Radiation Resistant Optical Fiber Research Articles

Radiation Damage Mechanisms and Research Status of Radiation-Resistant Optical Fibers: A Review.

In recent years, optical fibers have found extensive use in special environments, including high-energy radiation scenarios like nuclear explosion diagnostics and reactor monitoring. However, radiation exposure, such as X-rays, gamma rays, and neutrons, can compromise fiber safety and reliability. Consequently, researchers worldwide are focusing on radiation-resistant fiber optic technology. This paper examines optical fiber radiation damage mechanisms, encompassing ionization damage, displacement damage, and defect centers. It also surveys the current research on radiation-resistant fiber optic design, including doping and manufacturing process improvements. Ultimately, it summarizes the effectiveness of various approaches and forecasts the future of radiation-resistant optical fibers.

Optical properties of thin films monitored in real-time at high gamma radiation doses using long period fiber gratings

In this work, we report an all-optical-fiber-based method to monitor in real-time the changes in thin film optical properties when exposed to harsh environments such as high doses of gamma radiation. The method is based on a long period grating (LPG) inscribed in a radiation resistant optical fiber, which is coated with a thin film to be analyzed. Due to impact of the environment on the film properties, the transmission spectrum of the LPG changes. To validate this methodology, we deposited oxides of various metals, i.e. aluminum (Al2O3), titanium (TiO2), and tantalum (Ta2O5), as well as a polymeric film, namely polystyrene (PS), on the LPG surface and measured the resonant wavelength shift induced by high doses of gamma exposure (dose rate of 2.3 kGy/h, up to a total dose of 46 kGy). The changes could be observed in real-time up to maximum reached dose and during the recovery period. The results are significantly dependent on thin film material. Among the oxides, TiO2 thin film demonstrated the highest susceptibility to irradiation, whereas Al2O3 exhibited the least impact. Additionally, a good recovery potential for Ta2O5 thin film was observed, hinting at its promising application in dosimetry. Conversely, the PS film exhibited a permanent effect induced by irradiation. This is the first real-time experimental study of the impact of high dose gamma radiation on thin film optical properties using a universal optical-fiber-based device. The findings pave the way for assessing radiation hardness of thin film materials or utilizing such a method to optimize material treatment involving ionizing radiation.

Paramagnetic Point Defect in Fluorine-Doped Silica Glass: The E^{'}(F) Center.

Fluorine-doped silica is a key material used in all low-loss and/or radiation-resistant optical fibers. Surprisingly, no fluorine-related radiation-induced point defects have been identified. By using electron paramagnetic resonance, we report the first observation of F-related defects in silica. Their fingerprint is a doublet with 10.5mT splitting due to hyperfine coupling (hfc) to ^{19}F nuclear spins. An additional 44.4mT hfc to the ^{29}Si nucleus indicates that this defect belongs to the "E^{'} center" family and has a structure of a fluorine-modified Si dangling bond: 3-coordinated Si atoms with an unpaired electron in an sp^{3} orbital, bonded to a glass network by 2 bridging oxygen atoms and to a F atom.

Progress of Gamma Ray Irradiation Experiments on ITER Diagnostics from JADA

The Japan domestic agency (JADA) is responsible for procuring five diagnostic systems for ITER: the microfission chamber (MFC), poloidal polarimeter (PoPola), edge Thomson scattering (ETS), divertor impurity monitor (DIM), and divertor infrared thermography (IRTh) systems. Components of these systems that will be installed in high radiation zones must undergo radiation resistance tests to ensure reliability. The JADA diagnostic group has been conducting gamma ray irradiation experiments on diagnostic components at QST since 2018. The MFC is a neutron diagnostic system that uses uranium fission chambers, the mineral-insulated cables of which were evaluated for corrosion resistance. In-situ observations of the MFC preamplifier have been launched. The PoPola provides the plasma current profile by detecting the polarizations of far-infrared laser beams at their inlets and outlets. Irradiation tests confirmed the durability of PoPola piezo actuators. The ETS is a laser-aided diagnostic to measure electron temperature and density in plasmas from scattered spectra. Laser-induced damages to the optical elements caused by irradiation were investigated. The DIM is a spectroscopic system having a wavelength range of 200 nm to 1000 nm. The effects of irradiation on optical devices, metal mirrors, and radiation-resistant optical fibers were investigated. The IRTh is an infrared thermography system to observe the surface temperature of the divertor. The optical elements and electrical devices of the IRTh have undergone irradiation experiments. The progress of the gamma ray irradiation experiments on the ITER diagnostic systems from JADA are reported.

Polarization-maintaining and radiation resistant optical fiber with germanosilicate elliptical core

This paper aims to consider fabrication of single-mode polarization-maintaining (PM) optical fibers with elliptical core, doped with 20 mol. % GeO2 and to study their optical properties and radiation resistance. The optical fiber preform was fabricated by chemical vapor deposition method. The low-oxygen central piece of the core in the preform was removed by high-temperature chemical gas-phase etching. The single-mode optical fibers 125 µm in diameter, with 65 µm thick polymer protection coating were drawn. The results of measurements of the optical properties at a wavelength of 1.3–1.55 μm confirmed that the highly-doped GeO2 optical fiber waveguides have a low optical loss and high radiation resistance owing to gas phase etching. Polarization-maintaining factor (h-parameter) of ≈ 8∙10-6 m−1 was achieved. As to the radiation resistance, our single-mode PM optical fiber with elliptical core appears to be quite competitive to the known PANDA PM optical fibers with a core made of pure silica glass.

MCVD method for manufacturing polarization-maintaining and radiation resistant optical fiber with germanosilicate elliptical core

The aim of this work was to develop a fabrication process of single-mode polarization-maintaining germanosilicate optical fibers with elliptical core (GOFEC) doped with 20 mol % GeO2. The fiber preform was fabricated by MCVD method. The low-oxygen central piece of the core in the preform was removed by high-temperature chemical gas-phase etching. The influence of γ-radiation with a dose rate of 1 Gy/s on the optical losses in GOFEC at a wavelength of 1550 nm and at 25°C and −60°C were investigated. Their radiation resistance at −60°C is proved to surpass that of the existing analogous fibers. It has been found that the radiation-induced attenuation in such highly doped GeO2 single-mode fibers is higher than that in multimode fibers. In contrast to multimode fibers, radiation resistance in single-mode fibers depends on the material of the core and cladding. As to the radiation resistance, these GOFEC are comparable with the fiber of PANDA type with a pure silica glass core.

Radiation-resistant optical fiber with oxygen-deficient silica glass core

Oxygen deficiency in a silica glass core of fluorosilicate optical fiber manufactured by the modified chemical vapor deposition method provides extra high level of its radiation resistance. Gamma-radiation-induced attenuation (RIA) in such a fiber increases with decreasing both the test temperature (from + 25 to minus 60 °C) and the wavelength (from 1.55 to 1.31 μm). After exposure to radiation, RIA completely disappears at the room temperature. At the temperature of minus 60 °C, the optical losses restore much worse. RIA increases due to the superposition of Rayleigh scattering and absorption, with the latter decreasing with increasing wavelength.

Effect of Temperature and Gamma-Ray Irradiation on Optical Characteristics of Fiber Bragg Grating Inscribed Radiation-Resistant Optical Fiber

A new radiation-hard germano-silicate glass optical fiber with a pure silica glass buffer and a boron-doped silica glass inner cladding was fabricated for temperature sensor application based on the fiber Bragg grating (FBG) under γ-ray irradiation environment. The temperature dependences of optical attenuation at 1550.5 nm and Bragg reflection wavelength shift from 18 °C to 40 °C before the γ-ray irradiation were about 4.57×10−4 dB/ °C and 5.48 pm/ °C, respectively. The radiation-induced optical attenuation at 1550.5 nm and the radiation-induced Bragg reflection wavelength shift under the γ-ray irradiation with the total dose of 22.85kGy at 35 °C were about 0.03dB/m and 0.12nm, respectively, with the γ-ray irradiation sensitivity of 5.25×10−3 pm/Gy. The temperature and the γ-ray irradiation dependence of optical attenuation at 1550.5nm in the FBG written fiber with boron-doped silica glass inner cladding were about 6 times and 4 times lower than that in the FBG written fiber without boron-doped silica glass inner cladding under a temperature change from 18 °C to 40 °C and the γ-ray irradiation with the total dose of 22.85 kGy at 35 °C, respectively. Furthermore, the effect of temperature increase on the Bragg reflection wavelength of the FBG written fiber with boron-doped silica inner cladding was much larger about 1000 times than that of the γ-ray irradiation. However, no influence on the reflection power of the Bragg wavelengths and the full width at half maximum (FWHM) bandwidth under temperature and the γ-ray irradiation change was found. Also, after the γ-ray irradiation with the dose of 22.85kGy, no significant change in the refractive index was found but the residual stresses developed in the fiber were slightly relaxed or retained.

Отечественные радиационно-стойкие волоконные световоды

Отечественные радиационно-стойкие волоконные световоды

Radiation tolerant fiber Bragg gratings for high temperature monitoring at MGy dose levels

We report a method for fabricating fiber Bragg gratings (FBG) resistant to very severe environments mixing high radiation doses (up to 3 MGy) and high temperatures (up to 230°C). Such FBGs have been written in two types of radiation resistant optical fibers (pure-silica and fluorine-doped cores) by exposures to a 800 nm femtosecond IR laser at power exceeding 500 mW and then subjected to a thermal annealing treatment of 15 min at 750°C. Under radiation, our study reveals that the radiation induced Bragg wavelength shift (BWS) at a 3 MGy dose is strongly reduced compared to responses of FBGs written with nonoptimized conditions. The BWS remains lower than 10 pm for temperatures of irradiation ranging from 25°C to 230°C without noticeable decrease of the FBG peak amplitude. For an applicative point of view, this radiation induced BWS corresponds to an additional error on the temperature measurements lower than 1.5°C, opening the way to the development of radiation-tolerant multi-point temperature sensors for nuclear industry.

An electron beam profile instrument based on FBGs.

Along with the dose rate and the total irradiation dose measurements, the knowledge of the beam localization and the beam profile/energy distribution in the beam are parameters of interest for charged particle accelerator installations when they are used in scientific investigations, industrial applications or medical treatments. The transverse profile of the beam, its position, its centroid location, and its focus or flatness depend on the instrument operating conditions or on the beam exit setup. Proof-of-concept of a new type of charged particle beam diagnostics based on fiber Bragg gratings (FBGs) was demonstrated. Its operating principle relies on the measurement of the peak wavelength changes for an array of FBG sensors as function of the temperature following the exposure to an electron beam. Periodically, the sensor irradiation is stopped and the FBG are force cooled to a reference temperature with which the temperature influencing each sensor during beam exposure is compared. Commercially available FBGs, and FBGs written in radiation resistant optical fibers, were tested under electron beam irradiation in order to study their possible use in this application.

Development of radiation-resistant optical fiber for application to observation and laser spectroscopy under high radiation dose

In the Fukushima Daiichi Nuclear Power Station, it is necessary to survey the locations and conditions of fuel debris inside reactor pressure vessels or primary containment vessels under water and radiation environment in preparation for removing fuel debris. An optical fiber is well known for features such as signal transmission, light weight, superior insulation performance, water resistance and electromagnetic noise resistance. These features allow the optical fiber to simplify the instrumentation systems for in-vessel inspection, as long as provide that the optical fiber can be used under high radiation dose environment. The radiation resistance of an optical fiber was improved by increasing the amount of hydroxyl up to 1000 ppm in pure silica fiber. The improved optical fibers were irradiated with γ-ray up to 1 × 106 Gy using a 60Co source. They indicated a large peak around 600 nm and a peak tail from ultraviolet region, but no large absorption in infrared region except a hydroxyl absorption peak of 945 nm. We have confirmed that the optical fiber containing 1000 ppm hydroxyl has enough radiation resistance for radiation-induced transmission losses, and the infrared imaging is effective for observation under high radiation doses.

Origin of the visible absorption in radiation-resistant optical fibers

In this work we investigated the point defects at the origin of the degradation of radiation-tolerant optical fibers used in the visible part of the spectrum for plasma diagnostics in radiation environments. For this aim, the effects of γ-ray irradiation up to the dose of 10 MGy(SiO2) and post-irradiation thermal annealing at 550°C were studied for a Fluorine-doped fiber. An absorption peaking around 2 eV is mainly responsible for the measured radiation-induced losses, its origin being currently debated in the literature. On the basis of the unchanging shape of this band with the radiation dose, its correlation with the 1.9 eV photoluminescent band and the thermal treatment results we assign the asymmetric absorption around 2 eV to an unique defect, the NBOHC, instead of a set of various defects.

Development and Application of Radiation-Resistant Optical Fiber for Heavy Irradiation Environment

Development and Application of Radiation-Resistant Optical Fiber for Heavy Irradiation Environment

Radiation-resistant optical fiber/scintillator system for gamma-ray monitor

A scintillator-based gamma-ray detection system that uses a radiation-resistant optical fiber was developed. The system consisted of two radiation-resistant optical fibers—one, a fiber with a scintillator, and the other, a fiber without a scintillator—which were used to obtain the gamma-ray dose rate at the measurement point. This system demonstrated a linear response with respect to the gamma-ray dose rate from 0.005 to 1.5Gy/h and a good radiation resistance over an absorbed dose of more than 300kGy.

Application of optical fibers to nuclear power systems―Development of radiation-resistant optical fibers for nuclear application―

Application of optical fibers to nuclear power systems―Development of radiation-resistant optical fibers for nuclear application―

Radiation resistant optical fiber with a high birefringence

A radiation resistant optical fiber with a high birefringence is fabricated on the basis of nitrogen-doped silica glass using the PANDA technology and studied. The loss in this fiber for an absorbed @[gamma]-radiation dose of 2–10 kGy does not exceed 5–10 dB/km, which is an order of magnitude lower than that of standard telecommunication fibers with a germanium silicate core.

Search for luminescent materials under 14 MeV neutron irradiation

A radiation detection system utilizing radiation-resistant optical fibers and luminescent materials will have several advantages, such as compactness and robustness, and can be a strong candidate for diagnostics of fusion neutrons. Luminescent materials – important components of an optical system – that exhibit luminescence under fast neutron irradiation were studied. Commercially available luminescent materials, such as ZnS:Ag, ZnS:Cu, SrAl 2O 4:Eu 2+, Dy 3+, and Sr 4Al 14O 25:Eu 2+, Dy 3+ exhibit luminescence under 14 MeV neutron irradiation. The materials excluding ZnS:Ag showed radiation resistance for a fast neutron fluence of up to 10 14 n/cm 2. The luminescence characteristics of Sr 4Al 14O 25:Eu 2+, Dy 3+ that have three apparent peaks were also examined under proton irradiation. The compounds exhibited the same luminescence peaks under fast neutron irradiation, which can be attributed to their dopants, namely, Dy 3+ and Eu 2+, and the intensity ratio of Eu 2+ to Dy 3+ showed dependence on incident energy and radiation.

In-situ ex-core monitoring using optical fibers with scintillators

In-situ radiation monitoring in the outside region of a reactor core has been experimentally demonstrated using radiation-resistant optical fibers with scintillators. To avoid influences of luminescence (400-450 nm) from the fibers by radiation, Y/sub 3/A/sub 15/O/sub 12/:Ce scintillators were adopted because the luminescence has its peak around 550 nm. In this method, low radiation field was monitored with a pulse counting method, while high field with an integral method. The demonstration experiments shows that radiation intensity outside a reactor core can be well monitored with the system from the reactor power of 1 kW to 3.5 MW. The vertical radiation intensity distribution around the reactor core was also measured at 3.5 MW.

Round-robin irradiation test of radiation resistant optical fibers for ITER diagnostic application

Fused silica core optical fibers are expected to play crucial roles especially in the size-reduced International Thermonuclear Experimental Reactor (ITER-FEAT). Several radiation resistant optical fibers have been developed in Japan and the Russian Federation. The task force on radiation effects in diagnostic components in the ITER-EDA (engineering and design activity) promoted international round-robin irradiation experiments on the developed optical fibers. Ten different optical fibers were tested in a cobalt-60 gamma-ray irradiation facility and in the Japan Materials Testing Reactor. The paper reports results obtained on five different optical fibers, which include purified, hydrogen loaded, and fluorine doped ones. Results show that the developed optical fibers could be deployed in remote handling and out-of-vessel applications. But, for the in-vessel diagnostics in the visible range optical spectroscopy, further improvement of the radiation resistance of optical fibers will be needed.