Single-mode low frequency fluctuations in vertical cavity surface emitting lasers with polarization-filtered feedback

Abstract

Low Frequency Fluctuations (LFF) are defined by an abrupt (1 ns) drop-out of the emitted power followed by a gradual (50 ns) build-up of the power until the next drop-out event, when the laser with feedback is biased close to threshold. In this paper experimental and theoretical results on a vertical-cavity surface-emitting laser (VCSEL) with polarized optical feedback are presented. Experimentally, we observe single-mode low frequency dynamics when the VCSEL is biased below the solitary laser threshold. We can choose one of the two typical polarization modes (PM) of the VCSEL to be lasing, by an adequate choice of the polarization direction in the external cavity. Our theoretical analysis is based on a model developed by Loiko et al. which is an extension of the Spin-Flip model. We confirm the appearance of single-mode LFF and also reproduce the response of the orthogonal polarization mode above the solitary laser threshold, both deterministically and in presence of noise. This analysis shows that aiming the feedback at the passive mode (in absence of feedback) forces the active mode to react with short pulses, due to parasitic carrier theft, while targeting the feedback at the active mode induces a smaller response from the orthogonal polarization mode. This difference in response allows us to conclude that the secondary polarization does not play an essential role in the LFF dynamics.