We present a non-destructive optical technique for a full characterization of rare-earth-doped optical preforms. Specifically, a combined profiling of refractive-index and active-dopant was carried out in the same region of optical preforms by performing ray deflection and photoluminescence projection measurements, respectively. In this way, the optical core, delineated by the refractive index profile, was used to define the actual active dopant distributions within the core. Using the same experimental set-up, it was also possible to uniquely provide the maximum value of active-ion concentration reached inside the core. The study was carried out on an optical fiber preform sample doped with Yb<sup>3+</sup> ions in high concentration. Comparison with independent measurements, such as those performed by a commercial refractive index profiler and microstructural secondary-ion mass spectrometry analysis, confirms the accuracy of the proposed technique in the optical features evaluation.
We investigated the radiation hardening of optical fiber amplifiers operating in space environments. Through a real-time analysis in active configuration, we evaluated the role of Ce in the improvement of the amplifier performance against ionizing radiations. Ce-codoping is an efficient hardening solution, acting both in the limitation of defects in the host glass matrix of RE-doped optical fibers and in the stabilization of lasing properties of the Er<sup>3+</sup>-ions. On the one hand, in the near-infrared region, radiation induced attenuation measurements show the absence of radiation induced P-related defect species in host glass matrix of the Ce-codoped active fibers; on the other hand, in the Ce-free fiber, the higher lifetime variation shows stronger local modifications around the Er<sup>3+</sup>-ions with the absence of Ce.
Er/Yb doped fibers and amplifiers have been shown to be very radiation sensitive, limiting their integration in space. We
present an approach including successive hardening techniques to enhance their radiation tolerance. The efficiency of our
approach is demonstrated by comparing the radiation responses of optical amplifiers made with same lengths of different
rare-earth doped fibers and exposed to gamma-rays. Previous studies indicated that such amplifiers suffered significant
degradation for doses exceeding 10 krad. Applying our techniques significantly enhances the amplifier radiation
resistance, resulting in a very limited degradation up to 50 krad. Our optimization techniques concern the fiber
composition, some possible pre-treatments and the interest of simulation tools used to harden by design the amplifiers.
We showed that adding cerium inside the fiber phosphosilicate-based core strongly decreases the fiber radiation
sensitivity compared to the standard fiber. For both fibers, a pre-treatment with hydrogen permits to enhance again the
fiber resistance. Furthermore, simulations tools can also be used to improve the tolerance of the fiber amplifier by
helping identifying the best amplifier configuration for operation in the radiative environment.
Rare-earth doped optical fibers have been shown to be very sensitive to radiations, limiting the integration of fiber-based
systems in space missions. In this paper, we present the characterization of two amplifiers based on a set of prototype
active Erbium/Ytterbium codoped double clad fibers developed by Ixfiber SAS. One of these fibers has been codoped
with cerium inside its core to enhance its radiation tolerance whereas the other is a classical phosphosilicate Er/Yb fiber.
The two amplifiers based on these fibers have been exposed to γ-rays at a low dose rate (0.3 rad/s) and to doses up to
90 krad. Previous studies indicated that Er/Yb amplifiers using this type of fiber suffered significant degradation for
cumulated dose above 5-10 krad. We observed, on the contrary, that with our radiation hardened fiber, the degradation
of the fiber amplifier's output power can be limited to less than 30% after an exposure dose of ~90 krad.
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 Er<sup>3+</sup> 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 H<sub>2</sub>-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 Er<sup>3+</sup> ions
In this paper, we reviewed our previous work concerning the responses of rare-earth (RE) doped fibers (Yb, Er and
Er/Yb) to various types of radiations like γ-rays, X-rays and protons. For all these harsh environments, the main
measured macroscopic radiation-induced effect is an increase of the linear attenuation of these waveguides due to the
generation of point defects in the RE-doped core and silica-based cladding. To evaluate the vulnerability of this class of
optical fibers for space missions, we characterize the growth and decay kinetics of their radiation-induced attenuation
(RIA) during and after irradiation for various compositions. Laboratory testing reveals that this class of optical fibers is
very sensitive to radiations compared to passive (RE-free) samples. As a consequence, despite the small length used for
space applications, the understanding of the radiation-induced effects in this class of optical fibers becomes necessary
before their integration as part of fiber-based systems like gyroscopes or communication systems. In this paper, we more
particularly discussed about the relative influence of the rare-earth ions (Er<sup>3+</sup> and/or Yb<sup>3+</sup>) and of the glass matrix
dopants (Al, P, ...) on the optical degradation due to radiations. This has been done by using a set of five prototype
optical fibers designed by the fiber manufacturer iXFiber SAS to enlighten the role of these parameters. Additional
spectroscopic tools like confocal microscopy of luminescence are also used to detect possible changes in the
spectroscopy of the rare-earth ions and their consequences on the functionality of the active optical fibers.