Modelocked integrated external-cavity surface emitting laser

A modelocked integrated external-cavity surface emitting laser (MIXSEL) is a novel type of ultrafast semiconductor laser that integrates a saturable absorber directly into a vertical external cavity surface-emitting laser. The saturable absorber requirements and integration challenges to obtain self-starting and stable pulse formation are discussed. One single quantum dot absorber layer was optimised for this application. Since the first feasibility demonstration of an optically pumped MIXSEL, the authors have further improved the average output power to 185 mW with 32 ps pulses at around 3 GHz pulse repetition rate at a centre wavelength of sime957 nm. The authors analyse and discuss the challenges for further power scaling and pulse shortening. The MIXSEL concept appears suitable for cost-efficient wafer-scale mass production when the external cavity is defined by a transparent wafer into which the curved output coupler can be etched. The semiconductor MIXSEL structure would then be glued to such a transparent wafer. The potential for electrically pumped MIXSELs will make this laser technology even more attractive.