Timing synchronization of optical pulse train from passively mode-locked semiconductor lasers by phase-locked loop

The timing synchronization of pulse trains is demonstrated, and the timing jitter is discussed with reference to both temporal pulse-train traces and frequency spectra of the mode-locked signal. Timing synchronization of pulse trains to an electrical oscillator by using a PLL has been demonstrated for passively mode-locked semiconductor lasers with an external cavity laser (ECL) configuration. The jitter estimated from the temporal trace of the pulse train has been compared with the one evaluated from the laser phase noise derived from the RF spectra of the mode-locked signal.