Fiber-optical 3D shape sensing

Fiber Bragg grating (FBG) technology is well known since more than three decades. It started in 1978 with the discovery of photosensitivity in optical fibers by Ken Hill et al. [1] when illuminating germanium-doped silica fibers with visible argon ion laser radiation. In this context, first periodic refractive index variation was introduced into the core of such special optical fibers. However, for nearly one decade, there was found no real application of these fundamental observations. The major breakthrough for Bragg gratings came in 1988 with the report on holographic writing applying single-photon absorption in the ultraviolet by Metz et al. [2]. They demonstrated reflection gratings using two interfering laser beams imaged into the fiber core. This was the starting point for several applications of FBGs ranging from reflection gratings used in telecommunication, high reflectivity end reflectors in fiber lasers, or sensor applications for monitoring mechanical strain and temperature.