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.

Titanium oxynitride (TiON) thin films are fabricated using reactive magnetron sputtering. The mechanism of their growth formation is explained, and their optical properties are presented. The films grown when the level of residual oxygen in the background vacuum was between 5 nTorr to 20 nTorr exhibit double epsilon-near-Zero (2-ENZ) behavior with ENZ1 and ENZ2 wavelengths tunable in the 700-850 and 1100-1350 nm spectral ranges, respectively. Samples fabricated when the level of residual oxygen in the background vacuum was above 2 × 10 Torr exhibit nonmetallic behavior, while the layers deposited when the level of residual oxygen in the background vacuum was below 5 × 10 Torr show metallic behavior with a single ENZ value. The double ENZ phenomenon is related to the level of residual oxygen in the background vacuum and is attributed to the mixture of TiN and TiON and TiO phases in the films. Varying the partial pressure of nitrogen during the deposition can further control the amount of TiN, TiO, and TiON compounds in the films and, therefore, tune the screened plasma wavelengths. A good approximation of the ellipsometric behavior is achieved with Maxwell-Garnett theory for a composite film formed by a mixture of TiO and TiN phases suggesting that double ENZ TiON films are formed by inclusions of TiN within a TiO matrix. These oxynitride compounds could be considered as new materials exhibiting double ENZ in the visible and near-IR spectral ranges. Materials with ENZ properties are advantageous for designing the enhanced nonlinear optical response, metasurfaces, and nonreciprocal behavior.

Several new plasmonic materials have recently been introduced in order to achieve better temperature stability than conventional plasmonic metals and control field localization with a choice of plasma frequencies in a wide spectral range. Here, epitaxial SrRuO3 thin films with low surface roughness fabricated by pulsed laser deposition are studied. The influence of the oxygen deposition pressure (20–300 mTorr) on the charge carrier dynamics and optical constants of the thin films in the near-infrared spectral range is elucidated. It is demonstrated that SrRuO3 thin films exhibit plasmonic behavior of the thin films in the near-infrared spectral range with the plasma frequency in 3.16–3.86 eV range and epsilon-near-zero wavelength in 1.11–1.47 μm range that could be controlled by the deposition conditions. The possible applications of these films range from the heat-generating nanostructures in the near-infrared spectral range, to metamaterial-based ideal absorbers and epsilon-near-zero components, where the interplay between real and imaginary parts of the permittivity in a given spectral range is needed for optimizing the spectral performance.

During the course of the recent work, we have found a typo in a Matlab code used for plotting analytical dispersions of the modes. This has led to a wrong axis scale in Fig. 3 (b,d) and wrong mode number assignment in Fig. 4 (c) and Fig. 6 (a,e,f). The corrected figures are presented below.The discussion of Figure 3 should read (the last 2 sentences of the 1 st paragraph on p. 348): "In contrast, the hyperbolic dispersion allows modes with q>4, with practical limits eventually imposed by both losses and the geometry of the nanorod composite as the EMT breaks down for wavevectors near the boundary of the Brillouin zone. For the considered example (Fig. 3d), the modes are confined to the metamaterial (waveguided modes)."Figure 3 (a) and (b) Isofrequency contours in the first Brillouin zone calculated for a frequency corresponding to a free-space wavelength λ 0 = 700 nm for an infinite Au nanorod metamaterial with p = 0.5 for (a) ordinary, TE, and (b) extraordinary, TM, modes. In the elliptic regime (a), the dispersion is bounded and corresponds to that of a typical anisotropic dielectric. The isofrequencies contours in the superstrate (air) and the substrate (glass) are also shown. (c) and (d) The mode position of a metamaterial slab (400 nm in thickness) shown as dots corresponding to intersection of the isofrequency contours of the infinite metamaterial with the quantized values of k z = q(π/l), where q = ± 1, ± 2, ± 3, . . . resulting from the finite size of the slab in the z-direction. (e) and (f) Angular spectra of reflectance of the metamaterial slab as in (c) and (d) for λ 0 = 700 nm calculated using TMM. The position of the modes obtained analytically is shifted to higher wavevectors due to the analytic model assumptions, influencing the confinement of the modes.

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