Xueqin Huang

Dirac cones induced by accidental degeneracy in photonic crystals and zero-refractive-index materials

A zero-refractive-index metamaterial is one in which waves do not experience any spatial phase change, and such a peculiar material has many interesting wave-manipulating properties. These materials can in principle be realized using man-made composites comprising metallic resonators or chiral inclusions, but metallic components have losses that compromise functionality at high frequencies. It would be highly desirable if we could achieve a zero refractive index using dielectrics alone. Here, we show that by employing accidental degeneracy, dielectric photonic crystals can be designed and fabricated that exhibit Dirac cone dispersion at the centre of the Brillouin zone at a finite frequency. In addition to many interesting properties intrinsic to a Dirac cone dispersion, we can use effective medium theory to relate the photonic crystal to a material with effectively zero permittivity and permeability. We then numerically and experimentally demonstrate in the microwave regime that such dielectric photonic crystals with reasonable dielectric constants manipulate waves as if they had near-zero refractive indices at and near the Dirac point frequency.

Dirac cones at k→=0 in acoustic crystals and zero refractive index acoustic materials

We show that two-dimensional acoustic crystals (ACs) can be designed to exhibit Dirac cone dispersion at k→=0. Effective medium theory finds that some of these ACs can have effectively zero reciprocal of bulk modulus 1/κeff and zero mass density ρeff, and thus zero refractive indices at the Dirac point. Numerical simulations are used to demonstrate various phenomena associated with the zero spatial phase change inside such materials.

Dirac cones at k → = 0 in phononic crystals

We show that two-dimensional phononic crystals exhibit Dirac cone dispersion at

Three-photon near-infrared quantum splitting in β-NaYF4:Ho3+

\stackrel{P\vec}{k}=0

Physics of the zero- photonic gap: fundamentals and latest developments

by exploiting dipole and quadrupole accidental degeneracy. While the equifrequency surface of Dirac cone modes is almost isotropic, such systems exhibit super-anisotropy, meaning that only transverse waves are allowed along certain directions, while only longitudinal waves are allowed along some other directions. Only one mode, not two, is allowed near the Dirac point, and only two effective parameters, not four, are needed to describe the dispersion. Effective medium theory finds that the phononic crystals have effectively zero mass density and zero

On the time evolution of the cloaking effect of a metamaterial slab

1/{C}_{44}^{\mathrm{eff}}

Dirac cone and double zero materials

at the Dirac point. Numerical simulations are used to demonstrate the unusual elastic wave properties near the Dirac point frequency.

Effective impedance for predicting the existence of surface states

We report on three-step sequential three-photon near-infrared (NIR) quantum splitting in β-NaYF4:Ho3+, where one absorbed ultraviolet photon is split into three NIR photons with wavelengths 850, 1015, and 1180 nm. The underlying mechanism is analyzed by static and dynamic photoemission and excitation spectroscopy. An internal quantum yield of 124% is estimated on the basis experimental data and theoretical considerations. Further development of an efficient triply splitting NIR phosphor might open up an approach in achieving efficient photonic devices, which enables more photons emitted than absorbed in the excitation process.

Enhancement of polarizabilities of cylinders with cylinder-slab resonances

Abstract A short overview is presented on the research works related to the zero- gap, which appears as the volume-averaged refraction index vanishes in photonic structures containing both positive and negative-index materials. After introducing the basic concept of the zero- gap based on both rigorous mathematics and numerical simulations, the unique properties of such a band gap are discussed, including its robustness against weak disorder, wide-incidence-angle operation and scaling invariance, which do not belong to a conventional Bragg gap. We then describe the simulation and experimental verifications on the zero- gap and its extraordinary properties in different frequency domains. After that, the unusual photonic and physical effects discovered based on the zero- gap and their potential applications are reviewed, including beam manipulations and nonlinear effects. Before concluding this review, several interesting ideas inspired from the zero- gap works will be introduced, including the zero-phase gaps, zero-permittivity and zero-permeability gaps, complete band gaps, and zero-refraction-index materials with Dirac-Cone dispersion.

Conical dispersions induced interface states in two-dimensional photonic crystals

We investigated the time evolution of the cloaking behavior of a small particle placed in front of a meta-material slab with ε=μ=-1+iδ. We found that the dipole excitation would be suppressed in the long time limit. While on the way to being cloaked, the excitation will exhibit oscillatory behavior as the result of the interference between particle-slab resonances and high density-of-states surface modes.