An Absolute Displacement Sensor Using Moire Fringe Techniques With Multimode Optical Fibres

Abstract

The feasibility of the use of optical fibres to supply light to, and relay information from, an absolute moiré fringe displacement sensor has been demonstrated and a prototype built.Fringe interpolation techniques are employed which reduce the susceptibility of the sensor to adventitious intensity fluctuations.The system is designed to operate over a displacement range of 100 µm and can resolve displacements down to 12 nm: nonlinearity is ±0.8,,um, while hysteresis and repeatability are better than 0.3 um.The system is largely immune to intensity variations on the input light channel, however differential attenuation between any of the four return light channels more seriously affects the measurement. In order to try and avoid this problem an optical arrangement has been investigated in which intensity information corresponding to four quadrature points on the moiré-fringe profile is carried in a single return optical fibre using wavelength separation.