Engineering silica optical fibers by nanoparticle doping
is a promising
technology that allows the introduction of new functionalities and
extends their applicable fields. However, the knowledge gap about
the impact of the extreme fabrication temperatures on the nanoparticle
features prevents field progress. Herein, we demonstrate that the
particularities of fiber fabrication, such as fast-heating rates and
quenching heat treatments, can be leveraged to explore unlikely phenomena
at the nanoscale under standard laboratory conditions. Tetragonal
cubic-shaped and monoclinic rod-shaped YPO4 nanocrystals
are in situ nucleated in a silica-based fiber core
glass, slightly modified with Ge and P, which shows for the first
time, the possibility of doping optical fibers with this type of nanostructures,
in terms of shape, composition, and structure of the nanocrystals.
Structural and anisotropic differences allow engineering differently
their shape and composition in the fiber core by tailoring the drawing
temperature, as revealed by a thorough study consisting of scanning
electron microscopy (SEM), high-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM), electron energy loss
spectroscopy (EELS), and high-resolution transmission electron microscopy
(HRTEM). This work demonstrates, for the first time, the possibility
of doping optical fibers fabricated by modified chemical vapor deposition
(MCVD) with anisotropic nanostructures, as well as the stability of
the monoclinic YPO4 phase. These findings open up new avenues
to study shape-dependent properties of rare-earth orthophosphate (REPO4) nanostructures in optical fibers which will allow incorporating
unprecedented functionalities and will have an impact in several fields
of application, such as fiber lasers and optical fiber amplifiers,
among others.
Rayleigh scattering enhanced nanoparticles-doped optical fibers are highly promising for distributed sensing applications, however, the high optical losses induced by that scattering enhancement restrict considerably their sensing distance to few meters. Fabrication of long-range distributed optical fiber sensors based on this technology remains a major challenge in optical fiber community. In this work, it is reported the fabrication of low-loss Ca-based nanoparticles doped silica fibers with tunable Rayleigh scattering for long-range distributed sensing. This is enabled by tailoring nanoparticle features such as particle distribution size, morphology and density in the core of optical fibers through preform and fiber fabrication process. Consequently, fibers with tunable enhanced backscattering in the range 25.9–44.9 dB, with respect to a SMF-28 fiber, are attained along with the lowest two-way optical losses, 0.1–8.7 dB/m, reported so far for Rayleigh scattering enhanced nanoparticles-doped optical fibers. Therefore, the suitability of Ca-based nanoparticles-doped optical fibers for distributed sensing over longer distances, from 5 m to more than 200 m, becomes possible. This study opens a new path for future works in the field of distributed sensing, since these findings may be applied to other nanoparticles-doped optical fibers, allowing the tailoring of nanoparticle properties, which broadens future potential applications of this technology.
A structural and compositional characterization of fast‐sintered Na‐rich feldspar is carried out by means of the confocal Raman microscopy. The analysis of the main Raman modes (νa = 512 cm−1 and νb = 480 cm−1) determines that feldspar crystallizations correspond to a sodic‐plagioclase group, with an anorthite proportion estimated of 25–45%. The presence of alkali and alkaline earth in the formulated composition leads to albite type feldspar with slightly Al–Si disordered distribution in tetrahedral sites. Raman shift of the main Raman mode νa reveals differences in crystal stresses between nanograins and micrograins. The Rayleigh light‐scattering microscopy shows up lamellar domains of ~2–3 μm resulting from unmixing by spinodal decomposition. Combining Raman spectroscopy and X‐ray diffraction versus temperature significant structural changes are confirmed. This structural change correlates with a stress release and thermally activated conduction. This research gives fundamental understanding of structure, chemical composition, and micro‐nanostructure of engineered glass–ceramics, which may allow tailoring them: for example, to modulate spinodal decomposition regions and interphases.
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