One-dimensional quasi bound states in the continuum in the {\omega}~k space for nonlinear optical applications

TL;DR

This paper introduces a new type of one-dimensional quasi-BIC resonances in photonic structures that are distributed continuously over a broad spectral band, enabling enhanced light-matter interactions across multiple wavelengths.

Contribution

The authors demonstrate a novel binary grating design supporting continuous QBIC resonances along a line in w~k space, expanding the applicability of BICs in nonlinear optical processes.

Findings

Support for broad, continuous QBIC resonances in the w~k space.

Enhanced light-matter interactions at arbitrary frequencies along the dispersion line.

Potential applications in nonlinear optics such as frequency generation.

Abstract

The phenomenon of bound state in the continuum (BIC) with infinite quality factor and lifetime has emerged in recent years in photonics as a new tool of manipulating light-matter interactions. However, most of the investigated structures only support BIC resonances at very few discrete points in the w~k space. Even when the BIC is switched to a quasi-BIC(QBIC) resonance through perturbation, its frequency will still be located within a narrow spectral band close to that of the original BIC, restricting their applications in many fields where random or multiple input frequencies beyond the narrow band are required. In this work, we demonstrate that a new set of QBIC resonances can be supported by making use of a special binary grating consisting of two alternatingly aligned ridge arrays with the same period and zero-approaching ridge width difference on a slab waveguide. These QBIC resonances are distributed continuously over a broad band along a line in the w~k space and can thus be considered as one-dimensional QBICs. With the Q factors generally affected by the ridge difference, it is now possible to choose arbitrarily any frequencies on the dispersion line to achieve significantly enhanced light-matter interactions, facilitating many applications where multiple input wavelengths are required, e.g. sum or difference frequency generations in nonlinear optics.