چكيده به لاتين
Metamaterials offer unprecedented flexibility for manipulating the optical properties of matter. Recently, metamaterials with near-zero refractive index have drawn much attention. Light inside such materials experiences no spatial phase change and extremely large phase velocity, properties that can be applied for realizing directional emission, tunneling waveguides, large area single mode. However, at optical frequencies previously demonstrated zero- or negative refractive index metamaterials require the use of metallic inclusions, leading to large ohmic loss, a serious impediment to device applications. Here, we demonstrate an impedance matched zero-index metamaterial at optical frequencies based on purely dielectric constituents. We show how one may obtain conical Dirac dispersions in photonic crystals, and in some cases such conical dispersions can be used to create a metamaterial with an effective zero refractive index. We show specifically that in two-dimensional photonic crystals we can adjust the system parameters to obtain accidental triple degeneracy at Γ point, whose band dispersion comprises two linear bands that generate conical dispersion surfaces and an additional flat band crossing the Dirac-like point. If this triply degenerate state is formed by monopole and dipole excitations, the system can be mapped to an effective medium with permittivity and permeability equal to zero simultaneously, and this system can transport wave as if the refractive index is effectively zero. However, not all the triply degenerate states can be described by monopole and dipole excitations and in those cases, the conical dispersion may not be related to an effective zero refractive index. Then, by using 𝐶𝑂𝑀𝑆𝑂𝐿 𝑀𝑢𝑙𝑡𝑖𝑝ℎ𝑦𝑠𝑖𝑐𝑠 software, we demonstrate in the optical regime that such dielectric photonic crystals with reasonable dielectric constants manipulate waves as if they had near-zero refractive indices. By simulating this model, we examine the wave behavior in this system. Also, by using this simulator, we design a zero refractive index waveguide in the optical range and compare how the wave behaves in this waveguide with the zero refractive index waveguides made of metal components.
