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

Bismuth (Bi)-doped glasses and fibers have been regarded as the most promising gain medium for broadband optical amplifiers. However, the Bi-doped glasses and fibers still meet low gain and insufficient efficiency due to the volatilization, uneven distribution, and uncontrollable valence states of Bi ions in the high-temperature (~2000°C) modified chemical vapor deposition process. Herein, we modified the sol-gel method and synthesized uniform Bi-doped glass with a doping concentration of 0.5wt.% Bi ions at 1300°C. Employing an 808nm LD as a pump, the Bi-doped glass showed a broadband fluorescence with the emission peak at 1413nm and a FWHM of 112nm. On this basis, the Bi-doped fibers were fabricated by rod-in-tube method. The background loss was measured to be 0.27dB/m at 1550nm. A 40m Bi-doped fiber amplifier was constructed by 808nm backward pumping. The maximum on-off gain at 1395nm reached 36dB, heralding the potential of our modified sol-gel method for high-gain Bi-doped glass and fiber fabrication.