Journal of Photonics The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Fabric Defect Detection Using Local Homogeneity Analysis and Neural Network Tue, 17 Mar 2015 13:34:52 +0000 In the textile manufacturing industry, fabric defect detection becomes a necessary and essential step in quality control. The investment in this field is more than economical when reduction in labor cost and associated benefits are considered. Moreover, the development of a wholly automated inspection system requires efficient and robust algorithms. To overcome this problem, in this paper, we present a new fabric defect detection scheme which uses the local homogeneity and neural network. Its first step consists in computing a new homogeneity image denoted as -image. The second step is devoted to the application of the discrete cosine transform (DCT) to the -image and the extraction of different representative energy features of each DCT block. These energy features are used by the back-propagation neural network to judge the existence of fabric defect. Simulations on different fabric images and different defect aspects show that the proposed method achieves an average accuracy of 97.35%. Ali Rebhi, Issam Benmhammed, Sabeur Abid, and Farhat Fnaiech Copyright © 2015 Ali Rebhi et al. All rights reserved. Concept of Bee-Eyes Array of Fresnel Lenses as a Solar Photovoltaic Concentrator System Mon, 02 Mar 2015 09:37:20 +0000 This paper presents a proposal of a new configuration of an optical concentrator for photovoltaic application which may enhance the efficiency of solar cells. Bee-eyes array Fresnel lenses concentrator proposed here provide high concentration factor which is greater than1000x at the 20th zone. In addition, the system also provides room for increasing the number of zones to achieve the high concentration factor if needs arise. The transmission efficiency greater than 90% has been achieved with f-number of 1.25. Mathematical relations derived to obtain flux distribution at the absorber plane and the transmission efficiency as well as the position of the solar cell were used in the ray tracing simulations for 6, 18, 36, 60, 90, 126, 168, 216, 270, and 330 suns concentration systems. A transmission efficiency is linearly decreasing with the increase in the number of arrays in which the transmission efficiency of 94.42% was recorded at the array of 6 suns and 74.98% at 330 suns. Nura Liman Chiromawa and Kamarulazizi Ibrahim Copyright © 2015 Nura Liman Chiromawa and Kamarulazizi Ibrahim. All rights reserved. Highly Effective Crosstalk Mitigation Method Using Counter-Propagation in Semiconductor Optical Amplifier for Remodulation WDM-PONs Sun, 19 Oct 2014 08:54:36 +0000 Remodulation-induced crosstalk mitigation in WDM-PON using remodulation approach is presented in this paper. Utilizing all-optical signal processing, the proposed method has been able to significantly improve system performance in terms of bit error rate (BER) and bit rate distance product. Moreover, the proposed method could be used for both baseband and modulated downstream electrical signals. Quang Thai Pham Copyright © 2014 Quang Thai Pham. All rights reserved. Graphene Embedded Modulator with Extremely Small Footprint and High Modulation Efficiency Wed, 28 May 2014 11:27:58 +0000 By embedding graphene sheet in the silicon waveguide, the overall effective mode index displays unexpected symmetry and the electrorefraction effect has been significantly enhanced near the epsilon-near-zero point. An eight-layer graphene embedded Mach-Zehnder Modulator has been theoretically demonstrated with the advantage of ultracompact footprint (4 × 2 μm2), high modulation efficiency (1.316 V·μm), ultrafast modulation speed, and large extinction ratio. Our results may promote various on-chip active components, boosting the utilization of graphene in optical applications. Ran Hao and Jia-Min Jin Copyright © 2014 Ran Hao and Jia-Min Jin. All rights reserved. Wet Chemical Preparation of Nanoparticles ZnO:Eu3+ and ZnO:Tb3+ with Enhanced Photoluminescence Thu, 17 Apr 2014 13:11:53 +0000 ZnO doped with Eu3+ and Tb3+ had been successfully prepared by wet chemical method with the assistance of microwave. The influence of reaction conditions such as temperature, time, content of Eu3+, Tb3+ ion, and annealing treatment on the structure and luminescent characteristics was studied. The analysis of energy dispersive spectroscopy (EDS) and photoluminescence spectra measurements indicated that Eu3+ and Tb3+ exist in host lattice and create the new emission region compared to ZnO crystalline host lattice. The field emission scanning electron microscope (FE-SEM) studies show the Eu3+, Tb3+ doped ZnO nanoparticles have a pseudohexagonal shape. The particle size was 30–50 nm for ZnO:Eu3+ and 40–60 nm for ZnO:Tb3+. Photoluminescence excitation (PLE) and photoluminescence (PL) spectra at room temperature have been studied to recognize active centers for characteristic luminescence of ZnO:Eu3+ and ZnO:Tb3+. The characteristic luminescent lines of Eu3+ (5D0-7Fj) and Tb3+ (5D4-7Fj) were determined. It has been demonstrated that the wet chemical synthesis method with microwave assistance can strongly enhance the luminescent intensity of nanoparticles ZnO:Eu3+ in red and ZnO:Tb3+ in green. Tran Kim Anh, Dinh Xuan Loc, Nguyen Tu, Pham Thanh Huy, Le Minh Anh Tu, and Le Quoc Minh Copyright © 2014 Tran Kim Anh et al. All rights reserved. A New Design for All-Normal Near Zero Dispersion Photonic Crystal Fiber with Selective Liquid Infiltration for Broadband Supercontinuum Generation at 1.55 μm Wed, 16 Apr 2014 12:47:53 +0000 A new design of all-normal and near zero flattened dispersion based on all-silica photonic crystal fibers (PCFs) using selectively liquid infiltration technique has been proposed to realize smooth broadband supercontinuum generation (SCG). The investigation gives the details of the effect of different geometrical parameters along with the infiltrating liquids on the dispersion characteristics of the fiber. Numerical investigations establish a dispersion value of −0.48 ps/nm/km around the wavelength of 1.55 μm. The optimized design has been found to be suitable for SCG around the C band of wavelength with flat broadband wavelength band (375 nm bandwidth) and smooth spectrum with only a meter long of the PCF. The proposed structure also demonstrates good tunable properties that can help correct possible fabrication mismatch towards a better optimization design for various optical communication systems. Partha Sona Maji and Partha Roy Chaudhuri Copyright © 2014 Partha Sona Maji and Partha Roy Chaudhuri. All rights reserved. Simulation and Measurement of Solar Harvesting Enhancement of Silver Plasmonic Nanoparticles on GaSb Nanodots Mon, 24 Mar 2014 08:06:32 +0000 The performance of a plasmonic antireflection layer which can be utilized for deep-space radiationresistant GaSb solar cells is investigated numerically and experimentally. The layer consists of nanodots made by plasma etching of a GaSb substrate and subsequent physical vapor deposition of Ag nanoparticles on the nanodot tips, in a partially ordered configuration determined by the plasma energy level. This technique is readily applicable to patterning of silicon. We measure the substrate reflectivity and model the reflection and absorption of the substrates using the 3D finite difference time domain (FDTD) method, which are realistically imported as 3D layers from the scanning electron microscopy (SEM) images. The variation of the height of the Ag nanoparticles on top of the GaSb pillars shows that the plasmonic effect remarkably enhances the absorption. The presence of GaSb pillars enhances absorption and tunes the maximum absorption wavelength peak. Lorenzo Rosa, Mukesh Ranjan, Mukul Bhatnagar, Daryoush Mortazavi, Subroto Mukherjee, and Saulius Juodkazis Copyright © 2014 Lorenzo Rosa et al. All rights reserved. Heat Conduction Modeling of Fiber Fuse in Single-Mode Optical Fibers Mon, 24 Feb 2014 09:16:31 +0000 The unsteady-state thermal conduction process in single-mode optical fiber was studied theoretically with the explicit finite-difference method. We assumed that the vitreous silica optical fiber underwent pyrolysis at elevated temperatures to form (). We also proposed a model in which the optical absorption coefficient of the core layer increased with increasing molar concentration of . The core-center temperature changed suddenly and reached over  K when a 1.064-μm laser power of 2 W was input into a short core layer of 40 μm length, which was heated at 2923 K. This thermal wave, that is, a fiber fuse, increased in size and propagated toward the light source at a rate of about 0.54 m/s. The calculated propagation velocity of the fiber fuse was in agreement with the experimental value. Moreover, the average temperature of the radiated region of the core layer gradually approached a temperature of about 5700 K. It was found that the final average temperature was close to the experimentally reported values. Yoshito Shuto Copyright © 2014 Yoshito Shuto. All rights reserved. Bragg Gratings Induced in Birefringent Optical Fiber with an Elliptical Stress Cladding Wed, 11 Dec 2013 15:18:47 +0000 The paper presents the results of writing of type I and high-performance type II fiber Bragg gratings in birefringent optical fiber with an elliptical stress cladding by a single 20 ns pulse of KrF excimer laser (248 nm). The gratings’ efficiency produced by a single pulse was up to 100%. Experimental results on visualization of these gratings are presented. I. K. Meshkovskiy, V. E. Strigalev, A. V. Kulikov, and S. V. Varzhel' Copyright © 2013 I. K. Meshkovskiy et al. All rights reserved. DQOBSR Protocol with QoS Provisioning for OBS Metro Rings Thu, 12 Sep 2013 10:04:12 +0000 Optical burst switching (OBS) is the switching technology that enables optical internet with current technology. OBS networks are capable of operating with or without optical buffers and wavelength converters. Hence, medium access control (MAC) protocol plays an important role in resolving contention in such networks. Distributed Queue OBS Ring (DQOBSR) is one MAC protocol proposed for OBS ring networks. In this paper, the quality of service (QoS) provisioning scheme for DQOBSR protocol is presented. For the proposed protocol, service differentiation for different classes of traffic in terms of throughput and access delay is verified through simulation. A mathematical model is also presented for the computation of classwise mean access delay. The results obtained using the model are found to be in good agreement with the simulation results. M. Thachayani and R. Nakkeeran Copyright © 2013 M. Thachayani and R. Nakkeeran. All rights reserved. Monitoring of Moisture in Transformer Oil Using Optical Fiber as Sensor Wed, 24 Jul 2013 09:29:25 +0000 This paper describes an optical fiber sensor and temperature sensor-based instrumentation system to measure the moisture content in transformer oil. The sensor system consists of (i) Diode Laser Source, (ii) a bare and bent multimode fiber as sensor probe, (iii) an LDR as detector, (iv) LM35-based temperature sensor, and (v) microcontroller system having a trained ANN for processing and calibration. The bare and bent optical fiber sensor and the temperature sensor LM35 are used to provide the measures of refractive index (RI) and temperature of a transformer oil sample. An ATmega32-microcontroller-based system with trained ANN algorithm has been developed to determine the moisture content of the transformer oil sample by sampling the readings of the bare bent optical fiber sensor and the temperature sensor. S. Laskar and S. Bordoloi Copyright © 2013 S. Laskar and S. Bordoloi. All rights reserved. Tunable Optical Filter Based on Mechanically Induced Cascaded Long Period Optical Fiber Grating Mon, 17 Jun 2013 17:38:40 +0000 We have proposed and demonstrated experimentally a novel and simple tunable optical filter based on mechanically induced and cascaded long period optical fiber gratings. In this filter variable FWHM and center wavelength is provided by cascading long period and ultralong period optical fiber gratings with different periods in a novel fiber structure. We report here for the first time to our knowledge the characterization of mechanically induced long period fiber gratings with periods up to several millimeters in novel multimode-single-mode-multimode fiber structure. We have obtained maximum loss peak of around 20 dB. Sunita P. Ugale and Vivekanand Mishra Copyright © 2013 Sunita P. Ugale and Vivekanand Mishra. All rights reserved.