Analysis of Force Sensor Using Polymer Optical Fiber Based on Twisting Structure

This article highlights an intensity variation-based force sensor for polymer optical fiber (POF) that relies on the twisting structure. The sensing phenomena of the sensor rely on cladding mode frustrated total internal reflection (CMFTIR). A portion of two POFs is twisted in the middle where the light source is connected with illuminating fiber, and the power meter is connected with the forward end of the second fiber. Thus, the force measurement is taken from the second fiber by observing the variation of coupled intensity in which the applied force is up to 0-20 N. The sensor is analyzed on straight fiber, twisted fiber with bend, and without bend (considering the sensor's sensitivity). The experimental results show that the sensor has higher sensitivity in the twisted with-bend structure, and the bending radius also affects the sensor sensitivity. Moreover, a multipoint and multiaxis force sensor is also presented. The POF is twisted up to 100 cm for multipoint sensing, and force is applied at five different points, whereas the cascading scheme is adopted for multiaxis to achieve the individual response of each axis. This study provides an alternative way to measure force based on intensity changes and has an additional advantage of being cheaper than fiber Bragg gratings and other systems.