An 80km open path Brillouin optical time domain analysis with far-end probe light

The sensing fiber in Brillouin optical time-domain analysis (BOTDA) is usually in a two-end accessed, close path form, which may be only half utilized in application. In this work, we propose a long-range open path BOTDA with far-end probe light. The sensing fiber is two-end accessed, open path, and the probe wave is provided by a remote dedicated light source via the far-end of fiber. Injection locking is employed in the pump light side to synchronize the laser frequency of both sides. 127-bit Simplex encoding (with 80 averaging) is also introduced to enhance the performance. In the demonstration experiment, the BOTDA achieves 0.79 MHz frequency resolution and 5.0 m spatial resolution at the farend of 80 km fiber in open path.