X-ray irradiation influence on prototype Er3+-optical fibers: confocal luminescence study

Abstract : The integration of rare-earth doped optical fibers as part of fiber-based systems in space implies the development of waveguides tolerant to the radiation levels associated with the space missions. We report the spatial distribution, the photoluminescence (PL) properties of color centers and the related changes induced by X-rays radiation at different doses (50, 500 and 1000 krad) for two different prototypes of Er-doped optical fibers. Each sample (in the version pristine, X-irradiated and H2 loaded prior to radiation exposure) was characterized by confocal microscopy luminescence (CML) measurements in Visible range with Visible (488 nm) or UV (325 nm) laser light excitation. The set of tested fibers allowed us to obtain information on the radiation responses of the silica-based host matrix and on the transitions between the energy states of rare-earth ions. Under Vis-excitation, the luminescence spectrum of the core revealed the typical emission pattern of Er3+ ions, with an increase of the emission intensity around 520 nm due to the radiation treatment; whereas no spectroscopic change induced by radiation was observed when a particular sensitizing element is added to the core composition or when the fiber was previously H2-loaded. The PL-core spectra under UV-excitation showed the behavior of the ODC, typical of the silica-based host matrix. For these spectra, addition of the sensitizing element annihilates the depressions that characterize the profile of ODC emission and that are due to the Er3+ ions absorption.