Study On Optical Characteristics Of Two-Dimensional Composite Photonic Crystals Based In Metal-Dielectric Multilayer Structure

Extraordinary optical transmission?EOT?have been observed in metal films with periodic arrays of subwavelength apertures.Light can be controlled at subwavelength scales by changing structural parameters,which extends the application of surface plasmon polaritons?SPP?to biosensor detection,filters,light modulators,etc.Therefore,the structure of metal with holes has gradually become popular topic for research.In this work,the transmission of electromagnetic wave and the generation mechanism of SPP in the porous structure of metal-dielectric compound photonic crystals are described.By using the finite-difference time-domain?FDTD?method,we study the influence of material properties and parameters on the electric field intensity and optical characteristics,which has certain reference value for the research and application of plasma nanostructures based on EOT.The optical characteristics of compound photonic crystals with circular holes drilled in metal-dielectric layers are studied.Effects of refractive index of the substrate on the excitation modes of plasma and optical properties of the photonic crystals are analyzed.The surface plasma dispersion is sensitive to the refractive index of the substrate adjacent to the metal film.The transmittance is reduced as the energy difference between the surface plasma modes on both sides of the metal film increases.Moreover,the transmission peaks,reflection valleys and absorption peaks in the optical curve exhibit red shift.In infrared band,the optical characteristics of compound photonic crystals with circular holes drilled in SiO₂-Ag-SiO₂ are simulated and analyzed.By increasing the size of nanoholes to microscale,the plasmonic resonance in the metal film can be shifted from visible to infrared range.The transmission peaks,reflection valleys and absorption peaks have a blue shift as the lattice constant decreases,the intensity of transmission peak increases.With the increase of hole radius,the coupling between SPP and localized surface plasmon?LSP?resonance is enhanced,and the intensity of transmission peak is increased.By adjusting the hole radius and lattice constant of the structure to ensure its ratio,light can be selectively allowed to transmit at a specific wavelength with a similar EOT spectrum.A new structure of photonic crystals with Pacman holes is proposed.The structure is also based on SiO₂-Ag-SiO₂ layers and optical characteristics of EOT are analyzed by changing the structural parameters.Compared with the simple circular hole structure,the new structure with Pacman holes has a higher main transmission peak,so the application potential of the new structure is better.The LSP resonance at the sharp angle of the Pacman holes has obvious influence on the optical properties of the structure.With the increase of hole radius,the transmission intensity is increased by the interaction of SPP resonance and LSP resonance,significantly,and the position of transmission peaks exhibit red shift.The red shift depends on the radius of the Pacman holes.With the increase of the angle of the Pacman holes,the position of the transmission peaks has a blue shift,and the maximum intensity of the transmission peak is obtained when the angle is 90°.When the thickness of silver film increases,the resonance coupling of SPP on the upper and lower surfaces of silver film decreases,the position of transmission peaks has a blue shift,the intensity of transmission peak decreases,and the transmission peak sharpens.These results can be used for reference in the new application of photonic crystals.