Photonic Spin-Hall Effect at Generic Interfaces

Although the photonic spin-Hall effect (PSHE) at optical interfaces has been widely studied in past years, its physical origin remains obscure. Here, through studying the scatterings of circularly polarized beams obliquely incident on a series of junctions linking two homogenous optical media, how the physical origin of the PSHE evolves as the interface changes from a slowly varying junction to a step-like sharp one is explored. Beams transmitted through a generic interface consist of two modes, a spin-maintained normal mode carrying a spin-redirection Berry (SRB) phase and a spin-flipped abnormal mode exhibiting a Pancharatnam-Berry (PB) phase. Under linear-polarization incidence, a spin-polarized beam transmitted through each junction is generally an interference of normal and abnormal modes corresponding to two different incident circular polarizations, and thus the resulting PSHE is dictated by the interplay and competition between two effects dictated by SRB and PB phases, respectively. Shrinking the interfacial region can increase the strength of the abnormal mode, making the measured PSHE change from the SRB-dominated one to the PB-dominated one. The results establish a unified framework to understand the PSHE at generic interfaces, offering practical ways to control the PSHE by "designing" the abnormal scatterings on optical interfaces.