Resonance-Enhanced Optical Property Of Metal-dielectric Nanostructures

Driven by advances in material science and progress in photonic integration technology, scientists are in hot pursuit of the manipulation of light waves at will. As it is well known, conventional dielectric materials have advantages of low loss and wide transparent band, while metals themselves possess large ohmic loss but plasmonic waves in metal surfaces enable extreme light concentration. When the metal surfaces are structured at nanoscale, it can result in many exotic phenomena and peculiar applications for light emitters, detectors, solar cells etc. A common challenge in these photonic devices is to precisely control transmission and absorption of light. Sometimes it is even required that the devices with excellent optical transmission should also maintain good conductivity. In this thesis, we demonstrate that metal-dielectric nanostructures can be artificially tailored as either highly absorptive or transparent materials in the visible and near-infrared regions.We first propose two types of absorbers, an extremely narrowband absorber and a double-sided absorber for optical absorption from two directions in space. The narrowband absorber is composed of alternative metal and dielectric layers. Owing to Fabry-Perot resonance and metal’s inherent loss, an ultra-narrow spectral range of light can be entirely trapped in the structure while the others will be totally reflected back. Theoretical calculations and experimental results show that the absorption wavelength can be flexibly tuned in the visible and near-infrared regions, and the minimal absorption bandwidth can be reduced to 2 nm. The other absorber is based on surface plasmon resonance and it is derived from the classical absorber with "metal-insulator-metal" architecture. Here, two different metal arrays are adopted to sandwich a dielectric film, which enables simultaneously efficient near-infrared absorption from both directions. Moreover, the absorption is insensitive to the polarization of incident light.Inspired by the "metal-insulator-metal" absorbers, we then achieve a polarization-insensitive antireflective coating with wide-angle operation in the visible and near-infrared regions. Different from the phenomenon of extraordinary optical transmission through a metallic film perforated by nanohole arrays, high transmission through a seamless metal film is obtained here. Simulation results show that the transmission of our designed nanostructure at 1030 nm reaches 70% while that of a bare silver film of 20 nm thickness at the same wavelength is only about 15%. Taking into account precision of nanofabrication, we redesign and optimize the nanostructures with 20 nm seamless gold film. Experimental results indicate that transmission of a bare gold film has been increased to 40% at 930 nm, which is 8 times larger than that of a metal-dielectric-metal layered structure.Overall, this thesis aims to enhance optical absorption or transmission of metal-dielectric nanostructures based on electromagnetic resonances. All these devices have potential applications in the fields of solar energy utilization, thermal radiation, optical filtering, and optical sensing.