Contents 1 INTRODUCTION
Modern lumped and travelling-wave electroabsorption modulators (EAMs) have bandwidths greater than 100 GHz, high operational speed and efficacy and are commonly used in both analogue and digital high-speed fibre-optic links. Due to their low operational voltage and compatibility with semiconductor lasers they can be effectively used both as an external modulator or as a part of integrated laser modulator. In lumped EA modulators an applied electric field causes the multiple quantum wells (MQWs), embedded in the optical waveguide, to change the insertion loss of the optical guide, typically in the range of around 15–20 dB/mm [1]. The distinctive feature of TW modulators is that the modulating microwave signal propagates in the same direction and at a speed close to that of the optical signal, causing the phase modulation induced by the microwave signal to accumulate along the propagation length. However, modern TW-EAMs exhibit certain problems, namely mismatch of the microwave and optical field velocities, chirp and unwanted effects caused by photo current generation during operation. These problems limit the bandwidth of the device and its performance at higher speeds. It is crucial to solve these problems if higher frequencies and bandwidths are to be achieved. Measurement-based approaches that have been reported accurately describe the modulator's parameters but are unable to predict the behaviour of devices with different sets of parameters [2].
