Passive Mode-Locking and Tilted Waves in Broad-Area Vertical-Cavity Surface-Emitting Lasers

We show experimentally and theoretically that an electrically biased 200-μm multitransverse mode vertical-cavity surface-emitting laser can be passively mode-locked using optical feedback from a distant resonant saturable absorber mirror. This is achieved when one cavity is placed at the Fourier plane of the other. Such nonconventional optical feedback leads to the formation of two tilted plane waves traveling in the external cavity with opposite transverse components and alternating in time at every round-trip. Each of these plane waves gives birth to a train of mode-locked pulses separated by twice the external cavity round-trip, while the two trains are time shifted by a round-trip. A large portion of the transverse section of the device contributes to mode-locked emission leading to pulses of approximately 1-W peak power and 10-ps width. We discuss how inhomogeneities in the transverse section of the saturable absorber select the emitted tilted waves, thus leading to tunable emission over 4 nm.