Abstract

Although bulk optic torsional vibrometers are commercially available [1], similar sensors based on optical fibre technology have not been reported, to our knowledge. Fibre-optic torsional vibrometers represent a class of extrinsic fibre-optic sensor [2]. We have developed two new fibre-optic sensors which may be classified as either differential or reference instruments. These are based on the Laser Doppler principle and are fabricated with single mode fibres and associated components. The major advantage of basing the instrument on optical fibres is that it allows both a flexible light guide between the optical source and processing electronics and the possibility of a miniature but rugged lightweight probe to be deployed in the measurement volume, greatly enhancing the applicability of the technique. The instrument can be used conventionally in a 'line of sight mode' or deployed in inaccessible areas. It would be feasible to design a probe which could be mounted inside an engine to monitor the rotation of internally mounted shafts etc. The differential mode, like bulk torsional vibrometers, has the advantage of direction independent instantaneous measurement. The reference mode has similar applications and the advantage that measurements can be made with significantly lower optical power when compared to the differential mode.

© 1992 Optical Society of America