A further strand concerns optical receiver analysis, in particular with respect to the use of optical preamplifiers. To operate a system including an optical preamplifier it is necessary to reduce the amplified spontaneous emission (ASE) noise by use of a filter. It is common to utilise a Fabry-Perot (FP) filter in either bulk or fibre versions and thus an extra component is required at the receiver.

Work in the group has focussed on bit error rate analyses including realistic filter characteristics and pulse shapes. Furthermore, approximation techniques for rapid receiver analysis have also been developed. The use of different wavelengths, that is colours, of light or wavelength division multiplexing (WDM) offers an increasingly attractive path for upgrading the digital telecommunications access network to cope with increasing customer bandwidth requirements.

The economic aspects of service provision in this portion of the network are such that low cost methods of generating a range of wavelengths are necessary. One option is to use an optical filter to provide narrow slice of a broadband noise source producing an approach commonly known as spectral or spectrum slicing (SS). This provides a cost-effective alternative to laser diode sources for WDM systems but introduces excess intensity noise due to the source incoherence. Modelling work in this area produced has led to several significant insights, including demonstrating that SS systems are limited by the interference between pulses (intersymbol interference) before the excess noise becomes the greatest problem.

Block diagram of an optical transmission system employing spectral slicing

• S. B. Sun and M. S. Leeson “Performance of Adaptive Low-Density Parity Check Codes in a Low Cost Spectrum-Sliced WDM Network”, IET Optoelectronics, vol. 5, no. 2, pp. 83-92, 2011.
• S. B. Sun and M. S. Leeson “High-order dispersion mitigation for spectrum-sliced FFH-OCDMA using adaptive prime-hop codes”, Photonic Network Communications, vol. 21, no. 2, pp. 107-116, 2011.
• S. B. Sun and M. S. Leeson “Spectrum-sliced WDM Systems with Optical Preamplifiers”, Fiber and Integrated Optics, vol. 28, no. 6, pp. 417-429, 2009.
• M. S. Leeson and S. Sun and “Spectrum Slicing for Low Cost Wavelength Division Multiplexing”, Mediterranean Journal of Electronics and Communications, vol. 5, no.4, pp. 114-119, 2009.