We report on theoretical analysis and experimental validation of the applicability of the effective medium approximation
to deeply subwavelength (period ⩽λ/30) all-dielectric multilayer structures. Following the theoretical prediction of the
anomalous breakdown of the effective medium approximation [H. H. Sheinfux et al., Phys. Rev. Lett. 113, 243901
(2014)] we thoroughly elaborate on regimes, when an actual multilayer stack exhibits significantly different properties
compared to its homogenized model. Our findings are fully confirmed in the first direct experimental demonstration of
the breakdown effect. 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 (up to 0.5) for structures with different layers ordering and different but still deeply
subwavelength thicknesses. Such big reflectance difference values resulted from the special geometrical configuration
with an additional resonator layer underneath the multilayers employed for the enhancement of the effect. Our results are
important for the development of new homogenization approaches for metamaterials, high-precision multilayer
ellipsometry methods and in a broad range of sensing applications.
By now superresolution imaging using hyperbolic metamaterial (HMM) structures – hyperlenses – has been demonstrated both theoretically and experimentally. The hyperlens operation relies on the fact that HMM allows propagation of waves with very large transverse wavevectors, which would be evanescent in common isotropic media (thus giving rise to the diffraction limit). However, nearly all hyperlenses proposed so far have been suitable only for very strong scatterers – such as holes in a metal film. When weaker scatterers, dielectric objects for example, are imaged then incident light forms a very strong background, and weak scatterers are not visible due to a poor contrast.
We propose a so-called dark-field hyperlens, which would be suitable for imaging of weakly scattering objects. By designing parameters of the HMM, we managed to obtain its response in such way that the hyperlens structure exhibits a cut-off for waves with small transverse wavevectors (low-k waves). This allows the structure to filter out the background illumination, which is contained in low-k waves. We numerically demonstrate that our device achieves superresolution imaging while providing the strong contrast for weak dielectric scatterers. These findings hold a great promise for dark-field superresolution, which could be important in real-time dynamic nanoscopy of label-free biological objects for example.
We theoretically investigate general existence conditions for broadband bulk large-wavevector (high-k) propagating waves (such as volume plasmon polaritons in hyperbolic metamaterials) in arbitrary subwavelength periodic multilayers structures. Treating the elementary excitation in the unit cell of the structure as a generalized resonance pole of reflection coefficient and using Bloch’s theorem, we derive analytical expressions for the band of large-wavevector propagating solutions. We apply our formalism to determine the high-k band existence in two important cases: the well-known metaldielectric and recently introduced graphene-dielectric stacks. We confirm that short-range surface plasmons in thin metal layers can give rise to hyperbolic metamaterial properties and demonstrate that long-range surface plasmons cannot. We also show that graphene-dielectricmultilayers tend to support high-k waves and explore the range of parameters, where this is possible, confirming the prospects of using graphene for materials with hyperbolic dispersion. The suggested formalism is applicable to a large variety of structures, such as continuous or structured microwave, terahertz (THz) and optical metamaterials, optical waveguide arrays, 2D plasmonic and acoustic metamaterials.
Photoelectric properties of metamaterials comprising asymmetrically shaped, similarly oriented metallic nanoparticles embedded in a homogeneous semiconductor matrix are theoretically and numerically studied. The asymmetric shape of the nanoparticles is found to result in the existence of a preferred direction where “hot” photoelectrons are emitted from the nanoparticle surface under the action of the localized plasmonic resonance excited in the nanoparticles. The resulting directional photocurrent flow occurring when nanoparticles are uniformly illuminated by a homogeneous plane wave is the direct analogy of the photogalvanic effect known to exist in naturally occurring non-centrosymmetric media. This plasmonic bulk photovoltaic effect is intermediate between the inner photoelectric effect in bulk media and the outer photoelectric effect at macroscopic interfaces. The results obtained are valuable for characterizing photoemission and photoconductive properties of plasmonic nanostructures. They can find many uses for photodetection-related and photovoltaic applications.
In this work, we show theoretically and confirm experimentally that thin metal membranes patterned with an array of
slot dimers (or their Babinet analogue with metal rods) can function as a versatile spectral and polarization filter. We
present a detailed covariant multipole theory for the electromagnetic response of an arbitrary dimer based on the Green
functions approach. The theory confirms that a great variety of polarization properties, such as birefringence, chirality
and elliptical dichroism, can be achieved in a metal layer with such slot-dimer patterning (i.e. in a metasurface). Optical
properties of the metasurface can be extensively tuned by varying the geometry (shape and dimensions) of the dimer, for
example, by adjusting the sizes and mutual placement of the slots (e.g. inter-slot distance and alignment angle). Three
basic shapes of dimers are analyzed: II-shaped (parallel slots), V-shaped, and T-shaped. These particular shapes of
dimers are found to be sensitive to variations of the slots lengths and orientation of elements. Theoretical results are well
supported by full-wave three-dimensional simulations. Our findings were verified experimentally on the metal
membranes fabricated using UV lithography with subsequent Ni growth. Such metasurfaces were characterized using
time-domain THz spectroscopy. The samples exhibit pronounced optical activity (500 degrees per wavelength) and high
transmission: even though the slots cover only 4.3 % of the total membrane area the amplitude transmission reaches 0.67
at the resonance frequency 0.56 THz.
Propagation of large-wavevector bulk plasmonic waves in multilayer hyperbolic metamaterials (HMMs) with two levels of structuring is theoretically studied. It is shown that when the parameters of a subwavelength metal-dielectric multilayer (“substructure”) are modulated (“superstructured”) on a larger, wavelength scale, the propagation of bulk plasmon polaritons in the resulting multiscale HMM is subject to photonic band gap phenomena. A great degree of control over such plasmons can be exerted by varying the superstructure geometry. As an example, Bragg reflection and Fabry-Perot resonances are demonstrated in multiscale HMMs with periodic superstructures. More complicated, aperiodically ordered superstructures are also considered, with fractal Cantor-like multiscale HMMs exhibiting characteristic self-similar spectral signatures in the high-k band. The multiscale HMM concept is shown to be a promising platform for using high-k bulk plasmonic waves as a new kind of information carriers, which can be used in far-field subwavelength imaging and plasmonic communication.
Based on analysis of light propagation in multiple cavity aperiodic structures, a filter with three narrow passbands with high transmission is designed. The design is implemented for use in express early-stage oral cancer screening by means of Raman spectroscopy. A combination of SiO2/Nb2O5 is used in a vacuum deposition process to ensure high refractive index contrast and durability of materials. The approach enables the development of simple and affordable Raman testers for multiple medical, forensic, and environmental applications.
Bistable lasing in twin coupled microcavities is demonstrated analytically and numerically, underlying a new principle of a
multiple-wavelength microlaser where the lasing wavelength is switched by locking into the desired mode in a multimode
resonator. The bistability appears due to an interplay between coherent and incoherent mode interaction processes, assisted
by similarity between the spatial intensity distribution of the modes in the gain region. The wavelength switching dynamics
in a model system of twin defects in a photonic crystal is explained on the basis of the theoretical analysis presented.
Spectral and localization properties of electromagnetic wave propagation in fractal nanostructures have been reviewed and summarized. Quarter-wave binary multilayer structures have been chosen as a simplest model that would allow to isolate effects pertaining to the geometrical organization of the structure. Intra- and inter-generation scaling relations have been obtained and compared to those known for quasiperiodic structures. Localization patterns have been shown to have an intermediate form between extended and localized eigenstates.
Influence of material anisotropy and gyrotropy on optical properties of fractal multilayer nanostructures is theoretically investigated. Gyrotropy is found to uniformly rotate the output polarization for bi-isotropic multilayers without any changes in transmission spectra. When introduced in a polarization splitter based on a birefringent
fractal multilayer, isotropic gyrotropy is found to resonantly alter output polarizations without shifting of transmission peak frequencies. The design of frequency-selective absorptionless polarizers for polarization-sensitive integrated optics is outlined.
Transmission properties of ultra-short pulses propagating through 1-D photonic crystals (PCs) with multiple cavities were experimentally investigated. Coupling between cavities is responsible for a wide resonance, inside the PC gap, suitable to distortion free propagation of 70 fs pulses at 800 nm. Geometry induced anomalous dispersion across the resonance allows chirp compensation of 70 fs pulses. We use an autocorrelator set-up in order to investigate chirp compensation effect by measuring the time duration of input and output pulses. Measurements are performed for different incidence angle. Results show that complete chirp compensation of 10 fs chirping occurs for an incidence angle of 20 deg.
We propose to represent complex non-periodic deterministic multilayer nanostructures as numbers in base equal to the number of constituent layer types, e.g., binary numbers for binary multilayers. We have shown that such numbers have correlation with geometrical and spectral properties of nanostructures in question. Possible applications for number identification and information coding are discussed. Numbers corresponding to fractal multilayers (fractal numbers) are shown to possess distinct factorization properties, which can be applied in non-symmetric cryptography. Using multilayers as reverse engineering proof optical keys or embedded identification elements is also considered.
We have studied biaxial, birefringent, one-dimensional multilayer structures and found a wavelength region where the phase of one specific polarizatin component of the transmitted field increases with wavelength, giving rise to unusual polarization dependent dispersive effects of the input beam. We have analysed the delay obtained with birefringent one-dimensional multilayer structures and the effect of the dispersion in the materials to generate anomalous phase in the spectrum.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.