Brillouin Time-Domain and Correlation-Domain Analyses Combined

A distributed fiber sensor for temperature and strain with an increased number of high-resolution points and a reduced acquisition time is presented, using a combination of Brillouin optical time domain analysis (B-OTDA) and Brillouin optical correlation domain analysis (B-OCDA) techniques. Both Brillouin pump and signal waves are co-modulated by a high-rate binary phase sequence, which restricts the Brillouin interaction to a discrete set of narrow correlation peaks according to the B-OCDA principle. In addition, amplitude pulse modulation is overlaid on the pump wave. With careful choice of the pump pulse duration, the SBS amplification taking place at multiple correlation peaks can be temporally resolved in measurements of the output signal power, much like in a B-OTDA. Using the proposed method, Brillouin gain spectra are acquired over a 4 km-long fiber with 2 cm resolution. 99.5% of the potential 200,000 resolution points are successfully mapped, using only 499 spatial scans of the correlation peaks positions.