편광유지 광자 결정 광섬유에 새겨진 장주기 광섬유 격자 기반 비틀림 센서

Abstract

Here we experimentally demonstrate a fiber-optic torsion sensor with twist direction discrimination capability by using a long-period fiber grating (LPFG) inscribed on polarization-maintaining photonic crystal fiber (PMPCF), of which the resonance dip shows a nearly temperature-insensitive twist response. An LPFG formed on PMPCF, referred to as a PMPC-LPFG, has an input-polarization-dependent resonance dip, and two separated resonance dips, designated as shorter wavelength-dip (SWD) and longer wavelength-dip (LWD), which are obtained with respect to orthogonal input polarizations. A torsion response of a sensor head was investigated in a wide twist angle range from －220° to 220° for the two resonance dips. Highly linear torsion responses of the SWD and LWD could be obtained with the adjusted R2 values of ~0.9960 and ~0.9967, respectively, in the twist angle range from －160° to 160°, when their transmittance values measured in a logarithmic scale were converted into a linear scale. Also, the temperature response of the sensor head was examined in the temperature range from 35 °C to 85 °C with a step of 5 °C. The experimental results corroborate that the proposed sensor can perform nearly temperature-insensitive torsion measurement with twist direction discrimination capability and good linearity in wide measurement range.