Optical Fibre Sensors - Chapter 8: Principles and Components

Abstract

Optical fibres have some degree of sensitivity to a wide range of external parameters. On the other hand the effects are usually small and are minimised as far as possible in fibres designed for telecommunications. Furthermore it is often difficult to differentiate between a number of small responses which may occur simultaneously. Considerable advantages can be gained in sensor applications by appropriate selection of core and cladding materials and by novel fibre structures and designs.

Thus by spinning the preform during fibre drawing a high degree of circular birefringence can be introduced whilst the linear birefringence becomes negligible. Such fibres can behave as sensors of magnetic fields and electric currents. By introducing a high degree of linear birefringence fibre gyroscopes capable of measuring angular rotation become possible. The introduction of rare-earth materials into the core produces absorption bands with steep edges which have a strong wavelength sensitivity to changes in temperature. This produces the basis for distributed sensors which cover a wide range of temperatures.

A variety of novel types of optical fibres are presently being explored for potential application to sensors and transducers.

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