TABLE OF CONTENTS In the following sections some recent advances on amplitude, wavelength, phase and polarisation modulating sensors are discussed. Although such division is general, as some recent techniques use many modulation principles simultaneously to separate efficiently the coupled parameters of interest, it still provides a basic framework for the design engineer to choose which technology may be the most appropriate for the solution of a particular problem.
In cases where optical fibres rather than free-space propagating beams are used, optical fibre sensors may be divided into extrinsic or intrinsic ones. This is dependent on whether the light signal is modulated inside or outside the fibre.
Examples of extrinsic fibre optic sensors include encoder plates or disks that measure linear or angular position, reflection and transmission configurations to measure pressure, flow and damage, total internal reflection sensors, for measuring pressure and liquid level, grating based sensors for measuring pressure and vibration, fluorescence sensors for temperature, viscosity and chemical analysis applications, evanescent sensors for monitoring temperature and strain, laser Doppler velocimetry sensors for flow measurement, pyrometers, for sensing temperature, and sensors based on photoelastic effects for monitoring pressure, acceleration, vibration and rotary position.
Examples of intrinsic fibre optic sensors include microbend sensors for measuring strain, pressure and vibration, blackbody sensors for measuring temperature, and distributed sensors. The latter can be further divided into Rayleigh sensors for measuring strain and temperature, Raman sensors for measuring temperature, mode-coupling sensors for measuring strain, pressure and temperature and quasi-distributed sensors for...
