Characterisation of a polymer-based eccentric FBG 3D shape deformation sensor

Abstract

We report on the systematic investigation of a polymer-optical fiber Bragg grating (POFBG) sensor for shape deformation with regard to its temperature and humidity sensitivity under various bending conditions and additionally with regard to strain and torsion, which are all relevant effects in the designated application in a novel 3D shape detection sensor system. The concept relies on the fast and simple inscription of Bragg gratings in graded-index multimode cyclic transparent optical polymer (CYTOP) fibers with the phase mask method and a krypton-fluoride excimer laser in the UV. When the fibers undergo deformation such as strain, torsion or bending or are affected by environmental effects, the lattice constant of the FBGs as well as the optical components can change and the spectral position of the Bragg peak shifts accordingly into the red or blue wavelength region. While the cross-sensitivity to humidity is relatively small over the full range from 10% to 98% relative humidity and, therefore, negligible, the cross-sensitivity to temperature is relevant and lies in the range from 17.2 pm/K (straight position) to 45.6 pm/K (upward bending position). The effect of strain on the sensor can be observed by the shift of the Bragg peak to the red wavelength region. Also, the impact from torsion on the sensor is clearly observable, even after multiple turns of the fiber, and the functionality of the sensor is preserved when plastic deformation occurs. The presented results offer the potential to use the sensor in everyday applications and specifically to track the motion of human hands. For example, sensor gloves can be used to detect early stage of motion impairment of focal dystonia patients in medical diagnostics or for augmented and virtual reality devices.