Displacement measurement using a focusing chromatic modulator

A novel, optical-fibre-based, displacement sensing system is described and its properties and behaviour investigated experimentally and theoretically. The system utilises the chromatic modulation principle in conjunction with a spherical modulator element which economically combines both modulating and focusing functions. A computer design package based upon a two-dimensional ray model is used to illustrate the behaviour of the sensing element and to establish optimised sensor element designs. The system is shown to offer a number of advantages which include simplicity and in-built insensitivity to variations in light intensity. A resolution of 1 in 10 4 is shown to be achievable. No quadrature referencing is needed for direction discrimination.