Differential Brillouin gain for improving the temperature accuracy and spatial resolution in a long-distance distributed fiber sensor.

We demonstrate a 12 km differential pulse-width pair Brillouin optical time-domain analysis (DPP-BOTDA) using 40 ns and 50 ns pulses with DC-coupled detection. A spatial resolution of 1 m and a narrowband Brillouin gain spectrum of 33 MHz are obtained simultaneously compared with 88 MHz with the use of 10 ns pulses in a conventional BOTDA. The experimental results show that the differential Brillouin gain of a 40/50 ns pulse pair is 7 times stronger than the direct Brillouin gain of BOTDA with the use of a 10 ns pulse, and the temperature uncertainty is 0.25 degrees C compared with 1.8 degrees C for a 10 ns pulse. As the pulse-width difference decreases from 10 ns to 1 ns, corresponding to a spatial resolution from 1 m to 10 cm, the prediction of temperature uncertainty will only increase from 0.25 degrees C to 0.8 degrees C for DPP-BOTDA over a 12 km long single-mode fiber.