Alain Pastouret

Radiation-resistant erbium-doped-nanoparticles optical fiber for space applications

We demonstrate for the first time a radiation-resistant Erbium-Doped Fiber exhibiting performances that can fill the requirements of Erbium-Doped Fiber Amplifiers for space applications. This is based on an Aluminum co-doping atom reduction enabled by Nanoparticules Doping-Process. For this purpose, we developed several fibers containing very different erbium and aluminum concentrations, and tested them in the same optical amplifier configuration. This work allows to bring to the fore a highly radiation resistant Erbium-doped pure silica optical fiber exhibiting a low quenching level. This result is an important step as the EDFA is increasingly recognized as an enabling technology for the extensive use of photonic sub-systems in future satellites.

How do traces of thulium explain photodarkening in Yb doped fibers

Ytterbium doped fiber lasers are known to be impacted by the creation of color centers during lasing so called photodarkening. This defect creation was investigated in a spectroscopic point of view, showing the presence of thulium traces (ppb) in the ytterbium doped fiber. Moreover, this contamination exhibit luminescence in the UV range under 976 nm excitation of the ytterbium-doped fiber. In adding more thulium to an ytterbium-doped fiber it was shown that thulium strongly impact the defects creation process, involved in photodarkening.

Quenching investigation on New Erbium Doped Fibers using MCVD Nanoparticle Doping Process

Ever demanding network implementations brought new requirements to be addressed to offer cost effective and power efficient solutions with smaller footprints. This general trend together with the constant need to improve L-band optical amplification efficiency account for the renewed interest on highly doped Erbium fibers. Erbium doped fiber amplifiers (EDFAs) performance degradation with Er3+ concentration increase has extensively been studied1 and is attributed to additional losses due to energy transfers between neighbouring ions. Experimental observations have been interpreted by the homogeneous up-conversion (HUC) and pair-induced quenching (PIQ) models, which account for pump power penalty and unsaturable absorption respectively. For a given Er3+ concentration, studies have also showed that both fiber manufacturing process and core matrix composition have a strong impact on quenching parameters. In 2009, we introduced a new doping concept involving Al2O3Er nanoparticles (NP) in a MCVD-compatible process showing improved performances in terms of erbium homogeneity along the fiber length for standard doping levels.2 In this paper, we address our most recent work on concentration quenching encountered in both standard and NP Erbium doped fibers.

Nanoparticle Doping Process: towards a better control of erbium incorporation in MCVD fibers for optical amplifiers

Germano-silica and alumino-silica Erbium Doped Fibers have been fabricated through a new Nanoparticles Doping process with MCVD technology. These fibers have been characterized in WDM amplification experiments in both C and L band.

Recent developments in optical fibers and how defense, security and sensing can benefit

For many years, fiber manufacturers have devoted research efforts to develop fibers with improved radiation resistance, keeping the same advantages and basic properties as standard fibers. Today, both single-mode (SMF) and multimode (MMF) RadHard (for Radiation-Hardened) fibers are available; some of them are MIL-49291 certified and are already used, for example in military applications and at the Large Hadron Collider (LHC) in CERN or in certain nuclear power plants. These RadHard fibers can be easily connected to standard optical networks for classical data transfer or they can also be used for command control. Using some specific properties (Raman or Brillouin scattering, Bragg gratings...), such fibers can also be used as distributed sensing (temperature or strain sensors, etc) in radiation environments. At least, optical fibers can also be used for signal amplification, either in telecom networks, or in fiber lasers. This last category of fibers is called active fibers, in opposition to passive fibers used for simple signal transmission. Draka has also recently worked to improve the radiation-resistance of these active fibers, so that Draka can now offer RadHard fibers for full optical systems.

Benefit of Rare-Earth "Smart Doping" and Material Nanostructuring for the Next Generation of Er-Doped Fibers

Erbium-doped fiber amplifiers (EDFAs) for harsh environments require to develop specific fabrication methods of Er 3+-doped fibers (EDFs) so as to limit the impact of radiation-induced absorption. In this context, a compromise has to be found between the concentration of Erbium and the glass composition. On the one hand, high concentration of Er 3+ ions helps to reduce the length of the EDF and hence the cumulated attenuation but generally leads to luminescence quenching mechanisms that limit the performances. On the other hand, so as to avoid such quenching effect, glass modifiers like Al 3+ or P 5+ ions are used in the fabrication of commercial EDFs but are not suitable for applications in harsh environment because these glass modifiers are precursors of radiation-induced structural defects and consequently of optical losses. In this work, we investigate the concept of smart doping via material nanostructuring as a way to fabricate more efficient optical devices. This approach aims at optimizing the glass composition of the fiber core in order to use the minimal content of glass modifiers needed to reach the suited level of performances for EDFA. Er 3+-doped alumina nanoparticles (NPs), as precursor of Er 3+ ions in the preform fabrication process, were used to control the environment of rare-earth ions and their optical properties. Structural and optical characterizations of NP-doped preforms and optical fibers drawn from such preforms demonstrate the interest of this approach for small concentrations of aluminum in comparison to similar glass compositions obtained by a conventional technique.

Core-shell nanoparticle erbium-doped fibers for next generation amplifiers

New generation systems are expected to include more intelligent amplifiers able to adapt to many conditions including different gains, channel load, temperature, aging and transient events.1 To face the challenge and meet these new requirements, having an accurate control on the Er environment within the fiber core matrix has never appeared to be so necessary and predominant as it is the case now. Unlike conventional solution doping techniques where Erbium ions are randomly incorporated in the fiber core, our process makes use of a soft chemical synthesis to initially produce Erbium-doped nanoparticles (NPs). Erbium ions are therefore incorporated in the fiber core together with their local environment. So far, our investigations2 first showed that, from the material point of view, quenching levels are intimately linked to the design of the NPs through their chemical composition. Then, from the system perspective, we evidenced the higher power conversion efficiencies exhibited by NP fibers when compared to their conventional counterparts in high power amplifier configurations. In this paper, we address our most recent work focusing on the NP optimisation towards quenching-free Erbiumdoped fibers with a particular focus on core-shell alumino-silicate NPs. Completing our first amplifier results obtained in high power configurations, we also explore new NP fiber profiles that extend the range of their applications. Gain and noise characteristics of typical WDM operating points serve as key indicators on the benefits our NP doping process could provide.

Performance Characterization of New Erbium-Doped Fibers using MCVD Nanoparticle Doping Process

In 2009, we introduced a new doping concept involving Al2O3/rare-earth nanoparticles (NP) in a MCVD-compatible process finding potential applications in Erbium-, Ytterbium- or Erbium-Ytterbium-doped fiber amplifiers and lasers.1 This approach, motivated by the need for increased efficiencies and improved attributes, is characterized by the ability to control the rare-earth ion environment independently from the core composition. The NP matrix can therefore be viewed as an optimized sub-micronic amplifying medium for the embedded rareearth ion. The first experimental evidence to support this idea is reported in a comparative study with a standard process2 where homogeneous up-conversion (HUC) and pair-induced quenching (PIQ) levels are extracted from Er3+ unsaturable absorption measurements. NP-based fibers are found to mitigate the effects of the Er3+ concentration increase seen in standard heavily-doped fibers. This conclusion is particularly clear when focusing on the HUC coefficient evolution since, for a given type of NP, its level is independent from the Er3+ concentration in the doped zone. In this paper, we address our most recent work completing these preliminary results. First, we investigate the quenching signature of a new NP design and its behavior when incorporated in different core matrices. The interplay is further analysed by relating this set of measurements to practical EDFA performances. Gain and noise characteristics of typical WDM amplifiers operating points serve as key benchmarking indicators to identify the benefits of NP Erbium-doped fibers in the wide variety of EDFAs implementations.

Broadband Radiation-Resistant Erbium-Doped Optical Fibers for Space Applications

We explore how radiation-resistant broadband erbium-doped fibers (EDFs) can be achieved by using a carefully selected chemical composition, without specific coating or specific packaging. In this framework, we define a factor of merit, an appropriate and effective tool to design a radiation-hardened EDF amplifier (EDFA) based on a mature technology. We focus on specialty fibers, with a finely tuned composition in aluminum and erbium, guaranteeing the optimal operation of an EDFA (a 20-nm bandwidth and an optical output power level of at least 18 dBm) in the classical booster configuration throughout the entire geostationary mission. These performances are estimated thanks to a standard accelerated test, with a 300-Gy dose deposition at a dose rate of 0.4 Gy/h. We also confirmed, based on experiments and modeling, the importance of the radiation-induced absorption at pump wavelength on the EDFA degradation under irradiation.

Evidence of two erbium sites in standard aluminosilicate glass for EDFA

Site distributions of Er(3+)-doped aluminosilicate preforms of standard EDFA were studied by the low temperature Resonant Fluorescence Line Narrowing (RFLN) spectroscopy. Two erbium concentration samples with the same glass base were investigated. At very low erbium concentration, two classes of sites were identified, related to the number of AlO(6) octahedral linked by two oxygen edge-sharing to Er(3+) in the coordination sphere. As erbium concentration is increased, the high AlO(6) coordinated class of sites is smeared out by the optical response of the one AlO(6) coordinated class of sites.