High-Spatial-Resolution Brillouin Optical Correlation Domain Analysis Using Short-Pulse Optical Sources

High-spatial-resolution distributed optical fiber sensing based on Brillouin optical correlation domain analysis (BOCDA) using short-pulse optical sources is demonstrated. Short optical pulses phase-modulated with a pseudo random bit stream (PRBS) are used for pump and Stokes probe lights for the correlation-domain measurement of distributions of local Brillouin frequency shift (BFS). Because the excitation of acoustic wave is tightly confined in short length along the fiber owing to the short pulse duration, spatial resolution of the measurement is improved as compared with the case using not-return-to-zero pulses. In this experiment, BFS variation in a 2 mm standard single-mode fiber section is clearly detected by the use of an external cavity mode-locked semiconductor laser emitting 3 ps pulses as the light source. Spatial resolution shorter than 1 mm is obtained. Scanning of measurement location is achieved electrically by changing the clock speed of the PRBS, which is an advantage of the proposed scheme over the high-spatial-resolution BOCDA using amplified spontaneous emission as a light source. Theoretical estimation of Brillouin gain that the short-pulse Stokes probe light acquires is presented.