Mode-locking in modeless laser cavity.

We demonstrate experimentally that random phase modulation of an erbium-doped fiber ring-laser with an intra-cavity electro-optic phase modulator did not inhibit ultra-short pulse operation (so-called mode-locking). Stable mode-locking was achieved even when the phase modulator was driven with random sequences sufficiently fast and strong to render the cavity modeless, as determined by heterodyne measurements. No significant change in the pulse characteristics was observed. The insensitivity to the random phase modulation is expected, given the lack of phase-sensitive elements in the cavity.