Fibre-Coupled Remote Optical Vibrometry

摘要

This report covers the work performed at the Southampton Optoelectronics ResearchCenter into fibre optic remote vibrometry in the period 1991-1994. A number of instruments have been constructed including a passive homodyne scheme based on 3X3 coupler with digital signal processing, a simple lead insensitive heterodyne system employing a single birefringent fibre connecting the probe bead with the processing optics and a scheme using a single frequency fibre laser operating at a wavelength of 1.5 microns as an optical source. In addition we have investigated the effects of noise in the detector circuits and of laser linewidth on the fundamental sensitivity of such vibrometers and have presented the results in terms of effects on minimum detectable phase. The usage of erbium-doped fibre amplifiers (EDFAs) in interferometric sensors of the type used in vibrometry has been considered theoretically. The conclusions are that provided an ASE filter of modest width (of the order of 1 GHz) is used at the output, the use of an EDFA in the signal arm of the interferometer is highly desirable as the low levels of received light will in general make it difficult to get close to shot noise limited detector performance. (AN).