Surface Plasmon Polariton Nano-Optics

The continuous miniaturization of existing optical and opto-electronic devices is exptected to meet fundamental limitations in near future. These limitations are due to diffraction limiting the spatial resolution to a value given by about half the light wavelength. A potental solution to this problem is the use of surface plasmon polaritons (SPPs) for optical functionality. SPPs are collective electron oscillations coupled to a light field which are propagating along the interface of a metal and a dielectric. As a surface wave, SPP modes feature properties essentially different from light field modes in all-dielectric structures. These properties allow in principle the realization of quasi two-dimensional photonic devices and SPP waveguiding in metal structures with subwavelength cross- sections. On this basis we study experimentally SPP optical elements. The starting point is the precise control of nanoscale metal geometries by means of lithographic methods. Lithography is complemented by various schemes for SPP field imaging and local light/SPP coupling to constitute a powerful toolbox for the realization of SPP optics. The fabrication of basic optical nanoelements in analogy to conventional optics, as beamsplitters or mirrors has been demonstrated already to be feasible. The logical next step is the quantification of SPP reltaed phenomena, i.e. the analysis of optical SPP elements in quantitative and efficiency terms. Especially the interaction of a propagating SPP mode with the nanostructures that constitute the SPP optical elements has to be thouroughly understood in quantitative terms - what is the role of nanostructure geometry and localised plasmon resonances? For this aim we developed an experimental technique called leakage radiation imaging during the first year of the present project. As demonstrated by our results this approach provides quantitative data on the spatial SPP field profile. It therefore forms the basis for the former development and optimization of subwavelength SPP based optical devices in analogy to conventional optics, as mirrors, beamsplitters, etc. While we could already demonstrate, e.g., SPP reflection coefficients as high as 80 % our work program aims at the optimisation of further optical SPP elements as beamsplitters or frequency selective filters. Besides the basic research interest this project will thereby contribute to the realization of SPP optical devices, the development of which is currently already tackled with a view to commerical application.