Tle Design And Sensitivity Study Of Multilayer Planar Optical Waveguide Gas Sensor

With the rapid development of high-speed information technology(such as 5G),we have gradually entered the era of artificial intelligence.Various communication technologies are continuously upgraded,speeded up and expanded,which directly promotes the progresses of sensor technology.The smart era relies on many sensors to interconnect everything and form the next generation network----the internet of things,which will profoundly change people`s lives and our thinking ways.Optical waveguide sensor is one of many sensors with unique advantages,which is a necessary sensor in the optical network.This thesis focuses on the planar multi-layer optical waveguide gas sensor and its gas detection sensitivity,which explores the feasibility for practical applications in the future.This thesis theoretically analyzes the relationship between the multi-layer planar optical waveguide structure and the gas to be measured.The structure design of the asymmetric five-layer optical waveguide is optimized by simulations,and the structure parameters of an asymmetric five-layer planar optical waveguide(thin film refractive index,thickness of each layer,etc.)used for gas measurement is obtained,which proves that the optimized optical waveguide can produce a clear interference pattern.We analyzed the influence factors of the effective refractive index of the upper and lower waveguide modes of the waveguide structure on the sensitivity of the waveguide sensor,and the influence on the movement of the interference fringes generated from the upper and lower waveguide layers.Then,a gas mixture method was used to prepare and to calibrate a mixed gas fo four liquids,such as ethanol,acetone,isoamyl acetate and water,in order to obtain a low-concentration gas used in interference testing.Based on the improvement of the experimental test system,the moving value of interference fringes generated from the waveguide structure was measured when the asymmetric five-layer optical waveguide structure was exposed to the isoamyl acetate and ethanol gases with differentconcentrations.The minimum volume concentration of ethanol gas measured by the gas sensors is 16.64 ppm,the sensitivity is S(28)0.00366mm/ ppm.The minimum volume concentration of isoamyl acetate gas measured by the gas sensor is 34.78 ppm,the sensitivity is S(28)0.00045mm/ ppm.As the testing gas volume concentration increases,the sensor sensitivity decreases.The experimental results show that measuring the low concentration gas using the waveguide structure achieves high sensitivity,which proves a certain practical prospects.