Researche On Botda Distributed Optical Fiber Temperature Measurement System

Distributed optical fiber Brillouin sensor is one of the most promising sensing technology in the international research in recent years, the technology has very important application value in the large engineering structure health monitoring such as oil pipeline, Bridges, dams, subway, tunnel and so on. This paper mainly includes the following aspects:1) We outlined the research situation of Brillouin fiber optic sensing system, analyzed the principle of Brillouin scattering in optical fiber and the characteristics of thermosensitivity, established the the function relation of Brillouin temperature and frequency shift.2) A new method that use electro-optic modulation (EOM) frequency shift technique for distributed fiber Brillouin temperature sensing was proposed, which solved the problem that system structure complicated and the work is not stable when using two lasers. Through observed the output light of electro-optic modulation, presented the way of avoid the electro-optic modulation double sideband influence on the sensing system.3) We designed and developed a photoelectric conversion circuit, background light control circuit, the programmable gain amplifier circuit, filter circuit and the narrow pulse generating circuit, and tested the detection ability of photoelectric conversion circuit, the test results show that the circuit can detect narrow pulse signal with the power of20nw, which meet the needs of Brillouin weak signal detection.4) We raised the mothed of using digital average technology process the Brillouin signal for the low signal-to-noise ratio, analysis the measurement principle of digital average method, implementation method and algorithm, the data acquisition is realized by using VB programming language processing.5) Theoretically and experimentally studied the stimulated Brillouin scattering threshold in the Standard single mode fiber and get the result of the4km of ordinary single mode optical fiber input threshold of7mw. At last, combining with the designed of hardware and software, we seted the distributed brillouin optical fiber temperature sensor system experiment device, and conducted the temperature measurement experiment and the temperature distribution measurement experiment with standard single-mode F-28optical fiber, then measured the temperature coefficient is1M/℃; the spatial resolution is about20m.