Distributed Temperature and Strain Measurement Based on Brillouin Gain Spectrum and Brillouin Beat Spectrum

A novel fast measurement method based on Brillouin gain spectrum (BGS) and Brillouin beat spectrum (BBS) in a complex index profile fiber has been proposed to realize simultaneous measurement of distributed temperature and strain. An interesting phenomenon that the temperature/strain sensitivities of the power on the BGS slope and the power on the BBS peak are very different has been discovered and utilized for temperature and strain sensing. By means of only measuring the power trace of the BGS slope and the power trace of one BBS peak along the sensing fiber, the distributed temperature and strain can be measured by using the Brillouin optical time-domain reflectometry (BOTDR) without scanning the Brillouin spectrum. The temperature and strain measurement uncertainties of the proposed method are one order of magnitude lower than that of the BBS-based measurement method. In a proof-of- concept experiment, the temperature and strain of the 2 km large effective area fiber (LEAF) are measured at a spatial resolution of 3 m within 18 s.