Extreme Radiation Sensitivity of Ultra-Low Loss Pure-Silica-Core Optical Fibers at Low Dose Levels and Infrared Wavelengths

Abstract

We report here the response of a commercial ultra-low loss (ULL) single-mode (SM) pure silica core (PSC) fiber, the Vascade EX1000 fiber from Corning, associated with 0.16 dB/km losses at 1.55 µm to 40 keV X-rays at room temperature. Today, among all fiber types, the PSC or F-doped ones have been demonstrated to be the most tolerant to the radiation induced attenuation (RIA) phenomenon and are usually used to design radiation-hardened data links or fiber-based point or distributed sensors. The here investigated ULL-PSC showed, instead, surprisingly high RIA levels of ~3000 dB/km at 1310 nm and ~2000 dB/km at 1550 nm at a limited dose of 2 kGy(SiO2), exceeding the RIA measured in the P-doped SM fibers used for dosimetry for doses of ~500 Gy. Moreover, its RIA increased as a function of the dose with a saturation tendency at larger doses and quickly recovered after irradiation. Our study on the silica structure suggests that the very specific manufacturing process of the ULL-PSC fibers applied to reduce their intrinsic attenuation makes them highly vulnerable to radiations even at low doses. From the application point of view, this fiber cannot be used for data transfer or sensing in harsh environments, except as a very efficient radiation detector or beam monitor.

Photobleaching Effect on the Radiation‐Induced Attenuation of an Ultralow Loss Optical Fiber at Telecommunication Wavelengths

“…For all the investigated power levels, after the irradiation starts, RIA kinetics quickly grow as the dose increases up to %3.3 kGy, where they reach a peak, and then begin to decrease. This behavior, typical of strain-assisted STH (s-a STH) bands at 660 and 760 nm, [15,16] points out an extreme sensitivity to radiations of this OFs class, allowing the RIA to reach magnitudes beyond those already achieved in literature by typical radiation-sensitive OFs, [5] as phosphosilicate and aluminosilicate OFs typically used for dosimetry applications, [17][18][19] usually characterized by a RIA of the order of %10-200 dB km À1 for accumulated doses of about hundreds of Gy.…”

“…Different pristine samples of the fiber under test (FUT), each about 1 m long and whose chemical composition and attenuation spectra can be found in ref. [5], were simultaneously irradiated being coiled into monolayer circles with a %6 cm radius and centered to the X-ray beam, in such a way to be homogeneously exposed. The online RIA was investigated at 1310 and 1550 nm with different power levels of the probing signal, ranging from 100 nW to %1 mW.…”

“…presumably linked to the generation of self-trapped holes (STHs). [5,6] The reason for this increased radiation sensitivity of this type of OFs is still uncertain. As already pointed out in ref.…”

“…As already pointed out in ref. [5], a reasonable hypothesis may lie in the introduction of very low quantity (below the energy dispersive X-ray analysis detection limit) of alkali metals as codopants, to decrease the fictive temperature of the glass and, thereby, the 1550 nm optical losses.…”

Near‐IR Radiation‐Induced Attenuation of Aluminosilicate Optical Fibers

“…[ 1–4 ] Most of the past efforts focused on the identification of the most tolerant fiber compositions against the observed fiber darkening (radiation‐induced attenuation [RIA]) to build radiation tolerant or radiation‐hardened data links or sensors. [ 5–7 ] However, today, it is well known that some of the fiber compositions render the glass very sensitive to radiations, allowing its use as a radiation detector [ 8,9 ] or even as a dosimeter when this high sensitivity is combined with no RIA dependence on the other irradiation parameters: dose rate and temperature. The most studied radiation sensitive optical fibers are the ones co‐doped with phosphorus that present very interesting features for dosimetry applications.…”