MgO-modified glass network enabling enhanced NIR photoemission in highly Bi-doped phosphate glasses and fibers for broadband fiber amplifiers

Bismuth (Bi)-doped glasses have emerged as promising broadband gain media due to their exceptional ultra-broadband optical response spanning the low-loss transmission window of silica fibers. In this study, phosphate glass matrix capable of accommodating high Bi doping levels was selected, and a glass network engineering strategy was proposed to enhance near-infrared (NIR) luminescence via controlled incorporation of MgO. Owing to its depolymerizing effect and high cation field strength, MgO effectively modulates the glass structure, facilitating the homogeneous dispersion and activation of Bi luminescent centers. The resulting glass exhibits a 4.2-fold enhancement in broadband near-infrared emission. Notably, this composition can be readily drawn into optical fibers via the rod-in-tube technique. The fabricated fibers demonstrate clear broadband On-off gain in the O-band, achieving a maximum gain of 14 dB at 1330 nm. These findings underscore the potential of highly Bi-doped phosphate glass fibers as gain media for next-generation broadband optical amplifiers.