High-efficiency broadband blazed metagrating working in visible light

A simple 1D blazed metagrating is proposed. The metagrating consists of SiO2 film sandwiched by Ag substrate and Ag nanostrips, which can achieve high-efficiency −1st-order diffraction in the range of 550 nm to 700 nm, and the peak efficiency is nearly 98%. The SiO2 dielectric layer in previous designs is used chiefly as a waveguide layer to support a guided mode. In comparison, it is introduced here to suppress the unwanted diffraction order (zero-order), which helps achieve high-efficiency diffraction at a high diffraction order. For analysis, the metagrating is disassembled into two parts, including a flat plate and a grating. By analysing the far-field radiation pattern of scattered waves and the reflection phase of a specific mode for these two parts, we conclude that the cause of high-efficiency blazing draws support from suppressing zero-order based on destructive interference. This work provides an intuitive physical image for this type of metagrating and an idea to design high-efficiency diffraction and beam deflection devices from the perspective of interference.