Topological Singularity in a Non-Interleaved Bidirectional Transmissive Metasurface Consisting of Weakly Coupled Resonators

Exceptional points (EPs), marked by eigenvalue-eigenstate coalescence, exhibit a robust topologically protected 2π phase upon encirclement, thereby supplying an additional phase-engineering mechanism that enables intriguing asymmetric wave manipulation. Here, based on a framework of two weakly coupled resonators, a novel mechanism is proposed for localizing the topological singularity in a two-dimensional parameter space, which establishes a deterministic geometry-EP mapping and provides an efficient, closed-form design route. By invoking reciprocity and synthesizing the topological exceptional (ET) phase with the Pancharatnam-Berry (PB) phase, asymmetric responses are engineered in the bidirectional circular-polarization conversion channels. As a proof of concept, we demonstrate two λ/14-thick non-interleaved metasurfaces in the microwave regime for near-field holographic manipulation and far-field beam steering, respectively. Both numerical simulations and experimental measurements confirm that each metasurface exhibits asymmetric wave manipulation under bidirectional right-circularly polarized wave (RCP) illumination: the meta-hologram generates distinct holographic patterns, while the far-field metasurface demonstrates asymmetric beam deflection angles. Our findings provide new routes to localize topological singularities and substantially expand the bidirectional wave-control capacities of topological metasurfaces, paving the way for geometry-programmable EP control in compact duplex communication, polarization-multiplexed holography, and secure information encoding.