Long Distance Distributed Fiber Raman Temperature Sensor

Abstract:Distributed optical fiber temperature sensor is a new type temperature sensor that developed in1980’s.It can monitor many points’temperature along a single optical fiber at the same time, and can locate the position of temperature field. Comparing to the traditional temperature sensing technology, distributed optical fiber temperature sensing technology has many advantages, such as anti-electromagnetic interference, lightning proof, high temperature resistance, corrosion-proof, etc., which are widely believed to be the promising new temperature sensing technology in the new century.The current situation and the development trend of the distributed optical fiber temperature sensor are analyzed, as well as the parameters and components which greatly affect the sensing performance of the distributed optical fiber temperature sensing system. In this paper, the fundamental operating principles and the temperature measurement principles using Raman back scattering are also detailed explanation. Combined with the project of the cross-river tunnel of Qiantang River, this paper analysis the key technologies involved in view of engineering applications. Long distance distributed fiber Raman photons sensor integrated Raman amplifier and distributed fiber Raman photons sensor based on pulse code modulated sources are the main objects of this thesis. The main research contents of this thesis include the following two points:1Integrated Raman amplifiers long distance distributed fiber Raman photons sensor.With Raman amplifier embedding in distributed fiber Raman temperature sensor, the light intensity is greatly strengthened in the sensing fiber. This solution solved the problem that the optical signal could not transmit long distance because of the high transmission loss. The temperature measurement of the system is more stable and precise as the improvement of the signal-to-noise ratio of the system.2Distributed fiber Raman photons sensor based on pulse code modulated sources.By coding and decoding laser pulses, the signal-to-noise ratio (SNR) of optical fiber distributed temperature sensors can be enhanced without impairing the spatial resolution and the measurement time. Thus the length of the sensing fiber is significantly increased. Through reducing a single pulse peak level, the fiber nonlinearities can be reduced effectively by the system. The results show that the SNR is improved by2.5times as using the83bits coding technique to measure temperature in a single-mode fiber with the length of10km.