Rothnie, Derek Malcolm; (1998) Link optimisation for optical WDM transmission systems. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis investigates the optimal transmission parameters required for wavelength division multiplexing (WDM) of high bit-rate channels over non-linear, dispersion managed fibre. With the availability of high powered laser sources, the advent of optical amplifiers and the long distances of some fibre networks the nonlinearity of the fibre medium can no longer be neglected. The non-linear optical Kerr effect is introduced in the context of fibre transmission and the three effects resulting from this non-linearity are presented, viz. Self-Phase Modulation (SPM), Cross-Phase Modulation (XPM) and Four-Wave Mixing (FWM). The non-linear scattering processes of Stimulated Brillouin Scattering (SBS) and Stimulated Raman Scattering (SRS) are also outlined. The detrimental impact of fibre dispersion is given and various schemes proposed to manage fibre dispersion are discussed with emphasis placed upon the use of Dispersion Compensating Fibre (DCF) for upgrading existing, embedded standard fibre. To accurately model signal propagation over such complex links the numerical Split-step Fourier method was employed to solve the Non-Linear Schrodinger Equation. The limitations inherent in this method are investigated, specifically the step-size effect which determines the accuracy of the calculations. The initial investigations by simulation concern the propagation of a single channel over the various dispersion managed systems. The maximum distances achievable in terms of channel bit-rate and channel power due to the combined action of dispersion and non-linearity (from SPM) are compared. The limitations from FWM and XPM on multi-channel propagation are then examined and optimisation of the WDM parameters: channel spacing, channel power and channel bit-rate, are determined. The conclusion draws together the results obtained and presents optimal operating parameters for WDM systems. Possible avenues for further research are then explored.

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