Title:  Applications of nonlinear dynamics in semiconductor lasers with time-delayed feedback in microwave photonics

Committee: 

Dr. Citrin, Advisor

Dr. Locquet, Co-Advisor

Dr. Voss, Chair

Dr. Declercq

Abstract: The objective of the proposed research is to investigate the dynamical phenomena and applications of a laser diode subjected to time-delayed feedback. In such a system, some light from the laser is converted to photocurrent that is fed back into the laser injection terminal, which can then display periodic oscillations in its optical intensity. We demonstrate experimental evidence that, as the feedback level is varied, a step-wise change in the oscillation frequency manifests itself in the output optical intensity. These transitions in the dynamics can either correspond to an abrupt jump between two limit cycles, associated with a subcritical torus bifurcation of a limit cycle, or a progressive switching mediated by an intermediate quasiperiodic state. Finally, when ramping the feedback level down, hysteresis is observed in the sequence of switching events between the limit cycles. Moreover, optoelectronic feedback on a laser diode is demonstrated to generate two distinct modes of periodic pulse-train formation depending on the injection current $J$ of the laser leading to microwave combs in two distinct regimes. For $J$ close to the threshold current $J_{th}$, the pulse repetition rate $f_{\rm rep}$ is the inverse of the loop delay. This behavior is attributed to feedback-induced gain-switching and leads to comb spacings in the tens of MHz range. In contrast, for $J \simeq 2J_{th}$, the repetition rate $f_{\rm rep}$ is observed to be related to the relaxation-oscillation frequency $f_{\rm RO}$. The potential to generate pulse trains and associated microwave combs may find use in metrology, optical communications, optical sampling, and spectroscopy.