Radiation-induced Attenuation Levels Research Articles

Combined Photobleaching and Temperature Effects on 1550 nm Radiation-Induced Attenuation of Germanosilicate Optical Fiber

Combined temperature and photobleaching (PB) effects on the 1550 nm radiation-induced attenuation (RIA) levels and kinetics of a commercial Ge-doped single-mode optical fiber have been investigated. The main goal of this study was to evaluate if synergetic effects could impact the performances of free space optical communication links in space. For this, we performed accelerated (0.5 Gy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s) irradiation runs with 100 kV X rays up to the total ionizing dose of 150 kGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), varying the irradiation temperature between -80 °C and 80 °C. First, we evaluate the irradiation temperature effects: infrared RIA largely increases at negative temperatures. Second, the effects of injecting different optical powers at the different temperatures have been characterized: if at temperatures exceeding room temperature (RT), PB effects are almost negligible, a PB effect is clearly observable at lower temperatures where the germanosilicate optical fiber present large RIA levels due to the contribution of metastable defects absorbing at 1550 nm. Increasing the injected powers allows reducing the concentration of these radiation-induced unstable defects, but not as much as thermal treatment consecutive to the irradiation. These results highlight the complex physics of radiation induced defects absorbing at 1550 nm in Ge-doped optical fiber, but also the vulnerability of this class of fiber for space telecommunication links. Regarding the unstable nature of point defects causing the RIA at lower temperature, it seems possible to mitigate the loss excess by thermal cycles at RT or higher temperatures. We also could expect that our accelerated tests represent a worst-case scenario in terms of RIA levels at the maximum dose.

Temperature Dependence of Radiation-Induced Attenuation of a Fluorine-Doped Single-Mode Optical Fiber at Infrared Wavelengths

Harsh environments can combine radiations and extreme temperature constraints, which can both degrade the optical performances of silica-based optical fibers. Among the different types of optical fibers, the ones having a core in pure-silica or doped with Fluorine are known to present, generally, the lowest steady state radiation-induced attenuation (RIA) to high cumulated doses (> 10 kGy) at room temperature. In this work, we investigate how the RIA levels and kinetics of a radiation hardened F-doped single-mode optical fiber depend on the irradiation temperature. To achieve this, we performed a systematic study on the combined temperature (from -80°C to 80°C) and steady state X-ray radiation (up to 100 kGy) effects on a F-doped single-mode fiber with a high temperature acrylate coating in the infrared domain. We then discuss the basic mechanisms at the origin of the RIA and its temperature dependence.

Investigation of radiation response on pure silica large core fibers at low dose levels

The radiation responses of three large core silica fibers with low OH contents were investigated with a high Dose rate (105 Gy/s), low total dose (1 mGy) pulsed X-rays, and low Dose rate (0.054 Gy/s) steady state gamma rays, respectively, to develop a fast radiation detector based on silica fiber and scintillator. The radiation-induced emission (RIE) and radiation-induced attenuation (RIA) of these fibers from a 350 nm–550 nm spectrum range were evaluated. All of them presented low RIA levels, and the Cherenkov radiation and individual peak fluorescence emission centered at 460 nm, being the primary contributors to RIE. In addition, the spectral decomposition of RIAs is performed using known Gaussian absorption bands associated with a few point defects; such as Si-related defects (Non-bridging-oxygen hole center-NBOHC, Si-ODC(II) Self-trapped hole-STH), and chlorine related defects (Cl0 and Cl2). The performances of these point defects at various irradiation doses are analyzed.

Radiation responses of ultra-low loss pure-silica-core optical fibers in the visible to infrared domains

–We investigated the origins of the steady state X-ray radiation-induced attenuation (RIA) in the visible to infrared spectral domains of an ultra-low loss Telecom-grade single-mode optical fiber. This pure-silica core optical fiber presents very high RIA in this spectral range, larger than so-called radiation sensitive optical fibers. The RIA is mainly caused by the appearance of two broad absorption features around 600 nm and 1200 nm, both leading to RIA levels of ∼2 dB/m at 2 kGy(SiO2) at room temperature. While the infrared-RIA may be attributed to the absorption bands at 0.93 eV and 1.2 eV of possible variants of Self-Trapped Holes, the exact nature of the large 600 nm absorption around remains unclear. It could not be only related to a very efficient generation of Non-Bridging Oxygen Hole Centers but our analysis suggests the presence of another defect structure associated with an absorption band around 2.14 eV (FWHM = 0.52 eV), stable at room temperature, but that can be passivated by post irradiation hydrogen-loading treatment.

Temperature Dependence of Radiation Induced Attenuation of Aluminosilicate Optical Fiber

We investigated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> the temperature influence on X-ray radiation-induced attenuation (RIA) levels and kinetics of an Al-doped single-mode optical fiber (OF) in the visible (vis) and near-infrared (NIR) spectral domains (400 nm– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2~\mu \text{m}$ </tex-math></inline-formula> , from room temperature (RT) up to 300 °C). The RIA spectra in the visible show no significant variation up to 200 °C. Above this temperature, the induced losses begin to decrease. The NIR RIA, on the other hand, appears to be more temperature-dependent, showing a monotonic decrease with increasing temperature throughout the whole investigated range. By studying the RIA growth kinetics at 1550 nm at the various temperatures, a linear dependence was found between the RIA levels and doses at which a steady state is reached, suggesting a direct generation process of the induced defects. Finally, the combination of the measurements led to the attribution of the RIA in the NIR domain to a single absorption component, whose generation process is correlated with the defects absorbing in the visible and characterized by a continuum of absorption states.

Temperature Dependence of Low-Dose Radiation-Induced Attenuation of Germanium-Doped Optical Fiber at Infrared Wavelengths

Ge-doped optical fibers (OFs) are considered radiation-tolerant waveguides. Even if their transmission in the infrared (IR) domain is degraded under irradiation, for most of the applications, their radiation-induced attenuation (RIA) remains acceptable. Space harsh environment is characterized by low dose and dose-rate constraints meaning that germanosilicate fibers are often employed for data links. However, the temperature can largely vary in space and is known to impact the RIA levels and kinetics. We studied here systematically the combined temperature and radiation effects induced on the transmission, at the telecom wavelengths, of a Ge-doped fiber, between −80 °C and 80 °C up to a total ionizing dose (TID) of 10 kGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )–1 Mrad. Our measurements highlight larger RIA levels at low temperatures than at room temperature (RT). At our highest TID, it increases by a factor of ~40 and ~20, respectively, at 1310 and 1550 nm, when the irradiation is performed at −80 °C instead of RT. A model is reported to study the activation energy of the radiation-induced point defects responsible for the IR-RIA. This simple model could help in predicting the fiber vulnerability for various mission profiles.

Temperature Influence on the Radiation Responses of Erbium‐Doped Fiber Amplifiers

The gain degradations of an Er‐doped fiber amplifier (EDFA) during the exposure of its active Er‐doped fiber to 40 keV X‐rays (≈2.7 mrad(SiO2) s−1 up to 300 krad) at three different temperatures: −40, 25, and 120 °C, are characterized. The spectral dependence of the fiber radiation‐induced attenuation (RIA) is monitored in situ in the 900–1600 nm spectral range, highlighting a combined temperature and radiation effect on the near‐infrared RIA levels and kinetics. At the system level, the kinetics of EDFA gain degradation are only slightly affected by varying the irradiation temperature for the tested backward pumping EDFA configuration. On the theoretical side, a homemade computer code based on the particle swarm optimization and the rate equations to model the radiation behavior of EDFA is used, considering only the RIA impact on its gain. Despite a good agreement between experimental and simulation results below the dose of 70 krad corresponding to current space missions, the comparison between the modeled and measured gain degradation kinetics at higher doses shows that a more precise modeling of the temperature impact on the absorption properties of the erbium ions is necessary to better reproduce the EDFA radiation behavior for future space missions.

Radiation Effects on Pure-Silica Multimode Optical Fibers in the Visible and Near-Infrared Domains: Influence of OH Groups

Signal transmission over optical fibers in the ultraviolet to near-infrared domains remains very challenging due to their high intrinsic losses. In radiation-rich environments, this is made even more difficult due to the radiation-induced attenuation (RIA) phenomenon. We investigated here how the number of hydroxyl groups (OH) present in multi-mode (MM) pure-silica core (PSC) optical fibers influences the RIA levels and kinetics. For this, we tested three different fiber samples: one “wet”, one “dry” and one with an intermediate “medium” OH content. The RIA of the three samples was measured in the 400–900 nm (~3 eV to ~1.4 eV) spectral range during and after an X-ray irradiation at a dose rate of 6 Gy(SiO2) s−1 up to a total accumulated dose of 300 kGy(SiO2). Furthermore, we evaluated the H2-pre-loading efficiency in the medium OH sample to permanently improve both its intrinsic losses and radiation response in the visible domain. Finally, the spectral decomposition of the various RIA responses allows us to better understand the basic mechanisms related to the point defects causing the excess of optical losses. Particularly, it reveals the relationship between the initial OH groups content and the generation of non-bridging oxygen hole centers (NBOHCs). Moreover, the presence of hydroxyl groups also affects the contribution from other intrinsic defects such as the self-trapped holes (STHs) to the RIA in this spectral domain.

Extreme Radiation Sensitivity of Ultra-Low Loss Pure-Silica-Core Optical Fibers at Low Dose Levels and Infrared Wavelengths.

We report here the response of a commercial ultra-low loss (ULL) single-mode (SM) pure silica core (PSC) fiber, the Vascade EX1000 fiber from Corning, associated with 0.16 dB/km losses at 1.55 µm to 40 keV X-rays at room temperature. Today, among all fiber types, the PSC or F-doped ones have been demonstrated to be the most tolerant to the radiation induced attenuation (RIA) phenomenon and are usually used to design radiation-hardened data links or fiber-based point or distributed sensors. The here investigated ULL-PSC showed, instead, surprisingly high RIA levels of ~3000 dB/km at 1310 nm and ~2000 dB/km at 1550 nm at a limited dose of 2 kGy(SiO2), exceeding the RIA measured in the P-doped SM fibers used for dosimetry for doses of ~500 Gy. Moreover, its RIA increased as a function of the dose with a saturation tendency at larger doses and quickly recovered after irradiation. Our study on the silica structure suggests that the very specific manufacturing process of the ULL-PSC fibers applied to reduce their intrinsic attenuation makes them highly vulnerable to radiations even at low doses. From the application point of view, this fiber cannot be used for data transfer or sensing in harsh environments, except as a very efficient radiation detector or beam monitor.

Infrared radiation Induced attenuation of radiation sensitive optical fibers: influence of temperature and modal propagation

Abstract We investigate the X-ray (40 keV) and γ-ray (1.2 MeV) radiation responses of three different radiation sensitive Optical Fibers (OFs) up to 100 Gy(SiO2). In particular, we study the Radiation Induced Attenuation (RIA) in the Near Infrared domain (NIR) for single mode OFs doped with Phosphorus (P), Aluminum (Al) and Phosphorus/Cerium (PCe) in their cores at three temperatures up to 50 °C. RIA levels and kinetics strongly depend on the operating wavelength and fiber composition. For both P and PCe-doped fibers, the P1 defects are the main contributors to the RIA, with Ce-codoping inducing a decrease of radiation sensitivity. For the Al-doped fiber, no specific absorption bands can be discriminated in the NIR. Both X- and γ-rays lead to the same RIA levels and kinetics. The RIA spectral dependences on dose and temperature highlight the potential of the three investigated fibers for radiation detection and dosimetry. To better discuss the properties of point defects responsible for the NIR RIA, we analyze how the fundamental mode propagation influences the RIA spectra of each fiber type. By reasonably assuming that the core RIA exceeds largely the cladding RIA and by calculating the mode Confinement Factor (CF), the RIA spectra of the core material are reconstructed and the spectral characteristics of defects are discussed for each type of fibers.

Transient and Steady-State Radiation Response of Phosphosilicate Optical Fibers: Influence of H2 Loading

The radiation response of a phosphorus-doped multimode optical fiber is investigated under both transient (pulsed X-rays) and steady-state ( $\gamma $ - and X-rays) irradiations. The influence of a H2 preloading on the fiber radiation-induced attenuation (RIA) in the 300–2000-nm wavelength range has been characterized. To better understand the impact of this treatment, online behaviors of fiber samples containing different amounts of gas are compared from glass saturation (100%) to less than 1%. In addition to these in situ experiments, additional postirradiation spectroscopic techniques have been performed such as electron paramagnetic resonance or luminescence measurements to identify the different point defects responsible for the induced losses and their H2 dependence. All our data at room temperature (RT) highlight a strong positive impact of H2, even at very low concentrations, on the RIA. Hydrogen quickly passivates ( $t s) most of the defects responsible for the visible–near-IR RIA, mainly phosphorus oxygen hole centers (POHC) and P1 defects. However, 1 year after the H2 loading at RT or when operating at liquid nitrogen temperature, the RIA levels of the not-treated and H2-loaded fiber become comparable. The obtained results provide a better understanding of the potential and limitations of H2-loading treatment to design radiation-hardened fiber links.

Influence of Self‐Trapped Holes on the Responses of Fluorine‐Doped Multimode Optical Fibers Exposed to Low Fluences of Protons

The radiation vulnerability of various classes of multimode silica‐based optical fibers is investigated for space applications operating from the ultraviolet up to near‐infrared spectral domains. For this, radiation‐induced attenuation (RIA) levels and kinetics in the 300 ÷ 1100 nm wavelength range are monitored during and after steady state 105 MeV proton exposure at room temperature (RT, equivalent dose of ∼250 Gy(SiO2)). The responses of three types of “radiation hardened” optical fibers with either a pure‐silica core (PSC) or fluorine‐doped cores are compared to the one of a Telecom‐grade germanosilicate optical fiber. RIA growth during irradiation and decay after irradiation (recovery phase) reveal that the highly fluorine (2 wt.%)‐doped optical fiber, manufactured by axial vapor deposition process, presents higher RIA levels above 600 nm than other tested optical fibers. Indeed, if the high F‐doping level reduces the UV‐RIA related to SiE’, NBOHC or chlorine‐related centers this composition appears as associated with a strong RIA increase in the visible‐near‐IR through the more efficient generation of RT unstable strain‐assisted or inherent self‐trapped holes.

Radiation Effects on Aluminosilicate Optical Fibers: Spectral Investigations From the Ultraviolet to Near‐Infrared Domains

Online X‐ray radiation induced attenuation (RIA) has been performed in aluminosilicate optical fibers having different Al concentrations. The studied UV‐visible spectral range revealed the presence of absorption bands related to Al defects. Their generation is shown to be not noticeably dependent on the dose rate. Furthermore, the Al content (2–4 wt%), the core sizes, and the manufacturing processes (SPCVD or MCVD) of the preforms have no significant influence on the RIA levels and kinetics, as well as the drawing parameters within the range used for specialty fiber production. The Aluminum–Oxygen Hole Center (Al–OHC) presence was proved by their 2.3 eV absorption band and by their electron paramagnetic resonance (EPR) signature. The growth kinetic of their concentration versus dose is linear up to 2–3 kGy (SiO2). While, at higher doses, EPR data highlight a saturation, suggesting that the Al–OHC generation results from a process involving precursors. To explain the E'Si growth kinetic with the dose, two processes are necessary, the first is from precursors and the second by breaking SiOSi links. The study of the RIA induced in the NIR demonstrates that the tail of the 2.3 eV Al–OHC band cannot explain the fiber degradation and that additional defects contribute to the induced losses.

Irradiation temperature influence on the in-situ measured radiation induced attenuation of Ge-doped fibers

We report an experimental investigation on the radiation-induced attenuation (RIA) in the ultraviolet-visible domain for Ge-doped optical fibers, during X-ray (10 keV) exposure at different temperatures. The objective is to characterize the impact of the irradiation temperature on the RIA levels and kinetics. Our data highlight that for dose exceeding 1 kGy(SiO2) the RIA spectrum changes with the irradiation temperature. In particular, for wavelengths below 470 nm the RIA depends both on the dose and on the irradiation temperature, whereas at higher wavelengths the RIA depends only on the dose. From the microscopic point of view the origin of this behavior is explained by a larger impact of the irradiation temperature on the Ge(1) defects generation mechanism with respect to the one of GeX defects, which appears as poorly temperature sensitive in the tested range. This finding prevents us from easily establishing a conclusive relation between the generation mechanisms of these two types of defects. The lower content of radiation induced Ge(1), in fiber irradiated at higher temperature, is supported by the electron paramagnetic resonance (EPR) results acquired after the irradiation. In situ RIA and postmortem EPR data show a significant correspondence of the Ge(1) growth as a function of the dose. Confocal microscopy luminescence experiments indicate that the non-bridging oxygen hole center concentration is higher at 473 K in comparison with those observed at 300 and 373 K.

Transient and Steady State Radiation Responses of Solarization-Resistant Optical Fibers

We investigated the responses of several solarization-resistant (SR) multimode optical fibers to high dose-rate (> 100 Mrad/s), low dose-rate (5 krad/s) X-rays and very low dose-rate (0.3 rad/s) 1 MeV γ-rays. We characterized the radiation-induced attenuation (RIA) and radiation-induced emission (RIE) phenomena in the spectral range 200-1100 nm. These commercial fibers, optimized for the transport of high power of ultraviolet (UV) light, present good radiation tolerance to transient and steady state environments compared to other classes of multimode optical fibers with pure or doped cores (Ge, P, F). The different tested SR fibers present similar behaviors for both gamma-rays and X-rays. These fibers present low transient and permanent RIA levels for wavelengths greater than 300 nm. Our results showed that RIE can become an important factor of the fiber degradation, especially for high dose-rate irradiation. The induced losses in these fibers can be explained by the generation of Si-related defects like the SiE', Si-NBOHCs or STHs and also to chlorine-related centers like Cl0.

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 Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (7-10 wt.%) during proton and gamma-ray exposures. We have simultaneously measured the radiation-induced attenuation (RIA) around the Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ion pumping wavelength (980 nm) and the associated changes of the Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> emission around 1530 nm. The three erbium-doped fibers show similar radiation responses. All fibers exhibit RIA levels between 9 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and 1.7 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> dB m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> Gy <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 980 nm and between 4 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and 1.1 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> dB m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> Gy <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> 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 Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ion properties seem to be mainly unaffected by proton exposure, suggesting a solvation shell around the Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ion formed by Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> species.

Pulsed X-Ray and Continuous Gamma Radiation Effects on Erbium Doped Optical Fibers Properties

The radiation responses of two erbium doped fibers are studied in harsh pulsed X-ray and gamma ray environments. Their transient and continuous responses were measured in the near-infrared spectral range. The online transmission measurements of radiation-induced attenuation (RIA) show no detectable change in the 1450-1600 nm erbium-ions-absorption domain, whereas the background losses from the silica-based host matrix are strongly increased by the creation of point defects. For both harsh environments, the rare-earth doped samples exhibit higher RIA levels compared than standard passive optical fibers. From all our measurements, we proposed that the main contribution to the induced losses is due to the radiation-induced changes of the host matrix rather than changes related to erbium ions. Photo-luminescence analyses confirm the generation of NBOHC in erbium doped fibers and suggest the existence of energy transfer between the radiation-induced point defects and the Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions.

Gamma and UV Radiation-Induced Color Centers in Optical Fibers

Radiation-induced losses and paramagnetic centers were investigated in phosphorusdoped and P-free multimode germanosilicate optical fibers after g-rays (~1 MeV) and ultraviolet (5 eV) exposures. After both types of irradiation, the same defects seem to be responsible of the fiber absorption in the spectral range 400 to 1650 nm. In particular, the P1 centers and the Phosphorus Oxygen Hole centers are created in both cases in the phosphorus-doped fibers and explain the high permanent radiation-induced attenuation levels observed in this fiber type. Luminescence and electron spin resonance measurements (77 K, ~9.38 GHz) on irradiated samples confirm that the GeE’, SiE’ and NBOHC defects are also generated in the different irradiated samples. From this study, it seems that the pertinence of a multimode fiber for nuclear space or civil applications could be estimated through low-cost ultraviolet measurements.

Pulsed X-ray and /spl gamma/ rays irradiation effects on polarization-maintaining optical fibers

We studied the sensitivities at 1.55 /spl mu/m of three polarization-maintaining (PM) and three unstressed single-mode (SM) optical fibers under pulsed X-ray (/spl sim/1 MeV) and steady-state /spl gamma/-ray (/spl sim/1 MeV) radiation. Our results showed no differential radiation-induced attenuation (RIA) between the two orthogonal polarization axes of PM fibers for times ranging from 10/sup -6/ s to 100 s after ionization pulse (dose 1MGy/s). The two inner cladding phosphorus-codoped PM fibers and their corresponding SM fibers exhibited the same RIA levels and kinetics after both irradiation types. Their radiation responses could be explained by their compositions and by the properties of the absorbing phosphorus-related defects generated in the light guiding region (core and inner cladding). The inner cladding fluorine-codoped PM fiber showed radiation-tolerant properties compared with its SM counterpart. We assumed, therefore, that the outer stress applying region dopants could have an impact on the fiber radiation sensitivity under both irradiation types. More particularly, we showed that the cladding phosphorus-codoping far from the light guiding region reduces the RIA related to the germanium defects in the fiber core. This effect could be due to the donor nature of the double phosphorus-oxygen bond and could be exploited to design radiation-hardened polarization-maintaining and single-mode optical fibers.

Gamma-rays and pulsed X-ray radiation responses of nitrogen-, germanium-doped and pure silica core optical fibers

The sensitivities of three single-mode optical fiber types were characterized under γ(∼1 MeV)-rays and pulsed X(∼1 MeV)-ray radiation environments at room temperature. The radiation-induced attenuation (RIA) time dependent changes were measured at 1.55 and 1.31 μm for undoped, germanium- and nitrogen-doped core fibers. The nitrogen-doped core fiber exhibited the lowest RIA level for the time range 10 −6 to 10 +2 s after pulse and a non-linear RIA dose dependence for our tested dose range 0.01–1 kGy (SiO 2). This fiber showed also a good radiation response under steady-state γ-irradiation. The tested pure silica core fiber was the most resistant fiber under γ-rays, but had the highest RIA levels after a pulsed X-ray one. The radiation-properties of the germanosilicate fibers depend greatly on their cladding composition. The phosphorus-codoping of these fibers suppressed their pulsed X-ray RIA peaks but was responsible for the highest permanent RIA levels after both types of irradiation. Our results showed that the two environments lead to the same RIA levels in germanosilicate and nitrogen-doped fibers, implying that the same mechanisms and color centers are involved at the different dose rates. We proposed some explanations, based on spectroscopic measurements, concerning the influence of the different tested core dopants.