Combined time-domain and correlation-domain Brillouin analysis with 1600 meters range and 2 centimeters resolution

A combined time-domain and correlation-domain Brillouin sensing scheme is demonstrated. Pump and signal waves are phase modulated by a high-rate, perfect Golomb code, which confines their interaction to discrete, 2 cm-long correlation peaks. The properties of the code substantially reduce off-peaks interactions. The pump wave is also amplitude modulated by a single pulse, so that amplifications at different correlation peaks can be separated in the time domain. The Brillouin gain spectra at all 80,000 resolution points of a 1,600 m-long fiber are reconstructed experimentally, using only 127 scans per frequency. A 3 cm-long hot spot is recognized.