Haitao Jiang

Omnidirectional gap and defect mode of one-dimensional photonic crystals containing negative-index materials

We show theoretically that a one-dimensional photonic crystal containing a negative-index material has an omnidirectional gap, owing to the mechanism of zero (volume) averaged refractive index. In contrast to the Bragg gap, the edge of such a zero-n gap is insensitive to incident angle and polarization. When an impurity is introduced, a defect mode appears inside the zero-n gap with a very weak dependence on incident angle and invariant with scaling.

Dielectric properties and relaxor behavior of rare-earth (La, Sm, Eu, Dy, Y) substituted barium zirconium titanate ceramics

Based on the Ti-vacancy defect compensation model, (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 (Ln=La,Sm,Eu,Dy,Y) ceramics have been fabricated via the conventional solid-state reaction method. The microstructures, dielectric properties, and ferroelectric relaxor behavior of (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 ceramics have been investigated. The results indicate that rare-earth ions with various ionic radii enter the unit cell to substitute for A-site Ba2+ ions and inhibit the grain growth. The typical ferroelectric relaxor behavior is induced due to the rare-earth ions substitution. The diffuseness of the phase transition and the degree of ferroelectric relaxor behavior are enhanced, the TC is remarkably shifted to lower temperature, and the tunability is suppressed with the increase of x value and substituted ionic radius for (Ba1−xLnx)Zr0.2Ti0.8−x∕4O3 (x=0.005–0.04, Ln=La,Sm,Eu,Dy,Y) ceramics. Tunable ferroelectric materials with moderate dielectric constant and low dielectric loss can be obtained by manipulating the doping am...

Tunneling modes of photonic heterostructures consisting of single-negative materials

We show theoretically that heterostructures consisting of single-negative materials can possess tunneling modes inside forbidden gaps, owing to the resonant coupling of the evanescent-wave-based interface modes. The tunneling modes appear when the heterostructure becomes nihility. They are independent of incident angles and polarizations and have zero phase delay, which can be utilized to design zero-phase-shift omnidirectional filters.

Raman and dielectric study of Ba0.4Sr0.6TiO3–MgAl2O4 tunable microwave composite

(1−x)Ba0.4Sr0.6TiO3–xMgAl2O4 (x=0.00, 0.05, 0.10, 0.20, and 0.30) composite ceramics have been synthesized by the solid-state reaction, and its structural and dielectric properties have been systematically characterized. Two crystalline phases, a cubic perovskite structure Ba0.4Sr0.6TiO3 (BST) and a face-centered-cubic spinel structure MgAl2O4 (MA), are clearly visible for x≥0.05. As the MA content increases, the composite ceramics show an increased degree of deviation from the Curie–Weiss law and an increased diffuseness of the dielectric peak. Meanwhile, the tunability of composite ceramics increases. Raman analysis clearly indicates that the incorporation of MA lowers the permittivity and degrades the quality factor of BST composites, which is ascribed to the deterioration on B-site ordering of ABO3 perovskite structure.

Compact high-Q filters based on one-dimensional photonic crystals containing single-negative materials

A mechanism to design compact high-Q filters is proposed in this paper, based on the properties of a defect mode in a one-dimensional (1D) photonic crystal composed of alternating layers of negative-permeability material and negative-permittivity material. The eigenfrequency equation for the defect mode is derived by means of the transfer-matrix method, and then, the dependence of the eigenfrequency on the thicknesses of the two host layers and the defect layer is calculated. In contrast to the case for a filter based on a conventional 1D photonic crystal (with positive refractive indices), we find that the quality factor Q of the filter involved in this paper can be boosted noticeably while the volume of the filter decreases.

TUNABLE SINGLE-NEGATIVE METAMATERIALS BASED ON MICROSTRIP TRANSMISSION LINE WITH VARACTOR DIODES LOADING

In this paper, tunable single-negative (TSNG) metamate- rials based on microstrip with varactor diodes loading are investigated. By tuning the external voltage, our structure can provide either an epsilon-negative or a mu-negative band gap, with varying gap width (the ratio of bandwidth to center frequency can be from 0 to over 100%) and depth (from 0dB to about i30dB). Moreover, the tun- neling mode in a heterostructure constructed by epsilon-negative and TSNG metamaterials is also studied. The results show that its trans- mission, Q-factor, and electromagnetic localization can also be con- trolled conveniently. All these properties make our structure promising to be utilized as a practical switching device, or a suitable platform for the study of nonlinear efiect in metamaterials.

Multichanneled filter based on a branchy defect in microstrip photonic crystal

A multichanneled filter based on a branchy defect in a microstrip photonic crystal is proposed. By introducing a branchy structure across the defect region, multiple defect modes will appear inside the photonic gap, leading to the multichanneled filtering phenomenon. In comparison with the conventional multichanneled filters, the proposed structure is more compact and tunable as far as the device volume and fabrication are concerned. The microwave experiment results are found in agreement with simulation results.

Rabi splitting with excitons in effective (near) zero-index media

We study theoretically the properties of a thin film of a semiconductor embedded in the interface of two kinds of single-negative materials. At some frequencies the structure with suitable size is equivalent to an effective (near) zero-index medium. The coupling of exciton resonance in the semiconductor and the interface mode in a zero-index medium leads to Rabi splitting. Compared with Rabi splitting observed in cavities, the splitting modes in zero-index media are robust against the scaling change of the length and direction of incident wave.

Dielectric relaxation in MgO-doped tunable Ba0.4Sr0.6TiO3?MgAl2O4 composite ceramics

xMgO?0.70(1 ? x)Ba0.4Sr0.6TiO3 (BST)?0.30(1 ? x)MgAl2O4 (MA) (x = 0, 1, 2, 5, 10?wt%) composite ceramics have been prepared by solid state reactions. Three phases, corresponding to the BST, MA and MgO phases, are clearly visible in the composite ceramics when x is equal to or more than 5?wt%. A dielectric peak with very strong frequency dispersion is observed for all samples. With increasing x, the composite shows an increased degree of deviation from the Curie?Weiss law and an increased diffuseness of the dielectric peak. The permittivity exhibits relaxor behaviour with the frequency-dependent temperature of the permittivity peak Tm satisfying the Vogel?Fulcher formula. As MgO increases, the activation energy Ea moves from 39.1 to 65.6?meV, possibly due to more defect pairs and . The room-temperature permittivity decreases from ~390 for x = 0.01 to ~280 for x = 0.10 while the tunability still remains constant ~9.0% under 30?kV?cm?1 biasing.

Two-dimensional complete band gaps in one-dimensional metal-dielectric periodic structures

It is widely believed that a one-dimensional (1D) periodic layered structure with ordinary materials can only have a band gap for certain propagation directions. However, we reveal that a 1D metal-dielectric periodic structure can trap transverse magnetic waves for any angle of propagation in a plane, owing to the existence of a two-dimensional (2D) complete band gap. The complete gap comes from Bragg scattering together with the cutoff effect of the metal-dielectric-metal waveguide. We discuss the criteria for the geometric and material parameters to realize a 2D complete gap and illustrate the complete band-gap effects with real structures.