Advances in OptoElectronics https://www.hindawi.com The latest articles from Hindawi © 2017 , Hindawi Limited . All rights reserved. Fundamental Transverse Mode Selection (TMS#0) of Broad Area Semiconductor Lasers with Integrated Twice-Retracted 4f Set-Up and Film-Waveguide Lens Thu, 14 Dec 2017 00:00:00 +0000 http://www.hindawi.com/journals/aoe/2017/5283850/ Previously we focused on fundamental transverse mode selection (TMS#0) of broad area semiconductor lasers (BALs) with two-arm folded integrated resonators for Fourier-optical spatial frequency filtering. The resonator had a round-trip length of 4f, where f is the focal length of the Fourier-transform element (FTE), that is, a cylindrical mirror in-between the orthogonal resonator branches. This 4f set-up can be called “retracted once” due to the reflective filter after 2f; that is, the 2f path was used forwards and backwards. Now the branches are retracted once more resulting in a compact 1f long linear resonator (called “retracted twice”) with a round-trip length of 2f. One facet accommodates the filter, while the other houses the FTE, now incorporating a film-waveguide lens. The BAL facet with the filter represents both the Fourier-transform plane (after 2f, i.e., one round-trip) as well as the image plane (after 4f, two round-trips). Thus filtering is performed even after 4f, not just after 2f. Experimental results reveal good fundamental TMS for pump currents up to 20% above threshold and a one-dimensional beam quality parameter = 1.47. The BALs are made from AlGaInAsSb, but the concept can equally well be employed for BALs of any material system. Henning Fouckhardt, Ann-Kathrin Kleinschmidt, Johannes Strassner, and Christoph Doering Copyright © 2017 Henning Fouckhardt et al. All rights reserved. Method Research of Coal Mine Roof Strain Detection Based on the Fiber Bragg Grating Sensor with Thermodynamic Couple Numerical Condition Thu, 03 Aug 2017 00:00:00 +0000 http://www.hindawi.com/journals/aoe/2017/2153409/ In order to solve the problem that the measure precision of coal roof rock strain amount detection using traditional electric sensor is insufficient, a kind of High Sensitive Surface-Pasted Fiber Bragg Grating Strain Sensor based on rock bolting is designed for substitution. Furthermore, a kind of Reference Grating Zero-Strain method based on sensitivity matrix coefficient is proposed for solving FBG strain-temperature cross-sensitivity problem and realizing the better separation relevant to strain and temperature. It is proved that the sensitivity and measurement precision and anti-interference ability of FBG strain sensors are better than traditional electricity class sensors, being able to realize the real-time and online detection for coal roof surrounding rock strain. Zhang Jian, Lu Chuan, and Lin De-Shu Copyright © 2017 Zhang Jian et al. All rights reserved. Broadband Enhancement of Optical Frequency Comb Using Cascaded Four-Wave Mixing in Photonic Crystal Fiber Wed, 12 Jul 2017 00:00:00 +0000 http://www.hindawi.com/journals/aoe/2017/1365072/ A cascaded intensity modulator (IM) and phase modulator (PM) are used to modulate a continuous-wave (CW) laser and generate an optical frequency comb (OFC). Thus, the generated comb is utilized as an initial seed and combined with another CW-laser to generate four-wave mixing (FWM) in photonic crystal fiber (PCF). Results show that an initial flat 30 GHz OFC of 29, 55 lines within power fluctuation of 0.8 dB and 2 dB, respectively, can be achieved by setting the ratio of the DC bias to amplitude of sinusoidal signal at 0.1 and setting the modulation indices of both IM and PM at 10. Moreover, the 1st order of FWM created through 14 m of PCF has over 68 and 94 lines with fluctuation of 0.8 dB and 2 dB, respectively. Hence, the generated wavelengths of 1st left and right order of FWM can be tuned in a range from ~1500 nm to ~1525 nm and ~1590 nm to ~1604 nm, respectively. Tawfig Eltaif Copyright © 2017 Tawfig Eltaif. All rights reserved. DWT versus WP Based Optical Color Image Encryption Robust to Composite Attacks Mon, 05 Jun 2017 09:02:15 +0000 http://www.hindawi.com/journals/aoe/2017/9802751/ Intensive studies have been done to get robust encryption algorithms. Due to the importance of image information, optical encryption has played a vital role in information security. Many optical encryption schemes have been proposed but most of them suffer from poor robustness. In this paper six proposed algorithms will be presented for optical encryption to be robust to severe attacks: composite attack. Three of these approaches are based on one level Discrete Wavelet Transform (DWT) and the others are based on Wavelet Packet (WP). Not only will new techniques be presented but also a new proposed chaotic map has been developed as random keys for all algorithms. After extensive comparative study with some traditional techniques, it has been found that the novel algorithms have achieved better performance versus conventional ones. Also it has been found that WP based algorithms have achieved better performance than DWT based ones against severe composite attacks. M. A. Mohamed, Ahmed Shaaban Samrah, and Mohamed Ismail Fath Allah Copyright © 2017 M. A. Mohamed et al. All rights reserved. Cavity Formation Modeling of Fiber Fuse in Single-Mode Optical Fibers Sun, 14 May 2017 08:50:56 +0000 http://www.hindawi.com/journals/aoe/2017/5728186/ The evolution of a fiber-fuse phenomenon in a single-mode optical fiber was studied theoretically. To clarify both the silica-glass densification and cavity formation, which have been observed in fiber fuse propagation, we investigated a nonlinear oscillation model using the Van Der Pol equation. This model was able to phenomenologically explain both the densification of the core material and the formation of periodic cavities in the core layer as a result of a relaxation oscillation. Yoshito Shuto Copyright © 2017 Yoshito Shuto. All rights reserved. Propagation in Diagonal Anisotropic Chirowaveguides Wed, 08 Mar 2017 09:20:12 +0000 http://www.hindawi.com/journals/aoe/2017/9524046/ A theoretical study of electromagnetic wave propagation in parallel plate chirowaveguide is presented. The waveguide is filled with a chiral material having diagonal anisotropic constitutive parameters. The propagation characterization in this medium is based on algebraic formulation of Maxwell’s equations combined with the constitutive relations. Three propagation regions are identified: the fast-fast-wave region, the fast-slow-wave region, and the slow-slow-wave region. This paper focuses completely on the propagation in the first region, where the dispersion modal equations are obtained and solved. The cut-off frequencies calculation leads to three cases of the plane wave propagation in anisotropic chiral medium. The particularity of these results is the possibility of controlling the appropriate cut-off frequencies by choosing the adequate physical parameters values. The specificity of this study lies in the bifurcation modes confirmation and the possible contribution to the design of optical devices such as high-pass filters, as well as positive and negative propagation constants. This negative constant is an important feature of metamaterials which shows the phenomena of backward waves. Original results of the biaxial anisotropic chiral metamaterial are obtained and discussed. S. Aib, F. Benabdelaziz, C. Zebiri, and D. Sayad Copyright © 2017 S. Aib et al. All rights reserved. Temperature Dependence Study of Mesa-Type InGaAs/InAlAs Avalanche Photodiode Characteristics Thu, 12 Jan 2017 00:00:00 +0000 http://www.hindawi.com/journals/aoe/2017/2084621/ Avalanche photodiodes (APDs) are key optical receivers due to their performance advantages of high speed, high sensitivity, and low noise. The most critical device parameters of APD include the avalanche breakdown voltage and dark current. In this work, we study the temperature dependence of the breakdown voltage and dark current of the mesa-type APD over a wide temperature range of 20–145°C. We institute an empirical model based on impact ionization processes to account for the experimental data. It is shown that highly stable breakdown characteristics of mesa-type APD can be attained with the optimization of the multiplication layer design. We have achieved excellent stability of avalanche breakdown voltage with a temperature coefficient of 0.017 V/°C. The temperature dependence of dark current is attributed to generation-recombination mechanism. The bandgap energy is estimated to be about 0.71 eV based on the temperature variation of dark current, in good agreement with the value for InGaAs. Jack Jia-Sheng Huang, H. S. Chang, Yu-Heng Jan, C. J. Ni, H. S. Chen, and Emin Chou Copyright © 2017 Jack Jia-Sheng Huang et al. All rights reserved. Coupling Characteristics of Fused Optical Fiber Coupler Formed with Single-Mode Fiber and Photonic Crystal Fiber Having Air Hole Collapsed Taper Thu, 24 Nov 2016 14:31:23 +0000 http://www.hindawi.com/journals/aoe/2016/6219895/ Fused coupler forming with a single-mode fiber (SMF) and a photonic crystal fiber (PCF) is one of the solutions for optical coupling from a light source to a PCF. In this paper, we presented coupling characteristics of a fused fiber coupler formed with an ordinary SMF and a PCF having air hole collapsed taper. A prototype of SMF-PCF coupler with air hole collapsed taper was fabricated using CO2 laser irradiation. The coupling efficiency from SMF to PCF was −6.2 dB at 1554 nm wavelength in the fabricated coupler. The structure of the SMF-PCF coupler to obtain high coupling efficiency was theoretically clarified by beam propagation analysis using an equivalent model of the coupler with simplification. It was clarified that appropriately choosing the prestretched or etched SMF diameter and the length of air hole collapsed region was effective to obtain high coupling efficiency that was a result of high extinction ratio at cross port and low excess loss. We also demonstrated that the diameter of prestretched SMF to obtain high coupling efficiency was insensitive to the air hole diameter ratio to pitch of the PCF in the air hole collapsed SMF-PCF coupler. Hirohisa Yokota, Hirotomo Yashima, Yoh Imai, and Yutaka Sasaki Copyright © 2016 Hirohisa Yokota et al. All rights reserved. An Iterative Method for the Uniformity Improvement of Edge-Lit Backlight Wed, 28 Sep 2016 14:08:21 +0000 http://www.hindawi.com/journals/aoe/2016/1760260/ A simple iterative optimization method is developed to improve the exiting light uniformity of the edge-lit backlight module. The method uses the relative deviation of the average luminous flux of the entire light guide plate (LGP) and the luminous flux of each region as constraint criterion and the ratio of the luminous flux of each region to the average luminous flux of the LGP as adjustment coefficient to adjust the density of the microstructures in each region. This process loops until the relative deviations of all regions meet a prespecified threshold value. A LGP based on microprism structure is presented to validate the method. The initial values, which represent the size of the microstructures manufactured on the bottom surfaces of the LGP, -dependent luminous fluxes, microstructure size distributions, iterations of the LGP, and the relative deviation of each region are discussed. The simulation results show that it is a very practical method for the uniformity improvement of the backlight when an appropriate initial value is selected and the final uniformity is better than 90% after optimization. Jin-Ren Yan, De-Cong Li, Zhi-Kun Wang, and Wen-Ping Rao Copyright © 2016 Jin-Ren Yan et al. All rights reserved. Characteristics of Highly Birefringent Photonic Crystal Fiber with Defected Core and Equilateral Pentagon Architecture Mon, 29 Aug 2016 14:12:15 +0000 http://www.hindawi.com/journals/aoe/2016/5301372/ A novel high birefringence and nearly zero dispersion-flattened photonic crystal fiber (PCF) with elliptical defected core (E-DC) and equilateral pentagonal architecture is designed. By applying the full-vector finite element method (FEM), the characteristics of electric field distribution, birefringence, and chromatic dispersion of the proposed E-DC PCF are numerically investigated in detail. The simulation results reveal that the proposed PCF can realize high birefringence, ranging from 1 to 1 orders of magnitude, owing to the embedded elliptical air hole in the core center. However, the existence of the elliptical air hole gives rise to an extraordinary electric field distribution, where a V-shaped notch appears and the size of the V-shaped notch varies at different operating wavelengths. Also, the mode field diameter is estimated to be about 2 μm, which implies the small effective mode area and highly nonlinear coefficient. Furthermore, the investigation of the chromatic dispersion characteristic shows that the introduction of the elliptical air hole is helpful to control the chromatic dispersion to be negative or nearly zero flattened over a wide wavelength bandwidth. Fei Yu, Zhenpeng Wang, Wenhao Yang, and Chongyang Lv Copyright © 2016 Fei Yu et al. All rights reserved. Polarization Sensitive Reflection and Dielectric Spectra in GaSe Thin Films Sun, 31 Jul 2016 10:10:40 +0000 http://www.hindawi.com/journals/aoe/2016/7182303/ The light polarization effects on the optical reflective and dielectric spectra of GaSe thin films are studied in the incident light wavelength range of 200–1100 nm. In this range of measurement, the angle of incidence () of light was varied between 30° and 80°. In addition, at of 30° the light polarizing angle () was altered in the range of 0–90°. Regardless of the value of , for all , the total reflectance sharply decreased with increasing . In addition, when is fixed at 30° and was varied, the amplitudes ratio of the polarized waves exhibits a resonance-antiresonance phenomenon at a wavelength that coincides with the film’s thickness (800 nm). This behavior was assigned to the coupled interference between incident and reflected waves and to the strong absorption effects. Two main resonance peaks are observed as response to -polarized and normal incident beam: one is at ~540 (556 nm) and the other at ~420 THz (714 nm). The dielectric constant of the GaSe films exhibits anisotropic characteristics that nominate it for use as multipurpose optoelectronic devices. Hazem K. Khanfar and Atef A. Qasrawi Copyright © 2016 Hazem K. Khanfar and Atef A. Qasrawi. All rights reserved. Study of a Linear Acoustooptic Laser Modulator Based on All-Fibre Sagnac Interferometer Mon, 25 Jul 2016 07:51:56 +0000 http://www.hindawi.com/journals/aoe/2016/5606417/ The feasibility of polarization-maintaining photonic crystal fibre (PM-PCF) strategy for acoustooptic modulation using all-fibre Sagnac interferometer is demonstrated. The principal constraint to apply the strategy is defined by a linear laser acoustooptic modulator (AOM) for 1550 nm. The intensity of incident acoustic waves over the PM-PCF loop segment affected the signal interference transmission; here, modulation by birefringence variation around was observed. It is discovered that, through mathematical analysis, two operation points in the spectrum, , operate in a linear region, and expressions for spectral gain and sensibility are also discovered. AOM has a bandwidth from 0.1 Hz to 20 kHz, and its dynamic range is from 0.0 to 43.5 dB. G. Trinidad García, E. Molina Flores, B. A. Ramírez Solís, and H. Azucena Coyotecatl Copyright © 2016 G. Trinidad García et al. All rights reserved. Noise Gain Features of Fiber Raman Amplifier Tue, 12 Jul 2016 14:30:36 +0000 http://www.hindawi.com/journals/aoe/2016/5843636/ The formation dynamics of the optical noise in a silica single mode fiber (SMF) as function of the pump power variation in the counter pumped fiber Raman amplifier (FRA) is experimentally studied. The ratio between the power of amplified spontaneous emission and the power of incoherent optical noise is quantitatively determined by detailed analysis of experimental data in the pump powers range of 100–300 mW within the full band of Stokes frequencies, including FRA working wavelengths over the C + L transparency windows. It is found out the maximum of Raman gain coefficient for optical noise does not exceed ~60% of corresponding peak at the gain profile maximum of coherent signal. It is shown that the real FRA noise figure may be considerably less than 3 dB over a wide wavelength range (100 nm) at a pump power of several hundreds of mW. Georgii S. Felinskyi and Mykhailo Y. Dyriv Copyright © 2016 Georgii S. Felinskyi and Mykhailo Y. Dyriv. All rights reserved. A Grooming Nodes Optimal Allocation Method for Multicast in WDM Networks Thu, 18 Feb 2016 10:47:48 +0000 http://www.hindawi.com/journals/aoe/2016/1978617/ The grooming node has the capability of grooming multicast traffic with the small granularity into established light at high cost of complexity and node architecture. In the paper, a grooming nodes optimal allocation (GNOA) method is proposed to optimize the allocation of the grooming nodes constraint by the blocking probability for multicast traffic in sparse WDM networks. In the proposed GNOA method, the location of each grooming node is determined by the SCLD strategy. The improved smallest cost largest degree (SCLD) strategy is designed to select the nongrooming nodes in the proposed GNOA method. The simulation results show that the proposed GNOA method can reduce the required number of grooming nodes and decrease the cost of constructing a network to guarantee a certain request blocking probability when the wavelengths per fiber and transmitter/receiver ports per node are sufficient for the optical multicast in WDM networks. Chengying Wei, Qinren Shen, Huanlin Liu, and Yong Chen Copyright © 2016 Chengying Wei et al. All rights reserved. Physics of Internal Photoemission and Its Infrared Applications in the Low-Energy Limit Thu, 28 Jan 2016 11:17:35 +0000 http://www.hindawi.com/journals/aoe/2016/1832097/ Internal photoemission (IP) correlates with processes in which carriers are photoexcited and transferred from one material to another. This characteristic allows characterizing the properties of the heterostructure, for example, the band parameters of a material and the interface between two materials. IP also involves the generation and collection of photocarriers, which leads to applications in the photodetectors. This review discusses the generic IP processes based on heterojunction structures, characterizing -type band structure and the band offset at the heterointerface, and infrared photodetection including a novel concept of photoresponse extension based on an energy transfer mechanism between hot and cold carriers. Y. F. Lao and A. G. U. Perera Copyright © 2016 Y. F. Lao and A. G. U. Perera. All rights reserved. Mathematical Verification for Transmission Performance of Centralized Lightwave WDM-RoF-PON with Quintuple Services Integrated in Each Wavelength Channel Tue, 29 Dec 2015 11:36:15 +0000 http://www.hindawi.com/journals/aoe/2015/183675/ Wavelength-division-multiplexing passive-optical-network (WDM-PON) has been recognized as a promising solution of the “last mile” access as well as multibroadband data services access for end users, and WDM-RoF-PON, which employs radio-over-fiber (RoF) technique in WDM-PON, is even a more attractive approach for future broadband fiber and wireless access for its strong availability of centralized multiservices transmission operation and its transparency for bandwidth and signal modulation formats. As for multiservices development in WDM-RoF-PON, various system designs have been reported and verified via simulation or experiment till now, and the scheme with multiservices transmitted in each single wavelength channel is believed as the one that has the highest bandwidth efficiency; however, the corresponding mathematical verification is still hard to be found in state-of-the-art literature. In this paper, system design and data transmission performance of a quintuple services integrated WDM-RoF-PON which jointly employs carrier multiplexing and orthogonal modulation techniques, have been theoretically analyzed and verified in detail; moreover, the system design has been duplicated and verified experimentally and the theory system of such WDM-RoF-PON scheme has thus been formed. Shuai Chen, Wei Nai, Fangqi Zhang, Shaoyin Wang, Decun Dong, and Yi Yu Copyright © 2015 Shuai Chen et al. All rights reserved. Target Tracking Algorithm Using Angular Point Matching Combined with Compressive Tracking Tue, 10 Nov 2015 07:06:20 +0000 http://www.hindawi.com/journals/aoe/2015/420183/ To solve the problems of tracking errors such as target missing that emerged in compressive tracking (CT) algorithm due to factors such as pose variation, illumination change, and occlusion, a novel tracking algorithm combined angular point matching with compressive tracking (APMCCT) was proposed. A sparse measurement matrix was adopted to extract the Haar-like features. The offset of the predicted target position was integrated into the angular point matching, and the new target position was calculated. Furthermore, the updating mechanism of the template was optimized. Experiments on different video sequences have shown that the proposed APMCCT performs better than CT algorithm in terms of accuracy and robustness and adaptability to pose variation, illumination change, and occlusion. Jing Luo, Tingting Dong, Chunyuan Zi, Chunbo Xiu, Huixin Tian, and Jiangtao Xi Copyright © 2015 Jing Luo et al. All rights reserved. All-Optical Surface Micropatterning by Electric Field Intensity Gradient Thu, 05 Nov 2015 07:47:47 +0000 http://www.hindawi.com/journals/aoe/2015/917029/ In this report an all-optical photo-induced formation of surface relief gratings is shown. For the surface patterning of As2S3 and As4S1.5Se4.5 films a direct holographic recording setup with a 532 nm wavelength Nd:YAG CW laser light was used. Our investigations have shown that the light-induced mass transfer process strongly depends on the material itself and on the polarization of the light. It has been shown that an electric field intensity gradient has to be obtained to achieve a direct patterning. The evolution of a surface relief in relation to recording parameters and thickness of the sample has been investigated in detail. U. Gertners and J. Teteris Copyright © 2015 U. Gertners and J. Teteris. All rights reserved. Analysis of the Interference Modulation Depth in the Fourier Transform Spectrometer Sun, 04 Oct 2015 16:34:22 +0000 http://www.hindawi.com/journals/aoe/2015/472852/ Based on the principle of the Michelson interferometer, the paper briefly describes the theoretical significance and calculates and deduces three expressions of the interference modulation depth. The influence of the surface shape error of plane mirror on modulation depth is analyzed, and the tolerance of error is also pointed out. Moreover, the dependence of modulation depth on the reflectance change of beam splitter interface is also analyzed, and the curve is given. It is concluded that this paper is of general significance for the Fourier transform spectrometer based on the principle of the Michelson two-beam interference. Rilong Liu Copyright © 2015 Rilong Liu. All rights reserved. Effective Evaluation of the Noise Factor of Microchannel Plate Thu, 27 Aug 2015 06:13:40 +0000 http://www.hindawi.com/journals/aoe/2015/781327/ To improve the noise performance of microchannel plate (MCP), we have presented a method using the sine random signals with Poisson distribution as the noise-excitation for electron source. By using this method, the effective evaluation of noise characteristics of MCP has been implemented through measuring and analyzing its noise factor. The results have demonstrated that the noise factor of filmed MCP is lower than 1.8. Additionally, as the open area ratio and the input electron energy are 72% and 400 eV, respectively, the noise characteristics of unfilmed MCP are improved evidently. Moreover, larger open area ratio, higher input electron energy, and higher voltage across the MCP all can reduce effectively the noise factor within a certain range. Meanwhile, the ion barrier film extends the life of image tube but at the cost of an increased noise factor. Therefore, it is necessary that a compromise between the optimum thickness of ion barrier film, open area ratio, input electron energy, and voltage across the MCP must be reached. Honggang Wang, Yujie Du, Yu Feng, Yang Lv, Xiaoming Hu, and Yunsheng Qian Copyright © 2015 Honggang Wang et al. All rights reserved. Gain Incorporated Split-Ring Resonator Structures for Active Metamaterials Wed, 26 Aug 2015 14:19:43 +0000 http://www.hindawi.com/journals/aoe/2015/247630/ We present a systematic study of split-ring resonator (SRR) structures that are used as the basic building blocks of active metamaterials with incorporated gain. The active split-ring resonator (aSRR) structures with gain elements can in theory have similar unusual electromagnetic responses such as negative effective permeability near their resonance of the artificial magnetic response just like their passive counterparts. At the same time aSRRs can have reversed imaginary part of the effective permeability and, therefore, mitigate the loss of passive SRRs. We explored in detail both passive and active SRRs through analytic theory, numerical simulations, and lab experimentation and demonstrated that aSRRs can have the similar negative effective permeability responses while reducing and even reversing the loss. Jordan Chaires, David Schumerth, Cole Drawdy, and Weiguo Yang Copyright © 2015 Jordan Chaires et al. All rights reserved. Fivefold Symmetric Photonic Quasi-Crystal Fiber for Dispersion Compensation from S- to L-Band and Optimized at 1.55 μm Mon, 03 Aug 2015 14:20:46 +0000 http://www.hindawi.com/journals/aoe/2015/417401/ A highly dispersive dual core quasi-periodic photonic crystal fiber is proposed for chromatic dispersion compensation. The dispersion for the dual concentric core fiber is optimized to compensate the chromatic dispersion with a high negative dispersion, accomplishing the communication bandwidth from S-band (1460 nm) to L-band (1625 nm). By precise control of structural parameter we have achieved a maximum dispersion of −18,838 ps/nm-km with the phase matching wavelength centred around 1.55 μm. We also numerically investigate the influence of structural parameter and doping effects and its response on peak dispersion parameter. Sivacoumar Rajalingam and Zachariah C. Alex Copyright © 2015 Sivacoumar Rajalingam and Zachariah C. Alex. All rights reserved. Optimization of Multiband White-Light Illuminants for Specified Color Temperatures Mon, 25 May 2015 11:10:53 +0000 http://www.hindawi.com/journals/aoe/2015/263791/ This paper describes an effective approach for the optimization of multiband spectra to produce prospective white-light spectra having specific color temperatures. The optimization process employs a genetic algorithm known as differential evolution, which aims to minimize the color rendering differences between a prospective white-light spectrum and its corresponding reference illuminant. Color rendering is assessed by calculating the CIEDE2000 color difference (ΔE00) for 14 CIE test colors under the two sources. Optimized white-light spectra were matched to three CIE standard illuminants, that is, A (2856 K), D50 (5003 K), and D65 (6504 K). Optimal solutions for three- and four-band 25 and 50 nm Gaussian spectra are presented and analyzed, together with mixed 4-LED spectra that were optimized in the same way. In all cases, the simulated sources were shown to provide color rendering of such quality that ΔE00av ≤ 2.24 units. Such white-light sources would likely find wide acceptance in numerous lighting applications. Snjezana Soltic and Andrew Neil Chalmers Copyright © 2015 Snjezana Soltic and Andrew Neil Chalmers. All rights reserved. Block-Based Compressed Sensing for Neutron Radiation Image Using WDFB Thu, 02 Apr 2015 14:11:34 +0000 http://www.hindawi.com/journals/aoe/2015/496863/ An ideal compression method for neutron radiation image should have high compression ratio while keeping more details of the original image. Compressed sensing (CS), which can break through the restrictions of sampling theorem, is likely to offer an efficient compression scheme for the neutron radiation image. Combining wavelet transform with directional filter banks, a novel nonredundant multiscale geometry analysis transform named Wavelet Directional Filter Banks (WDFB) is constructed and applied to represent neutron radiation image sparsely. Then, the block-based CS technique is introduced and a high performance CS scheme for neutron radiation image is proposed. By performing two-step iterative shrinkage algorithm the problem of norm minimization is solved to reconstruct neutron radiation image from random measurements. The experiment results demonstrate that the scheme not only improves the quality of reconstructed image obviously but also retains more details of original image. Wei Jin, Zhen Liu, and Gang Li Copyright © 2015 Wei Jin et al. All rights reserved. Unusual Blueshifting of Optical Band Gap of CdS Nanocrystals through a Chemical Bath Deposition Method Thu, 05 Mar 2015 12:04:57 +0000 http://www.hindawi.com/journals/aoe/2015/317108/ CdS nanocrystals are synthesized through a chemical bath deposition method. After annealing, these nanocrystals are enlarged according to Scherrer’s formula. Small nanocrystals display wide band gaps as a result of the quantum effect experienced by nanocrystals of a certain size. However, the absorption edge and green and red emissions of annealed CdS nanocrystals show obvious blueshift compared with the as-grown ones. After annealing, the intensity ratio of these green and red emissions increases, which indicated that the defect states are reduced. Therefore, the improvement in crystalline quality and the reduced strain contribute to the unusual blueshifting of the optical band gap and of the green and red emissions. Shu Qing Yuan, Peng Fei Ji, Yong Li, Yue Li Song, and Feng Qun Zhou Copyright © 2015 Shu Qing Yuan et al. All rights reserved. A Microring Temperature Sensor Based on the Surface Plasmon Wave Sun, 15 Feb 2015 09:13:17 +0000 http://www.hindawi.com/journals/aoe/2015/696749/ A structure of microring sensor suitable for temperature measurement based on the surface plasmon wave is put forward in this paper. The sensor uses surface plasmon multilayer waveguiding structure in the vertical direction and U-shaped microring structure in the horizontal direction and utilizes SOI as the thermal material. The transfer function derivation of the structure of surface plasmon microring sensor is according to the transfer matrix method. While the change of refractive index of Si is caused by the change of ambient temperature, the effective refractive index of the multilayer waveguiding structure is changed, resulting in the drifting of the sensor output spectrum. This paper focuses on the transmission characteristics of multilayer waveguide structure and the impact on the output spectrum caused by refractive index changes in temperature parts. According to the calculation and simulation, the transmission performance of the structure is stable and the sensitivity is good. The resonance wavelength shift can reach 0.007 μm when the temperature is increased by 100 k and FSR can reach about 60 nm. This structure achieves a high sensitivity in the temperature sense taking into account a wide range of filter frequency selections, providing a theoretical basis for the preparation of microoptics. Wenchao Li, Xiaopeng Sha, Dongyang An, and Zhiquan Li Copyright © 2015 Wenchao Li et al. All rights reserved. Performance of Series Connected GaAs Photovoltaic Converters under Multimode Optical Fiber Illumination Sun, 21 Dec 2014 00:10:03 +0000 http://www.hindawi.com/journals/aoe/2014/824181/ In many military and industrial applications, GaAs photovoltaic (PV) converters are connected in series in order to generate the required voltage compatible with most common electronics. Multimode optical fibers are usually used to carry high-intensity laser and illuminate the series connected GaAs PV converters in real time. However, multimode optical fiber illumination has a speckled intensity pattern. The series connected PV array is extremely sensitive to nonuniform illumination; its performance is limited severely by the converter that is illuminated the least. This paper quantifies the effects of multimode optical fiber illumination on the performance of series connected GaAs PV converters, analyzes the loss mechanisms due to speckles, and discusses the maximum illumination efficiency. In order to describe the illumination dependent behavior detailedly, modeling of the series connected PV array is accomplished based on the equivalent circuit for PV cells. Finally, a series of experiments are carried out to demonstrate the theory analysis. Tiqiang Shan and Xinglin Qi Copyright © 2014 Tiqiang Shan and Xinglin Qi. 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.