Colour-Modulation Optical Displacement Sensors

In the choice of techniques for optical sensing, colour measurementoffers the attraction of intensity independence so that connector and other variable losses are not important. The use of diffraction gratings and zone plates for displacement sensing is well known but the use of such dispersive elements in low cost systems is sometimes precluded by poor temperature stability or high cost. This paper describes an approach to solving these constraints so that colour measurement techniques can find wider application. Colour filters offer a very simple means whereby the perceived colour of light can be varied. Their temperature stability will limit the accuracy of devices built around such filters and experimental data on a variety of filters is presented. A number of examples of the use of filters in sensor designs are given and the limitation of accuracy and resolution discussed. The advantages of the use of filters for colour modulation optical displacement sensors include the inherent flexibility offered by the design and their potentially low cost.