Measurement of the probability distribution of DFB laser phase-induced intensity noise

It is experimentally demonstrated that laser phase-induced intensity noise (PIIN) distributions are in general highly non-Gaussian and in fact often bimodal, thus empirically confirming early theoretical predictions. Specifically, it is shown that when multipath optical systems are driven by sources whose linewidth Δν is small compared to the detection system's electrical bandwidth B, the amplitude distribution of the PIIN is non-Gaussian and has extremely short tails. This is true of the photocurrents generated by self-heterodyne and self-homodyne spectrum analyzers, for which B ≫ Δν is a requirement. It is also true of broadband communication links using externally modulated distributed-feedback (DFB) lasers. One consequence for such links is that when PIIN is their dominant noise sources, they can exhibit a low BER at significantly smaller SNR values than Gaussian statistics predict.