Doubly resonant photonic crystal cavity using merged bound states in the continuum

TL;DR

This paper proposes a novel doubly resonant photonic crystal cavity utilizing merged bound states in the continuum to significantly enhance second harmonic generation efficiency, achieving a 6000% increase compared to isolated BICs.

Contribution

It introduces a method to merge BICs in photonic crystal cavities, leading to higher quality factors and improved nonlinear optical performance.

Findings

Merged BICs exhibit high quality factors in finite-size photonic crystals.

The SHG efficiency near merged BICs is approximately 6000% W-1.

Design of heterostructure PhC cavity enables mode matching with merged BICs.

Abstract

In this work, a doubly resonant photonic crystal (PhC) cavity using the merged bound states in the continuum (BICs) is proposed to obtain a higher second harmonic generation (SHG) efficiency. Firstly by scanning geometry parameters the accidental BICs and a band-edge mode outside the light cone can be obtained. Then as the lattice constant or the thickness of the slab is adjusted the accidental BICs will merge. A supercell with large and small holes is constructed and the band-edge mode outside the light cone can be mode-matched with the merged BICs mode. Finally the heterostructure PhC cavity is designed. The merged BICs show a high quality factor for the photonic crystal with finite size. Consequently, the SHG efficiency of the lattice constant near merged BICs of ~6000% W-1 is higher than the one of the isolated BIC.