Mode configurations in second-order mode-locked lasers

An analysis of the mode frequencies and phases of lasers that are self-pulsing due to second-order mode locking is presented. It is shown that locking can occur with the modes arranged in several different configurations with different pulsing frequencies corresponding to the beat notes between different combinations of longitudinal modes. The experimental observations of the transition between two of these configurations in a self-pulsing GaAs junction laser is reported.