Power Scaling of Ytterbium-doped Fiber Superfluorescent Sources

Power scaling of ytterbium-doped fiber superfluorescent sources based on single-stage and two-stage cladding-pumped fiber configurations is reported. For the single-stage configuration, a novel fiber-end termination scheme was employed to suppress laser oscillation in combination with a simple all-fiber scheme for achieving a predominantly single-ended output. The fiber was cladding-pumped by a diode stack at 976 nm and yielded $\sim 62$ W of single-ended amplified spontaneous emission output for 119 W of launched pump power, limited by the onset of parasitic lasing. At pump powers in excess of 40 W, the slope efficiency with respect to the launched pump power was 67%. The emission spectrum spanned the wavelength range from 1030 to 1100 nm and the bandwidth (FWHM) was 12 nm. Scaling to higher power levels was demonstrated using a two-stage cladding-pumped fiber configuration comprising of a low-power fiber superfluorescent seed source and a high-power amplifier. The two-stage source yielded 122 W of amplified spontaneous emission output (limited by available pump power) in a beam with $M^{2}\approx 2.1$. The slope efficiency for the amplifier with respect to the launched pump power was 77%. The prospects for further improvement in performance and output power are considered.