Abstract
Hyperbolic metamaterials comprised of an array of plasmonic nanorods provide a unique platform for designing optical sensors and integrating nonlinear and active nanophotonic functionalities. In this work, the waveguiding properties and mode structure of planar anisotropic metamaterial waveguides are characterized experimentally and theoretically. While ordinary modes are the typical guided modes of the highly anisotropic waveguides, extraordinary modes, below the effective plasma frequency, exist in a hyperbolic metamaterial slab in the form of bulk plasmon-polaritons, in analogy to planar-cavity exciton-polaritons in semiconductors. They may have very low or negative group velocity with high effective refractive indices (up to 10) and have an unusual cut-off from the high-frequency side, providing deep-subwavelength (λ0/6–λ0/8 waveguide thickness) single-mode guiding. These properties, dictated by the hyperbolic anisotropy of the metamaterial, may be tuned by altering the geometrical parameters of the nanorod composite.
Highlights
Light interacts with a resonant medium by forming polaritonic waves
We have introduced the effective plasma frequency of the metamaterial to characterize their metal-like behavior for TM-polarized fields via the free-electron Drude model [15]: Re(εzeff(ωpeff)) = 0
Experimentally and theoretically, the mode structure of finite-thickness hyperbolic metamaterial slabs
Summary
Light interacts with a resonant medium by forming polaritonic waves. These are mixed excitations of the electromagnetic field (photons) with quasiparticles related to material resonances. When electromagnetic fields propagate in resonant media, polaritonic waves are formed and their behavior is governed by the dispersion determined by the material resonances around which negative permittivity can be observed [1]. Both phononpolariton and exciton-polaritons can exist in the bulk of the material and at the interface with the adjacent medium as surface electromagnetic waves (surface polaritons). Bulk plasmon-polaritons of an anisotropic plasmonic metamaterial slab can be considered in analogy to exciton-polaritons in a semiconductor cavity Such bulk plasmon-polariton modes can be tailored by controlling the geometry of the metamaterial design, and their properties can be utilized in applications requiring sensitive control over both groupand phase-velocity dispersion, such as waveguides, sensors or nonlinear optical devices.
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