Extending the Sensing Range of Brillouin Optical Time-Domain Analysis Combining Frequency-Division Multiplexing and In-Line EDFAs

We demonstrate a high-performance Brillouin optical time-domain analysis (BOTDA) system with an extended sensing range by combining frequency-division multiplexing and in-line Erbium doped fiber amplifiers (EDFAs). The frequency-division multiplexing BOTDA features multiple sections of fibers with different Brillouin frequency shifts, and it reduces the effective Brillouin interaction length to one resonant Brillouin frequency section rather than the entire length of the sensing fiber, so that the power of CW probe of BOTDA can be increased to enhance the Brillouin signal within individual sections and consequently extend the sensing range combined with high strain or temperature resolution with negligible pump depletion. In addition, in-line EDFAs placed between spans are used to compensate the fiber loss for similar Brillouin gains in each span. In experiment, a 150-km sensing range is achieved by dividing the sensing fibers into two spans of equal length and using two types of fibers in each span. Using the differential pulse-width pair technique, a 100/120 ns pulse pair is used to realize a 2-m spatial resolution and a measurement accuracy of 1.5 degrees C/30 mu epsilon at the end of the sensing fibers.