Nonlinear Dynamics in Semiconductor Lasers - Abstract

Columbo, Lorenzo

Self-pulsing and self-frequency combs generation in single section Quantum Dots ring lasers. A theoretical analysis.

We theoretically studied coherent phenomena in the multi-mode dynamics of single section semiconductor ring lasers with Quantum Dots (QDs) active region. In the unidirectional ring configuration our simulations show the occurrence of self-pulsing in the system leading to ultra-short pulses (sub-picoseconds) with a THz repetition rate. The linear stability analysis of the continuous wave solutions (CW) is in good agreement with the numerics and it allows to establish an analogy between the observed CW instability and the well-known Risken-Nummedal-Graham-Haken instability consisting in the amplification of the Rabi frequency of the system and affecting the multi-mode dynamics of two-level lasers [1], [2]. In the temporal domain semiconductor lasers operating in self-pulsing regime are breakthrough alternatives to passive and active mode-locked devices for applications to time resolved measurements of e.g. fast molecular dynamics. In the frequency domain the self-pulsing regime corresponds to a frequency comb, i.e. a set of narrow and equally spaced optical lines with almost equal amplitude much sought after for a number of applications in metrology, molecular spectroscopy, high-data rate optical interconnections and in the emerging field of long-range, high-capacity wireless communication based on combined THz photonics and THz electronics [3]. We finally show that self-pulsing in unidirectional ring QD lasers is robust and controllable phenomenon over a wide range of bias currents, device lengths and degree of inhomogeneous broadening. In the bidirectional ring configuration we observed a much lower CW instability threshold associated to spatial hole burning due to the standing wave pattern in the carriers density that cannot be washed out by diffusion in low dimensional active media such as QDs and Q-Dashes. Coherent dynamics leading to self-frequency comb generation is found for sizable intervals of the bias current, but it does not correspond to the emission of optical pulses.