Advances in OptoElectronics http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Preparation of Compensation Ions Codoped SrTiO3:Pr3+ Red Phosphor with the Sol-Gel Method and Study of Its Luminescence Enhancement Mechanism Sun, 14 Dec 2014 07:22:32 +0000 http://www.hindawi.com/journals/aoe/2014/674780/ SrTiO3:Pr3+ is the most representative titanate matrix red phosphor for field emission display (FED). The red luminous efficiency of SrTiO3:Pr3+ will be greatly improved after the compensation ions codoping, so SrTiO3:Pr3+ red phosphor has been a research focus at home and abroad. SrTiO3:Pr3+, SrTiO3:Pr3+, Mg2+, and SrTiO3:Pr3+, Al3+ phosphors are synthesized by a new sol-gel method. Crystal structure, spectral characteristics, and luminescence enhancement mechanism of the sample were studied by XRD and PL spectra. The results showed that after co-doped, SrTiO3:Pr3+ phosphor is single SrTiO3 cubic phase, the main emission front is located at 614 nm, corresponding to Pr3+ ions 1D23H4 transition emission. SrTiO3:Pr3+, Mg2+ and SrTiO3:Pr3+, Al3+ phosphor luminescence intensity is enhanced, but the main luminescence mechanism is not changed. Acceptor impurity = Mg2+, Al3+ will replace Ti bit after being doped into the crystal lattice to form charge compensation corresponding defect centers to reduce the demand of Sr2+ or Ti3+ vacancy. While Sr-doped Pr will make lattice distortion and transition energy of 4f-5d is very sensitive to crystal electric field changes around Pr atom. Doping different impurities will make electric field distribution around the icon have a different change. It increases energy transfer of 4f-5d transition and improves the luminous intensity of SrTiO3:Pr3+ red phosphor. Dan Guo, Xiaodong Zhang, and Jiangni Yun Copyright © 2014 Dan Guo et al. All rights reserved. Combination of Transverse Mode Selection and Active Longitudinal Mode-Locking of Broad Area Semiconductor Lasers Sun, 13 Jul 2014 00:00:00 +0000 http://www.hindawi.com/journals/aoe/2014/293590/ Experimental results of the combination of transverse mode selection and active mode-locking with anti-reflection-coated broad area lasers (BALs) are presented. The BALs are subject to feedback from a free-space external Fourier-optical 4-setup with a reflective spatial frequency filter in the Fourier-plane for transverse mode selection. Driving the BALs with a high frequency modulated pump current above threshold active longitudinal mode-locking is achieved. Pulse durations as low as 88 ps are obtained, while the Gaussian-like fundamental or a higher order transverse mode up to mode number 5 is selected on purpose. Pulse duration and shape are nearly independent of the selected transverse mode. Christoph Doering and Henning Fouckhardt Copyright © 2014 Christoph Doering and Henning Fouckhardt. All rights reserved. Signal Processing Algorithms for Down-Stream Traffic in Next Generation 10 Gbit/s Fixed-Grid Passive Optical Networks Sun, 22 Jun 2014 06:25:42 +0000 http://www.hindawi.com/journals/aoe/2014/296781/ We have analyzed the impact of digital and optical signal processing algorithms, that is, Volterra equalization (VE), digital backpropagation (BP), and optical phase conjugation with nonlinearity module (OPC-NM), in next generation 10 Gbit/s (also referred to as XG) DP-QPSK long haul WDM (fixed-grid) passive optical network (PON) without midspan repeaters over 120 km standard single mode fiber (SMF) link for downstream signals. Due to the compensation of optical Kerr effects, the sensitivity penalty is improved by 2 dB by implementing BP algorithm, 1.5 dB by VE algorithm, and 2.69 dB by OPC-NM. Moreover, with the implementation of NL equalization technique, we are able to get the transmission distance of 126.6 km SMF for the 1 : 1024 split ratio at 5 GHz channel spacing in the nonlinear region. Rameez Asif, Rabeea Basir, and Ramshah Ahmad Copyright © 2014 Rameez Asif et al. All rights reserved. Highly Nonlinear and Birefringent Spiral Photonic Crystal Fiber Wed, 11 Jun 2014 12:21:07 +0000 http://www.hindawi.com/journals/aoe/2014/464391/ We propose and design a spiral photonic crystal fiber with elliptical air holes for achieving high birefringence, large nonlinearity, and negative dispersion. The structure is designed using chalcogenide glass (As2S3) for different ellipticity ratios of air holes in the cladding and the effect on various properties is observed. The proposed structure has birefringence of the order 10−2, nonlinearity of 26739.42 W−1 m−1, and dispersion of −1136.69 at 0.85 μm. An accurate numerical approach based on finite element method is used for the design and simulation of the structure. Due to high birefringence and negative dispersion, the proposed structure can be used for polarization control and dispersion compensation, respectively. S. Revathi, Srinivasa Rao Inbathini, and Rizwan Ali Saifudeen Copyright © 2014 S. Revathi et al. All rights reserved. The CdS/CdSe/ZnS Photoanode Cosensitized Solar Cells Basedon Pt, CuS, Cu2S, and PbS Counter Electrodes Thu, 27 Feb 2014 11:06:56 +0000 http://www.hindawi.com/journals/aoe/2014/397681/ Highly ordered mesoporous TiO2 modified by CdS, CdSe, and ZnS quantum dots (QDs) was fabricated by successive ionic layer adsorption and reaction (SILAR) method. The quantity of material deposition seems to be affected not only by the employed deposition method but also and mainly by the nature of the underlying layer. The CdS, CdSe, and ZnS QDs modification expands the photoresponse range of mesoporous TiO2 from ultraviolet region to visible range, as confirmed by UV-Vis spectrum. Optimized anode electrodes led to solar cells producing high current densities. Pt, CuS, PbS, and Cu2S have been used as electrocatalysts on counter electrodes. The maximum solar conversion efficiency reached in this work was 1.52% and was obtained by using Pt electrocatalyst. CuS, PbS, and Cu2S gave high currents and this was in line with the low charge transfer resistances recorded in their case. Tung Ha Thanh, Dat Huynh Thanh, and Vinh Quang Lam Copyright © 2014 Tung Ha Thanh et al. All rights reserved. Design and Optimization of Polarization Splitting and Rotating Devices in Silicon-on-Insulator Technology Thu, 06 Feb 2014 09:25:09 +0000 http://www.hindawi.com/journals/aoe/2014/490405/ We review polarization splitting and rotating photonic devices based on silicon-on-insulator technology platform, focusing on their performance and design criteria. In addition, we present a theoretical investigation and optimization of some rotator and splitter architectures to be employed for polarization diversity circuits. In this context, fabrication tolerances and their influences on device performance are theoretically estimated by rigorous simulations too. Benedetto Troia, Francesco De Leonardis, Mauro Lanzafame, Tommaso Muciaccia, Giuseppe Grasso, Giovanni Giannoccaro, Carlo Edoardo Campanella, and Vittorio M. N. Passaro Copyright © 2014 Benedetto Troia et al. All rights reserved. Burn-In Aging Behavior and Analytical Modeling of Wavelength-Division Multiplexing Semiconductor Lasers: Is the Swift Burn-In Feasible for Long-Term Reliability Assurance? Sun, 08 Dec 2013 09:46:16 +0000 http://www.hindawi.com/journals/aoe/2013/568945/ Effective and economical burn-in screening is important for technology development and manufacture of semiconductor lasers. We study the burn-in degradation behavior of wavelength-division multiplexing semiconductor lasers to determine the feasibility of short burn-in. The burn-in is characterized by the sublinear model and correlated with long-term reliability. Jia-Sheng Huang Copyright © 2013 Jia-Sheng Huang. All rights reserved. A Comprehensive Analysis of Plasmonics-Based GaAs MSM-Photodetector for High Bandwidth-Product Responsivity Tue, 24 Sep 2013 11:15:18 +0000 http://www.hindawi.com/journals/aoe/2013/793253/ A detailed numerical study of subwavelength nanogratings behavior to enhance the light absorption characteristics in plasmonic-based metal-semiconductor-metal photodetectors (MSM-PDs) is performed by implementation of 2D finite-difference time-domain (FDTD) algorithm. Due to the structure design and changes in the device physical parameters, various devices with different geometries are simulated and compared. Parameters like nano-grating height and duty cycle (DC) are optimized for rectangular and taper subwavelength metal nanogratings on GaAs substrate and their impact on light absorption below the diffraction limits are confirmed. The calculated light enhancement is ~32.7-times for an optimized device in comparison with a conventional MSM-PD. This enhancement is attributed to the plasmonic effects in the near-field region. Narottam Das, Farzaneh Fadakar Masouleh, and Hamid Reza Mashayekhi Copyright © 2013 Narottam Das et al. All rights reserved. Electronically Tunable Wide Band Optical Delay Line Based on InGaAs Quantum Well Microresonators Sun, 08 Sep 2013 08:44:20 +0000 http://www.hindawi.com/journals/aoe/2013/930369/ A novel electronically tunable optical delay line based on InGaAs quantum well microresonators is proposed for high frequency RF transmission. The device utilizes the charge-controlled blue shift of the absorption edge in InGaAs quantum wells to change the effective refractive indices of the resonators and couplers, therefore, provides an efficient way to produce variable time delay. A theoretical model based on measurements is used to analyze the device performance. Simulation results for five 3 × 27 μm2 cascaded resonators with bias voltages <0.7 V show a continuous tuning range of 7~68 ps, a ripple delay <1.5 ps, and a useable bandwidth of 39.3 GHz. Yan Zhang and Geoff W. Taylor Copyright © 2013 Yan Zhang and Geoff W. Taylor. All rights reserved. Initial Antinoise Performance Analysis of Pupil Phase Diversity Based on Genetic Algorithm Mon, 02 Sep 2013 11:25:28 +0000 http://www.hindawi.com/journals/aoe/2013/721420/ Pupil phase diversity (PPD) wavefront sensor is a new kind of phase-visualization methods, and the output signal of PPD represents the input pupil phase and shows a 1-1 mapping between the position of the wavefront error in the pupil and its position in the output signal. High-precisely wavefront measuring can be obtained under no noise by using appropriate phase restoration algorithm while performance of PPD under noise is unknown. We analyzed antinoise performance of PPD based on genetic algorithm (GA) through measuring the distorted wavefront under different noise level. Simulation results show that wavefront measuring is almost not affected by the existence of noise, which indicates that PPD based on GA can be used in applications with noise. Huizhen Yang and Yaoqiu Li Copyright © 2013 Huizhen Yang and Yaoqiu Li. All rights reserved. Design and Investigation of SST/nc-Si:H/M (M = Ag, Au, Ni) and M/nc-Si:H/M Multifunctional Devices Wed, 07 Aug 2013 13:58:36 +0000 http://www.hindawi.com/journals/aoe/2013/807542/ Hydrogenated nanocrystalline Silicon thin films prepared by the very high frequency chemical vapor deposition technique (VHF-CVD) on stainless steel (SST) substrates are used to design Schottky point contact barriers for the purpose of solar energy conversion and passive electronic component applications. In this process, the contact performance between SST and M (M = Ag, Au, and Ni) and between Ag, Au, and Ni electrodes was characterized by means of current-voltage, capacitance-voltage, and light intensity dependence of short circuit () current and open circuit voltage () of the contacts. Particularly, the devices ideality factors, barrier heights were evaluated by the Schottky method and compared to the Cheung's. Best Schottky device performance with lowest ideality factor suitable for electronic applications was observed in the SST/nc-Si:H/Ag structure. This device reflects a of 229 mV with an of 1.6 mA/cm2 under an illumination intensity of ~40 klux. On the other hand, the highest being 9.0 mA/cm2 and the of 53.1 mV were observed for Ni/nc-Si:H/Au structure. As these voltages represent the maximum biasing voltage for some of the designed devices, the SST/nc-Si:H/M and M/nc-Si:H/M can be regarded as multifunctional self-energy that provided electronic devices suitable for active or passive applications. A. F. Qasrawi, Salam M. Kmail, Samah F. Assaf, and Z. M. Saleh Copyright © 2013 A. F. Qasrawi et al. All rights reserved. Multiband Negative Permittivity Metamaterials and Absorbers Sun, 28 Jul 2013 08:19:43 +0000 http://www.hindawi.com/journals/aoe/2013/269170/ Design and characteristics of multiband negative permittivity metamaterial and its absorber configuration are presented in this paper. The proposed multiband metamaterial is composed of a novel multibranch resonator which can possess four electric resonance frequencies. It is shown that, by controlling the length of the main branches of such resonator, the resonant frequencies and corresponding absorbing bands of metamaterial absorber can be shifted in a large frequency band. Yiran Tian, Guangjun Wen, and Yongjun Huang Copyright © 2013 Yiran Tian et al. All rights reserved. A Viable Passive Optical Network Design for Ultrahigh Definition TV Distribution Thu, 16 May 2013 12:17:35 +0000 http://www.hindawi.com/journals/aoe/2013/219271/ International Telecommunication Union (ITU) has recently standardized ultrahigh definition television (UHD-TV) with a resolution 16 times more than the current high definition TV. An increase in the efficiency of video source coding or in the capacity of transmission channels will be needed to deliver such programs by passive optical network (PON). In this paper, a high capacity integrated PON infrastructure is proposed to overlay ultrahigh definition television by a complete passive coexistence of 10G-PON (XG-PON) and single carrier directly modulated, duo-binary 40G-PON (XLG-PON) signal. The simulation results show error-free transmission performance and further distribution to 32 optical network units (ONUs) on broadcast basis with negligible power penalty over 20 km of bidirectional standard single mode fiber. Shahab Ahmad Niazi, Xiaoguang Zhang, Lixia Xi, Abid Munir, Muhammad Idrees, and Yousaf Khan Copyright © 2013 Shahab Ahmad Niazi et al. All rights reserved. Preparation of Organic Zn-Phthalocyanine-Based Semiconducting Materials and Their Optical and Electrochemical Characterization Thu, 02 May 2013 10:05:06 +0000 http://www.hindawi.com/journals/aoe/2013/321563/ In order to increase the species of organic semiconductors, new Zn-phthalocyanines-based organic materials were synthesized and characterized. The new compounds have been characterized by 1H and 13C using NMR, FTIR, and UV-Vis. The absorption, fluorescence, and electrochemical properties were also studied. Green photoluminescence was observed in dilute solutions. In solid thin films, π-π* interactions influenced the optical properties, and redshifted photoluminescence spectra were obtained; red emissions for ZnPAL (647 nm) and ZnPTr (655 nm) were found. By cyclic voltammetry, the electrochemical band gap was estimated to be 1.94 and 1.17 eV for ZnPAl and ZnPTr, respectively. Single-layer diode devices of an indium tin oxide/Zn-phthalocyanine/aluminum configuration were fabricated and showed relatively low turn-on voltages (3.3 V for ZnPAl and 3 V for ZnPTr). Amira Hajri, Sarra Touaiti, and Bassem Jamoussi Copyright © 2013 Amira Hajri et al. All rights reserved. Germanium Doping to Improve Carrier Mobility in CdO Films Wed, 03 Apr 2013 11:32:09 +0000 http://www.hindawi.com/journals/aoe/2013/804646/ This investigation addresses the structural, optical, and electrical properties of germanium incorporated cadmium oxide (CdO : Ge) thin films. The focus was on the improvement in carrier mobility to achieve high transparency for near-infrared light and low resistivity at the same time. The properties were studied using X-ray diffraction, SEM, spectral photometry, and Hall measurements. All CdO : Ge films were polycrystalline with high texture orientation along [111] direction. It was observed that it is possible to control the carrier concentration () and mobility () with Ge-incorporation level. The mobility could be improved to a highest value of  cm2/V·s with Ge doping of 0.25 wt% while maintaining the electrical resistivity as low as  Ω·cm and good transparency % in the NIR spectral region. The results of the present work proved to select Ge as dopant to achieve high carrier mobility with low resistivity for application in transparent conducting oxide (TCO) field. Generally, the properties found make CdO : Ge films particularly interesting for the application in optoelectronic devices like thin-film solar cells. A. A. Dakhel Copyright © 2013 A. A. Dakhel. All rights reserved. The Effect of Electron versus Hole Photocurrent on Optoelectric Properties of Wz-GaN Reach-Through Avalanche Photodiodes Mon, 25 Mar 2013 08:56:58 +0000 http://www.hindawi.com/journals/aoe/2013/840931/ The authors have made an attempt to investigate the effect of electron versus hole photocurrent on the optoelectric properties of structured Wurtzite-GaN (Wz-GaN) reach-through avalanche photodiodes (RAPDs). The photo responsivity and optical gain of the devices are obtained within the wavelength range of 300 to 450 nm using a novel modeling and simulation technique developed by the authors. Two optical illumination configurations of the device such as Top Mounted (TM) and Flip Chip (FC) are considered for the present study to investigate the optoelectric performance of the device separately due to electron dominated and hole dominated photocurrents, respectively, in the visible-blind ultraviolet (UV) spectrum. The results show that the peak unity gain responsivity and corresponding optical gain of the device are 555.78 mA W−1 and , respectively, due to hole dominated photocurrent (i.e., in FC structure); while those are 480.56 mA W−1 and , respectively, due to electron dominated photocurrent (i.e., in TM structure) at the wavelength of 365 nm and for applied reverse bias of 85 V. Thus, better optoelectric performance of Wz-GaN RAPDs can be achieved when the photocurrent is made hole dominated by allowing the UV light to be shined on the -layer instead of -layer of the device. Moumita Ghosh, Mangolika Mondal, and Aritra Acharyya Copyright © 2013 Moumita Ghosh et al. All rights reserved. Important Effect of Defect Parameters on the Characteristics of Thue-Morse Photonic Crystal Filters Thu, 21 Mar 2013 13:46:02 +0000 http://www.hindawi.com/journals/aoe/2013/856148/ Design and characterization of optical filters based on photonic crystal Thue-Morse structures are theoretically examined using transfer matrix method. It is shown that by introducing defect layer in the original structure of the proposed filter, main characteristics of it are changed. The main advantage of this defect in Thue-Morse structure is its capability for DWDM communication applications. In other words, achievement of DWDM filter through the Thue-Morse photonic crystal structure is much easier. The desired wavelengths can be achieved by changing the defect parameter. High efficiency of the proposed filter is one of its benefits. The transmission efficiency of this structure is about 96% and the quality factor is more than 77000. Hamed Alipour-Banaei, Farhad Mehdizadeh, and Mahdi Hassangholizadeh-Kashtiban Copyright © 2013 Hamed Alipour-Banaei et al. All rights reserved. Quantum-Dot Semiconductor Optical Amplifiers: State Space Model versus Rate Equation Model Thu, 07 Mar 2013 13:57:49 +0000 http://www.hindawi.com/journals/aoe/2013/831852/ A simple and accurate dynamic model for QD-SOAs is proposed. The proposed model is based on the state space theory, where by eliminating the distance dependence of the rate equation model of the QD-SOA; we derive a state space model for the device. A comparison is made between the rate equation model and the state space model under both steady state and transient regimes. Simulation results demonstrate that the derived state space model not only is much simpler and faster than the rate equation model, but also it is as accurate as the rate equation model. Hussein Taleb, Kambiz Abedi, and Saeed Golmohammadi Copyright © 2013 Hussein Taleb et al. All rights reserved. Applications of Fianite in Electronics Wed, 19 Dec 2012 13:29:38 +0000 http://www.hindawi.com/journals/aoe/2012/907560/ Fianite or yttrium stabilized zirconia (YSZ) solid solutions single crystals were known worldwide as jewelry material. The review is devoted to novel applications of the material in the field of microelectronics. A number of modern aspects of the application of fianite in micro-, opto- and SHF-electronics were analyzed in this paper. It was demonstrated that fianite is an extremely promising multipurpose material for new electronic technologies due to unique combination of physical and chemical properties. As a substrate and buffer layer for the epitaxy of Si, Ge, GeSi and AIIIBV compounds (GaAs, InGaAs, GaSb, InAs, GaN, AlN), fianite has a number of advantages over the other dielectric materials. The use of fianite (as well as ZrO2 and HfO2 oxides) instead of SiO2 as gate dielectrics in CMOC technology seems to be of peculiar interest. The unique properties of fianite as protecting, stabilizing and antireflecting coatings in electronics and optoelectronic devices have been outlined. A comparative study of the performance characteristics of fianite and conventional materials has been carried out. Alexander N. Buzynin, Yury N. Buzynin, and Vitaly A. Panov Copyright © 2012 Alexander N. Buzynin et al. All rights reserved. Modern Trends in Metamaterial Applications Mon, 10 Dec 2012 10:01:29 +0000 http://www.hindawi.com/journals/aoe/2012/514270/ Ivan D. Rukhlenko, Pavel A. Belov, Natalia M. Litchinitser, and Alexandra Boltasseva Copyright © 2012 Ivan D. Rukhlenko et al. All rights reserved. Applications of Hyperbolic Metamaterial Substrates Thu, 06 Dec 2012 09:25:17 +0000 http://www.hindawi.com/journals/aoe/2012/452502/ We review the properties of hyperbolic metamaterials and show that they are promising candidates as substrates for nanoimaging, nanosensing, fluorescence engineering, and controlling thermal emission. Hyperbolic metamaterials can support unique bulk modes, tunable surface plasmon polaritons, and surface hyperbolic states (Dyakonov plasmons) that can be used for a variety of applications. We compare the effective medium predictions with practical realizations of hyperbolic metamaterials to show their potential for radiative decay engineering, bioimaging, subsurface sensing, metaplasmonics, and super-Planckian thermal emission. Yu Guo, Ward Newman, Cristian L. Cortes, and Zubin Jacob Copyright © 2012 Yu Guo et al. All rights reserved. Multiplexed FBG Monitoring System for Forecasting Coalmine Water Inrush Disaster Thu, 06 Dec 2012 07:51:50 +0000 http://www.hindawi.com/journals/aoe/2012/895723/ This paper presents a novel fiber-Bragg-grating- (FBG-) based system which can monitor and analyze multiple parameters such as temperature, strain, displacement, and seepage pressure simultaneously for forecasting coalmine water inrush disaster. The sensors have minimum perturbation on the strain field. And the seepage pressure sensors adopt a drawbar structure and employ a corrugated diaphragm to transmit seepage pressure to the axial strain of FBG. The pressure sensitivity is 20.20 pm/KPa, which is 6E3 times higher than that of ordinary bare FBG. The FBG sensors are all preembedded on the roof of mining area in coalmine water inrush model test. Then FBG sensing network is set up applying wavelength-division multiplexing (WDM) technology. The experiment is carried out by twelve steps, while the system acquires temperature, strain, displacement, and seepage pressure signals in real time. The results show that strain, displacement, and seepage pressure monitored by the system change significantly before water inrush occurs, and the strain changes firstly. Through signal fusion analyzed it can be concluded that the system provides a novel way to forecast water inrush disaster successfully. B. Liu, S. C. Li, J. Wang, Q. M. Sui, L. C. Nie, and Z. F. Wang Copyright © 2012 B. Liu et al. All rights reserved. Extension of the Multipole Approach to Random Metamaterials Sun, 25 Nov 2012 09:35:27 +0000 http://www.hindawi.com/journals/aoe/2012/161402/ Influence of the short-range lateral disorder in the meta-atoms positioning on the effective parameters of the metamaterials is investigated theoretically using the multipole approach. Random variation of the near field quasi-static interaction between metaatoms in form of double wires is shown to be the reason for the effective permittivity and permeability changes. The obtained analytical results are compared with the known experimental ones. A. Chipouline, S. Sugavanam, J. Petschulat, and T. Pertsch Copyright © 2012 A. Chipouline et al. All rights reserved. Rolled-Up Metamaterials Sun, 18 Nov 2012 09:50:09 +0000 http://www.hindawi.com/journals/aoe/2012/782864/ In this paper we review metamaterials fabricated from self-rolling strained metal-semiconductor layer systems. These systems relax their strain upon release from the substrate by rolling up into microtubes with a cross-section similar to a rolled-up carpet. We show that the walls of these microtubes represent three-dimensional optical metamaterials which so far could be used, for example, for the realization of broadband hyperlenses, fishnet metamaterials, or optically active three-dimensional metamaterials utilizing the unique possibility to stack optically active semiconductor heterostructures and metallic nanostructures. Furthermore, we discuss THz metamaterials based on arrays of rolled-up metal semiconductor microtubes and helices. Stephan Schwaiger, Andreas Rottler, and Stefan Mendach Copyright © 2012 Stephan Schwaiger et al. All rights reserved. Conditions of Perfect Imaging in Negative Refraction Materials with Gain Thu, 08 Nov 2012 09:48:31 +0000 http://www.hindawi.com/journals/aoe/2012/347875/ Light propagation is analyzed in a negative refraction material (NRM) with gain achieved by pumping. An inherent spatial “walk-off” between the directions of phase propagation and energy transfer is known to exist in lossy NRMs. Here, the analysis is extended to the case where the NRM acts as an active material under various pumping conditions. It is shown that the condition for perfect imaging is only possible for specific wavelengths under special excitation conditions. Under excessive gain, the optical imaging can no longer be perfect. Haowen Liang, Yifeng Shao, Jianying Zhou, Boris A. Malomed, and Gershon Kurizki Copyright © 2012 Haowen Liang et al. All rights reserved. Plasmonic Nanostructure for Enhanced Light Absorption in Ultrathin Silicon Solar Cells Mon, 05 Nov 2012 08:56:05 +0000 http://www.hindawi.com/journals/aoe/2012/592754/ The performances of thin film solar cells are considerably limited by the low light absorption. Plasmonic nanostructures have been introduced in the thin film solar cells as a possible solution around this issue in recent years. Here, we propose a solar cell design, in which an ultrathin Si film covered by a periodic array of Ag strips is placed on a metallic nanograting substrate. The simulation results demonstrate that the designed structure gives rise to 170% light absorption enhancement over the full solar spectrum with respect to the bared Si thin film. The excited multiple resonant modes, including optical waveguide modes within the Si layer, localized surface plasmon resonance (LSPR) of Ag stripes, and surface plasmon polaritons (SPP) arising from the bottom grating, and the coupling effect between LSPR and SPP modes through an optimization of the array periods are considered to contribute to the significant absorption enhancement. This plasmonic solar cell design paves a promising way to increase light absorption for thin film solar cell applications. Jinna He, Chunzhen Fan, Junqiao Wang, Yongguang Cheng, Pei Ding, and Erjun Liang Copyright © 2012 Jinna He et al. All rights reserved. Field Enhancement in a Grounded Dielectric Slab by Using a Single Superstrate Layer Wed, 31 Oct 2012 15:56:43 +0000 http://www.hindawi.com/journals/aoe/2012/439147/ The addition of a dielectric layer on a slab configuration is frequently utilized in various electromagnetic devices in order to give them certain desired operational characteristics. In this work, we consider a grounded dielectric film-slab, which is externally excited by a normally-incident Gaussian beam. On top of the film-slab, we use an additional suitably selected single isotropic superstrate layer in order to increase the field concentration inside the slab and hence achieve optimal power transfer from the external source to the internal region. We define a quantity of interest, called “enhancement factor,” expressing the increase of the field concentration in the film-slab when the superstrate is present compared to the case that it is absent. It is shown that large enhancement factor values may be achieved by choosing properly the permittivity, the permeability, and the thickness of the superstrate. In particular, it is demonstrated that the field in the film-slab is significantly enhanced when the slab is composed by an ϵ-near-zero (ENZ) or low-index metamaterial. Constantinos A. Valagiannopoulos and Nikolaos L. Tsitsas Copyright © 2012 Constantinos A. Valagiannopoulos and Nikolaos L. Tsitsas. All rights reserved. Numerical Simulation on Electrical-Thermal Properties of Gallium-Nitride-Based Light-Emitting Diodes Embedded in Board Wed, 24 Oct 2012 10:59:31 +0000 http://www.hindawi.com/journals/aoe/2012/495981/ The electrical-thermal characteristics of gallium-nitride- (GaN-) based light-emitting diodes (LED), packaged by chips embedded in board (EIB) technology, were investigated using a multiphysics and multiscale finite element code, COMSOL. Three-dimensional (3D) finite element model for packaging structure has been developed and optimized with forward-voltage-based junction temperatures of a 9-chip EIB sample. The sensitivity analysis of the simulation model has been conducted to estimate the current and temperature distribution changes in EIB LED as the blue LED chip (substrate, indium tin oxide (ITO)), packaging structure (bonding wire and chip numbers), and system condition (injection current) changed. This method proved the reliability of simulated results in advance and useful material parameters. Furthermore, the method suggests that the parameter match on Shockley's equation parameters, , , and , is a potential method to reduce the current crowding effect for the EIB LED. Junction temperature decreases by approximately 3 K to 10 K can be achieved by substrate thinning, ITO, and wire bonding. The nonlinear-decreasing characteristics of total thermal resistance that decrease with an increase in chip numbers are likely to improve the thermal performance of EIB LED modules. Xing-ming Long, Rui-jin Liao, and Jing Zhou Copyright © 2012 Xing-ming Long et al. All rights reserved. Realization of Radar Illusion Using Active Devices Wed, 24 Oct 2012 08:12:47 +0000 http://www.hindawi.com/journals/aoe/2012/736876/ A new method is proposed for realizing radar illusion of an electromagnetic target by using active devices. The devices are installed around the target but may closely cover the target or not, leading to closed or open configurations. The amplitudes and phases of the active devices are determined by using T-matrix method. The numerical computation is calculated using MATLAB, and the results show that this method is convenient, flexible, and efficient, which has important significances for implementation of novel electromagnetic devices. B. Z. Cao, L. Sun, and Z. L. Mei Copyright © 2012 B. Z. Cao et al. All rights reserved. Recent Advances in Multiband Printed Antennas Based on Metamaterial Loading Mon, 22 Oct 2012 11:32:38 +0000 http://www.hindawi.com/journals/aoe/2012/968780/ It is shown that printed antennas loaded with metamaterial resonators can be designed to exhibit multiband functionality. Two different antenna types and metamaterial loading are considered: (i) printed dipoles or monopoles loaded with open complementary split ring resonators (OCSRRs) and (ii) meander line or folded dipole antennas loaded with split ring resonators (SRRs) or spiral resonators (SRs). In the first case, multiband operation is achieved by series connecting one or more OCSRRs within the dipole/monopole. Such resonators force opens at their positions, and by locating them at a quarter wavelength (at the required operating frequencies) from the feeding point, it is possible to achieve multiple radiation bands. In the second case, dual-band functionality is achieved through the perturbation of the antenna characteristics caused by the presence of the metamaterial resonators. This latter strategy is specially suited to achieve conjugate matching between the antenna and the chip in radiofrequency identification (RFID) tags at two of the regulated UHF-RFID bands. F. Paredes, G. Zamora, S. Zufanelli, F. J. Herraiz-Martínez, J. Bonache, and F. Martín Copyright © 2012 F. Paredes et al. All rights reserved.