Improvement of refractive index measurement range using a plasmonic multi-angle tilted fiber Bragg grating

Abstract

Surface Plasmon resonance (SPR), which is a unique electro-magnetic phenomenon occurring at the interface between materials with opposite dielectric constants, is extremely sensitive to the surrounding refractive index (RI), and can be used for chemical and biochemical detection. In this work, a multi-angle tilted fiber Bragg grating (TFBG) coated by a gold film with thickness of 50 nm is proposed and experimentally demonstrated. In this structure, SPR on the gold film surface can be easily excited through the TFBG. By simultaneously inscribing several tilted angles of gratings in the fiber core, the measured range of RI can be improved in comparison to the conventional TFBG with only one tilted angle of grating. Experimental results show that the measured range of RI is 1.30–1.42 and the sensitivity is 523.41 nm/RIU (Refractive Index Unit), using the proposed multi-angle sensor. Furthermore, analysis based on the experimental results also indicates that the proposed sensor has high linearity in the measured range.