20 GHz Mode-Locked Laser Diodes With Integrated Optical Feedback Cavities in a Generic Monolithic InP Photonics Platform

We investigate integrated mode-locked laser diodes with distributed Bragg reflectors fabricated in the JePPIX-Oclaro indium phosphide photonics platform. The optical and radio-frequency (RF) characteristics of passively mode-locked lasers with and without monolithically integrated feedback cavities were measured and compared. The RF linewidth of the mode-locked laser could be reduced by integrating an optical feedback cavity of a particular length and a tunable magnitude of feedback. A maximum linewidth reduction factor of 1.9 was observed near the onset of mode locking, but increasing the laser optical power tended to lead to unstable operation. Increasing the drive current of the design without feedback also reduced the RF linewidth. A reduction factor of 7.6 was observed.