Plastic optical fibre with structural imperfections as a displacement sensor

An optical displacement sensor is presented. It is based on bending a multi-looped plastic optical fibre that has multi-structural imperfections on the outer side of its core. A theoretical model was developed which shows that losses of light in such fibres result from the attenuation of light in the structurally imperfect area. In this model, the structurally imperfect area is replaced by a uniform layer with a complex refractive index. The sensor was tested using two different types of imperfection geometry, and some experimental results are discussed. The sensor's highest sensitivity was achieved by multi-structural imperfections in the fibre's sensitive region. The sensitivity was improved even more by increasing the depth of the fibre's imperfections.