Stabilization and frequency control of a DFB laser with a tunable optical reflector integrated in a Silicon Photonics PIC

We investigate the effect of tunable filtered optical feedback on a commercial DFB laser edge coupled to a silicon photonic planar integrated circuit in which a tunable reflector has been implemented by means of a ring resonator-based add-drop multiplexer. Controlled optical feedback allows for fine-tuning of the laser oscillation frequency. Under certain conditions, it also allows suppression of bifurcation modes triggered by reflections occurring elsewhere on the chip. A semianalytical model describing laser dynamics under combined optical feedback from the input facet of the edge coupler and from the tunable on-chip reflector fits the measurements. Compensation of detrimental effects from reflections induced elsewhere on a transceiver chip may allow moving isolators downstream in future communications systems, facilitating direct hybrid laser integration in silicon photonic chips, provided a suitable feedback signal for a control system can be identified. Moreover, the optical frequency tuning at lower feedback levels can be used to form a rapidly tunable optical oscillator as part of an optical phase-locked loop, circumventing the problem of the thermal to free carrier effect crossover in the FM response of injection current-controlled semiconductor laser diodes.