Research On Distributed Optical Fiber Temperature Measurement System Based On Brillouin Scatering Efect

Temperature measurement involves many aspects of the national economy and society and is of great significance.With the development,the requirements for temperature measurement continue to increase.Due to the inherent point measurement and electrical design features of traditional electronic sensors,they inevitably have the disadvantages of existing measurement dead zones and being susceptible to electromagnetic interference,which seriously limits the development of temperature measurement technology.In recent years,the emergence of optical fiber sensing technology has provided a new solution for temperature measurement.Optical fiber sensing technology has many advantages such as long measuring distance,distributed measuring,anti-electromagnetic interference,intrinsic safety and long life.It is very suitable for engineering application scenarios such as building fire warning,transmission line work and safety status monitoring,oil and gas pipeline fault detection and mine safety monitoring.Among the optical fiber sensing technologies,the temperature detection technologies based on fiber Bragg grating,Brillouin scattering effect and Raman scattering effect can be used for temperature measurement.Among them,the temperature detection technology based on Brillouin scattering effect can realize distributed and long-distance temperature detection through conventional single-mode optical fibers,and because Brillouin scattering effect is sensitive to strain,the technology has the potential to simultaneously detect temperature and strain.At the meantime,BOTDR system has a single-end access characteristic suitable for engineering application,so this paper mainly studies the distributed optical fiber temperature measurement system based on BOTDR.First of all,this paper studies the temperature measurement principle of the system.The spontaneous Brillouin scattering in the fiber has the characteristic that the scattered light power and frequency are linear with the ambient temperature,so it can be used for temperature detection.Since the detection signal is a light pulse,the "time of flight method" can be used to obtain position information.The detection mechanism of coherent detection instead of direct detection is chosen to reduce the difficulty of detection and improve the detection accuracy.Brillouin frequency shift demodulation scheme based on FFT instead of frequency scanning technology is chosen to improve the system response speed.According to the detection mechanism and demodulation scheme,the overall design of the system is carried out.Secondly,this paper studies the design and implementation of temperature demodulation algorithm.The FFT is used to analyze the Brillouin scattering spectrum,and the Brillouin scattering spectrum is fitted by LM algorithm,and the temperature demodulation based on LabVIEW is designed and implemented.Finally,the paper uses the designed system to conduct temperature measurement experiments and analyze the performance of the system.By analyzing the parameter design of each part of the system,the key components required by the system are selected.The experimental system is built with the selected device as the main body.The experiment is carried out under certain conditions.The results show that the designed system performance index is: temperature range up to 30~80 °C,measurement accuracy up to 2 °C,space The resolution is up to 2 m and the sensing distance is up to 9.65 km.In addition,the performance of BOTDR system improved by high extinction ratio pulsed light modulation is also studied in this paper.The pulsed extinction ratio measurement scheme based on coherent detection is designed.The verification experiment results show that compared with the traditional pulse modulation scheme based on electro-optic modulator(EOM),the extinction ratio of detection pulse light is increased by 16 dB through using the pulse modulation scheme based on semiconductor optical amplifier(SOA).The Brillouin frequency shift fluctuation of BOTDR system at the end of 10.7 km sensing optical fiber is reduced from 10.6 MHz to 5.7 MHz,and the sensing distance under the same measuring conditions is increased from 10.7 km to 27 km.