Tuning the emission wavelength of semiconductor ring lasers with on-chip filtered optical feedback

In this paper we discuss the use and implementation of on-chip filtered optical feedback in order to tune the emission wavelength of a semiconductor ring laser. In this device, a directional coupler is used to couple part of the light emitted by the laser to a feedback section integrated on the same chip. The feedback section contains two arrayed waveguide gratings and a set of semiconductor optical amplifiers to provide filtering of particular longitudinal modes sustained by the ring cavity. Each of the two counter-propagating modes supported by the ring laser is coupled back into the same direction after filtering in the feedback section. We show that, for appropriate currents injected into the semiconductor optical amplifiers, the emission wavelength can be tuned and that single mode operation in both directions is achieved. We use a rate equation model in order to demonstrate tuning of the device theoretically.