Omnidirectional Band Research Articles

Reconfigurable (4, 62) and (4, 82) Archimedean plasma photonic crystals in dielectric barrier discharge

Archimedean photonic crystal has become a research area of great interest due to its various unique properties. Here, we experimentally demonstrate the realization of reconfigurable (4, 62) and (4, 82) Archimedean plasma photonic crystals (APPCs) by use of dielectric barrier discharges in air. Dynamical control on both the macrostructures including the lattice symmetry and the crystal orientation, and the microstructures including the fine structures of scattering elements has been achieved. The formation mechanisms of APPCs are studied by time-resolved measurements together with numerical simulations. Large omnidirectional band gaps of APPCs have been obtained. The tunable topology of APPCs may offer new opportunities for fabricating multi-functional and highly-integrated microwave devices.

Angular dependence of photonic band gap and omni-directional reflection in one-dimensional photonic crystal applied to a thermophotovoltaic device

In this work, we present a theoretical study and a numerical simulation on omnidirectional reflection in one-dimensional photonic crystal structures for a thermophotovoltaic device. The optical properties are determined using the transfer matrix method. The results show that the angular dependence of photonic bandgaps depends on refractive index contrast and, polarization. However, for both TE and TM polarization, a reflectivity peak with 100% reflectivity is observed. The Te/SiO2 structure is the one with the largest bandwidth of omnidirectional photonic band gap compared with the TiO2/SiO2 and Si/SiO2 structures. The results also show that by designing a giant birefringent optical the Brewster’s angle allows angle the control at any angle for both TE and TM mode.

Multi-Order Asymmetric Acoustic Metamaterials with Broad Bandgaps at Subwavelength Scales.

Noise manipulation at the subwavelength scale remains a challenging problem. To obtain better broadband sound isolation within the subwavelength range, a class of asymmetric acoustic metamaterials (AAMs) based on rotation is proposed, and this class of AAMs can further improve subwavelength sound isolation performance by introducing multi-orders. The influences of changing the alternate propagation length of the coiled channel and the square cavity in the unit cell on the band frequency distribution and the omnidirectional band structure were investigated. The effective parameters are calculated with the S-parameter retrieval method, and the generation and change mechanisms of the bandgaps were elucidated. The calculation of sound transmission characteristics showed that, in the asymmetric mode, the overall sound isolation performance of the structure was greatly improved, and the relative bandwidth expanded as the alternate propagation length of the coiled channel and square cavity increased. The omnidirectional bandgaps from the first-order to the third-order AAMs occupied 63.6%, 75.96%, and 76.84% of the subwavelength range, respectively. In particular, the first bandgap moves to the low frequency and becomes wider. Both the experimental results and numerical analyses consistently showed that disrupting structural symmetry enhances acoustic metamaterials for superior broadband sound isolation, inspiring broader applications for asymmetry in this field.

Blue-Noise-Based Disordered Photonic Structures Show Isotropic and Ultrawide Band Gaps

Spatially disordered but uniformly distributed point patterns characterized by so-called blue-noise long-range spatial correlations are of great benefit in computer graphics, especially in spatial dithering thanks to the spatial isotropy. Herein, the potential photonic properties of blue-noise disordered, homogeneous point processes based on farthest-point optimization are numerically investigated for silicon photonics. The photonic properties of blue-noise two-dimensional patterns are studied as a function of the filling fraction and benchmarked with photonic crystals with a triangular lattice. Ultrawide and omnidirectional photonic band gaps spanning most of the visible spectrum are found with estimates of gap–midgap ratios of up to 55.4% for transverse magnetic polarization, 59.4% for transverse electric polarization, and 32.7% for complete band gaps. The waveguiding effect in azimuthal defect lines is also numerically evaluated. These results corroborate the idea that long-range correlated disordered structures are helpful for engineering novel devices with the additional degree of freedom of spatial isotropy, and capable of bandgap opening even without total suppression of infinite-wavelength density fluctuations.

Transformation one-dimensional photonic crystal omnidirectional reflector

In this paper, a concept of transformation one-dimensional photonic crystal is proposed to design omnidirectional reflector, which has a reduced thickness compared with that of the omnidirectional reflector using conventional one-dimensional photonic crystal structure. At first, the omnidirectional reflection band of an original one-dimensional photonic crystal is simulated using the transfer matrix method for comparison. Next, the transformation one-dimensional photonic crystal is designed based on transformation optics. Simulation results indicate that the transformation one-dimensional photonic crystal structures with arbitrary shrunken thickness can omnidirectionally reflect the incident TM waves that operates in the same omnidirectional reflection band of the original one-dimensional photonic crystal structure. Such a concept of transformation one-dimensional photonic crystal also can be expanded to any omnidirectional reflector designed by using other multilayer dielectric systems.

Controllable and tunable plasma photonic crystals through a combination of photonic crystal and dielectric barrier discharge patterns

We report five types of patterns with square symmetry, including three novel types obtained by inserting a specially designed grid photonic crystal (PC) into a dielectric barrier discharge system. They are studied using an intensified charge-coupled device camera and photomultiplier tubes. The three novel types of patterns are a square pattern with one structure, a square superlattice pattern with four sublattices and a (1/4)K grid (K grid is the basic wave vector of the grid), and another square pattern with a complex inversion discharge sequence. From the application viewpoint, the five types of patterns can be used as plasma photonic crystals (PPCs). Their band diagrams under a transverse-magnetic wave simulated by the finite element method show that there are a large number of band gaps. Compared with the original PC with only a unidirectional band gap, the five types of PPCs have tunable and omnidirectional band gaps, which is very important in controlling the propagation of electromagnetic waves in the mm-wave region. The experimental results enrich the pattern types in the dielectric barrier discharge system and provide a method for obtaining PPCs with symmetry controllability and bandgap tunability.

Spatiotemporally controllable honeycomb superlattice plasma photonic crystals in dielectric barrier discharge

We present the experimental realization of tunable honeycomb superlattice plasma photonic crystals (PPCs) in dielectric barrier discharge by utilizing mesh-liquid electrodes. Fast reconfiguration among the simple honeycomb lattice, honeycomb superlattice, and honeycomb-snowflake superlattice is achieved. A dynamic control on the sizes of center scattering elements in the honeycomb superlattice has been realized. A phenomenological activator-inhibitor reaction diffusion model is established to demonstrate the formation and reconstruction of the honeycomb superlattice. The simulations reproduce well the experimental observations. The photonic band diagrams of different honeycomb PPCs are studied by using the finite element method. The addition of large center elements in honeycomb superlattice yields remarkable omnidirectional band gaps that are about 2.5 times larger than in the simple honeycomb lattice. We propose an effective scheme to fabricate spatiotemporally controllable honeycomb lattices that enable great improvement in band gap size and dynamic control of microwave radiations for wide applications.

Design of metasurfaces in 3D for omnidirectional band gaps: The scalar wave case

We discuss a comprehensive process for designing the material properties of three-dimensional periodic structures that are tasked to exhibit user-defined omnidirectional band gaps. To this end, we build upon the framework first posited in Goh and Kallivokas (2019) for two-dimensional metamaterials, and aim at engineering the dispersive properties of a metamaterial’s 3D unit cell using an inverse medium approach. The inversion is driven by forcing the vanishing of trial group velocities at the target band gap frequencies, subject to the satisfaction of the Floquet–Bloch eigenvalue problem defined over the unit cell’s IBZ. Omnidirectionality is controlled by enforcing the vanishing of the group velocities along the IBZ’s high-symmetry lines. Using an adjoint method, the unit cell’s properties are iteratively updated until the design goal is attained. Numerical examples for acoustic metamaterials and metasurfaces demonstrate the methodology.

Omnidirectional flat bands in chiral magnonic crystals

The magnonic band structure of two-dimensional chiral magnonic crystals is theoretically investigated. The proposed metamaterial involves a three-dimensional architecture, where a thin ferromagnetic layer is in contact with a two-dimensional periodic array of heavy-metal square islands. When these two materials are in contact, an anti-symmetric exchange coupling known as the Dzyaloshinskii–Moriya interaction (DMI) arises, which generates nonreciprocal spin waves and chiral magnetic order. The Landau–Lifshitz equation and the plane-wave method are employed to study the dynamic magnetic behavior. A systematic variation of geometric parameters, the DMI constant, and the filling fraction allows the examination of spin-wave propagation features, such as the spatial profiles of the dynamic magnetization, the isofrequency contours, and group velocities. In this study, it is found that omnidirectional flat magnonic bands are induced by a sufficiently strong Dzyaloshinskii–Moriya interaction underneath the heavy-metal islands, where the spin excitations are active. The theoretical results were substantiated by micromagnetic simulations. These findings are relevant for envisioning applications associated with spin-wave-based logic devices, where the nonreciprocity and channeling of the spin waves are of fundamental and practical scientific interest.

Nonreciprocal omnidirectional band gap of one-dimensional magnetized ferrite photonic crystals with disorder

Based on the transfer matrix method (TMM), the nonreciprocal omnidirectional band gaps (OBGs) of magnetized ferrite photonic crystals (MFPCs), consisting of the Yttrium iron garnet ferrite and general dielectric, are investigated. Herein, a disordered MFPC is modeled by rendering the thicknesses of the general dielectric in the Gauss distribution. With the introduction of D, t, and H0 to quantitatively describe the disorder degree, the average thicknesses of the general dielectric layers and the external magnetic field, the three parameters are adjusted for multifarious values. It is shown that the disorder effects (DEs) lead the OBGs to the pattern, that the widths primarily expand and then narrow down with the increasing D. Thereinto, the OBG of D = 0.1 attains the maximum. Also, on top of D = 0.2, the OBGs for the negative fully cover the OBGs for the positive. The OBGs are sensitive to the switches in t and H0 that the ranges vary irregularly with these two variables. For t = 0.2, the OBGs exhibit excellent nonreciprocity, with no overlapping bands in the OBGs for the positive and negative propagation. The results help assume the possible DEs on the OBGs of the MFPCs and give practical advice on the design of filters.

A theoretical study of optical transport properties’ considerations in three variants of one-dimensional Fibonacci-based plasma photonic crystals

ABSTRACT In this study, we considered the optical transmission properties of one-dimensional plasma photonic crystals according to the Fibonacci order. Here, three types of Fibonacci sequence-based structures with fixed total lengths were compared. It was found that type (1) and type (2) structures had the best and the worst frequency bandgaps, respectively. In the first type, barriers only changed with position according to the Fibonacci sequence, while the second and the third types varied dependently and independently according to the Fibonacci sequence, respectively. To obtain the numerical results, the transfer matrix method was used. We considered the effects of the number of layers, plasma density, total system length, and dielectric constant magnitude in the dielectric layers in the mentioned types of Fibonacci systems. The omnidirectional band gaps (OBG) have been also addressed. We showed that the OBGs were available in types (1) and (3) the Fibonacci systems, whereas they were absent in type (2).

Omnidirectional photonic band gap based on nonlinear periodic and quasi-periodic photonic crystals

Omnidirectional photonic band gap based on nonlinear periodic and quasi-periodic photonic crystals

High-Order Photonic Cavity Modes Enabled 3D Structural Colors.

It remains a challenge to directly print arbitrary three-dimensional shapes that exhibit structural colors at the micrometer scale. Woodpile photonic crystals (WPCs) fabricated via two-photon lithography (TPL) are elementary building blocks to produce 3D geometries that generate structural colors due to their ability to exhibit either omnidirectional or anisotropic photonic stop bands. However, existing approaches produce structural colors on WPCs when illuminating from the top, requiring print resolutions beyond the limit of commercial TPL, which necessitates postprocessing techniques. Here, we devised a strategy to support high-order photonic cavity modes upon side illumination on WPCs that surprisingly generate prominent reflectance peaks in the visible spectrum. Based on that, we demonstrate one-step printing of 3D photonic structural colors without requiring postprocessing or subwavelength features. Vivid colors with reflectance peaks exhibiting a full width at half-maximum of ∼25 nm, a maximum reflectance of 50%, a gamut of ∼85% of sRGB, and large viewing angles were achieved. In addition, we also demonstrated voxel-level manipulation and control of colors in arbitrary-shaped 3D objects constituted with WPCs as unit cells, which has potential for applications in dynamic color displays, colorimetric sensing, anti-counterfeiting, and light-matter interaction platforms.

Design and Optimization of One-Dimensional TiO2/GO Photonic Crystal Structures for Enhanced Thermophotovoltaics

In this paper, we theoretically explore the spectroscopic features of various one-dimensional photonic crystal (1D-PC)-based spectrally selective filters. The 1D-PC structure is composed of alternating layers of titanium dioxide (TiO2) and graphene oxide (GO). Employing the transfer matrix method (TMM), the impacts of the incidence angle, the number, and thicknesses of TiO2/GO layers in various 1D-PC stacks on the spectroscopic features of the filters are explored in detail. The proposed 1D-PC structures are designed for practical use for thermophotovoltaic (TPV) applications to act as filters that selectively transmit light below 1.78 μm to a GaSb photovoltaic cell, while light with longer wavelengths is reflected back to the source. The optimal design presented here consists of two Bragg quarter-wave 1D-PC filters with different central frequencies stacked to form a single structure. We demonstrate that our optimized 1D-PC filter exhibits a large omnidirectional stop band as well as a broad pass band and weak absorption losses. These features meet the fundamental exigencies to realize high-efficiency TPV devices. Additionally, we show that when integrated in a TPV system, our optimized filter leads to a spectral efficiency of 64%, a device efficiency of 39%, and a power density of 8.2 W/cm2, at a source temperature of 1800 K.

Omnidirectional reflection control of plane waves via giant magnetostrictive materials

The omnidirectional reflection behaviors of elastic waves and tuned by external magnetic fields are investigated in this paper. The projected band structures are used for analyzing omnidirectional reflection bands, which are also validated by the refraction spectra. It is demonstrated that the omnidirectional reflection phenomenon can be efficiently tuned via the external magnetic field imposed on the Terfenol-D layer. Furthermore, an absolute band gap can be achieved by constructing two superlattices in tandem with different magnetic fields. Our design scheme and the modulation methodology open a new prospect for designing active acoustic mirrors and filters with high quality.

Omnidirectional photonic band gaps in one-dimensional gradient refractive index photonic crystals considering linear and quadratic profiles

By using the transfer matrix formalism, in this work it is presented the study of the optical properties of 1D photonic structures constructed with M periods of bilayers of dielectric material and slabs with gradient refractive index (GRIN) profile of two types: linear and quadratic. By varying the profile parameters, preserving the average value of the refractive index for the GRIN slab, the results show the formation of new photonic band gaps whose bandwidths depends on the slope and the curvature of the linear and quadratic profile respectively. Also, it can be observed the formation of omnidirectional photonic bandgaps for the TE and TM polarizations, one for the linear profile and three for the quadratic one, for which their bandwidths depend linearly on the slope and the curvature of the GRIN profiles. It is expected that the presented results could be useful in the construction of optical devices based in their optical response under oblique incidence.

Tunable triangular and honeycomb plasma structures in dielectric barrier discharge with mesh-liquid electrodes

We demonstrate a method to generate tunable triangular and honeycomb plasma structures via dielectric barrier discharge with uniquely designed mesh-liquid electrodes. A rapid reconfiguration between the triangular lattice and honeycomb lattice has been realized. Novel structures comprised of triangular plasma elements have been observed and a robust angular reorientation of the triangular plasma elements with is suggested. An active control on the geometrical shape, size and angular orientation of the plasma elements has been achieved. Moreover, the formation mechanism of different plasma structures is studied by spatial-temporal resolved measurements using a high-speed camera. The photonic band diagrams of the plasma structures are calculated by use of finite element method and two large omnidirectional band gaps have been obtained for honeycomb lattices, demonstrating that such plasma structures can be potentially used as plasma photonic crystals to manipulate the propagation of microwaves. The results may offer new strategies for engineering the band gaps and provide enlightenments on designing new types of 2D and possibly 3D metamaterials in other fields.

Broad omnidirectional acoustic band gaps in a three-dimensional phononic crystal composed of face-centered cubic Helmholtz resonator network.

Broad omnidirectional band gaps in a three-dimensional phononic crystal consisting of a face-centered cubic array of spherical air voids connected by cylindrical conduits in solid background are numerically and experimentally demonstrated. With a low material filling fraction of 37.7%, the first bandgap covers 3.1-13.6 kHz frequency range with 126.1% gap-over-midgap ratio. Finite-element method is employed in band structure and numerical transmission analyses. Omnidirectional band gaps are observed in only two-period thick slabs in the 100, 110, and 111 orientations. Experimental transmission characteristics are in good agreement with numerical data. The phononic crystal can be employed in low-frequency sound proofing.

Three-Dimensional Trampolinelike Behavior in an Ultralight Elastic Metamaterial

Elastic metamaterials possess band gaps, or frequency ranges that are forbidden to wave propagation. Existing solutions for impeding three-dimensional (3D) wave propagation largely rest on high-volume fractions of mass inclusions that induce and tailor negative effective density-based local resonances. This study introduces a class of elastic metamaterials that achieve low-frequency band gaps with a volume fraction as low as 3% (mass density as low as $0.034\phantom{\rule{0.1em}{0ex}}\mathrm{g}/{\mathrm{cm}}^{3}$). The working of the proposed design hinges on a 3D trampolinelike mode behavior that gives rise to wide, omnidirectional, and low-frequency band gaps for elastic waves despite very low-mass densities. Such a 3D trampoline effect is derived from a network of overhanging nodal microarchitectures that act as locally resonating elements, which give rise to band gaps at low frequencies. The dynamic effective properties of the metamaterial are numerically examined, which reveal that the band gap associated with the trampoline effect is resulted from a negative effective modulus coupled with a near-zero yet positive effective density. The experimental characterization is then made possible by fabricating the metamaterial via a light-based printing system that is capable of realizing microarchitectures with overhanging microfeatures. This design strategy could be useful to applications where simultaneous light weight and vibration control is desired.

(Generalized) Bloch mode synthesis for the fast dispersion curve calculation of 3D periodic metamaterials

Metamaterials, i.e. artificial structures with unconventional properties, have shown to be highly potential lightweight and compact solutions for the attenuation of noise and vibrations in targeted frequency ranges, called stop bands. In order to analyze the performance of these metamaterials, their stop band behavior is typically predicted by means of dispersion curves, which describe the wave propagation in the corresponding infinite periodic structure. The input for these calculations is usually a finite element model of the corresponding unit cell. Most common in literature are 2D plane metamaterials, which often consist of a plate host structure with periodically added masses or resonators. In recent literature, however, full 3D metamaterials are encountered which are periodic in all three directions and which enable complete, omnidirectional stop bands. Although these 3D metamaterials have favorable vibro-acoustic characteristics, the computational cost to analyze them quickly increases with unit cell model size. Model order reduction techniques are important enablers to overcome this problem. In this work, the Bloch Mode Synthesis (BMS) and generalized BMS (GBMS) reduction techniques are extended from 2D to 3D periodic structures. Through several verifications, it is demonstrated that dispersion curve calculation times can be strongly reduced, while accurate stop band predictions are maintained.