Effect of Drawing Conditions on Optical Properties of Bismuth-Doped High-GeO2–SiO2 Fibers

The effect of drawing conditions on the optical properties of the bismuth-doped high-germania-glass core fibers has been studied. It was found that the gain characteristics of these fibers become better with the increase of the drawing speed from 10 to 100 m/min. The small-signal absorption spectra of the Bi-doped fibers obtained at drawing speeds lower than 1 m/min are characterized by a high level of the unsaturable loss and the presence of an unstructured band situated within a wavelength region of 1100 - 1250 nm. The variation of drawing temperature ranging from 1770 to 1830 °C almost did not affect the optical properties of the fibers studied. It was shown that an optimization of the drawing parameters can significantly increase the performance of the developed bismuth-doped fiber lasers.