Distributed sensing using Rayleigh scatter in polarization-maintaining fibres for transverse load sensing

Distributed transverse load sensing, along an extended length of polarization-maintaining (PM) fibre, has been demonstrated using high spatial resolution (2 cm) optical frequency domain reflectometry (OFDR) which is based on recording a characteristic Rayleigh scatter 'fingerprint' of a single mode fibre. Application of a transverse load to a PM fibre induces localized differential changes of the refractive index of slow and fast axes, which can be monitored simultaneously and separately. The magnitude of the refractive index variation affects the distributed Rayleigh scattering, permitting the determination of scale and/or direction of load, relative to the PM fibre axes, by cross correlation with a previously recorded 'fingerprint'. Load sensitivity as a function of load direction, relative to the PM fibre axes, and the linearity of induced refractive index changes with a load of up to 16 N mm−1 for the optimum load orientation are presented. The application of this technique towards a load-sensing mat is discussed.