Membrane-Free Fiber-Optic Fabry-Perot Gas Pressure Sensor With High-Resolution

Gas pressure monitoring has been applied to various fields in our life,such as aerospace,medical equipment,meteorological monitoring,marine exploration,national defense,military and industrial production.However,the traditional pressure sensor based on electricity,is difficult to miniaturize and sensitive to temperature and electromagnetic interference,which limits its practical application.Optical fiber gas sensors have the advantages of small size,light weight,anti-electromagnetic interference and intrinsic safety.Compared with the traditional gas pressure sensors based on electricity,they are more suitable under high temperature,high pressure,flammable and explosive fields,and strong electromagnetic interference.The optical fiber Fabry-Perot（F-P）gas pressure sensor has been widely studied and applied to environmental pressure monitoring due to its simple structure,low cost and high sensitivity.In this paper,the research status of optical fiber F-P gas pressure sensor is analyzed,and the advantages and disadvantages of optical fiber F-P gas pressure sensors with different structures are summarized.A membrane-free fiber-optic Fabry-Perot gas pressure sensor based on femtosecond laser micromachining and CO₂ laser welding is proposed and fabricated,and a thorough theoretical and experimental research on the performance of the proposed sensor is carried out.The research content of this paper is as follows:First,the principle and demodulation technology of optical fiber F-P sensing are deeply studied,and the expression of reflected light intensity of optical fiber F-P sensing is deduced.Several demodulation technologies,and a white light interference（WLT）demodulation method based on digital cross-correlation technology are introduced.A membrane-free fiber-optic F-Pgas pressure sensor based on femtosecond laser micromachining and CO₂ laser welding is proposed.On the basis of theoretical derivation,the performance of the sensor is analyzed by MATLAB software,and the relationship between the pressure and the optical cavity length of the sensor with different initial geometric cavity lengths is simulated.In theory,when the cavity length is 703μm,2062μm,and 2926μm,the sensitivity of the sensors is 1854.4 nm/MPa,5439.3 nm/MPa,7718.4 nm/MPa,respectively.The relationship between the sensitivity of the sensor and the initial geometric cavity length is analyzed,and the sensitivity is positively correlated with the initial geometric cavity length.Finally,the influence of temperature changes in the range 20℃to 70℃on the optical cavity length of the sensor is also analyzed.Second,the gas pressure sensing experimental system is built and the performance of the sensor is tested.Firstly,the equipment parameters used in the sensing system and gas pressure sensing process are introduced.Secondly,the reflection spectrum,sensitivity,repeatability and resolution of sensors with initial geometric cavity lengths of 703μm,2062μm and 2926μm are studied.According to the experiment data,the sensor with an initial geometric cavity length of 2926μm has a high sensitivity of 7702 nm/MPa and a high resolution of 4.9 Pa within the gas pressure test range of 0 MPa to 0.5 MPa,and has a good repeatability.The experimental results are consistent with the theoretical simulation results.Then,connecting a fiber Bragg grating（FBG）in series with the F-P pressure sensor to eliminate the temperature influence.The FBG temperature sensing calibration experiment is carried out,and the relationship between the temperature and the Bragg wavelength of the FBG is explored.Finally,a vacuum sensing experiment system is built,in the pressure range of 0.1 KPa to 88KPa,the sensors with initial geometric cavity lengths of 2078μm and 2926μm have a high sensitivity of 5.22 nm/KPa and 7.38 nm/KPa,respectively,and have a good repeatability.