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Accepted papers to appear in an upcoming issue

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Single Mode GaSb Diode Lasers for Sensor Applications in a new long Wavelength Regime

Tobias Milde, Christian Assmann, Alvaro Jimenez Galindo, Martin Honsberg, James O’GORMAN, Wolfgang Schade, and Joachim Sacher

Doc ID: 297147 Received 31 May 2017; Accepted 18 Aug 2017; Posted 18 Aug 2017  View: PDF

Abstract: The wavelength, λ, range between 1.8µm ≤ λ ≤ 3.5µm contains strong spectral absorption lines of many gases used in health, industry, safety and medicine and whose sensitive and quantitative detection is desirable. However, the performance of InP diode lasers markedly deteriorates beyond λ~2µm. In this paper we present new results on developing tunable high power single mode laser diodes based on the GaSb material system with emission in the wavelength range 1.8µm ≤ λ ≤ 3.5µm

Measurement of atmospheric carbon dioxide andwater vapour in urban built-up areas in theGandhinagar-Ahmedabad region in India using aportable tunable diode laser spectroscopy system

ANIRBAN ROY, NEETESH SHARMA, Arup Chakraborty, and abhishek upadhyay

Doc ID: 297228 Received 01 Jun 2017; Accepted 18 Aug 2017; Posted 18 Aug 2017  View: PDF

Abstract: This paper reports open-path in situ measurements of atmospheric carbon dioxide at Gandhinagar ( .2156°N,72.6369°E) and Ahmedabad ( .0225°N, 72.5714°E) in the heavily industrialized state of Gujarat in western India.Calibration-free second harmonic wavelength modulation spectroscopy (2f WMS) is used to carry out accurate andfully automated measurements. The mean values of mole fraction of carbon dioxide at four locations were 438ppm, 495 ppm, 550 ppm and 740 ppm respectively. These values are much higher than the current global averageof 406.67 ppm. A 1 mW, 2004 nm vertical cavity surface-emitting laser is used to selectively interrogate the R16transition of carbon dioxide at 2003.5 nm (4991.2585 cm-1). The 2f WMS signal corresponding to the gasabsorption line shape is simulated using spectroscopic parameters available in the HITRAN database and relevantlaser parameters that are extracted in situ from non-absorbing spectral wings of the harmonic signals. The molefraction of carbon dioxide is extracted in real-time by a MATLAB program from least-squares fit of the simulated 2fWMS signal to the corresponding experimentally obtained signal. A 10 mW, 1392.54 nm distributed feedback laseris used at two of the locations to carry out water vapour measurements using direct absorption spectroscopy. Thisis the first instance of a portable tunable diode laser spectroscopy system being deployed in an urban location inIndia to measure atmospheric carbon dioxide and water vapour under varying traffic conditions. Themeasurements clearly demonstrate the need to adopt tunable diode laser spectroscopy for precise long-termmonitoring of greenhouse gases in the Indian sub-continent.

2 µm laser oscillation of Ho3+:Tm3+ co-doped silica microsphere

Longxiang Peng, Yantang Huang, Yafan Duan, Shijian Zhuang, Tingdi Liao, and Xu Canhua

Doc ID: 297639 Received 07 Jun 2017; Accepted 18 Aug 2017; Posted 18 Aug 2017  View: PDF

Abstract: 2 µm laser oscillation with low threshold has been achieved in a Ho3+:Tm3+ co-doped silica microsphere (HTCSM). The Ho3+:Tm3+ co-doped sol-gel functionalization film is applied to the surface of a silica microsphere, and an optical tapered fiber (OTF) is adopted to couple an 808 nm continuous-wave (CW) laser served as a pump light source. Multi-mode and single-mode laser oscillations around 2 µm within the eye-safe waveband are observed due to the 5I7→5I8 transitions of Ho3+ ions sensitized by Tm3+. The morphology characteristics of microsphere determine the multi-mode laser oscillation spectrum. The free spectral range (FSR) is in good accordance with the calculated value based on the Mie scattering theory.The HTCSM laser oscillation shows characteristics of good capability, simple process, high flexibility and low cost.

Improvement of pointing accuracy for Risley prisms by parameters identification

Jinying Li, chen ke, peng qi, wang ke, jiang yang, fu chengyu, and ren ge

Doc ID: 290112 Received 27 Apr 2017; Accepted 17 Aug 2017; Posted 17 Aug 2017  View: PDF

Abstract: Risley prisms appear to be a promising solution to high-accuracy pointing and tracking. In order to improve thepointing accuracy of achromatic Risley prisms, an appropriate mathematical model is established, and the forwardand inverse solutions are proposed. Focusing on the sources of systematic errors, an optimization method based ongenetic algorithm is proposed to identify the parameters of the physical model, including wedge angles, refractiveindexes, and installations. Finally, the experimental platform is established. The pointing accuracy and the size ofthe blind zone are tested to prove the validity of the method. Experimental results show that the proposed methodis effective to reduce the influence of manufacturing, installation, and measurement errors. The optimized pointingaccuracy has been improved significantly. Within the maximum deflection angle of 3°, the maximum pointing erroris reduced from 33 arcsec to less than 1. And the angular dynamic range is found to be greater than 43 dB, whichcan meet the needs of the majority of applications. In addition, the test of the blind zone shows that the optimizedparameters are consistent with the actual system.

Suomi NPP VIIRS solar diffuser screen transmittance model and its applications

Ning Lei, Xiaoxiong Xiong, and Jeff McIntire

Doc ID: 296116 Received 16 May 2017; Accepted 17 Aug 2017; Posted 17 Aug 2017  View: PDF

Abstract: The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi National Polar-orbiting Partnership satellitecalibrates its reflective solar bands through observations of a sunlit solar diffuser (SD) panel. Sunlight passesthrough a perforated plate, referred to as the SD screen, before reaching the SD. It is critical to know whether theSD screen transmittance measured prelaunch is accurate. Several factors such as misalignments of the SD paneland the measurement apparatus could lead to errors in the measured transmittance and thus adversely impact onorbitcalibration quality through the SD. We develop a mathematical model to describe the transmittance as afunction of the angles that incident light makes with the SD screen, and apply the model to fit the prelaunchmeasured transmittance. The results reveal that the model does not reproduce the measured transmittance unlessthe size of the apertures in the SD screen is quite different from the design value. We attribute the difference to theorientation alignment errors for the SD panel and the measurement apparatus. We model the alignment errors andapply our transmittance model to fit the prelaunch transmittance to retrieve the “true” transmittance. To use thismodel correctly, we also examine the finite source size effect on the transmittance. Furthermore, we compare theproduct of the retrieved “true” transmittance and the prelaunch SD BRDF value to the value derived from on-orbitdata to determine whether the prelaunch SD BRDF value is relatively accurate. The model is significant in that itcan evaluate whether the SD screen transmittance measured prelaunch is accurate and help retrieve the truetransmittance from the transmittance with measurement errors, consequently resulting a more accurate sensordata product by the same amount.

Biconic White Multipass Cell Design Based on a Skew Ray-Tracing Model

Yin Guo and Liqun Sun

Doc ID: 300696 Received 22 Jun 2017; Accepted 17 Aug 2017; Posted 17 Aug 2017  View: PDF

Abstract: A biconic White multipass cell (bi-WMPC), designed as a compact, zero-geometrical-loss, anastigmatic optical system, capable used with an extended divergent source, is proposed. Firstly, a skew ray-tracing model is developed for a conventional White-type multipass cell (WMPC), base on which the astigmatism is calculated, together with its sensitivity coefficients in relation to all-important optical structural parameters in various configurations. Next, a generalized bi-WMPC is designed to suppress the astigmatism, which leads to much smaller reflection spots on the field mirror compared to the conventional design. The demonstration of an optimized bi-WMPC initialized from a commercial WMPC (52-pass with 0.8 m base length) suggests a 53-fold reduction of the Wavefront aberration from 79.187 λ to 1.493 λ, as well as the path-length to volume ratio (PVR) increase from 20.8 m/L to 35.2 m/L. These improvements are critical for the design of a compact WMPC with a path-length of tens to hundreds of meters. Present developed skew ray-tracing model for a WMPC can also be applied to other freeform surfaces to further compensate the inherent aberrations induced by multiple off-axis reflections.

Triple Brillouin frequency spacing multi-wavelengthfiber laser with double Brillouin cavities and theirapplication in microwave signal generation

zhen wang, Tianshu Wang, Qingsong Jia, Wanzhuo Ma, Qingchao Su, and Peng Zhang

Doc ID: 296933 Received 30 May 2017; Accepted 16 Aug 2017; Posted 17 Aug 2017  View: PDF

Abstract: We propose and experimentally investigate a multi-wavelength Brillouin fiber laser (MBFL) with triple frequencyspacing by employing a modular structure. In this scheme, we obtain optimized 9 channels with frequency spacingof 0.259 nm. The single, double and triple Brillouin frequency spacing for the MBFL can be easily realized byutilizing this modular structure. The impact of Brillouin pump (BP) power, BP wavelength anderbium-ytterbium-doped fiber amplifier (EYDFA) output power on the performance of the MBFL are investigated,respectively. Besides, we also study the generation of beating frequency microwave signals based on single, doubleand triple frequency spacing MBFL. 10.5 GHz, 21.48 GHz and 31.77 GHz microwave signals with 3 dB linewidth of16.4 MHz, 15.2 MHz and 12.8 MHz are generated, respectively.

Wavefront aberration metrology based on transmitted fringe deflectometry

Lili Jiang, Xiaodong Zhang, Fengzhou Fang, Xianlei Liu, and Linlin Zhu

Doc ID: 297429 Received 06 Jun 2017; Accepted 16 Aug 2017; Posted 17 Aug 2017  View: PDF

Abstract: A simple, precise and innovative technique for wavefront aberration measurement is presented in this paper. This technique is based on the transmitted fringe deflectometry (TFD), who used to measure wavefront slope and wavefront. The system measurement error when measuring wavefront aberration is analyzed, including the aberration of the reference wavefront caused by shape distribution and the tilt and decentration of the phase object. Based on this, the system error model is established and the system error compensation method is also presented. In addition, the system parameters calibration method is discussed in detail. Simulation and experimental results showed that the proposed TFD wavefront aberration measurement model can achieve high measurement accuracy.

Coherent laser phase retrieval in the presence of measurement imperfections and incoherent light

Anders Hansen

Doc ID: 300487 Received 20 Jun 2017; Accepted 15 Aug 2017; Posted 17 Aug 2017  View: PDF

Abstract: Phase retrieval is a powerful numerical method that can be used to determine the wavefront of laser beams based only on intensity measurements, without the use of expensive, low-resolution specialized wavefront sensors such as Shack-Hartmann sensors. However, phase retrieval techniques generally suffer from poor convergence and fidelity when the input measurements contain electronic or optical noise and/or an incoherent intensity contribution overlapped with the otherwise spatially coherent laser beam. Here, we present an implementation of a modified version of the standard multiple-plane Gerchberg–Saxton algorithm and demonstrate that it is highly successful at extracting the intensity profile and wavefront of the spatially coherent part of the light from various lasers, including tapered laser diodes, at a very high fidelity despite the presence of incoherent light and noise.

Scene reassembly after multimodal digitization and pipeline evaluation using photorealistic rendering

Jonathan Stets, Alessandro Dal Corso, Jannik Nielsen, Rasmus Lyngby, Sebastian Jensen, Jakob Wilm, Mads Doest, Carsten Gundlach, Eythor Runar Eiriksson, Knut Conradsen, Anders Dahl, Jakob Andreas Bærentzen, Jeppe Frisvad, and Henrik Aanaes

Doc ID: 295986 Received 23 May 2017; Accepted 15 Aug 2017; Posted 16 Aug 2017  View: PDF

Abstract: Transparent objects require acquisition modalities that are very different from the ones used for objects with more diffuse reflectance properties. Digitizing a scene where objects must be acquired with different modalities, requires scene reassembly after reconstruction of the object surfaces. This reassembly of a scene that was picked apart for scanning seems unexplored. We contribute with a multimodal digitization pipeline for scenes that require this step of reassembly. Our pipeline includes measurement of bidirectional reflectance distribution functions (BRDFs) and high dynamic range (HDR) imaging of the lighting environment. This enables pixelwise comparison of photographs of the real scene with renderings of the digital version of the scene. Such quantitative evaluation is useful for verifying acquired material appearance and reconstructed surface geometry, which is an important aspect of digital content creation. It is also useful for identifying and improving issues in the different steps of the pipeline. In this work, we use it to improve reconstruction, apply analysis by synthesis to estimate optical properties, and to develop our method for scene reassembly.

Negative influence of detector noise on ghost imaging based on photon counting technique at low light levels

Xiaohui Shi, Hengxing Li, Yanfeng Bai, and Xiquan Fu

Doc ID: 298217 Received 16 Jun 2017; Accepted 15 Aug 2017; Posted 16 Aug 2017  View: PDF

Abstract: The influence of detector noise on ghost imaging (GI) is investigated at low light levels. Based on the characteristics of the additive detector noise, we establish the analytical model and display the ghost images through numerical and experimental demonstrations. It is shown that the contrast-to-noise ratio (CNR) and visibility of reconstructed images are sharply affected by the detector noise. Following the increase of the ratio of average signal intensity to the average noise, the quality of reconstructions is enhanced. To reduce the measurement numbers and thus shorten the consuming time without sacrificing the imaging quality, we propose a sorting technique in traditional GI algorithm for a high-quality image reconstruction. The results demonstrated here will be favorable to the applications of low-light-level imaging.

Investigation of nonuniform surface properties of classically-manufactured fused silica windows

Christoph Gerhard, Daniel Tasche, Olivier Uteza, and Jörg Hermann

Doc ID: 295310 Received 05 May 2017; Accepted 15 Aug 2017; Posted 15 Aug 2017  View: PDF

Abstract: We report on investigations of the spatial variations of contamination, roughness and index of refraction of classically-manufactured polished fused silica surfaces. Therefore laser-induced breakdown spectroscopy was used to probe surface and subsurface impurities via the detection of aluminum. Measurements at different positions on the surface of the cylindrical fused silica windows evidenced an almost contamination-free center region whereas a relatively large contamination was found close to the edge. In-depth measurements verify the presence of aluminum atoms in the bulk until a depth of several tens of microns for the edge region. In addition, atomic force microscopic measurements show that the surface roughness is larger in the center region compared to the edge. Further, the index of refraction increases from the center region towards the edge as measured via ellipsometry. The results indicate a nonuniform impact of the grinding, lapping, and polishing tools on the surface. The findings turn out to be of specific interest for different applications, particularly for the realization of large-scale high performance coatings.

Sub-mm depth resolved digital holography

Joseph van Rooij and Jeroen Kalkman

Doc ID: 296247 Received 31 May 2017; Accepted 15 Aug 2017; Posted 15 Aug 2017  View: PDF

Abstract: We present sub-millimeter full-field depth from focus digital holography of surface topography of rough objects. For each pixel, the depth of the object is calculated from the variance of the intensity image over a set of reconstruction distances. First, we theoretically describe the axial resolution of this method and show that sub-millimeter resolution is feasible. Second, using a digital holography setup without magnifying optics or lateral scanning we experimentally demonstrate 100 micron axial resolution depth ranging and surface topography imaging. This is significantly better than what has previously been reported using digital holography and could make this technique useful for rapid characterization of surface topography of objects.

Compact fabrication-tolerant subwavelength-grating-based two-mode division (de)multiplexer

Zeinab Jafari, Abbas Zarifkar, and Mehdi Miri

Doc ID: 297420 Received 05 Jun 2017; Accepted 15 Aug 2017; Posted 15 Aug 2017  View: PDF

Abstract: Regarding the importance of bandwidth and capacity expansion in communication systems, a novel mode division (de)multiplexer based on subwavelength grating (SWG) is proposed. SWG-based devices could have smaller sizes, be much more fabrication tolerant and have much wider bandwidths due to the reduced confinement of the field and dispersion. It is also feasible to reduce the loss of a SWG-based device by tuning the duty cycle of the grating. Thanks to these properties of SWGs, we have designed a compact fabrication-tolerant two-mode division (de)multiplexer. A flat-top transmission of >0.89 (loss <0.5 dB) is obtained over 65 nm from 1500 to 1565 nm which completely covers the entire C-band used for dense wavelength division multiplexing (DWDM). Moreover, the cross-talk is <-10 dB for a broad bandwidth of ~120 nm over which the loss of the complete device including both multiplexer and de-multiplexer is <1 dB. Therefore, the proposed device is promising for high capacity optical communications in both conventional and entirely SWG-based silicon photonic circuits.

Convolutional neural network-based data pageclassification for holographic memory

Tomoyoshi Shimobaba, Naoki Kuwata, Mizuha Homma, Takayuki Takahashi, Yuki Nagahama, Marie Sano, Satoki Hasegawa, Ryuji Hirayama, Takashi Kakue, Atsushi Shiraki, Naoki Takada, and Tomoyoshi Ito

Doc ID: 301571 Received 04 Jul 2017; Accepted 14 Aug 2017; Posted 15 Aug 2017  View: PDF

Abstract: We propose a deep-learning-based classification of data pages used in holographic memory. Wenumerically investigated the classification performance of a conventional multi-layer perceptron (MLP)and a deep neural network, under the condition that reconstructed page data are contaminated by somenoise and are randomly laterally shifted. Under data pages are randomly laterally shifted, the MLP wasfound to have a classification accuracy of 93.02%, whereas the deep neural network was able to classifydata pages at an accuracy of 99.98%. The accuracy of the deep neural network is two orders of magnitudebetter than the MLP.

Using Refraction in Thick Glass Plates for Optical Path Length Modulation in Low Coherence Interferometry

Niklas Kröger, Jochen Schlobohm, Andreas Pösch, and Eduard Reithmeier

Doc ID: 296334 Received 18 May 2017; Accepted 14 Aug 2017; Posted 15 Aug 2017  View: PDF

Abstract: In Michelson interferometer setups the standard way to generate different optical path lengths between measurement and reference arm relies on expensive high precision linear stages such as piezo actuators.We present an alternative approach based on the refraction of light at optical interfaces using a cheap stepper motor with high gearing ratio to control the rotation of a glass plate.The beam path is examined and a relation between angle of rotation and change in optical path length is devised.As verification an experimental setup is presented and reconstruction results from a measurement standard are shown.The reconstructed step height from this setup lies within 0.12% of the expected value.

Reversible and irreversible alterations of the optical thickness of PQ/PMMA volume recording media samples. Part 1: Experiment

Boris MANUKHIN, Sergey CHIVILIKHIN, Irina Schelkanova, Natalia Andreeva, Daria Materikina, and Olga ANDREEVA

Doc ID: 294980 Received 02 May 2017; Accepted 13 Aug 2017; Posted 14 Aug 2017  View: PDF

Abstract: An experimental research into changes of the optical thickness of phenanthrenequinone-doped polymethylmethacrylate samples in the process of irradiation by the 473 nm laser is presented. It was demonstrated thatheating induced reversible changes lead to a decrease of the optical thickness. The temperature coefficient of therelative changes of the optical thickness was measured to be –1.40×10-5 К-1 that matches the data published byother authors. It is also established that the irreversible changes induced by the photochemical transformationlead to an increase of the optical thickness outside of the absorption band of the samples (λ>530 nm), relativechange of which at λ=532 nm is +3.7×10-5. It was demonstrated that the reversible and irreversible changes do notcompensate for each other in the process of samples’ exposure.

Bi-directional ultrasonic wave coupling to FBGs incontinuously-bonded optical fiber sensing.

Junghyun Wee, Drew Hackney, Philip Bradford, and Kara Peters

Doc ID: 297261 Received 02 Jun 2017; Accepted 13 Aug 2017; Posted 14 Aug 2017  View: PDF

Abstract: Fiber Bragg grating (FBG) sensors are typically spot-bonded on the surface of a structure to detect ultrasonic wavesin laboratory demonstrations. However, to protect the rest of the optical fiber from any environmental damageduring real applications, bonding the entire length of fiber, called continuous bonding, is commonly done. In thispaper, we investigate the impact of continuously-bonding FBGs on the measured Lamb wave signal. In theory, theultrasonic wave signal can bi-directionally transfer between the optical fiber and the plate at any adhered location,which could potentially produce output signal distortion for the continuous bonding case. Therefore, anexperiment is performed to investigate the plate-to-fiber and fiber-to-plate signal transfer, from which the signalcoupling coefficient of each case is theoretically estimated based on the experimental data. We demonstrate thatthe two coupling coefficients are comparable, with the plate-to-fiber case approximately 19% larger than the fiberto-plate case. Finally, the signal waveform and arrival time of the output FBG responses is compared between thecontinuous and spot bonding cases. The results indicate that the resulting Lamb wave signal output is only thatdirectly detected at the FBG location, however a slight difference in signal waveform is observed between the twobonding configurations. This paper demonstrates the practicality of using continuously-bonded FBGs for ultrasonicwave detection in structural health monitoring (SHM) applications.

Analysis and investigation of temperature andhydrostatic pressure effects on optical characteristicsof multiple quantum well slow light devices

Saeed Abdolhosseini, reza kohandani, and Hassan Kaatuzian

Doc ID: 300420 Received 20 Jun 2017; Accepted 13 Aug 2017; Posted 14 Aug 2017  View: PDF

Abstract: This paper represents the influences of temperature and hydrostatic pressure variations on GaAs/AlGaAs multiplequantum well slow light systems based on coherence population oscillations. An analytical model in non-integerdimension space is used to study the considerable effects of these parameters on optical properties of the slowlight apparatus. Exciton oscillator strength and fractional dimension constant have special roles on the analyticalmodel in fractional dimension. Hence, impacts of hydrostatic pressure and temperature on exciton oscillatorstrength and fractional dimension quantity are investigated theoretically in this article. Based on achieved results,temperature and hydrostatic pressure play key roles on optical parameters of the slow light systems such as slowdown factor and central energy of the device. It is found that the slope and value of the refractive index real partchange with alterations of temperature and hydrostatic pressure in the range of 5 to 40 degrees of Kelvin and 1 barto 2 kbar, respectively. Thus, the peak value of slow down factor can be adjusted by altering these parameters.Moreover, the central energy of the device shifts when the hydrostatic pressure is applied to the slow light deviceor temperature is varied. In comparison with previous reported experimental results, our simulations follow themsuccessfully. It is shown that the maximum value of slow down factor is estimated close to 5.5×104 with a fineadjustment of temperature and hydrostatic pressure. Meanwhile, central energy shift of the slow light device isrisen up to 27 meV, which provides an appropriate basis for different optical devices in which multiple quantumwell slow light is one of their essential subsections. This multiple quantum well slow light device has potentialapplications for using as tunable optical buffer and pressure/temperature sensors.

Vector mode conversion based on asymmetric fiber Bragg grating in few-mode fibers

an Mi, Haisu Li, and Guobin Ren

Doc ID: 300653 Received 21 Jun 2017; Accepted 13 Aug 2017; Posted 14 Aug 2017  View: PDF

Abstract: We propose a vector mode conversion approach based on asymmetric fiber Bragg gratings (AFBGs) written in step-index fiber and vortex fiber, respectively. The mode coupling properties of AFBG are numerically investigated. Comparing with step-index fiber, the large mode separation in vortex fiber is beneficial to extracting the desired vector mode at specific wavelength. In addition, polarization of incident light and attenuation coefficient of index change distribution of AFBG play critical roles in mode coupling process. The proposed AFBG provides an efficient method to realize high-order vector mode conversion, and it shows great potential for OAM multiplexing and fiber lasers with vortex beams output.

Novel Ultrashort Polarization Rotator Based on Spiral Photonic Crystal Fiber Aiding by Liquid Crystal

Lin Yu, LEI CHEN, Weigang Zhang, Yun-Shan Zhang, Song Wang, Yanxi Zhang, Tieyi Yan, and Jiang Yang

Doc ID: 301248 Received 28 Jun 2017; Accepted 13 Aug 2017; Posted 14 Aug 2017  View: PDF

Abstract: A novel polarization rotator (PR) is proposed based on a spiral photonic crystal fiber aiding by the liquid crystal. The proposed PR has an ultrashort length of only ~ 4.17μm and low crosstalk of ~-20.93 dB, and the proposed PR offers a nearly 100% polarization conversion efficiency for whole C-band. In addition, a large temperature tolerance of ~±5 °C and a large rotation angle tolerance of ~±4°can be accepted based on the full-vector finite-element method simulation. The proposed PR is a potentially effective polarization conversion device for applications in modern communication systems.

Microsphere-assisted phase-shifting profilometry

Stephane Perrin, Audrey LEONG-HOI, Sylvain Lecler, Pierre Pfeiffer, Ivan Kassamakov, Anton Nolvi, Edward Hæggström, and Paul Montgomery

Doc ID: 297757 Received 13 Jun 2017; Accepted 11 Aug 2017; Posted 14 Aug 2017  View: PDF

Abstract: In the present work, we have investigated the combination of super-resolution microsphere-assisted 2D imaging technique with low-coherence phase-shifting interference microscopy. The imaging performance of this technique is studied by numerical simulation in terms of the magnification and the lateral resolution as a function of the geometrical and optical parameters. The results of simulations are compared with the experimental measurements of reference gratings using a Linnik interference configuration. Additional measurements are also shown on nanostructures. An improvement by a factor of 4.7 in the lateral resolution is demonstrated in air, thus giving a more isotropic nanometric accuracy for full-field surface profilometry in the far field.

Design and simulation of a superposition compoundeye system based on hybrid diffractive-refractive lenses

Shuqing Zhang, Zhou Luyang, Changxi Xue, and Lei Wang

Doc ID: 296894 Received 30 May 2017; Accepted 11 Aug 2017; Posted 11 Aug 2017  View: PDF

Abstract: Compound eye offers a promising field of miniaturize imaging system. As one application of compound eye,superposition compound eye systems form a composite image by superposing the images produced by different channel. The geometric configuration of superposition compound eye systems is achieved by three MLAs (micro- lens arrays) with different pitches and focal lengths. High resolution is indispensable for the practicability of superposition compound eye system. In this paper, hybrid diffractive-refractive lenses are introduced into the design of compound eye system for this purpose. With the help of ZEMAX, two superposition compound eyeive lenses were separately designed. Then we demonstrate theeffectiveness of using hybrid diffractive-refractive lens to improve the image quality.

Highly Birefringent Highly Negative Dispersion Compensating Photonic Crystal Fiber

Animesh Bala, Kanan Roy Chowdhury, Md Borhan Mia, and Mohammad Faisal

Doc ID: 297892 Received 16 Jun 2017; Accepted 10 Aug 2017; Posted 11 Aug 2017  View: PDF

Abstract: A triangular lattice dispersion compensating photonic crystal fiber (DC-PCF) is presented in thispaper. The fiber produces high birefringence and operates at fundamental mode only. Full vector finite element method (FEM) with a perfectly matched absorbing layer boundary condition (PML) is applied to investigate the guiding properties of the proposed fiber. The designed fiber demonstrates that it is possible to obtain a very large negative dispersion of −9486. 1 ps/ (nm. km) at 1550 nm wavelength with a negative dispersion more than −7000 ps/(nm. km) over entire C band (1530-1565 nm), which is suitable for broadband dispersion compensation. The birefringence is about 4. 13 × 10-2 at 1550 nm wavelength which is also very high. All these properties endorse this fiber much suitable in the area of broadband dispersioncompensation and polarization maintaining applications.

Temperature Tunable One-dimensional PlasmonicPhotonic Crystals Based on a Single Graphene Layerand a Semiconductor Constituent

Abbas Ghasempour Ardakani and Marzieh Sedaghatnejad

Doc ID: 298185 Received 20 Jun 2017; Accepted 10 Aug 2017; Posted 11 Aug 2017  View: PDF

Abstract: We first investigate a graphene based 1-D plasmonic photonic crystal (PPC) composed of a graphene sheetdeposited on a SiO2 grating whose grooves are filled with air by using finite-element method software (COMSOLMultiphysics). The dispersion effect of SiO2 is considered in the simulation and we show that this effect significantlyaffects on the transmission spectrum of the proposed PPC. The transmission spectrum shows a stop band in themid-infrared region which is blue shifted with increasing the Fermi energy level of the graphene sheet. However,the transmission spectrum is not affected by variation of the ambient temperature. To achieve a temperaturetunable 1D graphene based PPC, we propose that the graphene sheet is placed on a grating composed of InAssemiconductor material. Our results confirm that the stop band in the proposed structure can be easily tuned withtemperature and moves to higher frequencies with increasing the ambient temperature. Moreover, we introduce adefect into the temperature tunable PPC to obtain a temperature tunable Fabry-Perot micro-cavity. It isdemonstrated that the resonance defect mode is easily controllable with changing the temperature and the Fermienergy level.

Instantaneous 3D-imaging of highly turbulent flames using Computed Tomography of Chemiluminescence (CTC)

Khadijeh Mohri, Simon Görs, Jonathan Schöler, Andreas Rittler, Thomas Dreier, Christof Schulz, and Andreas Kempf

Doc ID: 295005 Received 05 May 2017; Accepted 10 Aug 2017; Posted 11 Aug 2017  View: PDF

Abstract: The CTC technique was applied for the first time to a real highly turbulent swirl flame setup, using alarger number of CCD cameras (Nq = 24 views), to directly reconstruct the three-dimentional (3D) instantaneousand time-averaged checmilumienscence fields. The views were obtained from a 172.5o region (inone plane) around the flame, and the CTC algorithm (Floyd et al., Combust. Flame 158, 2011) was usedto reconstruct the flame by discretising the domain into voxels. We investigated how the reconstructionsare affected by the views’ arrangement and settings of the algorithm, and considered how the quality ofreconstructions should be assessed to ensure a realistic description of the technique’s capabilities. Thereconstructions using Nq 12 were generally better when the cameras were more equiangularly distributed.When Nq was severely low (e.g. 3), the reconstruction could be improved by using less voxels.The paper concludes with a summary of the strengths and weaknesses of the CTC technique for examininga real turbulent flame geometry and provides guidance on best practice.

Defect detection based on lensless reflective point diffraction interferometer

Wenhua Zhu, Lei Chen, Yiming Liu, Yun Ma, Donghui Zheng, Zhigang Han, and Jinpeng Li

Doc ID: 299373 Received 20 Jun 2017; Accepted 09 Aug 2017; Posted 09 Aug 2017  View: PDF

Abstract: We propose a defect detection system to identify phase defects on optics based on a lensless reflective point diffraction interferometer (LRPDI). The optics under test is illuminated by a collimated beam to produce signal wavefront carrying the defect information, and then the signal wavefront is recorded in a high carrier interferogram using the LRPDI. By lensless imaging, amplitude and phase defects as well as the accurate phase of a phase defect can be identified. The simulation and experiment demonstrate the success of the proposed system in detecting phase defects, and its high-accuracy and high-resolution dynamic detection ability are verified.

The theoretical imaging study of early caries bylaser induced Rayleigh wave

Ling Yuan, Song Mei, Shen Zhong-Hua, Xiaowu Ni, and Jian Lu

Doc ID: 291869 Received 04 May 2017; Accepted 09 Aug 2017; Posted 10 Aug 2017  View: PDF

Abstract: Vitro human teeth are scanned by computed tomography through the 3D-reconstructiontechnology. The geometric models of teeth are achieved. Based on it, a physical model of the acoustic waves on teeth induced by laser is established, and the finite element method was used to solve this physical model. As the velocity of Rayleigh wave is sensitive to the elastic modulus of the teeth, the parameters such as the position, depth and morphology of the caries as well as demineralization degree can be evaluated by the velocity field of Rayleigh wave on teeth. Furthermore, by the frequency domain characters of surface acoustic waves, the depth of the caries region can be evaluated. Therefore, the 3D evaluation method is established to develop the nondestructive and quantitative detection on the early caries.

Quantitative phase imaging by optimized asymmetric illumination

Yoshimasa Suzuki, mayumi odaira, Hisashi Ohde, and Yoshimasa Kawata

Doc ID: 297198 Received 23 Jun 2017; Accepted 09 Aug 2017; Posted 10 Aug 2017  View: PDF

Abstract: We have presented a simple approach for quantitative phase imaging by optimizing asymmetric illumination of a conventional microscope. With this illumination, the light intensity modulation accompanying refraction at the surface profile of phase objects occurs, and "phase-gradient information" can be derived by detecting it. Two images with phase-gradient information in different axes are converted into the two-dimensional phase distribution of the specimen by introducing the Phase Gradient Transfer Function, which is the intensity change due to refraction by the phase-gradient of a specimen. We confirm accurate and repeatable performance of our experimentally and demonstrate phase imaging of live cells.

Automated batch characterization of inkjet-printed elastomer lenses using a LEGO® platform

Yulung Sung, Jacob Garan, Hoang Nguyen, ZHENYU Hu, and Wei-chuan Shih

Doc ID: 297793 Received 12 Jun 2017; Accepted 09 Aug 2017; Posted 10 Aug 2017  View: PDF

Abstract: Small self-adhesive inkjet-printed elastomer lenses, have enabled smartphone cameras to image and resolve microscopic objects. However, the performance of different lenses within a batch is affected by hard-to-control environmental variables. We present a cost-effective platform to perform automated batch characterization of 300 lens units simultaneously for quality inspection. The system was designed and configured with LEGO® bricks, 3D printed parts, and a digital camera. The scheme presented here may become the basis of a high-throughput, in-line inspection tool for quality control purpose, and can also be employed for the optimization of manufacturing process.

Design, Fabrication and Demonstration of a Dielectric Vortex Waveguide in the Sub-THz Region

Nafiseh Aflakian, Tim LaFave Jr., Kenneth O, Solyman Ashrafi, and Duncan MacFarlane

Doc ID: 296759 Received 30 May 2017; Accepted 08 Aug 2017; Posted 08 Aug 2017  View: PDF

Abstract: A sub-terahertz vortex dielectric waveguide was designed and fabricated in the cyclic olefin copolymer, TOPAS, compound. The annular index profile was engineered using a holey cladding to support operation from approximately 200 to 300 GHz. The vortex waveguide was tested at 280 GHz using an OAM-endowed Laguerre-Gaussian mode generated by a stepped spiral phase plate.

Analyses of optical rays in KTN optical beamdeflectors for device design

Tadayuki Imai, Masahiro Ueno, Yuzo Sasaki, and Tadashi Sakamoto

Doc ID: 297372 Received 29 Jun 2017; Accepted 08 Aug 2017; Posted 09 Aug 2017  View: PDF

Abstract: The KTN optical beam deflector is an electrooptic deflector without any moving parts that works at frequencieshigher than 200 kHz. In this paper we discuss the performance parameters of this deflector. Optical beams are bentby the spatial distribution of the refractive index in the KTN crystal block used in this deflector. In addition to thedeflection function, the index distribution operates as a cylindrical convex lens. Therefore the deflector is oftenused with glass cylindrical lenses to cancel out the lens function. We analyzed optical rays curving in the blockbased on graded index lens theory. We describe the way in which such performance parameters as the deflectionangle change depending on both the choice of the compensating lenses and the parameters of the KTN block,namely its size and charge density. We concentrate especially on methods designed to improve the resolvable spotnumber, which is the most important figure of merit for optical deflectors. One way to achieve improvement is toinput a collimated beam or a slightly converging beam into the KTN block.

Determination of point of incidence for the case of reflection or refraction at spherical surface knowing two points lying on the ray

Antonin Miks and Pavel Novak

Doc ID: 298161 Received 16 Jun 2017; Accepted 08 Aug 2017; Posted 09 Aug 2017  View: PDF

Abstract: The paper is focused on the problem of determination of the point of incidence of a light ray for the case of the reflection or refraction at the spherical optical surface assuming two fixed points in space that the sought light ray should go through are given. The requirement is that one of these points lie on the incident ray and the other point on the reflected/refracted ray. Although at first glance it seems to be a simple problem, it will be shown that it has no simple analytical solution. The basic idea of the solution is given and it is shown that the problem leads to a nonlinear equation in one variable. The roots of the resulting nonlinear equation can be found by numerical methods of mathematical optimization. The proposed methods were implemented in MATLAB and the proper function of these algorithms was verified on several examples.

A line-scanning laser scattering system for fast defect inspection of large aperture surface

Jingtao Dong

Doc ID: 294477 Received 27 Apr 2017; Accepted 07 Aug 2017; Posted 07 Aug 2017  View: PDF

Abstract: Inspection of defects with micron-level on large aperture surfaces with hundreds of millimeters is one of the challenges in surface quality evaluation. Various microscopic imaging methods have been applied to inspect the surface defects, while they are time-consuming for the small field of view and the sub-aperture stitching. To tackle this problem, a high-speed line scanning system based on the dark-field laser scattering method is proposed. The laser beam is scanned by the rotating polygon mirror to a laser line for high throughput and then the telecentric f-theta lens converges each incoming laser beam to a focused spot that creates a high intensity to enhance the signal-to-noise ratio. The scattered light from surface defect is collected by the designed integrating sphere for low background noise and the scattering signal is detected for each focused spot at a proper acquisition rate by a PMT detector with extremely short response time. In the meanwhile, the tested surface is moving perpendicular to the laser line to realize high speed large area inspection. The defect inspection system is confirmed experimentally with laser line length of 60mm, minimum detectable size less than 0.5μm and figure of merit of 9.6 cm²s-¹μm-¹. The work put forward an effective method for automatic discovery of surface defects such as scratches, digs and contaminants on large aperture surfaces.

Validation of a gonio-hyperspectral imaging systembased on light-emitting diodes for the spectral andcolorimetric analysis of automotive coatings

Francisco Burgos, Meritxell Vilaseca Ricart, Esther Perales, Elisabet Chorro, Francisco Martínez-Verdú, José Fernández-Dorado, and Jaume Pujol

Doc ID: 296812 Received 26 May 2017; Accepted 07 Aug 2017; Posted 07 Aug 2017  View: PDF

Abstract: In this study, a novel gonio-hyperspectral imaging system based on light-emitting diodes for the analysisof automotive coatings was validated colorimetrically and spectrally from 368 nm to 1309 nm. A total of 30pearlescent, 30 metallic and 30 solid real automotive coatings were evaluated with this system, the BYKmacand X-Rite MA98 gonio-spectrophotometers and also with the SPECTRO 320 spectrometer for furthercomparison. The results showed very precise correlations, especially in the visible range. In conclusion,this new system provides a deeper assessment of goniochromatic pigments than current approaches dueto the expansion of the spectral range to the IR.

Decomposition and correction overlapping peaks of LIBS using an error compensation method combined with curve fitting

Bing Tan, Min Huang, Qibing Zhu, Ya Guo, and Jianwei Qin

Doc ID: 297189 Received 01 Jun 2017; Accepted 07 Aug 2017; Posted 07 Aug 2017  View: PDF

Abstract: Laser induced breakdown spectroscopy (LIBS) technique is an effective method to detect material composition byobtaining the plasma emission spectrum. The overlapping peaks in the spectrum are a fundamental problem in thequalitative and quantitative analysis of LIBS. Based on a curve fitting method, this paper studies an error compensationmethod to achieve the decomposition and correction of overlapping peaks. The vital step is that the fitting residual is fedback to the overlapping peaks and performing multiple curve fitting process to obtain a lower residual result. For thequantitative experiments of Cu, the Cu-Fe overlapping peaks in the range of 321-327nm obtained from the LIBSspectrum of five different concentrations of CuSO4·5H2O solution were decomposed and corrected using curve fittingand error compensation methods. Compared with the curve fitting method, the error compensation reduced the fittingresidual about 18.12%-32.64% and improved the correlation about 0.86%-1.82%. And then, the calibration curvebetween the intensity and concentration of the Cu was established. It can be seen that the error compensation methodexhibits a higher linear correlation between the intensity and concentration of Cu, which can be applied to thedecomposition and correction of overlapping peaks in LIBS spectrum.

Figuring porcess of KDP crystal using IBF technology

Li furen, Xuhui Xie, guipeng tie, Hao Hu, and Lin Zhou

Doc ID: 295319 Received 05 May 2017; Accepted 07 Aug 2017; Posted 08 Aug 2017  View: PDF

Abstract: Currently, ion beam figuring (IBF) technology has presented many excellent performances in figuring KDP crystals. Such as, it is a non-contact figuring process and it does not require polishing fluid. So it is a very clean figuring process and does not introduce any impurities. However, the ion beam energy deposited on KDP crystal will heat the KDP crystal and may generate cracks on it. So it is difficult directly using IBF technology to figure KDP crystal. As oblique incident IBF (OI-IBF) has lower heat deposition, higher removal rate and smoother surface roughness compared to normal incident IBF. This paper studied the process of using OI-IBF to figure KDP crystal. Removal rates and removal functions at different incident angles were first investigated. Then heat depositions on test work piece were obtained through experiments. In order to validate the figuring process, a KDP crystal with size of 200mm×200mm×12mm was figured by OI-IBF. After three iterations using OI-IBF process, the surface error decreases from the initial values with PV 1.986λ RMS 0.438λ to PV 0.215λ RMS 0.035λ. Experimental results indicate that OI-IBF is feasible and effective to figure KDP crystals.

Simplified paraboloid phase model based phase tracker for demodulation of a single complex fringe

Aohan He, Balakrishnan Deepan, and Chenggen Quan

Doc ID: 296081 Received 15 May 2017; Accepted 07 Aug 2017; Posted 08 Aug 2017  View: PDF

Abstract: Regularized phase tracker (RPT) is an effective method for demodulation of single closed fringe patterns. However,lengthy calculation time, specially designed scanning strategy, and sign-ambiguity problem caused by noise andsaddle points, reduce its effectiveness, especially for demodulating large and complex fringe patterns. In this paper,a simplified paraboloid phase model based regularized phase tracker (SPRPT) is proposed. In SPRPT, first andsecond phase derivatives are pre-determined by density-direction-combined method and discrete higher orderdemodulation algorithm (DHODA) respectively. Hence, cost function is effectively simplified to reduce thecomputation time significantly. Moreover, pre-determined phase derivatives improve the robustness of thedemodulation of closed complex fringe patterns. Thus, no specifically designed scanning strategy is needed;nevertheless it is robust against the sign-ambiguity problem. Paraboloid phase model also assures better accuracyand robustness against noise. Both the simulated and experimental fringe patterns (obtained using electronicspeckle pattern interferometry) are used to validate the proposed method, and a comparison of the proposedmethod with existing RPT methods is carried out. The simulation results show that the proposed method hasachieved the highest accuracy with less computational time. The experimental result proves the robustness andthe accuracy of the proposed method for demodulation of noisy fringe patterns and its feasibility for static anddynamic applications.

Integrated optical readout using hybrid plasmonicdirectional coupler in water

Ruozhou Li, Ying Yu, Xiaoyang Zhang, and Tong Zhang

Doc ID: 296303 Received 19 May 2017; Accepted 07 Aug 2017; Posted 08 Aug 2017  View: PDF

Abstract: Integrated polymer optical readout has been recognized as a promising route to obtain miniaturizedcantilever-based sensor works on static mode for various liquid-state chemical and biological measurements inportable lab-on-chip systems. For conventional optical readouts based on end-fire coupling mechanism, the mostsensitive region was limited to a cantilever deflection of several micrometers due to the Gaussian profile of themode in polymer waveguides. We proposed an integrated optical readout based on a hybrid plasmon directionalcoupler aiming at improving the sensitivity at sub-micrometer deflection region (<1 μm). The coupler consists of ashort-range surface plasmon waveguide and a polymer waveguide. We show that the coupling length and thepropagation loss of the coupler are ultra-sensitive to the deflection, which lead to improved sensitivity of thereadout. In addition, the dynamic range can be extended by integrating an array of hybrid plasmon directionalcouplers onto a single microcantilever. The proposed optical readout is beneficial to high sensitivitycantilever-based sensors for lab-on-chip applications, and allows for the design of more compact optical waveguidebased sensors in water.

MWIR thermal imaging spectrometer based on the acousto-optic tunable filter

Huijie Zhao, Zheng Ji, Guorui Jia, Ying Zhang, and Yansong Li

Doc ID: 291542 Received 28 Mar 2017; Accepted 07 Aug 2017; Posted 07 Aug 2017  View: PDF

Abstract: MWIR thermal imaging spectrometers are widely used in remote sensing, industrial detection and military applications. The acousto-optic tunable filter (AOTF) based spectrometer has the advantage of fast tuning, light weight and no moving parts, which is ideally suited in MWIR applications. However, when designing an AOTF imaging spectrometer, the traditional method used a refractive grating or parallel glass model in optical design software to simulate the AOTF, lowering the imaging performance of the optical system. In this paper, an accurate simulating model for an actual MWIR AOTF by using the user defined surface (UDS) function in ZEMAX is presented and an AOTF based MWIR thermal imaging spectrometer is designed and tested successfully. It is based on a MWIR tellurium dioxide (TeO2) AOTF with operational spectral range from 3.0 to 5.0 μm and spectral resolution of 30.8 nm at 3.392μm. The optical system employs a three-mirror off-axis afocal telescope with a 2.4°×2.0° field of view. The operation of the MWIR thermal imaging spectrometer and its image acquisition are computer controlled. Furthermore, the imaging spectrometer is tested in the laboratory and several experiments are also presented. The experimental results indicate that the proposed AOTF model is efficient, and meanwhile, show that the imaging spectrometer has the ability to distinguish the real hot target from the interfering target effectively.

Signal-to-Noise Ratio Enhancement of Hadamard Transform Spectrometer Using a 2-D Slit-array

Mingbo Chi, Yihui Wu, Fang Qian, peng hao, Wenchao Zhou, and Yongshun Liu

Doc ID: 296711 Received 31 May 2017; Accepted 06 Aug 2017; Posted 07 Aug 2017  View: PDF

Abstract: The encoding and decoding principle of the Hadamard transform spectrometer with a 2-D slit-array mask is described in this paper. Based on the Hadamard transform theory, the signal-to-noise ratio (SNR) enhancement of 2-D slit-array Hadamard transform spectrometer is deduced and verified experimentally. Affected by the optical system of the spectrometer, there are differences between the experimental results and theoretical calculations. In the end of this paper, we have discussed the influence of the spectrometer’s optical system on the SNR enhancement based on the spatial frequency analysis.

Fast and accurate phase unwrapping algorithm based on the Transport of Intensity Equation

J. Martinez-Carranza, Konstantinos Falaggis, and Tomasz Kozacki

Doc ID: 296032 Received 15 May 2017; Accepted 05 Aug 2017; Posted 07 Aug 2017  View: PDF

Abstract: The phase information of a complex field is routinely obtained using coherent measurement techniques as e.g. with interferometry or holography. The obtained measurement result is subject to a 2π ambiguity and is often referred to as wrapped phase. Phase unwrapping algorithms (PUAs) are commonly employed to remove this ambiguity, and hence, obtain the absolute phase. However, implementing PUAs can be computationally intensive and the accuracy of those algorithms may be low. Recently, the Transport of Intensity Equation (TIE) has been proposed as a simple and practical alternative for obtaining the absolute phase map. Nevertheless, an efficient implementation of this technique has not been made yet. In this work, we propose a Fourier-based accurate solution for the TIE-based PUA that improves significantly speed and accuracy. The proposed method calculates directly the axial derivative of the intensity from the wrapped phase when considering the correct propagation method. This is done in order to bypass the time-consuming wave-propagation techniques employed in similar methods. The analytical evaluation of this parameter allows obtaining an accurate solution when unwrapping the phase map with low computational effort. This work further shows that the use of a semi-iterative procedure that improves significantly the accuracy of the final absolute phase map. The utility of the developed TIE-unwrapping technique is proven both by numerical simulations and experiments for various objects.

1 kHz single-frequency 2.09 μm Ho:YAG ring laser

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

Doc ID: 297481 Received 05 Jun 2017; Accepted 04 Aug 2017; Posted 07 Aug 2017  View: PDF

Abstract: In this paper we report the experimental realization of a high-repetition rate single-frequency Ho:YAG ring laser at 2.09 μm. Single frequency operation of the ring laser is achieved by injection-seeding with a continuous wave (CW) Ho:YAG non-planar ring oscillator (NPRO) laser. The output energy of the ring laser is 6.24 mJ, with a pulse width of 172 ns and a repetition rate of 1 kHz. The beam quality M2-factor is measured to be ∼1.3 at the maximum output energy. The half-width of pulse spectrum is measured to be 2.61 MHz by a heterodyne technique.

Controllable direction of liquid jets generated by thermocavitation within a droplet

Juan Padilla Martinez, Julio Ramirez-San-Juan, Carla Berrospe-Rodriguez, Nikolai Korneev, Guillermo Aguilar, Placido Zaca, and Ruben Ramos-Garcia

Doc ID: 291679 Received 30 Mar 2017; Accepted 04 Aug 2017; Posted 07 Aug 2017  View: PDF

Abstract: A high-velocity fluid stream ejected from an orifice or nozzle is a common mechanism to produce liquid jets in inkjet printers or to produce sprays among other applications. In the present research, we show the generation of liquid jets of controllable direction produced within a sessile water droplet by thermocavitation. The jets are driven by an acoustic shock wave emitted by the collapse of a hemispherical vapor bubble at the liquid-solid/substrate interface. The generated shock wave is reflected at the liquid-air interface due to acoustic impedance mismatch generating multiple reflections inside the droplet. During each reflection, a force is exerted on the interface driving the jets. Depending on the position of generation of the bubble within the droplet, the mechanical energy of the shock wave is focused on different regions at the liquid-air interface, ejecting cylindrical liquid jets at different angles. The ejected jet angle dependence is explained by a simple ray tracing model of the propagation of the acoustic shock wave inside the droplet.

Reflectivity and transmissivity of a surface covered by a disordered monolayer of large and tenuous particles: Theory versus experiment

Omar Vazquez-Estrada and Augusto Garcia-Valenzuela

Doc ID: 293276 Received 19 Apr 2017; Accepted 03 Aug 2017; Posted 04 Aug 2017  View: PDF

Abstract: The main objective of this paper is to endorse a recently derived theoretical model for the coherent reflectance andtransmittance from a surface supporting a disordered monolayer of large and tenuous particles by comparisonwith experimental measurements. The model is based on the so-called anomalous-diffraction approximation and isassumed to be valid for small and moderate angles of incidence. We prepared disordered monolayers of sphericalpolystyrene particles of 1.8 μm diameter and of human red blood cells on glass microscope slides. In both cases,particles were immersed in a liquid of refractive index close to that of the particle. We measured the relativereflectivity and transmissivity of the samples versus the wavelength of light at normal incidence and the reflectivityand transmissivity versus the angle of incidence at a fixed wavelength, and compared with predictions of theanomalous-diffraction approximation model. For the polystyrene particles samples, we also compare the resultswith another available theoretical model developed some years ago do deal with disordered monolayers of highlyscattering particles. In the case of red blood cells monolayers, we also present measurements with a hemolyzedsample and a disordered multilayer film for comparison. We find that the anomalous diffraction model can befitted very well to the experimental curves, in some cases, even for high angles of incidence.

1018 nm Yb-doped high power fiber laser pumped by broadband pump sources around 915 nm with output power above 100 W

Yakup Midilli, Oyewole Efunbajo, Bartu Simsek, and Bulend Ortac

Doc ID: 297982 Received 16 Jun 2017; Accepted 03 Aug 2017; Posted 04 Aug 2017  View: PDF

Abstract: We demonstrate a 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources operating the broad absorption spectrum around 915 nm. In the experiment, two different pump diodes were tested to pump over a wide spectrum ranging from 904 nm to 924 nm by altering the cooling temperature of pump diodes. Across this so called pump wavelength regime having 20 nm wavelength span, the amplified stimulated emission (ASE) suppression of the resulting laser was generally around 35 dB showing good suppression ratio. Comparisons to the conventional 976 nm pumped 1018 nm ytterbium-doped fiber laser were also addressed in this study. Finally, we have tested this system for high power experiment and obtained 67% maximum optical to optical efficiency at approximately 110 W output power level. To the best of our knowledge, this is the first 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources around 915 nm, reported in detail.

Self-correction of projector nonlinearity in phase-shifting fringe projection profilometry

Fuxing LÜ, Shuo Xing, and Hongwei Guo

Doc ID: 298265 Received 20 Jun 2017; Accepted 03 Aug 2017; Posted 04 Aug 2017  View: PDF

Abstract: In phase-shifting fringe projection profilometry, the luminance nonlinearity of the used projector has been recognized as one of the most crucial factors decreasing the measurement accuracy. To solve this problem, this paper presents a novel self-correcting technique that allows us to suppress the effect of the projector nonlinearity in the absence of any calibration data regarding the projector intensities or regarding the phase errors. In its first step, the standard phase-shifting algorithm is used to recover the phases, as well as the background intensities and the modulations. Using these results enables normalizing the fringe patterns, for ridding them of the effects of the background and modulations. Secondly, we smooth the calculated phase map by use of a low-pass filter in order to remove the ripple-like phase errors induced by the projector nonlinearity. Thirdly, we determine a polynomial representing the projector nonlinearity by fitting the curve of the normalized fringe intensities against the cosine values of the smoothed phases. Finally, we correct the phase errors using the curve just obtained. Doing these steps in an iterative way eventually results in a phase map and further a 3D shape with their artifacts induced by the projector nonlinearity suppressed significantly. Experimental results demonstrate that this technique offers some advantages over others. It does not require a prior calibration to the projector thus being suitable for dealing with a time-variant nonlinearity; its pointwise operation protects the edges and details of the measurement results from being blurred; and it works well with very few fringe patterns and is efficient in image capturing.

Wander of the short-term spreading filter for partially coherent Gaussian beams through the anisotropic turbulent ocean

Yanqiu Yang, Lin Yu, Qiu Wang, and YiXin Zhang

Doc ID: 297208 Received 01 Jun 2017; Accepted 02 Aug 2017; Posted 02 Aug 2017  View: PDF

Abstract: The models of the short-term spreading and wander of the short-term spreading filter for partially coherent Gaussian (PCG) beams propagating in an anisotropic oceanic turbulence are established. The results of beam wander based on our model are larger than L. C. Andrews and R. L. Phillips's model which weakens the effect of irradiance fluctuations on the beam wander. The results of our model show that, the short-term spreading and wander of beams increase as the rate of dissipation of kinetic energy per unit mass of fluid and the emitting beam radius decrease, but they increase as the dissipation rate of temperature variance increases. As the temperature fluctuation of the oceanic turbulence gets stronger, the beam wander rises first and then turns into the wander saturation. The larger inner scale of turbulence will decrease the short-term spreading of the beam and increase the beam wander. It also indicates that the anisotropy can restrain the impact of the turbulence to some extend in the oceanic channel. The salinity fluctuation has a greater impact on both short-term spreading and wander of the beam than temperature fluctuation does in oceanic turbulence.

Double-sided telecentric zoom lens consisting of four tunable lenses with fixed distance between object and image plane

Antonin Miks and Pavel Novak

Doc ID: 300880 Received 23 Jun 2017; Accepted 02 Aug 2017; Posted 02 Aug 2017  View: PDF

Abstract: This work performs a paraxial analysis of the double-sided telecentric zoom lens consisting of four tunable lenses with fixed distance between object and image plane. Equations enabling calculation of paraxial parameters of such optical systems are derived and the calculation is presented on examples. To our knowledge the presented analysis is novel and such optical systems have not been investigated yet.

Demonstration of 3D computed tomography of chemiluminescence with restricted field of view

Hecong Liu, Tao Yu, man zhang, and Weiwei Cai

Doc ID: 297552 Received 16 Jun 2017; Accepted 01 Aug 2017; Posted 01 Aug 2017  View: PDF

Abstract: Three-dimensional imaging techniques have experienced surged research interests during the past a few years due to the advancements in both hardware i.e. the sensor arrays and data acquisition system, and new imaging concepts such as light field imaging and compressed sensing. Computed tomography of chemiluminescence (CTC) is an intriguing technique for combustion diagnostics due to its ease of implementation as no excitation source is required in measurements. It has been applied extensively for the retrieval of intermediate species such as CH*/OH* from which the flame topology can be obtained. However, all the previous demonstrations or applications were performed under the assumption that a complete field of view is available for all projections. However, this prerequisite cannot be guaranteed for some practical scenarios such as engine measurements in which optical access is extremely limited and a portion of the field of view is unavoidably blocked especially when a considerable number of projections are required. This work aims to develop an improved CTC modality that can handle projections with restricted field of view, and suggest the best strategy for tomographic reconstruction under such experimental conditions. Although this technique is discussed under the context of combustion diagnostics, it can also be useful and adapted for other tomographic areas such as biomedical imaging.

Improved generation method utilizing a modified Fourier spectrum for Airy beams with the phase-only filter technique

ling yong, yang yun, zhang xue, Qiang Lu, liu shuai, and guo zi

Doc ID: 296483 Received 22 May 2017; Accepted 01 Aug 2017; Posted 01 Aug 2017  View: PDF

Abstract: We present an improved method to generate Airy beams utilizing a liquid crystal on silicon (LCoS) device. In thismethod, the phase and amplitude information of a modified Fourier spectrum of Airy beam together with a Fresnelholographic lens is encoded onto the LCoS using the phase-only filter technique, thus a desired Airy beam is formedin the focal plane of the Fresnel holographic lens. In this paper, the principle of the proposed method is describedin detail. And both the excellent numerical simulations and experimental results for verifying this method aredemonstrated. It is shown that the new generation method is accurate and simple, particularly the setup is morecompact comparing with the conventional Fourier transform method, which only comprises the input polarizedlaser and a LCoS device. The meaningful method will further promote the investigations on the properties andapplications of Airy beam.

The investigation for connecting waveguide in off-planar integrated circuit

Jie Lin and zhifang Feng

Doc ID: 292176 Received 14 Apr 2017; Accepted 31 Jul 2017; Posted 01 Aug 2017  View: PDF

Abstract: The transmission properties of a vertical waveguide connected the different devices in off-planar integrated circuitare designed, investigated and analyzed in detail by the finite-difference time-domain method. The results showthat both guide band width and transmission efficiency can be adjusted effectively by shifting continuously thevertical waveguide. Especially surprised, the wide guide band (0.385[c/a]~0.407[c/a]) and well transmission (-6dB) are observed simultaneously in several directions when the vertical waveguide is located at the specificlocation. The results are very important for all-optical integrated circuit, especially in compact integration.

Enhanced 3 μm luminescence properties based oneffective energy transfer Yb3+: 2F5/2→Dy3+: 6H5/2 influoaluminate glass modified by TeO2

Fangwei Qi, Feifei Huang, Tao Wang, ying tian, Ruo Lei, Renguang Ye, Junjie Zhang, Long Zhang, and Shiqing Xu

Doc ID: 296563 Received 30 May 2017; Accepted 30 Jul 2017; Posted 01 Aug 2017  View: PDF

Abstract: Enhanced 3 μm luminescence of Dy3+ based on the effective process of Yb3+: 2F5/2→Dy3+: 6H5/2 with higher energytransfer coefficient of 7.36×10-39 cm6/s in fluoaluminate glass modified by TeO2 was obtained. The energy transferefficiency from Yb3+ to Dy3+ in Dy3+/Yb3+ co-doped was as high as 80%, indicating effective energy transfer of Yb3+.The higher temperature of glass transition (Tg) and larger characteristic temperatures (ΔT, Kgl) revealed betterthermal properties of the prepared glasses compared with the traditional fluoaluminate glasses, which is of greatbenefit to fiber drawing. The lower hydroxyl content (15.7 ppm) indicated better fluorescence properties of theglass. It was noted that the longer lifetime of 572 μs and higher emission cross section of 5.22×10-21 cm2 along withthe bandwidth of 245 nm around 3 μm proved potential applications in mid-IR laser materials of the present glass.

Ion-exchanged binary phase plates for mode multiplexing in graded-index optical fibers

Jesús Liñares, Carlos Montero-Orille, Vicente Moreno, Dolores Mouriz, María C. Nistal, and Xesús Prieto-Blanco

Doc ID: 296588 Received 23 May 2017; Accepted 29 Jul 2017; Posted 01 Aug 2017  View: PDF

Abstract: Few-mode graded-index optical fibers are being increasingly relevant in spatial division multiplexing. Likewise, multi-region binary phase plates are fundamental elements for some mode multiplexing schemes in such optical fibers. In this work we propose a coupling configuration for mode multiplexing based on collimating-focusing graded-index lenses together with binary phase plates, and calculate, in a fully analytical and quasi-analytical way, the theoretical conversion efficiencies and crosstalks between the fields generated by such plates and the Laguerre-Gaussian modes. These modes describe, directly or by a linear combination of them, the first optical modes of many graded-index optical fibers. The results obtained provide both the illumination conditions of the plates and their optical characteristics. The fabrication of the plates is made by using ion-exchange technology and their optical characterization by beam profilometry. The experimental conversion efficiencies are in agreement with the theoretical results.

Self-shading associated with an SBA system for measurement of water-leaving radiance and its correction

Zhehai Shang, Zhongping Lee, Qiang Dong, and Jianwei Wei

Doc ID: 296287 Received 18 May 2017; Accepted 29 Jul 2017; Posted 01 Aug 2017  View: PDF

Abstract: The shading error associated with the water-leaving radiance (Lw) measured via the Skylight Blocked Approach (SBA, Lee et al. 2013) is characterized by Monte Carlo simulations, and it is found this error is in a range of ~1-20% under most water properties and solar positions. A model for estimating this shading error is further developed, and eventually a scheme to correct this error based on the shaded measurements is proposed and evaluated. It is found that the shade-corrected value in the visible domain is within 3% of the true value, which thus indicates that with the SBA scheme, we can obtain not only high precision, but also high accuracy Lw in the field.

Error analysis of the calibration of a dual-rotating-retarder Mueller matrix polarimeter

Xuemin Cheng, Maolin Li, Jialing Zhou, Hui Ma, and Qun Hao

Doc ID: 297875 Received 13 Jun 2017; Accepted 29 Jul 2017; Posted 01 Aug 2017  View: PDF

Abstract: We previously developed a Mueller matrix microscope by combining a dual-rotating-retarder device with a commercial microscope, with promise for pathologic diagnosis applications. In practical applications, the signals to be measured are sensitive to systematic errors, and the measurement accuracy and the instrument calibration affect the capacity to characterize the data. In conventional calibration, the initial positions of the rotating devices are constrained, causing calibration instability. To improve the calibration, we examine the mathematical model of the calibration process using previous studies, and derive a calibration algorithm with reduced error magnification. Our experimental results show the proposed algorithm improves calibration accuracy, and provides more robust results.

Mean estimation empirical mode decompositionmethod for terahertz time-domain spectroscopy denoising

Xiao Qiao, Jiao Ren, Dandan Zhang, CAO GUOHUA, Xinming Zhang, and Lijuan Li

Doc ID: 296284 Received 18 May 2017; Accepted 28 Jul 2017; Posted 03 Aug 2017  View: PDF

Abstract: The wavelet-domain de-noising technique has many applications in terahertz time-domain spectroscopy (THz-TDS). However, it requires a complex procedure for the selection of the optimal wavelet basis and threshold, whichvary for different materials. Inappropriate selections can lead to de-noising failure. Here, we propose the MeanEstimation Empirical Mode Decomposition (ME-EMD) de-noising method for THz-TDS. First, the THz-TDS signaland the collected reference noise are decomposed into the intrinsic mode functions (IMFs); second, the maximumand mean absolute values of the noise IMF amplitudes are calculated and defined as the adaptive threshold andadaptive estimated noise value, respectively; finally, these thresholds and estimated noise values are utilized tofilter the noise from the signal IMFs and reconstruct the THz-TDS signal. We also calculate the signal–to-noise ratio(SNR) and mean square error (MSE) for the ME-EMD method, the ‘db7’ wavelet basis, and the ‘sym8’ wavelet basisafter de-noising, in both the simulation and the real sample experiments. Both theoretical analysis andexperimental results demonstrated that the new ME-EMD method is a simple, effective, and high-stability denoisingtool for THz-TDS pulses. The measured refractive index curves are compared before and after de-noising,and demonstrated that the de-noising process is necessary and useful for measuring the optical constants of asample.

Beam diameter thresholds as applying light depolarization for effective submicron and micron RMS roughness evaluation

Linsheng Liu and Kazuhiro Nonaka

Doc ID: 295887 Received 15 May 2017; Accepted 27 Jul 2017; Posted 01 Aug 2017  View: PDF

Abstract: In order to further study the microscopic mechanism and beam diameter effect during light depolarization (LDP),we developed a compact laser instrument (λ=632.8 nm) with adjustable beam diameter ≥ 18 μm (approximately28λ). Six nickel plate-samples with RMS roughness, Rq, of 42 nm ~ 2.3 μm (i.e., 0.067 ~ 3.7λ) fabricated by finehoningmethod are examined. To analyze the beam diameter effect as applying LDP for sub-micron and micron Rqevaluation, the cross-sectional beam-spot size (BSS) is adjusted from 20 to 650 μm during off-specular inspections.The results of BSS ≤ 40 μm (i.e. 60λ) have a 10 nm-level Rq sensitivity, while that of BSS ≥ 140 μm (220λ) have anabout 100 times weaker sensitivity. It means that BSS of 60 and 220λ should have instructional significance asapplying LDP for precision levels of 10 nm and 1 μm surface roughness analyses, respectively. In addition, since theinstrument is simple, portable, stable and has a low-cost, it has great potential for both LDP analyses and practicalonline roughness testing.

Optomechanical Design of Rotary Kaleidoscope for Bidirectional Texture Function Acquisition

Jiri Cap, Jan Hosek, Vlastimil Havran, Sarka Nemcova, and Kakolina Macuchova

Doc ID: 295427 Received 11 May 2017; Accepted 26 Jul 2017; Posted 27 Jul 2017  View: PDF

Abstract: Optical systems are traditionally used for accurate recording and measurement of the real world’s appearance. Present techniques allow us to form a computer based virtual world, which is used in a variety of technical fields. The crucial issue for future applications of virtual reality is the fidelity of rendered images to real world objects. This is strongly affected by the appearance of the rendered object’s surfaces. Currently, the most accurate method of describing a surface’s characteristics is bidirectional texture function, BTF. We have designed, optimized, built and tested a unique portable instrument based on a rotary kaleidoscope principle for BTF acquisition in situ. Such an instrument has never been used before to measure BTF of a surface. We enhanced a common static kaleidoscope by adding rotation, which allows us to get a larger number of images of the sample for more combinations of illumination directions and viewing directions. This results in a higher directional and spatial resolution of measured BTF data. In this paper we focus on the optomechanical design of the rotary BTF measurement instrument and issues related to its alignment to keep the desired mechanical precision.

Recent progress of quantum cascade laser research from 3-12 µm at the Center for Quantum Devices

Manijeh Razeghi, Wenjia Zhou, Steven Slivken, Quanyong Lu, Donghai Wu, and Ryan McClintock

Doc ID: 296920 Received 31 May 2017; Accepted 26 Jul 2017; Posted 27 Jul 2017  View: PDF

Abstract: The quantum cascade laser (QCL) is becoming the leading laser source in the mid-infrared (mid-IR) range, which contains two atmospheric transmission windows and many molecular fingerprint absorption features. Since its first demonstration in 1994, the QCL has undergone tremendous development of the output power, wall plug efficiency, wavelength coverage and tunability, beam quality, and for various applications based on QCL technology. At the Center for Quantum Devices, we have demonstrated high power continuous wave operation of QCLs covering a wide wavelength range from 3 to 12 μm, with power output up to 5.1 W at room temperature. Recent research has resulted in power scaling in pulsed mode with up to 203W output, electrically tunable QCLs based on monolithic sampled grating design, heterogeneous QCLs with a broad spectral gain, broadly tunable on-chip beam-combined QCLs, QCL-based mid-IR frequency combs and fundamental mode surface emitting quantum cascade ring lasers. The developed QCLs will be the basis for a number of next-generation spectroscopy and sensing systems.

Extra-cavity radiofrequency modulator for a lidar-radar designed for underwater target detection.

Nour ALEM, Fabrice Pellen, Guy Le Brun, and Bernard Le Jeune

Doc ID: 297245 Received 01 Jun 2017; Accepted 26 Jul 2017; Posted 27 Jul 2017  View: PDF

Abstract: Hybrid LIDAR Radar technique is commonly used for shallow underwater target detection. This technique requires a powerful blue-green RF modulated laser with stable microwave frequency. In this paper, a novel modulator design perfectly suited for this application is proposed. It consists in an extra-cavity modulator composed of two plane mirrors and a Second Harmonic Generator (SHG) stage within the cavity to maximize the energy efficiency. This modulator is coupled with a picosecond Nd:YAG infrared laser source to insure delivering a powerful pulse (up to 5 mJ). Results considering this architecture show stable modulation frequency and powerful modulated beam. As the emitted signal last only few nanoseconds, a range gating method can be used for target localization. This emitted signal has experimentally proven to preserve the input beam polarization which can be also employed to enhance the target return.

Breast density quantification using structured-light based diffuse optical tomography simulations

Jessica Kwong, Farouk Nouizi, Jaedu Cho, Jie Zheng, Yifan Li, Jeon-Hor Chen, Min-Ying Su, and Gultekin Gulsen

Doc ID: 301004 Received 26 Jun 2017; Accepted 26 Jul 2017; Posted 02 Aug 2017  View: PDF

Abstract: We present the feasibility of structured-light based diffuse optical tomography (DOT) to quantify the breast density with an extensive simulation study. This study is performed on multiple numerical breast phantoms built from magnetic resonance imaging (MRI) images. These phantoms represent realistic tissue morphologies and are given typical breast optical properties. First, synthetic data are simulated at five wavelengths using our structured-light based DOT forward problem. Afterwards, the inverse problem is solved to obtain the absorption images and subsequently the chromophore concentration maps. Parameters, such as segmented volumes and mean concentrations, are extracted from these maps and used in a regression model to estimate the percent breast densities. These estimations are correlated with the true values from MRI, r = 0.97, showing that our new technique is promising in measuring breast density.

Dependence of depth of focus on spherical aberration of optical systems

Antonin Miks and Jiri Novak

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

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

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