The work could guide the development of heavily doped Bi active fibers, which exhibit great potential for application in the next-generation optical amplifiers. Bi-dopants exhibit multi-chemical states and can transform into a deactivated state when the bulk is drawn into the fiber at high temperature, which limits the development of high-performance Bi-active fibers. "From the viewpoint of thermodynamics, the deactivation of Bi dopants cannot be prevented during the fiber drawing process, since the Bi-active center is not the thermodynamics stable at such temperatures," said Shifeng Zhou, corresponding author on the paper and professor at the South China University of Technology. "Thus, a kinetics strategy must be considered to suppress the transformation of the Bi-active center to an inactive state during the fiber drawing process. Controlling the temperature-dependent viscosity of the materials might be one of the effective kinetic approaches to suppress the deactivation of the Bi center." Bi-active fiber is now regarded as the most promising candidate for next-generation broadband optical amplifiers in high-capacity telecommunication systems. However, due to the easy deactivation of bi-centers, fabricating Bi-active centers remains a challenge. Nowadays, only a few groups worldwide can fabricate the Bi-active fiber using the modified chemical vapor deposition (MCVD) method. The complicated chemical vapor deposition (CVD) technique not only creates a significant technique barrier for the fabrication of Bi-active fiber but also limits the available glass fiber system and the doping concentration of Bi. The evolution of Bi dopant at different temperatures in glass systems with different viscous characteristics is systematically studied. It is found that the systems with a faster viscosity changing rate in the temperature range from 1.0 to 1.6 < I>Tg exhibit better anti-deactivation ability for Bi dopants. Based... |