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

Abstract

We performed a comparative study of Yb-doped double-clad large mode area ( M F D = 31 µ 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 ∼ 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 71 W (gain 32 dB, 74% slope efficiency). Efficient green light generation ( λ = 532 n m ) with 17 W average power (1.7 µJ) and 80 pm linewidth was demonstrated using the developed master oscillator power amplifier system.