A precision fiber optic displacement sensor based on reciprocal interferometry

A fiber optic nanometer range displacement sensor has been developed based on reciprocal interferometry, a concept widely used in fiber optic gyroscop es. Its configuration is similar to a Michelson interferometer but with onl y one of the two arms used. The principle of operation is the interference between the reflected light wave from the fiber end and that from a reflect ive object. As both the reference and the sensing light waves travel throug h the same optical path except for the air gap which is the distance to be sensed, the system is thus reciprocal and insensitive to perturbations intr oduced to the fiber path. While the system is very simple, it has demonstra ted substantially :improved immunity against environmental perturbations ov er the conventional Michelson interferometer. Our experimental results have shown that the interference behavior agrees well with its mathematical mod el. The system has demonstrated a resolution of 5 nm. The influence of temp erature change and PZT induced phase shift to the fiber has been studied an d the results have shown that the system is indeed insensitive to these per turbations. (C) 2000 Elsevier Science B.V. All rights reserved.