Fiber-optic Radiation Research Articles

Prompt-critical power excursion measurements with optical fibers in the CABRI experimental reactor

This paper presents our experimental work to assess the capability of estimating the transient-induced power distribution evolution in the CABRI experimental reactor, using Cherenkov radiation in optical fibers. The CABRI reactor is designed to produce power transients from 100 kW up to 21 GW in less than 100 ms, in order to irradiate a test fuel pin under conditions representative of a Reactivity Insertion Accident in pressurized water reactors. Because of the wide response range and short response time required to follow the reactor power evolution during a complete transient, the usual means of detection, such as ionization or fission chamber, are rendered inoperable, especially for in-core or core vicinity measurements. For this reason, we suggest measuring the Cherenkov light produced within the optical fibers. The Cherenkov light emission is linked to local electron production, which is proportional to local gamma flux through the Compton or pair production cross-section. In other words, the intensity of Cherenkov radiation is related to the photon flux intensity. Knowledge of the fission photons emitted by the reactor gives direct insight into the fission rate, hence a spatial power density distribution could be reconstructed by using the measurement of Cherenkov light at different points in the reactor. The radio-luminescence measurements taken using photodiodes show very good linearity with the reactor power monitoring system despite the transient radiation induced attenuation observed in the optical fibers. The radio-luminescent light shows steady values with around 5% of variations over the 15 transients for low OH fibers and high OH fibers. Low OH tends to overestimate the FWHM of the power peak by 1–4%.

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.

First demonstration of a single-end readout position-sensitive optical fiber radiation sensor inside the Fukushima Daiichi Nuclear Power Station based on wavelength-resolving analysis

We have developed a new position-sensitive optical fiber radiation sensor that achieves single-end readout and high dose rate application. The sensor determines the incident position of radiation on the optical fiber by using the wavelength dependence of light attenuation within the fiber. Through analysis of the wavelength spectrum output from the fiber end, the incident position of radiation on the optical fiber can be inversely estimated via spectrum unfolding. Using this optical fiber sensor, we measured the radiation distribution inside the Fukushima Daiichi Nuclear Power Station (FDNPS). The actual trend of the incident position of radiation was successfully reproduced in a high dose rate area, with the maximum dose rate exceeding 100 mSv/h. This validates the effectiveness of our new position-sensitive optical fiber radiation sensor.

Nonreciprocity in optical fiber radiation modes induced by spin–momentum locking

Nonreciprocity in optical fibers are opening new avenues for fields such as quantum computing and quantum photonics. In this study we explore the chiral properties of the radiation modes of optical fibers and show that whispering gallery mode resonances, as part of radiation modes, carry specific transverse spin angular momenta. The transverse spin angular momentum is different for forward and backward propagating radiation modes, hence indicating spin–momentum locking. As a result of spin–momentum locking, a nonreciprocity in the emission coupling of an atomic transition with a specific spin into the forward and backward propagating modes is observed. Modeling an atomic transition by a classical dipole that rotates clockwise or anticlockwise, we optimize the position of the dipole within the optical fiber to achieve maximum nonreciprocity between the coupling of the dipole emission into the forward or backward propagating mode. We find near-perfect nonreciprocity in both radiation and guided modes and further outline the fiber diameter and dipole position to achieve this state. This study not only shows the rich physics of fiber radiation modes within the context of light–matter interaction but also complements previous studies of nonreciprocity in subwavelength waveguides.

Comparison of existing and new optical fiber-based scintillation detectors for spent-fuel verification equipment

The Wolsung Nuclear Power Plant in Korea is under IAEA safeguards. During IAEA physical inventory verifications, the Optical Fiber radiation Probe System has been used since 2007 as the official instrument for verification of spent fuel. Its low sensitivity requires excessive time and labor to perform the IAEA safeguard activities and increases the operator load for preparing a dangerous and time-consuming secondary inspection. The objective of this paper is to develop a superior new optical fiber-based scintillation detector to deal with such issues. To increase the sensitivity of the instrument, a new optical fiber-based scintillation detector was developed by combining a p-terphenyl scintillator with a new type of optical fiber. A field test was carried out in the CANDU Wolsung Unit 1 to characterize the performance of the new detector. The field test showed that the OFPS using the new optical fiber-based scintillation detector has at least 100-times higher sensitivity and can also measure even very weak signals not measurable by the existing detector. From the experimental results, we can conclude that the newly developed OFPS detector would increase the effectiveness and efficiency of nuclear safeguards for verification of spent fuel in wet storage pools of CANDU reactors.

Characterization of a Fiber Optic Radiation Sensor Prototype for Nuclear Dismantling

The use of an active measurement system to localize contamination in concrete structures of nuclear facilities offers advantages such as an easy on-site analysis within a short measurement time. A measuring system based on a scintillation crystal connected to a long optical fiber with a large diameter could satisfy the demands of a measuring system for gamma-ray spectroscopy in boreholes. This work describes the development of a gamma-ray spectroscopy system using a fiber optic radiation sensor. A prototype was built with a GAGG scintillation crystal, which could reach an energy resolution of 33% at the 662-keV gamma-ray emission energy of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs. A minimal time for the detection of a contamination of a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs source with an activity of 21 kBq and a layer of 6-cm concrete between sensor and radiation source was determined to be under 1 min with three different evaluation methods. They were based on the decision threshold and the Kolmogorov–Smirnov test corresponding to the energy distribution and the distribution of time differences between detector events. In addition, it was possible to estimate the distance of a point-like source from the sensor by establishing a further analysis parameter comparing different energy regions of a spectrum.

First demonstration of a novel single-end readout type position-sensitive optical fiber radiation sensor based on wavelength-resolved photon counting

In this study, a single-end readout type position-sensitive optical fiber radiation sensor was developed. Using the wavelength dependency of light attenuation inside the optical fiber, the incident position of radiation at the fiber can be estimated reversely. Instead of a spectrometer, we employed bandpass filters and photon-counting head as a photodetector to improve detection efficiency. The detection efficiency of a 10 m long plastic scintillation fiber at the 5 m position from the readout end was evaluated to be in the range of 0.08–0.12 % for 662 keV gamma-rays from 137Cs and 2.6–3.9 % for beta-rays from 90Sr/90Y when a bandpass filter transmitting photons with a wavelength of 500 nm was used. A basic measurement test of radiation intensity distribution was conducted using a 90Sr/90Y radioactive point source. A field test was also performed at the difficult-to-return zone in Fukushima Prefecture, and the estimated dose rate distribution roughly agreed with the survey meter measurement.

Recent Advances in Optical Fiber Enabled Radiation Sensors.

Optical fibers are being widely utilized as radiation sensors and dosimeters. Benefiting from the rapidly growing optical fiber manufacturing and material engineering, advanced optical fibers have evolved significantly by using functional structures and materials, promoting their detection accuracy and usage scenarios as radiation sensors. This paper summarizes the current development of optical fiber-based radiation sensors. The sensing principles of both extrinsic and intrinsic optical fiber radiation sensors, including radiation-induced attenuation (RIA), radiation-induced luminescence (RIL), and fiber grating wavelength shifting (RI-GWS), were analyzed. The relevant advanced fiber materials and structures, including silica glass, doped silica glasses, polymers, fluorescent and scintillator materials, were also categorized and summarized based on their characteristics. The fabrication methods of intrinsic all-fiber radiation sensors were introduced, as well. Moreover, the applicable scenarios from medical dosimetry to industrial environmental monitoring were discussed. In the end, both challenges and perspectives of fiber-based radiation sensors and fiber-shaped radiation dosimeters were presented.

Miniature Otto Prism Coupler for Integrated Photonics

AbstractOne of the main issues in integrated photonics is the coupling of free‐space or optical fiber radiation to waveguides on the photonic chip surface. The ideal coupler is miniature, highly efficient, and provides a large number of addressable devices. Here, a new concept of 3D out‐of‐plane coupler is introduced, which is a microscale prism exploiting frustrated total internal reflection in the Otto configuration to excite surface electromagnetic waves or near‐surface waveguide modes. A method for designing the couplers operating at normal incidence is proposed and it is applied to excite Bloch surface waves (BSWs) in 1D photonic crystals. Polymer microprisms are printed using two‐photon laser lithography and allow transferring more than 40% of the incident light energy into BSWs. The couplers enable focusing BSWs simultaneously with their excitation. Advanced design prisms can provide nearly 100% efficiency, making the proposed concept an alternative to actual coupling concepts in integrated photonics.

Nonreciprocity in Optical Fiber Radiation Modes Induced by Spin-Momentum Locking

Nonreciprocity in Optical Fiber Radiation Modes Induced by Spin-Momentum Locking

Development of a fiber-optic system for testing instruments for monitoring nuclear power plants

The necessity of testing the equipment for monitoring the operation of nuclear power plants is justified. It is proposed to use optical fiber and pulsed laser radiation for these purposes. It is established that optical fiber is more resistant to radiation than other communication systems. The design of a fiber-optic emergency simulator is developed. The calculation of its characteristics is carried out. Their experimental research was carried out. It was found that with an optical signal delay of 98.6 microseconds, the loss is – 26 dB with an uneven frequency response of ± 2 dB. This makes it possible to test the entire set of equipment that uses optical signals used to control a nuclear power plant.

Distributed fiber optic radiation sensors

Abstract. The international research efforts focused on the development of radiation sensors based on optic fibers have their origins in the 1970s (Evans et al., 1978). Generally, the lightweight fiber optic sensors are immune to electromagnetic field interference and high voltages making them deployable in harsh environments at hard to reach areas where conventional sensors usually will not work at all. A further advantage of such radiation sensors is the possibility of remote and real-time monitoring (Huston et al., 2001). In this work, we present our results achieved in several research activities for development of fiber optic dosimeters. The findings show that both the measurement of the radiation-induced attenuation (RIA) along the entire sensing fiber and the accompanying change in the refractive index of the fiber core can be used for distributed radiation monitoring in the kGy and MGy range, respectively. Depending on the fiber type and material the RIA shows varying response to dose rates, environmental temperatures and the wavelength of the laser source used. Thereby, an operation with visible laser light provides most favorable performance in terms of high radiation sensitivity. Operating at these wavelengths, RIA monitoring could yield high-sensitivity dose measurement with sub-gray resolution and accuracy (Stajanca and Krebber, 2017b); however, conventional optical time-domain reflectometry (OTDR) systems for RIA measurements operating in the visible range suffer from low-spatial resolution, long measurement times and poor signal-to-noise (SNR) ratio. The limitations of the OTDR performance can be overcome by the incoherent optical frequency domain reflectometry (I-OFDR) developed by the Federal Institute of Materials Research and Testing (BAM, Liehr et al., 2009) with potential for dynamic real-time measurement. Over the years, several highly radiation sensitive fibers, such as perfluorinated polymer optical fibers (PF-POF, Stajanca and Krebber, 2017a), phosphorous-doped silica optical fibers (SOF, Paul et al., 2009), aluminium-doped SOF (Faustov et al., 2013) and erbium-doped SOF (Wosniok et al., 2016) have been identified and are commercially available. As mentioned before, the radiation-induced RIA increase is associated with an increase in the refractive index leading also to material compaction in the fiber core. The latter two effects can be used for measuring radiation distribution based on Brillouin scattering in the range of high radiation doses of several MGy (Phéron et al., 2012; Wosniok et al., 2016). When using fiber optic sensors for radiation monitoring, the existing post-irradiation annealing behavior of the optical fiber sensors must also be considered.

Morphological changes of veins and perivenous tissues during endovenous laser coagulation using 2-μm laser radiation and various types of optical fibers

ObjectiveTo determine the morphological changes in veins and perivenous tissues after endovenous laser coagulation (EVLC) using laser radiation with a wavelength of 1910 nm and different types of fibers (bare tip and radial). MethodsThe EVLC procedure was carried out on 22 surface veins of six sheep. The radiation source was a diode-pumped solid-state laser, which was based on a LiYF4:Tm crystal and had an emission wavelength of 1910 nm and a maximum output power of 10 W. Two types of optical fibers were used: (1) bare tip and (2) radial or radial with two rings. Histological and morphometric methods were used, and the statistical digital data were analyzed. ResultsThe use of a linear endovenous energy density of 20 J/cm and optical bare fibers for veins with diameters of 3-4 mm resulted in a slit-shaped or wide venous wall perforation. A thermal effect was observed on the perivenous connective tissue (PVCT), which caused damage to its structures. Wide perforations were accompanied by complete destruction of the PVCT in the projection of the formed defect. The distance between the remaining vein wall fragment, located opposite to the perforation, and injured small vessels was 257.7 ± 23.6 μm. The radius of thermal damage increased to 2073.5 ± 8.0 μm near the vessel perforation. Using optical radial fibers for veins with diameters of 3.9 ± 0.5 mm did not lead to perforations. The destructive effect of the laser on small vessels of the PVCT extended to a distance of 425.7 ± 22.0 μm. ConclusionsAnalysis of thermal vessel damage in perivenous tissue after EVLC with bare-tip fiber shows that in the projection of a wide perforation, the damaged vessels of the PVCT are located at a large distance from the coagulated vein wall. On the opposite side of the perforation, the distance from the coagulated vein wall to the damaged vessels of the PVCT is significantly reduced because of the minimal output of laser radiation energy through the poorly damaged part of the wall. Using an optical radial fiber facilitates the application of a uniform distribution of thermal energy to the vein wall and damage to all its layers; at the same time, it minimizes the thermal energy that extends beyond the vein wall and damages the surrounding tissue. Clinical RelevanceThe use of radiation with a wavelength of 1910 nm will make it possible to carry out endovenous laser coagulation of varicose veins at lower power values compared with radiation in the micron and one and a half micron regions of the spectrum. Understanding of morphological changes of veins and perivenous tissues after endovenous laser coagulation with 1910-nm laser radiation and different types of optical fibers (bare-tip, radial, radial 2ring) help predict possible complications and reduce their rate.

Investigation of the Incorporation of Cerium Ions in MCVD-Silica Glass Preforms for Remote Optical Fiber Radiation Dosimetry.

The incorporation of Ce3+ ions in silicate glasses is a crucial issue for luminescence-based sensing applications. In this article, we report on silica glass preforms doped with cerium ions fabricated by modified chemical vapor deposition (MCVD) under different atmospheres in order to favor the Ce3+ oxidation state. Structural analysis and photophysical investigations are performed on the obtained glass rods. The preform fabricated under reducing atmosphere presents the highest photoluminescence (PL) quantum yield (QY). This preform drawn into a 125 µm-optical fiber, with a Ce-doped core diameter of about 40 µm, is characterized to confirm the presence of Ce3+ ions inside this optical fiber core. The fiber is then tested in an all-fibered X-ray dosimeter configuration. We demonstrate that this fiber allows the remote monitoring of the X-ray dose rate (flux) through a radioluminescence (RL) signal generated around 460 nm. The response dependence of RL versus dose rate exhibits a linear behavior over five decades, at least from 330 µGy(SiO2)/s up to 22.6 Gy(SiO2)/s. These results attest the potentialities of the MCVD-made Ce-doped material, obtained under reducing atmosphere, for real-time remote ionizing radiation dosimetry.

Distributed X-Ray Dosimetry With Optical Fibers by Optical Frequency Domain Interferometry

This article reports on the first demonstration of in situ , real-time dosimetry realized with an enhanced backscattering optical fiber, and a high-resolution optical backscattering reflectometry measurement. This work is devised to overcome the current problems in monitoring radiotherapy treatments, in particular, the difficult evaluation of not only the actual X-ray dose that is accumulated on the target volume but also the distribution profile of the ionizing radiation beam. Overall, the research aims at developing a dose sensor with the most demanding features of small form factor, spatial profiling, and remote interrogation. The experiments have been conducted by evaluating the spatial profile of radiation-induced spectral shift of the Rayleigh backscattering along an optical fiber exposed to X-rays. The sensing element is a section of specialty optical fiber whose Rayleigh backscattering signature changes under ionizing radiation. The specialty fiber is designed to exhibit an enhanced backscattering, in order to overcome the poor sensitivity to radiation of standard optical fibers that are normally, used in telecommunications. The enhanced sensitivity is achieved by doping the core with either aluminum or magnesium nanoparticles, and two different fibers have been fabricated and tested. The experimental results show the capability of real time detection of the radiation profile from high-dose rates (700 Gy/min) to low-dose rates (2 Gy/min). Moreover, different sensing mechanisms and responses to high- and low-dose rates are evidenced. A comparison with a quasi-distributed sensing system based on an array of fiber Bragg gratings (FBGs) is discussed, highlighting the superior performance of the backscattering approach in terms of sensitivity and spatial resolution, whereas the array of FBGs exhibits an advantage in terms of sampling speed.

Boosting dispersive wave emission via spectral phase shaping in nonlinear optical fibers

Dispersive waves (DWs) radiation in optical fibers allow to excite frequencies in spectral regions that are otherwise difficult to access. However, the resonant emission is weak and phase matching inhibits its shaping, making it ineffective in many applications. Here, we numerically investigated that DWs generated from high-energy pulses propagating in nonlinear optical fibers can be controlled through spectral phase modulation. Using tunable asymmetric and oscillatory temporal pulse shapes obtained by cubic and quadratic spectral phase modulation, we excite a multiple emission process that strongly enhances the energy and peaks of DWs. Successive collisions between the shed soliton and multiple secondary peaks of the asymmetric pulse give the mechanism to stimulate various resonant frequencies. The whole process can be precisely controlled by simply adjusting the spectral phase modulation structure without the need to change the fiber length. This radiation is either reduced or enhanced by the Raman effect depending on whether the third-order dispersion is positive or negative. Our results provide a novel strategy to manipulate DWs emission and particularly to boost the DWs energy in optical fibers that may be relevant in the development of novel electromagnetic sources for broadband supercontinuum and on-chip frequency-comb generation.

Methods for Increasing the Spatial Resolution of a Distributed Beam-Loss Monitor Based on Cherenkov Radiation in an Optical Fiber

Abstract—The principle of operation of a distributed beam-loss monitor based on the Cherenkov radiation in optical fiber is considered. The monitor allows real-time monitoring the distribution of the beam loss along the entire accelerator. The methods for increasing the spatial resolution of the monitor implemented on the e–e+ Injection Complex at the Budker Institute of Nuclear Physics are experimentally studied. For a 15-m-long quartz fiber with a diameter of 550 μm and a microchannel plate-based photomultiplier as a radiation detector, a spatial resolution of 0.5 m is achieved.

Combined Temperature and Radiation Effects on Radiation-Sensitive Single-Mode Optical Fibers

We analyzed the simultaneous response to radiation and temperature exposure of radiation-sensitive optical fibers doped with aluminum, phosphorus and/or Germanium in the framework of the CERTYF (Combined Effects of Radiations, Temperature and hYdrogen on silica-based optical Fibers) project, whose aim is to build a predictive model based on intrinsic and extrinsic optical parameters.

Recent Advances in Silica Glass Optical Fiber for Dosimetry Applications

In this paper, we review the highly promising silica glass, fabricated as doped and undoped optical fiber for intended use in radiation dosimetry. The dosimetry techniques reviewed here, underpinned by intrinsic and extrinsic defects in silica glass, focus on Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Radioluminescence (RL), with occasional references to the much more established Radiation Induced Attenuation (RIA). The other focus in this review is on the various materials that have been reported earlier as dopants and modifiers used in silica glass optical fiber radiation dosimeters. This article also elaborates on recently reported optical fiber structures, namely, cylindrical fibers, photonic crystal fibers and flat fibers, as well as dimensions and shapes used for optimization of dosimeter performance. The various types of optical fiber radiation dosimeters are subsequently reviewed for various applications ranging from medical dosimetry such as in external beam radiotherapy, brachytherapy and diagnostic imaging, as well as in industrial processing and space dosimetry covering a dynamic dose range from μGy to kGy. Investigated dosimetric characteristics include reproducibility, fading, dose response, reciprocity between luminescence yield to dose-rate and energy dependence. The review is completed by a brief discussion on limitations and future developments in optical fiber radiation dosimetry.

Nonlinear Fourier transform for characterization of the coherent structures in optical microresonators.

We propose and demonstrate, in the framework of the generic mean-field model, the application of the nonlinear Fourier transform (NFT) signal processing based on the Zakharov-Shabat spectral problem to the characterization of the round trip scale dynamics of radiation in optical fiber- and microresonators.