Void Engineering in Silica Glass for Ultralow Optical Scattering Loss

Abstract

Optical losses in silica glass fibers remain a challenge in their applications. The main contributor to optical attenuation is Rayleigh scattering. This review discusses the recent studies and findings on voids in silica glass and their effects on the optical loss. Through experimental studies of pressure-quenching on glass at the melting temperature, void size shrunk, and the optical loss was reduced to approximately half of that of conventional optical fibers at 0.2 GPa. Our modeling results predicted that further reduction was expected, credited to the optimization of the glass network, called topological pruning, under high compressive pressures of up to 4 GPa.

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“…On the other hand, the decrease in Rayleigh scattering can also be attributed to a decrease in the magnitude of density fluctuations in the glass. This work concludes that the suppression of density fluctuations cannot be explained by a simple shrinkage of the entire glass network; instead, the applied pressure must have triggered preferential shrinkage of larger voids, which narrows the void distribution while keeping the SiO 2 tetrahedra intact …”

“…Decreasing the magnitude of density fluctuations, and the resulting Rayleigh scattering, can be achieved by decreasing the void size using a pressurization treatment or lowering the fictive temperature T f through thermal annealing. , Positron annihilation lifetime spectroscopy (introduced in section ) measurements on silica glass reveal that the void radius decreases continuously with increasing applied pressure during compression, as shown in Figure . This work by Ono also measured the Rayleigh scattering intensity using a 90° scattering measurement of compression and varying T f .…”

“…91,94 Positron annihilation lifetime spectroscopy (introduced in section 4.6) measurements on silica glass reveal that the void radius decreases continuously with increasing applied pressure during compression, as shown in Figure 60. 498 This work by Ono 498 also measured the Rayleigh scattering intensity using a 90°s cattering measurement of compression and varying T f . Figure 61 shows the Rayleigh scattering results versus the measured void radius, where the Rayleigh scattering loss is shown to be proportional to void radius for both the compression and varying T f studies.…”

“…This work concludes that the suppression of density fluctuations cannot be explained by a simple shrinkage of the entire glass network; instead, the applied pressure must have triggered preferential shrinkage of larger voids, which narrows the void distribution while keeping the SiO 2 tetrahedra intact. 498 To gain a systematic understanding of the effect of pressure on the silica glass network in terms of homogeneity at the atomistic level, Yang et al 137 used MD (see section 5.1) simulations to examine how the density fluctuations in SiO 2 glass change at various quench pressures P Q , including conditions beyond those achievable in experiments. At lower quench pressures (P Q < 4 GPa), the homogeneity of the silica glass is enhanced from pressurization owing to the reduction of the structural void size in the glass and narrowing of the void size distribution, as illustrated in Figure 62a.…”

“…Third lifetime component, τ 3 , and the corresponding void radius measured using PALS and plotted against the applied pressure. Adapted with permission from ref . Copyright 2021 IEEE.…”