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Accepted papers to appear in an upcoming issue

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Rectangular-core large-mode-area photonic crystalfiber for high power applications: Design and analysis

Ajeet Kumar, REENA DALAL, Than Singh Saini, Yogita Kalra, and Ravindra Sinha

Doc ID: 258618 Received 01 Feb 2016; Accepted 27 Apr 2016; Posted 28 Apr 2016  View: PDF

Abstract: A rectangular-core large-mode-area photonic crystal fiber structure has been designed based on the principle ofhigher-order mode filtering by introducing fluorine-doped material rods in the cladding region. The proposedstructure has an effective-mode-area of fundamental mode (FM) as large as 2147 μm2 at 1.064 μm with nominalloss of 1.36×10-2 dB/m and 9.34 dB/m at first higher order mode (FHOM) which confirms effective single-modeoperation after ~2.14 meter propagation length. The same structure offers effective-mode-area of 5688 μm2 atλ=1.55 μm with confinement loss of ~6.3×10-2 dB/m for FM and ~20. dB/m for FHOM. The loss of the FHOM isabove 8 dB/m from λ=1μm to λ=1.6 μm with very small loss in FM which offers extended single-mode operationwithin such broad spectral range.

Image interpolation used in three-dimensional rangedata compression

Shaoze Zhang, Jianqi Zhang, Xi Huang, and Delian Liu

Doc ID: 260840 Received 09 Mar 2016; Accepted 27 Apr 2016; Posted 28 Apr 2016  View: PDF

Abstract: Advances in the field of three-dimensional (3D) scanning have made the acquirement of 3D range data easier andeasier. However, the large size of 3D range data brings the challenge of storing and transmitting 3D range data. Toaddress this challenge, this paper presents a framework to further compress 3D range data using imageinterpolation. First of all, use a virtual fringe projection system to store 3D range data as images, and then apply theinterpolation algorithm to the images to reduce their resolution to further reduce the data size. When 3D rangedata are needed, the image of low resolution is scaled up to its original resolution by applying the interpolationalgorithm, and then the scaled-up image is decoded and the 3D range data are recovered according to the decodedresult. Experimental results show that the proposed method could further reduce the data size while maintaininglow error.

Color computer-generated hologram generation usingthe random phase-free method and color spaceconversion

Tomoyoshi Shimobaba, Michal Makowski, Yuki Nagahama, Yutaka Endo, Ryuji Hirayama, Daisuke Hiyama, Satoki Hasegawa, Marie Sano, Takashi Kakue, Minoru Oikawa, Takashige Sugie, Naoki Takada, and Tomoyoshi Ito

Doc ID: 260944 Received 10 Mar 2016; Accepted 27 Apr 2016; Posted 28 Apr 2016  View: PDF

Abstract: We propose two calculation methods of generating color computer-generated holograms (CGH) with therandom phase-free method and color space conversion in order to improve the image quality and acceleratethe calculation. The random phase-free method improves the improvement of the image quality inmonochrome CGH, but it is not performed in color CGH. We first aimed to improve the image qualityof color CGH using the random phase-free method and then to accelerate the color CGH generation witha combination of the random phase-free method and color space conversion method, which acceleratesthe color CGH calculation due to down-sampling of the color components converted by color space conversion.To overcome the problem of image quality degradation that occurs due to the down-sampling ofrandom phases, the combination of the random phase-free method and color space conversion method improvesthe quality of reconstructed images and accelerates the color CGH calculation. We demonstratedthe effectiveness of the proposed method in simulation, and in this paper discuss its application to lenslesszoom-able holographic projection.

110-W all-fiber picosecond MOPA based on largecore diameter Ytterbium-doped fiber

Wei Shi, Zhenhua Yu, Xinzheng Dong, Jinhui Li, Yizhu Zhao, and Huixian Liu

Doc ID: 261573 Received 21 Mar 2016; Accepted 27 Apr 2016; Posted 28 Apr 2016  View: PDF

Abstract: We demonstrate an all fiber picosecond fiber laser in master oscillator power amplifier (MOPA) configuration. The seed sourceis a soliton-type passively mode-locked Yb-doped fiber laser by a semiconductor saturable absorber mirror (SESAM) andchirped fiber bragg grating (CFBG). The pulse width of the seed laser is 4.5 ps with the repetition rate of 15 MHz. Highlydoped active fiber with large core diameter (50μm) is employed to boost the average power of the seed pulses to 117 W with11-ps pulse width and 709-kW peak power. The corresponding M2 at maximum output power is 3.7. The all fiber constructionof the whole laser system enables compact size and robust operation.

Automated Decomposition Algorithm for Raman Spectra Based on a Voigt Line-profile Model

Liankui Dai and Yunliang Chen

Doc ID: 261335 Received 17 Mar 2016; Accepted 26 Apr 2016; Posted 26 Apr 2016  View: PDF

Abstract: Raman spectra measured by spectrometers usually suffer from band overlap and random noise. In this paper, an automated decomposition algorithm based on a Voigt line-profile model for Raman spectra is proposed to solve this problem. In order to decompose a measured Raman spectrum, a Voigt line-profile model is introduced to parameterize the measured spectrum and a Gaussian function is used as the instrumental broadening function, and hence the issue of spectral decomposition is transformed into a multi-parameter optimization problem of the Voigt line-profile model parameters. The algorithm can eliminate instrumental broadening, obtain a recovered Raman spectrum, resolve overlapping bands and suppress random noise simultaneously. Moreover, the recovered spectrum can be decomposed to a group of Lorentzian functions. Experimental results on simulated Raman spectra show that the performance of this algorithm is much better than a commonly-used blind deconvolution method. The algorithm has also been tested on the industrial Raman spectra of ortho-xylene and proved to be effective.

Ultra-sensitive, real-time trace gas detection using a high-power, multi-mode diode laser and cavity ringdown spectroscopy

Gottipaty Rao, Andreas Karpf, and Yuhao Qiao

Doc ID: 259220 Received 16 Feb 2016; Accepted 26 Apr 2016; Posted 28 Apr 2016  View: PDF

Abstract: We present a simplified Cavity Ring-down (CRD) trace gas detection technique that is insensitive to vibration, andcapable of extremely sensitive, real-time absorption measurements. A high power, multi-mode Fabry-Perot (FP)diode laser with a broad wavelength range (􀪢􀫃􀢒􀢇􀢙􀢋􀢘 ~ 􀫙. 􀫟 􀜖􀜕) is used to excite a large number of cavity modes,thereby reducing the detector’s susceptibility to vibration and making it well suited for field deployment. Whendetecting molecular species with broad absorption features (􀪢􀫃􀢇􀢈􀢙􀢕􀢘􀢖􀢚􀢏􀢕􀢔 ≫ 􀪢􀫃􀢒􀢇􀢙􀢋􀢘), the laser’s broad linewidthremoves the need for precision wavelength stabilization. The laser’s power and broad linewidth allow the use ofon-axis cavity alignment, improving the signal-noise-ratio while maintaining its vibration insensitivity. The use ofa FP diode laser has the added advantage of being inexpensive, compact and insensitive to vibration. Thetechnique was demonstrated using a 1.1 Watt (λ = 400 nm) diode laser to measure low concentrations of NitrogenDioxide (NO2) in zero air. A sensitivity of 38 parts-per-trillion (ppt) was achieved using an integration time of 128ms; for single-shot detection, 530 ppt sensitivity was demonstrated with a measurement time of 60 μs which opensthe door to sensitive measurements with extremely high temporal resolution; to the best of our knowledge, theseare the highest speed measurements of NO2 concentration using CRDS. The apparatus’ reduced susceptibility tovibration was demonstrated by introducing small vibrations into the apparatus and observing that there was nomeasurable effect on the sensitivity of detection.

Reflection and transmission properties of a metasurface composed of resonant loaded wire dipoles

zeeshan awan

Doc ID: 259513 Received 24 Feb 2016; Accepted 26 Apr 2016; Posted 28 Apr 2016  View: PDF

Abstract: A considered metasurface is assumed to consist of a two dimensionalperiodic arrangement of inductively loaded wires. The effects of incident angles and inductive loads upon an equivalent surface impedance, reflection and transmission properties of this metasurface have been investigated using numerical simulations. It is shown that at particular frequency and angle, a metasurface can be cloaked for the incoming incident wave with nearly zero reflection. It is further studied that this approximate zero reflection is independent of inductances of inductively loaded wire dipoles.

Non-critically phase-matched fourth harmonicgeneration of Nd:glass lasers and design of final opticsassembly

Xiuqing Jiang, Lailin Ji, liu dong, Shunxing Tang, Bao-Qiang Zhu, and Zunqi Lin

Doc ID: 259675 Received 18 Feb 2016; Accepted 26 Apr 2016; Posted 26 Apr 2016  View: PDF

Abstract: The Non-critically phase-matched (NCPM) fourth harmonic generation (FHG) with partially deuterated dihydrogenphosphate (KD*P)crystal at an Nd:glass laser radiation wavelength of 1053.1nm has been confirmed. NCPM FHG hasbeen achieved in 70% and 65% deuterated KD*P crystal at the temperature of 17.7oC and 29.3oC, respectively. Theangular acceptance of 70% and 65% deuterated KD*P crystals fixed at their NCPM temperature were measured,which were 53mrad and 55mrad, respectively. The application of the NCPM FHG in high power laser facility forinertial confinement fusion is also discussed. Based on the theoretical analysis, the NCPM KD*P can be placed afterfocus lens, and thus the laser induced damage of fused silica lens at ultraviolet can be avoided.

Freeform illumination optics construction following anoptimal transport map

Zexin Feng, Brittany Froese, and Rongguang Liang

Doc ID: 260344 Received 01 Mar 2016; Accepted 25 Apr 2016; Posted 26 Apr 2016  View: PDF

Abstract: We present a modified optimal transport ray mappingapproach to design freeform optics for prescribed illuminations.After mapping the source intensity intoa virtual irradiance distribution under stereographicprojection, we employ an advanced optimal transportmap computation method with the ability to tacklenon-standard boundary conditions. Following the computedmap, we construct the freeformoptical surface directlyfrom normal vectors by requiring that the chordbetween two adjacent points is perpendicular to the averageof the two normal vectors at these two points andenforcing this relationship with a least squares method.Examples of designing freeform lenses for LED sourcesshow that we can produce various uniform illuminationpatterns with high optical efficiencies.

Polarization maintaining low-loss porous-core spiral photonic crystal fiber for THz wave guidance

Md. Rabiul Hasan, Md. Shamim Anower, Md. Ariful Islam, and S. M. Razzak

Doc ID: 260243 Received 29 Feb 2016; Accepted 25 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: A polarization maintaining spiral photonic crystal fiber (PCF) is proposed for efficient transmission of polarization maintaining terahertz (THz) waves. The finite element method (FEM) with perfectly matched layer (PML) boundary condition is used to characterize the guiding properties. It is demonstrated that by creating artificial asymmetry in porous-core, an ultra-high birefringence of 0.0483 can be obtained at the operating frequency of 1.0 THz. Moreover, a low effective material loss (EML) of 0.085 and very small confinement loss of 1.91×10-3 dB/cm are achieved for y-polarization mode with optimal design parameters. This article also focuses on some crucial design parameters such as power fraction, bending loss, and dispersion for usability in THz regime.

Wavelength Optimization Using Available Laser Diodes in Spectral Near-infrared Optical Tomography

Min-Chun Pan, MIN-CHENG PAN, Liang-Yu Chen, and CHUNG-CHEN YAN

Doc ID: 260272 Received 01 Mar 2016; Accepted 25 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: As employing optimized wavelengths, a near-infrared (NIR) tomographic imaging system with multi-wavelengths in continuous wave (CW) enables to provide accurate information of chromophores. In this paper, we discuss wavelength optimization with the selection from commercial laser diodes. Through theoretical analysis, we use the residual norm (R) and the condition number (κ) to represent the uniqueness of a matrix problem and the smooth singular-value distribution of each chromophore, respectively. The optimum wavelengths take place for large R and small κ. We considered totally 38 wavelengths of laser diodes in the range of 633-980 nm commercially available to discover optimum sets for a broad range of chromophore combinations. In the total 38 wavelengths, there exist 501,942 (C385), 2,760,681 (C386), and 12,620,256 (C387) combinations of five, six, and seven wavelength sets, respectively, for accurately estimating chromophores (HbO2, HbR, H2O, and lipid), water, lipid plus the scattering prefactor A. With the numerical calculation, top 10 wavelength sets were selected based on the principle of large R and small κ. In the study, the chromophore concentration for young and old women are investigated; finally, choosing the laser diodes with the wavelength of 650, 690, 705, 730, 870/880, 915 and 937 nm is recommended either for young or old women to construct a spectral NIR tomographic imaging system in the CW domain.

Parameter correction method for dual positionsensitive detector-based unit

Peng-Cheng Hu, Shuai Mao, Xuemei Ding, and Jiu Tan

Doc ID: 261071 Received 14 Mar 2016; Accepted 25 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: A dual position sensitive detector (PSD)-based unit can be used for angular measurements of amulti-degree-of-freedom measurement system and a laser interferometry-based sensing and trackingsystem. In order to ensure the precision of incident beam direction measurement for a PSD-based unit,model and auto-reflection alignment methods for correction of PSD-based unit parameters areproposed. Experimental results demonstrate the deviations between the angular measurementsobtained using a dual PSD-based unit and an auto-collimator varied by 70", 20" and 1" for three runs ofthe auto-reflection alignment method, respectively, and the model method deviations all varied by 1" inthe 1000" measurement range for three runs. It is therefore concluded that the model method is morereliable than the auto-reflection alignment method to ensure the accuracy of a dual PSD-based unit.

Detection of defects on the surface of a semiconductorby terahertz surface plasmon polaritons

li yi, Tao Yang, Y Zhu, Wei Huang, Rayko Stantchev, Yi-qiang QIN, and Xin-hui Zhou

Doc ID: 258548 Received 01 Feb 2016; Accepted 25 Apr 2016; Posted 26 Apr 2016  View: PDF

Abstract: We propose a new method for detecting small defects on the surface of a semiconductor by analyzing thetransmission spectrum of terahertz surface plasmon polaritons. The field distributions caused by detectingdifferent sized defects is simulated. Experimentally, using a terahertz time domain spectrometer, we measure thetransmission spectrum of terahertz surface plasmon polaritons passing through particles on the surface of anintrinsic InSb wafer. Our results show that the measured temporal waveform and frequency spectra are distinctlychanged due to the presence of the particles, thereby confirming the effectiveness of this method for detectingdefects. For increased detection efficiency, the frequency of the surface plasmon polaritons has to be slightly lowerthan the plasma frequency of the semiconductor. In comparison with traditional methods, our approach offers themerits of detecting both on-surface as well as sub-surface defects, which is critical in monitoring the quality ofsemiconductor wafers.

Gaussian beam propagation in anisotropic turbulencealong horizontal links: theory, simulation andlaboratory implementation

Xifeng Xiao, David Voelz, Italo Toselli, and Olga Korotkova

Doc ID: 258261 Received 26 Jan 2016; Accepted 25 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: Experimental and theoretical work has shown that atmospheric turbulence can exhibit “non-Kolmogorov”behavior including anisotropy and modifications of the classically-accepted spatial power spectral slope 11/3. Intypical horizontal scenarios, atmospheric anisotropy implies that the refractive index is more spatially correlatedin both horizontal directions than in vertical. In this work, we extend Gaussian beam theory for propagationthrough Kolmogorov turbulence to the case of anisotropic turbulence along horizontal direction. We also study theeffects of different power spectral slopes of turbulence on the beam propagation. A description is developed forthe average beam intensity profile and the results for a range of scenarios are demonstrated for the first time witha wave optics simulation and a spatial light modulator-based laboratory benchtop counterpart. Implementationdetails of the simulation and benchtop setup are described. The theoretical, simulation and benchtop intensityprofiles show good agreement and illustrate that an elliptically shaped beam profile can develop uponpropagation. For stronger turbulent fluctuation regimes and larger anisotropies, the theory predicts a slightlymore elliptical form of the beam than is generated by the simulation or benchtop setup. The theory also predictsthat the beam width becomes unbounded as the power spectral slope index α approaches a maximum value of 4.This behavior is not seen in the simulation or benchtop results because the numerical phase screens used for thesestudies do not model the unbounded wavefront tilt component implied in the analytic theory.

Characterization and simulation of soft gamma-ray mirrors for their use with spent fuel rods at reprocessing facilities

Jaime Ruz Armendariz, Marie-Anne Descalle, Jenifer Alameda, Nicolai Brejnholt, David Chichester, Todd Decker, Monica Fernández-Perea, Randy Hill, Roger Kisner, Alexander Melin, Bruce Patton, Regina Soufli, Holly Trellue, Scott Watson, Klaus-Peter Ziock, and Michael Pivovaroff

Doc ID: 259039 Received 19 Feb 2016; Accepted 25 Apr 2016; Posted 28 Apr 2016  View: PDF

Abstract: The use of a grazing incidence optic to selectively reflect K-shell fluorescence emission and isotope-specific lines from Special Nuclear Materials (SNM) is a highly desirable non-destructive analysis method for use in reprocessing fuel environments. Preliminary measurements have been performed and a simulation suite has been developed to give insight into the design of the X-ray optics system as a function of source emission, multilayer coating characteristics and general experimental configurations. Experimental results are compared to the predictions from our simulation toolkit to illustrate the ray-tracing capability and explore the effect of modified optics in future measurement campaigns.

A Branch and Bound Algorithm for AccurateEstimation of Analytical Isotropic BRDF Models

Sang Lee and Chanki Yu

Doc ID: 258495 Received 29 Jan 2016; Accepted 23 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: We present a reliable and accurate global optimization framework for estimating parameters of isotropic analyticalBRDF models. This approach is based on a branch-and-bound strategy with linear programming and interval analysis.Conventional local optimization is often very inefficient for BRDF estimation since its fitting quality is highlydependent on initial guesses due to the nonlinearity of analytical BRDF models. The algorithm presented in this paperemploys L1-norm error minimization to estimate BRDF parameters in a globally optimal way and interval arithmeticto derive our feasibility problem and lower bounding function. Our method is developed for the Cook-Torrance modelbut with several normal distribution functions such as the Beckmann, Berry and GGX functions. Experiments havebeen carried out to validate the presented method using 100 isotropic materials from the MERL BRDF database, andour experimental results demonstrate that the L1-norm minimization provides more accurate and reliable solutionthan the L2-norm minimization.

Double-Pulse 2-μm IPDA Lidar Airborne-Validation forAtmospheric Carbon Dioxide Measurement

Tamer Refaat, Upendra Singh, Jirong Yu, Mulugeta Petros, Ruben Remus, and Syed Ismail

Doc ID: 258615 Received 18 Feb 2016; Accepted 23 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: Field experiments were conducted to test and evaluate the initial atmospheric carbon dioxide (CO2) measurementcapability of an airborne, high energy, double-pulsed, 2-μm integrated path differential absorption (IPDA) lidar.This IPDA was designed, integrated and operated at NASA Langley Research Center onboard the NASA B-200aircraft. The IPDA was tuned to the CO2 strong absorption line at 2050.9670 nm, which is optimum for lowertropospheric weighted column measurements. Flights were conducted over land and ocean under differentconditions. Focusing on low surface reflectivity oceanic surface returns during full day background conditions, thefirst validation experiments of the IPDA for atmospheric CO2 remote sensing are presented. In these experiments,the IPDA measurements were validated by comparison to an airborne flask air sampling measurements conductedby NOAA Earth System Research Laboratory. IPDA performance modeling was conducted to evaluate measurementsensitivity and bias errors. The IPDA signals and their variation with altitude compare well with predicted modelresults. In addition, off-off-line testing was conducted, with fixed instrument settings, to evaluate the IPDAsystematic and random errors. Analysis show an altitude independent differential optical depth offset of 0.0769.Optical depth measurement uncertainty of 0.0918 compares well with the predicted value of 0.0761. IPDA CO2column measurement compare well with model driven near simultaneous air sampling measurements from theNOAA aircraft at different altitudes. With 10 second shot average, CO2 differential optical depth measurement of1.0054±0.0103 was retrieved from 6 km altitude and 4 GHz on-line operation. As compared to CO2 weightedaveragecolumn dry-air volume-mixing ratio of 404.08 ppm, derived from air sampling, IPDA measurementresulted in a value of 405.22±4.15 ppm with 1.02% uncertainty and 0.28% additional bias. Sensitivity analysis ofenvironmental systematic errors correlates the additional bias to water vapor. IPDA ranging resulted inmeasurement uncertainty of <3 m.

Thermal refocusing method for space-borne high resolution optical imagers

OZGUR SELIMOGLU, Mustafa Ekinci, and Ozgur Karci

Doc ID: 248555 Received 24 Feb 2016; Accepted 22 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: We describe the design of a thermal refocusing method for space-borne high resolution cameras where Korsch optical design is usually implemented. The secondary mirror is made of aluminum, a high thermal expansion coefficient material, instead of conventional zero expansion glass ceramics. In this way, radius of the curvature can be controlled by means of temperature change of the mirror. Change in the radius of curvature also changes the effective focal length of the camera which is used for compensation of the defocus occurred in space. We showed that 30 µm de-space of the secondary mirror in the optical system can be compensated by ~10 °C temperature change of the mirror while the image quality is maintained.

A fast and scalable algorithm for multiple Mie-scattering in optical systems

Oliver Kalthoff, Ronald Kampmann, Simon Streicher, and Stefan Sinzinger

Doc ID: 257846 Received 21 Jan 2016; Accepted 21 Apr 2016; Posted 22 Apr 2016  View: PDF

Abstract: The Monte Carlo simulation of light propagation in optical systems requires the processing of a large number of photons to achieve a satisfactory statistical accuracy. Based on classical Mie scattering we experimentally show that the independence of photons propagating through a turbid medium imposes a postulate for a concurrent and scalable programming paradigm of general purpose graphics processing units. This ensures that, without re-writing code, increasingly complex optical systems can be simulated if more processors are available in the future.

Unequal A Priori Probability Multiple Hypothesis Testing in Space Domain Awareness with the Space Surveillance Telescope

Tyler Hardy, Stephen Cain, and Travis Blake

Doc ID: 259035 Received 09 Mar 2016; Accepted 21 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: This paper investigates the ability to improve Space Domain Awareness (SDA) by increasing the number of detectable Resident Space Objects (RSOs) from space surveillance sensors. With matched filter based techniques the expected impulse response, or Point Spread Function (PSF), is compared against the received data. In the situation where the images are spatially undersampled, the modeled PSF may not match the received data if the RSO does not fall in the center of the pixel. This aliasing can be accounted for with a Multiple Hypothesis Test (MHT). Previously, proposed MHTs have implemented a test with an equal a priori prior probability assumption. This paper investigates using an unequal a priori probability MHT. To determine accurate a priori probabilities three metrics are computed; they are correlation, physical distance, and empirical. Using the calculated a priori probabilities, a new algorithm is developed and images from the Space Surveillance Telescope (SST) are analyzed. The number of detected objects by both an equal- and unequal- prior probabilities are compared while keeping the false alarm rate constant. Any additional number of detected objects will help improve SDA capabilities.

The Analysis of the feasibility the cascaded multi-dithering technique for coherent beam combining of a large number of beam elements

Heekyung Ahn and Hong Jin Kong

Doc ID: 260264 Received 01 Mar 2016; Accepted 21 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: The capacity of cascaded multi-dithering technique in terms of scalability is analyzed by developing equations and performing simulations, whose results are found to be in agreement with the earlier experimental result of a sixteen fiber beam combination using the cascaded multi-dithering technique.

Comparative Efficiency Analysis of Fiber-array and Conventional Beam Director Systems in Volume Turbulence

Mikhail Vorontsov, Grigory Filimonov, Vladimir Ovchinnikov, Ernst Polnau, Svetlana Lachinova, Thomas Weyrauch, and Joseph Mangano

Doc ID: 259890 Received 23 Feb 2016; Accepted 21 Apr 2016; Posted 21 Apr 2016  View: PDF

Abstract: The performance of two prominent laser beam projection system types is analyzed through wave-optics numerical simulations for various atmospheric turbulence conditions, propagation distances, and adaptive optics (AO) mitigation techniques. Comparisons are made between different configurations of both a conventional beam director (BD) using monolithic-optics-based Cassegrain telescope and a fiber-array beam director that uses an array of densely-packed fiber collimators. The BD systems considered have equal input power and aperture diameters. The projected laser beam power inside the Airy size disk at the target plane is used as the performance metric. For the fiber-array system, both incoherent and coherent beam combining regimes are considered. We also present preliminary results of side-by-side atmospheric beam projection experiments over a 7-km propagation path using both the AO-enhanced beam projection system with Cassegrain telescope and the coherent fiber-array BD composed of 21 densely-packed fiber collimators. Both wave-optics numerical simulation and experimental results demonstrate that, for similar system architectures and turbulence conditions, coherent fiber-array systems are more efficient in mitigation of atmospheric turbulence effects and generation of a hit spot of the smallest possible size on a remotely located target.

Simplified optical correlation-domain reflectometry without reference path

Yosuke Mizuno, Makoto Shizuka, Neisei Hayashi, and Kentaro Nakamura

Doc ID: 260502 Received 07 Mar 2016; Accepted 21 Apr 2016; Posted 21 Apr 2016  View: PDF

Abstract: We develop a simplified configuration for optical correlation-domain reflectometry (OCDR) without an explicit reference path. Instead, the Fresnel-reflected light generated at the distal open end of the sensing fiber is exploited as a reference light. After the fundamental demonstration, the optimal incident power is found to be approximately 8 dBm. We also show that the loss near the distal end should not be applied, unlike in the case of Brillouin-based OCDR.

An accurate calibration method for camera and projector in fringe patterns measurement system

Rui Chen, Jing Xu, Heping Chen, JIanhua Su, Zonghua Zhang, and ken chen

Doc ID: 260827 Received 09 Mar 2016; Accepted 20 Apr 2016; Posted 21 Apr 2016  View: PDF

Abstract: The 3D measurement system based on fringe patterns is widely applied in diverse fields. The measurement accuracy is mainly determined by camera and projector calibration accuracy. In the existing method, the system iscalibrated by a dot calibration board with the traditional image process algorithm. In this paper, an improved calibration method is proposed to increase camera and projector calibration accuracy simultaneously. To thisend, first, a sub-pixel edge detection method is proposed to improve the detection accuracy of reference features for coarse calibration; second, an iterative compensation algorithm is developed to improve the detection accuracy of the reference feature centers for fine calibration. The experimental results demonstrate that the proposed calibration method can improve the calibration accuracy and measurement accuracy

Measurement of Brillouin grating in a short optical fiber with a coherent frequency-modulated continuous wave reflectometer using complex Fourier transformation

Kazumasa Takada and Takahiro Yasuno

Doc ID: 261050 Received 15 Mar 2016; Accepted 20 Apr 2016; Posted 20 Apr 2016  View: PDF

Abstract: We report theoretical and experimental investigations of the measurement of a Brillouin grating induced by counter-propagating pump light waves with a coherent frequency-modulated continuous wave (FMCW) reflectometer utilizing a wavelength tunable laser source. We up-convert the frequency of the probe light by the Brillouin frequency before launching it into a fiber, and detect the Stokes light generated by the Brillouin grating in the same way that we derive the Fresnel and Rayleigh backreflections in the fiber by using the Fourier transformation. The only difference is that the frequency should sweep across the pumping frequency and a coherent spike-like noise is generated at the center in the signal waveform. A simple signal processing procedure is demonstrated successfully to reveal the original signal waveform and thus the reflection from a short fiber as a function of the frequency up-conversion

Photorefractive Two-Beam Coupling Joint Transform Correlator: Modeling and Performance Evaluation

George Nehmetallah, Jed Khoury, and Partha Banerjee

Doc ID: 256360 Received 23 Dec 2015; Accepted 20 Apr 2016; Posted 20 Apr 2016  View: PDF

Abstract: In this work a novel optical joint transform correlator based on photorefractive two-beam coupling is theoretically investigated and simulated, and its performance is analyzed through assessing the dependence of relevant standard figures of merit on the photorefractive gain coefficient and pump-probe beam ratio for a variety of reference and signal images. The photorefractive two-beam coupling joint transform correlator combines two features. The first is embedded semi-adaptive optimality which weighs the correlation against clutter and noise in the input and the second is the intrinsic dynamic range compression nonlinearity which improves several metrics simultaneously without metric tradeoff. The result shows that the two-beam coupling joint transform scheme is a very robust correlator with respect to standard evaluation metrics for different sets of data.

Noninvasive particle sizing using camera-based diffuse reflectance spectroscopy

Otto Abildgaard, Jeppe Frisvad, Viggo Falster, Alan Parker, Niels Jørgen Christensen, Anders Dahl, and Rasmus Larsen

Doc ID: 256952 Received 06 Jan 2016; Accepted 20 Apr 2016; Posted 20 Apr 2016  View: PDF

Abstract: Diffuse reflectance measurements are useful for noninvasive inspection of the optical properties of materials. Spectroscopic analysis of these optical properties can be used for particle sizing. Systems based on optical fiber probes are commonly employed, but their low spatial resolution limits the range of optical properties that they can deal with. To cover a wider range of optical properties, we use camera-based spectroscopic oblique incidence reflectometry. We develop a noninvasive technique for acquisition of apparent particle size distributions based on this approach. Our technique is validated using stable oil-in-water emulsions with a wide range of known particle size distributions. We also measure the apparent particle size distributions of complex dairy products. These results show that our tool, in contrast to those based on fiber probes, can deal with a range of optical properties wide enough to track apparent particle size distributions in a typical industrial process.


Juan Sánchez-Escobar, Liliana Ibeth Santillan, Javier Vargas Ubera, and J.Felix Aguilar

Doc ID: 258454 Received 29 Jan 2016; Accepted 20 Apr 2016; Posted 20 Apr 2016  View: PDF

Abstract: A stochastic inverse method is presented based on a hybrid evolutionary optimization algorithm (HEOA) to retrieve a particle-size distribution (PSD) from the angular distribution of scattered light. By solving an optimization problem, the HEOA (with the Fraunhofer approximation) retrieves the PSD from an intensity pattern generated by Mie theory. The analyzed light-scattering pattern can be attributed to unimodal normal, gamma, or lognormal distribution of spherical particles covering the interval of modal size parameters The HEOA ensures convergence to the near-optimal solution during the optimization of a real-valued objective function by combining the advantages of both a multi-member evolution strategy (MMES) and locally weighted linear regression (LWLR). The numerical results show that our HEOA can be satisfactorily applied to solve the inverse light-scattering problem avoiding the use of a priori information about the domain of the sought distribution.

Sum regression decomposition of spectral and angle-resolved Mueller matrices from biological reflectors

Roger Magnusson, Hans Arwin, Kenneth Jarrendahl, Enric Garcia-Caurel, and Razvigor Ossikovski

Doc ID: 258555 Received 29 Jan 2016; Accepted 20 Apr 2016; Posted 20 Apr 2016  View: PDF

Abstract: We show spectroscopic Mueller-matrix data measured at multiple incidence angles of the scarab beetle C. aurata. The Mueller matrix is decomposed by method of regression decomposition and it is shown that this Mueller matrix can be decomposed into a set of two matrices representing one polarizer and one dielectric reflector. We also report on a tentative decomposition of the beetle C. argenteola using the same method.

An optical remote sensor for peanut kernel abortion classification

Nisan Ozana, STAV BUCHSBAUM, Yael Bishitz, Yevgeny Beiderman, ZEEV SCHMILOVITCH, Ariel Schwarz, Amir Shemer, Josheph keshet, and Zeev Zalevsky

Doc ID: 260092 Received 01 Mar 2016; Accepted 20 Apr 2016; Posted 20 Apr 2016  View: PDF

Abstract: In this paper we propose a simple, inexpensive optical device for remote measurement of various agriculture parameters. The sensor is based on temporal tracking of back-reflected secondary speckle patterns generated when illuminating a plant with a laser and while applying periodic acoustic based pressure stimulation. By analyzing different parameters using a support vector machine based algorithm, peanuts kernel abortion can be detected remotely. This paper presents experimental tests which are the first step towards an implementation of a noncontact device for detection of agriculture parameters such as kernel abortion.

Visibility measurement using two-angle forward scattering by liquid droplets

Peng Peng and Chengwei li

Doc ID: 259012 Received 04 Feb 2016; Accepted 20 Apr 2016; Posted 21 Apr 2016  View: PDF

Abstract: This study presents a two-angle forward scattering (TAFS) method that can be used to detect atmosphere visibility and distinguish different weather phenomena. The visibility meter has two receivers arranged at the forward scattering angles of 35° and 90°, and the atmosphere visibility is measured by the first receiver (35°). We use the ratio between the scattering phase functions P(35°) and P(90°) to judge the asymmetry parameter of atmospheric particles and to distinguish the weather phenomenon. Compared with multi-angle forward scattering (MAFS) that can distinguish fog, haze, and mist, TAFS can determine additional weather phenomena (i.e., fine and rain) and has fewer receivers. Thus, we improve the instrument design of this method whose visibility error is smaller than that of MAFS during rainy days.

Analytical calculation of light-collection efficiency of optical emission spectrometer with effective solid-angle method

Jae Hahn and Minwook Kang

Doc ID: 260434 Received 04 Mar 2016; Accepted 19 Apr 2016; Posted 20 Apr 2016  View: PDF

Abstract: A method is proposed for calculating the optical emission spectrometer (OES) light-collection efficiency using the effective solid angle from an arbitrary point source. Based on the point source-OES relative positioning, the effective solid angle is derived for four cases: 1) on-axis and on the object plane, 2) on-axis and outside the object plane, 3) off- axis and on the object plane, and 4) off-axis and outside the object plane. The results were in good agreement with those obtained through Monte Carlo ray tracing. Calculating the OES geometrical collection efficiency with respect to the object plane distance in three different-sized cylindrical volume sources, we suggest a simple strategy to increase this efficiency in plasma process monitoring.

Spatial filtering velocimetry for real-time measurements of speckle dynamics due to out-of-plane motion

Michael Jakobsen and Anders Olesen

Doc ID: 258485 Received 29 Jan 2016; Accepted 19 Apr 2016; Posted 19 Apr 2016  View: PDF

Abstract: This paper describes an optical spatial-filtering-velocimetry technique that converts an expanding or contracting speckle pattern into a photocurrent. This photocurrent will have a quasi-sinusoidal dependency to this specific speckle motion. The spatial filter consists of series of concentric rings. Each ring divides the incoming light into two radial-wise almost even contributions and directs them by refraction towards two half rings of photodetectors, respectively. The corresponding two photocurrents are balanced and provide a differential photocurrent. In this paper the optical spatial-filtering-velocimetry technique is used to demonstrate real-time measurements of speckle dynamics due to out-of-plane motion.

High Security Communication by Coherence Modulation at the Photon Counting Level

William Rhodes, Yezid Torres, and Abdellatif Boughanmi

Doc ID: 259562 Received 16 Feb 2016; Accepted 19 Apr 2016; Posted 19 Apr 2016  View: PDF

Abstract: We show that key-specified interferometer pathlength difference modulation (often referred to as coherencemodulation), operating in the photon-counting regime with a broadband source, can provide a quantifiably highlevel of physics-guaranteed security for binary signal transmission. Each signal bit is associated with manyphotocounts, perhaps numbering in the thousands. Of great importance, the presence of an eavesdropper can bequickly detected. We first review the operation of key-specified coherence modulation at high light levels,illustrating by means of an example its lack of security against attack. We then show, using the same example, thatthrough the reduction of light intensities to photon-counting levels, a high level of security can be attained. Aparticular attack on the system is analyzed to demonstrate the quantifiability of the scheme's security, and variousremaining research issues are discussed. A potential weakness of the scheme lies in a possible vulnerability to lightamplification by an attacker.

Doppler shift generated by a moving diffraction grating under incidence by polychromatic diffuse light

Kokou Dossou

Doc ID: 260497 Received 04 Mar 2016; Accepted 19 Apr 2016; Posted 19 Apr 2016  View: PDF

Abstract: We consider the spectral response of moving diffraction gratings, in which the incident light extends over a broad angular range and where the diffracted light is observed from a specific angle. We show that the dispersion relation between the frequency perceived by an observer who is looking at a moving grating and the incident frequency can exhibit some unique features, such as a flat band (i.e., a local minimum). An observer can see the light diffracted into a non-specular diffraction order from a multitude of incident light rays and the angle of incidence of each ray is frequency-dependent; as a consequence, when the grating is moving, each incident ray experiences a Doppler shift in frequency that depends on its angle of incidence. We find that remarkable features appear near a Wood anomaly where the angle of incidence, for a given diffraction angle, can change very quickly with frequency. This means that light of multiple frequencies and incident from multiple angles can be mixed by the motion of the grating into the same diffracted ray and their frequencies can be compressed into a narrower range. The existence of a flat band means that a moving grating can be used as a device to increase the intensity of the perceived diffracted light due to spectral compression. The properties of a grating in motion in sunlight can also be relevant to the study of naturally occurring gratings which are typically in oscillatory motion.

Generation Regimes of Bidirectional Hybridly Mode-Locked Ultra-Short Pulse Erbium-doped All-Fiber Ring Laser with a Distributed Polarizer

Alexandr Krylov, Dmitry Chernykh, Natalia Arutunyan, Vyacheslav Grebenyukov, Anatoly Pozharov, and Elena Obraztsova

Doc ID: 261034 Received 11 Mar 2016; Accepted 19 Apr 2016; Posted 19 Apr 2016  View: PDF

Abstract: We report on the stable picosecond and femtosecond pulse generation from the bidirectional erbium-doped all-fiber ring laser hybridly mode-locked with a co-action of a Single-Walled Carbon Nanotube-based saturable absorber (SWCNT-SA) and Nonlinear Polarization Evolution that was introduced through the insertion of the short-segment polarizing fiber. Depending on the total intracavity dispersion value, laser emits conservative solitons, transform-limited Gaussian pulses or highly-chirped stretched pulses with almost 20-nm-wide parabolic spectrum in both – clockwise (CW) and counterclockwise (CCW) directions of the ring. Owing to the polarizing action in the cavity we have demonstrated for the first time to the best of our knowledge an efficient tuning of soliton pulse characteristics for both CW and CCW channels via an appropriate polarization control. We believe that the bidirectional laser presented may be highly-promising for gyroscopic and other dual-channel applications.

Simulating multiple diffraction in imaging systems using a path integration method

Beat Mout, Michael Wick, Florian Bociort, Joerg Petschulat, and H. Urbach

Doc ID: 260535 Received 07 Mar 2016; Accepted 18 Apr 2016; Posted 19 Apr 2016  View: PDF

Abstract: We present a method for simulating multiple diffraction in imaging systems based on the Huygens-Fresnel principle. The method accounts for the effects of both aberrations and diffraction and is entirely performed using Monte Carlo ray tracing. We compare the results of this method to those of reference simulations for field propagation through optical systems and for the calculation of point spread functions. The method can accurately model a wide variety of optical systems beyond the exit pupil approximation.

A three-element trap filter radiometer based on large active area silicon photodiodes

Saber Salim, Klaus Anhalt, Dieter Taubert, and Joerg Hollandt

Doc ID: 260368 Received 01 Mar 2016; Accepted 18 Apr 2016; Posted 18 Apr 2016  View: PDF

Abstract: This paper shows the opto-mechanical design of a new filter radiometer built at the Physikalisch-Technische Bundesanstalt (PTB), Germany, for the accurate determination of the thermodynamic temperature of high temperature blackbodies. The filter radiometer is based on a three-element reflection-type trap detector that uses three large active area silicon photodiodes. Its spectral coverage and field-of-view are defined by a detachable narrow-band filter and a diamond-turned precision aperture, respectively. The temperature of the filter radiometer is stabilized using a water-streamed housing and is measured using a thin-film platinum thermometer placed onto the first photodiode element. The trap ‘mount’ has been made as compact as possible, which, together with the large active area of the chosen photodiodes, allows a wide field-of-view. This work presents the design of the filter radiometer and discuses the criteria that have been considered in order for the filter radiometer to suit the application.

Automatic Arc Discharge Technology for Inscribing Long Period Fiber Gratings

Guolu Yin, Jian Tang, Changrui Liao, and Yiping Wang

Doc ID: 260775 Received 07 Mar 2016; Accepted 17 Apr 2016; Posted 18 Apr 2016  View: PDF

Abstract: We experimentally demonstrate an automatic arc discharge technology for inscribing high quality long period fiber gratings (LPFGs) with greatly improved inscription efficiency for both single mode fiber (SMF) and photonic crystal fiber (PCF). The proposed technology was developed by implementing an embedded program in a commercial fusion splicer. In addition, the improved technology employs an ultra-precision motorized translation stage, and the tensioning mass required by conventional technology was eliminated. While hundreds of arc discharges are generally required by conventional technology, only 30 and 60 arc discharges were required to inscribe LPFGs with dip attenuations of 30 and 20 dB for SMF and PCF, respectively.

LD-pumped dual-cavity high power fiber laser emitting at 1150nm employing hybrid gain

Yizhu Chen, jiangming xu, Hu Xiao, Jinyong Leng, and Pu Zhou

Doc ID: 257815 Received 19 Jan 2016; Accepted 17 Apr 2016; Posted 18 Apr 2016  View: PDF

Abstract: We demonstrate a laser-diode pumped dual-cavity high power fiber laser emitting at 1150nm. The laser employs Yb and Raman gain simultaneously. The fiber laser with simple structure achieves high efficiency operation while efficiently suppressing the amplified spontaneous emission and parasitic oscillation. The maximum output power at 1150nm is 110.8W with an optical-to-optical efficiency of 57%. Further power scaling at 1150nm is expected with optimization of the system design.

Speckle reduction algorithm for ultrasound images in complex wavelet domain using genetic algorithm-based mixture model

Muhammad Uddin, Murat TAHTALI, Andrew Lambert, Mark Pickering, Margaret Marchese, and Iain Stuart

Doc ID: 258131 Received 25 Jan 2016; Accepted 16 Apr 2016; Posted 18 Apr 2016  View: PDF

Abstract: Compared with other medical imaging modalities, ultrasound(US) imaging is a valuable way of examining the internal organs of a body, with two-dimensional (2D) imaging the most common technique used in clinical diagnoses. Conventional 2D US imaging systems are highly flexible, cost-effective imaging tools which permit operators to observe and record images of a large variety of thin anatomical sections in real time. Recently, 3D US imaging has also been gaining popularity due to its considerable advantages over 2D US imaging. It reduces dependency on the operator and provides better qualitative and quantitative information for an effective diagnosis. Furthermore, it provides a 3D view which allows the observation of volume information. The major shortcoming of any type of US imaging is the presence of speckle noise. Hence, speckle reduction is vital in providing a better clinical diagnosis. The key objective of any speckle reduction algorithm is to attain a speckle free image, whilst preserving the important anatomical features. In this paper, we introduce nonlinear multi-scale complex wavelet diffusion based algorithm for speckle reduction and sharp edge preservation of 2D and 3D US images. In the proposed method, we use Ryleigh and Maxwell mixture model for 2D and 3D US images respectively where genetic algorithm is used combined with expectation maximisation method to estimate mixture parameters. Experimental results using both 2D and 3D synthetic, physical phantom and clinical data demonstrate that our proposed algorithm significantly reduce speckle noise while preserving sharp edges without discernible distortions. The proposed approach performs better than the state-of-the-art approaches in both qualitative and quantitative measures.

Direct method of 3D imaging using the multiple-wavelengths range-gated active imaging principle

Alexis Matwyschuk

Doc ID: 258239 Received 26 Jan 2016; Accepted 16 Apr 2016; Posted 19 Apr 2016  View: PDF

Abstract: The tomography executed with mono-wavelength active imaging systems uses the recording of several images to restore the 3D scene. Thus, in order to show the depth in the scene, a different color is attributed to each recorded image. Therefore, the 3D restoration depends on the video frame rate of the camera. By using a multiple-wavelengths range-gated active imaging system, it is possible to restore the 3D scene directly in a single image at the moment of recording with a video camera. Each emitted light pulse with a different wavelength corresponds to a visualized zone with a different distance in the scene. The camera shutter opens just once during the light pulses emission with the different wavelengths. So the restoration can be executed in real time with regard to the video frame rate of the camera. From an analytical model and from a graphical approach, we demonstrated the feasibility of this new method of 3D restoration. The non-overlapping conditions between two consecutive visualized zones were analyzed. The experimental test results confirmed these different conditions and validated the theoretical principle to restore directly the 3D scene in a color image with a multiple-wavelengths laser source, a RGB filter and a triggerable intensified camera.

Measurement of mean thickness of transparent-samples using simultaneous phase shifting interferometry with four interferograms

Noel-Ivan Toto-Arellano, VICTOR H. FLORES-MUÑOZ, G. Rodríguez Zurita, A. MARTÍNEZ GARCÍA, Luis García Lechuga, and David Serrano García

Doc ID: 258507 Received 09 Feb 2016; Accepted 15 Apr 2016; Posted 21 Apr 2016  View: PDF

Abstract: In this research a novel interferometric system is reported, which allows the generation of four simultaneous interferograms with phase shifts of π/2, for calculating the mean thickness of static transparent samples. The system consists of three coupled interferometers: a rectangular Sagnac interferometer which generates an interference pattern with crossed circular polarizations, coupled to two Michelson interferometers which operate as a multiplexing system, generating replicas of the interference pattern. The two coupled Michelson interferometers generate four patterns retaining their polarization properties, which allow independent phase shifts by placing each replicated pattern on a linear polarizer, thereby, four interferograms with relative shifts of π/2 are obtained. The optical phase is calculated using the well-known four-step algorithm. With knowledge of the optical phase, different properties of the samples can be calculated or analyzed, in this case, by knowing the refractive index, we can calculate the mean thickness of test objects. The results obtained for static transparent samples are presented. The capability of the system to analyze dynamic events is showed when results for the calculation of OPD of a heat flow are presented.

Absolute distance measurement by multi-heterodyneinterferometry using frequency comb and a cavitystabilizedtunable laser

Hanzhong Wu, FuMin Zhang, tingyang liu, XingHua Qu, and Petr Balling

Doc ID: 258193 Received 26 Jan 2016; Accepted 15 Apr 2016; Posted 25 Apr 2016  View: PDF

Abstract: In this paper, we develop a multi-heterodyne system capable of absolute distance measurement using frequencycomb and a tunable diode laser locked to a Fabry-Perot cavity. Numerous beat components can be obtained bydown converting the optical frequency into the RF region with the multi-heterodyne interferometry. The distancescan be measured via the mode phases with a series of synthetic wavelengths. The comparison with the referenceinterferometer shows an agreement within 1.5 μm for the averages of five measurements, and 2.5 μm for the singlemeasurement, which is at 10-8 level in relative.

Direct optical imaging of structural inhomogeneities in crystalline materials

Alexander Grigorev

Doc ID: 261245 Received 17 Mar 2016; Accepted 15 Apr 2016; Posted 18 Apr 2016  View: PDF

Abstract: A method for optical imaging of structural inhomogeneities in crystalline materials is proposed, based on the differences in the optical properties of the structural inhomogeneity and the homogeneous material near the fundamental absorption edge of the crystalline material. The method can be used to detect defects in both semiconductors and insulators.

Characteristics of light transfer in the connected conical waveguides with the same symmetry axis

Arsen Babajanyan, Shant Araqelyan, Tigran Abrahamyan, and Khachatur Nerkararyan

Doc ID: 259737 Received 19 Feb 2016; Accepted 15 Apr 2016; Posted 15 Apr 2016  View: PDF

Abstract: The propagation of the light trough dielectric-metal-dielectric conical waveguide is described by the coupling modes between internal and external waveguides. The energy pumping from internal to the external waveguide has a resonant behavior and very sensitive to the variations of the system parameters. The simplified model of this process realization is the light flash at the end of conical metal covered tip of the optical fiber that crosses the liquid air interface. Here, as an external waveguide serves the liquid meniscus formed at tip of the optical fiber. In this conditions, the shift of liquid surface by 50 nm toward to tip end brings to significant changes in the transferred radiation power. Ability to register nanometric displacements (nano-vibrations) of the liquid surface opens up new ways to create sensitive sensors for different purposes.

Standard deviation index for stimulated Brillouin scattering suppression with different homogeneity

Yang Ran, Rongtao Su, Pengfei Ma, Xiaolin Wang, Pu Zhou, and Lei Si

Doc ID: 259856 Received 22 Feb 2016; Accepted 15 Apr 2016; Posted 15 Apr 2016  View: PDF

Abstract: We present a new quantitative index of standard deviation to measure the homogeneity of spectral lines in a fiber amplifier system, so as to find the relation between stimulated Brillouin scattering (SBS) threshold and the homogeneity of corresponding spectral lines. Theoretical model is built and simulation framework has been established to estimate the SBS threshold when input spectra with different homogeneity are set. In experiment, by setting the phase modulation voltage to a constant value and the modulation frequency to different values, spectral lines with different homogeneity can be obtained. Experimental results show that SBS threshold increases negatively with the standard deviation of the modulated spectrum, which is in good agreement with the theoretical results. When the phase modulation voltage is confined to 10 V and modulation frequency is set to be 80 MHz, the standard deviation of modulated spectrum equals 0.0051, which is the lowest value in our experiment. Thus, at this time, the relatively highest SBS threshold is achieved. This standard deviation can be a good quantitative index in evaluating the power scaling potential in a fiber amplifier system, which is also a design guideline in suppressing SBS in a better degree.

Multi-fields direct design method for ultrashort throw ratio projection optics with two tailored mirrors

Yunfeng Nie, Ruben Mohedano, Pablo Benitez, Julio Chaves, Juan Carlos Miñano, Thienpont Hugo, and Fabian Duerr

Doc ID: 260915 Received 11 Mar 2016; Accepted 14 Apr 2016; Posted 15 Apr 2016  View: PDF

Abstract: In this work, we present a multi-fields direct design method for an ultrashort throw ratio projection optics. The multi-fields design method allows to directly calculate two freeform mirror profiles, which are fitted by odd polynomials and imported into an optical design program as an excellent starting point. Afterwards, these two mirrors are represented by two rectangular aperture freeform surfaces for further optimization. The final configuration consists of an off-the-shelf projection lens and two freeform mirrors to greatly shorten the regular projection distance from 2m to 48cm for a 78.3 inch diagonal screen. The values of MTF for the optimized freeform mirror system are improved to over 0.6 at 0.5 lp/mm, in comparison with its rotationally symmetric counterpart’s 0.43, and the final distortion is less than 1.5%: showing a very good and well-tailored imaging performance over the entire field of view.

Comparison of Selective Transmitters for Solar Thermal Applications

Robert Taylor, Todd Otanicar, Yasitha Hewakuruppu, and Drew DeJarnette

Doc ID: 261003 Received 11 Mar 2016; Accepted 14 Apr 2016; Posted 14 Apr 2016  View: PDF

Abstract: Solar thermal collectors are radiative heat exchangers. Their efficacy is dictated predominantly by their absorption of short-wavelength solar radiation and, more importantly, by their emission of long-wavelength thermal radiation. In conventional collector designs, the receiver is coated with a selectively absorbing surface (Black Chrome, TiNOx, etc.) which serves both of these aims. As the leading commercial absorber, TiNOx consists of several thin, vapor deposited layers (of metals and ceramics) on a metal substrate. In this technology the solar absorption to thermal emission ratio can exceed 20. If a solar system requires an analogous transparent component – one which transmits the full AM1.5 solar spectrum, but reflects long wavelength thermal emission – the technology is much less developed. Bespoke ‘heat mirrors’ are available from optics suppliers at high cost, but the closest mass-produced, commercial technology is low-e glass. Low-e glasses are designed for visible light transmission and, as such, they reflect up to 50% of available solar energy. To address this technical gap, this study investigated selected combinations of thin films which could be deposited to serve as transparent, selective solar covers. A comparative numerical analysis of feasible materials and configurations was investigated using a non-dimensional metric, termed the ‘Efficiency Factor for Selectivity’ (EFS). This metric is dependent on the operation temperature and solar concentration ratio of the system, so our analysis covered the practical range for these parameters. It was found that thin films of indium tin oxide (ITO) and ZnS-Ag-ZnS provided the highest EFS. Of these, ITO represents the more commercially viable solution for large-scale development. Based on these optimized designs, proof-of-concept ITO depositions were fabricated and compared to commercial depositions. Overall, this study presents a systematic guide for creating a new class of selective, transparent optics for solar thermal collectors.

Spectral-overlap approach to multiframe superresolution image reconstruction

Richard Picard, Edward Cohen, and Peter Crabtree

Doc ID: 252634 Received 27 Oct 2015; Accepted 13 Apr 2016; Posted 15 Apr 2016  View: PDF

Abstract: Various techniques and algorithms have been developed to improve the resolution of sensor-aliased imagery captured with multiple subpixel-displaced frames on an under-sampled pixelated image plane. These de-aliasing algorithms are typically known as multiframe superresolution (SR), or geometric SR to emphasize the role of the focal-plane array. Multiple low-resolution (LR) aliased frames of the same scene are captured and allocated to a common high-resolution (HR) reconstruction grid, leading to the possibility of an alias-free reconstruction, as long as the HR sampling rate is above the Nyquist rate. Allocating LR-frame irradiances to HR frames requires the use of appropriate weights. Here we present a novel approach in the spectral domain to calculating exactly weights based on spatial overlap areas, which we call the spectral-overlap (SO) method. We emphasize that the SO method is not a spectral approach but rather an approach to calculating spatial weights which uses spectral decompositions to exploit the array properties of the HR and LR pixels. The method is capable of dealing with arbitrary aliasing factors and interframe motions consisting of in-plane translations and rotations. We calculate example reconstructed HR images (the inverse problem) from synthetic aliased images for integer and for fractional aliasing factors. We show the utility of the SO-generated overlap-area weights in both non-iterative and iterative reconstructions with known or unknown aliasing factor. We show how the overlap weights can be used to generate the Green’s function (pixel response function) for noniterative de-aliasing. In addition, we show how the overlap-area weights can be used to generate synthetic aliased images (the forward problem). We compare the SO approach to the spatial-domain geometric approach of O’Rourke and find virtually identical high accuracy but with significant enhancements in speed for SO. We also compare the SO weights to interpolated weights and find that the overlap-area weights lead to significantly smaller errors in iterative reconstructions. We consider how the SO method might be extended to account for the influence of the optical transfer function (OTF), more complex or space-variant motions, the registration process, and noise.

Super-resolution imaging of photonic crystals using the dual-space microscopy technique

Darshan Desai, Sanchari Sen, Maksym Zhelyeznyakov, Wedad Alenazi, and Luis Grave de Peralta

Doc ID: 261412 Received 17 Mar 2016; Accepted 13 Apr 2016; Posted 18 Apr 2016  View: PDF

Abstract: We present an experimental implementation of the recently proposed Dual-Space Microscopy (DSM), an optical microscopy technique based on simultaneous observation of an object in the position and momentum spaces, using computer-controlled hemispherical digital condensers. We demonstrate that DSM is capable of resolving structures below the Rayleigh resolution limit.

Improving Centroiding by Super-ResolutionReconstruction of Sodium Layer Density inShack-Hartmann Wavefront Sensors

Alexandre Mello and Daniel Pipa

Doc ID: 255126 Received 10 Dec 2015; Accepted 13 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: Adaptive optics in the new generations of large telescopes, over 24min diameter, presents new challenges.One of them is the spot elongation in Shack-Hartmann wavefront sensors when using laser guide stars.The laser brightness depends on the sodium layer density profile and this is reproduced in the format ofthe elongated spot. The pattern of the spot is a problem for centroiding techniques, and the knowledgeof the sodium layer profile is essential for an adequate centroiding. In this work, we propose a superresolutionreconstruction technique that combines the information available in various low resolutionelongated spots over the sub-apertures of the sensor to obtain a high resolution sodium layer densityprofile that can be used as a reference in centroiding. This is achieved with the information available inthe Shack-Hartmann wavefront sensor only, dispensing with external measurements. Finally, we presentsimulation results of an iterative method that yields a super-resolved sodium layer density profile jointlywith an improved centroiding.

Wavelength calibration model for prism-type echellespectrometer by reversely solving prism’s refractive indexin real time

Zhang Rui, xiaotian li, Yin Lu, jicheng cui, yang jin, sun ci, and ba yin

Doc ID: 256833 Received 05 Jan 2016; Accepted 12 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: In an echelle spectrometer equipped with a prism cross-dispersion element, wavelength calibration is very difficultbecause of the complex, non-linear interaction between the prism and the echelle grating.From the spectrometer geometry and thedispersion equations for the prism and the grating, a detailed mathematical model for wavelength calibration is derived that fits therefractive index of the prism in real time. An expression relating the refractive index, wavelength, and image coordinates is constructed,and standard wavelength sources and image positions are adopted to timely calculate the refractive index which is affected by ambientfactors such as temperature and air pressure. Experimental results indicate that the fitting accuracy of the refractive index in real timeapproaches 10-4,whilethe wavelength accuracy approaches 10-3 nm for the entire spectral range.

Effective parameters for film-free femtosecond laser assisted bioprinting

Hélène DESRUS, Bruno Chassagne, Francois Moizan, Raphael DEVILLARD, Stephane Petit, Rainer Kling, and Sylvain CATROS

Doc ID: 257364 Received 12 Jan 2016; Accepted 12 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: Optimal conditions for femtosecond laser bioprinting set-up are reported on, in terms of numerical aperture and accuracy of focal spot location, for different bioinks to deposit, without using a metallic absorbing layer.

Accurate alignment of optical axes of a biplate using a spectroscopic Mueller matrix ellipsometer

Shiyuan Liu, Honggang Gu, Xiuguo Chen, Hao Jiang, Chuanwei Zhang, and weiqi Li

Doc ID: 258252 Received 26 Jan 2016; Accepted 12 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: The biplate that consists of two single-waveplates made from birefringent materials with their fast axes oriented perpendicular to each other is one of the most commonly used retarders in many optical systems. The internal alignment of the optical axes of the two single-waveplates is a key procedure in the fabrication and application of a biplate to reduce the spurious artifacts of oscillations in polarization properties due to the misalignment error and to improve the accuracy and precision of the systems using such biplates. In this paper, we propose a method to accurately align the axes of an arbitrary biplate by minimizing the oscillations in the characteristic parameter spectra of the biplate detected by a spectroscopic Mueller matrix ellipsometer (MME). We derived analytical relations between the characteristic parameters and the misalignment error in the biplate, which helps us to analyze the sensitivity of the characteristic parameters to the misalignment error and to evaluate the alignment accuracy quantitatively. Experimental results performed on a house-developed MME demonstrate that the alignment accuracy of the proposed method is better than 0.01° in aligning the optical axes of a quartz biplate.

Spatial light coupled into a single-mode fiber by a Cassegrain antenna through atmospheric turbulence

Sichen Lei and zheng ke

Doc ID: 258389 Received 27 Jan 2016; Accepted 12 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: Cassegrains are widely used in free-space optical (FSO) communication. The coupling efficiency and variance of aCassegrain-fiber (single-mode) system distorted by atmospheric turbulence are numerically evaluated using second-orderand fourth-order moments under Von Karman spectrum. Considering the limited cost and size of the equipment, theCassegrain aperture should satisfy DA/ρS ≈7 (ρS approximates the characteristic atmospheric coherence length), and theobscuration ratio should be no more than 0.2.

Modeling absorption spectra for detection of combustion products of jet engines by laser remote sensing

Danila Kashirskii, Olga Voitsekhovskaya, Oleg Egorov, and Olga Shefer

Doc ID: 259976 Received 10 Mar 2016; Accepted 12 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: The absorption spectra of exhaust gases (H₂O, CO, CO₂, NO, NO₂, and SO₂) and aerosol (soot and Al₂O₃) particles were modeled at different temperatures for the first time and suitable spectral ranges were determined for conducting laser remote sensing of the combustion products of jet engines. The calculations were conducted on the basis of experimental concentrations of the substances and sizes of aerosol particles. The temperature and geometric parameters of jet engine exhausts were also taken from the literature. The absorption spectra were obtained using the line-by-line method, making use of the spectral line parameters from the authors’ own high-temperature databases (for NO₂ and SO₂ gases) and HITEMP 2010 database, and taking into account atmospheric transmission. Finally, the theoretical absorption spectra of the exhaust gases were plotted at temperatures of 400 K, 700 K, and 1000 K, and the impact of aerosol particles on the total exhaust spectra was estimated in the spectral ranges suitable for remote sensing applications.

Reshaping of Gaussian light pulses transmittedthrough one-dimensional photonic crystals with twodefect layers

Yuliya Dadoenkova, Nataliya Dadoenkova, Igor Lyubchanskii, and Dmitry Sementsov

Doc ID: 260391 Received 03 Mar 2016; Accepted 12 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: We present a theoretical study of reshaping of sub-picosecond optical pulses in the vicinity of the double-peakeddefect mode frequencies in the spectrum of a one-dimensional photonic crystal with two defect layers and calculatetime delay of the transmitted pulses. We used the transfer matrix method for evaluation of the transmittivityspectra, and the Fourier transform technique for calculation of the transmitted pulses envelopes. The mostconsiderable reshaping of the pulses takes place for pulses with the carrier frequency in the defect mode centerand with the spectrum, wider than the half-width of the defect mode. For the pulses with the carrier frequency atthe low- and high-frequency peaks of the defect mode, reshaping is strong for the twice wider pulses. The maximaltime delay of a spectrally narrow pulse is of the order of the pulse duration and demonstrates extrema at thefrequencies of the defect mode peaks. The time delay of a wide pulse doesn’t depend on the carrier frequency, butis one order of magnitude larger than the pulse duration.

Highly efficient Tm:CaYAlO4 laser in-band pumped bya Raman fiber laser at 1.7 μm

Weichao Yao, Fan Wu, Yongguang Zhao, Hao Chen, Xiaodong Xu, and Deyuan SHEN

Doc ID: 258752 Received 01 Feb 2016; Accepted 11 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: We report on high power and efficient operation of a Tm:CaYAlO4 (Tm:CYA) laser in-band pumped by a Ramanfiber laser at 1.7 μm. Laser characteristics of 4.0 at.% and 6.0 at.% doped Tm:CYA samples are investigated andcompared with both a-cut and c-cut configurations. Up to 6.8 W of output power has been generated at 1968.3 nmusing a 6.0 at.% doped and a-cut Tm:CYA crystal, corresponding to a slope efficiency with respect to incident pumppower of 52.3%. Laser output from both a- and c-cut samples are nearly linearly polarized with the polarizationextinction ratio (PER) reaching 24 dB for the a-cut sample.

Finely-engineered slow light photonic crystalwaveguides for efficient wideband wavelengthindependenthigher-order temporal solitons

Xiujian Li, meicheng fu, Jiali Liao, Zhengzheng Shao, Yuanda Zhang, Xiaochun Wang, and Matthew Matthew

Doc ID: 259080 Received 08 Feb 2016; Accepted 11 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: By orthogonally dual-shifting the air-hole rows in the triangular photonic crystal waveguide, a novel finelyengineeredslow light silicon photonic crystal waveguide is designed for higher-order temporal solitons and ultrashorttemporal pulse compression with a large fabrication tolerance. The engineering of dispersion provides thewaveguide a wide wavelength range with only-low anomalous dispersion covering, which makes the compressionratio wavelength-independent and stable even under ultra-low input pulse energy. The simulation results arebased on nonlinear Schrödinger equation (NLSE) modeling, which demonstrates that the input picosecond pulsesin the broad wavelength range with ultra-low pJ pulse energy can be stably compressed by a factor of 6 to higherordertemporal solitons in a 250 μm short waveguide.

Stochastic dual-plane on-axis digital holographicimaging on irregular surfaces

Fengpeng Wang, Dayong Wang, Lu Rong, Yunxin Wang, and Jie Zhao

Doc ID: 258900 Received 03 Feb 2016; Accepted 11 Apr 2016; Posted 11 Apr 2016  View: PDF

Abstract: An imaging method based on dual-plane on-axis digital holography is proposed for the situation when an object ison the irregular surface of a transparent medium. Light propagation of the object on the uneven surface of themedium is analyzed and simulated. The diffracted pattern of the object is deformed or destroyed by the refractedlight of the medium. Dual-plane on-axis digital holography is used to eliminate the twin-image. In order to retrievethe information lost in the reconstructed image due to destructive interference, the object is illuminated by astochastic beam that is a speckle wave produced by a ground glass. Simulated and experimental results arepresented, to demonstrate that the proposed method can be used for imaging on the irregular surface of atransparent medium.

Analytical Approximation for Photonic Array Modes in 2D Photonic Crystal Lattices

Vladislav Shteeman, Elena Smith, and Amos Hardy

Doc ID: 252196 Received 11 Feb 2016; Accepted 11 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: We present a comprehensive Analytical approximation for array modes (both the modal fields and their associated propagation constants) for the specific class of two-dimensional photonic crystal devices (namely, arrays of coupled waveguides, photonic crystal fibers (PCF), phased laser arrays etc.), where light propagates along the optical axis of the waveguides / lasers and is confined in the transverse plane. The approximation covers rectangular and hexagonal photonic lattices. Our approach allows for a fast (several minutes) and accurate numerical calculation of array modes and photonic band structure of 2D photonic devices, based on those lattices. It also allows for analytical predictions of some optical properties of those devices, such as a spatial distribution of modal envelopes (and, correspondingly, modal area), number of photonic bands, their upper and lower limits and bandwidth. Our computations show close agreement between the results, acquired with the Analytical approximation on the one hand and the standard coupled-mode formalism and the Helmholtz equation on the other hand.

Monolithic fiber end cap collimator for high powerfree-space fiber-fiber coupling

Zilun Chen, Xuanfeng Zhou, Zefeng Wang, and Jing Hou

Doc ID: 260704 Received 07 Mar 2016; Accepted 09 Apr 2016; Posted 11 Apr 2016  View: PDF

Abstract: In this paper, we present the design, build, and test of a monolithic fiber end cap collimator for high power freespacefiber-fiber coupling applications. The collimator is based on a large size fiber end cap and a spherical lensdesign on the output facet. Values of the spot size and working distance are theoretically analyzed based onGaussian approximation and ABCD transmission matrix. The free-space fiber-fiber coupling process is alsoanalyzed for different lens curvature radii and coupling distances. In experiment, a collimated laser beam is gotwith Rayleigh length of about 400 mm. High power laser with 1.1 kW output is tested for the end cap collimatorwhile only heating up by 7 °C at the output facet without actively cooled. Free-space fiber-fiber coupling betweentwo 20/400 μm fibers is achieved based on these collimators with measured coupling loss lower than 0.3 dB.

Multiple-3D-object secure information system basedon phase shifting method and single interference

Nam Kim and Wei-Na Li

Doc ID: 258692 Received 01 Feb 2016; Accepted 09 Apr 2016; Posted 13 Apr 2016  View: PDF

Abstract: We propose a multiple-3D-object secure information system for encrypting multiple three-dimensional (3D)objects based on the 3-step phase shifting method. During the decryption procedure, five phase functions (PFs) aredecreased to three PFs in comparison with our previous method, which implies that one cross beam splitter isutilized to implement the single decryption interference. Moreover, the advantages of the proposed scheme alsoinclude: each 3D object can be decrypted discretionarily without decrypting a series of other objects earlier; thequality of the decrypted slice image of each object is high according to the correlation coefficient values, none ofwhich is lower than 0.95; no iterative algorithm is involved. The feasibility of the proposed scheme is demonstratedby computer simulation results.

Colored adaptive compressed imaging with a singlephotodiode

Weiji He, Yiyun Yan, Huidong Dai, Xingjiong Liu, Guohua Gu, and Qian Chen

Doc ID: 257257 Received 11 Jan 2016; Accepted 08 Apr 2016; Posted 08 Apr 2016  View: PDF

Abstract: The computational ghost imaging (CGI) is mainly about the reconstruction of the grayscale images at present,while there are few researches aiming at the color images. In this paper, we both theoretically andexperimentally demonstrate a colored adaptive compressed imaging method focusing on YUV color space. Theproposed method adequately exploits the sparsity of U, V components in the wavelet domain, the human visualcharacteristics and the interdependence between luminance and chrominance components. The simulationand experimental results reveal that our method not only greatly reduces the measurements required but alsooffers better image quality. As the application of single photodiode increases, our method shows great potentialin many fields.

Temperature controlled photonic nanojet via VO₂ coating

Minghui Hong, Eugene Soh, Mengxue Wu, Guoqiang Gu, and Lianwei CHEN

Doc ID: 260419 Received 07 Mar 2016; Accepted 08 Apr 2016; Posted 08 Apr 2016  View: PDF

Abstract: In this work, a numerical investigation of how temperature can tune the full width at half maximum (FWHM) and working distance (WD) of a photonic nanojet (PNJ) is conducted. Vanadium (IV) Oxide (VO₂), a phase change material, is coated onto the top half surface of a glass microsphere and illuminated with incident light at a wavelength of 800 nm. As VO₂ changes from semi conducting to metallic phase, the refractive index of the VO₂ layer changes at its transition temperature of 68 °C. It is found that a coatingof 75 nm on a 5.0 µm diameter microsphere with a refractive index of 1.50 is the most optimal as it tunes the FWHM the greatest while remaining thin enough to have a high transmission. When temperature is raised from 20 to 90 °C, the FWHM varies from 0.43 to 0.37 µm, corresponding to a 14.0% change. The WD varies from 0.29 to 0.20 µm, corresponding to a 31.0% change. Tunable PNJs have potential applications in tunable nanolithography and imaging.

Cascaded gain fibers for increasing output power and the SBS threshold of narrow linewidth fiber Raman amplifiers

James Nagel, Valery Temyanko, Jeremy Dobler, Mikhail Likhachev, Mikhail Bubnov, Evgeny Dianov, and Nasser Peyghambarian

Doc ID: 259230 Received 10 Feb 2016; Accepted 07 Apr 2016; Posted 08 Apr 2016  View: PDF

Abstract: We show both experimentally and theoretically a method for increasing the stimulated Brillouin scattering (SBS) threshold and output power of narrow linewidth fiber Raman amplifiers. This method employs two or more fibers with varying concentrations of the Raman gain material dopant such as GeO₂ or P₂O₅ in silicate-based glasses, which are cascaded to form an amplifier gain stage, disrupting the buildup of SBS that normally occurs in single continuous fibers. A numerical model is presented which is applicable to arbitrary amplifier systems for gain stage optimization and increased power scaling. We give experimental results for phosphosilicate fibers which agree well with simulation predictions in support of the numerical model used.

All-fiber-integrated linearly-polarized fiber laser delivering 476 μJ, 50 kHz, nanosecond pulses for ultrasonic generation.

Zhang fei, xiaodong Xu, Hailong Yu, Rongtao Su, Wang Xiaolin, and Yang Lijia

Doc ID: 257536 Received 19 Jan 2016; Accepted 06 Apr 2016; Posted 07 Apr 2016  View: PDF

Abstract: We demonstrate a high-energy linearly-polarized pulsed fiber laser for ultrasonic generation based on master oscillator power amplification (MOPA) scheme, which delivers nanosecond pulses with duration of 4.8ns and pulse energy of 476μJ at the repetition rate of 50kHz. The MOPA is seeded by a gain switch semiconductor laser diode at 1064nm. In the Pre-amplification stages, double-pass amplification structure is designed and successfully applied to amplify the low power seed laser for the consideration of suppressing amplified spontaneous emission (ASE), decreasing the number of amplification stages and reducing the nonlinear effects. The highly ytterbium-doped fiber (YDF) is utilized in the Main amplifier to shorten the fiber length and then reducing the fiber nonlinearity. The average power is finally boosted to .8W with corresponding optical to optical efficiency of 66.9% and polarization extinction rate (PER) of ~10.5dB. The corresponding peak power is calculated to be 87.1kW. Finally, the established laser system is successfully used for ultrasonic generation based on line excitation and grating excitation configurations and clear surface acoustic wave (SAW) signals are detected. Greatly potential applications in laser ultrasonic can be foreseen.

10 GHz Pulse Repetition Rate Er:Yb:glass Laser Modelocked with Quantum Dot SESAM

Vesna Markovic, Bojan Resan, Sarah Kurmulis, Ziyang Zhang, Andreas Oehler, Markus Mangold, Thomas Sudmeyer, Ursula Keller, Richard Hogg, and Kurt Weingarten

Doc ID: 259395 Received 18 Feb 2016; Accepted 06 Apr 2016; Posted 07 Apr 2016  View: PDF

Abstract: Semiconductor saturable absorber mirror (SESAM) modelocked high pulse repetition rate (≥10 GHz) diode-pumped solid-state lasers are proven as an enabling technology for high data rate coherent communication systems owing to their low noise and high pulse-to-pulse optical phase-coherence. Compared to quantum well (QW), quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the first 10 GHz pulse repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting 2 ps pulse width from an Er-doped glass oscillator (ERGO). 10 GHz ERGO laser is modelocked with InAs/GaAs QD SESAM with saturation fluence as low as 9 µJ/cm2.

Passive Q-switching of Tm,Ho:KLu(WO4)2 microchip laser by a Cr:ZnS saturable absorber

Josep Maria Serres, Pavel Loiko, Xavier Mateos, Venkatesan Jambunathan, Anatol Yasukevich, Konstantin Yumashev, Valentin Petrov, Uwe Griebner, Magdalena Aguiló, and Francesc Diaz

Doc ID: 260487 Received 04 Mar 2016; Accepted 06 Apr 2016; Posted 07 Apr 2016  View: PDF

Abstract: A diode-pumped Tm,Ho:KLu(WO4)2 microchip laser passively Q-switched with a Cr:ZnS saturable absorber generated an average output power of 131 mW at 2063.6 nm with a slope efficiency of 11% and a Q-switching conversion efficiency of 58%. The pulse characteristics were 14 ns / 9 μJ at a pulse repetition frequency of 14.5 kHz. With higher modulation depth of the saturable absorber, 9 ns / 10.4 μJ / 8.2 kHz pulses were generated at 2061.1 nm corresponding to a record peak power extracted from a passively Q-switched Tm,Ho laser of 1.15 kW. A theoretical model is presented predicting the pulse energy and duration. The simulations are in good agreement with the experimental results.

67.9W high power white super-continuum all- fiber laser source

ge tingwu, Chang Sun, Siyuan Li, Na An, and Zhiyong Wang

Doc ID: 260016 Received 25 Feb 2016; Accepted 06 Apr 2016; Posted 07 Apr 2016  View: PDF

Abstract: We present a high power white super-continuum all-fiber laser source with average power of 67.9W, spectrum ranging from 500nm to 1700nm, spectral width below 10dB flatness exceeding 1000nm (except pump wavelength), and visible waveband energy (before 850nm) occupying about 21% of the total SC power. A 145W high power picosecond pulse fiber laser is designed specially with high repetition frequency of 656MHz in order to reducing the nonlinear effects. Meanwhile, a self-made high power mode field adaptor which can operate stably at hundreds of watts pulse power has 82% high coupling efficiency. To our knowledge, the 67.9W white super-continuum fiber laser source we achieved is the highest reported with such wide and flat optical spectrum.

Stray light effects in above-water remote sensing reflectance from hyperspectral radiometers

Marco Talone, Giuseppe Zibordi, Ilmar Ansko, Andrew Banks, and Joel Kuusk

Doc ID: 259535 Received 16 Feb 2016; Accepted 04 Apr 2016; Posted 07 Apr 2016  View: PDF

Abstract: Stray light perturbations are unwanted distortions of the measured spectrum due to the non-ideal performance of optical radiometers. Because of this, stray light characterization and correction is essential when accurate radiometric measurements are a necessity. In agreement with such a need, this study focused on stray light correction of hyperspectral radiometers widely applied for above-water measurements to determine the remote sensing reflectance (RRS). Stray light of sample radiometers was experimentally characterized and a correction algorithm was developed and applied to field measurements performed in the Mediterranean Sea. Results indicate that mean stray light corrections are appreciable, with values generally varying from -1% to +1% in the 400-700 nm spectral region for downward irradiance and sky radiance, and from -1 to +4% for total radiance from the sea. Mean corrections for data products such as the RRS exhibit values which depend on water type varying between -0.5 and +1% in the blue-green spectral region, with peaks up to 9% in the red in eutrophic waters. In addition, the possibility of using one common stray light correction matrix for the analyzed class of radiometers was investigated. Results centered on RRS support such a feasibility at the expenses of an increment of the uncertainty typically well below 0.5% in the blue-green and up to 1% in the red, assuming sensors are based on spectrographs from the same production batch.

Compact Lensless Digital Holographic Microscopy Using Curved Mirror for Enlarged Working Distance

Ervin Cheng, Joshua Ng, Choo Min Lim, and Weijuan Qu

Doc ID: 257404 Received 13 Jan 2016; Accepted 01 Apr 2016; Posted 08 Apr 2016  View: PDF

Abstract: A concave mirror has been presented to be used in lensless digital holographic microscopy (DHM)system to effectively enlarge the working distance and at the same time maintain the compact size of the whole system. A theoretical analysis of phase compensation between the object wave and the wave reflected from curved reference mirrors are given. Experimental demonstrations of the curved reference mirrors used in the DHM system have been obtained to support our idea.

Enabling high-speed wide-field dynamic imaging inmulti-focal photoacoustic computed microscopy: asimulation study

Hongying Wan, Yihang Zhou, Leslie Ying, Jing Meng, Liang Song, and Jun Xia

Doc ID: 258051 Received 22 Jan 2016; Accepted 29 Mar 2016; Posted 11 Apr 2016  View: PDF

Abstract: Photoacoustic-computed microscopy (PACM) is an emerging technology that employs thousands of optical foci toprovide wide-field high-resolution images of tissue optical absorption. A major limitation of PACM is the slowimaging speed, limiting its usage in dynamic imaging. In this study, we improved the speed through a two-stepapproach. First, we employed compressed sensing with partially known support to reduce the transducer elementnumber, which subsequently improved the imaging speed at each optical scanning step. Second, we use the highspeed low resolution image acquired without microlens array to inform dynamic changes in the high resolutionPACM image. Combining both approaches, we achieved high-resolution dynamic imaging over a wide field.

Automated Spoof-Detection for Fingerprints using Optical Coherence Tomography

Luke Darlow, Leandra Webb, and Natasha Botha

Doc ID: 257585 Received 15 Jan 2016; Accepted 29 Mar 2016; Posted 29 Mar 2016  View: PDF

Abstract: Fingerprint recognition systems are prevalent in high-security applications. As a result, the act of spoofing these systems with artificial fingerprints is of increasing concern. This research presents an automatic means of spoof-detection using Optical Coherence Tomography. This technology is able to capture a 3D representation of the internal structure of the skin, and is thus not limited to a 2D surface scan. The additional information afforded by this representation means that accurate spoof-detection can be achieved. Two features were extracted to detect the presence of: (1) an additional thin layer on the surface of the skin; and (2) a thicker additional layer or a complete artificial finger. An analysis of these features showed that they are highly separable, resulting in 100% accuracy regarding spoof-detection, with no false rejections of real fingers. This is the first attempt at fully-automated spoof-detection using OCT.

Nonlinear optical behavior of porphyrin functionalized nanodiamonds: an efficient material for optical power limiting

olivier muller, Vincent Pichot, Lionel Merlat, Loic Schmidlin, and Denis Spitzer

Doc ID: 256930 Received 07 Jan 2016; Accepted 29 Mar 2016; Posted 07 Apr 2016  View: PDF

Abstract: The nonlinear optical mechanisms and the optical limiting behavior of porphyrin functionalized detonation nanodiamonds are investigated and compared to the conventional detonation nanodiamonds (DNDs). The optical limiting behavior is characterized by means of nonlinear transmittance, Z-scan and scattered intensity measurements when submitted to a nanosecond pulsed Nd:YAG laser operating at the second harmonic wavelength. We found that the largest nonlinear attenuation was observed on the 4, 4’, 4’’, 4’’’ - (porphyrin – 5, 10, 15, 20 – tetrayl) tetrakis benzoic acid (PCOOH) suspension. Using Z-scan experiments, it is shown that nonlinear refraction predominates in the unfunctionalized DND suspension, while nonlinear absorption is the most relevant mechanism in the porphyrin-functionalized DNDs. Furthermore, a stronger backscattered intensity signal is highlighted for the unfunctionalized DNDs through nonlinear scattering measurements.

A Watermarking Scheme for Micro-lens Array basedFour-dimensional Light Field Imaging

Yucheng Lu, Suping You, Wei Zhang, Bo Yang, Runling Peng, and Songlin Zhuang

Doc ID: 260719 Received 07 Mar 2016; Accepted 28 Mar 2016; Posted 28 Mar 2016  View: PDF

Abstract: This paper proposes a watermark scheme for lenslet based light field imaging operating on its four-dimensionalFourier domain. In this scheme, the computational light field of the two-dimensional watermark is obtained at first.A slice of its frequency spectrum is then generated. After that, the watermark is embedded into the host light fieldby slice displacement. The experimental simulations show that the proposed scheme is simple in complexity, whilethe robustness is strong. In addition, it does not bring significant artifacts as well as distortions in the refocusedimage and the depth map.

Refractive index determination by coherence scanning interferometry

Hirokazu Yoshino, Piotr Kaminski, Michael Walls, Roger Smith, and Daniel Mansfield

Doc ID: 257911 Received 20 Jan 2016; Accepted 21 Mar 2016; Posted 22 Mar 2016  View: PDF

Abstract: Coherence scanning interferometry (CSI) is established as a powerful non-contact, three dimensional, metrology technique used to determine accurate surface roughness and topography measurements with sub-manometer precision. The helical complex field (HCF) function is a topographically defined helix modulated by the electrical field reflectance, originally developed for the measurement of thin films. An approach to extend the capability of the HCF function to determine the spectral refractive index of a substrate or absorbing film has recently been proposed. In this paper, we confirm this new capability, demonstrating it on surfaces of silicon, gold and a gold/palladium alloy using silica and zirconia oxide thin films. These refractive index dispersion measurements show good agreement with those obtained by Spectroscopic Ellipsometry.

Based on Point-Line-Face-Body theory preparing Zr65Al7.5Ni10Cu17.5 bulk metallic glasses

Wenxian Wang, Zexin Chang, and Yaqiong Ge

Doc ID: 258018 Received 21 Jan 2016; Accepted 21 Mar 2016; Posted 23 Mar 2016  View: PDF

Abstract: Zr65Al7.5Ni10Cu17.5 bulk metallic glasses was prepared based on point-line-face-body (PLFB) theory with the pre-laid powder method by laser processing, and the thickness of the prepared bulk amorphous alloy was about 1.6mm. The microstructure evolution, phase composition, chemical component distribution and corrosion behavior of the bulk amorphous alloy were investigated. The results showed that the amorphization ratio increased with the increase of the thickness of Zr65Al7.5Ni10Cu17.5 BMGs, furthermore, the volume fraction of amorphous phase in the bottom layer (1st layer), the middle layer (4th layer) and the surface layer (7th layer)was approximately 52%, 66% and 74% respectively. Due to the different thermal cycle during the PLFB forming process, the amorphous and crystallization co-existed in the deposited layers. For the corrosion property, the experiments of potentiodynamic polarization plots, Nyquist plots and the equivalent circuits were performed in 3.5 wt% sodium chloride solution. Attributing to higher amorphization ratio in the surface layer, the 7th layer exhibits better corrosion resistance performance than other layers.

Frequency-tunable metamaterial absorber usingvaractor-loaded fishnet-like resonatorresonator

Sungjoon Lim, Hyung Kim, and Dongju Lee

Doc ID: 259007 Received 04 Feb 2016; Accepted 14 Mar 2016; Posted 26 Apr 2016  View: PDF

Abstract: A frequency-tunable metamaterial absorber is designed with the unit cell consisting of a varactor-loaded fishnetlikeresonator. This geometry allows all cathode and anode pads of the unit cells to be connected to theircounterparts. Hence, only the ends of the periodic structure need to be biased, reducing the complexity of the biasnetwork. The absorber was modeled using a full-wave simulation tool and verified experimentally with a 20 × 20unit-cell prototype. Using free-space measurements, the absorber shows >90% absorption ratio from 3.96 GHz to5.29 GHz with a frequency tuning ratio of 28.7%, when the reverse voltage varied from 0 V to 19 V.

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