All-fiber ultra-short pulse hybrid mode-locked laser with high power amplifier

Ultra-short pulse (USP) fiber lasers have a great potential for their applications in various fields of science, industry and technology [1]. We have implemented MOPA (Master Oscillator Power Amplifier) configuration. Master oscillator (MO) is ring all-fiber laser with 92.6 fs parabolic spectra dechirped pulses at a central wavelength of 1560nm with 11.2mW average output power and 38.2MHz repetition rate [2]. The short pulses were realized with a hybrid mode-locking (ML) technique [3] that implies a co-action of two ML mechanisms — saturable absorber based on the Boron-Nitride-doped Single-Walled Carbon Nanotubes [4] and Nonlinear Polarization Evolution [5] in fibers. MO total cavity dispersion is D
T
≈ +0.01 ps
²
for the central wavelength λ
0
= 1560nm as it was estimated according to the measured dispersion of fibers. The pulse evolution in preamplifier and in MO ring cavity has a similar structure. Note that in preamplifier output average power was increased to 100mW with slight change of the pulse duration and spectrum shape after master oscillator. Thus, we suggest similariton generation in MO according to obtained measurements. For achieving high output power we used chirped pulse amplification technique and stretched the pulse in the high-power amplifier entrance. The active fiber of the high-power amplifier is single mode double-clad Er-doped (without Yb
³⁺
) fiber with mode field diameter ∼ 25 µm pumped at 980 nm. As a result, output power of 3.1W with a pulse duration ∼ 20 ps without compression was achieved after high power amplification corresponding to pulse energy of ∼ 80 nJ and peak power of ∼ 4 kW.