Temperature-Insensitive Fiber-Optic Refractometer Based on Immobilization of Polydimethilsiloxane Film

A temperature-insensitive fiber refractometer, which consists of a simple single-mode–multimode–single-mode fiber optic scheme, is theoretically proposed and experimentally demonstrated. The multimode section is involved with a segment of D-shaped no core fiber (Ds-NCF) while the surface of the Ds-NCF is partially coated with a thin layer of polydimethylsiloxane (PDMS) film. Owing to the opposite thermo-optic coefficients (TOC) of the silica and the PDMS, a compact structure with nearly zero temperature dependence is fabricated. Moreover, such refractometer benefits from simplicity and low-cost and achieves competitive refractive index sensitivities of 140.1 nm/RIU in the range of 1.32 to 1.37, and 1147 nm/RIU over a RI range from 1.38 to 1.44. These excellent characteristics would find wide potential applications, such as chemical, biological, medical detection, and other fields.