Optical-Fiber Refractometric Sensor with Semi-cylindrical Optical Detection Element for Measuring the Level of Gasoline

We present a novel optical fiber refractometric sensor with semi-cylindrical optical detection element. A pair of the multimode optical fibers is attached symmetrically to the element´s flat plane. The optical coupling of the two fibers due to internal reflection of light from the element´s cylindrical surface is sensitive to the refractive index of the surrounding medium. We exploit several internal reflections in series and partial focusing of the optical beam by the element´s cylindrical surface to achieve enhanced sensitivity to the refractive index of the surrounding medium and reduced intrinsic optical loss in the transducer. We show theoretically that the transducer, in particular, can discriminate between the air and gasoline. We also present experimental data obtained with plastic detection element, which confirm our theoretical results. A vertical array of such transducers employing a relatively long single semi-cylindrical detection element can access the level of gasoline in automobile tanks.