Photonic crystals (PBG) are artificial microstructures in which the refractive index is periodically modulated at a length scale comparable to the wavelength of light propagating in that structure. For specific crystal configurations, this index periodicity can lead to a complete photonic band gap, thus inhibiting wave propagation in one, two and even in three dimensions. Introduction of defects (breaking the symmetry of the periodic array by introducing a different element, in size, index of refraction, or both) may lead to the appearance of defect modes inside the stop band. This can lead to a multitude of effects one can take advantage of to control the flow of light: microcavities, waveguiding, omnidirectional mirrors. When some of the elements of the periodic structures or the defects are made of nonlinear materials a new set of effects may appear. Due to the periodicity of the array, which effectively acts as an extra degree of freedom in momentum space, it is possible to obtain phase-matched interactions, as second harmonic generation and other parametric processes. Through cascading one can even obtain (with high efficiency) third and fourth harmonic generation in a chi-2 material. The existence of spatial solitons has also been predicted.
Our studies are focussed on the possibility of enhancing the transfer of energy to or from the defect mode through coupling via a parametric signal, simultaneous multi-wave processes (like for example, simultaneous second and third harmonic generation), light diod based on the combined action of the periodic structure and the generation of a second harmonic.
We study the characteristics of nonlinear PBG crystals in terms of modes, band structure and the existence of localized structures. We investigate the possibility of switching between these localized structures and delocalized structures. We also plan to provided a systematic study of PBG structures based on piesoelectrics, materials which provide an efficient interaction between acoustic and electromagnetic waves, giving the possibility by this means to excite and control light (microwave) propagation by low-frequency acoustic waves.
The above studies are carried out in collaboration with the groups at the Institute for Radielectronics of Czech Academy of Scieces (Czech Republic) and Lukin's Institute of Physical Problems (Zelenograd, Russia).
For the related publications of the group see http://alf1.cii.fc.ul.pt/~konotop/Publications.htm.