An investigation of the modal coupling of simple branching semiconductor ring lasers

We have investigated, by simulation, the coupling efficiencies of a ring laser into a straight guide in terms of the power splitting ratio between the fundamental modes of the ring and straight output guide, as well as the proportion of power lost to higher-order excitations of the straight guide. The results show that the typical design for a branching ring laser can be optimized by offsetting the output guide position and choosing the proper guide width. This analysis also shows that the symmetrical dual output port design (i.e. tangential straight guide) can result in very poor output coupling efficiencies as compared to the single output port design