Le Peng Zhang

Bio: Le Peng Zhang is an academic researcher from Southeast University. The author has contributed to research in topics: Surface plasmon polariton & Plasmon. The author has an hindex of 6, co-authored 15 publications receiving 92 citations.

A plasmonic route for the integrated wireless communication of subdiffraction-limited signals.

Abstract: Perfect lenses, superlenses and time-reversal mirrors can support and spatially separate evanescent waves, which is the basis for detecting subwavelength information in the far field. However, the inherent limitations of these methods have prevented the development of systems to dynamically distinguish subdiffraction-limited signals. Utilizing the physical merits of spoof surface plasmon polaritons (SPPs), we demonstrate that subdiffraction-limited signals can be transmitted on planar integrated SPP channels with low loss, low channel interference, and high gain and can be radiated with a very low environmental sensitivity. Furthermore, we show how deep subdiffraction-limited signals that are spatially coupled can be distinguished after line-of-sight wireless transmission. For a visualized demonstration, we realize the high-quality wireless communication of two movies on subwavelength channels over the line of sight in real time using our plasmonic scheme, showing significant advantages over the conventional methods. The unique properties of surface plasmons enable wireless transmission of signals separated by less than one wavelength. Until recently, it was considered impossible to distinguish signals with sub-wavelength separation, due to the so-called diffraction limit. This limit can be overcome using artificial structures called metamaterials, but it is difficult to integrate these new components with conventional electronics. Now, Tie Jun Cui at Southeast University in Nanjing, China, and co-workers have shown that sub-wavelength signals can be transmitted using surface plasmon polaritons (SPPs)—combinations of electromagnetic waves and charge motion that travel on the surface of a metal. By encoding signals in ‘spoof’ SPPs that mimic natural SPPs, the team were able to wirelessly transmit two high-definition movies on channels just one-tenth of a wavelength apart, even with a concrete wall in the way.

Active digital spoof plasmonics

Abstract: Digital coding and digital modulation are the foundation of modern information science. The combination of digital technology with metamaterials provides a powerful scheme for spatial and temporal controls of electromagnetic waves. Such a technique, however, has thus far been limited to the control of free-space light. Its application to plasmonics to shape subwavelength fields still remains elusive. Here, we report the design and experimental realization of a tunable conformal plasmonic metasurface, which is capable of digitally coding and modulating designer surface plasmons at the deep-subwavelength scale. Based on dynamical switching between two discrete dispersion states in a controlled manner, we achieve digital modulations of both amplitude and phase of surface waves with nearly 100% modulation depth on a single device. Our study not only introduces a new approach for active dispersion engineering, but also constitutes an important step towards the realization of subwavelength integrated plasmonic circuits.

Design of Miniaturized Antenna Using Corrugated Microstrip

Abstract: We present a new method to design miniaturized antennas using a corrugated microstrip (CM) line, which shows good slow wave characteristic in the required frequency band. To achieve good radiating behavior and low profile simultaneously, CM is employed as the resonating part of the antenna. The impact of the CM propagation constant on the antenna is discussed in detail. The miniaturized antenna is designed and measured to verify the feasibility of the design method. The measured results show that the proposed antenna can achieve a beamwidth of 70° in E-plane and 75° in H-plane with a gain tolerance of 3 dB, and the realized peak gain level at the central frequency is 5.15 dBi, which have good agreements to the expected designs. Such results indicate that the proposed antenna exhibits excellent radiation characteristics at the resonant mode. The effective size of the proposed miniaturized antenna is $0.16\lambda _{0}\times 0.16 \lambda _{0}\times 0.04 \lambda _{0}$ at 9 GHz, in which $\lambda _{0}$ is the wavelength of the central frequency.

A novel spoof surface plasmon polariton structure to reach ultra-strong field confinements

Abstract: Ultrathin corrugated metallic structures have been proved to support spoof surface plasmon polariton (SPP) modes on two-dimension (2D) planar microwave circuits. However, to provide stronger field confinement, larger width of strip is required to load deeper grooves, which is cumbersome in modern large-scale integrated circuits and chips. In this work, a new spoof SPP transmission line (TL) with zigzag grooves is proposed. This new structure can achieve stronger field confinement compared to conventional one with the same strip width. In other words, the proposed spoof SPP TL behaves equivalently to a conventional one with much larger size. Dispersion analysis theoretically indicates the negative correlation between the ability of field confinement and cutoff frequencies of spoof SPP TLs. Numerical simulations indicate that the cutoff frequency of the proposed TL is lower than the conventional one and can be easily modified with the fixed size. Furthermore, two samples of the new and conventional spoof SPP TLs are fabricated for experimental demonstration. Measured S-parameters and field distributions verify the ultra-strong ability of field confinement of the proposed spoof SPP TL. Hence, this novel spoof SPP structure with ultra-strong field confinement may find wide applications in microwave and terahertz engineering.

A Wide-Angle Broadband Converter: From Odd-Mode Spoof Surface Plasmon Polaritons to Spatial Waves

Abstract: A wide-angle broadband converter from odd-mode spoof surface plasmon polaritons (SPPs) to spatial waves is proposed using spatially gradient Vivaldi-shaped flaring structure. We first show the dispersion, Eigen mode, and effective circuit topology of the designed SPP structure and show that it can support a propagating odd mode. A conversion structure between odd-mode spoof SPPs and spatial mode has been designed to realize smooth impedance and wavenumber transition. Through the full-wave simulation method, we obtained the optimized geometric parameters, from which we fabricate the converter using the print circuit board technology. The measured results from both far field and near field show that the proposed structure has successfully excited odd-mode spoof SPPs coming from an extremely wide-angle spatial radiation. The allowed azimuthal and pitched angle ranges are larger than 72°.

Reprogrammable plasmonic topological insulators with ultrafast control.

Abstract: Topological photonics has revolutionized our understanding of light propagation, providing a robust way to manipulate light. So far, most of studies in this field are focused on designing a static photonic structure. Developing a dynamic photonic topological platform to switch multiple topological functionalities at ultrafast speed is still a great challenge. Here we theoretically propose and experimentally demonstrate a reprogrammable plasmonic topological insulator, where the topological propagation route can be dynamically changed at nanosecond-level switching time, leading to an experimental demonstration of ultrafast multi-channel optical analog-digital converter. Due to the innovative use of electric switches to implement the programmability of plasmonic topological insulator, each unit cell can be encoded by dynamically controlling its digital plasmonic states while keeping its geometry and material parameters unchanged. Our reprogrammable topological plasmonic platform is fabricated by the printed circuit board technology, making it much more compatible with integrated photoelectric systems. Furthermore, due to its flexible programmability, many photonic topological functionalities can be integrated into this versatile topological platform. The development of fast and dynamic topological photonic platforms is an ongoing challenge. Here, the authors demonstrate a reprogrammable plasmonic topological insulator in which ultrafast electric switches allow for nanosecond-level switching time between different configurations.

Reprogrammable plasmonic topological insulators with ultrafast control

Abstract: Topological photonics has revolutionized our understanding of light propagation, but most of current studies are focused on designing a static photonic structure. Developing a dynamic photonic topological platform to switch multiple topological functionalities at ultrafast speed is still a great challenge. Here we demonstrate an ultrafast reprogrammable plasmonic topological insulator, where the topological propagation route can be dynamically steered at nanosecond-level switching time, namely more than 10^7 times faster than the current state-of-the-art. This orders-of-magnitude improvement is achieved by using ultrafast electronic switches in an innovative way to implement the programmability. Due to the flexible programmability, many existing photonic topological functionalities can be integrated into this agile topological platform. Our work brings the current studies of photonic topological insulators to a digital and intelligent era, which could boost the development of intelligent and ultrafast photoelectric devices with built-in topological protection.

Time-Resolved Nonlinear Ghost Imaging

Abstract: We propose a new type of THz Ghost-Imaging technique combining nonlinear pattern generation and time-resolved single-pixel measurements. Our approach allows to reconstruct the morphology and spectrum of the sample with deep subwavelength resolution.

Excitation of Surface Plasmon Resonance on Multiwalled Carbon Nanotube Metasurfaces for Pesticide Sensors.

Abstract: With the rapid advances in functional optoelectronics, the research on carbon-based materials and devices has become increasingly important at the terahertz frequency range owing to their advantages in terms of weight, cost, and freely bendable flexibility. Here, we report an effective material and device design for a terahertz plasmonic metasurface sensor (PMS) based on carbon nanotubes (CNTs). CNT metasurfaces based on silicon wafers have been prepared and obvious resonant transmission peaks are observed experimentally. The enhanced resonant peaks of transmission spectra are attributed to the surface plasmon polariton resonance, and the transmission peaks are further well explained by the Fano model. Furthermore, the different concentration gradients of pesticides (2,4-dichlorophenoxyacetic and chlorpyrifos solutions) have been detected by the designed PMSs, showing the lowest detection mass of 10 ng and the sensitivities of 1.38 × 10-2/ppm and 2.0 × 10-3/ppm, respectively. Good linear relationships between transmission amplitude and pesticide concentration and acceptable reliability and stability have been obtained. These materials and device strategies provide opportunities for novel terahertz functional devices such as sensors, detectors, and wearable terahertz imagers.

Perfect Control of Diffraction Patterns with Phase-Gradient Metasurfaces.

Abstract: Phase-gradient metasurfaces (PGMs) constitute an efficient platform for deflection of a beam in a desired direction. According to the generalized Snell's law, the direction of the reflected/refracted wave can be tuned by the spatial phase function provided by the PGMs. However, most studies on PGM focus only on a single diffraction order, that is, the incident wave can be reflected or refracted to a single target direction. Even in the case of multiple beams pointing in different directions, the beams are still in the same order mode, and the energy carried by different beams cannot be controlled. In addition, the energy ratio of multiple beams is generally uncontrollable. Here, we propose a general method to perfectly control diffraction patterns based on a multi-beam PGM. An analytical solution for arbitrarily controlling diffraction beams is derived through which the generation and energy distribution in high-order diffraction beams can be achieved. Three metasurfaces with different diffraction orders and energy ratios are designed and fabricated to demonstrate the proposed method. The efficiencies of diffraction for the desired channels are close to 100%. The simulated and measured far-field patterns are in good agreement with theoretical predictions, validating the proposed method that provides a new way to design multi-beam antennas and that has significance in wireless communication applications.