Research On Spectral Absorption And Optical Imaging In Visible Range With Metal-Dielectric Multilayer Materials

The optical properties of any micro-nano device are essentially derived from the optical properties of its constituent materials.The dielectric constant of metallic materials is less than zero in the visible and infrared range,and is opposite to that of the dielectric materials.When the micro-nano-scale metal and dielectric are combined together to interact with the electromagnetic field,different or even opposite optical phenomenon can be produced.In recent years,it has been found that the combination of metal and dielectric materials can convert incident electromagnetic waves into Surface Plasmon Polariton(SPP),thereby enhancing the ability of materials to regulate light at the nanometer scale.We use the surface plasmon resonance or other resonance effect of the metal-dielectric micro-nano structure to achieve enhanced resonance absorption of the electromagnetic wave in a specific wavelength range.In these structures,a multilayer structure based on metal-dielectric-metal due to its natural magnetic resonance characteristics can respond to an incident magnetic field and generate anti-parallel currents on both metal surfaces,thereby generating a local electromagnetic field in the medium and the absorption of electromagnetic waves by metals has a full absorptivity at a specific wavelength,forming a nanophotonic absorber device on a macroscopic scale.The first work of this paper is to design visible-range single-band and dual-band absorbers based on metal-dielectric multilayer structure.The single-band absorber has a nearly perfect absorptivity of 99.65%at 555 nm.According to the field distribution analysis,the absorption peak is formed by coupling the magnetic resonance mode and the cavity mode in the middle of the metal layer.In combination with the LC equivalent circuit,the law of absorption spectrum changes with material parameters can be interpreted qualitatively.In addition.We also quantify the absorption mechanism at this wavelength using the antisymmetric mode in the equivalent metal-insulator-metal waveguide.Later on for this single-frequency absorber,based on its angular dependence,we look forward to its application as a low-angle detector or collimator.In addition to the single-frequency absorber,the dual-frequency absorber designed in this paper can also achieve near-perfect absorption efficiency at 450 nm and 584 nm in the visible range.These two absorption peaks come from the symmetrical mode in the insulator-metal-insulator waveguide and the antisymmetric mode in the metal-insulator-metal waveguide,respectively.The change of the absorption spectrum with the structural parameters also verifies the correctness of the interpretation.Afterwards,we experimentally prepared and characterized absorbers with different periodic parameters and obtained corresponding results with simulations.The absorption of this one-dimensional grating structure can also be extended to a two-dimensional form,forming a dual-band absorber with insensitive polarization.The absorber based on this stacking structure effectively avoids the problems of large pitch size,difficulty in processing,and low space utilization of the planar composite structure,and is more advantageous for device miniaturization,integration,and large-scale production.In addition to the enhanced absorption characteristics resulting from magnetic resonance,the coupling of SPPs in metal-insulator-metal structures can also produce propagation modes having a negative refractive index.In this paper,the second work uses a metal-dielectric multilayer structure to design a full-angle negative-refractive index waveguide at 532 nm.The energy refractive index and phase refractive index of the waveguide are both close to-1.By adjusting the thickness of the metal and delectric film,this negative refractive index effect can be kept constant over a large range of angles.Using this negative refraction effect,the light source on the side of the waveguide can be image.The imaging resolution can reach 283 nm,close to the diffraction limit at this wavelength.In general,when a positive-refractive material converges light,a curved surface is needed to modulate the phase,but a multi-layered waveguide made of metal/dielectric materials can be imaged simply by a flat plate structure.This greatly simplifies the fabrication process and at the same time facilitates the integration into micro-nano photonic devices.