49-core rod-type Ytterbium-doped multicore fiber for high power operation

We present an Ytterbium-doped, multicore fiber with 7x7 cores. The fiber is realized in a rod-type geometry with step index cores and an air-cladding for pump guiding. Using a segmented-mirror beam splitter followed by a double-pass multicore pre-amplifier and a main-amplifier of 1 m length, the stretched femtosecond input pulses emitted from the frontend system are amplified. The cores of the main amplifier have a mode-field diameter of 28 µm. Operating at 10 MHz repetition rate, a high average power in excess of 1 kW with near single-mode operation is achieved.