Advances in Optical Technologies The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Robust Discrimination between Single Gold Nanoparticles and Their Dimers in Aqueous Solution for Ultrasensitive Homogeneous Bioassays Tue, 07 Apr 2015 12:21:47 +0000 We propose a robust method to distinguish isolated single gold nanoparticles (AuNP monomers) and their dimers under Brownian motion, a key for ultrasensitive homogeneous bioassays, including AuNP sandwich assays. To detect dimers and distinguish them from a larger number of monomers in aqueous solution, single-particle polarization microscopy was performed. For the accurate detection of individual particles, the optical anisotropy and rotational diffusion time are measured because a dimer is much more anisotropic than the nearly spherical monomer and the rotational diffusion time of a dimer is four times that of a monomer. By employing an autocorrelation analysis, we defined a measure of distinguishing that simultaneously enables high detection probability and low error probability. The detection platform offers homogeneous DNA hybridization assays and immunoassays at the subpicomolar level. Jun Kobayashi, Yukari Takeshita, Naoto Mizuno, Keio Esashika, and Toshiharu Saiki Copyright © 2015 Jun Kobayashi et al. All rights reserved. Nanophotonics: Fabrications and Application of Nanoscale Optics to Novel Photonic Devices Tue, 03 Feb 2015 07:30:50 +0000 Takashi Yatsui, Chennupati Jagadish, and Gilles Lerondel Copyright © 2015 Takashi Yatsui et al. All rights reserved. Switching the Localized Surface Plasmon Resonance of Single Gold Nanorods with a Phase-Change Material and the Implementation of a Cellular Automata Algorithm Using a Plasmon Particle Array Mon, 02 Feb 2015 10:39:11 +0000 We investigate the modulation of the localized surface plasmon resonance (LSPR) of a gold nanorod (AuNR) using a GeSbTe film as an active medium. We demonstrate high-contrast switching of LSPR in an AuNR/GST/Au thin film sandwich structure upon phase change. To go beyond this single-particle switching functionality, we consider a plasmon particle system interacting with a phase-change material (PCM) to discuss the possibility of parallel processing devices with memory functionality, exploiting the plasticity and threshold behavior that are inherent characteristics of PCMs. We demonstrate that the temporal and spatial evolution of a plasmon-PCM array system can be equivalent to a cellular automata algorithm. Takashi Hira, Takayuki Uchiyama, Kenta Kuwamura, Yuya Kihara, Tasuku Yawatari, and Toshiharu Saiki Copyright © 2015 Takashi Hira et al. All rights reserved. GaP Homojunction LEDs Fabricated by Dressed-Photon-Phonon-Assisted Annealing Mon, 02 Feb 2015 08:35:03 +0000 By using a homojunction-structured GaP single crystal, we generated a photon energy higher than the bandgap energy (2.26 eV). The device was fabricated by performing dressed-photon-phonon- (DPP-) assisted annealing, while applying a forward-bias current, on a p-n homojunction structure formed by implanting a dopant (Zn) into an n-type GaP substrate. The DPP-assisted annealing increased the light emission intensity in an energy band above 2.32 eV by at least 550% compared with that before annealing. Jun Hyoung Kim, Tadashi Kawazoe, and Motoichi Ohtsu Copyright © 2015 Jun Hyoung Kim et al. All rights reserved. Realization of Ultraflat Plastic Film Using Dressed-Photon-Phonon-Assisted Selective Etching of Nanoscale Structures Mon, 02 Feb 2015 08:24:00 +0000 We compared dressed-photon-phonon (DPP) etching to conventional photochemical etching and, using a numerical analysis of topographic images of the resultant etched polymethyl methacrylate (PMMA) substrate, we determined that the DPP etching resulted in the selective etching of smaller scale structures in comparison with the conventional photochemical etching. We investigated the wavelength dependence of the PMMA substrate etching using an O2 gas. As the dissociation energy of O2 is 5.12 eV, we applied a continuous-wave (CW) He-Cd laser ( nm, 3.81 eV) for the DPP etching and a 5th-harmonic Nd:YAG laser ( nm, 5.82 eV) for the conventional photochemical etching. From the obtained atomic force microscope images, we confirmed a reduction in surface roughness, , in both cases. However, based on calculations involving the standard deviation of the height difference function, we confirmed that the conventional photochemical etching method etched the larger scale structures only, while the DPP etching process selectively etched the smaller scale features. Takashi Yatsui, Wataru Nomura, and Motoichi Ohtsu Copyright © 2015 Takashi Yatsui et al. All rights reserved. Mass Screening of Vision in the Cinemas and a Maculascope for the Masses: Revival of Haidinger’s Brush Wed, 31 Dec 2014 10:37:50 +0000 Haidinger’s brush, an entoptic phenomenon, is very useful in checking central vision loss and eccentric fixation. Haidinger’s brush is also used to provide vision training for subjects affected by eccentric fixation/lazy eye. We propose the use of Haidinger’s brush for mass self-screening of vision in cinema theatres in one go and at no cost to the subjects. We also suggest a simple projection technology for mass vision screening of subjects in waiting rooms or at shop windows of eye-care practitioners. Finally, we propose a new affordable handheld device for vision training. The test and the devices that we propose would increase public awareness of eye health, improve vision in children, and help prevent blindness in the elderly. Kodikullam V. Avudainayagam and Chitralekha S. Avudainayagam Copyright © 2014 Kodikullam V. Avudainayagam and Chitralekha S. Avudainayagam. All rights reserved. Performance of All-Optical XNOR Gate Based on Two-Photon Absorption in Semiconductor Optical Amplifiers Wed, 31 Dec 2014 08:45:03 +0000 All-optical logic XNOR gate is realized by a series combination of XOR and INVERT gates. This Boolean function is realized by using Mach-Zehnder interferometers (MZIs) and exploiting the nonlinear effect of two-photon absorption (TPA) in semiconductor optical amplifiers (SOAs). The employed model takes into account the impact of amplified spontaneous emission (ASE), input pulse energy, pulsewidth, SOAs carrier lifetime, and linewidth enhancement factor (α-factor) on the gate’s output quality factor (Q-factor). The outcome of this study shows that the all-optical XNOR gate is indeed feasible with the proposed scheme at 250 Gb/s with both logical correctness and acceptable quality. Amer Kotb Copyright © 2014 Amer Kotb. All rights reserved. Optical Biosensor Based on Microbendings Technique: An Optimized Mean to Measure the Bone Strength Wed, 24 Dec 2014 13:52:06 +0000 Osteoporosis, a disease in humans, reduces bone mineral density. The microarchitecture of the bone gets deteriorated with change in variety of proteins in the bone. Therefore, a quantitative assessment of the strength of human bone, considering its structural properties and degradation due to aging, disease, and therapeutic treatment, becomes an integral part of the bioengineering studies. This paper presents a model of fiber optic biosensors (FOBs) which utilizes microbending technique to measure the strength of the bone. In parallel, an artificial neural network (ANN) based test bench has been developed for the optimization of FOBs strain measurement in orthoapplications using MATLAB. The performance accuracy of the given model appears to be considerable in ensuring the detection of the onset of osteoporosis. Preeti Singh and Abhishek Shrivastava Copyright © 2014 Preeti Singh and Abhishek Shrivastava. All rights reserved. Comparative Study of Fiber Bragg Gratings and Fiber Polarimetric Sensors for Structural Health Monitoring of Carbon Composites Tue, 18 Nov 2014 11:37:37 +0000 A comparative study is presented between Bragg grating (FBG) and polarimetric sensors (PS), two of the most promising fiber optic sensing techniques for the structural health monitoring of smart materials based on carbon fiber composites. The paper describes the realization of a test plate equipped with both types of sensors and reports the characterization under static and dynamic conditions, highlighting pros and cons of both technologies. The FBG setup achieves 1.15 ± 0.0016 pm/kg static load response and reproduces dynamic excitation with 0.1% frequency uncertainty; the PS system exhibits a sensitivity of 1.74 ± 0.001 mV/kg and reproduces dynamic excitation with 0.5% frequency uncertainty. It is shown that the PS technology is a good and cheap alternative to FBG for vibration-monitoring of small structures at high frequency. Massimo Olivero, Guido Perrone, Alberto Vallan, and Daniele Tosi Copyright © 2014 Massimo Olivero et al. All rights reserved. Implementation of a Phase Only Spatial Light Modulator as an Atmospheric Turbulence Simulator at 1550 nm Wed, 06 Aug 2014 07:50:27 +0000 Modeling and simulating atmospheric turbulence in a controlled environment have been a focus of interest for scientists for decades. The development of new technologies allows scientists to perform this task in a more realistic and controlled environment and provides powerful tools for the study and better understanding of the propagation of light through a nonstatic medium such as the atmosphere. Free space laser communications (FSLC) and studies in light propagation through the atmosphere are areas which constantly benefit from breakthroughs in technology and in the development of realistic atmospheric turbulence simulators, in particular (Santiago et al. 2011). In this paper, we present the results from the implementation of a phase only spatial light modulator (SLM) as an atmospheric turbulence simulator for light propagation in the short-wave infrared (SWIR) regime. Specifically, we demonstrate its efficacy for its use in an FSLC system, at a wavelength of 1550 nm. Carlos Font, Freddie Santiago, G. Charmaine Gilbreath, David Bonanno, Blerta Bajramaj, Christopher Wilcox, Sergio Restaino, and Scott Mathews Copyright © 2014 Carlos Font et al. All rights reserved. Emission Spectral Control of a Silicon Light Emitting Diode Fabricated by Dressed-Photon-Phonon Assisted Annealing Using a Short Pulse Pair Sun, 06 Jul 2014 10:44:24 +0000 We fabricated a high-efficiency infrared light emitting diode (LED) via dressed-photon-phonon (DPP) assisted annealing of a p-n homojunctioned bulk Si crystal. The center wavelength in the electroluminescence (EL) spectrum of this LED was determined by the wavelength of a CW laser used in the DPP-assisted annealing. We have proposed a novel method of controlling the EL spectral shape by additionally using a pulsed light source in order to control the number of phonons for the DPP-assisted annealing. In this method, the Si crystal is irradiated with a pair of pulses having an arrival time difference between them. The number of coherent phonons created is increased (reduced) by tuning (detuning) this time difference. A Si-LED was subjected to DPP-assisted annealing using a 1.3 μm ( eV) CW laser and a mode-locked pulsed laser with a pulse width of 17 fs. When the number of phonons was increased, the EL emission spectrum broadened toward the high-energy side by 200 meV or more. The broadening towards the low-energy side was reduced to 120 meV. Tadashi Kawazoe, Naoki Wada, and Motoichi Ohtsu Copyright © 2014 Tadashi Kawazoe et al. All rights reserved. A No-Reference Sharpness Metric Based on Structured Ringing for JPEG2000 Images Tue, 24 Jun 2014 12:32:49 +0000 This work presents a no-reference image sharpness metric based on human blur perception for JPEG2000 compressed image. The metric mainly uses a ringing measure. And a blurring measure is used for compensation when the blur is so severe that ringing artifacts are concealed. We used the anisotropic diffusion for the preliminary ringing map and refined it by considering the property of ringing structure. The ringing detection of the proposed metric does not depend on edge detection, which is suitable for high degraded images. The characteristics of the ringing and blurring measures are analyzed and validated theoretically and experimentally. The performance of the proposed metric is tested and compared with that of some existing JPEG2000 sharpness metrics on three widely used databases. The experimental results show that the proposed metric is accurate and reliable in predicting the sharpness of JPEG2000 images. Zhipeng Cao, Zhenzhong Wei, and Guangjun Zhang Copyright © 2014 Zhipeng Cao et al. All rights reserved. Implementation of a One-LLID-per-Queue DBA Algorithm in EPON Sun, 25 May 2014 06:11:36 +0000 The advantages of Ethernet passive optical network (EPON) are setting it to be a natural ubiquitous solution for the access network. In the upstream direction of EPON, the directional property of the splitter requires that the traffic flow be mitigated to avoid collision. A dynamic bandwidth allocation (DBA) scheme is desirable in optimizing the bandwidth usage further. In this paper, a global priority DBA mechanism is discussed. The mechanism aims to reduce the overall delay while enhancing the throughput and fairness. This study was conducted using MATLAB where it was compared to two other algorithms in the literature. The results show that the delay is reduced up to 59% and the throughput and fairness index are improved up to 10% and 6%, respectively. N. A. M. Radzi, N. M. Din, M. H. Al-Mansoori, and H. Zainol Abidin Copyright © 2014 N. A. M. Radzi et al. All rights reserved. Band Structure Engineering in 2D Photonic Crystal Waveguide with Rhombic Cross-Section Elements Mon, 12 May 2014 10:16:57 +0000 Two-dimensional photonic crystal (2D PhC) waveguides with square lattice composed of dielectric rhombic cross-section elements in air background, by using plane wave expansion (PWE) method, are investigated. In order to study the change of photonic band gap (PBG) by changing of elongation of elements, the band structure of the used structure is plotted. We observe that the size of the PBG changes by variation of elongation of elements, but there is no any change in the magnitude of defect modes. However, the used structure does not have any TE defect modes but it has TM defect mode for any angle of elongation. So, the used structure can be used as optical polarizer. Abdolrasoul Gharaati and Sayed Hasan Zahraei Copyright © 2014 Abdolrasoul Gharaati and Sayed Hasan Zahraei. All rights reserved. Demonstration of Controlling the Spatiotemporal Dynamics of Optical Near-Field Excitation Transfer in Y-Junction Structure Consisting of Randomly Distributed Quantum Dots Sun, 27 Apr 2014 07:25:46 +0000 Solution searching devices that operate on the basis of controlling the spatiotemporal dynamics of excitation transfer via dressed photon interactions between quantum dots have been proposed. Long-range excitation transfer based on dressed photon interactions between randomly distributed quantum dots is considered to be effective in realizing such devices. Here, we successfully controlled the spatiotemporal dynamics of excitation transfer using a Y-junction structure consisting of randomly dispersed CdSe/ZnS core-shell quantum dots. This Y-junction structure has two “output ends” and one “tap end.” By exciting one output end with control light, we observed increased excitation transfer to the other output end via a state-filling effect. Conversely, we observed reduced excitation transfer to the output ends by irradiating the tap end with control light, due to excitation of defect levels in the tap end. These results show the possibility of controlling the optical excitation transfer dynamics between multiple quantum dots. Wataru Nomura, Makoto Naruse, Masashi Aono, Song-Ju Kim, Tadashi Kawazoe, Takashi Yatsui, and Motoichi Ohtsu Copyright © 2014 Wataru Nomura et al. All rights reserved. Tunability of Triangular SRR and Wire Strip (TSRR-WS) Metamaterial at THz Sun, 27 Apr 2014 00:00:00 +0000 This paper adumbrates a novel tunable metamaterial consisting of triangular split ring resonator (TSRR) and wire strip (WS) at THz frequency. Ansoft high frequency structure simulator (HFSS) has been used to design and analyse the metamaterial having Rogers RT/duroid 5870 (  =  2.33) and FR4 (  =  4.4) as substrate material. Nicolson Ross Weir (NRW) method has been used to retrieve the material parameters from transmission and reflection coefficient. 4% maximization has been obtained in the location of the negative region (or resonance frequency for permeability) by using FR4 with 0.75 μm instead of 1.25 μm as substrate thickness. In addition, 18% minimization has been achieved by using FR4 with 0.25 μm instead of RT/duroid 5870 substrate with the same thickness. Tunability has been proved by showing dependence of resonant frequency over the substrate thickness and substrate material. Parul Dawar and Asok De Copyright © 2014 Parul Dawar and Asok De. All rights reserved. A Potential Candidate for Lamp Phosphor: Eu3+ Activated K2Y2B2O7 Thu, 10 Apr 2014 17:53:07 +0000 The novel phosphor K2Y2B2O7 doped with europium is studied for its photoluminescence properties. The studies show that the phosphor gives strong red emission (PL) at 613 nm related to 5D0-7F2 transition of Eu3+ under the 260 nm excitation (PLE) related to the charge transfer (CT) from the 2p orbital of the O2− ions to the 4f orbital of Eu3+ ions with CIE coordinates (; ). The results of PL and PLE spectra indicate the applicability of K2Y2B2O7:Eu as a red component in lamp phosphor. The phosphor is characterized through XRD pattern analysis, and morphology is explained on the basis of SEM image. Optimum concentration of Eu3+ required for the highest intensity of emission is also studied. K. A. Koparkar, N. S. Bajaj, and S. K. Omanwar Copyright © 2014 K. A. Koparkar et al. All rights reserved. Electromagnetic Imaging of Two-Dimensional Geometries by Multipulse Interference Using the Inverse FDTD Method Mon, 31 Mar 2014 00:00:00 +0000 The size, shape, and location of unknown objects in the ground and in the body can be estimated by an electromagnetic imaging technique. An imaging approach to clear detection of two-dimensional geometries is proposed in this paper. Based on the inverse finite-difference time-domain (FDTD) method, a phase interference technique using multidirectional pulses is employed. The advantage of the proposed method is that it can clearly reconstruct the geometry in a simple calculation. Sample imaging results are demonstrated. The analysis of the FDTD results shows that the detectable object size is limited by the incident wavelength and the measurement spacing and illustrates the detectability of multiple objects. Naoki Okada and James B. Cole Copyright © 2014 Naoki Okada and James B. Cole. All rights reserved. Role of Density Profiles for the Nonlinear Propagation of Intense Laser Beam through Plasma Channel Sun, 23 Mar 2014 14:01:59 +0000 In this work role of density profiles for the nonlinear propagation of intense laser beam through plasma channel is analyzed. By employing the expression for the dielectric function of different density profile plasma, a differential equation for beamwidth parameter is derived under WKB and paraxial approximation. The laser induces modifications of the dielectric function through nonlinearities. It is found that density profiles play vital role in laser-plasma interaction studies. To have numerical appreciation of the results the propagation equation for plasma is solved using the fourth order Runge-Kutta method for the initial plane wave front of the beam, using boundary conditions. The spot size of the laser beam decreases as the beam penetrates into the plasma and significantly adds self-focusing in plasma. This causes the laser beam to become more focused by reduction of diffraction effect, which is an important phenomenon in inertial confinement fusion and also for the understanding of self-focusing of laser pulses. Numerical computations are presented and discussed in the form of graphs for typical parameters of laser-plasma interaction. Sonu Sen, Meenu Asthana Varshney, and Dinesh Varshney Copyright © 2014 Sonu Sen et al. All rights reserved. All-Optical Logic Gates: Designs, Classification, and Comparison Wed, 19 Mar 2014 16:45:39 +0000 The paper reviews the current status and designs of all-optical gates. Various schemes with and without semiconductor optical amplifiers are discussed and compared. The optical gates are classified according to their design structures. It is divided into two major divisions that is, nonsemiconductor optical amplifier based gates and semiconductor optical amplifier based gates. In nonsemiconductor optical amplifier based gates, different schemes have been proposed to create non-linearity which is discussed. The semiconductor optical amplifier based gates of different design structures are discussed to show the probe pulse that is modulated in different ways to obtain results. Pallavi Singh, Devendra Kr. Tripathi, Shikha Jaiswal, and H. K. Dixit Copyright © 2014 Pallavi Singh et al. All rights reserved. Dynamic Range Analysis of the Phase Generated Carrier Demodulation Technique Mon, 17 Mar 2014 08:15:28 +0000 The dependence of the dynamic range of the phase generated carrier (PGC) technique on low-pass filters passbands is investigated using a simulation model. A nonlinear character of this dependence, which could lead to dynamic range limitations or measurement uncertainty, is presented for the first time. A detailed theoretical analysis is provided to verify the simulation results and these results are consistent with performed calculations. The method for the calculation of low-pass filters passbands according to the required dynamic range upper limit is proposed. M. J. Plotnikov, A. V. Kulikov, V. E. Strigalev, and I. K. Meshkovsky Copyright © 2014 M. J. Plotnikov et al. All rights reserved. Optical Response to Submicron Digital Elements Simulated by FDTD Wavelets with Refractive Impulse Tue, 04 Mar 2014 16:23:56 +0000 Accurate simulation from digital, submicron, optical elements is obtained by finite difference time domain (FDTD) results that are phase analyzed as sources for Huygens wavelets on fine scales much shorter than the wavelength used. Results, from the MIT electromagnetic evaluation program, are renormalized by a method here called “refractive impulse.” This is valid for polarized responses from digital diffractive and focusing optics. The method is employed with plane wave incidence at any angle or with diverging or converging beams. It is more systematic, more versatile, and more accurate than commercial substitutes. Antony J. Bourdillon Copyright © 2014 Antony J. Bourdillon. All rights reserved. Low-Frequency Raman Spectroscopic Monitoring of Supramolecular Structure in H-Bonded Liquids Tue, 04 Mar 2014 09:57:56 +0000 Effective density of vibrational states in H-bonded liquids was measured by Raman scattering method. Actuality of a low-frequency part of the spectrum of the intermediate (fracton) region, which obeys a power law, indicates the correct application of the percolation model. The dependence of exponent on binary solutions concentration has been studied. Existence of correlation of the fractal structure parameter and dynamic viscosity has been noted. Nataliia Kuzkova, Andrey Yakunov, and Mykola Bilyi Copyright © 2014 Nataliia Kuzkova et al. All rights reserved. Polarization Division Multiplexing of OFDM Radio-over-Fiber Signals in Passive Optical Networks Thu, 27 Feb 2014 14:16:17 +0000 This paper describes the state-of-the-art of polarization multiplexing for optical networks transmission. The use of polarization division multiplexing (PDM) permits to multiply the user capacity and increase the spectral efficiency. Combining PDM and orthogonal frequency division multiplexed (OFDM) modulation allows maximizing the optical transmission capacity. The experimental demonstration of transmitting OFDM signals following ECMA-368 ultrawide band (UWB) standard in radio-over-fiber using PDM in passive optical networks is herein reported. The impact of cross-polarization and cochannel crosstalk is evaluated experimentally in a three-user OFDM-UWB subcarrier multiplexed (SCM) configuration per polarization. Each SCM uses up to three OFDM-UWB channels of 200 Mbit/s each, achieving an aggregated bitrate of 1.2 Gbit/s with 0.76 bit/s/Hz spectral efficiency when using PDM transmission. The experimental results for the polarization-multiplexed SCM indicate that a 4 dB additional polarization crosstalk interference can be expected compared to a nonpolarization-multiplexed transmission system which translates to 2.4 dB EVM penalty in the UWB signals. The successful PDM transmission of SCM multiuser OFDM-UWB over a passive optical network of 25 km standard-single mode fiber (SSMF) reach is demonstrated. Maria Morant, Joaquin Pérez, and Roberto Llorente Copyright © 2014 Maria Morant et al. All rights reserved. Properties of the Band Gaps in 1D Ternary Lossy Photonic Crystal Containing Double-Negative Materials Thu, 13 Feb 2014 11:11:50 +0000 Theoretically, the characteristics matrix method is employed to investigate and compare the properties of the band gaps of the one-dimensional ternary and binary lossy photonic crystals which are composed of double-negative and double-positive materials. This study shows that by varying the angle of incidence, the band gaps for TM and TE waves behave differently in both ternary and binary lossy structures. The results demonstrate that, by increasing the angle of incidence for the TE wave, the width and the depth of zero-, zero-, and Bragg gap increase in both ternary and binary structures. On the other hand, the enhancement of the angle of incidence for the TM wave contributes to reduction of the width and the depth of the zero- and Bragg gaps, and they finally disappear for incidence angles greater than 50° and 60° for the binary structure and 40° and 45° for the ternary structures, respectively. In addition, the details of the edges of the band gaps variations as a function of incidence angle for both structures are studied. Alireza Aghajamali, Maryam Akbarimoosavi, and Mahmood Barati Copyright © 2014 Alireza Aghajamali et al. All rights reserved. Total Internal Reflection-Based High Efficiency Grating Design for a Metal-Free Polarizing Filter Applications Using Hybrid Optimization Procedure Mon, 10 Feb 2014 15:55:45 +0000 This paper presents a fast and rigorous design method for grating-based metal-free polarizing filter applications using two-step hybrid optimization techniques. Grating structures utilizing the total internal reflection in a lamellar configuration were used to achieve metal-free solution, which is a key technology in the chirped pulse amplification for high power laser system. Here two polarizing filters were designed: polarization sensitive and polarization insensitive. Those polarization performances were characterized by the rigorous coupled-wave analysis (RCWA), and the design parameters of grating structures, pitch, depth, and filling factor were optimized by two-step hybrid optimization procedure because the diffraction characteristics of grating-based polarizing filters are highly sensitive to small changes in design parameters. The Taguchi method is incorporated into selection process in the genetic algorithm, which indicates that the Taguchi method optimizes the design parameters in a coarse manner, and then, coarsely optimized parameters are finely optimized using the genetic algorithm. Therefore the proposed method could solve global numerical optimization problems with continuous variables. The proposed two-step hybrid optimization algorithm could effectively optimize the grating structures for the purpose of polarization filter applications, and the optimized grating structures could selectively filter the incident light up to 99.8% as to TE or TM waves. ChaBum Lee Copyright © 2014 ChaBum Lee. All rights reserved. Application of the Expansion Method in Ultrashort Pulses in Nonlinear Optical Fibers Wed, 11 Dec 2013 10:07:34 +0000 With the increasing input power in optical fibers, the dispersion problem is becoming a severe restriction on wavelength division multiplexing (WDM). With the aid of solitons, in which the shape and speed can remain constant during propagation, it is expected that the transmission of nonlinear ultrashort pulses in optical fibers can effectively control the dispersion. The propagation of a nonlinear ultrashort laser pulse in an optical fiber, which fits the high-order nonlinear Schrödinger equation (NLSE), has been solved using the expansion method. Group velocity dispersion, self-phase modulation, the fourth-order dispersion, and the fifth-order nonlinearity of the high-order NLSE were taken into consideration. A series of solutions has been obtained such as the solitary wave solutions of kink, inverse kink, the tangent trigonometric function, and the cotangent trigonometric function. The results have shown that the expansion method is an effective way to obtain the exact solutions for the high-order NLSE, and it provides a theoretical basis for the transmission of ultrashort pulses in nonlinear optical fibers. Jiang Xing-Fang, Wang Jun, Wei Jian-Ping, and Hua Ping Copyright © 2013 Jiang Xing-Fang et al. All rights reserved. Neural Network Modeling for Prediction of Weld Bead Geometry in Laser Microwelding Mon, 09 Dec 2013 16:40:31 +0000 Laser microwelding has been an essential tool with a reputation of rapidity and precision for joining miniaturized metal parts. In industrial applications, an accurate prediction of weld bead geometry is required in automation systems to enhance productivity of laser microwelding. The present work was conducted to establish an intelligent algorithm to build a simplified relationship between process parameters and weld bead geometry that can be easily used to predict the weld bead geometry with a wide range of process parameters through an artificial neural network (ANN) in laser microwelding of thin steel sheet. The backpropagation with the Levenberg-Marquardt training algorithm was used to train the neural network model. The accuracy of neural network model has been tested by comparing the simulated data with actual data from the laser microwelding experiments. The predictions of the neural network model showed excellent agreement with the experimental results, indicating that the neural network model is a viable means for predicting weld bead geometry. Furthermore, a comparison was made between the neural network and mathematical model. It was found that the developed neural network model has better prediction capability compared to the regression analysis model. Mohd Idris Shah Ismail, Yasuhiro Okamoto, and Akira Okada Copyright © 2013 Mohd Idris Shah Ismail et al. All rights reserved. Photonic Processing for Wideband Cancellation and Spectral Discrimination of RF Signals Thu, 05 Dec 2013 09:59:39 +0000 Photonic signal processing is used to implement common mode signal cancellation across a very wide bandwidth utilising phase modulation of radio frequency (RF) signals onto a narrow linewidth laser carrier. RF spectra were observed using narrow-band, tunable optical filtering using a scanning Fabry Perot etalon. Thus functions conventionally performed using digital signal processing techniques in the electronic domain have been replaced by analog techniques in the photonic domain. This technique was able to observe simultaneous cancellation of signals across a bandwidth of 1400 MHz, limited only by the free spectral range of the etalon. David M. Benton Copyright © 2013 David M. Benton. All rights reserved. Minimizing the Bright/Shadow Focal Spot Size with Controlled Side-Lobe Increase in High-Numerical-Aperture Focusing Systems Wed, 20 Nov 2013 14:29:10 +0000 Minimizing the bright/shadow focal spot size for differently polarized incident waves through the additional apodization of the focusing system output pupil by use of an optical element with the vortex phase dependence on angle and the polynomial amplitude dependence on radius is studied. The coefficients of the radial polynomial were optimized with the aim of fulfilling certain conditions such as the energy efficiency preservation and keeping the side lobes under control. The coefficients were chosen so as to minimize the functional using Brent’s method. S. N. Khonina and S. G. Volotovskiy Copyright © 2013 S. N. Khonina and S. G. Volotovskiy. All rights reserved.