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

Abstract: A beam splitter (BS) is one of the most critical building blocks in optical systems. Despite various attempts to miniaturize the conventional cube BS reported, it remains a challenge to realize an ultrathin BS with multi-port output, nonuniform splitting ratio and steerable outgoing directions. Herein, we have demonstrated a free-space optical multi-port beam splitter (MPBS) based on a polarization-independent all-dielectric metasurface. By utilizing an optimized phase-pattern paradigm via a gradient-descent-based iterative algorithm on amorphous silicon (a-Si) metasurfaces, we have prepared various MPBS samples with arbitrarily predetermined output port number (2~7), power ratio and spatial distribution of output beams. The experimental results reveal that the MPBSs could achieve high total splitting efficiency (TSE, above 74%) and beam-splitting ratio fidelity (SRF, above 0.992) within the bandwidth of 100nm (1500nm~1600nm). We envision that such MPBS could provide a fabulous flexibility for optical integrated systems design and diverse applications.