Bistability in Semiconductor Lasers With Polarization-Rotated Frequency-Dependent Optical Feedback

Abstract—Bistability in the emission frequency of a semicon-ductor laser subject to orthogonal-polarization optical feedback was recently observed experimentally by Farias et al. in 2005. A frequency-sensitive filter (Cs-vapor cell) was placed in the way of the feedback beam to spectrally modulate the feedback power. Two different emission frequencies with the same output power were observed. This observation was understood in terms of a model that took into account the line shape of the filter and the empirical linear relation between the feedback-induced frequency shift and the feedback intensity. The model allowed to calculate steady states but not time-varying solutions. Here we present a rate-equation model that takes into account thermal and gain-saturation effects, and predicts a linear variation of the laser frequency with the feedback strength, together with a small power modulation. This model allows to study time-dependent solutions, and in particular, the transition between the two coexisting states. We show that numerical simulations using this model correctly reproduce the previous observed dynamics, and we present new experimental results in good agreement with our model for the laser response under orthogonal feedback. Index Terms—Bistability, optical feedback, semiconductor lasers. I