed YSZ TBCs viaMueller matrix polarimetry. A rotating retarder Mueller matrix (RRMM) polarimeter was used to measure thepolarization properties of the plasma sprayed YSZ coatings with different porosity levels. From thesemeasurements, it was determined that a sample’s measured depolarization ratio is dependent on the sample’ssurface roughness and porosity level. To this end, we correlate the depolarization ratio with the samples’surface roughness, as measured by a contact profilometer, as well as the total porosity level, in percentagemeasured using a micrograph and stereological analysis. With the use of this technique, a full field and rapidmeasurement of porosity level can be achieved.

An infrared image enhancement algorithm based on adaptive histogram segmentation

Jun Huang, Ma Yong, ying zhang, and fan fan

Doc ID: 304652 Received 14 Aug 2017; Accepted 09 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: Contrast enhancement plays a crucial role in infrared image pre-processing. Compared with the increasingly popular local-mapping enhancement methods, the global-mapping enhancement methods have a unique feature that is reserving the thermal distribution information which is vital in some temperature-sensitive applications. However, the main challenge of the global-mapping methods is how to enhance the contrast effectively without suffering from over-enhancement of the background and the noise. To this end, we propose a novel global-mapping enhancement algorithm in this paper. First, the histogram is divided into several sub-histograms adaptively based on heat conduction theory. By designing a metric called AHV, the background and non-background sub-histograms are distinguished, then enhanced separately, where more grayscales are allocated to non-background sub-histograms than background sub-histograms. Meanwhile, the property of the human visual system described by Weber’s law is also taken into consideration during grayscales redistribution. The qualitative and quantitative comparisons with state-of-the-art methods on several databases demonstrate the advantages of our proposed method.

Retrieval of aerosol asymmetry factor from Sun-skyradiometer measurements: application to almucantargeometry and accuracy assessment

Lili Qie, Zhengqiang Li, Philippe Goloub, Li Li, Donghui LI, Kaitao LI, Ying Zhang, and Hua XU

Doc ID: 304713 Received 11 Aug 2017; Accepted 08 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: The Devaux-Vermeulen-Li method (DVL method) is a simple method that directly retrieves aerosol opticalparameters based on single-wavelength solar-sky radiation observations, without the assumption of aerosolmicrophysical properties. Inheriting the previous retrieval of single scattering albedo (SSA) and scattering phasefunction, the DVL method is modified to derive aerosol asymmetric factor (g) parameter. Interpolation methodswere proposed to estimate the phase function over the extreme forward and backward scattering regions whereinstrumental observations are missing; Thus, g could be derived from the phase function over the entire scatteringangle region. To evaluate the g accuracy from the DVL algorithm, especially for non-spherical aerosols, syntheticretrieval with typical aerosol models (water-soluble, biomass burning, dust-sphericity and dust-spheroid models)and retrievals from AERONET observations (Beijing site, from January 2011 to March 2015) were implemented at 4wavelengths (440, 675, 870 and 1020 nm). The numerical experiments showed that DVL retrieves g with errorsless than ± 0.02 under “error-free” conditions. When measurement uncertainties were present, all g errors werewithin ± 0.03, except for the angular pointing error from the coarse mode-dominated dust-sphericity/spheroidaerosols. Most importantly, g retrievals were not sensitive to the aerosol optical depth (AOD) and sky radianceerrors, which are important influencing factors for SSA retrieval. Comparison of DVL retrievals with AERONETversion 2 level 2.0 products (with AOD (440 nm) ˃0.2) show that the DVL g was well correlated with that ofAERONET, especially for the 675, 870 and 1020 nm bands, with RMSDs smaller than 0.02 and absolute values ofMBDs smaller than 0.01. Relatively larger deviations occurred at the 440 nm band, where g values wereunderestimated by approximately 0.03 compared to those of AERONET, with a higher RMSD of approximately0.035. Both the synthetic retrieval and comparison with AERONET indicated that the algorithm for large, nonsphericalparticles is comparable to that of other spherical aerosol particles in retrieving g.

Error of image saturation in the structured-light method

zhao shuai qi, Zhao Wang, Junhui Huang, xing chao, and Jianmin Gao

Doc ID: 302172 Received 13 Jul 2017; Accepted 08 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: In phase measuring structured-light method, image saturation will induce large phase errors. Usually, by selectingproper system parameters (such as the phase-shift number, exposure time and projection intensity etc), the phaseerror can be reduced. However, due to lack of complete theory of phase error, there is no rational principle or basisfor optimal system parameters selection. For this reason, the phase error due to image saturation is analyzedcompletely, and the effects of the two main factors, including the phase-shift number and saturation degree, on thephase error are studied in depth. In addition, the selection of optimal system parameters is discussed, including theproper range and the selection principle of the system parameters. The error analysis and the conclusion areverified by simulation and experiment results, and the conclusion can be used for optimal parameter selection inthe practice.

Full field-of-view digital lens-free holography forweak-scattering objects based on grating modulation

Wenhui Zhang, Liangcai Cao, Guofan Jin, and David Brady

Doc ID: 302561 Received 17 Jul 2017; Accepted 08 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: Grating based single-shot digital lens-free holography with spatial spectral multiplexing is proposed to realize fullfield of view (FOV) imaging for weak scattering objects. Multiple object waves are generated by a one-dimensionalgrating which is placed in near contact with the object to avoid the crosstalk among different diffraction ordersduring reconstruction. A multiplexed off-axis hologram is created by interference between the object waves andreference wave and captured by an image sensor in one shot. Multiple imaging areas corresponding to thecaptured object waves can be simultaneously retrieved during reconstruction. A formula which guarantees fullFOV imaging without crosstalk or information loss is presented. The imaging experiments of a USAF resolutiontarget are presented to demonstrate the feasibility of this method.

Iterative pixelwise approach applied to computergeneratedholograms and diffractive optical elements

Wei-Feng Hsu and Shih-Chih Lin

Doc ID: 302564 Received 17 Jul 2017; Accepted 08 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: This paper presents a novel approach to optimizing the design of phase-only computer-generated holograms (CGH)for the creation of binary images in an optical Fourier transform system. Optimization begins by selecting an imagepixel with a temporal change in amplitude. The modulated image function undergoes inverse Fourier transformfollowed by the imposition of a CGH constraint and the Fourier transform, to yield an image function associatedwith the change in amplitude of the selected pixel. In iterations where the quality of the image is improved, thatimage function is adopted as the input for the next iteration. In cases where the image quality is not improved, theimage function before the pixel changed is used as the input. Thus, the proposed approach is referred to as thePixelwise Hybrid Input-Output (PHIO) algorithm. The PHIO algorithm was shown to achieve image quality farexceeding that of the Gerchberg-Saxton (GS) algorithm. The benefits were particularly evident when the PHIOalgorithm was equipped with a dynamic range of image intensities, equivalent to amplitude freedom of imagesignal. The signal variation of images reconstructed from the GS algorithm was 1.02 , but only 0.2537 when usingPHIO, i.e., a 75% improvement. Nonetheless, the proposed scheme resulted in a 10% degradation in diffractionefficiency and signal-to-noise ratio.

Detecting Crop Population Growth Using ChlorophyllFluorescence Imaging

Heng Wang, Xiangjie Qian, Lan Zhang, Sailong Xu, Haifeng Li, Xiaojian Xia, Liankui Dai, Liang Xu, Jingquan Yu, and Xu Liu

Doc ID: 308279 Received 29 Sep 2017; Accepted 08 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: For both field and greenhouse crops, it is challenging to evaluate their growth information on a large area over along period of time. In this work, we developed a chlorophyll fluorescence imaging based system for croppopulation growth information detection. Modular design was used to make the system provide high intensityuniform illumination. This system can perform modulated chlorophyll fluorescence induction kineticsmeasurement and chlorophyll fluorescence parameter imaging over a large area up to 45 cm × 34 cm. The systemcan provide different lighting intensity by modulating the duty cycle of its control signal. Results of continuousmonitoring of cucumbers in nitrogen deficiency show the system can reduce the judge error of crop physiologicalstatus and improve monitoring efficiency. Meanwhile the system is promising in high throughout applicationscenarios.

Sub-Harmonic Injection Locking of Quantum DashLasers Using Spectral Enrichment from SemiconductorOptical Amplifiers

Manas Srivastava, Prince Anandarajah, Balaji Srinivasan, Sean O Duill, Deepa Venkitesh, and Pascal Landais

Doc ID: 308517 Received 03 Oct 2017; Accepted 08 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: We report sub-harmonic injection-locking of a 40 GHz passively mode-locked quantum dash (Q-dash) laser through spectral enrichment in a non-linear semiconductor optical amplifier (SOA). The proposed scheme is demonstrated for injection locking of the Q-dash passively mode-locked laser using data modulated with non-return to zero line-coding at 10 Gsymbols/s with both intensity and phase shift keying modulations.

Wavelength and fluence dependent third-order opticalnonlinearity of mono- and multi-layer graphene

Kwangjun Ahn, Ji Yoon Gwak, Byungjic Lee, Sun Young Choi, Mi Hye Kim, in hyung baek, Young Uk Jeong, and Fabian Rotermund

Doc ID: 309170 Received 16 Oct 2017; Accepted 08 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: The objective of this study is to investigate third-order optical nonlinearities of monolayer and randomlystacked bi- and four-layer graphene samples depending on wavelength and fluence of femtosecond laserpulses in the near-infrared spectral region. Nonlinear refractive indices and absorption coefficients, inconsequence, third-order susceptibilities of graphene samples are determined by z-scan measurementsat four different wavelengths and three fluence regimes categorized by nonlinear transmission measurements.In addition, nonlinear refractive indices are independently investigated by optical Kerr gate experiments,showing good agreement with z-scan results. Our study on third-order nonlinearities of monoandmulti-layer graphene samples is significant for understanding nonlinear optical characteristics ofgraphene and developing graphene-based nonlinear photonic devices.

Optimal design for the support structure of a cavity mirror in a COIL resonator

Ding Cui, Zhaoxiang Deng, Yuqiang Xian, Xiaoyang Hu, and Lin Zhang

Doc ID: 306712 Received 27 Sep 2017; Accepted 08 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: The dynamic characteristics of the cavity mirror support structure strongly influence the quality of the output beam. However, the contradiction between excellent dynamic performance and light weight make the design process challenging. To cope with the problems encountered in the original design, this article presents a two-dimensional adjustable support structure based on spherical constraints with large specific stiffness in the initial design phase. Subsequently, a two-level optimization strategy containing macro design and detailed design is adopted to optimize the initial structure. At the macro design stage, a two-step topology optimization procedure is introduced, in which the scale of the optimization model is dramatically reduced using the independent continuous mapping algorithm to improve the calculation speed in the first step, and the gray elements are eliminated using the bi-directional evolutionary structural optimization method to clearly obtain the optimal topology in the second step. This method is verified to overcome the defect of low efficiency while still eliminating gray elements. At the detailed design stage, an adaptive surrogate model and the multi-objective design optimization method are employed to seek the best compromise between lower weight and higher dynamic performance. The results from the application to the example of the cavity mirror support structure show that the mass is reduced by 41.8% and the dynamic performance requirement is fulfilled.

Analysis of Long-term Visual Quality with Numerical3D Ray Tracing after Corneal Cross-Linking Treatment

Staffan Schedin, Per Hallberg, and Anders Behndig

Doc ID: 307641 Received 21 Sep 2017; Accepted 07 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: A numerical 3D ray tracing model was used to evaluate the long-term visual effects of two regimens of cornealcrosslinking (CXL) treatment of 48 patients with the corneal degeneration keratoconus. The 3D ray tracinganalyses were based on corneal elevation data measured by Scheimpflug photography. Twenty-two patients weretreated with standard CXL applied uniformly across the corneal surface, whereas 26 patients underwent acustomized, refined treatment only at local zones on the cornea (Photorefractive Intrastromal Crosslinking; PiXL).Spot diagrams, spot RMS values and Strehl ratios were evaluated for the patients prior to and 1, 3, 6 and 12 monthsafter treatment. It was found that the group of patients treated with PiXL, in average, tended to attain a long-termimprovement of the corneal optical performance, whereas only minor changes of the optical parameters werefound for group treated with standard CXL. Our results confirmed that standard CXL-treatment stabilizes thecorneal optical quality over time, and thus halts the progression of the corneal degeneration. In addition tostabilization, the results showed that a significantly higher proportion of subjects treated with PiXL improved inRMS, 3, 6, and 12 months after treatment, compared to with CXL (p<0.05). This finding indicates that the PiXLtreatmentmight improve the optical quality over time.

Improved particle position accuracy from off-axisholograms using a Chebyshev model

Johan Ohman and Mikael Sjodahl

Doc ID: 302339 Received 12 Jul 2017; Accepted 07 Nov 2017; Posted 13 Nov 2017  View: PDF

Abstract: Side scattered light from micrometer sized particles is recorded using an off-axis digital holographic setup.From holograms a volume is reconstructed with information about both intensity and phase. Finding par- ticle positions are non-trivial since poor axial resolution elongates particles in the reconstruction. To over- come this problem the reconstructed wavefront around a particle is used to find the axial position. The method is based on the change in sign of the curvature around the true particle position plane. The wave- front curvature is directly linked to the phase response in the reconstruction. In this paper we propose a new method of estimating the curvature based on a parametric model. The model is based on Chebyshev polynomials and is fitted to the phase anomaly, compared to a plane wave, in the reconstructed volume. From the model coefficients, it is possible to find particle locations. Simulated results shows increased performance in the presence of noise compared to the use of finite difference methods. The standard deviation is decreased from 3 − 39µm to 6 − 10µm for varying noise levels. Experimental results shows a corresponding improvement where the standard deviation is decreased from 18µm to 13 .

New insight into aspheric-misfit with hard tools – mapping the island of low mid-spatial-frequencies

David Walker, Hsing-Yu Wu, Guoyu Yu, Hongyu Li, Wang Zhang, and Chunlian Lu

Doc ID: 297916 Received 18 Jul 2017; Accepted 07 Nov 2017; Posted 08 Nov 2017  View: PDF

Abstract: This paper addresses CNC polishing of aspheric or freeform optics. Prior CNC grinding of the asphere tends to produce mid-spatial frequencies (MSFs) at some level. PrecessionsTM polishing can rectify these, but the very ability of the bonnet-tooling to adapt to the local asphere, enables it to adapt at least in part to similar spatial frequencies in the MSFs. To accelerate smoothing, hard tools can in principle be used, but aspheric misfit is often assumed to preclude this. In this paper, we explore new insight into the role of abrasive particle size in accommodating misfit. Firstly, we report on a glass bending-rig to produce a continuous range of complex surfaces, whilst withstanding process-forces. Then, we describe how this was used to evaluate the triangle of misfit, abrasive size and MSFs produced, for hard rotating tools. This has revealed a regime where such tools can be used without introducing significant new MSFs, as evidenced by manufacture of prototype off-axis aspheric segments for the E-ELT project.

Holographic Display Methods for Volume Data : Polygon-based and MIP-based methods

Zixiang Lu and Yuji Sakamoto

Doc ID: 302552 Received 31 Jul 2017; Accepted 07 Nov 2017; Posted 08 Nov 2017  View: PDF

Abstract: Volume data are widely used in many areas, especially in biomedical science and geology. However, current visualization technologies of volume data can not satisfy the visual requirements of humans. In this study, we propose two holographic display methods for volume data. The first method is polygon-based and the other is MIP-based. Both methods are able to generate CGHs of volume data. The polygon-based method can obtain various and colorful holograms, while the MIP-based method can be quickly calculated. Both methods can generate holographic animations, which were displayed on an electro-holography device.

1.7 μm band narrow-linewidth tunable Raman fiberlasers pumped by spectrum-sliced amplifiedspontaneous emission

Peng Zhang, Di Wu, Quanli Du, Xiaoyan Li, Kexuan Han, lizhong zhang, Tianshu Wang, and Huilin Jiang

Doc ID: 303194 Received 24 Jul 2017; Accepted 07 Nov 2017; Posted 08 Nov 2017  View: PDF

Abstract: A 1.7 μm band tunable narrow-linewidth Raman fiber laser (RFL) based on spectrally sliced amplified spontaneousemission (SS-ASE) and multiple filter structures is proposed and experimentally demonstrated. In this scheme, aSS-ASE source is employed as a pump source in order to avoid stimulated Brillouin scattering (SBS). The ringconfiguration includes a 500 m long high nonlinear optical fiber (HNLF) and a 10 km long dispersion shifted fiber(DSF) as gain medium. A segment of un-pumped polarization-maintaining erbium-doped fiber (PM-EDF) is used tomodify shape of spectrum. Furthermore, a nonlinear polarization rotation (NPR) scheme is applied as thewavelength selector to generate lasers. A high-finesse ring filter and a ring filter are used to narrow the linewidthof laser respectively. We demonstrate tuning capabilities of single laser over 28 nm between 1652 nm and 1680 nmby adjusting polarization controller (PC) and tunable filter. The tunable laser has a 0.0 nm effective linewidthwith the high-finesse ring filter. The stable multi-wavelength laser operation of up to four wavelengths can beobtained by adjusting the PC carefully when the pump power increases.

Theoretical Investigation of a five-band terahertz absorber based on an asymmetric split-ring resonator

Tianhua Meng, Dan Hu, Hongyan Wang, Wei Zhang, and Zhenjie Tang

Doc ID: 305186 Received 21 Aug 2017; Accepted 07 Nov 2017; Posted 08 Nov 2017  View: PDF

Abstract: A simple five-band terahertz metamaterial perfect absorber, composed of an asymmetric double-gap square split-ring and a metallic ground plate spaced by a thin polyimide dielectric layer, is proposed and theoretically investigated. The results show that it can perform absorption peaks at five resonant frequencies whose peaks average 98.85%. The perfect absorption is mainly attributed to the combined effect of LC, dipole, and surface response of the structure. Compared with previously reported multi-band absorbers, our design only has a single and compact structure which can drastically simplify the design and fabrication process. Furthermore, the resonance absorption properties of the absorber can be tuned by changing the geometric parameters of the structure. Such a simple and effective design holds great promise for potential applications in spectroscopic imaging, biological sensing, and detecting of the drugs and explosive.

Angular distribution of laser-induced fluorescenceemission of active dyes in scattering media

Ali Bavali, Parviz Parvin, Mohammad Reza Tavassoli, and Mohammad Reza Mohebbifar

Doc ID: 305295 Received 21 Aug 2017; Accepted 07 Nov 2017; Posted 08 Nov 2017  View: PDF

Abstract: Angular dependence of the intensity and the emissive wavelength of the laser-induced fluorescence emission inhybrid media (fluorophores + nanoparticles) are investigated using various TiO2 densities as guest nanoscattererin the ethanolic solutions of the host Rd6G and Coumarine 4 (C4) molecules. It is shown that the intensity of thescattered photons varies in terms of the detection angle. When the nanoscatterer density increases at certainexcitation energy, then the angular anisotropy enhances. While the emissive wavelength exhibits the spectral shiftin terms of the angular variation for Rd6G fluorophores, it remains invariant for C4-based suspension. In theformer case, the emissive wavelength undergoes spectral shift in terms of angular variation. Several factors such asthe optical path length in the scattering media, the excitation volume and the re-absorption events of thefluorescence emissions by the non-excited molecules strongly affect the spectral features. In fact, the density ofscatterers, the dye concentration, and the interplay between Stokes shift rate and the overlapping betweenabsorption/emission spectra of the given fluorophores are taken into account as the major parameters to form theangular distribution.

Full-color digitized holography for large-scale holographic 3D imaging of physical and nonphysical objects

Kyoji Matsushima and Noriaki Sonobe

Doc ID: 302515 Received 14 Jul 2017; Accepted 07 Nov 2017; Posted 08 Nov 2017  View: PDF

Abstract: Digitized holography techniques are used to reconstruct three-dimensional (3D) images of physical objects using large-scale computer-generated holograms (CGHs). The object field is captured at three wavelengths over a wide area at high densities. Synthetic aperture techniques using single sensors are used for image capture in phase-shifting digital holography. The captured object field is incorporated into a virtual 3D scene that includes nonphysical objects, e.g., polygon-meshed CG-models. The synthetic object field is optically reconstructed as a large-scale full-color CGH using red-green-blue color filters. The CGH has a wide full-parallax viewing zone and reconstructs a deep 3D scene with natural motion parallax.

Analysis of high-resolution electro-optical beam steering by long-range surface plasmon resonance using ZnSe prism

APARUPA KAR, Nabamita Goswami, and Ardhendu Saha

Doc ID: 304512 Received 10 Aug 2017; Accepted 06 Nov 2017; Posted 08 Nov 2017  View: PDF

Abstract: A proposal on high-resolution electro-optical beam steering is conceptualized analytically using long-range surface plasmon resonance configuration comprising a liquid crystal layer of E44 for 1550nm wavelength. With the tuning of refractive index of E44 through variation of applied voltage from (0-10)V, an optical beam steering can be attained considering composite effect of spatial and angular Goos-Hanchen and Imbert-Fedorov shift. As compared with the existing beam shift processes in µrad by mechanical means, here computed angular resolution is 3.40 nrad. Proposed idea finds a new avenue in the field of pulse generation, optical sensors applications and atomic force microscopy mitigating existing drawbacks.

Carry-free full-symbol one-step modified signed-digitaddition

Shuai Kong, Junjie Peng, Youyi Fu, and Xinyu Wei

Doc ID: 304617 Received 15 Aug 2017; Accepted 06 Nov 2017; Posted 08 Nov 2017  View: PDF

Abstract: Optical computing has advantages over electronic computing for it can carry much more informationand deal with more data bits. Provided carry-look-ahead is applied in optical computing as electroniccomputing does to accomplish addition calculation, it will be much inefficient because of delay causedby a large number of serial carries. On the basis of the research on relations among the augend, addend,results and the redundancy of modified signed-digit (MSD) number, the implementation method of carryfreeone-step MSD addition is presented. Meanwhile, the corresponding logical light path scheme isdesigned in this paper. Extensive experimental results show that the implementation method of one-stepaddition proposed is correct and light path scheme designed is reasonable.

Sensitivity enhancement of a conventional gold grating assisted SPR sensor by using bimetallic configuration

ASHISH BIJALWAN and Vipul Rastogi

Doc ID: 306140 Received 31 Aug 2017; Accepted 06 Nov 2017; Posted 08 Nov 2017  View: PDF

Abstract: A surface plasmon resonance (SPR) based refractive index sensor using silver grating, fabricated over the gold film is proposed. The performance of the sensor has been evaluated on the basis of sensitivity, full width half maximum (FWHM) and dip strength of the reflection spectrum. Rigorous coupled wave analysis (RCWA) has been utilized to study the effect of grating parameters on sensing performance. Our systematic analysis exhibits that inappropriate grating parameters may lead to poor performance of the sensor. Sensitivity of conventional gold grating (grating engraved in gold) assisted SPR sensor is obtained to be 321º/RIU. Further, we have shown that sensitivity and FWHM could be improved by using a bimetallic structure that consists of a silver grating on a thin gold film and thereby increases the quality factor. Sensitivity of proposed structure is 346º/RIU with quality factor more than 97.46 RIU-¹.

Frequency-modulated multifunction lidar for anemometry, range finding and velocimetry – 1.Theory and signal processing

Patrick Feneyrou, Luc Leviandier, jean minet, Grégoire Pillet, Aude Martin, Daniel Dolfi, jean-pierre schlotterbeck, Philippe Rondeau, xavier lacondemine, alain rieu, and Thierry Midavaine

Doc ID: 303072 Received 21 Jul 2017; Accepted 05 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: Original waveforms and optimized signal processing are proposed for frequency-modulated continuous-wave lidar for range finding, velocimetry and laser anemometry. For range finding, the aim of this signal processing is to extend lidar range and reduce ambiguities. Moreover, the effect of moderate atmospheric turbulence on lidar efficiency is analyzed for both infinite and finite targets taking into account for the wind-induced bistatism. For laser anemometry, the aim is to measure air speed at the shortest distance farther than the rotor-induced turbulent volume around the helicopter and to avoid parasitic echoes coming from clouds or hard targets in the vicinity of an helicopter.

Frequency-modulated multifunction lidar for anemometry, range finding and velocimetry – 2.Experimental results

Patrick Feneyrou, Luc Leviandier, jean minet, Grégoire Pillet, Aude Martin, Daniel Dolfi, jean-pierre schlotterbeck, Philippe Rondeau, xavier lacondemine, alain rieu, and Thierry Midavaine

Doc ID: 303077 Received 02 Aug 2017; Accepted 05 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: Frequency-modulated continuous-wave lidar is evaluated for range finding, velocimetry and laser anemometry. An original signal processing and waveform calibration for range-finding leads to a reduction of computational effort while preserving capability for long range measurement. Multiple targets distance measurement is also demonstrated. For laser anemometry, the aim is to avoid parasitic echoes in the vicinity of a helicopter and measure the air speed at the shortest distance farther than the rotor-induced turbulent volume around the helicopter. Flight test of this functionality and vortex ring state warning are demonstrated.

Electrooptically induced topological reactions ofthe defects of optical indicatrix orientation anddefects of polarization state

Yurij Vasylkiv, Taras Kryvyy, Ihor Skab, and Rostyslav Vlokh

Doc ID: 306468 Received 06 Sep 2017; Accepted 05 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: We have studied the behavior of topological defects (TDs) of optical indicatrix orientation and polarizationstate, which appear when a divergent optical beam propagates through LiNbO3 crystals under external electricfield. We have found that the topological reaction of splitting of a central TD of optical indicatrix orientation,which occurs under the electric field EX, proceeds according to a scheme 1=1/2 + 1/2. This reaction splits adoubly charged optical vortex into two singly charged vortices. Increase in the electric field strength leads toangular displacement of the optical vortices, thus making it possible to operate spatial positions of the opticalvortices via a Pockels effect. We have found that the lateral TDs with the strengths ±½ represent the defects ofpolarization state and are not caused by defects of optical indicatrix orientation. They form topological dipolesand generate optical vortices. These topological dipoles undergo no topological reactions in the externalelectric field.

Designing a Low-Threshold Quantum-Dot Laser based on Slow Light Photonic Crystal Waveguide

Hosein Taleb and Mohammad Moravvej-Farshi

Doc ID: 303764 Received 01 Aug 2017; Accepted 03 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: We numerically investigate and design a compact photonic crystal waveguide (PCW) quantum dot (QD) laser. For this purpose, we propose a set of rate equations to model the performance of the PCW-QD-laser. In the proposed model, we take the effects of the homogeneous and inhomogeneous broadenings and the slow light effects on the modal gain and loss coefficient into taken account. Simulations show that threshold currents as low as ~50 µA can be achieved that is ~120 times smaller than that of the conventional QD-laser, with 150 times larger cross-sectional area and 50 times larger output power. Moreover, our results demonstrate that the turn-on delay time of this laser is about three times less than that of its conventional counterpart. The proposed edge emitting PCW-QD-laser is a promising light source for the off-chip and on-chip photonic network applications.

High photon conversion efficiency cw lasing in an optically pumped I2 hollow fiber gas laser in the visible region

Vasudevan Nampoothiri, Farzin Beygi Azar Aghbolagh, Benoît Debord, Frédéric Gérôme, Fetah Benabid, and Wolfgang Rudolph

Doc ID: 304975 Received 25 Aug 2017; Accepted 03 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: CW lasing in the visible spectral region from a molecular iodine filled hollow core photonic crystal fiber is demonstrated. More than an order of magnitude improvement in photon conversion efficiency has been achieved compared to previous non-fiber based geometries in this spectral region. The laser shows strong coupling of pump and laser polarization.

Rapid calibration of a projection-type holographiclight-field display using hierarchically upconvertedbinary sinusoidal patterns

Tomoya Nakamura and Masahiro Yamaguchi

Doc ID: 306166 Received 05 Sep 2017; Accepted 03 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: A projection-type holographic light-field (LF) display is a full-parallax, full-color, and glass-free threedimensional(3D) display with a holographic optical element (HOE) and a projector. The display hasunique characteristics, including transparency; however, a rapid calibration method has not yet beenestablished. In this paper, we propose a rapid calibration method for a holographic LF display withoutsacrificing its accuracy. The proposed method performs calibration via the projection of binary sinusoidalpatterns whose frequencies are iteratively and hierarchically upconverted. Compared to the conventionalmethod, in the proposed method, the required number of projections is reduced from linear to logarithmicwith the projector’s resolution. We confirm the successful reconstruction of the 3D image using theproposed method.

Focusing anomalies with binary diffractive opticalelements

Oussama Bouzid, Sofiane Haddadi, Michael Fromager, Emmanuel CAGNIOT, kouider Ferria, Andrew Forbes, and Kamel Ait-Ameur

Doc ID: 305641 Received 28 Aug 2017; Accepted 02 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: Binary diffractive optics have been extensively studied to date as tools for arbitrary laser beam shaping, andexperimentally implemented with etched transparent optics and spatial light modulators. Here we demonstratethat a simple one-step binary optic is able to enhance the intensity of a focused beam, displaying some counterintuitivefocusing anomalies. We explain these effects by considering the optical aberrations in binary diffractiveoptics, and outline how this may be exploited for further improvements in refractive/diffractive combinations forsuper-resolution microscopy.

Diffraction mechanism of a light-diffusing film with an alternate-polymer-layer structure

Yoshifumi Sekiguchi, Takahiro Ishinabe, Souichirou Seo, Yosei Shibata, and Hideo Fujikake

Doc ID: 305784 Received 07 Sep 2017; Accepted 02 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: A diffraction mechanism, and an optical model to reflect that mechanism, for a light-diffusing film with an alternate-polymer-layer structure was proposed and validated. According to this model, the film forms an angular distribution of light intensity that is almost constant in a certain scattering-angle (cut-off angle) range and drastically decreases outside that range; that is, the profile is similar to a trapezoid. Although the trapezoid intensity distribution (TID) is a fundamental distribution of the film, the mechanism to form the TID has not previously been clarified. A key mechanism is that the refractive-index distribution (RID) of the layer structure is expressed as stacked phase gratings, some of which should diffract zeroth-order light to higher orders strongly, and the repetition of this multiple diffraction spreads light over the whole cut-off angle range, thereby generating the TID. To verify the proposed mechanism, intensity distributions were calculated by using the proposed model. And the calculation results indicate that the proposed model reproduces the TID.

Detection of Uranyl Fluoride and Sand SurfaceContamination on Metal Substrates by Hand-HeldLaser Induced Breakdown Spectroscopy

Michael Shattan, Dory Miller, Matthew Cook, Ashley Stowe, John Auxier, Christian Parigger, and Howard Hall

Doc ID: 303324 Received 28 Jul 2017; Accepted 02 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: A hand-held device for laser-induced breakdown spectroscopy has been investigated for the determination ofuranyl fluoride surface contamination. This research demonstrates the ability to successfully detect uranium onsurfaces when using a low resolving power (λ/Δλ = 4000) spectrograph, with a 5mJ energy per 1 ns pulsed laserradiation, available as a commercially packaged hand-held system. Sand/uranyl fluoride mixtures are prepared tosimulate residue likely encountered during decontamination efforts at facilities that handle uranium hexafluoride.Detection limits are described for four uranium lines with one revealing the capability to detect uranium at a levelof 250 parts-per-million. Advantages of the studied compact device include that location specific information canbe obtained on-site to augment contamination identification.

Features of the non-collinear one-phonon anomalouslight scattering controlled by elastic waves withelevated linear losses: potentials for multi-frequencyparallel spectrum analysis of radio-wave signals

Alexandre Shcherbakov and Adan Omar Arellanes Bernabe

Doc ID: 297778 Received 09 Jun 2017; Accepted 02 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: During subsequent development of recently proposed multi-frequency parallel spectrometer for precise spectrumanalysis of wide-band radio-wave signals, we study potentials of new acousto-optical cells exploiting selectedcrystalline materials at the limits of their capabilities. Characterizing these wide-aperture cells is non-trivial due tonew features inherent in the chosen regime of an advanced non-collinear one-phonon anomalous light scatteringby elastic waves with significantly elevated acoustic losses. These features can be observed simpler in uniaxial,tetragonal and trigonal crystals possessing linear acoustic attenuation. We demonstrate that formerly studiedadditional degree of freedom, revealed initially for multi-phonon regimes of acousto-optical interaction, can beidentified within the one-phonon geometry as well and exploited for designing new cells. We clarify the role ofvarying the central acoustic frequency and acoustic attenuation using the identified degree of freedom. Therewith,we are strongly restricted by a linear regime of acousto-optical interaction to avoid the origin of multi-phononprocesses within carrying out a multi-frequency parallel spectrum analysis of radio-wave signals. Proof-ofprincipleexperiments confirm the developed approaches and illustrate their applicability to innovative techniquefor an advanced spectrum analysis of wide-band radio-wave signals with the improved resolution in an extendedfrequency range.

Wave properties in asymmetric single-negative-based photonic crystals

Tzu Chyang King, Yi-Huan Wu, Zhe-Wei Li, CHIH-HSI HUANG, and Chien-Jang Wu

Doc ID: 302349 Received 12 Jul 2017; Accepted 01 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: We theoretically study wave properties for one-dimensional defective asymmetric photonic crystals,air/(AB)MG(BA)N/air, air/(AQ)MG(QA)N/air, and air/(BQ)MG(QB)N/air, where A is a lossy epsilon-negative (ENG)material, B is a lossy mu-negative (MNG) material, G and Q are dielectrics with different refractive indexes, and Mand N are stack numbers with M ≠ N. Special attention has been paid on their absorption spectra. It is found thatat certain frequencies the absorption can exhibit unidirectional properties. Our calculated results show twokinds of unidirectional absorption peaks. One is a single absorption peak whose frequency depends on thethickness of defect layer G. For the other peaks, its frequency does not change when the defect layer’s thicknesschanges. In addition, in the second kind of peaks, the peak number for forward and backward propagation aredifferent, that is, there are (M – 1) absorption peaks for forward propagation while there are (N – 1) absorptionpeaks for backward propagation. When the two kinds of unidirectional absorption peaks are merged, some newpeaks appear, and both of forward and backward propagation will have (M + N – 1) absorption peaks.

On-site multi-kilowatt laser power meter calibration using radiation pressure

Paul Williams, Joshua Hadler, Brian Simonds, and John Lehman

Doc ID: 303100 Received 18 Aug 2017; Accepted 01 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: We have demonstrated the calibration of a thermal power meter against a radiation-pressure power meter in the range of 20 kW in a manufacturing test environment. The results were compared to a traditional calorimeter-based laboratory calibration undertaken at the National Institute of Standards and Technology. The results are reported and the effects of non-ideal conditions typical of measurements in low-stability environments are discussed.

Security Validation Based On Orthogonal Polarization Multiplexing In Three-dimensional Space

Chao Lin and Jiancun Ren

Doc ID: 306040 Received 30 Aug 2017; Accepted 01 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: To enhance the security and practicality of optical validation technique, a multiple-level security validation method is proposed based on the orthogonal polarization multiplexing in three-dimensional space. First, original image is partitioned into two complementary images. Each image is divided into several subblocks. Then, two phase-only masks are generated by adopting the multiple diffractive planes and multiple signal windows phase retrieval algorithm in order to reproduce a three-dimensional diffraction field with all of the subblocks randomly distributed in specific locations. One of the phase masks is taken as the system lock which is fixed. The other one is preserved to act as the validation key. At last, the two diffraction beams of two phase-only masks are converted into orthogonal polarization states when illuminated by a collimated wave. As a result, the simultaneous control of both intensity and polarization distributions in desired longitudinal planes and transversal positions is achieved. A three-dimensional polarization mapping protocol is established to generate the three-dimensional polarization key. During validation, only when both the validation key and the three-dimensional polarization key are correct, one can gain the access permission. Experimental results show that the proposal can achieve both an easy implementation and the multiple-level validation functionality.

Optical solution to the transport of intensity equation using Bessel sources

Tonmoy Chakraborty and Jonathan Petruccelli

Doc ID: 306233 Received 06 Sep 2017; Accepted 01 Nov 2017; Posted 06 Nov 2017  View: PDF

Abstract: Propagation-based phase imaging using the transport of intensity equation (TIE) allows rapid, deterministic phase retrieval from defocused images. However, computational solutions to the TIE suffer from significant low--frequency noise artifacts and is unique up to the application of boundary conditions on the phase. We demonstrate that quantitative phase can be imaged directly at the detector for a class of pure-phase samples by appropriately patterning the illumination to solve the TIE optically. This can reduce noise artifacts and obviates the need for user-supplied boundary conditions, and is demonstrated via simulation and experiment.

Wavelength measurement by Fourier analysis ofinterference fringes through a plane parallel plate

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

Doc ID: 306756 Received 08 Sep 2017; Accepted 01 Nov 2017; Posted 08 Nov 2017  View: PDF

Abstract: When a diverging laser beam passed through a plane parallel glass plate, interference fringes were observed;analysis of these fringes provided accurate estimation of the source wavelength. The fringes had a unique angularrange of uniform fringe density. Fourier transform of the fringes in this range directly provided wavelengthinformation. Reference lasers were used to establish a calibration between the fringe density and wavenumber,with which we estimated the wavelength of a test laser. An accuracy of 4.5×10−5 was obtained, which is better thanthat of conventional grating spectrometers, while providing a much broader free spectral range. Our method hasunique features, such as extreme simplicity of the set-up, fast analysis, and low-cost, which are great advantages inpractical wavelength meter applications.

Plasmon-induced transparency based on a trianglecavity coupled with an ellipse-ring resonator

Ali Akhavan, hassn ghafoorifard, Saeed Abdolhosseini, and hamidreza habibiyan

Doc ID: 303214 Received 24 Jul 2017; Accepted 31 Oct 2017; Posted 06 Nov 2017  View: PDF

Abstract: In this paper, a novel compact plasmonic system is introduced to realize the phenomenon of plasmon-inducedtransparency. Proposed device consists of a triangle defect coupled with an ellipse-ring resonator based on metalinsulator-metal platform. By the finite-difference time-domain method, the transmission characteristics arenumerically studied in details. In order to verify the simulation results, the coupled mode theory is utilized. In thefollowing, the effect of geometrical parameters, namely, the major and minor radii of ellipse-ring, and the gapbetween cavities are investigated. Moreover, the fundamental factors of transmission spectra including intrinsicDrude loss and refractive index of dielectric region are studied. As a result, the transmission peak is obtained near70 % and the full width at half maximum is close to 28 nm. The sensitivity and figure of merit of the proposedstructure are 860 nm/RIU and 31.6 RIU-1, respectively. The mentioned compact structure has the ability andpotential to be used in integrated optical circuits like slow light devices, nano-scale filters and nanosensors.

16 Gbps Random Bit Generation using Chaos inNear-Symmetric Erbium-doped Fiber Ring Laser

Akash Pandey, Ankit Sharma, and Pradeep Kumar Krishnamurthy

Doc ID: 303727 Received 01 Aug 2017; Accepted 31 Oct 2017; Posted 06 Nov 2017  View: PDF

Abstract: We demonstrate bias-free random bit generator at 16Gbps using chaos in a near-symmetric erbium dopedfiber (EDF) ring laser. The laser consists of two EDFs,each pumped at 980 nm, two intracavity filters of centralwavelength 1549.30 nm, and two 90:10 output couplers.The presence of chaos at the laser output is demonstratedby computing the largest Lyapunov exponentfor different embedding dimensions. The laser outputsare photodetected and subtracted to generate anelectrical difference signal which is then sampled at 2GSa/s and post-processed to extract random bits at 16Gbps. The random bits exhibit very low autocorrelation( ~10¨⁴) and have successfully passed all NISTand Diehard battery of tests.

Spectral response of Bragg gratings in multimode polymer waveguides

Aditya Bhuvaneshwaran, Stanislav Sherman, and Hans Zappe

Doc ID: 305210 Received 21 Aug 2017; Accepted 31 Oct 2017; Posted 06 Nov 2017  View: PDF

Abstract: A means to calculate the multimodal spectral response of Bragg gratings in general non-circular multimode waveguides is proposed. To illustrate the power of the technique, the spectra of two Bragg temperature sensors are numerically calculated in which coupling between 100 modes considered. It is shown how the Bragg wavelength in multimode Bragg grating waveguides is affected by the number of modes and energy distribution among them. Good matching of the simulated spectrum of a multimode Bragg grating on a planar inverted rib waveguide to the measured spectrum is seen.

Numerical simulation and experimental investigation of GaN-basedflip-chip LEDs and top-emitting LEDs

Xingtong Liu, Shengjun Zhou, Yilin Gao, Hongpo Hu, Yingce Liu, Chengqun Gui, and Sheng Liu

Doc ID: 306439 Received 06 Sep 2017; Accepted 31 Oct 2017; Posted 31 Oct 2017  View: PDF

Abstract: We demonstrate GaN-based flip-chip LED (FC-LED) with highly reflective indium-tin oxide (ITO)/distributed Braggreflector (DBR) Ohmic contact. Transparent ITO current spreading layer combined with Ta2O5/SiO2 double DBRstacks is used as reflective p-type Ohmic contact in the FC-LED. We develop a strip-shaped SiO2 current blocking layer,which is well aligned with p-electrode, to prevent current from crowding around p-electrode. Our combined numericalsimulation and experimental results revealed that the FC-LED with ITO/DBR has advantages of better current spreadingand superior heat dissipation performance as compared with top-emitting LEDs (TE-LED). As a result, the light outputpower (LOP) of FC-LED with ITO/DBR was 7.6% higher than that of TE-LED at 150 mA, and the light output saturationcurrent was shifted from 130.9 A/cm2 for TE-LED to 273.8 A/cm2 for FC-LED with ITO/DBR. Due to the high reflectance ofITO/DBR Ohmic contact, the LOP of FC-LED with ITO/DBR was 13.0% higher than that of conventional FC-LED with Ni/Ag at150 mA. However, due to the better heat dissipation of Ni/Ag Ohmic contact, the conventional FC-LED with Ni/Agexhibited higher light output saturation current as compared to the FC-LED with ITO/DBR.

Integrated Beam Shaping and Polarization Beam Combining Design for Fiber Coupled Semiconductor Laser Stacks System

He Yu, Xin Zhao, Xiao Wu, YONGGANG ZOU, Xiaohui Ma, Liang Jin, Yingtian Xu, and He Zhang

Doc ID: 307568 Received 28 Sep 2017; Accepted 31 Oct 2017; Posted 31 Oct 2017  View: PDF

Abstract: The beam quality mismatch in fast and slow axes of laser diode stacks limits their applications. An effective beam shaping method was proposed based on a pair of step prisms. Using this technique, we can eliminate the lightless areas and achieve polarization multiplexing of laser diode stacks. Two laser diode stacks consisting of eight bars were coupled into a fiber with a core diameter of 200 μm and an NA of 0.22. The simulation results demonstrated that the output power can reach 1083W and the optical-optical efficiency was 84.6%.

Piezooptic and elastooptic properties of monoclinic triglycine sulfate crystals

Bohdan Mytsyk, Natalya Demyanyshyn, ALESSANDRO ERBA ERBA, VIKTOR SHUT SHUT, SERGEY MOZZHAROV, YAROSLAV KOST, Oksana Mys, and Rostyslav Vlokh

Doc ID: 307751 Received 27 Sep 2017; Accepted 30 Oct 2017; Posted 31 Oct 2017  View: PDF

Abstract: For the first time we have experimentally determined all of the components of piezooptic tensor for monoclinic crystals. This has been implemented on a specific example of TGS crystals. Basing on the results obtained, the complete elastooptic tensor has been calculated. The acoustooptic figures of merit (AOFM) have been estimated for the case of acoustooptic interaction occurring in the principal planes of optical indicatrix ellipsoid and for the geometries in which the highest elastooptic coefficients are involved as effective parameters. It has been found that the highest AOFM value is equal to 6.8×10–15 s3/kg for the case of isotropic acoustooptic interaction with quasi-longitudinal acoustic waves in the principal planes. This AOFM is higher than the corresponding values typical for the canonic acoustooptic materials, which are transparent in the deep ultraviolet spectral range.

High-power Self-mode-locked Pr:YLF Visible Lasers

Saiyu luo, Bin Xu, Huiying XU, and Zhiping Cai

Doc ID: 308025 Received 27 Sep 2017; Accepted 30 Oct 2017; Posted 31 Oct 2017  View: PDF

Abstract: We demonstrate efficient self-mode-locked green and red lasers with repetition rate of tens and hundreds of MHz in a Pr:YLF crystal. Using double-end blue-diode-pumped geometry, more than 0.68 W average output power at 522 nm and more than 1.44 W at 639 nm are obtained, which are believed to be the highest average output power for mode locked lasers operating in visible wavelength region.

Tunable plasmon-induced absorption in integratedgraphene nanoribbon side-coupled waveguide

qi lin, Xiang Zhai, Yi Su, Hai-Yu Meng, and wang lingling

Doc ID: 307412 Received 22 Sep 2017; Accepted 30 Oct 2017; Posted 31 Oct 2017  View: PDF

Abstract: By designing a novel graphene plasmonic band-pass filter with two gold ribbons, we have numerically andanalytically investigated the transmission properties of plasmon-induced absorption (PIA) in compact graphenenanoribbon side-coupled waveguide. The formation and evolution of the PIA window are dependent on thesuperposition of super resonances and the near-field coupling intensity between the designed two resonators.Interestingly, the induced absorption window not only can be engineered longitudinally in intensity, but alsodynamically tuned horizontally in resonant wavelength by changing Fermi energy of graphene layers. Optical timedelay near 1.0 ps can be realized in the PIA window, which exhibits excellent slow light features. Double PIAresonance is also discussed. This result may have potential applications in graphene plasmonic switching andbuffering.

Relationship between phosphor properties andchromaticity of phosphor-in-glass

Sunil Kim, Fauzia Iqbal, and hyungsun KIM

Doc ID: 307673 Received 21 Sep 2017; Accepted 30 Oct 2017; Posted 30 Oct 2017  View: PDF

Abstract: SiO2-B2O3-ZnO-Li2O glass and four types of phosphors (Y3Al5O12:Ce3+, (Sr,Ba)Si2O2N2:Eu2+, CaAlSiN3:Eu2+, andLu3Al5O12:Ce3+) with different spectral distributions and thermal properties were prepared to achieve the desiredcolor point based on the relationship between the thermal properties of phosphors and the microstructure of thephosphor-in-glass (PIG). The glass frit was mixed with various contents of phosphors (2.5, 5.0, 7.5, and 10.0 vol%)and then sintered to form a PIG. It was confirmed that the different pore properties of each PIG, caused by thedifference in phosphor thermal properties, have a strong influence on the optical properties of the PIG. As the masschange of the phosphor increases, the scattering coefficient of the PIG also increases based on the variations in bothpore size and porosity inside the plate. It is apparent that the scattering coefficient is strongly related to the path ofconverted light and blue light from the light-emitting diode (LED) chip; therefore, the ratio of transmittance toreflectance of each PIG is different, even if each PIG has the same phosphor content. These results indicate thatachieving the target LED chromaticity is closely related to the phosphor characteristics and PIG’s pore properties.

Overlapped fiber optic Michelson interferometers forsimultaneous refractive index measurement at twosensing points

Ma. del Rosario Bautista-Morales, Rodolfo Martinez, and Carlos A. Pineda-Arellano

Doc ID: 307810 Received 25 Sep 2017; Accepted 30 Oct 2017; Posted 30 Oct 2017  View: PDF

Abstract: We present a fiber refractometer based on the implementation of overlapped Michelson interferometers; therefractometer allows simultaneous refractive index measurement at two-sensing-points for samplesdiscrimination. The fiber refractometer uses the Fresnel reflection in each fiber tip of the overlappedinterferometers to generate the interference signal. Experimental results, implementing the two sensing points, fordiscrimination between non-contaminated and contaminated distilled water are presented. Despite the simplicityof the presented system, resolution and repeatability of 3 x10-4 and 5x10-4 are obtained in a dip and readexperiments using both sensing points simultaneously for refractive index measurement.

Multi-Objective Vs. Single-Objective Optimization Frameworks for Designing Photonic Crystal Filters

Seyed Mohammad Mirjalili, Behnaz Merikhi, Seyedeh Zahra Mirjalili, Milad Zoghi, and Seyedali Mirjalili

Doc ID: 305760 Received 28 Aug 2017; Accepted 30 Oct 2017; Posted 31 Oct 2017  View: PDF

Abstract: This paper proposes a novel framework for multi-objective optimization of photonic crystal (PhC) filters and compares it with a single objective optimization approach. In this framework, an optimizer called Multi-Objective Gray Wolf Optimizer has been utilized to automatically find the optimal designs. The proposed method is able to design any kind of PhC filter. As a case study, a new structure of super defect PhC filter for application in the wavelength division multiplexer (WDM) is designed using the framework. The results show that the proposed framework is comprehensive and able to find a significantly wide range of optimal designs for general and specific application such as WDM with respect to each defined WDM standard.

Resolution optimization of an off-axis lensless digitalholographic microscope

Gene Serabyn, Kurt Liewer, and J. Kent Wallace

Doc ID: 303871 Received 02 Aug 2017; Accepted 28 Oct 2017; Posted 10 Nov 2017  View: PDF

Abstract: Microscopes aimed at detecting cellular life in extreme environments such as ocean-bearing solar system moonsmust provide high resolution in a compact, robust instrument. Here we consider the resolution optimization of acompact off-axis lensless digital holographic microscope (DHM) that consists of a sample placed between an inputpoint-source pair and a detector array. Two optimal high-resolution regimes are identified, at opposite extremes – alow-magnification regime with the sample located near a small-pixel detector array, and a high-magnificationregime with the sample near the input plane. In the former, resolution improves with smaller pixels, while in thelatter, the effect of the finite pixel size is obviated, and the spatial resolution improves with detector array size. Usingan off-axis lensless DHM with a 2k x 2k array of 5.5 μm-pixels in the high-magnification regime, and standardaberration correction software, a resolution of ~ 0.95 μm has been demonstrated, a factor of 5.8 smaller than thepixel size. Our analysis further suggests that with yet larger detector arrays, a lensless DHM should be capable ofnear wavelength-scale resolution.

Analysis of Dual Coupler Nested Coupled Cavities

George Adib, Yasser Sabry, and Diaa Khalil

Doc ID: 302069 Received 18 Jul 2017; Accepted 27 Oct 2017; Posted 27 Oct 2017  View: PDF

Abstract: Coupled ring resonators are becoming basic building block in several optical systems serving differentapplications. In many of these applications, a small full width half maximum is required along with alarge free spectral range. In this work, a configuration of passive coupled cavities constituting of dualcoupler,nested cavities is proposed. A theoretical study of the configuration is presented allowing toobtain analytical expressions of its different spectral characteristics. The transfer function of theconfiguration is also used to generate design curves while comparing these results with analyticalexpressions. Finally, the configuration is compared with other coupled cavities configurations.

Modeling of the petawatt PETAL laser chain using Miró code

Herve Coic, Jean Philippe Airiau, Nathalie Blanchot, E. Bordenave, and Claude ROUYER

Doc ID: 302270 Received 20 Jul 2017; Accepted 26 Oct 2017; Posted 27 Oct 2017  View: PDF

Abstract: Miró software has been used intensively to simulate LMJ laser with the treatment of amplification, frequency conversion and both temporal/spatial smoothing of the beam for ns pulses. We show that the software is able to model all the physical aspects of the Petawatt PETAL laser chain in sub-picosecond regime, from the front-end to the focal spot with a broadband treatment of the amplification and compression stages, including chromatism compensation in the laser chain, segmentation and recombination of the beams on the second compression stage and focusing by an off-axis parabola.

Spectral characterization of a supercontinuum source based on nonlinear broadening in an aqueous K2ZnCl4 salt solution

Timothy Robinson, Siddharth Patankar, Emma Floyd, Nicholas Stuart, Nicholas Hopps, and Roland Smith

Doc ID: 306464 Received 07 Sep 2017; Accepted 20 Oct 2017; Posted 23 Oct 2017  View: PDF

Abstract: Wereportoninvestigationsconcerningtheshot-to-shotspectralstabilitypropertiesofasupercontinuum sourcebasedonnonlinearprocessessuchasself-phasemodulationandopticalwave-breakinginahighlyconcentrated K2ZnCl4 double salt solution. The use of a liquid medium offers both damage resistance and high 3rd order optical nonlinearity. Approximately 40 µJ pulses spanning a spectral range between 390-960 nm were produced with 3.8% RMS energy stability, using infrared input pulses of 500 ± 50 fs FWHM durations and 2.42 ± 0.04 mJ energies with an RMS stability of 2%. The spectral stability was quantified via acquiring single-shot spectra and studying shot-to-shot variation across a spectral range of 200-1100 nm, as well as by considering spectral correlations. The regional spectral correlation variations were indicative of nonlinear processes leading to side-band generation. Spectral stability and efficiency of energy transfer into the supercontinuum were found to weakly improve with increasing driver pulse energy, suggesting that the nonlinear broadening processes are more stable when driven more strongly, or that self-guiding effects in a filament help to stabilize the supercontinuum generation.

Inverse conversion algorithm for all-optical depth coloring camera

Sungjin Lim, Daerak Heo, Kim Mugeon, GENSUB CHOI, and Joonku Hahn

Doc ID: 303998 Received 03 Aug 2017; Accepted 17 Oct 2017; Posted 02 Nov 2017  View: PDF

Abstract: Three-dimensional (3D) metrology has received lots of interests from academy and industry due to broad applications such as 3D contents, 3D printing, and autonomous driving. The all-optical depth coloring (AODC) camera has some benefits in computation load since it extracts depth information of the object fully optically. The AODC camera represents depth of the object as RGB color corresponding to a specific wavelength but one point measured in RGB color space is not generally assigned into the wavelength. In the AODC camera, the detected spectrum through the gating part has narrow bandwidth resulting from the width of slit in the projection part, so the color vector in RGB color space is convertible inversely into the wavelength after projection on the normalized rgb plane. In this paper, we present an inverse conversion algorithm from RGB color to depth for the AODC camera and experimental results are presented to confirm its feasibility. Also, some practical limitations are discussed resulting from the non-linearity of the response of the image sensor and the width of the slits in projection part and gating part.

A high-energy, stable single-frequency Ho:YAG ceramic amplifier system

YIXUAN ZHANG, Chunqing Gao, Qing Wang, Quanxin Na, gao mingwei, zhang meng, Qing Ye, Yujia Wang, and Jian Zhang

Doc ID: 302154 Received 10 Jul 2017; Accepted 13 Oct 2017; Posted 26 Oct 2017  View: PDF

Abstract: We demonstrate a 2090 nm single-frequency, high-energy, Q-switched Ho:YAG ceramic master oscillator and power amplifier system which contains two-stage amplifiers. The maximum single-frequency pulse energy is 55.64 mJ at a pulse repetition frequency of 200 Hz. The half-width of the pulse spectrum is measured to be 3.88 MHz by a heterodyne technique. To the best of our knowledge, 55.64 mJ is the highest single-frequency output energy obtained from the Ho:YAG laser.

Characterization of the reference wave in a compact digital holographic camera

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

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

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

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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