Transformation cavities with a narrow refractive index profile

TL;DR

This paper introduces a new method for designing transformation cavities with a narrower refractive index profile, maintaining high Q-factors and directional emission, which simplifies experimental realization.

Contribution

A novel design approach for transformation cavities that reduces the refractive index profile width by 50% without sacrificing performance.

Findings

Narrower refractive index profile achieved

High Q-factors maintained with new design

Directional emission preserved in the modified cavities

Abstract

Recently, gradient index cavities, or so-called transformation cavities, designed by conformal transformation optics have been studied to support resonant modes with both high Q-factors and emission directionality. We propose a new design method for transformation cavities to realize a narrower width of the refractive index profile, a great advantage in experimental implementations, without losing the benefits of conformal mapping. We study the resonant modes with both high Q-factor and directional emission in the newly designed transformation cavities, where the refractive index profile is 50 percent narrower than in previously proposed transformation cavities. By varying a system parameter with a fixed maximal value of the refractive index profile inside the cavity, the width of the refractive index profile narrows, the Q-factors become higher, and the near and far field patterns maintain their properties, namely conformal whispering gallery modes and bidirectional emission, respectively.