Synchronization of environmentally coupled, passively mode-locked fiber lasers

We have synchronized a pair of femtosecond, passively mode-locked Er-doped fiber lasers by active adjustment of the cavity length of one laser with an electronic servo. While each laser delivers pulses with durations of several hundred femtoseconds, they have been synchronized to within a relative timing jitter of 5 ps rms, as measured by cross correlation. This corresponds to a phase error of 30 arcsec. Low drift and jitter were accomplished by thermal and mechanical coupling of the two lasers.