Influence of temperature and dose rate on radiation-induced attenuation at 1542 nm in fluorine-doped fibers.

Radiation-induced attenuation (RIA) at 1542 nm of fluorine-doped fibers under gamma radiation source has been investigated for different dose rates and temperatures. Both the temperature and dose rate dependencies are unusual. First, the fiber presents an enhanced low dose rate sensitivity that is favored by increasing temperature. Furthermore, in certain conditions, RIA increases with irradiation temperature, which is a very rare phenomenon. We have built a phenomenological model that shows that these behaviors can be explained considering that two color centers previously identified in the literature are responsible for RIA: inherent and strain-assisted self-trapped holes.

Benefit of Rare-Earth "Smart Doping" and Material Nanostructuring for the Next Generation of Er-Doped Fibers.

Erbium-doped fiber amplifiers (EDFAs) for harsh environments require to develop specific fabrication methods of Er 3+-doped fibers (EDFs) so as to limit the impact of radiation-induced absorption. In this context, a compromise has to be found between the concentration of Erbium and the glass composition. On the one hand, high concentration of Er 3+ ions helps to reduce the length of the EDF and hence the cumulated attenuation but generally leads to luminescence quenching mechanisms that limit the performances. On the other hand, so as to avoid such quenching effect, glass modifiers like Al 3+ or P 5+ ions are used in the fabrication of commercial EDFs but are not suitable for applications in harsh environment because these glass modifiers are precursors of radiation-induced structural defects and consequently of optical losses. In this work, we investigate the concept of smart doping via material nanostructuring as a way to fabricate more efficient optical devices. This approach aims at optimizing the glass composition of the fiber core in order to use the minimal content of glass modifiers needed to reach the suited level of performances for EDFA. Er 3+-doped alumina nanoparticles (NPs), as precursor of Er 3+ ions in the preform fabrication process, were used to control the environment of rare-earth ions and their optical properties. Structural and optical characterizations of NP-doped preforms and optical fibers drawn from such preforms demonstrate the interest of this approach for small concentrations of aluminum in comparison to similar glass compositions obtained by a conventional technique.

Radiation-resistant erbium-doped-nanoparticles optical fiber for space applications.

We demonstrate for the first time a radiation-resistant Erbium-Doped Fiber exhibiting performances that can fill the requirements of Erbium-Doped Fiber Amplifiers for space applications. This is based on an Aluminum co-doping atom reduction enabled by Nanoparticules Doping-Process. For this purpose, we developed several fibers containing very different erbium and aluminum concentrations, and tested them in the same optical amplifier configuration. This work allows to bring to the fore a highly radiation resistant Erbium-doped pure silica optical fiber exhibiting a low quenching level. This result is an important step as the EDFA is increasingly recognized as an enabling technology for the extensive use of photonic sub-systems in future satellites.

How do traces of thulium explain photodarkening in Yb doped fibers?

Ytterbium doped fiber lasers are known to be impacted by the creation of color centers during lasing so called photodarkening. This defect creation was investigated in a spectroscopic point of view, showing the presence of thulium traces (ppb) in the ytterbium doped fiber. Moreover, this contamination exhibit luminescence in the UV range under 976 nm excitation of the ytterbium-doped fiber. In adding more thulium to an ytterbium-doped fiber it was shown that thulium strongly impact the defects creation process, involved in photodarkening.