Long-range open-path BOTDA with far-end probe light source and injection locking

In a conventional Brillouin optical time-domain analysis (BOTDA) system, the inherent two-end access architecture requires a roundtrip wiring layout for the fiber under test (FUT), which fundamentally limits the actual sensing range to half of the total fiber length. In this paper, an end-to-end topology configuration for a BOTDA system is proposed, with long range and open path. The pump light and the probe light are sent into the FUT from the opposite ends, while their generation modules are physically put at the near end and far end, respectively. The probe light is provided by a remote dedicated light source via the far end of the FUT. A portion of the backward-propagating probe light is utilized as a master light source for the pump wave, and injection locking is employed in the pump side to maintain the frequency synchronization between the two lights. The demonstration experiment is designed with an 80-km single-mode fiber, and 127-bit Simplex coding (with 80 averages) is introduced to enhance the performance, achieving 5.0 m spatial resolution and 0.85 MHz frequency uncertainty at the far end of the FUT.