Temperature sensitivity of microbending losses in radiation-resistant optical fibers

Thin F-doped cladding, pure silica core optical fibers might be excellent candidates for space applications due to their good resistance to high ionising radiation doses. However, besides radiation, thermally-induced microbending losses might also degrade the transmission of such polyimide-coated fibers at telecommunication wavelengths. In the infrared, this attenuation can reach levels comparable to radiation-induced loss in the visible. To evidence this effect, a worst-case experiment was conducted in which fiber samples (10 m) were wrapped around 54mm diameter aluminum mandrels and heated up to 60°C during irradiation. We compared the results with those obtained by in situ spectral measurements of transmission loss on similar but unirradiated samples. Here, the temperature was cycled between room temperature and 120°C. Infrared transmission loss increased with temperature but disappeared after cooling back to room temperature. At a wavelength of 1 tm, the temperature-induced loss (reference loss at room temperature) in a polyimide-coated fiber reached 0.4, 0.9 and 2.0 dB/m at 50°C, 73°C and 114°C respectively. Whereas the behavior of polyimide-coated radiation-resistant fibers is strongly influenced by temperature-induced microbending losses, acrylate-coated fibers, however, showed practically no sensitivity of transmission loss to temperature. An aluminium-coated radiation-resistant fiber showed an intermediate sensitivity.