Optical fibre interferometric system for Doppler effect measurement

A novel idea of optical fibre laser Doppler velocimetry especially useful for non-contact testing of rotation elements is presented. The main idea of the system is based on an application of interferometric measurement of Doppler effect by a specially constructed optical fibre interferometer. The standard single-mode coupler; connected with laser diode operated at 0.68 mum, has been used as the main optical element. A suitable selection of a target distance from the specially constructed optical head makes the system work as a single-reflection Fabry-Perot fibre interferometer Such device provided polarisation stability as well as good environmental shielding. The special numerical processing of interferometric output signals by a technique based on FFT gives a possibility of rotation element testing. The theoretical investigation was compared with experimental data obtained for the commercially available magnetic hard disc and the dynamically tuned electromechanical gym.