High-Sensitivity D-Shaped Dual-Groove Photonic Crystal Fiber SPR Sensor for Low-Refractive-Index Detection

In this paper, we propose a D-shaped dual-groove photonic crystal fiber (PCF) refractive index (RI) sensor based on surface plasmon resonance (SPR). The sensor employs microchannels with deposited gold (Au) as the plasmonic material to excite SPR effects, enabling highly sensitive detection in the low-RI regime. The proposed PCF sensor innovatively employs a dual-side groove configuration, which effectively enhances the SPR coupling strength and consequently improves the overall sensor performance. To analyze and optimize the performance of the PCF-SPR sensor, a systematic investigation was conducted using the finite element method (FEM) combined with perfectly matched layer boundary conditions. The effects of critical structural parameters—including gold film thickness, air hole diameter, and hole pitch—on sensor performance were thoroughly examined, followed by comprehensive numerical analysis and optimization. Simulation results demonstrate that the proposed sensor operates in the mid-infrared region with a wavelength range of 2110–2250 nm, capable of detecting analytes with refractive indices spanning from 1.20 to 1.28. Notably, when the analyte RI reaches 1.26, the sensor achieves a peak wavelength sensitivity of 7000 nm/RIU and a resolution of 1.43×10⁻⁵RIU. The designed sensor exhibits distinct advantages including high sensitivity, straightforward fabrication, and effective operation in the low-refractive-index regime, making it particularly suitable for organic solvent monitoring, biomolecule detection, and environmental pollutant analysis with significant application potential.