TABLE OF CONTENTS In Chapter 3, we have examined how optical amplification can be achieved in semiconductor lasers. We have seen that the formation of an active region due to population inversion in a forward biased p.n. junction will introduce optical gain, and a simple dielectric waveguide will be formed due to the resulting refractive index step. The semiconductor laser amplifier amplifies signals which travel across the active region via the dielectric waveguide. In this chapter, we will apply some of the mathematical principles of electromagnetics to analyse how optical signals propagate across a semiconductor laser amplifier by treating them as electromagnetic waves [ [1], [2]]. This investigation is important because the propagation characteristics of optical signals in the amplifier determine the electromagnetic field distribution inside the structure, which affects the photon density in the amplifier and is crucial in determining the amplifier gain, gain saturation and noise characteristics.
The electromagnetic analysis of a semiconductor laser amplifier (SLA) involves two steps. Firstly, one has to determine the transverse field distributions in the amplifier. This is affected by the dimensions of the active region on the x ? y plane of the dielectric optical waveguide formed in the active region [ [3], [4]]. Secondly, one has to determine the longitudinal field distributions. This is affected by the amplifier length and the boundary conditions along the direction of propagation of signals. Both of these field distributions in the amplifier depends on the group velocity of signals,...
