Processing and Optical Properties of YAG- and Rare-Earth-Aluminum Oxide-composition Glass Fibers
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Processing and Optical Properties of YAGand Rare-Earth-Aluminum Oxide-composition Glass Fibers Richard Weber, Johan Abadie, Thomas Key, April Hixson, Paul Nordine, Yannick Feillens1, Hiroshi Noguchi1, Jonathan Kurz,1 Brandon Wood,1 Michel Digonnet1, and Martin Fejer1. Containerless Research, Inc., Evanston, IL 60201, U.S.A. 1 Ginzton Laboratory, Stanford University, Stanford, CA 94304, U.S.A. ABSTRACT Rare-earth-aluminum oxide-composition glass fibers 5-50 µm in diameter and containing up to 50 mole % rare-earth oxide were drawn from undercooled liquids 550-650 K below the equilibrium melting point. The fibers have tensile strengths of ~6 GPa, glass transition temperatures of ~1150 K, and infrared transmission up to ~5500 nm. The optical properties of erbium-doped fibers containing up to 12.5 mole % Er2O3 were investigated. The 1/e lifetime of the 4I13/2 excited state was 0.8-7 ms, decreasing with increasing Er concentration. Amplified spontaneous emission measurements indicate extremely broadband spectra, up to 135 nm (3-dB width) in 0.5 mole % fibers. Although this result is encouraging, the gain bandwidth, which has not been measured, is likely narrower. Glass fibers were crystallized by heat treatment under tension at temperatures of 1300-1900 K to form flexible, creep resistant polycrystalline monofilaments with tensile strengths up to 2.4 GPa. INTRODUCTION Glass fibers are of interest in optical transmission, in fiber laser and amplifier device applications [1,2], as reinforcement materials [3], and as precursors for synthesis of crystalline structural fibers [4,5]. Most glass fibers contain silica (SiO2), which provides the network structure responsible for the high melt viscosity required for fiber drawing [6]. In spite of its exceptional processing characteristics, silica has some limitations as a host material for optically active ions [7] and does not provide the high temperature strength and creep resistance needed in structural materials. In optical applications, the limitations of silica-based glasses include: (i) a low solubility of rare-earth elements that leads to “clustering” of the ions even at concentrations as low as a few hundred ppm, and (ii) a high phonon energy, which leads to relatively poor infrared transmission. It also limits the lifetime of excited states and interferes with applications at wavelengths above about 2000 nm. Low rare-earth solubility is common to many of the network glass formers which typically phase separate by rejection of a dopant-rich component. Addition of 10-20 mole % aluminum oxide improves homogeneity in silicate glasses [8,9] but does not significantly affect infrared transmission. Heavy metal fluoride-based glasses have good infrared transmission and higher rare-earth solubilities, but they are mechanically weak, melt easily, tend to crystallize, and are prone to reaction with moisture [1]. In oxide fiber ceramic matrix composites, fibers that are chemically compatible with the matrix, that can withstand high temperature, and provide mechanical and chemical sta
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