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

摘要

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 ~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 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 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 Tb3+ photoluminescence. In the heavily doped materials, a UV/blue-to-green photo-conversion gain of ~43% is achieved. The lifetime of photoluminescence is ~2.2?ms at a stimulated emission cross-section σ _em of ~1.1 × 10?21?cm2 for ~ 5.0 × 1021?cm?3 Tb3+. This results in an optical gain parameter σ _em* τ of ~2.5 × 10?24?cm2s, what could be of interest for implementation of a Tb3+ fiber laser.