Watt-level cladding-pumped bismuth-doped fiber laser operating near 1.31 μ m

We report, to the best of our knowledge, the first CW bismuth-doped fiber laser operating at around 1.31 mu m with an output power of >1 W utilizing a cladding-pumping configuration with multimode semiconductor laser diodes emitting at a wavelength of 793 nm. The Bi-doped fiber (BDF) serving as an active medium of the laser was based on a pedestal-index design, where P2O5-SiO2 glass core surrounded by P-doped cladding. The BDF construction offers advanced gain characteristics and an increased mode size (similar to 13 mu m). The fiber preform was fabricated by the conventional modified chemical vapor deposition (MCVD) method combined with all gas-phase doping technique. The BDF with low-index polymer coating provided sufficient cladding peak absorption at 750 nm belonging to bismuth active centers associated with phosphorus atoms (BACs-P) that allowed to develop a continuous-wave laser with a linear cavity configuration and enable a maximum slope efficiency of similar to 4% with respect to the absorbed pump power. In addition, near-field spatial intensity distribution of optical beam has good quality (M-2<1.13) and close to Gaussian mode profile in x and y directions. The perspectives for optimization of BDF design and laser system configurations based on such fibers for further power scaling are discussed.