Effect of gain compression on the FM nonlinear distortion in semiconductor lasers

The FM intermodulation characteristics of directly modulated semiconductor lasers of relevance to the design of subcarrier multiplexed applications are investigated, "Adiabatic" chirp which has previously not been considered is shown to have a large impact on the reduction of the distortion levels at frequencies below half the resonance frequency of the laser. Results are presented showing that, in contrast to previous suggestions, FM modulation may be advantageous, imposing less requirements on laser linearity than IM modulation.