Ayoub Ladaci

Proton Irradiation Response of Hole-Assisted Carbon Coated Erbium-Doped Fiber Amplifiers

We investigated the behavior of a new class of erbium-doped fiber amplifier (EDFA) when exposed to 63 MeV protons. The EDFA is designed with a radiation hardened hole-assisted carbon coated (HACC) Er3 + -doped optical fiber. The particular structure of this HACC fiber allows to permanently incorporate an optimal amount of D2 or H2 gases into its core, reducing its radiation sensitivity without degrading the EDFA performances. Irradiations up to a fluence of 7.5 ×1011 p/cm2 confirm the excellent tolerance of this HACC-EDFA component. It exhibits a limited decrease of ~ 0.6 dB of its ~ 27 dB gain for this fluence corresponding to an ionization dose of 100 krad(Si). Such a device can then survive to the radiative environments associated with both todays space missions and future more challenging applications.

Optimization of rare-earth-doped amplifiers for space mission through a hardening-by-system strategy

Rare-earth doped optical fibers (REDF, Er or Er/Yb-doped) are a key component in optical laser sources (REDFS) and amplifiers (REDFA). The high performances of these fiber-based systems made them as promising solution part of gyroscopes, telecommunication systems… However, REDFs are very sensitive to space radiations, so their degradation limits their integration in long term space missions. To overcome this issue, several studies were carried out and some innovations at the component level were proposed by our group such as the Cerium co-doping or the hydrogen loading of the REDF. More recently we initiated an original coupled simulation/experiment approach to improve the REDFA performances under irradiation by acting at the system level and not only at the component itself. This procedure optimizes the amplifier properties (gain, noise figure) under irradiation through simulation. The optimization of the system is ensured using a PSO (Particle Swarm optimization) algorithm. Using some experimental inputs, such as the Radiation Induced Attenuation (RIA) measurements and the spectroscopic features of the fiber, we demonstrate its efficiency to reproduce the amplifier degradation when exposed to radiations in various experimental configurations. This was done by comparing the obtained simulation results to those of dedicated experiments performed on various REDFA architectures. Our results reveal a good agreement between simulations and experimental data (with <2% error). Finally, exploiting the validated codes, we optimized the REDFA design in order to get the best performances during the space mission and not on-ground only.

Optimized radiation-hardened erbium doped fiber amplifiers for long space missions

In this work, we developed and exploited simulation tools to optimize the performances of rare earth doped fiber amplifiers (REDFAs) for space missions. To describe these systems, a state-of-the-art model based on the rate equations and the particle swarm optimization technique is developed in which we also consider the main radiation effect on REDFA: the radiation induced attenuation (RIA). After the validation of this tool set by confrontation between theoretical and experimental results, we investigate how the deleterious radiation effects on the amplifier performance can be mitigated following adequate strategies to conceive the REDFA architecture. The tool set was validated by comparing the calculated Erbium-doped fiber amplifier (EDFA) gain degradation under X-rays at ∼300 krad(SiO2) with the corresponding experimental results. Two versions of the same fibers were used in this work, a standard optical fiber and a radiation hardened fiber, obtained by loading the previous fiber with hydrogen gas. Based on these fibers, standard and radiation hardened EDFAs were manufactured and tested in different operating configurations, and the obtained data were compared with simulation data done considering the same EDFA structure and fiber properties. This comparison reveals a good agreement between simulated gain and experimental data (<10% as the maximum error for the highest doses). Compared to our previous results obtained on Er/Yb-amplifiers, these results reveal the importance of the photo-bleaching mechanism competing with the RIA that cannot be neglected for the modeling of the radiation-induced gain degradation of EDFAs. This implies to measure in representative conditions the RIA at the pump and signal wavelengths that are used as input parameters for the simulation. The validated numerical codes have then been used to evaluate the potential of some EDFA architecture evolutions in the amplifier performance during the space mission. Optimization of both the fiber length and the EDFA pumping scheme allows us to strongly reduce its radiation vulnerability in terms of gain. The presented approach is a complementary and effective tool for hardening by device techniques and opens new perspectives for the applications of REDFAs and lasers in harsh environments.

Radiation influence on Er/Yb doped fiber amplifiers performances: high power and WDM architectures

The actual challenge for space researchers is to increase the free space telecommunications data speed transfer. One of the most promising solutions is the optical communication systems. This technology can be used for the inter-satellite and/or satellite-ground links, reaching the TB/s speed for data transfer in the case of Dense Wavelengths Division Multiplexing (DWDM) based technologies. However, to achieve such systems, two main issues need to be overcome: the first one is to validate that no unexpected radiation effect appears when the optical amplifier working in the DWDM configuration and the second one is to estimate the degradation of the Erbium/Ytterbium co-doped boost (High Power - HP) amplifier performances during the space mission lifetime. In this last case, the used high powers will result in a complex response of the amplifier due to photobleaching, photodarkening and thermal effects. In this work, we estimate the radiation effects on an Er/Yb co-doped boost amplifier operating in a Dense WDM configuration. Both radiation hardened and a conventional versions of EYDFA have been considered. The obtained results allow estimating the performances of our fibers under exposure in such amplification setup and also to validate its potential for use in an actual space mission. We demonstrate the good radiation resistance of Er/Yb co-doped 12 μm core diameter fibers reaching 20 W of output power for telecommunication applications. This core diameter provides a fewmode optical output signal (with low dispersion) and with enough power to ensure the signal propagation trough the atmosphere. This study is fundamental as several phenomena such as Photo/Thermal bleaching, photo-darkening… are in competition due to the high-power light density in the fiber core and the system radiation response cannot yet be predicted by actual simulation tools.