Progress in Asymmetric Resonant Cavities: Using Shape as a Design Parameter in Dielectric Microcavity Lasers

We report on progress in developing optical microresonators and microlasers based on deformations of dielectric spheres and cylinders. We review the different semiconductor and polymer dye microlasers which have been developed and demonstrated using this approach. All the lasers exhibit highly directional emission despite the presence of ray chaos in the system. Lasing has been demonstrated using both optical pumping and electrical pumping in the case of InGaP quantum cascade lasers and very recently in GaN MQW lasers. Lasing modes based on stable and unstable periodic orbits have been found as well as modes based on chaotic whispering gallery orbits; the lasing mode depending on the material, shape and index of refraction. The lasing from modes based on unstable orbits dominated for certain shapes in the GaN cylinder lasers, and is related to the “scarred” states known from quantum chaos theory. Extreme sensitivity of the emission pattern to small shape differences has been demonstrated in the polymer microlasers. Large increases in output power due to optimization of the resonator shape has been demonstrated, most notably in the quantum cascade “bowtie” lasers. Efficient numerical approaches have been developed to allow rapid calculation of the resonant modes and their directional emission patterns for general resonator shapes. These are necessary because the lasing modes are not usually amenable to standard analytic techniques such as Gaussian optical or eikonal theory. Theoretical analysis of the directional emission from polymer lasers has shown that highly directional emission is compatible with strongly chaotic ray dynamics due to the non-random character of the short-term dynamics. Very recently uni-directional emission and electrical pumping have been demonstrated in the GaN MQW system using a spiral-shaped resonator design, bringing this general approach in which shape is used as a design parameter closer to useful applications.