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Accepted papers to appear in an upcoming issue

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Learning-based focusing through scattering media

Ryoichi Horisaki, Takagi Ryosuke, and Jun Tanida

Doc ID: 291160 Received 22 Mar 2017; Accepted 24 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: We present a machine-learning-based method for light focusing through scattering media.In this method, the optical process in a scattering medium is computationally inverted based on a nonlinear regression algorithm with a number of training input-output pairs through the medium, and an input optimized for a target output is calculated.We experimentally demonstrate focusing through a process with a randomness by a scattering media and a nonlinearity by a double modulation with a spatial light modulator.Our approach realizes model-free control of optical fields, where optical processes or models are unknown.

Optimization method of star tracker orientation for sun-synchronous orbit based on space light distribution

Geng Wang, Fei Xing, Minsong Wei, Ting Sun, and Zheng You

Doc ID: 286123 Received 06 Feb 2017; Accepted 22 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: The star tracker, an optical attitude sensor with high precision, is susceptible to the space light from the sun and the earth albedo. Researches in this field relatively lack of a systematic analysis up to now. This paper proposed a pointing orientation method for the star tracker onboard the sun-synchronous orbit spacecraft, and analyzed the space light distribution by transforming the complicated relative motion among the sun, the earth and the satellite to the body coordinate system of the satellite. Meanwhile, the boundary-curve equations of the areas exposed in the stray light from the sun and earth albedo were calculated by the coordinate-transformation matrix under different maneuver attitudes, and the installation orientation of the star tracker was optimized based on the boundary equations, instead of the traditional iterative simulation method. The simulation experiment indicated that this pointing orientation method was more effective and precise, and could provide a theoretical foundation for the installation of the star tracker free from the stray light.

Movement Flatness Error Measurement based on Astigmatic Method

Xin Liang, Zhen Bai, and Jingsong Wei

Doc ID: 287483 Received 24 Feb 2017; Accepted 22 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: The movement flatness error is one of the critical parameters of motorized stage performance. In this work, the measurement of movement flatness error based on an astigmatic method is proposed, in which the focus error signal is detected and used to analyze the flatness error. The theoretical derivation and analysis are presented, and the experimental system is established accordingly. The experimental results indicate that our measurement method and established system exhibit an accuracy of less than ±100 nm. The movement flatness error of an x-y motorized stage is measured using the established system, and the movement flatness error profile is mapped; it was determined that the maximum flatness error is within 0.9 μm in our experiment. The proposed method is hence proven to be an effective way of measuring the movement flatness error of motorized stages.

Self-calibrating phase-shifting interferometry of three unequal phase-steps by fitting background light by a polynomial of degree K

Cruz Meneses-Fabian and Nydia Tejeda-Muñoz

Doc ID: 286236 Received 08 Feb 2017; Accepted 21 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: This paper presents a novel non-iterative and robust algorithm in phase-shifting interferometry of three unknown and unequal phase-steps. First, the modulation light and the object phase are algebraically eliminated, second, the background light is approximated, by a 2-D polynomial of degree K, and estimated by applying the least squares method, third the phase-steps are obtained, and finally, the object phase is computed. This idea is theoretically described and numerical and experimentally verified for several values of K

Interaction of two singular Lissajous lines in free-space

Haitao Chen, Zenghui Gao, and Wanqing Wang

Doc ID: 286071 Received 21 Feb 2017; Accepted 21 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: The interaction of two Singular Lissajous lines emergent from a polychromatic vector beam is studied. It is shown that singular Lissajous lines disappear with propagation,meanwhile Lissajous singularities take place. In addition, the handedness reversal, the changes in the shape of Lissajous figures and the degree of polarization of Lissajous singularities, as well as the creation and annihilation of single or pairs of Lissajous singularities may appear by varying the propagation distance, off-axis distance, wavelengths, or amplitude factors.

Inflight observation of Bottlinger's rings

Joseph Shaw

Doc ID: 287781 Received 28 Feb 2017; Accepted 21 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: On the morning of 5 November 2013 a bright subsun was consistently visible during a flight from Bozeman, Montana to Salt Lake City, Utah. Just after passing over the Wasatch Mountains and beginning to descend into the Salt Lake Valley, the subsun expanded to a rare display of Bottlinger’s rings – an elliptical halo surrounding the subsun. The rings remained visible for one minute or less. This paper shows photographs of tbe sequence, along with meteorological data from a nearby radiosonde. The display occurred in virga below clouds at an air temperature in the approximate range from -8 to -12 °C, in air saturated with respect to ice, at an altitude of approximately 2600-3600 m above mean sea level.

Optimization technique for rolled edge control process based on the acentric tool influence functions

Hang Du, Ci Song, Shengyi li, Mingjin Xu, and Xiaoqiang Peng

Doc ID: 285327 Received 23 Jan 2017; Accepted 21 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: In the process of computer controlled optical surfacing (CCOS), the uncontrollable rolled edge restricts the further improvement of the machining accuracy and efficiency. Two reasons are responsible for the rolled edge problem during small tool polishing. One is the edge areas cannot be processed because of the orbit movement. The other is that the tool influence function (TIF) changing is difficult to compensate in algorithm since pressure step appears in the local pressure distribution at the surface edge. In this paper, an acentric tool influence function (A-TIF) is designed aiming at the rolled edge after CCOS polishing. The model of A-TIF is analyzed theoretically. Combine with a control point translation dwell time algorithm to make the full aperture of workpiece can be covered by the peak removal point of tool influence functions. Thus surface residual error in full-aperture can be corrected effectively. Finally, a quartz glass of 100mm×100mm is polished by this designed A-TIF. The residual error converges from 0.09μm RMS, 0.6μm PV to 0.03μm RMS, 0.38μm PV. The ability to suppress the rolled edge of the designed A-TIF has been confirmed.

Ultra-compact air mode photonic crystal nanobeam cavity integrated with bandstop filter for refractive index sensing

Fujun Sun, Zhongyuan Fu, Chunhong Wang, Zhaoxiang Ding, Chao Wang, and Huiping Tian

Doc ID: 285361 Received 23 Jan 2017; Accepted 20 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: We propose and investigate an ultra-compact air mode photonic crystal nanobeam cavity (PCNC) with ultra-high quality factor-to-mode volume ratio (Q/V) by quadratically tapering the lattice space of the rectangular holes from the center to both ends while other parameters remain unchanged. By using three dimensional finite-difference time-domain (3D-FDTD) method, an optimized geometry yields a Q of 7×10⁶ and a V ~ 0.026(λ/n)³ in simulations, resulting an ultrahigh Q/V ratio exceeding 108(λ/n)-³. When the number of holes on either side is 8, the cavity possesses a high sensitivity (S) of 252nm/RIU (refractive index unit), a high calculated Q-factor of 1.27×10⁵ and an ultra-small effective V of ∼0.018(λ/n)³ at the fundamental resonant wavelength of 1522nm. Particularly, the footprint is only about 8×0.7μm². However, inevitably our proposed PCNC has several higher-order resonant modes in the transmission spectrum, which makes the PCNC difficult to be used for multiplexed sensing. Thus, a well-designed bandstop filter with weak sidelobes and broad bandwidth based on photonic crystal nanobeam waveguide is created to connect with the PCNC to filter out the high-order modes. Therefore, the integrated structure presented in this work is promising for building ultra-compact lab-on-chip sensors array with high density and parallel-multiplexing capability.

Analysis and manipulation of the induced changes in the state of polarization by mirror scanners

Anna Petrova-Mayor and Sarah Knudsen

Doc ID: 285996 Received 01 Feb 2017; Accepted 20 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: The induced polarization effects of metal-coated mirrors were studied in the configurations of one- and two-mirror lidar scanners as a function of azimuth and elevation angles. The theoretical results were verified experimentally for three types of mirrors (custom enhanced gold, off-the-shelf protected gold, and protected aluminum). A method was devised and tested to maintain a desired polarization state (linear or circular) of the transmit beam for all pointing directions by means of rotating wave-plates in the transmit and detection paths. Alternatively, the mirror coating can be optimized to preserve the linear polarization state of the transmitted beam. The compensation methods will enable ground-based scanning lidars to produce absolutely calibrated depolarization measurements.

Nanoparticle Classification in Wide-field Interferometric Microscopy by Supervised Learning from Model

Oguzhan Avci, Celalettin Yurdakul, and Selim Unlu

Doc ID: 290361 Received 10 Mar 2017; Accepted 20 Apr 2017; Posted 20 Apr 2017  View: PDF

Abstract: Interference enhanced wide-field nanoparticle imaging is a highly sensitive technique that has found numerous applications in labeled and label-free sub-diffraction-limited pathogen detection. It also provides unique opportunities for nanoparticle classification upon detection. More specif- ically, the nanoparticle defocus images result in a particle-specific response that can be of great utility for nanoparticle classification, particularly based on type and size. In this work, we com- bine a model based supervised learning algorithm with a wide-field common-path interferometric microscopy method to achieve accurate nanoparticle classification. We verify our classification schemes experimentally by using gold and polystyrene nanospheres.

Mapping of spectral signatures with snapshot spectral imaging

Michael Golub, Oren Pe'eri, and Menachem Nathan

Doc ID: 284366 Received 09 Jan 2017; Accepted 20 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: We propose a snapshot spectral imaging method that enables direct reconstruction of spatial maps for spectral signatures of given materials using a monochromatic image sensor. An image-plane array of dispersive shapers converts an aerial image of an object into a tailored mixture of spectral and spatial data that is sensed and digitally processed to reconstruct weight coefficients of the spectral signatures. The feasibility of the method is proven by computer simulations.

>1 kW All-Fiberized Narrow-Linewidth Polarization-Maintained Fiber Amplifier with Wavelength Spanning from 1065 nm to 1090 nm

Yakun Liu, Rongtao Su, Pengfei Ma, Xiaolin Wang, hanwei zhang, Pu Zhou, and Lei Si

Doc ID: 285652 Received 01 Feb 2017; Accepted 20 Apr 2017; Posted 20 Apr 2017  View: PDF

Abstract: We demonstrate all-fiberized, kilowatt-level, narrow-linewidth, Yb-doped and polarization-maintained (PM) amplifiers with central wavelength spanning from 1065 nm to 1090 nm. The laser system consists of a tunable single-frequency laser seed and multi-stage PM fiber amplifiers in the master oscillator power amplifier (MOPA) configuration. The SBS effect is suppressed by phase modulation based on a white noise source (WNS). The linewidth (∆λ ~ 0.12 nm @ 1 kW), polarization extinction ratio (PER > 13 dB) and beam quality (M2 ~ 1.2) are well maintained during the power scaling process and the slope efficiency of this system is 70.8 %. To the best of our knowledge, this is the first demonstration of the spectral tunable, all-fiberized, narrow-linewidth, linear-polarized and near diffraction limited amplifiers at kW power-level.

An opto-mechanical design of a dispersive artificial eye

Mark Coughlan, Toshifumi Mihashi, and Alexander Goncharov

Doc ID: 286038 Received 02 Feb 2017; Accepted 20 Apr 2017; Posted 20 Apr 2017  View: PDF

Abstract: We present an opto-mechanical artificial eye that can be used for examining multi-wavelength ophthalmic instruments. Standard off-the-shelf lenses and a refractive index matching fluid were used in the creation of the artificial eye. In addition to dispersive properties, the artificial eye can be used to simulate refractive error. To analyze the artificial eye, a multi-wavelength Hartmann-Shack aberrometer was used to measure the longitudinal chromatic aberration and the possibility of inducing refractive error. Off-axis chromatic aberrations were also analyzed by imaging through the artificial eye at two discrete wavelengths. Possible extensions to the dispersive artificial eye are also discussed.

1kHz, 96W pulse-bursts picosecond laser system with 6 equal amplitude and spacing pulses in a 4 ns

Mingliang Long, G Li, and Meng Chen

Doc ID: 287869 Received 08 Mar 2017; Accepted 20 Apr 2017; Posted 20 Apr 2017  View: PDF

Abstract: An average power of 96 W, six pulses in a burst picosecond Nd:YAG laser system at a pulse repetition frequency of 1 kHz was reported. The six pulses in a burst have equal amplitude and pulse spacing, pulse spacing between each other was 800 ps, which repetition rate was up to gigahertz, the beam quality of M² factor was less than 3, pulse width was 50 ps. Beam splitter mirrors split and combined the pulse beam, making the single pulse divided into six pulses. A volume-bragg-gratings, serrated aperture, Nd:YAG regenerative amplifier and two stage of single passed high gain Nd:YAG amplifier were applied.

Fabrication of asymmetric long-period gratings in polarization-maintaining fiber with CO2 laser

Wang Qingquan, Yunqi Liu, Liang Zhang, and Tingyun Wang

Doc ID: 287830 Received 02 Mar 2017; Accepted 20 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: We propose the fabrication of the long-period fiber gratings (LPFGs) in a panda polarization-maintaining fiber (PMF) using two-step CO2 laser writing method. The first laser irradiation was aligned along one of axes of the PMF and the grating with high contrast can be written after several laser scannings. The second irradiation could be performed by rotating the PMF so that the other axis of the fiber aligning toward to the laser exposure. New transmission dips can be observed when the first irradiation is along the slow axis and the second one is along the fast axis of the PMF. The stress relaxation effect of the stress-applying parts was investigated theoretically and experimentally, which is believed to be dominant for the fabrication of the LPFGs in the PMFs by CO2 laser.

Mid-infrared supercontinuum generation in multimode As2Se3 chalcogenide photonic crystal fiber

Amani Ben Khalifa, Amine Ben Salem, and Rim Cherif

Doc ID: 287568 Received 27 Feb 2017; Accepted 19 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: We report a mid-infrared supercontinuum generation (SCG) in a multimode chalcogenide photonic crystal fiber (PCF). An interesting behavior is observed due to the strong nonlinear coupling between six modes when taking into account two-fold degeneracy. By solving the multimode generalized nonlinear Schrödinger equation (MM-GNLSE), we predict the generation of a very broadband supercontinuum in both polarizations of the fundamental mode where the energy is transferred from the excited mode HE11a to mode HE11b. The obtained SCG spans from 2 to 11 µm in only 5 cm PCF length when injecting a 500 fs pulse with a relatively high peak power of 50 kW at 4.1 µm. Moreover, a high order supercontinuum is generated in both HE31 polarized modes where the energy has been transferred from the excited HE31a mode to HE31b mode. Our results confirm that energy transfer occurs only between optical degenerate modes when propagating in a multimode chalcogenide PCF in the mid-infrared region.

High-order rainbows of a spherical particle produced by near-grazing incident light

James Lock

Doc ID: 285005 Received 17 Jan 2017; Accepted 19 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: This study is concerned with the formation of high-order rainbows by near-grazing light incident on a spherical particle. As the number of internal reflections involves increases, the incident Descartes ray strikes the sphere surface increasingly closer to its edge where the predictions of ray theory and Airy theory become invalid. The deflection angle of the confluence of the stationary points of the phase of the partial wave scattering amplitudes is studied as a function of rainbow order and sphere radius. It is found that as the rainbow order increases, the angular interval over which the upper supernumerary ray stationary point occurs shrinks to zero. In addition, for deflection angles beyond the confluence of the upper supernumerary ray with the tunneling ray, intensity oscillations are due to interference of the field of the lower supernumerary ray with that of the edge region Fock transition, rather than interference between the upper and lower supernumerary rays.

Laser characteristics of Nd3+-doped calcium bariumniobate ferroelectric crystal at 1.06 and 1.34 μm

Jinglong Lan, Xiaoxu Huang, Xiaofeng Guan, Bin Xu, Huiying XU, Zhiping Cai, Xiaodong Xu, Dongzhen Li, and Jun Xu

Doc ID: 285947 Received 31 Jan 2017; Accepted 18 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: We report on diode-pumped Nd3+-doped calcium barium niobate ferroelectric crystal (Nd:CBN-28) lasers at 1.06 and 1.34 μm. The maximum output power of the 1.06 μm laser reaches 0.69 W in continuous-wave regime, which is believed to be the highest output power ever obtained with Nd:CBN-28 crystal. Using a chopper to modulate the pump, the highest output power further improves to 0.77 W. Preliminary Q-switched laser operation at 1.06 μm, using a Cr:YAG saturable absorber, is realized with maximum average output power of 89 mW, pulse width of 220 ns and pulse energy 10.8 μJ, for the first time to our knowledge. Quasi-continuous-wave laser at 1.34 μm with chopper is also demonstrated with maximum output power of 56 mW. The scaled output power in fundamental wave should be favorable for the investigation on broadband nonlinear self-frequency conversion into visible.

Calibration and data extraction in non-optimized Mueller matrix polarimeters

Omar Rodriguez-Nuñez, Juan Lopez-Tellez, Oscar Rodriguez Herrera, and Neil Bruce

Doc ID: 287029 Received 17 Feb 2017; Accepted 18 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: We present a method for calibration and data-extraction for a non-optimized Mueller matrix polarimeter. The advantage of this type of method is a reduction in measurement time for multi-wavelength systems or in systems with slow response times. The calibration process requires the measurement of four known polarization devices. Here we use free-space transmission, a horizontal and a vertical linear polarizer, and a quarter-wave retarder with its fast axis at 30° to the horizontal. Experimental measurements of rotating quarter-wave and half-wave retarders show that accurate results can be obtained with the proposed method.

A potential material for fabricating optical mirrors: polished diamond coated silicon carbide

Xinchang Wang, Chengchuan Wang, Xiaotian Shen, and Fanghong Sun

Doc ID: 287161 Received 23 Feb 2017; Accepted 18 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: Polished diamond coated silicon carbide can be a potential candidate material for making optical mirrors, due to the excellent properties. At present, five typical types of diamond films are deposited on RB-SiC substrates by HFCVD, and then polished by mechanical polishing. It is found that the boron doped micro-crystalline and undoped nano-crystalline composite diamond (BDMC-UNCCD) coated specimen performs the best before, during and after polishing. The film surface composed of nano-sized diamond grains has relatively low surface roughness and hardness, which are beneficial for the efficient polishing, and under the present condition only such the surface can be completely polished to a homogeneous mirror surface. The micro-sized diamond grains and the boron incorporation in the underlying BDMCD layer can enhance the film-substrate adhesion, which plays an important role in the film integrity during the polishing or subsequent applications. In conclusion, the polished BDMC-UNCCD coated RB-SiC specimen indeed shows low surface roughness (Ra = 5.41 nm), high hardness (71.47 GPa), high elastic modulus (746 GPa), favorable surface shape accuracy (RMS = 0.083λ) and considerable reflectivity in the short-wavelength range.

Cascaded chirped narrow bandpass filter with flat-top based on two-dimensional photonic crystals

Yu Zhuang, He-ming Chen, and Ke Ji

Doc ID: 287384 Received 23 Feb 2017; Accepted 18 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: We propose a structure of cascaded chirped narrow bandpass filter with flat-top based on 2-D photonic crystals (PhCs). The filter brought up here consists of three filter units that each has a resonator and two reflectors. Coupled mode theory (CMT) and transfer matrix method (TMM) are methodologies applied in the analysis of the features. The calculations show that the bandwidth of the filter can be adjusted by changing the distances between resonators and reflectors, based on which a flat-top response can be achieved by chirped-cascading the filter units. According to the theoretical model, we design a narrow bandpass filter based on 2-D PhCs with triangular lattice of air holes, the parameters of which are calculated using finite difference method (FEM). The simulation results show that the filter has a center frequency of 193.40 THz, an insertion loss of 0.18 dB, a flat bandwidth of 40 GHz, and ripples about 0.2 dB in the passband. The performance of the filter is suitable for dense-wavelength-divison-multiplexed (DWDM) optical communication systems with a 100-GHz channel spacing.

Measurement of water vapor using an imaging field-widened spatial heterodyne spectrometer

Jeffery Langille, Brian Solheim, Adam Bourassa, Doug Degenstein, Stephen Brown, and Gordon Shepherd

Doc ID: 284104 Received 05 Jan 2017; Accepted 18 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: Spatial Heterodyne Spectroscopy (SHS) has been successfully applied to measure variations in water vapor pressure in the lab. An imaging system is combined with a monolithic field-widened SHS to observe a white light source through a 1 m length water vapor cell that is designed to produce predictable variations in the water vapor pressure. The performance of the spectrometer design is examined by comparing spectra simulated using a radiative transfer model to observed spectra at several cell pressures. The intended application of the instrument to vertically resolve the water vapor profile in the Upper Troposphere and Lower Stratosphere using limb scattered radiation in a vibrational band of water (1363 nm – 1366 nm) is also introduced.

Scanning high power continous wave laser generated bulk acoustic waves

Zheng Li, shiling yan, Qingnan Xie, Chenyin Ni, and Shen Zhong-Hua

Doc ID: 284309 Received 17 Jan 2017; Accepted 17 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: The ultrasonic bulk waves generated by a high power continuous laser scanning along the surface of aluminum material were theoretically investigated. Although the temperature rise generated by this scanning laser irradiation was small, it provided a large temperature gradient, which was able to generate measurable ultrasonic waves. Detailed discussions were given to the influence of scanning speed on the generation propagation direction and the amplitude of wavefront. The longitudinal and transverse waves would be generated in the material, only when the scanning speeds reached a certain range. What’s more, the amplitude of wavefronts were significantly enhanced if the wavefront angle controlled by scanning speed matched with the propagation direction of the ultrasound. In summary, it expounded a method to obtain the ultrasonic signal of direction controlled from the perspective of numerical simulation, as long as the scanning speed met the requirements.

Generating superimposed Bessel beams with a volume holographic axicon

Raphael Guerrero and Alvie Asuncion

Doc ID: 285900 Received 30 Jan 2017; Accepted 17 Apr 2017; Posted 17 Apr 2017  View: PDF

Abstract: Quasi-Bessel beams (QBB) with different profiles are generated with an axicon-telescope system. Beam profiles are found to vary with different axicon-telescope distance δ. QBBs are stored as volume holograms in a photorefractive crystal. Reconstructions of the QBBs are focused by the recording axicon to produce superimposed Bessel beams (SBBs) with oscillating cores. SBBs formed through this method have different oscillation periods that range from 4.3 cm to 6.1 cm. We demonstrate that periodicity is dependent on δ. Our method allows tunability of SBB period through a simple rearrangement of optical elements.

Blue sun glints on water viewed through a polarizer

Joseph Shaw and Michael Vollmer

Doc ID: 286798 Received 15 Feb 2017; Accepted 17 Apr 2017; Posted 18 Apr 2017  View: PDF

Abstract: Sun glints are formed by specular reflections of the sun from capillary waves formed by wind blowing over water. These glints are normally colorless for a high sun or take on the color of the light source, such as orange-red during sunset or sunrise. However, when the glints are highly polarized by reflection near the Brewster angle, i.e. with relatively high sun they can change from colorless to a blue appearance caused by blue light leakage through a polarizing filter oriented orthogonal to the plane of polarization of the reflected light. Measurements are shown of crossed-polarizer transmission spectra exhibiting blue and near infrared light leakage for photographic polarizing filters and polarized sunglasses. A variety of photographs are shown to confirm blue light leakage as the source of the blue glint color.

Integrated FP/RFBG Sensor with Micro-channel for dual-parameter Measurement under High Temperature

yaxin wang, haihong bao, ZengLing Ran, jingwei huang, and shuang zhang

Doc ID: 287430 Received 15 Mar 2017; Accepted 17 Apr 2017; Posted 18 Apr 2017  View: PDF

Abstract: An integrated sensor via overlapping a micro Fabry-Pérot (MFP) cavity with micro-channel on a regenerated fiber Bragg grating (RFBG) is constructed for dual-parameter sensing of temperature, strain and gas pressure under high temperature (600℃). The MFP is fabricated by using a 157 nm laser machining on H2-loaded bend insensitive fiber. A fiber Bragg grating (FBG) is inscribed at the same position of the MFP using 248nm laser exposure, and then successfully regenerated after a required annealing process which enhances the strain sensitivity of MFP more than 3 times. The micro-channel created on the MFP is used to improve gas pressure sensitivity of the MFP nearly 100times. Since the MFP and RFBG have different sensitivity to gas pressure, strain and temperature, the sensor head could be used to perform dual-parameter measurement by simultaneous measurement of high-temperature and strain, and high-temperature and gas pressure.

Optimized Calibration Methodology of VIIRS Day-Night Band Using a Solar Diffuser

Junqiang Sun and Menghua Wang

Doc ID: 287773 Received 02 Mar 2017; Accepted 17 Apr 2017; Posted 24 Apr 2017  View: PDF

Abstract: An enhanced methodology of the standard on-orbit calibration of the day-night band (DNB) of the Visible Infrared Imaging Radiometer Suite (VIIRS) on-board the Suomi National Polar-orbiting Partnership (SNPP) satellite is presented. The range of the “sweet spot” for the fully illuminated scans in the calibration events is expanded from 4° to 7.8° in order to increase the number of fully illuminated scans to 72, which then permits a complete calibration of the DNB to be carried out within one orbit for all 36 aggregated modes and the two mirror sides. This improves over the current operational methodology, which is with a more restricted range for the sweet-spot that requires multiple orbits to complete a calibration. The expansion necessarily requires the expansion of a key calibration input, the product of the bidirectional reflectance factor (BRF) of the solar diffuser (SD) with the vignetting function (VF) describing the transmission of the attenuation screen in front of the SD port, or BVP for short. The expanded BVP is derived by fitting the function in three separate intervals and joining them smoothly to form a single function. Additional enhancements include the adaptation of the previously improved SD degradation and all other improvements developed for reflective solar bands in previous work. The time-dependent relative spectral response (RSR) is also characterized and implemented, and its impact and improvements are studied and discussed. The result shows that the improved DNB calibration coefficients are more stable, smooth and less noisy.

Estimation of order parameter of a Liquid crystalvariable retarder using Haller’s approximation

Alok Tiwary, Raja Bayanna Ankala, and Shibu Mathew

Doc ID: 287833 Received 02 Mar 2017; Accepted 16 Apr 2017; Posted 18 Apr 2017  View: PDF

Abstract: We use a liquid crystal variable retarder (LCVR) for polarization modulation of the input beam in a po-larimeter intended for solar observations. It is known that the retardance of LCVR depends on the voltageand temperature. Voltage at a constant temperature is used for fast modulation. However, fluctuations inthe temperature reduces the accuracy in the polarimetric measurements. In order to understand these, we have performed calibration of the LCVR with respect to temperature and estimated the different param-eters, critical exponent (β), maximum retardance (δ 0 ) and order parameter (S) of the liquid crystal using Haller’s approximation. We also study the dependence of these parameters with voltage. It is observedthat the change in order parameter with change in temperature varies linearly with voltage in the range of 1-7 volts.

A Dispersed Fringe Accumulation based Left Subtract Right method for fine co-phasing of dispersed fringe sensor

Yang Li, Shengqian Wang, and Changhui Rao

Doc ID: 280572 Received 10 Nov 2016; Accepted 16 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: The dispersed fringe sensor is usually used to detect the piston errors (optical path difference) between different segmented mirrors or synthetic aperture telescopes. In this paper, a Dispersed Fringe Accumulation (DFA) based Left Subtract Right (LSR) piston estimation method is proposed for Dispersed Fringe Sensor in the fine co-phasing stage, and it abbreviated DFA-LSR. In this method, the dispersed fringe image is accumulated in the dispersed direction, and then the LSR method is used to detect the piston error. The DFA-LSR makes up for the shortcoming of the main peak position (MPP) method which lacks engineering practicality. The analysis and experiment results show that the proposed method can keep relatively better performance even at the condition of poor signal noise ratio, compared with the MPP method in fine co-phasing stage.

Scattering of cylindrical waves by a chiral coated cylindrical reflector placedin chiral background

zeeshan awan

Doc ID: 288057 Received 03 Mar 2017; Accepted 15 Apr 2017; Posted 20 Apr 2017  View: PDF

Abstract: The scattering of cylindrical waves by a chiral coated cylindrical reflectorplaced in chiral background has been investigated using numerical simula-tions. The expressions for electric and magnetic fifields inside chiral coatingand in chiral background have been derived using wave fifield decompositionapproach. It is studied that the scattering gain can be controlled by varyingthe cylindrical wave source location, thickness of coating, chirality of coatingand chirality of background medium. It is shown that by increasing the chirality of coating for a chiral coated cylindrical reflector placed in free space, the scattering gain in the forward direction increases whereas the scattering gain in the backward direction decreases. It is further investigated that a strong chiral coated cylindrical reflector placed in certain chiral background guide most of the scattered fifield toward rear side of the reflector. It is also observed that the scattering gain pattern becomes isotropic provided that if chiral, strong chiral and chiral nihility coated cylindrical reflectors are placed in chiral nihility background. A cloaking phenomenon associated with a chiral coated reflector placed in chiral background at a specificfic observation angle is also discussed

Coherent beam combining of fiber lasers using CDMA-based single-frequency dithering technique

Min Jiang, Rongtao Su, Zhang Xin, Yanxing Ma, Xiaolin Wang, and Pu Zhou

Doc ID: 285161 Received 18 Jan 2017; Accepted 14 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: Coherent beam combination (CBC) is a promising method to obtain high-power and high-brightness laser output. In this paper, we present a novel single-frequency dithering technique based on code division multiple access (CDMA). By using orthogonal phase control signals, the phase control speed in the coherent beam combination system can be boosted and the number of channels can be increased. The design method of orthogonal signals is introduced and the relevant simulations and experiment of the designed signals have been demonstrated. In the experiment, we design four orthogonal coding signals and realize the phase locking of five channels. When the phase control system is in the closed loop, the residual phase error is less than λ/30 and the phase control speed of CBC system is increased compared with that of the single-frequency dithering technique.

Equivalence of internal and external mixture schemes of single scattering properties in vector radiative transfer

Lipi Mukherjee, Pengwang Zhai, Yongxiang Hu, and David Winker

Doc ID: 285540 Received 24 Jan 2017; Accepted 13 Apr 2017; Posted 13 Apr 2017  View: PDF

Abstract: Polarized radiation fields in a turbid medium is influenced by single scattering properties of scatterers. It is common that media contain two or more types of scatterers, which makes it essential to properly mix single scattering properties of different types of scatterers in the vector radiative transfer theory. The vector radiative transfer solvers can be divided into two basic categories: the stochastic and deterministic methods. The stochastic method is basically the Monte Carlo method which can handle scatterers with different scattering properties explicitly. This mixture scheme is called the external mixture scheme in this paper. The deterministic methods, however, can only deal with a single set of scattering properties in the smallest discretized spatial volume. The single scattering properties of different types of scatterers have to be averaged first before they are input to deterministic solvers. This second scheme is called the internal mixture scheme. The equivalence of these two different mixture schemes of scattering properties has not been demonstrated so far. In this paper polarized radiation fields for several scattering media are solved using the Monte Carlo and Successive Order of Scattering (SOS) methods and scattering media contain two types of scatterers: molecules and aerosols. The Monte Carlo and SOS methods employ external and internal mixture schemes of scatterers, respectively. It is found that the percentage differences between radiances solved by these two methods with different mixture schemes are of the order of 0.1%. The differences of Q/I, U/I, and V/I are of the order of 10^-5 ∼ 10^-4, where I, Q, U and V are the Stokes parameters. Therefore the equivalence between these two mixture schemes is confirmed to the accuracy level of the radiative transfer numerical benchmarks.

Supernumerary arcs of rainbows: the theory of interference

Philip Laven

Doc ID: 285088 Received 13 Feb 2017; Accepted 13 Apr 2017; Posted 14 Apr 2017  View: PDF

Abstract: Supernumerary arcs on rainbows are historically important because in the early 1800s they provided evidence in favor of the wave theory of light. The success of Airy’s rainbow integral has overshadowed the earlier contribution from Young, who proposed that supernumerary arcs were caused by interference between two geometrical rays that emerge from the raindrop at the same scattering angle. Airy dismissed Young’s idea as “the imperfect theory of interference” because it predicted supernumerary arcs at the wrong angles. Young was unaware that a light ray crossing a caustic suffers a phase shift of 90°. If these phase shifts are taken into account, the theory of interference becomes surprisingly accurate.

Electrically tunable all optical diode in one-dimensional photonic crystal structure

Kazem Jamshidi-Ghaleh and Fatemeh Moslemi

Doc ID: 285808 Received 27 Jan 2017; Accepted 13 Apr 2017; Posted 14 Apr 2017  View: PDF

Abstract: All optical diode (AOD) tunability with external applied voltage in a one dimensional photonic crystal (1DPC) structure is investigated. An asymmetric hybrid Fabry-Perot resonator with arrangement of (BA)5/AgLiNbO3Ag/(AB)5(AABB)5, composed of linear (B) and nonlinear (A) materials, is proposed in which, the LiNbO3, (LNO) sandwiched with two pairs of Ag layers used as a defect. The linear electro-optical (EO) effect and the optical nonlinear response of LNO is considered in calculations. The linear transmittance (LT) spectrum, nonlinear transmission (NT) curves and field distribution inside of structure, around the defect mode frequency, for left to right (L-R) and right to left (R-L) light incidences, at different applied voltages, are graphically, illustrated. Results show that, with increasing the applied voltage, the NT curves from L-R and R-L deflect, amplify and compress in comparison of zero applied voltage. For negative voltages, because of accumulating the EO effect and dynamical shifting due to nonlinearity, the variations are more sensitive. Electro-optical effect in LNO causes to tunability of LT spectrum and intensity dependent refractive index in nonlinear layers dynamically tunes the optical bistability (OB) threshold. The results of this study can be useful in designing the externally tunable AOD for all optoelectronic devices.

Astigmatic transforms of an optical vortex for measurement of its topological charge

Victor Kotlyar, Alexey Kovalev, and Alexey Porfirev

Doc ID: 286125 Received 03 Feb 2017; Accepted 13 Apr 2017; Posted 14 Apr 2017  View: PDF

Abstract: We obtain analytical expressions for the complex amplitudes of optical vortices deformed by astigmatic transforms, i.e. passed either through a cylindrical lens or through an inclined spherical lens. We also obtain similar analytical expressions describing propagation of an optical vortex generated when a Gaussian beam illuminates an inclined spiral phase plate (SPP) or when an elliptic Gaussian beam illuminates a SPP (not inclined). All these optical vortices with a topological charge (TC) n are described by the n-th order Hermite polynomial with a complex argument. It is shown that the argument is real only on a straight line in the transverse plane of the laser beam. There are n intensity nulls on this line. The treated here astigmatic transforms are used to determine the integer TC of optical vortices. We conduct a comparative experimental study of different astigmatic transforms and we show that the transform with a cylindrical lens is the best for determining the TC. Unlike other similar works, in this study we achieve transformation of n-degenerate intensity null of an optical vortex with the TC n = 100 into n isolated first order intensity nulls.

Adaptive Reconstruction for Coded Aperture Temporal Compressive Imaging

Yueting Chen, Chaoying Tang, Zhihai Xu, Qi Li, Min Cen, and Huajun Feng

Doc ID: 286818 Received 15 Feb 2017; Accepted 13 Apr 2017; Posted 14 Apr 2017  View: PDF

Abstract: This paper presents an adaptive reconstruction method for coded aperture temporal compressive imaging. A pixel-wise equal-exposure coding strategy is firstly designed, which brings regional motion objects within the captured coded image a shot-noise-like speckle feature. By taking advantage of this phenomenon, a motion area detecting method is proposed. Then the adaptively segmented motion areas will be reconstructed to a series of video frames and filled back into the static clear background. Both simulation and real experiment results demonstrate that the proposed method significantly reduces the time consumption of video reconstruction and maintains high image quality.

Beam drift error and control technology for scanning beam interference lithography

wang wei, ying song, Shan Jiang, mingzhong pan, and heshig bayan

Doc ID: 285587 Received 26 Jan 2017; Accepted 12 Apr 2017; Posted 13 Apr 2017  View: PDF

Abstract: To improve the quality of grating masks made by scanning beam interference lithography, this article established a mathematical model of step-scanning exposure and analyzed the effects of the beam drift error on the interference image. Beam angle drift can be decomposed into the drift error δx in the exposure plane (XOZ plane) and the drift error δy perpendicular to the plane. Analysis shows that the δx has a major impact on the interference fringes during exposure, which may affect the precision of phase lock. δy leads to the appearance of deflected interference strips and affects the exposure dose. When a low-frequency drift error appears in the light path, the exposure contrast on the photoresist will decrease with the exposure process, which makes the fabrication of large-size diffraction gratings difficult. Furthermore, taking advantage of the characteristics of a scanning beam interference lithography system, an exposed beam stable system was designed that can effectively suppress the low-frequency drift of the beam. The total beam angle control accuracy is better than the 2.7 μrad, and position control accuracy is better than 3.9 μm (both for 1σ), which achieves the expected goal of the design.

Field diversity phase retrieval method for wavefront sensing in monolithic mirror space telescopes

Guohao JU, Changxiang Yan, Dan Yue, and Zhiyuan Gu

Doc ID: 287386 Received 23 Feb 2017; Accepted 12 Apr 2017; Posted 12 Apr 2017  View: PDF

Abstract: To guarantee the uniqueness of the solution, a series of intensity images with known phase diversities are usually needed in the current phase retrieval wavefront sensing methods. However, to obtain these intensity images with the deliberately added diversity phases, some additional instruments (e.g. beam splitters) or operations (e.g. adjustment of the focus) are usually needed, which can pose a challenge for wavefront sensing in space telescopes. This paper proposes a new concept for retrieving the wavefront phase of monolithic mirror space telescopes with perturbation, where the intensity measurements with phase diversities are directly obtained from different field positions of one image, without the need for any additional instruments or operations. To realize this new concept, we present a modified phase diversity method to account for the unknown phase diversities between these intensity measurements based on an in-depth understanding of the net aberration fields induced by misalignments and figure errors. Relevant simulations for different cases are performed to demonstrate the feasibility and accuracy of the proposed method. Since in this method the phase diversities between different intensity measurements are mainly induced by the diversities in the field position, we name it as field diversity phase retrieval method. This work can present great facility for wavefront sensing in monolithic mirror space telescopes.

A Phase-Sensitive Optical Time-Domain Reflectometric System Based on a single-source Dual Heterodyne Detection scheme

Miao Yu, Minhan Liu, Tianying Chang, Jinpeng Lang, Jiandong Chen, and Hong-Liang Cui

Doc ID: 290150 Received 08 Mar 2017; Accepted 12 Apr 2017; Posted 13 Apr 2017  View: PDF

Abstract: With increasing sophistication and expanding fields of application, new technical demands on the phase-sensitive optical time-domain reflectometry (φ-OTDR ) system in terms of higher recognition rate and real-time responsiveness for vibration detection, as well as more stable and accurate intensity, frequency and phase information acquisition of the signal must somehow be met. Current system architecture is not believed to meet such demands without modification and improvement. A system based on dual homologous heterodyne coherent detection is proposed and demonstrated, which can single out a pure vibration signal from the inherently present residual frequency and phase fluctuations caused by less strictly synchronous clock, inherent characteristics of the laser and the acousto-optical modulator, and environment temperature changes. With less burden on data processing, higher real-time performance is achieved as well. Using probe light pulses of 4 kHz repetition rate, and 80 ns pulse width, a 9 m spatial resolution has been achieved on a 24.6 km sensing fiber, with a detectable frequency range from 5 Hz to 1.715 kHz, with a SNR > .5 dB. All the above parameters are close to the maximum theoretical values. The drastically improved system demodulation characteristics foreshadow better performance and improved reliability in engineering applications.

Advanced modelling of a moderate-resolution holographic spectrograph

Eduard Muslimov, Gennady Valyavin, Sergei Fabrika, and Nadezhda Pavlycheva

Doc ID: 283230 Received 20 Dec 2016; Accepted 12 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: In the present article we consider an accurate modeling of spectrograph with cascade of volume-phase holographic gratings. The proposed optical scheme allows to detect spectra in an extended wavelength range without gaps providing relatively high and constant spectral resolution and high throughput. However, modeling and minimization of possible cross-talks between gratings and stray light in such a scheme represents a separate task. We use analytical equations of coupled wave theory together with rigorous coupled wave analysis to optimize the gratings parameters and further apply the latter together with non-sequential raytracing algorithm to model propagation of beams through the spectrograph. The results show relatively high throughput up to 53% and absence of any significant cross-talks or ghost images even for ordinary holograms recorded on dichromated gelatin.

The development of multi-band photoacoustic tomography imaging system based on a novel capacitive micromachined ultrasonic transducer (CMUT) array

jian zhang, Sio Pun, Yuanyu Yu, DUYANG GAO, Jiujiang Wang, PENG MAK, KIN FONG LEI, CHING-HSIANG CHENG, and Zhen Yuan

Doc ID: 286115 Received 03 Feb 2017; Accepted 12 Apr 2017; Posted 12 Apr 2017  View: PDF

Abstract: Photoacoustic (PA) imaging as a hybrid technology combines the high optical contrast and high acoustic resolution in a single imaging modality. However, most of the available PA imaging systems can not character biological system at multiple length scales due to a limited bandwidth of the piezoelectric ultrasonic transducer. In this study, we fabricated a novel multi-band capacitive micromachined ultrasonic transducer (CMUT) array, and first developed a CMUT-based multi-band photoacoustic tomography (MBPAT) imaging system. The MBPAT imaging system was examined by the phantom experiments, and then was successfully applied to image the zebrafish in vivo. The imaging results indicated that CMUT array based MBPAT can provide a more comprehensive and accurate characterization of biological tissues, which exhibit the potential of MBPAT/CMUT in various areas of biomedical imaging.

Method for simultaneously calibrating peak retardation and static retardation of a photoelastic modulator

wei quan, Qinghua Wang, Yueyang Zhai, Liwei Jiang, Lihong Duan, and Ye Wu

Doc ID: 287409 Received 23 Feb 2017; Accepted 11 Apr 2017; Posted 12 Apr 2017  View: PDF

Abstract: A method for simultaneously calibrating the peak retardation and static retardation of a photoelastic modulator (PEM) is proposed. By optimizing the polarization modulation system, the normalized fundamental frequency components of the modulation signals are obtained to calculate the peak retardation and static retardation of the PEM. The calibration result is immune to fluctuations of the incident light intensity and can be used to correct the deviation of the photoelastic modulation detection results. In our experiments, the average deviation between measured peak retardations and corresponding set values is 0.0339 rad. The standard deviation between the measured static retardations and the average measured value is 0.0003 rad. The calibration method has a high sensitivity since the large gradient of the first order Bessel function when the peak retardation is less than 1 rad. The experimental results consist well with the theoretical analysis.

Influence of residual carbon impurity in the heavily Mg-doped GaN contact layer on the Ohmic contact

Feng liang, De Zhao, Desheng Jiang, Liu Zongshun, Jian zhu, Ping Chen, J. Yang, Wei Liu, Xiang Li, Shuangtao Liu, xing yao, Liqun Zhang, Mo Li, and Jian Zhang

Doc ID: 287850 Received 02 Mar 2017; Accepted 11 Apr 2017; Posted 12 Apr 2017  View: PDF

Abstract: The influence of residual carbon impurity incorporated into the heavily Mg-doped GaN layer has been studied systematically according to the relation between the carbon concentration and specific contact resistance. Furthermore, the results of temperature-dependent current-voltage characteristics and the photoluminescence spectra indicate that a proper concentration of residual carbon impurity can improve the performance of Ohmic contact through introducing deep level defects to enhance the variable range hopping conduction.

Effect of Cu/Ga ratio on deep-level defects in CuGaSe2 thin films studied by photocapacitance measurements with two-wavelength excitation

Xiaobo Hu, Juanjuan Xue, Jiao Tian, Guoen Weng, and Shaoqiang Chen

Doc ID: 290758 Received 16 Mar 2017; Accepted 11 Apr 2017; Posted 12 Apr 2017  View: PDF

Abstract: Effect of Cu/Ga ratio on properties of deep-level defects in CuGaSe2 thin films were studied using photocapacitance methods with two-wavelength excitation. Transient photocapacitance method using a monochromatic probe light determined two kinds of defects locating at 0.8 eV and 1.5 eV above the valence band, respectively, the position of which almost kept constant regardless of Cu/Ga ratio. Then, in addition to the probe light, laser light with a wavelength of 1550 nm, corresponding to 0.8 eV, was then used to study the saturation effect of the deep-level defect at 0.8 eV above the valence band. The results suggest that the defect level at 0.8 eV acts as a recombination center at room temperature, and it becomes more effective in CuGaSe2 films with lower Cu/Ga ratio.

Study of the influence of the agarose hydrogel layer thickness on sensitivity of the coated silica microspehre resonator to humidity

arun mallik, Gerald Farrell, Qiang Wu, and Yuliya Semenova

Doc ID: 284793 Received 13 Jan 2017; Accepted 11 Apr 2017; Posted 12 Apr 2017  View: PDF

Abstract: In this paper, we investigate both theoretically and experimentally the influence of the Agarose hydrogel layer thickness on sensitivity of a proposed relative humidity (RH) sensor based on a silica microsphere resonator coated with Agarose hydrogel. The operating principle of the sensor relies on excitation of whispering gallery modes (WGMs) in the coated silica microsphere using the evanescent field of a tapered fiber. A change in the ambient relative humidity is detected by measuring the wavelength shift of the WGMs in the transmission spectrum of the tapered fiber. Using perturbation theory, we analyze the influence of the Agarose coating thickness on the sensitivity of the proposed sensor and compare the results of numerical simulations with experimental findings for different coating layer thickness. We demonstrate that an increase in the coating layer thickness initially leads to an increase in the sensitivity to RH and reaches saturation at higher values of the Agarose layer thickness. The results of the study are useful for the design and optimization of microsphere sensors parameters to meet a particular performance specification.

Invertible propagator for plane wave illumination of forward-scattering structures

Gregory Samelsohn

Doc ID: 284985 Received 17 Jan 2017; Accepted 11 Apr 2017; Posted 11 Apr 2017  View: PDF

Abstract: Propagation of directed waves in forward-scattering media is considered. It is assumed that the evolution of the wave field is governed by the standard parabolic wave equation. An efficient one-step momentum-space propagator, suitable for a tilted plane wave illumination of extended objects, is derived. It is expressed in terms of a propagation operator that transforms (the complex exponential of) a linogram of the illuminated object into a set of its diffraction patterns. The invertibility of the propagator is demonstrated, which permits a multiple-shot scatter correction to be performed, and makes the solution especially attractive for either projective or tomographic imaging. As an example, high-resolution tomograms are obtained in numerical simulations implemented for a synthetic phantom, with both refractive and absorptive inclusions.

Characterization and Control of the electro-optic phase dispersion in lithium niobate modulators for wide spectral band interferometry applications in the mid-infrared

samuel heidmann, gwenn ulliac, Nadège COURJAL, and Guillermo Martin

Doc ID: 286079 Received 03 Feb 2017; Accepted 11 Apr 2017; Posted 11 Apr 2017  View: PDF

Abstract: Mid Infrared wideband modulation is achieved in an electro-optic Y-junction using Lithium Niobate waveguides. Comparison between external (scanning mirror) and internal (electro-optical) modulation allows to study the chromatic polynomial dependence of the relative phase. We propose an improved dispersion model and apply this effect to show active dispersion compensation in wide band fringe modulation in the mid infrared. This can be useful for long baseline interferometry applications

Bow-shaped Caustics from Conical Prisms: a 13th Century Account of Rainbow Formation from Robert Grosseteste's De iride

Joshua Harvey, Hannah Smithson, Clive Siviour, Giles Gasper, Sigbjorn Sonnesyn, Brian Tanner, and Tom McLeish

Doc ID: 287109 Received 28 Feb 2017; Accepted 11 Apr 2017; Posted 20 Apr 2017  View: PDF

Abstract: The rainbow has been the subject of discussion across a variety of historical periods and cultures, and numerous optical explanations have been suggested. Here, we further explore the scientific treatise De iride [On the Rainbow] written by Robert Grosseteste in the thirteenth century. Attempting to account for the shape of the rainbow, Grosseteste bases his explanation on the optical properties of transparent cones, which he claims can give rise to arc-shaped projections through refraction, i.e. caustics. By stating that atmospheric phenomena are reducible to the geometric optics of a conical prism, the De iride lays out a coherent and testable hypothesis. Through both physical experiment and physics-based simulation we present a novel characterization of cone-light interactions, demonstrating that transparent cones do indeed give rise to bow-shaped caustics; a nonintuitive phenomenon that suggests Grosseteste's theory of the rainbow is likely to have been grounded in observation.

Design of a coaxial light guide producing a wide-angle light distribution

Hiroshi Ohno

Doc ID: 286921 Received 17 Feb 2017; Accepted 10 Apr 2017; Posted 11 Apr 2017  View: PDF

Abstract: A compact light-emitting diode (LED) lighting module with a coaxial light guide that can produce a wide-angle light distribution is proposed. The structure of the coaxial light guide has a scattering area inside it and a tapered outer surface that is able to concentrate all of the rays on the scattering area owing to the total internal reflection. The rays diffused and reflected by the scattering area are refracted by the tapered outer surface and emitted in a wide-angle light distribution. A prototype of the LED lighting module was able to produce a point-like compact light source that radiates rays with half-intensity angle of 274 degrees and lighting efficiency of 91%.

Illumination-Direction Multiplexing Fourier Ptychographic Microscopy Using Hemispherical Digital Condensers

Maged Alotaibi, Sueli Skinner Ramos, Ali Alamri, Bader Alharbi, Mohammed Alfarraj, and Luis Grave de Peralta

Doc ID: 290217 Received 08 Mar 2017; Accepted 10 Apr 2017; Posted 11 Apr 2017  View: PDF

Abstract: Simulations were conducted to explore a broader collection of possible illumination patterns realizable using a white-light-emitting hemispherical digital condenser. Several simple, but practical, illumination patterns were selected and used in experiments where a sample was illuminated simultaneously from different directions. The illumination-direction multiplexing (IDM) Fourier ptychographic microscopy (FPM) method was successfully used for imaging and phase-recovery. This study suggests that IDM-FPM can be used for imaging photonic crystals with subwavelength periods using traditional microscope condensers with variable numerical aperture.

Single-pixel compressive diffractive imaging with structured illumination

Ryoichi Horisaki, Hiroaki Matsui, and Jun Tanida

Doc ID: 283175 Received 20 Dec 2016; Accepted 10 Apr 2017; Posted 11 Apr 2017  View: PDF

Abstract: We present a method for diffractive imaging with a single photodetector and structured illumination based on compressive sensing. A complex-amplitude object is sequentially illuminated with randomly structured coherent light patterns, and the intensities of each propagating field are measured with a single photodetector. This measurement process does not use any reference light or imaging optics. The object field is reconstructed from the sequentially measured intensities with an algorithm in which compressive sensing and phase retrieval are integrated. We demonstrate the proposed method experimentally.

A compact, semi-passive, beam steering prism array for solar concentrators

Cheng Zheng, Qiyuan Li, Gary Rosengarten, Evatt Hawkes, and Robert Taylor

Doc ID: 286118 Received 03 Feb 2017; Accepted 10 Apr 2017; Posted 13 Apr 2017  View: PDF

Abstract: In order to maximize solar energy utilization in a limited space (e.g. rooftops), solar collectors should track the sun. As an alternative to rotational tracking systems, this paper presents a compact, semi–passive, beam steering prism array which has been designed, analysed and tested for solar applications. The proposed prism array enables a linear concentrator system to remain stationary so that it can integrate with a variety of different solar concentrators and which should be particularly useful for systems which require a low profile (namely rooftop mounted systems). A case study of this prism array working within a specific rooftop solar collector demonstrates that it can boost the average daily optical efficiency of the collector by 48% and expand its effective working time from 6 hours to 7.33 hours. Overall, the proposed design provides an alternative way to ‘follow’ the sun for a wide range of solar thermal and photovoltaic concentrator systems.

Drifts in real-time partial wavefront correction and how to avoid them

Ivan Marin-Franch, Antonio J. Del Águila-Carrasco, Xavier Levecq, and Norberto Lopez-Gil

Doc ID: 286284 Received 07 Feb 2017; Accepted 10 Apr 2017; Posted 12 Apr 2017  View: PDF

Abstract: In visual experiments that require real-time partial correction of wavefront aberrations, small errors occur that accumulate over time and lead to drifts in Zernike coefficients of the uncorrected aberrations. A simple algorithm that does not require the inclusion of an additional optical path to obtain independent measurements of the eye’s aberrations is described here and its effectiveness in preventing these drifts demonstrated

A plasmonic wavelength demultiplexer with a ring resonator using high-order resonant modes

Chia-Ti Wu, Chia-Chih Huang, and Yeun-Chung Lee

Doc ID: 287997 Received 03 Mar 2017; Accepted 09 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: In this paper, we propose a novel wavelength demultiplexer based on metal-insulator-metal (MIM) plasmonic waveguides with a nanoscale ring resonator. Its transmission characteristics are numerically studied using finite element method (FEM) simulations, and the eigen wavelengths of the ring resonator are theoretically calculated. For the proposed structure, we found that the ratio of the resonance wavelengths for two different high-order modes of the ring resonator is close to the ratio of the two communication wavelengths 1310 nm and 1550 nm. These resonance wavelengths of the demultiplexer are effortlessly tuned by varying the refractive index of the material in the ring resonator and the geometrical parameters of the structure. The results simulated by FEM agree well with those from the resonant theory of the ring resonator. The presented structures will have significant potential applications in highly integrated plasmonic devices.

Efficient self-frequency-doubling Nd:GdCOB green laser at 545 nm pumped by 796 nm laser diode

Lunhua Li, Yufei Wang, Yun Liu, Shaoyu Zhao, and Wan-hua Zheng

Doc ID: 285392 Received 26 Jan 2017; Accepted 09 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: A 796-nm laser-diode (LD) pumped self-frequency-doubling Nd:GdCa4O(BO3)3 (Nd:GdCOB) green laser is first demonstrated. With 2.93 W of 796 nm LD pump power, a maximum power of 460 mW green laser at 545 nm has been achieved. The optical conversion efficiency of 15.8% is higher than that pumped with 808 nm LD. The relationships of output power and optical conversion efficiency with the pump wavelength shifting toward 796 nm are presented.

Very Accurate Temperature Control of Bones by CO₂ Laser for Medical Applications.

Luc Levesque and Alek Robaczewski

Doc ID: 286776 Received 15 Feb 2017; Accepted 09 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: In this report we are showing that temperature of porcine bone samples can be maintained to a constant value within the range 40ºC to 75ºC. For the afore-mentioned temperature range, it was also shown that a porcine bone sample could be kept at a given temperature within a fraction of a degree Celsius. This method relies on a real-time feedback computer-control between a non-contact sensor and a CO₂ laser operating at a typical repetition rate within the 5 kHz-20 kHz range. Results are shown for domesticated porcine bones that are strongly absorbing the CO₂ radiation at λ= 10.6 µm.

Comparative Assessment of Erbium Fiber Ring Lasers and Reflective SOA Linear Lasers for Fiber-Bragg Grating Dynamic Strain Sensing

Heming Wei and Sridhar Krishnaswamy

Doc ID: 286906 Received 17 Feb 2017; Accepted 09 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: Fiber Bragg Grating (FBG) dynamic strain sensors using both an Erbium-based fiber ring laser configuration and a reflective semiconductor optical amplifier (RSOA) based linear laser configuration are investigated theoretically and experimentally. Fiber laser models are first presented to analyze the output characteristics of both fiber laser configurations when the FBG sensor is subjected to dynamic strains at high frequencies. Due to the differences in the transition times of Erbium and the semiconductor (InP/InGaAsP), EDFA- and RSOA-based fiber lasers exhibit different responses and regimes of stability when the FBG is subjected to dynamic strains. The responses of both systems are experimentally verified using an adaptive photorefractive two wave mixing (TWM) spectral demodulation technique. The experimental results show that the RSOA-FBG fiber linear cavity laser is stable and can respond to dynamic strains at high frequencies. An example application using a multiplexed TWM interferometer to demodulate multiple FBG sensors is also discussed.

Numerical investigation of a microfiber-plane-grating composite optical waveguide for gas refractive index sensing

Chengju Ma, Liyong Ren, wenge guo, Fu Wei, Yiping Xu, Liu Gang, and Jin Wen

Doc ID: 287334 Received 22 Feb 2017; Accepted 08 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: In this paper, we propose a microfiber-plane-grating composite optical waveguide (MPGCOW), which is formed by immobilizing a tapered microfiber on the surface of a plane grating with one defect, for gas refractive index (RI) sensing. Its optical properties and gas RI sensing properties are investigated by the finite difference time domain (FDTD) method. Results show that the MPGCOW has a photonic stop band, and is very sensitive to the ambient gas RI variation. The largest gas RI sensing sensitivity of 486.67nm/RIU and detection limit of 2×10-6 are obtained by immersing the structure in the mixture gas of N2 and He with various mixture ratios.

Rainbows in elliptically deformed drops. II. The appearance of supernumeraries of higher-order rainbows in rain showers

Gunther Konnen and James Lock

Doc ID: 285003 Received 17 Jan 2017; Accepted 08 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: The appearance of supernumeraries of higher-order rainbows in heavy rain showers is explored for rainbows up to order five (p=6). This is done by using a combination of the ray-theory-based first-order Mobius approximation for higher-order rainbows with the Airy approximation of the rainbow radiance distribution. We conclude that supernumerary formation of rainbows of order three, four, and five is possible in natural rain showers. Supernumeraries of the third-order and fourth-order rainbows are preferentially formed near the bottom of these rainbows. A strategy for observing supernumeraries of high-order rainbows is proposed.

Background oriented schlieren measurement of the refractive index field of air induced by a hot, cylindrical measurement object

Rüdiger Beermann, lorenz quentin, Andreas Pösch, Eduard Reithmeier, and Markus Kaestner

Doc ID: 283508 Received 23 Dec 2016; Accepted 07 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: To optically capture the topography of a hot measurement object with high precision, the light deflection by the inhomogeneous refractive index field - induced through the heat transfer from the measurement object to the ambient medium - has to be considered.We are using the 2d background oriented schlieren method (BOS) with illuminated wavelet background, optical flow algorithm and Ciddor's equation to quantify the refractive index field located directly above a red-glowing, hot measurement object. Provided no forced, external flow is disturbing the shape of the convective flow originating from the hot object,a laminar flow can be observed, resulting in a sharply bounded, inhomogeneous refractive index field.

The color design model of high CRI white-light LED module

Shang-Ping Ying, Han-Kuei Fu, Hsin-Hsin Hsieh, and Kun-Yang Hsieh

Doc ID: 286628 Received 13 Feb 2017; Accepted 07 Apr 2017; Posted 13 Apr 2017  View: PDF

Abstract: The traditional white-light light-emitting diode is packaged with single chip and single phosphor, but the disadvantage is poor color rendering index. The next generation package is two chips and single phosphor with high color rendering index and retaining the high luminous efficacy. This study adopts two chips and two phosphors to improve the tunable ability of color with varied proportions of two phosphors and varied densities of phosphor silicone. The color design model is established for color fine tune of white-light light-emitting diode module. The result shows that the maximum difference between measurement and color design model is about 0.0063 for CIE 1931 color coordinates (x, y) around correlated color temperature of 2500 K. This study provides a quick method to obtain color fine tune with white-light light-emitting diode module of high color rendering index and high luminous efficacy.

Quantitative measurements of turbid liquids via SLIPI where absorption spectrophotometry fails

GUY-OSCAR REGNIMA, THOMAS KOFFI, Bagui Olivier, ABAKA KOUACOU, Elias Kristensson, Jeremie Zoueu, and Edouard Berrocal

Doc ID: 287460 Received 27 Feb 2017; Accepted 07 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: A comparison between the commonly used absorption spectrophotometry and a more recent approach known as Structured Laser Illumination Planar Imaging (SLIPI) is presented for the characterization of scattering and absorbing liquids. Water solutions of milk and coffee are respectively investigated for 10 different levels of turbidity. For the milk solutions scattering is the dominant process, while the coffee solutions have a high level of absorption. Measurements of the extinction coefficient are performed at both λ = 450 nm and λ = 638 nm and the ratio of their values has been extracted. We show that the turbidity limit of valid transmission measurements is reached at an optical depth of OD ~2.4 corresponding here to an extinction coefficient, µe = 0.60 mm-1, when using a standard absorption spectrometer having a spatial Fourier filter prior to detection. This limitation is due to both the loss of non-scattered light as well as the contribution of scattered and multiply scattered photons reaching the detector. On the contrary the SLIPI measurements were found to be very reliable even for an extinction coefficient 3 times as high where µe = 1.80 mm-1. This improvement is due to the capability of the technique in efficiently suppressing the contribution from multiple light scattering.

Antitwilight II: Monte Carlo Simulations

Steven Richtsmeier, David Lynch, and David Dearborn

Doc ID: 287554 Received 27 Feb 2017; Accepted 07 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: For this paper, we employ the Monte Carlo Scene (MCScene) radiative transfer code to elucidate the underlying physics giving rise to the structure and colors of the antitwilight, i.e., twilight opposite the sun. MCScene calculations successfully reproduce colors and spatial features observed in videos and still photos of the antitwilight taken under clear, aerosol-free sky conditions. We examine the effects of solar elevation angle, Rayleigh scattering, molecular absorption, aerosol scattering, multiple scattering, and surface reflectance on the appearance of the antitwilight. We also compare MCScene calculations with predictions made by the MODTRAN radiative transfer code for a solar elevation angle of +1°.

Porosity and optical properties of zirconia films prepared by plasma ion assisted deposition

Christian Franke, Olaf Stenzel, Steffen Wilbrandt, Sven Schröder, Luisa Coriand, Nadja Felde, and Andreas Tünnermann

Doc ID: 286555 Received 10 Feb 2017; Accepted 07 Apr 2017; Posted 07 Apr 2017  View: PDF

Abstract: The porosity of zirconia films prepared by plasma ion assisted deposition has been investigated by means of optical (spectrophotometric) and non-optical analytic techniques such as transmission electron microscopy, X ray reflection XRR and energy dispersive X ray spectroscopy EDX. A discrimination between large (open) and small (closed) pores was achieved by means of measurement of the thermal and vacuum-to-air shift. Depending on the level of plasma assistance during film preparation, the porosity was found to vary between thirty and nearly zero volume percent. With decreasing porosity, the surface roughness determined by atomic force microscopy AFM tends to decrease as well.

Full-color reflector using vertically stacked liquid crystal guided-mode resonators

Chun-Ta Wang, Ping-Chien Chang, Jia-Jin Lin, Mao Chou Tai, Yung-Jr Hung, and Tsung-Hsien Lin

Doc ID: 286347 Received 08 Feb 2017; Accepted 07 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: In this work, we proposed a full-color reflector using three stacked red (R), green (G), and blue (B) reflection gratings hybrid with the tunable 90o twisted nematic liquid crystals (TNLCs). The color reflector based on guided-mode resonance (GMR) gratings reflects strongly at the resonance wavelength. The optical reflectivity of GMR gratings can then be controlled by utilizing 90o TNLCs to change the polarization of incident light. The optical characteristics and the chromaticity of the designed reflectors were evaluated by simulation. Individual RGB chip with/without LC was demonstrated experimentally. The fabricated GMR reflector for red exhibits a high TE/TM polarization ratio of >10:1 and 80% optical reflectivity at resonant wavelength, while the GMR reflector for blue only allows 60% optical reflectivity and a degraded polarization ratio of 3:1 mainly due to high optical absorption of silicon. Nevertheless, silicon-based GMR reflector enables a wide reflection bandwidth, so a full-color reflector can be realized by vertically stacking RGB tunable reflectors. The proposed full-color reflector therefore exhibits a wide-gamut color space with low driving voltage of <3V, showing its promise for use in energy-saving reflective information systems.

Detection of heavy metal Cd in polluted fresh leafy vegetables by laser induced breakdown spectroscopy

Mingyin Yao, Muhua Liu, Lin Huang, tianbing chen, gangfu rao, and hui yang

Doc ID: 286569 Received 14 Feb 2017; Accepted 07 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: For seeking a novel method with the ability of green analysis in monitoring toxic heavy metals residue of fresh leafy vegetables, laser induced breakdown spectroscopy (LIBS) was applied to prove its capability in performing this work. The spectra of fresh vegetables samples polluted in lab were collected by optimized experimental setup, and the reference concentrations of Cd from samples were obtained by conventional atomic absorption spectroscopy (AAS) after wet digestion. The direct calibration employing intensity of single Cd line and Cd concentration exposed the weakness of this calibration method. Furthermore, the accuracy of linear calibration can be improved a little by triple Cd lines as characteristic variables, especially after the spectra were pretreated. However, it is not enough in predicting Cd in samples. Therefore, partial least-squares regression (PLSR) was utilized to enhance the robustness of quantitative analysis. The results of PLSR model showed that the prediction accuracy of Cd target can meet the requirement of determination in food safety. This investigation presented that LIBS is a promising and emerging method in analyzing toxic compositions in agricultural products, especially while suitable chemometrics combined with.

Extracting and compensating for FOG vibration error based on improved EMD with masking signal

Wei Wang and xiyuan chen

Doc ID: 280870 Received 15 Nov 2016; Accepted 07 Apr 2017; Posted 07 Apr 2017  View: PDF

Abstract: Vibration is an important error source of Fiber-Optic Gyroscope (FOG), and the extraction and compensation of vibration signal are important means to eliminate the error and improve the accuracy of FOG. To decompose the vibration signal better, a new algorithm based on Empirical Mode Decomposition (EMD) with masking signal is proposed in this paper, which is called AM-EMD. First, the optimal frequency value of masking signal and the range of it are analyzed and presented. Second, an optimal decomposition of the vibration signal is obtained by using the particle swarm optimization (PSO) to obtain the optimal frequency and amplitude of masking signal. Finally, the extraction and compensation of the vibration signal are completed according to the mean value of intrinsic mode functions (IMFs) and the correlation coefficients between IMFs and the vibration signal. Experiments show that the new method can decompose the signal more accurately compared to the traditional methods, and the precision of compensation is higher.

Wide-angle, polarization-insensitive and broadband metamaterial absorber based on multilayered metal-dielectric structures

Tian Lan and Pinwei Liu

Doc ID: 287390 Received 23 Feb 2017; Accepted 07 Apr 2017; Posted 07 Apr 2017  View: PDF

Abstract: Wide-angle, polarization-insensitive and broadband metamaterial absorber (MA) based on multilayered metal-dielectric structures was designed and investigated using finite-different time-domain solution. The device exhibited polarization-insensitive absorption in the 475 – 592 nm range, with the absorption higher than 95%. At the same time, the broadband absorption was nearly non-affected for incident angles below 50°. To understand this absorption mechanism of this broadband MA, we investigated the magnetic field distributions at the resonance wavelength. Different metallic layers yielded different resonant wavelengths, leading to the observed high absorption in the broadband spectrum. For broadband MAs, the absorption spectrum can be expanded by adjusting structural parameters.

Image restoration in fiber-coupled imagers using space-variant impulse response characterization

Nojan Motamedi, Vitaliy Lomakin, and Joseph Ford

Doc ID: 278997 Received 18 Oct 2016; Accepted 07 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: Fiber coupled image sensors have attracted interest in recent years for high-resolution conformal image transfer, including mapping of the spherical image surface of a monocentric wide-angle lens to one or more flat focal plane sensors. However, image resolution is lost due to fiber bundle defects, moiré from lateral fiber-sensor misalignment, and blur due to the non-zero gap between fiber bundle and the image sensor. Here we investigate whether sub-pixel impulse response characterization of the strongly shift-variant impulse response can be used with existing image processing techniques to recover the resolution otherwise lost in image transfer. We show that the sub-micron impulse response is experimentally repeatable, and can be used to recover image data and reveal fine features of the input surface structure of a 2.5 µm pitch fiber bundle.

Mountain Shadows Revisited

John Adam

Doc ID: 285083 Received 19 Jan 2017; Accepted 07 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: Using purely geometric considerations a sequence of mountain shadow models is considered. The observer is located at the summit of idealized mountains with several different cross-sectional profiles. The result for a triangular profile is generalized to the case of an off-summit observer. We also examine the case of a conical mountain. In addition a simple geometric model is formulated for mountain ‘spikes’ in terms of the differences in shadow length and contrast for an off-summit observer within the shadow. An Appendix is devoted to the notion of ‘umbral volume’.

Simulation of small- and wide-angle scattering properties of glass-bead retroreflective materials

Dalma Héricz, Tamás Sarkadi, Gabor Erdei, Théo Lazuech, Sándor Lenk, and Pal Koppa

Doc ID: 285370 Received 10 Feb 2017; Accepted 07 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: Retroreflective materials are extensively used as traffic signs and security patterns. These goods are often realized by spherical glass-beads attached to some reflective substrate. New applications, especially 3D projection requires the precise evaluation and design of the characteristics of light backscattered from retroreflective screens. Simulation of such materials is not straightforward due to the different optical processes taking place: direct retroreflection involving small-angle diffraction effects, and multiple scattering resulting in wide-angle diffuse light. We propose a new complex method to describe the backscattering properties of glass-bead retroreflectors, which uniquely combines diffraction calculations with ray-tracing based on the microscopic properties of the retroreflector screen. The simulation method was validated with our measurements performed on commercial retroreflective screens.

Comparative study of fully 3D reconstruction algorithms for lens-free microscopy

Anthony Berdeu, Fabien Momey, Bastien Laperrousaz, Thomas Bordy, Xavier Gidrol, Jean-Marc Dinten, Nathalie Picollet-D'hahan, and Cédric ALLIER

Doc ID: 285743 Received 26 Jan 2017; Accepted 05 Apr 2017; Posted 06 Apr 2017  View: PDF

Abstract: We propose a 3D imaging platform based on lens-free microscopy to perform multi-angle acquisitions on 3D cell cultures embedded in extracellular matrices. Lens-free microscopy acquisitions present some inherent issues such as the lack of phase information on the sensor plane and a limited angular coverage. We developed and compared three different algorithms based on the Fourier diffraction theorem to obtain fully 3D reconstructions. These algorithms present an increasing complexity associated with a betterreconstruction quality. Two of them are based on a regularised inverse problem approach. To compare the reconstruction methods in terms of artefacts reduction, signal-to-noise ratio and computation time, we tested them on two experimental datasets: an endothelial cell culture and a prostate cell culture grown in a 3D extracellular matrix with large reconstructed volumes up to ~5 mm^3 with a resolution sufficient to resolve isolated single cells. The lens-free reconstructions compare well with standard microscopy.

Improving Chemical Species Tomography of Turbulent Flows Using Covariance Estimation

Samuel Grauer, Paul Hadwin, and Kyle Daun

Doc ID: 286543 Received 10 Feb 2017; Accepted 05 Apr 2017; Posted 06 Apr 2017  View: PDF

Abstract: Chemical species tomography (CST) experiments can be divided into limited-data and full-rank cases. Both require solving ill-posed inverse problems and thus the measurement data must be supplemented with prior information in order to carry out reconstructions. The Bayesian framework formalizes the role of additive information, expressed as the mean and covariance of a joint-normal prior probability density function. We present techniques for estimating the spatial covariance of a flow under limited-data and full-rank conditions. Our results show that incorporating a covariance estimate into CST reconstruction via a Bayesian prior increases the accuracy of instantaneous estimates. Improvements are especially dramatic in real-time limited-data CST, which is directly applicable to many industrially-relevant experiments.

How clean is the solvent you use to clean your optics? A vibrational sum-frequency-generation study.

Amanda Souna, John Bender, and John Fourkas

Doc ID: 288059 Received 10 Mar 2017; Accepted 05 Apr 2017; Posted 10 Apr 2017  View: PDF

Abstract: Solvents for cleaning optics often come into contact with plastic and/or rubber during storage and transfer. To explore the effects that exposure to these materials can have on solvents, we used vibrational sum-frequency-generation spectroscopy to study a silica optic following cleaning with solvents that had come into contact with either low-density polyethylene, high-density polyethylene, or rubber. Our studies show that even brief contact of acetone, methanol, or isopropanol with plastic or rubber can cause otherwise pure solvents to leave a persistent residue.

High resolution flash three-dimensional LIDAR Systems based on polarization modulation

Peng Zhang, Du Ping, Jiguang Zhao, Yishuo Song, and Hang Chen

Doc ID: 287537 Received 27 Feb 2017; Accepted 04 Apr 2017; Posted 06 Apr 2017  View: PDF

Abstract: Two high resolution flash LIDAR systems based on polarization modulation are demonstrated in this paper. One utilizes a polarization beam splitter and two CCD arrays; the other utilizes a micro-polarizer array and a CCD array. Compared with the traditional flash LIDAR systems, the main idea of the presented flash LIDAR systems is to replace high bandwidth detectors with a polarization modulator and low bandwidth detectors. The polarization modulator is used to modulate the polarization state of the received laser pulse in time and mapping range information onto intensity. The distance between the target and the system can be derived from intensity images which can be read out using low bandwidth detectors. Comparisons of the two systems indicate that they have the same range precision. Both the two demonstrated systems can achieve a high range precision of several millimeters. The system using a polarization beam splitter and two CCD arrays can obtain higher resolution images, but it is crucial to align the two CCD arrays precisely.

Investigation of High Optical Gain in Complex Type-II InGaAs/InAs/GaAsSb Nano-Scale Heterostructure for MIR Applications

Nisha Yadav, Garima Bhardwaj, Syed Anjum, Saurabh Dalela, M. J. Siddiqui, and Parvej Alvi

Doc ID: 285736 Received 26 Jan 2017; Accepted 04 Apr 2017; Posted 19 Apr 2017  View: PDF

Abstract: This paper reports a comprehensive theoretical study of W - shaped complex type-II InGaAs/InAs/GaAsSb nano-scale heterostructure consisting of two quantum wells of InAs material using the six band k.p theory. The entire structure has been supposed to be grown on InP substrate. In order to optimize the optical gain, the probability densities of electrons and holes were optimized in the heterostructure. Following these calculations, dispersion relations for electron and hole energies; and transverse electric (TE) and transverse magnetic (TM) polarizations dependent dipole matrix elements and momentum matrix elements were calculated and finally the optical gain in both the polarization modes were calculated. For this optimized complex heterostructure, a very high optical gain of the order of ~ 4500 cm-1 in the regime of mid-infrared wavelength ~ 3.2 µm has been achieved. The results suggest that the designed nano-heterostructure may be utilized for MIR applications such as chemical and bio-molecular sensing of molecules, for the applications of spectroscopy in the “Fingerprint Region” of molecular science and for detection of atmospheric gases which respond to 3.2 µm wavelength.

Mirages at Lake Geneva: the Fata Morgana

Andrew Young and Eric Frappa

Doc ID: 286520 Received 16 Feb 2017; Accepted 03 Apr 2017; Posted 05 Apr 2017  View: PDF

Abstract: Fata Morgana mirages are frequently seen at Lake Geneva. We show the first photographs of them, including a real-time video, and explain their main features, which are due to the very turbulent entrainment zones of capping inversions, especially in valley circulations.

On the discrimination of multiple phytoplankton groups from light absorption spectra of assemblages with mixed taxonomic composition and variable light conditions

Emanuele Organelli, Caterina Nuccio, Luigi Lazzara, Julia Uitz, Annick Bricaud, and Luca Massi

Doc ID: 284979 Received 17 Jan 2017; Accepted 30 Mar 2017; Posted 07 Apr 2017  View: PDF

Abstract: According to recommendations of the international community of Phytoplankton Functional Type algorithm developers, a set of experiments on marine algal cultures was conducted to: (i) investigate uncertainties and limits in phytoplankton group discrimination from hyperspectral light absorption properties of assemblages with mixed taxonomic composition; and (ii) evaluate the influence of light-driven spectral modifications. Results showed that spectral absorption signatures of multiple species can be extracted from mixed assemblages, even at low relative contributions. Errors in retrieved pigment abundances are, however, influenced by the co-occurrence of species with similar spectral features. Plasticity of absorption spectra due to changes in light conditions weakly affects inter-specific differences, with errors <21% for retrievals of pigment concentrations from mixed assemblages.

Spectral measurement and modeling of natural rainbows

Raymond Lee

Doc ID: 286110 Received 03 Feb 2017; Accepted 29 Mar 2017; Posted 05 Apr 2017  View: PDF

Abstract: Although quantitative observations of rainbow spectra, colors, and luminances are needed for any comprehensive analysis of rainbow scattering theory, very little such data has been published. But new remote sensing tools now make possible the detailed spectral and colorimetric measurement of natural rainbows, which here are defined as bows seen in sunlit rain or water-drop sprays. To measure these often short-lived phenomena, both multispectral tools (colorimetrically calibrated RGB cameras) and hyperspectral tools (imaging spectrometers) are used to examine the spectral and angular fine structure of natural rainbows. Airy theory for aerodynamically flattened drops helps to explain some of these bows’ observed features, such as the reduced color gamuts caused by smaller drop sizes and low sun elevations h0. However, other features such as the distinct blues seen in rainbows at higher h0 are not well explained.

Experimental measurements of the magnitude and phase response of high frequency modulated light undewater

Brandon Cochenour, Kaitlin Dunn, Alan Laux, and Linda Mullen

Doc ID: 286250 Received 10 Feb 2017; Accepted 28 Mar 2017; Posted 10 Apr 2017  View: PDF

Abstract: The propagation behavior of high frequency intensity modulated signals through turbid water is of significant interest for underwater laser ranging, imaging, and communications. Prior experimental mea- surements have focused only on the magnitude response of the underwater optical channel to forward scattered and unscattered modulated light. In this study we include, for the first time in our knowledge, both the magnitude and phase of the underwater optical channel to forward scattered light. The magnitude and phase response is measured out to 1 GHz, using three different artificial scattering agents in scattering environments in excess of 25 attenuation lengths. The phase response provides additional insight into the behavior of forward scattered light carrying high frequency intensity modulation.

Alignment sensing for optical cavities using radio frequency jitter modulation

Paul Fulda, Daniel Voss, Chris Mueller, Luis Ortega, Giacomo Ciani, Guido Mueller, and D. Tanner

Doc ID: 287112 Received 21 Feb 2017; Accepted 27 Mar 2017; Posted 06 Apr 2017  View: PDF

Abstract: Alignment sensing is often required in precision interferometry applications such as Advanced LIGO in order to achieve the optimum performance. Currently favored sensing schemes rely on the use of two separate RF quadrant photodetectors and Gouy phase telescopes to determine the alignment of a beam relative to an optical cavity axis. In this paper we demonstrate and alternative sensing scheme that has potential advantages over the currently standard schemes. We show that by using electro-optic beam deflectors to impose RF jitter sidebands on a beam it is possible to extract full alignment signals for two in-line optical cavities from just one single-element photodetector in reflection of each cavity.

Hafgerðingar and giant waves

Siebren van der Werf

Doc ID: 285673 Received 26 Jan 2017; Accepted 26 Mar 2017; Posted 27 Mar 2017  View: PDF

Abstract: A thirteenth century text in Old Norse, Konungs Skuggsjá, (translated as The Kings Mirror) tells about a phenomenon that may be encountered in the Greenland Sea. It is called Hafgerdingar (sea fences). The horizon is raised and from there three giant waves come rolling in. Recently Lehn and Schroeder have explained the phenomenon as a superior mirage. I extend their analysis by introducing a periodic time dependence in the properties of the inversion layer, and show that also the illusion of incoming waves and an immediate danger may so be explained.

Thermal stress and end-bulging in monoclinic crystals: The case study of double tungstates

Konstantin Yumashev and Pavel Loiko

Doc ID: 282009 Received 01 Dec 2016; Accepted 26 Mar 2017; Posted 07 Apr 2017  View: PDF

Abstract: An analytical description of the thermal stress and end-bulging component of the thermal lensing is presented for monoclinic laser crystals, taking into account the anisotropy of their optical, thermal and elastic properties, for the first time, to the best of our knowledge. The geometry of longitudinal diode-pumping (plane stress approximation) is considered. The developed approach is applied to the monoclinic double tungstates (MDTs), Yb:KGW, Yb:KYW and Yb:KLuW, yielding values of normal and shear stresses, tensile stress, and the end-bulging term. We show that for low-symmetry crystals, end-bulging is responsible for the astigmatism of the thermal lens. The geometry of this astigmatism is explained in terms of the principal meridional planes. We show that the crystal cut of the MDTs along the optical indicatrix axis Ng (propagation direction) provide low thermal stress, purely positive and weakly astigmatic thermal lens which is a key condition for power scaling and diffraction-limited laser output.

Differentiation of soot particulates in air using polarized light scattering method

Li Da, Nan Zeng, Dongjian Zhan, Yuerong Chen, Zeng mao, and Hui Ma

Doc ID: 283803 Received 30 Dec 2016; Accepted 25 Mar 2017; Posted 30 Mar 2017  View: PDF

Abstract: Soot is the main absorbent particle in visible range. Light scattering and absorption by particles in air can change optical polarization state, and the information upon polarization can reflect the component of particles. In this article, a polarized scattering method with the reference to a commercial instrument has been developed for the feasibility study concerning about differentiating soot out of the sand and salt. Simulated results indicate that S₂/S₀ at the scattering angle of 115º can identify the soot particles from salt and sand. Single component experiments for the three types of particles have verified the characteristic scattering angle and polarized parameter, then double composition experiments about soot mixing with sand and salt are carried out, it implies the potential of characterizing the mass fraction of soot. The preliminary field measurement has been conducted and compared with other carbon aerosol measuring instrument, it is believed that polarization method can be used to characterized soot.

Tropospheric haze and colors of the clear twilight sky

Raymond Lee and Duncan Mollner

Doc ID: 285879 Received 31 Jan 2017; Accepted 23 Mar 2017; Posted 24 Mar 2017  View: PDF

Abstract: At the earth’s surface, clear-sky colors during civil twilights depend on the combined spectral effects of molecular scattering, extinction by tropospheric aerosols, and absorption by ozone. Molecular scattering alone cannot produce the most vivid twilight colors near the solar horizon, for which aerosol scattering and absorption are also required. However, less well known are haze aerosols’ effects on twilight sky colors at larger scattering angles, including near the antisolar horizon. To analyze this range of colors, we compare 3D Monte Carlo simulations of skylight spectra with hyperspectral measurements of clear twilight skies over a wide range of aerosol optical depths. Our combined measurements and simulations indicate that: (a) the purest antisolar twilight colors would occur in a purely molecular, multiple-scattering atmosphere, whereas (b) the most vivid solar-sky colors require at least some turbidity. Taken together, these results suggest that multiple scattering plays an important role in determining the redness of the antitwilight arch.

Calibration method for a large-scale structured light measurement system

Peng Wang, jianmei wang, Jing Xu, Yong Guan, Guanglie Zhang, and ken chen

Doc ID: 285289 Received 23 Jan 2017; Accepted 23 Mar 2017; Posted 12 Apr 2017  View: PDF

Abstract: The structured light method is an effective non-contact measurement approach. The calibration greatly affects the measurement precision of structured light systems. To construct a large-scale structured lightsystem with high accuracy, a large-scale and precise calibration gaugeis always required, which leads to an increased cost. To this end, in thispaper, a calibration method with a planar mirror is proposed to reducethe calibration gauge size and cost. An out-of-focus camera calibration method is also proposed to overcome the defocusing problem caused by the shortened distance during the calibration procedure. The experimental results verify the accuracy of the proposed calibration method.

Rainbows in elliptically deformed drops. I. Mobius shift for higher-order rainbows

Gunther Konnen and James Lock

Doc ID: 285001 Received 17 Jan 2017; Accepted 22 Mar 2017; Posted 19 Apr 2017  View: PDF

Abstract: Using ray theory, the Mobius shift of the (p-1)-order rainbow angle for a particle having an elliptical cross section is obtained to first order in the ellipticity as a function of the tilt of the ellipse with respect to the propagation direction of the incoming rays. The result is then adapted to the geometry of scattering of light rays from the sun by a falling water drop as a function of the sun height angle. The variation in the angular spacing between the supernumeraries is determined as a function of location along the rainbow arc, the conditions under which the rainbow angle is insensitive to drop flattening were determined, and the dependence of the Mobius shift on the drop refractive index is shown for rainbows up to fourth order (p=5).

Demodulation of multi-modulation artefacts in Fourier-transform infrared spectroscopy

Jurgen Stohner and Mathias Schilling

Doc ID: 287105 Received 21 Feb 2017; Accepted 21 Mar 2017; Posted 07 Apr 2017  View: PDF

Abstract: Fourier-transform infrared (FTIR) spectra can show artefacts, for example in the vicinity of the overtonewhen light is doubly modulated. Technical approaches, e.i. modifications to the spectrometer set-up, hadbeen devised in the past in order to reduce those artefacts. Elimination of the artefacts were achievedonly partly but to the expense of a loss of intensity or an increase of the noise level. We devised a computationaldemodulation scheme which is capable to almost fully reduce the artefacts neither with a lossof spectroscopic information nor an increase of the noise level. This has been demonstrated for the FTIRabsorption spectra in the overtone regions of HCl(g) and CH4(g).

Sinusoidal phase-modulating interferometer with ellipse fitting and correction method

Chang NI, Ming Zhang, zhu yu, Chuxiong Hu, Siqi DING, and Zhe JIA

Doc ID: 280489 Received 09 Nov 2016; Accepted 02 Feb 2017; Posted 06 Apr 2017  View: PDF

Abstract: In sinusoidal phase-modulating interferometer, sinusoidal modulation to the phase of the laser or the reference wave is necessary. However, modulation of the phase also involves an intensity modulation of the light, which leads to the measurement error if a conventional signal processing is used. In addition, the error of modulation depth and the phase delay of demodulation also increase the measurement error. A novel signal processing with ellipse fitting and correction method is proposed to correct the error caused by them. Numerical simulation results and experimental results prove that the novel signal processing can compensate the measurement error caused by the intensity modulation, the error of modulation depth and the phase delay of demodulation.

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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