Refining High-Resolution Brillouin Optical Correlation-Domain Reflectometry Using Polymer Fibers by Modeling Refractive Index Differences in Optical Paths

High-spatial-resolution Brillouin optical correlation-domain reflectometry (BOCDR) in perfluorinated graded-index polymer optical fibers (PFGI-POFs) is gaining attention for structural health monitoring. A major challenge has been accurately predicting Rayleigh noise behavior, which constrains the modulation amplitude and spatial resolution. However, prior models did not consider differences in optical path lengths caused by the refractive indices of silica fibers (used in circulators) and PFGI-POFs. We refine the noise model to incorporate these differences. Experiments with varying fiber lengths show that the revised model more accurately predicts Rayleigh noise bandwidth, especially with longer circulator fibers. Errors of up to 120 MHz in the conventional model are reduced to within 25 MHz, showing the importance of proper optical path modeling in BOCDR. © 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.