H. T. Jiang

Metamaterial analog of quantum interference: From electromagnetically induced transparency to absorption

With a metamaterial structure, the phenomenology observed in quantum electromagnetically induced transparency is reproduced. Through the parametric comparison between quantum and classical systems, the physical mechanism of this novel phenomenon has been explained directly in our analysis. In addition, we use another metamaterial structure to mimic a tripod four-level atom and reveal the analog of electromagnetically induced absorption. Our theoretical and experimental studies may not only bring an intuitive understanding of quantum interference in atomic system, but also provide useful guidelines for the design of microwave devices based on metamaterials.

Transmission properties near Dirac-like point in two-dimensional dielectric photonic crystals

We study the wave transport properties near the Dirac-like point at the Brillouin zone center in two-dimensional dielectric photonic crystals with finite thickness. Both simulations and microwave experiments confirm that the transmittance is nearly inversely proportional to the length (L) of the samples in the propagation direction near the Dirac-like point. This transmittance law comes from the conically shaped dispersion. Since the conical singularity at the Brillouin zone center corresponds to zero refractive index, the field at the Dirac-like point contains a basic component of nearly uniform field. In contrast, the field at the Dirac point in the corner of the hexagonal Brillouin zone contains a basic component of inhomogeneous standing-wave–like field.

Anomalous transmission of disordered photonic graphenes at the Dirac point

The transmission properties of disordered photonic graphenes are investigated in microwave experiments. In the weak-localization regime, we found that, in the passbands the transmission decreases as the random degree increases, owing to the enhanced coherent backscattering effect. However, at the Dirac point, with the increase of the random degree, the transmission increases rather than decreasing. This observed anomalous transportation, also called weak antilocalization, provides the important experimental clue that the Berry phase associated with the Dirac point may suppress the coherent backscattering effect in a random system.

Ultra-deep stopband induced by spontaneous-emission-cancellation–like interference between two side-coupled zero-index-metamaterial–based resonators

In this paper, two side-coupled zero-index-metamaterial?based resonators that mimic the spontaneous-emission cancellation (SEC) effect are investigated numerically and experimentally. It is found that an interference-induced stopband as deep as ?70?dB can be observed in a microstrip SEC structure whose size is even less than 0.5?cm2. More simulations about the electrical-field distributions demonstrate intuitively the underlying physics, i.e., the destructive interference between two side-coupled zero-index-metamaterial?based resonators. Our method of realizing ultra-deep stopband properties in a miniaturized filter may find potential applications in both microwave and optical-communication systems.

Position-independent normal-mode splitting in cavities filled with zero-index metamaterials.

We study the normal-mode splitting when an oscillator is placed in a two-dimensional photonic crystal microcavity embedded with an impedance-matched or an impedance-mismatched zero-index medium (ZIM). Because of the (nearly) uniform localized fields in the ZIM, the normal-mode splitting remains (almost) invariant no matter where the oscillator is. When a split ring resonator is coupled to a transmission-line- based effective ZIM at various locations, nearly position-independent mode splitting is observed.

Experimental realization of subwavelength flux manipulation in anisotropic near-zero index metamaterials

Recently, it has been theoretically shown that anisotropic metamaterials with a near-zero index can flexibly control electromagnetic flux in the subwavelength scale. Here, by using two-dimensional transmission lines with lumped elements, we design and fabricate a type of anisotropic metamaterial with a near-zero permeability component. By further introducing spatial variations into the system, we experimentally realize the subwavelength flux manipulation in such a highly anisotropic environment, which is conducted via evanescent scattered waves. The experimental results agree well with the simulation. Our work verifies the feasibility of subwavelength flux manipulation in near-zero index materials.

Experimental investigation of bistable transmission with nonlinear meta-atoms in waveguide configuration

We experimentally investigate the low-threshold and high-contrast bistable transmission of the nonlinear two-level and three-level meta-atom within the waveguide. Such subwavelength meta-atoms may find applications in integrated nanophotonic circuits.