Theoretical Analysis of Unidirectional Operation and Reflection Sensitivity of Semiconductor Ring or Disk Lasers

We theoretically and numerically analyze the unidirectional behavior of ring or disk lasers coupled to a bus waveguide with a relatively strong reflector on one side and find analytical expressions for the ratio of the powers in clockwise and counter clockwise modes. At low bias levels, this ratio depends on the coupling coefficients that determine the coupling between clockwise and counterclockwise modes, whereas at high bias levels it also depends strongly on the gain suppression. We also theoretically and numerically investigate the feedback sensitivity of such lasers and come to the conclusion that ring or disk lasers are generally much more sensitive to external reflections than traditional Fabry-Perot, DFB, or DBR lasers. At high bias levels, the feedback sensitivity also depends strongly on the gain suppression, and at high enough power levels, it can be better than that of traditional edge-emitting lasers.