Multi-wavelength emission using compact semiconductor ring laser with filtered optical feedback

Laser diodes that emit multiple wavelengths simultaneously are needed in a range of applications including wavelength division multiplexing, high speed optical networks and tera-hertz generation. In this work we report on an integrated approach to obtain multi-wavelength emission from a semiconductor ring laser based on on-chip filtered optical feedback. Semiconductor ring laser have the advantage that they can be easily integrated with other optical components as they do not require mirrors to form the cavity. Moreover, no thermal control of the wavelength emission is needed and therefore the device can be in principle fast. The filtered optical feedback is realized by employing two arrayed waveguide gratings to split/recombine light into different wavelength channels. Semiconductor optical amplifiers are placed in the feedback loop in order to control the feedback strength of each wavelength channel independently. Experimental observations [Khoder et al, Optics. Lett. 38, 2608-2610, 2013] have shown that the effective gain is the key parameter that has to be balanced using the feedback in order to achieve multi-wavelength emission. This can be achieved by tuning the injection current in each amplifier which will change the feedback phase and strength. Numerical simulations using rate equations reproduce the experimental results and show the effects of feedback phase and strength on the multi-wavelength emission.