Numerical analysis of an ultra-broadband and highly efficient beam splitter in the visible region.

We report a quasi-continuous beam splitter with highly efficient equal-power beam splitting in a wide spectral range. It consists of rhombic aluminum antimonide nanorods standing on a silica substrate. Firstly, a beam splitter based on discrete structures is designed, and the structures are optimized to obtain the quasi-continuous beam splitter. The beam splitter achieves a splitting efficiency of over 80% within the region of 675-786 nm (bandwidth = 111 nm), where the splitting angle can vary in the range of 97.2°-121.8°. In particular, the splitting efficiency reaches 93.4% when the wavelength is 690 nm. Overall, the proposed beam splitter potentially paves the way for realizing broadband metasurfaces and high-performance quasi-continuous metasurface-based devices.