Simultaneous generation and manipulation of terahertz waves based on nonlinear leaky-waveguide antennas with integrated bianisotropic metasurfaces

We hereby propose and theoretically investigate a new scheme for simultaneous generation and manipulation of terahertz (THz) waves through difference frequency generation facilitated by a metasurface-assisted nonlinear leaky waveguide antenna. The proposed structure integrates a nonlinear optical waveguide, composed of multiple Al_xGa_1−xAs layers, with a THz leaky waveguide, wherein a bianisotropic metasurface realizes the radiating aperture. By explicitly utilizing the electric, magnetic, and magnetoelectric coupling responses of the metasurface, we demonstrate that the generated THz wave can be induced as a tightly confined, phase-matched guided mode for efficient generation of the THz wave. Additionally, this approach allows the THz wave to be transformed into a directive beam, radiating at a user-defined leakage rate and direction. Our numerical analyses suggest that THz beams ranging from 2.85 THz to 3.05 THz can be steered from 4^◦ to 40^◦, utilizing the inherent beam-steering capabilities of the leaky-waveguide antenna. Within this THz frequency spectrum, the phase matching condition is achieved by adjusting the optical wavelengths between 1.6µm and 1.52µm. In particular, the nonlinear conversion efficiency is 2.9 × 10⁻⁵ [1/W] at 3 THz.