OPTICAL BISTABILITY IN INTERDIGITATED SEMICONDUCTOR LASERS

Abstract

Saturable absorber in semiconductor lasers was extensively studied since 1964 when Lasher proposed a bistable semiconductor laser based on inhomogeneous current injection. The main characteristics of saturable absorber is bistability in the light versus current curve. This research project examines in detail the effects of saturable absorber using a new device structure developed in this centre. The device, called the interdigitated contact semiconductor laser, has all the characteristics of a laser with saturable absorbers and is yet the most flexible structure studied to elate. lt. has two contacts and allows the amount, of saturable absorbers to be altered electrically. Additionally, light can be injected in the transverse direction through the unmetalised regions to interact with the carriers for optical switching. In this work, a 2D computer simulation program was developed to simulate the effects of parametric variations on the bistable behaviour. Some of the factors include current spreading, carrier diffusion, differential gain ratio, carrier lifetime ratio, absorber length and gain region length. The effect of longitudinal and transverse light injection was also simulated. A comprehensive theory on the mechanism behind the bistable behaviour was developed in this work. It allows the effect of the parametric variations to be explained consistently. The simulation results were shown to agree with the experimental results by some pioneers in this field and is often more thorough than the earlier works. The device was also fabricated and bistable behaviour was observed. We have additionally demonstrated the effect of transverse light injection which is a new development in this field. The functionality of the device is wide and applications include Optoelectronics AND gate, optical memory element, optical NOT gate, Optoelectronic bistable switch, light signal power limiter, light signal booster and optical bistable switch.