Architecture for high-power thulium-doped fiber amplifier

A method comprising:

• generating pumplight using each of multiple thulium-doped pumping fiber lasers;
• generating a seed signal using a seed laser source;
• receiving the pumplight from the multiple thulium-doped pumping fiber lasers and the seed signal from the seed laser source at a thulium-doped pumped fiber laser, wherein:
• receiving the pumplight and the seed signal at the thulium-doped pumped fiber laser comprises receiving the pumplight from the multiple thulium-doped pumping fiber lasers and the seed signal from the seed laser source at a signal combiner comprising multiple pigtail fibers;
• each of the multiple pigtail fibers comprises a cladding and a core, the cladding of each pigtail fiber longitudinally down-tapered such that a diameter of the cladding of the pigtail fiber decreases along at least a portion of a length of the pigtail fiber while a diameter of the core remains substantially constant;
• and
• an overall combined first cross-sectional dimension of the multiple pigtail fibers substantially matches a second cross-sectional dimension of a fiber gain medium of the thulium-doped pumped fiber laser;
• and
• amplifying the seed signal based on the pumplight using the thulium-doped pumped fiber laser;
• wherein the multiple thulium-doped pumping fiber lasers forward-pump the thulium-doped pumped fiber laser so that an output from the thulium-doped pumped fiber laser has a longer wavelength than the pumplight;
• wherein the fiber gain medium comprises a core doped with thulium and a cladding, the fiber gain medium being longitudinally up-tapered such that a diameter of the core and a diameter of the cladding of the fiber gain medium increase along at least a portion of a length of the fiber gain medium;
• wherein the seed signal is provided to the core of the fiber gain medium by the signal combiner and the pumplight is provided to the cladding of the fiber gain medium by the signal combiner;
• and
• wherein the signal combiner supports tandem pumping of the thulium-doped pumped fiber laser using the multiple thulium-doped pumping fiber lasers while transporting predominately single-transverse-mode beams.

A system comprising:

• multiple thulium-doped pumping fiber lasers each configured to generate pumplight;
• a seed laser source configured to generate a seed signal;
• a thulium-doped pumped fiber laser configured to receive the pumplight from the multiple thulium-doped pumping fiber lasers and the seed signal from the seed laser source, the thulium-doped pumped fiber laser also configured to amplify the seed signal using the pumplight and generate an output beam having an average power level of at least 1 kW, wherein the thulium-doped pumped fiber laser comprises:
• a signal combiner comprising multiple pigtail fibers configured to receive the pumplight from the multiple thulium-doped pumping fiber lasers and the seed signal from the seed laser source, wherein each of the multiple pigtail fibers comprises a cladding and a core, the cladding of each pigtail fiber longitudinally down-tapered such that a diameter of the cladding decreases along at least a portion of a length of the pigtail fiber while a diameter of the core remains substantially constant, wherein the signal combiner is configured to support tandem pumping of the thulium-doped pumped fiber laser using the multiple thulium-doped pumping fiber lasers while transporting predominately single-transverse-mode beams;
• and
• a fiber gain medium connected to an output of the signal combiner, the fiber gain medium comprising a core configured to receive the seed signal from the signal combiner and a cladding configured to receive the pumplight from the signal combiner;
• wherein an overall combined first cross-sectional dimension of the multiple pigtail fibers substantially matches a second cross-sectional dimension of the fiber gain medium;
• wherein the multiple thulium-doped pumping fiber lasers are configured to forward-pump the thulium-doped pumped fiber laser so that an output from the thulium-doped pumped fiber laser has a longer wavelength than the pumplight;
• and
• wherein the core of the fiber gain medium is doped with thulium, the fiber gain medium being longitudinally up-tapered such that a diameter of the core and a diameter of the cladding of the fiber gain medium increase along at least a portion of a length of the fiber gain medium.