Recent advances in high-speed lasers and amplifiers based on 1.5 µm QD/QDash material

A review is given on the recent progress in the epitaxy of 1.55 μm QD/QDash laser material and its application in lasers and semiconductor optical amplifiers. By choosing different growth modes by using either A_s4 or A_s2, the shape of InAs islands grown on AlGaInAs surfaces can be strongly influenced from dash-like to dot-like geometries. This shape change is accompanied by a strong reduction of the size fluctuation, which increases significantly the modal gain of lasers. This has a large impact on the response time of lasers allowing record values of the modulation speed of InP based QD lasers of 15 GBit/s. On the other hand dash-like structures allow ultra-high speed responses in optical amplifiers due to their local relaxation but remaining coupling to continuum states. By two-photon absorption phenomena instantaneous gain can be obtained on the sub-ps time scale.