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Online ISSN 1751-8776 Print ISSN 1751-8768

IET Optoelectronics

Volume 6, Issue 5, October 2012

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Volume 6, Issue 5

October 2012

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    • Multifunctional microwave photonic filter based on a single fibre Bragg grating
      • Author(s): B. Luo ; J. Dong ; Y. Yu ; X. Wang ; X. Zhang
      • Source: IET Optoelectronics, Volume 6, Issue 5, p. 201 –206
      • DOI:  10.1049/iet-opt.2011.0062
      • Type: Article
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      • p. 201 –206 (6)
        Multifunctional microwave photonic filters (MWPFs) have potential applications in flexible and various microwave signal processing. The authors propose and demonstrate a MWPF, including all-pass filter, band-pass filter and notch filter based on a single fibre Bragg grating. A high Q band-pass filter with a Q factor of 235 and a rejection ration exceeding 30 dB, and a notch filter with a flat top and a rejection ratio exceeding 25 dB are experimentally achieved.
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      Modelling of one-dimensional magnetoplasmonic periodic structures by the effective refractive index method
      • Author(s): S. Hosseinzadeh
      • Source: IET Optoelectronics, Volume 6, Issue 5, p. 207 –214
      • DOI:  10.1049/iet-opt.2011.0043
      • Type: Article
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      • p. 207 –214 (8)
        An external DC magnetic field may change the dispersion diagram of periodic structures, so that tunable reciprocal and non-reciprocal plamonic components may be constructed. In this study, the effect of an external DC magnetic field on the dispersion diagram of plasmonic periodic structures will be investigated by the effective refractive index method. Investigations are focused on the Voigt and Faraday configurations, although it can be extended to other configurations. In this regard, the wave equation for both structures is solved, eigenpropagation constants and eigenpolarisation are derived. Then, the effective propagation constant and finally, the dispersion diagram for the Voigt and Faraday structures will be derived. The effect of the bias field is investigated on the aforementioned structures. It is seen that tunable periodic structures can be achieved by the magnetoplasmonic configurations. Different dispersion diagrams can be obtained for different modal waves. For both structures, there is a transmission band for frequencies below the plasma frequency, especially for extremely low frequencies, where in the absence of a magnetic field, wave transmission is impossible. There is no limit on the period of structure, the period of structure in the simulation varies from zero to 1.6λp.
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      Spectral efficiency analysis of bipolar spectral-amplitude coding optical code-division multiple-access systems using different one-dimensional codes
      • Author(s): H.M.R. Al-Khafaji ; S.A. Aljunid ; H.A. Fadhil
      • Source: IET Optoelectronics, Volume 6, Issue 5, p. 215 –222
      • DOI:  10.1049/iet-opt.2011.0051
      • Type: Article
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      • p. 215 –222 (8)
        In this study, the spectral efficiency (SE) of bipolar spectral-amplitude coding optical code-division multiple-access (SAC-OCDMA) systems operating with incoherent sources is analysed. The analytical expressions of the model were derived to assess the performance of SAC-OCDMA systems, taking into account the intensity noise as the primary source of noise. Four different SAC codes were used to evaluate and compare the SE against the number of active users and code length for a bit-error rate (BER) of 10−11. The investigated codes are Hadamard, modified quadratic congruence (MQC), balanced incomplete block design (BIBD) and zero cross-correlation (ZCC). Our analytical results revealed that ZCC code has the ability to support more users at a high data rate up to 2.5 Gbps and offers significant SE enhancement in bipolar SAC-OCDMA system over other SAC codes under investigation. In addition, bipolar encoding improves the SE compared with unipolar technique, for example bipolar ZCC has 7.7-dB SE advantage than unipolar ZCC. Furthermore, when BER requirement of the system decreases, the SE can be increased.
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      Passive all-optical tree architecture-based scheme for conversion of 2n radix-based number to its binary form
      • Author(s): M.K. Das ; J.N. Roy ; T. Chattopadhyay
      • Source: IET Optoelectronics, Volume 6, Issue 5, p. 223 –229
      • DOI:  10.1049/iet-opt.2011.0088
      • Type: Article
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      • p. 223 –229 (7)
        In this study, a simple but efficient all-optical conversion scheme of 2n radix-based form to its binary equivalent is proposed and described with the help of passive all-optical tree architecture. The proposed design is more efficient in terms of speed and hardware complexity. Here, the authors describe the different schemes that can perform conversion of any 2n radix-based number to its binary equivalent such as hexadecimal to binary, ASCII to binary and so on. The model can be extended for studying a more complex all-optical circuit of enhanced functionality in which binary conversion scheme is the basic building block.
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      Engineering method for predicting junction temperatures of high-power light-emitting diodes
      • Author(s): X. Luo ; Z. Mao ; J. Yang ; S. Liu
      • Source: IET Optoelectronics, Volume 6, Issue 5, p. 230 –236
      • DOI:  10.1049/iet-opt.2011.0004
      • Type: Article
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      • p. 230 –236 (7)
        In order to evaluate the reliability of a high-power light-emitting diode (LED) module, it is important to obtain junction temperature of high-power LED modules in various applications. However, until recently, there were no simple and effective methods to obtain the junction temperature of LEDs. In this study, an engineering method to estimate the junction temperature of typical LED packaging modules by using an analytical solution was proposed. Simple experiments were used to help determine boundary conditions for thermal modelling. Simulations for obtaining thermal resistance and junction temperature of LED packaging modules in the same boundary conditions were also carried out by commercial software COMSOL. On comparing the junction temperatures obtained by the two methods, it can be seen that the proposed model is able to estimate junction temperatures well.
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      Simulation of transient temperature for mixture of two materials in the selective laser sintering process
      • Author(s): X. Jian  and  R.S. Rana
      • Source: IET Optoelectronics, Volume 6, Issue 5, p. 237 –241
      • DOI:  10.1049/iet-opt.2011.0058
      • Type: Article
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      • p. 237 –241 (5)
        In the process of rapid prototyping by the method of selective laser sintering, transient temperature has a direct effect upon the sintering performance. In the present work, a model is developed to predict the three-dimensional transient temperature field. It uses the finite element method to model the variation of thermal properties and solid–liquid two-phase interface in sintering the mixture of Al2O3-coated ceramic powder and polystyrene powder. A high-speed charge-coupled device image temperature measurement system is used to obtain real data from laser sintering experiments for comparison. The test results validate the simulation data and imply that the modelling method is useful in predicting the transient sintering temperature when correct thermal properties and key factors of two-phase interface are main concerns. The performance characteristics of the sintering process are predicted by the modelling method.
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      Analysis of electrical and optical characteristics of InGaSb PIN photodiodes
      • Author(s): M. Tanzid  and  F.M. Mohammedy
      • Source: IET Optoelectronics, Volume 6, Issue 5, p. 242 –249
      • DOI:  10.1049/iet-opt.2011.0101
      • Type: Article
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      • p. 242 –249 (8)
        This study represents an analysis of electrical and optical characteristics of InGaSb PIN photodiodes. The electrical characteristics are analysed by depicting a model of zero-bias resistance–area product (R0A) of such photodiodes. The effects of dislocation and temperature on R0A are also included in the model. Different optoelectronic properties of the material are extracted by fitting the obtained models with experimental data. The extracted dislocation density is 6.67×108 cm−2, which is close to the measured value of 2.4(±0.2)×108 cm−2. Through the dislocation and temperature-dependent modelling, maximum R0A is found to be 1.85 Ω cm2 at 139 K. Experimental data obtained at 300 and 363 K are fitted with theoretical model. The optical properties are analysed by the modelling of responsivity, quantum efficiency and detectivity. Cutoff wavelength is found to be 2271 nm, which is within ±5 nm of the experimentally obtained data. The present analysis gives a photodiode responsivity is 0.47 A/W, quantum efficiency is 28.86% and detectivity is 1.53×109 cm Hz1/2/W1 at a particular wavelength of λ=2.0 µm, which are agreeable to the experimentally obtained data.
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      Peak-to-average power ratio reduction using coded signal in optical-orthogonal frequency division multiplexing systems
      • Author(s): E K. Singh Bhatia ; T.S. Kamal ; R.S. Kaler
      • Source: IET Optoelectronics, Volume 6, Issue 5, p. 250 –254
      • DOI:  10.1049/iet-opt.2011.0089
      • Type: Article
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      • p. 250 –254 (5)
        A new coding scheme is proposed using a variable rate for an all-optical sampling orthogonal frequency-division multiplexing system, to minimise the peak-to-average power ratio. Cyclic rotation and code rate variation are shown to improve the peak envelope power. The proposed idea comprises of searching for a variable code rate selection for the binary input data and cyclic rotation, followed by codeword inversion.
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      Test system for comprehensive evaluation of infrared-guided missiles
      • Author(s): A.K. Maini  and  V. Agrawal
      • Source: IET Optoelectronics, Volume 6, Issue 5, p. 255 –262
      • DOI:  10.1049/iet-opt.2012.0002
      • Type: Article
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      • p. 255 –262 (8)
        Electro-optically guided munitions, which include infrared (IR)-guided and laser-guided munitions, are the most widely used precision strike weapons on a variety of military platforms. To ensure 100% hit accuracy for these weapons, it is imperative that these are tested comprehensively at regular intervals. IR-guided missiles of the 1970s and 1980s used single colour IR seekers that respond to 3–5-µm band of the IR signatures of the target aircraft. State-of-the-art IR-guided missiles use two colour seekers that employ both 3–5- and 8–12-µm bands to offer improved false alarm rejection and greater immunity to deception by flares. This study presents a new design concept that can be used to build a test system capable of carrying out comprehensive characterisation of IR-guided missiles employing non-imaging type single colour or dual colour IR seekers. The study begins with a brief outline on the requirements of comprehensive characterisation and then discusses the proposed design concept along with its implementation in experimental hardware. The experimental hardware is evaluated by measuring different performance parameters. Test results obtained with prototype hardware are also presented in the study.
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