Distributed fibre optic sensors for humidity and hydrocarbon detection.

A novel distributed fibre optic sensor that incorporates liquid swellable polymers to transduce the swelling into a microbend loss is presented. Interrogation of the sensor using standard optical time domain reflectometry (OTDR) instruments provides the possibility of detecting target chemicals and fluids at any location along the sensor length. The location of multiple events along a sensor, which may extend to 4 km is readily achievable. In this paper we present an overview of the work conducted on the characterisation of a distributed optical fibre water sensor. Following a discussion of the basic principles of the water sensor and the underlying technology we present a review of the significant developments achieved. Tests incorporating the sensor in civil engineering applications, which range from monitoring of concrete curing to leak detection in highways, are described. In addition to this, more recent developments to utilise the sensor technology to detect other fluids are discussed, in particular for the monitoring of pH changes and liquid hydrocarbons. We discuss some of the significant advantages in using this type of sensor construction and areas in which it can be practically used.