Harmonically mode-locked fiber laser with fine repetition rate tuning through continuous wave injection

Fiber ring laser harmonically mode-locked through nonlinear polarization evolution with the pulse repetition rate up to 6.75 GHz is demonstrated. We report on a new method of fine repetition rate tuning with the use of external continuous wave injected into the ring laser cavity. With this method, we have shown experimentally that the pulse repetition rate of the harmonically mode-locked laser can be tuned over a few GHz range with the minimal possible step equal to the fundamental frequency of the ring cavity.