High power fused pump/signal combiner for reverse pumping of active double clad fibers

We present a new type of combiner based on a fused pump/signal fiber bundle. We obtain a record high signal-to-pump isolation of more than 46dB from a device optimized for high power counter directional pumping of Ytterbium-doped large mode area airclad fibers. The compact device combines more than 100W of light from 14 pcs. of 105μm NA=0.15 fibers into the pump cladding of an airclad fiber with a coupling efficiency of 90%. The signal light is delivered through the center of the combiner ensuring the exceptional isolation. The high level of isolation, measured for a 60W amplifier configuration, is essential to ensure the reliability of the pump diodes in a high power pulsed system. The combiner is compatible with PM and non-PM systems and we demonstrate both a CW and a pulsed configuration.