Symmetrical Core-Offset Fiber SPR Sensor With Superior Comprehensive Performance: Mechanism Analysis and Experimental Realization

Abstract

Optical fiber surface plasmon resonance (SPR) sensors have significantly limited their development in high-precision biochemical detection due to the difficulty in balancing sensitivity, full width at half maximum (FWHM), and resonance depth. In order to solve this problem, a symmetrical core-offset SPR sensor based on multimode-single mode-multimode (MSM) structure is proposed and fabricated in this article. Analysis using the finite-difference beam propagation (FD-BPM) and eigenmode expansion (EME) method reveals that an appropriate core-offset not only reduces the effective refractive index of cladding mode thus improving the sensor sensitivity, but also decreases the cladding modes which narrows the FWHM. In addition, light energy leakage into the cladding of the single-mode fiber (SMF) is increased, which deepens the resonance spectrum. The experimentally fabricated sensor achieves a reasonable figure of merit (RFOM) of 12.16/RIU, which represents 3.68 times the value of traditional MSM structure. The symmetrical core-offset structure achieves the balance of sensitivity and spectrum characteristics as verified by simulation and experiment. Moreover, the sensor is simple to fabricate and has high mechanical strength, which shows great prospect for high-precision biochemical detection.