Enhancement of SPR effect and sensing characteristics in D-shaped polished grapefruit microstructured optical fiber with silver film

Abstract

The microstructured optical fiber (MOF) sensor based on the surface plasmon resonance (SPR) has a compact structure, high sensitivity, and real-time monitoring advantages. Beyond that, the SPR effect could improve the sensitivity of the sensor. In this paper, the self-made grapefruit MOF was polished in a D-shaped and coated with a silver film on the polished surface by silver mirror reaction. After that, the MOF was spliced with the multimode fiber (MMF) and finally formed the MMF–MOF–MMF sensing structure. The experimental study found that the resonance coupling between the cladding mode and the metal film can be enhanced, and the SPR effect between the transmission field and the silver film can be strengthened by D-shaped polishing. According to that, the highest sensitivity of the sensor was increased from 4821 nm/RIU to 5431 nm/RIU when the refractive index is 1.3921, and the polished sensor can reach the highest sensitivity of 6338 nm/RIU when the refractive index is 1.4083. In addition, the analyte’s measurement range was extended from 1.33-1.3921 to 1.33-1.4083. In addition to the high sensitivity and wide measurement range, the proposed D-shaped sensor also has the advantages of easy manufacturing, good stability, and compact structure.