High-resolution Brillouin fiber sensing using random phase coding of the pump and probe waves

Distributed temperature measurements with 1.2 cm resolution based on stimulated Brillouin scattering (SBS) in standard fibers are reported. High resolution is achieved by phase-coding both pump and probe waves with a high-rate, pseudo-random binary phase code. The SBS interaction is effectively confined to narrow correlation peaks. The separation between adjacent peaks, signifying the unambiguous measurement range, scales with the length of the modulation code and can therefore be made arbitrarily long. Measurements were performed over 40 meters of fiber, or 3300 resolution points. The technique is applicable to distributed measurements of birefringence and Brillouin frequency shift over polarization maintaining fibers.