Fabrication and spectroscopic properties of Bi-doped glass and fiber based on modified sol-gel method

Bismuth (Bi)-doped glasses and fibers are the most promising gain media to solve the capacity crisis in optical communication systems due to their broadband near-infrared luminescence covering O-U bands. To date, only Bi-doped fibers prepared by the modified chemical vapor deposition method have been well-developed, providing net gain performance. However, the crucial technological challenges have not been fully resolved, such as the high fabrication cost and the balance among unsaturated loss, doping concentration, and unit gain. In this work, we propose a modified sol-gel method for low temperature synthesis of highly homogeneous Bi-doped glasses. By using HF and HCl as the coordinated catalysis, a series of uniform Bi-doped glasses with low OH- content (similar to 4.5 ppm) was prepared at 1300 C-degrees within 3.5 days. The Bi-doped glasses present broadband luminescence covering the O-U band, attributed to the superposition of multiple bismuth active centers (BACs), and provide relatively high fluorescence lifetimes (657-735 mu s). On this basis, Bi-doped GeO2-SiO2 fibers (BGSFs) were prepared via the rod-in-tube method. Utilizing a 40 m BGSF as the gain media, an amplifier was constructed using backward pumping. As the pump power of 808 nm laser diode reached 100 mW, positive gain was obtained in the range of 1200-1600 nm with a maximum on-off gain of 0.9 dB/m at 1395 nm. These results suggest that our modified sol-gel method holds promising potential for flexible fabrication of Bi-doped glasses and fibers.