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

Abstract

Among the various advantages of optical fibers (OFs), low attenuation remains one of the most significant features, especially in the second and third telecom windows (around 0.5 and 0.2 dB km À1 ) at 1.31 and 1.55 μm wavelengths. [1] Ongoing studies are underway to limit as much as possible optical losses to overcome the limitations encountered in the design of telecommunication systems, to transfer information over longer distances (trans-oceanic transmission) without repeaters and/or signal regeneration. To date, the aforementioned attenuation limit, typically referring to commercial germanosilicate OFs (as the Corning SMF-28 and its latest enhanced versions) has been passed by a new generation of ultralow loss (ULL) OFs, whose core is composed essentially of pure silica (PSC-pure-silica core) with a low fluorine codoping. [2] With an appropriate and optimized manufacturing process, this new class of waveguides allows reducing the disorder in the microscopic glass structure and, as a result, the Rayleigh scattering losses that mostly explained the attenuation at Telecom windows. Losses as low as 0.14 dB km À1 at 1550 nm are today achieved. [2] When OFs are integrated in harsh environments associated with radiation constraints (e.g., space applications, fusiondevoted facilities, nuclear waste repositories), new sources of optical losses are added to the fiber intrinsic attenuation. In fact, radiations degrade the signal propagation inside the OF by generating radiation-induced point defects in the silica glass matrix. [3] These defects are associated with different absorption bands peaking in the ultraviolet, visible and infrared domains, reducing the silica transparency. This phenomenon, called radiation-induced attenuation (RIA), then logically depends on the OF intrinsic characteristics (chemical composition, geometry, and manufacturing process), on the environmental constraints (nature of particles, dose, dose rate, and temperature) as well as on the fiber profile of use (probing wavelength, signal power, and temperature). Indeed, all these parameters influence the defect generation efficiency or recovery processes through thermal or photo-assisted processes.From literature, it is known that PSC and F-doped OFs are, in terms of RIA, among the most radiation-resistant waveguides. [3,4] However, a new commercial ULL-PSC OF, the Corning Vascade EX1000, was recently found to be characterized by very high radiation-induced losses (up to a few dB m À1 after kGy dose levels) located in the infrared range of the spectrum. These losses were attributed to the presence of two overlapping absorption bands peaked around 1030 nm (%1.2 eV) and 1330 nm (%0.9 eV),

Radiation Monitoring With Radiosensitive Pure-Silica Core Ultralow Loss Optical Fiber

“…This comes at the cost of a lower sensitivity per unit length, but this can be very easily compensated with a longer sample length. The sensitivity is also tunable by adapting the fiber profile of use as seen in a previous work [8]. The results in this article ultimately show the promise of this ULL-PSCF to serve as the active element of a dose rate monitor, e.g.…”

“…The reduction in sensitivity and thus the lower detection capability of a dosimeter like this can be easily compensated with more fiber length, as the results presented in this paper for the IR-RIA were achieved with only 24 cm of fiber. The RIA response to dose rate can also be tuned with the choice of the light source used for the interrogation system, as the PB effect discussed in [8] shows that a stronger injected power can mitigate part of the losses of this optical fiber. The results shown in Fig.…”

“…As the main actors for these transient losses are metastable defects, most of the transient losses are expected to anneal once the irradiation is over, which explains the observed strong recovery. In recent studies, the IR-RIA levels and kinetics of this fiber were also demonstrated to strongly depend on the dose rate and on the injected light power, since this latter can favor a light-assisted recombination phenomenon of the defects, the photo-bleaching [8]. The comparison at different light powers proposed in [8] highlights the complex RIA dose, dose rate and PB dependence for such fiber.…”

“…In recent studies, the IR-RIA levels and kinetics of this fiber were also demonstrated to strongly depend on the dose rate and on the injected light power, since this latter can favor a light-assisted recombination phenomenon of the defects, the photo-bleaching [8]. The comparison at different light powers proposed in [8] highlights the complex RIA dose, dose rate and PB dependence for such fiber. The dependence on the injected light power introduces an interesting tuning possibility for the implementation of this OF as a radiation detector.…”

Pulsed X‐Ray Radiation Response of Ultralow Loss Pure‐Silica‐Core Optical Fibers

“…Moreover, considering the power of the probing energy (of the order of few μW), photo-bleaching phenomena may occur, as already observed in ref. [28], under X-ray steady-state irradiation condition.…”