Metallo-dielectric Photonic Band Gap Research Articles

Semiconductor-based superlens for subwavelength resolution below the diffraction limit at extreme ultraviolet frequencies

We theoretically demonstrate negative refraction and subwavelength resolution below the diffraction limit in the UV and extreme UV ranges using semiconductors. The metal-like response of typical semiconductors such as GaAs or GaP makes it possible to achieve negative refraction and superguiding in resonant semiconductor/dielectric multilayer stacks, similar to what has been demonstrated in metallodielectric photonic band gap structures. The exploitation of this basic property in semiconductors raises the possibility of yet-untapped applications in the UV and soft x-ray ranges.

Tailoring metallodielectric structures for superresolution and superguiding applications in the visible and near-ir ranges

We discuss propagation effects in realistic, transparent, metallodielectric photonic band gap structures in the context of negative refraction and super-resolution in the visible and near infrared ranges. In the resonance tunneling regime, we find that for transverse-magnetic incident polarization, field localization effects contribute to a waveguiding phenomenon that makes it possible for the light to remain confined within a small fraction of a wavelength, without any transverse boundaries, due to the suppression of diffraction. This effect is related to negative refraction of the Poynting vector inside each metal layer, balanced by normal refraction inside the adjacent dielectric layer: The degree of field localization and material dispersion together determine the total momentum that resides within any given layer, and thus the direction of energy flow. We find that the transport of evanescent wave vectors is mediated by the excitation of quasistationary, low group velocity surface waves responsible for relatively large losses. As representative examples we consider transparent metallodielectric stacks such as $\mathrm{Ag}∕{\mathrm{TiO}}_{2}$ and $\mathrm{Ag}∕\mathrm{GaP}$ and show in detail how to obtain the optimum conditions for high transmittance of both propagating and evanescent modes for super-guiding and super-resolution applications across the visible and near IR ranges. Finally, we study the influence of gain on super-resolution. We find that the introduction of gain can compensate the losses caused by the excitation of surface plasmons, improves the resolving characteristics of the lens, and leads to gain-tunable super-resolution.

Theoretical analysis of a palladium-based one-dimensional metallo-dielectric photonic band gap structure for applications to H2 sensors

In this paper we report a numerical study of a palladium-based metallo-dielectric photonic band gap structure for the purpose of detecting H2. In particular, and as an example, we will explore applications to the diagnosis of lactose malabsorption, more commonly known as lactose intolerance condition. This pathology occurs as a result of an incomplete absorption or digestion of different substances, causing an increased spontaneous emission of H2 in human breath. Palladium is considered in order to exploit its well known ability to absorb hydrogen spontaneously. The proposed structure is particularly able to detect the lactose malabsorption level of the patient with relatively high sensitivity and rapidity.

Tunable absorption resonance in electromechanical one-dimensional metallodielectric photonic band gap structures

We present the results of an experimental study of an electromechanical, one-dimensional, metallodielectric photonic band gap structure. We monitor the reflectance as a function of the thickness of an air gap located inside the stack. The results suggest that, by changing the thickness of the air gap by approximately 20 nm, a large contrast can be achieved between high- and low-reflectance states, as reflectance switches from a fraction of a percent to about 70%. Using this approach, we are able to selectively remove a relatively narrow but tunable wavelength range from the reflected spectrum, thus making possible applications to accelerometers, linear optical switches, modulators, and other specialized filters in the visible range. The characteristic absorption spectrum can be controlled by varying air gap and dielectric layer thicknesses.

Design, Fabrication, Linear and Nonlinear Optical Properties of Metal-Dielectric Photonic Bandgap Structures

The linear and the nonlinear optical properties of metallodielectric photonic bandgap (MD-PBG) structures were studied by using linear absorption spectroscopy and a femtosecond nonlinear transmission method. The MD-PBG structure consisted of three bilayers of MgF2(250 nm)/Ag(30 nm). It was prepared by evaporating MgF2 and Ag layers alternatively onto a glass plate. The optical transmission spectrum of the prepared MD-PBG structure was found to exhibit several pass bands and a broad photonic bandgap. The photonic bandgap extended throughout most of the visible region from 475 nm to 780 nm. Interestingly, there existed transmissive pass bands corresponding to the Bragg resonances: λ1 = 410 nm (T = 53.9 %), λ2 = 449 nm (T = 42.9 %), λ3 = 802 nm (T = 39.6 %) and λ4 = 878 nm (T = 16.9 %). The observed transmission spectra could be described by applying the optical transfer matrix formalism to the periodic metallodielectric multilayer. The number of pass bands was found to increase with increasing number of metal-dielectric pairs, and the band width of PBG was found to increase with increasing dielectric layer thickness. At high laser intensity, the MD-PBG structure exhibited a large nonlinear absorption. The enhanced optical nonlinearity is thought to be due to a bathochromic shift of the low-energy band edge of PBG by the saturable absorption of each metallic layer.

One-dimensional heterostructural metallodielectric photonic band gap material for the modification of emission spectrum of BaF2 scintillator

One-dimensional metallodielectric heterostructural photonic band gap (PBG) material is designed to reach high transmittance band in short wavelength, broad and deep forbidden band in long wavelength, especially sharp cutoff edge between the transmission and forbidden bands. The designed PBG material is applied to modify the emission spectrum of a BaF2 scintillator and is proved to be adequate to suppress the slow component of the scintillation light. The suppression ratio of the slow to the fast component reaches 28dB with a tolerable attenuation of the fast component.

Photonic bandgap surfaces with interdigitated corrugations

For a given operational frequency, the unit cell surface area of a metallo–dielectric photonic bandgap structure (MBPG) is reduced by increasing the capacitance between adjacent unit cell elements. An MPBG structure possessing interdigitated corrugations is proposed in order to achieve this increase. The structure is incorporated, as the ground plane, in a microstrip transmission line and it is experimentally characterised over the 50 MHz–4 GHz frequency band.

Preparation of Silver-Coated Polystyrene Composite Particles

We report a feasible approach to the preparation of monodispersedmetal-shell composite microspheres based on a combination of surfacereaction and surface seeding techniques. The method was implemented forcoating polystyrene (PS) spheres with silver shell having a variablethickness by controlling the amount of reagents in the reactionprocedure. These composite spherical particles in dimensions of thesubmicrometer range may become attractive building blocks for thecreation of metallo-dielectric photonic band gap materials when theyare organized into crystals.

Accessing the optical limiting properties of metallo-dielectric photonic band gap structures

The optical limiting properties of a one-dimensional, transparent metallodielectric photonic band gap structure are studied. Due to light confinement in the structure that enhances the nonlinear response of the layers, a nonlinear transmission dependence on the incident light intensity is found. Experimental results are reported for a four period sample where the single period consists of ZnO and Ag layers 109 and 17 nm thick, respectively. The structure was designed to exhibit a transmission resonance at 532 nm. Under the action of a Q-switched frequency doubled Nd:yttrium–aluminum–garnet laser, a decrease in transmission of approximately 50% is obtained for a maximum incident light intensity of 2 GW/cm2. These results are explained in terms of a dynamic change of the absorption coefficient due to the enhancement of the two-photon absorption process. These results suggest that the structure is suitable for optical limiting applications in the visible range.

Dipole and tripole metallodielectric photonic bandgap (MPBG) structures for microwave filter and antenna applications

A photonic band gap structure made from periodic arrays of conducting dipoles and tripoles on a dielectric is presented. Using the proposed structures, several example devices have been demonstrated for microstrip resonators and filters as well as patch antennas. Measured and predicted frequency responses of a microstrip line using a dual dipole metallodielectric photonic bandgap (MPBG) structure show a 40% band width centred at 10 GHz. A planar microstrip resonator using a dipole MPBG shows a slower wave performance and a higher Q factor when compared with the conventional half-wavelength resonator. Three patch antenna designs on different dielectric constant substrates using a tripole MBPG produce better return loss, higher boresight gains (up to 3 dB) and smoother radiation patterns as a result of surface wave suppression.

Artificial versus natural crystals: effective wave impedance of printed photonic bandgap materials

Printed metallo-dielectric photonic bandgap (PBG) materials are analyzed using an analytical approach based on multipole expansions for the scattered fields of individual scatterers and a transfer-matrix method for reconstructing the total scattered fields created by successive lattice planes of the artificial crystal. An effective description of the PBG medium is derived and its correspondence with natural crystals is further advanced through an analysis based on Lorentzian response functions, which characterize natural crystals. The effective wave impedance and bulk reflection coefficient of the medium are provided and their properties inside and outside the bandgaps are examined. The presented treatment for these effective response functions extends far beyond the traditional effective medium theory (EMT) limits.

Electromagnetic properties of periodic and quasi-periodic one-dimensional, metallo-dielectric photonic band gap structures

We discuss some of the electromagnetic properties of one-dimensional, metallo-dielectric photonic band gap structures. In our considerations, we include discussions of the transmissive and reflective properties of multilayer stacks, and the density of electromagnetic field modes for the structure. In particular, we highlight and contrast the role of quasi-periodic structures with respect to periodic structures, in the form of Cantor Fibonacci sets, and a `chirped' set.

Electromagnetic scattering from a PBG material excited by an electric line source

A general procedure Is presented to determine the fields scattered by a periodic structure due to a complex excitation in terms of the structure's plane-wave response. Specifically, the scattered field from an electric line source over a semiinfinite metallo-dielectric photonic bandgap (PBG) material is described. An effective description for the artificial crystal's plane-wave response is used, consisting of angularly parameterized response functions. A methodology for analyzing the electromagnetic response of such a material to a nonplane-wave excitation is provided, whereby a general complex excitation is spectrally decomposed into an integral over a continuous spectrum of homogeneous and inhomogeneous plane waves. An analytic solution for the scattering of each plane wave by the PBG material half-space is then utilized. The complete scattered field is given in a closed integral form, which is computed both numerically and in the asymptotic limit. The effect of the PBG crystal half-space on the scattered field due to an electric line source is presented for frequencies that correspond, for a normally incident plane wave, to a transmission bandgap, a transmission band edge, and an antireflecting plateau. The focusing effects and electric- and magnetic-wall behavior of the PBG crystal are demonstrated. The presented approach promotes both the physical understanding of PBG material systems and the efficiency of the numerical modeling of these systems at frequencies beyond the quasi-static limit of the traditional effective medium theories.

3D Metallo-Dielectric Photonic Crystals with Strong Capacitive Coupling between Metallic Islands

We introduce a new type of metallo-dielectric photonic band gap structure (PBG), intentionally incorporating very strong capacitive interactions between the periodic metallic islands. The band gaps become huge, with the lower band edge frequency being pushed down by the capacitive interaction between metallic islands, while the upper band edge frequency continues to depend primarily on the lattice constant, as in normal PBG’s. With this new type of photonic crystal, the spatial periodicity can be much smaller than the corresponding electromagnetic wavelength, allowing PBG structures to play a role at radio frequencies. [S0031-9007(98)05629-4] PACS numbers: 42.70.Qs, 41.20.Jb, 78.70.Gq, 84.40. ‐ x