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International audience; We analyze the quantum dynamics of a two-level emitter in a resonant microcavity with optical feedback provided by a distant mirror (i.e., a half-cavity) with a focus on stabilizing the emitter-microcavity subsystem. Our treatment is fully carried out in the framework of cavity quantum electrodynamics. Specifically, we focus on the dynamics of a perturbed dark state of the emitter to ascertain its stability (existence of time oscillatory solutions around the candidate state) or lack thereof. In particular, we find conditions under which multiple feedback modes of the half cavity contribute to the stability, showing certain analogies with the Lang-Kobayashi equations, which describe a laser diode subject to classical optical feedback.

International audience; It is well known that external-cavity lasers (ECLs) subjected to optical feedback undergo bifurcations which lead to chaos. The most commonly cited route is a quasi-periodic route. We show here that the previously claimed quasi-periodic route is not the typical route given by the Lang-Kobayashi equations. Further, we demonstrate the mechanisms which lie behind this route to chaos. Laser diodes subjected to optical feedback from a distant reflector have been studied intensely for decades as an experimental testbed for nonlinear dynamics [1], as well as, their promise in high-speed, high energy-efficiency applications [2]. The dynamics behind such systems can be characterized by three variables: photon number, carrier number, and optical phase. Previously, most experiments have focused on the optical intensity and carrier number [3-4]. One example of all three being measured is for a fixed optical feedback [5]. Here we measure all three variables simultaneously and vary the optical feedback to see how the dynamics unfold [4-7]. We uncover that the previously identified quasi-periodic route is unlike the LK equations and present an interpretation of the route to chaos that differs from the previous one [3]. The dynamics observed in these systems are manifested from the interplay of two main frequencies, the relaxation oscillation and external cavity frequencies. The relaxation oscillation frequency results from the exchange between photon and carrier populations in the cavity. The external cavity frequency is given by the inverse of the delay time between the laser field and the field re-injected by the external reflective surface. The external-cavity frequency gives the location in optical frequency of attractors known as external cavity modes (ECMs). The separation between each ECM is given by the external cavity frequency and ECMs are labeled with integer numbers. Positive (negative) integers correspond to a higher (lower) frequency from the free running optical frequency of the laser which is labeled ECM 0. These steady state solutions form an ellipse in the optical phase and carrier population plane, which is a projection of phase space. In our experiments for low levels of feedback, the optical intensity, carrier number, and optical phase are characterized by stable operation around a single attractor ECM 0. As feedback is increased, an instability occurs in which the laser operates stably around ECM +1 and the laser’s optical frequency moves between ECM +1 and negative ECMs as seen in Fig. 1. As the laser’s optical frequency is moving toward negative ECMs, the photon and carrier populations undergo periodic oscillations near the relaxation oscillation frequency. We observe that the laser switches periodically between stable emission around ECM +1 and movement toward negative ECMs. For larger feedback, the laser moves around ECM +2 and the laser is characterized in the photon and carrier populations by limit cycles near the relaxation oscillation frequency, while the optical phase is stably around ECM 2.

International audience; Semiconductor laser diodes subjected to recurrent optical feedback are of interest in many high-speed applications. Here we exploit the chaotic terminal voltage dynamics in order to generate random bit streams. Further, a comparison of the voltage dynamics to the commonly utilized optical intensity is performed, and it is found that the voltage is a superior source for generating random numbers because the dynamics suppress the delay-signature and its distribution is more symmetric. Importantly, the system demonstrated here is significantly simpler to implement by eliminating the need for optical to electrical conversion and can be connected directly into electronic applications where GS/s random bit streams are desired