Yi Ren

Polarization detection is crucial for advanced electromagnetic applications, yet conventional Stokes-based methods are often bulky and complex. This letter proposes a universal, compact approach for detecting arbitrary polarization states on the Poincaré sphere using a spoof surface plasmon polariton (SSPP) platform. Leveraging the spin-momentum locking property of SSPPs, the design incorporates only two spiral shaped scatterers coupled to a single SSPP waveguide. Incident polarization is decomposed into left- and right-handed circular components, which are separated directionally and collected at two output ports. The signal ratio between these ports yields the full polarization state via a derived analytical relation, eliminating the need for multi-element cascades or Stokes parameter retrieval. Simulated and measured deviations are below 0.9 ° and 8.5 °, respectively. The proposed platform offers a fabrication-friendly, planar architecture suited for on-chip integration, providing a robust miniaturized solution for polarization sensing, communication, and imaging.

Traditional phase shifters are mainly focused on phase performance and rarely consider the phase shift between different electromagnetic (EM) modes, limiting their widespread applications. Spoof surface plasmon polaritons (SSPPs) support EM waves with strong field confinements, giving rise to the time delay of signals. Due to the flexible dispersion behaviors, SSPPs can be engineered at will by designing the plasmonic structure parameters. Benefitting from these characteristics, here we propose a multi-mode and reconfigurable SSPP phase shifter loaded with varactor diodes. By controlling the dispersion behaviors, phase differences between different SSPP modes can be realized, and the phase shift of each mode can be reconfigured. Experimental results show that the proposed SSPP phase shifter can achieve about 240°, 241°, and 340° phase shifts among the fundamental (even) modes, the high-order (odd) modes, and the fundamental and high-order modes, respectively, by switching the bias voltages applied to the varactors. Additionally, the proposed SSPP phase shifter has the capability to continuously tune the phase difference in each mode. Simulations and measurements have a good consistency. This work lays the groundwork for SSPP applications in large-scale integrated circuits and wireless communication systems and has a promising application in Terahertz circuits.

The ability of spoof surface plasmon polaritons (SSPPs) to confine electromagnetic fields in a subwavelength regime enables the design of miniaturized antennas. However, the impedance matching scheme for miniaturized spoof plasmonic antennas has not been studied systematically. In this paper, we propose a general method in the antenna design based on SSPPs, providing a feasible solution to impedance matching at the feeding point of miniaturized spoof plasmonic antennas. To verify the method, a prototype of a planar spoof plasmonic dipole antenna is simulated, fabricated and measured, of which the dipole arm length is reduced by 35.2% as compared with the traditional dipole antenna. A peak gain level of 4.29 dBi and the radiation efficiency of about 94.5% were measured at 6 GHz. This general method can be extended to solve the impedance matching problem in the design of other spoof plasmonic devices.

Plasmon antennas allow subwavelength confinement and enhancement of electromagnetic fields at the “hotspot” where the radiation efficiency of emitters can be substantially enhanced. Such enhancement, however, is often polarization dependent. Consequently, the radiation behaviors (e.g., radiation pattern and polarization states) of the emitter placed at the hotspot are also modified significantly. Enhancing the radiation efficiency without altering the original radiation pattern and polarization state of the emitter is highly desired for many sought-after applications involving chiral emitters but remains a challenging task, especially at low frequencies. To this end, spoof-plasmon antennas with fourfold and sixfold rotational symmetries are designed and realized experimentally. These plasmon antennas support polarization-independent localized plasmon resonances, which can significantly enhance the local density of photonic states at the structural center without changing the polarization state of the emitter. As a typical example, the structure with sixfold rotational symmetry is coupled with a half-wave dipole antenna. The measurement results show that the far-field radiation pattern of the dipole antenna is maintained with the radiation efficiency enhanced by more than 2 orders of magnitude, irrespective of the dipole orientation.

The dual band filtering characteristics of a spoof surface plasmonic waveguide (WG) loaded with a composite slot structure are studied in the present paper. The proposed composite slot structure enables the plasmonic WG to work at dual bands in the microwave region, where the working bandwidth can be flexibly adjusted with a broad isolation band between them. In particular, the second bandwidth can be adjusted independently without affecting the first passband by controlling the special parameter of the composite slot. As a demonstration, the measurement results of the proposed prototype filter illustrate that the plasmonic filtering WG has a dual bandpass performance with excellent frequency selectivity, where the insertion loss of the dual-band filter is less than −3 dB in the frequency from 2.7 GHz to 6.7 GHz and 7.7 GHz to 9.1 GHz, and the stopband rejection level is lower than −10 dB from 6.9 GHz to 7.5 GHz. Compared with the traditional dual band plasmonic filtering WG, the proposed filter has compact physical size, lower insertion loss in the passband and stronger isolation ability between the two passbands.

Spoof plasmonic metamaterials enable the transmission of electromagnetic energies with strong field confinement, opening new pathways to the miniaturization of devices for modern communications. The design of active, reconfigurable, and nonlinear devices for the efficient generation and guidance, dynamic modulation, and accurate detection of spoof surface plasmonic signals has become one of the major research directions in the field of spoof plasmonic metamaterials. In this article, we review recent progress in the studies on spoof surface plasmons with a special focus on the active spoof surface plasmonic devices and systems. Different design schemes are introduced, and the related applications including reconfigurable filters, high-resolution sensors for chemical and biological sensing, graphene-based attenuators, programmable and multi-functional devices, nonlinear devices, splitters, leaky-wave antennas and multi-scheme digital modulators are discussed. The presence of active SSPPs based on different design schemes makes it possible to dynamically control electromagnetic waves in real time. The promising future of active spoof plasmonic metamaterials in the communication systems is also speculated.

We propose to suppress high-power microwave pulses (HPMPs) using nonlinear dispersion and filtering natures of spoof surface plasmon polaritons (SSPPs). Frequency components of a short HPMP are distributed in time domain due to different group velocities and partly cutoff on SSPP transmission lines (TLs), leading to peak suppression of HPMP. To illustrate the protection mechanism in real microwave engineering, an SSPP mono-pulse antenna is designed. Sum and difference beam functions of the antenna are demonstrated by both simulations and experiments. For easy comparison, a microstrip mono-pulse antenna is also fabricated. HPMP incidences from the main lobe directions of the sum beam and difference beam are considered. Compared to the microstrip antenna, obvious suppression of HPMPs is observed in the SSPP mono-pulse antenna in different cases, which verifies the better performance to prevent HPMP damages by SSPPs. The proposed technology to suppress HPMPs by using SSPPs can find wide applications in radar and communication systems in the electronic warfare environment.