Local chirality of optical waves in ultrasmall resonators

TL;DR

This paper demonstrates how wave optics effects in ultrasmall deformed microcavities break local chiral symmetry, enabling controlled unidirectional emission and improved collection efficiency through spatial separation of CW and CCW modes.

Contribution

It reveals the role of wave optics in breaking local chirality and controlling emission directionality in ultrasmall resonators, a novel insight for photonic device design.

Findings

Spatial separation of CW and CCW modes leads to unidirectional emission.

Evanescent coupling directionality depends on the coupling position.

Local chirality control enhances emission collection efficiency.

Abstract

The local chiral symmetry between clockwise (CW) and counter-clockwise (CCW) propagating light in a deformed microcavity can be broken by wave optics effects, which become significant as the cavity size approaches the wavelength. We show that the spatial separation of the CW and CCW ray orbits underlying the high quality factor resonant modes results in unidirectional emission in free space. In the presence of a waveguide, evanescent coupling also becomes directional, and the output direction can be varied by selecting the coupling position along the cavity boundary. Our results demonstrate that the local chirality can be utilized to control the output directionality and enhance the collection efficiency of emission from ultrasmall resonators.