Giant asymmetric second-harmonic generation in bianisotropic metasurfaces based on bound states in the continuum

TL;DR

This paper theoretically demonstrates highly asymmetric second-harmonic generation in bianisotropic AlGaAs metasurfaces, achieving a four-order magnitude difference in SHG power for forward and backward illumination, enabled by bound states in the continuum.

Contribution

It introduces a novel approach to achieve highly asymmetric SHG in bianisotropic metasurfaces using bound states in the continuum, advancing nonlinear optical control.

Findings

Achieved up to four orders of magnitude difference in SHG power between forward and backward directions.

Demonstrated that geometrical tuning near quasi-bound states in the continuum enhances asymmetry.

Provided a theoretical framework for directional higher-order wave generation.

Abstract

Bianisotropy is a powerful concept enabling asymmetric optical response, including asymmetric reflection, absorption, optical forces, light trapping, and lasing. The physical origin of these asymmetric effects can be understood from magnetoelectric coupling and asymmetrical field enhancement. Here, we theoretically propose highly asymmetric second-harmonic generation (SHG) in bianisotropic AlGaAs metasurfaces. We show that around four orders of magnitude second-harmonic power difference for the forward and backward illuminations can be obtained by altering geometrical parameters that coincide with quasi-bound states in the continuum. Our study paves the way towards a directional generation of higher-order waves and can be potentially useful for nonlinear holograms.