Computer controlled harmonic FM mode-locking of 40 GHz repetition rate fiber laser

摘要

We developed a new method of harmonic FM mode-locking of a fiber laser. The method is based on computer control of the modulation frequency generated by an external RF synthesizer and applied to the phase modulator inside the laser cavity. The developed software tunes the modulation frequency to follow the fluctuations of the laser cavity length in order to keep the laser mode-locked. As a feedback the program used the DC component of the mixed signal from a fast photodiode measuring the laser output intensity and the signal from the synthesizer. The program performed approximately two auto-tuning steps per second. The presented method allows very simple, reliable and stable computer controlled harmonic mode-locking of a fiber laser. We achieved pulse duration of 2.6 ps and side mode suppression of 55 dB at 40 GHz repetition rate.