Wavy optical grating: wideband reflector and Fabry-Perot BICs

TL;DR

This paper explores how a wavy dielectric optical grating can serve as a wideband reflector and support Fabry-Perot BICs, with tunable Q-factors and potential for on-demand control via vibrational waves.

Contribution

It introduces a novel wavy grating design that enables wideband reflection and tunable BICs, expanding the capabilities of optical resonator and reflector technologies.

Findings

Wavy gratings produce high reflectance over large bandwidths.

Double-layer wavy gratings can host Fabry-Perot BICs with tunable Q-factors.

The Q-factor inversely relates to the amplitude of the wavy shape.

Abstract

In this study, we theoretically and numerically investigate the resonant modes and reflectance of an optical grating consisting of a wavy dielectric slab by applying the spectral element method. The presence of the wavy shape transforms the waveguide modes into leaky resonant modes. A few resonant modes with specific longitudinal wave number have infinitely large Q factor, while the other resonant modes have finite Q factor. For the leaky resonant mode with zero longitudinal wave number, the Q factor is inversely proportional to the amplitude of the wavy shape. An array of multiple low-Q wavy gratings has a high reflectance in a large bandwidth. A double-layer wavy grating forms a Fabry-Perot cavity, which hosts Fabry-Perot bound states in the continuum (BICs) at the resonant frequency. The Q-factor of the Fabry-Perot cavity can be tuned by adjusting the distance between the two wavy slabs. The wavy shape could be generated by a vibrational wave in a flat dielectric slab so that the BICs mode and wideband reflectance could be controlled on-demand.