High spectral contrast chiral second-harmonic generation from multilayer gallium selenide coupled to silicon holey disk metasurfaces

Abstract

We present electromagnetic design and analysis of hybrid metasurfaces composed of multilayer gallium selenide (GaSe) coupled to silicon holey disk arrays for achieving high spectral contrast chiral second-harmonic generation (SHG). The silicon holey disk structures are designed to support electromagnetically induced transparency (EIT)-like optical resonances in the 1.5–1.8 µm wavelength range in the vicinity of electric and toroidal dipole scattering modes. The fundamental electric field enhancement above the silicon structures shows right-circularly polarized (RCP)- and left-circularly polarized (LCP)-like characteristics at distinct wavelengths resulting in two prominent peaks for the LCP and RCP resolved SHG from the GaSe layer above the holey disks. This results in high contrast SHG degree of circular polarization spanning − 1 to + 1 over the fundamental excitation spectral range considered. The chiral SHG response is also found to be strongly influenced by the unit-cell lattice arrangement with square or hexagonal lattice exhibiting very different chiral SHG response. This observation is consistent with the circular polarization state selection rules for the harmonic generation process considering the rotational symmetry of the underlying metasurface lattice arrangement. Two-dimensional (2D) material–dielectric resonant metasurface hybrid systems exhibit nonlinear optical polarization selection rules, which differ from the native 2D material, making them an interesting platform for realizing engineered chiral nonlinear photonic devices.