Dispersion-tuned harmonically mode-locked fiber ring laser for self-synchronization to an external clock

The stable operation of a high-repetition-rate dispersion-tuned harmonically mode-locked erbium-doped fiber ring laser is reported for the first time to our knowledge. The dispersion causes a round-trip delay that varies with wavelength, so synchronism with the amplitude modulator is passively maintained at a wavelength that is synchronous with the modulation frequency (external clock). One can tune the laser by simply changing the cavity length. A 10-GHz train of transform-limited, 6.5-ps duration pulses is obtained over an 8-nm tuning range. Pulse energy equalization can be achieved by the interplay of normal dispersion, self-phase modulation, and amplitude modulation.