A study on an actively mode-locked picosecond pulsed ytterbium-doped fibre laser with dispersion controlled by a photonic crystal fibre

We report on the generation of picosecond pulses in a modulator-based actively mode-locked ring cavity ytterbium-doped fibre laser by means of numerical simulation. A photonic crystal fibre (PCF) with large anomalous group velocity dispersion (GVD) and small nonlinearity can compensate the large normal GVD in the cavity accumulated by the ytterbium-doped fibre and the single mode fibre. Numerical models of the laser are established and solved by a simulation program. We study the laser behaviour and simulate the forming of the mode-locked pulses. The laser can easily produce stable pulses with 11.5 ps pulse width, 0.73 nJ pulse energy and 2.67 GHz repetition rate at 1 μm, which indicates that this laser can perfectly meet the demands of smaller pulse width and higher pulse energy as a seed laser. More numerical simulations are performed to test several key parameters, such as the small signal gain, the mode-locking order and the GVD coefficient of the PCF. The results show how these parameters affect the output pulses and help us to optimize the laser performance. The numerical simulation plays a guiding role in optimal design for later experiments.