Fractal antennas for light collection

In a recent collaboration between Stanford and ICFO, Farzaneh Afshinmanesh in the Brongersma group and Alberto Curto of the Molecular NanoPhotonics group led by ICREA professor Niek van Hulst, have fabricated Si-photo-detectors with transparent metallic fractal electrodes. The detectors show superior performance both in broad-band and flat polarization response. The work was published in NanoLetters.

Fractal patterns are prevalent throughout nature because they combine two functional properties. First repetition of patterns at many size scales results in exceptional surface area/volume ratios, ideally suited for collection of solar energy. Second fractal patterns have high connectivity properties, ideal for compact and efficient electrical contacting. Now Farzaneh Afshinmanesh and Alberto Curto have seized this prospective to merge photonic and electronic functionality in one fractal nanostructure. They fabricated transparent nanostructured aluminium electrodes with optimized space-filling fractal geometries displaying a broadband spectral transmission and flat polarization response. On Si-photodiodes the fractal design outperforms periodic square and linear patterns. Nanofractals might be interesting for several optoelectronic applications, such as solar cells, light emitting diodes, electronic displays, for which combined electronic and optical access is required.