Rational-Harmonically Mode-Locked Fiber Ring Laser Driven by Regenerated Subharmonic Clock

The authors experimentally demonstrate rational-harmonically mode-locking of a fiber ring laser driven by the subharmonic clock extracted from the laser output. The ring laser comprised of polarization-maintaining components including an erbium-doped fiber amplifier and a semiconductor optical amplifier showed self-pulsing with a repetition frequency of 21.32 GHz, where the electrical signal of 10.66 GHz driving the mode-locker was extracted from the detected pulse train through downconversion by an electrical frequency divider. The mode of operation greatly depended on the bias point of the optical modulator. The rational-harmonically mode-locking with the rational harmonic order of the second was observed when the modulator was biased in the vicinity of the voltage providing either the maximum or the minimum transmission, where the bias in the vicinity of the minimum transmission showed better performance in favor of the uniformity of the pulses.