Abstract
We investigated the optical transmission properties of a metamaterial system in which a natural dielectric is inserted between metallic sub-wavelength slit arrays that behave as an artificial dielectric when the incident light wavelength is longer than the slit periodicity. Transmission spectra were measured using terahertz time-domain spectroscopy, and the experimental results were analyzed by simulations based on the finite-difference time-domain method. We revealed that the resonance characteristics are defined by the two diffraction-limit frequencies for the inner and outer openings of the slits, which are different for the insertion of the dielectric. We also determined further details on the blue-shift behavior specific to the even-order resonance modes by accounting for the refractive index of the inserted intermediate dielectric. In addition, we experimentally demonstrated that insertion of a dielectric having a high refraction index enhances the frequency repulsion at the anticrossing, i.e., the coupling strength, between the symmetric and antisymmetric optical modes. These experimental and theoretical results will be essential for understanding and developing applications for hybrid systems composed of dielectrics with both fixed and widely tunable refractive indices.
Highlights
Metallic sub-wavelength slit arrays exhibit remarkable Fabry–Perot-like waveguide resonances when the incident wavelength is longer than the slit periodicity, i.e., below the Rayleigh–Wood diffraction-limit frequency for the slit openings.[1,2,3,4] The effective refractive index of such perforated metallic plates is determined by the ratio of the slit periodicity to the slit width.[2]
No apparent repulsions are found in the control spectra [Figs. 2(a) and 2(b)]. These results prove experimentally that the insertion of a material with a high refractive index enhances the coupling strength between the odd- and even-order resonance modes, and were achieved owing to the use of artificial dielectrics, which have a sufficiently higher effective refractive index than that of the intermediate region
We have investigated experimentally and theoretically the optical transmission properties of a hybrid multi-layered system where a natural dielectric material is sandwiched between artificial dielectrics, i.e., sub-wavelength cut-through metallic slit-array plates
Summary
Metallic sub-wavelength slit arrays exhibit remarkable Fabry–Perot-like waveguide resonances when the incident wavelength is longer than the slit periodicity, i.e., below the Rayleigh–Wood diffraction-limit frequency for the slit openings.[1,2,3,4] The effective refractive index of such perforated metallic plates is determined by the ratio of the slit periodicity to the slit width.[2] Such artificial dielectrics, which have effective indices that can, in principle, be designed to be anywhere within the range from 1 to ∞ by controlling their geometrical parameters, have potential applications in novel functional devices, and can enable research on the optical properties of systems containing transparent materials with very high refractive indices. Systems.[11,12,13,14,15] In this work, we measured the optical transmission spectra of a hybrid system, in which a natural dielectric was inserted between artificial dielectrics formed by metallic sub-wavelength slit arrays, using terahertz time-domain spectroscopy. We experimentally demonstrated that the mode coupling between the even- and odd-order modes is enhanced by the insertion of a material with a high refractive index
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