Mitchell, John Edward; (2000) Beat noise and related phenomena in optical networks. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

This thesis is concerned with the characterisation and modelling of spurious signals created in wavelength division multiplexed optical networks. The main focus of this work considers interferometric noise in various optical network scenarios. Simulation tools and analytic techniques are described and developed to produce performance metrics for the systems involved. Interferometric noise has been recognised as a significant limitation in many forms of network, yet primarily only simplistic studies have been performed. A theoretical analysis of interferometric beat noise is presented which uses an accurate statistical characterisation to evaluate system performance. This allows comparison with published results and techniques and enables system factors such as extinction ratio and crosstalk-crosstalk beating to be included which have previously either been ignored or approximated. It is shown that accepted approximations can lead to erroneous results and the prediction of counter intuitive network trends. The results are supported by simulation using the Signal Processing Worksystem (SPW) which exploits custom written blocks to model optical devices. The study of interferometric noise is extended to systems transporting signals with modulation formats other than intensity modulation. Quadrature amplitude modulation is selected for detailed consideration as it is the preferred format for many hybrid fibre radio systems. Results are presented concerning the tolerable crosstalk levels using this scheme for optical generation of millimetre waves using a heterodyne mixing technique as employed in the MODAL system. The tools and techniques described are used to explore two specific illustrative network examples. 1. The use of incoherent light in a technique called spectrum slicing is investigated for the transport of analogue signals 2. The potential effects of interferometric noise in optical beamforming networks are identified, with the main parameters shown to be source wavelength separation and receiver filter order. System performance metrics are presented demonstrating the component characteristics required for acceptable operation.

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