Chirality-Assisted Aharonov-Anandan Geometric-Phase Metasurfaces for Spin-Decoupled Phase Modulation

In this work, a quasi-nondispersive and spin-decoupled phase modulation strategy was proposed based on the chiral structure. Owing to the spin-dependent response of the chiral structure, the evolution of the Aharonov-Anandan (AA) geometric phase can be controlled by tuning different structural parameters independently. Additionally, the chiral structure was designed nonresonant or weak-resonant to minimize the influence of strong resonant absorption and large dispersive propagation phase shift, leading to an efficiently quasi-nondispersive phase modulation. To prove the validity of the strategy, a series of umbrella-shaped reflection-Type metal-insulator-metal structures were designed as the unit cells and simulated with the finite element method. Moreover, the metasurfaces were designed based on such unit cells to generate broadband orbital angular momentums with different topological charges and spin-switchable holograms, respectively. Simulated and experimental results are in good agreement with the theoretical results. To the best of our knowledge, broadband spin-dependent phase modulation has been achieved without intentionally merging other types of phases for the first time in this work. We believe that this strategy provides a flexible approach for complex spin-or polarization-related applications in optical communication, integrated optics, optical sensing, and other related fields.