METAMATERIALS  &  PLASMONICS RESEARCH  LABORATORY

One major obstacle in developing plasmonic devices is dissipative loss. Structural waveguide dispersion offers a route to tackle this problem. Although long range propagation of surface waves using this concept is recently reported, experimental realizations of localized surface plasmon resonances with suppressed dissipative loss still remain elusive. In this paper, effective localized surface plasmons in a bounded waveguide filled with only positive dielectrics are modeled theoretically and demonstrated experimentally. Theoretical analysis based on cylindrical wave expansion shows that the effective surface modes are induced by structural dispersion of transverse electric modes. Owing to dramatically suppressed metallic loss, the designed structure can support multipolar sharp plasmonic resonances, which are difficult to attain with natural plasmons at optical frequencies. To probe the characteristics of these resonances in the experiment, a deepsubwavelength open resonator is fabricated and the transmission spectrum at the boundary of the structure is measured. The results reveal that structured-dispersion-induced localized surface plasmons are quite sensitive to the background refractive index but relatively robust to the size and shape of the resonator. These findings open up a new avenue for designer localized surface waves at low frequencies and may find applications in miniaturization of microwave resonators, filters, and terahertz biosensors.

Recent theoretical and experimental works demonstrate that effective surface plasmon polaritons (ESPPs) induced by structural dispersion in bounded waveguide are perfect low-frequency counterpart of optical SPPs both for the double-layered and multi-layered systems. In all these efforts, the lateral dimension of each layer was assumed to be the same and the dispersion of the ESPPs was only tuned by the dielectric permittivity in each layer. Inevitably, the dielectric loss will deteriorate the transmission performance of ESPPs due to the huge field confinement and enhancement. In this work, we propose a simple but robust scheme to dramatically enhance the transmission efficiency of ESPPs by introducing a double-layered air-filled plasmonic waveguide with different lateral dimensions. Simulation and experimental results demonstrate that an ultra-low loss plasmonic waveguide with tunable bandwidth can be easily built by changing the lateral dimension of the upper air layer. This work provides valuable guidance for flexible design of low-loss plasmonic devices and systems at microwave and terahertz frequencies.

Backward phase matching, which describes counterpropagating fundamental and harmonic waves in a negative‐index medium, is one of the most intriguing phenomena in nonlinear metamaterials. Predicted theoretically decades ago, however, it is still a challenging task to be applied for efficient second harmonic (SH) generation in a nonlinear metamaterial with ultrathin geometry and ultralow loss. Here, a negative‐index spoof plasmonic metamaterial is reported, which is composed of an ultrathin symmetrical corrugated metallic strips loaded with nonlinear active devices. The simulated and measured power spectra and surface near‐field distributions show that a peak SH signal can be generated at the backward phase‐matched frequency point in a 120° curved surface with high efficiency, thanks to the ultrathin flexible geometry, significant confinement effect, and large propagation length of the spoof surface plasmons. The results open new technological challenges from nano‐ and micro‐nonlinear photonics to science and engineering of compact, broadband, and efficient frequency‐mixing metamaterials and electromagnetic devices.

Congratulations to Jiajia Song for her paper presented in IEEE EMC Conference

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Abstract:

The field uniformity in most reverberation chambers (RC) generally cannot meet the standards  ofIEC61000-4-21 in the frequency range between 80MHz and 200MHz, which is lower than the lowest usable frequency (LUF) of the RCs. In this paper, we demonstrate that by coating the RCs walls with judiciously designed metasurfaces the field uniformity in the RCs between 80MHz and 200MHz can be effectively improved. Actually, the reflective metasurfaces can be designed to tune the phase of scattering waves fromthe walls and increase the mode numbers in the RCs, thus improving the field uniformity and generating statistically homogeneous, isotropic, incoherent and random fields. Simulation results validate our idea.

Prof. Yijun Feng gave us a fantastic talk on Metamaterials and Metasurface in his group.

Recently, effective surface plasmon polaritons (ESPPs) induced by structural dispersion in bounded waveguides were theoretically demonstrated and experimentally verified. Despite the theoretical and experimental efforts, whether ESPPs can mimic real SPPs in every aspect still remains an open question. In this work, we go one step further to study the hybridization of ESPPs in multilayer systems. We consider transverse electric (TE) modes in a conventional rectangular waveguide and a parallel-plate waveguide (PPW) and derive analytically the dispersion relations and asymptotic frequencies of the corresponding ESPPs modes in sandwiched structures consisting of alternating dielectrics of different permittivities. Our results show that the ESPPs can be categorized into odd and even parities (owing to the ‘plasmon’ hybridization) in a similar way as natural SPPs supported by the insulator/metal/insulator (IMI) and metal/insulator/metal (MIM) heterostructures in the optical regime. The similarities and differences between ESSPs and their optical counterparts are also discussed in details, which may provide valuable guidance for future application of ESPPs at the microwave and terahertz frequencies.

Prof. Yumao Wu give a wonderful talk on High Frequeny EM Scattering, Multiphysics Modeling and High Performance Methods

​The concept of metasurfaced reverberation chamber (RC) is introduced in this paper. It is shown that by coating the chamber wall with a rotating 1-bit random coding metasurface,it is possible toenlarge the test zone of the RC while maintaining the field uniformity as good as that in a traditional RC with mechanical stirrers. A 1-bit random coding diffusion metasurface is designed to obtainall-direction backscattering under normal incidence.Three specific cases are studied for comparisons, including a (traditional) mechanical stirrer RC, amechanicalstirrer RC with a fixed diffusion metasurface, and a RC with a rotating diffusion metasurface. Simulation results show that the compact rotating diffusion metasurface can act as a stirrer with good stirring efficiency. By using such rotating diffusion metasurface,the test region of the RC can be greatly extended.

Advances in metamaterials have offered the opportunity of engineering electromagnetic properties beyond the limits of natural materials. A typical example is the “spoof” surface plasmon polaritons (SPPs)that mimic features of SPPs without penetrating into metal but only with periodic corrugations on metal surfaces. They hold considerable promise in device applications from microwave to far infrared, where the real SPPs modes do not exist. The original spoof SPPs concept was derived from the description of corrugated surfaces by an effective medium (metamaterial) that hosts an effective plasma frequency. Here we extend the concept of spoof SPPs beyond the metamaterial limit and propose the concept of surface-wave photonic crystal to describe spoof SPPs modes with the band structure theory. Moreover, as inspired by the development of topological framework in condensed matter physics, the topological description of spoof SPPs has been used to propose topologically protected waveguiding phenomena.

Challenges and solvers to the multiphysics analysis and modeling.

Congratuations to Yunhe Sun, Hengyi, Sun and Yang Zhang for receiving the Innovation Award of Ministry of industry and Information!

Structural Dispersion Induced ESPPs and ELSPs

Welcome Mr. Yulei Ji and Mr. Man Tao to join our group!

When light hits a metal, it generates electromagnetic waves that travel along the surface of the metal. These waves, called surface plasmon polaritons (SPPs), can be harnessed to make powerful sensors and ultra-compact devices that relay data almost instantaneously. One major obstacle in developing plasmonic devices, however, is dissipative loss. SPPs decay as they travel along the metal due to the conversion of optical energy to heat. These losses severely limit the performance of metal-based plasmonic devices at optical frequencies. To overcome this problem, some scientists have proposed using waveguides – structures that confine and convey waves – that are made of only dielectric materials. These could enable modal-dispersioninduced effective SPPs that do not suffer dissipative losses.