Laser diode-pumped femtosecond erbium-doped fiber laser with a sub-ring cavity for repetition rate control

It is shown for the first time that the pulse repetition rate of a femtosecond erbium-doped fiber laser with a nonlinear amplifying loop mirror can be controlled by attaching a sub-ring linear cavity to the main cavity. The transit time in the sub-ring cavity is set as an inverse integer of that in the main cavity, resulting in an increase in the repetition rate of the output pulse. The pulse thus obtained has a width of 315 fs, a peak power of 12.7 W, and a repetition rate of 125 MHz.