Preparation and spectral characteristics of Bi-doped double cladding fiber

Bi-doped double cladding fiber preform is prepared by modified chemical vapor deposition and solution doping process. The absorption spectrum of preform and the near-infrared (NIR) luminescence spectrum of fiber are experimentally investigated. The luminescence spectrum of the fiber shows a peak emission band at 1140 nm with a full-width at half-maximum (FWHM) of 130 nm under 976 nm LD exciting. Under 808 or 793 nm LD exciting, an ultra-broad NIR emission with an FWHM of more than 250 nm is observed in the Bi-doped fiber, and the range of luminescence spectrum is from 1000 to 1700 nm. After the heat treatment of the Bi-doped fiber preform slice under 900 C for 1 h, under 808 nm LD exciting, the fluorescence intensity is about 4 times higher than that of the perform slice without heat treatment. The results indicate that the Bi-doped double cladding fiber is a promising gain medium used for ultrashort fiber lasers and tunable fiber lasers.