Optical feedback-induced quasiperiodic cascade in optically injected semiconductor lasers

Optical injection (OI) is a widely used technique for stabilizing the frequency and linewidth of lasers, as well as for enhancing nonlinear dynamical behaviors. When optical feedback (OF) is added to an optically injected laser, the injection-locking (IL) region is modified, typically shifting toward negative detunings, while the system exhibits more complex and richer unlocked dynamics. Although asymptotic analyses predict that OF leads to an oscillatory IL boundary, this phenomenon has not yet been observed experimentally. Recent numerical investigations have shown that optical feedback significantly alters the transition to locking, resulting in a cascade of quasiperiodic bifurcations. We confirm experimentally that as the driving frequency is tuned, the slave laser alternates between periodic, quasiperiodic, and chaotic regimes, with the feedback delay playing a key role in this sequence. Such hybrid OI-OF configurations are promising for applications in random number generation and neuromorphic photonics, highlighting the importance of a deeper understanding of their underlying dynamics.