Cover story: Liu SQ, Chen SZ, Wen SC, Luo HL. Photonic spin Hall effect: fundamentals and emergent applications. Opto-Electron Sci 1, 220007 (2022).

The reflection and refraction of plane-waves at optical interfaces is a fundamental optical process, which can be governed by reflection law and Snell’s law in geometrical optics. However, the finite-width beams in practical situation are mostly treated as the superposition of many plane-waves with slightly different diffractions, whose propagation evolution no longer exactly obeys the prediction of geometrical optics. As is known, an arbitrary linearly polarized beam consists of a superposition of its right-circularly and left-circularly polarized components. After such a beam is reflected (refracted) from an optical interface or propagating through an inhomogeneous medium, photons with opposite spin angular momenta will separate with each other and manifest itself as the spin-dependent splitting. The photonic spin Hall effect can also be regarded as an analogue of the SHE in electronic systems, where the two circularly polarized components play the role of spin-up and spin-down electrons, and the refractive index gradient replaces the electric field, respectively. Fundamentally, the photonic spin Hall effect originates from the spin-orbit interaction of photons which related to two kinds of geometric phases, i.e., the Rytov-Vlasimirskii-Berry phase in momentum space and the Pancharatnam-Berry phase in Stokes parameter space. The unique properties of the photonic spin Hall effect, for instance the high sensitivity to optical parameters and its powerful ability to manipulate the photons, nowadays, make it a hotspot in modern optics and a useful tool in precision metrology, analog optical computing, quantum imaging, and microscopy imaging. This review provides a brief framework to describe the fundamentals and advances of the photonic spin Hall effect, and presents the emergent applications of this phenomenon in different scenes.