3D shape-sensor based on integrated optics in ultra-thin glass

Abstract

3D shape sensors find important applications in industries, e.g. structural health monitoring and medical technology. (Fiber-)Optical shape sensors possess various advantages such as miniature size, high sensitivity and low costs. Current challenges are the necessary increase of stability and reproducibility and the lack of application cases. We present a 3D shape sensor based on an ultra-thin glass (100 um) approach which allows both a stable and reproducible measurement. The 3D shape sensor presented here is part of the development of a novel and flexible X-ray detector, which serves as a practical application. Femtosecond laser pulses are used for the optical integration of both light waveguides and Bragg gratings into the ultra-thin glass. Bragg gratings serve as strain and ultimately curvature sensors (0 to 20/m) as they are integrated parallel to the neutral bending axis (20-30 um). The Bragg gratings are organized in a bi-directional network at known positions as all Bragg gratings can be integrated in a single step. The 3D shape sensor has to be calibrated only a single time as it can be mounted on and removed from surfaces without the need of a direct adhesion, resulting in easier integration and higher reproducibility as the neutral bending axis is not moved. A 3D reconstruction algorithm provides a 3D point cloud, which allows the calculation of the shape of the surface (here the detector surface). As the positions of Bragg gratings are well known, a more precise 3D shape recalculation is possible compared to fiber Bragg gratings.