Pulse Coding Technique in Differential Cross-Spectrum BOTDR for Improving the Brillouin Frequency Accuracy and Spatial Resolution

We propose a novel technique to deploy Golay code in our previously reported differential cross-spectrum BOTDR (DCS-BOTDR) fiber sensor technique to improve the Brillouin frequency shift (BFS) resolution measurement. The conventional DCS-BOTDR uses two pulsed probes having slightly different in pulse duration; the duration difference between the pulses enables sub-meter spatial resolution. In the new coded DCS-BOTDR, the narrow pulse was modulated with Golay code via intensity modulation scheme to achieve higher BFS resolution and at the same time attain sub-meter spatial resolution. By using 8 bits of Golay code in the proof-of-concept experiment, we have achieved 40 cm spatial resolution and 3.47 MHz Brillouin frequency accuracy in measuring a 1280 m fiber.