Pulsed X‐Ray Radiation Responses of Solarization‐Resistant Optical Fibers

Abstract

The transient radiation‐induced attenuation (RIA) of two different versions of pure‐silica‐core (PSC) multimode optical fibers (so‐called “solarization‐resistant” fibers) exposed to nanosecond 1 MeV X‐ray pulses are investigated. On‐line RIA spectra measurements at both room temperature (RT) and liquid nitrogen temperatures (LNT) in the range 1–3.5 eV are performed. Following the RIA kinetics, the properties of the metastable defects that are bleached just after the pulse are discussed. The spectral decomposition of the RIA is performed using known Gaussian bands associated to point defects absorbing in this spectral range. For both fiber types, the generation and the post‐irradiation kinetics of the self‐trapped holes (STHs) that are the main contributor to the transient RIA are investigated particularly. Moreover, thanks to the measurements performed at low temperatures the complex temperature dependence of the kinetics of self‐trapped holes and some chlorine‐related species is characterized.

Radiation Effects on Pure-Silica Multimode Optical Fibers in the Visible and Near-Infrared Domains: Influence of OH Groups

“…However, to achieve a good quality of the fit, we were obliged to introduce the Gaussian absorption band related to the STH2 point defect. The introduction of this band is well supported by the literature, where it has been found that a higher OH concentration corresponds to a higher STH2 relative contribution [34]. In addition, the inset of Figure 6a reports the same fitting routine but with the NBOHC considered as a single Gaussian absorption band centered around 2 eV.…”

“…where A is the area of the band, E C is the center of the optical absorption band, while the standard deviation σ is related to the Full Width at Half Maximum (FWHM) as FWHM = 2 √ 2 ln 2σ. While to date the decomposition of RIA in the UV-visible range of silica-based materials is rather well known and understood, still a number of issues need to be clarified with regard to certain color centers typically identified in OFs, such as strain-assisted selftrapped holes (s-a STH) [34][35][36]. To the fit purpose, the values used for the E C Gaussians centers and for their FWHMs remain fixed parameters, whereas the amplitude A is left as a free parameter eVolving during the irradiation.…”

“…with regard to certain color centers typically identified in OFs, such as strain-assisted selftrapped holes (s-a STH) [34][35][36]. To the fit purpose, the values used for the Gaussians centers and for their FWHMs remain fixed parameters, whereas the amplitude A is left as a free parameter evolving during the irradiation.…”

Influence of Self‐Trapped Holes on the Responses of Fluorine‐Doped Multimode Optical Fibers Exposed to Low Fluences of Protons

“…Due to the particularities of these defects (see for a review), F‐doped and some pure‐silica‐core fibers that are radiation‐tolerant to high doses (> 100 kGy) can present large Vis/near‐IR RIA levels due to the presence of STHs at lower dose levels. Furthermore, as previous and recent studies show that IR‐absorbing species, tentatively identified as STHs, can also be responsible for the RIA at higher wavelengths (2 nd and 3 rd Telecom windows) in the so‐called radiation hardened optical fibers, the particular impact of these defects for space applications needs to be carefully investigated to avoid underestimation of the fiber degradation for the future space missions.…”

“…Some manufacturing processes allow to simultaneously reduce both chlorine and OH amounts to a few ppm. In this case, several researchers have shown that part of the produced fibers exhibit high RIA levels at lower doses, especially after exposure to a high dose rate and low dose (< 200 Gy) X‐ray pulse or during the first times of steady state γ‐ray irradiation at lower dose rates . Their unexpected behaviors can be explained by room‐temperature unstable defects: the self‐trapped holes (STHs) .…”