Accepted papers to appear in an upcoming issue
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Nonlinear Diffusion Model for Annealed Proton-Exchanged Waveguides in Zirconium-Doped Lithium Niobate
Carsten Langrock, Rostislav Roussev, Giovanni Nava, Paolo Minzioni, Nicola Argiolas, cinzia Sada, and Martin Fejer
Doc ID: 263625 Received 21 Apr 2016; Accepted 26 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: Photorefractive-damage (PRD) resistant zirconium-oxide-doped lithium niobate is investigated as a substrate for the realization of annealed proton-exchanged (APE) waveguides. Its advantages are a favorable distribution coefficient, PRD resistance comparable to magnesium-oxide-doped lithium niobate, and a proton diffusion behavior resembling congruent lithium niobate. A 1-D model for APE waveguides was developed based on a previous model for congruently melting lithium niobate. Evidence for a nonlinear index dependence on concentration was found.
High sensitivity optical waveguide accelerometer based onFano resonance
Tong Zhang, Feng-Hua Wan, Qian guang, Ruozhou Li, and Jie Tang
Doc ID: 264682 Received 05 May 2016; Accepted 26 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: An optical waveguide accelerometer based on tunable asymmetrical Fano resonance in a ring-resonator-coupled Mach-Zehnderinterferometer (MZI) is proposed and analyzed. Fano resonance accelerometer have a relative large workspace of couplingcoefficient with high sensitivity which has potential application in inertial navigation, missile guidance and attitude control ofsatellite. Due to the interference between a high-Q resonance pathway and a coherent background pathway, a steep asymmetricline shape is generated which greatly improve the sensitivity of this accelerometer. The sensitivity of the accelerometer is about111.75 mW/g. A 393-fold increase in sensitivity is achieved compared with conventional MZI accelerometer, and approximatelyequal to the single ring structure.
Optical scattering modelling of etched ZnO:Al superstrates and device simulation studies of a-Si:H solar cells with different texture morphologies
Xia Yan, Weimin Li, Armin Aberle, and Selvaraj Venkataraj
Doc ID: 264632 Received 05 May 2016; Accepted 25 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: Transparent conductive oxide (TCO) materials have been widely used as the front electrodes of thin-film amorphous silicon (a-Si:H) solar cells. To improve the performance of solar cells, textured front TCO is required as the optical layer which effectively scatters the incoming light and thus enhances the photon absorption within the device. One promising TCO material is aluminium-doped zinc oxide (AZO), which is most commonly prepared by magnetron sputtering. After deposition, sputtered AZO films are typically wet-chemically etched using diluted hydrochloric (HCl) or hydrofluoric (HF) acid to obtain rough surface morphologies. In this paper, we report the effects of a textured AZO front electrode on the performance of a-Si:H solar cells based on optical scattering modelling and electrical device simulations, involving four different AZO surface morphologies. The simulated light scattering behaviours indicate that a better textured surface not only scatters more light, but also allows more light get transmitted into the absorber (~90% of visible light), due to greatly reduced front reflection by the rough surface. Device simulation results show that the two-step AZO texturing process should give improved a-Si:H solar cell performance, with an enhanced short-circuit current density of 16.5 mA/cm², which leads to a high photovoltaic (PV) efficiency of 9.9%.
Demonstration of random projections applied to theretrieval problem of geophysical parameters fromhyper-spectral infrared observations
Carmine Serio, Guido Masiello, and Giuliano Liuzzi
Doc ID: 266975 Received 24 May 2016; Accepted 25 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: The random projections statistical technique has been used to reduce the dimensionality of the radiancedata space generated from high spectral resolution infrared observations. The mathematical inversionof the physical radiative transfer equation for geophysical parameters has been solved in this space ofreduced dimensionality. The great advantage of using random projections is that they provide an unifiedtreatment of instrument noise and forward model error, which can be comprehensively modeled with asingle variance term. The result is a novel retrieval approach, which combines computational efficiencyto possibly improved accuracy of the retrieval products. The novel approach has been demonstratedthrough application to the Infrared Atmospheric Sounder Interferometer. We have found that state-of-artspectroscopy and related line-mixing treatment for the ν2 CO2 absorption band, i.e. the fundamental bandfor temperature retrieval, show an excellent consistency with satellite observations.
Generating perfect polarization vortices throughencoding liquid-crystal display devices
Shiyao Fu, Tonglu Wang, and Chunqing Gao
Doc ID: 268158 Received 13 Jun 2016; Accepted 25 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: Perfect polarization vortices (PPVs) are a new kind of vector beams with identical diameters. In this paper, wepropose an approach that using encoded liquid-crystal display devices to generate PPVs, which is based on theFourier transformation of high-order Bessel-Gaussian (BG) beams. The liquid-crystal display device used here is aphase-only liquid-crystal spatial light modulator (SLM). In the experiment, a hologram consists of a holographicaxicon and a spiral phase plate is encoded on a SLM to generate high-order BG beams. Then, another SLM and aconvex lens, can realize the transformation from BG beams into PPVs. We analyze the diameter of the PPV obtainedby our approach, and find it will be impacted by the focal length of the lens as well as the period of the holographicaxicon, but will be little influenced by the polarization order.
Calibration and 3-D reconstruction of underwater objects with non-single view projection model by structured light stereo imaging
Yexin Wang, Murat Aykin, and Shahriar Negahdaripour
Doc ID: 266552 Received 20 May 2016; Accepted 24 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: Establishing the projection model of imaging systems is critical in 3-D reconstruction of object shapes from multiple 2-D views. When deployed underwater, these are enclosed in waterproof housings with transparent glass ports that generate non-linear refractions of optical rays at interfaces, leading to invalidation of the commonly assumed single-viewpoint (SVP) model. In this paper, we propose a non-SVP ray tracing model for the calibration of a projector-camera system, employed for 3-D reconstruction based on the structured light paradigm. The projector utilizes dot patterns, having established that the contrast loss is less severe than for traditional stripe patterns in highly turbid waters. Experimental results are presented to assess the achieved calibrating accuracy.
Design and daytime performance of laser-inducedfluorescence spectrum (LIFS) lidar for simultaneousdetection of multiple components, dissolved organicmatter, phycocyanin and chlorophyll, in river water
Yasunori Saito, Kei Kakuda, Mizuho Yokoyma, Tomoki Kubota, Takayuki Tomida, and Ho-Dong Park
Doc ID: 265159 Received 16 May 2016; Accepted 24 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: In this work, we developed mobile laser-induced fluorescence spectrum (LIFS) lidar based on preliminaryexperiments on Excitation-Emission-Matrix of water sample and method for reducing solar background light usingsynchronous detection technique. The combination a UV short pulse laser (355 nm, 6 ns) for fluorescenceexcitation with a 10-100 ns short time synchronous detection using a gated image-intensified multi-channel CCD ofthe fluorescence made the LIFS lidar operation possible even in daytime. The LIFS lidar with this constructiondemonstrated the potential of natural river/lake water quality monitoring at the Tenryu River/Lake Suwa. Threemain components in the fluorescence data of the water, dissolved organic matter (DOM), phycocyanin, andchlorophyll were extracted by spectral analysis using the standard spectral functions of these components. Theirconcentrations were estimated by adapting experimentally calibrated data. Results of long term field observationsusing our LIFS lidar from 2010 to 2012 show the necessity of simultaneous multi-component detection tounderstand the natural water environment.
Analytical model for radiative transfer including theeffects of a rough material interface
Thomas Giddings and Anthony Kellems
Doc ID: 264012 Received 26 Apr 2016; Accepted 24 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: The reflected and transmitted radiance due to a source located above a water surface is computed basedon models for radiative transfer in continuous optical media separated by a discontinuous air-water interfacewith random surface roughness. The air-water interface is described as the superposition of random,unresolved roughness on a deterministic realization of a stochastic wave surface at resolved scales. Underthe geometric optics assumption, the bidirectional reflection and transmission functions for the air-waterinterface are approximated by applying regular perturbation methods to Snell’s law and including theeffects of a random surface roughness component. Formal analytical solutions to the radiative transferproblem under the small-angle scattering approximation account for the effects of scattering and absorptionas light propagates through the atmosphere and water and also capture the diffusive effects due tothe interaction of light with the rough material interface that separates the two optical media. Resultsof the analytical models are validated against Monte Carlo simulations, and the approximation to thebidirectional reflection function is also compared to another well-known analytical model.
Influence of Target Reflection on 3D Range GatedReconstruction
Xin Wang, Sing Yee Chua, Ningqun Guuo, and Ching Seong Tan
Doc ID: 264244 Received 10 May 2016; Accepted 24 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: Range gated has been a promising laser ranging method which is widely used in different fields suchas surveillance, industry, and military. In a range gated system, reflected laser pulse returned fromthe target scene contains the key information for range reconstruction which directly affects the systemperformance. Therefore, it is necessary to study the characteristics and effects of target reflection factor.In this paper, theoretical and experimental analysis are performed to investigate the influence of targetreflection on three-dimensional (3D) range gated reconstruction. Based on the Laser Detection AndRanging (LADAR) and bidirectional reflection distribution function (BRDF) theory, a 3D range gatedreconstruction model is derived and the effect on range accuracy is analysed from the perspectives oftarget surface reflectivity and angle of laser incidence. Our theoretical and experimental study showthat the range accuracy is proportional to the target surface reflectivity but decreases when the angleof incidence increases adheres to the BRDF model. The presented findings establish a comprehensiveunderstanding of target reflection in 3D range gated reconstruction which is of interest to variousapplications such as target recognition and object modelling. This paper provides a reference for futureimprovement works to perform accurate range compensation or correction.
Nonlinear evolution of Airy-like beams generated by modulated waveguide arrays
Xinyuan Qi, Zheng Cao, qinggui tan, and Xiaojun Li
Doc ID: 265305 Received 17 May 2016; Accepted 23 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: We numerically study the formation of modulated waveguide generated Airy-like beams and theirsubsequent evolution in homogeneous medium. The results show that the Airy-like beams could begenerated from narrow Gaussian beams propagating in one dimensional transverse separation modulatedunbent, cosine bent or logarithm bent waveguide arrays, respectively. The waveguide-generated Airylikebeams maintain their characteristics when propagating without nonlinearity or under the selfdefocusingnonlinearity in homogeneous medium. While the beams are distorted under the self-focusingnonlinearity. The deformation depends on the waveguide bending and the outgoing angles of the Airylikebeams. Our results provide a new way to generate and manipulate the Airy-like beam.
Terahertz ultrathin film thickness sensor below λ/90 based on metamaterial
Meng Chen, Fei Fan, Si Shen, Xianghui Wang, and Shengjiang Chang
Doc ID: 267917 Received 07 Jun 2016; Accepted 22 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: The film thickness sensing based on metamaterial is investigated in the terahertz (THz) region. We fabricated the metamaterial sensor, and demonstrated its resonance by using the THz time-domain spectroscopy system. According to the corresponding moving of the resonance dependent on the different thickness of the film on the sensor, the thickness sensing can be achieved. Its sensitivity is up to 13.5GHz/μm with the applicable film thinner than λ/90. Meanwhile, the limitation of the sensor is also explained with the electric dipole resonant field distribution, which leads to the nonlinear sensing property. This simple and flexible method can realize the thickness sensing of ultrathin film in THz region, and has the applied potential in the real-time monitoring of sample quality.
Remote picometer FBG demodulation using a dual-wavelength source
Carlos Fernandez-Pousa, Germán Torregrosa, Haroldo Maestre Vicente, and Juan Clement Bellido
Doc ID: 268084 Received 15 Jun 2016; Accepted 22 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: We report on the self-referenced, intensity-based, remote and passive interrogation of a fiber Bragg grating (FBG) for point sensing, by use of a reconfigurable dual-wavelength source composed of a tunable wavelength and subsequent suppressed-carrier, electro-optic amplitude modulation. The demodulation procedure is based on the measurement of the reflected power at two different wavelengths within the FBG spectral response. The grating was interrogated by use of conventional spectral analysis, and also after 32.9 km of single-mode fiber using a dispersive incoherent OFDR technique. Both procedures provide picometer resolution in the determination of Bragg wavelength shifts at a comparatively similar scan time (~1 s) and received power (-16 dBm). The main limitations in each interrogation scheme have been identified. These results show the feasibility of interrogation systems incorporating relatively simple frequency combs at a calibrated, and eventually reconfigurable, wavelength grid with an, at least, similar performance to that of commercial FBG interrogators.
Fusion of infrared and visible images for night-vision context enhancement
Zhi Zhou, Ming Dong, Xiao Xie, and Zhi Gao
Doc ID: 263009 Received 11 Apr 2016; Accepted 22 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: Because of the poor lighting conditions at night time, visible images are often fused with corresponding infrared (IR) images for context enhancement of the scenes in night vision. In this paper, we present a novel context enhancement technique through visible and infrared image fusion for night vision applications with the guided filter. Firstly, to enhance the visibility of poorly illuminated details in the visible image before the fusion, an adaptive enhancement method is developed by incorporating the processes of dynamic range compression and contrast restoration based on the guided filter. Then, the important IR spectral information from the infrared image is injected into the visible image, while simultaneously the details and background scenery of the visible image are persevered by using a novel fusion method based on a multi-scale decomposition with the guided filter. Moreover, in order to obtain the fused image more suitable for human perception, an automatic parameter selection method based on the human vision system (HVS) is proposed to determine a proper amount of the IR spectral information injected into the visible image, for which a new metric of perceptual saliency is created to compare the saliency of perceptual information contained in the infrared and visible images. Experimental results show that the proposed technique is able to achieve better context enhancement in night vision.
Electrically controlled spatial-polarization switch based on patterned photoalignment of nematic liquid crystals
Elena Melnikova, Alexei Tolstik, Irina Rushnova, OLGA KABANOVA, and Alexander Muravsky
Doc ID: 263520 Received 20 Apr 2016; Accepted 22 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: A switching scheme for two orthogonal modes of laser radiation that is based on the total internal reflection effect realized at the interface of two liquid crystal regions with the orthogonal director orientations is proposed. To create the photorefractive interface within the bulk of a liquid crystal, an original technique based on self-alignment of azo dye photoalignment and absorbing electrode patterns has been developed. Spatial separation of the orthogonally polarized light beams and their switching (when the positions of reflected and transmitted light beams are switched) due to the voltage applied has been experimentally realized.
Optical Turbulence in Confined media: Part I, TheINdoor TurbulENce SEnsor (INTENSE) instrument
Julien Chabé, Flavien Blary, Aziz Ziad, Julien Borgnino, Yan FANTEI-CAUJOLLE, Arnaud Liotard, and Frederic Falzon
Doc ID: 263541 Received 19 May 2016; Accepted 22 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: Optical system performances can be affected by local optical turbulence created by its surroundingenvironment (telescope dome, clean room, atmospheric surface layer). We present our newinstrument INTENSE (INdoor TurbulENce SEnsor) dedicated to this local optical turbulence characterization.INTENSE consists of using several parallel laser beams separated by non redundant baselinesbetween 0.05 and 2.5 m and measuring Angle-of-Arrival fluctuations from spots displacements on a CCD.After introducing the theoretical background, we give a description of the instrument including a detailedcharacterization of instrumental noise and finally give the first results for the characterization ofthe turbulence inside clean rooms for optical systems studies.
Towards the Recognition of Wall Materials throughActive Thermography coupled with NumericalSimulations
Mauro Mameli, Francesca Pietrarca, Sauro Filippeschi, and Fabio Fantozzi
Doc ID: 264051 Received 26 Apr 2016; Accepted 22 Jul 2016; Posted 27 Jul 2016 View: PDF
Abstract: In the framework of historical buildings, the wall thickness as well as the wall constituents are not often known apriori and active IR thermography can be exploited as a non-intrusive method for detecting what kind of material liesbeneath the external plaster layer. In the present work, the wall of a historical building is subjected to a heatingstimulus and the surface temperature temporal trend is recorded by an IR camera. A hybrid numerical model isdeveloped in order to simulate the transient thermal response of wall made of different known materials underneaththe plaster layer. Only when the numerical thermal contrast together with the appearance time match with theexperimental thermal images, the material underneath the plaster can be qualitatively identified.
Interferometric measurement of surface shape bywavelength tuning suppressing random intensity error
Yangjin Kim, Kenichi Hibino, Naohiko Sugita, and Mamoru Mitsuishi
Doc ID: 266727 Received 20 May 2016; Accepted 21 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: In this research, the susceptibility of the phase shifting algorithms to the random intensity error was formulatedand estimated. The susceptibility of the random intensity error of conventional windowed phase shiftingalgorithms was discussed and the 7N – 6 phase shifting algorithm was developed to minimize the random intensityerror using the characteristic polynomial theory. Finally, the surface shape of the transparent wedge plate wasmeasured using the wavelength tuning Fizeau interferometer and 7N – 6 algorithm. The experimental resultsindicated that the surface shape measurement accuracy for the transparent plate was 2.5 nm.
Study of a micro-CPV system based on Cu(In,Ga)Se2 microcells array
Sebastien Jutteau, Jean-Francois Guillemoles, and Myriam Paire
Doc ID: 263185 Received 02 Jun 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: We study a micro-CPV system based on micro solar cells made from a thin film technology, Cu(In,Ga)Se2. Wedesigned, using the ray-tracing software Zemax OpticStudio 14, an optical system adapted and integrated to themicrocells, with only spherical lenses. The designed architecture has a magnification factor of 100x for an opticalefficiency of 85% and an acceptance angle of +/- 3.5°, without antireflective coating. An experimental study isrealized to fabricate the first generation prototype on a 5x5cm² substrate. A mini-module achieved a concentrationratio of 72x under AM1.5G, and an absolute efficiency gain of 1.8% for a final aperture area efficiency of 12.6%.
Effect of codoped interface layer on passively Q-switched laser performance of composite crystals
Jun Dong and Jie Xu
Doc ID: 265490 Received 17 May 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: By using combinations of appropriate laser crystals, we simulated Yb:YAG/Cr4+:YAG composite crystal with Cr,Yb:YAG interface layer. The effect of Cr,Yb:YAG interface layer on laser performance of Yb:YAG/Cr4+:YAG composite crystal has been investigated for the first time to our best knowledge. The formation of Cr,Yb:YAG interface layer in Yb:YAG/Cr4+:YAG composite crystal has a negative impact on average output power, optical efficiency as well as single pulse energy and peak power. In addition, Cr,Yb:YAG interface layer also leads to a strong mode competition, resulting in the decrease of the longitudinal mode number, the widening of the longitudinal mode separations and the poor stability of laser pulse trains. The results of this study are of theoretical and practical importance to develop novel types of Yb:YAG/Cr4+:YAG composite crystals which could be used to obtain laser pulses with high peak power and high optical efficiency.
Frequency spacing switchable multi-wavelengthBrillouin Erbium fiber laser utilizing cascaded Brillouingain fibers
Wang Xiaorui, Yanfu Yang, Meng Liu, yijun yuan, Yunxu Sun, Yinglong Gu, and Yong Yao
Doc ID: 267077 Received 25 May 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: A new hybrid Brillouin Erbium fiber laser scheme that employing cascaded multiple Brillouin gain fibers in a ringcavity to realize multi-wavelength laser output with switchable frequency spacing is proposed and experimentallyinvestigated. The multiple frequency down-shifting processes introduced by multiple stimulated Brillouinscattering (SBS) effects in one round trip of the cavity make it possible to realize multi-wavelength output withfrequency spacing which is an integer multiple of SBS frequency shifting. With two cascaded SBS fibers, thefrequency spacing can be switched between single and double SBS frequency shifting by properly adjustingBrillouin pump power. Multi-wavelength outputs with triple or quadruple SBS frequency spacing are alsodemonstrated by employing three or four SBS gain fibers, respectively.
Compact KGd(WO₄)₂ picosecond pulse-train synchronously pumped broad-band Raman Laser
Xiaoqiang Gao, meng chen, and Mingliang Long
Doc ID: 267215 Received 27 May 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: We demonstrated an efficient approach realizing extra-cavity synchronously pumped stimulated Raman cascaded process under low repetition frequency (1 kHz) pump condition. We also constructed compact KGd(WO₄)₂ (also KGW) crystal picosecond Raman laser which has been configured as the developed method. Pulse-train green laser pumped the corresponding 120mm long KGW crystal Raman cavity, in which the pulse-train contains 6 pulses for every millisecond with about 800ps distance separated thus it can realize synchronously pumping between pump pulse and the pumped Raman cavity. The investigated system produced collinear Raman laser output which includes 6 laser lines covering 532nm to 800nm spectra and it’s the first report on the high-average-power picosecond collinear multi-wavelength (more than three laser components) generation to our knowledge. The method has never been reported before wherein synchronously-pumped stimulated Raman scattering (SRS) realm.
Application of Gaussian beam ray-equivalent modeland back-propagation artificial neural network in laserdiode fast axis collimator assembly
Guido Perrone, HAO YU, Andrea Braglia, and Giammarco Rossi
Doc ID: 267394 Received 31 May 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: The paper presents the development of a tool based on a back-propagation artificial neural network to assistin the accurate positioning of the lenses used to collimate the beam from semiconductor laser diodesalong the so-called fast axis. After training using a Gaussian beam ray-equivalent model, the network iscapable of indicating the tilt, decenter and defocus of such lenses from the measured field distribution,so the operator can determine the errors with respect to the actual lens position and optimize the diodeassembly procedure. An experimental validation using a typical configuration exploited in multi-emitterdiode module assembly and fast axis collimating lenses with different focal lengths and numerical aperturesis reported.
Simulation of optical caustics associated with the tertiary rainbow of oblate droplets
guan lu, Haitao Yu, Jianqi Shen, and Cameron Tropea
Doc ID: 268085 Received 10 Jun 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: In the present paper, vector-ray tracing (VRT) model is used to simulate optical caustic structures, including rainbow and hyperbolic umbilic (HU) fringes, in the tertiary rainbow region of light scattering from oblate spheroidal droplets. In order to apply the optical caustic structures to particle diagnostics, the evolutions of rainbow fringe and HU fringe with the increase of aspect ratio of oblate spheroidal droplets are investigated in detail and the curvature of rainbow fringe is also calculated. Then, on the basis of VRT model, the location of cusp caustics is calculated and compared with theoretical prediction.
Extrinsic Calibration of Non-overlapping Camera Network Based on Close-range Photogrammetry
Shuai Dong, Xinxing Shao, Xin Kang, Fujun Yang, and Xiaoyuan He
Doc ID: 264697 Received 06 May 2016; Accepted 21 Jul 2016; Posted 21 Jul 2016 View: PDF
Abstract: In this paper, an extrinsic calibration method for a non-overlapping camera network is presented based on close-range photogrammetry. The method does not require calibration targets or the cameras to be moved. The visual sensors are relatively motionless and do not see the same area at the same time. The proposed method combines the multiple cameras using some arbitrarily distributed encoded targets. The calibration procedure consists of three steps: reconstructing the three-dimensional (3D) coordinates of the encoded targets using a hand-held digital camera, performing the intrinsic calibration of the camera network and calibrating the extrinsic parameters of each camera with only one image. A series of experiments, including 3D reconstruction, rotation and translation, are employed to validate the proposed approach. The results show that the relative error for the 3D reconstruction is smaller than 0.003%, the relative errors of both rotation and translation are less than 0.066%, and the re-projection error is only 0.09 pixels.
GRASSP: A Spectrograph for the Study of Transient Luminous Events
María Passas Varo, Justo Sanchez, Ernesto Sanchez-Blanco, Alejandro Luque, and F Gordillo-Vazquez
Doc ID: 262890 Received 08 Apr 2016; Accepted 21 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: We present the main parameters, design features and optical characterization of GRASSP, a ground-based spectrographic system intended for the analysis of the spectroscopic signature of transient luminous events (TLEs) occurring in the mesosphere of the Earth. It has been designed to measure the spectra of the light emitted from TLEs with a mean spectral resolution of 0. 5 nm and 0.07 nm/px dispersion in the wavelength range between 700 and 800 nm.
Half-Disordered Photonic Crystal Slabs
Jacob Keilman, David Citrin, and Vincent Beque
Doc ID: 254326 Received 29 Feb 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016 View: PDF
Abstract: Optical transmission spectra of finite-thickness slabs of two-dimensional triangular-lattice photonic crystals of air holes in a dielectric matrix with various concentrations of randomly located vacancies (absent air holes) are studied. We focus on structures in which only one half of the structure—the incidence or transmission side—is disordered. We find vacancy-induced scattering gives rise to a strong difference in the two cases; for light incident on the disordered side, high transmission within the photonic pseudogap at normal incidence is predicted, in strong contrast to the opposite case, where low transmission is predicted throughout the pseudogap, as is observed in the case of an ideal structure with no defects.
An ultra-broadband polarization splitter based on three-core photonic crystal fiber with a modulation core
Tongtong Zhao, shuqin lou, Zhenggang Lian, Xin Wang, and Min Zhou
Doc ID: 262920 Received 11 Apr 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016 View: PDF
Abstract: We design an ultra-broadband polarization splitter based on three-core photonic crystal fiber. A modulation core and two fluorine-doped cores are introduced to achieve an ultra-wide bandwidth. The properties of three-core photonic crystal fiber are modeled by using the full-vector finite element method along with full-vector beam propagation method. Numerical results demonstrate that an ultra-broadband splitter with 320 nm bandwidth with an extinction ratio as low as -20 dB can be achieved by using 52.8 mm long three-core photonic crystal fiber. This splitter also has high compatibility with standard single-mode fibers as the input and output ports due to low splicing loss of 0.02 dB. All the air holes in the proposed structure are circular holes and arranged in a triangular lattice that makes it easy to fabricate.
Diffractive fan-out elements for wavelength-multiplexing subdiffraction-limit spot generation in three dimensions
Yusuke Ogura, Masahiko Aino, and Jun Tanida
Doc ID: 264748 Received 11 May 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016 View: PDF
Abstract: Wavelength-multiplexing generation of subdiffraction-limit spots in three dimensions using propagating light was demonstrated and evaluated. Our previous design algorithm [Y. Ogura et al., Opt. Exp. 22, 25196 (2014)] was extended to consider multiple output planes and multiple wavelengths by integrating modulation distributions for individual wavelengths. A diffractive fan-out element that generates subdiffraction limit spot arrays with two wavelengths on two planes was demonstrated. Spot sizes were reduced to 79% of that of the diffraction limit spot on average. Numerical calculations showed that seven-wavelength multiplexing is achievable, and the crosstalk suppression conditions are effective for crosstalk suppression between wavelengths.
Transmittance properties in a magnetized cold plasma-superconductor periodic multilayer
Doc ID: 265256 Received 16 May 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016 View: PDF
Abstract: This study theoretically investigates the transmittance properties in a one-dimensional photonic crystal containing magnetized cold plasma and high temperature superconductor materials. The cutoff frequency as a function of the magnetic field and the electron density of the plasma layer and the temperature will be investigated. The results illustrate that the temperature, the electron density, and the variations of the magnetic field affect the cutoff frequency. In addition, the shift trend in the cutoff frequency proves to be dependent on the polarization due to the presence of polarization-dependent magnetized cold plasma. Moreover, in temperature-dependent transmittance, weak oscillation and intensity can be seen at higher temperatures, which is in sharp contrast with low temperature superconductor-dielectric structure. The proposed structure could certainly provide helpful information for designing new types of antennas, reflectors, and high pass filters at microwave frequency.
Cavity-dumped Yb:YAG ceramic in the 20 W, 12 mJ range at 6.7 ns operating from 20 Hz - 5 kHz with fluorescence feedback control
Christian Fries, Marco Weitz, Christian Theobald, Patric v. Loewis of Menar, Jürgen Bartschke, and Johannes Lhuillier
Doc ID: 266868 Received 24 May 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016 View: PDF
Abstract: Increasing data acquisition rates in metrology applications based on optical parametric oscillators (OPOs) can accelerate measurement processes. To achieve this, flash-lamp systems with low pulse repetition frequency of 10-100 Hz used as pump source for the OPOs could be replaced by diode-pumped solid state lasers in the kHz range. We demonstrate a 969 nm pumped Yb:YAG ceramic laser, yielding 21.6 W output power, 12.5 mJ pulse energy and excellent beam quality. A fluorescence feedback control, developed from gain dynamics simulations in two operating regimes, allows stable operation at 6.7 ns from 20-5000 Hz. Third harmonic generation to 343 nm yields 3.24 W at 2 kHz. The system provides constant pulse duration in a huge repetition rate interval, which is beneficial for a pump source for future metrology devices.
Transmission characteristics and transmission line model of metal-insulator-metal waveguide with a stub modified by cuts
yueke wang, Xinru shen, Xin Yan, lin yuan, and Tian Sang
Doc ID: 267038 Received 25 May 2016; Accepted 20 Jul 2016; Posted 21 Jul 2016 View: PDF
Abstract: We propose a structure of Metal-Insulator-Metal (MIM) waveguide with a stub modified by cuts. Our simulation results, conductedby finite element method, show that the wavelengths of transmission dip vary with the position of the cuts and form the zigzag lines.A transmission line model is also presented, and it agrees with simulation results well. It is believed that our findings provide a smartway to design plasmonic waveguide filter at communication region based on MIM structures.
Flexible Calibration of Phase-to-Height Conversion in Fringe Projection Profilometry
Jin Lu, Rong Mo, Huibin Sun, and Chang Zhiyong
Doc ID: 267039 Received 27 May 2016; Accepted 19 Jul 2016; Posted 21 Jul 2016 View: PDF
Abstract: A flexible new technique is presented to calibrate the monocular system of phase-based fringe projectionprofilometry, which is made of a camera, a projector and a computer. The proposed algorithm mainly consists of amore flexible phase-to-height conversion (PHC) model and a minimum norm solution, followed by a nonlinearoptimization based on the maximum likelihood criterion. In the whole calibration procedure, this method onlyrequires the camera to capture a few two-dimensional (2D) checkerboard target images and several deformedfringe images at least three different orientations. And the proposed technique neither subjects to certainlimitations nor measures additional geometry parameters in advance. Also, no high precise gage blocks or no extrareference phases are involved. In contrast with the existing methods, the proposed technique is easier to use andmore flexible. Experiments have been performed to validate the performance of this technique.
Canceling the momentum in a phase-shifting algorithm to eliminate spatially uniform errors
Kenichi Hibino and Yangjin Kim
Doc ID: 267604 Received 02 Jun 2016; Accepted 19 Jul 2016; Posted 21 Jul 2016 View: PDF
Abstract: In phase-shifting interferometry, phase modulation nonlinearity causes both spatially uniform and non-uniform errors in the measured phase. Conventional error-compensating algorithms only eliminate the spatially variable error component. The uniform error is proportional to the inertial momentum of the data-sampling weight of a phase-shifting algorithm. This paper proposes a design approach to cancel the momentum by using characteristic polynomials in the Z-transform space, and shows that an arbitrary M-frame algorithm can be modified to a new (M + 2)-frame algorithm that acquires new symmetry to eliminate the uniform error.
Strain and high temperature discrimination using a type II fiber Bragg grating and a miniature fiber Fabry-Pérot interferometer
Yajun Jiang, Dexing Yang, Yuan Yuan, Jian Xu, Dong Li, and Jianlin Zhao
Doc ID: 269328 Received 27 Jun 2016; Accepted 19 Jul 2016; Posted 21 Jul 2016 View: PDF
Abstract: A novel method for simultaneous measurement of strain and high temperature using a type II fiber Bragg grating (FBG) and a miniature fiber Fabry-Pérot interferometer (MFFPI) is proposed. The MFFPI is produced by fusion splicing a short section of quartz capillary tube with two single mode fibers, and then it is exposed by focused femtosecond laser and a phase mask to inscribe a type II FBG nearby. The reflection spectrum of this sensor is the superposition of reflection spectrum of the FBG and interference fringe of the MFFPI. This sensor shows perfect high temperature and strain responses. Due to the different responses to the uniform variations of strain and temperature, by measuring the reflection peak of FBG and one of the interference dips of MFFPI, strain and temperature can be determined simultaneously. The resolutions of this particular sensor in measuring strain and temperature are estimated to be ±8.4 με and ±3.3 °C in the range from 0 με to 1122 με and from °C to 600 °C.
Preparation and transmission characteristics of mid-infrared ATR hollow waveguide based on stainless steel capillary tube
Xu Wang, Hong Guo, Lin Wang, Fangyu Yue, Chengbin Jing, and Junhao Chu
Doc ID: 265443 Received 17 May 2016; Accepted 19 Jul 2016; Posted 19 Jul 2016 View: PDF
Abstract: Stainless steel (SUS) capillary tubes were examined as a category of structural tube for establishing a metallic ATR GeO2 hollow waveguide. GeO2 films were grown on the inner wall of SUS tubes by different liquid phase deposition (LPD) cycles. FTIR spectra, SEM and transmission loss for CO2 laser were measured to investigate the effects of the LPD cycles on the transmission behavior of the hollow waveguide samples. The film thickness and surface roughness increase with every LPD cycle. The 2 LPD cycled sample has a film thickness equivalent to the CO2 laser wavelength while the surface roughness is acceptable. This sample has the lowest transmission loss (0.27dB/m) among these samples. The bending loss, output beam profile and full divergence angle (FDA) were further studied. Higher-order modes are excited by bending the sample, inducing additional loss, decentralized beam profile and larger FDA.
Metal powder absorptivity: modeling and experiment
Charles Boley, Scott Mitchell, Alexander Rubenchik, and Sheldon Wu
Doc ID: 265226 Received 16 May 2016; Accepted 19 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: We present results of numerical modeling and direct calorimetric measurements of the powder absorptivity for a number of metals. The modeling results generally correlate well with experiment. We show that the powder absorptivity is determined, to a great extent, by the flat-surface absorptivity. Our results allow the prediction of the powder absorptivity from normal flat-surface absorptivity measurements.
Effects of small misalignments on the intensity and Strehl ratio for a laser beam focused by an Off-Axis Parabola
Luca Labate, Paolo Ferrara, Leonida Gizzi, and Lorenzo Fulgentini
Doc ID: 263874 Received 06 May 2016; Accepted 18 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: A general procedure is described to calculate the intensity and Strehl ratio, at a generic plane in the focalregion, of a beam focused by an off-axis parabolic mirror in the presence of small misalignments. Thegeneral theoretical framework is first developed, which allows a full vector diffraction treatment in thecase of general misalignments. Then, a parametric numerical study is reported, aimed at highlighting thetolerances of both the intensity and Strehl ratio for small misalignments, for different focusing and offaxisparabola parameters. A set of experimental measurements aimed at validating the theoretical modelis also discussed.
Experimental demonstration of optical stealth transmission over WDM network
Tao Pu, Huatao Zhu, Rong Wang, Tao Fang, Peng Xiang, Jilin Zheng, Yeteng Tang, and Dalei Chen
Doc ID: 267516 Received 01 Jun 2016; Accepted 18 Jul 2016; Posted 19 Jul 2016 View: PDF
Abstract: We propose and experimentally demonstrate an optical stealth transmission system over 200 GHz-grid WDM network. The stealth signal is processed by spectral broadening, temporal spreading and power equalizing. The public signal is suppressed by multi-band-notch filtering at the stealth channel receiver. The interaction between the public and stealth channel is investigated in terms of public signal to stealth signal ratio, data rate, notch filter bandwidth and public channel number. The stealth signal can transmit over 80 km single mode fiber with error free. Our experimental results verifies the feasibility of optical steganography used over the existing WDM based optical network.
Novel integral imaging system using an adaptive lens array
Kwan-Hee Yoo, minho song, Ji-Seong Jeong, Munkh-Uchral Erdenebat, Ki-Chul Kwon, and Nam Kim
Doc ID: 263978 Received 26 Apr 2016; Accepted 18 Jul 2016; Posted 19 Jul 2016 View: PDF
Abstract: We produced an adaptive lens array composed of multiple flat lens arrays arranged in a curved shape with an adjustable radius of curvature, in order to overcome the hardware problem of the conventional flat or curved lens array-based systems. The manufactured adaptive lens array is applied to an integral imaging system. The gap mismatch that occurs when using a curved lens array is resolved by computing the exact display mapping position of element images through each lens. The results of the experiment demonstrate that the adaptive lens array-based integral imaging system successfully generated elemental images according to the curvature transformation of the adaptive lens array and they were reconstructed as 3D images.
Mid-infrared supercontinuum generation in silica photonic crystal fibers
Meisong Liao, wanjun bi, Juanjuan Gao, Xia Li, and Liangming Xiong
Doc ID: 264532 Received 04 May 2016; Accepted 18 Jul 2016; Posted 19 Jul 2016 View: PDF
Abstract: Mid-infrared supercontinuum (SC) light source, which has important applications in many fields, is extensivelyinvestigated in soft glass fibers. However, the poor instinct properties of soft glass fibers and the development ofultra-short pulse lasers left an opportunity to the mid-infrared SC generation in silica fiber. Until now, silica fiber isthe commonly used medium for SC generation due to its outstanding properties. In this paper, mid-infrared SCgeneration in short silica photonic crystal fibers (PCFs) is investigated theoretically and systematically. In case of1550 nm pump, the soliton self-frequency shift effect is utilized to extend the long wavelength edge of SC. Adoptinga fiber which has a zero dispersion wavelength away from the pump pulse is benefit for the suppression of bluespectral component and the energy distribution in the long wavelength band. In case of 1950 nm pump, thegeneration of red-shifted dispersive wave (DW) is an efficient way to extend the long wavelength edge of SC.Additionally, the coherence for femtosecond pulse pumping is discussed in this paper. Finally, the long wavelengthedge of SC is beyond 3000 nm when 1950 nm femtosecond pump pulse propagates in a PCF with negativedispersive slope around the pump pulse.
High-precision broadband measurement of refractive index by picosecond real-time interferometry
Zheng Jie Tan, Dafei Jin, and Nicholas Fang
Doc ID: 267901 Received 07 Jun 2016; Accepted 18 Jul 2016; Posted 26 Jul 2016 View: PDF
Abstract: Refractive index is one of the most important quantities that characterize a material's optical properties. However, it is hard to measure this value over a wide range of wavelengths. Here, we demonstrate a new technique to achieve a spectrally broad refractive index measurement. When a broadband pulse passes through a sample, different wavelengths experience different delays. By comparing the delayed pulse to a reference pulse, the zero path difference (ZPD) position for each wavelength can be obtained and the material's dispersion can be retrieved. Our technique is highly robust and accurate, and can be miniaturized in a straightforward manner.
Analyzing the propagation behavior of coherence and polarization degrees of a phase-locked partially coherent radial flat-topped array laser beam in underwater turbulence
F Kashani and Masoud Yousefi
Doc ID: 265035 Received 11 May 2016; Accepted 17 Jul 2016; Posted 19 Jul 2016 View: PDF
Abstract: In this research, based on an analytical expression for Cross- Spectral Density (CSD) matrix elements, coherence and polarization properties of phase-locked partially coherent flat-topped (PCFT) radial array laser beams propagating through weak oceanic turbulence are analyzed. Spectral degrees of coherence and polarization are analytically calculated using CSD matrix elements. Also, the effective width of spatial degree of coherence (EWSDC) is calculated numerically. The simulation is done by considering the effects of source parameters (such as radius of array setup’s circle, effective width of the spectral degree of coherence and wavelength) and turbulent ocean factors (such as the rate of dissipation of the turbulent kinetic energy per unit mass of fluid and relative strength of temperature and salinity fluctuations, Kolmogorov micro-scale, and rate of dissipation of the mean squared temperature) in detail. Results indicate that, any change in the amount of turbulence factors that increase the turbulence power, reduces the EWSDC significantly and causes the reduction in the degree of polarization occurs at shorter propagation distances but with smaller magnitudes. In addition, being valid for all conditions, the degradation rate of the EWSDC of Gaussian array beams are more in comparison with the PCFT ones. The simulation and calculation results are shown by graphs.
Design and fabrication of a tunable wavelength-selective polarization grating
Kotaro Kawai, Moritsugu Sakamoto, Kohei Noda, Tomoyuki Sasaki, Nobuhiro Kawatsuki, and Hiroshi Ono
Doc ID: 265347 Received 16 May 2016; Accepted 17 Jul 2016; Posted 19 Jul 2016 View: PDF
Abstract: Tunable wavelength-selective diffraction with polarization conversion is realized by the design of a liquid crystal (LC) grating containing a twisted nematic alignment structure that is fabricated by an efficient one-step photoalignment method. The diffraction efficiency strongly depends on the wavelength of the incident beam, and this property can be controlled by adjusting the birefringence of the nematic LC using a thermal control. These properties are well described by a theoretical analysis based on the Jones calculus and are experimentally demonstrated using 488-, 532-, and 633-nm wavelength incident polarized laser beams. The resultant LC grating has potential application as diffractive optical elements that can simultaneously control the parameters of light such as amplitude, wavelength, and polarization.
Fourier ptychographic microscopy using an infrared-emitting hemispherical digital condenser
Sanchari Sen, Ishtiaque Ahmed, Batool Aljubran, Ayrton Bernussi, and Luis Grave de Peralta
Doc ID: 264781 Received 16 May 2016; Accepted 16 Jul 2016; Posted 19 Jul 2016 View: PDF
Abstract: Fourier ptychographic microscopy is demonstrated in the near-infrared spectral range using a computer-controlled hemispherical digital condenser comprising multiple 940 nm wavelength light emitting diodes. This technique was used to image periodic patterned samples (photonic crystals). Experimental and simulated results using a phase retrieval algorithm were found to be in excellent correspondence. We show that for samples with a single period in each direction, the resolution of the obtained high-resolution near-infrared images is limited by the Rayleigh criteria.
Fabrication of Phase Transmission Holographic Optical Element in Polycarbonate and its Characterization
Vadivelan. V Varadarajan and Chander Bellan
Doc ID: 264226 Received 28 Apr 2016; Accepted 16 Jul 2016; Posted 19 Jul 2016 View: PDF
Abstract: The phase transmission holographic optical element in silver halide holographic emulsion especially for holographic weapon sight is fabricated and obtained desired diffraction efficiency with very high transmission. One of a main drawback of these holograms are become dark by exposed under Sun light, it is drastically reduce the visible transmission and diffraction efficiency of a holographic optical element, hence it is not suitable for weapon sight application. To overcome this problem, we transferred holographic optical element with reticle image from silver halide into polycarbonate by using electroforming and recombination techniques. The holographic optical element in polycarbonate have many advantages, the details method of fabrication, transfer and its characterization are presented. The very interesting result of diffraction efficiency variation with angle obtained in polycarbonate is discussed.
Temperature drift Modeling and compensation of Fiber Optical Gyroscope Based on improved support vector machine and particle swarm optimization algorithms
Wei Wang and xiyuan chen
Doc ID: 264686 Received 06 May 2016; Accepted 15 Jul 2016; Posted 15 Jul 2016 View: PDF
Abstract: Temperature drift is one of the main error sources of fiber optic gyroscope (FOG). Modeling and compensation of temperature drift is an important method to improve the precision of FOG. In this paper, a new method of modeling and compensation for FOG based on improved particle swarm optimization (PSO) and support vector machine (SVM) algorithms is proposed, which is called PSO-RBFP, and the experiment results show the validity and practicability of the method. The convergence speed and reliability of PSO are improved by introducing dynamic inertia factor. The regression accuracy of SVM is improved by introducing the combined kernel function with parameters. The regression accuracy of PSO-RBFP is further improved by introducing the algorithm of piecewise regression, and the algorithm is called PSO-RBFP-P. The steps to model and compensate the temperature drift of FOG are as follows. Firstly, the parameters of the combined kernel function are optimized by the improved PSO algorithm. Secondly, the new kernel function of SVM is used to carry out piecewise regression of temperature drift, and the regression model is also obtained. Thirdly, the temperature drift is compensated by the regression model and regression data. The experimental results show that the method proposed in this paper can effectively compensate the temperature drift of FOG. The regression accuracy of temperature drift (in the case of MAPE indicators) increased by 89% compared to the traditional SVM.
Eye-Safe Transmitter for Ground-Based, Integrated Path Differential Absorption LIDAR Measurement of CO₂, CH₄, and H₂O near 1.6 μm
David Plusquellic and Gerd Wagner
Doc ID: 262752 Received 07 Apr 2016; Accepted 15 Jul 2016; Posted 15 Jul 2016 View: PDF
Abstract: The eye-safe transmitter of a ground-based, integrated path, differential absorption light detection and ranging (IPDA LIDAR) system is described and specified in detail. The transmitter is based on an actively stabilized, continuous-wave, single-frequency external-cavity diode laser (ECDL) operating from 1.60 μm to 1.65 μm. The ECDL is microwave (MW) sideband tuned using an electro-optical phase modulator (EOM) driven by an arbitrary waveform generator (AWG) and filtered using a confocal cavity to generate a sequence of 1 frequencies separated by 300 MHz. The scan sequence of single sideband frequencies of 600 ns duration covers a 37 GHz region across absorption lines of CO₂, CH₄, and H₂O at a spectral scan rate of 10 kHz (100 μs per scan). Simultaneously, an eye-safe backscatter LIDAR system at 1.064 μm is used to monitor the atmospheric boundary layer. IPDA measurements of the CO₂ and CH₄ dry air mixing ratios are presented in comparison with those from a commercial cavity ring-down (CRD) instrument. Differences between the IPDA and CRD concentrations in several cases are well correlated with the atmospheric aerosol structure from the LIDAR measurements. IPDA dry air mixing ratios of CO₂ and CH₄ are determined with fit uncertainties of 2.7 μmol/mol (ppm) for CO₂ and 0.025 μmol/mol (ppm) for CH₄ over 30 s measurement periods. For longer averaging times (up to 1200 s), improvements in these detection limits by up to 3-fold are estimated from Allan variance analyses. Two sources of systematic error are identified and methods to remove them are discussed, including speckle interference from wavelength decorrelation and the seed power dependence of amplified spontaneous emission. Absolute accuracies of CO₂ and CH₄ are estimated at 1.6 μmol/mol (0.4 % of ambient levels) and 0.042 μmol/mol (2 %), respectively.
Multispecies Absorption Spectroscopy of Detonation Events at 100 kHz using a Fiber-Coupled, Time-Division-Multiplexed Quantum-Cascade-Laser System
Keith Rein, Sukesh Roy, Scott Sanders, Andrew Caswell, Frederick Schauer, and James Gord
Doc ID: 263202 Received 26 Apr 2016; Accepted 15 Jul 2016; Posted 15 Jul 2016 View: PDF
Abstract: A mid-infrared fiber-coupled laser system constructed around three time-division-multiplexed quantum-cascade lasers capable of measuring the absorption spectra of CO, CO2, and N2O at 100 kHz over a wide range of operating pressures and temperatures is demonstrated. This system is first demonstrated in a laboratory burner and then used to measure temperature, pressure, and concentrations of CO, CO2, and N2O as a function of time in a detonated mixture of N2O and C3H8. Both fuel-rich and fuel-lean detonation cases are outlined. High-temperature fluctuations during the blowdown are observed. Concentrations of CO are shown to decrease with time for fuel-lean conditions and increase for fuel-rich conditions.
Performance estimation of dual-comb spectroscopy in different frequency-control schemes
Honglei YANG, Haoyun Wei, Hongyuan Zhang, Kun Chen, Li Yan, Viktor Smolski, and Konstantin Vodopyanov
Doc ID: 267714 Received 03 Jun 2016; Accepted 15 Jul 2016; Posted 19 Jul 2016 View: PDF
Abstract: Dual-comb spectroscopy (DCS) has shown unparalleled advantages but at the cost of highly mutual coherence between comb lasers. Here, we investigate spectral degradation induced by the laser frequency instability and improvement benefited from active laser stabilization. Mathematical models of DCS in the cases of direct radio-frequency (RF) locking and optical phase-stabilization were separately established first. Numerical simulations are utilized to study the impact of laser intrinsic stability and the improvement by different locking strategies on spectral performance in the following. Finally, both simulations are proven by corresponding experiments. It shows that optical phase-stabilized system owns a better immunity of laser frequency perturbation than direct RF-stabilized one. And the performance improvement by the feedback servos is also more effective in the optical phase-stabilized system. In addition, the simulations could instruct optimal design and system improvement.
Visual and instrumental correlation of sparkle by themagnitude estimation method
Omar Gomez, Esther Perales, Elisabet Chorro, Valentin Viqueira, and Francisco Martínez-Verdú
Doc ID: 267073 Received 25 May 2016; Accepted 15 Jul 2016; Posted 19 Jul 2016 View: PDF
Abstract: Most real surfaces and objects show variation in appearance with viewing and illumination directions. Besidesangular dependency, they also show spatial variation in color; i.e. they exhibit some sort of texture. Of the surfaceswe see, surfaces colored by special-effect pigments produce several complex visual effects, like change in color andlightness with viewing and illumination angles, and effects like sparkle and gloss on other textures.In the last two decades, different commercial devices have appeared to help ensure the proper characterization ofmaterials with special-effect pigments. However, the instrumental characterization of sparkle is currently availableonly by a commercial device integrated into a multi-angle spectrophotometer. As it is difficult to find completeopen original studies about the sparkle effect for designing and calibrating this commercial instrument, the mainobjective of this work was to check whether a good visual and instrumental correlation exists between the sparklethat the observer perceives and the sparkle value provided by the device using some subsets of goniochromaticsamples with different types of special-effect pigments and colors. Visual assessments were made by aconventional magnitude estimation method in a directional lighting booth, which belonged to the same companyowner of the sparkle instrument, in different geometries and at distinct illuminance levels.The results revealed that there was a good visual correlation of the sparkle-grade value. By separately analyzingthe factors used in its instrument algorithm, such as sparkle intensity and sparkle-area values, it was clearly shownthat the correlation was not good or simply did not exist. Consequently, and perhaps as regards choice of newspecial-effect pigments, such as synthetic mica and other future ones, we generated herein even more questionsabout current mathematical algorithms, and only recognized calculating this texture effect at the industrial level.
Terahertz polarization splitter based on a dual-elliptical-core polymer fiber
Guofeng Yan, Erik Forsberg, Sailing He, and Hongzhi Chen
Doc ID: 264517 Received 03 May 2016; Accepted 13 Jul 2016; Posted 15 Jul 2016 View: PDF
Abstract: A terahertz (THz) polarization splitter based on a dual-elliptical-core polymer fiber is proposed and theoretically optimized. Dual-elliptical cores of subwavelength-scale diameters are independently suspended within the fiber, which not only support two orthogonal polarization modes being single-mode guided with low absorption losses, but also allow them to switch from one core to the other, with different coupling lengths. As a consequence, the two polarizations can be easily separated by choosing a suitable transmission length at a desired operation frequency. Here, the transmission modes, coupling lengths for x- and y-polarization, as well as the performance of the proposed polarization splitter at a center-frequency of 0.6 THz are investigated and numerically analyzed. A 1.43 cm long splitter with an ultra-low loss of 0.4 dB, a high extinction ratio (ER) better than -10 dB and a bandwidth of 0.02 THz is achieved.
Analysis of autostereoscopic three-dimensionalimages with horizontal parallax using multiviewwavelets
Vladimir Saveljev and Irina Palchikova
Doc ID: 267162 Received 27 May 2016; Accepted 13 Jul 2016; Posted 15 Jul 2016 View: PDF
Abstract: We propose the multiview wavelets which can be used in the real-time processing of the multiview images. The reference functions for the synthesis/analysis of multiview images are described. The synthesized binary image was observed experimentally as a three-dimensional visual image. The wavelets are built basing on the reference functions as scaling functions of the wavelet analysis. The locations recognized in the continuous wavelet transform correspond to the layout of the testing object. The proposed wavelets can be applied to the multiview images with the horizontal parallax, and in a generalized two-dimensional form, to the integral and plenoptic images.
Two-way shift of wavelength in holographic sensing of organic vapor in nano-zeolites dispersed acrylamide photopolymer
Yu Dan, Mao Dongyao, Geng yaohui, Hongpeng Liu, Zhou ke, and Xian Lihong
Doc ID: 266658 Received 20 May 2016; Accepted 12 Jul 2016; Posted 12 Jul 2016 View: PDF
Abstract: Holographic sensing of alcohol organic vapor is characterized in detailed at transmission and reflection geometries in Y nanozeolites dispersed acrylamide photopolymer. Two-way shift of diffraction spectrum and its temporal evolution with various vapor concentrations are measured. Obvious blue shifts of diffraction spectrum peaks are observed and analyzed in transmission recording geometry. The competition mechanism between decreasing of average refractive index and swelling of grating space are proposed for exploring the wavelength shift mechanism. In reflection grating, as organic vapor increases, the red shift after blue shift of wavelength peaks are observed clearly. It is further demonstrated the significance of this competition mechanism. In low concentration region, at transmission <700ppm and reflection <200pmm, the blue shift of wavelength is a significant factor for identify organic vapor with low refractive index. These experimental results provide a probability for improving the applicability of holographic sensor. This work can accelerates the development of holographic sensing strategy and provide a novel identification method for organic vapor.
Demonstration of a Homogeneous Yb-Doped Core Fully-Aperiodic Large-Pitch-Fiber Laser
Romain Dauliat, Aurélien Benoit, dia darwich, Raphael Jamier, Jens Kobelke, Stephan Grimm, Kay Schuster, and Philippe Roy
Doc ID: 264579 Received 11 May 2016; Accepted 12 Jul 2016; Posted 13 Jul 2016 View: PDF
Abstract: The first demonstration of a 40 µm core homogeneously ytterbium-doped fully-aperiodic large-pitch-fiber (FA-LPF) laser is reported on here. In this concept, the amplification of unwanted high-order modes is prevented by means of an aperiodic inner cladding structure, while the core and inner cladding material has a higher refractive index than pure silica. In a laser configuration, up to 252 W of extracted power, together with an optical-to-optical efficiency of 63 % with respect to the incident pump power, have been achieved. While an average M² of 1.4 was measured, the emitted power becomes temporally unstable when exceeding 95 W, owing to the occurrence of modal instabilities.
Phase control of optical bistability and multistability in tripod four-level atomic medium
Xionghui Hu, Hongjun Zhang, Sun Hui, Yaohua Lei, Wei Liu, and Huijing Li
Doc ID: 265288 Received 16 May 2016; Accepted 12 Jul 2016; Posted 13 Jul 2016 View: PDF
Abstract: Optical bistability and multistability behaviors are investigated in a tripod four-level atomic configuration including a unidirectional ring cavity. We find that optical bistability and multistability can be obtained by changing the relative phase of the driven fields and the intensity of the microwave filed. In addition, we can switch optical bistability to optical multistability by adjusting the relative phase of the driven fields or vice versa and the threshold can be controlled via changing the parameters of the scheme.
Large Range Manipulation of Exciton Species in Monolayer WS2
Tian Jiang, Ke We, Yu Liu, Hang Yang, and Xiang'ai Cheng
Doc ID: 267100 Received 26 May 2016; Accepted 12 Jul 2016; Posted 13 Jul 2016 View: PDF
Abstract: Unconventional emissions from exciton and trion in monolayer WS2 are studied by photoexcitation. Excited by 532nm laser beam, the carrier species in the monolayer WS2 is affected by the excess electrons escaping from photoionization of donor impurity, the concentration of which varies with the location of the sample. Simply increasing the excitation power at room temperature, the excess electron and thus the intensity ratio of excited trion and exciton can be continuously tuned over a large range from 0.1 to 7.7. Furthermore, this intensity ratio can also be manipulated by varying temperature. However, in this way the resonance energy of the exciton and trion show red-shifts with increasing temperature due to electron−phonon coupling. The binding energy of the trion is determined to be ~ meV and independent to temperature, indicating strong Coulomb interaction of carriers in such 2D materials.
Passive vibration compensation in scanning white-light interferometry
Stanislav Tereschenko, Peter Lehmann, Angelika Bruecker-Foit, and Lisa Zellmer
Doc ID: 267390 Received 31 May 2016; Accepted 11 Jul 2016; Posted 12 Jul 2016 View: PDF
Abstract: We present a passive vibration compensation approach in scanning white-light interferometry (SWLI). A pointwise distance measuring interferometer (DMI) obtains fast temporal distance changes during the white-light depth-scan of an areal measuring Michelson white-light interferometer for topography measurement. Both interferometers share a part of the optical path so that the measurement spot of the DMI is within the field of view of SWLI. With the real positions of the interferometer with respect to the measuring object during the depth scan known from DMI measurements we can compensate for the influence of unintentional distance changes caused by environmental vibrations or scanner nonlinearities. By reordering of the captured image frames and improved correlogram interpolation, we are able to reconstruct correct signals from completely distorted (and unusable) SWLI signals. Although the basic idea of the system already has been published, we improved the signal reconstruction technique, so that the specimen’s topography measurement can be obtained with the same accuracy as without any vibrations or scan distortions influece. In addition we demonstrate the feasibility of the approach by different practical measurements with and without vibrations.
Measurement of refractive index dispersion of a fused silica plate using Fabry-Perot interference
Myoungsik Cha, Choonghwan Lee, Heejoo Choi, and Jonghan Jin
Doc ID: 262857 Received 11 Apr 2016; Accepted 11 Jul 2016; Posted 12 Jul 2016 View: PDF
Abstract: We used Fabry-Perot interferometry to measure the refractive indices of a fused silica plate at four different wavelengths ranging from 544 nm to 1550 nm, giving a detailed analysis on the uncertainty of this experimental method. Because of a small expanded uncertainty of 2.7 × 10^−5 (k = 1.96) obtained using the experimental method, it was possible to make corrections to the existing Sellmeier formula [I. H. Malitson, J. Opt. Soc. Am., 55, 1205 (1965)] for our fused silica sample. The corrected Sellmeier formula resulted in a group index value larger than that evaluated using the Malitson's Sellmeier formula by 3 × 10^−4. We verified this by comparing it with the group index measured with spectral domain interferometry at 1530 nm.
Temperature dependence of Birefringence in ethanol-filled suspended core fibre
Jose Luis Vilas, Jose Sanchez-Martin, and Eusebio Bernabeu Martinez
Doc ID: 264511 Received 04 May 2016; Accepted 11 Jul 2016; Posted 12 Jul 2016 View: PDF
Abstract: The temperature dependence of the birefringence in a Suspended Core Fibre (SCFs) has beenexperimentally analyzed by using a polarimetric setup. The used configuration consists on two linearpolarizers and the SCF as birefringent medium. A theoretical study based on Jones matrices has been carriedout to analyze the experimental observed behavior. For this, it was used a polarimetric all-fibre configurationwhose sensitivity depends on the wavelength variation with temperature. Results obtained show that it isstrongly affected when the air-holes of SCF are partially-filled with ethanol.
Modified Iterative Vector Similarity Measure for Particle Size Analysis Based on Forward Light Scattering
Tian‘en Wang, Jianqi Shen, and Chengjun Lin
Doc ID: 264664 Received 05 May 2016; Accepted 11 Jul 2016; Posted 12 Jul 2016 View: PDF
Abstract: The vector similarity measure (VSM), originally applied to information retrieval, has been recently introduced to analyze particle size distribution (PSD) based on forward light scattering. The VSM technique can predict the PSD with low sensitivity to the experimental errors. However, the simulations and experiments of multimodal distributed particle system were not satisfying. In this paper, a modified inverse algorithm is presented to improve the VSM technique. Simulated results and experimental evidence show that, with this modification, the VSM technique can re-construct the PSD more efficiently.
Surface deformation and friction characteristic of nano scratch at ductile-removal regime for optical glass BK7
Chen Li, Feihu Zhang, Ye Ding, and Lifei Liu
Doc ID: 265472 Received 20 May 2016; Accepted 11 Jul 2016; Posted 12 Jul 2016 View: PDF
Abstract: Nano scratch for optical glass BK7 based on ductile-removal regime was carried out and the influence rule of scratch parameters on surface deformation and friction characteristic were analyzed. Experimental results showed that with increase of the normal force the deformation of burrs in the edge of the scratch was more obvious, and with increase of the scratch velocity the deformation of micro-fracture and burrs in the edge of the scratch was more obvious similarly. The residual depth of the scratch was measured by the atomic force microscope. The experimental results also showed that with the increase of the normal force, the residual depth of the scratch increased linearly while the elastic recovery rate decreased. Furthermore, with the increase of the scratch velocity, the residual depth of the scratch decreased while the elastic recovery rate increased. The scratch process of the Berkovich indenter was divided into the cutting process of many large negative rake faces based on the improving cutting model, and the friction characteristic of the Berkovich indenter and the workpiece was analyzed. The analysis showed that the coefficient of friction increased and then tended to be stable with the increase of normal force. Meanwhile, the coefficient of friction decreased with the increase of scratch velocity and the coefficients, kln(v) and μ0, were introduced to improve the original formula of friction coefficient.
Real-Time Two-Dimensional Beam Steering with Gate-Tunable Materials: A Theory Design Investigation
Jierong Cheng, Samad Jafar-Zanjani, and Hossein Mosallaei
Doc ID: 264690 Received 06 May 2016; Accepted 10 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: A leaky wave antenna is proposed that furnishes two-dimensional beam scanning in both elevation and azimuth planes via electrical control in real-time, and at a single frequency. The structure consists of a graphene sheet on a metal-backed substrate. The two-dimensional beam scanning performance is achieved through proper biasing configuration of graphene. Traditional pixel-by-pixel electrical control makes the biasing network a huge challenge for chip-scale designs in the terahertz regime and beyond. The method presented here enables dynamic control by applying two groups of one-dimensional biasing on the sides of the sheet. They are orthogonal and decoupled, with one group offering monotone impedance variation along one direction, and the other sinusoidal impedance modulation along the other direction. The conductivity profile of the graphene sheet for certain radiation angle, realized by applying proper voltage to each pad underneath the sheet, is determined by holographic technique, and can be reconfigured electronically and desirably. Such innovative biasing design makes the real-time control of the beam direction and beamwidth simple and highly integrated. The concept is not limited to graphene-based structures, and can be generalized to any available gate-tunable material system.
Scintillation analysis of multiple-input single-output underwater optical links
Muhsin Gökçe and Yahya Baykal
Doc ID: 267016 Received 25 May 2016; Accepted 10 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: Multiple-input single-output (MISO) techniques are employed in underwater wireless optical communication(UWOC) links to mitigate the degrading effects of oceanic turbulence. In this paper, we consider a MISO UWOC system which consists of a laser beam array as transmitter and a point detector as receiver. Our aim is to find the scintillation index at the detector in order to quantify the system performance. For this purpose, the average intensity and the average of the square of the intensity are derived in underwater turbulence by using the extendedHuygens - Fresnel principle. The scintillation index and the average bit-error-rate ( BER ) formulas presented inthis paper depend on the oceanic turbulence parameters such as the rate of dissipation of mean-squared temperature, rate of dissipation of kinetic energy per unit mass of fluid, Kolmogorov microscale, and the ratio of temperature to salinity contributions to the refractive index spectrum, the link length and the wavelength. Recently, we have derived an equivalent structure constant of atmospheric turbulence and expressed it in terms ofin this paper, this equivalent structure constant isutilized which enables us to employ the existing similar formulation valid in atmospheric turbulence.
All-fiber, narrow linewidth and linearly-polarized fiber laser in a single-mode-multimode-single-mode cavity
Xijia Gu, Man Jiang, Haiyang Xu, Pu Zhou, and Guomin Zhao
Doc ID: 267308 Received 30 May 2016; Accepted 10 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: We report the design of an all-fiber, linearly-polarized Yb-doped fiber laser at 1064 nm with a narrow linewidth and high output power required by the master oscillator of the amplifier for high power spectral beam combining. The laser has achieved linearly-polarized output with a polarization extinction ration of dB, a narrow linewidth of ≤ 52 pm and an output power of 32.7W. Such a performance was obtained by the cavity design that incorporated a wavelength shifted PM fiber Bragg grating pair and single-mode-multimode-single-mode structure
Defects evaluation system for spherical optical surfaces based on microscopic scattering dark-field imaging method
Yongying Yang, Yihui Zhang, Chen Li, Fan Wu, Huiting Chai, Kai Yan, Lin Zhou, Yang Li, Dong Liu, Jian Bai, and Yibing Shen
Doc ID: 264561 Received 04 May 2016; Accepted 09 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: In the field of the automatic optical inspection (AOI), it is imperative to measure the defects on the spherical optical surfaces. So a novel spherical surface defect evaluation system (SSDES) is established in this paper to evaluate defects on optical spheres. In order to ensure the microscopic scattering dark-field imaging of optical spheres with different surface shape and radius of curvature, the illumination with variable aperture angle is employed. Besides the scanning path of sub-apertures along the parallels and meridians is planned to detect the large optical spheres. Since analysis shows that the spherical defect information could be lost in the optical imaging, the three-dimensional correction based on pin-hole model is proposed to recover the actual spherical defects from the captured two-dimensional images. Given the difficulty of sub-apertures stitching and defects features extracting in the three-dimensional space after the correction, the 3D sub-apertures are transformed into a plane to be spliced through geometric projection. And then methods of the surface integral and the calibration are applied to quantitatively evaluate the spherical defects. Furthermore, the 3D panorama of defect distribution on the spherical optical components can be displayed through the inverse projective reconstruction. Finally, the evaluation results are compared with the OLYMPUS microscope, testifying the micron resolution and the detection error is less than 5%.
Field experiment and image reconstruction using aFourier Telescopy imaging system over a 600-m-longhorizontal path
Yu Shuhai, Lei Dong, Xinyue Liu, lin xudong, Haoran Meng, and Xing Zhong
Doc ID: 259940 Received 26 Feb 2016; Accepted 09 Jul 2016; Posted 22 Jul 2016 View: PDF
Abstract: To confirm the effect of uplink atmospheric turbulence on FourierTelescopy (FT), we designed a system for far-field imaging, utilizing aT-type laser transmitting configuration with commercially availablehardware, except for a green imaging laser. The horizontal lighttransmission distance for both uplink and downlink was ~300 m. Forboth the transmitting and received beams, the height upon the groundwas below 1 m. The imaging laser’s pointing accuracy was ~9.3 μrad. Anovel image reconstruction approach was proposed, yieldingsignificantly improved quality and Strehl ratio of reconstructed images.From the reconstruction result, we observed that the tip/tilt aberrationis tolerated by the FT system even for Changchun’s atmosphericcoherence length parameter (r0) below 3 cm. The resolution of thereconstructed images was ~0.615 μrad.
Annealing effects on microstructure and laser induced damage threshold of HfO₂/SiO₂ multilayer mirror
Shuvendu Jena, Raj Tokas, Divakar Kompalli, Sudhakar Thakur, and Naba Sahoo
Doc ID: 264069 Received 27 Apr 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: HfO₂/SiO₂ periodic multilayer high reflection mirrors have been prepared by reactive electron-beam evaporation technique. The deposited mirrors were annealed in the temperature range from 300ºC to 500ºC. The effects of annealing on optical, microstructural and laser induced damage characteristics of the mirrors have been investigated. The high reflection band of the mirror shifts towards shorter wavelength with increasing annealing temperature. As-deposited and annealed mirrors show polycrystalline structure with monoclinic phase of HfO₂. Crystalinity and grain size increase upon annealing. The roughness of the mirror increases with annealing up to 400ºC and decreases at 500ºC. The laser induced damage threshold (LIDT) has been assessed using 532 nm pulsed laser at a pulse width of 7 ns. The LIDT value of the multilayer mirror increases from 44.1 J/cm² to 77.6 J/cm² with annealing up to 400ºC. The improvement of LIDT with annealing is explained through oxygen vacancy as well as grain size dependent thermal conductivity. Finally the observed laser damage morphology such as circular scalds and ablated multilayer stacks with terrace structure are analyzed.
CW and QCW Thulium-doped all-fiber laser: implementation on kidney stone fragmentation
ATASI PAL, DEBASIS PAL, Aditi Ghosh, and Ranjan Sen
Doc ID: 264584 Received 04 May 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: A continuous-wave (CW) as well as quasi continuous wave (QCW) thulium-doped all-fiber laser at 1.94 µm has been designed targeting application in Urology. The thulium-doped active fiber with octagonal-shaped inner cladding is pumped at 793 nm to achieve a stable CW laser power of 10 W with 32% lasing efficiency (against launched pump power).The linear variation of laser power with pump offers scope of further power scaling. A QCW operation with variation of duty cycle from 0.5% to 90%; repetition rate from 0.1 Hz to 1 KHz and pulse width from 40 µs to 2s has been presented. Laser power of 9.5 W in CW mode of operation and average power of 5.2 W with energy range of 10.4 to 104 mJ in QCW mode of operation has been employed to fragment COM kidney stones (size of 1.5-4 cm) having different color and composition. Dependence of ablation threshold, ablation rate and average fragmented particle size on the average power and energy has been studied. 1 min of laser exposure results fragmentation of stone surface with ablation rate of 8 mg/min having minimum particle size of 6.54 µm with an average size of 20-100 µm ensuring the natural removal of fragmented parts through the urethra.
Study of Evaluating Beam Quality of double-cladding fiber laser in application
Qirong Xiao, Xuejiao Wang, Ping Yan, and Mali Gong
Doc ID: 264599 Received 04 May 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: We put forward a new βFL factor which is used exclusively in fiber laser to assess beam quality and choose LP01 mode as the new suitable ideal beam. We present a new simple measurement method and verify the reasonability of βFL factor in experiment in 20/400 μm fiber laser. Furthermore, we use the new βFL factor to evaluate the beam quality of the 3 kW level fiber laser. It can be concluded that βFL is a key factor not only for assessing the performances of the high power fiber laser that we mainly concern, but also for the simple measurement.
50-kHz, 50-ns UV pulse generation by diode-pumped frequency doubling Pr3+:YLF Q-switch laser with a Cr4+:YAG saturable absorber
Fumihiko Kannari, Hiroki Tanaka, Ryosuke Kariyama, and Kodai Iijima
Doc ID: 264644 Received 05 May 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: We demonstrate intracavity second harmonic generation at 320 nm of a diode-pumped praseodymium-doped YLF laser Q-switched by a Cr4+:YAG crystal. By employing two 3.5-W high power blue InGaN diode lasers as the pump source, we obtained 50-ns Q-switched pulses with a pulse energy of 1.54 μJ at a repetition rate of 50 kHz. A rate equation analysis shows good agreement with the experimental results.
Climatology of aerosol optical properties over four locations in the Indo-Gangetic plains
Humera Bibi, Khan Alam, Thomas Blaschke, Samina Bibi, and Muhammad Jawed Iqbal
Doc ID: 268103 Received 13 Jun 2016; Accepted 08 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: The emphasis of the present work lies on the examination of the distribution and spectral behavior of the optical properties of atmospheric aerosols in the Indo-Gangetic Plains (IGP). Measurements were performed using an AErosol RObotic NETwork (AERONET) Sun photometer at four sites (Karachi, Lahore, Jaipur and Kanpur) with different aerosol environments during the period 2007-2013. The Aerosol Optical Depth (AOD) and angstrom exponent (α) were measured, and the results revealed a high AOD with a low α value over Karachi and Jaipur in July, while a high AOD with a high α value was reported over Lahore and Kanpur during October and December. The pattern of the aerosol Volume Size Distribution (VSD) was similar across all four sites, with a prominent peak in coarse mode at a radius of 4.0-5.0 um, and in fine mode at a radius of 0.1-4.0 um, for all seasons. On the other hand, during the winter months, the fine-mode peaks were comparable to the coarse mode, which was not the case during the other seasons. The Single Scattering Albedo (SSA) was found to be strongly wavelength-dependent during all seasons and for all sites, with the exception of Kanpur, where the SSA decreases with increasing wavelength during winter and post-monsoon. It was found that the phase function of the atmospheric aerosol was high at a small angle and stable around a scattering angle of 90-180º at all sites and during all seasons. Spectral variation of the ASYmmetry parameter (ASY) revealed a decreasing trend with increasing wavelength, and this decreasing trend was more pronounced during summer, winter and post-monsoon as compared to pre-monsoon. Furthermore, extensive measurements suggest that both real (RRI) and imaginary (IRI) parts of the Refractive Index (RI) show contrasting spectral behavior during all seasons. Finally, the analysis of the NOAA HYSPLIT back trajectory revealed that the seasonal variation in aerosol types was influenced by contribution of air masses from multiple source locations.
Linearity enhancement of scale factor in optical interrogated micromechanical accelerometer
Li Shuang Feng, Yu Zhang, Xiao Wang, and yang wang
Doc ID: 265388 Received 16 May 2016; Accepted 07 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: A method to reduce the residual stress of support arms in optical interrogated micromechanical accelerometer is proposed in order to enhance the linearity of scale factor of accelerometer. Firstly, the behavior of residual stress in support arms is analyzed in detail, and the simulation of shape curvature caused by residual stress in aluminum-made support arms is completed using finite element analysis (FEA). Then, by comparing two different materials of support arms (aluminum-made and silicon-made support arms), a modified fabrication is introduced in order to reduce the unexpected residual stress in support arms. Finally, based on contrast experiments, the linearity of scale factor of accelerometers with aluminum-made and silicon-made support arms are measured using force feedback test system, respectively. Results show that the linearity of scale factor of accelerometer with silicon-made support arms is 0.85%, which is reduced about an order of magnitude than that of accelerometer with aluminum-made support arms with the linearity of scale factor of 7.48%, linearity enhancement of scale factor is validated in optical interrogated micromechanical accelerometer. This allows accuracy improvement of accelerometer in the application of inertial navigation and positioning.
Performance of low-cost few-mode FBG sensor systems: polarization sensitivity and linearity of temperature and strain response
Denis Ganziy, Bjarke Rose, and Ole Bang
Doc ID: 264060 Received 26 Apr 2016; Accepted 07 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: We evaluate whether 850nm FBG sensor systems can use low-cost 1550 nm telecom fibers, in other words, how detrimental the influence of higher-order modes is to the polarization stability and the linearity of the strain and temperature response. We do this by comparing polarization sensitivity of a few-mode 850nm FBG sensor to a strictly single-mode 850nm FBG sensor system using 850 nm single-mode fibers. We also compare the performance of the FBGs in strain and temperature tests. Our results show that the polarization stability and the linearity of the response degrade due to the presence of the higher-order modes. We demonstrate that using simple coiling of the 1550 nm fiber one can regain the performance of the few-mode system and make it usable for high precision measurements.
A Comparison of Three Dimensional Particle Tracking and Sizing using Plenoptic Imaging and Digital In-line Holography
Daniel Guildenbecher, Brian Thurow, and Elise Hall
Doc ID: 264468 Received 03 May 2016; Accepted 07 Jul 2016; Posted 14 Jul 2016 View: PDF
Abstract: Digital in-line holography and plenoptic photography are two techniques for single-shot, volumetric measurement of 3D particle fields. Here we present a comparison of the two methods by applying plenoptic imaging to experimental configurations that have been previously investigated with digital in-line holography. These experiments include the tracking of secondary droplets from the impact of a water drop on a thin film of water and tracking of pellets from a shotgun. Both plenoptic imaging and digital in-line holography successfully quantify the 3D nature of these particle fields. This includes measurement of the 3D particle position, individual particle sizes, and three-component velocity vectors. For the initial processing methods presented here, both techniques give out-of-plane positional accuracy of approximately 1-2 particle diameters. For a fixed image sensor, digital holography achieves higher effective in-plane spatial resolutions. However, collimated and coherent illumination makes holography susceptible to image distortion through index of refraction gradients, as demonstrated in the shotgun experiments. On the other hand, plenoptic imaging allows for a simpler experimental configuration and, due to the use of diffuse, white-light illumination, plenoptic imaging is less susceptible to image distortion in the shotgun experiments.
Optical reflectance of pyrheliometer absorption cavities: progress towards SI-traceable measurements of solar irradiance
Heather Patrick, Thomas Germer, Clarence Zarobila, Catherine Cooksey, and Howard Yoon
Doc ID: 263998 Received 20 May 2016; Accepted 06 Jul 2016; Posted 20 Jul 2016 View: PDF
Abstract: We have accurately determined the absorptance of three pyrheliometer cavities at 532 nm by measuring the residual reflectance using an angle-resolved bidirectional reflectometer. Measurements were performed at normal incidence as a function of viewing angle and position on the cavity cone. By numerically integrating the measured angle resolved scatter (ARS) over both direction and position and accounting for an obstructed view of the cavity, we determined that the effective cavity reflectance was between 8 × 10-4 and 9 × 10-4. Thus, the absorptance of the three cavities ranged from 0.99909 (0.00014) to 0.99922 (0.00012) where the values in parentheses indicate the k = 2 expanded uncertainties. These measurements, when extended over the spectral range of operation of the pyrheliometer, are required to establish SI traceability for absolute solar irradiance measurements.
Development of an immersive virtual reality headmounteddisplay with high performance
Yunqi Wang, Weiqi Liu, xiangxiang Meng, Hanyi Fu, Daliang Zhang, kang si, Rui Feng, Wei Zhonglun, Xiuqing Zhu, and Jiang Guohua
Doc ID: 263921 Received 25 Apr 2016; Accepted 05 Jul 2016; Posted 27 Jul 2016 View: PDF
Abstract: To resolve the contradiction between large field of view and high resolution in immersive virtual reality (VR)head-mounted displays (HMDs), an HMD monocular optical system with a large field of view and high resolution wasdesigned. The system was fabricated by adopting aspheric technology with CNC grinding and a high-resolution LCD as theimage source. With this monocular optical system, an HMD binocular optical system with a wide-range continuouslyadjustable inter-pupillary distance was achieved in the form of partially overlapping fields of view (FOV) combined with ascrew adjustment mechanism. A fast image processor-centered LCD driver circuit and an image preprocessing system werealso built to address binocular vision inconsistency in the partially overlapping FOV binocular optical system. Thedistortions of the HMD optical system with a large field of view were measured. Meanwhile, the optical distortions in thedisplay and the trapezoidal distortions introduced during image processing were corrected by a calibration model forreverse rotations and translations. A High performance non-fully transparent VR HMD device with high-resolution(1920×1080) and large-FOV (141.6° (H) ×73.08° (V)) was developed. The full field-of-view average value of angularresolution in pixels per degree is 18.6 pixels/degree. With the device, high-quality VR simulations can be completed undervarious scenarios, and the device can be utilized for simulated trainings in aeronautics, astronautics, and other fields withcorresponding platforms. The developed device has positive practical significance.
High Raman-to-fluorescence ratio of Rhodamine6G excited with 532nm laser wavelength Using a closely-packed, self-assembled monolayer of silver nanoparticles.
Seyed Hassan Tavassoli, Najmeh Sadegh, and Hossein Khadem
Doc ID: 260435 Received 10 Mar 2016; Accepted 03 Jul 2016; Posted 11 Jul 2016 View: PDF
Abstract: Highly efficient Raman to fluorescence ratio of Rhodamine6G obtained by means of 532nm laser wavelength which is in close proximity of the dye's absorption maximum. Closely-packed, gap-filled self-assembled monolayers of silver nanoparticles were produced to observe the Raman signals of rhodamine 6G. Two mechanisms contribute to detect the Raman signals of the fluorescent sample: Surface Enhanced Raman Scattering (SERS) and Nanomaterial Surface Energy Transfer (NSET). Self-assembled monolayers of silver nanoparticles with different coverage densities and also those filled with probe molecules were prepared through variation of substrate's immersion time in nanoparticle solution and drying the substrate, respectively. Examination of the effects of these two factors on the plasmonic response and SERS efficiency of substrate revealed that in a gap-filled dense coverage, near-field interactions dominate, which remarkably increase the Raman-to-fluorescence ratio (RFR). To have a perfect dense coverage, the efficient immersion time was obtained about 48 hours. Drying the substrates also caused further enhancement in RFR through filling inter-particle spaces with dye molecules and, accordingly, an increase in NSET efficiency.
Oversaturated part-based visual tracking via Spatio-temporal Context learning
liu wei, Jicheng Li, Zhiguang Shi, Xiaotian Chen, and Xiao Chen
Doc ID: 263446 Received 18 Apr 2016; Accepted 27 Jun 2016; Posted 29 Jun 2016 View: PDF
Abstract: Partial occlusion is one of the key challenging factors in a robust visual tracking method. To solve this issure, part-based trackers are widely explored, while most of which are computationally expensive and therefore infeasible for real-time applications. Context information around the target has been used in tracking, which is renewed by spatio-temporal context (STC) tracker recently, the Fast Fourier Transform adopted in STC equips it with high efficiency. However, the global context used in STC alleviates the performance when dealing with occlusion. In this paper, we propose an oversaturated part-based tracker based on spatio-temporal context learning (OPSTC), which tracks objects based on selected parts with spatio-temporal context learning respectively. Furthermore, a structural layout constraint and a novel model update strategy are utilized to enhance the tracker’s anti-occlusion ability and deal with other appearance changes effectively. Extensive experimental results demonstrate our tracker’s superior robustness against the original STC and other state-of-art methods.
Development of an optical microscopy system for automated bubble cloud analysis.
Daniel Wesley, Stuart Brittle, and Daniel Toolan
Doc ID: 260966 Received 11 Mar 2016; Accepted 22 Jun 2016; Posted 08 Jul 2016 View: PDF
Abstract: Recently, the number of uses of bubbles has begun to increase dramatically, with medicine, biofuel production and wastewater treatment just some of the industries taking advantage of bubble properties, such as high mass transfer. As a result, more and more focus is being placed on the understanding and control of bubble formation processes and there are currently numerous techniques utilised to facilitate this understanding. Acoustic bubble sizing (ABS) and laser scattering have long held the advantage over photographic methods due to the high levels of automation. This paper demonstrates how photographic methods can be improved upon utilising machine vision to yield high levels of automation, comparable to the other techniques outlined. We also discuss the added benefits of the photographic system and how it is possible to obtain considerable additional information above and beyond that which ABS and laser scattering can supply. This work could easily be exploited by both industrial scale operations and small scale laboratory studies, as the simplistic and cost effective approach is highly transferrable and intuitive to use.