Search

We demonstrate a concept and fabrication of lithography-free layered metal-SiO2 thin-film structures which have reduced reflectivity (black appearance), to as low as 0.9%, with 4.9% broadband reflectance (8.9% for soda lime) in the 500&ndash, 1400 nm range. The multi-layered (four layers) thin-film metamaterial is designed so that optical impedance matching produces minimal reflectance and transmittance within the visible and infra-red (IR) spectral region for a range of incident angles. The structure has enhanced absorbance and is easily tuned for reduced minimal transmission and reflection. This approach should allow for novel anti-reflection surfaces by impedance matching to be realized.

In this contribution, we show how it is possible to exploit the exotic response of arrays of plasmonic nanoparticles (NPs) to design ultra-thin optical absorbers and color filters. First, it is shown that an array of electrically small spheroidal NPs may be effectively characterized using a complex-valued surface impedance tensor. Then, the model is exploited to design optical Salisbury-like screens able to absorb all the impinging light within a desired frequencies range. Finally, an innovative nanoscale color filter able to selectively absorb the light in a narrow frequencies band while being transparent in the rest of the IR and optical spectrum is proposed.

Optical absorbers have been a topic of intense research due to their importance in many applications. In particular, multi-band and perfect absorption features in a desired frequency range are essential in broadband applications. In this work, we numerically studied the absorption properties of subwavelength metallic gratings coated with a dielectric layer. Here, the structure is considered to be an integration between a resonant cavity and a subwavelength metallic grating. Two appropriately designed structures can exhibit multi-band absorption properties. In addition to the numerical simulation results, we elaborate on determining the appropriate structural parameters that yield the desired spectral absorption profile in the visible range. We also numerically identify critical coupling conditions for perfect absorption.