Study On Tapered Fiber Liquid Sensors

With the development of fiber sensor technology, fiber sensors have already been used in many fields. Liquid sensors based on optical fiber, because of many advantages, have been widely applied.The theory of light-wave propagation in tapered fiber is analyzed by employing the geometry theory. A sort of liquid sensors, using the tapered fiber as sensing head, are proposed in this thesis. Two kinds of sensors are designed, i.e. reflected light detecting sensors and transmitting light detecting sensors. The beam propagation method is adopted to model and simulate light-wave transmission and refection of tapered fiber in order to validate theoretical results. Electrical arc melting method and hydrogen-oxygen blaze heating up method are used in making different tapered angles of fibers. The transmition-type sensors can measure the level of liquid continuously. The reflection-type sensors can measure the level of liquid discretely as well as detect dropping-speed of liquid.It is experimentally demonstrated that tapered fiber liquid sensors have high sensitivity, reliability and immunity from interferes. The liquid level measurement by tapered fibers is immune to the fluctuation of the liquid surface and the foam on the liquid surface. The dropping-speed monitoring sensors can detect dropping of liquid exactly and quickly. At the same time, tapered fiber sensing head can be used to analyze and inspect liquid in medical and biochemical fields. This kind of sensors will have promising prospect in many other fields.