Mode-locking of an InGaAs VCSEL in an external cavity

Mode-locking of vertical cavity surface emitting lasers (VCSELs) has already been achieved by electrically pumping a VCSEL in an external cavity at the cavity frequency. This cavity was formed using a butt-coupled fibre and 24 ps pulses were generated at a repetition rate of 821 MHz. It has also been suggested that self-pulsations could be produced by the introduction of a saturable absorber in the VCSEL structure. Here we report the generation of 36 ps pulses at a repetition rate of 2.46 GHz by mode-locking a VCSEL placed in an external cavity and for the first time to our knowledge we report on the measurement of a transform-limited time-bandwidth product. If the mirror forming the external cavity is replaced by a second VCSEL a small self-oscillation has been observed when the lasers are DC biassed. Furthermore, pseudo-random pulses have been generated by modulation of the gain or loss of the coupled VCSEL system.