Chirping noise of laser diodes under small signal modulation

Distributed feedback laser diodes are of high modulation frequency response. They can be used as light sources and be directly modulated for high bit rate optical communication. As the case of conventional laser diodes, direct intensity modulation of DFB laser diodes brings about chirping, which affects the performance of optical transmission systems. In this paper, chirping characteristics of DFB laser diodes under small signal modulation are studied. Chirping amplitude and phase changing with the modulation frequency are presented. The factors and improvements on the chirping are briefly introduced; The qualitative comparison between the frequency chirping of laser and IM response is made, which validated the similarity between the peak frequency of the frequency chirping and relaxation oscillation frequency, then the conclusion is obtained that any measures to come to attenuation of relaxation oscillation can be used to reduce the chirp; The theoretical relationship of the ratio CPR between the chirping and modulation power has been derived; and have an analysis about the impact for chirping on communication system. It provides the basis for optimization design and improvement on the device performance.