Reducing the sensitivity of semiconductor ring lasers to external optical injection using selective optical feedback

We numerically investigate the influence of an integrated filtered optical feedback on the behavior of a semiconductor ring laser subject to external optical injection. The optical injection is spectrally directed at one of the non-lasing longitudinal modes of the laser. This so-called side-mode injection can cause wavelength switching, directional switching, and changes in the dynamical regime of the semiconductor ring laser. Such changes are often unwanted as they can affect the stability and the performance of the semiconductor ring laser. We investigate to what extent these undesired effects can be avoided by stabilizing the laser using on-chip filtered feedback. A two-directional mode model is used to investigate the dynamical behavior of the semiconductor ring laser under the simultaneous effect of the external optical injection and the integrated feedback. The results show that on-chip filtered optical feedback can be used to reduce the sensitivity of the semiconductor ring laser to external optical injection.