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The cladding-pumping scheme has made the power scalability of rare-earth-doped fiber lasers up to record levels possible by distributing the pump absorption along much longer fiber lengths. However, in addition to increasing the fiber cost and the cavity losses, a longer cavity length leads to enhanced detrimental nonlinear effects such as stimulated Raman scattering. As a way to reduce the required length of such lasers, we propose here an all-fiber laser architecture that makes use of a femtosecond-written chirped inner-cladding Bragg grating (ICBG) as a residual pump reflector. We report a 73% reflectivity of the pump power propagating in the highly multimode 125 μm-diameter inner cladding of the fiber made out of pure silica. This component was inscribed by using 400 nm femtosecond pulses and the phase-mask technique. Such a reflectivity was reached by optimizing the chirp of the grating and by inserting the fiber inside a hollow capillary with an outside diameter of 1 mm during the inscription. The latter reduces greatly the impact of the fiber’s curvature on the refraction of the writing beam. A larger writing area and consequently a stronger reflectivity could therefore be reached. The presence of this component at the output of a 21 m long erbium-doped silica fiber laser operating at 1.6 μm increased its slope efficiency from 20.5 to 25.1 % with respect to the injected pump power and increased its output from 22.8 to 29 W at 115 W of pump power.
Lauris Talbot,Louis-Charles Michaud,Vincent Boulanger,Pascal Paradis, andMartin Bernier
"Inner-cladding pump reflector based on chirped volume Bragg gratings", Proc. SPIE 11261, Components and Packaging for Laser Systems VI, 112610R (21 February 2020); https://doi.org/10.1117/12.2546707
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Lauris Talbot, Louis-Charles Michaud, Vincent Boulanger, Pascal Paradis, Martin Bernier, "Inner-cladding pump reflector based on chirped volume Bragg gratings," Proc. SPIE 11261, Components and Packaging for Laser Systems VI, 112610R (21 February 2020); https://doi.org/10.1117/12.2546707