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Accepted papers to appear in an upcoming issue

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Laboratory calibration for star sensors using global refining method

tao ye, fei yang, and jianfeng xie

Doc ID: 331022 Received 07 May 2018; Accepted 16 Aug 2018; Posted 17 Aug 2018  View: PDF

Abstract: Laboratory calibration is critical to ensure the precise attitude determination ofstar sensors. Existing laboratory star sensor calibration methods exhibit disadvantages forlarge-field-of-view star sensors and large amounts of calibration data. Inspired by theleast-squares and Li’s methods, a global refining method is proposed to overcome theinherent disadvantages by simultaneously obtaining all of the star sensor’s parameters. Itfirst employs the maximum likelihood estimation method to optimize the initialestimation of the principal point and focal length. Next, a linear least-squares solution wasused to initially estimate the star sensor distortion. Taking the installation error intoaccount, we conduct a maximum likelihood estimation to estimate the installation anglesfrom the estimated parameters of the first two steps. Finally, we determine a globallyoptimal solution to refine the star sensor parameters. Compared with the traditionalmethod and Li’s method under the same conditions, both the simulation and real dataresults demonstrate that the proposed method is more robust and can achieve highprecision. In addition, the experimental results show that the calibration method cansatisfy the precision requirement for large-field-of-view star sensors.

External versus induced and free versus bound electric currents and related fundamental questions of the classical electrodynamics of continuous media: discussion

Vadim Markel

Doc ID: 328856 Received 25 Apr 2018; Accepted 10 Aug 2018; Posted 10 Aug 2018  View: PDF

Abstract: Standard textbooks on classical electrodynamics frequently operate with the notions of free and bound currents (charges). Alternative terminology of external and induced currents also exists. However, a clear physical definition of these physical objects is rarely given. The term "free current" can refer in some cases to the conductivity current, which is subject to constitutive relations in a material sample. In other cases, free current refers to the current that is completely extrinsic to a given material sample and is assumed to be known a priori or manipulated by the experimentalist at will. Although one can argue that all currents flowing in material media are subject to some constitutive relations, there is a clear distinction in the construction of the classical electrodynamics between the external and the induced currents. The aim of this article is to clarify this distinction while pointing out that the traditional distinction between free and bound currents is arbitrary and can be abandoned. In addition, the article considers some relevant fundamental questions of classical electrodynamics including the derivation of macroscopic Maxwell's equations, properties of the external currents and physical interpretation of some auxiliary fields such as the field of polarization P.

Bit error rate of pulse position modulated optical wireless communication links in oceanic turbulence

Yahya Baykal

Doc ID: 331084 Received 07 May 2018; Accepted 08 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: Upper bound of the average bit error rate (BER) of a pulse position modulated (PPM) optical wireless communication (OWC) link operating in oceanic turbulence is formulated. BER variations against the changes in the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature and the rate of dissipation of kinetic energy per unit mass of fluid are found at various data bit rates, average current gains of the avalanche photodiode (APD) and M values of the M-ary PPM. It is found that under any oceanic turbulence parameters, BER performance of PPM OWC system becomes favorable at smaller data bit rates, M values, and at larger average current gains of APD.

Disparity Selective Stereo Matching Using Correlation Confidence Measure

Kim SiJung, Jinbeum Jang, Jaeseung Lim, Joonki Paik, and sangkeun lee

Doc ID: 324934 Received 06 Mar 2018; Accepted 08 Aug 2018; Posted 10 Aug 2018  View: PDF

Abstract: Recently, the cost-volume filtering methods for local stereomatching provide fast and accurate results compared to those of theother method. However, it still causes incorrect results in theocclusion and texture-free regions. Especially, cost aggregation bypixel units consumes high computation because of depending on theimage resolution and search range. This paper presents a robuststereo matching method for occluded regions. First, we generate costvolumes using the CENSUS transform and the scale-invariant featuretransform (SIFT). Then, label-based cost volumes are aggregatedusing adaptive support weight and SLIC scheme from generated twocost volumes. In order to obtain optimal disparity by twolabel-based cost volumes, we select the disparity corresponding tohigh confidence similarity of CENSUS or SIFT with minimum costpoint. Experimental results show that our method estimates theoptimal disparity in occlusion information which exists only inscene of one of the stereo pairs.

Solving analytically the simplified spherical harmonicsequations in cylindrical turbid media

Ehsan Edjlali and Yves Berube-Lauziere

Doc ID: 334329 Received 04 Jun 2018; Accepted 07 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: A methodology is presented for analytically solving the simplified spherical harmonics equations (SPN)in a finite homogeneous absorbing and scattering cylindrical medium. The SPN equations are a reliableapproximation to the radiative transfer equation for describing light propagation inside turbid media.They consist of a set of coupled partial differential equations (PDEs). The analytical solution developedhere is for a steady-state isotropic point source located at an arbitrary point inside a cylindrical turbidmedium. Partial reflection boundary conditions are considered, as they realistically model the refractiveindex mismatch between a turbid medium and its surroundings (air), as occurs in practice in biomedicaloptics. The eigen method is used to decouple the set of SPN PDEs. The methodology is applied to the SP3,which has proved to be sufficiently accurate in practice, but it is readily generalizable to higher orders.The solution is compared to the analytical solution of the diffusion equation as well as to gold standardMonte Carlo simulations for validation, against which it shows good agreement. This work is importantas it provides a further tool for validating numerical solutions of the SPN equations for curved geometries,namely cylindrical shapes which are often used in practice.

Formation of high-quality vortex laser beams withdifferent orbital angular momentums in the laserresonator

Liying Zhang, Tao Geng, Xiumin Gao, Songlin Zhuang, and Jinling Lian

Doc ID: 331511 Received 11 May 2018; Accepted 06 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: A scheme for forming high-quality vortex laser beams by employing spiral phase elements inside the laserresonator is presented theoretically. The calculated results show that the purity of the generated mode willdecrease slightly as the mode order increases. However, the purity can achieve higher than 0.97 even for the highorder mode. More important, the value of the orbital angular momentum is controllable. Then, the influence ofproduction and alignment errors, including the number of phase levels of the spiral phase elements, the surfaceroughness of the reflective mirrors, and the decenter of the reflective mirrors are discussed in detail. The resultsshow that the diffraction loss of the proposed system is more sensitive to production errors, and the purity of thegenerated mode is more sensitive to alignment errors. Thus, we estimate that the height of one step of the spiralstructure should be less than one fifteenth of the wavelength, the maximum surface fluctuation should be less thanone twentieth of the wavelength, and the vertical distance between the centers of the two reflective mirrors shouldbe less than 20 micrometers if one wants to obtain the high-quality vortex laser beams with high efficiency. Therequirements for precision are acceptable for existing microfabrication and operation technologies.

Transmission of polychromatic electromagnetic multi-Gaussian Schell-model beam in an inhomogeneous gradient-index fiber

Serkan Sahin, Minghui Zhang, Yahong Chen, and Yangjian Cai

Doc ID: 335980 Received 25 Jun 2018; Accepted 04 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: We derive analytical expressions for the cross-spectral density matrix of polychromatic electromagnetic multi-Gaussian Schell-model (EMGSM) beam transmission through a gradient-index fiber. The space-spectrum evolution properties for the spectral density, spectral shift, degree of polarization, and electromagnetic coherence state of a polychromatic EMGSM beam with Lorentzian line type spectrum and central wavelength $\lambda_0 = 1550$~nm propagation in a Silica-clad germania core inhomogeneous graded-index fiber are studied in detail. We show that these statistical properties exhibit periodicity in the fiber, caused by the focusing property of square-law media, which can be reminiscent of the self-imaging effect of optical fields. The effects of the nonconventional correlation functions of the polychromatic EMGSM beam on the transmission properties are also investigated.

X-ray tomography of extended objects: a comparison of data acquisition approaches

Ming Du, Rafael Vescovi, Kamel Fezzaa, Chris Jacobsen, and Doga Gursoy

Doc ID: 331496 Received 11 May 2018; Accepted 03 Aug 2018; Posted 06 Aug 2018  View: PDF

Abstract: The penetration power of x-rays allows one to image large objects. For example, centimeter-sized specimens can be imaged with micron-level resolution using synchrotron sources. In this case, however, the limited beam diameter and detector size preclude the acquisition of the full sample in a single take, necessitating strategies for combining data from multiple regions. Object stitching involves the combination of local tomography data from overlapping regions, while projection stitching involves the collection of projections at multiple offset positions from the rotation axis followed by data merging and reconstruction. We compare these two approaches in terms of radiation dose applied to the specimen, and reconstructed image quality. Object stitching involves an easier data alignment problem, and immediate viewing of subregions before the entire dataset has been acquired. Projection stitching is more dose-efficient, and avoids certain artifacts of local tomography; however, it also involves a more difficult data assembly and alignment procedure, in that it is more sensitive to accumulative registration error.

Three-dimensional localized chirped Airy-Circular wave packets in free space

Guanwen Zhao, Shijie Chen, zhengzhong Huang, and Dongmei Deng

Doc ID: 326963 Received 26 Mar 2018; Accepted 03 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: By solving the (3+1) dimensional free space Schrödinger equation in circular cylindrical coordinates, we have systematically analyzed the propagation of the chirped Airy-Circular (CAiCi) wave packets. The complex amplitude of the CAiCi wave packets is constructed by the Airy function, the Gaussian function and the confluent hypergeo-metric function. We find that the CAiCi wave packets are some coaxial ring pulses stacked along the temporal domain in the initial position, which are modulated by the chirped factor, the initial velocity, the distribution factor and the propagation distance. Meanwhile, the wave packets will appear to intensity attenuation, diffusion, convergence and so on. And we also can modulate the shape of the wave packets and change their optical properties by altering the mode numbers. Furthermore, we analyze the evolution properties of the wave packets in detail from the aspects of the gradient force, the scattering force, phase, the Poynting vector and the angular momentum, and find some interesting phenomena.

Focal shift in tightly focused hybridlypolarized Laguerre–Gaussian vector beamswith zero radial index

Yi Chen, Sujuan Huang, Musheng Chen, and xianpeng liu

Doc ID: 331699 Received 18 May 2018; Accepted 02 Aug 2018; Posted 03 Aug 2018  View: PDF

Abstract: Hybridly polarized Laguerre-Gaussian vector beams (HPLGVB) with zero radialindex are obtained based on the third type Laguerre Gaussian vector beams (LGVB).Polarization distributions of HPLGVB are controlled by the phase retardation of a wave plate.The ellipticity angle and polarization orientation angle are used to describe the polarizationdistributions of the HPLGVB. The electric field intensity distributions of tightly focusedHPLGVB are analyzed in the focal plane by the Richards-Wolf vectorial diffraction method.It is found that the tightly focused HPLGVB exist a focal shift phenomenon. The dependenceof the focal shift of HPLGVB on the different parameters is discussed in detail. Thesimulation results show that the magnitude of the focal shift is related to the polarizationdistribution, and the focal shift is quite obvious for large azimuthal mode index, long focallength, large numerical aperture and narrow beam waist. The effective control of the focalshift will have great potential applications in optical micro-manipulation.

Optical image processing with metasurface darkmodes

Ann Roberts, Daniel Gomez, and Timothy Davis

Doc ID: 331364 Received 09 May 2018; Accepted 27 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: Here we consider image processing using optical modes of metasurfaces that are excited with a dependence on the angle of incidence of a plane wave. These spatially dispersive modes can be used to directly manipulate the spatial frequency content of an incident field suggesting their use as ultra-compact alternatives for analog optical information processing. A general framework for describing the filtering process in terms of the optical transfer functions is provided and specific examples presented.

Optimized angular selective filtering of direct solar radiation

Rustam Zakirullin

Doc ID: 335526 Received 19 Jun 2018; Accepted 25 Jul 2018; Posted 25 Jul 2018  View: PDF

Abstract: A method to optimize angular selective filtering of direct solar radiation by minimization of light transmission of a window at preset date and time of day taking into account orientation of the window to the cardinal, the latitude of building, the seasonal and daily distribution of solar radiation intensity is described. Optimization is carried out due to using an optical filter with two thin-film surface gratings with alternating transmissive and non-transmissive parallel strips. Optimal slope angle of strips to horizontal, widths of strips, shift of input and output gratings relative to each other, angular characteristics of light transmittance are calculated.

Tensor-based predictive control for extremelylarge-scale single conjugate adaptive optics

Baptiste Sinquin and Michel Verhaegen

Doc ID: 326616 Received 21 Mar 2018; Accepted 25 Jul 2018; Posted 26 Jul 2018  View: PDF

Abstract: In this paper we propose a data-driven predictive control algorithm for large-scale single conjugate adaptiveoptics systems. At each time sample, the Shack-Hartmann wavefront sensor signal sampled on aspatial grid of size N N is reshuffled into a d-dimensional tensor. Its spatial-temporal dynamics aremodeled with a d-dimensional autoregressive model of temporal order p where each tensor storing pastdata undergoes a multilinear transformation by factor matrices of small sizes. Equivalently, the vectorform of this autoregressive model features coefficient matrices parametrized with a sum of Kroneckerproducts between d factor matrices. We propose an Alternating Least Squares algorithm for identifyingthe factor matrices from open-loop sensor data. When modeling each coefficient matrix with a sum of rterms, the computational complexity for updating the sensor prediction online reduces from O(pN4) inthe unstructured matrix case to O(prdN2(d+1)d ). Most importantly, this model structure breaks away fromassuming any prior spatial-temporal coupling as it is discovered from data. The algorithm is validatedon a laboratory testbed that demonstrates the ability to decompose accurately the coefficient matrices oflarge-scale autoregressive models with a tensor-based representation, hence achieving high data compressionrates and reducing the temporal error especially for large Greenwood per sample frequency ratio.

Hybrid Cameras Array based Calibration for Computer Generated Integral Photography Display

Guowen Chen, Hanpeng Wang, Mengfei Liu, and Hongen Liao

Doc ID: 318847 Received 04 Jan 2018; Accepted 24 Jul 2018; Posted 25 Jul 2018  View: PDF

Abstract: Integral photography (IP) is one of the most promising 3D displays, which can achieve full parallax 3D display without glasses. There is a great need to render a correct, high precision 3D image from IP display. To achieve a correct 3D display, calibration is needed to correct optical misalignment and optical aberrations while it is challenging to achieve a correct mapping between (micro-lens array) MLA and matrix display. We proposed an IP calibration method for 3D auto-stereoscopic integral photography display based on a sparse cameras array. Our method distinguish itself with previous methods by estimating parameters for a dense correspondence map of IP display with relative flexible setup and high precision in reasonable time cost. We also propose a workflow to enable our method to handle both visible and invisible micro-lens array and get great outcome. One prototype is fabricated to evaluate feasibility of proposed method. Moreover, we evaluated our proposed method in both geometry accuracy and image quality.

M-Pulse Amplitude Modulation of Flat-Topped Beam for Aeronautical Laser Communications

Hamza Gerçekcioglu

Doc ID: 325271 Received 06 Mar 2018; Accepted 18 Jul 2018; Posted 19 Jul 2018  View: PDF

Abstract: Using Rytov method, bit error rate ( ) performances of M-Pulse Amplitude Modulation (M-PAM) are investigated for the flat-topped beam when such a beam is employed in aeronautical laser communication system operating in vertical paths having weak atmospheric turbulence. By using the on-axis scintillation index and the log-normal distributed intensity, the average bit error rate ( ) is evaluated for M-PAM when . The scintillation indices of collimated flat-topped beams of various flatness orders N are compared against propagation lengths, source sizes, zenith angle for laser communication vertical paths, including uplink and downlink. Also, versus the average signal to noise ratio ( ) is examined for various beam flatness orders. It is shown that as the flatness order increases, the scintillation index decreases. Taking one of best flatness order value N=15 for reducing the scintillations, versus propagation lengths, source sizes, zenith angle and are found for various values of M. When M is increased, is found to deteriorate.

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