Configurational Entropy Engineering of Bi‑Doped Glass Fiber Enabling Ultrabroadband Emission

ABSTRACT Near‐infrared (NIR) broadband amplification and lasers are pivotal for high‐capacity optical communications and gas detection, yet their advancement is restricted by the performance limits of current gain materials. Bismuth (Bi)‐doped silica, the most promising candidate for the L‐band and beyond, is fundamentally hindered by the thermodynamic aggregation of inactive bismuth ions. These ions form detrimental atomic clusters that act as quenching centers, inducing high unsaturable loss (UL). Here, configurational entropy engineering is reported to overcome this limitation in Bi‐doped silica fiber. Distinct from compositional high‐entropy alloys, this approach utilizes kinetic manipulation to trap the glass network in a high‐energy, disordered configurational state. This effectively suppresses the growth of element aggregation domains, preventing energy dissipation from the bismuth active center. Consequently, the fabricated entropy‐engineered Bi‐doped fiber exhibits a dramatic reduction in background loss (from 400 to 210 dB/km) and suppressed UL (from 33.5% to 25.8%). Leveraging this high‐performance medium, broadband amplification with >20 dB net gain is demonstrated across the 1680–1750 nm range, alongside tunable laser output at 1650 and 1720 nm. These findings establish configurational entropy engineering as a general thermodynamic and kinetic strategy for manipulating the structure of amorphous materials, unlocking the potential of amorphous functional materials.