In this research area we investigate the integration of nanostructures on macroscale systems. The goal is to enhance the performance and functionalize such systems with unique properties of nanostructures. This multi-scale approach enables physical response for all incorporated lengthscales. Potential application includes integrated diffractive solar concentrators.
Antireflective In-Plane Solar Concentrator
In addition to the antireflection effects, photonic nanostructures can also be used to trap light. We are investigating the use of such nanostructures on a glass window to re-direct and concentrate ambient sunlight to the edge, where it can be captured by a solar cell (as shown above) [1]. This effectively functionalizes windows are solar harvesters, which can serve as a building energy source. The nanostructures can also selectively trap a certain color wavelength, enabling spectra splitting to bandgap-matching solar cells. We have demonstrated 2% energy conversion efficiency, which can be improved by optimizing for structure geometry. These structures can be applied to existing windows and can be one aspect of the progress towards zero-emission buildings.
Gradient-Index Antireflection Diffractive Optics
Similar to planar surfaces, diffractive optical elements also suffers from Fresnel losses which takes the form of reflected diffracted orders. Using the same bio-inspired principles, it is possible to design a nanostructured gradient-index (GRIN) medium where the reflected orders can be suppressed, transfering all energy into transmissed orders [2]. The above figure illustrates the simulated electric field magnitude of reflected orders for a diffraction grating without (left) and with (right) the optimized nanostructures (click on figures to show simulated movie).
Such a nanostructured GRIN element can be fabricated using a combined lithographic and self-assembly approach, as shown in the above figure. The micrographs depict a diffractive microstructure with engineered nanoscale surface texture. The Fresnel losses are over two orders of magnitude lower than a traditional element over broad wavelength band and large incident angles [3].
