Passive mode locking of buried heterostructure lasers with nonuniform current injection

In this letter we report on a novel method to passively mode lock a semiconductor laser. We present experimental results of GaAlAs buried heterostructure semiconductor laser with a split contact coupled to an external cavity. The split contact structure is used to introduce a controllable amount of saturable absorption which is necessary to initiate passive mode locking. Unlike previous passive mode locking techniques, the method presented does not rely on absorption introduced by damaging the crystal and is consequently inherently more reliable. We have obtained pulses with a full width at half-maximum of 35 ps at repetition frequencies between 500 MHz and 1.5 GHz.