Surface Plasmon Polariton Transmission Research Articles

Spoof surface plasmon polaritons transmission lines with line‐width reduction based on miniature unit structures

Spoof surface plasmon polaritons transmission lines with line‐width reduction based on miniature unit structures

Propagation and excitation properties of nonlinear surface plasmon polaritons in a rectangular barrier

We propose a scheme to study the nonlinear propagation properties of nonlinear surface plasmon polaritons (SPPs) in a three level $\Lambda$ type electromagnetically induced transparency (EIT) system with modulation of a rectangular barrier. Based on the multi scale method, the nonlinear Schr\"odinger equation (NLSE) describing nonlinear propagation of SPPs is derived, and the rectangular barrier affecting propagation of nonlinear SPPs is provided by an off-resonance Stark field. For the single nonlinear SPPs incident case, by adjusting the height and half width of the barrier, we can realize transmission, trapping and reflection of the nonlinear SPPs. For two nonlinear SPPs symmetrical incident case, we find that a periodic intensity distribution in transverse direction mode can be excited in the rectangular barrier, and we study the relationship between propagation properties of such excited modes in the barrier with nonlinearity, half width of the barrier and phase difference of the initial nonlinear SPPs. In addition, we design an optical switch of nonlinear SPPs based on the above results. The results obtained here not only provide a theoretical basis for the study of the interaction between nonlinear SPPs and external potentials, but also have broad application prospects in the field of optical information at micro/nano scale.

Ultra-compact on-chip spoof surface plasmon polariton transmission lines with enhanced field confinements

On-chip transmission lines (TLs) for spoof surface plasmon polariton (SSPPs) have been proved to suppress on-chip channel crosstalk in terahertz band due to their field confinement property. But the contradiction between strong field confinement and miniaturization limits the application of the on-chip SSPP TLs in millimeter and terahertz bands. Here, an ultra-compact on-chip SSPP TL with strong field confinement is proposed using 0.18 μm CMOS technology. The proposed SSPP TL reduces the cutoff frequency down to 435 GHz in a very limited TL width. Broadband feeding without using gradient transition structures is presented to guarantee the compact size. Compared to microstrip and the typical SSPP TLs, outstanding field confinement of the novel on-chip SSPP TL is demonstrated by the electrical-field- intensity distributions. Measured result matches to simulated one well. It is shown that the proposed on-chip SSPP TL possesses the lowest cutoff frequency and the smallest width relative to the cutoff wavelength, compared to the microstrip and the typical SSPP TLs. Thus the ultra-compact on-chip SSPP TL with strong field confinement may be widely used in the future miniaturized monolithic microwave integrated circuits.

An Ultra‐Compact Spoof Surface Plasmon Polariton Transmission Line and Its Signal Integrity Analysis

An ultra‐compact spoof surface plasmon polariton (UCSSPP) transmission line (TL) based on a meander line is proposed, which can achieve almost the same transmission performance as the conventional rectangular‐groove SSPP TL, but the linewidth is greatly reduced by more than 40%. The coupling effect between two UCSSPP TLs in different line arrangements has been well studied, revealing that excellent crosstalk suppression can be achieved when two TLs are arranged back‐to‐back, while strong coupling occurs when they are arranged face‐to‐back or face‐to‐face. The signal integrity of back‐to‐back UCSSPP TLs is analyzed and demonstrated, which shows that the signal integrity can be greatly improved compared with microstrip (MS) TLs. In addition, based on the principle of mode mismatch, MS and UCSSPP TLs are arranged alternately to solve the mutual coupling problem in multi‐line systems. In contrast, benefiting from the strong coupling of face‐to‐face UCSSPP TLs, an ultra‐miniaturized SSPP coupler working at 9 GHz is designed, whose size can be reduced by over 75% compared with conventional MS coupler. The measurement results show good agreement with full‐wave simulations, indicating that the proposed UCSSPP TL has significant advantages in signal integrity and device miniaturization over previously reported SSPP TLs.

Compact Folded SSPP Transmission Line and Its Applications in Low-Pass Filters

This paper proposes two compact folded spoof surface plasmon polariton (SSPP) transmission lines (TL) with single-sided grooves (Type A) and double-sided grooves (Type B), and their cut-off frequencies are 17.55 GHz and 19.52 GHz, respectively. Due to large number of units, the proposed SSPP TLs have steep sideband and excellent upper band suppression (<-48 dB). The compact folding solution could reduce the lateral size to nearly 2/5 of the original one, and to a certain extent solve the layout difficulties associated with traditional SSPP TLs due to their slender structure. The cut-off frequency can be independently regulated by stub length and width. The proposed components are fabricated and tested. The experimental results are in good agreement with the simulated results, demonstrating the possibility of compact folded SSPP TLs and greatly improving the potential of SSPP use in miniaturized and highly integrated circuit systems.

T-shaped double-strip spoof surface plasmon polariton transmission lines and application to microwave resonators

A microwave double-strip spoof surface plasmon polariton (DS SSPP) is proposed for high-speed interconnects and high-performance microwave circuits. Based on the dispersion analysis, a T-shaped double-strip structure is designed to provide strong surface- and slow-wave properties from very low to very high frequencies (~ 40 GHz). It allows the tight field confinement and greatly reduces the electromagnetic wave leakage. It exhibits broadband performance with reduced ripples in the insertion loss. It also shows more constant group delay and impedance than counterpart single-strip SSPP. The compact coaxial-to-microstrip-to-DS SSPP transition are designed using gradient grooves. The measurement shows that the DS SSPP lines can exhibit the lower coupling and lower insertion loss than the microstrip lines, so that the former is well-suited for the densely packed high-speed interconnects. The designed DS SSPP is utilized for high quality (Q)-factor microwave ring resonator. The measured unloaded Q-factor is 107.9 at the resonant frequency of 8.7 GHz, which is 1.3 times higher than the microstrip ring resonator. It is found to be caused by the reduction of the radiation loss, according to the loss analysis. The size is also reduced due to the short wavelength, occupying 56.8% of that of the microstrip ring resonator. Therefore, the proposed T-shaped DS SSPP can be also applied for high-performance miniaturized microwave circuits.

A novel plasmonic waveguide for the dual-band transmission of spoof surface plasmon polaritons

A novel plasmonic waveguide for the dual-band transmission of spoof surface plasmon polaritons

A Back-Fire to Forward Wide-Angle Beam Steering Leaky-Wave Antenna Based on SSPPs

We demonstrate an efficient back-fire to forward wide-angle beam steering leaky-wave antenna (LWA) based on a large dispersion gradient planar spoof surface plasmon polariton (SSPP) transmission line (TL) with split-ring units. To convert the highly confined SSPP waveguiding mode to a radiation mode, two arrays of metallic patches are periodically arranged on both sides of the SSPP TL. The patches are designed as two combined half-elliptical shapes to mitigate the open stopband effect and enhance the radiation performance. We propose a theoretical method to interpret the mechanism and predict the directional pattern of the LWA. To verify the proposed method, the SSPP TL and LWA prototypes are fabricated and measured. The calculation, simulation, and experimental results match well and show that the main beam of the LWA can steer a wide range of 112&#x00B0; from back-fire (&#x2212;90&#x00B0;) to the forward quadrant of 22&#x00B0; passing through the broadside in 6.3&#x2013;11 GHz, demonstrating a large scanning rate of 2.07&#x00B0;/&#x0025;. Furthermore, the LWA also possesses the advantages of low profile, high average gain (12 dBi), high average efficiency (95&#x0025;), and low sidelobe level (&#x003C;&#x2212;13 dB). This work provides an alternative route to achieving wide-angle LWAs for promising microwave radar and wireless communication applications.

High-Efficiency Excitation of Spoof Surface Plasmon Polaritons Through Rectangular Waveguide Using Dipole Antenna

In this communication, a high-efficiency rectangular waveguide-to-spoof surface plasmon polaritons transmission line (SSPPs TL) transition operating within terahertz frequencies is demonstrated. Terahertz signal fed by the rectangular waveguide is first coupled to the planar circuit through the dipole antenna. And then a taper and double-sided SSPPs TL are used to transform the resonant mode in the dipole antenna to the SSPPs mode and achieve impedance and momentum matching. The high transmission performance of the SSPPs TL is obtained by etching a series of periodically corrugated grooves on the metal strip in the top layer and a ground pad connected to the convexity of the rectangular waveguide is employed in the bottom layer. A back-to-back transition prototype was fabricated on a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$50~\mu \text{m}$ </tex-math></inline-formula> -thickness quartz substrate and designed for a terahertz device with WR-4.3 standard rectangular waveguide. The measured results show that the insertion loss is lower than 2 dB from 195 to 250 GHz, and the in-band return loss is better than 10 dB. To the best of our knowledge, this work presents the rectangular waveguide-to-SSPPs TL transition using a dipole antenna for the first time, which has potential applications for plasmonic-integrated circuits and systems in the terahertz range.

Embroidered Spoof Surface Plasmon Polariton Transmission Line for Wireless Body Sensor Network

A wearable Spoof Surface Plasmon Polariton Transmission Line (SSPP TL) operating at 2.45 GHz designed for embroidery production and on-body communication is proposed. The SSPP TL supports both even and odd modes launched by near field coupling with a dipole antenna perpendicular and parallel to the TL, respectively. First, the experimental dispersion curves and transmission for the even and odd modes are favourably compared to simulations. Then, experimental transmission for each mode is compared with the Line-Of-Sight (LOS) transmission between two parallel-oriented antennas. At 2.45 GHz, a transmission enhancement of 16 dB is measured for the even mode and it reaches up to 37 dB for the odd mode. A transmission enhancement of 30 dB is also measured at 2.45 GHz between two antennas with orthogonal orientations. Performances of the SSPP TL for Wireless Body Sensor Network are evaluated. Transmission is sustained for the SSPP TL under curvature and right angle bending. Transmission measured when both an arm and a copper plate obstacle between antennas were surrounded by the curved SSPP TL is compared with the obstructed LOS transmission. Measurements show a transmission enhancement up to 22 and 25 dB for the even and odd modes, respectively.

Compact transition enabled broadband propagation of spoof surface plasmon polaritons based on the equivalent circuit model

In this paper, a strategy to develop a compact transition of the spoof surface plasmon polariton (SSPP) transmission line (TL) is proposed. First, an equivalent distributed circuit model is employed for the theoretical analysis and optimization design of the SSPP unit. The mapping relation between the unit performance and the geometric parameters is deduced from the transmission matrix. The calculated results are compared with the numerical ones from the three-dimensional (3D) simulations for validation. Then, a compact transition (only 0.26λ g) is built with only two matching units and a tapered strip through optimizations. The optimizations are implemented with the circuit simulations based on the equivalent model, which can remarkably save time in comparison with the 3D simulations. The transition principle is also explained by quantitatively extracting the dispersion properties and impedance characteristics. Finally, a prototype of the proposed SSPP TL is fabricated and measured for demonstration. The measured operating band (0–7.7 GHz) is almost up to the cut-off frequency (about 8 GHz), which remains the inherent broadband low-pass transmission characteristics. Meanwhile, the measured in-band return loss is almost higher than 10 dB, which verifies the high-efficiency propagation. This work can pave the way for building up a new SSPP-based framework of microwave circuits.

Design of Compact Sub-Terahertz Spoof Surface Plasmon Polariton Transmission Line Based on InP Technology

Design of Compact Sub-Terahertz Spoof Surface Plasmon Polariton Transmission Line Based on InP Technology

Annular Surface Plasmon Polariton-Based Frequency-Scanning Leaky-Wave Antenna for Full Azimuth Coverage

This article presents a single-layered annular surface plasmon polariton (SPP)-based leaky-wave antenna (LWA) for full azimuth beam scanning in 60 GHz applications. The groundless annular SPP transmission line (TL) has a special feeding mechanism that can be operated at 60 GHz in the SPP mode. Periodically radiating circular patches with gradually smaller sizes near the TL create an additional momentum that helps convert the slow wave SP mode into the radiating leaky mode. This results in frequency-dependent continuous beam scanning in the azimuth plane. The theoretical, numerical, and experimental results of the proposed device agree well. The antenna has an overall scanning range of 268°, −10 dB impedance BW of 15.33%, and a peak gain of 19.7 dBi with an average sidelobe level (SLL = −10 dB) and a cross-polar level of −20 dB. Owing to the low-profile compactness and improved performance, the proposed single-layered LWA is a promising candidate for 60 GHz V-band millimeter (mm)-wave applications.

A wide‐angle forward to backward scanning wideband leaky‐wave antenna based on microstrip spoof surface plasmon polaritons

In this work, a wide-angle forward to backward scanning wideband leaky-wave antenna (LWA) based on the microstrip spoof surface plasmon polaritons (SSPPs) transmission line (TL) is proposed. The proposed microstrip SSPP TL has tapered corrugations on both sides of the metallic strip conductor. After designing an efficient transition with a good transition occupation ratio and excellent transmission efficiency, a wide-angle scanning LWA is realised. A methodology of achieving high gain and wide-angle scanning by adjusting a large number of radiating elements in a compact area is proposed. The proposed antenna operates in the frequency range of 8.9–12.7 GHz having fractional bandwidth of 35.18% with a continuous scanning range from −35° to +51°. The maximum gain of 19.03 dBi with a maximum radiation efficiency of 90% is achieved from the structure. The proposed antenna can easily be integrated with planar wireless communication systems due to the presence of an unbroken ground plane.

Guiding and routing surface plasmons with transformation-invariant metamaterials

Rough metallic surfaces cause severe scattering to surface plasmon polaritons (SPPs), thereby limiting SPP transmission efficiency. Here, we propose a general scheme to design ultracompact plasmonic routers that can confine and guide SPPs on an arbitrarily shaped rough surface. Our strategy makes use of recently proposed transformation-invariant metamaterials (TIMs). To illustrate the advantages of this approach, we perform finite-element simulations, showing that the performance of the designed surface wave router is robust against the change in thickness. As a result, a λ/6 thick TIM layer can significantly suppress scattering from arbitrarily shaped metallic bumps or crevices. We also give a blueprint to implement such ultracompact surface wave routers based on periodic metal/epsilon-near-zero material stackings.

Generation of dual-band rejection filtering function in two frequency bands developed by spoof surface plasmon polaritons

In this paper, we propose the generation of dual-band rejection filters based on the interaction between spoof surface plasmon polaritons transmission line and -type resonator cells. By selecting a suitable value of spacing inside them, the -type resonator cells generate excellent dual-band band rejection filter on combining with spoof SPP transmission line in lower frequency band. A simple parametric calculation based on varying the value of spacing inside -type resonator cells, has been performed for the conversion of dual-band band rejection filter from lower frequency band to higher frequency band. Greater value of spacing results in larger LC coupling which deteriorate filtering performance by leaving us with dual-band rejection filtering function in lower frequency band. By choosing smaller value of spacing converts it into dual-band rejection filtering function in upper frequency band because of significant reduction in LC coupling, and hence leading to much improved broadband filtering performance. In short, the formation of dual-band rejection filter in lower frequency band and its conversion into dual-band rejection filter in upper frequency band can be fully controlled by just adjusting the value of vertical width inside -type resonator cells. The simulation results demonstrate the outstanding performance of the proposed filters and can play a crucial role in developing integrated plasmonic circuits at microwave and terahertz frequencies.

Suppressed Transmission of Long-Range Surface Plasmon Polariton by TE-Induced Edge Plasmon.

Work on controlling the propagation of surface plasmon polaritons (SPPs) through the use of external stimuli has attracted much attention due to the potential use of SPPs in nanoplasmonic integrated circuits. We report that the excitation of edge plasmon by TE-polarized light passing across gapped-SPP waveguides (G-SPPWs) leads to the suppressed transmission of long-range SPPs (LRSPPs) propagating along G-SPPWs. The induced current density by highly confined edge plasmon is numerically investigated to characterize the extended radiation length of decoupled LRSPPs by the TE-induced edge plasmon. The suppressed transmission of LRSPPs is confirmed using the measured extinction ratio of the plasmonic signals which are generated from the modulated optical signals, when compared to the extended radiation length calculated for a wide range of the input power. It is also shown that LRSPP transmission is sensitive to the excited power of edge plasmon in the gap through the permittivity change near the gap. Such a control of SPPs through the use of light could be boosted by the hybridized edge plasmon mode and a huge field enhancement using nanogap, gratings or metasurfaces, and could provide opportunities for ultrafast nano-plasmonic signal generation that is compatible with pervasive optical communication systems.

Frequency controlled beam scanning characteristic realized using a compact slow wave transmission line.

To simplify the design of a beam scanning device, we present a simple and compact structure to realize the frequency scanning characteristic based on a hybrid waveguide consisting of a spoof surface plasmon polariton (SSPP) transmission line and half-mode substrate integrated waveguide (HMSIW). Additionally, the radiation characteristic is implemented using periodically modulated slots. The scanning angle range covers backward to forward directions without an open stop band at the broadside. The results from both simulations and measurements show that the total scanning angle reaches 117° for a frequency range of 9-11.4 GHz. Owing to the inherent features of the HMSIW and the unique design of the SSPP transmission line, the entire structure is only 139.2mm×15mm in size. Moreover, the average gain is approximately 6.5 dBi. Overall, the compact size and good performance ensure that the proposed design is favorable for planar integrated communication systems.

Short-circuited stub-loaded spoof surface plasmon polariton transmission lines with flexibly controllable lower out-of-band rejections.

This Letter proposes an approach to develop a spoof surface plasmon polariton (SSPP) transmission line (TL) by loading short-circuited (SC) shunt stubs. Lower out-of-band rejections can be flexibly controlled without affecting the upper cutoff frequency by independently modifying the stubs. Dispersion analysis of the SSPP unit is realized by theoretical calculation and circuit simulation to predict the upper cutoff frequency of the proposed SSPP TL simultaneously. Also, parametric sweeping of the SC shunt stubs is performed based on circuit simulation to investigate their impacts on the lower and upper out-of-band rejections of the proposed SSPP TL. In addition, electric field distributions of different types of TLs are simulated and compared to study the transmission characteristics of the proposed SSPP TL. The lower cutoff frequency can be flexibly tuned in a wide range, from 1.2 to 2.1 GHz, in the simulations. The measured 3-dB fractional bandwidth is about 128.1%, covering a range from 1.19 to 5.43 GHz. The numerical and experimental results are compatible, which verifies the feasibility of the proposed approach. This approach can offer more convenience and flexibility for controlling the rejections of the SSPP by introducing up to four tuning parameters. More importantly, the proposed SSPP TL avoids using the substrate integrated waveguide (SIW) technique, which shows the potential to decrease the transverse width (0.44λg), especially at lower frequencies (e.g., 1.2 GHz), and to reduce the complexity in designing the high-efficiency transition. This work paves the way for the development of novel SSPP-based microwave devices.

Tilted-Beam Antenna Based on SSPPs-TL with Stable Gain.

In this paper, a titled-beam antenna based on spoof surface plasmon polaritons (SSPPs) transmission lines (TLs) is proposed. The parallel SSPPs-TL is a slow-wave TL, which is able to limit waves in the TL strictly. By periodically introducing a set of tapered stubs along the SSPPs-TL, the backward endfire beams are formed by the surface waves in the slow-wave radiation region. Then, through the placement of a big metal plate below the endfire antenna, the backward endfire beams are tilted, and the tilted angle of the beams are steered by the distance of the metal plate and antenna. Over the band of 5.7 GHz~7.0 GHz, the tilted antenna performs constant shapes of radiation patterns. The gain keeps stable at around 12 dBi and the 1-dB gain bandwidth is 20%. The measured results of the fabricated prototypes confirm the design theory and simulated results.