This paper presents a high-performance energy-selective structure (ESS) design methodology based on a stacked slotline. By leveraging the unique characteristics of three-dimensional stacked structures, the method efficiently converts spatial waves into guided waves in slotline transmission lines, which can be tailored via lumped-circuit design to achieve precise energy-selective functionality. The proposed design approach systematically extends previous work by providing a clear theoretical foundation for decoupling and independently optimizing multiple ESS performance indicators. This allows the design of structures with flexibly selectable frequency bands and high shielding efficiency. Two prototypes were fabricated to validate the method. Prototype I targets bandwidth expansion, achieving an operational range from 2.2 to 8.2 GHz (115.4% relative bandwidth), with less than 1 dB insertion loss and over 10 dB shielding effectiveness across the band. Prototype II emphasizes shielding performance, reaching a shielding efficiency greater than 33 dB between 3.9 and 6.3 GHz, with a maximum of 40.3 dB. Both prototypes were fabricated and validated through experimental measurements, showing agreement with the simulation results. The performance of the two designed structures far exceeds other existing ESSs in terms of broadband or high shielding efficiency, indicating that the comprehensive design method has great potential to significantly improve the design of targeted technical specifications.
The design of large-scale coding metasurfaces poses significant computational challenges, often limited by the prohibitive time required for full-wave simulations necessary for optimization. This paper proposes an efficient design strategy based on a Hybrid Genetic Algorithm, validated through the design, fabrication, and characterization of an X-band metasurface for Radar Cross Section reduction. The proposed design strategy relies on a two-stage optimization process: a fast pre-optimization phase, based on the analytical Huygens-Fresnel principle, generates a preliminary solution which is subsequently refined by a second optimization stage utilizing fullwave simulations. Specifically, the optimization targets a 1-bit coding scheme, where meta-atoms switch between two distinct states with a phase difference of 180 +/- 37 degrees. This hybrid approach demonstrates optimal convergence, reducing computational time by 25% compared to traditional full-wave-only techniques. Furthermore, a novel "spiralling cross" unit cell topology is introduced. Owing to its delay-line geometry, this structure provides additional degrees of freedom for spectral tuning and supports intermediate phase shifts, thus enabling encoding schemes beyond traditional 1-bit configurations. Experimental results confirm the validity of the proposed approach, demonstrating how the combination of versatile geometry and hybrid optimization effectively overcomes the trade-offs between numerical accuracy and computational efficiency.
Accurate simulation of partially coherent imaging is crucial for computational lithography, with Abbe and Hopkins as the two main formulations being used. Although the two methods are equivalent in theory, practical simulators making independent choices between Abbe and Hopkins could hardly produce consistent results that match the desired accuracy owing to the inherently different ways of numerically representing, discretizing, and truncating the illumination source and lens pupil function, etc. Moreover, classical Hopkins models require prior construction and/or eigen decomposition of the high-dimensional transmission cross coefficient (TCC), the prohibitive costs of which hinder timely model verification. To address these challenges, we developed a unified Abbe-Hopkins formulation in conjunction with a TCC-free Hopkins pointwise sampler for efficient cross-model validation. Our formulation supports both Abbe and Hopkins modeling in a single unified framework, with the two simulation modes using exactly the same numerical representations of the illumination source and projection lens. Cross-model verification for randomly sampled points is performed efficiently by evaluating the Hopkins quadratic form through a fast Fourier transform of an image and a few pointwise multiplications between images, without ever explicitly constructing a TCC and eigen-analyzing it. Numerical tests show that the Abbe and Hopkins results agree up to the machine precision level.
We present a review of homogenization models of microwave wire media with different geometries. We begin with a simple (uniaxial) wire medium and then consider more complex types of wire media - double, triple, and interlaced wire media - which remain underexplored. We discuss boundary problems with wire media and the most important physical effects revealed using the reviewed homogenization models.
This paper reviews recent advances in acoustic computation and modeling, specifically bridging effective medium theory (EMT) and biomedical ultrasound imaging. To achieve this, we examine how EMT provides the physical foundation for wave-based imaging through homogenized parameters, focusing on image reconstruction across diverse systems ranging from single pulse-receivers to multi-input and multi-output (MIMO) tomography. Furthermore, we highlight cross-disciplinary insights from computational optics, such as the transport of intensity equation and ptychography, while addressing acoustic-specific challenges like aberration correction and wave interference. In light of these challenges, emerging solutions are discussed, including ultrasound matrix imaging (UMI) via transfer matrix methods, inverse-designed matching layers, and hardware-accelerated approaches like the Krimholtz-Leedom-Matthaei (KLM) electro-acoustic model for ultrafast imaging. Ultimately, by integrating physical understanding of effective media with advanced computational algorithms, these developments provide a robust framework for the future of high-resolution 3D ultrasonography and acoustic holography.
Free-space electromagnetic waves can be coupled into on-chip propagating surface waves (SWs), a process that holds great promise for receiver front ends in wireless communication systems. However, it has traditionally faced challenges in terms of coupling efficiency and controlling the on-chip wavefront of SWs. To address these challenges, we designed and experimentally demonstrated SW couplers operating in the terahertz regime based on metal-insulator-metal resonators. Our devices achieve not only broadband and highly efficient coupling, with an efficiency exceeding 60% over a 20 GHz bandwidth, but also enable the directional steering of the excited SWs to designated on-chip ports. Thus, mode conversion and on-chip routing functionalities are seamlessly integrated into a single compact component. Based on this design, we fabricated devices and implemented corresponding terahertz wireless communication links, successfully demonstrating 16-QAM data transmission in both single-link and dual-link configurations.
To achieve synchronous and uniform amplification of dense multi-carrier signals, this paper proposes a multi-frequency nondegenerate parametric amplifier (PA) based on a nonlinear spoof surface plasmon polariton (SSPP) waveguide. By engineering the dispersion characteristics of a varactor-diode-loaded waveguide, we realize an SSPP platform that exhibits minimized phase mismatch for three distinct signal-idler pairs under a constant pump frequency (13.348 GHz) and a fixed bias voltage. Experimental results show that the amplifier delivers highly uniform gains exceeding 20 dB for three closely spaced carriers at 6.363, 6.489, and 6.549 GHz, effectively emulating a three-frequency-shift keying (3FSK) signal. This work demonstrates a fixed-condition amplification scheme that requires no dynamic tuning, offering a promising solution for amplifying densely spaced carriers in integrated communication systems.
The control of all of light's degrees of freedom and its harnessing for applications is captured by the emergent field of structured light. The modern toolkit includes external modulation of light with devices such as metasurfaces and spatial light modulators, their intra-cavity insertion for structured light directly at the source, and their deployment to engineer quantum structured light at the single photon and entangled state regimes. Historically, this control has involved linear optical elements, with nonlinear optics only recently coming to the fore. This has opened unprecedented functionality while revealing new paradigms for nonlinear optics beyond plane waves. In this review, we look at the recent progress in structured light with nonlinear optics, covering the fundamentals and the powerful applications they are facilitating in both the classical and quantum domains.
Investigations into the nature of electromagnetic fields produced by dipole sources over homogeneous flat ground or impedance surfaces date back many years. In general, at a long distance r from the source, the near-surface field is mostly contributed by the geometrical optics term (describing the radiation pattern), a guided wave, and a higher-order reactive contribution referred to as the Norton wave. In the special case of a perfect magnetic conductor interface, the first two terms vanish; thus, the residual Norton wave determines the steepest achievable field decay profile of r-3/2 (for a two-dimensional horizontal magnetic dipole). In this paper, we reveal that in the presence of a non-local metasurface described by the second-order impedance boundary condition, the field decay can be further accelerated by suppressing the Norton wave (approaching the profiles r-5/2 and r-7/2 for the electric and magnetic fields, respectively). In a proposed practical realization of a nonlocal metasurface, the effect is numerically verified and shown to reduce the edge diffraction effects by 10 dB for a shield diameter of only one wavelength, paving the way for compact antenna systems.
Plasmonic designs for mid-infrared extraordinary optical transmission (EOT), a direct route to tailored filtering with broadband out-of-band rejection, have long been constrained by a fundamental trade-off between high transmission efficiency and narrow linewidths, a challenge rooted in the material properties of noble metals. Here, we theoretically propose and numerically demonstrate a versatile design paradigm that resolves this challenge by functionally decoupling the tasks of light coupling and resonant filtering. Our approach uses a dual-stacked noble metal-dielectric grating architecture to surpass the intrinsic limitations of single-layer structures. This paradigm provides the flexibility to engineer devices for ultra-high spectral selectivity and transmission efficiency. We demonstrate this with distinct designs: one at 10 mu m with a quality factor (Q-factor) > 2000 and > 91% transmission; a high-Q design at 4 mu m and > 80% transmission; and a high-efficiency design at 4 mu m with > 92% transmission over a uniquely broad spectral-angular range. These generic designs produce solitary, narrow EOT peaks originating from a "triple-coupling" mechanism that mitigates reflection and absorption losses, with symmetry-broken configurations capable of exceeding Q-factors of 16,000 while maintaining a peak transmission efficiency > 60%. Crucially, these compact two-layer designs exhibit exceptional robustness against fabrication variations, offering a broadly applicable route to ultra-compact, low-cost infrared components, enabling advanced architectures such as angular sensing, spectro-polarimetric imaging, and isotope-resolved gas diagnostics.
With increasing demand for renewable energy, perovskite solar cells (PSCs) have emerged as a promising alternative due to their high efficiency and solution-based manufacturing processes. However, the fabrication of PSCs in ambient conditions, as opposed to inert environments, remains challenging due to environmental factors such as moisture and oxygen that degrade perovskite materials. Developing air-processed PSCs is therefore critical for reducing fabrication cost, simplifying manufacturing infrastructure, and enabling scalable production compatible with industrial processes. Moreover, air processing represents a key step toward realistic deployment, bridging the gap between laboratory demonstrations and commercial applications. This perspective discusses the progress of air-processed PSCs, highlights the environmental challenges related to stability and performance, and outlines potential strategies for future research, including precursor chemistry, solvent and additive engineering, and interface optimization. In addition, emerging scalable deposition techniques, automated platforms, and machine learning-assisted control are expected to accelerate device optimization and reproducibility. Despite remaining challenges, commercializing air-processed PSCs is increasingly viable, promising a sustainable and efficient approach for solar energy technology.
Temporal metasurfaces offer a promising platform for new-architecture wireless communications by enabling fast modulation of both electromagnetic waves and digital information. Optical control of these metasurfaces is particularly attractive as it establishes a direct physical bridge between optical and microwave signals, forming the foundation for optoelectronic hybrid communication systems. However, existing schemes are confined to static pre-alignment of the laser beam with the metasurface, lacking real-time spatial alignment capability essential for real-world mobile applications. Here, we propose and realize a mobile hybrid wireless communication system based on the designed laser-tracking-modulated microwave temporal metasurface. This communication system is constructed by integrating a photodiode-based microwave temporal metasurface, a vision-assisted laser-tracking transmitter, and a microwave receiver, enabling direct laser-to-microwave signal conversion sustained by dynamic alignment. Experimental results demonstrate that the system successfully maintains a stable hybrid communication link while the laser transmitter is in motion. This work provides a viable strategy for establishing stable hybrid wireless links for moving platforms and drones in high-mobility scenarios.
Complex beams hold significant value in radar and communication systems due to their distinctive propagation characteristics. Digital metasurfaces, which can dynamically control electromagnetic (EM) waves, play an important role in realizing complex beams. Conventional analytic and optimization methods face challenges in synthesizing complex beams of low-bit digital metasurfaces due to the quantization error and the high computational complexity. Here, we propose a statistical method to realize complex beams with phase-only digital metasurfaces. To this end, we introduce tailored quantization probabilities to design the discrete random phase distributions, which approximate the continuous excitation coefficients derived from analytic methods. Based on the proposed method, we analyze the error between the realized and target patterns. These findings offer critical insights into the accuracy of random quantization. Complex patterns with cosecant, prescribed null, flat-top, and dual-beam are designed and validated in combination with a 2-bit phase coding digital metasurface. The experimental results are in good agreement with the theoretical analysis. This work pioneers the application of random phase approximation and statistical synthesis in digital metasurfaces, providing a fast and efficient route for realizing complex beams in modern radar and wireless communication technologies.
The modulation of topological polarization singularities in momentum space in photonics has attracted much attention due to their relations with bound states in the continuum (BICs), unidirectional guided resonances, and chirality. Current modulation strategies that rely on structural symmetry breaking or phase-change materials are challenging to achieve dynamic and flexible modulation of polarization singularities. Recently, magneto-optical (MO) modulation of light provides a promising theoretical strategy for the dynamic modulation of polarization singularities. However, the dynamics of transverse electric (TE)/transverse magnetic (TM)-mode singularities under varying magnetic fields remain elusive in the MO photonic crystal (PhC) slab. Herein, we systematically investigate the dynamic modulation of topological polarization singularities in the PhC slabs with square arrays of square air holes and deformed square air holes based on the MO effect. In-plane (x/y) magnetic fields have no effect on the TE mode of the MO PhC slab. However, the fields induce splitting and separation of vortex polarization singularity (V point) of the TM mode into a pair of circular polarization points (C points), enabling extrinsic chirality without breaking the structural symmetry. A magnetic field along the z direction enables near-unity circular dichroisms (CDs) over a broad angular range when circular polarizations are formed at off-Gamma points for the TE and TM modes. Furthermore, by introducing single symmetry breaking (in-plane symmetry breaking for TE, out-of-plane symmetry breaking for TM) with magnetic field tuning, one of the C points can be shifted to the Gamma point, resulting in intrinsic chiral quasi-BICs (QBICs) with ultrahigh Q-factors and near-unity CDs. This study provides a dynamic and flexible modulation approach for polarization singularities, which enhances light-matter interactions for applications in advanced chiral photonic devices and tunable optoelectronic devices.
