Study On Fiber Optic Gas Sensing Based On Infrared Absorption

With the attention of people to the quality of living environment and production safety,gas monitoring and analysis instruments or technologies have been rapidly developed.In this paper,erbium-doped photonic crystal fiber with excellent optical properties is used as gain medium.The sensing mode of optical fiber gas sensor and the influence of sensing light source on the sensing sensitivity of the system are studied.Firstly,according to the working principle of gas detection,the common gas trace technology is summarized,the advantages and disadvantages of various technologies are analyzed,and the advantages of optical analysis compared with other gas sensing technologies are pointed out.The fine characteristics of optical fiber gas sensing equipment and scheme based on spectral absorption are described,and the research status of optical fiber sensing technology at home and abroad is summarized.From the point the view of application,the advantages of fiber ring cavity laser in gas sensing are analyzed.Based on the energy level theory of erbium ion,the formation process of laser is described.The expressions of the number of inversion particles and the number of photons in a fiber laser ring cavity are derived by using the laser rate equation.Based on the sensing principle of infrared absorption spectroscopy,the method of improving the sensitivity of gas sensing is analyzed by combining the expression of photon number and absorption intensity,and the influence of the pump mode of laser on the gas sensing system is discussed.Finally,the absorption spectra of common gases in low loss window of near infrared quartz fiber are analyzed.Then,the relationship between absorption spectrum and environmental change was studied.The working principle and output characteristics of broadband laser source are analyzed theoretically and experimentally.It is pointed out that there is an optimal pump power of gas sensing in broadband laser source.The key devices and their functions in the system are introduced.Under the optimal pump power of gas sensing,the effect of the output coupling ratio of coupler on the measurement sensitivity and measurement error of external cavity and intra cavity gas sensing systems is described.The influence of gas pressure on the sensitivity of two gas sensing methods was studied.The experimental calibration and retrieving concentration of acetylene are carried out,and the sensing performance of the two gas sensing methods was compared.A distributed Bragg reflectance fiber laser with good output performance is constructed by using fiber Bragg grating(FBG).The output center wavelength is close to the acetylene absorption peak at 1532.82 nm.The sensing performance of this light source was investigated by using acetylene as gas sample in the mode of external transmission of the cavity.Because the absorption peak was located at the edge of the laser spectrum,the gas sensing performance was not satisfactory.To solve this problem,a tunable narrow linewidth fiber laser is developed based on nonlinear polarization rotation effect.The tuning principle and output characteristics of the laser are analyzed in detail.In the experiment of acetylene sensing,there is a good linear response relationship between the acetylene concentration and the output peak power of the tunable fiber laser.