Spoof Spoof Surface Plasmon Polaritons Research Articles

Absolute and global instabilities driven by Cherenkov interaction between magnetized electron beam and spoof surface plasmon polaritons

In this study, we examine absolute and global instabilities driven by the Cherenkov interaction between a magnetized electron beam and spoof surface plasmon polaritons (SPPs) with an azimuthal mode number m. The absolute and global instabilities are induced in long and short lengths of the cylindrical corrugated waveguides (CCWs), respectively. The temporal and spatial growth rates have different dominant modes of spoof SPPs that, respectively, affect the absolute and global instabilities. In the experiment, the G-band radiation, which corresponds to the dominant mode in the spatial growth rate, is observed with the short length CCW. In the long CCW, the G-band radiation vanishes because the dominant mode in the temporal growth rate has lower frequency than the G-band cutoff frequency of the detecting system. Our results demonstrate that the instability and the multimode radiation are changed by the length of the CCW.

Ultracompact terahertz plasmonic mode division multiplexer.

In this Letter, an ultracompact terahertz (THz) mode division multiplexer based on THz spoof surface plasmon polaritons (SPPs) is proposed. Compared with traditional optical multiplexing devices, the proposed mode multiplexer can be designed with a reduced footprint by exploiting more degrees of freedom in the parameters of the unit cell, namely a rectangular metallic pillar. The ultracompact mode division multiplexer can simultaneously support the propagation of four mode channels: the TM0, TM1, TM2, and TM3 modes. Then, we numerically evaluate the performance of a cascaded plasmonic mode division circuit composed of a mode multiplexer and demultiplexer. The cross talk and excess loss of the whole circuit are lower than -15 dB and 3.7 dB, respectively, for all four mode channels at a center frequency of 0.65 THz. The footprint of the whole device is about 27 × 2.3 mm and the length of each coupling region is about 2.7 mm. For the first time, to the best of our knowledge, a mode division multiplexer based on THz spoof SPPs is reported, which will form core devices for future THz on-chip multimode communication systems.

Measurement Method for the Dispersion Curves of a Spoof SPP Transmission Line Using a Single Sample

Research works on spoof surface plasmon polariton (SPP) transmission lines (TLs) have been carried out toward the goal of achieving flexible control of dispersion. The existing measurement methods for the dispersion of the spoof SPPs require two SPP TL samples with different numbers of units and transition structures, which makes the process more difficult and expensive. This work proposes a new approach for measuring the dispersion curve of a spoof SPP TL by using experimental near-field data. A mathematical model is presented to describe the relation between the wavenumber <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> and the near-field data by considering the presence of reflected waves. The high efficiency and accuracy of this method are verified by the good agreement obtained between the measured dispersion curve and the eigenmode simulation result for a typical spoof SPP TL. Hence, the proposed method makes it possible to measure the dispersion curve of a spoof SPP TL based on a single sample, providing significant progress toward decreasing testing error and cost.

Cascaded plasmon-induced transparency in spoof surface plasmon polariton waveguide

Manipulating spoof surface plasmon polaritons (SPPs) effectively has promising applications in developing ultracompact plasmonic circuits. Research on versatile components in planar spoof SPP waveguides has attracted widespread attention over the decades. In particular, cascaded chip-scale devices play an important role in enhancive buffering, highly-sensitive sensing and nonlinear interaction. Herein, we propose a novel strategy to manipulate the switching and slow wave features of spoof SPPs on the basis of plasmon-induced transparency (PIT) spectral responses. A combined module consisting of split square-ring resonators and electric-LC resonators is loaded with a spoof SPP waveguide along the propagating trajectory, where the destructive interference between the two resonators contributes to the PIT behavior and the group delay of the spoof SPPs. A modulation contrast of up to 16.2 dB is achieved for the spoof SPP transmission at the PIT peak frequency. The measurements are consistent with both full-wave simulations and theoretical calculations. Cascaded capabilities performed by installing multiple PIT modules at an interval of an equivalent wavelength are accomplished in the planar spoof SPP waveguide. The proposed strategy opens up fascinating prospects on highly integrated plasmonic circuits and networks.

Realization of broadband coherent perfect absorption of spoof surface plasmon polaritons

In this work, we propose and demonstrate a scheme to realize broadband coherent perfect absorption of spoof surface plasmon polaritons (SPPs) using an ultrathin conductive film vertically placed on a plasmonic metasurface that supports spoof SPPs. When the conductive film possesses an appropriate sheet resistance, two incident coherent beams of spoof SPP waves can be simultaneously absorbed over a broad spectrum. By tuning the phase difference between the two incident beams from 0 to π, the absorption can be gradually changed from near-100% to near-zero, as verified in full-wave simulations and microwave experiments. Our work extends the theory of coherent perfect absorption from propagating waves to spoof SPPs with a significant advantage of broad working bandwidth.

Spoof Surface Plasmon Polariton Endfire Antenna Possessing Bidirectional and Unidirectional Radiation Pattern

A simple approach is proposed to design a new type of endfire antenna, which simultaneously possesses bidirectional and unidirectional radiation pattern in wideband. By the dispersion engineering, different frequency bands spoof surface plasmon polariton (SPP) modes are excited at the two ports of a proposed splitter structure, and the two ports of the splitter structure are directly connected with two radiator structures, which are utilized to decouple the different frequency bands spoof SPP to free space wave by dispersion mismatching, achieving bidirectional and unidirectional radiation pattern in different frequency bands. From 8.4 to 21.6 GHz, this designed spoof SPP antenna possesses bidirectional endfire radiation pattern, and from 21.6 to 45.0 GHz, this designed spoof SPP antenna possesses unidirectional endfire radiation pattern. This designed spoof SPP antenna has an average gain over 10.6 dB in the whole working bandwidth, and the relative bandwidth of this antenna is 137%. Both the simulation and measurement results verify that the stable bidirectional and unidirectional radiation pattern of this proposed endfire spoof SPP antenna in wide bandwidth are achieved.

A 13.5-Gb/s 140-GHz Silicon Redriver Exploiting Metadevices for Short-Range OOK Communications

The effort to confine the electromagnetic field by silicon passive metadevices has made the design of an on-chip wideband sub-terahertz (sub-THz) I/O redriver feasible, paving a new way toward energy-efficient and crosstalk-immune ON–OFF keying (OOK) communications. Two metadevices, namely spoof surface plasmon polaritons (SPPs) metawaveguide and split-ring resonator (SRR), are exploited to build the sub-THz low-crosstalk silicon channel and high-ON–OFF-ratio modulator, respectively. A sub-THz signal source combining the merit of spoof SPPs and SRR is introduced. A 140-GHz dual-channel redriver composed of these metadevices is fully integrated in a 65-nm CMOS technology. The redriver realizes both 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> –1 and 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup> –1 13.5 Gb/s/lane for dual-channel OOK modulation. The measured energy efficiency is 2.6 pJ/bit/lane and the bit error rate (BER) is ≤10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−12</sup> , demonstrating a crosstalk-immune sub-THz I/O system. The power consumption is 35.1 mW/lane and the active area of the redriver is 0.23 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Ultrawideband Spoof Surface Plasmon Polariton Bidirectional Endfire Antenna Based on Wave Vectors Mismatching

In this work, an ultrawideband spoof surface plasmon polariton (SPP) bidirectional endfire antenna is proposed based on wave vectors’ mismatching. One splitter structure connects two radiator structures to form the proposed antenna, and two types of slot lines are used to design the splitter structure and the two radiator structures. Although the spoof SPP can transmit to the two radiator structures from the splitter structure, the wave vectors of the spoof SPP in the splitter structure and radiator structures are mismatched. Thus, the spoof SPP from the splitter structure will not be bounded mode when it propagates at the two radiator structures and will be decoupled by the two radiator structures, thereby realizing a bidirectional endfire radiation pattern. The bandwidth of the proposed antenna depends on the decoupling bandwidth of the spoof SPP based on wave vectors’ mismatching, which is determined by the working band of the splitter structure and the dispersion of radiator structures. This proposed antenna has a relative bandwidth of 120% from 9.6 to 40.00 GHz, average efficiency of 93%, and an average gain of over 9.2 dB, having great potential in microwave and millimeter communications.

Terahertz multi-frequency splitter and spoof SPPs switch

In this paper, a spoof surface plasmon polaritons (SPPs)-based multi-frequency splitter in the terahertz (THz) band is realized by designing different grating heights. The structure is composed of an incident aperture waveguide and a composite gratings structure placed on both sides of the incident aperture waveguide. The composite grating structure has different grating heights, which is used to transmit and guide THz waves of different frequencies in different directions. Simulation results show that a mixed incident light consisting of three frequencies, of 0.5 THz, 0.7 THz and 1 THz, can be effectively separated by this splitter. Furthermore, the function of the spoof SPPs switch can be realized by increasing the number of incident aperture waveguides. The simple structure and small size, means that this multi-frequency splitter and switch can be conveniently integrated into THz sensing or THz communication systems.

Multi frequency multi bit amplitude modulation of spoof surface plasmon polaritons by schottky diode bridged interdigital SRRs

Multi-frequency multi-bit programmable amplitude modulation (AM) of spoof surface plasmon polaritons (SPPs) is realized at millimeter wave frequencies with interdigital split-ring resonators (SRRs) and In-Ga-Zn-O (IGZO) Schottky diodes. Periodic SRRs on a metal line guide both SRR mode and spoof SPP mode, the former of which rejects the spoof SPP propagation at the SRR resonant frequencies. To actively modulate the amplitude of spoof SPPs, IGZO Schottky diodes are fabricated in the SRR gaps, which continuously re-configure SRRs to metallic loops by applying bias. Interdigital gaps are designed in SRRs to increase the capacitance, thus red shifting the resonant frequencies, which significantly broadens the operation bandwidth of multi-frequency AM. Thus, cascading different kinds of interdigital SRRs with Schottky diodes enables multi-frequency multi-bit AM programmable. As a demonstration, a dual-frequency device was fabricated and characterized, which achieved significant multi-bit AM from −12.5 to −6.2 dB at 34.7 GHz and from −26 to −8.5 dB at 50 GHz independently and showed programmable capability.

Terahertz Circularly- and Linearly Polarized Leaky-Wave Antennas Based on Spin–Orbit Interaction of Spoof Surface Plasmon Polaritons

In this article, we present terahertz circularly polarized (CP) and linearly polarized (LP) leaky-wave antennas based on spin-orbit interaction of spoof surface plasmon polaritons (SPPs). Besides the strong field confinement, spoof SPP waveguides inherently have longitudinal and transverse electric fields with phase quadrature, which means that the electric fields along spoof SPP waveguides have spin property. Based on the spin-orbit interaction, two terahertz CP leaky-wave antennas are achieved with periodic cylinders: 1) by loading cylinders on top of the spoof SPP waveguide, it can excite symmetrical right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) radiations in the transverse plane and 2) when the cylinders are loaded along the side of spoof SPP waveguide, RHCP radiation can be generated in the longitudinal plane; when the cylinders are replaced by cuboids, the RHCP radiation will become right-hand elliptical. Based on the field superposition theory, LP radiation is achieved by elliptically polarized waves with opposite handedness, generating by symmetrically loading periodic cuboids on both sides of the SPP waveguide. Finally, the terahertz LP leaky-wave antenna was fabricated and experimented. It achieves 14.5-17.5 dBi gain and scans from -18° to +12° in the operating frequency band of 145-220 GHz with |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -10dB.

Variable Operating Frequencies Spoof SPP Filter Based on Double-Layers Structure

A novel variable operating frequencies spoof surface plasmon polariton (SPP) filter is proposed in this letter. This proposed spoof SPP filter is adopted double-layers structure, the bandwidths of this proposed filter can be freely designed by loading corresponded upper layer. Dielectric layer and I-shape structure layer are utilized to design the upper layer of the proposed filter, then, wide-range continuous variable operating frequencies spoof SPP filter is achieved. The cut-off frequency of this filter can continuously shift from 2.40GHz to 11.35GHz when corresponding I-shape structure layers are designed. Both simulation and experiment results verify our design. This wide-range continuous variable operating frequencies spoof SPP filter presents the improvement and convenience in practice applications.

Ultra-compact terahertz plasmonic wavelength diplexer.

Terahertz (THz) spoof surface plasmon polariton (SPP) waveguides can provide subwavelength confinement, which makes it possible for the THz waves to transmit at low loss over long distances along a metallic surface. This work reports on the design and actualization of an ultra-compact wavelength diplexer formed by THz spoof SPP waveguiding structures. By adding a certain number of periodic pillars in the coupling part of the directional coupler, the refractive index of the anti-symmetrically distributed odd modes can be engineered, thereby adjusting the coupling length. By adjusting the periodic pillar parameters properly, the SPP modes at two target frequencies will be coupled in the device for an odd or even number of times, so that the SPP modes at these two frequencies can be coupled out from different ports. The length of the wavelength diplexer is 1.6 mm, which is about 12.8% of its traditional counterpart. Minimum simulated transmittances of -24.34dB and -26.27dB can be obtained at 0.637 THz and 0.667 THz, respectively. The insertion losses at the two operating frequencies are less than 0.46 dB, and the extinction ratios are both better than 19 dB. By cascading the proposed diplexers, a compact wavelength demultiplexer with more channels can be obtained, which has important applications for future THz integrated communication systems.

Broadband and High-Efficiency Excitation of Spoof Surface Plasmon Polaritons Through Rectangular Waveguide

Spoof surface plasmon polaritons (SPPs) are highly localized surface waves that can be supported on metal surfaces with subwavelength decorations. Mode matching and momentum matching have been investigated so as to efficiently excite the spoof SPPs through conventional planar waveguides (WGs) such as the microstrip (MS) line and the co-planar waveguide (CPW). In this work, a smooth and wideband bridge between the conventional rectangular waveguide and the plasmonic waveguide of spoof SPPs has been proposed and experimentally demonstrated. High efficiency is achieved in both simulation and experiment in a wide frequency range from 12 to 18 GHz. The high-efficiency and broadband excitation of spoof SPPs through rectangular waveguide has great potentials in microwave, millimeter-wave and terahertz circuits and systems.

Integrated multi-scheme digital modulations of spoof surface plasmon polaritons

The future wireless communications require different kinds of modulation functions to be integrated in a single intelligent device under different scenarios. Here, we propose a multi-scheme digital modulator to achieve this goal based on integrated spoof surface plasmon polaritons (SPP) in different frequency bands. By constructing switchable spoof SPP units, the propagating wave in the proposed spoof SPP waveguide can be manipulated in amplitude domain, frequency domain, and phase domain. As a proof of concept, the integrated multi-scheme digital modulator is experimentally verified to achieve at least three kinds of modulations, including amplitude shift keying, phase shift keying, and frequency shift keying, in a single digital spoof plasmonic waveguide. The simulated and measured results show that the modulator has excellent property of field confinement and is capable of frequency-domain modulation. Hence, the multi-scheme modulation property makes the proposed SPP digital modulator be an effective and reliable candidate for efficient manipulations of SPP waves and for advanced modulation technology

Crosstalk Noise Suppression Between Single and Differential Transmission Lines Using Spoof Surface Plasmon Polaritons

Crosstalk noise suppression is a crux in the high-speed integrated circuit design, which requires weak-coupling between transmission lines (TLs) over a wide band. To overcome the difficulty, this article presents a novel method to suppress the broadband crosstalk noise between a single TL and the differential pair based on spoof surface plasmon polaritons (SPPs). Due to the subwavelength feature of spoof SPP TLs, a natural mode mismatching between the spoof SPP TL and conventional microstrip (MS) brings a broadband suppression of near-field coupling. In order to verify the crosstalk suppression effect, four different kinds of prototypes are discussed and compared. The simulated and measured results in the frequency domain and time domain demonstrate that the proposed scheme achieves more than 83% far-end noise peak suppression than the traditional MS technology by replacing the single MS TL to the spoof SPP TL. Accordingly, the time-domain crosstalk noise is significantly suppressed without any extra costs, demonstrating its potential applications in ultracompact high-speed integrated circuits.

High-Gain Millimeter-Wave Antennas Based on Spoof Surface Plasmon Polaritons

High-gain millimeter-wave antennas based on spoof surface plasmon polaritons (SPPs) are proposed in this article. Since the dispersion of spoof SPP modes supported by metallic grooves is insensitive to their lateral width, we propose two millimeter-wave antennas with wide SPP grooves, namely an SPP tapering rod antenna and an SPP leaky-wave antenna. The widened grooves enlarge the aperture size of the antennas, enhancing the antenna gains. Both antennas are fed by a standard waveguide and are fabricated by 3-D printing with surface metallization. Based on the similar principle of conventional dielectric rod antennas, the proposed SPP rod antenna achieves broadband and high gain. The measured |S11| is below −16.5 dB from 50 to 75 GHz, and the antenna gain varies from 16.06 to 19.3 dBi. By employing periodic modulation, the SPP leaky-wave antenna operates from 50 to 70 GHz for |S11| below −10 dB. This leaky-wave antenna with 24 modulated periods achieves 20.1–23.9 dBi gain in the operating band with a beam-scanning range from −39° to −3°.

Half-Mode Substrate Integrated Waveguide Dispersion Tailoring Using 2.5-D Spoof Surface Plasmon Polaritons Structure

In this article, a half-mode substrate integrated waveguide (HMSIW) combined with 2.5-D spoof surface plasmon polaritons (SPPs) structure is proposed to tailor the dispersion features and cutoff frequency of the HMSIW. The proposed HMSIW-SPP structure has a smaller longitudinal dimension since the dispersion of the proposed structure can be tailored by adjusting the geometric parameters of the 2.5-D spoof SPP arbitrary. Simultaneously, the proposed structure has a smaller lateral width than that of the classical HMSIW because the 2.5-D spoof SPP introduces extra capacitance in the waveguide. Moreover, an equivalent circuit model is proposed and used to analyze the design principles. The structure exhibiting the cutoff frequency of 6.0 GHz is designed and fabricated under the printed circuit board process. Measurement and simulation results show that the proposed HMSIW-SPP structure decreases the longitudinal dimension by more than 50% and the lateral width by 25% without sacrificing its transmission performance. Due to the reduced cutoff frequency and effective wavelength, the proposed structure enables extreme miniaturization and can be applied in the design of miniaturized microwave circuits.

Programmable Multifunctional Device Based on Spoof Surface Plasmon Polaritons

The spoof surface plasmon polariton (SPP) waveguide, which could support well-confined surface waves along an ultrathin corrugated metallic strip, is one of the most advantageous candidates in integrated circuits due to the remarkable properties of low crosstalk, low loss, and packaging minimization. Many devices based on the spoof SPP waveguide have emerged, but it is still a challenge to manipulate the SPP waves freely in real-time. Here, we propose a programmable multifunctional spoof SPP device by loading varactor diodes between adjacent metallic teeth of SPP waveguides. By programming the bias voltages of the varactor diodes dynamically, the coupling waves propagating on two SPP waveguides can be freely controlled. Simulations and experiments demonstrate that the programmable SPP device can realize high-efficiency SPP through transmission, unequal coupling, 3 dB direction coupling, and crossover transmission with better isolation effect. Different functions and operational frequency ranges can be reconfigured in real-time. The proposed method lays the groundwork for applications in large-scale microwave integrated circuits and digital communication systems.

Filtering microwave differential signals through odd-mode spoof surface plasmon polariton propagation

Recently, spoof surface plasmon polaritons (SPPs) have been successfully applied to microwave signal propagation in ultra-thin planar circuits, due to their unique features of electromagnetic (EM) wave confinement in deep subwavelength scale and controllable dispersive properties. Both even and odd modes can be supported in symmetric spoof SPP structures. However, most device applications employ even mode propagation due to its easy stimulation. In this paper we investigate the dispersion characteristics and EM field patterns of both even and odd modes in a symmetric H-shaped spoof SPP structure. We concentrate on odd modes with an anti-symmetric electric field distribution, and their application to the propagation and filtering of differential signals. With odd modes, a balanced bandpass filter (BPF) can be constructed with a designable passband depending on the dispersion engineering of the odd modes in the spoof SPP structures. Pure odd mode propagation provides an ideal platform for differential signal transmission, with effective rejection of the common mode and an ultra-wide upper stopband in the designed filters. To validate the proposed design, two balanced BPFs operating at 2.3 GHz and 4 GHz are designed and implemented. There is good agreement between the simulated and measured results. We believe that the proposed method may encourage alternative applications of differential signal filtering with flexible frequency responses, and may play an important role in device development in wireless communication systems.