Research And Design Of CO₂ Detection System Based On Broadband Light Source And FP Cavity

In recent years,a dramatic increase in CO₂ emissions caused a series of climate problems.Human beings know little about the relationship between CO₂ and climate change.For understanding the relationship among CO₂,climate change and the human activities,the atmospheric carbon source and carbon sink need to be detected accurately.This paper focuses on active optical atmospheric CO₂detection technology and completes the design of CO₂ detection system based on broadband light source and FP cavity filtering.This paper first introduces the background and significance of the research and explains the necessity of CO₂ atmospheric detection.The history and current situation of CO₂ detection are introduced,including satellites on orbit and active optical system under study.Based on the interaction between atmosphere and optical radiation,the working principle of differential absorption lidar system,this paper introduces the new system including the broadband light source used as the emitting light source and the FP cavity filter used as the receiver filter.At last,the new system achieves the CO₂ detection.According to the principle of wide band light source-FP cavity filter system and the target of CO₂ detection,the paper design the specific components and parameters.Combined with the characteristics of atmospheric detection CO₂,for abundant CO₂ transmission spectrum and small water vapor effect,the system used 1567¹574nm as the working band.SLED is chosen as the lighting source,SLED's output power is 24mW,ripple is 50dB.Two optical amplification schemes of OPO and EDFA are compared,EDFA is more appropriate as the optical power amplifier.The transmitter and the receiver shared an optical window,including three port optical fiber Circulator and optical fiber focusing/collimating system.The collimator crosstalk of circulator is 50dB.The collimating/focusing system uses single lens structure with focal length100mm and aperture 25.4mm.The receiver uses optical fiber splitter to divide light.First channel used optical fiber FP cavity filter and In GaAs PIN detector.The FP cavity uses the intrinsic optical fiber FP cavity,the reflectivity of the cavity reflector is 0.9,the length of cavity is 24.6mm.The detector uses optical fiber input.There are three experiments for FP cavity,detector and whole system.Using tunable laser as input of single frequency light source,the transmittance of FP cavity filter is tested.The optical fiber power meter is used as a reference to calibrate the detector.The single frequency light input is used to test the response of the whole system at single frequency wavelength.At last,ground test system is designed,including single frequency light source system and long path gas absorption cell.The last chapter summarizes the completed work,analyzes the problems existing in the system at present,and forecasts the future research of active optical CO₂ detection system.This paper has made innovations in system composition and error analysis.It proposes a CO₂detection system with all fiber structure.The introduction of optical fiber FP cavity ensures the optical seal of the whole structure,simplifies the system and greatly improves the energy utilization ratio.In the aspect of error analysis,this paper separates the detection error from the inversion error,which helps to understand the source of error and further improve the system's working ability.