Ultra-large core birefringent Yb-doped tapered double clad fiber for high power amplifiers

We present a birefringent Yb-doped tapered double-clad fiber with a record core diameter of 96 μm. An impressive gain of over 38 dB was demonstrated for linearly polarized CW and pulsed sources at a wavelength of 1040 nm. For the CW regime the output power was70 W. For a mode-locked fiber laser a pulse energy of 28 μJ with 292 kW peak power was reached at an average output power of 28 W for a 1 MHz repetition rate. The tapered double-clad fiber has a high value of polarization extinction ratio at 30 dB and is capable of delivering the linearly polarized diffraction-limited beam (M² = 1.09).