Transmission-line delay limitations of laser bandwidths

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