Hafnia-yttria-alumina-silica based optical fibers with diminished mid-IR (>2 µm) loss

Fabrication details and basic characteristics of a set of novel multimode hafnia-yttria-alumina-silicate (HYAS) core-glass based fibers, one of which is co-doped with bismuth (Bi), for the mid-IR (> 2 µm) spectral range are reported. It is demonstrated that fibers of this type possess low fundamental loss in the spectral range beyond 2 µm, lowered by fewer times as compared to conventional silica-based ones, even at moderate (units of mol.%) co-doping with hafnium. This makes them attractive for versatile mid-IR applications. Furthermore, HYAS core-glass fiber co-doped with Bi is revealed to have all the signs of ‘active’ (fluorescing) Bi-related centers, thus being suitable for lasing/amplifying in the near-IR spectral range.