Single Mode Broad Area PT-Symmetric Microring Lasers

Abstract: Single-transverse mode lasing is demonstrated in a broad-area PT-symmetric semiconductor microring arrangement. The proposed scheme is versatile, robust to fabrication errors, and allows for high brightness operation while maintaining spectral purity. OCIS codes: (140.3570) Lasers, single-mode; (140.3948) Microcavity devices; (140.3410) Laser resonators Broad-area lasers provide high output powers while managing the thermal load and reducing the impact of optical nonlinearities [1,2]. Unfortunately, enlarging the cross section of a waveguide inevitably introduces higher order transverse modes and leads to undesired filamentation [3], thus compromising the spectral and spatial fidelity of the laser and limiting the brightness of the output beam. These limitations exist on all scales, and may even be exacerbated in chip-scale semiconductor lasers, where the large gain bandwidths afforded by the active media already pose a challenge in promoting single-mode operation. Tapering along the direction of propagation and/or engineering the refractive index in the cross section have been extensively pursued as possible techniques to enforce single mode operation in such broad area semiconductor arrangements. Despite their success in suppression of higher order modes, the application of these techniques is quite limited because of their inherent sensitivity to perturbations. Lately, the selective breaking of parity-time (PT) symmetry has been proposed as a viable strategy for obtaining single transverse mode operation [4]. Along these lines, by pairing an active resonator/waveguide with a lossy but otherwise identical partner, it is possible to enforce single-spatial-mode performance, even in the presence of strong mode competition i