Bound State in the Continuum Supported Asymmetric Dome-shaped Dielectric Metasurface: Crossing and Avoided Crossing of Transmission with Applications

TL;DR

This paper investigates a dielectric dome-shaped metasurface supporting bound states in the continuum, demonstrating resonance crossing, avoided crossing phenomena, and applications in sensing and nonlinear optics.

Contribution

It introduces a novel all-dielectric dome-shaped metasurface supporting high-Q BICs, exploring symmetry breaking effects and demonstrating enhanced third harmonic generation.

Findings

High-Q quasi-BICs with Q-factor > 10^4 observed

Resonance crossing and avoided crossing phenomena demonstrated

300-fold increase in third harmonic generation efficiency

Abstract

This work examines a symmetry-protected bound state in the continuum (BIC) supported unique all-dielectric dome-shaped metasurface (MS). The simple unit MS is made up of four dome-shaped nanobars of silicon in the top layer and silica glass as the substrate. Two strong transmission dips denoted as an electric dipole (ED) and magnetic dipole (MD) quasi-BIC with a high Q-factor that surpasses the value of 104 are observed after the symmetry between the nanobars is broken by a small angle from their initial position. A crossover between the ED and MD resonances is noticed when the periodicity of the MS is changed in the y direction. In addition, transmission spectra show the avoided-crossing phenomenon of dipole quasi-BIC resonances when the superstrate's refractive index (RI) is reduced from its initial value. Other widely used dielectric materials are additionally employed in dome-shaped nanobars to evaluate their performances in terms of sharpness and near-zero transmission. Moreover, Other forms of symmetry breakdown such as diagonal width and length asymmetry have been investigated for their impact on the Q-factor. Finally, we have demonstrated two significant applications, including refractometric glucose sensing and third harmonic generation (THG). Our dome-shaped MS is roughly 300 times more efficient at generating third harmonics than a flat rectangular silicon film MS. Our proposed BIC and q-BIC-facilitated MS may provide a method for enhancing the functionality of biological sensors, multimodal lasing, optical switches, and nonlinear optics.