Terbium-containing aluminoborate glasses and fibers for magneto-optical applications

New glass compositions for magneto-optical devices have been synthesized and characterized. In this work, alumino-borate glasses containing up to 13 mol % of Tb 4 O 7 have been obtained. While the glass transition temperatures do not change as a function of the increasing rare earth content, the thermal stability parameter (Tx-Tg) reaches 259 o C for the most stable composition. The observed increasing in density and refractive index are attributed to the polarizability of the Terbium electron cloud and the generation of non-bridging oxygens (NBOs). Both Raman and DSC data indicate a progressive structural modification of the glass matrix. While the presence of Tb is fundamental for the glass formation, there is a competition between the network depolymerization caused by NBOs and the compensation caused by the strong electrostatic attraction of the ions, which stabilizes the structure and sustains the glass transition. The glasses exhibit a broad optical window extending from 0.5 μm to 1.5 μm, limited by the presence of 4f-4f absorption bands of Tb 3+ ions. The magneto-optical constant (V b ) increases with the terbium content reaching -110 rad T -1 m -1 for the sample containing 13 mol% of Tb 4 O 7 at 633 nm. Due to thermal stability of the glasses, it was possible to obtain a multimode core-cladding optical fiber using the rod-in-tube technique. The preliminary characterizations of the fiber, including optical losses, are reported and discussed.