Yunlong Shi

Transmission properties of lossy single-negative materials

We study the transmission properties of structures with one or two kinds of lossy single-negative (permittivity-negative and permeability-negative) material. Analytic results show that the transmission of the structure depends on the material absorption and reflection. In sharp contrast to lossy dielectrics, the reflection of the lossy single-negative material(s) can decrease as the dissipation coefficient increases. As a result, the transmission of the lossy single-negative material(s) will be nonmonotonic as the dissipation coefficient varies. In particular, the transmission can be enhanced even when the dissipation coefficient increases.

Enhancement of Faraday rotation effect in heterostructures with magneto-optical metals

We theoretically study the transmission and Faraday rotation effect in the heterostructure composed of an all-dielectric photonic crystal and a magnetic metal. Under the tunneling mechanism, the electromagnetic fields can totally enter the structure and localize at the interface between photonic crystal and magnetic metal. Because of the localized electromagnetic fields, the transmission and Faraday rotation in the heterostructure are simultaneously boosted.

Highly localized mode in a pair structure made of epsilon-negative and mu-negative metamaterials

In this paper, the tunneling phenomenon occurring in a pair structure made of epsilon-negative (ENG) and mu-negative (MNG) metamaterials is experimentally studied. The ENG and MNG metamaterials are fabricated using coplanar waveguide loading with lumped-element series capacitors and shunt inductors. The properties of the tunneling mode are investigated by means of the transfer-matrix method, based on the experiment parameters of effective permittivity and permeability. The results show that the tunneling frequency is independent of the pair length and the electric field is highly localized at the interface of the ENG-MNG pair. These features illustrate that the pair behaves as a cavity with strongly enhanced electric field and with dimensions beyond the half-wavelength limit.

Observation of valley-dependent beams in photonic graphene.

Valley-dependent propagation of light in an artificial photonic hexagonal lattice, akin to electrons in graphene, is investigated in microwave regime. Both numerical and experimental results show that the valley degeneracy in the photonic graphene is broken when the frequency is away from the Dirac point. The peculiar anisotropic wave transport property due to distinct valleys is analyzed using the equifrequency contours. More interestingly, the valley-dependent self-collimation and beam splitting phenomena are experimentally demonstrated with the armchair and zigzag interfaces, respectively. Our results confirm that there are two inequivalent Dirac points that lead to two distinct valleys in photonic graphene, which could be used to control the flow of light and might be used to carry information in valley polarized beam splitter, collimator or guiding device.

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.

Tunnelling-based Faraday rotation effect enhancement

The transmission and Faraday rotation effect of a heterostructure composed of an all-dielectric magnetophotonic crystal and a magneto-optical metal are theoretically studied. When impedance and phase matching conditions are satisfied in the heterostructure, the transmission and Faraday rotation effect can simultaneously be enhanced due to the slow-wave effect of the localized electric field at the interface between the magnetophotonic crystal and the magneto-optical metal layer.

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.

Valley-dependent beams controlled by pseudomagnetic field in distorted photonic graphene

The generation and control of valley pseudospin currents are the core of valleytronics. Here, the photonic analogy for generation and control of valley pseudospin currents using the pseudomagnetic fields induced in strained graphene is investigated in a microwave regime. In photonic graphene with uniaxial distortion, photons in two different valleys experience pseudomagnetic fields with opposite signs, and valley-dependent propagations in bended paths are observed. The external-field-free photonic transportation behavior may be very useful in controlling the flow of light in future valley-polarized devices.

Multi-channeled filtering properties of the sandwich structures composed of epsilon-negative metamaterials

Multi-channeled filtering properties are found in the sandwich structure composed of two e-negative layers with dielectric permittivity described by Drude model separated by another normal material layer. Epsilon-negative metamaterials are successfully realized by using composite right/left-handed transmission line, based on which the Fabry–Perot (FP) cavity was also constituted. The single resonant mode is split into some discrete resonant peaks, leading to the multi-channeled filtering phenomenon through the several coupled FP cavity resonators. In comparison with the conventional multichanneled filters, the proposed structure is more compact and tunable. The microwave experiment results are found in agreement with simulation results.

Microwave propagation in a graphenelike photonic crystal slab

In this paper, we investigate the transport properties of microwaves in a two-dimensional (2D) graphenelike photonic crystal (PC) slab. We realize a narrow electromagnetic (EM) beam by using a grounded coplanar waveguide with better direction, which is beneficial to the study of the transport properties of (2D) PCs. The extremal transmission of the microwave near the Dirac point in a graphenelike PC slab, being inversely proportional to the thickness of the sample, is demonstrated by means of numerical simulation. Furthermore, we verify experimentally that some certain EM field modes for photonic bands cannot be excited in the PC slab.