All‐Dielectric Asymmetric Metagrating for Broadband and Wide‐Angle Terahertz Beam Steering with High Efficiency

Abstract Efficient terahertz (THz) beam steering is crucial for advancing next‐generation wireless communication, radar, and imaging systems. However, achieving high efficiency across broad frequency bands and wide deflection angles remains challenging due to the limited degrees of freedom in conventional dipolar‐based Huygens metasurfaces and gradient‐phase designs. Here, an all‐dielectric asymmetric metagrating composed of four‐silicon‐pillar unit cells with high resistivity is proposed and experimentally demonstrated. Unlike dipole‐based or reflective configurations, this asymmetric mechanism excites strong electric and magnetic octupoles, inducing both longitudinal and transverse scattering asymmetries (bi‐asymmetry) while suppressing guided‐mode resonances, thereby realizing broadband and wide‐angle anomalous refractive diffraction. The device achieves a frequency scanning range from −36° to −22° with diffraction efficiencies exceeding 80% over a 15% relative bandwidth, and maintains efficiency above 70% across deflection angles ranging from −62° to −27° at the central working frequency. Excellent agreement between simulation and experimental measurements confirms the metagrating's robust capability in directing energy into the −1st transmission diffraction order. This work establishes a compact and scalable route toward high‐performance THz photonic components with superior efficiency and angular versatility.