Helical Long-Period Gratings in Four-Core Fiber for Multiparametric Monitoring of Directional Bending, Torsion and Temperature
Yunhe Zhao, Huiqin Peng, Yuehui Ma, Yunqi Liu, Yongsheng Yang, Zuyuan He
Abstract
We demonstrate the multiparametric monitoring of directional bending, torsion, and temperature based on helical long-period gratings (HLPGs) in a triangular four-core fiber (FCF) using CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser irradiation. The simulations investigated the stress-relaxing effect of the stress-applying parts due to CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> laser heating. In the experiments, the HLPGs with a period of 435 μm and a period number of 60 induced in FCF have been investigated for multiparametric monitoring. The directional bending sensing characteristics of FCF-HLPGs exhibit that at the curvature ranges A and B, the maximum bending sensitivities are −47.24 and 48.47 dB/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> obtained at −60°, respectively. And their sensitivities show the sine function behavior with curvature directions from −180° to 180°. The torsion sensitivity based on coupling efficiency variation is −0.16%/(rad/m) in the range from −10 to 10 rad/m. The temperature sensitivity based on wavelength variation is 0.123 nm/°C, and the intensity response on temperature can be negligible. The proposed FCF-HLPGs is potential in practical application for multiparametric monitoring.