Cladding Etched Strongly Coupled Seven-Core Fiber Modal Interferometer for Highly Sensitive Refractive Index Sensing

In this paper, we have proposed and demonstrated a highly sensitive refractive index (RI) sensor based on cladding- etched strongly-coupled seven-core fiber (SCSCF). We spliced a 30-mm-long piece of SCSCF into two standard single mode fibers to form a supermode interferometer. The SCSCF is sensing element, and the degree of interaction between SCSCF and its surroundings can be enhanced by etching the thick cladding. For the diameter of SCSCF ranging from 30.1 um to 26.5 μm, the measured RI sensitivity distinctively increases from 194.5 nm/RIU (refractive index unit) to 366.0 nm/RIU around RI 1.33, which agree well with the simulated RI sensitivities.