Contents I. Introduction
Considerable efforts have been expended on the investigation of the modulation speed of quantum-well (QW) lasers [1]–[4]. This quantity is of great importance for long-wavelength lasers, employed in long-haul optical communication links. It has been expected that an additional carrier confinement, like with quantum wires (QWRs) or quantum dots (QDs), can provide increased differential gain, higher modulation bandwidth, and narrower spectral linewidth [5] than with QW structures. However, this approach does not consider the effect of the environment in which the device itself is embedded nor does it account for the impediment by a limited optical confinement which is particularly obvious with V-groove-shaped quantum wires (V-QWRs) [6]. Schematic of a stack of V-QWRs oriented along the direction of light propagation (not drawn to scale). A solution to the latter problem is a stack of V-QWRs leading to a corresponding increase of the confinement factor. Additionally, an array of QWRs or stacks thereof can be fabricated which are oriented perpendicularly to the direction of light propagation [7], [8], resulting in a further improvement. This arrangement offers the potential of fabricating a distributed feedback laser if the period the V-QWRs is properly chosen [7]. In the present case we consider a possible structure as schematically represented in Fig. 1. Several V-QWRs are arranged on top of each other in an orientation along the propagation direction of the radiation, confined by the two cleaved mirrors at a distance with the reflexion coefficients and [9]. The laser cavity is laterally (in the direction) defined by an etched mesa structure supported by a substrate (not drawn to scale). Fig. 1(b) displays a section through this structure with a scaled-up V-QWR of cross section . The well material InGaAs (deeper shade) is matched in its composition to the lattice constant of the surrounding barrier material InP.
