Polarization-Maintaining Fiber Long-Period Grating Based Vector Curvature Sensor

Abstract

We propose and demonstrate an optical fiber vector curvature sensor based on a long-period fiber grating (LPFG) inscribed in Panda type polarization-maintaining fiber (PMF) using CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -laser heating and tapering system. The uniform heating approach removes the necessity of CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -laser exposure alignment along the axis of PMFs during grating fabrication. A serial of PMF-LPFGs with grating period from 350 to 490 μm with a step of 20 μm have been fabricated experimentally. The curvature response of the fast and slow axis resonance dips for the LPFG with a period of 450 μm was investigated in the curvature range from 0 to 4.137 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at four bending orientations. The maximum curvature sensitivities were measured to be 9.26 and -6.89 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for the fast and slow axis LP15 modes, respectively. The sensor can achieve 2-dimensional bending direction recognition. The proposed grating has potential application as a vector curvature sensor.