International Journal of Optics The latest articles from Hindawi Publishing Corporation © 2016 , Hindawi Publishing Corporation . All rights reserved. Analytical Approach to Polarization Mode Dispersion in Linearly Spun Fiber with Birefringence Mon, 23 May 2016 08:15:35 +0000 The behavior of Polarization Mode Dispersion (PMD) in spun optical fiber is a topic of great interest in optical networking. Earlier work in this area has focused more on approximate or numerical solutions. In this paper we present analytical results for PMD in spun fibers with triangular spin profile function. It is found that in some parameter ranges the analytical results differ from the approximations. Vinod K. Mishra Copyright © 2016 Vinod K. Mishra. All rights reserved. Gas Bubbles Investigation in Contaminated Water Using Optical Tomography Based on Independent Component Analysis Method Mon, 16 May 2016 07:03:03 +0000 This paper presents the results of concentration profiles for gas bubble flow in a vertical pipeline containing contaminated water using an optical tomography system. The concentration profiles for the bubble flow quantities are investigated under five different flows conditions, a single bubble, double bubbles, 25% of air opening, 50% of air opening, and 100% of air opening flow rates where a valve is used to control the gas flow in the vertical pipeline. The system is aided by the independent component analysis (ICA) algorithm to reconstruct the concentration profiles of the liquid-gas flow. The behaviour of the gas bubbles was investigated in contaminated water in which the water sample was prepared by adding 25 mL of colour ingredients to 3 liters of pure water. The result shows that the application of ICA has enabled the system to detect the presence of gas bubbles in contaminated water. This information provides vital information on the flow inside the pipe and hence could be very significant in increasing the efficiency of the process industries. Mohd Taufiq Mohd Khairi, Sallehuddin Ibrahim, Mohd Amri Md Yunus, and Mahdi Faramarzi Copyright © 2016 Mohd Taufiq Mohd Khairi et al. All rights reserved. Differences in Nanosecond Laser Ablation and Deposition of Tungsten, Boron, and WB2/B Composite due to Optical Properties Wed, 11 May 2016 12:07:14 +0000 The first attempt to the deposition of WB3 films using nanosecond Nd:YAG laser demonstrated that deposited coatings are superhard. However, they have very high roughness. The deposited films consisted mainly of droplets. Therefore, in the present work, the explanation of this phenomenon is conducted. The interaction of Nd:YAG nanosecond laser pulse with tungsten, boron, and WB2/B target during ablation is investigated. The studies show the fundamental differences in ablation of those materials. The ablation of tungsten is thermal and occurs due to only evaporation. In the same conditions, during ablation of boron, the phase explosion and/or fragmentation due to recoil pressure is observed. The deposited films have a significant contribution of big debris with irregular shape. In the case of WB2/B composite, ablation is significantly different. The ablation seems to be the detonation in the liquid phase. The deposition mechanism is related mainly to the mechanical transport of the target material in the form of droplets, while the gaseous phase plays marginal role. The main origin of differences is optical properties of studied materials. A method estimating phase explosion occurrence based on material data such as critical temperature, thermal diffusivity, and optical properties is shown. Moreover, the effect of laser wavelength on the ablation process and the quality of the deposited films is discussed. Tomasz Moscicki Copyright © 2016 Tomasz Moscicki. All rights reserved. Center Symmetric Local Multilevel Pattern Based Descriptor and Its Application in Image Matching Wed, 11 May 2016 11:49:05 +0000 This paper presents an effective local image region description method, called CS-LMP (Center Symmetric Local Multilevel Pattern) descriptor, and its application in image matching. The CS-LMP operator has no exponential computations, so the CS-LMP descriptor can encode the differences of the local intensity values using multiply quantization levels without increasing the dimension of the descriptor. Compared with the binary/ternary pattern based descriptors, the CS-LMP descriptor has better descriptive ability and computational efficiency. Extensive image matching experimental results testified the effectiveness of the proposed CS-LMP descriptor compared with other existing state-of-the-art descriptors. Hui Zeng, Xiuqing Wang, and Yu Gu Copyright © 2016 Hui Zeng et al. All rights reserved. The Impact of Pixel Resolution, Integration Scale, Preprocessing, and Feature Normalization on Texture Analysis for Mass Classification in Mammograms Tue, 12 Apr 2016 08:09:50 +0000 Texture analysis methods are widely used to characterize breast masses in mammograms. Texture gives information about the spatial arrangement of the intensities in the region of interest. This information has been used in mammogram analysis applications such as mass detection, mass classification, and breast density estimation. In this paper, we study the effect of factors such as pixel resolution, integration scale, preprocessing, and feature normalization on the performance of those texture methods for mass classification. The classification performance was assessed considering linear and nonlinear support vector machine classifiers. To find the best combination among the studied factors, we used three approaches: greedy, sequential forward selection (SFS), and exhaustive search. On the basis of our study, we conclude that the factors studied affect the performance of texture methods, so the best combination of these factors should be determined to achieve the best performance with each texture method. SFS can be an appropriate way to approach the factor combination problem because it is less computationally intensive than the other methods. Mohamed Abdel-Nasser, Jaime Melendez, Antonio Moreno, and Domenec Puig Copyright © 2016 Mohamed Abdel-Nasser et al. All rights reserved. Experimental Research of Reliability of Plant Stress State Detection by Laser-Induced Fluorescence Method Thu, 03 Mar 2016 13:32:29 +0000 Experimental laboratory investigations of the laser-induced fluorescence spectra of watercress and lawn grass were conducted. The fluorescence spectra were excited by YAG:Nd laser emitting at 532 nm. It was established that the influence of stress caused by mechanical damage, overwatering, and soil pollution is manifested in changes of the spectra shapes. The mean values and confidence intervals for the ratio of two fluorescence maxima near 685 and 740 nm were estimated. It is presented that the fluorescence ratio could be considered a reliable characteristic of plant stress state. Yury Fedotov, Olga Bullo, Michael Belov, and Viktor Gorodnichev Copyright © 2016 Yury Fedotov et al. All rights reserved. Synthesis, Optical Characterization, and Thermal Decomposition of Complexes Based on Biuret Ligand Thu, 25 Feb 2016 15:50:27 +0000 Four complexes were synthesized in methanol solution using nickel acetate or nickel chloride, manganese acetate, manganese chloride, and biuret as raw materials. The complexes were characterized by elemental analyses, UV, FTIR, Raman spectra, X-ray powder diffraction, and thermogravimetric analysis. The compositions of the complexes were [Ni(bi)2(H2O)2](Ac)2·H2O (1), [Ni(bi)2Cl2] (2), [Mn(bi)2(Ac)2]·1.5H2O (3), and [Mn(bi)2Cl2] (4) (bi = NH2CONHCONH2), respectively. In the complexes, every metal ion was coordinated by oxygen atoms or chlorine ions and even both. The nickel and manganese ions were all hexacoordinated. The thermal decomposition processes of the complexes under air included the loss of water molecule, the pyrolysis of ligands, and the decomposition of inorganic salts, and the final residues were nickel oxide and manganese oxide, respectively. Mei-Ling Wang, Guo-Qing Zhong, and Ling Chen Copyright © 2016 Mei-Ling Wang et al. All rights reserved. Optical, Thermal, and Mechanical Properties of L-Serine Phosphate, a Semiorganic Enhanced NLO Single Crystal Wed, 24 Feb 2016 11:38:13 +0000 Single crystals of L-serine phosphate (LSP) were grown by slow evaporation technique. The optical studies reveal the transparency of the crystal in the entire visible region. Grown crystal was subjected to single crystal XRD diffraction technique. Thermal studies of LSP confirm the thermal stability of the crystal and it is stable up to 210°C. The functional groups and optical behaviour of the crystal were identified from FT-IR and UV-Vis analysis. The crystals were also characterized by microhardness and photoconductivity to determine the mechanical strength and the optical conductivity. Laser damage threshold and nonlinear optical activity of the grown crystal were confirmed by Q-switched Nd : YAG laser beam. K. Rajesh, A. Mani, V. Thayanithi, and P. Praveen Kumar Copyright © 2016 K. Rajesh et al. All rights reserved. Nonparaxial Propagation of Vectorial Elliptical Gaussian Beams Thu, 18 Feb 2016 15:41:39 +0000 Based on the vectorial Rayleigh-Sommerfeld diffraction integral formulae, analytical expressions for a vectorial elliptical Gaussian beam’s nonparaxial propagating in free space are derived and used to investigate target beam’s propagation properties. As a special case of nonparaxial propagation, the target beam’s paraxial propagation has also been examined. The relationship of vectorial elliptical Gaussian beam’s intensity distribution and nonparaxial effect with elliptic coefficient and waist width related parameter has been analyzed. Results show that no matter what value of elliptic coefficient is, when parameter is large, nonparaxial conclusions of elliptical Gaussian beam should be adopted; while parameter is small, the paraxial approximation of elliptical Gaussian beam is effective. In addition, the peak intensity value of elliptical Gaussian beam decreases with increasing the propagation distance whether parameter is large or small, and the larger the elliptic coefficient is, the faster the peak intensity value decreases. These characteristics of vectorial elliptical Gaussian beam might find applications in modern optics. Wang Xun, Huang Kelin, Liu Zhirong, and Zhao Kangyi Copyright © 2016 Wang Xun et al. All rights reserved. Irradiance Scintillation Index for a Gaussian Beam Based on the Generalized Modified Atmospheric Spectrum with Aperture Averaged Wed, 17 Feb 2016 11:38:49 +0000 This paper investigates the aperture-averaged irradiance scintillation index of a Gaussian beam propagating through a horizontal path in weak non-Kolmogorov turbulence. Mathematical expressions are obtained based on the generalized modified atmospheric spectrum, which includes the spectral power law value of non-Kolmogorov turbulence, the finite inner and outer scales of turbulence, and other optical parameters of the Gaussian beam. The numerical results are conducted to analyze the influences of optical parameters on the aperture-averaged irradiance scintillation index for different Gaussian beams. This paper also examines the effects of the irradiance scintillation on the performance of the point-to-point optical wireless communication system with intensity modulation/direct detection scheme. Chao Gao, Yang Li, Yiming Li, and Xiaofeng Li Copyright © 2016 Chao Gao et al. All rights reserved. Disorder Improves Light Absorption in Thin Film Silicon Solar Cells with Hybrid Light Trapping Structure Mon, 08 Feb 2016 14:03:59 +0000 We present a systematic simulation study on the impact of disorder in thin film silicon solar cells with hybrid light trapping structure. For the periodical structures introducing certain randomness in some parameters, the nanophotonic light trapping effect is demonstrated to be superior to their periodic counterparts. The nanophotonic light trapping effect can be associated with the increased modes induced by the structural disorders. Our study is a systematic proof that certain disorder is conceptually an advantage for nanophotonic light trapping concepts in thin film solar cells. The result is relevant to the large field of research on nanophotonic light trapping which currently investigates and prototypes a number of new concepts including disordered periodic and quasiperiodic textures. The random effect on the shape of the pattern (position, height, and radius) investigated in this paper could be a good approach to estimate the influence of experimental inaccuracies for periodic or quasi-periodic structures. Yanpeng Shi, Xiaodong Wang, and Fuhua Yang Copyright © 2016 Yanpeng Shi et al. All rights reserved. Corollaries of Point Spread Function with Asymmetric Apodization Tue, 26 Jan 2016 11:06:05 +0000 Primary energy based corollaries of point spread function with asymmetric apodization using complex pupil function have been studied in the case of three-zone aperture. Merit function like semicircled energy factor, excluded semicircled energy, and displaced semicircled energy were analyzed with respect to Airy case in terms of phase and amplitude apodization. Analytical results have been presented for the optimum parameters of phase and amplitude asymmetric apodization. Naresh Kumar Reddy Andra, Udaya Laxmi Sriperumbudur, and Karuna Sagar Dasari Copyright © 2016 Naresh Kumar Reddy Andra et al. All rights reserved. Development of Combinatorial Pulsed Laser Deposition for Expedited Device Optimization in CdTe/CdS Thin-Film Solar Cells Sun, 17 Jan 2016 13:48:06 +0000 A combinatorial pulsed laser deposition system was developed by integrating a computer controlled scanning sample stage in order to rapidly screen processing conditions relevant to CdTe/CdS thin-film solar cells. Using this system, the thickness of the CdTe absorber layer is varied across a single sample from 1.5 μm to 0.75 μm. The effects of thickness on CdTe grain morphology, crystal orientation, and cell efficiency were investigated with respect to different postprocessing conditions. It is shown that the thinner CdTe layer of 0.75 μm obtained the best power conversion efficiency up to 5.3%. The results of this work shows the importance that CdTe grain size/morphology relative to CdTe thickness has on device performance and quantitatively exhibits what those values should be to obtain efficient thin-film CdTe/CdS solar cells fabricated with pulsed laser deposition. Further development of this combinatorial approach could enable high-throughput exploration and optimization of CdTe/CdS solar cells. Ali Kadhim, Paul Harrison, Jake Meeth, Alaa Al-Mebir, Guanggen Zeng, and Judy Wu Copyright © 2016 Ali Kadhim et al. All rights reserved. Optical Image Encryption Using Devil’s Vortex Toroidal Lens in the Fresnel Transform Domain Thu, 31 Dec 2015 14:41:44 +0000 We have carried out a study of optical image encryption in the Fresnel transform () domain, using a random phase mask (RPM) in the input plane and a phase mask based on devil’s vortex toroidal lens (DVTL) in the frequency plane. The original images are recovered from their corresponding encrypted images by using the correct parameters of the and the parameters of DVTL. The use of a DVTL-based structured mask enhances security by increasing the key space for encryption and also aids in overcoming the problem of axis alignment associated with an optical setup. The proposed encryption scheme is a lensless optical system and its digital implementation has been performed using MATLAB 7.6.0 (R2008a). The scheme has been validated for a grayscale and a binary image. The efficacy of the proposed scheme is verified by computing mean-squared-error (MSE) between the recovered and the original images. We have also investigated the scheme’s sensitivity to the encryption parameters and examined its robustness against occlusion and noise attacks. Hukum Singh, A. K. Yadav, Sunanda Vashisth, and Kehar Singh Copyright © 2015 Hukum Singh et al. All rights reserved. Impact of Strong Raman Self-Frequency Shift on Bound State of Dissipative Solitons Wed, 16 Dec 2015 14:26:36 +0000 Bound dissipative solitons are numerically studied by implementing strong Raman self-frequency shift (RSFS) in an all-normal-dispersion (ANDi) Yb-doped fiber laser. Results demonstrated that overstrong RSFS had no filter-like effect in the ANDi fiber laser when a bandpass filter was present in the intracavity. However, overstrong RSFS could cause the bandpass filter to destabilize the ANDi fiber laser. For the first time in the field, we have demonstrated that strong RSFS could destabilize bound DS pulses and generate noise-like bound pulses. Furthermore, the generation mechanism of destabilized noise-like bound pulses in the fiber laser with intracavity filter is different from the noise-like pulses in the fiber lasers without a bandpass filter. Cong Xu Copyright © 2015 Cong Xu. All rights reserved. Longest Path Reroute to Optimize the Optical Multicast Routing in Sparse Splitting WDM Networks Tue, 15 Dec 2015 06:43:48 +0000 Limited by the sparse light-splitting capability in WDM networks, some nodes need to reroute the optical packet to different destination nodes with the high cost of routing for reducing packet loss possibility. In the paper, the longest path reroute optimization algorithm is put forward to jointly optimize the multicast routing cost and wavelength channel assignment cost for sparse splitting WDM networks. Based on heuristic algorithms, the longest path reroute routing algorithm calls multiple longest paths in existing multicast tree to reroute the path passing from the nodes which are violating the light-splitting constraint to the nodes which are not violating light-splitting constraint with few wavelength channels and low rerouting cost. And a wavelength cost control factor is designed to select the reroute path with the lowest cost by comparing the multicast rerouting path cost increment with the equivalent wavelength channel required cost increment. By adjusting wavelength cost control factor, we can usually get the optimized multicast routing according to the actual network available wavelength conversion cost. Simulation results show that the proposed algorithm can get the low-cost multicast tree and reduce the required number of wavelength channels. Huanlin Liu, Hongyue Dai, Fei Zhai, Yong Chen, and Chengying Wei Copyright © 2015 Huanlin Liu et al. All rights reserved. Optical Characterization of Zinc Modified Bismuth Silicate Glasses Wed, 09 Dec 2015 13:05:06 +0000 The optical characterization of glass samples in the system 40SiO2 · ZnO · ()Bi2O3 with , 5, 10, 15, 20, 25, 30, 35, and 40 prepared by conventional melt-quench technique has been carried out in the light of Hydrogenic Excitonic Model (HEM). The absorption coefficient spectra show good agreement with theoretical HEM for the present glass system and the values of different parameters like , , , , and have been estimated from fitting of this model. The values of energy band gap estimated from fitting of HEM with experimental data are in good agreement with those obtained from Tauc’s plot for direct transitions. The band gap energy is found to increase with increase of ZnO content. The decrease in values of Urbach energy with increase in ZnO content indicates a decrease in defect concentration in the glass matrix on addition of ZnO content. Optical constants and obey - consistency and the dielectric response of the studied glass system is similar to that obtained for Classical Electron Theory of Dielectric Materials. The calculated values of the metallization criterion () show that the synthesized glasses may be good candidates for new nonlinear optical materials. Rajesh Parmar, J. Hooda, R. S. Kundu, R. Punia, and N. Kishore Copyright © 2015 Rajesh Parmar et al. All rights reserved. Bessel Beam Diffraction by an Aperture in an Opaque Screen Thu, 26 Nov 2015 14:19:55 +0000 The scattering of the Bessel beam by a circular aperture in an opaque screen is investigated by the geometrical theory of diffraction approach. The geometrical optics and diffracted and scattered fields are obtained. The effect of the aperture to the scattering process is analyzed. The uniform versions of field expressions are derived. The geometrical optics and diffracted and scattered fields are examined numerically. Husnu Deniz Basdemir Copyright © 2015 Husnu Deniz Basdemir. All rights reserved. A Novel Coupled Resonator Photonic Crystal Design in Lithium Niobate for Electrooptic Applications Wed, 18 Nov 2015 08:50:53 +0000 High-aspect-ratio photonic crystal air-hole fabrication on bulk Lithium Niobate (LN) substrates is extremely difficult due to its inherent resistance to etching, resulting in conical structures and high insertion losses. Here, we propose a novel coupled resonator photonic crystal (CRPC) design, combining a coupled resonator approach with that of Bragg gratings. CRPC design parameters were optimized by analytical calculations and FDTD simulations. CRPC structures with optimized parameters were fabricated and electrooptically tested on bulk LN annealed proton exchange waveguides. Low insertion loss and large electrooptic effect were observed with the fabricated devices, making the CRPC design a promising structure for electrooptic device applications. Birol Ozturk, Ozgur Yavuzcetin, and Srinivas Sridhar Copyright © 2015 Birol Ozturk et al. All rights reserved. Free Space Optics: Current Applications and Future Challenges Tue, 17 Nov 2015 08:23:33 +0000 FSO is a communication system where free space acts as medium between transceivers and they should be in LOS for successful transmission of optical signal. Medium can be air, outer space, or vacuum. This system can be used for communication purpose in hours and in lesser economy. There are many advantages of FSO like high bandwidth and no spectrum license. The transmission in FSO is dependent on the medium because the presence of foreign elements like rain, fog, and haze, physical obstruction, scattering, and atmospheric turbulence are some of these factors. Different studies on weather conditions and techniques employed to mitigate their effect are discussed in this paper. Aditi Malik and Preeti Singh Copyright © 2015 Aditi Malik and Preeti Singh. All rights reserved. Integrated Wavelength-Tunable Light Source for Optical Gas Sensing Systems Mon, 16 Nov 2015 14:27:02 +0000 A compact instrument consisting of a distributed feedback laser (DFB) at 1.65 μm was developed as a light source for gas sensing systems using tunable diode laser absorption spectroscopy (TDLAS) technique. The wavelength of laser is tuned by adjusting the laser working temperature and injection current, which are performed by self-developed temperature controller and current modulator respectively. Stability test shows the fluctuation of the laser temperature is within the range of ±0.02°C. For gas detection experiments, the wavelength is tuned around the gas absorption line by adjusting laser temperature and is then shifted periodically to scan across the absorption line by the laser current modulator, which generates a 10 Hz saw wave signal. In addition, the current modulator is able to generate sine wave signal for gas sensing systems using wavelength modulation spectroscopy (WMS) technique involving extraction of harmonic signals. The spectrum test proves good stability that the spectrum was measured 6 times every 10 minutes at the constant temperature and current condition. This standalone instrument can be applied as a light source for detection systems of different gases by integrating lasers at corresponding wavelength. Bin Li, Qi-Xin He, Hui-Fang Liu, and Yi-Ding Wang Copyright © 2015 Bin Li et al. All rights reserved. Synthesis and Optical Characterization of Mixed Ligands Beryllium Complexes for Display Device Applications Wed, 28 Oct 2015 11:31:29 +0000 Synthesis and photoluminescent behaviour of mixed ligand based beryllium complexes with 2-(2-hydroxyphenyl)benzoxazole (HPB) and 5-chloro-8-hydroxyquinoline (Clq) or 5,7-dichloro-8-hydroxyquinoline (Cl2q) or 2-methyl-8-hydroxyquinoline (Meq) or 8-hydroxyquinoline (q) are reported in this work. These complexes, that is, [BeHPB(Clq)], [BeHPB(Cl2q)], [BeHPB(Meq)], and [BeHPB(q)], were prepared and their structures were confirmed by elemental analysis, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and thermal analysis. The beryllium complexes exhibited good thermal stability up to ~300°C temperature. The photophysical properties of beryllium complexes were studied using ultraviolet-visible absorption and photoluminescence emission spectroscopy. The complexes showed absorption peaks due to and electronic transitions. The complexes emitted greenish blue light with peak wavelength at 496 nm, 510 nm, 490 nm, and 505 nm, respectively, consisting of high intensity. Color tuning was observed with changing the substituents in quinoline ring ligand in metal complexes. The emitted light had Commission Internationale d’Eclairage color coordinates values at and for [BeHPB(Clq)], and for [BeHPB(Cl2q)], and for [BeHPB(Meq)], and for [BeHPB(q)]. Theoretical calculations using DFT/B3LYP/6-31G(d,p) method were performed to reveal the three-dimensional geometries and the frontier molecular orbital energy levels of these synthesized metal complexes. Vandna Nishal, Devender Singh, Raman Kumar Saini, Vijeta Tanwar, Shri Bhagwan, Sonika Kadyan, Ishwar Singh, and Pratap Singh Kadyan Copyright © 2015 Vandna Nishal et al. All rights reserved. Gait Recognition Using GEI and AFDEI Sun, 11 Oct 2015 08:14:54 +0000 Gait energy image (GEI) preserves the dynamic and static information of a gait sequence. The common static information includes the appearance and shape of the human body and the dynamic information includes the variation of frequency and phase. However, there is no consideration of the time that normalizes each silhouette within the GEI. As regards this problem, this paper proposed the accumulated frame difference energy image (AFDEI), which can reflect the time characteristics. The fusion of the moment invariants extracted from GEI and AFDEI was selected as the gait feature. Then, gait recognition was accomplished using the nearest neighbor classifier based on the Euclidean distance. Finally, to verify the performance, the proposed algorithm was compared with the GEI + 2D-PCA and SFDEI + HMM on the CASIA-B gait database. The experimental results have shown that the proposed algorithm performs better than GEI + 2D-PCA and SFDEI + HMM and meets the real-time requirements. Jing Luo, Jianliang Zhang, Chunyuan Zi, Ying Niu, Huixin Tian, and Chunbo Xiu Copyright © 2015 Jing Luo et al. All rights reserved. Analytical Model for Optical Scattering of Infrared Laser by Nonspherical Raindrops Mon, 05 Oct 2015 13:59:07 +0000 Analytic model was developed to investigate the interaction of infrared laser with nonspherical raindrops. The method based on Fraunhofer diffraction and geometrical optics was presented to obtain the analytic solution for single-scattering properties by approximate ellipsoid raindrops. Light scattering patterns were obtained for different drop sizes and shapes. Computational results demonstrate that the scattering of raindrops was contributed by both Fraunhofer diffraction and geometric scattering, and the results obtained from analytic formulas were consistent with the conclusions of using Monte Carlo ray tracing approach. Jing Guo, He Zhang, and Xiang-jin Zhang Copyright © 2015 Jing Guo et al. All rights reserved. Automated 3D Scenes Reconstruction Using Multiple Stereo Pairs from Portable Four-Camera Photographic Measurement System Mon, 17 Aug 2015 06:03:33 +0000 An effective automatic 3D reconstruction method using a portable four-camera photographic measurement system (PFCPMS) is proposed. By taking advantage of the complementary stereo information from four cameras, a fast and highly accurate feature point matching algorithm is developed for 3D reconstruction. Specifically, we first utilize a projection method to obtain a large number of dense feature points. And then a reduction and clustering treatment is applied to simplify the Delaunay triangulation process and reconstruct a 3D model for each scene. In addition, a 3D model stitching approach is proposed to further improve the performance of the limited field-of-view for image-based method. The experimental results tested on the 172 cave in Mogao Grottoes indicate that the proposed method is effective to reconstruct a 3D scene with a low-cost four-camera photographic measurement system. Qi Peng, Lifen Tu, Kaibing Zhang, and Sidong Zhong Copyright © 2015 Qi Peng et al. All rights reserved. Investigation on the Effect of Underwater Acoustic Pressure on the Fundamental Mode of Hollow-Core Photonic Bandgap Fibers Sun, 29 Mar 2015 08:02:08 +0000 Recently, microstructured optical fibers have become the subject of extensive research as they can be employed in many civilian and military applications. One of the recent areas of research is to enhance the normalized responsivity (NR) to acoustic pressure of the optical fiber hydrophones by replacing the conventional single mode fibers (SMFs) with hollow-core photonic bandgap fibers (HC-PBFs). However, this needs further investigation. In order to fully understand the feasibility of using HC-PBFs as acoustic pressure sensors and in underwater communication systems, it is important to study their modal properties in this environment. In this paper, the finite element solver (FES) COMSOL Multiphysics is used to study the effect of underwater acoustic pressure on the effective refractive index of the fundamental mode and discuss its contribution to NR. Besides, we investigate, for the first time to our knowledge, the effect of underwater acoustic pressure on the effective area and the numerical aperture (NA) of the HC-PBF. Adel Abdallah, Zhang Chaozhu, and Zhong Zhi Copyright © 2015 Adel Abdallah et al. All rights reserved. Performance Comparison of Wavefront-Sensorless Adaptive Optics Systems by Using of the Focal Plane Thu, 08 Jan 2015 06:49:15 +0000 The correction capability and the convergence speed of the wavefront-sensorless adaptive optics (AO) system are compared based on two different system control algorithms, which both use the information of focal plane. The first algorithm is designed through the linear relationship between the second moment of the aberration gradients and the masked far-field intensity distribution and the second is stochastic parallel gradient descent (SPGD), which is the most commonly used algorithm in wavefront-sensorless AO systems. A wavefront-sensorless AO model is established with a 61-element deformable mirror (DM) and a CCD. Performance of the two control algorithms is investigated and compared through correcting different wavefront aberrations. Results show that the correction ability of AO system based on the proposed control algorithm is obviously better than that of AO system based on SPGD algorithm when the wavefront aberrations increase. The time needed by the proposed control algorithm is much less than that of SPGD when the AO system achieves similar correction results. Additionally, the convergence speed of the proposed control algorithm is independent of the turbulence strength while the number of intensity measurements needed by SPGD increases as the turbulence strength magnifies. Huizhen Yang, Zhen Zhang, and Jian Wu Copyright © 2015 Huizhen Yang et al. All rights reserved. On Optimal Frequencies for Reconstruction of a One-Dimensional Profile of Gradient Layer’s Refractive Index Tue, 16 Dec 2014 07:24:37 +0000 The problem of reconstruction of a one-dimensional profile of gradient layer’s refractive index is investigated. An algorithm for choosing a right frequency, at which a scattered field is measured, is proposed. It is concluded that at the correct choice of frequency one measurement must be sufficient. Moreover, in this case, regularization parameters of the residual functional are chosen as zero. It is shown that in case of measurements being carried out with errors, residual terms must be added to the functional. Dmitrii Tumakov Copyright © 2014 Dmitrii Tumakov. All rights reserved. Omnigradient Based Total Variation Minimization for Enhanced Defocus Deblurring of Omnidirectional Images Mon, 08 Dec 2014 11:24:36 +0000 We propose a new method of image restoration for catadioptric defocus blur using omnitotal variation (Omni-TV) minimization based on omnigradient. Catadioptric omnidirectional imaging systems usually consist of conventional cameras and curved mirrors for capturing 360° field of view. The problem of catadioptric omnidirectional imaging defocus blur, which is caused by lens aperture and mirror curvature, becomes more severe when high resolution sensors and large apertures are used. In an omnidirectional image, two points near each other may not be close to one another in the 3D scene. Traditional gradient computation cannot be directly applied to omnidirectional image processing. Thus, omnigradient computing method combined with the characteristics of catadioptric omnidirectional imaging is proposed. Following this Omni-TV minimization is used as the constraint for deconvolution regularization, leading to the restoration of defocus blur in an omnidirectional image to obtain all sharp omnidirectional images. The proposed method is important for improving catadioptric omnidirectional imaging quality and promoting applications in related fields like omnidirectional video and image processing. Yongle Li and Jingtao Lou Copyright © 2014 Yongle Li and Jingtao Lou. All rights reserved. A Novel Shared Protection Scheme Based on Aggregate Wavelength in High Speed Networks Thu, 20 Nov 2014 00:00:00 +0000 We propose novel analytical model of dynamic link cost evaluation in IP over WDM networks. We suggest disjoint path algorithm for the primary and backup path based on wavelength aggregate information, to provide shared backup. We show the optimality of pair selected because of joint optimization of the pair paths. The shareable capacity factor is introduced to establish the effect of load balancing on resources. We compared our simulation results with that of separate protection at connection and showed improvement on resource utilization performance of the network. We also study the blocking probability of proposed scheme. Anshu Oberoi, J. S. Sohal, and R. S. Kaler Copyright © 2014 Anshu Oberoi et al. All rights reserved.