Radiation Effects on Ytterbium- and Ytterbium/Erbium-Doped Double-Clad Optical Fibers

We characterize by different spectroscopic techniques the radiation effects on ytterbium- (Yb) and ytterbium/erbium (Yb/Er)-doped optical fibers. Their vulnerability to the environment of outer space is evaluated through passive radiation-induced attenuation (RIA) measurements during and after exposure to 10 keV X-rays, 1 MeV $\gamma$-rays, and 105 MeV protons. These fibers present higher levels of RIA (1000×) than telecommunication-type fibers. Measured RIA is comparable for $\gamma$-rays and protons and is on the order of 1 dB/m at 1.55 $\mu$ m after a few tenths of a kilorad. Their host matrix codoped with aluminum (Al) and/or phosphorus (P) is mainly responsible for their enhanced radiation sensitivity. Thanks to the major improvements of the Er-doped glass spectroscopic properties in case of Yb-codoping, Yb/Er-doped fibers appear as very promising candidates for outer space applications. In the infrared part of the spectrum, losses in P-codoped Yb-doped fibers are due to the $\hbox {P}_{1}$ center that absorbs around 1.6 $\mu$ m and are very detrimental for the operation of Er-codoped devices in a harsh environment. The negative impact of this defect seems reduced in the case of Al and P-codoping.