Experimental investigation of the cavity modulation frequency detuning effect in an active harmonically mode-locked fiber laser

We report the results of our recent experimental investigation of the cavity modulation frequency detuning effect on the output pulse dynamics in an active harmonically mode-locked erbium fiber laser. Our experimental study, which was carried out over a wide frequency detuning range, shows the existence of three different operating modes that depend on the degree of frequency detuning: (i) harmonic mode-locking, (ii) Q-switched harmonic/fundamental mode-locking, and (iii) a sinusoidal wave modulation mode. For this particular experimental laser configuration, the harmonic mode-locking mode is maintained over the frequency detuning range within ±15 kHz, and then the Q-switched harmonic/fundamental mode-locking mode appears over the frequency detuning range from ±16 to ±36 kHz. It is found that the Q-switched harmonic/fundamental mode-locking mode always produces both harmonic and fundamental repetition rate mode-locked pulses within a Q-switching envelope. A detailed experimental characterization of the output pulses in each operating mode is performed in terms of average power, pulse peak power, pulse width, and temporal width and repetition rate of the Q-switching envelope.