Online ISSN
1751-8776
Print ISSN
1751-8768
IET Optoelectronics
Volume 6, Issue 6, December 2012
Volumes & issues:
Volume 6, Issue 6
December 2012
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- Author(s): C. Reis ; L. Costa ; A. Bogoni ; A. Maziotis ; A. Teixeira ; C. Kouloumentas ; D. Apostolopoulos ; D. Erasme ; G. Berrettini ; G. Meloni ; G. Parca ; H. Brahmi ; I. Tomkos ; L. Poti ; M. Bougioukos ; P.S. André ; P. Zakynthinos ; R. Dionisio ; T. Chattopadhyay ; H. Avramoupoulos
- Source: IET Optoelectronics, Volume 6, Issue 6, p. 263 –276
- DOI: 10.1049/iet-opt.2012.0012
- Type: Article
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p.
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This study provides a review of all-optical flip-flops (AOFFs) technologies, and their possible experimental implementation solutions, for a variety of applications in optical communication networks. A description of the state-of-the-art experimental implementations and validation testing of the technologies used in different AOFFs schemes is made, presenting to the interested reader an overview of the up to date AOFFs design schemes. Some of the research results presented in this study were performed under the EU NoE EURO-FOS project consortium. This study also provides researchers working on this topic with interesting trends that are worth considering in their own research studies. - Author(s): N.-M. Lin ; S.-C. Shei ; S.-J. Chang
- Source: IET Optoelectronics, Volume 6, Issue 6, p. 277 –281
- DOI: 10.1049/iet-opt.2011.0075
- Type: Article
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p.
277
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This study reports the development of GaN-based light-emitting diodes (LEDs) with Ni/Ag (1 nm±0.2 nm/100 nm±2 nm) layers underneath an insulating layer of SiO2. The results of this study confirm the thermal stability of a Ni/Ag mirror with reflectance of 90.6±1.5% following thermal annealing at 500°C for 5 min. This approach achieves far superior current spreading and prevents the absorption of light through the use of an opaque p-pad electrode. With 20-mA current injection, the output power of the LED with SiO2/Ni/Ag layers was 6.5 and 12.1% greater than that of LEDs with and without a SiO2 layer, respectively. Furthermore, the 20-mA forward voltage increased only slightly from 3.03±0.01 to 3.05±0.01 V for LEDs with SiO2/Ni/Ag layers. Good reliability is also achieved for LEDs with SiO2/Ni/Ag layers. - Author(s): Y.-C. Kuo ; Y.-J. Luo ; L.-J. Liu
- Source: IET Optoelectronics, Volume 6, Issue 6, p. 282 –289
- DOI: 10.1049/iet-opt.2012.0027
- Type: Article
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p.
282
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In this study, a digital solar energy harvesting integrated circuit and system synthesis tool is developed with visual basic software. Using this synthesis tool, the design time to market can be significantly reduced. A metering technique is also developed to combine the solar energy harvesting system with an online system. Therefore users can obtain the proposed system's information at any time and from anywhere. Meanwhile, there is no need to buy any additional scope or metre to undertake the measurements. Computer simulations and experimental results demonstrate the accuracy and the superior performance of the proposed technique. - Author(s): N. Avlonitis and P.B. Charlesworth
- Source: IET Optoelectronics, Volume 6, Issue 6, p. 290 –297
- DOI: 10.1049/iet-opt.2011.0098
- Type: Article
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290
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A method for the evaluation of performance of free space optical communications systems utilising modulating retro reflectors under weak turbulence is presented. The model considers the effects of system physical parameters, such as the modulating retro reflector effective size and receiver aperture diameter, on the bit-error rate (BER) and the capacity. Different spatial spectrums are used with the model and the effect of aperture averaging is evaluated directly from the normalised spatial covariance in each case. The log-normal distribution is adopted for the evaluation of BER in the weak fluctuation regime. Finally, for the first time the capacity of a system using modulated retro reflectors is calculated using a recently proposed closed-form expression. The model can be used as a performance metric in network routing algorithms. - Author(s): A.A. Jasim ; S.W. Harun ; K.S. Lim ; B.M.A. Rahman ; H. Ahmad
- Source: IET Optoelectronics, Volume 6, Issue 6, p. 298 –302
- DOI: 10.1049/iet-opt.2012.0025
- Type: Article
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p.
298
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The authors demonstrate a microfibre Mach–Zehnder interferometer (MMZI) using a single silica optical microfibre fabricated using flame-heated-drawing technique. The microfibre was cut into two parts: the first part is stretched straight, whereas the second part is bent and manipulated to form an MMZI. The fabricated MMZI shows good interference fringes with the highest extinction ratio of 14 dB. The free spectral range (FSR) of the interferometer can be tuned from 0.14 to 0.75 nm by micromanipulating the path-length difference of the MMZI under an optical microscope. It is also observed that the FSR is unaffected by the volatility of the surrounding air. The MMZI is also used to demonstrate a compact current sensor. The proposed sensor uses a copper wire, which touching one arm of the MMZI so that the wavelength shift is linearly proportional to the square of the amount of the flowing current. The slope efficiency of the sensor is obtained at 60.17 pm/A2. - Author(s): S. Li ; D.S. Kuo ; C.H. Liu ; S.C. Hung ; S.J. Chang
- Source: IET Optoelectronics, Volume 6, Issue 6, p. 303 –306
- DOI: 10.1049/iet-opt.2012.0019
- Type: Article
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The authors propose a simple direct wet etching method to texture the indium-tin-oxide (ITO) p-contact layer of GaN-based light-emitting diodes (LEDs). It was found that high density ITO nanorods with average diameter of 140 nm and average height of 120 nm were formed after the LED samples were immersed in a solution consists of HCl (30%), FeCl3 (30%) and de-ionised water (40%) for 2 min at room temperature. It was also found that output power of the LEDs with 2 min direct wet etching was 21% higher than that of conventional LEDs. Furthermore, it was found that such enhancement should be attributed to the enhanced photon extraction from the front surface of the LED chip. - Author(s): J.P. Ding and Y.F. Ji
- Source: IET Optoelectronics, Volume 6, Issue 6, p. 307 –317
- DOI: 10.1049/iet-opt.2012.0044
- Type: Article
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p.
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Visible-light communication system that utilises white light-emitting diode (LED) lighting equipment has been proposed and expected to provide uniform wireless communications and illumination simultaneously. Owing to multipath transmission channel characteristics, up to now, it is still challenging to obtain uniform signal-to-noise ratio (SNR) for each position within the indoor environment. In this study, an evolutionary algorithm (EA)-based alternative scheme is proposed to optimise the SNR distribution for indoor visible-light communication systems. Presented analysis shows that in three distributed lighting configurations, when the optical powers of individual white LED lighting equipment are dynamically controlled by tailored EA, the dynamic range of SNR referenced against the peak SNR can be reduced by up to about 24.7% whereas the uniformity illuminance ratio is improved from less than 0.63 to over 0.70 with the impact to root-mean-square delay spread is negligible. Furthermore, the relationship between the field of view of receivers and the optimisation performance is presented as well. - Author(s): D. Zhang ; W. Liu ; Z. Xue ; Z. Zhang ; Y. Zhang ; L. Chen ; Q. Hu ; C. Guan
- Source: IET Optoelectronics, Volume 6, Issue 6, p. 318 –326
- DOI: 10.1049/iet-opt.2012.0020
- Type: Article
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p.
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A reconfigurable demodulator for both differential-phase-shift keying (DPSK) and differential-quadrature-phase-shift keying (DQPSK) formats is theoretically and experimentally presented. In this crystal-based demodulator, a rotatable quarter-wave plate is implemented to switch the operation of the device between DPSK and DQPSK modes. To mitigate polarisation-dependent-frequency shift (PDFS), the authors control uniformity of optical path length differences for the orthogonal polarisation states in the delay crystal, a liquid crystal phase-tuning retarder is used to improve the tuning time. The design and fabrication consideration of this device are also discussed. The packaged device has a low PDFS of within ±0.2 GHz over C-band, fast tuning time of 20.5 ms, error-free demodulation of optical transponder unit-3 DPSK and DQPSK signals can be achieved.
Evolution of all-optical flip-flops and their applications in optical communications networks
GaN-based light-emitting diodes with a thermally stable mirror structure underneath an insulating SiO2 layer
Synthesis design of digital solar energy harvesting integrated circuits and systems
Performance of retro reflector-modulated links under weak turbulence
Microfibre Mach–Zehnder interferometer and its application as a current sensor
Efficiency improvement of GaN-based light-emitting diodes by direct wet etching of indium-tin-oxide layer
Evolutionary algorithm-based optimisation of the signal-to-noise ratio for indoor visible-light communication utilising white light-emitting diode
Reconfigurable crystal-based demodulator for both differential-phase-shift keying and differential-quadrature-phase-shift keying formats: principle, design and performance
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