Interferometric, direct fiber-optic shape sensing with six degrees of freedom

Fiber-optic shape sensing is a specialized measurement method for the direct detection of shape changes in a sensor, which does not require an external observer, such as a camera. This sensor is characterized by its compact design and can be directly integrated into various objects to capture their shape changes. This opens up promising potential applications in minimally invasive surgery, continuum robotics, and structural monitoring.

The sensor consists of an arrangement of prepared optical fibers, in which multiple pairs of reflectors function as independent interferometers. The signal evaluation is performed using the range-resolved-interferometry method[1], which enables multiplexing and thereby facilitates the separation of the interferometer signals. This results in spatially resolved measurements of the differential strain along the fiber arrangement, from which the shape changes of the sensor can be directly determined (see figure).

The current state of the art is capable of shape sensing with four degrees of freedom. However, torsion of the sensor can lead to the loss of the coordinate system, resulting in significant measurement errors. The goal of this research project is to develop a system that enables the measurement of all six degrees of freedom, thereby expanding shape sensing to include the torsion and longitudinal strain of the sensor. The project is being worked on by our doctoral student Dipl.-Ing. Marvin Henkel.