Dynamical Control of Non-Hermitian Coupling between Subthreshold Nanolasers Enables Q-Switched Pulse Generation

Abstract

Non-Hermitian photonics provides a framework to engineer the gain and loss of optical modes in open systems, enabling the control of their spectral and dynamical properties. In particular, the ability to dynamically tune modal losses offers a route to implement functionalities traditionally relying on cavity Q-factor modulation, such as Q-switching, within nanophotonic platforms. Here, we demonstrate the generation of short optical pulses in a pair of phase-coupled photonic crystal nanolasers by exploiting non-Hermitian coupling. Two waveguide-coupled nanocavities are operated below their individual lasing thresholds and subjected to asymmetric optical pumping such that a transient carrier-induced detuning modifies the interference conditions between them. This dynamically controls the gain and loss of collective modes. Upon crossing a resonance condition, this leads to the rapid release of stored carrier energy as an optical pulse. A rate-equation model captures the interplay between carrier dynamics and modal coupling and reproduces the observed behavior. Experiments performed on an indium phosphide platform show pulse generation from cavities that do not lase efficiently on their own in continuous-wave operation with temporal characteristics governed by carrier dynamics. These results indicate that non-Hermitian coupling can be used to control the effective cavity losses over time, providing a route to pulse generation in integrated photonic systems.