Semiconductor Laser Diode Gain Switching Techniques and Laser Diode Equivalent Circuit Modelling in Spice

Abstract

In developing a compact electro-optic sampling system for industrial use it is desirable to utilize a semiconductor laser diode as the light source since these devices are compact and economical. This thesis investigates several novel laser driver techniques for generating extremely short optical gain switched pulses from a semiconductor laser diode. These techniques include a novel bias control scheme in which the bias to a semiconductor laser diode, that is being driven with a step recovery diode pulse generator circuit, is turned on and off in order to switch the gain switched optical pulses on and off as desired. The second technique involves a mono-cycle scheme that allows a step recovery diode pulse generator circuit, which is customarily driven by a fixed frequency oscillator, to be driven by a mono-cycle pulse train of variable repetition rate. An equivalent circuit model of a laser diode based on the mono-mode rate equations is discussed and implemented in SPICE for the purpose of studying the interaction of the laser driver circuit electronics and the laser diode. The laser diode equivalent circuit is benchmarked against analytical solutions of the rate equations. A qualitative agreement between the measurements of the laser diode optical and terminal voltage responses and the SPICE simulations of the laser diode equivalent circuit model are demonstrated.