Polarized Luminescence of Bismuth Active Centers in Phosphosilicate Glasses

The polarization properties of bismuth active centers (BACs) are important for many applications of bismuth-doped fibers, but they are still lacking in study. In this paper, we present the measurements of polarized luminescence (PL) of the BACs formed in a Bi-doped phosphosilicate glass matrix. This research was performed on phosphosilicate fiber preforms used for the drawing of active bismuth-doped fibers for efficient optical amplifiers and lasers. The degree of polarization (DOP) of luminescence of the BACs associated with phosphorus and silica (BAC-P and BAC-Si) is provided and discussed. The DOP of luminescence at the 1320 nm wavelength appeared to be around 19%, 0% and 7.5% for pumps at 1240 nm, 762 nm and 425 nm, respectively. The DOP of PL caused by resonant excitation may be described in terms of a model of a partially anisotropic oscillator with the parameters represented by the principal axes of an ellipsoid. For the resonant excitation at 1240 nm, the ratio of the major principal axis to the minor one turned out to be 5.1 and 3.0 for BAC-P and BAC-Si, respectively.