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Early Posting

Accepted papers to appear in an upcoming issue

OSA now posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Frequency domain phase noise analysis of dualinjection-locked optoelectronic oscillators

Sajad Jahanbakht

Doc ID: 263908 Received 25 Apr 2016; Accepted 30 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: introduced as a means to achieve very low noise microwaveoscillations while avoiding the large spurious peaks which occur in thephase noise of the conventional single-loop OEOs. In these systems twoOEOs are inter-injection-locked to each other. The OEO with the longeroptical fiber delay line is called the master OEO and the other is calledthe slave OEO. Here a frequency domain approach for simulating thephase noise spectrum of each of the OEOs in a DIL-OEO system ispresented which is based on the conversion matrix approach. Thevalidity of the new approach is verified by comparing its results withpreviously published data in the literature. In the new approach firstlyin each of the master or slave OEOs, the power spectral densities(PSDs) of two white and 1/f noise sources are optimized such that theresulting simulated phase noise of any of the master or slave OEOs inthe free-running state matches the measured phase noise of that OEO.After that the proposed approach is able to simulate the phase noisePSD of both OEOs at the injection-locked state. Because of the shortrun-time requirements, especially compared to previously proposedtime domain approaches, the new approach is suitable for optimizingthe power injection ratios (PIRs), and potentially other circuitparameters, in order to achieve good performance regarding the phasenoise in each of the OEOs. Through various numerical simulations theoptimum PIRs for achieving good phase noise performance arepresented and discussed which are in agreement with the previouslypublished results. This further verifies the applicability of the newapproach. Moreover some other interesting results regarding the spurlevels are also presented.

Multi-User 3D Film on a Time-Multiplexed Side-Emission Backlight System

Yi-Pai Huang, CHIH-HUNG TING, Yu-Cheng Chang, Chun-Ho Chen, and HAN-WEN TSAI

Doc ID: 264506 Received 13 May 2016; Accepted 30 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: The desirable features for a portable 3D display include displaying 2D and 3D images without resolution degradation for multiple users, a 2D/3D switchable functionality, and, in particular, a compact volume. Here, a multi-user 3D film is proposed to combine with a side-emission backlight system that has a directional-sequential light distribution to produce a portable 3D display with these desirable features. According to the simulation and experimental results, the multi-user 3D film successfully uses an inverted trapezoid structure to separate the rays of each light source and increases the number of observers from one to three. Additionally, the specification of the inverted trapezoid structure can be determined via equations for different designated viewing positions of the side observer and for the ratio of light intensities for the central observer and the side observer.

Gravity-immune liquid-filled tunable lens with reduced spherical aberration

pengpeng zhao, Caglar Ataman, and Hans Zappe

Doc ID: 266642 Received 20 May 2016; Accepted 30 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: The performance of uniform-thickness membrane lenses is severely compromised due to the inherent trade-off between spherical aberration for thick-membranes and the sensitivity of thin ones to gravity effects. This problem can be eliminated by engineering the membrane thickness profifile, such that a sufficiently thick membrane can be deformed into a perfect optical surface under uniform pressure load. We present here a membrane-based liquid-tunable aspherical lens capable of diffraction-limited performance at nominal focal length which has two orders-of-magnitude smaller wavefront error compared to conventional tunable lenses, regardless of the lens orientation, by use of a non-uniform thickness profifile of the flexible membrane. The lens has an aperture size of 3 mm, with a nominal focal length of 8mm and a theoretical diffraction-limited tuning range between 7.2mm to 8.8mm. Between 6mm to 12mm, the cut-off frequency remains above 50% of the diffraction limit, demonstrating a drastic reduction in spherical aberration compared to conventional liquid-tunable lenses.

Directional view method for a time-sequential autostereoscopic display with full resolution

Xiao Wei Sun, Zhenfeng Zhuang, Lei Zhang, philip Surman, Song Guo, BIN CAO, and Yuanjin Zheng

Doc ID: 267470 Received 02 Jun 2016; Accepted 30 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: A time-sequential autostereoscopic three-dimensional (3D) display using a set of cylindrical optical elements (COEs) as the backlight steering is proposed. The operation principle of the system and its detailed design approach of the system are described. In our system, the COEs control the direction of the backlight for the proposed system of the user’s right and left views. Additionally, the displayed images can be observed under ambient lighting by implementing the high density light-emitting diode (LED) arrays. Compared to the first-generation array display, the image resolution is greatly improved by the addition of the time multiplexing technique. A prototype system using a set of COEs, LED arrays, two linear Fresnel lenses and an elliptical diffuser is constructed. Here, the directional backlight beams are synchronized with the right and left images alternately displayed on the liquid crystal display (LCD) screen and two convergent viewing zones are formed alternately in front of the user’s eyes, then 3D images are perceived because of persistence of the vision of human eye. The experimental results show that the proposed method is a potential technology for the 3D applications, such as 3D television.

Large-aperture transparent beam-steering screen based on LCMPA

Hongjuan Wang, Oleg YAROSHCHUK, xiangyu zhang, Zhenfeng Zhuang, philip Surman, Xiao Wei SUN, and Yuanjin Zheng

Doc ID: 267850 Received 09 Jun 2016; Accepted 30 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: A large aperture transmissive step-steering screen composed of a liquid crystal micro-prism array (LCMPA) deflector and a 90° twist nematic liquid crystal (TN LC) polarization modulator is developed. The designed 3 inches device provides steering angle of 0.95° that differs from the projected value by only 1.26% and the angular difference caused by dispersion less than 5%. Using two-layer cascaded screens a three direction beam steering system for stereoscopic displays is achieved with a steering step of 0.95°, residual un-desired polarization contrast less than 2% and high optical uniformity.

Revealing the radial modes in vortex beams

Bereneice Sephton, Angela Dudley, and Andrew Forbes

Doc ID: 267851 Received 06 Jun 2016; Accepted 30 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: Light beams that carry orbital angular momentum are often approximated by modulating an initial beam, usually Gaussian, with an azimuthal phase variation to create a vortex beam. Such vortex beams are well defined azimuthally, but the radial profile is neglected in this generation approach. Here we show that a consequence of this is that vortex beams carry very little energy in the desired zeroth radial order, as little as only a few percent of the incident power. We demonstrate this experimentally and illustrate how to overcome the problem by complex amplitude modulation of the incident field.

Harnessing diffraction grating in an in-plane switching cell submitted to zigzag lattice

Vincent Odent, Ernesto Berrios-Caro, and Marcel Clerc Gavilán

Doc ID: 267941 Received 09 Jun 2016; Accepted 30 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: Programmable diffraction gratings are relevant in the optical data processing. One of the adequate device candidates is the In-Plane Switching liquid crystal cell. This technology, developed initially for liquid crystal screens, has been also studied with two inter-digital electrodes, as diffraction grating. Recently, it has been reported the apparition of programmable zigzag wall lattices in an in-plane switching configuration. Here, we report a theoretical and experimental study of programmable diffraction grating in an in-plane switching cell.

An improved method to fully compensate the spatial phase nonuniformity of LCoS devices with a Fizeau interferometer

Qiang Lu, Lei Sheng, Fei Zeng, Shi-jie GAO, and Yanfeng Qiao

Doc ID: 269517 Received 30 Jun 2016; Accepted 30 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: Liquid crystal on silicon (LCoS) devices usually show spatial phase nonuniformity (SPNU) in applications of phase modulation, which comprises the phase retardance nonuniformity (PRNU) as a function of the applied voltage, and inherent wavefront distortion (WFD) introduced by the device itself. We propose a multipoint calibration method utilizing a Fizeau interferometer to compensate SPNU of the device. Calibration of PRNU is realized by defining a grid of 3×6 cells onto the aperture, and calculating phase retardance of each cell versus a gradient gray pattern. With designing an adjusted gray pattern calculated by the calibrated multipoint phase retardance function, compensation of inherent WFD is achieved. The peak to valley value of the residual WFD compensated by multipoint calibration method is significantly reduced from 2.5λ to 0.140λ, while the global calibration method is only 0.364λ. Experimental results of the generated finite-energy 2D Airy beams in Fourier space demonstrate the effectiveness of this multipoint calibration method.

Active thermography inspection of laser scanning head glass contamination

Jiri Skala, Michal Svantner, Jiri Tesar, and Aleš Franc

Doc ID: 269635 Received 30 Jun 2016; Accepted 30 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: Industrial lasers are an expanding technology of welding and other material processing. Lasers are often used withoptical scanning heads which provide more versatility, accuracy and speed. The output part of the scanning head is covered bya protective glass which might get contaminated by various particles from the laser processing. This decreases the transmissivity ofthe glass and it can affect the production quality. The contamination needs to be checked regularly but a visual inspection might notalways be effective. This paper proposes two alternative methods of inspecting the protective glass – flash-pulse activethermography and laser active thermography. They are based on the thermal excitation of the glass and measuring the responsewith an infrared camera. The experimental setup and practical results are described and the advantages and disadvantages arediscussed. The presented methods proved to be effective in detecting the contamination of the glass.

Diffraction and Polarization Effects in Earth Radiation Budget Measurements

James Mahan, Anum Barki, and Kory Priestley

Doc ID: 270297 Received 11 Jul 2016; Accepted 30 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: Thermal radiation emitted and reflected from the Earth and viewed from near-Earth orbit may be characterized by its spectral distribution, its degree of coherence, and its state of polarization. The current generation of broadband Earth radiation budget instruments has been designed to minimize the impacts of diffraction and polarization on science products. Monte-Carlo ray-trace (MCRT) models which treat individual rays as quasi-monochromatic, polarized entities are used to explore the possibility of improving the performance of such instruments by including measures of diffraction and polarization during calibration and operation. Discernible diffraction and polarization sensitivity associated with typical Earth radiation budget instrument design features suggests that the quest for improved accuracy in future Earth radiation budget instruments might need to involve measures of coherence and, perhaps with less urgency, polarization.

Pr3+:YLF mode-locked laser at 640 nm directly pumped by InGaN-diode lasers

Fumihiko Kannari, Kodai Iijima, Ryosuke Kariyama, and Hiroki Tanaka

Doc ID: 270321 Received 12 Jul 2016; Accepted 29 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: We attain stable mode-locking of an InGaN-laser diode pumped Pr3+:YLF laser with pump power of 2.8-W using a semiconductor saturable absorption mirror (SESAM). Maximum averaged output power of 65 mW was obtained with a 45-ps pulse width at a pulse repetition rate of 108 MHz. We also attempted Kerr-lens mode-locking by employing an SF57 glass in a cavity as a Kerr-medium.

Simultaneous interferometric measurement of linear coefficient of thermal expansion and temperature-dependent refractive index coefficient of optical materials

James Corsetti, William Green, Jonathan Ellis, Greg Schmidt, and Duncan Moore

Doc ID: 270170 Received 11 Jul 2016; Accepted 29 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: Characterizing the thermal properties of optical materials is necessary for understanding how to design an optical system for changing environmental conditions. A method is presented for simultaneously measuring both the linear coefficient of thermal expansion and the temperature-dependent refractive index coefficient of a sample interferometrically in air. Both the design and fabrication of the interferometer is presented as well as a discussion of the results of measuring both a steel and a CaF2 sample.

Chirp evaluation of semiconductor DFB lasers through a simple Interferometry-Based (IB) technique

Jacopo Nanni, Marina Barbiroli, Franco Fuschini, Diego Masotti, Jean-Luc Polleux, Catherine Algani, and Giovanni Tartarini

Doc ID: 267968 Received 07 Jun 2016; Accepted 29 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: Direct modulation of the laser source is often utilized in realizing optical fiber connections where lowlevels of the cost of the entire system must be kept. An undesired consequence of this choice is the onsetof the laser frequency chirp effect, which is detrimental in case of either digital or analog links, and must be evaluated with precision in order to perform an accurate design of the whole system. Various methods of evaluation of the chirp parameters have been proposed, and the choice among them is typically done on the basis of the laboratory equipments available at the moment. This paper adds a further element to the set of possible choices, since it presents a method for the evaluation of the adiabatic chirp factor in DFB laser sources, which exploits a simple interferometric scheme, guarantees low cost, and shows, at the same time, good accuracy of the results.

Retrieval of the particle size distribution function from the data of lidar sensing under the assumption of known refractive index

Iogannes Penner, Svetlana Samoilova, and Michael Sviridenkov

Doc ID: 267443 Received 02 Jun 2016; Accepted 29 Aug 2016; Posted 30 Aug 2016  View: PDF

Abstract: We suggest a method for retrieval of the particle size distribution function from the data of vertical lidar sensing. We have used the data obtained at the Zvenigorod AERONET site obtained in 2011–2012, 462 models altogether. For each laser shot both fine (with particle sizes in the range from 0.05 to 0.6 um) and coarse aerosol fractions (from 0.6 to 10 um) were considered, with emphasize on the coarse fraction. The suggested method is the improvement of the Tikhonov method. The Tikhonov method is not optimal for coarse particles, because its stabilizer does not account for and cannot account for the presence of the coarse mode (in fact, the data on the presence of several extrema of the particle size distribution function). The components of the matrix located in quadrants II and IV are sensitive to the change of these parameters. The neglect of this fact will lead again to arbitrariness of estimating the contribution of the coarse particles even for exact values on the main diagonal and two diagonals adjacent to it. The suggested method allows the coarse fraction up to 2.5 um to be determined unambiguously. For larger particles (> 2.5 um) it is recommended to use the available sets of the coefficients, but with level of values to be determined.

Improving wavefront sensing with a Shack-Hartmanndevice

Martin Rais, Jean-Michel Morel, Carole Thiebaut, Jean-Marc Delvit, and Gabriele Facciolo

Doc ID: 269017 Received 24 Jun 2016; Accepted 29 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: In order to achieve higher resolutions, current earth-observation satellites use larger lightweight primarymirrors that can deform over time, impacting on image quality. We evaluated the possibility ofcompensating these deformations directly in the satellite by combining a deformable mirror with aShack-Hartman wavefront sensor (SHWFS). The performance of the SHWFS depends entirely on theaccuracy of the shift estimation algorithm employed, which should be computationally cheap to beexecuted on-board. We analyzed the problem of fast accurate shift estimation in this context and proposea new algorithm, based on a global optical flow method that estimates the shifts in linear time. In ourexperiments, our method proved to be more accurate and stable, as well as less sensitive to noise than allcurrent state-of-the-art methods, permitting a more precise on-board wavefront estimation.

A New Approach To Inverting Backscatter and Scatter from Photon-Limited Lidar Observations

Willem Marais, Robert Holz, Yu Hen Hu, Ralph Kuehn, Edwin Eloranta, and Rebecca Willett

Doc ID: 259412 Received 16 Feb 2016; Accepted 29 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: Atmospheric lidar observations provide a unique capability to directly observe the vertical column of cloud and aerosol scattering properties. However, detector and solar background noise hinder the ability of lidar systems to provide reliable backscatter and extinction (scatter) estimates. Standard methods for solving this inverse problem are only effective with high signal-to-noise ratio observations that are only available at low-resolution in uniform scenes. This paper describes a novel method for solving the inverse problem with high-resolution, lower signal-to-noise ratio observations that are effective in non-uniform scenes. Specifically, the noise associated with photon-counting lidar observations can be modeled using a Poisson distribution, and state-of-the-art tools for solving Poisson inverse problems are adapted to the atmospheric lidar problem. It is demonstrated through photon-counting HSRL (High Spectral Resolution Lidar) simulations that the proposed algorithm yield inverted backscatter and scatter cross-sections (per unit volume) with smaller MSE (Mean Squared Error) values at higher spatial resolutions, compared to the standard approach. A limited case study of real experimental data is also provided where the proposed algorithm is applied on HSRL observations and the inverted optical depths are compared against those of AERONET. In addition, three case studies on real data are also provided to juxtapose the inversion results of the new and the standard approaches.

Tilt performance evaluation of ground settlement sensor configured in a fiber-optic low-coherent interferometer

Pinglei Zhang, Heming Wei, and Jingjing Guo

Doc ID: 262248 Received 20 Apr 2016; Accepted 28 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: Ground settlement (GS) is one of the causes to destroy the durability of the reinforced concrete structures. It could lead to a deteriorationin structural basement and increase the risk of collapse. The methods used for GS monitoring were mostly electronic-based sensors byreading the changes in resistance or resonant frequencies etc. These sensors often bear low accuracy in a long term. Our published workdemonstrated that a fiber-optic low coherent interferometer configured in a Michelson interferometer was designed as a GS sensor and amicro-meter resolution in the room environment was approached. However, the designed GS sensor, which based on a hydraulicconnecting vessel in principle, has to suffer from a tilt degeneration problem due to a strictly vertical requirement in practical installment.Here, we made a designed in the GS sensor based on its robust tilt performance. The experimental tests shown that the sensor can workwell within a ±5°tilt. This could meet the requirements in the most designed GS sensor installments applictaions.

Atmospheric Propagation and Combining of High-Power Lasers: Response to Comments.

William Nelson, Phillip Sprangle, and Christopher Davis

Doc ID: 270071 Received 06 Jul 2016; Accepted 28 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: Response to comments.

Optimization of a dispersion-tuned wavelength-swept fiber laser for optical coherence tomography

Yuya Takubo, Takuma Shirahata, and Shinji Yamashita

Doc ID: 268535 Received 21 Jun 2016; Accepted 27 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: We optimized parameters of the dispersion-tuned wavelength-swept fiber laser by numerically analyzing dynamic characteristics. The optimized laser is experimentally demonstrated and applied to the swept-source optical coherence tomography (SS-OCT) system. Dispersion-tuned wavelength-swept laser (DT-WSL) is an unique tunable fiber laser, whose lasing wavelength can be tuned rapidly without any mechanical tunable filters. Although the wavelength of a DT-WSL can be swept rapidly and widely, the broadening of the instantaneous spectral width at high sweep rate has been a critical drawback for SS-OCT applications. Numerical simulations have shown that higher modulation frequencies for active mode-locking lead to narrower instantaneous spectral widths. However, a lower modulation frequency is needed to achieve a wider wavelength tuning range. Pulse modulation is employed to solve the trade-off between instantaneous spectral width and wavelength tuning range. In this paper, the characteristics of a sinusoidally-modulated and a pulse-modulated DT-WSL are compared numerically and experimentally. The numerical simulation results show that a pulse-modulated laser can achieve spectral widths as narrow as that of the sinusoidally-modulated laser with >5GHz modulation frequency, even when the pulse modulation frequency is as low as 500MHz. We also study the difference in the laser characteristics with different sweep direction and discover that a positive wavelength sweep leads to a narrower instantaneous spectral width. We also experimentally confirmed that pulse-modulation can indeed achieve a narrower spectral width as expected from our numerical simulation results. The pulse-modulated DT-WSL is then used in an SS-OCT system and successfully achieve a coherence length of 1.3mm, whereas that of a sinusoidally-modulated DT-WSL is limited to only 0.7mm. Furthermore, we experimentally compare the performance difference in OCT imaging with different wavelength sweep direction, and the results proved that it is advantageous to apply a positive wavelength sweep, as predicted by our numerical simulation.

Temporal and frequency characteristics of a narrow light beam in sea water

Mikhail Kirillin and Alexander Luchinin

Doc ID: 268538 Received 17 Jun 2016; Accepted 27 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: The structure of a light field in sea water excited by a unidirectional point-sized pulsed source is studied by Monte Carlo technique. The pulse shape registered at the distances up to 120 m from the source on the beam axis and in its axial region is calculated with a time resolution of 1 ps. It is shown that with the increase of the distance from the source the pulse splits into two parts formed by components of various scattering orders. Frequency and phase responses of the beam are calculated by means of the fast Fourier transform. It is also shown that for higher frequencies, the attenuation of harmonic components of the field is larger. In the range of parameters corresponding to pulse splitting on the beam axis, the attenuation of harmonic components in particular spectral range exceeds the attenuation predicted by Bouguer law. In this case, the transverse distribution of the amplitudes of these harmonics is minimal on the beam axis.

Full-field 3D deformation measurement: comparison between speckle phase and displacement evaluation

davood khodadad, Alok Singh, Giancarlo Pedrini, and Mikael Sjodahl

Doc ID: 268826 Received 20 Jun 2016; Accepted 26 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: The objective of this paper is to describe a full field deformation measurement method based on 3D speckle displacements. The deformation is evaluated from the slope of the speckle displacement function that connects the different reconstruction planes. For our experiment, a symmetrical arrangement with four illuminations parallel to the planes (x, z) and (y, z) was used. Four sets of speckle patterns were sequentially recorded by illuminating an object from four directions, respectively. A single camera is used to record the holograms before and after deformations. Digital speckle photography is then used to calculate relative speckle displacements in each direction between two numerically propagated planes. The 3D speckle displacements vector is calculated as a combination of the speckle displacements from the holograms recorded in each illumination direction. Using the speckle displacements, problems associated with phase wrapping are avoided. In our experiment, the procedure is shown to give the theoretical accuracy of 0.17 pixels yielding the accuracy of 2×10-³ in the measurement of deformation gradients.

Overview of Advanced LIGO Adaptive Optics

Aidan Brooks, Benjamin Abbott, Muzammil Arain, Giacomo Ciani, Ayodele Cole, Greg Grabeel, Eric Gustafson, Christopher Guido, Matthew Heintze, Alastair Heptonstall, Mindy Jacobson, Won Kim, Eleanor King, Alexander Lynch, Stephen O'Connor, David Ottaway, Ken Mailand, Guido Mueller, Jesper Munch, Virginio Sannibale, Zhenhua Shao, Michael Smith, Peter Veitch, Thomas Vo, Cheryl Vorvick, and Phil Willems

Doc ID: 269484 Received 07 Jul 2016; Accepted 26 Aug 2016; Posted 26 Aug 2016  View: PDF

Abstract: This is an overview of the adaptive optics used in Advanced LIGO (aLIGO), known as the thermal compensation system (TCS). The thermal compensation system was designed to minimize thermally-induced spatial distortions in the interferometer optical modes and to provide some correction for static curvature errors in the core optics of aLIGO. The TCS is comprised of ring heater actuators, spatially tunable CO2 laser projectors and Hartmann wavefront sensors. The system meets the requirements of correcting for nominal distortion in Advanced LIGO to a maximum residual error of 5.4nm, weighted across the laser beam, for up to 125W of laser input power into the interferometer.

Carbon fiber composites inspection and defect characterization using active infrared thermography: numerical simulation and experimental results

Henrique Fernandes, Hai Zhang, Alisson Figueiredo, Clemente Ibarra-Castanedo, Gilmar Guimarares, and Xavier Maldague

Doc ID: 269596 Received 01 Jul 2016; Accepted 26 Aug 2016; Posted 26 Aug 2016  View: PDF

Abstract: Composite materials are widely used in the industry. One of the reasons is because they have strength and stiffness comparable to metals with the added advantage of significant weight reduction. Infrared thermography (IT) is a safe non-destructive testing (NDT) technique that has a fast inspection rate. In active IT an external heat source is used to stimulate the material being inspected in order to generate a thermal contrast between the feature of interest and the background. In this paper carbon fiber-reinforced polymers (CFRP) are inspected using IT. More specifically, carbon/PEEK (Polyether ether ketone) laminates with square Kapton® inserts of different sizes and at different depths are tested with three different IT techniques: pulsed thermography, vibrothermography and line scan thermography. The finite element method (FEM) is used to simulate the pulsed thermography experiment. Numerical results displayed a very good agreement with experimental results.

Robust infrared small target detection via non-negativity constraint based sparse representation

Minjie Wan, Guohua Gu, Weixian Qian, Kan Ren, and qian Chen

Doc ID: 270787 Received 19 Jul 2016; Accepted 26 Aug 2016; Posted 26 Aug 2016  View: PDF

Abstract: Infrared (IR) small target detection is one of the vital techniques in many military applications, including IR remote sensing, early warning and IR precise guidance. Over-complete dictionary based sparse representation is an effective image representation method which can capture geometrical features of IR small targets by the redundancy of the over-complete dictionary. In this paper, a robust infrared small target detection method motived by sparse representation is presented. First, a frequency saliency detection based pre-processing is developed to extract suspected regions that may possibly contain the target so that the subsequent computing load is decreased. Second, a target over-complete dictionary is constructed by a varietal two-dimensional Gaussian model which has an extent feature constraint and takes background effects into consideration simultaneously. Third, a sparse representation model with a non-negativity constraint is proposed for the suspected regions to calculate the corresponding coefficient vectors. Fourth, the detection problem is skillfully converted to an l1-regularized optimization via an accelerated proximal gradient (APG) method. Finally, based on the distinct sparsity difference, an evaluation index called sparse rate (SR) is presented to extract the real target by an adaptive segmentation directly. Large numbers of experiments demonstrate both effectiveness and robustness of our method.

A Highly Sensitive Raman System for Dissolved Gas Analysis in Water

Yang Dewang, Jinjia Guo, Qingsheng Liu, Zhao Luo, Jingwen Yan, and Ronger Zheng

Doc ID: 269272 Received 27 Jun 2016; Accepted 26 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: The detection of dissolved gases in seawater plays an important role in ocean observation and exploration. As a potential technique for oceanic applications, Raman spectroscopy has already proved its advantages in simultaneous detection of multiple species during previous deep sea explorations. Due to the low sensitivity of conventional Raman measurements, there were many reports of Raman application on direct seawater detection in high concentration areas, but few on undersea dissolved gas detection. In this work, we have presented a Highly Sensitive Raman Spectrometer (HSRS) prototype with a special designed gas chamber for small amount of underwater gas extraction. Systematical experiments have been carried out for system evaluation, and the results have shown that the Raman signals obtained by the innovation of near concentric cavity was about 21 times stronger than those of conventional single-pass Raman measurements. Based on this prototype, we have achieved a low limit of detection (LOD) of 2.32 and 0.44 μmol/L for CO₂ and CH₄ respectively in the lab. A test-out experiment has also been accomplished with a gas-liquid separator coupled to the Raman prototype, and signals of O₂ and CO₂ were detected after one hour of degasification. This system has shown new potentials of Raman spectroscopy in ocean observation, and further work would be done for the improvement of in-situ detection.

Quantitative measurement of dynamic nano-strain based on Φ-OTDR

Xi Chen, Yong Kang Dong, Erhu Liu, cheng fu, Hongying Zhang, and Zhiwei Lu

Doc ID: 270684 Received 26 Jul 2016; Accepted 25 Aug 2016; Posted 29 Aug 2016  View: PDF

Abstract: A sensing system is proposed for quantitative measurement of large-range dynamic nano-strain based on phase-sensitive optical time domain reflectometer (Φ-OTDR), where the coherent detection and IQ demodulation methods are employed to demodulate both the phase and the amplitude of the Rayleigh scattering light in real-time. A nano-positioning translation stage is utilized to apply precise nano-strain to fiber. By measuring phase differences between two adjacent sections, the quantitative nano-strain with a large measurement range is demonstrated; while it is also a novel method to measure the strain-parameter of refractive index. For the Panda polarization-maintaining fiber under test in the experiment, the strain parameter of phase is measured to be 8.714 mrad/(nε·m), while the strain parameter of refractive index is measured to be -0.3751 ε-¹. As a proof of the concept, the dynamic strain sensing with a range of 10-1000 nε is experimentally demonstrated, and the strain resolution is 1 nε or 2 nε corresponding to 5 m or 2.5 m spatial resolution, respectively. The experimental measurement also shows a triangular wave with a 12-Hz vibrating frequency and a 100-nε strain amplitude as well as a 188-Hz resonant signal of the tensile section.

Spectral design methods for multi-channel LED lightsources based on differential evolution algorithm

fuzheng zhang, Haisong Xu, and Zhehong Wang

Doc ID: 269122 Received 24 Jun 2016; Accepted 25 Aug 2016; Posted 26 Aug 2016  View: PDF

Abstract: The methods were proposed to design the spectra of light sources with multi-channel LEDs based on differentialevolution (DE) algorithm. Specifically, to produce a desired illuminance level while matching a specific spectrum, amatching method combining the DE algorithm and photometry was verified by matching CommissionInternationale de l’Eclairage (CIE) standard illuminant A and D65 at the two desired illuminance levels (500 and1000 lx) with a multi-channel LED array. Furthermore, considering that correlated color temperature (CCT),illuminance, and color rendering are of practical importance to general lighting, on the basis of photometry andcolorimetry, the DE algorithm integrating a mechanism dealing with constraints was developed to optimize CIEgeneral color rendering index of light sources under a joint target of CCT and illuminance. Sixteen selected targets(eight CCTs from 2800 to 6500 K at 500 and 1000 lx, respectively) were realized with the LED array. The resultsindicate that the relative errors of CCT and illuminance are less than 0.7% and 1.5%, respectively, while achievingexcellent or even perfect color rendering. These methods also enable a practical tool for smart and dynamiclighting.

Optical nonsubsampled contourlet transform

Liang Han, Wenli Zhang, Xiujuan Pu, Wanqi Chen, and Xia Liu

Doc ID: 270163 Received 08 Jul 2016; Accepted 25 Aug 2016; Posted 26 Aug 2016  View: PDF

Abstract: The nonsubsampled contourlet transform(NSCT) is a fully shift-invariant, multiscale, and multidirection expansion and implemented in optics using the Fourier transform of its filters. In this paper, we propose a novel optical NSCT filter design method and the corresponding post-processing method to avoid the use of holographic techniques. The novel optical NSCT filter has real and non-negative Fourier transform. The input image is placed in input plane of 4f correlator and these real and non-negative Fourier transform NSCT filters are placed in the Fourier transform plane of 4f correlator respectively. Then the NSCT result is captured by CCD in output plane of 4f correlator and its perfect reconstruction is theoretically possible, which are demonstrated by both simulation and optical experiment.

Nonsubsampled contourlet transform method for optical fringe pattern analysis in profilometry and interferometry

Sikun Li, Xiangzhao Wang, Feng Tang, Yang Bu, and Osami Sasaki

Doc ID: 269110 Received 24 Jun 2016; Accepted 25 Aug 2016; Posted 25 Aug 2016  View: PDF

Abstract: A method based on nonsubsampled contourlet transform, which is an overcomplete transform with multiresolution, directionality and shift-invariance properties, is proposed to extract the fundamental frequency component of an optical fringe pattern in profilometry and interferometry. The nonsubsampled contourlet transform method overcomes the disadvantages of the original contourlet transform method, which lacks of shift-invariance property, as well as improves the frequency selectivity. A strategy is developed to automatically determine the optimal decomposition scale for removing the background intensity and suppressing the noise of the fringe pattern. The proposed method is precise, effective and possesses a strong noise immune ability. Simulations and experiments verify the validity, and show the superiorities of the proposed method.

Femtosecond pulse generation with an a-cut Nd:CaYAlO4 disordered crystal

shande Liu, Lulu Dong, Yan Xu, Xiao Zhang, Tingqi Ren, Xiaodong Xu, Yandong Peng, Yuping Zhang, huiyun zhang, Dehua Li, Baitao Zhang, and Jingliang He

Doc ID: 269327 Received 27 Jun 2016; Accepted 25 Aug 2016; Posted 25 Aug 2016  View: PDF

Abstract: We experimentally demonstrated a diode-pumped 587 fs ultrafast laser by using an a-cut Nd:CaYAlO4 crystal. Pumped by an 808 nm fiber-coupled laser diode, a stable continuous-wave mode-locked ultrafast laser was achieved with a semiconductor saturable absorber. The ultrafast pulses had a repetition rate of 75 MHz at the center wavelength of 1080.8 nm. A maximum average output power of the mode-locked laser reached 375 mW delivering a slope efficiency of 9%.

Statistical accuracy in super resolution optical fluctuation imaging

xuehua wang, danni Chen, Bin Yu, and Hanben Niu

Doc ID: 265232 Received 16 May 2016; Accepted 24 Aug 2016; Posted 24 Aug 2016  View: PDF

Abstract: The super resolution optical fluctuation imaging (SOFI) technique enhances image spatial resolution by calculating the spatiotemporal cumulants of independent stochastic intensity fluctuations of emitters. Ideally, SOFI eliminates any noise that is not correlated over time, but in practice, due to limited data length, the statistical uncertainty of cumulants will affect the continuities and homogeneities of SOFI images. Since variance and signal to noise ratio (SNR) characterize cumulant statistical uncertainty, we determined theoretical expressions for these based on a single dataset. From a simulation of temporal fluctuations of blinking fluorescent emitters, we calculated the quantitative relation between SNR of cumulants and multiple parameters of the blinking signal, such as the on-time ratio, acquisition fame to average blinking rate ratio, sequence length, and photon amplitude, which not only provides a physical interpretation for SOFI phenomena, but also theoretical guidance to achieve optimal practical outcomes.

Laser marking thermal effects on stainless steel microstructure and corrosion properties

Michal Svantner, Martin Kučera, Eva Smazalová, Šárka Houdková, and Radomír Čerstvý

Doc ID: 268212 Received 13 Jun 2016; Accepted 24 Aug 2016; Posted 25 Aug 2016  View: PDF

Abstract: Laser marking is an advanced application of surface optical properties modification. Influence of laser marking processing parameters on stainless steel corrosion properties is shown in this contribution. Processes during the laser beam-surface interaction cause structure and colour changes and can be also responsible for undesirable reduction of corrosion resistance of the surface. Corrosion tests, roughness, microscopic and EDX analyses, GIXRD analyses and ferrite content analyses were carried out. It was found, that the increasing heat input is the most crucial parameter regarding the degradation of stainless steel corrosion resistance. The pulse length and pulse frequency are the other relevant parameters. A correlation between laser processing parameters, GIXRD results, ferrite content and affected surface corrosion resistance was found. Possibilities and limitations of laser marking of stainless steel in the context of its corrosion resistance reduction are discussed.

Robustness of a coherence vortex

Alcenisio Silva, Eduardo Fonseca, and Cleberson Alves

Doc ID: 269153 Received 05 Jul 2016; Accepted 23 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: We study experimentally and theoretically, the behavior of a coherence vortex after its transmission through obstacles. Notably, we find that such vortex survives and preserves its effective topological charge. Despite suffering changes on the modulus of the coherence function, these changes disappear along propagation.

Detection and counting of a nanoparticle in liquid flow by self-mixing microchip Yb:YAG laser velocimetry

Takayuki Ohtomo, Kenju Otsuka, and Seiichi Sudo

Doc ID: 269233 Received 27 Jun 2016; Accepted 23 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: We observed the peculiar output waveform of a laser modulated by backscattering light from a single nanoparticle moving in the flow channel using a self-mixing microchip Yb:YAG laser Doppler velocimeter. This modulated waveform superimposed on noise-driven relaxation oscillations and appeared intermittently associated with the passage of a single particle across the laser beam focus. Single particle counting, which obeys the Poisson distribution, was performed successfully over a long period of time. The experimental results have been reproduced by a numerical simulation. The sensitivity to detect a single particle was increased by aligning the light axis of laser beam along the flow direction.

Off-axis digital holographic particle positioning basedon polarization-sensitive wavefront curvatureestimation

Johan Öhman and Mikael Sjodahl

Doc ID: 269569 Received 30 Jun 2016; Accepted 23 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: Poor axial resolution in holographic particle imaging applications makes particle positioning in 3D spacemore complex since the positions are not directly obtained. In this paper we estimate the axial positionof micrometer particles by finding the location where the wavefront curvature from the scattered lightbecomes zero. By recording scattered light at 90◦ using off-axis holography the complex amplitude of thelight is obtained. By reconstruction of the imaged scene a complex valued volume is produced. Fromthis volume phase gradients are calculated for each particle and used to estimate the wavefront curvature.From simulations it is found that the wavefront curvature became zero at the true axial position of theparticle. We applied this metric to track an axial translation experimentally using a telecentric off-axisholographic imaging system with a lateral magnification of M = 1.33. A silicon cube with moldedparticles inside was used as sample. Holographic recordings are performed both before and after a 100μmaxial translation. From the estimated positions it was found that the mean displacement of particlesbetween recordings was 105.0μm with a standard deviation of 25.3μm.

The impact of nonzero boresight pointing errors on the performances of relay-assisted free-space optical communication system over exponentiated Weibull fading channels

Ping Wang, Xiaoxia Liu, Tian Cao, Huihua Fu, Ranran Wang, and Li-xin Guo

Doc ID: 270747 Received 19 Jul 2016; Accepted 23 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: The impact of nonzero boresight pointing errors on the system performances of decode-and-forward protocol based multihop parallel optical wireless communication system is studied. For the aggregated fading channel, the atmospheric turbulence is simulated by exponentiated Weibull model and pointing errors are described by one recently proposed statistical model including both boresight and jitter. The binary phase-shift keying (BPSK) subcarrier intensity modulation-based analytical average bit error rate (ABER) and outage probability expressions are achieved for a non-identically and independently distributed system. The ABER and outage probability are then analyzed with different turbulence strengths, receiving aperture sizes, structure parameters (P and Q), jitter variances and boresight displacements. The results show that aperture averaging offers almost the same system performance improvement with boresight included or not, despite of the values of P and Q. The performance enhancement owing to the increase of cooperative path (P) is more evident with nonzero boresight than that with zero boresight (jitter only), whereas the performance deterioration because of the increasing hops (Q) with nonzero boresight is almost the same as that with zero boresight. Monte Carlo simulation is offered to verify the validity of ABER and outage probability expressions.

Comparative analysis of autofocus functions in digitalin-line phase-shifting holography

Elsa Fonseca, Paulo Fiadeiro, Manuela Pereira, and António Pinheiro

Doc ID: 267006 Received 31 May 2016; Accepted 23 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: Numerical reconstruction of digital holograms relies on a precise knowledge of the original object position. However, there are a number of relevant applications where this parameter is not known in advance and an efficient autofocusing method is required. This paper addresses the problem of finding optimal focusing methods for use in reconstruction of digital holograms of macroscopic amplitude and phase objects, using digital in-line phase-shifting holography in transmission mode. Fifteen autofocus measures,including spatial, spectral and sparsity based methods, were evaluated for both synthetic and experimental holograms. The Fresnel transform and the angular spectrum reconstruction methods were compared. Evaluation criteria included unimodality, accuracy, resolution, and computational cost. Autofocusing under angular spectrum propagation tend to perform better with respect to accuracy and unimodality criteria. Phase objects are, generally, more difficult to focus than amplitude objects. The normalized variance, the standard correlation and the Tenenbaum gradient are the most reliable spatial based metrics, combining computational efficiency with good accuracy and resolution. A good trade-off between focus performanceand computational cost was found for the Fresnelet sparsity method.

25 W/m2 collection efficiency stationary solar-pumped Nd:YAG laser

Dawei Liang, Joana Almeida, and Cláudia Vistas

Doc ID: 267982 Received 09 Jun 2016; Accepted 23 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: A large aspheric fused silica lens was used to couple efficiently the concentrated solar radiation from the focal zone of a 1.5 m diameter primary concentrator into a 4mm diameter, 35mm length Nd:YAG single-crystal rod within a conical pump cavity. 29.3 W continuous-wave laser power was measured, attaining 25.0 W/m2 record-high collection efficiency for a stationary solar laser, corresponding to 119% enhancement over the previous record. Its laser beam figure of merit of 0.04W is 6.25 times higher than that of direct tracking solar laser with 30 W/m2 collection efficiency. Strong dependency of solar laser power on laser resonant cavity length was found.

Off-axis holographic lens spectrum splitting photovoltaic system for direct and diffuse solar illumination conversion

Shelby Vorndran, Benjamin Chrysler, Brian Wheelwright, Roger Angel, Raymond Kostuk, and zachary holman

Doc ID: 268366 Received 20 Jun 2016; Accepted 23 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: A high-efficiency spectrum splitting PV module is described that uses an off-axis volume holographic lens to focusand disperse incident solar illumination to a rectangular shaped high bandgap indium gallium phosphide cellsurrounded by strips of silicon cells. The holographic lens design allows for efficient collection of both direct anddiffuse illumination to maximize energy yield. Volume diffraction characteristics are modeled using rigorouscoupled wave analysis, and system performance is simulated using non-sequential raytracing and PV cell data fromthe literature. Under AM 1.5 illumination conditions the simulated module obtains 30.6% conversion efficiency.This efficiency is a 19.7% relative improvement compared to the more efficient cell in the system (silicon). Themodule is also simulated under a typical meteorological year of direct and diffuse irradiance in Tucson, AZ andSeattle, WA. Compared to a flat panel silicon module, the holographic spectrum splitting module obtains a relativeimprovement in energy yield of 17.1% in Tucson and 14.0% in Seattle. An experimental proof-of-concept volumeholographic lens is also fabricated in dichromated gelatin to verify the main characteristics of the system. The lensobtains an average first-order diffraction efficiency of 85.4% across the aperture at 532 nm.

Methane detection using scattering material as the gas cell

Hongze Lin, Chunsheng Yan, Fei Gao, Yujian Ding, and Sailing He

Doc ID: 268433 Received 16 Jun 2016; Accepted 22 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: A compact methane (CH4) detection system is presented and developed by using an alumina ceramic scattering material as its gas cell. Due to the material’s high scattering performance, the optical path length of the gas cell at 1653.7nm can reach 15.96 cm although its physical length along the light transmission direction is only 0.50cm. The wavelength modulation spectroscopy technique is employed to enhance the detection sensitivity, and the second harmonic gas absorption signal with low noise is detected and processed. The long-term stability of the system is investigated by the Allan deviation analysis method. Detection limits of 4.5 ppm and 2.6 ppm are achieved at averaging times of 20s and 200s, respectively. The dynamic gas exchange performance is also experimentally studied. The experimental results indicate that our system is a good choice for practical applications owing to its small volume, high sensitivity and stability.

Optically stabilized Erbium-fiber comb with hybrid mode-locking and a broad tunable range of repetition rate

Honglei Yang, Xuejian Wu, Hongyuan Zhang, Shijie Zhao, Lijun Yang, Haoyun Wei, and Yan Li

Doc ID: 268940 Received 30 Jun 2016; Accepted 22 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: We present an optically stabilized Erbium-fiber frequency comb with a broad repetition rate tuning range based on a hybrid mode-locked oscillator. We lock two comb modes to narrow-linewidth reference lasers in turn to investigate the best performance of control loops. The control bandwidth of fast and slow piezo-electric transducers reaches 70 kHz, while that of pump current modulation with phase-lead compensation is extended to 32 kHz exceeding laser intrinsic response. Eventually, simultaneous lock of the both loops are realized to totally phase-stabilize the comb, which will facilitate precision dual-comb spectroscopy, laser ranging and timing distribution. In addition, a 1.8-MHz span of the repetition rate is achieved by an automatic optical delay line that is helpful to manufacture a secondary comb with a similar repetition rate. The oscillator is housed in a home-made temperature-controlled box with an accuracy of ±0.02 K, which not only keeps high signal-to-noise ratio of the beat notes with reference lasers, but also guarantees self-start at the same mode-locking every time.

Notch Filtering Using a Multiple Passband AOTF in SWIR Region

Neelam Gupta and Dennis Suhre

Doc ID: 268061 Received 10 Jun 2016; Accepted 22 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: Notch filtering operation was accomplished using a TeO2 AOTF with 16 simultaneous overlapping passbands in the SWIR wavelength region. By switching off specific RF signals applied to the AOTF, laser wavelengths corresponding to the inactive passbands are rejected, providing see-through capability with the remaining wavelengths. The rejection level is determined by leakage through the sidelobes of adjacent passbands, as was shown by theory and corresponding measurements. By switching off multiple passbands near the laser wavelength, the rejection level can be increased at the expense of reduced see-through capability. The AOTF imaging system used a telecentric confocal optics that compensates for AOTF aberrations, which are severe at high sidelobe operation.

Compact fiber optic dual-detection confocal displacement sensor

Hongki Yoo, Dong-Ryoung Lee, Suin Jang, and Min Woo Lee

Doc ID: 267363 Received 07 Jun 2016; Accepted 22 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: We propose a dual-detection confocal displacement sensor (DDCDS) with a compact fiber-based optical probe. This all-fiber-optic sensor probe is simple and robust, since it only requires simple alignment of a gradient refractive index (GRIN) lens and a double clad fiber (DCF). The DDCDS is composed of two point detectors, one coupled to a single mode fiber (SMF) and the other coupled to a multi-mode fiber (MMF), and is used to measure the light intensity from a core and an inner clad of a DCF. The ratio of the axial response curves, measured by the two detectors, can be used to obtain a linear relationship between the axial position of the object plane and the ratio of the intensity signals. We demonstrate the performance of the proposed method by measuring micro-movement and fast vibration.

Intensity-symmetric accelerating caustic beams

zhijun ren, Hongzhen Jin, Huanhuan Dai, and Yile Shi

Doc ID: 267956 Received 07 Jun 2016; Accepted 22 Aug 2016; Posted 23 Aug 2016  View: PDF

Abstract: We construct and generate symmetric accelerating caustic beams (ACBs) using a 3/2-order phase-only mask with elliptical contour based on optical caustics and diffraction theory. ACBs are a type of bimodal accelerating caustic beams with two quasi-constant intensity peaks, very similar to combination of two face-to-face Airy-like beams judging by appearance. Their fundamental optical morphology and force properties of particles in ACBs are subsequently provided. The unique optical properties of ACBs can be exploited for practical uses, such as accelerating electrons and clearing micrometer-sized particles as laser micrometer-sized ‘water pump’ instead of laser micrometer-sized ‘snowblower’ of accelerating Airy beams.

Hybrid algorithm for phase retrieval from a single spatialcarrier fringe pattern

Zhichao Dong and Haobo cheng

Doc ID: 270534 Received 13 Jul 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: A hybrid algorithm is proposed in this study for demodulating a single spatial carrier fringe pattern (FP) of interferometricmeasurement, which essentially combines spatial carrier phase shift (SCPS) method and Fourier transform(FT) method. It firstly extracts three phase-shifted FPs from a single spatial carrier FP, and then employs FTmethod and a subtraction operation to determine the phase shift of three phase-shifted FPs, and finally retrievesthe phase map using a least square phase shift algorithm. The subtraction operation could considerably mitigatethe inherent edge error of FT method, resulting in an increase of accuracy compared with FT method. It also doesnot require the background and modulation amplitude of the spatial carrier FP to be constant, thus it is robust andquite suitable for engineering. The factors that may influence the performance of the proposed algorithm are analyzed,including the random and speckle noise, carrier frequency, the shape of the background and modulationamplitude. The feasibility of the proposed algorithm is validated by two experiments, comparing with temporalphase-shifted method. The proposed algorithm is expected to be used in interferometric measurement under adverseenvironments.

A simple transfer calibration method for CIMEL Sun-Moon photometer: calculating lunar calibration coefficients from sun calibration constants

Kaitao LI, Zhengqiang Li, Donghui LI, Jiuchun YANG, Hua XU, Philippe Goloub, and Stéphane Victori

Doc ID: 268025 Received 09 Jun 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: The CIMEL new technologies allow now both day and night time Aerosol Optical Depths (AOD) measurements.Although the daytime AOD calibration protocols are well established, the accurate and simple nighttime calibrationis still a challenging task. Standard Lunar-Langley and intercomparison calibration methods both require specificconditions in terms of atmospheric stability and site condition. Additionally, the lunar irradiance model has alsosome known limits on its uncertainty. This paper presents a simple calibration method that transfers the direct-Sun calibration constant, V0,Sun, to the lunar irradiance calibration coefficient, CMoon. Our approach is a purecalculation method, independent of site limits, e.g. Moon phase. The method is also not affected by the lunarirradiance model limitations, which is the largest error source of the traditional calibration methods. Besides, thisnew transfer calibration approach is easy to use in the field since CMoon can be obtained directly, once V0,Sun is known.Error analysis suggests that the average uncertainty on CMoon over 440-1640 nm bands obtained with the transfermethod is 2.4-2.8% depending on V0,Sun approaches (Langley or intercomparison), which is comparable with that ofLunar-Langley approach, theoretically. In this paper, the Sun-Moon transfer and the Langley methods arecompared based on site measurements in Beijing and the day-night measurement continuity and performance areanalyzed.

Intensity fluctuations of asymmetrical optical beams in anisotropic turbulence

Yahya Baykal

Doc ID: 268712 Received 17 Jun 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: Intensity fluctuations of asymmetrical optical beams are examined when such beams propagate through anisotropic turbulence.Anisotropic turbulence is modeled by non-Kolmogorov von Kármán spectrum. The variations of the scintillation index are observedagainst the changes in the asymmetry factor of the Gaussian beam, power law exponent of non-Kolmogorov spectrum, anisotropic factorsin the transverse direction, and the link length. It is found that for all the conditions, asymmetry in the optical beam is a disadvantage butthe anisotropy in the atmosphere is an advantage for reducing the intensity fluctuations in an optical wireless communications linkoperating in the atmosphere.

From Image-pair to Computer Generated Hologram for Real-world Scene

Sihao Ding, Siyang Cao, Yuan Zheng, and Robert Ewing

Doc ID: 269339 Received 30 Jun 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: We propose an approach to produce computer generated holograms (CGH) from image-pairs of a real-world scene. The ratio of the 3D physical size of the object is computed from the image-pair to provide the correct depth cue. A multi-layer wavefront recording plane method completed with a two-stage occlusion culling process are carried out for wave propagation. Multiple holograms can be generated by propagating the wave towards the desired angles, to cover the circular-views that are wider than the viewing angle restricted by wave length and pitch size of a single hologram. The impact of the imperfect depth information extracted from the image-pair on CGH is examined. The approach is evaluated extensively on image-pairs of real-world 3D scenes and the results demonstrate that the circular-view CGH can be produced from a pair of stereo images using the proposed approach.

Stripe-shaped apertures in confocal microscopy

Wei Gong, Shuhao Shen, Bingzhao Zhu, Yao Zheng, and Ke Si

Doc ID: 256483 Received 06 Jun 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: It is theoretically verified that, compared with the aperture shapes of previous re-search, when two stripe-shaped apertures are combined in a confocal microscope with a finite-sized pinhole, the axial resolution is improved to a certain extent. Noticing the fact that different stripe shapes can bring about different effects, we also investigate the relationships among resolution, shapes, pinhole size and signal-to-background ratio.

Compact silicon photonic interleaver based on self-coupled optical waveguide

Sinan Lai, Boyu Liu, Xu Zhen, and Jiayang Wu

Doc ID: 264220 Received 09 Jun 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: We propose and experimentally demonstrate a new scheme to realize an on-chip silicon photonic interleaver by using self-coupled optical waveguide (SCOW). Benefiting from high-order filtering property of multi-stage SCOW resonator, the device footprint can be reduced and the fabrication tolerance can also be improved compared to conventional ring-assisted Mach-Zehnder interferometer (MZI) interleavers. The operation principle of the proposed interleaver is theoretically analyzed. The designed device is fabricated on a silicon-on-insulator (SOI) wafer under standard complementary metal oxide semiconductor (CMOS)-compatible fabrication processes. Experimental results show that about 20 dB extinction ratio and 8 dB insertion loss can be achieved in the C-band, verifying the effectiveness of the proposed device as an on-chip interleaver with compact footprint and high extinction ratio.

Ideal luminous efficacy and color spatial uniformity of package-free LED based on packaging phosphor-coated geometry

Tsung-Xian Lee and Chien-Feng Chou

Doc ID: 267181 Received 27 May 2016; Accepted 22 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: This paper presents the optical analysis of the luminous efficacy of radiation (LER) and color spatial uniformity (CSU) of a package-free white LED conducted to boost the LER and improve the CSU simultaneously. According to the simulation results, the main effect on the LER and CSU was the change in the geometrical ratio of phosphor coating. Regardless of the packaging size, when the ratio of the top coating to the sidewall coverage of the phosphor layer thickness was in the range from 0.9 to 1.1, the maximum LER and optimal CSU can be obtained analytically. Besides, effectively increasing the volume of the overall packaging dimension to be 30 times the size of the chip can enable package-free LED to achieve maximum LER without affecting the CSU.

Two-layer anti-reflection coating with mullite and polyimide foam for large-diameter cryogenic infrared filters

Yuki Inoue, Takaho Hamada, Masaya Hasegawa, Masashi Hazumi, Yasuto Hori, Aritoki Suzuki, Takayuki Tomaru, Tomtoake Matsumura, Toshifumi Sakata, Tomoyuki Minamoto, and Tohru Hirai

Doc ID: 270364 Received 11 Jul 2016; Accepted 22 Aug 2016; Posted 25 Aug 2016  View: PDF

Abstract: We have developed a novel two-layer anti-reflection (AR) coating method for large-diameter infrared (IR) filters made of alumina, for the use at cryogenic temperatures in millimeter wave measurements. Thermally-sprayed mullite and polyimide foam (Skybond Foam) are used as the AR material. An advantage of the Skybond Foam is that the index of refraction is chosen between 1.1 and 1.7 by changing the filling factor.Combination with mullite is suitable for wide-band millimeter wave measurements with sufficient IR cutoff capability. We present the material properties, fabrication of a large-diameter IR filter made of alumina with this AR coating method, and characterizations at cryogenic temperatures. This technology can be applied to a low-temperature receiver system with a large-diameter focal plane for next-generation cosmic microwave background (CMB) polarization measurements, such as POLARBEAR-2 (PB-2).

Minimization of temperature for laser cooling of Yb ion-doped crystals

Andrei Ivanov, Yuri Rozhdestvensky, and Evgenii Perlin

Doc ID: 267555 Received 01 Jun 2016; Accepted 21 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: In this paper, quantum mechanical calculations of cooling characteristics for the Yb3+:YLF system with use of the vibronic model of laser cooling are presented. Dynamics of the laser cooling process for the seven-level system of an Yb ion is described by the density-matrix formalism. Dependences of the cooling characteristics on the pump intensity are obtained for various temperatures and absorption coefficients of impurity ions. It is shown that the pump intensity, at which the net cooling power has a maximum, depends on temperature. Thus, choosing the intensities, which correspond to the net cooling power maximum over the entire temperature range, we achieve lower sample temperature at a shorter time than in the case of using the constant intensity throughout the cooling process. Calculations are performed for the parameters of the Yb3+:YLF system.

Detecting defects in marine structures by using eddycurrent infrared thermography

Waldemar Swiderski

Doc ID: 267648 Received 21 Jun 2016; Accepted 21 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: Eddy current infrared (IR) thermography is a new nondestructive testing (NDT) technique used for thedetection of cracks in electro-conductive materials. By combining the well-established inspection methods of eddycurrent NDT and IR thermography, this technique uses induced eddy currents to heat test samples. In this way, IRthermography allows visualization of eddy currents distribution which is distorted in defect sites. The paper discussesthe results of numerical modelling of eddy current IR thermography procedures in application to marine structures.

SNPP VIIRS Polarization Sensitivity Analysis

Junqiang Sun, Xiaoxiong Xiong, Eugene Waluschka, and Menghua Wang

Doc ID: 267776 Received 06 Jun 2016; Accepted 21 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: The Visible Infrared Imaging Radiometer Suite (VIIRS) is one of five instruments onboard the Suomi National Polar-orbiting Partnership (SNPP) satellite that launched from Vandenberg Air Force Base, California, on October 28, 2011. It is a whiskbroom radiometer that provides ±56.28⁰ scans of the Earth view (EV). It has 22 bands, among which 14 are Reflective Solar Bands (RSB). The RSB cover a wavelength range from 410 nm to 2250 nm. The RSB of a remote sensor are usually sensitive to the polarization of incident light. For VIIRS, it is specified that the polarization factor should be smaller than 3% for 412 nm and 862 nm bands and 2.5% for other RSB for the scan angle within ±45⁰. Several polarization sensitivity tests were performed prelaunch for SNPP VIIRS. The first few tests either had large uncertainty or were less reliable, while the last one was believed to provide the more accurate information about the polarization property of the instrument. In this paper, the measured data in the last polarization sensitivity test are analyzed and the polarization factors and phase angles are derived from the measurements for all the RSB. The derived polarization factors and phase angles are band, detector, and scan angle dependent. For near-infrared bands, they also depend on half angle mirror (HAM) side. Nevertheless, the derived polarization factors are all within the specification although the strong detector dependence of the polarization parameters was not expected. Compared to the Moderate Resolution Imaging Spectroradiometer (MODIS) on both Aqua and Terra satellites, the polarization effect on VIIRS RSB is much smaller.

Selective visual attention based clutter metric with HVS adaptability

Bo Zheng, wang xiaodong, Jian Wang, Yang Jiang, and Jingtao Wang

Doc ID: 267063 Received 26 May 2016; Accepted 21 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: Most existing clutter metrics are proposed based on fixed structural features and experienced weight measures. In this paper, we identify the clutter as selective visual attention effects and propose new type of clutter metric. Firstly adaptive structural features are extracted from the blocks with edge-structure similarity to target. Then the confusing blocks are selected by the similarity threshold based on the attention guidance map. The clutter is estimated by quantifying the effects of confusing blocks on target acquisition performance. The comparative field experiments, with Search_2 dataset, show that the proposed metric is consistent with the adaptability of HVS and outperforms other metrics.

A linear approximation of Rayleigh-Brillouin scattering spectra

Ioannis Binietoglou, Paris Giampouras, and Livio Belegante

Doc ID: 269681 Received 05 Jul 2016; Accepted 21 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: Rayleigh-Brillouin scattering is the basis of many remote sensing techniques, including high spectral resolution lidar measurements of aerosols and wind. Rayleigh-Brillouin spectra can be accurately estimated using models like the so-called Tenti's S6 and Pan's S7 models. Unfortunately, these are computationally expensive and can be the bottleneck for real-time lidar processing and iterative parameter estimation problems. This short article describes a very efficient linear approximation of the Rayleigh-Brillouin spectra based on Principal Component Analysis (PCA). Using PCA, the outputs of the above models can be approximated with very high accuracy using a single matrix multiplication. The described method can be applied to the output of any detailed scattering model, so it can be used for a wide range of problems, e.g. for scattering from different gases (Air, N₂, O₂, ...) and for different ranges of temperature and pressure. The accuracy of the approximation can be tuned to the requirements of the studied problem, and can easily exceed other uncertainties in the scattering calculations.

Design quadrilateral apertures in binary CGHs of large space bandwidth product

Yunlong Sheng and Jing Wang

Doc ID: 268348 Received 14 Jun 2016; Accepted 21 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: A new approach for designing the binary computer‐generated hologram (CGH) of very large number of pixels is proposed. Diffraction of the CGH apertures is computed by the analytical Abbe transform and considering theaperture edges as the basic diffracting elements. The computation cost is independent of the CGH size. The arbitrary‐shaped polygonal apertures in the CGH consist of quadrilateral apertures, which are designed by assigning the binary phases using the parallel Genetic Algorithm with local search followed by optimizing locations of the co‐vertices with direct search. The design results in high performance with low image reconstruction error.

A Multi-wavelength Laser and its Application in Digital Holography

Staffan Tjörnhammar, Finn Klemming Eklöf, Zhangwei Yu, davood khodadad, Emil Hällstig, Mikael Sjodahl, and Fredrik Laurell

Doc ID: 269459 Received 29 Jun 2016; Accepted 20 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: In this paper we present a tailored multi-wavelength Yb-fiber laser source in the 1.03 µm spectral region for spatially multiplexed digital holographic acquisitions. The wavelengths with bandwidths below 0.1 nm were spectrally separated by approximately 1 nm by employing fiber Bragg gratings for spectral control. As a proof of concept, the shape of a cylindrically shaped object with a diameter of 48 mm was measured. The holographic acquisition was performed in dual-wavelength mode with a synthetic wavelength of 1.1 mm and the accuracy was estimated to 3 % of the synthetic wavelength.

Geometric analysis of influence of fringe directions on phase sensitivities in fringe projection profilometry

Hongwei Guo, ruihua zhang, and Anand Asundi

Doc ID: 269471 Received 30 Jun 2016; Accepted 19 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: In fringe projection profilometry, the phase sensitivity is one of the important factors affecting the measurement accuracy. In this paper, we perform a strict analysis in theory about the dependence of the phase sensitivities on the fringe directions. We use the epipolar geometry as the tool to derive the relationship between the fringe distortions and the depth variations of the measured surface, and further formularize the phase sensitivity as a function of the angle between the fringe direction and the epipolar line. The results reveal that, using the fringes perpendicular to the epipolar lines enables achieving the maximum phase sensitivities; whereas if the fringes have directions along the epipolar lines, the phase sensitivities decline to 0. Based on these results, we suggest the optimal fringes being circular-arc-shaped and centered at the epipole, which enable giving the best phase sensitivities over the whole fringe patterns; and the quasi-optimal fringes being straight and perpendicular to the connecting line between the fringe pattern center and the epipole, which can achieve satisfyingly high phase sensitivities over whole fringe patterns in the situation that the epipole locates far away from the fringe pattern center. Experimental results demonstrate that our analyses are practical and correct, and that our optimized fringes are effective in improving the phase sensitivities and further the measurement accuracies.

Design considerations of high-performance InGaAs/InP single-photon avalanche diodes for quantum key distribution

Jun Zhang, Jian Ma, Bing Bai, Liu-Jun Wang, Cunzhu Tong, Ge Jin, and Jian-Wei Pan

Doc ID: 269901 Received 05 Jul 2016; Accepted 19 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: InGaAs/InP single-photon avalanche diodes (SPADs) are widely used in practical applications requiring near-infrared photon counting such as quantum key distribution (QKD). Photon detection efficiency anddark count rate are the intrinsic parameters of InGaAs/InP SPADs, due to the fact that their performances cannot be improved using different quenching electronics given the same operation conditions. After modeling these parameters and developing a simulation platform for InGaAs/InP SPADs, we investigate the semiconductor structure design and optimization. The parameters of photon detection efficiency and dark count rate highly depend on the variables of absorption layer thickness, multiplication layer thick-ness, excess bias voltage and temperature. By evaluating the decoy-state QKD performance, the variables for SPAD design and operation can be globally optimized. Such optimization from the perspective of specific applications can provide an effective approach to design high-performance InGaAs/InP SPADs.

Temporal characterization of a petawatt class laser in Shen Guang II facility

Xiaoping Ouyang, Yong Cui, Jian Zhu, Bao-Qiang Zhu, and Jianqiang Zhu

Doc ID: 270279 Received 11 Jul 2016; Accepted 19 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: Temporal characterization is important in diagnosis and measurement of a petawatt class laser. The V curve of pulse width versus grating position was obtained by a pulse width measurement with a mirror image configuration. Its temporal range was 18ps with 0.05ps resolution. The pulse contrast between -60ps and -6ps of the petawatt class laser in the SG-II facility was measured within a single shot. The pulse contrast between -91ps and -60ps was also measured after expanding the temporal range. The temporal range of our pulse contrast measurement is 70ps with a dynamic range of 8 orders of magnitude.

High Repetition Rate Ultrashort Pulsed Fiber Ring Laser Using Hybrid Mode-Locking

Xiang Zhang, Hongyu Hu, Wenbo Li, and Niloy Dutta

Doc ID: 268822 Received 20 Jun 2016; Accepted 19 Aug 2016; Posted 22 Aug 2016  View: PDF

Abstract: We propose and demonstrate a hybrid mode-locked erbium-doped fiber ring laser by combining the rational harmonic mode-locking technique and passive mode-locking based on nonlinear polarization rotation (NPR) in a highly nonlinear photonic crystal fiber (PCF). By carefully adjusting the modulation frequency and the polarization controllers (PCs) in the cavity, a 30 GHz pulse train with improved stability and narrower pulse width is generated. The pulse width at 30 GHz using rational harmonic mode locking alone is 5.8 ps. This hybrid scheme narrows the pulse width to 1.9 ps at the repetition rate of 30 GHz. Numerical simulation has been carried out, which shows good agreements with the experimental results.

Modular pump head design of diffused, metal and hybrid pump geometry for diode-side-pumped high power Nd:YAG laser


Doc ID: 268671 Received 21 Jun 2016; Accepted 19 Aug 2016; Posted 19 Aug 2016  View: PDF

Abstract: In this paper we present a comparative study on pump head for high power diode side pumped Nd:YAG laser. Pump head is modular type, which are in the form of discs, with each disc holding three pump diodes kept at 1200 with respect to each other. Unabsorbed pump light from the active medium is reflected by reflectors mounted adjacent to the pump diodes. Performance of high power pump head made of modular discs mounted with specular or diffused type reflectors was studied. Hybrid pump geometry was also investigated where in the pump head is made up of discs loaded with metal and diffused reflectors alternately. The discs are loaded around the active medium in such a way that successive discs are rotated by sixty degrees with respect to each other. Fluorescence profiles, thermal lensing, laser output power and M2 values were studied for pump head made up of metal, diffused and hybrid type reflectors. All the pump heads were studied for three different resonator lengths to maximize the output power with best beam quality. The experimental results show that the diffused reflector based geometry in sixty degree rotated configuration produced maximum output power and best beam quality in terms of M2 value.

Radiation hardening of sol-gel derived silica fiber preforms through fictive temperature reduction

Matthieu Lancry, B. Hari Babu, Nadège Ollier, HICHAM EL HAMZAOUI, Mohamed Bouazaoui, and Bertrand Poumellec

Doc ID: 269811 Received 07 Jul 2016; Accepted 18 Aug 2016; Posted 18 Aug 2016  View: PDF

Abstract: The impact of fictive temperature (Tf) on the evolution of point defects and optical attenuation in non-doped and Er3+-doped sol-gel silica glasses was studied and compared to Suprasil F300 and Infrasil 301 glasses, before and after γ-irradiation. To this aim, sol-gel optical fiber preforms have been fabricated by densification of erbium salt-soaked nanoporous silica xerogels through polymeric sol-gel technique. These γ-irradiated fiber preforms have been characterized by infrared (FTIR), UV-Vis-NIR absorption spectroscopy, electron paramagnetic resonance and photoluminescence measurements. We showed that a decrease in the glass fictive temperature leads to a decrease in the glass disorder and strained bonds. This mainly results in a lower defect generation rate and thus less radiation-induced attenuation in the UV-Vis range. Furthermore, it was found that γ-radiation "hardness" is higher in Er3+-doped sol-gel silica compared to un-doped sol-gel silica and standard synthetic silica glasses. The present work demonstrates an effective strategy to improve the radiation resistance of optical fiber preforms and glasses through glass fictive temperature reduction.

High-power and high-efficiency diode-pumped Nd:LuYAG mixed crystal lasers operating at 939 and 946 nm

Bin Xu, Qin Cui, Jinglong Lan, Zhi Lin, Huiying XU, Zhiping Cai, Xiaodong Xu, Jian Zhang, and Jun Xu

Doc ID: 267913 Received 07 Jun 2016; Accepted 18 Aug 2016; Posted 19 Aug 2016  View: PDF

Abstract: We report on high-performance infrared lasers at 0.94 μm based on quasi-three-level transition of 4F3/2 → 4I9/2 in Nd:LuYAG mixed crystal, for the first time to our knowledge. The maximum output power was achieved to 5.64 W with slope efficiency of about 52.5% at 946 nm. Simultaneous dual-wavelength laser at 939 and 946 nm is also obtained with maximum output power of 3.61 W and slope efficiency of 34.8% by introducing a glass etalon into the cavity. Moreover, a 2.0-W single-wavelength laser at 939 nm can be further attained by suitably tilting the etalon. Finally, thermal focal length of the laser crystal is estimated by using a flat-flat laser cavity.

An Efficient Patch-based Approach for Compressive Depth Imaging

Xin Yuan, Xuejun Liao, and Patrick Llull

Doc ID: 268465 Received 17 Jun 2016; Accepted 18 Aug 2016; Posted 19 Aug 2016  View: PDF

Abstract: We present efficient camera hardware and algorithms to capture images with extended depth of field. The camera moves its focal plane via a liquid lens and modulates the scene at different focal planes by shifting a \emph{fixed} binary mask, with synchronization achieved by using the same triangular wave to control the focal plane and the pizeoelectronic translator that shifts the mask. Efficient algorithms are developed to reconstruct the all-in-focus image and the depth map from a single coded exposure, and various sparsity priors are investigated to enhance the reconstruction, including group sparsity, tree structure, and dictionary learning. The algorithms naturally admits a parallel computational structure due to the independent patch-level operations. Experimental results on both simulation and real datasets demonstrate the efficacy of the new hardware and the inversion algorithms.

Spectral tuning of C-shaped microfiber taper interferometer with a nanosized liquid crysal overlay

Haimei Luo, Changjing Wang, Yinghua Ji, Wen Yuan, Guoping Zhang, Yifan Wang, Zehua Hong, and XianPing Wang

Doc ID: 265307 Received 16 May 2016; Accepted 17 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: In this paper, the tuning characteristics of C-shaped microfiber taper covered with a nanosized high-refractive index (HRI) liquid crystal (LC) layer under different temperatures and electric-field intensities have been theoretically analyzed and experimentally investigated. C-shaped microfiber taper interferometer with a waist diameter of ~3.72 μm is fabricated by using flame brushing technique, followed by bending the transition region of the taper to form a modal interferometer and later by placing a ~200 nm LC layer over the uniform taper waist region. Experimental results indicate that a high-efficiency thermal or electric tuning of LC coated C-shaped microfiber taper interferometer could be achieved. This suggests a potential application of this device as tunable all-fiber photonic devices, such as filters, modulators and sensing elements.

A colorless beat interference cancellation receiver for the orthogonally polarized SSB-OOFDM signal with reduced guard band

Jianxin Ma and Ying Zhang

Doc ID: 267591 Received 02 Jun 2016; Accepted 17 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: In the paper, we have proposed a novel optical orthogonal frequency division multiplexing (OOFDM) link scheme with the colorless beat interference cancellation receiver (BICR) structure for the single-sideband OOFDM (SSB-OOFDM) signal with orthogonally polarized optical carrier and sideband, which is generated by using a polarization modulator and an optical band-pass filter. The BICR, employing only a polarization beam splitter and a balanced photodiode pair, can mitigate colorlessly the signal-signal beat interference (SSBI) induced by the square-law detection in a photodiode and thus the spectral efficiency (SE) is improved by reducing the guard band (GB) between the optical carrier and OOFDM signal. A simulation link for the 40Gbit/s 16-QAM SSB-OOFDM signal with reduced GB is built to demonstrate the feasibility of our proposed scheme. The simulation results indicate that the link has a higher SE compared to the conventional intensity modulation and direction detection scheme and the BICR exhibits a better performance to suppress SSBI according to the error vector magnitude and the constellation diagrams.

GPU acceleration of Monte Carlo simulations for polarized photon scattering in anisotropic turbid media

Hui Ma, Pengcheng Li, Celong Liu, Xianpeng Li, and Honghui He

Doc ID: 268215 Received 16 Jun 2016; Accepted 17 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: In earlier studies, we have developed scattering models and the corresponding CPU based Monte Carlo (MC) simulation programs to study the behavior of polarized photons as they propagate through complex biological tissues. To study the simulation results in high degrees of freedom raised the demand for massive simulation tasks. In this paper, we report a parallel implementation of the simulation program based on the compute unified device architecture (CUDA) running on graphics processing unit (GPU). Different schemes for sphere-only simulations and sphere-cylinder mixture simulations were developed respectively. Diverse optimizing methods were employed to achieve the best acceleration. The final version GPU program is hundreds of times faster than the CPU version. Dependence of the performance on input parameters and precision were also studied. It is shown that using single precision in the GPU simulations results in very limited losses in the accuracy. Consumer level graphics cards, even those in laptop computers, are more cost-effective than the scientific graphics cards for single precision computation.

Method for Predicting Junction Temperature Distribution in High Power Laser Diode Bar

Bongtae Han, Dae-Suk Kim, Caleb Holloway, and Avram Bar-Cohen

Doc ID: 268935 Received 21 Jun 2016; Accepted 17 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: A hybrid experimental/numerical method is proposed for predicting the junction temperature distribution in a high power laser diode (LD) bar with multiple emitters. A commercial water-cooled LD bar with multiple emitters is used to illustrate and validate the proposed method. A unique experimental setup is developed and implemented first to measure the average junction temperatures of the LD bar emitters. After measuring the heat dissipation of the LD bar, the effective heat transfer coefficient of the cooling system is determined inversely. The characterized properties are used to predict the junction temperature distribution over the LD bar under high operating currents. The results are presented in conjunction with the wall-plug efficiency and the center wavelength shift.

Influence of the microstructure geometry of patterned sapphire substrate on the light extraction efficiency of GaN LEDs

Yuh-Jen Cheng, Chien-Ting Kuo, Lung-Hsing Hsu, Bo-Hsin Huang, Hao-chung Kuo, and Chien-Chung Lin

Doc ID: 269005 Received 24 Jun 2016; Accepted 17 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: The influence of the microstructure geometry of patterned sapphire substrate (PSS) on the light extraction efficiency (LEE) of GaN LED is numerically analyzed. Cone structure of various dimensions as well as dome and mixed microstructures are studied. LEE is found to mainly depend on the microstructure surface slope. LEE rises quickly as slope increases and flattens out at slope above 0.6. The scale down of microstructure has little effect on LEE. Light rays are found to travel longer distance in PSS LED, as compared with LEDs grown on flat substrate. Keeping GaN absorption loss low is important for LEE optimization.

Monochromatic Measurements of the JPSS-1 VIIRS Polarization Sensitivity

Jeff McIntire, David Moyer, Steven Brown, Keith Lykke, Eugene Waluschka, Hassan Oudrari, and Xiaoxiong Xiong

Doc ID: 269091 Received 29 Jun 2016; Accepted 16 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: Polarization sensitivity is a critical property that must be characterized for spaceborne remote sensinginstruments designed to measure reflected solar radiation. Broadband testing of the first JointPolar-orbiting Satellite System (JPSS-1) Visible Infrared Imaging Radiometer Suite (VIIRS) showedunexpectedly large polarization sensitivities for the bluest bands on VIIRS (centered between 400 nmand 600 nm). Subsequent ray trace modeling indicated that large diattenuation on the edges of thebandpass for these spectral bands was the driver behind these large sensitivities. Additional testingusing the National Institute of Standards and Technology’s (NIST’s) Traveling Spectral Irradiance andRadiance Responsivity Calibrations Using Uniform Sources (T-SIRCUS) was added to the test programto verify and enhance the model. The testing was limited in scope to two spectral bands at two scan angles;nonetheless, this additional testing provided valuable insight into the polarization sensitivity. Analysishas shown that the derived diattenuation agreed with the broadband measurements to within an absolutedifference of about 0.4 % and that the ray trace model reproduced the general features of the measureddata. Additionally, by deriving the spectral responsivity, the linear diattenuation is shown to be explicitlydependent on the changes in bandwidth with polarization state.

The disparity between online and offline tests in accelerated aging tests of LED lamps under electric stress

wang yao, Lei Jing, Hong-Liang Ke, Hao Jian, Qun Gao, Xiaoxun Wang, Qiang Sun, and Zhi-Jun XU

Doc ID: 270656 Received 15 Jul 2016; Accepted 16 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: The accelerated aging tests under electric stress for one type of LED lamps are conducted, and the differences between online and offline tests of the degradation of luminous flux is studied in this paper. The transformation of the two test modes is achieved with an adjustable AC voltage stabilized power source. Experimental results show that the exponential fitting of the luminous flux degradation in online tests possesses a higher fitting degree for most of lamps, and the degradation rate of the luminous flux by online tests is always lower than that by offline tests. Bayes estimation and Weibull distribution are used to calculate the failure probabilities under the accelerated voltages, and then the reliability of the lamps under rated voltage of 220V is estimated by use of the inverse power law model. Results show that the relative error of the lifetime estimation by offline tests increases as the failure probability decreases, and it cannot be neglected when the failure probability is less than 1 %. The relative errors of lifetime estimation are 7.9%, 5.8%, 4.2% and 3.5%, at the failure probabilities of 0.1%, 1%, 5% and 10%, respectively.

Three-dimensional measurement with light field camera: from disparity map to absolute distance

Peng Yang, Zhaomin Wang, Weijuan Qu, Hongying Zhao, Anand Asundi, Lei Yan, and y y

Doc ID: 268137 Received 30 Jun 2016; Accepted 16 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: A new approach to measure 3D profile of texture object is proposed utilizing light field imaging, in which three keysteps are required: a disparity map is first obtained by detecting the slopes in the epipolar plane image with themulti-label technique; the intrinsic parameters of the light field camera are then extracted by camera calibration;at last, the relationship between disparity values and real distances is built up by depth calibration. In the last step,a linear calibration method is proposed to achieve accurate results. Furthermore, the depth error is alsoinvestigated and compensated by reusing the checkerboard pattern. The experimental results are in goodagreement with the 3D models, and also indicate that the light field imaging is a promising 3D measurementtechnique.

Thermal effects in the DKDP Pockels cells in the 215-300K temperature range

Alexey Starobor and Oleg Palashov

Doc ID: 267860 Received 07 Jun 2016; Accepted 16 Aug 2016; Posted 16 Aug 2016  View: PDF

Abstract: The thermal and electro-optical effects in Pockels cells with DKDP crystals in the 215-300K temperature rangewere investigated. Half-wave voltage decreases linearly with cooling, thereby it reduces 7 times (up to 1 kW) withcooling to 215K. The optical power of the thermally induced lens falls twice on cooling to 215K from 300K;thermally induced depolarization is almost independent on temperature and determined by input radiationpower. A significant reduction of the thermally induced depolarization in DKDP crystal with axis inclined to thepolarization plane of the beam was demonstrated numerically and experimentally. Thus, the DKDP crystals cooledto 215K allow the creation of a low-voltage Pockels cell working with a high average and peak laser power.

The focal length measurement based on Fresnel diffraction from a phase plate

Masoomeh Dashtdar and S. Mohammad Ali Hosseini Saber

Doc ID: 265041 Received 20 May 2016; Accepted 16 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: A method based on the Fresnel diffraction of light from the phase step is introduced for measuring effective focal length (EFL) and back focal length (BFL) of the optical imaging systems. It is shown that, as a transparent plane-parallel plate is illuminated at a boundary region by a monochromatic beam of light, Fresnel diffraction occurs because of the abrupt change in phase imposed by the finite change in refractive index at the plate boundary. Variation of incident angle in convergent (or divergent) beam of light causes the periodic intensity along the central fringe of the diffraction pattern. The measurement of extrema position of the intensity distribution provides the EFL and BFL, accurately. The technique is easy to apply, and can measure a wide range of both positive and negative focal lengths. The measuring setup can be very compact with low mechanical and optical noises. As examples of this technique, the EFLs of five different lenses are experimentally obtained. The results are quite consistent with the values indicated by the lens manufacturer.

Gold Nanobipyramids Q-switched Nd:LGGG eye-safe laser operating at 14 .4 nm

huanian Zhang, Bowen Li, and JIE LIU

Doc ID: 270557 Received 14 Jul 2016; Accepted 15 Aug 2016; Posted 16 Aug 2016  View: PDF

Abstract: The performance of a laser diode (LD) pumped passively Q-switched Nd:LGGG laser at 14 .2 nm with goldNanobipyramids (Au-NBPs) as saturable absorber was demonstrated. The average output power of 125 mW wasobtained at the pump power of 12.2 W, corresponding to an optical-to-optical conversion efficiency of 1.36% and aslope efficiency of 1.78%. The minimum pulse width of 514 ns at the pulse repetition rate of 98.6 kHz was obtainedat the pump power of 12.2 W. To the best of our knowledge, this is the fisrt report focusing on the applications ofgold Nanobipyramids using as saturable absorber for pulse laser operation in eye-safe region.

EXAFS studies on Gd doped ZrO2 thin films deposited by r.f. magnetron sputtering

DIBYENDU BHATTACHARYYA, S Jha, Naba Sahoo, Sk Haque, and S Tripathi

Doc ID: 264496 Received 03 May 2016; Accepted 15 Aug 2016; Posted 16 Aug 2016  View: PDF

Abstract: ZrO2 thin films with 0, 7, 9, 11, 13% Gd doping have been prepared by RF magnetron sputtering and have been characterized by several techniques viz., grazing incidence X-ray diffraction (GIXRD), grazing incidence X-ray reflectivity (GIXR), spectroscopic ellipsometry and optical transmission measurements to probe their structural and optical properties. Extended X-ray absorption fine structure (EXAFS) measurements have also been carried out on the samples at the Zr K-edge and Gd L3-edges. It has been observed that Gd goes to Zr sites up to 9%-11% doping concentration and for Gd doping concentration beyond 11%, Gd precipitates out as a separate Gd2O3 phase. The local structure information surrounding the Zr and Gd sites obtained from the analysis of the EXAFS studies, have also been used to explain the macroscopic optical properties of the samples.

Foveated scanning: dynamic mono-dimensional enlargement of resolved field-of-view in lenses of scanner systems

farhang javaherian and Bizhan Rashidian

Doc ID: 267300 Received 30 May 2016; Accepted 15 Aug 2016; Posted 16 Aug 2016  View: PDF

Abstract: An inconsistency between the circular symmetric geometry of conventional optical imagers and the geometry of long linear sensors used in today line scan cameras results in suboptimal separate design of optics and electronics of scanner systems.Based on the method of foveated optical imaging, a technique named Foveated Scanning (FS) is proposed in this paper. The FS technique is employed to enlarge the one dimensional resolved field of view (RFOV) of conventional lenses and permits optimized performance on a Line-of-Interest (LOI) in the image plane where the opto-electronic sensor is located.The achieved enlargement of RFOV is verified on a proof-of-concept basic telephoto lens. Both MTF analysis and the imaging simulation of a standard target have been performed. Results show a 2-fold increase in RFOV by this technique.

Noise in adaptive interferometric fiber sensors based on population dynamic grating in erbium doped fiber

Serguei Stepanov, Marcos Plata, and Eliseo Hernandez-Hernandez

Doc ID: 267314 Received 31 May 2016; Accepted 15 Aug 2016; Posted 16 Aug 2016  View: PDF

Abstract: Experimental investigations of the main noise sources which limit the sensitivity of the adaptive interferometricall-fiber sensors operating in the communication wavelength region are reported. Adaptive properties (i.e. theauto-stabilization of an optimal operation point of the interferometer) are enabled by the dynamic populationgrating recorded in a segment of the erbium-doped fiber (EDF) at mW scale cw power in the 1480-1560nmspectral range. The utilized symmetric Sagnac configuration with low light internal reflections ensures reducedsensitivity of the sensor to phase noise of the laser, while intensity noise is reduced to insignificant level by thebalanced detection scheme. It is shown that the fluorescence from the erbium ions, excited by the counterpropagatingwaves recording the grating, increases the noise level from the fundamental shot noiseapproximately by factor of 2-3 only. It is also shown that conventional communication DFB semiconductor laserswith MHz linewidth are not suitable for high sensitivity applications of such sensors. Because of inevitable backreflections from the output terminal devices (photodiodes, insulators, circulator..) the above-mentionedfundamental noise level is increased by two orders of magnitude due to high phase noise of the DFB laser.

All-Optical Processes in Double Quantum Dot Structure

Amin Al-Khursan and ektefaa rehman

Doc ID: 268811 Received 20 Jun 2016; Accepted 15 Aug 2016; Posted 16 Aug 2016  View: PDF

Abstract: Ladder-plus-Y double quantum dot (DQD) structure was modeled for all-optical processing by combining the density matrix theory with the pulse width description of the applied pulse. The momentum matrix elements are calculated including wetting layer (WL). Ladder-plus-Y structure exhibits pattern-free output with high bit rate (50Tbps) which is critical in optical communication applications. It is shown that very high ground state occupation with periodic shape for state occupations are critical in obtaining pattern-free eye diagram.

Laser-induced breakdown spectroscopy of liquid solutions: A comparative study on the forms of liquid surface and liquid aerosol

Xiangyou LI, xinyan yang, Lianbo Guo, Jiaming Li, Rongxing Yi, Zhong Qi Hao, Meng Shen, Ran Zhou, Kuohu Li, Yongfeng Lu, and Xiaoyan Zeng

Doc ID: 269345 Received 27 Jun 2016; Accepted 15 Aug 2016; Posted 16 Aug 2016  View: PDF

Abstract: Liquid surface and liquid aerosol as the traditional liquid form for Laser-induced breakdown spectroscopy (LIBS) and inductively coupled plasma (ICP), respectively, have been used to analyze chromium (Cr) and cadmium (Cd) elements using LIBS in liquid solution. The spectral differences, the effect of laser frequency, the accumulated number of laser pulses, and gate delay time, and the quantitative analyses for liquid surface and liquid aerosol were compared. The results showed that, the liquid surface demonstrated a lower plasma threshold, higher optical emission intensity, and higher SNR. Moreover, RSDs of intensities of liquid aerosol are better than those of the liquid surface. Furthermore, quantitative analyses results of Cr I 357.86 nm and Cd I 361.05 nm of liquid surface are close to those of liquid aerosol. The limit of detections (LoDs) of Cr and Cd of liquid surface were 2.764 and 86.869 μg/mL, which were close to 2.847 μg/mL of Cr and 97.635 μg/mL of Cd of liquid aerosol. For both liquid surface and liquid aerosol, the coefficient of determination R2 of the calibration curve for Cr and Cd were above 0.98, and the average RSDs of Cr and Cd of liquid surface were 0.028 and 0.059, which were similar to the 0.024 of Cr and 0.042 of Cd of liquid aerosol. These results suggest that both the liquid surface and aerosol have similar detection ability for water quality monitoring.

Integrated Backlight Module to provide a collimated and uniform planar light source

bingle huang and Tailiang Guo

Doc ID: 263953 Received 25 Apr 2016; Accepted 15 Aug 2016; Posted 15 Aug 2016  View: PDF

Abstract: We introduce a novel integrated backlight module (IBLM), which consists of a compound optical film (COF) and a light guide plate (LGP) without any microstructure. The COF comprises functions of a conventional microstructure that adjusts the emergent light and two cross brightness enhancement films (BEF). The four surfaces of the LGP is coated with highly reflective film. The COF can not only adjust the distribution of the output light by varying the density of the microstructure on the COF, but also can collimate the two cross direction light into the normal direction. The vertical and horizontal full width at half maximum (FWHM) of angular intensity of the IBLM with the proposed COF for the optimal case are of 24 and 14 degrees, respectively. And the spatial uniformity and total optical efficiency of the IBLM reaches 85% and 77.2%, respectively. Comparing with the conventional edge-lit backlight module, the optical efficiency improves to 1.3-times and the on-axis luminance improves to 5.1-times by using the COF backlight module. Most importantly, the proposed film just needs to collocate with a relatively low-cost and easily-manufactured LGP, therefore, the backlight adopting the proposed COF can be extended for large-sized application.

Measurement of reflection phase using thick-gap Fabry Perotetalon

Wing Yim Tam, Tsz Kit Yung, Wensheng Gao, Ho Ming Leung, Qiuling Zhao, and Xia Wang

Doc ID: 267915 Received 07 Jun 2016; Accepted 15 Aug 2016; Posted 15 Aug 2016  View: PDF

Abstract: We report measurement of reflection phase of dielectric (glass) / titanium (Ti) surface in thevisible wavelength using a thick-gap Fabry Perot interferometry technique. Using a two-beaminterference model for the reflection peaks and troughs of the Fabry Perot etalon, we obtain theair-gap spacing of the etalon and, more importantly, the reflection phase of the etalon substrate.We find systematic dependence of the as-measured reflection phase on the air-gap spacing dueto numerical aperture effect of the measuring objective. However, the relative reflection phaseof Ti with respect to glass is independent of the air-gap spacing. As a demonstration of ourapproach in the optical characterization of small metamaterial samples, we also measure thereflection phase of micron-sized 2D Au sawtooth nano-array. The experiment is in goodagreement with model simulation.

To extend depth-of-field for hybrid imaging systems via using both dark and dot point spread functions

Le Nhu

Doc ID: 268883 Received 21 Jun 2016; Accepted 13 Aug 2016; Posted 15 Aug 2016  View: PDF

Abstract: In this paper, we propose one method based on the use of both dark and dot point spread functions (PSFs) toextend depth-of-field in hybrid imaging systems. Two different phase modulations of two phase masks areused to generate both dark and dot PSFs. The quartic phase mask (QPM) is used to generate the dot PSF. Acombined phase mask between the QPM and angle for generating the dark PSF is investigated. Thesimulation images are shown that the proposed method can produce superior to imaging performance ofhybrid imaging systems in extending depth of field.

Dual-wavelength common-path digital holographic microscopy for quantitative phase imaging based on lateral shearing interferometry

Jianglei Di, Ying Li, Min Xie, Jiwei Zhang, Chaojie Ma, Teli Xi, Enpu Li, and Jianlin Zhao

Doc ID: 269955 Received 22 Jul 2016; Accepted 13 Aug 2016; Posted 16 Aug 2016  View: PDF

Abstract: A dual-wavelength common-path digital holographic microscopy based on a single parallel glass plate is presented to achieve quantitative phase imaging, which combines dual-wavelength technique with lateral shearing interferometry. The two illumination laser beams with different wavelengths (λ₁=532nm and λ₂=632.8nm) are reflected by the front and back surface of the parallel glass plate to create the lateral shear and form the digital hologram, and then the hologram is reconstructed to obtain the phase distribution with a synthetic wavelength Λ=3339.8nm. The experimental configuration is very compact with the advantages of vibration resistance and measurement range extension. Experiment results of laser ablated pit, groove and staircase specimens show the feasibility of the proposed configuration.

Developing Integrated Photonic System with a Simple Beamforming Architecture for Phased-Array Antennas

Weimin Zhou, Michael Stead, Steven Weiss, OLUKAYODE OKUSAGA, Lingjun Jiang, Stephen Anderson, and Zhaoran Huang

Doc ID: 269999 Received 08 Jul 2016; Accepted 12 Aug 2016; Posted 15 Aug 2016  View: PDF

Abstract: We have designed a simplified true-time-delay beamforming architecture using integrated photonics for phased-array antennas. This architecture can independently control multiple RF beams simultaneously with only a single tuning-parameter to steer the beam in each direction for each beam. We have made a proof-of-the-principle demonstration of an X-band, 304-elements, fiber-optics-based beamformer for one-dimensional steering in transmission mode. The goal is to develop a semiconductor based integrated photonic circuit so that a 2D beamforming-array for both transmit and receive can be made on a single chip. For that, we have designed a Si based integrated waveguide circuit using two types of “slow-light” waveguide for tunable time-delays for 2-dimensional steering.

Optofluidic 2-D grating volume refractive index sensor

Anirban Sarkar, Shivakiran Bhaktha B.N., and Sugata Khastgir

Doc ID: 266891 Received 24 May 2016; Accepted 11 Aug 2016; Posted 12 Aug 2016  View: PDF

Abstract: We present an optofluidic reservoir with 2-D grating for lab-on-a-chip volume refractive index sensor. The observed diffraction pattern from the device resembles the analytically obtained fringe pattern. The change in the diffraction pattern has been monitored in the far-field for fluids with different refractive indices. Reliable measurement of refractive index variations, with an accuracy of 6 × 10-3 refractive index units, for different fluids establishes the optofluidic device as a potential on-chip tool for monitoring dynamic refractive index changes.

Traceability of solar UV measurements using the Qasume reference spectroradiometer

Gregor Hülsen, Julian Gröbner, Saulius Nevas, Peter Sperfeld, Luca Egli, Geiland Porrovecchio, and Marek Smid

Doc ID: 268096 Received 10 Jun 2016; Accepted 11 Aug 2016; Posted 12 Aug 2016  View: PDF

Abstract: One major objective of the European Joint Research Project "Traceability for surface spectral solarultraviolet (UV) radiation" was to reduce the uncertainty of spectral UV measurements. The measurementinstrument used for this work was the portable UV European reference spectroradiometer QASUME.The calibration uncertainty of this instrument was decreased and validated by a comparison of directcalibrations against a primary standard for spectral irradiance, a high temperature blackbody radiator,and against a reference detector using a spectrally tunable laser as a monochromatic source. The spectralirradiance responsivity of the reference detector is traceable to the primary standard of optical power,realized through a cryogenic radiometer, and to the SI unit of meter.The measuring technique was improved by the construction of a new reference spectroradiometer,QASUMEII. An improved input optics removes the dependences of the measured solar irradiance on theangle of incident for solar zenith angle smaller than 75 degrees. Moreover, a hybrid photon detectionsystem enables continuous tracking of the instrument’s responsivity changes.For both spectroradiometer systems an uncertainty budget was calculated. The improvements havereduced the measurement uncertainties of solar spectral UV irradiance measurements from 4.8 % in 2005to 2.0 % (k=2) in the spectral region above 310 nm. The largest sources of uncertainty were the absolutespectral irradiance responsivity calibration, the angular response uncertainty, and the instrument stabilityusing the hybrid detector, which were reduced from 3.6 % to 1.1 %, from 1.2 % to 0.6 %, and from 0.65 %to 0.4 %, with respect to the situation prior to the project.The new instrument was validated during a four month intercomparison relative to the QASUMEreference. The mean ratio of the solar irradiance scans between the two reference spectroradiometer hasan offset of +0.7 % and a standard deviation of ±1.5 % for wavelength greater than 305 nm - which is wellwithin the combined uncertainty of 3.7 % calculated from the uncertainties of the two systems.

Simulation study of Dual-Space Microscopy

Darshan Desai, Maksym Zhelyeznyakov, Shaima Alanzi, and Luis Grave de Peralta

Doc ID: 268132 Received 16 Jun 2016; Accepted 11 Aug 2016; Posted 12 Aug 2016  View: PDF

Abstract: We explore the convergence of the dual-space microscopy (DSM) phase-recovery algorithm. DSM is an optical microscopy technique based on simultaneous observation of an object in the position and momentum spaces. We present one-dimensional (1D) simulations of this technique, demonstrating that DSM technique is capable to resolve periodic and non-periodic structures with a resolution well below the Rayleigh resolution limit. Using simple and faster 1D version of the full 2D DSM algorithm, we simulated DSM technique for thousands of different samples. Our results demonstrate that the DSM algorithm always converges rapidly to the correct optical disturbance.

Far-field characteristics of the square grooved-dielectric lens antenna for terahertz band

Wei Zeng and Wu Pan

Doc ID: 268578 Received 16 Jun 2016; Accepted 11 Aug 2016; Posted 12 Aug 2016  View: PDF

Abstract: In order to improve the gain and directionality of the terahertz antenna, the square grooved-dielectric lens antenna based on Fresnel zone plate is proposed. First, a diagonal horn which is adopted as the primary feed antenna is designed. Then, the far-field characteristics of the lens antenna is studied by using Fresnel-Kirchhoff diffraction theory and the paraxial approximation. The effects of the full-wave period, the focus diameter ratio, the sub-region and the dielectric substrate thickness on radiation characteristics are studied. The experimental results show that the proposed lens antenna has axisymmetric radiation patterns. The gain is over 26.1dB and the 3dB main lobe beamwidth is lower than 5.6° across the operation band. The proposed lens antenna is qualified for the applications in terahertz wireless communication systems.

Nonuniformity correction for division of focal plane polarimeters with calibration method

Zhang Chao, Luo Haibo, Hui Bin, and Chang Zheng

Doc ID: 268847 Received 24 Jun 2016; Accepted 11 Aug 2016; Posted 12 Aug 2016  View: PDF

Abstract: Division of Focal Plane (DoFP) polarimeters are composed of nanometer polarization elements overlaid upon a focal plane array (FPA) sensor. Manufacturing flaws of polarization grating and each detector in the FPA having a different photo-response can introduce nonuniformity errors when reconstructing the polarization image without correction. A new calibration method is proposed to mitigate nonuniformity errors in the visible waveband. We correct nonuniformity in the form of vector. The correction matrix and offset vector are calculated for the following correction. The performance of the proposed method is compared with the state of the art by employing simulated data and real scenes. Experimental results showed that the proposed method can effectively mitigate nonuniformity errors and achieve better visual results.

Characteristics of spectral lines with crater development during laser-induced breakdown spectroscopy

Xiangyou LI, Kuohu Li, Lianbo Guo, Zhong Qi Hao, Jiaming Li, xinyan yang, Meng Shen, Qingdong Zeng, Yongfeng Lu, and Xiaoyan Zeng

Doc ID: 269626 Received 30 Jun 2016; Accepted 11 Aug 2016; Posted 12 Aug 2016  View: PDF

Abstract: To study the characteristics of spectral lines with crater development during laser-induced breakdown spectroscopy, the changes in the spectral-line intensities of iron (Fe) and chromium (Cr) during the development of crater were investigated. Images of the plasmas formed during crater development were captured, and the temperatures and electron densities of the plasmas were calculated. The results showed that, with the development of crater, the intensities of the ion lines decreased, and the intensities of the atomic lines increased. This is because the plasmas generated in crater have higher initial emission intensity and more rapid cooling with the crater development. These two effects lead to changes in the rate of decrease of ion and atomic line intensity over time. Therefore, the changes in intensities of the ion lines caused by crater development differs from that of the atomic lines.

Harmonics analysis of the photonic time stretch system

Yuan Mei, Boyu Xu, Hao Chi, Tao Jin, Shilie Zheng, Xiaofeng Jin, and Xianmin Zhang

Doc ID: 260698 Received 07 Mar 2016; Accepted 10 Aug 2016; Posted 10 Aug 2016  View: PDF

Abstract: Photonic time stretch (PTS) has been intensively investigated in recent decades due to its potential application to ultra-wideband analog-to-digital conversion. A high-speed analog signal can be captured by an electronic analog-to-digital converter (ADC) with the help of PTS technique which slows down the speed of signal in the photonic domain. Unfortunately, the process of the time stretch is not a linear process due to the nonlinear modulation of the electro-optic intensity modulator in the PTS system, which means the undesired harmonics distortion. In this paper, we present an exact analytical model to fully characterize the harmonics generation in the PTS systems, for the first time to the best of our knowledge. We obtain concise and closed-form expressions for all harmonics of the PTS system with either a single-arm Mach-Zehnder modulator (MZM) or a push-pull MZM. The presented model can largely simplify the PTS system design and the system parameters estimation, such as system bandwidth, harmonics power, time-bandwidth product, and dynamic range. The correctness of the mathematic model is verified by numerical and experimental results.

Model-based restoration using light vein for range-gated imaging system

canjin wang, Tao Sun, Tingfeng Wang, rui wang, Jin Guo, and yuzhen tian

Doc ID: 269505 Received 30 Jun 2016; Accepted 10 Aug 2016; Posted 10 Aug 2016  View: PDF

Abstract: The images captured by airborne range-gated imaging system are degraded by lots of factors such as light scattering, noise, defocus of optical system, atmospheric disturbance, platform vibration and so on. The characteristics of low illumination, few details and high noise make art-of-state restoration method fail. In this article we present a restoration method especially for range-gated imaging system. The degradation process is divided into two parts: static part and dynamic part. For the static part, we establish the physical model of the imaging system according to the laser transmission theory, and estimate the static PSF. For dynamic part, a so-called light vein feature extraction method is presented to estimate the fuzzy parameter of the atmospheric disturbance and platform movement, which make contributions to the dynamic PSF. At last, combined with static and dynamic PSF, an iterative updating framework is used to restore the image. Compared with the state-of-art methods, the proposed method can effectively suppress ringing artifacts and achieve better performance in range-gated imaging system.

Optical amplification and reshaping based on the Peregrine rogue wave

Wang yan, Lijun Song, and Li Lu

Doc ID: 269806 Received 05 Jul 2016; Accepted 10 Aug 2016; Posted 10 Aug 2016  View: PDF

Abstract: Based on the characteristic of the Peregrine rouge wave, the amplification and the reshaping of soliton are investigated. The numerical results show that the amplification and the reshaping of soliton can be realized by injecting a CW and filtering the CW at suitable positions. The combination of continuous wave pump and spectral filter placed suitably in fiber plays a role of amplifier, whichcan be used to long-haul transmission of soliton. As an example, long-haul transmission with four amplification periods is demonstrated.

Proximity Operators for Phase Retrieval

Ferréol Soulez, Eric Thiebaut, Antony Schutz, André Ferrari, Michael Unser, and Frédéric Courbin

Doc ID: 264969 Received 03 Jun 2016; Accepted 10 Aug 2016; Posted 11 Aug 2016  View: PDF

Abstract: We present a new formulation of a proximity operator that generalizesthe projector step for phase retrieval. This proximity operator for noisyintensity measurements can replace the classical``noise free' projection in any projection-based algorithm. It isderived from a maximum likelihood formulation and admits a closed formsolution for both the Gaussian and the Poisson cases. In addition, we extendthese proximity operators to undersampled intensity measurements.To assesstheir performance, these operators are exploited in a classical Gerchberg Saxtonalgorithm. We present numerical experiments showing that the reconstructedcomplex amplitudes with these proximity operators perform always better thanusing the classical intensity projector while their computational overhead ismoderate.

Removal of all mosaic grating errors in a single interferometer system by a phase-difference reference window

yuxian lu, Xiangdong Qi, xiaotian li, haili yu, Shan Jiang, heshig bayan, and Yin Lu

Doc ID: 265116 Received 13 May 2016; Accepted 10 Aug 2016; Posted 11 Aug 2016  View: PDF

Abstract: An interference method to remove all mosaic grating errors using a phase-difference reference window without compensations for coupled mosaic errors or analyzing the far-field diffraction intensity patterns is proposed. The reference window is achieved by adding a small-aperture prism, therefore the incident light on the mosaic gratings contains two incident angles and optical paths, eliminating the uncertainty of longitudinal mosaic error in the interferometer. The mathematical model of the method is established and optical structure is designed. Interference fringes with reference window and alignment process are simulated, and the accuracy for mosaic errors are analyzed. The result shows that our method can eliminate longitudinal mosaic error and all other mosaic grating errors. The accuracy of angle mosaic errors can be less than 1μrad and position mosaic errors can be to nanometer level. Compared with far-field diffraction intensity patterns method, our method reduces the complexity of the optical structure and ensures the measuring accuracy.

Array illumination of Fresnel-Dammann zone plate

Yayao Ma, Chaochao Ye, Jie Ke, Junyong Zhang, Jianqiang Zhu, and Zunqi Lin

Doc ID: 265331 Received 17 May 2016; Accepted 09 Aug 2016; Posted 11 Aug 2016  View: PDF

Abstract: Traditional Dammann grating (DG) is phase-only modulation, and its theoretical foundation is based on the far-fielddiffraction. Here we extend the traditional Fresnel zone plate (FZP) into a Fresnel-Dammann zone plate (FDZP),which is considered as a FZP with Dammann modulation in essence. Different from Dammann grating, a single FDZPcan generate array illumination from near field to far field by means of amplitude-only modulation in the absence ofphase modulation. We then give some array illumination operated in water window to validate the feasibility andvalidity. This kind of wave-front modulation technology can be applied to array focusing and imaging from x-ray toEUV region.

Detection and localization of gold nanoshells inside cells: Near-Field approximation

Mario D'Acunto, Antonio Cricenti, Serena Danti, Simone Dinarelli, Marco Luce, Davide Moroni, and Ovidio Salvetti

Doc ID: 268090 Received 10 Jun 2016; Accepted 09 Aug 2016; Posted 10 Aug 2016  View: PDF

Abstract: The optical properties of metal nanoparticles play a fundamental role for their use in a wide range of applications. In hyperthermia treatment, for example, the gold nanoshells (NSs, dielectric core + gold shell) pre-embedded in a cancer cell absorb energy when exposed to appropriate wavelengths of a laser beam and heat up thus destroying the cancer cell. In this process, nevertheless, the healthy tissues (not targeted by the NSs) along the laser path are not affected; this is because most biological soft tissues have a relatively low light absorption coefficient in the near-infrared (NIR) regions, characteristic known as the tissue optical window. Over such window, NIR light transmits through the tissues with the scattering-limited attenuation and minimal heating avoiding damages to the healthy tissues. As a consequence, the identification of NSs assumed a fundamental role for the further development of such cancer treatment. Recently, we have demonstrated the possibility to identify 100-150nm diameter gold NSs inside mouse cells using a scanning near-optical microscope (SNOM). In this paper, we provide numerical demonstration that the SNOM is able to locate NSs inside the cell with a particle-aperture distance of about 100nm. This result was obtained developing an analytical approach based on the calculation of the dyadic Green function in near-field approximation. The implications of our findings will remarkably affect further investigations on the interaction between NSs and biological systems

FSO System Performance under Atmospheric Scattering and Turbulence for 850 nm and 1550 nm Operation

Amr El-Wakeel, Nazmi Mohammed, and Mostafa Hussein Aly

Doc ID: 267280 Received 01 Jun 2016; Accepted 08 Aug 2016; Posted 09 Aug 2016  View: PDF

Abstract: In this work, a Free Space Optical Communication (FSO) link is proposed and utilized to explore and evaluate, the FSO link performance under the joint occurrence of the atmospheric scattering and turbulence phenomena for 850 nm and 1550 nm operation. Diffraction and non-diffraction limited systems are presented and evaluated for both wavelengths operation considering far-field conditions under different link distances. Bit error rate (BER), pointing error angles, beam divergence angles and link distance are the main performance indicators that are used to evaluate and compare the link performance under different system configurations and atmospheric phenomena combinations. A detailed study is performed to provide the merits of this work. For both far-field diffraction limited and non-diffraction limited systems, it is concluded that 1550 nm system operation is better than 850 nm for the whole presented joint occurrences of atmospheric scattering and turbulence.

(ARL) Measurement of back-scattering patterns from single laser trapped aerosol particles in air

Yongle Pan, Chuji Wang, Leonid Beresnev, Alex Yuffa, Gorden Videen, David Ligon, and Joshua Santarpia

Doc ID: 272251 Received 22 Jul 2016; Accepted 05 Aug 2016; Posted 10 Aug 2016  View: PDF

Abstract: We demonstrate a method for measuring elastic back-scattering patterns from single, laser-trapped, micron-sized particles, spanning the scattering angle range of θ=〖167.7〗^∘-〖180〗^∘and ϕ=0^∘-〖360〗^∘in spherical coordinates. We calibrated the apparatus by capturing light-scattering patterns of 10µm-diameter Borosilicate glass microspheres and comparing their scattered intensities with Lorenz-Mie theory. Back-scattering patterns are also presented from a single, trapped Johnson grass spore, two attached Johnson grass spores, and a cluster of Johnson grass spores. The method has potential use in characterizing airborne aerosol particles, and may be used to provide back-scattering data for LIDAR applications.

Detection capability of pulsed micro-laser linethermography on submillimeter porosity in carbonfiber reinforced polymer composites by experimentand simulation

Hai Zhang, Henrique Fernandes, FRANK BILLY DJUPKEP DIZEU, Ulf Hassler, Julien Fleuret, Marc Genest, Clemente Ibarra-Castanedo, Francois Robitaille, Simon Joncas, and Xavier Maldague

Doc ID: 267654 Received 03 Jun 2016; Accepted 05 Aug 2016; Posted 08 Aug 2016  View: PDF

Abstract: In this article, pulsed micro-laser line thermography (pulsed micro-LLT) was used to detect the submillimeterporosities in 3D preformed carbon fiber reinforced polymer composite (CFRP) specimen. X-raymicro-computed tomography (micro-CT) was used to verify the thermographic results. Then, finite elementanalysis (FEA) was performed on the corresponding models on the basis of the experimental results.The same infrared image processing techniques were used for the experimental and simulation resultsfor comparative purposes. Finally a comparison of experimental and simulation post-processing resultswas conducted. In addition, an analysis of probability of detection (PoD) was performed to evaluate thedetection capability of pulsed micro-LLT on submillimeter porosity.

Systematic afterpulsing-estimation algorithms forgated avalanche photodiodes

Carlos Wiechers Medina, Roberto Ramírez-Alarcón, Oscar Muñiz-Sánchez, Pablo Daniel Yepiz Graciano, Alejandro Arredondo-Santos, Jorge Hirsh, and Alfred U'Ren

Doc ID: 267727 Received 06 Jun 2016; Accepted 05 Aug 2016; Posted 08 Aug 2016  View: PDF

Abstract: We present a method designed to efficiently extract optical signals from InGaAs avalanche photodiodes(APDs) operated in gated mode. In particular, our method permits an estimation of the fraction of countswhich actually results from the signal being measured, as opposed to being produced by noise mechanisms,specifically by afterpulsing. Our method in principle allows the use of InGaAs APDs at highdetection efficiencies, with the full operation bandwidth, either with or without resorting to the applicationof a dead time. As we show below, our method can be used in configurations where afterpulsingexceeds the genuine signal by orders of magnitude, even near saturation. The algorithms which we havedeveloped are suitable to be used either in real-time processing of raw detection probabilities or in postprocessingapplications, after a calibration step has been performed. The algorithms which we proposehere can complement technologies designed for the reduction of afterpulsing.

Error Correction for Rotationally Asymmetric Surface Deviation Testing Based on Rotational Shears

Weibo Wang, Pengfei Lui, yaolong xing, Jiubin Tan, and Jian Liu

Doc ID: 268509 Received 16 Jun 2016; Accepted 05 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: We present a practical method for absolute testing of rotationally asymmetric surface deviation based on rotation averaging, additional compensation and azimuthal errors correction. The neglected information on errors of angular order kNθ in the traditional multi-angle averaging method can be reconstructed and compensated with the help of least-squares fitting of Zernike polynomials by an additional rotation measurement. The estimation algorithm adopts least squares technique to determine the true azimuthal positions of part rotation and consequently eliminates testing errors caused by rotation inaccuracy. The unknown relative alignment of the measurements can be estimated through the differences in measurement results at overlapping areas. The method proposed combines the advantages of single-rotation method and multi-angle averaging method, and realizes a balance between the efficiency and accuracy of the measurements. Experimental results show that the method proposed can obtain high accuracy even with fewer rotation measurements.

High-resolution, dual-depth SD-OCT with interlaced detection for whole-eye imaging

Hyung-Jin Kim, Pilun Kim, Min Gyu Hyeon, jeehyun kim, and Beop-Min Kim

Doc ID: 266531 Received 20 Jun 2016; Accepted 04 Aug 2016; Posted 04 Aug 2016  View: PDF

Abstract: Dual-depth spectral-domain optical coherence tomography (SD-OCT) enables high-resolution in vivo whole-eye imaging. Two orthogonally polarized beams from a source are focused simultaneously on two axial positions of the anterior segment and the retina. For the detector arm, a 1 × 2 ultrafast optical switch sequentially delivers two spectral interference signals to a single spectrometer, which extends the in air axial depth range up to 9.44 mm. An off-pivot complex conjugate removal technique doubles the depth range for all anterior segment imaging. The graphics processing unit based parallel signal processing algorithm supports fast two- and three-dimensional image displays. The obtained high-resolution anterior and retinal images are measured biometrically. The dual-depth SD-OCT system has an axial resolution of ~6.4 µm in air and the sensitivity is 91.79 dB at 150 µm from the zero-delay line.

Analysis of wavefront coding imaging with cubic phase mask decenter and tilt

yijian wu, Liquan Dong, Yuejin Zhao, Ming Liu, Xuhong Chu, Wei Jia, xiaohu guo, and Yun Feng

Doc ID: 269147 Received 27 Jun 2016; Accepted 03 Aug 2016; Posted 04 Aug 2016  View: PDF

Abstract: This manuscript has examined how the decenter and tilt of cubic phase mask plate influence the imaging of wavefront coding system. The calculated phase term of pupil function with mask decenter and tilt indicates that both decenter and tilt change the shape of the system modulation transfer function (MTF) in a predictable way by changing the phase and defocus parameters. The simulation in an on-axis three-mirror Cassegrain (TMC) system is presented to confirm the calculated formula result. Experimental results for mask decenter are also presented. The results demonstrate that the decenter of phase mask have less effect on PSF by z direction than x and y direction.

An architecture for one-shot compressive imagingusing computer-generated holograms

Alexander Macfaden, Stephen Kindness, and Timothy Wilkinson

Doc ID: 258774 Received 04 Mar 2016; Accepted 03 Aug 2016; Posted 03 Aug 2016  View: PDF

Abstract: We propose a synchronous implementation of compressive imaging. This method is mathematically equivalent to prevailing sequential methods [Takhar et al. Proc. SPIE 6065, 2006], but uses a static holographic optical element to create a spatially distributed spot array from which the image can be reconstructed with an instantaneous measurement. We present the holographic design requirements and demonstrate experimentally that the linear algebra of compressed imaging can be implemented with this technique. This technique has the potential to be integrated with optical metasurfaces allowing newcompressive sensing methods to be developed.

Measurement of the inter-modal crosstalk of a bend multimode waveguide

JIAN Wang, Changyun Zhao, Bing Wei, wang Gencheng, Tingge Dai, Yuehai Wang, Xiaoqing Jiang, Yubo Li, and Jianyi Yang

Doc ID: 272769 Received 29 Jul 2016; Accepted 03 Aug 2016; Posted 08 Aug 2016  View: PDF

Abstract: We quantitatively investigate the main source of the inter-modal crosstalk of the silicon-based bend multimode waveguide by experiment. The measurement is performed through the time-domain scanning low-coherence interferometry (LCI). From the measurement results, one can not only calculate the modal crosstalk, but also locate the position where the crosstalk appears. The results indicate that the modal mismatch at the points where the curvature of the waveguide changes is the main origin of the modal crosstalk. For a two-mode waveguide with a bending radius of 5 μm at 1310 nm, the crosstalk is as high as -20 dB and -16 dB for the fundamental and first-order mode, respectively. This work gives us a deep insight into how the guided modes actually propagate through the bend waveguide.

Master Slave Optical Coherence Tomography Imaging of Eyelid Basal Cell Carcinoma

Catherine Chin, Adrian Bradu, Rongxuan Lim, Mona Khandwala, John Schofield, Adrian Podoleanu, and Lasse Leick

Doc ID: 264513 Received 04 May 2016; Accepted 03 Aug 2016; Posted 09 Aug 2016  View: PDF

Abstract: Optical coherence tomography (OCT) is fast emerging as an additional non interventional modality for skin tumour detection and diagnosis. A master/slave (MS) flying spot OCT configuration was assembled to detect periocular basal cell carcinomas (BCC). A swept source at 1300 nm and sweeping speed of 50 kHz was used A three step process was involved. First, 384 memories of channelled spectra from a mirror were stored for 384 optical path differences at the Master stage. Then, the stored channelled spectra (masks) were correlated with the channelled spectrum from the BCC tissue to produce 384 en-face OCT images (200x200 pixels) for the optical path difference (OPD) values used to acquire the masks. Finally, these en-face slices were stacked to form a volume to cross-reference BCC tumour margins in orthogonal plane. With the MS-OCT method, 200x200 lateral pixels, several en-face images are produced in 3.2 s per eyelid sample. Combination of en-face view with the cross sectioning views allow for better discrimination of BCCs comparable to using cross-sectional (B-scan) alone as previously reported using the conventional fast Fourier Transform (FFT) based OCT techniques.

High Sensitivity and resolution Integrated OpticalSystem for Portable Raman Spectrometer

Ming Tang, Xin Wang, Fan guang, Wei Li, Ying Xu, Jing Que, Jian He, and Yong Zuo

Doc ID: 262408 Received 12 Apr 2016; Accepted 03 Aug 2016; Posted 04 Aug 2016  View: PDF

Abstract: An integrated optical system with high sensitivity and resolution was presented. This was made possible by coupling probeto monochromator directly, using an aspheric lens in collection path, using an achromatic lens in coupling path, using adichroic filter with high transmission and steep transitional zone as beam splitter, increasing the throughput ofmonochromator and optimizing the structure parameters of monochromator. This optical system has a high sensitivity, thetested spectrogram of glass rod demonstrated that the signal to noise ratio measured by the integrated optical system wasalmost four times as high as independent probe and monochromator. The optical system also has the advantages of highresolution (4cm-1 or 0.28 nm), low cost and portable size. This work makes a good preparation for the development of highsensitivity, high resolution and low cost integrated portable Raman spectrometer.

Transmittance Derived Line Width and Line Shift inPolycrystalline Nd:YAG

Ryan Springer and Michael Thomas

Doc ID: 266680 Received 27 May 2016; Accepted 02 Aug 2016; Posted 08 Aug 2016  View: PDF

Abstract: Temperature dependent transmittance derived line width and line shift measurements are conductedon polycrystalline 1% and 6% Nd doped YAG in the 293K to 473K range. Single crystal temperaturedependent line width model is adapted for polycrystalline YAG. Comparison between line widthmeasurement techniques was conducted and transmittance method is preferred for ground state linewidth measurements. Polycrystalline YAG material is found to have broader intrinsic line width thansingle crystal material. Polycrystalline YAG material should provide mode locking advantages of shorterminimum pulse length than single crystal YAG.

The Study on Intelligent Recognition Detection Technology of Debond Defects for Ceramic Matrix Composites (CMC) Based on THz-TDS

Jiao Ren, Li Li, Dan Zhang, and Xiao Qiao

Doc ID: 264962 Received 16 May 2016; Accepted 01 Aug 2016; Posted 03 Aug 2016  View: PDF

Abstract: With the wide use of high-temperature resistant CMC in aviation and space flight, it is urgent to detect the quality of the bonding. This paper used the Terahertz (THz) time-domain spectroscopy non-destructive testing technology to inspect the bonding defects of the CMC. The paper put forward a method-Extraction Method, which applied to make samples to simulate the bonding defect of CMC by embedding the PTFE sheets with 0.12mm thickness into the adhesive layer, and extracting it after curing and presetting the bonding defects. On the basis of the classical and analytical algorithm such as the maximum in time-domain, power spectrum integration, etc., through the further study in the THz spectral characteristics of bonding samples for CMC, specifically introduce the upper de-bonding coefficient, lower de-bonding coefficient, average absorption coefficient for frequency domain, centroid coefficient for frequency domain and other characteristics; By optimizing to build the THz detection characteristics set, as a sample, adopt the neural network intelligent recognition algorithm to detect the upper and lower de-bonding defect in samples and realize the intelligent identification for CMC de-bonding defect.

Atmospheric propagation and combining of high power lasers: comment

Gregory Goodno and Joshua Rothenberg

Doc ID: 263228 Received 26 Apr 2016; Accepted 31 May 2016; Posted 29 Aug 2016  View: PDF

Abstract: Nelson et al [Appl. Opt. 55, 1757 (2016)] recently concluded that coherent beam combining and remote phase-locking of high power lasers are fundamentally limited by the laser source linewidth. These conclusions are incorrect and not relevant to practical high power coherently combined laser architectures.

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