Enhanced photonic spin Hall effect in a GST/HMM composite structure for optical encoding and refractive index sensing

Conventional photonic devices are functionally frozen after fabrication, lacking dynamic reconfigurability. Hence, developing reconfigurable multi-functional devices on a single platform has become an urgent issue. The photonic spin Hall effect (PSHE), arising from spin-orbit interaction, offers a promising platform due to its sensitivity to external stimuli. In this work, we propose a PSHE-based multi-functional device with a GST/HMM composite structure, which enables dynamic switching between two-bit optical encoding and refractive index sensing by controlling the phase state of GST layer via external stimuli. In the amorphous GST state, the device enables two-bit encoding and wide-range refractive index sensing (1.0-1.5 RIU) with a sensitivity of 4.08×10^-6 m/RIU. Switching GST to the crystalline state enhances the sensitivity to 5.32×10^-5 m/RIU, more suitable for high-precision detection within a narrow-range of 1.00-1.10 RIU. These findings validate that the GST phase transition enables effective mode switching of the device, which paves the way for compact, multi-functional, and reconfigurable photonics.