Broadband and highly efficient enhancement of photonic spin Hall effect at a quasi-bound state in the continuum

The efficiency of the photonic spin Hall effect (PSHE) has attracted increasing attention, as it plays a key role in the development of spin-selective devices. However, highly efficient enhancement of PSHE has always been achieved at a single wavelength. Here, we propose a method to achieve highly efficient enhancement of the photonic spin Hall effect over a broadband operating wavelength by utilizing a magnetic dipole quasi-bounded state in the continuum (q-MDBIC) with a high refractive index. Under both horizontal and vertical polarization incidence, when the wavelength is 50.9–51.9 μm and the incident angle is 0.5°–10°, the transverse shift of PSHE can reach 1.7λ–37λ, with high efficiency of more than 90%. Meanwhile, the quality (Q) factor can also be maintained around 55. Furthermore, different metasurface lattice periods can achieve different broadband PSHE, which provides favorable conditions for the control of broadband PSHE. Our work will have wide applications in devices with efficient spin selection.