| The leakage of H2S gas can easily cause extremely serious consequences on the environment and human body.Therefore,it is important to develop a rapid,high sensitivity and reliable hydrogen sulfide gas sensor in order to monitor the concentration of H2S gas under particular environment.The use of evanescent waves to detect gases is a typical optical detection technique in which the sensor sensitive elements are separated from the optical input/output waveguide sections,and the test signal is not disturbed by the input and output optical waveguide coupling.Meanwhile,the technique has advantages such as high sensitivity,immunity to electromagnetic interference,wide frequency band for the transmittable signal,point-like or distributed measurement and long-distance transmission of signal compared to conventional methods.A ridge-shaped optical waveguide structure sensitive to hydrogen sulfide gas was proposed.The polymer was polyethylenimine(PEI)and polymethyl methacrylate(PMMA)blended in a certain proportion.PEI contains a large number of amino groups that can react with hydrogen sulfide gas,so it has a strong adsorption effect on hydrogen sulfide,and improves the unevenness of the application of hydrogen sulfide sensitive material in the sensor core layer of the sensor.The ridge waveguide structure can make the sensor device smaller and facilitate system integration.It can also increase the waveguide cross section and reduce the coupling loss with the optical fiber or other devices.By properly designing the ridge waveguide size,the distribution of the guided wave light field can be controlled,the contact between the evanescent field and hydrogen sulfide gas can be increased,and the strong adsorption of hydrogen sulfide by PEI can increase the signal of hydrogen sulfide gas concentration detected by the evanescent field.The details are as follows:The principle of detecting the concentration of H2S gas by the evanescent field of the optical waveguide was analyzed.As the sensitive element of the evanescent field sensor,the optical waveguide has a great influence on the performance of the sensor,so materials of the waveguide and the principle of response and absorption to H2S gas were analyzed.Starting from the electromagnetic theory of light,wave mode theory was used to analyze the mode characteristics of the three-layer slab waveguide.Using the effective refractive index method,the propagation mode characteristics of the ridge waveguide guided mode were analyzed based on the guided mode theory of three-layer slab waveguide which will provide a theoretical basis for the designation of the organic polymer ridge waveguide.The single mode criterion of the ridge waveguide was analyzed to obtain the relationship between the parameters of the ridge waveguide structure.Specifically for the study of PEI/PMMA blended organic polymers,the reasonable structural dimensions of the designed organic polymer ridge waveguide are inner ridge height H=4.5?m,outer ridge height h=2.5?m,and ridge width W=4.2?m.Finally the model and field distribution of the organic polymer ridge waveguide were simulated and the optimal structural parameters of the organic polymer ridge waveguide for H2S gas detection were obtained.The preparation method of organic polymers was studied and found the suitable solvent for dissolving PMMA and PEI was glacial acetic acid.The effect of PEI content on the hydrogen sulfide response of the films was analyzed by UV transmission spectrum,and the effect of temperature on the response of the films was studied by UV absorption spectroscopy.The film-forming properties of blended organic polymers and the manufacturing process of organic polymer ridge waveguides were explored.A ridge waveguide with a designed size was developed.An optical system was constructed and the transmission mode of the ridge waveguide was tested. |
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