Integrated spoof surface plasmon devices and circuits

Recent progress on metamaterials: From effective medium model to real-time information processing system

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.

Beam-frequency-scanning detection and point-to-point communication typically differ significantly in bandwidth and polarization characteristics, requiring two separate antennas in conventional designs. This paper proposes a method to integrate a dual-mode radiation of narrowband circular polarization (CP) into a broadband linearly polarized (LP) beam-scanning leaky-wave antenna (LWA) using a full spoof surface plasmon polariton (SSPP) system. First, a grooved SSPP unit and its complementary structure are used with periodic mode modulation to achieve continuous vertically polarized (V-pol) dual-beam scanning from backward to forward. By periodically embedding spoof localized surface plasmon (SLSP) units, strong coupling between SLSPs and SSPPs is enabled under resonant conditions. Then, CP radiation is generated due to the rotating electric-field vectors of SLSPs. Experiment and simulation results demonstrate continuous V-pol beam scanning from −30° to 22° across 4.25–6.75 GHz, including effective broadside radiation. Notably, at 5.4 GHz, the antenna radiates right-handed circularly polarized (RHCP) and left-handed circularly polarized (LHCP) waves in opposite broadside directions. Compared with existing technologies, the insertable CP radiation allows the antenna to enable two significantly different operating modes, which can be applied in combined beam-scanning detection and narrowband satellite emergency communication, greatly improving system integration.

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.

In this brief, we propose a spoof surface plasmon polariton (SPP) filter with reconfigurable dual and non-linear notched frequencies. The SPP waveguide with asymmetrical geometry leads to asymmetrical field confinement depending on the groove orientation. By loading half-wavelength SPP resonators along the weaker field confinement side of the asymmetrical SPP waveguide, dual notches can be generated in the SPP transmission. Meanwhile, since the dispersion of SPP cell is not linear, the dual notched frequency locations are also non-linearly spaced. Varactor diodes, with voltage controllable capacitance, are incorporated into the SPP resonators to engineer the SPP non-linear dispersion. Thus, the SPP effective wavelength can be altered and the dual-notched frequencies be tuned. Two reconfigurable notched frequencies are achieved at 4.29/5.69, 4.045/5.27 and 3.765/4.85 GHz with 16, 4.5 and 0 V bias, respectively.

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.

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.

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.

We propose a duplexer based on spoof surface plasmon polaritons (SSPPs) transmission lines (TLs). The duplexer consists of two domino SSPP TLs with different lower cut-off and higher cut-off (asymptotic) frequencies, forming the two frequency band channels. The low frequency band channel is the domino SSPP TL with higher unit height. For the branch of the high frequency band channel, which is based on a SSPP TL with lower unit height, multiple SSPP TL sections functioning as band-stop structures are placed aside the SSPP TL to realize satisfying out-of-band rejection below the lower cut-off frequency. The two branches are fed through a common rectangular waveguide. Different transition length of the two branches as well as a shifted placement from the center is designed to achieve efficient transition for both branches at respective bands.

In this paper, the spoof surface plasmon polaritons (SSPPs) transmission line (TL) of periodical grooved bow-tie cells is proposed. The complex propagation constant and characteristic impedance of the SSPPs TLs and microstrip lines (MLs) are extracted using the analytical method of generalized lossy TL theory. The properties of the SSPPs TLs with different substrates and the same geometrical configuration are experimented. Then, for comparison, two ML counterparts are also experimented, which shows that the SSPPs TL is less sensitive to the thickness, dielectric constant and loss tangent of the chosen substrate below the cutoff frequency, compared with the ML ones. The single-conductor co-planar quasi-symmetry unequal power divider based on this SSPPs TL is presented in microwave frequencies. For experimental validation, the 0-dB, 2-dB, and 5-dB power dividers are designed, fabricated, and measured. Both simulated and measured results verify that the unequal power divider is a flexible option, which offers massive advantages including single-conductor co-planar quasi-symmetry structures, wide-band operation, and convenient implementations of different power-dividing ratios. Hence, it can be expected that the proposed unequal power dividers will inspire further researches on SSPPs for future design of novel planar passive and active microwave components, circuits and systems.

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.

A novel millimeter-wave spoof surface plasmon polaritons (SSPPs)-fed dual-polarized microstrip patch antenna array is proposed in this article. A dual-polarized single-layered square patch antenna fed by SSPPs is investigated first acting as the radiators. A method of directly connecting two orthogonal SSPPs with two edges of the square patch is introduced to excite the TM10 and TM01 modes and to achieve promising performance simultaneously. The fabricated antenna element has a measured overlapped impedance bandwidth of 13.7%, an isolation of more than 15 dB between the two inputs, a gain of up to about 6 dBi, and stable dual-polarized radiation patterns. With the use of two SSPPs branches printed on different sides of the substrate, a compact SSPPs power divider with adjustable power dividing ratio is then investigated for realizing the series SSPPs feed network, whose design considerations are discussed in detail. By combining the feed network with the patch elements, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times $ </tex-math></inline-formula> 4 SSPPs-fed dual-polarized microstrip patch antenna array is fulfilled. The fabricated prototype confirms a bandwidth of 15% and dual-polarized broadside radiations. Benefitted from the simple single-layered geometry without the metallic ground plane over the major region of array geometry and the dual-polarized unidirectional radiation, the presented designs are valuable to emerging millimeter-wave applications.

Realizing fine control of surface plasmon polaritons (SPPs) and spoof surface plasmon polaritons (SSPPs) is highly desired in many integrated photonic and microwave applications, but the flexibility to control the wavefront of SPPs and SSPPs still need addressing. In this paper, a Pancharatnam–Berry (PB) phase manipulating metasurface (PMM) was designed to achieve SSPPs excitation and wavefront control. Under circular polarization (CP) incidence, simply by designing the rotation angle of the unit cells the reflection phase spatial distribution can be manipulated. By means of different phase profiles on the 2D unit cells array, the SSPPs can be excited with various wavefront shapes, without the need of special excitation structure pattern. Meanwhile, a plasmonic metal is also designed to support SSPPs with both TE and TM polarizations, which can efficiently guide out the energies from the input CP waves. As a proof of concept, a PB PMM composed of N-shape metallic structure was designed. Through designing the rotation of the unit cells, two typical phase profiles were designed to excite SSPPs in arbitrary slant direction or focusing. This scheme could be used to achieve SSPPs excitation with many other wavefront shapes, and would also enable promising applications in other spectra.

The feasibility of realizing an active terahertz (THz) switch by utilizing artificially corrugated perfect conductor metamaterials is reported in this paper by demonstrating that the strongly localized THz spoof surface plasmon polariton (SSPP) modes can be easily controlled by changing the refractive index of dielectrics inside a longitudinal metallic structure with a periodic array of grooves. Specifically, this paper shows that incorporation of electrooptical material such as a nematic liquid crystal into the plasmonic gap leads to a highly compact and efficient THz switch that is activated by a low-voltage control-signal. The optimal design of the SSPP switch enabled by this novel method shows: 1) a strong subwavelength SSPP localization; 2) relatively high extinction ratio; and 3) small damping attenuation. Furthermore, the design flexibility associated with simple micrometer-scale architecture provides a promising method toward controlling or steering the subwavelength THz signal in the future SSPP-based compact digital circuit.

High-order spoof surface plasmon (SSP) mode on corrugated metallic surfaces can find many interesting applications, such as in imaging, sensing, transmission and enhanced radiation source, etc. In this paper, an efficient excitation method of the high-order SSP mode by using an injected electron beam on the uniform rectangular metallic grating is proposed and investigated numerically. Based on the matched wave momentum between the SSP mode and the electron beam, both the fundamental and high-order SSP modes can be excited on the structure by using a single injected electron beam. Numerical simulation results indicate that the maximum electric field intensity of the generated high-order SSP mode is about two orders higher than that of the fundamental SSP mode. In addition, the peak power of the excited high-order SSP mode is almost two times that of the fundamental SSP mode power by the same energy electron beam, which demonstrates the obvious advantage of the high-order SSP electronic excitation approach compared to the previous fundamental SSP mode excitation on the structure. The central working frequency of high-order SSP power spectrum is about three times that of the fundamental SSP power spectrum. Moreover, the influences of the injected electron beam energy on the excited SSP power spectrum are analyzed specifically. It is shown that the generated SSP power spectrum demonstrates a blue shift with the decreased working voltage of the electron beam simultaneously, with its peak power increasing. However, the working bandwidth is narrowed with decreased beam voltage, which further reveals its working mechanism of presented electronic excitation of the SSP mode. The presented studies provide a new method to excite a high-order SSP mode on the metallic grating, which can find some potential applications in high-sensitivity sensing, deep sub-wavelength waveguide, and many others in terahertz spectra.