Full-polarization high-efficiency enhancement of the photonic spin Hall effect via a q-BIC metasurface.

The efficiency and Q-factor of the photonic spin Hall effect (PSHE) are crucial for spin-selective optoelectronic devices, yet this enhancement of PSHE is typically limited to linear polarization or polarization-dependent scenarios. Here, we propose an all-dielectric C4v metasurface to realize the high efficiency and Q-factor enhancement of PSHE under full-polarization (arbitrary polarization states) incidence by leveraging the quasi-bound states in the continuum (q-BIC). Due to the C4v symmetry of the metasurface, the q-BIC resonance becomes polarization-independent, simultaneously satisfying the conditions of |rₛ| = |rₚ| = 1 and zero phase difference for any incident polarization. Under full-polarization incidence (including arbitrary linear, circular, and elliptical polarizations) at a wavelength of 1181 nm and an incident angle of 0.5°, the transverse displacement of PSHE can reach 36.4λ. Meanwhile, the efficiency remains above 92.5%, while maintaining a high-Q-factor of 785. This strategy offers viable opportunities for applications in high-efficiency and Q-factor spin-selective devices.