Continuous Liquid Level Sensor Based on Coupled Light Diffusing Fibers

A continuous liquid level fiber optic sensor has been devised, developed, and tested. The sensor is based on two coupled light-diffusing glass fibers. The light from a laser diode is diffused out from the first fiber by scattering and coupled, always by the scattering, to the second fiber. The working wavelength has been selected in order to be strongly absorbed by most common liquids. The optical power measured at the ends of the collection fiber depends on liquid level. Both co-propagation and counter-propagation coupling configurations have been theoretically analysed and experimentally tested. Differently from counter-propagation configuration, co-propagation configuration exhibits a linear response with the liquid level and allows level measurements with a resolution in the order of millimetres over 1 m range.