The theoretical foundations of laser action were laid by Einstein in the very beginning of the twentieth century, when he structured light-matter interaction into three main mechanisms: absorption, spontaneous emission and stimulated emission. The possibility of obtaining stimulated emission from semiconductor junctions was first proposed in 1961, and realised in a GaAs p-n junction by different groups soon after that. However, a major step was only taken when Z.I. Alferov and H. Kroemer realised that semiconductor lasers would only be efficient when the stimulated emission was confined to a small region. They were awarded the Nobel prize in Physics in 2000 for "developing semiconductor heterostructures used in high-speed micro- and opto-electronics". As the Nobel Committee remarked, modern information system components must be fast, so that large volumes of information can be generated and transferred in a short time, and small, so that they can fit in an office, a briefcase, a PC, etc. Semiconductor microlasers nowadays indeed drive the flow of information on internet's fibre optic cables. They are found in CD players, printers and many other applications.
In 1979, Iga presented a radically different design for semiconductor lasers: Vertical-Cavity Surface-Emitting Lasers (VCSELs) are now the world's most produced laser type. We want to study the behaviour of semiconductor lasers in general, focussing (but not exclusively) on VCSELs in particular. First of all, we want to study semiconductor lasers as a stand-alone device, studying their polarisation and mode properties, as well as their noise behaviour. All these properties are of course very important when one wants to modulate these devices at high bit rates. Then we will also study their behaviour when they are put into contact with perturbations from the external world: optical feedback and optical injection, that both give rise to a rich and interesting dynamical behaviour. Finally, we want to study some advanced laser concepts like e.g. VCSELs incorporating photonic crystal structures that are nowadays developed for specific applications, or to overcome specific problems.
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