Cladding-pumped bismuth-doped fiber lasers operating at a wavelength region of 1.4–1.5 µm

This article reports the results on development and study of the output characteristics of bismuth-doped fiber lasers for the near-IR range, which are pumped into a cladding using multimode laser diodes emitting at a wavelength of 808 nm. The active medium of such lasers was bismuth-doped germanosilicate glass fibers with various shapes (circular and square sections) of the inner cladding coated with a polymer having a refractive index of 1.396. On the basis of such fibers, a series of lasers generating radiation in the wavelength range 1.4–1.5 μm was developed, and their spectral and power characteristics were studied. Numerical simulation was also carried out aimed at finding the optimal configuration of such lasers in order to determine the maximum achievable characteristics of these devices. A good agreement between the calculated data and the experimental results has been obtained. As a result, using a bismuth-doped active fiber with a square cross section of ~80 μm and a core diameter of ~11 μm, a fiber laser was created that operated at a wavelength of ~1460 nm, with a slope efficiency of about 5% and a maximum output power of more than 250 mW.