Coherence Recovery in a Hybrid Partially Mode Locked III-V-on-Silicon Laser

Abstract

We analyse the spectral properties of an optical frequency comb emitted by a III-V-on-silicon ring laser operated in the hybrid mode-locking regime. We demonstrate that the mode-locked laser has disparate responses to an external RF modulation depending on the saturable absorber bias and pump current. Firstly, we show that, when the mode-locking is fully achieved, the hybrid operation maintains the full mode-locking characteristics across the whole locking region. Secondly, starting from an incomplete passive mode-locking regime, and using the modulation frequency as a control parameter, we demonstrate the gradual improvement of the mode-locking characteristics within the locking tongue. This effect is maximized at the RF locking tongue boundary and manifests in an increase of the spectral width and a diminution of the modal linewidth dispersion.