Recent developments in nanotechnology have provided methods for structuring and modifying materials on a length scale of nanometers. This has led to new possibilities for controlling the interaction between light and matter on a very fundamental level, with profound consequences for basic science and technology.
The VKR Centre of Excellence is a unique opportunity of gathering internationally recognized Danish research groups in a focused and ambitious effort to explore nanophotonics for terabit communications. It is an area of research that entails fundamental problems within nanotechnology, physics of light-matter interaction, experimental characterization on ultrashort time scales, communication systems working at fundamental limits, condensed matter theory and mathematical optimization of nonlinear systems.
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Fig. 1.Quantum dots on a surface.
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Fig. 2. Photonic crystal structure. |
Quantum dots, often referred to as man-made atoms, are semiconductur structures so small that quantum mechanics only allows the existence of discrete energies for the electrons. Changing the quantum dot size thus allows controlling the energies of these states – and thereby the frequencies at which photons can be emitted. On the other hand, by incorporating periodic arrays of holes in the materials one can synthesize photonic crystals, where the propagation of photons is prohibited, or only allowed, at certain frequencies in certain spatial regions. In this way light can, for instance, be trapped in an ultra-small cavity. Combining quantum dots and photonic crystals, an example of metamaterials, one can realise situations never before encountered in Nature. For instance, an electron in an excited level of an atom decays, in vacuum, by spontaneous emission of a photon. However, if the atom is replaced by a quantum dot and contained in a photonic crystal, this decay may not be possible at all! This result is not contained in Einstein’s fundamental postulates on light-matter interaction, but has been experimentally observed by one of the researchers of the proposed centre [P. Lodahl et al., Nature 430, 654 (2004)].
The example above serves to illustrate the fundamental possibilities offered by nanophotonic structures. By controlling both the electronic and the photonic modes, a new degree of light-matter control can be exercised and new paradigms may emerge. In the NATEC centre we will investigate the properties of nanophotonic structures at ultrashort time scales and explore the possibility for manipulating and processing photons at very high speeds. There is a fierce, world-wide, race to increase the speed of the devices and systems that form the core of our information society,
i.e., the computers become faster and the data rates at which we access and exchange information over the internet continuously increase. The higher the data rate, the more beneficial it is to use optical communications, i.e., representing data as light pulses and transmitting these on optical fibres. The fundamental reasons for this are that fibres have very low loss and extremely large bandwidth. Optical fibres, therefore, constitute the backbone of communication networks and are getting closer and closer to our homes. However, it is now clear that conventional techniques to scale the capacity will fail to meet the demand within the next two decades [E. Desurvire, J. Lightwave Technol. 24, 4697 (2006)]. Consequently, major breakthroughs are needed. In particular, there is a need to develop photonic chips – i.e., integrated structures that allow generating and processing photons, much like the way electrons are used in conventional electronic chips.
It may seem a paradox, but even slow-light phenomena are envisioned to be of prime importance for the realization of ultra-fast optical devices. In particular, slow-light enables enhanced light-matter interactions and manipulation of light in nano-scale devices. One example is demonstrated in a recent Nature paper by some of the applicants, where slow-light effects are used to make a more efficient modulator [R. Jacobsen et al., Nature 441, 199 (2006)].