KW monolithic PCF fiber amplifers for narrow linewidth and single mode operation
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We report on the progress towards the development and performance of Photonic Crystal Fiber (PCF) based multi-kW fiber amplifiers that are both narrow linewidth and have near diffraction limited beam quality for government and industrial applications that are both reliable and highly affordable. These amplifiers based on the foundation of Photonic Crystal Fibers along with a novel multi fiber-coupled laser diode stack and a monolithic 6+ l×l large fiber pump/signal multiplexer. The pixilated nature of the PCF fabrication process allows for the inclusion of precise index of refraction control so designs to control SBS, prevent modal instabilities and integrate large quantities of pump light can be realized, The precisely aligned 2-D laser diode emitter array found in laser diode stacks is utilized by way of a simple in-line imaging process with no mirror reflections to process a 2-D array of 380-450 elements into 3 400/440μm 0.22NA pump delivery fibers. The fiber combiner is an etched air taper design that transforms low numerical aperture (NA), large diameter pump radiation into a high NA, small diameter format for pump injection into an air-clad large mode area PCF, while maintaining a constant core size through the taper for efficient signal coupling and throughput. A completely monolithic amplifier utilizing these components has been demonstrated at 967W of output power at 1085nm.