A Temperature-Insensitive Bidimensional Curvature Sensor Employing C-Fiber-Based Fabry–Pérot Air Cavity

Abstract

A bidirectional curvature sensor based on C-fiber-based Fabry-Pérot interferometer (FPI) is proposed and validated in this work. Well-established glass processing techniques and fiber drawing procedures are used to fabricate the C-fiber, which is then fusing-spliced between two single-mode fibers (SMFs) to form an FPI. When the FPI cavity undergoes bending deformation, the variation of the optical path will cause a change of the interference phase difference, resulting in a spectral shift. The shifting direction of the interference spectrum could also be used to identify the bending direction. Moreover, the FPI cavity length has a direct influence on the curvature sensing performance of the proposed sensor, and the smaller the length, the higher the sensitivity. Bending measurement and orientation recognition are experimentally investigated in two opposite directions, namely, the 0°and 180°direction. The maximum sensitivity as high as 3.434 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> is obtained within a curvature range of 0.373-1.585 m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> in the 0°direction using a FPI cavity length of 104.81 um. It also features a low thermal sensitivity of 0.893 pm/°C. The proposed sensor is ultra-compact, easy-to-fabricate and cost effective, which makes it a promising candidate for the bending monitoring at some specific points or ultra-short distances, such as the bend-determination of joint of a robot arms or micron-scale thin films.