Radiation-induced Attenuation Research Articles

High Precision Radiation Induced Attenuation Measurements Enabled by Improved Phase Shifted Fiber Loop Ring-Down System

High Precision Radiation Induced Attenuation Measurements Enabled by Improved Phase Shifted Fiber Loop Ring-Down System

Measurement of radiation induced attenuation in irradiated active fibers using optical frequency domain reflectometry

Radiation induced attenuation (RIA) is a major factor affecting the performance of fiber laser systems operated in adverse environments. To investigate the output characteristics of lasers with irradiated active fibers, measurement of detailed RIA profiles is required. Here, a novel method is proposed to explore the attenuation characteristics of irradiated active fibers using optical frequency domain reflectometry (OFDR), which enables propagation loss measurement by acquiring the spatial-resolved backscattered optical signals. With this technique, the RIA data of Yb-doped fibers (YDFs) under uniform radiation is derived by linear fitting of the OFDR traces. And, conventional optical transmission (OT) method is also exploited for comparison. Analysis show that the measured results of the two approaches are consistent. Then, the capability of OFDR is further verified for non-uniform RIA profile measurement of YDFs. For a pump bleached YDF, an upward parabolic RIA profile is attained by taking derivative of the smoothed polynomial fitting of the OFDR trace. Finally, the impacts of RIA profile on the output characteristics of Yb-doped fiber lasers are examined theoretically with a multiphysics thermal model, further validating the necessity of RIA profile measurement.

Temperature Cycling Effects on Infrared Radiation-Induced Attenuation of Silica-based Optical Fibers

Temperature Cycling Effects on Infrared Radiation-Induced Attenuation of Silica-based Optical Fibers

Influence of Hydrogen on the Radiation-Induced Attenuation of Ge-doped Optical Fibers

Influence of Hydrogen on the Radiation-Induced Attenuation of Ge-doped Optical Fibers

Combined Radiation and Temperature Effects on Brillouin-Based Optical Fiber Sensors

The combined effects of temperature (from −80 °C to +80 °C) and 100 kV X-ray exposure (up to 108 kGy(SiO2)) on the physical properties of Brillouin scattering and losses in three differently doped silica-based optical fibers, with varying dopant type and concentration (4 wt%(Ge), 10 wt%(Ge) and 1 wt%(F)), are experimentally studied in this work. The dependencies of Brillouin Frequency Shifts (BFS), Radiation-Induced Attenuation (RIA) levels, Brillouin gain attenuation, Brillouin frequency temperature (CT) and strain (Cε) sensitivity coefficients are studied under X-rays in a wide temperature range [−80 °C; +80 °C]. Brillouin sensing capabilities are investigated using a Brillouin Optical Time Domain Analyzer (BOTDA), and several properties are reported: (i) similar behavior of the Brillouin gain amplitude decrease with the increase in the RIA; (ii) the F-doped and heavily Ge-doped fibers do not exhibit a temperature dependence under radiation for their responses in Brillouin gain losses. Increasing Ge dopant concentration also reduces the irradiation temperature effect on RIA. In addition, Radiation-Induced Brillouin Frequency Shift (RI-BFS) manifests a slightly different behavior for lower temperatures than RIA, presenting an opportunity for a comprehensive understanding of RI-BFS origins. Related temperature and strain sensors are designed for harsh environments over an extended irradiation temperature range, which is useful for a wide range of applications.

Near-infrared radiation induced attenuation in nested anti-resonant nodeless fibers.

This Letter reports the first, to the best of our knowledge, spectral radiation induced attenuation (RIA) measurements of nested anti-resonant nodeless hollow-core fibers (NANFs). A 5-tube NANF, alongside a solid-core single-mode radiation resistant fiber (SM-RRF), was irradiated under γ-ray up to 101 kGy (SiO2) and under x-ray up to 241 kGy (SiO2). No RIA was observed in the NANF in the second half of the O-band, the S-band, the C-band, and the L-band. The NANF showed a reduction of absorption bands associated with water and HCl under irradiation. Three new attenuation peaks were radiolytically induced and are attributed to the creation of HNO3. These peaks are centered respectively at 1441 nm, 1532 nm, and 1628 nm, with a full width at half maximum (FWHM) of, respectively, 10 nm, 12 nm, and 12 nm. These results demonstrate that the wide bandwidth range of NANFs is essentially unaffected by radiation, but the internal gas contents of the NANF must be managed to avoid producing undesirable spectral features through radiolytic reactions. Wide spectral regions almost unaffected by the ionizing radiation could open new possibilities for the use of NANF in harsh radiation environments.

Radiation-resistant cerium co-doped erbium-doped fibers for C- and L-band amplifiers in a high-dose gamma-radiation environment.

We experimentally demonstrate a comparative study on the radiation-resistant cerium (Ce) co-doped erbium-doped fiber amplifiers (EDFAs) exposed to a high-dose gamma-radiation environment of 1.8 kGy/h dose rate in the C and L bands. Our results show that Ce is an effective co-dopant in the aluminosilicate EDFs for suppressing radiation-induced attenuation (RIA) of more than an order of magnitude lower than the Ce-free EDF. After exposure to a high-dose gamma-radiation of up to 10 kGy, the Ce co-doped EDF still exhibits good radiation tolerance, providing 41.6 ± 2.9 dB gain and 5 ± 0.8 dB NF from 1535-1560 nm for a -25 dBm input signal. In the L-band, we report, for the first time, the radiation-resistant EDFA with the radiation-induced gain degradation (RIGD) of 3.7 dB under 2.5 kGy irradiation and 4.4 dB under 10 kGy irradiation at 1600 nm. Also, the radiation-dependent gain coefficient and gain saturation were studied in the C and L bands. A comparison of different Ce co-doped EDFs exposed to different total gamma doses reveals the radiation impact on the amplifier performance, indicating the feasibility of using Ce co-doped EDFs for space-based optical communications, requiring robust radiation stability.

Experimental–Simulation Analysis of a Radiation Tolerant Erbium-Doped Fiber Amplifier for Space Applications

Research on optical amplifiers has highlighted how ionizing radiation negatively impacts the performance of erbium-doped fiber amplifiers (EDFAs), through the degradation of their gain. The amplitudes and kinetics of this degradation are mainly explained by the radiation-induced attenuation (RIA) phenomenon at the pump and signal wavelengths. In this work, the gain degradation of a radiation tolerant EDFA (exploiting a cerium-co-doped active optical fiber) induced by ionizing radiation up to 3 kGy (SiO2), at two dose rates, 0.28 Gy/s and 0.093 Gy/s, is studied through an experimental/simulation approach. Using a home-made simulation code based on the rate and power propagation equations and including the RIA effects, the radiation-dependent performance of EDFAs were estimated. The variations in the spectroscopic parameters caused by irradiation were also characterized, but our results show that they give rise to EDFA gain degradation of about 1%. To overcome the issue of overestimating the RIA during the radiation tests on the sole active rare-earth-doped fiber, a new RIA experimental setup is introduced allowing us to better consider the photobleaching mechanisms related to the pumping at 980 nm. A good agreement between experimental and simulated gain degradation dose dependences was obtained for two different irradiation conditions, thus also validating the simulation code for harsh environments applications.

Radiation Induced Attenuation and Luminescence Study in Radioluminescent Optical Fibers

We present experimental characterization of both RIA (Radiation Induced Attenuation) and RL (Radioluminescence) of differently doped optical fibre radiation sensors. We present data for different sample lengths and Total Ionizing Dose (TID) up to 600 kGy (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) under X-rays. Combined RIA and RL responses are used to attempt explaining the variation of the RL signal with TID on those fibres.

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.

Calibration in the Visible and Infrared Domains of Multimode Phosphosilicate Optical Fibers for Dosimetry Applications

We systematically explore the suitability of two radiation-sensitive multimode optical fibers with either P or GeP-doped cores, to serve as the sensing elements in point or distributed dosimeters. To this end, we measured the dependences of their spectral Radiation-Induced Attenuation (RIA) in the visible and near-infrared (near-IR) domain (400 - 2100 nm) up to total ionizing dose (TID) of 5 kGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), while varying the irradiation temperature from -80 °C to +80 °C and the dose rate between 1 mGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s and 10 Gy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s. To assess the fiber radiation sensitivity calibration coefficients, we studied the linearity of the RIA vs TID response across our whole spectral range. Once confirmed, their “radiation sensitivity calibration” curves are obtained in the tested ranges of environmental parameters, including the dispersion related to dose rate and temperature. Both fibers present very similar curves despite their different chemical compositions. We then studied the recovery kinetics at the different temperatures of the two fibers to investigate the stability of the RIA response. Our results show that the Ge-codoping only slightly increases the IR sensitivity related to P1 defects while keeping unchanged the visible – near-IR RIA, where the contribution of phosphorus-oxygen-hole centers (POHC) is dominant. On the contrary, after the irradiation the responses of the two fibers differ, as the recovery kinetics of the GeP fiber are strongly affected by temperature, limiting its dosimetry capabilities with respect to the P fiber.

Investigations on Ionizing Dose Deposition in Thin-Layered Devices: Sample-to-Sample Variability and Electronic Equilibrium Dependence

The impact of photon energy spectrum on dose deposition variability is investigated using dosimetry, charge collection experiments on electronic and opto-electronic devices, and Radiation-Induced Attenuation (RIA) measurements in optical fibers. Geant4 calculations are performed to discuss the influence of photon energy spectrum, sensitive layer thickness and of the irradiated material. Implications for radiation test of electronic and optical equipment are discussed to ensure the effective TID is reached in irradiated devices.

Proton Dosimetry Using Radiation-Induced Luminescence in Micrometer-Core Germanosilicate Optical Fibers

We investigated the radiation-induced luminescence of 62.5 μm, 10 μm and 3 μm germanosilicate single- and multi-mode telecom-grade optical fibers for use as high-resolution dosimeters at dose rates ranging between 5 Gy s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 120 Gy s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> using proton beams of varying currents and energies. Only one of the two single-mode fibers under investigation had a detectable light yield, with a dose rate threshold around 20 Gy s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . All tested multi-mode fibers showed a detectable response over the whole accessible dose rate range. All tested multi-mode fibers displayed a linear dose rate response when the proton beam energy was fixed. However, the slope of the response curve showed a strong dependence on the proton beam energy. Geometry and material differences, as well as radiation-induced attenuation effects have been ruled out as sources for the observed proton energy dependence of the dose rate response.

Gamma irradiation of Ge-doped and radiation-hard silica fibers at cryogenic temperatures: Mitigating the radiation-induced attenuation with 1550 and 970 nm photobleaching

We investigated the effects of gamma irradiation on radiation-induced attenuation (RIA) in photosensitive (Ge-doped) and radiation-hard (F-doped) fibers at cryogenic temperatures (77 K) under different photobleaching conditions. We show that increasing the probe power (1550 nm) and injecting lower wavelength light (970 nm) both resulted in a significant reduction in RIA in both fiber types, where radiation-hard fibers were intrinsically more resistant to the RIA. Deconvolution of RIA growth curves revealed that the RIA was composed of transient and long-term growth components that were correlated with distinct radiation-induced defects specific to each fiber composition. The 1550 nm light more effectively suppressed the transient RIA, while 970 nm more effectively suppressed the long-term RIA. Ultimately, we show that cryogenic RIA may be effectively managed in fiber optic sensing systems using radiation-hard fibers and dual-wavelength photobleaching strategies.

Radiation-induced attenuation in single-mode pure-silica-core optical fibers two years after high-fluence reactor irradiation

Single-mode pure-silica-core optical fibers (PSFs) coated with different materials (aluminum, copper, polyimide, or acrylate) and reactor-irradiated 2 years ago to the fast-neutron fluence of 1.8·1020n/cm2 and γ-dose of 2.3·109 Gy with evacuation to 0.005–0.25 Pa were OTDR-tested at wavelengths λ = 1.31 and 1.55 µm. Metal-coated PSFs demonstrated virtually the same radiation-induced attenuation (RIA) at λ = 1.55 µm as was measured 1 day after the irradiation (∼2–4 dB/m), whereas RIA in the polyimide-coated PSF that survived the irradiation went down from ∼4.3 to 1.8 dB/m. Fiber microbending originating from radiation-induced coating decay (not mechanical failure of the fiber itself) was argued to be the source of the catastrophic RIA rise in the polyimide- and acrylate-coated PSFs during the reactor irradiation in vacuum.

Novel methodology for interpolation of radiation-induced attenuation in optical fibers

When irradiated with ionizing radiation, glass undergoes a darkening (or coloring), often referred to as Radiation-Induced Attenuation (RIA). This degradation is disadvantageous for many applications requiring optical fibers in radiative environments. In many cases, RIA growth follows a power-law with deposited dose. However, this law is descriptive and cannot be used to extrapolate or interpolate RIA in other experimental conditions. In this work, a methodology based on response surface methodology is suggested to interpolate the power-law in the region of experimentation. More specifically, the methodology leads to a single equation that approximates the RIA of the fiber inside this region. It might be useful to provide more information on the behavior of RIA regarding experimental parameters based on a batch of experiments.

Toward local core outlet temperature monitoring in gas-cooled nuclear reactors using distributed fiber-optic temperature sensors

Gas-cooled nuclear reactors operate at temperatures up to 950 ℃ with significant spatial variations in power generation and coolant flow through hundreds of parallel flow channels, resulting in complex mixing at the core outlet. The high temperatures and complex mixing can damage downstream components, challenge reactor calorimetry for power determination, and result in significant conservatism in calculated peak fuel temperatures, which ultimately limits the total power output. Directly measuring each gas stream individually is unrealistic using single point thermocouples, requiring more robust sensing techniques. Fiber-optic sensors are resilient to high temperatures (up to 1,000 ℃) and radiation damage. Moreover, distributed measurements can be made along the length of one fiber, making them potential candidates for monitoring local core outlet temperatures to improve core calorimetry and identify hot channels. To the authors’ knowledge, this manuscript is the first to report spatially distributed fiber optic temperature measurements to quantify mixing at the outlet of a relevant orifice plate under prototypic temperature and flow regimes to assess the feasibility of using fiber-optic sensors for distributed measurements of coolant temperature in gas-cooled reactors. A single optical fiber captured dynamic changes in local temperatures, whereas the mixed outlet temperature exhibited a muted response and could not identify which channels were responsible for the change in the mixed outlet temperature. The discussion focuses on potential challenges for deploying distributed optical fibers in gas-cooled reactors, including the effects of vibrations, radiation-induced signal attenuation and drift, and routing of the fiber while minimizing flow obstructions.

Influence of Pre-Radiation and Photo-Bleaching on the Yb-Doped Fiber Laser Radiated with Gamma-ray

To improve the radiation resistance of Yb-doped fiber lasers, we investigate the influence of pre-radiation and photo-bleaching on the gamma-radiated laser’s performance. When the gamma radiation dose is within 10 krad(Si) with a radiation dose rate less than 0.4 rad(Si)/s, compared to the output power of a non-pre-radiated Yb-doped fiber laser, the pre-radiation technique could enhance the radiation resistance against gamma-ray. However, the mode instability threshold was decreased, which was caused by the cumulated radiation-induced attenuation of pre-radiation and radiation. Based on an electronic probe micro-analyzer, the Yb-doped active fiber was Yb-doped aluminophosphosilicate ternary fiber; therefore, the radiated defects were mainly hole-related defects. A laser diode centered at 532 nm was chosen as the photo-bleaching laser source, which could recover 45.2% of the radiated-induced attenuation and increase the mode instability threshold. This work demonstrates the influence of pre-radiation and photo-bleaching on the radiation resistance against the gamma-ray of Yb-doped fiber lasers, which are of significance in the design and fabrication of related fiber lasers.

Influence of spin–orbit coupling on the gamma-ray induced attenuation in high-OH silica fibers

There is an ever-increasing demand for radiation-tolerant optical systems in space and nuclear applications. This motivates leveraging advanced modeling techniques for the rational design of radiation-hard, application-specific optical materials. Here we used molecular dynamics, density functional theory, and solution of Maxwell’s equations to understand the role of point-defects on the radiation-induced attenuation in wet fused silica (a-SiO2:OH). We apply this approach to study γ-irradiated optical fibers, and find theoretical evidence that non-bridging oxygen-hole centers (NBOHC) are the primary microscopic defect responsible for radiation-induced attenuation in the visible-range. The nature of the defect states and implications for fiber efficiency are discussed. Spin–orbit coupling is found to play an important role in defining the optical properties of gamma-ray induced defects.

A technique for conducting of reactor in-situ tests of optical fibres and FBG-sensors intended for in-vessel applications in thermonuclear facilities

A method for in-situ studies of the optical fibres (OFs) and the fibre Bragg grating (FBG) sensors radiation resistance under irradiation at the IVG.1 M research reactor (Kurchatov, Kazakhstan) was developed. For this purpose, an irradiation ampoule device (AD) was developed that makes it possible to carry out joint irradiation of investigated samples with a fast neutron flux of up to 2.4 1013 n/(cm2·s) and a dose rate of up to 1.57 kGy/s in the temperature range from 200 to 700 °C and pressures of 10–80 Pa.Studies of radiation-induced attenuation (RIA) of single-mode OF in various protective coatings (copper, aluminium and polyimide at a wavelength of 1.55 μm and in the spectral range from 1.1 to 1.7 μm were carried out. Fast neutron fluence and absorbed dose were ФE>0.1MeV=1.72·1017 n/cm2 and Dγ=11.3 MGy, respectively. It has been established that the method of fibre winding in AD has a critical influence and leads to a parasitic contribution of temperature-induced stress-related losses to optical losses arising during reactor irradiation.The operability of FBG sensors up to a temperature of 500 °C has been demonstrated.The developed methods make it possible to conduct in-situ studies of the radiation resistance of fibre-optic components under conditions close to their applications in thermonuclear and nuclear facilities.