Surface plasmon resonance refractive index sensor with progressive fiber expander

In this letter, a refractive index sensor based on surface plasmon resonance (SPR) with progressive fiber expander is presented and verified. The coupler is fabricated by continuously splicing multi-mode fibers of different core diameter in front of the no core fiber (NCF), which enhanced the evanescent field reaching to the metal surface. Experimental results indicate that, the sensor achieves a maximum sensitivity of 7307.64 nm/RIU within the RI range of 1.33-1.42. Furthermore, the proposed SPR sensing exhibits excellent repeatability, high mechanical strength, and cost-effectiveness, offering possibilities for designing high-performance SPR sensors.