Liquid-level sensing method based on differential pulse-width pair Brillouin optical time-domain analysis and a self-heated high attenuation fiber.

A liquid-level sensing method based on differential pulse-width pair Brillouin optical time-domain analysis (DPP-BOTDA) combining with a self-heated high attenuation fiber (HAF) is proposed, where the principle is to locate the temperature abruption position at the interface between liquid and air caused by their different thermal diffusion rates. A Panda polarization-maintaining fiber is used as the sensing optical fiber, which is tightly glued alongside a laser-powered HAF. Heated by a high-power laser, the temperature of the HAF can increase and exhibits approximately exponential attenuation with the light propagation direction, which induces a similar temperature distribution over the sensing fiber. By using a 5-cm spatial resolution DPP-BOTDA and a 1.4-W heating light, temperature distributions of the sensing fiber are measured for different water levels, and the results indicate that distributed liquid-level sensing with a range of 20 cm and a resolution of 1 cm is realized using our method.