Metasurface-Based Free-Space Multi-Port Beam Splitter with Arbitrary Power Ratio

A beam splitter (BS) is one of the most critical building blocks in optical systems. Despite various attempts of flat-type BSs to miniaturize the conventional cube BS reported, it remains a challenge to realize an ultrathin optical BS with multi-port output, non-uniform splitting ratio, and steerable outgoing directions. Herein, a free-space optical multi-port beam splitter (MPBS) based on a polarization-independent all-dielectric metasurface is demonstrated. By applying an optimized phase-pattern paradigm via a gradient-descent-based iterative algorithm to amorphous silicon (alpha-Si) metasurfaces, a variety of MPBS samples with arbitrarily predetermined output port number (2-7), power ratio, and spatial distribution of output beams are prepared. The experimental results reveal that the fabricated MPBSs can achieve high total splitting efficiency (TSE, above 74.7%) and beam-splitting fidelity (similarity, above 78.4%) within the bandwidth of 100 nm (1500-1600 nm). Such proposed MPBS can provide fabulous flexibility for optical integrated system and diverse applications.

Automated summary

This study demonstrates a free-space optical multi-port beam splitter based on a polarization-independent all-dielectric metasurface. By applying an optimized phase-pattern paradigm, amorphous silicon metasurfaces are used to prepare multi-port beam splitter samples with arbitrarily predetermined output port number, power ratio, and spatial distribution. The experimental results show that the fabricated beam splitters can achieve high total splitting efficiency and beam-splitting fidelity within a certain bandwidth. Such proposed beam splitter provides great flexibility for optical integrated systems and diverse applications.