High‐Efficiency Beam Splitters with Tailored Split Ratios Enabled by Phase‐Engineered Multilayer Metasurfaces

Abstract Metasurface‐based beam splitters have attracted significant attention in communities of spectroscopy, optical communications, and so on for their strong capability to manipulate electromagnetic waves. However, achieving precise control over split ratios under high efficiency conditions remains a significant challenge. In this work, a phase engineering strategy based on multilayer metasurfaces is presented to tailor the split ratios of beam splitters with high efficiency. By engineering the reflection phase and its dispersion of the multilayer films, rather than the upper metasurfaces, the proposed approach exploits the longitudinal degrees of freedom to substantially enhance the design flexibility and performance of beam splitters. Using this strategy, high‐efficiency beam splitters is demonstrated with tailored split ratios and equal‐power beam splitters with customized operational bandwidths, respectively. As a proof of concept, a 2D four‐channel circularly‐polarized beam splitter is experimentally realized with a high efficiency exceeding 21% per channel. These results provide a new pathway for promoting the performance and flexibility of metasurface‐based beam splitters.