Rotational photonic spin Hall effect.

Multidimensional manipulation of photonic spin Hall effect (PSHE) has attracted considerable interest due to its potential in a wide variety of spin-based applications. Plenty of research efforts have been devoted to transverse or longitudinal spin-dependent splitting; however, the splitting pattern that can self-rotate in a three-dimensional (3-D) space appears to be missing in literature. In this paper, we introduce a novel 3-D rotational PSHE, which can be realized and tuned using well-designed Pancharatnam-Berry phase metasurfaces. To demonstrate this phenomenon, we first show that when a single dielectric metasurface is used, the lobe-structured spin-splitting patterns on the transverse planes rotate and evolve along the propagation path. Then, we present that under two cascaded metasurfaces, the rotation angle of the splitting patterns are tunable by adjusting the relative rotation angle between the two metasurfaces. Finally, we manifest that the lobe number of the two spin-dependent splitting patterns can be independently controlled once we introduce a dynamic phase, which produces an asymmetrical rotational PSHE. The demonstrated phenomena can be used to achieve active manipulation of spin photons in multiple dimensions, and the developed device might find potential applications in various areas, e.g., optical microscopy.