Abstract
A major development in telecommunications is due to the Er-doped optical fiber amplifier (EDFA) utilizing the I13/2 → I15/2 emission transition at about 1.54 μm of Er3+ (see e.g. [1] and references therein). Wavelength division multiplexing (WDM), which is based on EDFA, requires that the Er3+ dopants have a broad and flat spectrum, which results in increased transmission capacity of WDM [1]. Recently it was realized that ultra-transparent oxy-fluoride glass-ceramics (GC) can be manufactured, including in fiber form with 100 dB/ km optical loss, see e.g. [2] and references therein. Thus, in addition to the enhanced up-conversion emission capability of rare-earth doped GC [3], potential applications as fiber lasers and optical amplifiers have emerged. In this paper we report the synthesis of Er3+ doped GC, which are ultra-transparent as evidenced by optical transmission spectroscopy and by observation of ultra-low frequency (4 and 7 cm−1) Raman scattering peaks. The chemical composition of our precursor glass (SiO2)(Al2O3)(CdF2)(PbF2)(ZnF2), when undoped, was close to the one reported in [2]. However, in addition, we used Er3+ as a rare-earth dopant (up to 5 mol% of ErF3) and did not use YF3. GC were obtained by heat-treatment of the precursor glass at 25–70 ◦C above the glass transition temperature, Tg, for 3–5 h resulting in typically about 2–12 nm size β-PbF2 crystals [4] hosting Er3+ dopants. Intensity, width and Stark-splitting of emission (I13/2 → I15/2 transition) and absorption (I15/2 → I13/2 transition) spectra of Er3+-dopants at 1.5 μm changed with the size of nano-crystals. In particular, we could obtain the broadest and flattest emission spectrum of Er3+ for the I13/2 → I15/2 transition to date. We also reached the largest wavelength divergence between the maximum of emission and absorption spectra for I13/2 ↔ I15/2 transitions to date, which is of primary importance for reduction of self-absorption and respective noise in the EDFA. Differential thermal analysis (DTA) of our precursor doped and undoped glasses indicated that the
Published Version
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