The Study Of The Fabrication Of Gas Sensing Hollow Core Waveguide With Liquid Film In Near-infrared Spectrum

With the development of socio-economic and industrialization, atmosphericpollution becomes serious. People want the high quality of life. The demand of highperformance of environmental monitoring is becoming more. The new type of gas sensoris the hotspot in the research of sensor. In this field, the spectral absorption sensor candectect wide range gas concentration with high precision and good selectivity. Because ofthe high performance of resistance to electromagnetic interference, and good selectivity,the less transmission loss, optical fiber sensing technology gained much attention. In the1970s, hollow core waveguide(HCW) was invented. The hollow core is used as bothwaveguide and spectral absorption room. The less transmission loss, high sensitivity andgood selectivity make this structure reach the requirement of gas detection. HCW withdielectric film is used in gas sensing. This HCW use the different of refractive index ofdielectric film to reduce the transmission loss in some window regions of mid-infraredspectroscopy. The research of near-infrared spectroscopy is neglected in a long time.Although the information of near-infrared is more than mid-infrared and the most ofcompound have spectral absorption in near-infrared, the absorption is co-frequencyabsorption or double frequency absorption. The absorption is weak, because of the size ofwavelength, the scattering loss is more in near-infrared.In the research, we put forward a new structure of HCW with liquid film. The liquidfilm HCW increase the gas absorption in near-infrared relatively. The liquid HCW isbased on Ag film HCW, we use liquid film(a kind of stationary liquid) instead of delectricfilm. According to the theory of similarity and intermiscibility of gas and liquid, when theliquid and gas have a same polarity, the liquid film HCW can increase the concentrationof gas in HCW. So the gas absorption become strong.We choose the quartz as the material of base core. According to Miyagi theory, weget the inside diameter of base core. We choose Ag as the material of reflection film to geta small transmission loss coefficient. In this research, we get the rule of Ag growing indifferent temperatures and in different long time. The process to make liquid film HCW isexplained in details. According to Miyagi theory, we get the thickness of liquid film. We tested the liquid film HCW transmission loss. The liquid film HCW has a flattransmission loss in near-infrared relatively. The liquid film HCW is a good gas sensingHCW in near-infrared relatively, and has a wide region near-infrared to detect gas.In the research, we made a system of liquid HCW gas sensing and tested differentconcentrations of gas, such as methane and acetylene. We found that liquid film HCW hasa increased effect to the gas which has the same polarity with liquid film and no increasedeffect to the gas which has the opposite polarity. In our study, the liquid film can detectacetylene above1000PPM concentration. We prove the liquid film HCW is a HCW whichcould be use repeatedly.