Coupled experiment/simulation approach for the design of radiation-hardened rare-earth doped optical fibers and amplifiers

Abstract

We developed an approach to design radiationhardened rare earth-doped fibers and amplifiers. This methodology combines testing experiments on these devices with particle swarm optimization (PSO) calculations. The composition of Er/Yb-doped phosphosilicate fibers was improved by introducing Cerium inside their cores. Such composition strongly reduces the amplifier radiation sensitivity, limiting its degradation: we observed a gain decreasing from 19 dB to 18 dB after 50 krad whereas previous studies reported higher degradations up to 0°dB at such doses. PSO calculations, taking only into account the radiation effects on the absorption efficiency around the pump and emission wavelengths, correctly reproduce the general trends of experimental results. This calculation tool has been used to study the influence of the amplifier design on its radiation response. The fiber length used to ensure the optimal amplification before irradiation may be rather defined and adjusted to optimize the amplifier performance over the whole space mission profile rather than before integration in the harsh environments. Both forward and backward pumping schemes lead to the same kind of degradation with our active fibers. By using this promising coupled approach, radiation-hardened amplifiers nearly insensitive to radiations may be designed in the future.

Radiation Effects on Silica-Based Optical Fibers: Recent Advances and Future Challenges

“…Another possibility to increase the fiber radiation tolerance consists of using new deposition techniques allowing removing Al and P from the manufacturing process of Er-doped optical fibers [160]. In addition to the hardening of the fiber, the fiber amplifiers can also be hardened by design for a given space mission with the approach presented in [161].…”

“…Different techniques allow us to calculate this modal distribution, even in complex fiber structures like double clad Er/Yb fibers or Hollow core fibers. At this time, such modeling has been done essentially for Rare-earth based optical fibers and amplifiers [161]. The different developed codes can be validated through comparison with experimental results from spectroscopic techniques such as Electron Paramagnetic Resonance (EPR), time or spatially-resolved luminescence or absorption, Raman spectroscopy ……”

Radiation hardening techniques for rare-earth-based optical fibers and amplifiers

“…To optimize amplifiers, researchers used these tools to identify the optimal amplifier design parameters (active fiber length, pumping scheme, RE concentration, refractive-index, geometrical parameters of the fiber transversal section) that maximize the amplification around 1550 nm. However, as the characteristics of the fiber will change with radiations, it can be clearly seen that such calculation tools, if they include radiation effects, may also be used to enhance the amplifier performance not only before irradiation but also, for example, for a space mission by a more judicious choice of these "optimal" parameters [15]. Furthermore, such an optimization of the amplifier can only be performed through simulations as it will require a too large number of samples and radiation experiments to identify the optimal system at reasonable costs.…”