Accurate estimation of measurement position in Brillouin optical correlation-domain reflectometry based on Rayleigh noise spectral analysis

Brillouin optical correlation-domain reflectometry (BOCDR) is unique in its ability to measure distributed strain and temperature changes along a fiber under test (FUT) from a single end, offering random access and relatively high spatial resolution, making it promising for infrastructure monitoring. BOCDR achieves spatial resolution through frequency modulation of the laser output, and this modulation frequency determines the measurement position, necessitating accurate association of modulation frequencies with positions on the FUT. However, a practical method to precisely correlate modulation frequency values with FUT positions has not yet been proposed. This study introduces a method utilizing the change in Rayleigh noise spectrum with modulation frequency to accurately associate these frequencies with positions on the FUT. The effectiveness of this method is proved through distributed strain and temperature measurements.