Pump-gain integrated functional laser fiber towards 10 kW-level high-power applications

To incorporate sufficient pump energy from multi-hundred watt-level 976 nm commercial laser diodes, a new kind of (8  +  1)-type pump-gain integrated functional laser ((8  +  1)-PIFL) fiber was fabricated by our newly optimized special fiber assembly and coating techniques for the first time. This (8  +  1)-PIFL fiber allowed for 10.66 kW aggregated pump power at 976 nm from six counter-pump ports in a master oscillator power amplifier laser setup and stably presented 8.72 kW laser output at 1079.4 nm with a high optical-to-optical efficiency of 81.0%. This is the highest power of the fiber amplifiers pumped by commercial laser diodes that has been reported so far, and only limited by the available pump power. Up to this power level, pure output spectrum with narrow 3 dB bandwidth Δλ _{3 dB} of 2.76 nm and without any sign of stimulated Raman scattering and amplified spontaneous emission was obtained. Neither roll over of output power nor obvious thermal issue was observed with increased pump power, indirectly justifying strong photodarkening and transverse mode instability suppression. With another ten pump ports to collect more pump power, a further power scaling towards 10 kW or above can be expected. (letter)