Interlocking of Optical Frequency Combs From a III-V-on-Si Mode-Locked Laser

We investigate the emission spectrum of a semiconductor III-V-on-Si laser operating in a passively mode-locked regime. We find a situation where the laser emits on two mode-locked states characterized by a spectrum of two separated lobes having slightly different repetition rates. As we vary the pump power or the saturable absorber bias voltage, the laser can either emit in one of the two mode-locked states or the two states coexist in a simultaneous dual-comb lasing. Applying active modulation to the saturable absorber bias, we test the coupling between the two combs in a hybrid mode-locked regime. We reveal the possibility to realize a complete synchronisation, or interlocking, of the dual lobes to the RF modulation.