Research And Development Of Distributed Optical Fiber Gas Sensor System

Today with the increasingly air pollution, it is particularly important to monitor the gas concentration around us real-time online. Conventional gas test method such as wet chemical method with long sampling time, complicated process, many interference factors, system is not easy to update and other shortcomings, it has great significance to discuss a fast, real-time online gas detection method for environmental protection, production safety and national economy. We report on distributed optical fiber gas sensor on theory of spectral absorption of gases and optical time domain reflectometer (OTDR),with hollow-suspended-core optical fiber as sensing fiber. We did theoretical research and experimental tests, this project has a high sensitivity, distributed detection, fast response, anti-interference ability, real-time online continuous monitoring and so on.Firstly, we study on the theory of spectral absorption of gas molecules and the principle of optical time domain reflectometer (OTDR).Based on the principle of optical time domain reflectometry gas distributed detection method and the absorption of gases on optical fiber evanescent field of the light wave we proposed this distributed detection method. In order to improve the gas detection sensitivity, we design a hollow-suspended-core fiber. We establish this fiber model, study on this fiber production methods and sensitization increasing methods.Also we do research on waveguide coupling theory, design a coupling method with the ordinary single-mode fiber and hollow-suspended-core fiber suspension. Finally ,we design and made a distributed optical fiber gas sensor system to test acetylene, using distributed feedback semiconductor laser (DFB LD) as a light source, avalanche photodiode (APD) as a detector, high-speed optical switch as a light intensity modulator and we do functional test of the source drive, wavelength locking, driver and signal processing detectors, modulators,high-speed data acquisition card. Using Visual C++ to write software for data acquisition and processing and experimental testing of the distributed optical fiber gas sensor system.