3.1 Introduction

In Chapter 2, the major characteristics of optical amplifiers were explored. These characteristics are important in determining the ultimate performance of any optical communication system using optical amplifiers [ ^[1]]. However, as discussed in the previous chapter, the exact performance requirements of an optical amplifier vary with its type and the application for which it is used. In this chapter, we continue our discussion by considering how optical amplification can be achieved in semiconductor lasers. This will help us to understand the physical processes which determine the characteristics of semiconductor laser amplifiers (SLAs), and hence the performance requirements in different SLA applications. The mechanisms of optical gain in semiconductor materials will first be reviewed, and we will discuss how optical amplification can be realised in semiconductor laser structures. A summary of the historical development of SLAs from literature will then be reviewed, and different types of semiconductor laser amplifiers will also be examined. Finally, a review of current research trends in different applications, and the subsequent performance requirements of SLAs, will be presented.

3.2 Principles of Optical Amplification in Semiconductor Lasers

It is well known in linear systems theory that an oscillator is essentially an amplifier with positive feedback. The same is true for laser diode oscillators. The gain of an amplifier with positive feedback as mentioned in Chapter 2 is given by:

where G _s is...