NOISE EFFECTS IN POSITION MEASUREMENT USING A WHITE-LIGHT INTERFEROMETRIC SYSTEM LINKED WITH DIFFERENT CORE DIAMETER MULTIMODE FIBERS

An optical fibre sensing system comprising two Michelson interferomete rs linked with a multimode fibre has been investigated. The signal to noise ratio of the output, when linking fibres of a range of core diam eters were used, was measured and the system analyzed. The signal to n oise ratio of the system in the 100 mu m fibre case is higher than tha t with a 50 mu m core diameter fibre, these results being obtained whi le the linking fibre in the system was perturbed to induce noise in a known and reproducible way. The repeatability of the displacement meas urement with 50 mu m, 100 mu m, and 200 mu m core diameter linking fib re has been obtained by using the maximum visibility method, this bein g seen to increase as the core diameter of the linking fibre increases , and for 200 mu m core diameter fibre it was measured to be about 22. 5 nm (3 standard deviations) under the conditions described.