The role of viscoelastic properties in strain testing using microstructured polymer optical fibres (mPOF)

Optical fibre sensors have conventionally been made of silica. Polymers however have a much lower Young's modulus and higher elastic limit than silica, and can be incorporated into a larger range of materials. Whilst these properties make them attractive for using in mechanical sensing, using polymers also brings complexity because of their viscoelastic response. In this work, we use long period gratings (LPG) in microstructured polymer optical fibre (mPOF) as a mechanical optical sensor. The effects of stress and strain on the sensor are decoupled and analysed independently. Through experiments and modelling we show that the effect of stress (as opposed to strain), and the relaxation of stress in the optical fibre during loading have a minimal effect.