Periodic Dielectric Structures Research Articles

Combined dielectric and plasmon resonance for giant enhancement of Raman scattering

Combined dielectric/metal resonators for colossal enhancement of inelastic light scattering are developed and their properties are investigated. It is shown that a record enhancement factor of 2 × 108 can be obtained using these structures. The dielectric resonators are fabricated on Si/SiO2 substrates where periodic arrays of square 10- to 200-nm-high dielectric pillars are produced via electron-beam lithography and plasma etching. The lateral size a of the pillars varies between 50 and 1500 nm, and their period in the array is 2a. To make a combined dielectric/metal resonator, a nanostructured layer of silver is deposited onto the fabricated periodic dielectric structure by thermal evaporation. It is established that, for a fixed height of the dielectric pillars, the Raman scattering enhancement factor experiences pronounced oscillations as a function of the period (and size) of the pillars. It is shown that these oscillations are determined by the modes of the dielectric resonator and governed by the relation between the excitation laser wavelength and the planar size of the dielectric pillars.

Photonic realization of topologically protected bound states in domain-wall waveguide arrays

We present an analytical theory of topologically protected photonic states for the two-dimensional Maxwell equations for a class of continuous periodic dielectric structures, modulated by a domain wall. We further numerically confirm the applicability of this theory for three-dimensional structures.

Guided-mode resonator for thin InGaAs P-i-N short-wave infrared photo-diode

We investigate a resonant photodiode transferred onto a gold mirror. This comprises a backside dielectric subwavelength periodic structure and an absorbing region as thin as 90 nm. Electro-optical characterizations of individual pixels featuring focal-plane array-compatible geometries are fully explained by electro-magnetic simulations. In particular, we observe a near perfect collection of the photo-carriers and external quantum efficiency of up to 71% around 1.55 μm.

2D-ordered dielectric sub-micron bowls on a metal surface: a useful hybrid plasmonic-photonic structure.

Recently, it has been demonstrated that the combination of periodic dielectric structures with metallic structures provides an efficient means to yield a synergetic optical response or functionality in the resultant hybrid plasmonic-photonic systems. In this work, a new hybrid plasmonic-photonic structure of 2D-ordered dielectric sub-micron bowls on a flat gold surface was proposed, prepared, and theoretically and experimentally characterized. This hybrid structure supports two types of modes: surface plasmon polaritons bound at the metallic surface and waveguided mode of light confined in the cavity of bowls. Optical responses of this hybrid structure as well as the spatial electric field distribution of each mode are found to be strongly dependent on the structural parameters of this system, and thus could be widely modified on demand. Importantly, compared to the widely studied hybrid systems, namely the flat metallic surface coated with a monolayer array of latex spheres, the waveguided mode with strong field enhancement appearing in the cavities of bowls is more facilely accessible and thus suitable for practical use. For demonstration, a 2D-ordered silica sub-micron bowl array deposited on a flat gold surface was fabricated and used as a regenerable platform for fluorescence enhancement by simply accommodating emitters in bowls. All the simulation and experiment results indicate that the 2D-ordered dielectric sub-micron bowls on a metal surface should be a useful hybrid plasmonic-photonic system with great potential for applications such as sensors or tunable emitting devices if appropriate periods and materials are employed.

Analysis and optimization of matching two-dimensionally periodic dielectric structures with cone-shaped cavities

The problem of scattering of plane electromagnetic waves by two-dimensionally periodic dielectric structures with cone-shaped cavities placed on a homogeneous dielectric substrate is considered. A modified hybrid projection method for solving this problem, which combines the coupled-wave method (incomplete Galerkin method), the projection field matching on domains’ boundaries, and the one-dimensional finite-element method, is proposed. The modified method enables one to avoid the use of the excessive number of unknown expansion coefficients, typical for the previous versions. The method is used for calculating the effective permittivity of a dielectric layer of finite thickness with cylindrical holes and for optimizing the parameters of conical cavities providing the matching of a dielectric half-space for various incidence angles.

Circular Split Ring Meta-Surfaces Variation Study as Surface Wave Suppressor

This work focuses on three different edge variation modified on the same circular split ring (CSR) longest arm of metallo dielectric periodic structure and its corresponding electromagnetic bandgap (EBG) behaviour as an alternative step to suppress surface wave. Three variants of circular split ring were studied to fulfill the requirements: Normal edge, triangular tip and tapered tip. These structures were optimized using Eigenmode Solver (EmS) with Advanced Krylov Subspace (AKS) method for full wave dispersion diagram. Final results shows a stable and good EBG region achieved from this CSR specifically within the 5.9 to 6 GHz region. The normal tip CSR that has a stable and good bandgap exits from 5.9265 GHz to 5.9516 GHz in between mode 5 and 6. While the triangular tip CSR bandgap is from 6.0214 GHz to 6.0378 GHz and tapered tip is from 6.0214 GHz to 6.0378 GHz.

3D periodic dielectric composite homogenization based on the generalized source method

The article encloses a new Fourier space method for rigorous optical simulation of three-dimensional (3D) periodic dielectric structures. The method relies upon a rigorous solution of Maxwell’s equations in complex composite structures by the generalized source method. Extremely fast graphics processing unit-enabled calculations provide a possibility for an efficient search of eigenmodes in 3D periodic complex structures on the basis of a rigorously obtained resonant electromagnetic response. The method is applied to the homogenization problem, demonstrating anisotropic dielectric tensor retrieval.

Structural Color for Security Printing: Patterned Robust Colloidal Crystals

Structural color is a unique optical property of nano- or microstructured materials with periodic dimensions similar to the wavelength of visible light. Characteristic color is produced through reflectance, interference, scattering, diffraction or refraction of incident light of a specific wavelength in visible spectrum, thereby producing a specific color or so-called structural color. Structural color is seen throughout nature, notably Morpho butterflies and opals present a striking sheen and accompanying vivid hue. Prior analysis of minerals and organisms that produce these distinctive colors allows for continuing analysis of color developing mechanisms [1]. Recently, with improvements in micro-fabrication, trial reproduction of these naturally occurring structural colors is proceeding across the field of Biomimetics [2]. Mono-dispersed micro-particles, structured in an ordered arrangement, are called colloidal crystals. Through Bragg reflection they exhibit structural color with a vivid hue. Colloidal crystals are relatively easy to produce by self-organization, and since dielectric periodic structures can be used as a photonic crystal for controlling electromagnetic waves, it has been extensively studied as a structural color element and photonic crystal. Some of the methods for manufacturing colloidal crystals include capillary method, electric electrophoresis, spin coating, spray coating, and substrate raising [3 - 6]. The color developing mechanism for structural color differs from pigment and does not absorb a specific wavelength, therefore in principle, fading from UV rays should be reduced. These materials can be used in applications that require pigments with excellent light-resistance and durability. In addition, since these colored micro-particle aggregates are non-toxic with a high level of safety, they show promise for wide use in printed materials. Here we present research results involving the formation of a pattern of stable colloidal crystals on various substrates and exploring their suitability for use in printed materials. Monodisperse silica nano-particles with a diameter of 300 nm were dispersed in a highly polar solvent. As the solvent evaporates the particles self-assemble into colloidal crystals. By depositing this dispersed suspension as an ink with a direct write printer (aerosol jet) we confirmed the ability to print colloidal crystals with structural color in any pattern. The cohesion of self-assembled colloidal crystals relies on electrostatic attraction making them extremely brittle with limited practical use. As such, a polymer was added to the suspension to reinforce the colloidal crystal structure with limited influence on the self-assembly mechanism. Thus, a strong coating is produced while also producing the desired color effect. Printed colloidal crystals produced by this method are difficult to reproduce by color copying and traditional printing methods considering the color and gloss change depending on the viewing angle. Figure 1 shows a feature printed using the colloidal crystal ink under various lighting/viewing conditions. Also, since it is possible to direct print any pattern, the method is amenable to variable data printing, providing a tamper prevention effect. Thus, these materials are attractive for use in security printing applications.

Skew Incidence Plane-Wave Scattering From 2-D Dielectric Periodic Structures: Analysis by the Mortar-Element Method

A full-wave simulator of 2-D dielectric periodic structures under skew plane wave incidence is presented in this paper. A differential formulation is used and the boundary value problem is solved by means of a multi-domain spectral method. Suitable mappings allow the efficient analysis of dielectric elements with rounded corner cross sections. A comparison with the results obtained by the method of moments and with a commercial simulator is presented for an array of dielectric rods and for a surface-relief diffraction grating.

An enhanced photonic crystal biosensor‐based immunodiagnostic assay for detection of soluble transferrin receptor as a biomarker of iron deficiency (813.7)

Identification of populations at risk for iron deficiency is of critical concern. Studies on the detection of soluble transferrin receptor (sTfR) using a PC biosensor assay are presented. sTfR (85kDa) is a favorable biomarker of iron status as it is less confounded by inflammation related factors. PCs are periodic dielectric surface structures designed to reflect a narrow band of wavelengths when illuminated by a broadband light source. Adsorption and binding of biomolecules on the PC surface elicits a wavelength shift (PWV) measured in nm. The PC surface of 384‐well microplate was functionalized with silane for immobilization of capture antibodies (Ab), followed by a blocking step. sTfR antigen was added before secondary Ab was dispensed in standard and control wells. Secondary Ab was functionalized with iron‐oxide nanoparticles (30 nm) to enhance signal‐to‐noise ratio. Antigen‐Ab interactions were followed using the BIND system. A sTfR standard curve (200‐5 ng/ml) was created and compared against a commercial ELISA kit. Ab selectivity, limit of detection (LOD), and dose‐response were evaluated (two experiments, n=4/sample). The PC biosensor showed a LOD of 28 ng/ml, a linear response ([PWV=0.8 + 8.4(ug/ml)‐1]; R2=0.98) and limited non‐specific binding against BSA. This study demonstrates the feasibility of the PC biosensor as an immunodiagnostic assay for sTfR detection.Grant Funding Source: ACES VISION 20/20 Grant

Metamaterial band theory: fundamentals & applications

Remarkable progress has been made over the past decade in controlling light propagation and absorption in compact devices using nanophotonic structures and metamaterials. From sensing and modulation, to on-chip communication and light trapping for solar cells, new device applications and opportunities motivate the need for a rigorous understanding of the modal properties of metamaterials over a broad range of frequencies. In this review, we provide an overview of a metamaterial band theory we have developed that rigorously models the behavior of metamaterials made of dispersive materials such as metals. The theory extends traditional photonic band theory for periodic dielectric structures by coupling the mechanical motion of electrons in the metal directly to Maxwell’s equations. The solution for the band structures of metamaterials is then reduced to a standard matrix eigenvalue problem that nevertheless fully takes into account the dispersive properties of the constituent materials. As an application of the metamaterial band theory, we show that one can develop a perturbation formalism based on this theory to physically explain and predict the effect of dielectric refractive index modulation or metallic plasma frequency variation in metamaterials. Furthermore, the metamaterial band theory also provides an intuitive physical picture of the source of modal material loss, as well as a rigorous upper bound on the modal material loss rate of any plasmonic, metamaterial structure. This in turn places fundamental limits on the broadband operation of such devices for applications such as photodetection and absorption.

Étude comparative des plaques verrouillées anatomiques (3,5 mm versus 4,5 mm) dans le traitement des fractures articulaires de l’extrémité proximale du tibia

In this paper, the first two total omnidirectional photonic band gaps (OBGs) of one-dimensional (1D) superconductor–dielectric photonic crystals (SDPCs) which composed of dielectric–dielectric and superconductor–dielectric periodic structures have been investigated theoretically by using the transfer matrix method (TMM). Those OBGs originate from Bragg gaps. From the analysis, it is found that this kind of heterostructure has wider frequency ranges of total OBGs for both polarizations in comparison to the dielectric photonic crystals (DPCs) or SDPCs, and the bandwidths of OBGs can be notably enlarged by increasing the thickness of superconductor layer and decreasing the ambient temperature.

Anomalous Refractions Based on Photonic Band Modulation of Photonic Crystals

Due to the existence of photonic bandgap derived from the periodical dielectric structure in wavelength scale, many novel optical phenomena can be demonstrated in photonic crystals (PhCs). Anomalous propagation of electromagnetic waves in X-band is demonstrated experimentally in a two-dimensional triangular lattice PhC. The experimental measurements of electric field are carried out in a near-field scanning system. The phenomena of anomalous refractions are observed and analyzed in respect of anisotropy of equal frequency surfaces in the PhC. The analysis results of numerical simulation are compared with the experimental measurements and good agreements are obtained.

Fractional tunnelling resonance in plasmonic media.

Metals can transmit light by tunnelling when they possess skin-depth thickness. Tunnelling can be resonantly enhanced if resonators are added to each side of a metal film, such as additional dielectric layers or periodic structures on a metal surface. Here we show that, even with no additional resonators, tunnelling resonance can arise if the metal film is confined and fractionally thin. In a slit waveguide filled with a negative permittivity metallic slab of thickness L, resonance is shown to arise at fractional thicknesses (L = Const./m; m = 1,2,3,…) by the excitation of ‘vortex plasmons'. We experimentally demonstrate fractional tunnelling resonance and vortex plasmons using microwave and negative permittivity metamaterials. The measured spectral peaks of the fractional tunnelling resonance and modes of the vortex plasmons agree with theoretical predictions. Fractional tunnelling resonance and vortex plasmons open new perspectives in resonance physics and promise potential applications in nanotechnology.

Dynamic Changes in Structural Color of a Lamellar Block Copolymer Photonic Gel during Solvent Evaporation

A high molecular weight, lamellar block copolymer (BCP) can exhibit a photonic stop band in the visible range of wavelengths due to the one-dimensional periodic dielectric layer structure. After dissolving a high molecular weight BCP in a neutral solvent, solvent evaporation causes microphase separation, forming a so-called “photonic gel” at a quite low polymer concentration (∼10 wt %). Moreover, by allowing the solvent to further evaporate, the reflected color can be tuned over the entire range of the visible spectrum. Here, a polystyrene–polyisoprene diblock (PS-b-PI) is dissolved in cumene, and the solution was placed between two glass substrates. The radial concentration gradient during slow evaporation of the cumene generates a “rainbow-like” set of reflected colors from the photonic gel. Based on local measurement of the reflectivity along the radial direction of the photonic gel, the radial solvent composition was calculated and the experimentally observed reflectivity was compared to results simul...

Volume integral equation for analysis of three-dimensional scattering from dielectric frequency-selective structures

The space-domain volume integral equation method is presented for the analysis of three-dimension scattering from dielectric frequency-selective structures involving homogeneous and inhomogeneous lossy materials. The method directly solves for the electric field in order to easily enable the periodic boundary conditions in the spatial domain. The special basis and test functions are introduced to deal with the current continuity in periodic boundaries. The computation of the spatial domain periodic Green’s function (PGF) is accelerated by the modified Ewald transformation, so that a very thick periodic structure can also be analyzed efficiently and accurately. The PGF mentioned above is of free-space type and very smooth and amenable to interpolation. Thus, optimized interpolation procedures for the PGFs can be applied, resulting in a considerable reduction of matrix-filling time without any significant influence on the accuracy. A study of the scattering parameters of a multilayered dielectric periodic structure is accomplished by imposing the boundary conditions in terms of the multimode scattering matrix. Numerical examples show the reliability and accuracy of the proposed method.

Ballistic charge transport in graphene and light propagation in periodic dielectric structures with metamaterials: A comparative study

We explore the optical properties of periodic layered media containing left-handed metamaterials. This study is based on several analogies between the propagation of light in metamaterials and charge transport in graphene. We derive the conditions for these two problems become equivalent, i.e., the equations and the boundary conditions when the corresponding wave functions coincide. We show that the photonic band-gap structure of a periodic system built of alternating left- and right-handed dielectric slabs contains conical singularities similar to the Dirac points in the energy spectrum of charged quasiparticles in graphene. Such singularities in the zone structure of the infinite systems give rise to rather unusual properties of light transport in finite samples. In an insightful numerical experiment (the propagation of a Gaussian beam through a mixed stack of normal and meta-dielectrics) we simultaneously demonstrate four Dirac point-induced anomalies: (i) diffusion-like decay of the intensity at forbidden frequencies, (ii) focusing and defocussing of the beam, (iii) absence of the transverse shift of the beam, and (iv) a spatial analogue of the Zitterbewegung effect. All of these phenomena take place in media with non-zero average refractive index, and can be tuned by changing either the geometrical and electromagnetic parameters of the sample,or the frequency and the polarization of light.

Lasing action in strongly coupled plasmonic nanocavity arrays

Periodic dielectric structures are typically integrated with a planar waveguide to create photonic band-edge modes for feedback in one-dimensional distributed feedback lasers and two-dimensional photonic-crystal lasers. Although photonic band-edge lasers are widely used in optics and biological applications, drawbacks include low modulation speeds and diffraction-limited mode confinement. In contrast, plasmonic nanolasers can support ultrafast dynamics and ultrasmall mode volumes. However, because of the large momentum mismatch between their nanolocalized lasing fields and free-space light, they suffer from large radiative losses and lack beam directionality. Here, we report lasing action from band-edge lattice plasmons in arrays of plasmonic nanocavities in a homogeneous dielectric environment. We find that optically pumped, two-dimensional arrays of plasmonic Au or Ag nanoparticles surrounded by an organic gain medium show directional beam emission (divergence angle <1.5° and linewidth <1.3nm) characteristic of lasing action in the far-field, and behave as arrays of nanoscale light sources in the near-field. Using a semi-quantum electromagnetic approach to simulate the active optical responses, we show that lasing is achieved through stimulated energy transfer from the gain to the band-edge lattice plasmons in the deep subwavelength vicinity of the individual nanoparticles. Using femtosecond-transient absorption spectroscopy, we verified that lattice plasmons in plasmonic nanoparticle arrays could reach a 200-fold enhancement of the spontaneous emission rate of the dye because of their large local density of optical states.

Unlocked evanescent waves in periodic structures

We predict the existence of evanescent modes with unlocked phases in two-dimensional (2D) dielectric periodic structures. Contrary to what is known for one-dimensional structures, where evanescent fields lock to the host modulation, we show that in 2D systems a new class of evanescent modes exists with an unlocked real part of the wave vector. Hence, beams constructed from such unlocked evanescent waves can exhibit spatial effects. A significant focalization of a beam propagating within the band gap of a flat photonic crystal slab is also shown. The predicted phenomenon is expected to be generic for spatially modulated materials.

Periodic dielectric structures for light-trapping in InGaAs/GaAs quantum well solar cells

We study dielectric diffraction gratings for light-trapping in quantum well solar cells and compare their performance with plasmonic and Lambertian light-trapping structures. The optimum structural parameters are identified for symmetric uni-periodic, symmetric bi-periodic and asymmetric bi-periodic gratings. The enhancement in short-circuit current density from the quantum well region with respect to a reference cell with no diffraction grating is calculated. The ratio of this enhancement to the maximum achievable enhancement (i.e. no transmission losses) is 33%, 75% and 74%, respectively for these structures. The optimum asymmetric and symmetric bi-periodic structures perform closest to Lambertian light-trapping, while all three optimum grating structures outperform optimum plasmonic light-trapping. We show that the short-circuit current density from the quantum well region is further enhanced by incorporating a rear reflector.