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Early Posting

Accepted papers to appear in an upcoming issue

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

Three-visible-light Wave Combiner Based on Photonic Crystal Microcavities

Yiling Sun, Xiaoyi Zhou, liu Dingwen, and Zhengbiao Ouyang

Doc ID: 238401 Received 23 Apr 2015; Accepted 02 Jul 2015; Posted 02 Jul 2015  View: PDF

Abstract: We propose a three-visible-light wave combiner based on two-dimensional square-lattice photonic crystal microcavities. The transmission characteristic of light wave in photonic crystals with point defects is analyzed. The resonant wavelengths correspond to different radiuses of point defect. As an example, a combiner for combining light waves of 488, 532 and 635 nm, which are commonly used as the three primary colors in laser display system, is designed and demonstrated through finite-difference time-domain method. The three visible light of 488, 532 and 635 nm output at the same port with transmittances of 97.6%, 98.1% and 90.0%, respectively. The results show that the proposed device can perform efficient synthesis and the method for the designing are useful for other combiners based on photonic crystals made of dispersion materials.

Effect of charged-particle surface excitations on near-field optics

Miroslav Kocifaj, Frantisek Kundracik, Gorden Videen, and Jozef Klacka

Doc ID: 241652 Received 25 May 2015; Accepted 02 Jul 2015; Posted 02 Jul 2015  View: PDF

Abstract: The mechanism of charge on the near-field intensity distribution is revealed for metallic and dielectric particles with sizes ranging from 10 nm to 10 m. The theoretical foundation of near-field intensity perturbations is in the discontinuity of the tangential components of the magnetic fields on either side of the interface between the particle and its surrounding medium, since excess electrons form a thin metal-like layer with elevated conductivity. We have shown that the local fields alter marginally if charges are imposed on a surface of a metallic particle. But an intensity amplification is identified in the vicinity of charged dielectric particles with sizes smaller than the wavelength. Specifically, we have demonstrated that the electromagnetic field is amplified near the poles of the particle as a result of the oriented electric and incident fields. In contrast, a dielectric particle that is large compared to the wavelength becomes opaque with a deep shadow at the side opposite to the beam incidence. As a result, intensity damping is identified near a charged sphere in the geometric optics regime. At significant charge densities, the physical properties of a conductive layer play a dominant role in forming the 3D intensity distribution independent of conductivity or permittivity of the particle core. These findings suggest that some electrically chargeable particles have the potential to be used as optical devices with properties tunable through their net surface charge.

Photometry based estimation of the total number of stars in the Universe

Lazo Manojlovic

Doc ID: 241802 Received 26 May 2015; Accepted 02 Jul 2015; Posted 02 Jul 2015  View: PDF

Abstract: A novel photometry based estimation of the total number of stars in the Universe is presented. The estimation method is based on the energy conservation law and actual measurements of the extragalactic background light levels. By assuming that every radiated photon is kept within the Universe volume, i.e. by approximating the Universe with an integrating cavity without the losses the total number of stars in the Universe of about 6×1022 has been obtained.

Correction of pathlength amplification in the filter-pad technique for measurements of particulate absorption coefficient in the visible spectral region

Dariusz Stramski, Rick Reynolds, Julia Uitz, Guangming Zheng, and Slawomir Kaczmarek

Doc ID: 237332 Received 02 Apr 2015; Accepted 01 Jul 2015; Posted 01 Jul 2015  View: PDF

Abstract: Spectrophotometric measurement of particulate matter retained on filters is the most common and practical method for routine determination of the spectral light absorption coefficient of aquatic particles, ap(λ), at high spectral resolution over a broad spectral range. The use of differing geometrical measurement configurations and large variations in the reported correction for pathlength amplification induced by the particle/filter matrix have hindered adoption of an established measurement protocol. We describe results of dedicated laboratory experiments with a diversity of particulate sample types to examine variation in the pathlength amplification factor for three filter measurement geometries; the filter in the transmittance configuration (T), the filer in the transmittance-reflectance configuration (T-R), and the filter placed inside an integrating sphere (IS). Relationships between optical density measured on suspensions (ODs) and filters (ODf) within the visible portion of the spectrum were evaluated for the formulation of pathlength amplification correction, with power functions providing the best functional representation of the relationship for all three geometries. Whereas the largest uncertainties occur in the T method, the IS method provided the least sample-to-sample variability and the smallest uncertainties in the relationship between ODs and ODf. Fifty percent of our IS data points of ODs measured for six different samples with 1 nm resolution within the light wavelength range from 400 to 700 nm is predicted from the power function with an error smaller than 7.1%. The relationships established for the three filter-pad methods are applicable to historical and ongoing measurements; for future work, the use of the IS method is recommended whenever feasible.

Simultaneous Super-resolution and Nonunifomity Correction for Infrared Imaging Systems

Pablo Meza, Sergio Torres, Esteban Vera, Cesar San Martin, and Guillermo Machuca

Doc ID: 238166 Received 15 Apr 2015; Accepted 01 Jul 2015; Posted 01 Jul 2015  View: PDF

Abstract: In this article, we present a novel algorithm to achieve simultaneous super-resolution and nonuniformity correction from a sequence of infrared images. We propose to use spatial regularization terms that exploit both non-local means and the absence of spatial correlation between the scene and the nonuniformity noise sources. We derive an iterative optimization algorithm based on a gradient descent minimization strategy. Results from infrared image sequences corrupted with simulated and real fixed-pattern noise show a competitive performance compared to state-of-the-art methods. A qualitative analysis on the experimental results obtained with images from a variety of infrared cameras indicates that the proposed method provides super-resolved images with significantly less fixed-pattern noise.

Better 3D Inspection with Structured Illumination: Signal Formation and Precision

Zheng Yang, Gerd Haeusler, and Alexander Kessel

Doc ID: 238349 Received 20 Apr 2015; Accepted 01 Jul 2015; Posted 01 Jul 2015  View: PDF

Abstract: 3D-metrology faces increasing demands for higher precision and larger space-bandwidth-speed-product SBSP (number of 3D-points/sec). In this paper we consider Structured-Illumination Microscopy (SIM) as a means for satisfying these demands, developing a theoretical model of the signal formation for both optically smooth and optically rough surface. The model allows us to investigate physical limits on precision and to establish rules that allow sensor parameter optimization for greatest precision or highest speed.

Extended X-ray Absorption Fine Structure (EXAFS) measurements on Asymmetric Bipolar Pulse DC magnetron sputtered Ta2O5 thin films

DIBYENDU BHATTACHARYYA, Sk Haque, P Sagdeo, D Shinde, J Misal, S Jha, and N Sahoo

Doc ID: 239803 Received 27 Apr 2015; Accepted 01 Jul 2015; Posted 01 Jul 2015  View: PDF

Abstract: Tantalum pent oxide (Ta2O5) thin films have been deposited on fused silica substrates using a novel Asymmetric Bipolar d.c. (ABPDC) magnetron sputtering technique under a mixed ambient of oxygen and argon. Films have been prepared at different oxygen to argon ratios in the sputtering ambient and optical properties of the films have been investigated by spectroscopic elliposmetry technique while the structural analysis of the films have been carried out by Grazing Incidence X-ray diffraction (GIXRD) and Extended X-ray absorption fine structure (EXAFS) measurements. The concentration of oxygen and tantalum in the Ta2O5 films has been estimated by Rutherford Backscattering Spectrometry (RBS) technique. The variation of optical constants of the films with change in deposition parameters has been explained in the light of the change in average Ta-O bond lengths and oxygen coordination around Ta sites as obtained from EXAFS measurements. The trend in variation of oxygen to tantalum ratio in the films obtained from RBS measurement, as a function of oxygen partial pressure used during sputtering, is found to follow the trend in variation of oxygen co-ordination number around Ta sites obtained from EXAFS measurement.

Microphysical Characterization of Free Space Optical Link due to Hydrometeor and Fog Effects

Frank Marzano and Saverio Mori

Doc ID: 239931 Received 28 Apr 2015; Accepted 01 Jul 2015; Posted 01 Jul 2015  View: PDF

Abstract: Free space optics (FSO) channel availability is affected by atmospheric water particles which may introduce severe path attenuation. A unified Microphysically-oriented Atmospheric Particle Scattering (MAPS) model is proposed and described to simulate particle scattering effects on FSO links. Atmospheric particles, such as raindrops, graupel particles and snowflakes together with fog droplets are considered. Input data to characterize liquid and frozen water particle size distribution, density and refractivity are derived from available literature data and measurements. Scattering, absorption and extinction coefficients as well as asymmetry factor are numerically simulated for each particle class and then parametrized with respect to particle water content, fall rate and visibility, spanning from visible to infrared wavelengths. Both single and multiple scattering effects are discussed and quantified by using a radiative transfer model for small-angle approximation. MAPS simulations confirm that fog layers are those causing the largest power extinction on FSO links, but also several decibels of attenuation can be attributed to snow and rain conditions. Multiple scattering effects, especially due to fog droplets, heavy rain and dry snowflakes, typically tend to reduce the total attenuation by increasing the received power. An estimate of these effects, parameterized to single-scattering extinction, is proposed for near-infrared FSO link design.

Z-scan measurement of nonlinear optical properties of BiOCl nanosheets

Tian Jiang, Runze Chen, Xin Zheng, Yangwei Zhang, and Tang Yuhua

Doc ID: 240653 Received 11 May 2015; Accepted 30 Jun 2015; Posted 02 Jul 2015  View: PDF

Abstract: Bismuth oxyhalides (BiOX), such as Bismuth oxyhlorides (BiOCl), are layered materials with [Bi2O2]2+ layers sandwiched between two sheets of Cl ions. Much work has focused on its protential to be photocatalysts, but its nonlinear optical properties are rarely studied. In this work, the nonlinear refractive index of BiOCl nanosheets has been characterized with Z-scan measurement under 800nm femtosecond pulsed laser excitation. A shift from saturable absorption to reverse saturable absorption was observed at higher input pump intensities in the experiments. The transition process was analyzed using a phenomenological model based on saturable absorption and multi-photon absorption.

Assessment of minimum permissible geometrical parameters of a near-to-eye display

Sergiy Valyukh and Oleksandr Slobodyanyuk

Doc ID: 235442 Received 02 Mar 2015; Accepted 30 Jun 2015; Posted 30 Jun 2015  View: PDF

Abstract: Light weight and small dimensions are some of the most important characteristics of near-to-eye displays (NEDs) which consist of two basic parts: a microdisplay for generation an image and supplementary optics to be able to see the image. Nowadays, the pixels size of microdisplays may be less than 4µm that makes the supplementary optics as the major factor defining restrictions on a NED dimensions, or at least on the distance between the microdisplay and eye. The goal of the present work is to give answers on the following two questions: how small this distance can be in principle and what is the microdisplay minimum resolution possible to see through the supplementary optics placed in immediate vicinity of the eye. To explore the first question, we consider an aberrations free magnifier that is the initial stage in elaboration of a real optical system. In this case the paraxial approximation and the transfer matrix method are ideal tools for simulation of light propagation from the microdisplay through the magnifier and the human eye’s optical system to the retina. The human eye is considered according to the Gullstrand model. Parameters of the magnifier, its location with respect to the eye and the microdisplay, depth of field that can be interpreted as the tolerance of the microdisplay position are determined and discussed. The second question related to the microdisplay maximum resolution is investigated by using the principles of wave optics.

New Mathematical Model for Hybrid and Panoramic Stereovision Systems: Panoramic to rectilinear conversion model

Aymen Arfaoui and Simon Thibault

Doc ID: 237629 Received 08 Apr 2015; Accepted 29 Jun 2015; Posted 30 Jun 2015  View: PDF

Abstract: This paper introduces a new generic model for a stereovision system composed either of a perspective camera and a panoramic camera, or of two panoramic cameras. We present a new simple model in order to establish matching images and to formulate 3D reconstruction. Indeed, we show that composed cubic splines functions are suitable for conventional and wide-angle cameras and model accurately tangential and radial distortions. Matching is greatly simplified using this technique and classical methods can be used to evaluate the relationship between image pairs and to achieve 3D reconstruction. Such a technique allows to model complex forms of distortions as is the case for panomorph lenses.

Extension of light transmission distance of single-mode fiber using a microaxicon lensed fiber end

Yuanzheng Chen, Jiwen Cui, and Jiubin Tan

Doc ID: 240451 Received 06 May 2015; Accepted 29 Jun 2015; Posted 30 Jun 2015  View: PDF

Abstract: The light signal through single-mode fiber is unstable, rapidly decays as it propagates, and has limited effective transmission distance. In this study, to extend its transmission distance a microaxicon was designed at single-mode fiber end and the emitted light analyzed via simulations and experiments. Results indicate that an 80 μm maximum transmission distance is achievable with the microaxicon at a 45° base angle. Further, the divergence angle of the light is reduced from 4.1° to 0.47°, its stability is improved by 97%, and the light spot is sharp at 70–80 μm away from the fiber end.

Intensity distribution of the parhelic circle and embedded parhelia at zero solar elevations: theory and experiments

Markus Selmke and Sarah Borchardt

Doc ID: 240195 Received 04 May 2015; Accepted 29 Jun 2015; Posted 29 Jun 2015  View: PDF

Abstract: We describe the individual contributions to the intensity distribution of the parhelic circle for plate-oriented hexagonal ice crystals at exactly zero solar elevation using geometrical optics. An experimental as well as theoretical study of in-plane ray-paths provides details on the mechanism for several halos, including the parhelia, the $120^{\circ}$ parhelia, a blue edge and the Liljequist parhelia. Azimuthal coordinates for associated characteristic features in the intensity distribution are compared to experimental data obtained using a spinning hexagonal glass prism.

Perceptual quality measurement of 3D images based on binocular vision

Wujie Zhou and Lu Yu

Doc ID: 240866 Received 12 May 2015; Accepted 29 Jun 2015; Posted 29 Jun 2015  View: PDF

Abstract: Three-dimensional (3D) technology has become immensely popular in recent years. Moreover, it has been widely adopted in various applications. Hence, perceptual quality measurement of symmetrically and asymmetrically distorted 3D images has become an important, fundamental, and challenging issue in 3D imaging research. In this paper, we propose a binocular vision based 3D image quality measurement (IQM) metric. Consideration of the 3D perceptual properties of the primary visual cortex (V1) and the higher visual areas (V2) for 3D-IQM is the major technical contribution of this research. To be more specific, first, the metric simulates the receptive fields of complex cells (V1) using binocular energy response and binocular rivalry response, and the higher visual areas (V2) using local binary patterns (LBP) features. Then, three similarity scores of 3D perceptual properties between the reference and distorted 3D images are measured. Finally, by using support vector regression (SVR), three similarity scores are integrated into an overall 3D quality score. Experimental results for two public benchmark databases demonstrate that, in comparison with most current 2D and 3D metrics, the proposed metric achieves significantly higher consistency in alignment with subjective fidelity ratings.

Precise Design of Two-dimensional Diffractive Optical Elements for Beam Shaping

Huarong Gu, Weidong Qu, Qiaofeng Tan, and Guofan Jin

Doc ID: 241967 Received 28 May 2015; Accepted 28 Jun 2015; Posted 01 Jul 2015  View: PDF

Abstract: Diffractive optical elements (DOEs) for beam shaping are widely used in many fields, and there are many kinds of optimization algorithm to design the DOEs for beam shaping. However, only the intensity distribution of the selected sampling points is controlled by these optimization algorithms. The intensity distribution of other points on the output plane is always far away from the ideal distribution. The reason is that the sampling interval on the output plane is not small enough. In this paper, a new modified GS algorithm is presented with a small enough sampling interval on the output plane. A two-dimensional DOE for beam shaping is designed, and the simulation results and the experimental results demonstrate the good performance of this algorithm.

Synthesis of statistical properties of randomly fluctuating polarized field

VINU RV and Rakesh Singh

Doc ID: 240226 Received 04 May 2015; Accepted 27 Jun 2015; Posted 29 Jun 2015  View: PDF

Abstract: An experimental technique for the synthesis of statistical properties of randomly fluctuating polarized field is investigated and experimentally demonstrated. The technique offers the controlled synthesis of coherence and polarization and subsequent analysis of the synthesized field is carried out by making use of two point intensity correlation and speckle holographic technique. The controlled synthesis is achieved by using an aperture of specific size at the source plane and generating a vortex in one of the orthogonal polarization components of the polarized field, thereby producing a singularity in off diagonal elements of the coherence - polarization matrix.

Improving the Performance of Gold Nanohole Arrays BioSensors by Controlling the Optical Collimation Conditions

jacson de Menezes, Anderson Thesing, chiara valsecchi, luis Armas, and Alexandre Brolo

Doc ID: 240240 Received 04 May 2015; Accepted 27 Jun 2015; Posted 29 Jun 2015  View: PDF

Abstract: An experimental investigation on both the bulk and surface sensitivities of gold nanohole arrays fabricated by interference lithography (IL) on the degree of white light beam collimation is presented. The optical transmission response of nanohole arrays has been recorded by focused and collimated beam transmission spectra. The results show that both the bulk and surface sensitivities for the collimated case are much larger than for the focused case. In particular, the shape of the spectra was dependent on the degree of beam collimation. The results showed that improved sensing performance (around 3.5 times) and higher FoM (around 4.4 times) can be obtained by simply adjusting the incident/collection experimental conditions in transmission measurements.

Nonresonant and resonant cloaking of an electrically large dielectric spherical object by a multilayer isotropic metamaterial cover

Ahmed Abouelsaood, Islam sayed, and Islam Eshrah

Doc ID: 237889 Received 13 Apr 2015; Accepted 27 Jun 2015; Posted 29 Jun 2015  View: PDF

Abstract: Mie theory and genetic algorithms are used to determine the parameters and performance of cloaks made of homogeneous isotropic metamaterials that would hide a spherical dielectric object of size comparable to the incident radiation wavelength. A single-layer cover with negative permittivity and permeability can produce a much greater reduction in the extinction efficiency than one with the permittivity and permeability of positive or opposite signs. Minimization of the extinction efficiency in the former case leads to both nonresonant and resonant solutions. Adding a second layer to the cover can lead to a significant enhancement of the bandwidth, but only to a modest reduction in the extinction efficiency at the design wavelength. In the single-layer case, Debye's scattering series is used to show that the nonresonant and resonant minima of the extinction efficiency correspond to scattering phase shifts approximately equal to zero and -π respectively, and to understand the simple approximate expressions for the cloak parameters of the nonresonant solutions. The series also explains the value of the outer radius of a multilayer cloak, provides a link to a previously studied isotropic approximation to a transformation optics cloak and indicates that a cloak consisting of an odd number of alternate double-negative and double-positive layers will probably give the best possible performance.

Numerical Simulations of Holographic Spatiospectral Traces of Spatiotemporally Distorted Ultrashort Laser Pulses

Zhe Guang, Michelle Rhodes, and Rick Trebino

Doc ID: 239762 Received 27 Apr 2015; Accepted 26 Jun 2015; Posted 29 Jun 2015  View: PDF

Abstract: We simulate traces for a catalog of spatiotemporally complex pulses measured using the only single-shot complete spatiotemporal pulse-measurement technique ever proposed and that we recently developed, called Spatially and Temporally Resolved Intensity and Phase Evaluation Device: Full Information from a Single Hologram (STRIPED FISH). STRIPED FISH measures the complete spatiotemporal intensity I(x,y,t) and phase Φ(x,y,t) of an arbitrary laser pulse using an experimentally recorded trace consisting of multiple digital holograms, one for each frequency present in the pulse. To understand the effects of various spatiotemporal distortions on the STRIPED FISH trace, we numerically investigate STRIPED FISH trace features for a catalog of pulses, including the spatially and temporally transform-limited pulse, temporal and spatial double pulses, spherically focusing and diverging pulses, self-phase modulated and self-focusing pulses, spatiotemporally coupled pulses and pulses with complex structures. Also, as a practical example, we analyze an experimentally recorded trace of a focusing pulse with spatial chirp. Overall, we find that, from STRIPED FISH’s informative trace, significant spatiotemporal characteristics of the unknown pulse can be immediately recognized from the camera frame. This, coupled with its simple pulse-retrieval algorithm, make STRIPED FISH an excellent technique for measuring and monitoring ultrafast laser sources.

(NRL) Review of infrared fiber-based components

Rafael Gattass, Rajesh Thapa, Frederic Kung, Lynda Busse, Brandon Shaw, and Jasbinder Sanghera

Doc ID: 241920 Received 28 May 2015; Accepted 26 Jun 2015; Posted 29 Jun 2015  View: PDF

Abstract: The infrared range of the optical spectrum is attractive for its use in sensing, surveillance and material characterization. The increasing availability of compact laser sources and detectors in the infrared range stands in contrast to the limited development of optical components for this optical range. We highlight developments of infrared components with a particular focus on fiber-based components for compact optical devices and systems.

An Experimental Assessment of SU-8 Optical Waveguides Buried in Plastic Substrate for Optical Interconnections

Hanan Hamid, David Thiel, and Thomas Fickenscher

Doc ID: 238268 Received 16 Apr 2015; Accepted 25 Jun 2015; Posted 29 Jun 2015  View: PDF

Abstract: Multimode polymer waveguides have been developed to create low cost high speed on board optical interconnects. Buried optical waveguides made from SU-8 in a polymethyl methacrylate polymer (PMMA) substrate covered with a thin PMMA sheet is a low cost option for electro-optical interconnects. The propagation losses for a 600×600 µm² straight waveguide were 1.96 dB/cm, 1.32 dB/cm and 1.39 dB/cm, respectively at three different wavelengths (850 nm, 1310 nm and 1550 nm). The bending loss for a 15 mm bending radius is as high as 6 dB/cm. Transition and radiation losses dominate overall loss when the bending radius is less than 30 mm. The waveguide was excited using a multimode 850 nm VCSEL transmitter and detected using a butt-coupled and a lens coupled receiver. The coupling loss was about 1 dB for the butt coupling technique and 2 dB for lens coupling. The response bandwidth and the group delay of direct modulated (IF) signal were independent of the channel waveguide for communication speeds up to more than 3 GHz. This technique is viable for low cost, short length, buried optical waveguides.

The fabrication, measurement and application of excellent 20/400 Yb-doped fiber

Nengli Dai, Liao Lei, Wang Yibo, Ying Xing, Haiqing Li, Jinggang Peng, and Jinyan Li

Doc ID: 231018 Received 17 Dec 2014; Accepted 25 Jun 2015; Posted 26 Jun 2015  View: PDF

Abstract: We have demonstrated an excellent 20/400 Yb-doped fiber from fabrication and measurement to application in this work. To obtain good laser property, some crucial parameters that include the refractive index profile, geometrical morphology and coating require precise controlling. Through a 7:1 pump combiner with six 120W 915 nm fibercoupled pump diodes modules, single all-fiber laser oscillator generating 500W of continuous wave (CW) signal power at 1080nm with 76.4% slope efficiency that is close to the theory limit. The signal power showed no evidence of roll-over and the highest output power was limited only by available pump power. The excellent 20/400 Ybdoped fiber could realize the application for the higher power fiber laser.

The transmitting characteristics of the polarization information under seawater

Zhongyi Guo, Qiang Xu, Qiangqiang Tao, Xinshun Wang, Weiyan Jiao, Shiliang Qu, and Gao Jun

Doc ID: 238133 Received 14 Apr 2015; Accepted 25 Jun 2015; Posted 26 Jun 2015  View: PDF

Abstract: We have presented the performance evaluation for light communication under water based on the polarization information. In particular, we focused on the transmitting characteristics of the polarized lights under different conditions of water types and link distances. The trajectories of transmitted photons propagating in water channel can be simulated based on the Monte Carlo (MC) algorithm. The simulated results demonstrate that the intensity of the polarized light after being transmitted in underwater decrease sharply as the transmission distance increase, but the degree of polarization (DoP) of the transmitted lights remains above 0.75. The polarization retrieve (PR) method is used for reducing the scattering impact on DoP of the light, and the maximal enhancement of linear degree of polarization (LDoP) can be obtained about 16%. Meanwhile, the modified PR method with different retrieval Mueller matrix deriving from different distances ( l ) of transmission channel has also been investigated, which shows that the retrieval accuracy will be enhanced with the increase of transmission distance of retrieval Mueller matrix (RMM).

In vivo tissue injury mapping using OCT based methods

Utku Baran, Yuandong Li, and Ruikang Wang

Doc ID: 239655 Received 27 Apr 2015; Accepted 25 Jun 2015; Posted 26 Jun 2015  View: PDF

Abstract: An injury causes changes in the optical attenuation coefficient of light beam travelling inside a tissue. We report a method called tissue injury mapping (TIM), which utilizes a non-invasive in vivo optical coherence tomography approach to generate optical attenuation coefficient and microvascular map of the injured tissue. Using TIM, the infarct region development in mouse cerebral cortex during stroke is visualized. Moreover, we demonstrate the changes in human facial skin structure and microvasculature during an acne lesion development from initiation to scarring. The results indicate that TIM may be used to aid in the characterization and the treatment of various diseases by enabling a high resolution detection of tissue structural and microvascular changes.

Imaging the local acoustic pressure in microchannels

Jorick van 't Oever, Raimond Frentrop, Daniel Wijnperlé, Herman Offerhaus, Dirk van den Ende, Jennifer Herek, and Frieder Mugele

Doc ID: 241195 Received 18 May 2015; Accepted 25 Jun 2015; Posted 26 Jun 2015  View: PDF

Abstract: A novel method for determining the spatially resolved acoustic field inside a water-filled microchannel is presented. The acoustic field, both amplitude and phase, is determined by measuring the change of index of refraction of the water due to the local pressure using stroboscopic illumination. The pressure distributions are measured for the fundamental pressure resonance in the water and two higher harmonic modes. By combining measurement at a range of excitation frequencies a frequency map of modes is made, from which the spectral line width and Q-factor of individual resonances can be obtained.

Thermal and Optical Design Analyses, Optimizations, and Experimental Verification for a Novel, Glare-free LED Lamp for Household Applications

Nisa Khan

Doc ID: 236366 Received 17 Mar 2015; Accepted 25 Jun 2015; Posted 25 Jun 2015  View: PDF

Abstract: Light emitting diode (LED) technologies are undergoing very fast developments to enable household lamp products with improved energy efficiency and lighting properties at lower cost. Although many LED replacement lamps are claimed to provide similar or better lighting quality at lower electrical wattage compared to general-purpose incumbent lamps, certain lighting characteristics important to human vision are neglected in this comparison, which include glare-free illumination and omni-directional or sufficiently broad light distribution with adequate homogeneity. In this paper, we comprehensively investigate the thermal and lighting performances and tradeoffs for several commercial LED replacement lamps for the most-popular Edison incandescent bulb. For the first time in the literature, we present simulation and analysis for thermal and optical performance tradeoffs for an LED lamp at the chip and module granularity level. In addition, we present a novel, glare-free, and production-friendly LED lamp design optimized to produce very desirable light distribution properties as demonstrated by our simulation results, some of which are verified by experiments.

Demonstration of an extended capture range for JWST phase retrieval

Elizabeth Carlisle and Daniel Acton

Doc ID: 237133 Received 31 Mar 2015; Accepted 25 Jun 2015; Posted 25 Jun 2015  View: PDF

Abstract: A geometrical phase retrieval (GPR) algorithm is applied to the problem of image stacking, in order to extend the capture range of normal phase retrieval (PR) on JWST, and potentially eliminate a lengthy Image Stacking process that is based on centroids. Computer simulations are used to establish the capture range of the existing PR algorithm for JWST and demonstrate that it is dramatically increased when combined with GPR, guaranteeing PR capture 95% of the time. An experiment using a scale optical model of JWST was conducted to demonstrate the effectiveness of the GPR algorithm in both coherent and incoherent imaging.

A fast weighted centroid algorithm for single particle localization near the information limit

Jan Scrimgeour and Jeremie Fish

Doc ID: 238246 Received 05 May 2015; Accepted 25 Jun 2015; Posted 25 Jun 2015  View: PDF

Abstract: A simple weighting scheme that enhances the localization precision of center of mass calculations for radially symmetric intensity distributions is presented. The algorithm effectively removes the biasing that is common in such center of mass calculations. Localization precision compares favorably with other localization algorithms in super resolution microscopy while significantly reducing processing time and memory usage. We expect that the algorithm presented will be of significant utility when fast computationally lightweight particle localization or tracking is desired.

Plastic Identification Using Multi-Spectral Infrared Spectroscopy

Abraham Vázquez-Guardado, Debashis Chanda, Mason Money, and Nathaniel McKinney

Doc ID: 238391 Received 21 Apr 2015; Accepted 24 Jun 2015; Posted 25 Jun 2015  View: PDF

Abstract: Identification and classification of plastics plays an important role in waste management and recycling process. Present electrical and optical sorting techniques lack required resolution for accurate identification in a high throughput manner for divers set of plastics commonly found in municipal waste. Multi-spectral infrared spectroscopic measurements are shown to uniquely identify all common as well as specialized plastics based on vibrational resonances. This simple optical technique in combination with a spectral signature library will enable high throughput and accurate detection of various plastics from recovered solid waste.

(NRL) Microwave Photonic Delay Line Signal Processing

John Diehl, Joseph Singley, Vincent Urick, and Christopher Sunderman

Doc ID: 240004 Received 01 May 2015; Accepted 24 Jun 2015; Posted 25 Jun 2015  View: PDF

Abstract: This paper provides a path for the design of state-of-the-art fiber-optic delay lines for signal processing. The theoretical forms for various RF system performance metrics are derived for four modulation types: push-pull and asymmetric Mach-Zehnder Modulators, phase modulator with asymmetric Mach-Zehnder Interferometer, and polarization modulator with control waveplate and polarizing beam splitter. Each modulation type is considered to cover the current and future needs for ideal system designs. System gain, compression point, and third-order output intercept point are derived from the transfer matrices for each modulation type. A discussion of optical amplifier placement and fiber-effect mitigation is offered. The paper concludes by detailing two high-performance delay lines, built for unique applications, which exhibit performance levels an order of magnitude better than commercial delay lines. This paper should serve as a guide to maximizing the performance of future systems, and offer a look into current and future research being done to further improve photonics technologies.

(NRL) Coherent light transmission properties of commercial photonic crystal hollow core optical fiber

Geoffrey Cranch and Gary Miller

Doc ID: 240018 Received 29 Apr 2015; Accepted 24 Jun 2015; Posted 25 Jun 2015  View: PDF

Abstract: Photonic crystal hollow core fiber (PC-HCF) has enabled many exciting new applications in nonlinear optics and spectroscopy. However, to date there has been less impact in coherent applications where preservation of optical phase over long fiber lengths is crucial. This manuscript presents characteristics of three commercially available PC-HCFs relevant to coherent applications including higher order mode analysis, birefringence and polarization dependent loss and their impact on coherent light transmission in PC-HCF. To demonstrate the potential of PC-HCF in high performance sensing, a Mach-Zehnder interferometer (MZI) incorporating 10 m of PC-HCF in each arm is characterized and demonstrates a phase resolution (59×10¯⁹ rad/Hz½ at 30 kHz) close to the shot noise limit, which is better than can be achieved in a MZI made with the same length of singlemode solid core fiber because of the limit set by fundamental thermodynamic noise (74×10¯⁹ rad/Hz½ at 30 kHz).

Comparison of bandwidth and sensitivity of long-period gratings in single-mode and few-mode fibers

Florence Yuen Ming Chan and Gopinath Mudhana

Doc ID: 224898 Received 13 Oct 2014; Accepted 24 Jun 2015; Posted 25 Jun 2015  View: PDF

Abstract: We present a comparative study of the bandwidth and the sensitivity of the resonance wavelength of long-period gratings (LPGs) to external perturbation fabricated in single-mode fibers (SMFs) and few-mode fibers (FMFs) and their dependencies on the group indices and the dispersion properties of the phase-matched modes. Unlike SMFs, a relatively large core size of FMFs invariably leads to non-uniform index modulation across the fiber cross-section under UV exposure, enabling the coupling between modes having dissimilar azimuthal symmetry. Simple analytical formulas for the group/effective index difference, dispersion difference, bandwidth, and wavelength sensitivities are derived for the case of SMFs where light is coupled from the fundamental core mode to the symmetrical cladding modes. Our results show that a two-mode fiber operating at a V-number close to 3 is capable of producing LPGs with broader bandwidth and higher sensitivity as compared with their SMF counterparts except for a few special cases. Our analyses provide insights into the characteristics of LPGs and facilitate their designs for specific applications.

Dynamic Point Shifting with Null-Screens using Three LCD’s as Targets for Corneal Topography

Martin Rodriguez Rodriguez, J. Rufino Diaz-Uribe, and Alberto Jaramillo-Núñez

Doc ID: 236222 Received 16 Mar 2015; Accepted 24 Jun 2015; Posted 24 Jun 2015  View: PDF

Abstract: In this paper the use of three LCD’s as a target for a corneal topographer is proposed. The main advantage is that the geometrical pattern in the target can be modified without moving any mechanical part to apply the Dynamic Point Shifting (DyPoS) method. Some results on the capabilities of the LCD’s, obtained with photo frames, for measuring a 6.37 mm radius of curvature (ROC) calibration sphere, and applying the DyPoS method are presented. It is shown that the error in measuring the ROC with DyPoS is reduced to 3% of the real value and the RMS in elevation or sagitta differences is around 15 micrometers; 30% and 66% of the values obtained without DyPoS, respectively.

Noise analysis of the Vernier anode

Airong Zhao, Qiliang Ni, and Weixing Yu

Doc ID: 237946 Received 13 Apr 2015; Accepted 24 Jun 2015; Posted 24 Jun 2015  View: PDF

Abstract: In this work, the partition noise and electronic noise of the Vernier anode were thoroughly analyzed based on the theory of the statistical variation and the error analysis. At the same time, a new method of calculating the inter-electrode capacitance of the Vernier anode was proposed since it is the main factor to influence the electronic noise. The effect of the inter-electrode capacitance on the electronic noise was discussed in detail, which is useful for the optimal design of a Vernier anode in the image charge mode. It is found that the calculated results of the inter-electrode capacitance for a 0.891 mm period Vernier anode is in good agreement with the experimental results.

Direct detection of aggregates in highly turbid colloidal suspensions of polystyrene nanoparticles

Samir Bali, Jason Berberich, Jonathan Scaffidi, Rey Ducay, Nathan Phillip, Jordan Boivin, Patrick Judge, and Lalit Bali

Doc ID: 238026 Received 14 Apr 2015; Accepted 23 Jun 2015; Posted 24 Jun 2015  View: PDF

Abstract: We demonstrate a total internal reflection based method which detects for the first time to the best of our knowledge, directly without any sample dilution or special sample preparation, the presence of aggregates in highly turbid aqueous suspensions of polystyrene nanospheres. Aggregation is induced either by changing the sample pH or ionic strength. The polystyrene mass density in our samples is two orders of magnitude higher than previously reported polystyrene aggregation studies. For the case that aggregates have formed but do not yet occupy a significant fraction of the sample volume, our sensor outperforms in sensitivity state of the art techniques such as dynamic light scattering. On the other hand, when the sample volume is dominated by aggregates, our sensor is not as effective.

Controlling mid-spatial frequency errors in magnetorheological jet polishing with simple vertical model

Haobo cheng, Tan Wang, H. Y., W.T. W., and Honyuen Tam

Doc ID: 241042 Received 14 May 2015; Accepted 23 Jun 2015; Posted 24 Jun 2015  View: PDF

Abstract: The mid-spatial frequency (MSF) errors are always yielded in magnetorheological jet polishing (MJP) with simple vertical jetting model, and require a control during the process. The relation between surface with MSF errors and power spectral density (PSD) is analyzed. Based on this, the various concepts and methods are developed to restrain the MSF errors in MJP. With the cut-off frequency, the appropriate removal function is adopted. And the dedicated path with uniform character is designed for polishing. The weighted iterative algorithm is proposed to get a continuous and effective dwell time map. The doublication ratio is utilized to increase the non-uniform of the surface. The experiments are deployed in a MJP run. Not only the PV (Peak to Valley) and RMS (Root Mean Square) of surface are reduced from 0.384λ, 0.077λ (λ=632.8nm) to 0.054λ, 0.007λ, but also the smooth PSD curves are yielded with low and smooth distribution.

Stimulated Raman scattering signal recorded using an optical imaging technique

Eynas Amer, Mikael Sjodahl, and Per Gren

Doc ID: 239757 Received 28 Apr 2015; Accepted 23 Jun 2015; Posted 23 Jun 2015  View: PDF

Abstract: In this paper the stimulated Raman scattering (SRS) signal has been recorded using an optical imaging technique based on spatial modulation. A frequency doubled Q-switched Nd-YAG laser (532 nm) has been used to pump a polymethyl methacrylate (PMMA) target. The frequency tripled (355 nm) beam from the same laser is used to pump an optical parametric oscillator (OPO). The Stokes beam (from the OPO) has been tuned to 631.27 nm so that the frequency difference between the pump and the Stokes beams fits a Raman active vibrational mode of the PMMA molecule (2956 cm-1). The pump beam has been spatially modulated with fringes produced in a Michelson interferometer. The pump and the Stokes beams were overlapped on the target resulting in a gain of the Stokes beam of roughly 2.5 % and a corresponding loss of the pump beam through the SRS process. To demodulate the SRS signal, two images of the Stokes beam without and with the pump beam fringes present were recorded. The difference between these two images is calculated and Fourier transformed. Then the gain of the Stokes beam has been separated from the background in the Fourier domain. The results show that spatial modulation of the pump beam is a promising method to separate the weak SRS signal from the background.

Fabrication of Fast MIR Photodetector Based on Hybrid Graphene-PbSe Nanorods

Mahboubeh Dolatyari, Ali Rostami, ghassem rostami, Hamideh Talebi, Amir Manzuri, and Mohammad Mahmudi

Doc ID: 239838 Received 27 Apr 2015; Accepted 23 Jun 2015; Posted 23 Jun 2015  View: PDF

Abstract: Weak light absorption of graphene has limited the responsivity of graphene-based photodetectors. On the other hand, slow response of PbSe as mid infrared range (MIR) detector makes this type of detectors unsuitable as commercial detectors. Here, we report a fast MIR detector based on hybrid graphene-PbSe nanorods. For this purpose, a few layer graphene is synthesized using a simple, scalable, and economical method on cobalt layer and the synthesized graphene was transferred on a interdigitated copper electrodes and synthesized nanorods were spin coated on the transferred graphene. Strong and tunable light absorption in the quantum-dot layer creates electric charges which are transferred to the graphene, and due to the high charge mobility of graphene and long trapped-charge lifetimes in the quantum dot layer they re-circulate many times. The fabricated device has high speed and responsivity. The gain of fabricated detectors based on hybrid graphene-QD is 10.3 times more and its response time is 14.3 times faster and responsivity is 10 times more than conventional nanorods based detectors. From point of view of spectral selectivity, tuning the size of nanorods helps optical detection from infrared to midinfrared.

Optical study of diffraction grating/Fresnel lens combinations applied to a spectral splitting solar concentrator for space applications

Céline Michel, Serge Habraken, Jerome Loicq, and Tanguy Thibert

Doc ID: 234461 Received 11 Feb 2015; Accepted 23 Jun 2015; Posted 24 Jun 2015  View: PDF

Abstract: This paper presents a new design of a planar solar concentrator with spectral splitting of light for space applications. This concentrator spectrally splits the incident light into mainly two parts. Each part is then focused onto specifific spatially separated photovoltaic cells, allowing for independent control of respective cells output power. These advantages of both spectral splitting and light focusing are here combined thanks to a specifific diffraction grating superimposed on a Fresnel lens. The theoretical principle of the optical design is presented, with optimization of each element and improvement steps, including optimization of grating period evolution along the lens, and testing of two kinds of gratings (a blazed and a lamellar one). First numerical results are presented, highlighting the possibility to design a concentrator at about 10x or more for each cell, with an optical efficiency larger than 70% and less than 10% of losses for tracking errors up to 0.8°. Some experimental results are also presented.

An On-orbit Calibration Approach for Star Camera based on the Iteration Method with Variable Weights

Yufeng Cheng, Mi Wang, Bo Yang, and Xiao Chen

Doc ID: 235968 Received 11 Mar 2015; Accepted 23 Jun 2015; Posted 24 Jun 2015  View: PDF

Abstract: To perform on-orbit calibration for star camera efficiently, we developed an attitude-independent calibration approach for global optimization and noise removal by least-square estimation using multiple star images, with which the optimal principal point, focal length, and the high-order focal plane distortion can be obtained in one step in full consideration of the interaction among star camera parameters. To avoid the problem when stars could be misidentified in star images, iteration method with variable weights is introduced to eliminate the influence of misidentified star pairs. The approach can increase the precision of least-square estimation and use fewer star images. The proposed approach has been well verified precise and robust in three experiments.

Gate-controlled diode structure based electro-optical interfaces in standard Silicon-CMOS integrated circuitry

Kaikai Xu, Haitao Liu, and z z

Doc ID: 233039 Received 23 Jan 2015; Accepted 22 Jun 2015; Posted 26 Jun 2015  View: PDF

Abstract: In this paper, we discuss the emission of visible light by a monolithically integrated silicon gate-controlled diode with the p-n junction reverse-biased. Since the MOS-like diode utilizes the field effect to modulate the optical output, the modulation speed will benefit from this mechanism obviously. Hence, a silicon gate-controlled diode structure for optical modulation analyzed its modulation principle and dynamic characteristics is presented, and the bandwidth of the device is considered to approaching GHz in theory due to the field induced emission mechanism. The prototype MOS-like diode opens up the design of multi-terminal silicon light emitting devices (LEDs), where gate electrodes with more than one gate contact overlap several junctions with different junction intersection geometries. The device appears as a good candidate for optical modulation in the high frequency domain within silicon technology.

Inscription of long period gratings using an ultraviolet laser beam in the diffusion doped microstructured polymer optical fiber

Dominik Kowal, Gabriela Statkiewicz-Barabach, Pawel Mergo, and Waclaw Urbanczyk

Doc ID: 236789 Received 24 Mar 2015; Accepted 22 Jun 2015; Posted 23 Jun 2015  View: PDF

Abstract: We show that diffusion of azobenzene from the solution in methanol into a cladding of a polymer fiber facilitates fabrication of long period gratings by the use of a He-Cd focused laser beam. We have measured a diffusion rate into PMMA cladding of the microstructured fibers annealed in advance at different temperatures and showed that the diffusion rate is strongly affected by temperature treatment of the fiber. We have also investigated an impact of the azobenzene diffusion on fiber spectral loss and cladding surface quality. Furthermore, we have examined a temporal stability of the fabricated long period gratings and their response to temperature and tensile strain.

Synthetic-wavelength interferometry improved with frequency calibration and unambiguity range extension

Claudius Weimann, Markus Fratz, Harald Woelfelschneider, Wolfgang Freude, Heinrich Hoefler, and Christian Koos

Doc ID: 240424 Received 12 May 2015; Accepted 22 Jun 2015; Posted 23 Jun 2015  View: PDF

Abstract: We improve the accuracy of distance measurements with synthetic-wavelength interferometry by referencing the spectral spacing of the free-running light sources to a high-precision radio-frequency (RF) oscillator. In addition, we increase the unambiguity range with a time-of-flight technique. Distances to scattering technical surfaces can be measured with micrometer accuracy and an unambiguity range of 1.17 m. The measurement rate amounts to 300 Hz.

A simple method to remove the first-order optical nonlinearity in the heterodyne laser interferometer

Haijin Fu, Jiubin Tan, Peng-Cheng Hu, and Fan Zhigang

Doc ID: 236145 Received 13 Mar 2015; Accepted 22 Jun 2015; Posted 22 Jun 2015  View: PDF

Abstract: A simple method was proposed by using a tunable attenuator fitted in the reference or measurement arm of a heterodyne laser interferometer to adjust the values of mixing laser beams while the spectrum of the measurement signal is monitored using a signal analyzer. The effectiveness of the proposed method in reducing the first-order optical nonlinearity was verified through experiments. Results indicated that the peak-to-peak value of the first-order optical nonlinearity could be reduced form 5.15 nm to 0.24 nm. It was therefore concluded that the proposed method was applicable to ultra-precision laser interferometry.

High-speed Phase-Shifting Interferometry using Triangular Prism for Time-resolved Temperature Measurement

Eita Shoji, Atsuki Komiya, Junnosuke Okajima, Hiroshi Kawamura, and Shigenao Maruyama

Doc ID: 238248 Received 17 Apr 2015; Accepted 21 Jun 2015; Posted 22 Jun 2015  View: PDF

Abstract: This study proposes a high-speed phase-shifting interferometer with an original optical prism. This phase-shifting interferometer consists of a polarizing Mach-Zehnder interferometer, an original optical prism, a high-speed camera and an image processing unit for a three-step phase-shifting technique. The key aspect of the application of the phase-shifting technique to high-speed experiments is an original prism, which is designed and developed specifically for high-speed phase-shifting technique. The arbaa prism splits an incident beam into four output beams with different information. The interferometer was applied for quantitative visualization of transient heat transfer. In order to test the optical system for measuring high speed phenomena, the temperature during heat conduction was measured around a heated thin tungsten wire (diameter of 5 μm) in water. The visualization area is approximately 90 μm ×210 μm and the spatial resolution is 3.5 μm at 300000 fps of the maximum temporal resolution with a high speed camera. The temperature fields around the heated wire were determined by converting phase-shifted data using the inverse Abel transform. Finally, the measured temperature distribution was compared with numerical calculations to validate the proposed system; a good agreement was obtained.

A broadband wavelength and angle resolved scattering characterization system for nanophotonics investigations

David Payne, Darren Bagnall, and Martin Charlton

Doc ID: 235956 Received 11 Mar 2015; Accepted 21 Jun 2015; Posted 22 Jun 2015  View: PDF

Abstract: The characterization of scattered light is complex and relatively non-standardized despite being of great importance to many optical technologies. Whilst total scatter can be efficiently measured using integrating sphere based techniques, a detailed determination of the full bidirectional scattering distribution function (BSDF) is far more challenging, often requiring complicated and expensive equipment as well as substantial measurement time. Due to this, many research groups rely on simpler, angle resolved scatter (ARS) measurements, yet these are typically carried out using a single wavelength source, therefore providing limited information. Here, we demonstrate a custom-built broadband angle resolved optical spectrometer (BAROS), which utilizes a supercontinuum white light laser source combined with a custom automated goniometer and a Si CCD array spectrometer in order to carry out broad spectral measurements of angle resolved scatter. The use of a collimated supercontinuum allows for small area measurements which are often crucial for investigation of nanophotonic samples created using expensive fabrication techniques. The system has been tested and calibrated, and accuracy and reproducibility has been verified by integrating wavelength and angle resolved scattering (WARS) data over the angular range and comparing to calibrated integrating sphere measurements.

Error analysis of aspheric surface with reference datum

Peng Yanglin, Yifan Dai, Shanyong Chen, Ci Song, and Shi Feng

Doc ID: 240239 Received 04 May 2015; Accepted 21 Jun 2015; Posted 30 Jun 2015  View: PDF

Abstract: Severe requirements of location tolerance provide new challenges for optical component measurement, evaluation and manufacture. Form error, location error and the relationship between form error and location error need to be analyzed together during error analysis of aspheric surface with reference datum. Based on the least-squares optimization method, we develop least-squares local optimization method to evaluate form error of aspheric surface with reference datum, and then calculate the location error. According to the error analysis of machined aspheric surface, the relationship between form error and location error is revealed, and the influence on machining process is stated. In different radius and aperture of aspheric surface, the change laws are simulated by superimposing normally distributed random noise on ideal surface. It establishes linkages between machining and error analysis, and provides effective guideline for error correcting.

Enhanced interference-pattern visibility using multislit optical superposition method for imaging-type two-dimensional Fourier spectroscopy

Wei QI, Yo Suzuki, Shun Sato, Masaru Fujiwara, Natsumi Kawashima, Satoru Suzuki, Pradeep Abeygunawardhana, Kenji Wada, Akira Nishiyama, and Ichirou Ishimaru

Doc ID: 235669 Received 05 Mar 2015; Accepted 20 Jun 2015; Posted 22 Jun 2015  View: PDF

Abstract: A solution is found for the problem of phase cancellation between adjacent bright points in wavefront-division phase-shift interferometry. To this end, a design is proposed that optimizes the visibility of the interference pattern from multiple slits. The method is explained in terms of Fraunhofer diffraction and convolution imaging. Optical simulations verify the technique. The final design can be calculated using a simple equation.

Auto-focus method for scanning remote sensing cameras

hengyi Lv, cheng han, Xucheng Xue, Cheng Yao, and chang hu

Doc ID: 239874 Received 27 Apr 2015; Accepted 20 Jun 2015; Posted 22 Jun 2015  View: PDF

Abstract: Auto-focus methods are conventionally based on capturing the same scene from a series of positions of the focal plane. As a result, it was difficult to apply this technique to scanning remote sensing cameras where the scenes change continuously. In order to realize auto-focus in scanning remote sensing cameras, a novel auto-focus method is investigated in this paper. Instead of introducing additional mechanisms or optics, the overlapped pixels of the adjacent CCD sensors on the focal plane are employed. Two images, corresponding to the same scene on the ground, can be captured at different time. Further, one step of focusing is done during the time interval so that the two images can be obtained at different focal plane positions. Subsequently, the direction of the next step of focusing is calculated based on the two images. The analysis shows that the method investigated operates without restriction of the time consumption of algorithm and realizes a total projection for general focus measures and algorithms from DC(digital still cameras) to scanning remote sensing cameras. The experiment results show that the proposed method is applicable to the entire focus measure family, and the error ratio is averagely no more than 0.2%, and drops to 0% by reliability improvement, which is lower than that of prevalent approaches(12%). The proposed method is demonstrated to be effective and has potential in other scanning imaging applications.

Zernike-like systems in polygons and polygonal facets

José López, Chelo Ferreira, Ester Pérez Sinusía, and Rafael Navarro

Doc ID: 237028 Received 14 Apr 2015; Accepted 19 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: Zernike polynomials are commonly used to represent the wavefront phase on circular optical apertures, since they form a complete and orthonormal basis on the unit disk. In [Diaz et all, 2014] we introduced a new Zernike basis for elliptic and annular optical apertures based on an appropriate diffeomorphism between the unit disk and the ellipse and the annulus. Here, we present a generalization of this Zernike basis for a variety of important optical apertures, paying special attention to polygons and the polygonal facets present in segmented mirror telescopes. On the contrary to ad hoc solutions, most of them based on the Gram-Smith orthonormalization method, here we consider a piece-wise diffeomorphism that transforms the unit disk into the polygon under consideration. We use this mapping to define a Zernike-like orthonormal system over the polygon. We also consider ensembles of polygonal facets that are essential in the design of segmented mirror telescopes. This generalization, based on in-plane warping of the basis functions, provides a unique solution, and what is more important, it guarantees a reasonable level of invariance of the mathematical properties and the physical meaning of the initial basis functions. Both, the general form and the explicit expressions for a typical example of telescope optical aperture are provided.

Suppression of TPL and ASE in Ti:sapphire amplifier by Polarization-selection pump

Xiaoyan Liang, YuXi Chu, Biao Gan, Lianghong Yu, Lu Xu, Ruxin Li, and Zhizhan Xu

Doc ID: 237470 Received 03 Apr 2015; Accepted 19 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: Based on the polarized-dependent absorption characteristic of Ti:S crystals, we propose a method to reduce the absorption coefficient of Ti:S by using σ-polarized pump. For Ti:S crystals, the absorption cross section of σ-polarized pump light is approximately half that of π-polarized pump light, which reduces the excited state density near the surface of the amplifier crystal results in reducing transverse parasitic lasing (TPL) and amplified spontaneous emission (ASE). The experimental results based on diameter of 80mm Ti:S confirmed the proposed method with different index-matched cladding materials [ethanol and bromonaphthalene(BN)]. In the case of an ethanol cladding, the maximum amplified output energies for π- and σ-polarized pumping are 20.8 and 26.8 J, respectively; corresponding to 28.8% energy improvement achieved by the σ-polarized pump. In the case of a BN cladding, the maximum amplified output energies achieved by π- and σ-polarized pumping are 40 and 44 J, respectively; this result corresponds to about 10% energy improvement achieved by the σ-polarized pump. This method can be used in larger size Ti:S amplifiers.

Focus-tunable low power electrowetting lenses with thin parylene films

Alexander Watson, Kevin Dease, Soraya Terrab, Chris Roath, Juliet Gopinath, and Victor Bright

Doc ID: 237971 Received 13 Apr 2015; Accepted 19 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: Electrowetting lenses with record low power consumption (μW) have been demonstrated using high quality Parylene AF-4 dielectric layers and large dodecyl sulfate ions. Water and propylene glycol are interchanged as the polar liquid to enable diverging and converging lens operation achievable with the application of 15 V. The optical quality of the lenses is comparable to conventional microlenses and the tuning exhibits very little (< 0.5°) contact angle hysteresis.

NaCl ion detection using a silica toroid microcavity

Takasumi Tanabe, Jiro Nishimura, Misako Kobayashi, and Ryusuke Saito

Doc ID: 238482 Received 21 Apr 2015; Accepted 19 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: An optical-microcavity-based sensor is an important building block for an optofluidics system, because it allows us to fabricate smaller devices with higher sensitivity. Here we describe the detection of NaCl and pH in water using a silica toroid microcavity. First we demonstrate the detection of NaCl particles, and show that a detection sensitivity of 0.38 mM is possible with a sample volume of 0.03 nL. Then, we report the detection of NaCl ions in liquid and demonstrate a sensitivity of 3.20 mM and also, in principle, the detection of pH with a sensitivity of 0.14 pH. Finally, we integrate a tapered optical fiber, a silica toroid microcavity, and a fluidic channel for future optofluidics applications.

Absolute Spherical Surface Metrology by Differencing Rotation Maps

Weibo Wang, Jiubin Tan, mengqian zhang, siwen yan, and Fan Zhigang

Doc ID: 238530 Received 29 Apr 2015; Accepted 19 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: A simple, novel method for the absolute interferometric testing of spherical surfaces is presented. This approach yields an estimate for the test surface errors without changing experimental settings, such as cavity length, that may affect the apparent reference errors. The test surface is tested in three orientations-a basic position and two rotation positions. Full-surface absolute maps for each test piece are determined with the proposition that any arbitrary wavefront of circular cross section may be expressed as a linear combination of polynomial terms and a data-processing technique based on differencing rotation maps of the rotated surface. An optimized numerical reconstruction algorithm employing the least squares technique to determine the true azimuthal positions of part rotation is used to reconstruct the rotational data. The technique does not require any assumptions about the surfaces under test and additional measurements. It is simple, accurate and can consequently eliminate testing errors caused by rotation inaccuracy. Experimental results are presented comparing the method proposed to the classic two-sphere method.

Visualization of the influence of the air conditioning system to the higher power laser beam quality with the modulation coherent imaging method

Liu Cheng, Hua Tao, Suhas Veetil, Xingchen Pan, and Jianqiang Zhu

Doc ID: 240229 Received 04 May 2015; Accepted 19 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: Air conditioning system can lead to dynamic phase change in the laser beams of high power laser facility for the inertial confinement fusion (ICF), and this kind of phase change can’t be measured by most of commonly employed Hartmann wavefront sensor or interferometry due to some uncontrollable factors. It is demonstrated that this problem can be solved using a scheme based on modulation coherent imaging (MCI), and thus the influence of the air conditioning system to the performance of the high power facility can be evaluated directly.

Fast temporal phase unwrapping method for the fringe reflection technique based on the orthogonal grid fringes

Bo Li, Suodong Ma, and Yang Zhai

Doc ID: 240353 Received 05 May 2015; Accepted 18 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: In traditional Temporal Phase Unwrapping (TPU) algorithms, the wrapped phases with different frequencies are obtained from several groups of phase shift fringes to calculate the unwrapped phase. Therefore the necessary quantity of the captured fringes is very large, especially for the Fringe Reflection Technique (FRT) since a pair of phases should be unwrapped to get the slopes of two perpendicular directions. In this paper we propose a fast TPU algorithm based on the orthogonal grid fringes by which only one image is needed to extract the two integer phases for each frequency instead of two groups of phase shift fringes, and then they can be added into the wrapped phases separately to complete the unwrapping. There are ridge errors in the direct unwrapped phases, but they are suppressed significantly by our pseudo phase shift strategy without any extra captured fringes. The proposed method is robust and effective where the used fringes amount is approximately only 1/4 of the previous similar algorithm and 1/6~1/8 of the traditional TPU methods. The algorithm is validated by the experiments, which still works well for the severely defocusing fringes or complex specimen.

Conditions for having identical aberration behaviors of various thick lenses

Chaohsien Chen

Doc ID: 241148 Received 18 May 2015; Accepted 18 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: Two optical lenses with the same focal length but different lens thicknesses and principal plane locations can provide equivalent first-order optics on imagery if the marginal and chief ray heights and slope angles at their principal planes are equal, resulting the same system magnification, object and image distances. In this paper, we will prove that if these lenses have same primary aberrations (including Seidel aberrations, chromatic aberrations and secondary spectrum) corresponding to the same marginal and chief rays then they must have same new aberrations for any same new rays. This theorem is useful when designers would like to redesign a lens group in a system. The influence on the movements among lens groups, the special aberration properties of plane parallel plates and afocal lens groups are also discussed.

Creating unconventional geometric beams with large depth of fifield using double freeform-surface optics

ZeXin Feng, Rongguang Liang, Chih-Yu Huang, Brittany Froese, and Donglin Ma

Doc ID: 239724 Received 28 Apr 2015; Accepted 17 Jun 2015; Posted 17 Jun 2015  View: PDF

Abstract: Conventional geometric-optics based beam shaping optics are mostly constructed in simple symmetries such as rotational or rectangular. Here, we consider generating a complex-shaped flat-top beam whilst maintaining the wavefront flat by employing double freeform optical surfaces. The output beam is designed with continuous variations from the flat-top to almost zero near the boundaries to resist the diffraction influence on its propagation. We solve this challenging problem by naturally incorporating an optimal transport mapping computation scheme for non-conventional boundary conditions with a simultaneous point-by-point surface construction approach. We demonstrate experimentally the generation of a long range propagated triangular beam through a plano-freeform lens pair fabricated by a diamond-tuning machine.

A Long-range Vibration Detection System using Heterodyne Interferometry

John Rzasa, Kyuman Cho, and Christopher Davis

Doc ID: 239923 Received 29 Apr 2015; Accepted 16 Jun 2015; Posted 17 Jun 2015  View: PDF

Abstract: We present the design and performance of an extremely sensitive coherent remote vibration detection system using optical heterodyne vibration of phase shifts produced by laser light scattered off a remote target. The resulting phase-modulated intermediate RF frequency of 200 MHz, which carries the vibrational motion of the target, is de-modulated down to base band using an RF IQ demodulator. Acquisition and calculation of the target phase angle is carried out on a custom-made control board which utilizes high resolution A/D converters, variable gain amplifiers and a Spartan-6 FPGA.

(NRL) Gain and Loss as a Function of Current Density and Temperature in Interband Cascade Lasers

Igor Vurgaftman, Charles Merritt, William Bewley, Chul Soo Kim, Chadwick Canedy, Jerry Meyer, and Mijin Kim

Doc ID: 240072 Received 04 May 2015; Accepted 16 Jun 2015; Posted 17 Jun 2015  View: PDF

Abstract: We characterize the internal efficiency, internal loss, and optical gain vs. current density in 7-stage interband cascade lasers (ICLs) operating at λ = 3.1 and 3.45 μm using a cavity-length study of the external differential quantum efficiency (EDQE) and threshold current density at temperatures between 300 and 345 K. We find that the pronounced “efficiency droop” of the EDQE at high current densities is primarily due to an increase in the internal loss rather than a reduction in the internal efficiency. On the other hand, if the current density J is fixed, the temperature variation of the EDQE at that J is due primarily to a decrease of the internal efficiency. The gain vs. current density is fit well by a logarithmic relationship, although the magnitude of the experimental gain is >20% below the theoretical estimate.

Metal crack propagation monitoring by photoluminescence enhancement of quantum dots

Ziming Zhao, Weiling Luan, Shaofeng Yin, and Juergen Brandner

Doc ID: 240978 Received 14 May 2015; Accepted 16 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: A visualization method for monitoring minor metal crack propagation is presented in this paper. Through CdS@ZnS core-shell quantum dots (QDs) enhanced emission of photoluminescence (PL), this crack detection method provides a visualization signal in a real-time and through a non-contact fashion. The crack of the CdS@ZnS core-shell QDs-epoxy resin kept a synchronous propagation with the metal crack. Detection of the tip growth in the film layers demonstrated that the actual crack propagation on the metal surface could be deduced from the tips in the film layers. The fluorescence peak tended to increase along the crack from the initial opening to the tip. Crack width as small as 10 μm can be detected with a precision of 0.1 μm and the minimum crack tip width of the QDs-epoxy resin was measured as 0.72 μm.

Channel density and efficiency optimization of volume Bragg grating based spectral beam combining systems in sequential and multiplexed arrangements

Gregory Ingersoll and James Leger

Doc ID: 235928 Received 10 Mar 2015; Accepted 16 Jun 2015; Posted 17 Jun 2015  View: PDF

Abstract: Spectral beam combining (SBC) systems utilizing multiple volume Bragg gratings must be carefully analyzed to maximize channel density and efficiency, and thus output radiance. This analysis grows increasingly difficult as the number of channels in the system increases, and heuristic optimization techniques are useful tools for exploring the limits of these systems. We explore three classes of multi-grating SBC systems: “cascaded” where each grating adds a new channel to the system in sequence, “sandwiched” where several individual gratings are placed together and all channels enter the system at the same facet, and “multiplexed” where all of the gratings occupy the same holographic optical element (HOE). Loss mechanisms differ among these three basic classes, and our optimization algorithm shows that the highest channel density for a given minimum efficiency and fixed operating bandwidth is achieved for a cascaded-grating system. The multiplexed-grating system exhibits the lowest channel density under that same constraints but has the distinct advantage of being realized by a single HOE. For a particular application, one must weigh channel density and efficiency versus system complexity when choosing among these basic classes of SBC system. Additionally, one may need to consider the effects of finite-width input beams. As input beam radius is reduced, angular clipping effects begin to dominate over spectral interference and crosstalk effects, limiting all three classes of SBC systems in a similar manner.

Creating optical filters with angular-selective light transmission

Rustam Zakirullin

Doc ID: 236268 Received 16 Mar 2015; Accepted 16 Jun 2015; Posted 17 Jun 2015  View: PDF

Abstract: A simple method for designing and calculating grating optical filters with angular-selective light transmission is presented. The selectivity is provided by the relative positions of two surface gratings formed by directionally transmissive strips, alternating with absorptive, reflective, or scattering strips. As the incidence angle changes, the proportion of radiation that passes through both gratings also changes. Geometric and optical filter parameters are calculated to achieve a light transmittance with a predetermined angular dependence. This method can be used to create neutral-density, frequency, and spatial filters pre-adapted to incidence angles that change when the light source moves relative to the filter.

Novel time-of-flight fiber dispersion measurement technique using supercontinuum light sources and acousto-optical tunable filters

Steven Wagner and Niels Göran Blume

Doc ID: 237391 Received 03 Apr 2015; Accepted 16 Jun 2015; Posted 17 Jun 2015  View: PDF

Abstract: Long-distance fiber links require precise knowledge of the fiber dispersion characteristic. Similar dispersion characteristics are necessary for supercontinuum broadband laser absorption spectroscopy (SCLAS) to allow proper data evaluation and species concentration determination as well as numerous other applications. In this work, a novel time-of-flight approach to measure the dispersion characteristic of fibers with supercontinuum laser light sources (SCL) and acousto-optical tunable filters (AOTF) is presented. Broadband emission of the SCL is filtered with a narrow-band AOTF and dispersed in time by the fiber under test. Using the wavelength-specific delay the dispersion characteristic can be calculated. The technique was verified against a state-of-the-art phase-shift-based dispersion measurement system. Advantages of the new approach include solely utilizing SCLAS system components as well as a high level of automation and wide spectral coverage ranging from 1100 to 1700 nm in a single measurement setup.

Fast high-time-resolution differential discrimination with multiple returns for time of flight system

Dongxian Geng, Wei Wang, Pengfei Du, and Mali Gong

Doc ID: 237927 Received 10 Apr 2015; Accepted 16 Jun 2015; Posted 17 Jun 2015  View: PDF

Abstract: A differential discriminator has been proposed in this paper to make a fast discrimination from multi-returns in the time-of-flight systems. The time resolution of the classical direct discrimination in a laser time-of-flight system has been analyzed. Theoretical model of the differential discriminator has been established. And as theoretical calculations and numerical simulations have shown, the time resolution can be improved by using differential discriminator instead of classical direct discriminator, especially with large-amplitude signals. However, the relationship between the time resolution and the amplitude is not monotonic. The time resolution decreases as the amplitude when the signals are very small. But through further analysis and simulations, a method to find an appropriate parameter to optimize the relationship curve has been proposed. The theory and the simulations were verified by the electrical circuit experiments and the optical circuit experiments taken with two close targets of about 8.3m. The full width at half maximum (FWHM) of the laser is about 50ns. The measured time resolution was better than 54.7ns when the amplitude is 200mV.

Numerical wave propagation in ImageJ

Jorge Garcia-Sucerquia, Juan Piedrahita-quintero, and Raul Castañeda

Doc ID: 238292 Received 16 Apr 2015; Accepted 16 Jun 2015; Posted 17 Jun 2015  View: PDF

Abstract: An ImageJ plugin for numerical wave propagation is presented. The plugin powers the well-known software for image processing ImageJ with the capability of computing numerical wave propagation by the use of angular spectrum, Fresnel and Fresnel-Bluestein algorithms. The plugin enables the numerical wave propagation within the robust environment provided by the complete set of built-in tools to image processing available in ImageJ. The plugin can be used for teaching and research purposes. We illustrate the use of the plugin to numerically recreate Poisson’s spot, Babinet’s principle and in the numerical reconstruction of digitally recorded holograms from millimeter-sized and pure phase microscopic objects.

Simultaneous multichannel CSRZ-to-NRZ format conversion using a fiber Bragg grating

Hui Cao, Javid Atai, Jun Zuo, Yu Yu, Gbadebo Adenowo, bangyun xiong, PeiYing Liang, Ya Gao, Xuewen Shu, and Jie Hou

Doc ID: 238411 Received 22 Apr 2015; Accepted 15 Jun 2015; Posted 17 Jun 2015  View: PDF

Abstract: A novel multi-channel CSRZ-to-NRZ format conversion scheme based on a single custom-designed fiber Bragg grating (FBG) with comb spectra is proposed. The spectral response of each channel is designed according to the algebraic difference between the CSRZ and NRZ spectra outlines. The tailored group delays are introduced to minimize the maximum refractive index modulation. Numerical results show that four-channel 200GHz-spaced CSRZ signals at 40 Gbits/s can be converted into NRZ signals with high Q-factor and wide-range robustness. It is shown that our proposed FBG is robust to deviations of bandwidth and central wavelength detuning. Another important merit of this scheme is that the pattern effects are efficiently reduced owing to the well-designed spectra response.

Scene distance measurement method based on lightfield imaging

Fei Yan, Wenxing Fu, Zijun Ren, and Kang Chen

Doc ID: 235562 Received 03 Mar 2015; Accepted 15 Jun 2015; Posted 15 Jun 2015  View: PDF

Abstract: Because a light field camera first takes an image and then refocuses it, we propose a scene distance measurement method based on light field imaging spatial refocusing principles, which was used to generate sequences of refocused images of the raw spatial scene images taken by the Lytro1 light field camera. Then selected the window of the object whose scene distance needed to be measured, used image resolution evaluation functions to choose one of the clearest images among the refocused image sequences, and used the Gaussian formula to deduce the scene distance measurement formula. Finally used the scene distance measurement method to measure an object on the scene and analyzed its measurement range and accuracy theoretically. The experimental results showed that this scene distance measurement method can obtain the scene distance information.

Experimental demonstration of all-optical weak magnetic field detection using beam-deflection of single-mode fiber coated with cobalt-doped nickel ferrite nanoparticles

Partha Roy Chaudhuri and Somarpita Pradhan

Doc ID: 240460 Received 06 May 2015; Accepted 15 Jun 2015; Posted 15 Jun 2015  View: PDF

Abstract: We experimentally demonstrate single-mode optical-fiber-beam-deflection configuration for weak magnetic-field-detection using an optimized (low coercive-field) composition of cobalt-doped nickel-ferrite nanoparticles. Devising a fiber-double-slit type experiment, we measure the surrounding magnetic field through precisely measuring interference-fringe yielding a minimum detectable field ~100mT and we procure magnetization data of the sample that fairly predicts SQUID measurement. To improve sensitivity, we incorporate etched single-mode fiber in double-slit arrangement and recorded a minimum detectable field ~30mT. To further improve, we redefine the experiment as modulating fiber-to-fiber light-transmission and demonstrate the minimum field as 2.0mT. The device will be unique for electrically or otherwise hazardous environment.

Particle Size Distribution of River-Suspended Sediments Determined by In Situ Measured Remote-Sensing Reflectance

Yuanzhi Zhang, Zhaojun Huang, Chuqun Chen, and Yijun He

Doc ID: 233250 Received 28 Jan 2015; Accepted 15 Jun 2015; Posted 17 Jun 2015  View: PDF

Abstract: Suspended sediments in water bodies are classified into organic and inorganic matters and have been investigated by remote-sensing technology for years. Focusing on inorganic matters, however, detailed information such as grain size of these matters was not provided yet. In this study, we present a new solution for estimating inorganic suspended sediments size distribution in highly complex Case 2 waters by using a simple spectrometer sensor rather than a backscattering sensor. An experiment was carried out in the Pearl River Estuary (PRE) in the dry season to collect remote-sensing reflectance (Rrs) and particle size distribution (PSDs) of inorganic suspended sediments. Based on Mie theory, PSDs in the PRE waters were retrieved by Rrs, colored dissolved organic matter (CDOM) and phytoplankton. The retrieved median diameters in 12 stations show a good agreement with those of laboratory analysis at an RMSE 2.604μm (27.63%), bias 1.924μm (20.42%) and MAE 2.298μm (24.37%). The retrieved PSDs and previous PSDs were compared and the features of PSDs in the PRE waters were concluded.

Resonant Cavity Effect Optimization of III-Nitride Thin-Film Flip-Chip Light-Emitting Diodes with Microsphere Arrays

Peifen Zhu and Nelson Tansu

Doc ID: 240584 Received 11 May 2015; Accepted 15 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: Comprehensive studies were carried out to investigate the light extraction efficiency of thin-film flip-chip (TFFC) light-emitting diodes (LEDs) with anatase TiO2 microsphere arrays by employing finite-difference time-domain method. The quantum well position and the resonant cavity effect were studied to obtain optimum light extraction for the planar TFFC LED. Further enhancement in light extraction was achieved by depositing microsphere arrays on the TFFC LED. The calculation results showed that the diameter of sphere, the sphere packing density and packing configuration have significant effect on the light extraction efficiency. A maximum light extraction efficiency of 75% in TFFC LEDs with microsphere arrays has been achieved. This study demonstrates the importance of optimizing the quantum well position, the cavity thickness, sphere diameter, sphere packing density, and packing configuration for enhancing the light extraction efficiency of TFFC LED with microsphere arrays.

Design of D Flip-flop and T Flip-flop using Mach-Zehnder interferometers for High Speed Communication

Santosh Kumar, Gurdeep Singh, Angela Amphawan, and Ashish Bisht

Doc ID: 235447 Received 04 Mar 2015; Accepted 12 Jun 2015; Posted 22 Jun 2015  View: PDF

Abstract: The speed of the electrical component is major constraint in high speed communications. To overcome this constraint electrical components are now being replaced by optical components. The application of optical switching phenomena has been used to construct the design of D Flipflop and T Flip-flop based on electro-optic effect in Mach-Zehnder interferometer (MZI). The MZI structures show the powerful ability to switch the optical signal from one output port to the other output port. Hence, it is possible to construct some complex optical combinational digital circuits using the electro-optic effect based MZI structure as a basic building block. The paper constitutes the mathematical description of proposed device and thereafter compilation using MATLAB. The study is carried out by simulating the proposed device with Beam propagation method (BPM).

Miniature cryogenic camera using thin integrated optics

Tatiana GRULOIS, Guillaume DRUART, Hervé SAUER, Mathieu Chambon, Nicolas Guerineau, Serge Magli, Gilles Lasfargues, and Pierre Chavel

Doc ID: 235830 Received 24 Mar 2015; Accepted 09 Jun 2015; Posted 10 Jun 2015  View: PDF

Abstract: We designed a compact infrared cryogenic camera using only one lens mounted inside the detector area. In the field of cooled infrared imaging systems, the maximal detector area is determined by the dewar. It is generally a sealed and cooled environment dedicated to the infrared quantum detector. By integrating an optical function inside it, we improve the compactness of the camera as well as its performances. The originality of our approach is to use a thin integrated optics which is a high quality Fresnel lens on a thin germanium substrate. The aim is to reduce the additional mass of the optical part integrated inside the dewar to obtain almost the same cool down time as a conventional dewar with no imaging function. A prototype has been made and its characterization has been carried out.

A Heat-Stop structure design with high cooling efficiency for large aperture size ground based solar telescope

Yangyi Liu, Changhui Rao, Naiting Gu, and Cheng Li

Doc ID: 236691 Received 30 Mar 2015; Accepted 09 Jun 2015; Posted 10 Jun 2015  View: PDF

Abstract: Heat-Stop is one of the most important thermal control devices for large ground based solar telescope. For controlling the internal seeing effect, the temperature difference between the Heat-Stop and the ambient environment need to be reduced, and a Heat-Stop with high cooling efficiency is required. In this paper, a novel design concept for Heat-Stop is proposed, and it is designed as a multi-channel loop cooling system to obtain a higher cooling efficiency. To validate the design, we analyze and compare the cooling efficiency for the multi-channel and existing single-channel loop cooling system under same conditions. Comparative results show that the new design enhances the cooling efficiency of the Heat-Stop obviously, and the novel design based on the multi-channel loop cooling system is obviously better than the existing design by increasing the thermal transfer coefficient..

Dual-wavelength narrow-linewidth linearly polarized seed source and the SBS suppression in its high-power fiber amplification

Yaqian Ding, Jun Zhou, Lei Zhang, Baoling Guo, Rui Wang, Guanghui Chen, Yunfeng Qi, and Yuan Liu

Doc ID: 236007 Received 11 Mar 2015; Accepted 06 Jun 2015; Posted 08 Jun 2015  View: PDF

Abstract: In this paper, we demonstrate a dual-wavelength narrow-linewidth linearly polarized all-fiber amplifier emitting 1035-nm and 1030-nm wavelengths with a high power of 80.0W. The seed source features two sets of fiber Bragg gratings(FBG) fabricated on PM fibers and a Ytterbium doped fiber as the gain medium. Two wavelengths propagate in one overlapping cavity and the power ratio can be tuned by a coiling fiber setup. Master oscillator power amplifier (MOPA) system consisting of two stage amplifier is employed. Longitudinally varied strains are applied on the gain fiber to suppress the back-scattered Stokes light in main amplifier stage. With appropriate seed power ratio, we are able to generate the amplification power to 80.0W comprised of 1035nm and 1030nm light while achieve at least 6 times increase of the stimulated Brillouin scattering threshold. Since both frequencies are propagating in one cavity and amplified in one gain medium, the 1035nm and 1030nm lasers have good temporal and spatial overlapping characteristics. This high-power MHz-level linearly polarized structure affords a compact, novel and high-efficiency approach to different frequency generation (DFG) of mid-infrared or terahertz emission.

Characterization of the Temporal Phase Fluctuations in a Weak Atmospheric Turbulence Regime as a Random Bit-Stream Generator

Carlos Font, G. Gilbreath, Sergio Restaino, David Bonanno, Blerta Bajramaj, and Kristen Nock

Doc ID: 233925 Received 09 Feb 2015; Accepted 02 May 2015; Posted 25 Jun 2015  View: PDF

Abstract: This paper investigates the extent to which atmospheric turbulence can be exploited as a random bit generator. Atmospheric turbulence is considered an inherently random process due to the complex inhomogeneous system composition and its sensitivity to changes in pressure, temperature, humidity and wind conditions. A self-calibrating Mach-Zehnder interferometer was used to collect phase fluctuations in the temporal domain introduced to an optical beam propagating through the atmosphere. The recorded phase fluctuations were converted into bit streams that were further analyzed in order to search for evidence of randomness. Empirical data and results which characterize the degree of randomness produced in the temporal phase component of an optical wave propagating through the atmosphere are presented.

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