Improving the spatial resolution and signal-to-noise ratio of BOTDR using double-pulse coding

The spatial resolution of conventional Brillouin optical time domain reflectometry (BOTDR) is intrinsically limited by the relaxation time of phonons in the fiber. To make use of the narrow pulse width for higher spatial resolution, the double-pulse probe can induce interference between two acoustic waves, making it possible to determine the Brillouin frequency shift from the oscillating Brillouin gain spectrum. However, the signal-to-noise ratio (SNR) is restricted since the pulse width is quite narrow. In this paper, we propose to combine the double-pulse technique with coding pulse to improve the SNR while maintaining high spatial resolution. The complementary return-to-zero (RZ) Golay codes are employed in the experiment, and every code element is expanded to contain the entire form of double-pulse. Thus, the interference pattern from the double-pulse interaction is guaranteed, and the decoding process can be correctly conducted. Experimental results demonstrate a significant SNR enhancement with a submeter-level spatial resolution.