Recent experiments with an excitable VCSEL micropillar laser with delayed optical feedback demonstrated that the system is able to sustain trains of optical pulses. The laser has two layers of gain and one layer of absorption in the VCSEL cavity, and it is an excitable single longitudinal and transverse mode laser. With optical feedback, a past pulse can trigger a new pulse, creating a pulse train with repetition rate given by the delay time. It is possible to trigger and retime pulses by appropriate external perturbations, in the form of appropriately timed short optical pulses. In particular, several pulse trains can be triggered independently by optical perturbations, and sustained simultaneously in the external cavity, with different timing in between pulses. Such dynamics are also called localised structures, and are investigated here theoretically.
It has been verified experimentally and theoretically that the phase of the electric field is not relevant. The Yamada model – a well-established system of ordinary differential equations for intensity, gain and absorption – is thus a suitable model. As we show, the Yamada model with delayed intensity feedback describes the pulsing micropillar laser system in good agreement with the experiment.
A bifurcation analysis of this model shows that several pulsing periodic solution with different repetition rates coexist and are stable. Although coexisting pulse trains can seem independent on the timescale of the experiment, we show that they correspond here to extremely long transient dynamics toward one of the stable periodic solutions, with equidistant pulses.
Soizic Terrien, Bernd Krauskopf, Neil G. R. Broderick, Louis Andréoli, Foued Selmi, Grégoire Beaudoin, Isabelle Sagnes, and Sylvain Barbay, "Pulse train control in an excitable micropillar laser with delayed optical feedback (Conference Presentation)," Proc. SPIE 10515, Vertical External Cavity Surface Emitting Lasers (VECSELs) VIII, 1051507 (Presented at SPIE LASE: January 29, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2288047.5751416167001.
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