Terahertz Silicon Metagratings: High-Efficiency Dispersive Beam Manipulation above Diffraction Cone

Optical wavefront engineering is essential for the development of next-generation integrated photonic devices. It is used for reflecting terahertz waves in a predesigned nonspecular direction with near-unitary efficiency, which is a longstanding challenge for high-performance functional devices. Recently, metagratings have offered an efficient solution for beam steering at large angles without the need for a discretization phase or impedance profile. Here, all-dielectric metagratings fabricated using a silicon cuboid complex lattice are proposed and demonstrated experimentally to achieve anomalous terahertz beam reflections above the diffraction cone with unitary diffraction efficiency. For the bipartite metagrating system, a single dispersive scatterer per unit is effective for achieving broadband beam steering because of Brillouin zone folding, and another perturbative synergetic scatterer is introduced to slightly tailor the array coupling and improve the performance. High-efficiency beam steering, including both retroreflection under oblique incidence and one-way diffraction under normal incidence, can be achieved by breaking structural symmetry and coherently suppressing unnecessary radiation channels. Moreover, silicon metagratings with spatially dispersive response features show perfect anomalous reflection operation in the broadband region, which is promising for leveraging terahertz spatially separated devices.

Automated summary

Optical wavefront engineering is essential for the development of next-generation integrated photonic devices. Recent advances in metagratings have provided an efficient solution for beam steering without the need for phase modulation or impedance profiles. All-dielectric metagratings fabricated with a complex lattice structure demonstrate unitary diffraction efficiency in anomalous terahertz beam reflections, making them promising for high-performance functional devices.