Distributed temperature measurement with Brillouin optical correlation-domain reflectometry at 8.5mm spatial resolution

We explore Brillouin optical correlation-domain reflectometry (BOCDR) at modulation frequencies near the theoretical limit defined by the Brillouin bandwidth—about 30 MHz for silica single-mode fibers. By measuring the Brillouin gain spectrum (BGS) in this frequency range, we find that above ~25 MHz, a periodic wave originating from the modulation frequency starts to overlay the BGS, posing a challenge for quantitative distributed measurements. Consequently, the upper limit of viable modulation frequencies depends not on the Brillouin bandwidth itself but on the range in which no periodic waves are superimposed on the BGS. Using this new insight, we set a modulation frequency limit at around 20 MHz, enabling an 8.5 mm spatial resolution—the world’s highest reported in BOCDR-based distributed measurement—to detect temperature changes in a 9 mm-long heated section of a silica single-mode fiber.