Controlling the symmetry of the photonic spin Hall effect by an optical vortex pair

A pair of vortices, one of the multiple vortices, exhibits more adjustable parameters and attractive characteristics compared with a single vortex. By introducing a vortex pair on the Gaussian beam, we not only realize both longitudinal and transverse asymmetrical spin splittings, but also achieve the symmetrical ones via the purely optical strategy. Namely, the symmetries of the spin splittings can be controlled flexibly by the tunable vortices, offering another degree of freedom for the photonic spin Hall effect. Based on the geometric phase theory, physical insights into the symmetry-controllable spin Hall shifts involving the initial phase from the incident vortex beam are provided. These findings reveal the influence of vortices on the symmetry of the photonic spin Hall effect and provide further potential methods for developing spin-based nanophotonic applications.