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Optoelectronics, IET

Issue 1 • Date February 2009

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Displaying Results 1 - 6 of 6
  • Discrete mode lasers for communication applications

    Page(s): 1 - 17
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1549 KB)  

    The authors present a novel, low cost laser transmitter for telecommunication systems. This device, called discrete mode (DM) laser, is basically a ridge waveguide Fabry-Perot (FP) laser, whose wavelength spectra has been modified to obtain a single mode operation. This is achieved by perturbing the effective refractive index of the guided mode along very small sections of the laser cavity, by etching features into the ridge waveguide. Suitable positioning of these interfaces allows the mirror loss spectrum of an FP laser to be manipulated in order to achieve single longitudinal mode emission. The waveguide structure requires only a single growth stage and uses optical lithography to realise the ridge. In addition, the fabrication process is re-growth free. Despite this simple and low cost fabrication process, the DM lasers portray many advantages over the distributed feedback and distributed Bragg reflector lasers, such as very high side mode suppression ratio, stable operation over a large temperature range, narrow linewidth and low sensitivity to optical feedback. View full abstract»

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  • Electronic distortion equalisation by using decision-feedback/feed-forward equaliser for transient and adiabatic chirped directly modulated lasers at 2.5 and 10 Gb/s

    Page(s): 18 - 29
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    A thorough study on the beneficial use of electronic distortion equalisation (EDE) in the transmission performance enhancement of conventional low-cost directly modulated lasers (DMLs) is provided. The studies focus first on the compensation of the chromatic dispersion effect and then on the compensation of cascaded filtering effects of DML generated transmission signals in a system, by means of the feed-forward and decision-feedback equalisers (FFE/DFE). The reported studies consider DMLs with different chirp characteristics operating at 2.5 and 10 Gb/s, using parameters that have been extracted from real lasers, previously verified by simulations and experiments. The performance efficiency of EDE is evaluated in terms of eye-opening penalty degradation associated with the signal transmission over a standard single mode fibre. Extensive simulations reveal significant performance improvement for all the examined cases by using the FFE/DFE. Furthermore, the results show that the equalisation efficiency strongly depends on the chirp characteristics of DMLs. View full abstract»

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  • Performance enhancement of outdoor visible-light communication system using selective combining receiver

    Page(s): 30 - 39
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    New generation of high-intensity aluminium gallium arsenide (AlGaAs) and aluminium indium gallium phosphide (AlInGaP) light-emitting diodes (LEDs) which have permitted the replacement of incandescent-based traffic lights with LED-based traffic lights, unfolds the potential of implementing visible-light communication (VLC) system on outdoor environment. The feasibility of outdoor VLC system is undoubtedly questionable because of the significant ambient-light noise caused by daylight. Existing performance studies related to this system have not taken into account the effect of ambient-light noise which varies largely from day time to night time. The authors propose an analytical daylight noise model based on a modified Blackbody radiation model to capture the effect of ambient-light noise and conduct an in-depth study on the impact of daylight on the system performance. The proposed daylight noise model allows us to perform analytical analysis which produces relatively accurate results with less complexity, as compared to the existing time-consuming simulation. The authors also introduce a new receiver structure employing the selective combining technique to significantly reduce the effect of background noise. From numerical analysis, the authors show that the new receiver structure is able to achieve a signal-to-noise ratio (SNR) improvement of approximately 5 dB and establish a stable communication link at any time of the day. View full abstract»

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  • Development of street lighting system-based novel high-brightness LED modules

    Page(s): 40 - 46
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (546 KB)  

    The development of high-power light emitting diode (LED) for street lighting is growing continuously owing to its greater energy efficiency, long operating life and light control. Users of street lighting are compelled to adopt this technology over traditional light sources. An alternative solution based on a novel 9LEDM (9-LED module) and adaptive driver is shown. The design of the 9LEDM is derived from the thermal, photometric, power electronics techniques to meet the application of street lighting. The 9LEDM performances with a price less than 1$/Watt (W) and luminous flux higher than 110 Lumens (Lm)/W compared with traditional ones. Furthermore, several restrictions of driving the solid-state lighting loads are overcome by an adaptive street lighting driver with an AC/DC converter of a quasi-resonant operation flyback topology and with Soft Startup, Full ON, Half ON functions by sensing the ambient light and working temperature. Finally, a high performance/cost 50 W pole head as a design example is conducted to illustrate the complete design process, and the results from the demonstration projection with two pole heads of 50 W for a 12 m pole show a luminous intensity range from 38 to 19 lux with a heat sink temperature of 58degC and an energy saving more by 72% compared with conventional street lighting after three months of running. View full abstract»

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  • Optimum mapping in an optical multiple pulse position modulation link using a maximum likelihood sequence detection scheme

    Page(s): 47 - 53
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (259 KB)  

    The performance analysis of any multiple pulse position modulation (PPM) system is extremely time consuming because of the effects of different detection errors on the multiple PPM alphabet. In a small multiple PPM system such as (2 12), there are 64 codewords and each one can have ten possible false alarms, two possible erasures and four possible wrong-slot errors. The situation is worse if higher-order codes are considered. A novel algorithm, which reduces the time taken to predict the sensitivity of a multiple PPM system from almost 2 h of analysis to under a second, is presented. Results obtained using this method agree with those obtained using a full mathematical model. The authors also present a methodology that obtains a close to optimum mapping for any multiple PPM system. Detailed results show the effectiveness of this mapping routine. View full abstract»

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  • Angle relations inside a bent waveguide for a wedge display

    Page(s): 54 - 60
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (746 KB)  

    Owing to the physical limitations of the tools used to manufacture waveguides, a some amount of bending occurs. For a wedge display, such bending would cause problems for the final picture presented as the angles of light injection into the wedge are susceptible to changes in curvature. The right-angled triangle approximation shows that a 5deg bending might be tolerable in the display, but significant distortion occurs for greater bending. View full abstract»

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Aims & Scope

IET Optoelectronics covers but is not limited to the following topics: Optical and optoelectronic materials; Light sources, including LEDs, lasers and devices for lighting; Optical modulation and multiplexing; Optical fibres, cables and connectors; Optical amplifiers; Photodetectors and optical receivers; Photonic integrated circuits; Nanophotonics and photonic crystals; Optical signal processing; Holography; Displays.

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IET Research Journals