Spoof Surface Plasmon Polariton Filter With Reconfigurable Dual and Non-Linear Notched Characteristics

In this paper, two novel waveguides with ELC like-shaped and Z-shaped grooves have been proposed to achieve highly efficient and strongly confined spoof surface plasmon polaritons (SSPPs) propagation. Low-dispersion bands can be realized by such structures with tight field confinement of SSPPs, resulting in size miniaturization of the proposed waveguides. Specifically, our method yields deep physical insight into the effect that the geometrically induced modifications of the supporting structure has on the dispersion properties and field confinement capabilities of SSPPs. In comparison, SSPP waveguide results presented in Aziz (2021 Results Opt. 5 100116) are given which is regarded to have stronger SSPPs field confinement as compared to previously reported different grooves shapes based SSPP waveguides. It is found that the dispersion and waveguide propagation characteristics can be directly manipulated by varying the geometrical parameters of the horizontal and slanted slits of Z-shaped and ELC-like shaped plasmonic waveguides without increasing the lateral dimension of the waveguides. Based on this waveguiding scheme, the proposed waveguides exhibit much lower asymptotic frequency of the dispersion relation and even tighter SSPPs field confinement than I-shaped plasmonic waveguide. Then, broadband transitions with a tapered metallic strip and an array of graded height ELC-like and Z-shaped units with good impedance matching and high mode conversion efficiency are designed. Fully controlled field enhancement functionality has been performed, by using such metamaterial particles in the form of grooves, decorated in SSPP waveguide. Simulated results have demonstrated that the proposed SSPP waveguides have much stronger field confinement than the highly efficient I-shaped grooves based SSPP waveguide. The proposed waveguides can be a significant contribution towards the advancement of plasmonic functional devices and integrated circuits in microwave frequencies.

Spoof surface plasmon polaritons (SPPs) are kinds of special surface wave modes, which have attracted wide interest of researches. However, the studies on odd-mode spoof SPPs are very limited, although it is proved to provide more tightly field confinements than the common spoof SPPs. In this paper, an odd-mode spoof SPP complementary waveguide is proposed. The dispersion analysis indicates that stronger ability of the field confinements can be obtained by trapezoid corrugations. To excite the odd-mode SPPs, a conversion structure is designed, and its outstanding transition efficiency between microstrip and the SPP waveguide is demonstrated by full-wave simulations. The near-field distributions of electric fields are also presented to show the good transmission of odd-mode SPPs on the proposed waveguide.

Spoof Surface Plasmon Polariton (SSPP) transmission line is a novel type of surface wave structure in microwave and terahertz frequency range. For limited electromagnetic field between corrugated metal and dielectric, SSPP transmission lines and components have the advantages of wideband adjustment, miniaturization and high integration. In this paper, the influence of several geometric parameters on the dispersion curves of the oral-ring SSPP unit is analyzed. And then, the attenuation constant of the oval-ring transmission line is calculated. Finally, the SSPP splitters with oval-ring unit cell are reviewed.

This paper presents an approach to develop spoof surface plasmon polaritons (SSPPs) in substrate integrated waveguides (SIWs) with simple geometries (arrays of rectangular holes). Dispersion properties of both SSPPs based on a SIW with a rectangular hole and the traditional SSPPs based on a single-conductor metallic strip with the same hole are compared. Moreover, a smooth transition built by stepped impedance transmission lines with gradient holes is designed for high-efficiency mode conversion. Consequently, an SSPP waveguide is constructed by a SIW with uniform holes and the proposed transition, and the frequency responses of the waveguide are simulated for validation. The simulated bandwidth can reach as up to 100.1% covering a range from 4.34 to 13.05 GHz, which agrees well with the dispersion diagram.

Effective spoof surface plasmon polariton (SSPP) bandpass filtering with a simple structure based only on SSPP transmission lines (TLs) is proposed, which has a different working principle from previous versions. SSPP sections are placed beside a main SSPP TL, introducing resonances leading to transmission zeros to the main SSPP TL. By utilizing the SSPP TL sections’ strong dispersion characteristics to merge transmission zeros, a continuous stopband is obtained ensuring good out-of-band rejection and selectivity at the lower band. A domino SSPP working in the microwave band is adopted to demonstrate the idea. A prototype is designed and fabricated to confirm the validity of the proposed method.

Ultra-wideband spoof surface plasmon polaritons (SSPPs) based on compact balanced coplanar stripline (CPS) waveguides are proposed. Compared with the conventional CPS-based terahertz (THz) SSPP unit cell, the proposed one has achieved a size reduction of 55.2% under the condition of the same asymptotic frequency. The propagation and attenuation characteristics of the proposed SSPP waveguide can be easily manipulated by adjusting the geometry dimensions of the SSPP unit cell. It indicates that the cut-off frequency of the SSPP waveguide has its tunable flexibility thereby facilitating the filter design. To further validate the proposed idea, a similar topology in microwave regime is designed and measured, where the microwave feeding can be easily realized by embedding a balun structure from unbalanced microstrip line to balanced CPS. The measurement of the microwave filter prototype illustrates ultra-wideband bandpass filtering characteristics with return losses of over 10 dB and average insertion losses of 3.2 dB in the passband of 1.9-14 GHz. The presented work may have significant potentials to develop the miniaturization of various planar plasmonic devices and integrated circuits in microwave and THz regimes.

The next‐generation wireless communications and intrachip and interchip communications require high‐speed terahertz (THz) interconnects. The interconnects based on spoof surface plasmon polaritons (SSPPs) provide a possible route to achieve this goal. Recently, some THz plasmonic devices are explored, but they suffer from bulk sizes and/or single function. Herein, planar multifunctional THz plasmonic devices based on the interaction between SSPPs and spoof localized surface plasmon (SLSPs) including the functions of pass‐through transmission, multifrequency resonances, and phase shift are proposed and experimentally demonstrated. The pass‐through transmission can be realized on the SSPP waveguide by increasing the loss of the coupled SLSP resonator; the multifrequency resonances are obtained by placing the SU‐8 films with different thicknesses on the SLSP resonator due to its high sensitivity; and the phase shift can be achieved by integrating the SU‐8 film on the SSPP waveguide due to the flexible dispersion behaviors of SSPPs. The proposed multifunctional THz plasmonic devices hold great promise for the THz on‐chip integrations, wireless communications, and sensing systems.

Spoof surface plasmon polaritons(SSP) on the corrugated metallic surfaces can find many interesting applications from microwave to terahertz band. In this paper, we propose a new excitation method of high-order SSP mode on a lamellar grating by injected electron beam. The dispersion characteristics and field confinement of SSP modes on the structure are presented by theoretical and numerical methods at terahertz frequencies. Besides, the excitation of high-order SSP mode by injected electron beam are modeled and implemented by numerical simulations based on FDTD algorithm. It is shown that the needed beam energy is much higher than the previously shown fundamental SSP mode excitation with metallic grating. Thus, it is very challenging to excite higher-order SSP mode by electron beam in the structure. Also, the output performances of the excited high-order SSP mode are also analyzed. The presented studies on the excitation of high-order SSP mode by electron beam pave the ways for the development of novel terahertz radiation source which can operate at higher frequency band and/or multi-frequency spectrum.

Two compact spoof surface plasmon polariton (SSPP) waveguides are proposed with simple configurations and good performance. Compared with the conventional SSPP structure having same asymptotic frequency, a new design of the tilted-stub structure occupies less transversal space. Moreover, this design can be applied in the SSPP cases with small period values, which will facilitate the longitudinal miniaturization. Then, an improved SSPP structure is constructed to realize the transversal size reduction of 58% compared with the conventional corrugated SSPP waveguide. For these two proposed waveguides, smooth transitions from microstrip lines to SSPPs are designed with seamless connection. Two experimental prototypes have been fabricated, whose measurements are in good agreement with the simulated ones. The proposed designs will have significant potentials for the miniaturization of plasmonic devices and circuits.

Periodically patterned conductor surfaces can transmit electromagnetic modes similar to surface plasmon polaritons, which are called spoof surface plasmon polaritons (SSPPs). In this paper, noncoplanar dentate complementary structure units are proposed. In this case, the fundamental SSPP is split into two modes, of which the mode in the high‐frequency side exhibits negative group velocity (NGV) near the cutoff frequency. The dispersion characteristics of NGV modes can be controlled by manipulating the symmetry of the complementary structure. It is confirmed that the actual transmission wave in the SSPP waveguide is the superposition result of the two split‐mode wave components.

A range of alternative approaches to traditional digital hardware have been explored for the implementation of artificial neural networks, including optical neural networks and diffractive deep neural networks. Spoof surface plasmon polariton waveguides, which operate at microwave and terahertz frequencies, can offer low crosstalk, low radiation loss and easy integration, and are of potential use in the development of an alternative technology for artificial neural networks. Here, we report a programmable surface plasmonic neural network that is based on a spoof surface plasmon polariton platform and can detect and process microwaves. The approach uses a parallel coupled spoof surface plasmon polariton cell integrated with varactors. The weight coefficients of the cell can be adjusted by tuning the voltages of the varactors, and the activation function of the neural network can be programmed by detecting the input intensity and feeding back the threshold to an amplifier. We show that a two-layer fully connected surface plasmonic neural network consisting of four input cells and four output cells can perform a vector classification task. The surface plasmonic neural network can also be used to create a wireless communication system to decode and recover images. In addition, we show that partially connected surface plasmonic neural networks can classify handwritten digits with high accuracy. A spoof surface plasmon polariton platform can be used to create a surface plasmonic neural network with programmable weights and activation functions.

In this presentation, I will review recent advances of spoof surface plasmons in the microwave, millimeter wave, and terahertz frequencies based on ultrathin metallic strictures. In details, I will introduce an ultrathin transmission line of spoof surface plasmon polaritons (SPPs) on corrugated metallic strip, which can be printed on ultrathin and flexible dielectric film to support conformal surface plasmons; an ultrathin corrugated metallic disk to support spoof localized surface plasmons (LSPs); passive SPP devices; active SPP devices for amplifying SPP signals and generating the second harmonics of SPPs; and the combined SPP and LSP circuits. Experimental results are presented for the SPP and LSP devices and circuits.

Dual beam scanning (DBS) antenna exited by two different spoof surface plasmon polaritons (SSPPs) transmission lines is proposed in this paper. The antenna is constructed by placing three rows of circular patches on both sides of two different planar SSPPs waveguide. These patches convert the SSPP guided waves into radiating waves. This simple single-layer antenna is characterized by dual without need to use switches or other complex configurations. It is designed to support application of several 5G sub-6 GHz bands (3.5 (n78) GHz, 3.7 (n77) GHz, and 4.5 (n79) GHz). The proposed antenna realizes the dual beam scanning by controlling the dispersion properties and field confinement along two different SSPPs transmission lines, based on different propagation constant. Numerical simulations are carried out by CST Microwave Studio and Ansys HFSS. These numerical simulations are verified by experimental results over the operating frequency band from 1 GHz to 6 GHz.

In search of new technologies for optimizing the performance and space requirements of electronic and optical micro-circuits, the concept of spoof surface plasmon polaritons (SSPPs) has come to the fore of research in recent years. Due to the ability of SSPPs to confine and guide the energy of electromagnetic waves in a subwavelength space below the diffraction limit, SSPPs deliver all the tools to implement integrated circuits with a high integration rate. However, in order to guide SSPPs in the terahertz frequency range, it is necessary to carefully design metasurfaces that allow one to manipulate the spatio-temporal and spectral properties of the SSPPs at will. Here, we propose a specifically designed cut-wire metasurface that sustains strongly confined SSPP modes at terahertz frequencies. As we show by numerical simulations and also prove in experimental measurements, the proposed metasurface can tightly guide SSPPs on straight and curved pathways while maintaining their subwavelength field confinement perpendicular to the surface. Furthermore, we investigate the dependence of the spatio-temporal and spectral properties of the SSPP modes on the width of the metasurface lanes that can be composed of one, two or three cut-wires in the transverse direction. Our investigations deliver new insights into downsizing effects of guiding structures for SSPPs.

Interconnects have become a major obstacle in chip scaling. Spoof surface plasmon polariton (SSPP) modes have gained attention for their ability to manipulate light beyond diffraction limits at a given frequency, leading to SSPP interconnects. This article investigates the transmission characteristics of SSPP interconnect pairs placed side by side in the terahertz frequency range with comprehensive performance analysis. The proposed SSPP waveguide pair exhibits a maximum transmission coefficient of around −0.05 dB in the −3 dB band in the terahertz frequency range. Due to field confinement near the metal–dielectric interface, energy remains confined for the designed SSPP interconnect pair system. The proposed SSPP structure shows several bands in the terahertz frequency range, whereas conventional interconnects shows almost zero transmission at such frequencies. Additionally, the effect of geometric parameters on transmission coefficients (S21) and coupling coefficients (S41) has been investigated. Moreover, it has been shown that the bandwidth, as well as the upper cutoff frequency, can be tuned by varying the geometric parameters such as groove height, groove width and groove density. Since global interconnects undergo bending in actual circuits during distant data transmission on chips, geometric mismatches may occur between adjacent pairs of SSPP interconnects. Hence, it has also been examined how bending and mismatches affect transmission and coupling coefficients. Several SSPP schemes have been simulated, among which the best performance is obtained with 2 μm mismatch in groove height. For this optimized design, two corrugated metal interconnects are considered with groove heights of 20 μm and 22 μm, respectively, a groove width of 3 μm, a period of 20 μm, and the number of grooves at 50. For this particular configuration, an ultra-wide passband is found having a bandwidth of almost 400 GHz, with a signal reflection of below −12 dB and little insertion loss of ∼−1.43 dB.