Subwavelength structures in photonic devices - Patterning of dielectric materials by shaped femtosecond laser pulses
Optical elements with structures smaller than the target wavelenth provide unique effects which base mainly on two principles. Guided-mode resonances in slab waveguides that are introduced by a periodic nanostructure are applied for narrowband spectral filters or polarizers. Furthermore, structures with dimensions far below the targeted wavelength are used to generate artificial refractive indices.
In this case light waves average the material properies of volume elements which consist to a certain ratio of base material and subwavelength air holes. Goal of this research project is the investigation on fabrication methods for these sub-100 nm structures using fs-laser pulses. In particular this approach owns a clear advantage and high potential regarding dielectric materials which are commonly used in all fields of optics. There are no charging problems as they are known from most established process, e.g. electron beam lithography.The research project is focused on narrowband optical filters for the visible spectral range, based on the guided-mode resonance effect and photonic crystal structures having a artificially generated, gradually varying refractive index distribution. Additionally, selective material processing of thin films and a thorough comparative study with the standard fabrication methods are adressed.
These investigations are subject of our close cooperation with the group of Prof. Baumert as part of the DFG Priority Program 1327 - "Optisch erzeugte Sub-100-nm-Strukturen für biomedizinische und technische Applikationen"