Velocity mismatch limits in semiconductor lasers and amplifiers

As modulation bandwidths for semiconductor lasers continue to increase, distributed effects become more important. The velocity mismatch between the optical field and the microwave field has long been known to be an important limit to the bandwidth of modulators, but this effect has so far been ignored in lasers and amplifiers. However, with bandwidths above 40 GHz lasers are now operating in a regime where the wavelength of the microwave field is comparable to the length of the device. Consequently, we can no longer treat the device as a lumped element, but have to consider the propagation effects, i.e. velocity mismatch and microwave propagation loss. In this work we use a simple numerical model to investigate the bandwidth limits set by the velocity mismatch, and compare the performance to that of the ideal, velocity matched case