Recent advances in radiation-hardened fiber-based technologies for space applications

International audience; In this topical review, the recent progress on radiation-hardened fiber-based technologies is detailed, focusing on examples for space applications. In the first part of the review, we introduce the operational principles of the various fiber-based technologies considered for use in radiation environments: passive optical fibers for data links, diagnostics, active optical fibers for amplifiers and laser sources as well as the different classes of point and distributed fiber sensors: gyroscopes, Bragg gratings, Rayleigh, Raman or Brillouin-based distributed sensors. Second, we describe the state of the art regarding our knowledge of radiation effects on the performance of these devices, from the microscopic effects observed in the amorphous silica glass used to design fiber cores and cladding, to the macroscopic response of fiber-based devices and systems. Third, we present the recent advances regarding the hardening (improvement of the radiation tolerance) of these technologies acting on the material, device or system levels. From the review, the potential of fiber-based technologies for operation in radiation environments is demonstrated and the future challenges to be overcome in the coming years are presented

Radiation Characterization of Optical Frequency Domain Reflectometry Fiber-Based Distributed Sensors

We studied the responses of fiber-based temperature and strain sensors related to Optical Frequency Domain Reflectometry (OFDR) and exposed to high γ-ray doses up to 10 MGy. Three different commercial fiber classes are used to investigate the evolution of OFDR parameters with dose, thermal treatment and fiber core/cladding composition. We find that the fiber coating is affected by both thermal and radiation treatments and this modification results in an evolution of the internal stress distribution inside the fiber that influences its temperature and strain Rayleigh coefficients. These two environmental parameters introduce a relative error up to 5% on temperature and strain measures. This uncertainty can be reduced down to 0.5% if a pre-thermal treatment at 80°C and/or a pre-irradiation up to 3 MGy are performed before insertion of the fiber in the harsh environment of interest. These preliminary results demonstrate that OFDR fiber-based distributed sensors look as promising devices to be integrated in radiation environments with associated large ionizing doses

Automatic Fracture Characterization Using Tactile and Proximity Optical Sensing

This paper demonstrates how tactile and proximity sensing can be used to perform automatic mechanical fractures detection (surface cracks). For this purpose, a custom-designed integrated tactile and proximity sensor has been implemented. With the help of fiber optics, the sensor measures the deformation of its body, when interacting with the physical environment, and the distance to the environment's objects. This sensor slides across different surfaces and records data which are then analyzed to detect and classify fractures and other mechanical features. The proposed method implements machine learning techniques (handcrafted features, and state of the art classification algorithms). An average crack detection accuracy of ~94% and width classification accuracy of ~80% is achieved. Kruskal-Wallis results (p < 0.001) indicate statistically significant differences among results obtained when analysing only integrated deformation measurements, only proximity measurements and both deformation and proximity data. A real-time classification method has been implemented for online classification of explored surfaces. In contrast to previous techniques, which mainly rely on visual modality, the proposed approach based on optical fibers might be more suitable for operation in extreme environments (such as nuclear facilities) where radiation may damage electronic components of commonly employed sensing devices, such as standard force sensors based on strain gauges and video cameras

Optical Fiber Based Sensors for Harsh Environments

The primary objective of this study is to develop optical fiber-based sensors that are capable of operating in extreme conditions. Silica-based optical fibers are well known for their resilience to harsh environments. Whether they are integrated into distributed sensing schemes or as point sensors, optical fibers offer low-costs, highly accurate sensing platforms for various physical quantities. In this dissertation, state-of–the-art Al-doped radiation sensitive optical fibers for distributed ionizing radiation measurements are presented for the first time. This optical fiber sensor, coupled with a Rayleigh scattering-based optical frequency domain reflectometry (OFDR) scheme, was used to monitor and quantitate ionizing gamma radiation from a 60Co radioactive isotope. An alternative multi-core optical fiber was deployed to simultaneously monitor two different parameters. The dual-core fiber has been fabricated with two distinct optical cores to allow for differences between the cores’ temperature and strain coefficients. With such differences, temperature and strain changes were discriminated using a Brillouin scattering time domain analyzer (B-OTDA). Ultrafast lasers are commonly used to inscribe thermally stable nanostructures on optical fibers’ cores. IR laser-induced structures inscribed on low-loss, radiation-hard silica fibers were used to develop point and distributed sensors for in-pile nuclear reactor measurements. The sensors were subjected to, arguably the most challenging of artificial environments, with temperatures above 600°C, and high neutron fluxes at levels above 1.2×1014 n/s/cm2. The sensors were also used to monitor the temperature distribution inside of a solid oxide fuel cell (SOFC). The information obtained from the operational SOFC can be used to prolong its lifetime and increase its efficiency. Lastly, additive manufacturing embedding of optical fibers into metallic parts were attempted. A nickel-iron alloy, Invar-36, was investigated as a coating material for silica. The coefficient of thermal expansion (CTE) of Invar-36 can be carefully engineered to be close to that of silica. With a reduced CTE mismatch at the glass-metal interface, problems of adhesion and delamination can be deterred to extreme conditions. The proposed sensor designs and implementations would allow monitoring complex structures, and harsh environments like in SOFCs, gas turbines, robotics, or in high performance machinery, with minimal invasiveness

Recent Progress in Optical Fiber Research

This book presents a comprehensive account of the recent progress in optical fiber research. It consists of four sections with 20 chapters covering the topics of nonlinear and polarisation effects in optical fibers, photonic crystal fibers and new applications for optical fibers. Section 1 reviews nonlinear effects in optical fibers in terms of theoretical analysis, experiments and applications. Section 2 presents polarization mode dispersion, chromatic dispersion and polarization dependent losses in optical fibers, fiber birefringence effects and spun fibers. Section 3 and 4 cover the topics of photonic crystal fibers and a new trend of optical fiber applications. Edited by three scientists with wide knowledge and experience in the field of fiber optics and photonics, the book brings together leading academics and practitioners in a comprehensive and incisive treatment of the subject. This is an essential point of reference for researchers working and teaching in optical fiber technologies, and for industrial users who need to be aware of current developments in optical fiber research areas

Advanced trends in nonlinear optics applied to distributed optical-fibre sensors

The distributed optical-fibre sensors based on the properties of Brillouin scattering is the central object of this thesis. In the past decade, optical fibres have gained a large interest as sensors: attractive solutions based on the non-linear stimulated Brillouin scattering have been proposed in the early 90s and the possibility to achieve long-range fully distributed strain measurements has been extensively demonstrated. The Brillouin interaction is responsible for the coupling between two optical waves and an acoustic wave when a resonance condition is fulfilled. Since the resonance condition is strain and temperaturedependent, by determining the resonance frequency we directly get a measure of temperature or strain. Local information about the acousto-optical resonance condition is typically obtained by using pulsed lightwaves and a classical time-of-flight technique (BOTDA technique). The main goal of this work has been the development of an innovative technique for the generation of optical signals, using a set of locked lasers – instead of the traditional techniques using external modulators. The utilisation of the injection-locking of semiconductor lasers is the key of the entire set-up and represents an entirely new and original approach, since it brings significant improvements in terms of SNR and costs. As long as intense pulses propagate along the fibre, the optical signals can be seriously degraded by several nonlinear interactions occurring inside the fibre; we show that the nonlinear effect exhibiting the lowest threshold power is the modulation instability (MI) process. From the study of the dynamic behaviour of MI we could observe the Fermi-Pasta-Ulam (FPU) recurrence over few periods in very comfortable conditions. One original application of Brillouin sensing has been the dosimetric measurement of ionising radiations in a nuclear environment. The measurement campaign has not only shown that distributed sensors based on Brillouin spectral analysis are radiation tolerant up to very high doses, but has also revealed the first observation – to our knowledge – of the negative compaction of silica in fibres. Distributed fibre sensors based on stimulated Brillouin scattering offer a unique capability for the analysis of optical signals and nonlinear phenomena in optical fibres. We present a generalised theoretical approach to the problem of localised sensing and report on the first distributed measurement – to our knowledge – of the parametric gain in a single-pump fibre-optics parametric amplifier (FOPA)

Technical Readiness and Gaps Analysis of Commercial Optical Materials and Measurement Systems for Advanced Small Modular Reactors

This report intends to support Department of Energy’s Office of Nuclear Energy (DOE-NE) Nuclear Energy Research and Development Roadmap and industry stakeholders by evaluating optical-based instrumentation and control (I&C) concepts for advanced small modular reactor (AdvSMR) applications. These advanced designs will require innovative thinking in terms of engineering approaches, materials integration, and I&C concepts to realize their eventual viability and deployability. The primary goals of this report include: 1. Establish preliminary I&C needs, performance requirements, and possible gaps for AdvSMR designs based on best available published design data. 2. Document commercial off-the-shelf (COTS) optical sensors, components, and materials in terms of their technical readiness to support essential AdvSMR in-vessel I&C systems. 3. Identify technology gaps by comparing the in-vessel monitoring requirements and environmental constraints to COTS optical sensor and materials performance specifications. 4. Outline a future research, development, and demonstration (RD&D) program plan that addresses these gaps and develops optical-based I&C systems that enhance the viability of future AdvSMR designs. The development of clean, affordable, safe, and proliferation-resistant nuclear power is a key goal that is documented in the Nuclear Energy Research and Development Roadmap. This roadmap outlines RD&D activities intended to overcome technical, economic, and other barriers, which currently limit advances in nuclear energy. These activities will ensure that nuclear energy remains a viable component to this nation’s energy security