Temperature-Insensitive Curvature Sensor With Plane-by-Plane Inscription of Off-Center Tilted Bragg Gratings in CYTOP Fibers

We demonstrate of an off-centered tilted fiber Bragg grating (FBG) inscribed in cyclic transparent optical polymer (CYTOP) fiber as a curvature sensor. The gratings were inscribed using a femtosecond (fs) laser with the direct write, plane-by-plane method due to its high flexibility and suitability for customization, particularly for the development of a single-peak spectrum in multimode CYTOP fiber. The grating is applied to curvature sensing, where the spectral features, namely the wavelength shift and reflected optical power, are analyzed with respect to the curvature angle on the optical fiber. The off-center and tilted FBG response as a function of the angle is compared with a centered and uniform FBG inscribed in CYTOP fiber using the same inscription method and laser parameters. Results show a significant improvement for the off-center grating when the wavelength shift information is considered and lower optical power sensitivity as a function of the angle with respect to the centered FBG. In addition, the temperature sensitivity differences of the two gratings, enables the development of temperature-insensitive angle sensor using a single off-center tilted FBG.