Mode selection and unidirectional emission in multiple-deformed microcavity through dynamic tunneling

Abstract

Microcavity holds great promise in demonstrating coherent light sources and photonic circuits due to its superior properties such as high-quality factor, small mode volume, etc. Generally, the rotationally symmetric geometry of microcavity naturally makes its output beams isotropic, which is hard to efficiently collect the emissions. Though several solutions have been proposed to tackle this issue, for instance, boundary deformation, nanoparticle scattering, and mode coupling, at the cost of quality (Q)-factor degradation, large divergence angle of output beams, and complex designs, therefore, which more or less hinders the practical potential of microcavity. Herein, to examine the possibility of simultaneously achieving high-Q and unidirectional emission with narrow angular divergence, we employ a spirally deformed quadrupolar microcavity to manipulate the intracavity physics. Our numerical results show that the chaotic-to-regular tunneling and unstable manifolds synergistically dominate the chirality and the corresponding far-field patterns. The spiral implies sufficient backscattering onto the chaotic modes, which sequently breaks the balance of clockwise and counterclockwise waves and brings such non-equivalence into diamond modes without spoiling their Q-factors. Then strong chirality is formed in the chaotic microcavity that initially reduces the output beams. Meanwhile, the geometry deformation from pristine quadrupolar further alters the unstable manifolds, finally yielding highly unidirectional emission with narrower divergence angle (≤30°). As a result, mode selection and unidirectional emission are constructed simultaneously in the presented microcavity through a simple but robust method. This research is of great significance to the research of microcavity and the practical application of optical sensing and single-photon sources.