12.1 Introduction

Wavelength conversion has received much attention recently due to its potential to increase the capacity of a wavelength division multiplexing (WDM) communication system by assigning dynamic links between channels. A semiconductor laser amplifier (SLA) with high non-linearity and short carrier lifetime has the potential to achieve all-optical wavelength conversion. The wide gain bandwidth travelling-wave SLA provides the necessary broad wavelength conversion span and the lifetime of the carriers provides the speed necessary for high bit-rate wavelength conversion. The three main techniques of achieving wavelength conversion in a SLA are (i) Cross-Gain Modulation (XGM) [ ^{[1] [2] [3] [4]}], (ii) Cross-Phase Modulation (XPM) [ ^{[5] [6] [7] [8]}] and (iii) Four Wave Mixing (FWM) [ ^{[9] [10] [11]}]. The prime objective of a wavelength converter is to achieve conversion rate for a signal of 10 Gb/s and above with a high extinction ratio, low noise factor and high conversion efficiency. Wavelength conversion using cross gain saturation in SLAs is the most straightforward method among the various proposed methods. It is simple to implement. Polarisation insensitive amplifiers can be employed in order to minimize the polarisation effects of the device. Recently, experimental and theoretical results have shown that wavelength conversion using XGM in SLAs has the potential to handle data transmission rates ranging from 10 to 40 Gb/s [ ^{[12] [13] [14] [15] [16]}]. However, the disadvantage of the XGM is the extinction ratio degradation for conversion to longer wavelengths. The output extinction ratio for shorter...