Intensity modulated optical fibre sensor system for measuring up to 20 mm of linear displacement

The development of an intensity modulated optical fibre sensor system is described which was configured to provide referencing against the major sources of error likely to be present within such a system. A single broadband LED source is utilised to provide two separate narrow-band wavelength signals, one as the measurand and a second as the reference. Both wavelength signals are extracted by using optical bandpass filters to spectrally slice the LED emission. The sensor system provides an output fully referenced for all major common-mode variations arising from the optical propagation effects as well as those due to the LED instability. The optical sensor employs a Graded-Index (GRIN) rod microlens together with an interference filter and a moving mirror element. The performance characteristics of the prototype dual wavelength sensor system show a linear displacement range of up to 20 mm