Dynamic properties of push-pull DFB semiconductor lasers

Using the spatially dependent multimode rate equations, we present a systematic study of small-signal dynamics of push-pull DFB lasers. The various spatial effects such as the longitudinal spatial hole burning, nonlinear gain compression, side-mode contribution, and push-pull modulation are all analyzed in a self-consistent manner. With the closed form expressions for the AM and FM responses, we show explicitly that the resonance frequency and the first cut-off frequency of push-pull DFB lasers are determined by the frequency spacing and the threshold gain difference between the lasing mode and its closest antisymmetric side mode, respectively. Numerical results reveal that a high modulation speed with a very low frequency chirp can be achieved with the push-pull DFB lasers.