We report the active mode locking of the emission from a GaAs buried optical guide laser in an external ring cavity. The two counter rotating pulses interact in the laser which in addition to the gain medium contains a saturable absorber at one facet introduced by proton bombardment at 600 keV with a 3×1015cm−2dosage level. Bursts of pulses with 0.56 psec FWHM at a 625‐MHz repetition rates have been obtained.