Highly sensitive, multi-stage, and mid-infrared refractive index sensor based on photonic spin Hall effect

Surface polaritons, as surface electromagnetic waves propagating along the surface of a medium, have played a crucial role in enhancing photonic spin Hall effect (PSHE) and developing highly sensitive refractive index (RI) sensors. Among them, the traditional surface plasmon polariton (SPP) based on noble metals limits its application beyond the near-infrared (IR) regime due to the large negative permittivity and optical losses. In this contribution, we theoretically proposed a highly sensitive PSHE sensor with the structure of Ge prism-SiC-Si:InAs-sensing medium, by taking advantage of the hybrid surface plasmon phonon polariton (SPPhP) in mid-IR regime. Here, heavily Si-doped InAs (Si:InAs) and SiC excite the SPP and surface phonon polariton (SPhP), and the hybrid SPPhP is realized in this system. More importantly, the designed PSHE sensor based on this SPPhP mechanism achieves the multi-stage RI measurements from 1.00025–1.00225 to 1.70025–1.70225, and the maximal intensity sensitivity and angle sensitivity can be up to 9.4 × 10⁴ μm/RIU and 245 °/RIU, respectively. These findings provide a new pathway for the enhancement of PSHE in mid-IR regime, and offer new opportunities to develop highly sensitive RI sensors in multi-scenario applications, such as harmful gas monitoring and biosensing.