Calibration Of Refractive Index Of Low Concentration Gas And Sensing Characteristics Of Interference

Gas sensing has always been one topic attracting many researchers in sensor research,optical waveguide sensor has advantages,such as high sensitivity,easy integration and immune to electromagnetic interference,so it has important application prospects in the fields of toxic,flammable,explosive gas detection and atmospheric environmental protection.The refractive index of gas is an important optical parameter to describe the gas characteristics,and the physical parameters such as dispersion,purity,and concentration of gas can be understood by means of the refractive index.Therefore,the refractive index measurement of gas and the index change can be used to describe the change of gas concentration.The optical waveguide gas sensor designed by the refractive index change of the waveguide layer provides theoretical and experimental basis for developing waveguide gas sensor with high sensitivity.The main contents and research results of the paper are as follows:1.Optimizing the gas generator to obtain gas concentration with a wide range.Low gas concentrations for ethanol,isoamyl acetate,acetone and water were prepared based on the diffusion tube in dynamic gas distribution method.2.Measuring the refractive index of gas and its variation by interferometric method.Under the conditions permitted by laboratory conditions,four gas chambers of different lengths were designed and fabricated to ensure sufficient variation of optical path difference.The gas chamber was placed in Michelson interference system.After many measurements,the relationship between the gas refractive index and the gas concentration was obtained.3.The integrated interference chip was designed and fabricated by using the optical waveguide mode theory.With the help of the waveguide dual channel of the integrated chip,the fringes with high interference contrast fringes are obtained.Within the experimental error,the detection sensitivity of the chip to isoamyl acetate gas was about 200ppm,when the external environment of the chip changes,the index change measurement of small refractive is achieved,which a simple?repeatable and accurate.The effect of external gas refractive index change on the contrast of interference fringes is simulated and calculated,which is shown that in a small range of refractive index variation,the change of gas refractive index has no obvious effect on the contrast of interference fringes.It is proved that the optical waveguide sensor has high sensitivity to the low gas concentration,and the integrated interference chip can be used to detect low gas concentration,which provides a development platform for the high sensitive gas sensors.