Ming Kang

Asymmetric transmission for linearly polarized electromagnetic radiation

Metamaterials have shown to support the intriguing phenomenon of asymmetric electromagnetic transmission in the opposite propagation directions, for both circular and linear polarizations. In the present article, we propose a criterion on the relationship among the elements of transmission matrix, which allows asymmetrical transmission for linearly polarized electromagnetic radiation only while the reciprocal transmission for circularly one. Asymmetric hybridized metamaterials are shown to satisfy this criterion. The influence from the rotation of the sample around the radiation propagation direction is discussed. A special structure design is proposed, and its characteristics are analyzed by using numerical simulation.

Tunable slow light in semiconductor metamaterial in a broad terahertz regime

We demonstrate theoretically and numerically that tunable slow light can be realized in planar semiconductor metamaterials with the unit cell composed of two different elements in a broad terahertz regime. In the unit cell, one element is a semiconductor split ring resonator and another one is a semiconductor cut wire. The interaction between the two elements of the unit cell, induced directly or indirectly by the incident electromagnetic wave, leads to a transparent window, resembling the classical analog of electromagnetically induced transparency. This transparent window, caused by the coupling of bright-bright modes or dark-bright modes, can be continuously tuned in a broad frequency regime. The strong normal phase dispersion in the vicinity of this transparent window results in the slow light effect. This scheme provides an alternative way to achieve tunable slow light in a broad frequency band and can find important applications in active and reversibly tunable slow light devices.

Twisted vector field from an inhomogeneous and anisotropic metamaterial

We propose a metamaterial design for realizing inhomogeneous and anisotropic effective media based on the localized waveguide resonance mechanism. Such a design can be easily achieved in experiment and enables us to simultaneously manipulate the wavefront and the state of polarization of the transmitted electromagnetic field by the polarization-sensitive extraordinary optical transmission. Numerical simulations, including the generation of the hybridized vector fields (especially twisted vector fields that are azimuthally polarized carrying a helical phase), prove the feasibility of our proposal. It could be expected as a good candidate of the specially designed subwavelength element for creating the exotic vector fields beyond the functionality of the existing vector fields in a wide spectral regime, especially the terahertz and radio regimes.

Unidirectional optical transmission in dual-metal gratings in the absence of anisotropic and nonlinear materials

We predict the unidirectional optical transmission in dual-metal grating structures composed of two gratings with different structures in the absence of anisotropy and nonlinearity. The zero-order unidirectional transmission is achieved. Based on the unique property and by modulating the structural parameters, the transmittance approaches to 0% and 60% in the two opposite directions, respectively.

Fano–Feshbach resonance in structural symmetry broken metamaterials

Metamaterials support optically excitable dark-plasmon modes featured by antisymmetric surface current oscillations, which can be explained by Fano-type resonance and can be tailored by controlling the embedded structural geometry. In this article, we numerically investigate the Fano-type resonance in complex metamaterials, and demonstrate the presence of Fano–Feshbach resonances due to the interaction between two Fano-type resonances in the overlapping region, implemented by breaking and tuning the symmetric properties of the resonant metallic element. Features of the resonance are discussed. This work shows that the domain of dark-plasmon mode based metamaterial system supports rich physics and can lead to various potential applications.

Slow light from sharp dispersion by exciting dark photonic angular momentum states.

A photonic angular momentum state (PAMS) with a topological charge of m≠±1 is dipole forbidden at all polarizations of free-space incidence due to the existence of a unique helical phase. We show that by indirectly exciting dark PAMSs through coupling with a bright resonant element, a sharply variant transmission behavior and strong dispersion can be achieved. This behavior can subsequently be utilized in slow light. A metamaterial design, in which a group index n(g) greater than 500 can be achieved, is present.

Optical spin-dependent angular shift in structured metamaterials

The physics behind the spin (polarization)-dependent electromagnetic hot-spot phenomenon is due to the presence of the geometric phase resulting from the optical spin-orbit interaction in the interaction of light with the subwavelength microstructures. Unlike the tiny spin-dependent shift of light associated with the usual spin-Hall effect of light, here we present the distinct polarization-dependent angular shift by employing an array of subwavelength metallic apertures. More importantly, this novel electromagnetic precession is accompanied by the extraordinary optical transmission phenomenon and offers the exciting possibilities for novel applications for subwavelength structured metallic systems.

Enhanced optical angular momentum in cylinder waveguides with negative-index metamaterials

The optical angular momentum (AM) of helical electromagnetic (EM) modes in cylinder waveguides with negative-index metamaterials (NIM) is investigated. The AM density in NIM is shown to be negative valued with respect to the azimuthal mode index, in sharp contrast to that in regular dielectrics and vacuum. Furthermore, the AM flux per single-photon flux is found to be greatly enhanced in the NIM waveguides; its value depends on the form of EM momentum used in the AM. This interesting phenomenon is shown to be associated with the unique trapped EM modes in the NIM waveguides. Our investigation results could contribute to many potential applications, especially in realizing high density optical memory and buffers, and in solving the Abraham–Minkowski dilemma.

Second-harmonic generation in one-dimensional metal gratings with dual extraordinary transmissions

We investigate the enhanced second-harmonic generation (SHG) in nonlinear metal gratings with simultaneously extraordinary optical transmissions (EOTs) for the fundamental and the second-harmonic wavelengths, i.e., dual EOTs. We show that the strongly temporal and spatial dispersions at Wood’s anomalies, the asymmetry in the grating structure and the intrinsic dispersion of the media are of great importance in achieving dual-EOT SHG. Metal gratings with dual EOTs are present and the maximum enhancement on SHG is around 20. Weak points of dual-EOT SHG, potential improvement and future applications are discussed.

Spin-sensitive distribution of electromagnetic field via spin-orbit interaction in structured metamaterials

We investigate the spin-sensitive distribution of electromagnetic (EM) field from a kind of defective inhomogeneous anisotropic metamaterial, with azimuthally distributed subwavelength rectangular holes within a distribution angle of Φ<2π. This structure supports the spin-orbit interaction in the optical angular momentum, induced by the Pancharatnam-Berry phase from the manipulation of the spin states of polarization. Spin-sensitive distributions of electric field intensity, spin states of polarization, and transverse energy flow in the transmitted EM field are investigated. Importance of this investigation and the possible applications are discussed.