Optical sensors for the location of buried optical cables and disturbances acting on extended lengths of optical fibre
The work presented in this thesis, investigating two novel optical fibre sensor systems, was carried out as part of industrially sponsored (Radiodetection Ltd) and supported applied research project. The first sensor determines the longitudinal position of acoustic disturbances acting on an extended length of optical fibre cable and the second system locates the lateral position of a buried dielectrically-sheathed fibre cable. The second system is believed to be the first optically-based sensor for the location of buried fibre optic cables. An RF electromagnetic field, emitted from above the cable, radiates through the ground and modulates the polarisation state of the light guided by the optical fibre, via the Faraday effect. The lateral position of the buried cable can then be inferred by observing the peak in the amplitude of modulation as the locator is traversed across the buried position of the fibre allowing, for the first time, dielectrically-sheathed optical cables to be located non-intrusively.