Temperature insensitive refractive index sensor based on a combination interference structure

A sensing head consisting of fiber loop mirror inscribed with a highly birefringence photonic crystal fiber (HiBi-PCF) was proposed and experimentally demonstrated. The HiBi-PCF was completely collapsed near the splicing points, thus the cladding mode in the HiBi-PCF would be excited, which was sensitive to the refractive index (RI) of surrounding medium. Owing to the low thermo-optic and thermo-expansion coefficient of the HiBi-PCF, the sensing head in our design was temperature insensitive. High sensitivity of 306.6 ± 0.2 nm/RIU (refractive index unit) and a resolution of 6.5 × 10−5 RIU have been achieved for the proposed liquid refractive index sensor.