FM and IM intermodulation distortions in directly modulated single-mode semiconductor lasers

Intermodulation distortion in directly-modulated semiconductor lasers is described with the aid of a nonlinear differential equation for the photon density. Both frequency modulation (FM) and intensity modulation (IM) have been investigated. Curves are presented of the magnitudes of the intermodulation products relative to the carriers intensity. Second order distortions are also reported. The comparison of the Bessel function analysis and the perturbation method is quite successful. Finally, laser´s FM and IM modulation characteristics are compared, and these theoretical results show that distortion levels would be stronger in FM than in direct IM, when the same operating conditions are adopted