Designing All-Electric Subwavelength Metasources for Near-Field Photonic Routings

Unique Huygens-Fresnel electromagnetic transportation of chiral Dirac wavelet in topological photonic crystal

Light propagates in various ways depending on environment, including uniform medium, surface/interface and photonic crystals, which appears ubiquitously in daily life and has been exploited for advanced optics technology. We unveiled that a topological photonic crystal exhibits unique electromagnetic (EM) transport properties originating from the Dirac frequency dispersion and multicomponent spinor eigenmodes. Measuring precisely local Poynting vectors in microstrips of honeycomb structure where optics topology emerges upon a band gap opening in the Dirac dispersion and a p-d band inversion induced by a Kekulé-type distortion respecting C_6v symmetry, we showed that a chiral wavelet induces a global EM transportation circulating in the direction counter to the source, which is intimately related to the topological band gap specified by a negative Dirac mass. This brand-new Huygens-Fresnel phenomenon can be considered as the counterpart of negative refraction of EM plane waves associated with upwardly convex dispersions of photonic crystals, and our present finding is expected to open a new window for photonic innovations.

Optical properties of symmetry breaking of the self-similar order in triadic Cantor photonic crystals

In general, the photonic crystal (PC) is a periodical optical structure, but there are some studies considering aperiodic structures. If we insert a defect layer into a one-dimensional periodic PC to break its translational symmetry order (TSO), some peaks, called defect modes, appear in the transmittance spectrum. The defect layer thickness governs the frequencies of these defect modes but almost does not affect the other part of the spectrum. The discovery of quasi-crystals tells us that not only the TSO but also other orders can produce Bragg diffraction. It is well known that triadic Cantor set (TCS) PCs, which lack TSO but have a self-similar symmetry order (SSO), still exhibit narrow transmission peaks. In this work, we try to break the SSO in TCS PCs and find the resulting optical phenomena, where single-negative materials and dielectrics are chosen as the constituents of PCs. The study method is the transfer matrix method, and the calculation results show that the background intensity of the transmittance spectrum rather than the frequency of peaks obviously periodically changes with the break of SSO. It follows that the SSO does have physical meaning, and not only the transmission peaks but also the background should be treated as a significant optical property.

Fledgling Quantum Spin Hall Effect in Pseudo Gap Phase of Bi2212

We studied the emergence of the quantum spin Hall (QSH) states for the pseudo-gap (PG) phase of Bi2212 bilayer system, assumed to be D-density wave (DDW) ordered, starting with a strong Rashba spin-orbit coupling (SOC) armed, and the time reversal symmetry (TRS) complaint Bloch Hamiltonian. The presence of strong SOC gives rise to non-trivial, spin-momentum locked spin texture tunable by electric field. The emergence of quantum anomalous Hall effect with TRS broken Chiral DDW Hamiltonian of Das Sarma et al. is found to be possible.

Observation of elastic spin with chiral meta-sources

Directional routing of one-way classical wave has raised tremendous interests about spin-related phenomena. This sparks specifically the elastic wave study of pseudo-spin in meta-structures to perform robust manipulations. Unlike pseudo-spin in mathematics, the intrinsic spin angular momentum of elastic wave is predicted quite recently which exhibits selective excitation of unidirectional propagation even in conventional solids. However, due to the challenge of building up chiral elastic sources, the experimental observation of intrinsic spin of elastic wave is still missing. Here, we successfully measure the elastic spin in Rayleigh and Lamb modes by adopting elaborately designed chiral meta-sources that excite locally rotating displacement polarization. We observe the unidirectional routing of chiral elastic waves, characterize the different elastic spins along different directions, and demonstrate the spin-momentum locking in broad frequency ranges. We also find the selective one-way Lamb wave carries opposite elastic spin on two plate surfaces in additional to the source chirality.

’Following up on the recent theoretical demonstration here the authors bring us a step closer to the real implementation of efficient ultrasonic chiral sources. They experimentally demonstrate the presence of elastic spin waves, Rayleigh and Lamb waves, generated by a chiral-meta source, characterizing their basic properties.

Conceptual-based design of an ultrabroadband microwave metamaterial absorber

While microwave absorption is a widely pursued topic, a conceptual-based design can offer a theoretical basis for generalization and improvements. We offer a design recipe for ultrabroadband absorption based on the use of electrical dipole resonance in a metallic ring to generate, via interaction with its image resonance, two high-impedance resonances. Impedance matching over the frequency range in between the two resonances is obtained by adding resistance to the metallic ring. To extend the absorption to an ultrabroadband spectrum, we employ a double-layer self-similar structure in conjunction with absorption of the diffracted waves at the higher frequency end. The resulting absorber pushes the overall performance close to the causality limit over a large absorption bandwidth.

By introducing metallic ring structural dipole resonances in the microwave regime, we have designed and realized a metamaterial absorber with hierarchical structures that can display an averaged −19.4 dB reflection loss (∼99% absorption) from 3 to 40 GHz. The measured performance is independent of the polarizations of the incident wave at normal incidence, while absorption at oblique incidence remains considerably effective up to 45°. We provide a conceptual basis for our absorber design based on the capacitive-coupled electrical dipole resonances in the lateral plane, coupled to the standing wave along the incident wave direction. To realize broadband impedance matching, resistive dissipation of the metallic ring is optimally tuned by using the approach of dispersion engineering. To further extend the absorption spectrum to an ultrabroadband range, we employ a double-layer self-similar structure in conjunction with the absorption of the diffracted waves at the higher end of the frequency spectrum. The overall thickness of the final sample is 14.2 mm, only 5% over the theoretical minimum thickness dictated by the causality limit.

Chiral interaction of an atom in a sandwiched waveguide

The chiral interaction between light and matter is mainly caused by the spin-momentum locking and makes the chiral quantum optics enter a vigorous development stage. Here, we explore the condition of the perfect chiral interaction between an atom possessing circular dipole and the surface plasmon polariton (SPP) mode. The realization of the perfect chiral interaction must satisfy the following two conditions at the same time. First, the SPP mode should possess the transverse circular polarization; and second, the atom decays mainly into the SPP mode, while the decay through other channel can be ignored. In this paper, we adopt a simple but effective structure to satisfy both of requirements, which is the sandwiched waveguide made of metal. We found that the transverse circular polarization of SPP mode might be achieved within the structure possessing multiple interfaces instead of the interface separating two semi-infinite materials. In our model, the decay rate into SPP mode overwhelms that through traveling wave, which provides higher quantum efficiency. What's more, we found that only the symmetric TM-polarized SPP mode might get the transverse circular polarization. For the sandwiched structure containing metal, the existence of two SPP modes weakens the overall chiral interaction. However, the structure containing left-handed materials (LHMs), which can only support one symmetric TM-polarized SPP mode, can get the nearly perfect chiral interaction. We measure the chiral interaction through the decay rate, radiation field distribution and the unidirectional rate through the energy flux. Our work provides a reference for exploring the perfect chiral interaction in more complex structures and has potential and wide applicability to other optical processes.

Reconfigurable magnetic near-field distributions based on the coding metasurfaces in MHz band

Magnetic near-field control has attracted extensive attention and have a wide range of applications in filters, sensors, and energy-transfer devices. Coding metamaterial has the convenience of miniaturization and integration, which not only provides a bridge between physics and information science, but also exploits a whole new perspective for magnetic near-field control. In this work, we theoretically propose and experimentally verify that the coding metasurface can realize the reconfigurable magnetic near-field distributions. By adjusting the digital voltage signals which drive the resonant units of metasurface, capacitance of the resonator can be dynamically controlled, thus the dynamic modulation of magnetic near-field distribution can be achieved. Specially, this magnetic near-field control can be explained with the help of coupled mode theory and coherent superposition method. Moreover, simulated annealing algorithm is employed to determine working frequency of the whole modulation system, which can avoid time-consuming frequency scanning process. The experimental results are in good agreement with the calculated results. This work reveals the significant potential of coding metasurface for the experimental study of the magnetic near-field control and promotes the use of metasurface for numerous integrated functional devices.