Microwave modulation of laser diodes with optical feedback

It is shown theoretically and experimentally that significant variations in the microwave modulation responses of laser diodes occur due to optical feedback from the transmission fiber. These variations decrease if the laser spectrum is less coherent; this can be achieved, for example, by increasing the intensity modulation index. In a recent letter the authors (1989) discussed the small-signal transfer functions; large deviations in the amplitude and the phase response resulted from optical feedback. For large-signal modulation, weaker feedback-induced deviations of the transfer function were predicted by W.I. Way and M.M. Choy (1988). The microwave modulation characteristics are considered in more detail, including the effects of higher modulation indexes. For a typical intensity modulation index of 26%, variations of up to 3 dB in amplitude and 60° in phase were observed