We report on a bifurcation scenario from which emerges oscillations at a frequency higher than the relaxationoscillation frequency in an edge-emitting laser diode subjected to polarized optical feedback; these oscillations appear in the square-wave regime. The study has been performed experimentally and numerically based on Lang-Kobayashi model. We unveil bifurcation diagrams showing a clear bifurcation point that marks the transition between sustained and damped oscillations on the plateaus of square-waves. We extend this first bifurcation study by providing additional analytical insight to characterize the main parametric dependence of the frequency of these undamped oscillations.
Vertical Cavity Surface Emitting Lasers (VCSELs) with isotropic optical feedback are studied especially in the so-called low frequency fluctuations regime. Correlation properties between linear polarizations are analyzed both analytically and numerically. The RF spectrum shows a double peak structure close to the external cavity frequency which can be predicted by our adapted Spin-Flip Model (SFM). We provide here numerical evidence of the interplay between modes and anti- modes which are solutions of the stability analysis of the VCSEL with feedback and demonstrate that this interplay is responsible for the double peak structure.