Subharmonic bifurcations and irregular pulsing behavior of modulated semiconductor lasers

We report the observation of subharmonic bifurcations and irregular pulsing behavior in the output of directly modulated diode lasers. The bifurcation sequence differs from the predicted scenarios most noticeably in the presence of large intrinsic fluctuations which impede any stable period-two oscillations for non-self-pulsing lasers and period-four oscillations for self-pulsing lasers. The nondeterministic noise makes it difficult to observe high-period bifurcation and chaotic behavior in semiconductor lasers by direct current modulation.