| Abstract [eng] |
During the past years there has been a rapid development of various complex nanostructures which led to an emergence of novel type optical elements. These compact and flat elements can control and shape wavefront, can be used in place of conventional lenses or as polarisation sensitive devices. The purpose of this work is to design a cluster of nanoparticles which could be used as a single meta-atom for a more complex metasurface. Here we engineer collective vector response to the polarisation of the source beam by using the concept of geometrical phase. In this way we can design such elements as S-waveplates, top hat converters, flat axicons etc. For numerical simulations we use Lumerical's Finite-Difference Time-Domain (FDTD) and T-Matrix methods. We use the T-matrix method which is faster to sweep different cluster parameters, but this method can accumulate rounding errors to a significant level. Therefore we use the Lumerical FDTD software for confirmation and visualisation of the results. The parameter space of three nanoparticles consists of dielectric constant, particle radius and inner geometry of the cluster. We find the optimal values and use such meta-atom for design of S-waveplate element. We have observed that one layer of meta-atoms is not sufficient, therefore multiple layers has been used. By varying the distance between 2 layers we have found that the most efficient distance between layers is equal to the wavelength of the incident beam. After simulating multiple layers we have observed that more layers produce better quality beam, but the overall transmission of the system decreases dramatically. |
