Complete band gaps in one-dimensional left-handed periodic structures

Omnidirectional nonreciprocal absorber realized by the magneto-optical hypercrystal

Photonic bandgap design is one of the most basic ways to effectively control the interaction between light and matter. However, the traditional photonic bandgap is always dispersive (blueshift with the increase of the incident angle), which is disadvantageous to the construction of wide-angle optical devices. Hypercrystal, the photonic crystal with layered hyperbolic metamaterials (HMMs), can strongly modify the bandgap properties based on the anomalous wavevector dispersion of the HMM. Here, based on phase variation competition between HMM and isotropic dielectric layers, we propose for the first time to design nonreciprocal and flexible photonic bandgaps in one-dimensional photonic crystals containing magneto-optical HMMs. Especially the zero-shift cavity mode and the blueshift cavity mode are designed for the forward and backward propagations, respectively. Our results show maximum absorption about 0.99 (0.25) in an angle range of 20-75 degrees for the forward (backward) incident light at the wavelength of 367 nm. The nonreciprocal omnidirectional cavity mode not only facilitates the design of perfect unidirectional optical absorbers working in a wide-angle range, but also possesses significant applications for all-angle reflectors and filters.

Computational Electromagnetics: A Miscellany

The paper presents a miscellany of unorthodox and, in some cases, paradoxical or controversial items related to computational and applied electromagnetics. The topics include a definition of the magnetic source field via a line integral, losses in electric power transmission vs. losses in photonics, homogenization of periodic electromagnetic structures, spurious modes, models of plasmonic media, and more. It is hoped that this assortment of subjects will be of interest to a broad audience of scientists and engineers.

Programmable stopbands and supratransmission effects in a stacked Miura-origami metastructure

Origami-based mechanical metamaterials and metastructure have been demonstrated to exhibit unique properties originating from their intricate geometries of folding. This research aims to extend the current investigation level from quasistatics to dynamics. In detail, this research focuses on the wave dynamics of a metastructure composed of stacked Miura-origami (SMO) units. The SMO unit could possess two stable configurations, endowing the metastructure with rich possibilities in the layout of its periodic repeating cell. Through linear dispersion analyses and numerical studies, we show that the long-desired stopband tunability and programmability of the metastructure along the three principal directions can be acquired by strategically programming the layout of the periodic cell. Based upon that, we further discover that energy supratransmission through the metastructure is possible within the stopband by increasing the driving amplitude. Through numerical means, the amplitude threshold of supratransmission is obtained. We demonstrate that the fundamental mechanism that triggers the supratransmission phenomenon is the transition of the responses from the low-energy intrawell oscillations to the high-energy interwell oscillations. Numerical studies also indicate that the supratransmission threshold can be effectively tailored by adjusting the periodic cell layout. The results of this research provide a wealth of fundamental insights into the origami wave dynamics and offer useful guidelines for developing origami metastructures with tunable and programmable dynamic characteristics.

Near-infrared tunable narrow filter in a periodic multi-nanolayer doped by a superconductor photonic quantum-well

The transfer matrix method is employed to theoretically investigate the near-infrared (NIR) narrow filter properties in a one-dimensional defective symmetric photonic crystal with a superconductor photonic quantum-well defect (PQW). The study investigates how the wavelength of the defect mode is affected by the stack number of the PQW defect structure, the thicknesses of PQW layers, the polarization, and the angle of incidence as well as the operating temperature. The results also show that the period of the PQW defect structure and the number of defect modes are independent of one another. This result differs from that of studies conducted on a common dielectric or metamaterial defect. It is noted that with an increase in the number of the defect period, the thickness of the superconductor layer, and the angle of incidence, the defect mode shows a blue-shift for both wave polarizations. On the other hand, an opposite trend is observed as the thickness of the air layer and the operating temperature increase. The results also reveal that new tunable narrow filters and optical communication devices can be achieved at NIR region in this proposed structure.

Transmittance properties in a magnetized cold plasma-superconductor periodic multilayer

This study theoretically investigates the transmittance properties of a one-dimensional photonic crystal containing magnetized cold plasma and high-temperature superconductor materials. The cutoff frequency, as a function of the magnetic field, electron density of the plasma layer, and temperature, will be investigated. The results illustrate that the temperature, electron density, and variations of the magnetic field affect the cutoff frequency. In addition, the shift trend in the cutoff frequency proves to be dependent on the polarization due to the presence of polarization-dependent magnetized cold plasma. Moreover, in temperature-dependent transmittance, weak oscillation and intensity can be seen at higher temperatures, which is in sharp contrast to low-temperature superconductor-dielectric structures. The proposed structure could certainly provide helpful information for the design of new types of antennas, reflectors, and high-pass filters at microwave frequency.

Single-negative metamaterial periodic multilayer doped by magnetized cold plasma

This study theoretically investigates the properties of the defect mode in a 1D defective single-negative photonic crystal containing a magnetized cold plasma defect layer. The considered photonic crystal structure is made of epsilon-negative and mu-negative metamaterials. We investigate the defect mode as a function of the thickness and the electron density of the defect layer and the magnetic field. The results show that the thickness, electron density, and variations of the magnetic field affect the frequency of the defect mode. In addition, the shift trend in the defect mode is shown to rely on the polarization due to the presence of polarization-dependent magnetized cold plasma. The results lead to some new information concerning the designing of new types of tunable narrowband filters at microwave frequency.

Radiation of a uniformly moving line charge in a zero-index metamaterial and other periodic media

Radiation of electromagnetic waves by a uniformly moving charge is the subject of extensive research over the last several decades. Fascinating effects such as Vavilov-Cherenkov radiation, transition radiation and the Smith-Purcell effect were discovered and studied in depth. In this letter we study the radiation of a line charge moving with relativistic constant velocity within an average zero index metamaterial consisting of periodically alternating layers with negative and positive refractive index. We observe a strong radiation enhancement, ~3 orders of magnitude, for specific combinations of velocities and radiation frequencies. This surprising finding is attributed to a gigantic increase in the density of states at the positive/negative index boundary. Furthermore, we shed light on radiation effects of such a line charge propagating within the more "traditional" structure of periodically alternating layers consisting of positive and different refractive index with focus on frequencies satisfying the quarter wave stack and the half wave stack conditions. We show that the quarter-wave-stack case results in emission propagating vertically to the line charge trajectory, while the half-wave-stack results in negligible radiation. All these findings were obtained using a computationally efficient and conceptually intuitive computation method, based on eigenmode expansion of specific frequency components. For validation purposes this method was compared with the finite-difference-time-domain method.

Electron transport and Goos-Hänchen shift in graphene with electric and magnetic barriers: optical analogy and band structure

Transport of massless Dirac fermions in graphene monolayers is analysed in the presence of a combination of singular magnetic barriers and applied electrostatic potential. Extending a recently proposed (Ghosh and Sharma 2009 J. Phys.: Condens. Matter 21 292204) analogy between the transmission of light through a medium with modulated refractive index and electron transmission in graphene through singular magnetic barriers to the present case, we find the addition of a scalar potential profoundly changes the transmission. We calculate the quantum version of the Goos-Hänchen shift that the electron wave suffers upon being totally reflected by such barriers. The combined electric and magnetic barriers substantially modify the band structure near the Dirac point. This affects transport near the Dirac point significantly and has important consequences for graphene-based electronics.

Guided modes near the Dirac point in negative-zero-positive index metamaterial waveguide

Motivated by the realization of the Dirac point (DP) with a double-cone structure for optical field in the negative-zero-positive index metamaterial (NZPIM), we make theoretical investigations of the guided modes in the NZPIM waveguide near the DP by using the graphical method. Due to the linear Dirac dispersion, the fundamental mode is absent when the angular frequency is smaller than the DP, while the behaviors of NZPIM waveguide are similar to the conventional dielectric waveguide when the angular frequency is larger than the DP. The unique properties of the guided modes are analogous to the propagation of electron waves in graphene waveguide [Appl. Phys. Lett., 94, 212105 (2009)], corresponding to the classical motion and the Klein tunneling. These results suggest that many exotic phenomena in graphene can be simulated by the relatively simple optical NZPIM.

Modulation of bistable lateral shifts in a one-dimensional nonlinear photonic crystal consisting of indefinite metamaterials

Nonlinear propagation characteristics are investigated theoretically in a one-dimensional photonic band-gap structure containing indefinite metamaterials. It is found that optical bistability can be achieved at very low threshold values of normalized input intensity in this composite structure when the indefinite metamaterial is a cut-off, anticut-off, and never cut-off medium. It is also found that there exists corresponding bistable lateral shift which is strongly dependent on the parameters of indefinite metamaterials.

Plasmon polaritons in photonic metamaterial superlattices: absorption effects

We discuss the propagation of electromagnetic waves in layered structures made up of alternate layers of air and metamaterials. The role played by absorption on the existence of electric and magnetic plasmon polaritons is investigated. Results show that plasmon-polariton modes are robust even in the presence of rather large absorption.

Quantum interference between two orthogonal transitions of an atom in one-dimensional photonic crystals

We find that the V-type three-level Zeeman atom has the complete quantum interference when it is embedded in one-dimensional photonic crystals (1D PCs) possessing the TM-polarized complete gap. To avoid the nonradiative decay related to dissipation and the decay through surface exciton, we add two phase compensators made of ideal left-handed materials on two sides of atom, and then the total structure is equivalent to a 1D PC supporting only the radiative modes. The parameter regions (epsilon, mu) leading to the TM-polarized complete gap have been sketched out, and the influence of absorption on the quantum interference is discussed.

Two-dimensional complete photonic gaps from layered periodic structures containing anisotropic left-handed metamaterials

We demonstrate that a two-dimensional complete photonic band-gap (PBG) can be realized in a layered periodic structure with a double-layer unit cell containing an anisotropic left-handed metamaterial layer. A set of criteria is derived for the geometric and material parameters to realize a two-dimensional complete PBG in such systems, and a detailed phase diagram is given. We discuss the underlying physics of the mechanism and illustrate the complete band-gap effects with several concrete examples.

Model system for a one-dimensional magnetic photonic crystal

We fabricate and characterize one-dimensional magnetic (rather than dielectric) photonic crystals for the first time. Our model system is a one-dimensional periodic lattice of gold-wire pairs. Each pair can be viewed as a magnetic coil with two slits and represents a "magnetic atom." Strong coupling between the resulting magnetic-dipole resonance and the Bragg resonance is accomplished by an adjacent dielectric slab waveguide, giving rise to an avoided crossing at near-infrared wavelengths. Our experimental findings are in excellent agreement with theory.

Optical properties of two-dimensional negative-phase-velocity-medium photonic crystals

By an extended plane-wave-based transfer-matrix method, the photonic band structure and the corresponding transmission spectrum have been calculated for a two-dimensional photonic crystal composed of negative-phase-velocity-medium (NPVM) cylindrical rods. Dispersionless anticrossing bands in the two-dimensional NPVM periodic structure are generated by the couplings among surface polaritons localized in the NPVM rods. In part of the negative-phase-velocity frequency region, the photonic band structures of the NPVM photonic crystal are characterized by a topographical continuous dispersion relationship accompanied by many anticrossing bands. The effect of the filling fraction of the NPVM rods on the optical properties of photonic crystals has also been studied.

Localized gap-edge fields of one-dimensional photonic crystals with an epsilon-negative and a mu-negative defect

We study the properties of one-dimensional photonic crystals with an epsilon-negative and a mu-negative defect. With suitable parameters, the pair defect is equivalent to a transparent material with zero effective refractive index. This special pair defect has no influence on the spectral gap formed by the interference of propagating waves in positive-refractive-index materials. However, the field distribution is modified noticeably by the decaying wave in the pair defect. Particularly, the gap-edge field can be a highly localized wave instead of the usual standing wave as the size of the pair defect increases. The localized gap-edge field can reduce the switching thresholds for bistability greatly when Kerr-type nonlinear mu-negative material is involved. A nonideal model when the epsilon-negative and mu-negative materials are dispersive and lossy is used to verify the unusual properties.

Large enhancement of interface second-harmonic generation near the zero-n(-) gap of a negative-index Bragg grating

We predict a large enhancement of interface second-harmonic generation near the zero-n(-) gap of a Bragg grating made of alternating layers of negative- and positive-index materials. Field localization and coherent oscillations of the nonlinear dipoles located at the structure's interfaces conspire to yield conversion efficiencies at least an order of magnitude greater than those achievable in the same length of nonlinear, phase-matched bulk material. These findings thus point to a new class of second-harmonic-generation devices made of standard centrosymmetric materials.

All-angle negative refraction for surface plasmon waves using a metal-dielectric-metal structure

We show that a metal-dielectric-metal structure can function as a negative refraction lens for surface plasmon waves on a metal surface. The structure is uniform with respect to a plane of incidence and operates at the optical frequency range. Using three-dimensional finite-difference time-domain simulations, we demonstrate the imaging operation of the structure with realistic material parameters including dispersions and losses. Our design should facilitate the demonstration of many novel effects associated with negative refraction on chip at optical wavelength ranges. In addition, this structure provides a new way of controlling the propagation of surface plasmons, which are important for nanoscale manipulation of optical waves.