Extreme events in detuned semiconductor lasers under delayed mutual injection

Single-mode semiconductor lasers support fast nonlinear dynamics for investigating extreme events. Although one laser subject to perturbation is sufficient for yielding extreme events, multiple lasers with mutual interactions have yet to be considered. Here, extreme events are found experimentally using two detuned lasers under delayed mutual injection. The mutually injected lasers each emit an intensity that exhibits locking to a constant, except for interruptions by intermittent pulses, including very strong ones as extreme events. Such extreme eruptions from a constant background under mutual injection are different from the continual chaotic oscillations usually obtained under unidirectional injections. By varying the detuning frequency between the lasers, the intermittent pulsations with extreme events are found in a route that involves regular switching between constant and periodic oscillatory intensities. By adopting space-time representation, the extreme events are observed to emerge stochastically, together with some partial repetitions of pulses corresponding to a slightly lengthened round trip. By optimizing the detuning, the maximal normalized occurrence of extreme events reaches 0.8%, which is relatively high among approaches on lasers without external modulations for excitations. On average, about six extreme events are yielded within one round trip of 130 ns, while their short pulse widths are of the order of 0.1 ns. Applicable to generating strong random electrical pulses, the experiments point to the importance of mutual interactions in single-mode lasers for extreme events.