Curvature, twist and pose measurements using fiber Bragg gratings in multi-core fiber: A comparative study between helical and straight core fibers

Abstract

This paper presents a technique to acquire measurements of curvature, twist and pose for two multi-core fibers; one with straight cores and the other with helical cores. Both the fibers have multiple fiber Bragg grating (FBG) sensors inscribed in the cores and the fibers are placed in known configurations in order to compare their measurement accuracy. For the curvature measurements both the fibers are placed in constant curvature slots; for the twist measurements, a set of twists are applied to each fiber and for the pose measurements the fibers are placed in molds of different shape. The mean curvature errors are 0.22 and 0.13 m−1, in the helical and straight core fiber respectively. For the twist measurement the mean errors are 26.57°/m and 146.50°/m in the helical and straight core fiber, respectively. Lastly, the pose measurement consists of position and orientation where the orientation is represented in the axis-angle form. The mean position errors are 0.49 and 0.27 mm, the mean axis orientation errors are 0.12° and 0.26° degrees and the mean angle orientation errors are 1.10° and 1.18°, for the helical and straight core fiber, respectively. The results show that the twist measurement error is significantly low with the helical core fiber, thus helical core fiber is better suited than straight core fiber for applications where twist measurements are required.