Analysis of the Influence of Macro-Bending Loss in Single-Mode Optical Fibers on OFDR Signal Quality.

This study investigates the influence of optical loss induced by the macro-bending of optical fibers on the signal quality of an optical frequency-domain reflectometry (OFDR) system. First, the finite element software COMSOL 5.3 was used to perform numerical simulations of the optical loss of single-mode fibers under different bending radii. The simulations revealed that when the bending radius is relatively small, the optical loss exhibits oscillation as the bending radius varies. Next, an optical backscatter reflectometer (OBR) was employed to measure the optical loss of the optical fiber under different bending radii and numbers of bending loops. The experimental results showed good consistency with the simulation results, and the variation law of optical loss under different bending radii and numbers of bending loops was clarified. An OFDR strain demodulator was used to demodulate the strain signals under loaded conditions with different fiber bending radii and numbers of bending loops. It was found that when the cumulative optical loss increases to a certain threshold, the demodulated signal quality degrades significantly-this confirms that macro-bending loss directly impacts the SNR of OFDR output signals. The findings of this study provide practical guidance for the bending-oriented deployment of optical fiber sensors, which was successfully validated through a real-world structural strain monitoring case.