Monitoring changes in the speckle field from an optical fibre exposed to low frequency acoustical vibrations

Some preliminary investigations are described of speckle fields produced from light propagation in a multimode optical fibre exposed to low frequency (100 Hz) acoustic vibrations. Measurements are presented that have been made with a photodiode detector and a CCD array, the results obtained with the latter being analysed using space domain chromatic techniques. Optimum operating conditions are considered for providing good sensitivity and repeatability for detecting low frequency vibration signals (not precise parameter measurements) with an ultimate objective of monitoring fault development from the vibration of a mechanical plant.