| Summary: | When a paraxial light beam is reflected from/ transmitted through an optical element with rotation symmetry, a tiny small incident angle can arise wave-vector-varying Pancharatnam-Berry (PB) phases, resulting in high-performance photonic spin Hall effect (PSHE). Differently, here we investigate the PSHE in photonic crystal slabs of square lattices constructed with air holes, and demonstrate that the C<sub>4v</sub> symmetry of the slabs enables giant PSHE in both isotropic and anisotropic band structures with a small incident angle. The guided-mode resonances of the subwavelength-thickness slab enhance the PSHE, allowing the spin separation to exceed the incident beam waist. Via changing the incident angle, wavelength and even the beam waist, the spin separation can be adjusted in a wide range, which makes our proposal more flexible in manipulation of spin photons.
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