Dual-Core Photonic Crystal Fiber Integrated SPR Sensor and Polarization Filter Based on Coupled Mode Theory

Abstract

Based on coupled mode theory, we propose a novel dual-polished photonic crystal fiber (PCF) designed to simultaneously achieve the dual-functionality of surface plasmon resonance (SPR) sensing and polarization filtering within a single platform. Unlike conventional works that rely strictly on fundamental modes, the primary novelty of this design lies in the strategic exploitation of supermodes to drive the device’s mechanisms. Owing to their characteristically larger mode areas, these supermodes exhibit exceptionally strong evanescent coupling with both the upper and lower gold (Au) thin films deposited onto the polished planes of the cladding regions. Using the finite element method (FEM), the dual-functional performance of the PCF structure was systematically analyzed. It demonstrated excellent performance in measuring the refractive index of various analytes with refractive indexes of 1.30 to 1.40, with a wavelength sensitivity (WS) of 8800 nm/RIU, a spectral resolution of 1.13636 × 10− 5 RIU and an amplitude sensitivity (AS) of 286 RIU⁻¹. When the refractive index of the analyte is 1.37, the maximum confinement loss for the Y-polarized odd mode is 143,160 dB/m. The polarization filter effect showed an extinction ratio of -65.85 dB at a propagation distance of 2 mm, which is considered good. Its simplicity and cost-effectiveness make this design superior to existing standards. The structure can detect various analytes, thus having high flexibility in practical applications such as biosensors and integrated photonic systems.