Large mode area double-clad ytterbium-doped spun tapered fiber

We performed a comparative study of Yb-doped double-clad large mode area (MFD = 31 mu m) spun tapered fibers with different pitch lengths. A novel type of spun tapered fibers with constant pitch lengths of 7.5, 15, and 30 mm, internal birefringence as low as similar to 10 8, and perfect output beam quality (M-2 < 1.2) has been manufactured and investigated. We demonstrated the efficient direct amplification of a picosecond pulsed signal (95 ps/100 MHz, 1064 nm) in the spun active tapered fiber with optimized geometry providing an average output power of 71W(gain 32 dB, 74% slope efficiency). Efficient green light generation (lambda = 532 nm) with 17W average power (1.7 mu J) and 80 pm linewidth was demonstrated using the developed master oscillator power amplifier system. (C) 2021 Optical Society of America