Abstract Chiroptics has gained significant interest due to its fundamental science and advanced applications in optical communications, quantum processing, and sensing. While optical bound states in the continuum (BICs) provide a powerful framework to generate optical chiral states, existing BIC platforms often suffer from limited tunability. In this study, a novel metasurface featuring chiral structures atop a thin film layer is demonstrated, supporting strong near‐ and far‐field chirality, characterized using the localized optical chirality formula and the generalized chiroptics theory. By preserving or breaking the rotational symmetry, the transition between the BIC‐associated vortex center and circularly polarized states is investigated. Notably, the upward and downward far‐field radiation remains identical, independent of geometric symmetry. More importantly, through in situ rotation of the upper‐layer structure within the meta‐atom, precise, all‐directional control over C points in momentum space around the Γ point is achieved, forming a Möbius‐like band. These findings provide a new strategy for tuning optical chiral states in a compact form, with potential implications for chiral sensing, structured light generation, and next‐generation optoelectronic devices.
Lin et al. (Mon,) studied this question.