We consider a VCSEL micropillar laser with an internal absorber section, which has been shown to show excitable behaviour before its threshold. The addition of optical feedback offers the possibility to generate a pulse train of low jitter with a repetition time that is controlled by the length of the feedback loop. We perform a bifurcation analysis of the governing Yamada equations for the intensity, gain and absorption and with delayed feedback. This reveals an increasing variety of new dynamics and a considerable degree of multistability when the delay time is increased.
More concretely, we present a bifurcation/stability diagram in the plane of feedback delay and feedback strength --- the two parameters of the external feedback loop. The organising feature is a winding curve of Hopf bifurcations, which develops an increasing amount of self-intersections as the delay of the feedback is increased. Along certain parts of the Hopf curve stable periodic solutions are created, which are physically self-pulsations with an increasing number of pulses in the external cavity. Several of these self-pulsations may coexist stably, and their basins of attractions are intermingled in a complicated way. As a result, the micropillar laser is very sensitive to small perturbations and noise while in such a multistable configuration. We also find multifrequency dynamics, where the amplitude of the self-pulsations is strongly modulated.
Bernd Krauskopf, Soizic Terrien, Neil Broderick, and Sylvain Barbay, "Dynamics of a micropillar laser with saturable absorber and delayed optical feedback (Conference Presentation)," Proc. SPIE 10515, Vertical External Cavity Surface Emitting Lasers (VECSELs) VIII, 1051506 (Presented at SPIE LASE: January 29, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2288076.5751425831001.
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