Optical characteristics and low linewidth enhancement factor in 1.2 μm quantum dot lasers

The QD density of states, which theoretically is a series of delta function spikes at the quantized energy levels, indicates that threshold current densities are not only low but also temperature independent. Another important property is the degree to which carrier density variations alter the index of refraction of the active layer. Large values of dn/dN can result in antiguiding in narrow stripe lasers, as well as self-focusing and filamentation in broad area emitters. The latter is often described by the linewidth enhancement parameter, α=-4π/λ(dn/dN)(dg/dN)^-1. For strained InGaAs single quantum well (QW) lasers, operating near 980nm, the value of α is typically 2 or higher at carrier densities corresponding to threshold. At the communications wavelengths of 1.3 μm and 1.55 μm α is usually much higher unless modulation doping or a large number of quantum wells are employed. However, the elimination or substantial reduction a may be realized by utilizing quantum dot lasers. α values are predicted to be low and even zero for certain conditions. Since one area of great interest is the production of QD devices at 1.3 μm, such structures may have a large applicability to wide bandwidth communications devices and high power amplifiers. We have designed, grown, and characterized quantum dot lasers that feature a layer of InAs quantum dots centered in a single 100 A In_0.2Ga _0.8As quantum well structure