Electroabsorption modulators for ultra high speed OTDM systems

Abstract

Reports on a fully packaged multiple quantum-well (MQW) electroabsorption modulator (EAM) of bandwidth >10 GHz and the characteristics which make it suitable for application in the short pulse generation and demultiplexing roles in a 4 channel optical time division multiplexing (OTDM) system whose aggregate bit rate of 40 Gbit/s exceeds that of commercially available drive electronics. An EAM must meet some exacting specifications if it is to fulfil these roles. Firstly it must be capable of generating optical pulses with a higher on:off ratio or modulation depth (>23 dB) than is required in either non return to zero systems or soliton systems not employing OTDM in order to avoid inter channel interference. Secondly if the pulse source is to be suitable for soliton transmission in a 4 channel OTDM system, then even if alternate pulses are transmitted in orthogonal polarisation states, transform limited sech/sup 2/ pulses with a duty ratio of <or=8% are required in order to minimise inter-soliton interactions. This duty ratio, which corresponds to a pulse duration of <or=8 ps at a 10 GHz repetition rate, is a factor of 2 smaller than in soliton systems not employing OTDM.