S. Girard

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

In this review paper, we present radiation effects on silica-based optical fibers. We first describe the mechanisms inducing microscopic and macroscopic changes under irradiation: radiation-induced attenuation, radiation-induced emission and compaction. We then discuss the influence of various parameters related to the optical fiber, to the harsh environments and to the fiber-based applications on the amplitudes and kinetics of these changes. Then, we focus on advances obtained over the last years. We summarize the main results regarding the fiber vulnerability and hardening to radiative constraints associated with several facilities such as Megajoule class lasers, ITER, LHC, nuclear power plants or with space applications. Based on the experience gained during these projects, we suggest some of the challenges that will have to be overcome in the near future to allow a deeper integration of fibers and fiber-based sensors in radiative environments.

New Insights Into Single Event Transient Propagation in Chains of Inverters—Evidence for Propagation-Induced Pulse Broadening

The generation and propagation of single event transients (SET) is measured and modeled in SOI inverter chains with different designs. SET propagation in inverter chains induces significant modifications of the transient width. In some cases, a propagation-induced pulse broadening (PIPB) effect is observed. Initially narrow transients, less than 200 ps at the struck node, are progressively broadened up to the nanosecond range, with the degree of broadening dependent on the transistor design and the length of propagation. The chain design (transistor size and load) is shown to have a major impact on the transient width modification.

Proton- and Gamma-Induced Effects on Erbium-Doped Optical Fibers

We characterized the responses of three erbium-doped fibers with slightly different concentrations of rare-earth ions (240-290 ppm) and Al2O3 (7-10 wt.%) during proton and gamma-ray exposures. We have simultaneously measured the radiation-induced attenuation (RIA) around the Er3+ ion pumping wavelength (980 nm) and the associated changes of the Er3+ emission around 1530 nm. The three erbium-doped fibers show similar radiation responses. All fibers exhibit RIA levels between 9 times 10-3 and 1.7 times 10-2 dB m-1 Gy-1 at 980 nm and between 4 times 10-3 and 1.1 times 10-2 dB m-1 Gy-1 at 1530 nm. Protons and gamma-rays lead to similar radiation damages, with small differences between the protons of different energies (50 MeV and 105 MeV). Furthermore, we have performed online measurements of the spectral dependence of RIA from 600 to 1600 nm and offline measurements from 1200 to 2400 nm. The three fibers exhibit the same spectral response. Losses decrease monotonically from the visible to the infrared part of the spectrum. We have performed spectral decomposition of these RIA curves with the help of absorption bands previously associated with radiation-induced point defects. Our analysis shows that the main part of the RIA (600-1700 nm) in erbium-doped glass can be explained by the generation of Al-related point defects. The other defects related to the germanium and phosphorus doping of the silica seem to have a lower contribution to the induced losses. The Er3+ ion properties seem to be mainly unaffected by proton exposure, suggesting a solvation shell around the Er3+ ion formed by Al2O3 species.

14-MeV Neutron,

In this paper, we investigate the mechanisms of absorbing defect generation by pulsed X-rays (~1 MeV), gamma-rays (~1.2 MeV) and 14-MeV neutrons in silica-based optical fibers. We measure the spectral and temporal dependence of the radiation-induced attenuation (RIA) from the ultraviolet to the near-infrared part of the spectrum (300-900 nm). The choice of the dopants incorporated in the fiber core and cladding strongly affects the fiber radiation tolerance. The structure and generation mechanisms of the point defects responsible for the fiber degradation are discussed on the basis of Gaussian decomposition of the RIA spectra with previously characterized absorption bands. In this spectral range, the absorption bands at 2.2, 2.5, and 3.1 eV (570, 510, and 400 nm) of phosphorus(P)-oxygen hole centers (POHC) explain the increase of losses in P-codoped fibers. For P-free fibers, our measurements showed that the RIA can be attributed to different germanium-related defects with absorption bands centered at 4.41, 2.61, and 1.97 eV (280, 475, and 630 nm) respectively, named Ge(1), GeX, and Ge-NBOHC centers. In the case of pulsed X-rays, another transient defect has been evidenced with an absorption band at 3.0 eV (400 nm, FWHM=0.60 eV) that has been associated in the literature with the [GeO4]- structure. Gamma-rays and 14-MeV neutrons globally lead to the same defect generation mechanisms and the same class of defects contributes to the induced losses. For a high dose rate environment and high-speed transmission measurements, very unstable defects, like self-trapped charges, have to be considered for the evaluation of the transient vulnerability of optical fibers

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We have studied the generation mechanisms of two different radiation-induced point defects, the Ge(1) and Ge(2) centers, in a germanosilicate fiber and in its original preform. The samples have been investigated before and after X-ray irradiation using the confocal microscopy luminescence and the electron paramagnetic resonance techniques. Our experimental results show the higher radiation sensitivity of the fiber as compared to the perform and suggest a relation between Ge(1) and Ge(2) generation. To explain our data we have used different models, finding that the destruction probability of the Ge(1) and Ge(2) defects is larger in fiber than in preform, whereas the generation one is similar. Finally we found that the higher radiation sensitivity of the fiber at low doses is essentially related to the presence of germanium lone pair center generated by the drawing.

-Ray, and Pulsed X-Ray Radiation-Induced Effects on Multimode Silica-Based Optical Fibers

We investigate the response of Ge-doped, P-doped, pure-silica, or Fluorine-doped fibers to extreme environments combining doses up to MGy(SiO 2) level of 10 keV X-rays and temperatures between 25 °C and 300 °C. First, we evaluate their potential to serve either as parts of radiation tolerant optical or optoelectronic systems or at the opposite, for the most sensitive ones, as punctual or distributed dosimeters. Second, we improve our knowledge on combined ionizing radiations and temperature (R&T) effects on radiation-induced attenuation (RIA) by measuring the RIA spectra in the ultraviolet and visible domains varying the R&T conditions. Our results reveal the complex response of the tested fibers in such mixed environments. Increasing the temperature of irradiation increases or decreases the RIA values measured at 25 °C or sometimes has no impact at all. Furthermore, R&T effects are time dependent giving an impact of the temperature on RIA that evolves with the time of irradiation. The two observed transient and stationary regimes of temperature influence will make it very difficult to evaluate sensor vulnerability or the efficiency of hardening approaches without extensive test campaigns.

Evolution of Photo-induced defects in Ge-doped fiber/preform: influence of the drawing

The radiation behavior of a commercially available Er-doped fiber is evaluated under varying gamma dose rates with in-situ spectral loss measurements. Complementary post-irradiation photoluminescence measurements allow us to better understand the radiation effects. Our results suggest that the microscopic environment of the Er/sup 3+/ ions is not much affected by the gamma irradiation, unlike the host matrix. We discuss the impact for potential applications of these commercially available fibers in radiation environments.

Combined High Dose and Temperature Radiation Effects on Multimode Silica-Based Optical Fibers

This paper investigates the single event upset sensitivity of Bulk SRAMs for terrestrial applications. The technology sensitivity is analyzed with both quasi-monoenergetic neutron and proton experiments in an energy range from 14 to 180 MeV. Analytical and simulation based correction methods of the neutron cross section are presented and validated. Then, neutron and proton cross section are compared. Soft Error Rate (for the terrestrial neutron spectrum) calculated with either proton or quasi-monoenergetic neutron data are also presented and compared

Gamma radiation effects in Er-doped silica fibers

The Laser Megajoule project is a major component of the French simulation program to study nuclear fusion by inertial confinement. The future Laser Megajoule facility requires control-command systems that will operate in a harsh radiative environment. Commercial off-the-shelf optical fiber data links are envisaged as a radiation tolerant solution for this application. In this paper, we present our preliminary study of their vulnerability. For this, we firstly have used an original method consisting of ultraviolet (/spl sim/5 eV) exposures of the fibers to identify the different germanosilicate optical fibers containing phosphorus, which leads them unacceptable for both steady state /spl gamma/-rays and successive pulsed X-ray irradiations. We have demonstrated the validity of the /spl gamma/-UV comparison by spectroscopic measurements. After this first selection, we have tested under pulsed X-rays (dose rate >10 MGy/s dose <0.5 kGy) the resistance of the P-free optical fibers at 1310 nm for the shortest times after an ionization pulse (10/sup -9/ to 10/sup -1/ s). Based on these results, we discuss the validity of the optical fiber data links for the control-command applications in LMJ facility.

Analysis of Quasi-Monoenergetic Neutron and Proton SEU Cross Sections for Terrestrial Applications

Transient radiation-induced effects in air-guiding photonic crystal fibers (Air-PCF) are investigated for the first time to our knowledge. We characterize the vulnerability of this kind of waveguide by measuring the time dependent changes of their radiation-induced attenuation (RIA) at 1.55 /spl mu/m. We compare their radiation response to those of two silica-based single-mode fibers with germanium-doped and pure-silica cores. An X-ray pulse induces globally the same effects in all waveguides: a strong and transient increase of RIA. For higher tested doses (10<D<100 Gy), Air-PCF exhibits an interesting saturation of RIA at /spl sim/0.1 dB/m. The possible mechanisms involved in this radiation response are discussed. In particular, we assume that the design of the photonic bandgap structure of the fiber, responsible for the light guidance in the air-core, could strongly affect the amplitude of RIA. The kinetics of RIA recovery depends predominantly on the point defects created at the air/silica interface and in the silica-based part of the microstructured cladding.