Bragg Gratings in Two-Core Rectangular Fiber for Discrimination of Curvature, Strain, and Temperature Measurements

Abstract

We report, for the first time, the development of a rectangular fiber with two cores consisting of different refractive indices for the discrimination of temperature effects during strain or curvature measurements using fiber Bragg gratings written in a single segment of fiber. Two cores with a diameter of 8 μm and a rectangular cladding with dimensions of 120 μm × 255 μm permit convenient splicing to conventional single-mode fiber and support easy identification of the orientation of the fiber. When placed in the desired orientation, each core of the two-core rectangular fiber experiences a different spectral shift in the presence of applied strain or curvature. The sensitivities of the two cores are 0.87 and 1.08 pm/με for strain, 126 and -128 pm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for curvature, and 10.05 and 10.40 pm/ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> C for temperature, respectively. In addition, the flat cladding structure of the fiber provides a large physical contact area between the sensing fiber and the substrate than a circular fiber and allows better strain coupling between the object and the fiber.