Covert infrared image encoding through imprinted plasmonic cavities

Brochosome-inspired binary metastructures for pixel-by-pixel thermal signature control

Microscale thermal signature control using incoherent heat sources remains challenging, despite recent advancements in plasmonic materials and phase-change materials. Inspired by leafhopper-generated brochosomes, we design binary metastructures functioning as pixel twins to achieve pixelated thermal signature control at the microscale. In the infrared range, the pixel twins exhibit distinct emissivities, creating thermal counterparts of "0-1" binary states for storing and displaying information. In the visible range, the engineered surface morphology of the pixel twins ensures similar scattering behaviors. This renders them visually indistinguishable, thereby concealing the stored information. The brochosome-like pixel twins are self-emitting when thermally excited. Their structure-enabled functions do not rely on the permittivities of specific materials, which distinguishes them from the conventional laser-illuminated plasmonic holographic metasurfaces. The unique combination of visible camouflage and infrared display offers a systemic solution to microscale spatial control of thermal signatures and has substantial implications for optical security, anticounterfeiting, and data encryption.

Tunable plasmonic superchiral light for ultrasensitive detection of chiral molecules

The accurate detection, classification, and separation of chiral molecules are pivotal for advancing pharmaceutical and biomolecular innovations. Engineered chiral light presents a promising avenue to enhance the interaction between light and matter, offering a noninvasive, high-resolution, and cost-effective method for distinguishing enantiomers. Here, we present a nanostructured platform for surface-enhanced infrared absorption-induced vibrational circular dichroism (VCD) based on an achiral plasmonic system. This platform enables precise measurement, differentiation, and quantification of enantiomeric mixtures, including concentration and enantiomeric excess determination. Our experimental results exhibit a 13 orders of magnitude higher detection sensitivity for chiral enantiomers compared to conventional VCD spectroscopic techniques, accounting for respective path lengths and concentrations. The tunable spectral characteristics of this achiral plasmonic system facilitate the detection of a diverse range of chiral compounds. The platform's simplicity, tunability, and exceptional sensitivity holds remarkable potential for enantiomer classification in drug design, pharmaceuticals, and biological applications.

Sub-Diffraction Readout Method of High-Capacity Optical Data Storage Based on Polarization Modulation

The big data era demands an efficient and permanent data storage technology with the capacity of PB to EB scale. Optical data storage (ODS) offers a good candidate for long-lifetime storage, as the developing far-field super-resolution nanoscale writing technology improves its capacity to the PB scale. However, methods to efficiently read out this intensive ODS data are still lacking. In this paper, we demonstrate a sub-diffraction readout method based on polarization modulation, which experimentally achieves the sub-diffraction readout on Disperse Red 13 thin film with a resolution of 500 nm, exceeding the diffraction limit by 1.2 times (NA = 0.5). Differing from conventional binary encoding, we propose a specific polarization encoding method that enhances the capacity of ODS by 1.5 times. In the simulation, our method provides an optical data storage readout resolution of 150 nm, potentially to 70 nm, equivalent to 1.1 PB in a DVD-sized disk. This sub-diffraction readout method has great potential as a powerful readout tool for next-generation optical data storage.

Whole-infrared-band camouflage with dual-band radiative heat dissipation

Advanced multispectral detection technologies have emerged as a significant threat to objects, necessitating the use of multiband camouflage. However, achieving effective camouflage and thermal management across the entire infrared spectrum, especially the short-wave infrared (SWIR) band, remains challenging. This paper proposes a multilayer wavelength-selective emitter that achieves effective camouflage across the entire infrared spectrum, including the near-infrared (NIR), SWIR, mid-wave infrared (MWIR), and long-wave infrared (LWIR) bands, as well as the visible (VIS) band. Furthermore, the emitter enables radiative heat dissipation in two non-atmospheric windows (2.5-3 μm and 5-8 μm). The emitter's properties are characterized by low emittance of 0.270/0.042/0.218 in the SWIR/MWIR/LWIR bands, and low reflectance of 0.129/0.281 in the VIS/NIR bands. Moreover, the high emittance of 0.742/0.473 in the two non-atmospheric windows ensures efficient radiative heat dissipation, which results in a temperature decrement of 14.4 °C compared to the Cr reference at 2000 W m-2 input power density. This work highlights the role of solar radiance in camouflage, and provides a comprehensive guideline for developing multiband camouflage compatible with radiative heat dissipation, from the visible to LWIR.

Visible and infrared dual-band anti-counterfeiting with self-assembled photonic heterostructures

Self-assembled photonic structures have greatly expanded the paradigm of optical materials due to their ease of access, the richness of results offered and the strong interaction with light. Among them, photonic heterostructure shows unprecedent advances in exploring novel optical responses that only can be realized by interfaces or multiple components. In this work, we realize visible and infrared dual-band anti-counterfeiting using metamaterial (MM) - photonic crystal (PhC) heterostructures for the first time. Sedimentation of TiO₂ nanoparticles in horizontal mode and polystyrene (PS) microspheres in vertical mode self-assembles a van der Waals interface, connecting TiO₂ MM to PS PhC. Difference of characteristic length scales between two components support photonic bandgap engineering in the visible band, and creates a concrete interface at mid-infrared to prevent interference. Consequently, the encoded TiO₂ MM is hidden by structurally colored PS PhC and visualized either by adding refractive index matching liquid or by thermal imaging. The well-defined compatibility of optical modes and facility in interface treatments further paves the way for multifunctional photonic heterostructures.

Polyaniline-Based Infrared Dynamic Patterned Encoder with Multiple Thermal Radiation Characteristics

A high-level infrared dynamic patterned encoder (IR-DPE) possesses prospective applications for energy-harvesting and information, but a simple and reliable method for fabrication remains challenging. Herein, we first report an IR-DPE with multiple thermal radiation characteristics based on polyaniline (PANI). Specifically, the electron-beam evaporation technique is introduced to obtain the divanadium pentoxide (V2O5) coating, and then the V2O5 film acts as an oxidant to drive in situ polymerization of the PANI film. During the process, we experimentally explore the relationship between the thickness of V2O5 and the emissivity of PANI to obtain up to six emissivity levels and achieve the IR pattern integrated into multiple thermal radiation characteristics. The device shows multiple thermal radiation characteristics at the oxidized state, realizing a pattern visible with the IR camera and the same thermal radiation properties at the reduced state, leading to the pattern concealed in the IR regime. In addition, the highest emissivity tunability of the device is to be tuned from 0.40 to 0.82 (Δε = 0.42) at 2.5-25 μm. Meanwhile, the device exhibits a maximum temperature control of up to 5.9 °C. The results show the enormous potential of IR-DPEs for IR information transfer and thermal management.

Enabling Active Nanotechnologies by Phase Transition: From Electronics, Photonics to Thermotics

Phase transitions can occur in certain materials such as transition metal oxides (TMOs) and chalcogenides when there is a change in external conditions such as temperature and pressure. Along with phase transitions in these phase change materials (PCMs) come dramatic contrasts in various physical properties, which can be engineered to manipulate electrons, photons, polaritons, and phonons at the nanoscale, offering new opportunities for reconfigurable, active nanodevices. In this review, we particularly discuss phase-transition-enabled active nanotechnologies in nonvolatile electrical memory, tunable metamaterials, and metasurfaces for manipulation of both free-space photons and in-plane polaritons, and multifunctional emissivity control in the infrared (IR) spectrum. The fundamentals of PCMs are first introduced to explain the origins and principles of phase transitions. Thereafter, we discuss multiphysical nanodevices for electronic, photonic, and thermal management, attesting to the broad applications and exciting promises of PCMs. Emerging trends and valuable applications in all-optical neuromorphic devices, thermal data storage, and encryption are outlined in the end.

Long-wavelength infrared selective emitter for thermal infrared camouflage under a hot environment

Thermal infrared camouflage as a kind of counter-surveillance technique has attracted much attention owing to the rapid development of infrared surveillance technology. Various artificial optical structures have been developed for infrared camouflage applications under cold ambient environment (low thermal radiation), but the realization of infrared camouflage under a hot environment (high thermal radiation) is also highly desirable and has been rarely reported. Here, a lithography-free, ultra-thin, high performance long-wavelength infrared (LWIR) selective emitter for thermal infrared camouflage in a high radiation environment is proposed and experimentally demonstrated. Experimental results show that our designed selective emitter exhibits average emissivity higher than 90% over the LWIR range from 8 to 14 µm and low emissivity less than 35% outside this window. Numerical simulations were performed to optimize the geometrical structures and reveal that such a selective emission effect is attributed to the combination of multiple hybrid plasmonic resonances. LWIR thermal images show that the selective emitter can perfectly blend into the high radiation backgrounds. Furthermore, it is found that the sample displays angle-independent emission properties, indicating that our emitter offers great potential for application in evading large-angle detection.

Noncontact human-machine interaction based on hand-responsive infrared structural color

Noncontact human-machine interaction provides a hygienic and intelligent approach for the communication between human and robots. Current noncontact human-machine interactions are generally limited by the interaction distance or conditions, such as in the dark. Here we explore the utilization of hand as an infrared light source for noncontact human-machine interaction. Metallic gratings are used as the human-machine interface to respond to infrared radiation from hand and the generated signals are visualized as different infrared structural colors. We demonstrate the applications of the infrared structural color-based human-machine interaction for user-interactive touchless display and real-time control of a robot vehicle. The interaction is flexible to the hand-interface distance ranging from a few centimeters to tens of centimeters and can be used in low lighting condition or in the dark. The findings in this work provide an alternative and complementary approach to traditional noncontact human-machine interactions, which may further broaden the potential applications of human-machine interaction.

The IR radiation from human hand can selectively interact with grating patterns in the generation of distinct IR structural colors, which can be used for human-machine interaction with flexible interaction distance in low or no light conditions.

Materials design of vertically coupled plasmonic arrays

Plasmonic metasurfaces have important applications in life science, optics, and catalysis. However, their industrial usage is limited by the challenges of high throughput nanofabrication. A promising solution is the transfer of a pattern into a substrate using block copolymers, nanostructured stamps or molds to create binary, three dimensional templates, which can then be decorated with plasmonically active metals. Here, we report on the optical properties of quasi-Babinet complementary arrays in the non-retarded regime investigated by finite-difference time-domain simulations. The structures consist of a nanopillar support, which is covered with metal disks on top of the pillars and a quasi-Babinet complementary hole array film at the base of the pillars. Strong vertical plasmonic coupling occurs for small separation distances of the plasmonic slabs. We present a comprehensive study of the near and far-field properties of such vertically coupled plasmonic arrays varying their critical geometric dimension and the employed metals with their intrinsic plasmonic material properties. In particular, we consider gold, silver, copper, aluminum, nickel, and palladium. Furthermore, the effect of the refractive index n of the nanopillar support between the range of n = 1.4 to n = 3.4 is investigated. The plasmonic slabs show tunable extraordinary transmission and large electric near-field enhancements, which are strongly dependent on the employed material and geometry. Further, we show that the templates are suitable for plasmonic heterostructures commonly used in plasmon-enhanced photocatalysis.

Metasurface-Driven Optically Variable Devices

Optically variable devices (OVDs) are in tremendous demand as optical indicators against the increasing threat of counterfeiting. Conventional OVDs are exposed to the danger of fraudulent replication with advances in printing technology and widespread copying methods of security features. Metasurfaces, two-dimensional arrays of subwavelength structures known as meta-atoms, have been nominated as a candidate for a new generation of OVDs as they exhibit exceptional behaviors that can provide a more robust solution for optical anti-counterfeiting. Unlike conventional OVDs, metasurface-driven OVDs (mOVDs) can contain multiple optical responses in a single device, making them difficult to reverse engineered. Well-known examples of mOVDs include ultrahigh-resolution structural color printing, various types of holography, and polarization encoding. In this review, we discuss the new generation of mOVDs. The fundamentals of plasmonic and dielectric metasurfaces are presented to explain how the optical responses of metasurfaces can be manipulated. Then, examples of monofunctional, tunable, and multifunctional mOVDs are discussed. We follow up with a discussion of the fabrication methods needed to realize these mOVDs, classified into prototyping and manufacturing techniques. Finally, we provide an outlook and classification of mOVDs with respect to their capacity and security level. We believe this newly proposed concept of OVDs may bring about a new era of optical anticounterfeit technology leveraging the novel concepts of nano-optics and nanotechnology.

Colloidal Self-Assembly Approaches to Smart Nanostructured Materials

Colloidal self-assembly refers to a solution-processed assembly of nanometer-/micrometer-sized, well-dispersed particles into secondary structures, whose collective properties are controlled by not only nanoparticle property but also the superstructure symmetry, orientation, phase, and dimension. This combination of characteristics makes colloidal superstructures highly susceptible to remote stimuli or local environmental changes, representing a prominent platform for developing stimuli-responsive materials and smart devices. Chemists are achieving even more delicate control over their active responses to various practical stimuli, setting the stage ready for fully exploiting the potential of this unique set of materials. This review addresses the assembly of colloids into stimuli-responsive or smart nanostructured materials. We first delineate the colloidal self-assembly driven by forces of different length scales. A set of concepts and equations are outlined for controlling the colloidal crystal growth, appreciating the importance of particle connectivity in creating responsive superstructures. We then present working mechanisms and practical strategies for engineering smart colloidal assemblies. The concepts underpinning separation and connectivity control are systematically introduced, allowing active tuning and precise prediction of the colloidal crystal properties in response to external stimuli. Various exciting applications of these unique materials are summarized with a specific focus on the structure-property correlation in smart materials and functional devices. We conclude this review with a summary of existing challenges in colloidal self-assembly of smart materials and provide a perspective on their further advances to the next generation.

Spectral Engineering of Tamm Plasmon Resonances in Dielectric Nanoporous Photonic Crystal Sensors

Model light-confining Tamm plasmon cavities based on gold-coated nanoporous anodic alumina photonic crystals (TMM-NAA-PCs) with spectrally tunable resonance bands were engineered. Laplacian and Lorentzian NAA-PCs produced by a modified Gaussian-like pulse anodization approach showed well-resolved, high-quality photonic stopbands, the position of which was precisely controlled across the visible spectrum by the periodicity in the input anodization profile. These PC structures were used as a platform material to develop highly reflective distributed Bragg mirrors, the top sides of which were coated with a thin gold film. The resulting nanoporous hybrid plasmonic-photonic crystals showed strong light-confining properties attributed to Tamm plasmon resonances at three specific positions of the visible spectrum. These structures achieved high sensitivity to changes in refractive index, with a sensitivity of ∼106 nm RIU-1. The optical sensitivity of TMM-NAA-PCs was assessed in real time, using a model chemically selective binding interaction between thiol-containing molecules and gold. The optical sensitivity was found to rely linearly on the spectral position of the Tamm resonance band, for both Laplacian and Lorentzian TMM-NAA-PCs. The density of self-assembled monolayers of thiol-containing analyte molecules formed on the surface of the metallic film directly contributes to the dependence of sensitivity on TMM resonance position in these optical transducers. Our findings provide opportunities to integrate TMM modes in NAA-based photonic crystal structures, with promising potential for optical technologies and applications requiring high-quality surface plasmon resonance bands.

Nonvolatile Optically Reconfigurable Radiative Metasurface with Visible Tunability for Anticounterfeiting

Control of thermal emission underpins fundamental science, as it is related to both heat and infrared electromagnetic wave transport. However, realizing nonvolatile reconfigurable thermal emission is challenging due to the inherent complexity or limitation in conventional radiative materials or structures. Here, we experimentally demonstrate a nonvolatile optically reconfigurable mid-infrared coding radiative metasurface. By applying laser pulses, infrared emissive patterns are directly encoded into an ultrathin (∼25 nm) Ge₂Sb₂Te₅ layer integrated into a planar optical cavity with the optically crystallized Ge₂Sb₂Te₅ spots, and the peak spectral emissivity is repeatedly switched between low (∼0.1) and high (∼0.7) values. In addition, the visible scattering patterns are independently modulated with submicron-sized bumps generated by high-power laser pulses. An anticounterfeiting label is demonstrated with spatially different infrared emission and visible light scattering information encoded. This approach constitutes a new route toward thermal emission control and has broad applications in encryption, camouflage, and so on.

Metasurface Holography in the Microwave Regime

Hologram technology has attracted a great deal of interest in a wide range of optical fields owing to its potential use in future optical applications, such as holographic imaging and optical data storage. Although there have been considerable efforts to develop holographic technologies using conventional optics, critical issues still hinder their future development. A metasurface, as an emerging multifunctional device, can manipulate the phase, magnitude, polarization and resonance properties of electromagnetic fields within a sub-wavelength scale, opening up an alternative for a compact holographic structure and high imaging quality. In this review paper, we first introduce the development history of holographic imaging and metasurfaces, and demonstrate some applications of metasurface holography in the field of optics. We then summarize the latest developments in holographic imaging in the microwave regime. These functionalities include phase- and amplitude-based design, polarization multiplexing, wavelength multiplexing, spatial asymmetric propagation, and a reconfigurable mechanism. Finally, we conclude briefly on this rapidly developing research field and present some outlooks for the near future.

Vanadium-dioxide microstructures with designable temperature-dependent thermal emission

We propose gold-vanadium dioxide microstructures for which the difference in thermally radiated power between the low and high temperature states can be tuned via structural design. We start by incorporating VO₂ in a gold-dielectric-gold waveguide to achieve a temperature-dependent mode effective index. We show that a cavity formed in this waveguide structure has a fundamental resonance wavelength that shifts with temperature. We calculate the thermal radiated power from the cavity at temperatures above and below the phase transition of VO₂ for wavelengths between 8 and 14 µm. We show that the difference in radiated power can be made positive, negative, or zero simply by adjusting the cavity length. Finally, we use our cavity to design thermally emissive metasurfaces with spatial emission patterns that can be inverted with temperature. Our emitters could serve as building blocks in the realization of metasurfaces enabling complex thermal radiation control.

Diffraction manipulation of visible light with submicron structures for structural coloration fabrication

The structural coloration of glass induced by submicron structures is eco-friendly, ink-free, and has profound scientific significance. However, it is difficult to manufacture the submicron structures for glass optics due to the high hardness of glass and the miniature size of the microstructures. In this paper, the diffraction manipulation mechanism of groove shape to structural coloration and optimization theory are studied by establishing the theoretical and simulation mode. Moreover, a newly-developed axial-feed fly-cutting (AFC) technology and the PGM technology are introduced to precisely create the designed submicron V-shape grooves and structural color pattern on a Ni-P mold and then replicating them on a glass surface. Between these two kinds of typical submicron grooves that can be machined by mechanical cutting technology, it is found that the diffraction intensity and efficiency of V-shape grooves are higher than these of jagged-shape grooves, which indicates that V-shape grooves is more suitable to be used for structural coloration with high brightness. The structural color resolution is dramatically increased with the reduction of groove spacing and can be flexibly regulated by AFC, which significantly contributes to the structural coloration manufacturing. Structural pixel segments composed of submicron grooves are arranged row-by-row to form color patterns, and the letters of different colors are fabricated on the mold and transferred to the glass surface. Methods of optical diffraction manipulation, flexible manufacturing of submicron structures, and structural color image construction proposed in this paper for the production of a structural color pattern are beneficial to a wide range of fields.

Peculiar polarization response in chiral liquid crystal stacks for multispectral camouflage

Chiral liquid crystals are self-organized Bragg reflectors which respond to circularly polarized light. Manipulation of the chiral structure has aroused great research interest. The x-y plane two-dimensional patterning of chiral liquid crystals leads to reflective planar optics, and the z-axis modulation results in a variety of photonic bandgap controls. Here, the optical properties of even-number left- and right-handed chiral liquid crystal stacks are investigated, with emphasis on the linear polarization response. Under certain conditions, a linearly polarized incidence can result in a linearly polarized reflected light. More intriguingly, the linear polarization has different forms of response to thick and thin chiral liquid crystal sublayers and responds to the rotation of liquid crystal alignment. Based on the peculiar polarization response, a new type of wavelength-response camouflage and anti-counterfeiting is conceptually proposed, which can hide two different images simultaneously within a small spectral range. Our work paves the way for three-dimensional manipulation of chiral liquid crystals and enlightens novel applications.

Spectrally and Spatially Selective Emitters Using Polymer Hybrid Spoof Plasmonics

Optimized thermal emitters using optical resonances have been attracting increased attention for diverse applications, such as infrared (IR) sensing, thermal imaging, gas sensing, thermophotovoltaics, thermal camouflage, and radiative cooling. Depending on the applications, the recently developed IR devices have been tailored to achieve not only spectrally engineered emission but also spatially resolved emission using various nanometallic structures, metamaterials, and multistacking layers, which accompany high structural complexity and prohibitive production cost. Herein, this article presents a simple and affordable approach to obtain spatially and spectrally selective hybrid thermal emitters (HTEs) based on spoof surface plasmons of microscaled Ag grooves manifested in encapsulation polymer layers. Theoretical analyses found that the polymer hybrid plasmonics allows diverse emission tuning within the long-wave IR (LWIR; 8-14 μm) region as follows: (1) spatially selective emission peaks only exist in the interface of Ag grooves and IR-transparent layers and (2) near-unity spectrally selective emission is obtained by refining inherent emissivity of a thin IR-opaque layer. Also, parametric studies computationally optimized the structural parameters for spatially and spectrally selective HTEs. Using the optimized parameters, the authors fabricated two HTEs and demonstrated the intriguing emission features in terms of infrared data encoding/decoding and radiative cooling, respectively. These successful demonstrations open up the applicability of HTEs for tailoring IR emission in a spatially and spectrally selective manner.

Hydroxypropyl Cellulose Adhesives for Transfer Printing of Carbon Nanotubes and Metallic Nanostructures

Transfer printing is one of the key nanofabrication techniques for the large-scale manufacturing of complex device architectures. It provides a cost-effective and high-throughput route for the integration of independently processed materials into spatially tailored architectures. Furthermore, this method enables the fabrication of flexible and curvilinear devices, paving the way for the fabrication of a new generation of technologies for optics, electronics, and biomedicine. In this work, hydroxypropyl cellulose (HPC) membranes are used as water soluble adhesives for transfer printing processes with improved performance and versatility compared to conventional silicone alternatives. The high-water solubility and excellent mechanical properties of HPC facilitate transfer printing with high yield for both metal and carbon nanotubes (CNTs) inks. In the case of metal inks, crack-free stripping of silver films and the simple fabrication of Moiré Plasmonic architectures of different geometries are demonstrated. Furthermore, HPC membranes are used to transfer print carbon nanotube films with different thicknesses and up to 77% transparency in the visible and near infrared region with potential applications as transparent conductive substrates. Finally, the use of prepatterned HPC membranes enables nanoscale patterning of CNT with feature resolution down to 1 µm.

Multiplexed Assembly of Plasmonic Nanostructures Through Charge Inversion on Substrate for Surface Encoding

Plasmonic nanomaterials are excellent and promising building blocks for information encoding and decoding. However, the positioning of multiplexed nanomaterials into recognizable structures remains a major challenge in nanotechnology. Herein, we developed a novel method for fabricating diversified nanostructures through surface charge inversion from amino-modified substrates to carboxyl-modified ones, as well as the corresponding electrostatic-induced assembly of metal nanoparticles. Under optimal conditions, the selected gold nanospheres (NSs) and peanut-like gold nanorods were successively located into patterns of spaced lines on the same substrate. Due to their unique optical properties, these two types of designed nanoarrays exhibited distinct color contrast and spectrum difference under dark-field scattering microscopy. Furthermore, this general strategy can be extended to wide ranges of nanoparticles with different morphologies and compositions for other multifunctional and high-demanding encoding applications.

Reversible decryption of covert nanometer-thick patterns in modular metamaterials

Continuous development of security features is mandatory for the fight against forgery of valuable documents and products, the most notable example being banknotes. Such features demonstrate specific properties under certain stimuli such as fluorescent patterns glowing under ultraviolet light. These security features should also be hard to copy by unlicensed people and be interrogated by anyone using easily accessible tools. To this end, this Letter demonstrates the development of an ideal security feature enabled by the realization of modular metamaterials based on metal-dielectric-metal cavities that consist of two separate parts: metal nanoparticles on an elastomeric substrate and a bottom mirror coated with a thin dielectric. Patterns generated by creating nanometer-thick changes in the dielectric layer are invisible (encrypted) and can only be detected (decrypted) by sticking the elastomeric patch on. The observed optical effects such as visibility and colors can only be produced with the correct combination of materials and film thicknesses, making the proposed structures a strong alternative to compromised security features.

Plasmon resonances in coupled Babinet complementary arrays in the mid-infrared range

A plasmonic structure with transmission highly tunable in the mid-infrared spectral range is developed. This structure consists of a hexagonal array of metallic discs located on top of silicon pillars protruding through holes in a metallic Babinet complementary film. We reveal with FDTD simulations that changing the hole diameter tunes the main plasmonic resonance frequency of this structure throughout the infrared range. Due to the underlying Babinet physics of these coupled arrays, the spectral width of these plasmonic resonances is strongly reduced, and the higher harmonics are suppressed. Furthermore, we demonstrate that this structure can be easily produced by a combination of the nanosphere lithography and the metal-assisted chemical etching technique.