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We reveal an outstanding potential of water as an inexpensive, abundant and bio-friendly high-refractive-index material for creating tunable all-dielectric photonic structures and metamaterials. Specifically, we demonstrate thermal, mechanical and gravitational tunability of magnetic and electric resonances in a metamaterial consisting of periodically positioned water-filled reservoirs. The proposed water-based metamaterials can find applications not only as cheap and ecological microwave devices, but also in optical and terahertz metamaterials prototyping and educational lab equipment.

We experimentally demonstrate the effect of anomalous breakdown of the effective medium approximation in all-dielectric deeply subwavelength thickness (d ∼ λ/160 − λ/30) multilayers, as recently predicted theoretically [H.H. Sheinfux et al., Phys. Rev. Lett. 113, 243901 (2014)]. Multilayer stacks are composed of alternating alumina and titania layers fabricated using atomic layer deposition. For light incident on such multilayers at angles near the total internal reflection we observe pronounced differences in the reflectance spectra for structures with 10-nm versus 20-nm thick layers, as well as for structures with different layers ordering, contrary to the predictions of the effective medium approximation. The reflectance difference can reach values up to 0.5, owing to the chosen geometrical configuration with an additional resonator layer employed for the enhancement of the effect. Our results are important for the development of new high-precision multilayer ellipsometry methods and schemes, as well as in a broad range of sensing applications.

We propose a graphene hyperlens for the terahertz (THz) range. We employ and numerically examine a structured graphene-dielectric multilayered stack that is an analogue of a metallic wire medium. As an example of the graphene hyperlens in action we demonstrate an imaging of two point sources separated with distance $\lambda_{0}/5$. An advantage of such a hyperlens as compared to a metallic one is the tunability of its properties by changing the chemical potential of graphene. We also propose a method to retrieve the hyperbolic dispersion, check the effective medium approximation and retrieve the effective permittivity tensor.Comment: 5 pages, 5 figure

Strongly confined surface plasmon-polariton modes can be used for efficiently delivering the electromagnetic energy to nano-sized volumes by reducing the cross sections of propagating modes far beyond the diffraction limit, i.e., by nanofocusing. This process results in significant local-field enhancement that can advantageously be exploited in modern optical nanotechnologies, including signal processing, biochemical sensing, imaging and spectroscopy. Here, we propose, analyze, and experimentally demonstrate on-chip nanofocusing followed by impedance-matched nanowire antenna excitation in the end-fire geometry at telecom wavelengths. Numerical and experimental evidences of the efficient excitation of dipole and quadrupole (dark) antenna modes are provided, revealing underlying physical mechanisms and analogies with the operation of plane-wave Fabry-Pérot interferometers. The unique combination of efficient nanofocusing and nanoantenna resonant excitation realized in our experiments offers a major boost to the field intensity enhancement up to ∼ 12000, with the enhanced field being evenly distributed over the gap volume of 30×30×10 nm 3 , and promises thereby a variety of useful on-chip functionalities within sensing, nonlinear spectroscopy and signal processing. [This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Nano Letters, c American Chemical Society after peer review. To access the final edited and published work see http://dx.doi.org/10.1021/acs.nanolett.5b03593.]Keywords: Surface plasmons polaritons, nanofocusing, field enhancement, tapered waveguide, phase-resolved near-field microscopy, optical antennasThe major aspect of focusing of electromagnetic radiation is the possibility of concentrating the energy in a small volume. Because of diffraction, the focusing of freepropagating optical waves is limited in size to the half of the light wavelength in the medium the diffraction limit of light.1 One approach to overcome this limit is to use surface plasmon polaritons (SPPs) surface electromagnetic modes bound to and propagating along metaldielectric interfaces, with electromagnetic fields in a dielectric being coupled to collective free electron oscillations in a metal.2 Spatial confinement of SPP modes in the cross section perpendicular to the propagation direction depends on the material composition and geometric configuration of a waveguiding structure. Notably, some SPP modes (supported, for example, by metal nanowires 3 ) exhibit a unique scaling property in their spatial confinement: the mode is progressively better confined for smaller lateral waveguide dimensions, opening thereby the possibility for guiding extremely confined (i.e., on a deep subwavelength scale) SPP modes 4 as well as for designing SPP-based nanoantennas.5 This feature can further be used for nanofocusing, which is the process of reducing the cross sections of propagating optical modes far beyond the diffraction limit, simply by gradually decreasing lateral waveguid...

Metamaterials (MTMs) claim a lot of attention worldwide. Description of the MTMs in terms of effective parameters is a simple and useful tool for characterisation of their electromagnetic properties. So a reliable effective parameters restoration method is on demand. In this paper we report about our activity and advances in the effective properties of metamaterials characterization.We present here the wave propagation retrieval method in two formulations: for MTMs with linear eigenwaves and for chiral MTMs with circular eigenwaves. The advantages and constraints of the method are noted. The case studies of the negative-index, ultra-high refractive index and chiral MTMs validate the method. Keywords: metamaterial, effective parameters, effective properties, restoration, retrieval, homogenisation INTRODUCTIONIn the recent years, metamaterials (MTMs) attracted a lot of attention worldwide due to their new flashing properties. The range of MTMs applications is very broad, starting from the negative-index superresolution lenses and nanocouplers [1], transformation optics [2] to the MTMs with giant gyrotropic effects, like optical activity [3] and circular dichroism [4]. In the cases when effective parameters (EPs) (refractive index n, impedance Z, permittivity and permeability µ) can be introduced in the correct way [5], a reliable retrieval procedure is on demand. Assigning some certain values to EPs is the simple and useful means, by which the properties of the MTM can be described and the performance of the MTM based devices predicted.Recently we have proposed a simple retrieval method based on the wave propagation phenomenon [19], which we refer to as the wave propagation retrieval method (WPRM). In this paper we show how WPRM works for negative index and high-index MTMs. We also extend the method to the case of chiral MTMs. The constraints and advantages of WPRM are mentioned as well.

We demonstrate the use of amplitude-and phase-resolved near-field mapping for direct characterization of plasmonic slot waveguide mode propagation and excitation with nanocouplers in the telecom wavelength range. We measure mode's propagation length, effective index and field distribution and directly evaluate the relative coupling efficiencies for various couplers configurations. We report 26-and 15-fold improvements in the coupling efficiency with two serially connected dipole and modified bow-tie antennas, respectively, as compared to that of the short-circuited waveguide termination. [This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Nano Letters, c American Chemical Society after peer review. To access the final edited and published work see http://dx.doi.org/10.1021/nl501207u.] Keywords: nanocoupler, surface plasmon, slot waveguide, nanoantenna, s-SNOM, near-field microscopy Great advantages offered by plasmonics to optical waveguiding are extreme subwavelength localization of guided modes close to the metal interface 1 together with electrical tunability of electromagnetic waves via intrinsic metallic contacts 2 . Plasmonic waveguides are therefore considered as a future generation of optical interconnects in integrated circuits for datacom technologies 3 . Inevitably, with the appearance of nanoscale waveguides, a new challenge has emerged: how to effectively couple the diffraction-limited optical waves into deep-subwavelength plasmonic waveguides. Various approaches have been utilized ranging from lenses to grating couplers 4 . However, the most compact solution is, an antenna based nanocoupler.Antenna is a common tool to capture free-space propagating radio-waves with more than a centurylong history 5 . Employment of metal-based antennas in photonics started only in the last two decades owing to the progress in high-resolution nanofabrication techniques 6,7 . Usage of plasmonic antennas 8 to couple light to plasmonic waveguides has been suggested theoretically 9-15 and then confirmed experimentally with cross-polarization microscopy measurements in the nearinfrared 16 and with near-field microscopy in optical 17 , telecom 18 and mid-infrared 19 ranges. Nevertheless, the amplitude-and phase-resolved measurements of the antenna-excited slot plasmons in the telecom range (with the free-space wavelength around 1.55 µm) have not been reported so far. It should be emphasized that the usage of phase-resolved near-field mapping is indispensable for direct characterization of the mode effective index as well as for revealing the symmetry of excited plasmonic modes 19 .In this Letter we report, for the first time to our knowledge, the amplitude-and phase-resolved near-field characterization of plasmonic slot waveguides and antenna based nanocouplers in the telecom wavelength range. Illumination with a wide laser beam excites both slot plasmons confined within a dielectric gap in a metal film and surface plasmon polaritons (SPP) propagating along ...

Homogenization of metamaterials is a crucial issue as it allows to describe their optical response in terms of effective wave parameters as e.g. propagation constants. In this paper we consider the possible homogenization of chiral metamaterials. We show that for meta-atoms of a certain size a critical density exists above which increasing coupling between neighboring meta-atoms prevails a reasonable homogenization. On the contrary, a dilution in excess will induce features reminiscent to photonic crystals likewise prevailing a homogenization. Based on Bloch mode dispersion we introduce an analytical criterion for performing the homogenization and a tool to predict the homogenization limit. We show that strong coupling between meta-atoms of chiral metamaterials may prevent their homogenization at all.