Research On Trace Gas Detection Based On Anti-resonant Hollow-core Fiber

Trace gas detection plays a vital role in many fields such as atmospheric environment monitoring,industrial process monitoring,human respiratory detection,and agricultural production.Optical gas detection is favored by domestic and foreign scholars for its advantages of fast,real-time and high sensitivity,and it is studied in depth.However,how to make the detection setup achieve miniaturization and high sensitivity at the same time,this problem has been restricting the further development of this technology.Anti-resonant hollow-core fiber is a new type of gas cell with micro-nano structure.It has the advantages of small size,easy bending,low loss,and fast response speed.It brings new ideas for integrating into a miniaturized,high-sensitivity trace gas detection setup.In this paper,the anti-resonant hollow-core fiber is the main research object,and the research of gas detection method based on anti-resonant hollow-core fiber is carried out with the exploration of miniaturized and high-sensitivity gas detection setup as the main line.Firstly,starting from the nature of gas molecules,two spectral detection techniques were discussed.Several common gas cells in the absorption spectrum were analyzed,and the advantages of the anti-resonant hollow-core fiber were expounded.The optical simulation software was used to model and simulate its structure,and its mode field and coupling efficiency are analyzed.Finally,a miniature trace gas detection setup was built,and methane was selected as the target gas to carry out experimental research and achieved good experimental results.The main work content of this article includes the following aspects:(1)Starting from the essence of gas molecules,the relevant physical parameters such as line intensity,line width,and line shape of the absorption spectrum are introduced.Based on the Lambert-Beer law,the direct absorption spectroscopy technology and the wavelength modulation spectroscopy technology were deeply analyzed.Several typical gas cell structures in laser absorption spectroscopy were introduced,and their advantages and disadvantages were analyzed in detail.After comparing several gas cells,it was found that anti-resonant hollow-core fiber as a gas cell could effectively reduce the size of the detection setup and improved the response time.(2)Based on the beam propagation method,the optical simulation software is used to model and simulate the anti-resonant hollow-core fiber.The mode field and coupling efficiency are analyzed.The optical transmission model of single-mode fiber and anti-resonant hollow-core fiber is established,and the change of coupling efficiency at different axial distances and radial distances is analyzed,which provides new ideas for the design of fiber coupling setups.(3)A trace gas detection setup was built based on anti-resonant hollow-core fiber.It mainly introduces the light source module,fiber selection and signal acquisition and processing module,and selects the key components of the detection setup.The inlet and outlet air chambers of the anti-resonant hollow-core fiber and the coupling setup with the single-mode fiber are designed,and the coupling efficiency and stability of the coupling setup are tested.(4)Carry out experimental analysis on the built detection setup.Methane gas was selected as the gas to be tested,and the wavelength modulation spectroscopy technique and the direct absorption technique were used to conduct experimental research on it.The experimental results showed that the gas detection device based on anti-resonant hollow-core fiber and wavelength modulation spectroscopy was suitable for the detection of trace gases with low concentration.The minimum detection limit of the detection device was 0.878ppm calculated by signal-to-noise ratio.