Fano resonance in thin-film optical coatings (Conference Presentation)

Abstract

We present a new class of thin-film based metamaterials that exhibits Fano resonance with wide range of potential applications. We realize Fano resonance via thin-film interference between a broadband (continuum) and a narrowband (discrete) light absorbers. Fano resonant optical coatings (FROCs) exhibit selective light reflection, similar to distributed bragg reflectors, with narrower bandwidth and overall significantly less thickness for a given wavelength range. Accordingly, FROCs produce vibrant colors superior to structural coloring via selective light absorption that has been demonstrated using metamaterials and thin-film cavities. We control the iridescence of the produced colors and can produce iridescent free, ultra-pure colors spanning the entire visible spectrum. Furthermore, we show that FROCs can be used as narrowband beam splitters, as opposed to being simple color filter similar to metal-dielectric cavities. Finally, we utilize the absorption/reflection properties of FROCs in energy applications and show that by selectively reflecting light within the absorption band of Si photovoltaic cell, while absorbing the rest of the solar spectrum, we obtain higher power from PV cells as opposed to a normal silver mirror, while increasing the FROC temperature significantly. Accordingly, FROCs can play a crucial role in hybrid, solar-PV and solar-thermal power generation which is of major importance in recent years due to limitation on electric energy storage. By coating an Aluminum sheet with FROC, while processing its back side to be superwicking, we demonstrate single-element spectral splitting that generate electricity from a PV cell while using the generated heat for water desalination.