High-power 120 fs pulses at 1.23 GHz from a single-mode Er/Yb-doped fiber laser

We present a compact single-mode erbium-doped master oscillator power amplifier (MOPA) fiber laser that can directly produce 100 fs pulses at 2.2 W and 120 fs pulses at 4.5 W average power. The laser operates at 1.2 GHz pulse repetition rate, with a central wavelength at around 1550 nm. The laser system consists of a passively mode-locked oscillator with a repetition rate of 77.6 MHz and an average power of 16.3 mW. Using a repetition rate multiplier consisting of five 50/50 couplers, we achieved pulses with a repetition rate of 1.23 GHz. The output was increased to an approximately 4.5 W average, corresponding to about 3.6 nJ pulse energy using only one amplifier stage comprising a cladding pump 10/125 erbium-ytterbium (Er/Yb) co-doped gain fiber. We characterized the system by measuring the optical spectrum and intensity autocorrelation at different output powers, 1.5 W, 2 W, 2.2 W, 3 W, 4 W, and 4.5 W. Finally, we used numerical simulations to study the pulse and optical spectrum evolutions in the fiber, and investigated the output pulse and spectrum at different output powers. We achieved a very good agreement with experimental results, inferring the pulse dynamics and its power scaling limitations.