Conventional optical elements achieve specific optical functions based on the gradual phase changes accumulated along the propagation path, leading to a large form factor that is not compatible with the miniaturized, lightweight, and compact systems [1,2]. Therefore, planar optics components have received extensive attention in recent years benefiting from the compact and ultrathin design and excellent manipulation capability in multi-dimensional physical parameters . The generalized laws of reflection and refraction offer the theoretical explanation for the principle of unique performance in planar optics components, leading to arbitrary wavefront modulation due to the phase discontinuities in light propagation . In general, the phase discontinuities can be implemented by geometric phase, dynamic phase, and so forth. Compared with the dynamic phase arising from the optical path difference in propagation, the geometric phase, also known as Pancharatnam–Berry (PB) phase, originates from the photonic spin–orbit interaction in asymmetric anisotropic structures [5,6]. In contrast with the dynamic phase that is adjusted by the equivalent refractive index of the material, the PB phase is a broadband non-dispersion phase modulation method that is only related to the rotation angle of the anisotropic structure . Therefore, PB phase has been widely used in multitudinous practical applications due to its precise phase control ability and robustness against fabrication tolerances.
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