Investigations of mode-locked Er-doped oscillators with record high-pulse energies

In our experiment, based on nonlinear polarization rotation (NPR), first, we demonstrate a large-energy square-wave mode-locked fiber laser under low pump power. The largest pulse energy of the square-wave pulses was 106.91 nJ. However, pulse breaking occurred when the pump power was higher than 1152 mW. Thus, under the maximum pump power of 2318 mW, several kinds of large-energy mode-locked operations were also investigated successfully. The maximum output pulse energy was recorded to be 881.34 nJ, which exhibits obvious enhancement in comparison with previous works. Additionally, in our work, we have successfully revealed that broadening of the pulse width, splitting of the pulse shape and increasing of the pulse repetition rate play significant roles in reducing the influence of large pulse energy and high peak power experimentally. Our experiment result will provide a useful guide for demonstrating large-energy pulse operations.