Large mode area double-clad ytterbium-doped tapered fiber with low birefringence

We developed ytterbium-doped double-clad large mode area (MFD = 30 μm) spun tapered fibers with low internal birefringence and perfect beam quality (M2 < 1.2). Picosecond MOPA system (95ps/100 MHz, 1064 nm) based on proposed active tapered fiber with output average power of 64 W (gain 32 dB) is demonstrated.