Faraday rotation and photoluminescence in heavily Tb(3+)-doped GeO(2)-B(2)O(3)-Al(2)O(3)-Ga(2)O(3) glasses for fiber-integrated magneto-optics

We report on the magneto-optical (MO) properties of heavily Tb(3+)-doped GeO(2)-B(2)O(3)-Al(2)O(3)-Ga(2)O(3) glasses towards fiber-integrated paramagnetic MO devices. For a Tb(3+) ion concentration of up to 9.7 × 10(21) cm(−3), the reported glass exhibits an absolute negative Faraday rotation of ~120 rad/T/m at 632.8 nm. The optimum spectral ratio between Verdet constant and light transmittance over the spectral window of 400–1500 nm is found for a Tb(3+) concentration of ~6.5 × 10(21) cm(−3). For this glass, the crystallization stability, expressed as the difference between glass transition temperature and onset temperature of melt crystallization exceeds 100 K, 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 Tb(3+) photoluminescence. In the heavily doped materials, a UV/blue-to-green photo-conversion gain of ~43% is achieved. The lifetime of photoluminescence is ~2.2 ms at a stimulated emission cross-section σ(em) of ~1.1 × 10(−21) cm(2) for ~ 5.0 × 10(21) cm(−3) Tb(3+). This results in an optical gain parameter σ(em)*τ of ~2.5 × 10(−24) cm(2)s, what could be of interest for implementation of a Tb(3+) fiber laser.