Research On Key Technologies Of Distributed Optical Fiber Raman Temperature Sensing System

Distributed fiber optic Raman temperature sensing system is a kind of temperature measuring system widely used nowadays.For example,it can be used in railway traffic,oil and gas pipelines,forest fires and other occasions in the early warning.The system is also capable of working in environments with long sensor length,high temperature and high pressure,strong corrosion and strong electromagnetic interference,such as nuclear power plants and ultra-high pressure.The two theoretical pillars of the distributed fiber Raman temperature sensing system are the sensitivity of the backraman scattering in the fiber to the temperature signal and the positioning technology in the fiber based on the optical time-domain reflection principle,which enables us to obtain continuous and stable temperature signals.However,in practical engineering practice,the light power of spontaneous Raman scattering light is 45 dBm to 60 dBm lower than that of incident light,which seriously affects the real-time detection function and measurement time of the whole system.This makes it necessary to find good signal processing methods.From this perspective,this paper analyzes the noise in the engineering practice of distributed optical fiber Raman temperature sensing system,analyzes the causes of the noise,such as the noise that may exist on the hardware of the system itself and the optical noise of the system,and selects the method to reduce the noise of the system based on these reasons.The method of deep learning is also explored to improve the signal-to-noise ratio of the system so as to improve the performance of the system.The work of this paper is as follows:(1)In this paper,we introduce the development status of distributed fiber Raman temperature sensor system at home and abroad.Then introduce the principle of Raman scattering,Rayleigh scattering,brillouin scattering and time domain reflection in optical fiber are introduced.We also compare and analyse the characteristics of the single path demodulation method based on anti-stokes light,the double path demodulation method based on Rayleigh scattering light and anti-stokes light,and the double path demodulation method based on stokes light and anti-stokes light.(2)In this paper we introduce the system construction,the main parameters of each module of the system and the performance indexes of the system,and analyze the causes of various noises in the distributed optical fiber Raman temperature sensingsystem.The principle of the cumulative average method and the fast independent component analysis method are also described.(3)The de-noising methods used in this paper include the traditional cumulative average algorithm and Fast independent component analysis(Fast-ICA)algorithm.Through experimental comparison,it is found that the denoising effect of fast-ICA method is relatively superior,which is helpful to improve the SNR of the system.