Complex systems are large aggregations of many smaller interacting parts. In such systems, such as e.g. spatially extended systems, interesting behavior can emerge which cannot be anticipated from the behavior of one of the constituents of the system alone. Emergent structures in such systems are patterns that appear spontaneously due to the interaction of each part with its immediate surroundings in space. Emergence does not arise if the various parts are simply coexisting; the presence and nature of the spatial interaction of these parts are central.
Master thesis subjects
Pattern formation and localized structures in spatially extended photonic systems
Physics and applications of metamaterials and nanophotonic devices
The success story of photonics is largely based on the precise control of the properties of light that is made possible by the interaction of electromagnetic waves with a variety of optical materials. Natural materials have, nevertheless, an important shortcoming: at optical frequencies, we cannot control the magnetic component of electromagnetic waves. Furthermore, photonics seems to be constrained by some fundamental limitations related to the wavelike nature of light.
Recently, scientists have succeeded to create a new class of materials that can overcome these limitations: metamaterials. These are artificial materials that contain small resonant electric circuits replacing the atoms as the basic units for the interaction with light. The circuits will often be designed such that the metamaterial has new electromagnetic properties that are not observed for natural materials, e.g., magnetic optical materials. Metamaterials allow for an unprecedented control over the propagation of light, such as in lenses with perfect resolution and optical invisibility cloaks.
Photonic Implementations of Reservoir Computing
Reservoir computing has recently been introduced as a generic name for a new research field in the domain of machine learning. These systems can be engaged to solve complex classification and recognition problems and are considered as a very promising approach for a new computation paradigm. The central part of the setup is traditionally a vast, distributed nonlinear network, the reservoir, with ports needed for information exchange. While the connections within the reservoir itself are kept constant, the connections to the output layer are trained.
Dynamics of semiconductor ring lasers
Modeling of spatially incoherent laser emission
Recently we have developed a unique technique to drive some types of semiconductor lasers into a regime of spatially incoherent laser emission. This high-power, spatially incoherent emission regime is quite uncommon for lasers but can be useful in illumination and projection systems as the low degree of spatial coherence helps to reduce speckle, which is the major noise source in images produced by a laser based projection system. the incoherent emission can be considered emission in multiple, independent, spatially seperated coherence islands.
Experimental investigation of multi-wavelength lasers based on filtered optical feedback
Today's trend in optical communications is towards bringing the optical fiber network closer to the end-user. In this context, a cheap and reliable tunable light source is required in order to fully exploit the bandwidth potential of optical fibres via wavelength division multiplexing.