Transmission-line delay limitations of laser bandwidths

Abstract

The paper describes the constraints placed on modulation bandwidths of horizontal-cavity semiconductor lasers by the dissipative and dispersive effects due to the transmission of electric signals along a narrow injection stripe. The calculations employ a distributed transmission-line model where the incremental small-signal laser equivalent circuit incorporates the effects of photon-carrier interactions represented in relaxation oscillations. At 150 μm cavity length, such as those feasible in strained quantum-well structures, the bandwidths appear to be limited to approximately 30 GHz even under the most idealised conditions. It is suggested that further improvements in bandwidths will require a judicious design of the laser travelling-wave structure. Vertical cavity laser structures may offer an alternative approach to increasing the bandwidth.