Double - Polarization Interferometer for Digital Displacement and Force Sensing by Fiber Tension - Bending

Abstract

lnterferometric fiber optical displacement and force sensors with incremental (digital) readout by fringe counting could be of advantage as elements in all fiber tactile sensor arrays of robotic grippers. Displacement to be measured is transferred to the sensing fiber via transverse - force -induced fiber tension bending, yielding a quadratic strain - displacement characteristic. This principle has been described previously for the sake of high resolution sensing of dc-measurands [1]. Here we are interested in low resolution remote sensing with large fiber strain (up to 0.5 %) and environmentally insensitive signal transfer. For eliminating the ambiguity of the counting procedure in remote readout of the interferometer, two phase - shifted orthogonally polarized interference signals are created employing the double - polarization method [2] [3]. The applicability of this method in the case of displacement sensing via axial stress applied to the fiber has been shown earlier [3]. The aim of the investigations reported here is to also demonstrate its applicability under the large changes in birefringence due to the transverse stress present under fiber tension bending.