Sub-wavelength resolution dynamics of semiconductor passively mode-locked lasers induced by optical feedback

We present a numerical analysis that focuses, for the first time to our knowledge, on the feedback-induced dynamics in a semiconductor passively mode-locked laser with sub-wavelength resolution. Our results and the corresponding theoretical explanations elucidate several aspects of the laser dynamics under self-injection including inherent properties of mode-locked lasers such as pulse intensity noise and timing jitter. We show that the dynamics of the laser exhibit a periodicity in the wavelength scale apparent only on integer multiples of the laser cavity and decays in the time scale of the pulse duration following the coherence of the mode-locked laser. The corresponding phenomena are dominant for external cavities that are shorter than the laser cavity and superimposed on the previously reported dynamics of the semiconductor mode-locked lasers for longer external delays. Since these dynamics are triggered by low feedback levels, our study could be useful for the optimization of the laser operation in cases where ultra-short external cavity lengths are involved (integrated designs, power collection with fiber tapers, etc.).