Expanding the Detection Range of SPR Liquid Refractive Index Sensor Based on Polarization Multiplexing

Conventional fiber-type liquid refractive index (RI) sensors based on surface plasmon resonance (SPR) typically operate with a single polarization mode for detection, which limits the detection range. In this study, a method based on polarization multiplexing is proposed to expand the RI detection range, and a birefringent photonic crystal fiber SPR sensing structure with a rectangular arrangement is designed. The sensor structure has been optimized and the key characteristics have been analyzed using the finite element method. The results indicate that the proposed sensing structure covers a detection range of 1.00-1.45 refractive index unit (RIU), i.e., the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i>-polarization covers 1.00-1.30 with a maximum wavelength sensitivity of 14,000 nm/RIU, while the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i>-polarization covers 1.06-1.45 with a maximum wavelength sensitivity of 11,300 nm/RIU. The proposed method can effectively expand the overall detection range of the sensor, and the corresponding structure has potential application in environmental monitoring, medical diagnosis, and food safety testing.