I. Introduction
Recent work on Opto Electronic Integrated Circuits (OEICs) has shown that it is possible to monolithically integrate a resonant tunnelling diode (RTD) with an optical waveguide electroabsorption modulator (RTD-EAM) [1] and a RTD with a laser diode (RTD-LD) [2]. Crucially the RTD introduces negative differential resistance (NDR) into the electrical characteristics of the RTD-EAM and the RTD-LD.