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Yb-doped fiber laser and amplifiers are strong contenders as combinable sources used in power-scalable spectral beam combined and coherent beam combined High Energy Laser (HEL) systems. Power levels well beyond 300kW is anticipated for HEL systems for DoD applications. Pumping these fiber amplifiers at 976 nm has become an imperative. Furthermore, technology demonstrations of HELs have resorted to slow turn-on time. This needs to change for fieldable HEL systems. The need for an “instant-on” of HEL beam on demand cannot be over emphasized. Pumping a fiber laser/amplifier on this strong absorption peak also leads to a reduction in cost due to the shorter fiber and higher threshold power for nonlinear effects such as Stimulated Raman Scattering (SRS) and Stimulated Brillouin Scattering (SBS). But the absorption band of Yb-doped fiber is very narrow (<5 nm) and very sharp drop-off occurs around the peak near 976 nm. nLIGHT has developed high-efficiency, OSL technology by incorporating into the semiconductor laser chip, a wavelength-selective element which forces the laser to operate only at the desired wavelength over all operating current (output power) and a wide range of operating temperature. Although wavelength-stabilization in semiconductor laser pumps have been done in the past using external Volume Bragg Gratings (VBGs) they are not as efficient for HEL application. Furthermore, VBG adds cost, mass and volume to the pump package. We have demonstrated nearly penalty-free wavelength-stabilized high power, high efficiency chips. These chips can be readily introduced into a fiber-coupled package without needing any modification to the opto-mechanical design of the package – a drop-in replacement to the current pump packages. We have packaged them in a low SWaP fiber-coupled packages to produce ⪆550W with 55% at 25C and ⪆530W with ⪆52% at 50C using wavelength-locked diodes with a narrow spectral bandwidth ⪅0.4 nm at FWHM. The center wavelength shifts at 0.065 nm/K. The full power-in-the-band (within ±2nm of Yb-absorption peak) can be achieved in millisecond time scale enabling instant-on capability for HEL systems. Wavelength-stabilized pumps will be an imperative in fielded HEL systems because these pumps will enable high efficiency, high fiber amplifier channel power, low SWAP, low cost and “instant on” over a wide operating temperature range.
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