Thermally Induced Bend Loss of Silica Optical Fiber

Multimode and single-mode silica fibers have been tested in a high-temperature setting, while simultaneously experiencing a bend. The range of temperature tested was 500 °C-1000 °C and the bend radii considered were 1.27, 2.54, and 3.81 cm (0.5, 1.0, and 1.5 in). Multimode fiber (MMF) was analyzed for transmission, while single-mode fiber (SMF) was both analyzed for transmission and interpreted by optical backscatter reflectometry. Attenuation was observed to increase in MMF with increasingly high temperatures and tighter bend radii. SMF was far more resilient to transmission loss than MMF, under similar conditions of temperature and curvature. Optical backscatter reflectometry was performed for bent SMF up to 1100 °C and revealed evidence that, at high temperatures, bends in fiber can enhance devitrification that can inhibit light transmission through the fiber. This paper suggests that the devitrification process begins at the surface of the fiber and moves inward. Moreover, this paper suggests that bend stress applied to surface flaws of the fiber leads to significantly higher crystallization rates at temperatures at which silica does not typically devitrify so rapidly.