Mid-infrared multimode fluoride fiber bend loss studies and FEM modeling-toward surgical applications

Mid-infrared (MIR) optical fibers have many applications in spectroscopy, sensors, and surgery. Metal fluoride optical fibers are excellent candidates for guiding MIR light sources due to their exceptionally low transmission loss. To guarantee the efficiency and safety of these fibers for high-power applications, it is necessary to characterize their macroscopic bend loss. In this work, we report experimental measurements and numerical modeling of macroscopic bend loss in multimode InF₃ and ZrF₄ optical fibers. Our results confirm that no significant bend loss occurs in the fibers for bend radii between 5 and 25 cm. This finding was consistent across both the physical measurements and the predictions from our COMSOL ray-tracing simulations. These results indicate that these multimode fluoride fibers are efficient and safe for high-power applications like spectroscopy and surgery.