InP-based quantum dash lasers for wide gain bandwidth applications

Self-assembled quantum dash (QDash) lasers based on InP with an emission wavelength of about 1.5 μm were grown by molecular beam epitaxy with solid-state sources. Two different approaches were investigated to further extend the broad gain bandwidth of QDash structures. One approach is based on layer thickness variations in a stacked QDash structure with thick barriers to avoid vertical strain coupling. In the alternative structure, the barrier thickness is reduced to allow strain coupling which modifies automatically the QDash size from layer to layer. With both approaches, the gain bandwidth could be significantly increased in comparison to structures with a single QDash layer. However, lasers based on active regions with reduced barrier widths show additionally a significant improvement of the device performance. Ridge waveguide lasers based on this new material show continuous wave (cw) operation up to 75 °C. At 20 °C, a threshold current of 65 mA was obtained for 2 mm long devices with 2.5 μm wide ridges.