Cladding-pumped bismuth-doped fiber laser

Abstract

For the first time, to the best of the authors’ knowledge, a cladding-pumped bismuth-doped fiber laser (BDFL) is demonstrated. A “home-made” Bi-doped germanosilicate fiber with a 125 µm circular outer cladding made of fused silica and coated by a low refractive index polymer is used as an active medium pumped by commercial multimode laser diodes with a total output power of 25 W at 808 nm. We find that the BDFL with a free-running cavity (when feedback is provided by ≈4% back reflection from two bare right-angle cleaved fiber ends) composed of a 100-m-long bismuth-doped fiber is capable of emitting at a wavelength of 1440 nm. A slope efficiency of 0.5% with respect to the absorbed pump power with a maximum output power of ≈50 mW is obtained in a BDFL with a cavity formed by a highly reflective Bragg grating at 1461 nm and a right-angle cleaved fiber end. The beam quality factors (M2) of the output BDFL in the horizontal and vertical directions are measured to be 1.18 and 1.13, respectively. The processes affecting the efficiency of the BDFLs are also discussed. The possible improvements for the output power scaling and increasing the efficiency of the cladding-pumped BDFLs are proposed.