Distributed detection of hydrogen and deuterium diffusion into a single-mode optical fiber with chirped-pulse phase-sensitive optical time-domain reflectometry

For some infrastructures like oil and gas extraction boreholes or radioactive waste repositories, where distributed optical fiber sensors are employed to grant the safety of the facilities, the presence of gas species such as hydrogen or deuterium is one more relevant parameter to monitor. The possibility of employing the same kind of sensors for this purpose is of special interest, reducing the cost by employing a single interrogator, able to measure more than one parameter by simply employing an adequate sensing fiber. To meet this goal, we present here a sensor based on Chirped Pulse Phase sensitive Optical Time Domain Reflectometry, which is able to detect these species while they diffuse into the silica fiber core. Its ability to measure the induced change of its refractive index with a sensitivity around 10 8 has allowed determining hydrogen concentration in the silica core with precision in the order of 10 3 mol/m3 and spatial resolution ~6 m, while also providing an indirect measurement of the solubility of deuterium in a standard telecom-grade optical fiber.Commission of the European Communities JointMinisterio de Economía y CompetitividadMinisterio de Ciencia, Innovación y UniversidadesComunidad de Madri

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 resistant single-mode fiber with different coatings for sensing in high dose environments

A radiation resistant single-mode optical fiber has been specifically developed for distributed sensing in harsh environments associated with MGy(SiO2) dose radiation. Different types of coating have been used: acrylate, polyimide, aluminum that allow extending the range of accessible temperatures up to 400°C. Various characterizations were performed: radiation inducted attenuation (offline and online), fiber mechanical strength and coating thermal degradation post irradiation. Safe operation is demonstrated for almost all coating types up to the MGy(SiO2) range of cumulated dose

Investigation of Coating Impact on OFDR Optical Remote Fiber-Based Sensors Performances for Their Integration in High Temperature and Radiation Environments

The response of OFDR-based temperature sensors is here investigated in harsh environments (high temperature, high radiation dose) focusing the attention on the impact of the fiber coating on the sensor performances in such environments. Our results demonstrate that the various coating types evolve differently under thermal treatment and/or radiations, resulting in a small (<5%) change in the temperature coefficient of the sensor. We identified a procedure allowing improving the sensor performances in harsh environments. This procedure consists in a pre-thermal treatment of the radiation tolerant fibers at its maximum coating operating temperature. This allows stabilizing the temperature coefficients when the fiber is exposed to the harsh constraints. Finally, we show that radiation does not affect scattering phenomenon, CT coefficients remain identical within 1% fluctuations up to 10 MGy, and that permanent RIA reached values stands for the development of high-spatial resolved distributed temperature for harsh environment associated with high temperature (up to 300 °C) and ionizing radiation up to the MGy dose level

Coating impact and radiation effects on optical frequency domain reflectometry fiber-based temperature sensors

Temperature response of radiation-tolerant OFDR-based sensors is here investigated, with particular attention on the impact of coating on OFS. By performing consecutive thermal treatments we developed a controlled system to evaluate the performances of our distributed temperature sensor and to estimate the radiation impact. We show an important evolution of the temperature coefficient measurements with thermal treatments for non-irradiated fiber and that the amplitude of this change decreases increasing radiation dose. As final results, we demonstrate that sensor performances are improved if we performed a pre-thermal treatment on the fiber-based system permitting to monitor temperature with an error of 0.05°C

Neutron-induced defects in optical fibers

We present a study on 0.8 MeV neutron-induced defects up to fluences of 1017 n/cm² in fluorine doped opticalfibers by using electron paramagnetic resonance, optical absorption and confocal micro-luminescence techniques. Our results allow to address the microscopic mechanisms leading to the generation of Silica-related point-defects such as E’, H(I), POR and NBOH Center

Radiation Vulnerability of Fiber Bragg Gratings in Harsh Environments

The difficulties encountered in the implementation of a temperature or strain sensor based on fiber Bragg grating (FBG) in a harsh radiative environment are introduced. We present the choices made to select both a radiation-resistant fiber in terms of transmission and also the grating inscription conditions necessary to write radiation tolerant FBGs in such fibers with a femtosecond laser. The radiation response of these gratings was also studied under radiation at dose up to 1 MGy. The comparison between Ge-free and Ge-doped fibers was highlighted