Large dynamic strain measurement via slope-assisted Brillouin optical time domain reflectometry using a frequency equalizer.

ABSTRACT

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 ∼1.94-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 13.1 Hz. The maximum measured errors of vibration frequency are 0.5 Hz@10.3 Hz and 0.8 Hz@13.1 Hz.