Improved High-Power Pump Couplers

Recent advances in fiber lasers have shown their potential for power scaling to Directed Energy (DE) levels. Many of the high-power, cladding-pumped, large-mode-area (LMA) fiber systems demonstrated in the laboratory have employed free-space optics to couple the diode-laser pump power into the pump cladding of the fiber. While the approach is useful for power-scaling demonstrations, it is not practical for operational lasers in terms of both reliability and ruggedness. In the work proposed here, we plan to develop and test high-power, all-fiber pump combiners to replace free-space optics for pump transport and allow construction of “all-glass” fiber lasers. The pump couplers must be compatible with polarization-maintaining (PM) LMA fibers used in the beam-combined systems needed to generate DE power levels. Also, given the interest, for some applications, in “eyesafer” DE systems, the couplers should work with not only Yb-doped fibers, but also with Tm-doped, 2-micron-wavelength fibers.