Infrared Electric Field Enhancement via a Hyperbolic-Metalens-Coupled Nanoantenna

Abstract

The development of near- and mid-infrared applications requires high enhancement of the electric field intensity (EFI) and a high absorption cross-section of the electric field. The high enhancement of EFI can be obtained by concentrating optical energy to areas much smaller than the diffraction limit or by using surface plasmon polaritons (SPPs). Noble metals such as gold (Au) or silver (Ag) are not feasible for infrared (IR) applications because of high losses, lack of tunability, low resolution, and low-intensity enhancement. Our methods to solve these problems are based on appropriate metamaterial selection and on coupling systems with optimization of their geometries. The high performance was achieved by introducing alternative metamaterials (AMM), a Fresnel zone plate (FZP), and nanoantennas. This dissertation demonstrates a novel metalens design in the near-infrared band from 1.5 µm to 3 µm, consisting of an FZP, which is called a plasmonic waveguide coupler (PWC), situated on a slab of type I hyperbolic metamaterial (HMM) that lies on a silicon substrate that has a silver nanodipole embedded within. The PWC is made of rings of indium tin oxide (ITO), and the type I HMM is constructed using a periodic stack of ITO and silicon layers that, through effective medium theory (EMT), act as a slab of type I HMM. Together the PWC and the HMM slab serve to focus incoming radiation onto a focal point marked by the location of the silver (Ag) nanodipole. The Ag nanodipole allows for high subwavelength confinement of optical modes because of the in-focal point component of the electromagnetic field vector coupled to the plasmonic resonance of the dipole. This dissertation also demonstrates a novel metalens in the mid-infrared range from 6.4 µm to 10 µm, consisting of a doped indium arsenide (InAs) which works as a plasmonic waveguide coupler (PWC) on a slab of type I hyperbolic metamaterial (HMM) on the top of a substrate of undoped InAs with an Au nanoantenna at the other end. The metalens focuses both propagating and evanescent waves into a focal point at which the field confinement and enhancement are improved using the plasmonic nanoantenna. Finally, ultrahigh mid-infrared electric field enhancement with a high absorption cross-section and a focusing resolution are obtained via gap nanoantenna plasmonic resonance coupled with the novel hyperbolic metalens. By combining the focal spot of the metalens with the excited plasmons of a gap nanoantenna, the resulting structure exhibits an ultrahigh field-intensity enhancement with a high absorption cross-section and a focusing resolution.