RESUMO
In this Letter, a method for measuring large dynamic strain via slope-assisted Brillouin optical time domain reflectometry (SA-BOTDR) is proposed. A linear artificial slope created by a frequency equalizer is used instead of the traditional slope of the Brillouin gain spectrum (BGS) as the linear response region between the Brillouin frequency shift (BFS) and signal intensity. This method makes the strain measurement range independent of the bandwidth of the BGS. The large dynamic strain with a maximum value of 3108 µÎµ and the spatial resolution of 5 m along the â¼1.94-km single-mode fiber (SMF) are obtained by means of the proposed technique. Meanwhile, a strong linear relationship is also established between the signal strength and strain at the vibration frequencies of 10.3 and 13.1â Hz. The maximum measured errors of vibration frequency are 0.5â Hz@10.3â Hz and 0.8â Hz@13.1â Hz.
RESUMO
A slope-assisted Brillouin optical time domain reflectometry system with large dynamic strain range was proposed and demonstrated using graded-index multi-mode fiber (GI-MMF) as sensing fiber. Analysis of the simulated and experimental results indicated that the Brillouin gain spectrum in GI-MMF could be broadened by controlling the coupling efficiency of optical and acoustic modes. The coupling efficiency could be controlled by adjusting lateral offset between single mode fiber (SMF) and GI-MMF. The system realized the maximum strain dynamic measurement of 3000 µÉ with the spatial resolution of 5 m along â¼1 km GI-MMF, and exhibited significant linear relationship between signal intensity and strain at vibrational frequency of 7.83 and 15.47 Hz. The measured error of vibration frequency was less than 0.2 and 1.5 Hz, respectively. The measured strain range of this system was more than three times that of traditional systems based on SMF and could be achieved at relatively low cost.
