All these effects, ranging from the interference of electromagnetic waves to material properties, are mapped to problem-specific models addressed by the group of Jens Förstner using physical equations. The variety of materials and geometries within one simulation leads to large and complex systems of equations requiring numerical evaluation. For this, the structures and the surrounding space is decomposed into many small spatial elements, which are then stored and processed in a computer. But often many elements are necessary that cannot completely fit into the memory of a single computer. Here, PC² comes into play.
Our model is distributed onto dozens to hundreds of computers, each storing and computing only a small part of the full space. However, since light travels between these parts, the computers have to exchange the relevant information – and therein lies the strength of high-performance computing centers like the PC² with their special and fast network interfaces.
The figures show examples for structures investigated by Förstner’s group. First, Fig. 2 illustrates a structure optimized to capture light from outside and to focus it into a small area (i.e., on the order of an embedded molecule). To achieve the best possible light concentration over 1,000 different models with a systematic variation of parameters, were simulated on the PC² computer cluster. The shown geometry performs several times better compared to existing solutions.
The structure in Fig. 3 represents an optical antenna – a miniaturization of a radio-frequency roof antenna to the nanoscale making it suitable for optical light. By using simulations on the PC² cluster it was possible to show that the proposed structure has a better directional characteristic compared to existing optical antennas. Although the calculations have only recently been finalized, there are already experimental results from co-workers which confirm the efficiency of the design. With this work, a wide spectrum of other photonic structures has been investigated by Förstner’s group including metamaterials, photonic crystals, quantum dots, integrated waveguides, biological structures – and even interplanetary dust.