Microwave Locking in a Semiconductor Laser With Optical Feedback for Repetitive Intermittent Signal Generation

Intermittent nonlinear dynamics is experimentally investigated for highly repetitive signal generation under microwave locking based on a laser with feedback. The optical feedback is implemented through a free-space cavity with a round-trip delay time τRT. The semiconductor laser exhibits intermittent dynamics to irregularly switch between stable self-locking and fast oscillations at the relaxation resonance frequency ƒr. The laser intensity manifests irregular on-off switching of the oscillations that allows for envelope extraction and binary thresholding to generate intermittent signals, where rough repetition in τRT is subsequently locked by a microwave modulation at 1/RT using an external source. Based on the laser with ƒr ≈ 9 GHz, the feedback supports up to about 20 irregular switches per round trip with τRT of only 3.2 ns. By space-time representation, the intermittent binary envelope signal without microwave locking is found to roughly repeat in every τRT with drifting over 105 round trips. By applying microwave locking, the drifting is significantly suppressed so that the repetition can be highly improved to cover more than 1010 round trips. By further applying random reinitializations, stochastic reproduction of the intermittent signals can be observed with correlation coefficients exceeding 0.7. Though limited to niche applications with stochastic reinitializations allowed, the approach can potentially replace some costly arbitrary waveform generators by probabilistically yielding the highly repetitive intermittent signals without requiring any fast electronics beyond 1/τRT, which is attributed to harnessing the locked nonlinear laser dynamics.