High Spatial and Spectral Resolution Long-Range Sensing Using Brillouin Echoes

High spatial ( cm) and spectral ( MHz) resolution Brillouin sensing is realized with enhanced signal to noise ratio using a pre-activated acoustic field and an optical phase control over the interrogating pulse. Pre-activation of the acoustic field preserves the Brillouin natural linewidth and a differential gain technique extends the method to long ranges. Experimentally, fully resolved measurements of the Brillouin frequency shift of a 5 cm spot perturbation at the far end of a 5 km fiber have been performed with a frequency resolution of 3 MHz (2) , using a 500 ps (5 cm) phase shift pulse.