Dynamic and highly sensitive photonic spin Hall effect sensor using quasi-bound states in the continuum

Abstract The photonic spin Hall effect (PSHE) has emerged as a promising platform for refractive index sensing due to its exceptional sensitivity of spin-dependent shifts (SDS) to nanoscale parameter variations. Nevertheless, current PSHE-based sensors suffer from limited measurement range, suboptimal sensitivity, and lack of active tunability for sensitivity modulation. To address these limitations, we propose a graphene-silicon cross-shaped metastructure-gas chamber structure. Symmetry breaking of the system is achieved by shifting the vertical segment of the cross-shaped plate along the X -direction by the distance dx , thereby generating symmetry-protected quasi-bound states in the continuum (q-BICs) with high quality factors. At this point, the near-zero reflection Fano resonance induced by q-BICs significantly enhances the photonic spin displacement. Simultaneously, the graphene Fermi level is exploited as a degree of freedom to dynamically modulate the sensitivity of the PSHE sensor in multi-gas environment (1.0–1.05) detection, achieving an optimal displacement sensitivity of 9040.36 μ m RIU −1 in the 1.01 gas environment. Through the dual synergistic mechanism of q-BICs and graphene Fermi level which allows the sensor to adapt its sensitivity by selecting an appropriate Fermi level according in different gas environments, this work establishes a new paradigm for the development of high-performance optoelectronic sensing architectures.