Geometry optimization of unidirectional integrated ring laser

Ring lasers, evanescently coupled to an adjacent optical waveguide, are essential components for the upcoming generation of integrated sources. In an ideally symmetric resonator, emission occurs from the both clockwise and counter-clockwise directions, resulting in a potential waste of emitted optical power, while unidirectional emission has been reported in different configurations, for example when asymmetric external reflectivities are used for the coupling waveguide. In the integrated form, a common approach consists in the inserting an S-bend waveguide in the ring, in such a way that the field propagating in the direction that we want to suppress is reinjected in the other direction. The S-bend waveguide must be carefully designed to reduce optical losses and to ensure a sufficient suppression of the undesired field. Using 2D finite- difference time-domain simulations performed with Synopsys RSoft