High efficiency low SWaP 793-nm diode lasers for pumping Tm fiber amplifiers

Tm-doped fiber amplifiers are good sources for high energy laser, DIRCM, LIDAR, remote sensing and spectroscopy. The reported Tm-doped amplifiers have efficiencies between 55% to 65%. The diode lasers that are commercially available at 793 nm produce about 35% ex-fiber efficiency. Therefore, the power conversion efficiency of Tm-doped amplifiers is only in the range of 20% - 23% which is less than half that of Yb-doped amplifiers. One straightforward way to improve the e-o power conversion efficiency of Tm-doped fiber amplifiers is to boost the efficiency of 793 nm diode pump from 35% to >55%. This will enable >36% efficient Tm-doped fiber amplifiers. With improvement in epitaxial design, we have demonstrated 64% at 15.5 W producing fiber-coupled package with 400 W in 225-μm/0.22 NA and 54% ex-fiber efficiency in packages with <0.63 kg/kW and <0.49 cc/W specific mass and specific volume, respectively. Further improvement is underway and we will update the latest results.