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Online ISSN 1751-8776 Print ISSN 1751-8768

IET Optoelectronics

Volume 3, Issue 5, October 2009

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Volume 3, Issue 5

October 2009

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    • Effect of self-phase-modulation on dispersion compensated absolute polar duty cycle division multiplexing transmission
      • Author(s): A. Malekmohammadi ; G.A. Mahdiraji ; A.F. Abas ; M.K. Abdullah ; M. Mokhtar ; M.F.A. Rasid
      • Source: IET Optoelectronics, Volume 3, Issue 5, p. 207 –214
      • DOI:  10.1049/iet-opt.2009.0008
      • Type: Article
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      • p. 207 –214 (8)
        The effect of self-phase modulation (SPM) on 40 Gb/s absolute polar duty cycle division multiplexing (AP-DCDM) is investigated and reported. The study includes the influence of launched power, number of channels and dispersion compensation method. Dispersion post-compensation and combination of dispersion pre- and post-compensation are used to manage the transmission links. At high powers, SPM degrades the pulse recompression process and provides an upper bound on the AP-DCDM transmitted pulse energy. It is demonstrated that the 40 Gb/s AP-DCDM system shows a 4.1 dB improvement and less than 1 dB penalty in terms of SPM tolerance in comparison to 40 Gb/s 4-ary and on–off-keying (OOK) systems, respectively. The SPM effect is stronger in the 100% post-compensated link than that in the combination of pre- and post-compensated links. Dispersion pre-compensation of 18–22% is found as the optimum range of pre-compensation ratio for AP-DCDM system, which makes optimisation of the launched power possible.
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      Jones matrix analysis of frequency mixing error in three-longitudinal-mode laser heterodyne interferometer
      • Author(s): S. Olyaee ; T.H. Yoon ; S. Hamedi
      • Source: IET Optoelectronics, Volume 3, Issue 5, p. 215 –224
      • DOI:  10.1049/iet-opt.2009.0015
      • Type: Article
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      • p. 215 –224 (10)
        In this study, the authors investigate theoretically a periodic non-linearity effect and its compensation in a three-longitudinal-mode heterodyne interferometer (TLMI). An analytical formula of the frequency mixing error in the TLMI is obtained based on the Jones calculus taking into account experimental parameters. We find that the non-ideal polarisation states and imperfect alignment of the optical setup play the major role to produce four- and eight-cycle non-linearities. The operation of non-linearity compensation system on the four- and eight-cycle non-linear errors is also presented.
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      Temperature estimation of high-power light emitting diode street lamp by a multi-chip analytical solution
      • Author(s): X. Luo ; W. Xiong ; T. Cheng ; S. Liu
      • Source: IET Optoelectronics, Volume 3, Issue 5, p. 225 –232
      • DOI:  10.1049/iet-opt.2008.0068
      • Type: Article
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      • p. 225 –232 (8)
        Light emitting diodes (LEDs) are now widely used in many fields including traffic lights, vehicle backlights and liquid crystal display (LCD) displays because of their long life, good illumination efficiency and low energy consumption. At present, LEDs are increasingly replacing the traditional lighting and are being used in general illumination such as the street lamp. For the high-power LED street lamps, good light extraction is the most important thing, but low junction temperature of the LED modules is also critical for achieving a long lifetime and a high optical efficiency. Actually, there have been many reports about early failures of street lamps, called dead lamps that have been regarded as a barrier in the public and administration acceptance of LED street lamps. Therefore temperature estimation is always a crucial issue for LED product development. A multi-chip spreading thermal resistance model was applied to estimate the temperature distribution of LED street lamp. The experiment was first done to obtain temperatures of several locations in a prototype LED street lamp. Then the multi-chip spreading resistance model was established to calculate the full temperature distribution. Comparison between the model calculation and experimental measurement showed a good agreement, which demonstrates that the present model can be used in engineering design to estimate the temperature distribution of high-power LED street lamps.
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      Synchronous optical code-division multiple access systems with constant multi-user interference
      • Author(s): L.-L. Jau ; Y.-H. Lee ; M.-H. Chuang ; C.-L. Yang ; Y.-G. Jan
      • Source: IET Optoelectronics, Volume 3, Issue 5, p. 233 –240
      • DOI:  10.1049/iet-opt.2008.0021
      • Type: Article
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      • p. 233 –240 (8)
        A synchronous optical code-division multiple access system with balanced encoder instead of on-off-keying (OOK) encoder is proposed. In the system, the multi-user interference is maintained constant during a frame, and the receiver estimates the interference frame by frame instead of bit by bit. The data rate of the proposed system is no longer severely limited by the electronic processing time in estimating the interference, and the structure of the proposed receiver is simpler than those in OOK systems. In the receiver, both linear and non-linear threshold estimators are introduced. Numerical results show that the proposed system has smaller bit error rate than OOK systems, especially when the number of training bits is increased.
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