Displacement sensor based on optical fibre with multiple overlapping imperfections

The concept of highly sensitive fibre optic displacement sensor is presented. It is based on macrobending step index polymer optical fibre with multiple overlapping surface-side imperfections. The theoretical principles of optical power losses in such fibres due to multiple curvatures are based on a surface that serves as a model for an imperfect layer and has the same optical properties. The sensing element was tested using two different types of roughness topologies and their combination. The various angles of imperfections (90 and 45 degrees) placed on the fibre's core were evaluated. We discuss some experimental results that confirm our prediction of considerable dependence of the output signal on the changing imperfections caused by bending the fibre. It was found that sensitivity to bending of the angular imperfections could be further increased by implementing multiple overlapping imperfections.