Efficient amplification of spoof surface plasmon polaritons (SPPs) is proposed at microwave frequencies by using a subwavelength‐scale amplifier. For this purpose, a special plasmonic waveguide composed of two ultrathin corrugated metallic strips on top and bottom surfaces of a dielectric substrate with mirror symmetry is presented, which is easy to integrate with the amplifier. It is shown that spoof SPPs are able to propagate on the plasmonic waveguide in broadband with low loss and strong subwavelength effect. By loading a low‐noise amplifier chip produced by the semiconductor technology, the first experiment is demonstrated to amplify spoof SPPs at microwave frequencies (from 6 to 20GHz) with high gain (around 20dB), which can be directly used as a SPP amplifier device. The features of strong field confinement, high efficiency, broadband operation, and significant amplification of the spoof SPPs may advance a big step towards other active SPP components and integrated circuits.

Artificial intelligence is facilitating human life in many aspects. Previous artificial intelligence has been mainly focused on computer algorithms (e.g. deep-learning and extremelearning) and integrated circuits. Recently, all-optical diffractive deep neural networks (D 2 NN) were realized by using passive structures, which can perform complicated functions designed by computer-based neural networks at the light speed. However, once a passive D 2 NN architecture is fabricated, its function will be fixed. Here, we propose a programmable artificial intelligence machine (PAIM) that can execute various intellectual tasks by realizing hierarchical connections of brain neurons via a multi-layer digital-coding metasurface array. Integrated with two amplifier chips in each meta-atom, its transmission coefficient covers a dynamic range of 35 dB (from -40 dB to -5 dB), which is the basis to construct the reprogrammable physical layers of D 2 NN, in which the digital meta-atoms make the artificial neurons alive. We experimentally show that PAIM can handle various deep-learning tasks for wave sensing, including image classifications, mobile communication coder-decoder, and real-time multi-beam focusing. In particular, we propose a reinforcement learning algorithm for on-site learning and discrete optimization algorithm for digital coding, making PAIM have autonomous intelligence ability and perform self-learning tasks without the support of extra computer.

In modern integrated circuits and wireless communication devices or systems, three key features need to be solved simultaneously to reach higher performance and more compact size: signal integrity, interference suppression, and miniaturization. However, the above-mentioned requests are almost contradictory using the traditional techniques. To overcome this challenge, here we propose time-domain spoof surface plasmon polaritons (SPPs) as the carrier of signals. By designing a special plasmonic waveguide constructed by printing two narrow corrugated metallic strips on the top and bottom surfaces of a dielectric substrate with mirror symmetry, we show that spoof SPPs are supported from very low frequency to the cutoff frequency with strong subwavelength effects, which can be converted to the time-domain SPPs. When two such plasmonic waveguides are tightly packed with deep-subwavelength separation, which commonly happens in integrated circuits and wireless communications due to limited space, we demonstrate theoretically and experimentally that SPP signals on such two plasmonic waveguides have better propagation performance and much less mutual coupling than the conventional signals on two traditional microstrip lines with the same size and separation. Hence the proposed method can achieve significant interference suppression in very compact space, providing a potential solution to break the challenge of signal integrity. KEYWORDS: surface plasmon polaritons, time domain, signal integrity, interference suppression S ignal interference suppression and signal integrity are two of the most challenging topics in physics and electrical engineering. Especially, the rapid developments of super-largescale integration of high-speed circuits and wireless communication systems/devices have brought forward higher requirements for signal interference suppression and signal integrity in the past decades. 1−3 Some special circuit strategies have been proposed to improve the signal quality, such as the equalization technique 4 and differential microstrip lines. 5 However, in the above techniques, additional areas of circuits and power consumptions are required, which make them rather difficult to utilize in high-frequency and/or high-speed circuits and systems. In fact, signal integrity, signal interference suppression, and miniaturization are three key features to be solved simultaneously to achieve higher performance and smaller size of complicated circuits and systems. But these factors are almost contradictory using the traditional transmission lines. To solve the challenges, we are forced to find new physics models beyond traditional transmission lines, and the surface plasmon polariton (SPP) approach is one of the possibilities due to its strong subwavelength effects.At optical frequencies, because of the negative permittivity behavior of the metal and positive permittivity of the dielectric, SPPs are formed by the interaction between free electrons and the electromagnetic field 6,7 and propagate in parallel to the metal−diele...

We propose a spoof surface plasmon polariton (SPP) emitter which is composed of ultrathin corrugated metallic strips, exhibiting the directional radiation property. The spoof SPP emitter provides a way to quickly convert the SPP mode to a radiated mode. By controlling phase modulations produced by the phase-gradient metasurface on the ultrathin metallic strips, we demonstrate theoretically and experimentally that spoof SPP waves are converted into spatial propagating waves with high efficiency, which are further radiated with flexible beam steering. The proposed method sets up a link between SPP waves and radiation waves in a highly controllable way, which would possibly open an avenue in designing new kinds of microwave and optical elements in engineering.

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