Simultaneous Measurement of Bending and Torsion in Optical Fiber Shape Sensor

Optical fiber shape sensing technology provides an excellent solution for the tracking and guiding of minimally invasive surgical instruments. However, when some large-deformed instrument operation tasks are involved, restricted by the operating environment, a significant torsion will be produced by the curved structure of the instrument, posing a threat to the accuracy of its shape reconstruction notably. In this paper we propose and experimentally illustrate a new distributed curvature and torsion measurement method based on optical frequency domain reflectometer using helical multi-core fibers. A theoretical model of total strain induced by the bending and torsion is established. Two diverse means of inverse algorithms to decouple bending and torsion are explored. The experimental results of two methods demonstrated that the torsion measurement errors are around 6.6% and 7.3%.