Sub pulse length event measurement in BOTDR system using slope assisted Brillouin frequency shift.

To overcome the limitations by pulse width on the event zone measurement capability, a novel temperature demodulation scheme was proposed and validated to measure sub-pulse length event zones based on the slope-assisted Brillouin frequency shift (SA-BFS). Unlike the conventional BFS-based methods, this approach leverages the BFS slope for temperature demodulation, enabling precise measurement of sub-pulse-length event zones. We developed a theoretical model that established a linear relationship between the BFS slope and temperature, validated through simulations and experiments across various event zone lengths and pulse widths. Ultimately, the system's measurement capability was improved from 2 to 0.49 m, achieving a temperature demodulation of 57.75 °C on a 10.2 km sensing fiber, with a temperature accuracy approximately ten times higher than that of conventional demodulation schemes. The method of SA-BFS provided a transformative approach to measure physical quantities along the fiber, serving as a valuable tool for distributed optical fiber sensors such as BOTDR and BOTDA.