All fiber-optic sensor for liquid level measurement

In this article, a simple intensity-modulated fiber optic sensor for liquid level measurement is presented. The sensor principle is based on frustrated total internal reflection effect caused by refractive index change of a medium surrounding an optical fiber. The end face of a step-index multimode optical fiber is polished to form a hemispherical tip so that a part of the forward propagating modes is reflected in the reverse direction by the effect of total internal reflection. The change of medium (due to contact of the tip with the liquid) modifies the critical angle for the back reflected light thus giving modulated output power. The experimental results of the sensor obtained for different liquids (pure water, ethanol) confirm the sensor potential for liquid level determination on with high accuracy nearly 5 mu m and repeatability. (C) 2008 Wiley Periodicals, Inc.