FPI-POFBG Angular Movement Sensor Inscribed in CYTOP Fibers With Dynamic Angle Compensator
Arnaldo Leal‐Junior, Antreas Theodosiou, Camilo A. R. Díaz, Letícia Avellar, Kyriacos Kalli, Carlos Marques, Anselmo Frizera
Abstract
We present the development and application of an angular movement sensor based on Fabry-Perot interferometer (FPI) in series with a fiber Bragg grating (FBG) inscribed in cyclic transparent optical polymer (CYTOP) using a femtosecond laser. The FPI was fabricated with UV-curable resin between the CYTOP and a silica pigtail, which provides flexibility and the possibility in situ fabrication. In this case, the FPI is an edge-filter for the FBG response, which presents both wavelength shift and optical power attenuation as the bending angle increases. A dynamic compensator for the material's viscoelastic response resulted in a six-fold reduction in the sensor's transient response error. The FPI-POFBG angular movement sensor was validated in knee angle monitoring during gait cycles, where the sensor presented errors as low as 2.5°. This is a low-cost sensor with high flexibility on fabrication and with the capacity of following subtle angle variations, as the ones commonly occurred in gait cycles.