TABLE OF CONTENTS Optical interferometry is a well established technique which is associated with high resolution optical spectrometry and the precise measurement of length. Apart from length, other important parameters can be derived such as velocity, acceleration, pressure and force. The requirement of good alignment of the optical components constituting the interfeometer has prohibited the use of this high resolution technique outside the laboratory in the past. This major restriction of the general application of interferometry has recently been relaxed with the development of all monomode fibre optic equivalents of the classical interferometers. Fibre-optic interferometric measurement systems can be classified as either intrinsic (where the measurement beam always remains within the fibre and the optical properties of the waveguide are changing) or extrinsic (where part of the measurement beam travels outside the waveguide). Of the intrinsic type, the differential (polarimetric) interferometers can be used for measurements of displacement but suffer from low resolution, unless special fibres are used. There are many extrinsic forms of interferometers but the main ones are the Fabry-Perot, the Mach-Zehnder, the Michelson and the Sagnac. External applications of interferometry include holography, laser velocimetry using double beam interferometry and measurements of displacement and vibration.
Fibre optic modulators are generally used for coherent applications such as interferometry. They provide a means of either stabilising an interferometer against environmental disturbances or of heterodyning to detect phase shift. Phase modulation is achieved by externally modulating the length of a fibre or the effective index of the...
