Bidirectional-pump-controlled reconfigurable nonlinear spoof plasmonic waveguide

Abstract

We present a dynamically reconfigurable spoof surface plasmon polariton (SSPP) waveguide capable of bidirectional switching between perfect absorption and perfect transmission through active control. Nonlinear varactor diodes are integrated into the waveguide, enabling degenerate phase matching between pump and signal waves via voltage-tuned dispersion engineering. Three-wave mixing processes are established, allowing bidirectional phase-controlled transitions from destructive to constructive interference. The proposed SSPP waveguide overcomes traditional pumping constraints with its bidirectional configuration, supporting both forward- and backward-propagating pump-signal configurations and permitting signal amplitude modulations at both the transmitter and receiver ends. Experimental characterization demonstrates remarkable signal gain tunability: the forward pumping configuration achieves a dynamic range spanning from −69.50 to +1.04 dB, while the backward configuration spans from −70.49 to +1.45 dB. This work provides new design paradigms for microwave coherent systems and advances the development of reconfigurable electromagnetic devices for adaptive energy harvesting and high-speed signal processing applications.

1. Introduction

Absorbers belong to a category of functional devices capable of selectively absorbing electromagnetic energy at specific frequency bands, which can suppress the adjacent-channel or noise interference in communication systems, enhance signal quality and system sensitivity, and convert electromagnetic energy into thermal or electrical energy. These capabilities endow absorbers with significant application value (Chong et al., 2010; Kats and Capasso, 2016; Baranov et al., 2017; Xomalis et al., 2019; Khurgin et al., 2024) in all-optical switches and logic gates (Fang et al., 2014, 2015; Kim et al., 2016; Papaioannou et al., 2016), photodetectors (Goykhman et al., 2011, 2012, 2016), sensing (Xiao SY et al., 2016; Li CW et al., 2019; Grimm et al., 2021; Zhang Y et al., 2023), imaging (Monticone et al., 2016; Zhao WL et al., 2023), heat transfer control (Li Y et al., 2022), non-destructive measurement (Zanotto et al., 2017), and other fields. Absorption can be achieved through various methods, such as electromagnetic resonance coupling (Liao et al., 2015; Wang P et al., 2021; Li YP et al., 2025), hot electron excitation (Khurgin et al., 2024), and coherent wave interference.

Compared to absorbers with fixed parameters, those with dynamically adjustable absorption characteristics (such as absorption rates or operational frequency bands) can significantly enhance the system adaptability and energy efficiency. For instance, in solar thermal collection systems, adjusting the absorption rates based on light intensity can improve the energy conversion efficiency while preventing overheating. These devices have become critical components in dynamic electromagnetic regulation systems.

Traditional absorption devices with tunable absorption rates typically rely on modifying the physical parameters of absorptive materials (e.g., thickness or loss) (Pu et al., 2012; Nie et al., 2014a; Zyablovsky et al., 2014; Bai et al., 2016; Jin and Yu, 2020) or adjusting the phase differences between the counter-propagating coherent waves (Wan et al., 2011; Nie et al., 2014a, 2014b; Yan et al., 2014; Wong et al., 2016; Zhao H et al., 2016; Xiao D et al., 2017; Huang et al., 2018; Guo and Argyropoulos, 2019, 2020; Alaee et al., 2020; Jin and Yu, 2020; Wang C et al., 2022; Chen JT et al., 2024; Zou et al., 2024). However, post-fabrication modification of the physical parameters of the materials is challenging, whereas coherent control over multiple incident waves is simple and can offer enhanced tunability. Notably, low absorption rates do not necessarily correspond to high transmission but may instead indicate high reflection. Conventional high-transmission schemes based on standard interference often induce waveform distortion. To address these limitations, a nonlinear