Alkali niobium borogermanosilicate optical fiber derived via the molten core method [Invited]

This is the authors' abstract. We don't add key points for this paper.

Herein, multicomponent glass optical fibers are produced using the molten core fiber fabrication method. A pre-melted glass of 30 K 2 O-20 Nb 2 O 5 -50 GeO 2 is used as a starting core material along with a low-alkali borosilicate (Duran) glass cladding. Some of the cladding dissolves into the core during the draw, and the final composition of the fiber core is a complex alkali borogermanosilicate with a little over 10 mol% Nb 2 O 5 . Although the germanium and niobium stay well confined within the core, potassium ions are observed to diffuse 10-15 μ m beyond the core into the borosilicate cladding. The fibers have a large numerical aperture greater than 0.6. Yb-doped versions were fabricated to gauge feasibility of this platform for fiber gain media. Forward amplified spontaneous emission was observed with no signal; then, a 0.49 dB/cm signal amplification at 1026 nm was achieved. A parasitic background absorption coefficient value of 0.7 dB/cm at 1080 nm was measured. The phonon energy of the base niobium germanate and a simulated fiber core glass was measured using Eu 3+ doped bulk glasses. The silicon and boron intrusion into the core does create high energy phonons around the rare-earth ions, but the niobium and/or germanium do appear to maintain strong influence over the excitation and the emission spectra in the Duran-diluted core glass composition.