Curvature Sensor Based on Hollow-Core Photonic Crystal Fiber Sagnac Interferometer

A fiber-optic curvature sensor based on hollow-core photonic crystal fiber (HC-PCF) Sagnac interferometer is demonstrated. The two ends of the 36 cm HC-PCF are spliced to the two arms of a 3 dB single-mode fiber coupler to form a Sagnac interferometer. The output spectra of the Sagnac interferometer under different curvatures are measured and analyzed. The results show that the wavelength shift has a linear relationship with the curvature, and the sensitivity of 0.232 nm·m is achieved in the curvature range of 0-9.9 m^-1. The temperature sensitivity is only 3.7 pm/^°C, and the cross sensitivity to the curvature measurement is ~ 0.016 m^-1/^°C. This merit of low sensitivity to temperature is very useful for the curvature measurement.