TABLE OF CONTENTS Currently due to potential applications in high-speed optical fibre communication and logic systems, amplification of ultrashort optical pulses in laser diode amplifiers have been the subject of considerable research interest. The large amplification bandwidth of the laser diode amplifier (LDA) which is about 6000 GHz (50 nm) at 1.55 ?m offers the possibility of amplifying ultrashort pulses without distortion [ [1]].
In a conventional straight cavity LDA, the carrier density reduces as the light intensity increases. This results in gain saturation of the amplifier, which severely limits its applications. The saturation output power can be increased by providing a larger cross-sectional area for the active region which provides a larger number of carriers and a lower optical intensity for a given optical power. However, a larger active-region cross-sectional area results in more than one transverse mode propagation. Bendelli et al. [ [2]] proposed a tapered-waveguide structure for the LDA active region to overcome this problem. In their structure the taper width increases gradually from the input to the output of the amplifier. This allows most of the power to be carried by the fundamental mode, and provides high saturation output power. It has been shown theoretically [ [2] [3] [4]] and experimentally [ [5] [6] [7] [8] [9] [10]] that a tapered-waveguide type LDA provides higher gain saturation compared to a conventional non-tapered travelling-wave LDA. Various tapered waveguides such as linear, exponential, quadratic and Gaussian have been proposed to improve the saturation...
