We report on an ytterbium-free, erbium-doped single-mode all-fiber laser reaching a record output power of 107 W at 1598 nm, with a slope efficiency of 38.6% according to the absorbed pump power at 981 nm. The erbium-doped gain fiber, co-doped with cerium, aluminum, and phosphorus, was fabricated in-house with adjusted doping concentrations to reduce erbium ions clustering, thereby increasing efficiency while keeping the numerical aperture low to ensure a single-mode laser operation. The addition of cerium co-dopant in the core glass of an erbium system is used for the first time, to the best of our knowledge, in order to adjust the fiber’s numerical aperture without increasing the erbium concentration. Numerical modeling, validated by the experimental results, demonstrates that adding aluminum and phosphorus at high concentration mitigates erbium ions clustering, with an estimated erbium paired ions of only 5.0% in the reported gain fiber.

A new, to the best of our knowledge, method for inscribing fiber Bragg gratings inside a fiber’s cladding based on the motorized rotation of the fiber is reported. By minimizing the aberrations induced by the fiber curvature on the femtosecond writing beam, this technique based on a phase mask allows to cover large transverse areas of a standard high-power fiber’s cladding. With this approach, a first-order Bragg grating was inscribed in the pure-silica inner cladding of a 20/400-µm fiber. It was then implemented as a pump reflector at the end of a 36-m-long Yb-doped fiber laser reaching 600 W of output power, confirming the power handling capabilities of such a component. Comparison of the laser performances with and without the pump reflector showcases its great potential for increasing pump absorption inside cladding-pumped fiber lasers, which paves the way for significantly reducing their active fiber length.

We report on the femtosecond inscription of multimode Bragg gratings inside large-core fibers and fibers' cladding. They are used as residual pump reflectors for cladding-pumped fiber lasers and as spectral stabilizers for high-power laser diodes.

Efficient wavelength stabilization of an off-the-shelf high-power laser diode operating at 976 nm is demonstrated by using a highly multimode fiber Bragg grating (FBG). This first-order grating is inscribed with 400 nm femtosecond pulses inside the 200 µm/0.22 NA pure silica core of the diode’s fiber pigtail. The FBG reduces the wavelength thermal drift of the 70 W diode by a factor of 12 while also reducing its emission linewidth by a factor of 2.8. At maximum output power, a power penalty of only 6% is measured. This promising approach offers a robust and compact scheme to stabilize the spectrum of high-power laser diodes that are particularly useful for fiber-laser pumping.