Optical Metamaterials Research Articles

Self-Assembly of Colloidal Dumbbell Isomers and Plasmonic Properties for Optical Metamaterials.

In this study, we explore the self-assembly of various colloidal symmetric dumbbell (DB) isomers, including dipole Janus, cis-Janus, trans-Janus, apolar-inward and polar-inward perpendicular Janus, and alternating perpendicular Janus DBs. Using dissipative particle dynamics (DPD) simulations under conditions mimicking experimental setups, we investigate cluster formation driven by emulsion droplet evaporation. Our findings reveal a diverse set of cluster structures, which are in good agreement with experimental and simulation results reported in the literature while also predicting the formation of novel cluster configurations. These structures, characterized by well-defined and predictable patterns, are potentially applicable to creating colloidal molecules and crystals. Furthermore, we examine the dynamics of cluster formation to gain insight into the mechanisms guiding the self-assembly of these diverse colloidal DBs. The study highlights the impact of particle isomerism on the resulting assembly structures. We further select a set of typical nanoclusters obtained, including a tetrahedral cluster, which is the simplest, to study its plasmonic properties. Our findings indicate that increasing the nanoparticle (NP) radius or decreasing the gap between NPs leads to a red shift in the plasmonic resonance wavelength and enhances the resonance strength. We identify critical parameter regions where the electric-dipole and magnetic-dipole resonances can be engineered to achieve negative dielectric permittivity and magnetic permeability, which are essential for developing negative-index metamaterials.

TIME REFRACTION and SPACETIME OPTICS

A review of recent advances in spacetime optics is given, with special emphasis on time refraction. This is a basic optical process, occurring at a temporal discontinuity or temporal boundary, which is able to produce various different effects, such as frequency shifts, energy amplification, time reflection, and photon emission. If, instead of a single discontinuity, we have two reverse temporal boundaries, we can form a temporal beam splitter, where temporal interferences can occur. It will also be shown that, in the presence of an axis of symmetry, such as a magnetic field, the temporal beam splitter can induce a rotation of the initial polarization state, similar to a Faraday rotation. Recent work on time crystals, superluminal fronts, and superfluid light will be reviewed. Time gates based on spacetime optical effects will be discussed. We also mention recent work on optical metamaterials. Finally, the quantum properties of time refraction, which imply the emission of photon from vacuum, are considered, while similar problems in high-energy QED associated with electron–positron pairs are briefly mentioned.

Surface Nanopatterning and Structural Coloration of Liquid Metal Gallium Through Hypergravity Nanoimprinting

AbstractNanoscale structuring of gallium‐based liquid metals has emerged as a promising approach for generating unique properties and functionalities in advanced materials and devices. However, their exceptionally high surface tension presents significant challenges for achieving surface nanostructuring using conventional fabrication techniques. Here, a hypergravity nanoimprinting method is introduced, which harnesses horizontal centrifugation to generate hypergravity fields that drive liquid gallium into nanoscale cavities on an elastic polymer stamp surface at subzero temperatures, where it solidifies and preserves imprinted features down to 100 nm lateral resolution. This surpasses previous limits of gallium patterning, enabling phenomena such as iridescent structural colors with a wide range of hues and high saturation. Numerical simulations reveal the intricate fluid dynamic behaviors and interfacial interactions during the imprinting process, providing valuable insights for process optimization and control. By synergistically combining advanced soft lithography techniques with the reversible solid‐liquid phase transition properties of liquid metals, hypergravity nanoimprinting offers a practical nanofabrication approach, facilitating the development of next‐generation nanoscale gallium devices with finely structured nanofeatures across diverse application domains, such as nanoelectronics and photonic metamaterials.

Surface Engineering of Polymeric Colloidal Crystals by Temperature - Pressure Annealing.

Polymer colloidal crystals (PCCs) have been widely explored as acoustic and optical metamaterials and as templates for nanolithography. However, fabrication impurities and fragility of the self-assembled structures are critical bottlenecks for the device's efficiency and applications. We have demonstrated that temperature-assisted pressure [ annealing results in the mechanical strengthening of PCCs, which improves with the annealing temperature. Here, the enhancement of elastic properties and morphological features of self-assembled PCC's is evaluated using Brillouin light scattering and scanning electron microscopy. The pressure-induced effects on the vibrational modes of PCCs are also illustrated at temperatures well below the polymer glass transition. While the PCCs colloid constituents display reversibility, the PCC material is strongly irreversible in the performed thermodynamic cycle. The effective elastic modulus enhances from 0.7GPa for the pristine sample to 0.8GPa, solely by pressure annealing at room temperature. [ annealing at higher temperatures leads to a maximum effective elastic modulus of 1.7GPa, more than twice the value in the pristine sample. Above a cross-over pressure, 725bar at 348K), the PCCs respond elastically and, hence, reversibly to pressure changes.

Photonic-Metamaterial-Based, Near-Field-Enhanced Biosensing Approach for Early Detection of Lung and Ovarian Cancer

Early detection of lung and ovarian cancers relies heavily on identifying tumor biomarkers, but current methods require large blood samples and complex genetic testing. This study presents a novel photonic-metamaterial-based biosensing approach that leverages near-field radiative enhancement to detect cancer biomarkers (CA 125, CEA, and CYFRA 21-1) with high sensitivity. By utilizing structured photonic metamaterials, we optimize specific wavelengths to identify these biomarkers in interstitial fluid, which can be easily collected via minimally invasive microneedle arrays. Integrating near-field interactions with wavelength-selective metamaterials amplifies the thermal response at the nanoscale, allowing for the detection of deficient concentrations of biomarkers. This photonic metamaterial technique provides a faster, more accessible, and affordable alternative to conventional blood-based methods, significantly improving early detection and monitoring of cancer. Ultimately, this approach offers a transformative tool for clinical and research applications in cancer diagnostics.

Macroscopic Monograin Nano-Gyroid Thin Films in 4-inch Scale Through Shear-Rolling and Subsequent Solvent Annealing.

The gyroid structure from self-assembly is highly attractive for optical applications such as photonic crystals and metamaterials. However, due to the direction-dependent nature of these applications, achieving a monograin-level structure over a large area has remained challenging. In this study, the fabrication of unidirectionally oriented anisotropic nanocylinders of polystyrene-block-polydimethylsiloxane (PS-b-PDMS) is reported block copolymer thin films up to a 4-inch scale via a shear-rolling process, followed by solvent annealing to induce phase transition to nearly monograin gyroid structures. Grazing-incidence small-angle X-ray scattering (GISAXS) analysis and cross-sectional scanning electron microscope (SEM) images in the direction parallel to the shear-rolling direction reveal the preferential orientation with the (111) plane onto the YZ axis of the film, while only the (110) plane on the YZ axis of the film is observed in the perpendicular direction, with grain sizes approaching single-grain levels. For metamaterial applications, the PDMS domain is selectively removed, and gold is electroplated to produce monograin gold gyroid films.

Achiral and chiral ligands synergistically harness chiral self-assembly of inorganics.

Chiral structures and functions are essential natural components in biominerals and biological crystals. Chiral molecules direct inorganics through chiral growth of facets or screw dislocation of crystal clusters. As chirality promoters, they initiate an asymmetric hierarchical self-assembly in a quasi-thermodynamic steady state. However, achieving chiral assembly requires a delicate balance between intricate interactions. This complexity causes the roles of achiral-chiral and inorganic components in crystallization to remain ambiguous. Here, we elucidate a definitive mechanism using an achiral-chiral ligand strategy to assemble inorganics into hierarchical, self-organized superstructures. Achiral ligands cluster inorganic building blocks, while chiral ligands impart chiral rotation. Achiral and chiral ligands can flexibly modulate the chirality of superstructures by fully using their competition in coordination chemistry. This dual-ligand strategy offers a versatile framework for engineering chiroptical nanomaterials tailored to optical devices and metamaterials with optical activities across a broad wavelength range, with applications in imaging, detection, catalysis, and sensing.

Synthesis of Chiral Ag, Pd, and Pt Helicoids inside Chiral Silica Mold.

Chiral inorganic nanomaterials hold significant promise for various applications, including enantioselective catalysis, polarization-controlling optical devices, metamaterials, and enantioselective molecular sensors. In our previous work, we presented a method for synthesizing chiral Au 432 helicoid III (Au helicoids) from peptides and amino acids, where helical gaps are intricately arranged with 432 symmetry within single cubic nanoparticles. In this study, we have achieved the fabrication of chiral silica molds through Au etching subsequent to the silica coating of Au helicoids. We demonstrate that these molds serve as geometrically confined reactors capable of producing chiral Ag, Pd, and Pt 432 helicoid III (Ag, Pd, and Pt helicoids). The morphology of the synthesized Ag, Pd, and Pt helicoids closely resembles that of the Au helicoids, exhibiting a superior g-factor compared to other reported chiral structures of each material. Notably, the Ag and Pd helicoids are found to be single-crystalline, with high-index planes exposed within the gaps. We believe that this silica mold-based approach can be generalized to synthesize chiral nanomaterials of various metal and even oxide materials.

Macro-Nanoporous Film with Cauliflower-Shaped Fibers for Highly Efficient Passive Daytime Radiative Cooling.

Passive daytime radiative cooling (PDRC) is a simple and effective cooling approach that does not consume any extra energy just by highly reflecting shortwave sunlight and highly radiating infrared heat through the atmospheric windows. In recent years, the application of photonic coolers and metamaterials for PDRC has been studied. However, they usually have complex processes and high precision requirements, which seriously limit large-scale fabrication. In this paper, a high-performance polyvinylidene difluoride-hexafluoropropylene (PVDF-HFP) PDRC fiber film was prepared by a simple and efficient electrospinning method combined with phase separation, and the obtained PVDF-HFP fibers have a cauliflower-shaped macro-nanoporous structure. The cauliflower-shaped structure provides more scattering sites of the fibers, and the fiber film with the macro-nanoporous morphology has a high scattering ability in the solar region, resulting in a high solar reflectivity of 99.65%. The PVDF-HFP porous film possesses an emissivity of 90.44% in the atmospheric window, and it can reach a maximum cooling temperature of 10.2 °C during the daytime. In addition, the excellent mechanical strength provides a guarantee for its large-scale practical application. This study offers an effective improvement strategy for the spectral performance of polymer fiber films, which is meaningful for green cooling management and reduction of carbon emission.

Investigating the potential of optical metamaterials with highly dispersive solitons in twin couplers with stochastic perturbations and white noise effects

This study emphasizes a unique contribution as we investigate the dimensionless version of the perturbed stochastic NLSE within an optical metamaterial-designed coupler. We employ Kudryashov's sextic-power law nonlinearity to present this formulation, and, for the first time, we introduce multiplicative white noise using the Ito interpretation. This study aims to bridge the gap in understanding the influence of stochastic effects on optical metamaterials and offers valuable insights for future research in this field. The methods introduced include enhancements to Kudryashov's approach and extensions to the modified sub-ODE technique. These methodologies are leveraged to derive a wide array of solutions, such as bright, dark, singular, and combined solitons, with some solutions presented using Jacobi and Weierstrass elliptic functions. The effectiveness of these methods in addressing various nonlinear partial differential equations is demonstrated through the results. The study further delves into how random noise impacts optical solitons and analyzes soliton behavior when subjected to different conditions. It is observed that white noise plays a crucial role in the formation of optical solitons within the coupler and that these solitons demonstrate highly dispersive properties under specific scenarios. These insights are pivotal for designing and innovating optical metamaterials for diverse technological uses.

Proximal High-Index Metamaterials based on a Superlattice of Gold Nanohexagons Targeting the Near-Infrared Band.

Plasmonic nanoparticles can be assembled into a superlattice, to form optical metamaterials, particularly targeting precise control of optical properties such as refractive index (RI). The superlattices exhibit enhanced near-field, given the sufficiently narrow gap between nanoparticles supporting multiple plasmonic resonance modes only realized in proximal environments. Herein, the planar superlattice of plasmonic Au nanohexagons (AuNHs) with precisely controlled geometries such as size, shape, and edge-gaps is reported. The proximal AuNHs superlattice realized over a large area with selective edge-to-edge assembly exhibited the highest-ever-recorded RI values in the near-infrared (NIR) band, surpassing the upper limit of the RI of the natural intrinsic materials (up to 10.04 at λ = 1.5µm). The exceptionally enhanced RI is derived from intensified in-plane surface plasmon coupling across the superlattices. Precise control of the edge-gap of neighboring AuNHs systematically tuned the RI as confirmed by numerical analysis based on the plasmonic percolation model. Furthermore, a 1D photonic crystal, composed of alternating layers of AuNHs superlattices and low-index polymers, is constructed to enhance the selectivity of the reflectivity operating in the NIR band. It is expected that the proximal AuNHs superlattices can be used as new optical metamaterials that can be extended to the NIR range.

Investigation of chirped solutions in optical metamaterials having parabolic law nonlinearity and space-time dispersion

Investigation of chirped solutions in optical metamaterials having parabolic law nonlinearity and space-time dispersion

Inverse design of metamaterial for dual-band infrared camouflage along with dual-band thermal management

The optical metamaterial for infrared camouflage with thermal management is an artificial structure available to not only evade the detection of various thermal imagers operating in distinct infrared wavebands but also ensure the thermal stability of the target. However, designing such an optical metamaterial is challenging due to the necessity to optimize numerous structural parameters simultaneously, especially metamaterials that are compatible with multiple functions. Herein, this paper proposes a novel inverse design method, combining African vultures optimization algorithm (AVOA) with rigorous coupled-wave analysis (RCWA), to design an optical metamaterial capable of achieving infrared camouflage and thermal management compatibly. The proposed metamaterial enables dual-band infrared camouflage for mid-wave infrared (MWIR, 3–5 μm) and long-wave infrared (LWIR, 8–14 μm), along with thermal management through dual-band non-atmospheric windows of 5–8 μm and 14–17 μm. Comparing to other intelligent optimization algorithms, the AVOA is exceptionally efficient, which only takes less time than others to get better results. This work not only provides theoretical guidance to design an optical metamaterial for infrared camouflage with thermal management, but also has the potential to solve the multi-objective optimization problems of multi-band or wide-band radiative modulation.

Non-Foster approach to broadband optical metamaterials based on Lorentzian gain materials

All passive metamaterials are inherently narrowband due to fundamental dispersion-energy constraints, and their dispersive properties are usually approximated by a Lorentz model. However, there are broadband active metamaterials in the radio frequency (RF) regime based on negative capacitors with non-Foster dispersion properties. Non-Foster dispersion is usually considered as an “electronic-engineering trick” that cannot be applied at optical frequencies. Here, we demonstrate that the dispersion relation of a RF non-Foster capacitor is similar to that of an optical gain material described by a Lorentz model. This insight paves the way to realize non-Foster optical metamaterial structures. As the simplest example, we develop a broadband non-Foster optical epsilon-near-zero slab with a 1:10 bandwidth.

Bright and dark optical solitons in optical metamaterials using a variety of distinct schemes for a generalized Schrodinger equation

Purpose The purpose of this study is to investigate the nonlinear Schrödinger equation (NLS) incorporating spatiotemporal dispersion and other dispersive effects. The goal is to derive various soliton solutions, including bright, dark, singular, periodic and exponential solitons, to enhance the understanding of soliton propagation dynamics in nonlinear metamaterials (MMs) and contribute new findings to the field of nonlinear optics. Design/methodology/approach The research uses a range of powerful mathematical approaches to solve the NLS. The proposed methodologies are applied systematically to derive a variety of optical soliton solutions, each demonstrating unique optical behaviors and characteristics. The approach ensures that both the theoretical framework and practical implications of the solutions are thoroughly explored. Findings The study successfully derives several types of soliton solutions using the aforementioned mathematical approaches. Key findings include bright optical envelope solitons, dark optical envelope solitons, periodic solutions, singular solutions and exponential solutions. These results offer new insights into the behavior of ultrashort solitons in nonlinear MMs, potentially aiding further research and applications in nonlinear wave studies. Originality/value This study makes an original contribution to nonlinear optics by deriving new soliton solutions for the NLS with spatiotemporal dispersion. The diversity of solutions, including bright, dark, periodic, singular and exponential solitons, adds substantial value to the existing body of knowledge. The use of distinct and reliable methodologies to obtain these solutions underscores the novelty and potential applications of the research in advancing optical technologies. The originality lies in the novel approaches used to obtain these diverse soliton solutions and their potential impact on the study and application of nonlinear waves in MMs.

Synergy between photonic metamaterials and AI.

Synergy between photonic metamaterials and AI.

A surrogate-assisted extended generative adversarial network for parameter optimization in free-form metasurface design

Metasurfaces have widespread applications in fifth-generation (5G) microwave communication. Among the metasurface family, free-form metasurfaces excel in achieving intricate spectral responses compared to regular-shape counterparts. However, conventional numerical methods for free-form metasurfaces are time-consuming and demand specialized expertise. Alternatively, recent studies demonstrate that deep learning has great potential to accelerate and refine metasurface designs. Here, we present XGAN, an extended generative adversarial network (GAN) with a surrogate for high-quality free-form metasurface designs. The proposed surrogate provides a physical constraint to XGAN so that XGAN can accurately generate metasurfaces monolithically from input spectral responses. In comparative experiments involving 20000 free-form metasurface designs, XGAN achieves 0.9734 average accuracy and is 500 times faster than the conventional methodology. This method facilitates the metasurface library building for specific spectral responses and can be extended to various inverse design problems, including optical metamaterials, nanophotonic devices, and drug discovery.

Distribution of Single-Particle Resonances Determines the Plasmonic Response of Disordered Nanoparticle Ensembles.

Understanding how colloidal soft materials interact with light is crucial to the rational design of optical metamaterials. Electromagnetic simulations are computationally expensive and have primarily been limited to model systems described by a small number of particles-dimers, small clusters, and small periodic unit cells of superlattices. In this work we study the optical properties of bulk, disordered materials comprising a large number of plasmonic colloidal nanoparticles using Brownian dynamics simulations and the mutual polarization method. We investigate the far-field and near-field optical properties of both colloidal fluids and gels, which require thousands of nanoparticles to describe statistically. We show that these disordered materials exhibit a distribution of particle-level plasmonic resonance frequencies that determines their ensemble optical response. Nanoparticles with similar resonant frequencies form anisotropic and oriented clusters embedded within the otherwise isotropic and disordered microstructures. These collectively resonating morphologies can be tuned with the frequency and polarization of incident light. Knowledge of particle resonant distributions may help to interpret and compare the optical responses of different colloidal structures, correlate and predict optical properties, and rationally design soft materials for applications harnessing light.

Novel highly dispersive soliton solutions in couplers for optical metamaterials: leveraging generalized Kudryashov’s Law of refractive index with eighth-order dispersion and multiplicative white noise

This article represents a significant advancement in the understanding of highly dispersive optical solitons within the context of optical metamaterials, leveraging a generalized form of Kudryashov’s law of refractive index. By integrating eighth-order dispersion and multiplicative white noise into the analysis, crucial elements in the development and optimization of sophisticated optical metamaterials are accounted for in this current paper for the first time. Through an improved direct algebraic method, a diverse range of soliton solutions are derived, encompassing bright, dark, singular, and straddled solitons. Moreover, the study goes beyond mere derivation by presenting exact solutions expressed using Jacobi and Weierstrass’s elliptic functions. This mathematical framework offers deeper insights into the dynamics of solitons within the investigated context. These findings substantially expand the theoretical underpinnings governing optical solitons in metamaterials, with direct implications for the design, and implementation of next-generation optical devices. The bridging of theoretical advancements with practical applications underscores the significance of this work. By elucidating precise control over soliton properties, it lays the groundwork for innovative solutions in optical communications and beyond. Also, this research serves as a crucial stepping stone towards realizing the full potential of optical metamaterials in shaping the future of optical technologies.

(Invited) Designing Plasmonic Photocatalysts

Nanostructured surfaces and colloids with designed optical functionalities - such as plasmonic and photonic nano and metamaterials - allow efficient harvesting of light at the nanoscale. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale [1-4]. One example are plasmonic and photonic catalysts, that can indeed confine solar energy into molecular regions [4-11].In this talk, I will present our recent efforts in order to understand the intricate realm of losses in plasmonic nanoparticles by studying this issue at the single-particle level. I will present a series of studies trying to correlate plasmonic photocatalytic activity with reactivity, temperature and field at the nanoscale. Our fundamental understanding of light-matter interaction in these systems can hopefully contribute to the rational design of future nanocatalysts; influencing diverse applications such as photocatalysis and temperature management, among others [1-11].