BW5B .2.pdf
2016 Photonics and Fiber Technology Congress (ACOFT, BGPP, NP) © OSA 2016
Improving optical fiber preform radiation resistance through fictive temperature reduction 1
Matthieu Lancry1*, B. Hari Babu1,2, Nadege Ollier2 and Bertrand Poumellec1 Institut de Chimie Moléculaire et des Matériaux d’Orsay, CNRS-UPSud, Université Paris Saclay, Bât.410, 91405 Orsay, France. 2 Laboratoire des Solides Irradiés, CEA-CNRS-Ecole Polytechnique, Université Paris-Saclay, Palaiseau, France.
[email protected]
Abstract: Sol-gel and Erbium-doped sol-gel glasses are fabricated through polymeric sol-gel technique. This work mainly demonstrates an effective strategy to improve the radiation resistance through glass fictive temperature reduction. The mechanisms are experimentally through UV-VisIR spectroscopic techniques. γ-irradiation leads to decrease of the frequency of Si-O-Si band that is likely due to an increase of the fictive temperature associated to an average reduction of bonding angle. Furthermore, we found that that γ-radiation "hardness" is higher in Er3+ doped sol-gel silica than that of standard synthetic or natural silica glasses. OCIS codes: (350.5610) Radiation; (060.2290) Fiber materials; (060.2410) Fibers, erbium; (160.6031) Silica
1. Introduction Nowadays, the radiation hardening of silica based glasses and optical fibers is a hot topic of research and addressing good platform for a wide range of photonic applications including space, optoelectronics, nuclear and military ones. The radiation resistance of passive and active optical fibers has been studied extensively in terms of radiation induced attenuation (RIA) and defect mechanisms both experimentally and theoretically. In the particular case of active fiber, radiations may decrease the amplification efficiency of the EDFAs [1]. Radiation resistance of optical fibers depend not only on the radiation conditions but also on mechanical properties (stress, strain and thus drawing tension) as well as the thermal history that can be define in term of fictive temperature, Tf. This is the temperature at which the glass structure is frozen-in [2]. In one of the rare study of Tf impact on the radiation resistance of glasses, Galeener et al. reported a reduction of defects concentration as fictive temperature (Tf) is substantially lowered. By using the electron paramagnetic resonance spectroscopic technique, Wang et al. investigated higher concentration of self-trapped hole (STH) centers formation taking place at higher fictive temperature in pure silica at 77K by ArF laser irradiation. However the state of art does not clearly delineate the glass thermal history, which should constantly improve the radiation tolerance, irrespective of the optical fiber composition, thermal history and glass manufacturing process. The main aim of this work is to investigate the characteristics of the radiation resistance of pure and Er3+-doped sol-gel silica glasses as a function of Tf. Our experimental results are compared with standard synthetic, Suprasil F300 and natural silica, Infrasil 301 with different fictive temperatures. 2. Experimental details The dense and crack-free silica optical fiber preforms were prepared by the polymeric sol-gel synthesis route and it was described in our earlier work [1]. Here, the suprasil F300 and Infrasil 301 were taken as a reference. All precursor glasses were subjected to thermal treatments in furnace at different temperatures (1000, 1100, 1200 and 1300°C), under air atmosphere during time exceeding their structural relaxation time. The glass samples were then quenched into the water at room temperature in order to fix their fictive temperature. The γ-irradiation was performed from a 60Co radioactive source with an accumulated dose of 5.9 kGy (dose rate of 14 Gy/min). The UV-Vis-NIR absorption spectra of all sol-gel silica glasses were recorded, before and after γ-irradiation, using Cary 5000 spectrophotometer and Nicolet Nexus 670 FT-IR spectrometer. Electron paramagnetic resonance (EPR) measurements were carried out at a frequency of 9.8 GHz. All EPR spectra are normalized by the sample mass for comparison of point defects. All measurements were carried out at room temperature (RT) except for STH defects study. 3. Results and discussion After 5.9 kGy γ-irradiation, a lower frequency of Si-O-Si asymmetric stretching band in all studied silica glasses can be found whatever the Tf may be (not shown here). This indicates that an average reduction of Si-O-Si bond angle variations takes place as a result of γ-irradiation. The most plausible explanation of the band frequency decrease, as compared to before γ-irradiation, could be an increase of the fictive temperature under γ-irradiation.
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BW5B .2.pdf
2016 Photonics and Fiber Technology Congress (ACOFT, BGPP, NP) © OSA 2016
The radiation induced attenuation (RIA) spectra of pure silica Sol-Gel glass were as reported in Fig. 1 (a) following with fictive temperature (1000-1300°C). The RIA spectrum is decomposed into eleven bands namely 5.8 eV (SiE’γ), non-bridging oxygen hole centers (6.7, 4.8 and 2.0 eV), Cl0 (3.28 eV), Cl2- defects (3.65 eV), selftrapped hole centers (2.6 eV for STH1 and 2.2 for STH2), peroxy radicals (1.97 eV), and an unknown band at 4.3eV [1,4,5]. In addition, the most intense band was identified at 5.4 eV band which can be attributed to the peroxy radicals (PRs) [4]. For all silica at Tf =1000°C, we identified mainly SiE’γ as well as a weak band associated with the NBOHC centers in Sol-gel silica and suprasil F300 samples. NBOHC defects were further study by additional photoluminescence measurements excited at 532nm. Beyond 1000°C, additional defects can be seen such as STHs, Cl0, Cl2 and peroxy radicals that were created in these samples. As it can be seen in Fig. 1(a), it appers that all defect concentrations are increasing with raising Tf except Cl-related defects. Indeed, 3.28 eV (Cl0) and 3.65 eV (Cl2) band intensity tend to decrease at 1300°C in sol-gel silica and suprasil F300 glass. Thus, a comparative study was carried out on the RIA results at a fixed fictive temperature (1100 °C) (see in the inset of Fig. 1(a)). From our experimental observations, sol-gel glasses and especially Er-doped sol-gel glass have a lower RIA when compared to the synthetic Suprasil F300 or Infrasil301 natural glasses. The EPR spectra of Tf-treated Suprasil F300 glasses were performed at 300K and 77K under 1mW power and modulation amplitude of 1Gauss before and after γ-irradiation. We confirm that there was no measurable defect centers before γ-irradiation in all Tf glasses. After irradiation, EPR spectrum of Suprasil F300 glass (Fig. 1(b)) possesses a complex signal that exhibits the characteristic features of the peroxy radicals (POR’s), self-trapped hole centers (STHs) and SiE’γ centers [1,6]. POR’s, STHs and SiE’γ were found to be decreases with the fictive temperature as shown in Fig. 1(b)). Similar results were observed in both sol-gel and synthetic silica glasses.
Fig. 1 (a) RIA spectra of pure silica solgel for different fictive temperature. Inset shows a comparison of Er-doped solgel, Suprasil F300 and Infrasil301 at Tf=11000C and (b) Low T EPR spectra recorded in Suprasil F300 for different Tf
4. Conclusions EPR analysis in combination with other spectroscopic techniques (FTIR, UV-Visible absorption and photoluminescence) show clearly that a lowering of the fictive temperature results in a lowering of defect concentration before and after irradiation and so to a smaller RIA. Consequently, our sol-gel silica glass materials present good radiation hardening behavior for all investigations to an equilibrium structure at the lowest practicable temperature Tf. Based on the experimental results, sol-gel silica glasses are promising materials for photonic applications in the harsh environment. 5. References [1] B. Hari Babu, N. Ollier, M. L. Pichel, H. El Hamzaoui, B. Poumellec, L. Bigot, I. Savelii, M. Bouazaoui, A. Ibarra, and M. Lancry, “Radiation hardening in sol-gel derived Er3+ doped silica glasses” J. Appl. Phys. 118, 123107 (2015). [2] M. Heili, B. Poumellec, E. Burov, C. Gonnet, C. L. Losq, D. R. Neuville and M. Lancry,”The dependence of the Raman defect bands in silica on densification revisited” J. Mater. Sci 51, 1659-1666 (2016). [3] K. Tsujikawa, K. Tajima and M. Ohashi, “Rayleigh scattering reduction method for silica-based optical fiber,” J. Light wave Tech. 18, 15281532 (2000). [4] L. Skuja, M. Hirano, H. Hosono and K. Kajihara, “Defects in oxide glasses,” Phys. Stat. Sol. (c) 2, 15-24 (2005). [5]S. Girard, J. Kuhnhenn, A. Gusarov, B. Brichard, M. Van Uffelen, Y. Ouerdane, A. Boukenter and C. Marcandella, “Radiation effects on silica-based optical fibers: Recent advances and future challenges,” IEEE Trans. Nucl. Sci. 60, 2015-2036 (2013). [6] D. L. Griscom, “Self-trapped holes in amorphous silicon dioxide”, Phys. Rev. B 40, 4224-4227 (1989).
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