  We investigate the effect of tunable optical feedback on a commercial DFB
laser edge coupled to a Silicon Photonics 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 semi-analytical 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 Photonics 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.
