Christian Waltermann

Point-by-point inscription of phase-shifted fiber Bragg gratings with electro-optic amplitude modulated femtosecond laser pulses.

Femtosecond laser pulses were used for the direct point-by-point inscription of phase-shifted fiber Bragg gratings (FBGs) in a single fabrication step without postprocessing. An electro-optic amplitude modulator is used in the setup to generate a defined delay between two identical laser pulse trains for the grating inscription. The grating structure with a central phase shift is formed by focusing the modulated laser pulses into the core of a fiber, while the fiber is translated with a constant velocity. The induced phase shift leads to a narrow transmission band with a bandwidth considerably below 10 pm within the stop band of the FBG. The inscribed FBGs show a birefringence of 3.9×10(-5) whereas their temperature and strain sensitivities are 10.4  pm/K and 1.4  pm/μstrain, respectively. The fabrication process is fast and offers a high grade of flexibility for the control of all grating parameters.

Femtosecond laser aided processing of optical sensor fibers for 3D medical navigation and tracking (FiberNavi)

A new concept for fiber-optical 3D shape sensing applying femtosecond laser technology for highprecision direct writing of Bragg gratings within the core and the cladding of single core standard telecom fibers is presented. This new technology enables a cost-efficient and real-time 3D shape sensing and navigation of medical catheters or endoscopes only by means of passive optical sensor elements. First prototypes showed the possibility to achieve absolute navigation accuracy of four mm per meter and have successfully been tested in clinical environment.

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.

Integration of fiber optical shape sensing with medical visualization for minimal-invasive interventions

We present a fiber optical shape sensing system that allows to track the shape of a standard telecom fiber with fiber Bragg grating. The shape sensing information is combined with a medical visualization platform to visualize the shape sensing information together with medical images and post-processing results like 3D models, vessel graphs, or segmentation results. The framework has a modular nature to use it for various medical applications like catheter or needle based interventions. The technology has potential in the medical area as it is MR-compatible and can easily be integrated in catheters and needles due to its small size.