Combined Photobleaching and Temperature Effects on 1550 nm Radiation-Induced Attenuation of Germanosilicate Optical Fiber

Combined temperature and photobleaching (PB) effects on the 1550 nm radiation-induced attenuation (RIA) levels and kinetics of a commercial Ge-doped single-mode optical fiber (OF) have been investigated. The main goal of this study was to evaluate if synergetic effects could impact the performances of free-space optical communication links in space. For this, we performed accelerated (0.5 Gy(SiO2)/s) irradiation runs with 100 kV X-rays up to the total ionizing dose of 150 kGy(SiO2), varying the irradiation temperature between −80 °C and 80 °C. First, we evaluate the irradiation temperature effects: infrared RIA largely increases at negative temperatures. Second, the effects of injecting different optical powers at different temperatures have been characterized: if at temperatures exceeding room temperature (RT), PB effects are almost negligible, a PB effect is clearly observable at lower temperatures where the germanosilicate OF present large RIA levels due to the contribution of metastable defects absorbing at 1550 nm. Increasing the injected powers allows for reducing the concentration of these radiation-induced unstable defects, but not as much as thermal treatment consecutive to the irradiation. These results highlight the complex physics of radiation-induced defects absorbing at 1550 nm in Ge-doped OF, but also the vulnerability of this class of fiber for space telecommunication links. Regarding the unstable nature of point defects causing the RIA at a lower temperature, it seems possible to mitigate the loss excess by thermal cycles at RT or higher temperatures. We also could expect that our accelerated tests represent a worst-case scenario in terms of RIA levels at the maximum dose.