A SPR Sensor with Wide RI Measuring Range and Narrow FWHM Based on PCF-Silver Film Structure

In order to reduce the full width at half maximum (FWHM) of the surface plasmon resonance (SPR) sensor and improve the detection accuracy, we propose to use the cladding mode of the photonic crystal fiber (PCF) to excite the surface plasmon resonance. First, the transmission spectra of the cladding mode and the fiber core mode in the excitation of the SPR effect are simulated using the finite element method. The results show that the SPR effect excited using the cladding mode is stronger, and the sensor has better loss peaks, which is more conducive to realizing the detection of the external environment. In addition, the cladding mode of PCF is used to excite the SPR effect without the need for post-processing techniques such as polishing and taper, which reduces the processing difficulty to a great extent. Subsequently, we constructed an experimental optical path and prepared two sensors, one to excite the resonance by the cladding mode of PCF and the other by the core mode of the no-core fiber. The experimental results show that the sensor based on the PCF cladding mode has better sensing performance with the narrowest FWHM of 58.45 nm, the highest sensitivity can reach 6549.93 nm/RIU, and the detection range of RI is 1.333-1.420. Therefore, the sensor fabricated by PCF cladding mode has the advantages of a wide RI measurement range, narrow FWHM, and high sensitivity. This is of high reference value in the experimental study of PCF-SPR sensors and has a broad application prospect in RI measurement of liquids.