Faraday rotation and photoluminescence in heavily Tb3+-doped GeO2-B2O3-Al2O3-Ga2O3 glasses for fiber-integrated magneto-optics

Abstract

We report on the magneto-optical (MO) properties of heavily Tb3+ -doped GeO2-B2O3-Al2O3-Ga2O3 glasses towards fiber-integrated paramagnetic MO devices. For a Tb3+ ion concentration of up to 9.7 × 1021 cm-3, the reported glass exhibits an absolute negative Faraday rotation of ∼120rad/T/m at 632.8nm. The optimum spectral ratio between Verdet constant and light transmittance over the spectral window of 400-1500nm is found for a Tb3+ concentration of ∼6.5 × 1021 cm-3. For this glass, the crystallization stability, expressed as the difference between glass transition temperature and onset temperature of melt crystallization exceeds 100K, which is a prerequisite for fiber drawing. In addition, a high activation energy of crystallization is achieved at this composition. Optical absorption occurs in the NUV and blue spectral region, accompanied by Tb3+ photoluminescence. In the heavily doped materials, a UV/blue-to-green photo-conversion gain of ∼43% is achieved. The lifetime of photoluminescence is ∼2.2ms at a stimulated emission cross-section Ï em of ∼1.1 × 1021 cm2 for ∼ 5.0 × 1021 cm-3 Tb3+. This results in an optical gain parameter σem ∗τ, of ∼2.5 × 1024 cm2 s, what could be of interest for implementation of a Tb3+ fiber laser.