Monomode optical fibre as a displacement sensor

Abstract

Three different mechanisms of small mechanical displacement detection, utilizing a single-mode optical fibre, have been developed. (1) The cylindrical body of the fibre is used as a microlens, which deflects the laser beam at different angles when at different positions relative to the beam axis. (2) The motion of the fibre core lobe into the focal spot of the beam will cause modulation of the coupled and hence of the transmitted light intensity. (3) When the focused beam is directed onto the lobe of the cladding or coating of the fibre at small incidence angles, multiply reflected leakage modes produce an interference pattern which is sensitive to the beam position. The techniques prove to be simple, robust and of submicron resolution.