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Accepted papers to appear in an upcoming issue

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Electrically tunable transmission type beam deflectorusing liquid crystal with high angular resolution

YOUNG KIM, KANGHEE WON, Yunhee Kim, Jungkwuen An, Hoon Song, Sunil Kim, Chil-Sung Choi, and Hong-Seok Lee

Doc ID: 318931 Received 05 Jan 2018; Accepted 23 May 2018; Posted 23 May 2018  View: PDF

Abstract: High efficient transmission type beam deflectors which have high angular resolution have been widely used forvarious applications. Especially, continuously tunable beam deflectors have been also needed for a lot of purposes.An indium-tin-oxide (ITO), widely used for transparent electrode, was placed on the upper and lower glasssubstrate. The ITO layer on the lower substrate was patterned by the contact mask aligner for relatively wide inputand output pad compare to main grating ITO patterns in active area. These input and output pads on the lowersubstrate are connected to each driving integrated circuit (IC) which has 360 channels for continuous control. Asmall pixel pitch of grating patterns of 6 μm, the electrode width is 3 μm with a 3 μm spacing, was developed andthe maximum diffraction angle is calculated and measured at 2.541O with a wavelength of 532 nm. A minimal cellgapof 2.5 μm was applied for the full 2 π phase modulation by using a high birefringence liquid crystal. Drivingmodule for continuous beam steering is also developed and applied to the beam deflector system. The diffractionefficiency of about 50.9% is observed at an angle of diffraction about 2.541O.

Continuously tunable true-time delay lines based onone-dimensional grating waveguide for beam steeringin phased array antennas

wang Gencheng, Tingge Dai, Jiang jianfei, Xiaoqing Guo, Bei Chen, Yuehai Wang, hui Yu, Xiaoqing Jiang, and Jianyi Yang

Doc ID: 320743 Received 26 Jan 2018; Accepted 23 May 2018; Posted 23 May 2018  View: PDF

Abstract: In this paper, we propose integrated one-dimensional (1D) grating waveguide based true-time delay (TTD) lines onsilicon-on-insulator (SOI) platform. Through optimizing the structure of the proposed waveguide, a time delay of77. ps/mm can be readily achieved in a wavelength tuning range from 1540.20 nm to 1558.97 nm. Compared toconventional photonic crystal waveguide based TTDs, the proposed waveguide occupies 70% less chip surface andhas much lower propagation loss when compared with 2D photonic crystal devices. Therefore, a larger time delaycan be achieved on-chip. To facilitate low loss coupling from strip waveguides to 1D grating waveguides and viceversa, a novel step taper is designed and shows a coupling efficiency of over 78%. Based on the 1D gratingwaveguide, a 1×4 beam steering module is designed and simulated. A wide beam steering angle from -67.84° to67.84° for the X-band 4 element phased array antenna (PAA) with an array pitch size of 1.25 cm is obtained.

Grating-assisted-cylindrical-resonant-cavities interlayer coupler

Congshan Wan, Thomas Gaylord, and Muhannad Bakir

Doc ID: 325562 Received 09 Mar 2018; Accepted 22 May 2018; Posted 23 May 2018  View: PDF

Abstract: A grating-assisted-cylindrical-resonant-cavities (GARC) interlayer coupler made of Si/SiO2 is designed and simulated to achieve efficient vertical interlayer coupling. This coupler consists of two cylindrical waveguide cavities connected by a high-index cylindrical via which functions as an interconnecting cavity. The interlayer coupling efficiency of this Si/SiO2 GARC coupler is simulated to be 71% (-1.5 dB, approximate single layer efficiency 84% or -0.76 dB) for TE polarization at 1.55 μm wavelength, which is generally higher than those of conventional rectangular SOI gratings with additional features such as reflectors, overlayers, chirped periods, dual-gratings, etc. The resonant strengths of the two cylindrical waveguide cavities are enhanced by circular Bessel-function-defined gratings and distributed Bragg reflectors. The waveguide cavities, in turn, are coupled to the high-index cylindrical via cavity. The GARC couplers are predicted to have favorable attributes compared with previous couplers including wider operational bandwidth (270 nm for 1 dB), larger tolerance to in-plane misalignment (±2 μm for 1 dB), easier fabrication (wider grating ridges and absence of adjacent-layer reflectors), smaller footprint (20 μm in diameter), and more flexible choices of interlayer distances (2 ~ 5 μm). A sensitivity analysis is also provided as a guide in fabrication. In general, it is found that the vertical dimensions of the GARC couplers need to be carefully controlled while the horizontal dimensions are less critical.

A 1.6:1 Bandwidth Two-Layer Antireflection Structure for Silicon Matched to the 190-310 GHz Atmospheric Window

Fabien Defrance, Cecile Jung-Kubiak, Jack Sayers, Jake Connors, Clare deYoung, Matthew Hollister, Hiroshige Yoshida, Goutam Chattopadhyay, Sunil Golwala, and Simon Radford

Doc ID: 326119 Received 16 Mar 2018; Accepted 22 May 2018; Posted 22 May 2018  View: PDF

Abstract: Although high-resistivity, low-loss silicon is an excellent material for THz transmission optics, its high refractive index necessitates antireflection treatment. We fabricated a wide-bandwidth, two-layer antireflection treatment by cutting subwavelength structures into the silicon surface using multi-depth deep reactive ion etching (DRIE). A wafer with this treatment on both sides has <-20 dB (<1%) reflectance over 190-310 GHz. We also demonstrated that bonding wafers introduces no reflection features above the -20 dB level, reproducing previous work. Together these developments immediately enable construction of wide-bandwidth silicon vacuum windows and represent two important steps toward gradient-index silicon optics with integral broadband antireflection treatment.

Active depth estimation from defocus using a camera array

Tianyang Tao, Qian Chen, Shijie Feng, Yan Hu, and Chao Zuo

Doc ID: 326220 Received 15 Mar 2018; Accepted 22 May 2018; Posted 22 May 2018  View: PDF

Abstract: This paper introduces an active depth estimation method from defocus using a camera array. High-frequency phase-shifted sinusoidal fringe patterns are projected onto the surface of the object, making low-texture areas of the object surface easily distinguishable. Based on the light-field measurement captured by a 5 × 5 camera array, synthetic aperture refocusing of the fringe images can be realized after the camera array is properly calibrated and rectified. The fringe modulations at different depth are calculated based on the computationally refocused images, which are used as depth cues to reconstruct the 3D shape of the measured object. Finally, the depth resolution of the 3D reconstruction is refined by combining the regular relationship between the fringe modulation and defocus cues. Compared with conventional methods, the pixel-wise fringe modulation analysis provides more accurate depth cues with higher spatial resolution and data density, while bypassing any complicated local analysis algorithms such as Laplacian operator or windowed Fourier transform (WFT). Because each spatial pixel from the measured data is processed independently from its neighbors, our approach is absent from error propagation problem existed in the global-optimization-based approaches. Some experiments are implemented to verify the effectiveness of the proposed method.

Holographic characterization of diffraction gratings modulation in photopolymers

Haoyu Li, Yue Qi, Changliang Guo, Ra'ed Malallah, and John Sheridan

Doc ID: 327402 Received 03 Apr 2018; Accepted 22 May 2018; Posted 23 May 2018  View: PDF

Abstract: It is known that in general the recorded holographic grating refractive index profiles are notidentical to the sinusoidal exposing pattern in photopolymer materials. During exposure highharmonics of the fundamental refractive index period are generated within the layer volume. Aset of equations to calculate the amplitudes of the higher harmonics of refractive index inducedin the grating are introduced. Then an algorithm involving the use of the 3-D nonlocal photopolymerizationdriven diffusion (NPDD) model is presented and applied to calculate theresulting grating diffraction efficiencies. The experimental observation results that the gratingdiffraction efficiency cannot reach the theoretical maximum value (ηmax = 100%) and that in thecase of over-modulation the minimum value (ηmin = 0%) is also never achieved, are explained(theoretically). The predictions of the simulations are also fit to measured experimental data foran Acrylamide/polyvinyl alcohol (AA/PVA) photopolymer material with good agreement beingachieved.

Numerical analysis of a multi-pass pumping Yb:YAGthick-disc laser with the minimizing heat generation

Wenguang Zhao, Guangzhi Zhu, Yongqian Chen, Biaoping Gu, Mu Wang, and Jing Dong

Doc ID: 326862 Received 26 Mar 2018; Accepted 21 May 2018; Posted 22 May 2018  View: PDF

Abstract: A theoretical model is established to describe the dynamic behavior and fractional thermal load of a multi-pass pumpingYb:YAG thick-disc laser, which is pumped at 1030nm and emits laser radiation at around 1048nm. The fractional thermalload, the temperature of the thick-disc crystal and the operational properties for different ambient temperatures anddifferent output coupler transmissions are investigated in details. The results show that the pump saturation effect andthe laser threshold are sensitive to the ambient temperature and the output coupler transmission, which affect thefractional thermal load and the laser extraction efficiency. Furthermore, a new design scheme is proposed to realize “ZeroThermal Load” (ZTL) throughout the output range by dynamically adjusting the output coupler transmission.


Isabel Pita, Mahendar Kumbham, Michael Schmidt, Matthew Gleeson, Kevin Ryan, Christophe Silien, and Ning Liu

Doc ID: 325491 Received 26 Mar 2018; Accepted 21 May 2018; Posted 21 May 2018  View: PDF

Abstract: The optimum geometry for waveguide propagation was determined by comparing bowtie and semicircle antennacuts to a standard plain waveguide with a 635 nm laser. The results of both experimental data and COMSOLsimulations proved that the bowtie antenna increased waveguide output in comparison to the plain waveguidewith the semicircle pattern showing no enhancement. It was also determined that the propagation was highestwhen the polarization direction of the laser was perpendicular to the direction of the waveguide for all patterns,while polarization along the propagation direction led to little or no output in all antenna and plain waveguidecases. The waveguide output of the bowtie antenna and plain structures was then measured using a tunable laserfor wavelengths from 570 nm to 958 nm under both parallel and perpendicular polarization conditions. Theresults indicated that the bowtie antenna performed better over the entire range with an average increase factor of2.12 ±0.40 over the plain waveguide pattern when perpendicularly polarized to the waveguide direction, and1.10±0.48 when parallel. The measured values indicate that the structure could have applications in broadbanddevices.

All-Optical wavelength conversion fortelecommunication mode-division multiplexingsignals in integrated silicon waveguides

Zijun Xu, Qiang Jin, Zhihua Tu, and Shiming Gao

Doc ID: 326722 Received 22 Mar 2018; Accepted 21 May 2018; Posted 21 May 2018  View: PDF

Abstract: An all-optical wavelength conversion method for telecommunication-band mode-division multiplexing (MDM)signals is proposed in integrated silicon waveguides by using the four-wave mixing (FWM) effect with a dual-modepump. By engineering the dispersion profile of the integrated silicon waveguide, the phase-matching conditionsare realized simultaneously for the TE01 mode and the TE11 mode of the MDM signal in telecommunication bandand they can be converted to the idler modes simultaneously. In a 1.2-cm-long waveguide, the 3-dB conversionbandwidth reaches 58 nm with a conversion efficiency of -22.3 dB pumped by a 100-mW TE01 and 105-mW TE11pump source.

Optical design of distributed zoom concentricmultiscale meteorological instrument

Yang Shen, hu wang, chenchen wang, Pan Yue, Yaoke Xue, zhe bai, and Xuewu Fan

Doc ID: 326976 Received 28 Mar 2018; Accepted 21 May 2018; Posted 21 May 2018  View: PDF

Abstract: Meteorological moderate resolution sensor requires large field of view (FOV) and low distortion imaging. Atpresent, fixed-focus camera combined with whiskbroom scanning mechanism or fixed-focus multi-cameracombined with pushbroom scanning mechanism is being used. Owing to fixed focal length of the camera, large FOVcauses the difference of imaging distance and ground imaging angle between the nadir point and the edge of FOV tobe significantly large, resulting in large different in the resolution between the nadir point and the edge of FOV. Thestudy proposes to adopt distributed zoom concentric multiscale system to realize large FOV, low distortion, andhigh imaging quality imaging, simultaneously, to coordinate with different compensation lenses to achievedifferent FOV corresponding to different focal lengths, the resolution drop between the nadir point and the edge ofFOV is reduced. To ensure same illumination of the entire FOV, the entire system possesses the same F #, differentfields of view exhibit different entrance pupil diameter. The study analyzes principle of aberration compensationof concentric multiscale system when both FOV and entrance pupil diameter are changed, and completes threegroups optical design of different focal lengths with uniform F #. The results indicate that the system hasadvantages of low distortion, and high imaging quality in the entire FOV. Moreover, the resolution drop in theentire FOV is reduced to approximately 50% of the traditional design scheme. To verify the implementability of thesystem, a set of prototype manufacturing and imaging experiments are conducted to prove that the system hassatisfactory implementability and the imaging quality is also satisfactory.

Non-pupil adaptive optics for visual simulation of acustomised contact lens

Mark Coughlan and Alexander Goncharov

Doc ID: 327479 Received 03 Apr 2018; Accepted 21 May 2018; Posted 21 May 2018  View: PDF

Abstract: We present a method for determining the deformable mirror profile to simulate the optical effect of acustomised contact lens in the central visual field. Using non-pupil conjugated adaptive optics allows awider field simulation compared to traditional pupil conjugated adaptive optics. For a given contact lens,the mirror shape can be derived analytically using Fermat’s principle of the stationary optical path, ornumerically using optimisation in ray-tracing programs. An example of an aspheric contact lens simulationis given to illustrate the method and the effect of eye misalignment with respect to the deformablemirror position is investigated. The optimal deformable mirror conjugation position is found to be nearthe posterior corneal surface. Chromatic aberration analysis is also presented and our findings indicatethe polychromatic simulation quality is similar to that of the monochromatic case, even though the mirroris a reflective component. The limitations of a single continuous surface deformable mirror to mimic acontact lens are outlined with some recommendations for improving the quality of simulation.

Cylinder-type Fiber-optic Vernier Probe Based onCascaded Fabry-Perot Interferometers with ControlledFSR Ratio

Lingxin Kong, Yanxi Zhang, Weigang Zhang, Yun-Shan Zhang, Lin Yu, Tieyi Yan, and Pengcheng Geng

Doc ID: 327539 Received 03 Apr 2018; Accepted 20 May 2018; Posted 21 May 2018  View: PDF

Abstract: We designed a cylinder-type fiber-optic Vernier probe based on cascaded Fabry-Perot interferometers (FPIs) inthis paper. It is fabricated by inserting a short single mode fiber (SMF) column into a large aperture hollow corefiber (LA-HCF) with the internal diameter of 150 μm, which structures a length adjusted air microcavity with thelead-in SMF inserted into the LA-HCF form the other end. The length of the SMF column is 537.9 μm. By adjustingthe distance between the SMF column and the lead-in SMF, the spectral change is displayed intuitively, and theVernier spectra are recorded and analyzed. In sensitivity analysis, the probe is encapsulated in the medical needleby UV glue as a small body thermometer when the length of the air microcavity is 715.5 μm. The experiment showsthat the sensitivity of the Vernier envelope is 12.55 times higher than that of the high frequency comb. This designcan effectively reduce the preparation difficulty of the optical fiber Vernier sensor based on cascaded FPIs, and canexpand the applied fields by using different fibers and materials.

Effect of noise-induced wavelength fluctuation intunable diode lasers on narrow-linewidth absorptionmeasurements

Yedhu Krishna, Sean O'Byrne, KANNAN MUNUSWAMY, and Gopalan Jagadeesh

Doc ID: 325647 Received 08 Mar 2018; Accepted 20 May 2018; Posted 21 May 2018  View: PDF

Abstract: Tunable diode laser absorption spectroscopy is being widely used to make sensors for diagnostic purpose invarious engineering applications. Since the wavelength of many diode lasers used in such sensors is sensitive to thedriving current, even noise as small as a few μArms in the driving current can cause a wavelength fluctuation of~ ± 0.5 pm which is large enough to interfere with sensitive absorption measurements. Although these fluctuationsare small, they can cause significant systematic error in measured absorption spectra in applications where theabsorption line probed is narrow, as is the case for low-density hypersonic flows. As an example, at a pressure of300 Pa and 297 K, the error in the full width at half maximum was ± 6.5 % in an absorption spectrum obtainedusing a system based on a vertical-cavity surface-emitting laser scanned at 10 kHz. This paper analyses the effect ofsuch systematic errors on measured temperature and velocity, and suggests some remedial measures.

Precise and robust binocular camera calibration basedon multiple constraints

Xia Liu, Zhenyu Liu, Guifang Duan, Jin cheng, xuetao jiang, and jianrong tan

Doc ID: 325640 Received 12 Mar 2018; Accepted 20 May 2018; Posted 23 May 2018  View: PDF

Abstract: Precise calibration of binocular vision system is the foundation of binocular vision measurement. In this paper, wepropose a high precise and robust binocular camera calibration method, which is devoted to minimize the errorbetween the geometric relation of 3D reconstructed feature points and the ground truth, such as adjacent distanceerror, collinear error and right-angle error. In addition, the reprojection error and epipolar are introduced tosatisfy the homography relation and epipolar geometry theory better. We optimize all intrinsic parameters,extrinsic parameters and distortion parameters to minimize the objective function which is the sum of a series ofnonlinear least squares terms. Levenberg-Marquardt iterative algorithm is used to find the optimal solution of thecamera parameters. To test the precision and robustness of the proposed method, both actual measurementexperiment and Gauss noise adding experiment are carried out. The experimental results show that comparedwith the other two calibration methods in the contrast experiment, the distance measurement error, collinearerror and right-angle error are reduced dramatically. It is noticeable that in Gauss noise adding experiments, thecalibration parameters estimated by the proposed method are more stable.

Large-area flexible infrared nanowire grid polarizer fabricated using nanoimprint lithography

Wei-dong Kang, Jinkui Chu, Xiang-wei Zeng, and fan yuanyi

Doc ID: 315269 Received 13 Dec 2017; Accepted 18 May 2018; Posted 18 May 2018  View: PDF

Abstract: We fabricated 4-inch large-area flexible infrared nanowire grid polarizer using nanoimprint and metal thermal evaporation process. To protect the Simaster template as well as to prolong the service life of it, we first fabricated nickel template as an alternative by electroforming process. Then thenanowire grid structure was transferred from this template to IPS substrate by thermal nanoimprint process. Finally, metal Al was deposited on the IPSnanowire structure by vertical thermal evaporation technology. The results of the infrared optical test reveal that the TM transmittance of the polarizeris greater than 60% in the 4-5.71 μm and 5.73-6.7 μm wavelength range, especially is greater than 70% in the wavelength range of 4.70-5.69 μm and5.75-6.59 μm, and the extinction ratio is more than 20 dB in the wavelength range of 3.6-6.7 μm, proving that the polarizer has good polarizationcharacteristics. The flexible infrared nanowire grid polarizer has potential applications in the fields of curved surface monitoring equipment and polarizedimaging equipment.

High Power Narrow Linewidth Discrete Mode Laser Diode Integrated with a Curved Semiconductor Optical Amplifier Emitting at 2051nm

Richard Phelan, Michael Gleeson, Diarmuid Byrne, John O'Carroll, Marta Nawrocka, Kevin Carney, Rob Lennox, Lina Maigyte, Phil Long, Chris Herbert, Jim Somers, and Brian Kelly

Doc ID: 327313 Received 29 Mar 2018; Accepted 18 May 2018; Posted 18 May 2018  View: PDF

Abstract: We report on a 2.051 μm InxGaAs/InP based Discrete Mode laser diode monolithically integrated with a curved tapered semiconductor optical amplifier for CO2 sensing applications. At a heat-sink temperature of 0°C, the laser emits a record InP value of more than 35mW continuous-wave output power in a single longitudinal mode.

Phase randomization for spatio-temporal averaging of unwanted interference effects arising from coherence

Fergal Shevlin

Doc ID: 327493 Received 03 Apr 2018; Accepted 18 May 2018; Posted 18 May 2018  View: PDF

Abstract: An approach to the reduction of unwanted interference effects, such as speckle and inhomogeneity, is to generate sequences of uncorrelated effects over the integration period of the sensor such that they are averaged. A moving diffuser is typically used. Dyoptyka's deformable mirror technology is presented as an alternative. Through phase randomization it achieves dynamic divergence of illumination without diffraction losses. It is shown to offer a unique combination of advantages over moving diffusers, including optical efficiency, speed, size, and reliability. Various applications are discussed.

Dynamics of two identical mutually delay-coupled semiconductor lasers in photonic integrated circuits

Masoud Seifikar, Andreas Amann, and Frank Peters

Doc ID: 327496 Received 03 Apr 2018; Accepted 18 May 2018; Posted 18 May 2018  View: PDF

Abstract: We theoretically investigate a system of two mutually delay-coupled semiconductor lasers, in a face to face configuration for integration in a Photonic Integrated Circuit. This system is described by single mode rate equations, which are a system of delay differential equations with one fixed delay. Several bifurcation scenarios involving multistabilities are presented, followed by a comprehensive frequency analysis of the symmetric and symmetry-broken, one-colour and two-colour states.

Reusable thin-film all-polymer couplers for vertical light-coupling to single-mode waveguides

pei li, Alex Dorn, Maher Rezem, Kirsten Honnef, and Hans Zappe

Doc ID: 325710 Received 08 Mar 2018; Accepted 17 May 2018; Posted 18 May 2018  View: PDF

Abstract: A reusable all-polymer coupler using gratings and tapers for vertical light coupling to single-mode planar waveguides is demonstrated. Numerical simulations were performed to optimize the tapers and gratings to increase the coupling efficiency. A hot-embossing replication technique is used for the fabrication of waveguide sensors and gratings, which is adaptable to mass production such as roll-to-roll processes. The external grating is reversibly bonded to the waveguide via van der Waals forces and the thus realized reusability reduces the fabrication costs. The utility of the structure was shown by using these grating couplers for testing of asymmetric Mach–Zehnder interferometers.

Laser Beam Imaging via Multiple Mode Operations of the Extreme Dynamic Range CAOS camera

Nabeel Riza and Mohsin Ali Mazhar

Doc ID: 325996 Received 14 Mar 2018; Accepted 17 May 2018; Posted 18 May 2018  View: PDF

Abstract: For the first time, demonstrated is laser beam imaging via multiple mode operations of the Digital Micro-mirror Device-based Coded Access Optical Sensor (CAOS) camera. Specifically, outlined are novel modes of software programmable CAOS imaging that includes the Time Division Multiple Access (TDMA) mode, the Code Division Multiple Access (CDMA) mode, the CDMA-TDMA mode, the Frequency Division Multiple Access (FDMA)-TDMA mode, the Frequency Modulation (FM)-CDMA-TDMA mode, FM-TDMA mode, and the FDMA-CDMA-TDMA mode. Engagement of FDMA and CDMA modes enables simultaneous multi-pixel improved signal-to-noise ratio photo-detection while use of TDMA prevents optical point detector saturation. The use of the FDMA and FM-modes creates high Digital Signal Processing (DSP) gain via temporal spectrum analysis to produce extreme dynamic range pixel-specific imaging. Using an un-attenuated 633 nm He-Ne laser near-Gaussian focusing beam, experimentally acquired are 13. 68 m spatial resolution laser beam map CAOS images with dynamic ranges of 44.78 dB, 45.28 dB, 83.90 dB, and 94.9 dB for the TDMA, CDMA, FM-CDMA-TDMA, and FM-TDMA modes, respectively. The FM-TDMA mode with its extreme dynamic ranging CAOS pixel mapping capability experimentally measures the non-Gaussian spatially oscillatory irradiance behavior predicted by Huygens-Fresnel diffraction theory. The demonstrated CAOS camera through software control allows high flexibility robust imaging of laser beams across different wavelength bands with widely varying beam irradiance levels and spatial signatures, thus empowering optical system designers to match overall system requirements that are highly dependent on accurate and reliable laser beam metrology.

Simulation of penetration depth of Bessel beams formultifocal optical coherence tomographycoherence tomography

Luying Yi, Liqun Sun, and Xianshun Ming

Doc ID: 325530 Received 08 Mar 2018; Accepted 17 May 2018; Posted 17 May 2018  View: PDF

Abstract: Multifocal Bessel Beam optical coherence tomography (MBOCT) combines the advantages of Bessel beam OCT andmultifocal OCT to increase imaging depth. For MBOCT, the penetration depth of the Bessel beam in highlyscatteringbiological tissue limits the final imaging depth. In this paper, we theoretically analyze the penetrationdepth of the Bessel beams with different parameters to explore which kind of Bessel beam is more suitable forMBOCT in scattering medium. The finite difference-time domain (FDTD) method is used to simulate the fielddistribution of Bessel beams in the medium. We find that the MBOCT for more focus based on Bessel beam with smallerFresnel number N has a higher penetration depth and light intensity when its lateral resolution is fixed. Moreover, the Besselbeam with N reversely closer to unity is more advantageous for penetrating the highly scattering medium for a certainimaging depth, and the Bessel beam has larger penetration depth when its lateral size is close to the size of object to be imaged.

Compressed sensing hyperspectral imaging in the 0.9-2.5 μm short-wave infrared wavelength range using digital micro-mirror device and InGaAs linear array detector

Masud Arnob, HUNG NGUYEN, Zhu Han, and Wei-chuan Shih

Doc ID: 326328 Received 21 Mar 2018; Accepted 17 May 2018; Posted 17 May 2018  View: PDF

Abstract: A hyperspectral imaging system based on compressed sensing has been developed to image in the 0.9-2.5 μm short-wave infrared (SWIR) wavelengths. With a programmable digital micromirror device (DMD) utilized as spatial light modulator, we have successfully performed spectrally-resolved image reconstruction with a 256-element InGaAs linear array detector without traditional raster-scanning or push-broom mechanism by compressed sensing (CS) single-pixel camera approach. The chemical sensitivity of the imaging sensor to near-infrared (NIR) overtone signatures of hydrocarbons was demonstrated using hydrocarbon and ink patterns on glass, showing spectral selectivity for the chemical components. Compared to point-by-point raster-scanning, we show that the CS scheme can effectively accelerate image acquisition with lower but reasonable quality. © 2018 Optical Society of America

Photoacoustic Imaging of Lamina CribrosaMicrocapillaries in Porcine Eyes

Thanadet Chuangsuwanich, Mohesh Moothanchery, Alvan Tsz Chung Yan, Leopold Schmetterer, Michael Girard, and Manojit Pramanik

Doc ID: 327787 Received 05 Apr 2018; Accepted 17 May 2018; Posted 17 May 2018  View: PDF

Abstract: Due to the embedded nature of the lamina cribrosa (LC) microcapillary network, conventional imaging techniqueshave failed to obtain high resolution images needed to assess the perfusion state of the LC. In this study, bothoptical resolution (OR) and acoustic resolution (AR) photoacoustic microscopy (PAM) techniques were used toobtain static and dynamic information about LC perfusion in ex-vivo porcine eyes. The OR-PAM system couldresolve a perfused LC microcapillary network with a lateral resolution of 4.2 μm, and also provided good depthinformation (33 μm axial resolution) to visualize through-thickness vascular variations. The AR-PAM system wascapable of detecting time-dependent perfusion variations. This study represents the first step towards using anemerging imaging modality (PAM) to study the LC’s perfusion, which could be a basis for further investigation ofthe hemodynamic aspects of glaucomatous optic neuropathy.

Ray Refraction in Uniaxial Crystals by Fermat’sPrinciple

Pengqian Wang

Doc ID: 325652 Received 08 Mar 2018; Accepted 16 May 2018; Posted 17 May 2018  View: PDF

Abstract: Fermat’s principle is used to study the refraction of extraordinary rays into and out of uniaxial crystalswith arbitrary optic axis orientations. The method produces direct formulas for the direction cosines ofthe refracted rays without the need of calculating intermediate quantities. The formulas are validated bycomparing them with previous ray-tracing methods.

Analytical model for active racetrack resonators withintra-cavity reflections and its application in Fanoresonance tailoring

Leonidas Dogkas, Thomas Kamalakis, and Dimitris Alexandropoulos

Doc ID: 327018 Received 27 Mar 2018; Accepted 16 May 2018; Posted 16 May 2018  View: PDF

Abstract: We present an analytical model for estimating the spectral properties of an active racetrack resonator/waveguide system. Under reasonable approximations, we show that the transfer function canbe approximated by a rational function, the coefficients of which are determined by the parameters ofthe structure. The model takes into account intra-cavity reflections which can provide additional degreesof freedom in the design. We identify conditions under which asymmetric transitions around a spectralpeak can occur which are characteristic of Fano-type resonances. The accuracy of our model is verified byrigorous transfer matrix numerical simulations. We also discuss how the model can be applied for tailoringthe transfer function in order to obtain sharper transitions from the spectral peaks to the minima inorder for the structure to be used for sensing applications.

Size effect of WSe2 on red passively Q-switched fiberlaser output performance

Duanduan Wu, Zhenrong Guo, Jian Peng, Jian Weng, Zhiping Cai, and Huiying Xu

Doc ID: 327271 Received 29 Mar 2018; Accepted 16 May 2018; Posted 16 May 2018  View: PDF

Abstract: Transition metal dichalcogenides (TMDs) possess direct bandgap in the visible frequency range and can be appliedas attractive visible saturable absorbers (SAs). In this paper, a new TMDs tungsten selenide (WSe2)-based red Qswitcheris fabricated and successfully used for Q-switched pulse generation in red Pr3+-doped ZBLAN fiber laser.The passive Q-switching fiber laser at 635.2 nm generates stable pulse with pulse duration of 504 ns, and averageoutput power of 4.91 mW, as well as tunable pulse repetition rate of 131.9-260.4 kHz. Furthermore, the size effectof WSe2 on the 635 nm passive Q-switching output performance is also investigated. Our work will provide acertain significance for the optimization of passive Q-switching red fiber lasers based on TMDs.

Label-free multimodal CARS analysis ofmicroparticles in unconstrained microfluidics.

Kevin O'Dwyer, Rabah Mouras, Aladin Mani, Daragh Rice, Matthew Gleeson, Ning Liu, Syed Tofail, and Christophe Silien

Doc ID: 327281 Received 29 Mar 2018; Accepted 15 May 2018; Posted 16 May 2018  View: PDF

Abstract: Fast, label-free optical identification and quantification of biomolecules and of other relevant biologicalmaterials in microfluidic devices and in the vascular system will play a major role in liquid biopsy and relateddiagnosis. An optical microscope probing simultaneously non-linear coherent anti-Stokes Raman scattering(CARS) and linear scattering (LS) was used to probe microparticles in aqueous solutions flowed unconstrainedin microfluidic channels. Despite the optical complexity of these systems, where out-of-focus microparticlesrandomly impede CARS and LS, and where water CARS generates a substantial background, we demonstratethat in-focus microparticles can be individually and unambiguously detected when CARS and LS are coanalysed.The ability to chemically discriminate microscale features in optically realistic flows supports therelevance of multimodal CARS platforms for liquid biopsy.

Ultra high-speed indirect X-ray imaging system withversatile spatio-temporal sampling capabilities

Emilio Escauriza, Margie Olbinado, Michael Rutherford, David Chapman, Alexander Rack, Daniel Eakins, and john jonsson

Doc ID: 327133 Received 29 Mar 2018; Accepted 15 May 2018; Posted 17 May 2018  View: PDF

Abstract: A new generation of cameras has made ultra highspeedX-ray imaging at synchrotron light sources a reality,revealing never-before-seen details of sub-surfacetransient phenomena. We introduce a versatile indirectimaging system capable of capturing — for thefirst time — hundreds of sequential X-ray pulses in 16-bunch mode at the European Synchrotron Radiation Facility,recording at 5.68 Mfps over dozens of microseconds,with an effective exposure of 100 ps. The versatilemultiplex camera construction of the system allowsfor various arrangements, including different scintillatorconfigurations, and simultaneous imaging with differentresolutions and regions of interest. Image resultsfrom a gas gun impact experiment, in which an additivemanufactured aluminium lattice was dynamically compressed,is presented as a demonstration of the system’scapabilities.

Color digital hologram compression based onmatching pursuit

Anas EL Rhammad, Patrick Gioia, Antonin Gilles, Marco Cagnazzo, and Beatrice Pesquet-Popescu

Doc ID: 321153 Received 02 Feb 2018; Accepted 15 May 2018; Posted 15 May 2018  View: PDF

Abstract: With the recent widespread interest for head-mounted displays applied to virtual or augmented reality,holography has been considered as an appealing technique for a revolutionary and natural 3D visualizationsystem. However, due to the tremendous amount of data required by holograms and to the verydifferent properties of holographic data compared to common imagery, compression of digital hologramsis a highly challenging topic for researchers. In this study, we introduce a novel approach for color hologramcompression based on matching pursuit and using an overcomplete Gabor’s dictionary. A detailedframework, together with a GPU-implementation, from hologram decomposition to bitstream generationis studied and the results are discussed and compared to existing hologram compression algorithms.

Spectral reflectance estimation from one RGB imageusing self-interreflections in a concave object

Rada DEEB, Damien Muselet, Mathieu Hébert, and Alain Tremeau

Doc ID: 325166 Received 05 Mar 2018; Accepted 15 May 2018; Posted 15 May 2018  View: PDF

Abstract: Light interreflections occurring in a concave object generate a color gradient which is characteristic of theobject’s spectral reflectance. In this paper, we use this property in order to estimate the spectral reflectanceof matte, uniformly colored, V-shaped surfaces from a single RGB image taken under directional lighting.First, simulations show that using one image of the concave object is equivalent to, and can even outperform,the state of the art approaches based on three images taken under three lightings with differentcolors. Experiments on real images of folded papers were performed under unmeasured direct sunlight.The results show that our interreflection-based approach outperforms existing approaches even when thelatter are improved by a calibration step. The mathematical solution for the interreflection equation andthe effect of surface parameters on the performance of the method are also discussed in this paper.

Differential interference contrast microscopy for cellsusing hard X-ray holography

Kiyofumi Matsuda, Juan Carlos Aguilar Lopez, Shakil Rehman, Masaki Misawa, Yoshio Suzuki, Akihisa Takeuchi, Masato Yasumoto, Kenichi Hibino, Maitreyee Roy, Ryohei Hanayama, and Katsuhiro Ishii

Doc ID: 325627 Received 07 Mar 2018; Accepted 15 May 2018; Posted 16 May 2018  View: PDF

Abstract: We propose a differential interference contrast method for cells using hard X-ray Gabor holography and knife-edgefiltering in the spatial frequency domain, without relying on beam shearing. A phase object is holographicallyrecorded and reconstructed by computer. Interference between the wavefronts of zeroth order weighted by 􀢋􀢐􀣊/􀫛in the positive frequency region produces a dark image. Similarly, interference between the wavefronts of thezeroth order weighted by 􀢋􀢐􀫜􀣊/􀫛 in the negative frequency region produces a bright image. By adding these twointensity distributions, good quality phase-contrast images of 8-μm-diameter polystyrene beads and human HeLacells were obtained.

Advancing Raman microspectroscopy for cellular and subcellular analysis: Towards in vitro high content spectralomic analysis

Hugh Byrne, Franck Bonnier, Alan Casey, Marcus Maher, Jennifer McIntyre, Esen Efeoglu, and zeineb farhane

Doc ID: 325846 Received 12 Mar 2018; Accepted 15 May 2018; Posted 16 May 2018  View: PDF

Abstract: In the confocal mode, Raman microspectroscopy can profile the biochemical content of biological cells at a subcellular level, and any changes to it by exogenous agents, such as therapeutic drugs or toxicants. As an exploration of the potential of the technique as a high content, label free analysis technique, this work monitors the spectroscopic signatures associated with the uptake and response pathways of commercial chemotherapeutic agents and polymeric nanoparticles by human lung cells. It is demonstrated that the signatures are reproducible and characteristic of the cellular event, and can be used, for example, to identify the mode of action of the agent as well as the subsequent cell death pathway, and even mechanisms of cellular resistance. Data mining approaches are discussed and a spectralomics approach is proposed.

Fast and wide-range optical beam steering with ultralowside lobes applying optimized multi-circularoptical phased array

Fangzheng Zhang, Daocheng Zhang, and Shilong Pan

Doc ID: 326115 Received 14 Mar 2018; Accepted 15 May 2018; Posted 16 May 2018  View: PDF

Abstract: A multi-circular optical phased array (OPA) is proposed and investigated through simulation to realize fast andwide-range optical beam steering with ultra-low side lobes. The proposed multi-circular OPA has a circularsymmetrical distribution, and its radical element spacings are optimized by a modified genetic algorithm toachieve the best side lobe suppression. Specifically, the peak side-lobe level (PSLL) of the far field pattern in 0°beam direction reaches as low as 0.0715 for a 73-element optimized multi-circular OPA, which is much better thana multi-circular OPA with uniform radical element spacing (the PSLL is 0.3686). The prominent feature of theproposed OPA is that, once the OPA is optimized towards a specific elevation direction by the modified geneticalgorithm, a wide-angle optical beam steering with nearly the same side lobe suppression can be achieved withoutupdating the OPA distribution, which makes it possible for fast optical beam steering over a wide scanning range.In the simulation, ultra-low side lobe beam steering with an elevation angle from 0° to 30° and an azimuth anglefrom 0° to 360° is achieved with the PSLL variation less than 0.001. The relationship between the optimized PSLLand the elevation angle used for OPA optimization is also investigated, which is helpful in achieving the best sidelobesuppression for different scanning ranges. The proposed OPA is expected to find applications such as laserradar, high-resolution display and free space optical communications.

Birefringence measurements of diamond space-variantsubwavelength gratings

Pierre Piron, Ernesto Vargas Catalan, Olivier Absil, and Mikael Karlsson

Doc ID: 326440 Received 23 Mar 2018; Accepted 15 May 2018; Posted 16 May 2018  View: PDF

Abstract: Subwavelength gratings are gratings with a period smaller than the incident wavelength, they possessform birefringence which depends on the grating parameters. This paper presents the results of an experimentalmethod designed to measure the birefringent properties of diamond subwavelength gratings inthe mid-infrared. The method consists in monitoring the intensity transmitted through one polarizer, asubwavelength grating and a second polarizer for various orientations of the first polarizer. By fitting theintensity variation as a function of the first polarizer orientation, one can compute the phase shift inducedby the grating, its local fast axis orientation and the ratio of the transverse electric on the transverse magnetictransmission efficiencies. The paper describes the method principle and its mathematical model.Then, several numerical simulations of different subwavelength gratings are presented and their resultsare discussed. Finally, the optical setup is described and the measurements of one subwavelength gratingare exposed and compared to the values expected from the manufacturing process.

Reference-plane-based fast pixel-by-pixel absolutephase retrieval for height measurement

Yidan Xing and Chenggen Quan

Doc ID: 324669 Received 27 Feb 2018; Accepted 14 May 2018; Posted 15 May 2018  View: PDF

Abstract: Absolute phase retrieval is essential for height measurement in digital fringe projection. However, projections ofadditional structured patterns that are normally required for phase unwrapping increase the measurementcomplexity. In this paper, we propose two reference-plane-based pixel-by-pixel absolute phase retrievaltechniques with as few projections as possible, suitable for different object depth ranges. The wrapped phase onobject is absolutely unwrapped by just referring to the absolute phase map on the reference plane. Singlefrequencyabsolute phase retrieval with one-reference-plane-based calibration is first proposed for objects withina height limit that equals to a calibrated system constant. To extend the measurement depth range, dual-frequencyabsolute phase retrieval with two parallel reference planes is further proposed. The additional low frequency isused to choose the unwrapping reference from the two reference plane phases for unwrapping the high-frequencyphase. Moreover, the proposed techniques are capable of high-frequency absolute phase unwrapping for objectswith step-height surface discontinuities. Experiments have been conducted to demonstrate the efficiency of theproposed two techniques respectively.

A Forward Fiber Fourier Transform SpectrometerModeling and Design with PZT Phase ModulationReal-time Compensation

Qinrui Cheng, Fajie Duan, Tingting Huang, and Jindong Wang

Doc ID: 325956 Received 12 Mar 2018; Accepted 14 May 2018; Posted 15 May 2018  View: PDF

Abstract: Piezoelectric ceramic transducer (PZT) is often applied in all-fiber Fourier transform spectrometer (FFTS) to realize phasemodulation. Combined with PZT and optical fiber features, a theoretical FFTS modeling is established. We systematicallydeduced the main causes of spectral errors and the factors of the instrumental resolution, then designed a new FFTS systemand provided real-time compensation methods for spectral errors. We creatively employed two Mach-Zenhderinterferometers by winding the sensing arms of the two on the same PZT cylinder, to realize the dual optical path experiencethe same and simultaneous phase modulation. Processing circuit is designed to achieve selective sampling of the testinterferogram, avoiding the spectral artifacts generated by the PZT phase discontinuities. The narrow line width of thereference spectrum is obtained at the same time for real-time calibration of spectral shift resulted from dispersion andother phase errors. By the comparison of the original interferogram and spectrum with those after compensation, theexperiments validated that the system design could effectively compensate for the spectral errors caused by PZT and opticalfiber physical limitations. Finally, the improved ideas are discussed if the FFTS prototype is to be applied to test gas real-timespectrum.

Modeling variation coefficient of wave-inducedunderwater irradiance for clear ocean and itsapplication to find the optimal detector size

Zao Xu and Dick Yue

Doc ID: 326831 Received 26 Mar 2018; Accepted 14 May 2018; Posted 14 May 2018  View: PDF

Abstract: In measuring the coefficient of variation (CV) of underwater wave-induced sunlight irradiance, the spatialintegration of irradiance signals due to the finite aperture size of irradiance detector usually causes anunderestimation of the measured variance. Since this spatial integration effect is strongly coupled withocean wave features, inherent optical properties (IOPs) of water, and atmospheric radiance conditions, directdeconvolution techniques from measured irradiance signals can lead to serious signal-to-noise degradationin a noisy upper ocean. On the other hand, choosing very small detector to guarantee CV accuracyis expensive. We address the intrinsic dependence of the CV on the detector size and choice of optimaldetector size for measuring irradiance variability in a turbid ocean environment. We present a new theoreticalmodel to directly obtain the form of the CV of the wave-induced scalar irradiance as the functionof the detector size, ocean surface wave parameters, and IOPs of ocean water. The model is derived underthe small-angle scattering approximation and the first-order assumption of the Snell’s law and Fresneltransmission coefficient. We demonstrate the validity and efficacy of the model for weakly-roughenedGaussian ocean surface conditions, by comparison to Monte Carlo radiative transfer simulations. Themodel shows that CV of wave-induced irradiance reaches an asymptotic with decreasing the detector size,and thereby providing an optimal or maximum detector size for given IOP and environmental conditions.

Multi-wavelength unidirectional forward scattering inthe visible range in all-dielectric silicon hollownanodisk

Jingwei Lv, Haiwei Mu, Qiang Liu, Xiaoming Zhang, Xianli Li, Chao Liu, Shasha Jiang, Tao Sun, and Paul K Chu

Doc ID: 327594 Received 03 Apr 2018; Accepted 13 May 2018; Posted 14 May 2018  View: PDF

Abstract: A dielectric nanoantenna with a relatively large refractive index possesses magnetodielectric properties that canoffer the unique opportunity to tailor unidirectional scattering. Herein we demonstrate that the interference fromelectric and magnetic multipoles in the silicon hollow nanodisk suppresses backscattering and enhances forward scatteringof light. This concept is implemented to design a lossless dielectric collector element which constitutes an enablingtechnology for applications which require backward scattering suppression such as nanoantennas andphotovoltaic devices.

Elemental Composition Analysis of Granite Rocksusing LIBS and LA-TOF-MS

Zeshan Umar, Nasar Ahmed, Rizwan Ahmed, Usman Liaqat, and Muhammad Baig

Doc ID: 325635 Received 09 Mar 2018; Accepted 13 May 2018; Posted 14 May 2018  View: PDF

Abstract: Qualitative and quantitative analysis of the raw granite rocks acquired from deposits in the Hunza district, Gilgitarea of Pakistan were studied using laser induced breakdown spectroscopy (LIBS) and laser ablation time of flightmass spectrometry (LA-TOF-MS). The optical emission spectra of the granite rocks, used in artificial jewelry and forflooring tiles, show the emission lines of (Si, Ca, K, Fe, Mg, Al, Na and Li) and (Si, Ca, K, Fe, Mg, Al, Ti, Na, Ba and Li)respectively. The mass spectra of these granite rocks were also studied with the LA-TOF-MS revealing analogouselemental compositions. The results obtained using LIBS and LA-TOF-MS for the raw granite samples display theirability as a powerful and complementary tools for the compositional analysis of the geological samples.

870fs, 448kHz pulses from an all-PM Yb-doped fiberlaser with a nonlinear amplifying loop mirror

Shangming Ou, Guanyu Liu, Liang Guo, Zhigang Zhang, and Qingmao Zhang

Doc ID: 325947 Received 12 Mar 2018; Accepted 13 May 2018; Posted 14 May 2018  View: PDF

Abstract: We demonstrate a mode-locked long all-polarization-maintaining fiber laser with a nonlinear amplifying loopmirror. The fiber oscillator directly delivers 221 ps chiped pulses at the repetition rate of 448 kHz. The pulses can be furtheramplified up to 134 nJ and compressed down to 870 fs by a grating pair. This kind of the laser is self-starting andlong-term stable, and it has potential application in high power fiber amplification for industrial application.

Two-dimensional shape retrieval from interferometricout-of-focus image of no-spherical particle - Part I:Theory

Huanhuan Shen, Lingyuan Wu, Yanglong Li, and Weiping Wang

Doc ID: 326586 Received 22 Mar 2018; Accepted 13 May 2018; Posted 14 May 2018  View: PDF

Abstract: Shape is one of the important characteristics of no spherical particle. Herein the two-dimensional shapesof several micrometer/millimeter sized particles with a variety of geometrical forms are retrieved fromsimulated interferometric out-of-focus images using the Hybrid Input-Output(HIO) algorithm. The particleconcerned can be either a single one, or a complex with separate parts. The impact of the axial size ofthe three-dimensional particle on the two-dimensional shape (i.e. the projection of the particle on the imagesensor) retrieval is analyzed, exhibiting that an increase of the axial size increases the deviation of lowfrequencies in the interferometric out-of-focus image, and eventually degrades the quality of the reconstructedshape. This study demonstrates the capability of the interferometric out-of-focus imaging technique,besides its size characterization, on the shape information retrieval of the micrometer/millimetersized no-spherical particle.

Optimization of a multi-blaze grating in reflectionusing free form profile

Bernard Sabushimike, HORUGAVYE Georges, and Serge Habraken

Doc ID: 323390 Received 15 Feb 2018; Accepted 13 May 2018; Posted 14 May 2018  View: PDF

Abstract: Diffraction gratings are very important in hyperspectral imaging. Their desired diffraction efficiency is dictated bythe sensitivity of the detector in the spectral band of interest and the luminance of the scene to be observed. If thedesired diffraction efficiency curve is established in this spectral band of interest, the remaining work is to design adiffraction grating that meets this demand. This paper is concerned with blazed gratings in reflection and thegeometry of the grating will therefore depend on this reference curve, the spectral band and the optimizationorder. The simplest form is a grating with a uniform profile that is optimized at a single blaze wavelength. It's amono-blaze grating. When such grating cannot meet the requirements in terms of diffraction efficiency a multiblazegrating optimized at several blaze wavelengths is required. The objective of this manuscript is to propose amethod of optimization of this multi-blaze grating i.e. how to find the number of blaze wavelengths necessary aswell as their value to answer the requirements in term of diffraction efficiency.

Temperature Field Investigation of Hydrogen/Air andSyngas/Air Axisymmetric Laminar Flames Using Mach-Zehnder Interferometry

Sadrollah Karaminejad, Mohammad Hossein Askari, and mehdi ashjaee

Doc ID: 324652 Received 27 Feb 2018; Accepted 13 May 2018; Posted 14 May 2018  View: PDF

Abstract: In this study, the optical method of Mach-Zehnder Interferometry (MZI) is utilized in order to explore the flame structure and temperature fieldof syngas/air and hydrogen/air flames. Two axisymmetric burners with inner diameters of 4 mm and 6 mm are used for temperature fieldmeasurement of hydrogen and syngas respectively. The effects of fuel composition, equivalence ratio and Reynolds number (Re) areinvestigated at ambient condition (P=0.87 bar, T=300K). Three different H2/CO fuel compositions with a hydrogen fraction of 30%, 50% and100% are studied. Temperature profiles are reported at four different sections above the burner tip. Measured temperatures usinginterferometry method are compared with thermocouple data and good agreement between them is observed. The results obtained in thisinvestigation indicated that the MZI can be applied for accurate determination of flame front and temperature field, especially for hightemperature flames where other methods can’t be properly utilized. Analyses of data reduction method revealed that, the exact determinationof the refractive index distribution and reference temperature is critical for accurate determination of temperature field. The results indicatedthat by increasing the Re, the maximum flame temperature enhances. Increasing the equivalence ratio, leads to expansion of the flame radialdistribution (at the same distance from the burner tip). At higher distances from burner tip, temperature increases uniformly from flameboundary toward flame axis, while at lower heights it shows reduction at the burner axis. By increasing CO content of fuel, the maximumflame temperature increases at all equivalence ratios except at stoichiometric condition, where SH100 illustrates the highest maximum flametemperature.

A Method for Defect Contour Extraction inTerahertz Non-destructive Testing Conductedwith a Raster-scan THz Imaging System

Cheng You, Cheng-Chang-Feng Lu, Tianyi Wang, Shun-Rong Qian, Zhenggang Yang, Kejia Wang, Jinsong Liu, and Shenglie Wang

Doc ID: 310054 Received 26 Oct 2017; Accepted 11 May 2018; Posted 11 May 2018  View: PDF

Abstract: In this article, a neoteric algorithm based on 2 dimensional (2D) continuous wavelettransform (CWT) is developed to get the defect contour in terahertz (THz) non-destructivetesting (NDT) result gained from a raster-scan frequency modulated continuous wave(FMCW) THz imaging system. In order to prove the method's validity, an experiment iscarried out. Result of the experiment shows that, the method allow one to extract defectcontour from the THz FMCW interference with severe stripe noises. Moreover, the relativeerror of defect area between the actual value and that gained from the extracted defectcontour is no more than 3.03%. That means, the method provided an effectively and exactlyway to extract defect contour in THz FMCW interference.

Impulse Response Modeling for Underwater OpticalWireless Channels

Yiming Li, Mark Leeson, and Xiaofeng Li

Doc ID: 325461 Received 06 Mar 2018; Accepted 11 May 2018; Posted 11 May 2018  View: PDF

Abstract: In underwater optical wireless communication (UOWC) channels, impulse response is widely used to describethe temporal dispersion of the received signals. In this paper, we propose a new function to modelthe impulse response in most realistic cases in UOWC channels. By exploiting the inherent propertiesof such channels, our newly proposed model is superior to the conventional weighted double Gammafunctions (WDGF) model in explaining the behavior of the channel. We use Monte-Carlo simulation toverify that our newly proposed model has a better accuracy of numerical fitting in most cases. Therefore,this new modeling approach offers a more convenient way to evaluate the performance of different kindsof UOWC channels.

Concept for Maritime Near-Surface Surveillance UsingWater Raman Scattering

Isaac Shokair, Mark Johnson, Randal Schmitt, and Shane Sickafoose

Doc ID: 326081 Received 14 Mar 2018; Accepted 11 May 2018; Posted 11 May 2018  View: PDF

Abstract: We discuss a maritime surveillance and detection concept based on Raman scattering of water molecules. Using arange-gated scanning lidar that detects Raman scattered photons from water, the absence or change of signalindicates the presence of a non-water object. With sufficient spatial resolution, a two dimensional outline of theobject can be generated by the scanning lidar. Because Raman scattering is an inelastic process, with a relativelylarge wavelength shift for water, this concept avoids the often problematic elastic scattering for objects at or veryclose to the water surface or from the bottom surface for shallow waters. The maximum detection depth for thisconcept is limited by the attenuation of the excitation and return Raman light in water. If excitation in the UV isused, fluorescence can be used for discrimination between organic and non-organic objects. In this paper wepresent a lidar model for this concept and discuss results of proof-of-concept measurements. Using published crosssection values, the model and measurements are in reasonable agreement and show that a sufficient number ofRaman photons can be generated for modest lidar parameters to make this concept useful for near-surfacedetection.

CO2 Laser Written Long-Period Fiber Grating with HighDiffractive Order Cladding Mode near Turning Point

Zuyao Liu, Yunqi Liu, Chengbo Mou, Fang Zou, and Tingyun Wang

Doc ID: 327369 Received 30 Mar 2018; Accepted 11 May 2018; Posted 11 May 2018  View: PDF

Abstract: We demonstrate the fabrication of long-period fiber grating (LPFG) in Boron-doped single-mode fiber (SMF) withhigh diffractive order cladding mode (HDCM) near turning point (TP). The simulations show that the LPFG withduty cycle less than 0.2 can couple light to HDCM. The LPFG with period more than 400 μm can achieve a strongmode coupling between fundamental mode and HDCM near TP. The effect of external refractive index (RI) on thetransmission spectrum of the LPFG with different grating period is investigated by simulations and experiments.With an increasing grating period, the spectral dip corresponding to HDCM travels faster than conventional dip andoverlapped dips appear in the transmission spectrum. High sensitivities up to 13497.7 nm/RIU and 0.77 nm/℃ of RIand temperature sensing can be achieved. Such LPFGs could be used potentially as optical filters and highsensitivity sensors.

Optical nonlinearities in LiKB₄O₇-Ag₂O and LiKB₄O₇-Ag₂O-Gd₂O₃ glasses containing Ag nanoparticles

Volodymyr Adamiv, Yaroslav Burak, Roman Gamernyk, Serhiy Malynych, Iryna Moroz, and Ihor Teslyuk

Doc ID: 314067 Received 06 Dec 2017; Accepted 11 May 2018; Posted 14 May 2018  View: PDF

Abstract: The results on optical studies of LiKB₄O₇–Ag₂O and LiKB₄O₇–Ag₂O–Gd₂O₃ glasses containing Ag nanoparticles formed during annealing in vacuum and air are presented. Strong bands that appear in optical transmission spectra of the samples correspond to plasmon excitations associated with Ag nanoparticles. The average radius of Ag nanoparticles was retrieved from FWHM of the plasmon bands and found to be 1.8…3.8 nm. Nonlinear-optical properties of the glasses were studied by single-beam Z-scan technique. In particular, influence of Ag nanoparticles on nonlinear refraction n₂ and nonlinear absorption β coefficients was investigated

Optical Modeling of Superconducting Nanowire SinglePhoton Detectors Using the Transfer Matrix Method

Kristen Sunter and Karl Berggren

Doc ID: 322653 Received 12 Feb 2018; Accepted 11 May 2018; Posted 14 May 2018  View: PDF

Abstract: We present optical modeling of SNSPD devices using an analytical approach based on the transfer matrixmethod. We find that the optimal dielectric layer thicknesses vary slightly with the thickness and fillfactor of the NbN layer and explore novel device geometries that can be described as a stack of thin films,such as devices on multilayered substrates, free-standing membranes, and optical fiber facets. In addition,the analytical results here show the importance of accounting for coherence correctly when an integratedcavity is included in the device structure and the relative insignificance of an anti-reflection coating inmost cases.

Calibration method for division of focal plane polarimeters

fei huang, Ming Li, wei cong chen, rui zhang, and chao shuai chen

Doc ID: 326122 Received 14 Mar 2018; Accepted 10 May 2018; Posted 10 May 2018  View: PDF

Abstract: The division of focal plane polarimeters is fabricated out of nanowire polarization filters attached to the surface of a focal plane (FPA). Due the limitations of the manufacturing process, the transmissivity of each nanowire polarization filter is different, resulting in a combination of inhomogeneities in transmittance and detector response. This yields the problem of polarization imaging uniformity more complicated than traditional intensity imaging. This study presented a brand new nonuniformity correction method for solving the correction inaccuracies in the traditional method. The method corrected the polarization filter transmittance with detector bias based on a new method for calculating the degree of linear polarization (DoLP). This paper included the theoretical derivation, experimental testing, and numerical simulation. In this simulation environment, the DoLP value was accurately calculated.

Precision fringe period metrology using LSQ sine fitalgorithm

xiansong Xiang, Minkang Li, Chunlong Wei, and Changhe Zhou

Doc ID: 325066 Received 27 Feb 2018; Accepted 10 May 2018; Posted 14 May 2018  View: PDF

Abstract: High precision grating fabrication is a precondition of the grating-based displacement measurement techniques.Likewise, the high precision fringe period value is an essential parameter in the grating fabrication process,especially in Scanning Beam Interference Lithography. In this paper, a procedure for measuring the fringe periodof interference beams are introduced. The procedure includes signal acquisition and signal processing. Theprecision of both the configuration for acquisition and the algorithm for processing are discussed. Experiments forfringe period measurement are also conducted, and the result average value of 564.374 nm with 1.5 picometerstandard deviation is obtained, reaching 2.6 ppm repeatability. The precision period value lays a solid foundationfor the high precision grating fabrication.

Theoretical large positive and negative lateral beamshift of the metal cladding waveguide in the midinfraredregion

Xiaofei Wang, qiaobo ye, Yingjie Zhou, Yan Li, hui Yu, Jianyi Yang, and Xiaoqing Jiang

Doc ID: 326262 Received 16 Mar 2018; Accepted 09 May 2018; Posted 09 May 2018  View: PDF

Abstract: A large negative and positive lateral beam shift is presented in the mid-infrared region based on the penetrationenhancement effect of the ultra-high order modes in the metal-cladding waveguide. The characteristics of lateralbeam shift have been discussed in theory, and the performance of the ultra-high order modes is confirmed in anexperiment at 5.4 um. The negative and positive lateral shift depends on the derivative of the imaginary part of thepropagation constant.

A Tunable 360° Microwave Photonic Multichannel Phase Shifter with Frequency Quadrupling

Weilei Wang, Aijun Wen, Zhaoyang Tu, Dong Liang, Mei Chen, Xiaoyan Li, and jinbo xiao

Doc ID: 322925 Received 16 Feb 2018; Accepted 09 May 2018; Posted 10 May 2018  View: PDF

Abstract: In this paper, a photonic scheme to generate a frequency-quadrupled microwave signal with full-range 360° tunable phase shift is proposed and experimentally demonstrated. Pure ±2nd-order sidebands with carrier suppressed are generated by the dual-parallel Mach-Zehnder modulator (DPMZM). The two sidebands are separated by a Fiber Bragg Grating (FBG) with the polarization state of one sideband rotated by 90 degrees via a Faraday rotating mirror (FRM) and then recombined to obtain a pair of orthogonally-polarized wavelengths. The two orthogonally polarized optical sidebands are aligned into the same polarization direction by using a polarizer (Pol). Finally, an RF signal with frequency-quadrupling is obtained by beating the ±2nd-order sidebands at a photodetector (PD). Moreover, the phase of the frequency-quadruped RF signal can be independently and arbitrarily adjusted from 0° to 360°through controlling the polarization direction. Experiments are carried out to demonstrate this scheme, frequency-quadrupled microwave signals at 12 GHz and 16 GHz are generated. A continuous phase shift from 0° to 360°of the frequency-quadrupled signal at 12GHz is also proved. The proposed scheme not only has the merits of large operation bandwidth and simple structure, but also can be extended to the multi-channel applications.

Second-order interferometric autocorrelation formeasuring group velocity dispersion and pulsebroadening of femtosecond pulses

Mojtaba Narimousa, Mohammad Sabaeian, Seyed Mehdi Mousavi, and omid panahi

Doc ID: 321053 Received 30 Jan 2018; Accepted 09 May 2018; Posted 15 May 2018  View: PDF

Abstract: Femtosecond pulse broadening and group velocity dispersion (GVD) were measured using a second-order interferometric autocorrelationtechnique. Two reference laser pulses of 36 and 55 fs were generated first in an Ti:Sapphire oscillator and then passed through the opticalelements of Ti:sapphire crystal and BK7 and fused silica glasses. For rectangular Ti:sapphire crystal and BK7 and fused silica slabs, materialdispersion and for fused silica prisms, material as well as angular dispersions were systematically measured. The experimental results werethen compared with theoretical models showing excellent agreement. The result of this work shows that one can rely very well on theoreticalexpressions to calculate the GVD of materials mentioned in this work and femtosecond pulse broadening.

Simultaneous measurement of phase transmission and birefringence of an object under test

Sergej Rothau, Klaus Mantel, and Norbert Lindlein

Doc ID: 326635 Received 21 Mar 2018; Accepted 09 May 2018; Posted 10 May 2018  View: PDF

Abstract: This publication presents a novel interferometric method for the simultaneous spatially resolved analysis of an object under test regarding the phase transmission function and the magnitude and orientation of the (uniaxial) birefringence. The measurement strategy is based on variations of the phase and polarization and processing the interference patterns so obtained. With this method, that is very similar to the classical phase shifting interferometry, a complete analysis of birefringent properties of the object and its impact on the phase of the incoming light can be done in one measurement cycle. The theoretical description of the investigated methods and their experimental implementation are presented.

Freeform imaging spectrometer design using a pointby-point design method

Tong Yang, Dewen Cheng, and Yongtian Wang

Doc ID: 326832 Received 26 Mar 2018; Accepted 09 May 2018; Posted 10 May 2018  View: PDF

Abstract: In this paper, we present a novel design method of freeform imaging spectrometers. All the freeform surfacesincluding the grating surface are generated point-by-point. The rays coming from multiple wavelengths, multiplefields and different pupil coordinates are all used, and the refractive/reflective as well as the diffraction of gratingare considered simultaneously in the design process. In addition, this method can be easily used in the design ofspecial nonsymmetric configurations. The system designed by this method can be taken as a good starting point forfurther optimization. To demonstrate the feasibility of the proposed method, we successfully designed a compactfreeform reflective imaging spectrometer working under the visible and near infrared (VNIR) band. Highperformance and small distortion have been achieved.

Bessel beam generation using a segmenteddeformable mirror

Xiaoming Yu, Ankesh Todi, and Hongmei Tang

Doc ID: 320728 Received 26 Jan 2018; Accepted 08 May 2018; Posted 08 May 2018  View: PDF

Abstract: Bessel beams with tunable spot size are desirable for many applications such as laser material processing, opticaltrapping, and imaging. In this paper, we report experimental and simulation results of using a segmenteddeformable mirror to generate zero- and higher-order Bessel beams that have controllable transverse andlongitudinal shape. The tilt angle and piston position of the mirror segments are optimized to recreate the phasestructure of a reflective axicon. Zero-order Bessel beams are generated at various beam converging angles, andtheir core diameter, peak intensity and depth-of-focus are found to agree with the calculated results. By applying aphase ramp along the azimuthal direction, the first-order Bessel beam is generated with the characteristic annularshape. Because deformable mirrors have low absorption and dispersion, and operate at a fast frame rate, they are apromising candidate for spatial beam shaping of high-power ultrafast lasers that are used in material processingapplications.

Fabrication and Characterization of Modulation Masks for Multimodal Spatial Frequency Modulated Microscopy

Nathan Worts, Michael Young, Jeffrey Field, Randy Bartels, Jason Jones, and Jeffrey Squier

Doc ID: 324592 Received 22 Feb 2018; Accepted 08 May 2018; Posted 08 May 2018  View: PDF

Abstract: Spatial frequency modulated imaging (SPIFI) is a powerful imaging method that when used in conjunction with multiphoton contrast mechanisms has the potential to improve the spatial and temporal scales that can be explored within a single nonlinear optical microscope platform. Here we demonstrate for the first time, it is possible to fabricate inexpensive masks using femtosecond laser micromachining that can be readily deployed within the multiphoton microscope architecture to transform the system from a traditional point scanning system to SPIFI, and gain the inherent advantages that follow.

Two-step carrier-wave stitching method for aspheric and freeform surfaces measurement with a standard spherical interferometer

Qun Hao, Shaopu Wang, Yao Hu, Yifeng Tan, Tengfei Li, and Shanshan Wang

Doc ID: 325413 Received 05 Mar 2018; Accepted 08 May 2018; Posted 08 May 2018  View: PDF

Abstract: Measurement of aspheric and freeform surfaces remains challenging due to the various shapes of the surface under test (SUT), especially when the SUT has a large aperture and strong deviation from the spherical surface. This paper proposes a two-step carrier-wave stitching method to enlarge the measurement bandwidth of Digital Moiré interferometry. Then measurements of aspheric and freeform surfaces with a standard spherical interferometer without phase shifting mechanism are demonstrated. Experimental results with a root-mean-square repeatability of better than 1/200 λ present good consistency to UA3P contact measurement results. Further simulation results with different residual wavefronts confirm measurement accuracies of peak-to-valley (PV) value of 10-3λ. The method is effective for large residual wavefront and thus is potential for flexible measurement of aspheric and freeform surfaces.

Propagation properties of hypergeometric-Gaussiantype-II beams through the quadratic-index medium

Bin Tang and Lirong Bian

Doc ID: 327651 Received 04 Apr 2018; Accepted 08 May 2018; Posted 08 May 2018  View: PDF

Abstract: The analytical expressions of hypergeometric-Gaussian type-II (HyGG-II) beams propagating in thequadratic-index medium are deduced based on the ABCD optical transformation matrix method. Thepropagation properties of HyGG-II beams in the quadratic-index medium are numerically and theoreticallyanalyzed in detail. The intensity distribution and the second-order moment-based beam width varyperiodically when the HyGG-II beams pass through the quadratic-index medium. The interactions of twoHyGG-II beams are also discussed graphically.

Multi-channel optical fiber refractometer based on tree topology structure

pan Niu, junfa zhao, Cheng Zhang, and Hua Bai

Doc ID: 328370 Received 16 Apr 2018; Accepted 08 May 2018; Posted 08 May 2018  View: PDF

Abstract: A multi-channel optical fiber refractometer based on S fiber taper (SFT) cascaded with fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The compact SFT acts as an in-line Mach-Zehnder interferometer (MZI) to be used as a band-pass filter (BPF) to tailor the FBG reflection, whose transmission spectrum is sensitive to the surrounding refractive index (SRI). Thus the peak power of the FBG reflection is modulated by the SRI. The three-channel SRI monitor can be achieved by discriminating the different centre wavelength and peak power variation of the FBG reflections. Experimental results show that the RI sensitivities of the three-channel are 345.54 dB/RIU, 349.57 dB/RIU and 463.60 dB/RIU, respectively. Moreover, the temperature cross-sensitivity can be solved by interrogating the centre wavelength of the FBG reflection.

Composited holograms for the generation of cylindrical optical lattice and flower mode

Enliang Wang, Yonghao Liang, Hailiang Li, and Changqing Xie

Doc ID: 327713 Received 06 Apr 2018; Accepted 07 May 2018; Posted 08 May 2018  View: PDF

Abstract: We present composited holograms to realize the azimuthal interference of cylindrical optical lattice and flower mode of Fourier transform-truncated Bessel beams. Three types of binarization operations are evaluated for the composited holograms generated by two Fourier transform-truncated Bessel beams with independent topological charges l₁ and l₂ and the same radial index p=1. Both numerical solutions and experimental results demonstrate that four types of cylindrical optical lattice and flower mode, namely, conventional cylindrical optical lattice, interleaved cylindrical optical lattice, flower-core and polygon-core flower mode, can be produced by the Fourier transformation of the composited holograms with same radial index p=1 and topological combinations |(|l₁|-|l₂ |)|<2, |(|l₁ |-|l₂|)|=2, |(|l₁|-|l₂ |)|=3 and|(|l₁ |-|l₂|)|=4, respectively. Moreover, a modified hologram with a scalar factor is introduced for further tailoring these multi-ring azimuthal distribution profile. The evolutions of the intensity profiles for various values of scale factor are presented. Our results indicate that the modified hologram are capable of in-depth exploration of the desired intensity profile of cylindrical optical lattice and flower mode, providing a flexible platform for light potential probe and microscopy.

Compact multichannel infrared camera integrated in an operational detector dewar cooler assembly

Florence de la Barrière, Guillaume Druart, Nicolas Guerineau, Frederic Champagnat, Aurélien Plyer, Gilles Lasfargues, and Serge Magli

Doc ID: 327745 Received 05 Apr 2018; Accepted 07 May 2018; Posted 07 May 2018  View: PDF

Abstract: We present an ultra-compact infrared cryogenic camera integrated inside a standard SOFRADIR’s Detector Dewar Cooler Assembly (DDCA) and whose field of view is equal to 120°. The multichannel optical architecture produces four non-redundant images on a single SCORPIO detector with a pixel pitch of 15µm. This ultra-miniaturized optical system brings a very low additional optical and mechanical mass to be cooled in the DDCA: the cool-down time is comparable to the one of an equivalent DDCA without an imagery function. Limiting the number of channels is necessary to keep the highest number of resolved points in the final image. However, optical tolerances lead to irregular shifts between the channels. This paper discusses the limits of multichannel architectures. With an image processing algorithm, the four images produced by the camera are combined to process a single full-resolution image with an equivalent sampling pitch equal to 7.5µm. Experimental measurements on MTF and NETD show that this camera achieves good optical performances.

Adaptive Filter Design via Gradient ThresholdingAlgorithm for Compressive Spectral Imaging

Nelson Diaz, Hoover Rueda, and Henry Fuentes

Doc ID: 320542 Received 24 Jan 2018; Accepted 07 May 2018; Posted 08 May 2018  View: PDF

Abstract: Sensing a spectral image data cube has been traditionally a time-consuming task since it requires a scanningprocess. In contrast, compressive spectral imaging (CSI) has attracted widespread interest since itrequires fewer samples than scanning systems to acquire the data cube, thus improving the sensing speed.CSI captures linear projections of the scene, and then a reconstruction algorithm estimates the underlyingscene. One notable CSI architectures is the colored coded aperture snapshot spectral imager (C-CASSI)which employs pixelated filter arrays as the coding patterns, to spatially and spectrally encode the incominglight. Up to date works on C-CASSI have used non-adaptive colored coded apertures. Non-adaptivesampling ignores prior information about the signal to design the coding patterns. Therefore, this workproposes a method to adaptively design the colored coded aperture, such that, the quality of image reconstructionis improved. In more detail, this work introduces a gradient thresholding algorithm (GTA)which computes the consecutive colored coded aperture from a rapidly reconstructed low-resolution versionof the data cube. The successive adaptive patterns enable recovering a data cube in presence ofGaussian noise with higher image quality. Real reconstructions and simulations evidence an improvementin up to 3 dB in the quality of image reconstruction of the proposed method in comparison withstate of the art non-adaptive techniques.

Relaxation oscillation suppressed, narrow linewidth,high beam quality 1319nm long-pulsed duration laser

Xiafei Xu, Yanhua Lu, Lei Zhang, Huaijin Ren, and Xiaoming Chen

Doc ID: 325153 Received 28 Feb 2018; Accepted 07 May 2018; Posted 08 May 2018  View: PDF

Abstract: We firstly report a 1319nm long-pulsed duration laser with relaxation oscillation suppressed byplacing a LBO crystal into the laser cavity. Two more etalons were added into the laser cavity tofurther increase the difference of cavity loss between oscillating and nonoscillating mode. Withvery little reduction of average output laser power, the smooth temporal profile laser pulse wasobtained with a pulse duration of 150μs. The average output power was 5.45W and the beamquality Mx2 and My2 were 1.12 and 1.20.

Preparation and quantitative characterization of Polydimethylsiloxane optical phantomswith Zinc-Phthalocyanine dye absorbers

Adamo Monte, Arnaldo Reis, Luismar Junior, and Andrea Antunes

Doc ID: 326388 Received 19 Mar 2018; Accepted 07 May 2018; Posted 08 May 2018  View: PDF

Abstract: We described a method for the preparation of polydimethylsiloxane (PDMS) phantoms tomimic the optical properties of biologic tissues at distinct wavelengths ranging from thevisible to the near-infrared spectra. The present method for fabricating solid optical tissuephantoms using Zinc-Phthalocyanine chromophores has demonstrated high photostabilitywith optical absorption coefficients up to 1.0 mm−1, making this phantom proper withabsorption bands ranging from 600 to 850 nm. It also happens that the chromophoreabsorption coefficient is linear as a function of its concentration inside the previous opticalwindow. The optical scattering properties were quantitatively selected by adding TiO2particle concentrations to the PDMS phantom. Thus, the quantitative optical properties ofabsorption and scattering for a large batch fabrication were demonstrated, making the Zinc-Phthalocyanine phantoms suitable for use as a reference standard.

Rb vapor-cell clock demonstration with a frequencydoubledtelecom laser

Nil Almat, Matthieu Pellaton, William Moreno, Florian Gruet, Christoph Affolderbach, and Gaetano Mileti

Doc ID: 325708 Received 12 Mar 2018; Accepted 07 May 2018; Posted 07 May 2018  View: PDF

Abstract: We employ a recently developed laser system, based on a low-noise telecom laser emitting around 1.56 μm, toevaluate its impact on the performance of a Rb vapor-cell clock in continuous-wave double-resonance scheme. Theachieved short-term clock instability below 2.5·10−13∙τ−1/2 demonstrates, for the first time, the suitability of afrequency-doubled telecom laser for this specific application. We measure and study quantitatively the impact oflaser amplitude and frequency noises and of the ac Stark shift, which limit the clock frequency stability on shorttimescales. We also report on the detailed noise budgets and demonstrate experimentally that, under certainconditions, the short-term stability of the clock operated with the low-noise telecom laser is improved by a factor ofthree compared to clock operation using the direct 780-nm laser.

Photometric optimization and comparison of hybridwhite LEDs for mesopic road lighting

CHUANWEN ZHANG, LICAI XIAO,, ping zhong, and Guoxing He

Doc ID: 326863 Received 26 Mar 2018; Accepted 06 May 2018; Posted 07 May 2018  View: PDF

Abstract: The photometric model for the mesopic luminous efficacy (LEm) of hybrid white LEDs, including the radiantefficiency of both blue and red LEDs as well as the overall quantum efficiency of the phosphor layer or the QDsfilm,was developed. The optimal spectral parameters of integrated with quantum dots (QD-WLED), phosphorconvertedwhite LED (pc-WLED) with red LEDs instead of red phosphor (pc/R WLED) for both color fidelity index(Rf) and color rendering index (Ra) above 70, 80, and 90 at correlated color temperatures of 2700 K to 6500 K wereobtained by maximizing the average LEm of four road lighting standards. By comparing between pc-WLED, QDWLED,and pc/R WLED, it was suggested that the pc/R WLEDs make strong candidates for mesopic road lighting.The requirements of the overall efficiency of QDs film were presented if the QD-WLEDs were competitive to the pc-WLEDs. Finally, the three real pc/R WLEDs with both Rf and Ra about 80 at CCTs of 2982 K, 4560 K, and 5683 Kwere demonstrated.

Water surface-clutter suppression method based oninfrared polarization information

Jianan Liang, Xia Wang, Yujie Fang, JingJing Zhou, Si He, and Weiqi Jin

Doc ID: 320680 Received 25 Jan 2018; Accepted 06 May 2018; Posted 07 May 2018  View: PDF

Abstract: Targeting star-like water surface clutter, a clutter suppression method based on infrared polarization informationis proposed. First, the clutter is suppressed from the global perspective using infrared polarization imagingtechnology and a basic clutter-suppressed image is obtained. Then, using the Reed–Xiaoli anomaly detectionalgorithm, the remaining clutter positions in the basic image are determined from the polarization intensity imageand basic image. Finally, an image filtering algorithm is utilized to further suppress the remaining clutter in thebasic image. In experiment, the proposed method can not only improve the signal-to-clutter ratio as much as 152%,but also preserve the target information and background texture features effectively, indicating clear superiorityof our method over existing clutter suppression algorithms. Clutter suppression and target detail preservation canenhance observer understanding of a scene significantly, so this method is applied to the detection and recognitionof targets on the water surface.

Pulse propagation in hollow core fiber at highpressure regime: application to compression of tensμJ pulses and determination of nonlinear refractiveindex of Xe at 1.03μm

Shu-Zee Lo, Lin Wang, and Zhi-Heng Loh

Doc ID: 325288 Received 02 Mar 2018; Accepted 06 May 2018; Posted 07 May 2018  View: PDF

Abstract: Classical expression for propagation constant and absorption coefficient derived by Narcatilli and Schmeltzer forhollow core fiber (HCF) has been slightly modified to account for noble gas material dispersion at high gaspressure. As a proof of concept, nonlinear refractive index of xenon gas has been investigated by numerically fittingto experimentally obtained spectral broadening in HCF under intense high repetition rate pulses. By varying thexenon pressure inside the HCF, a pressure dependent nonlinear refractive index value of( ) 20 2κ 2 50.1 0.3 10 cm W atm = ± × − at 1.03 μm is obtained, which compared favorably with literature reportedvalues. Finally, temporal compression of 50 μJ, 320 fs pulses at 0.6 MHz repetition rate to 61 fs with 0.29 GW peakpower in a HCF filled with 5 bars of Xe gas has been demonstrated using a single HCF compression stage.

Refractive index of adipose tissue and lipid dropletmeasured in a wide spectral and temperature ranges

Irina Yanina, Ekaterina Lazareva, and Valery Tuchin

Doc ID: 319766 Received 09 Feb 2018; Accepted 06 May 2018; Posted 08 May 2018  View: PDF

Abstract: This study presents refractive index measurements of human and porcine adipose tissues and lipid droplet contentin the visible and NIR. The coefficients of Sellmeier formula were calculated for approximation tissue dispersion.For the first time, the phase transition temperatures andtemperature increments dn/dT of adipose tissue werequantified for a wide wavelength range from 480 to 1550 nm and from room temperature up to 50°C.For humanabdominal adipose tissue, the refractive index increment averaged across all wavelengths is dn/dT=–(3.54±0.15)×10–4 °C–1, for porcine tissue dn/dT=–7.92 (0.74)×10–4 °C–1, and for porcine lipid droplet dn/dT=–6.01(0.29)×10–4 °C–1. Data available in literature for refractive indices of adipose tissues measured by differenttechniques are summarized and compared with the received data.

Optical design of low-cost polarimetric back-scatter sondes

Murray Hamilton

Doc ID: 325747 Received 12 Mar 2018; Accepted 03 May 2018; Posted 03 May 2018  View: PDF

Abstract: The optical design of a simple low-cost polarimetric balloon-borne backscatter sonde for detecting cloud thermodynamic phase is described. Simulations are performed to determine the best choice of polarisation, and the layout of the detectors with respect to the emitter.The variety of scattering angles of the detected photons, due to finite size detectors, has at least as great an effect as multiple scattering in determining the the ratio of cross-polarised to co-polarised signal.The problem with aligned flat plate ice crystals giving similar depolarisation to spherical scatterers, noted in the context of cloud lidar, also occurs here even with a cloud of randomly oriented large plates. Nevertheless we find that configurations of the instrument that can distinguish liquid droplets from a wide variety of ice crystal habits, including plates, are possible.

Direct bleaching of a Cr4+:YAG saturable absorber in apassively Q-switched Nd:YAG laser

Baichao Zhang, Ying Chen, Pengyuan Wang, Yanchao Wang, Jinbo Liu, Shu Hu, Xusheng Xia, Youbao Sang, Hong Yuan, Xianglong Cai, Dong Liu, Baodong Gai, and jingwei Guo

Doc ID: 326775 Received 23 Mar 2018; Accepted 03 May 2018; Posted 03 May 2018  View: PDF

Abstract: In this work, the anisotropy of non-linear absorption in a crystal Q-switch was considered when we establishedcoupled rate equations of passively Q-switched laser. A [100]-cut Cr4+:YAG crystal, with initialtransmission T0 = 40%, was used as the Q-switch to evaluate the theoretical model, and the results ofsimulation were in good accordance with the experiment. In order to control timing jitter of the passivelyQ-switched laser, an actively Q-switched Nd:YAG laser was applied to directly bleach the [100]-cutCr4+:YAG crystal. The timing jitter was more than one microsecond without bleaching light. While therewas a bleaching light, the time lag between the laser pulse and the bleaching light was less than one hundrednanoseconds, which meant the timing jitter decreased. The pulse width of the passively Q-switchedlaser was found to decrease from 45 ns to 35 ns due to the existing of bleaching light. As the peak powerof bleaching light was increased, the laser pulse energy increased from 18.2 mJ to 24.6 mJ, which meanta 35% increment in the pulse energy. The increase in pulse energy can be explained by the increase of acoefficient, and the results of simulation agreed well with the experiment.

Spatio-temporal analysis of glass volume processingusing ultrashort laser pulses

Klaus Bergner, Brian Seyfarth, Kim Lammers, Tobias Ullsperger, Sven Döring, Matthias Heinrich, Malte Kumkar, Daniel Flamm, Andreas Tünnermann, and Stefan Nolte

Doc ID: 325716 Received 08 Mar 2018; Accepted 02 May 2018; Posted 02 May 2018  View: PDF

Abstract: Ultrashort laser pulses allow for the in-volume processing of glass through non-linear absorption resultingin permanent material changes and the generation of internal stress. Across the manifold potentialapplications of this technology, process optimization requires a detailed understanding of the laser-matterinteraction. Of particular relevance are the deposition of energy inside the material, and the subsequentrelaxation processes. In this article, we investigate the spatio-temporal evolution of free carriers, energytransfer and the resulting permanent modifications in the volume of glass during and after exposure tofemtosecond and picosecond pulses. For this purpose, we employ time-resolved microscopy in order toobtain shadowgraphic and interferometric images that allow to relate the transient distributions to therefractive index change profile. Whereas the plasma generation time is given by the pulse duration, thethermal dynamics occur over several microseconds. Among the most notable features is the emergence ofa pressure wave due to the sudden increase of temperature and pressure within the interaction volume.We show how the structure of the modifications, including material disruptions as well as local defects,can be directly influenced by a judicious choice of pulse duration, pulse energy and focus geometry.

Determination of the refractive index and Abbe numberof glass of spherical lenses

Antonin Miks and Michal Šmejkal

Doc ID: 326557 Received 21 Mar 2018; Accepted 02 May 2018; Posted 02 May 2018  View: PDF

Abstract: The article deals with the problem of determination of basic parameters of unknown spherical lenses, namely theirradii of curvature, thicknesses and refractive indices of materials, for example, optical glasses, from which theselenses are made. Four methods are proposed to obtain these parameters and mathematical relations are derivedthat allow us to determine the refractive index and Abbe number of lens material based on the measured radiusvalues, the thickness, and the position of the focal point or the focal length.

Determining the size and refractive index of homogeneousspherical aerosol particles using Mie resonancespectroscopy

Nugent Lew, Michelle Ting, and Thomas Preston

Doc ID: 320940 Received 29 Jan 2018; Accepted 01 May 2018; Posted 02 May 2018  View: PDF

Abstract: Methods for determining the size and refractive index of single, homogeneous, micron-sizedaerosol particles using Mie resonance spectroscopy are studied using measurements from opticallytrapped particles and light scattering calculations based on Mie theory. We considerboth single particle broadband light scattering and cavity-enhanced Raman scattering (CERS)and demonstrate that, when resonances observed in either type of spectroscopy are fitted usingMie theory, the accuracy of the best-fits are similar. However, broadband measurements canyield more resonances than CERS, thus reducing the uncertainty in the retrieved parametersof best-fit and increasing the range of particles that can be characterized. Resonance fittingmethods are also compared to methods that fit the entire Mie scattering spectrum. Throughcalculations, it is shown that measured scattering spectra are sensitive to small changes in howlight is collected while Mie resonance positions are much less sensitive. This means that additionalparameters are required to accurately fit entire light scattering spectra using Mie theorybut these parameters are not needed to accurately determine Mie resonance positions.

Transmission-Enabled Fiber Fabry-Pérot Cavity Based On Deeply-Etched Slotted Micromirror

Muhammad Othman, Yasser Sabry, Mohamed Sadek, Ismail Nassar, and Diaa Khalil

Doc ID: 324773 Received 27 Feb 2018; Accepted 01 May 2018; Posted 02 May 2018  View: PDF

Abstract: In this work we report the analysis, fabrication and characterization of optical cavity built using Bragg-coated fiber (BCF) mirror and metal-coated MEMS slotted micromirror, where the latter allows transmission output from the cavity. Theoretical modeling, using Fourier optics analysis for the cavity response based on tracing the propagation of light back and forth between the mirrors is presented. Detailed simulation analysis is carried out for the spectral response of the cavity under different design conditions. MEMS chips are fabricated using deep reactive ion etching (DRIE) of a silicon-on-insulator (SOI) substrate with different device etching depths of 150 µm and 80 µm with aluminum and gold metal coating, respectively, of the slotted micromirror. The cavity is characterized as an optical filter using a BCF with reflectivity that is larger than 95 % in a 300-nm range across the E-band and the L-band. Versatile filter characteristics were obtained for different values of the MEMS micromirror slit width and cavity length. A free spectral range (FSR) of about 33 nm and a quality factor of about 196 were obtained for a 5.5-µm width aluminum slit, while an FSR of about 148 nm and a quality factor of about 148 were obtained for a 1.5-µm width gold slit. The presented structure opens the door for wide spectral response transmission-type MEMS filters.

Spectral refractive index technique for monitoring thebeer mashing process

Francilaine Silva Almeida, Alex Cesar Pereira Rocha, Sandro Lima, and Luis Andrade

Doc ID: 324644 Received 16 Mar 2018; Accepted 27 Apr 2018; Posted 02 May 2018  View: PDF

Abstract: During beer production, the mashing process is fundamental for extraction of the main sugars from the starch. Thequantification of these fermentable sugars during the process provides a measure of the alcoholic content of the finalbeer. Therefore, monitoring of the sugar composition during beer production is very important for obtaining a qualityproduct. This paper demonstrates the potential of white light interferometry (WLI) for monitoring the extraction ofsugars in different mashing processes, by observing the refractive index of the mixture. All the mashings presented linearincreases of the refractive index during the temperature steps, which were influenced by the concentrations of sugarsproduced in each step. Cauchy parameters obtained by refractive index interpretation showed the influence ofcarbohydrates on absorption in the infrared region, and amino acids on absorption in the ultraviolet region. Strongcorrelation was obtained between the refractive index and °Bx values, indicating that the WLI technique is a potentialanalytical method for monitoring the mashing process during beer production.

A directional coupler based on elliptic cylindrical nanowire hybrid plasmonic waveguide

de zheng zeng, Li Zhang, Qiulin Xiong, and ma junxian

Doc ID: 325943 Received 12 Mar 2018; Accepted 25 Apr 2018; Posted 25 Apr 2018  View: PDF

Abstract: We present a novel directional coupler based on elliptic cylindrical nanowire hybrid plasmonic waveguide. Using finite element method (FEM), the electric field distributions of y-polarized symmetric and antisymmetric modes of the coupler are compared, and the coupling and transmission characteristics are analyzed, then the optimized separation distance between the two parallel waveguides 100 nm is obtained. This optimized architecture fit in the weak coupling regime. Furthermore, the energy transfer is studied, and the performances of the directional coupler are evaluated, including excess loss, coupling degree and directionality. The results show that when the separation distance is set to 100 nm, the coupling length reaches to the shorter value of 1.646 μm, and the propagation loss is as low as 0.076 dB/μm, and the maximum energy transfer can reach 80%. The proposed directional coupler features good energy confinement, ultracompact and low propagation loss, which has potential application in dense PICs and other photonic devices.

Single shot phase retrieval based on beamsplitting

He Xi, Xingchen Pan, Liu Cheng, and Jianqiang Zhu

Doc ID: 320726 Received 29 Jan 2018; Accepted 23 Apr 2018; Posted 25 Apr 2018  View: PDF

Abstract: A kind of beam splitting based single shot phase retrieval is proposed, where thetransmitted field of a sample to be observed is diffracted into many replicas by a Dammann gratingand then incident on a weakly-scattering phase plate with known structure, and the exiting beamspropagate roughly along their original directions and form a diffraction-pattern array on thedetector. All sub-diffraction-patterns isolated with each other were recorded with a singlemeasurement, and the complex amplitude of the radiation incident on the grating and accordinglythat transmitted from sample can be iteratively reconstructed from the recorded diffraction patternsarray iteratively. Since the weakly scattering plate is accurately measured in advance, fastconvergence and high accuracy can be achieved with a small number of sub-diffraction patterns. Thefeasibility of this proposed method is verified with experiments using visible light.

Dependence of temperature and far-field beamquality on substrate thickness of spectral beamcombining grating with 13.4kW/cm2 laser irradiation

Jiao Xu, Junming Chen, Peng Chen, yonglu wang, Yibing Zhang, Fanyu Kong, jin yunxia, and Jianda Shao

Doc ID: 325067 Received 06 Mar 2018; Accepted 17 Apr 2018; Posted 17 Apr 2018  View: PDF

Abstract: In previous research, the thermal distortion and far-field beam quality of spectral beam combining grating wereanalyzed by theory and experiment under the irradiation of high-power continuous-wave (CW) laser. It wasconcluded that the thermal expansion of the substrate was the main cause of the grating distortion and decrease inthe beam quality. However, there was no further study to determine a method to decrease the heat deposition onthe grating surface and far-field beam quality factor, M2. In this paper, we theoretically simulate the influence of thesubstrate thickness on the temperature field distribution and far-field beam quality of a multilayer dielectricgrating. An experimental setup is proposed to verify the theoretical calculations. The experimental results are ingood agreement with the calculations. The conclusions indicate that the temperature rise of the grating and M2, areeffectively reduced by increasing the thickness of the substrate.

Comment: Diffracted Radiance Not Proven to be Fundamental Quantity in Nonparaxial Scalar Diffraction Theory

David Zissa

Doc ID: 304505 Received 11 Aug 2017; Accepted 01 Apr 2018; Posted 11 May 2018  View: PDF

Abstract: A paper asserting that the squared modulus of the Fourier transform of the complex amplitude distribution emerging from the diffracting aperture is radiance rather than irradiance relies on an unproven statement. Thus it is not necessary to reinterpret this quantity as radiance.

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

Rajab Nasehi and Mohammad Mahmoudi

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

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

Dependence of depth of focus on spherical aberration of optical systems

Antonin Miks and Jiri Novak

Doc ID: 267338 Received 31 May 2016; Accepted 05 Jul 2016; Posted 06 Jul 2016  View: PDF

Abstract: This paper presents a theoretical analysis and computation of aberration coefficients of the third and fifth order of transverse spherical aberration of an optical system, which generates a ray bundle with a diameter of a geometric-optical circle of confusion smaller than a predetermined limit value. Equations were derived for the calculation of aberration coefficients of an optical system, which satisfy given conditions, and for the determination of the maximum possible depth of focus for given conditions.

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