Fabry–Perot interference-based fiber-optic sensor for small displacement measurement

A simple fiber-optic sensor based on Fabry–Perot interference for small displacement measurement is investigated both theoretically and experimentally. A broadband light source is coupled into a Fabry–Perot cavity formed by the surfaces of a sensing fiber end and the measured object. The interference signals from the cavity are reflected back into the same fiber. A small displacement via changes in cavity length can be obtained by measuring the wavenumber spacing of the interference fringes. The experimental data meet with the theoretical values very well. Given the light source bandwidth of 40 nm and the initial distance of 30 μm, the proposed displacement sensing system could achieve high resolution measurement of 16 nm.