TABLE OF CONTENTS Semiconductor laser diode amplifiers (SLDAs) have been developed mainly to replace complex optoelectronic regenerating systems. Some of their main functions are to act as: (i) post-amplifiers for the optical transmitter, (ii) inline amplifiers and (iii) preamplifier for optical receivers [ [1]]. Recently, the development of the erbium doped fibre-amplifiers (EDFAs) has challenged many of the applications of SLDAs. The limitation of the SLDA is the difficulty in achieving high gain, low polarisation sensitivity, low noise figure and low coupling loss at the same time [ [2]]. However, SLDAs have the advantage of small size, low power consumption and low cost (when mass produced), and can be integrated monolithically with other photonic devices like lasers or detectors. Moreover, they are also available at a wavelength of 1.3 ?m and perform other functions such as switching, pulse-shape regeneration and wavelength conversion.
Combinations of antireflection coating, window facet and angle facet structures [ [3]] have made it possible to reduce the facet reflectivity of the SLDA to a negligible value, hence resulting in an almost ideal travelling wave semiconductor laser amplifier (TW-SLDA). Compared with a Fabry-Perot laser diode amplifier, which has a facet reflectivity of about 30% [ [4]], a TW-SLDA has a wider bandwidth, higher gain and is less sensitive to (i) state of polarisation of the input signal and (ii) fluctuations in current and temperature.
Gain saturation in TW-SLDAs severely limits many of its applications. In a wavelength division multiplexing system, the gain...
