Periodic Dielectric Structures Research Articles

Effect of random structural variations on the optical properties of honeycomb photonic crystals

Periodic dielectric structures called photonic crystals are being used in various sensors and devices. Since photonic crystals are designed to operate within certain frequency ranges, accuracy in structure becomes important. In this work, we investigate the effects of two types of randomness, surface roughness and positional randomness, on the optical properties of the honeycomb photonic crystal. We employed the plane wave expansion method to investigate the effects of random perturbations of the shape and the position of the structure on the density of states. We also employ the finite-difference time-domain method to calculate the transmission spectrum as a consistency check. We find that both surface roughness and positional imperfections cause significant changes in the DOS. As the degree of randomness is increased, transverse electric and transverse magnetic gaps are narrowed and complete gaps totally disappear at 45 % of surface roughness.

Optothermal‐Enabled Reconfigurable Colloidal Photonic Crystals for Color and Spectrum Manipulation

AbstractColloidal photonic crystals (CPCs) are extensively utilized in nanoscale light manipulation due to their periodic dielectric structure. However, achieving spatial reconfigurability in CPCs remains a significant challenge, despite its importance for broader photonic applications in colloidal science. In this study, an optically induced thermoelectric field is generated by adding ionic surfactants to the solution, leading to the efficient formation of tightly assembled nanoparticles that exhibit the characteristics of CPC, which is termed optothermo‐CPC. Specifically, this CPC exhibits excellent spatial reconfigurability through the tuning of the optically induced thermoelectric field. This allows for the remote control of its position and shape, in a real‐time and high‐precision manner. Additionally, by changing the particle size, it is possible to tune the transmission spectrum and color. Additionally, optothermo‐CPC can navigate obstacles and possess a robust self‐healing ability. These highly adaptable and reconfigurable properties endow CPCs with significant potential for various photonic applications within complex fluidic environments.

Фотонные кристаллы: оптимизация характеристик и перспективы оптических приложений

Background: Photonic crystals (PCs) have emerged as a new material for light manipulation, providing unprecedented control over light-matter interaction. This unique capacity is due to their periodic dielectric structure, which may produce photonic band gaps that impact photon transmission. Objective: The article summarizes current advances in photonic crystal design and use, focusing on their significance in creating next-generation optical systems. Methods: The article performed a complete literature analysis, concentrating on the most recent PC production and characterization approaches. Innovative techniques like 3D printing, nanoimprint lithography, self-assembly, and advanced computational modelling were studied in depth to optimize their optical characteristics. Results: Recent studies show that PC manufacturing accuracy has increased significantly, allowing for more effective light manipulation and enhanced optical device functioning. Applications such as ultrasensitive sensors, improved optical fibers, and innovative laser designs demonstrate PCs' rising value. Conclusion: The ongoing advancement of photonic crystal technology is laying a solid basis for the next generation of optical devices. These developments improve existing applications and provide opportunities to investigate new functionality in optical and other electromagnetic systems. Incorporating PCs into numerous technical sectors holds the prospect of significant advances in both commercial and scientific fields.

Stealthy and hyperuniform isotropic photonic band gap structure in 3D.

In photonic crystals, the propagation of light is governed by their photonic band structure, an ensemble of propagating states grouped into bands, separated by photonic band gaps. Due to discrete symmetries in spatially strictly periodic dielectric structures their photonic band structure is intrinsically anisotropic. However, for many applications, such as manufacturing artificial structural color materials or developing photonic computing devices, but also for the fundamental understanding of light-matter interactions, it is of major interest to seek materials with long range nonperiodic dielectric structures which allow the formation of isotropic photonic band gaps. Here, we report the first ever 3D isotropic photonic band gap for an optimized disordered stealthy hyperuniform structure for microwaves. The transmission spectra are directly compared to a diamond pattern and an amorphous structure with similar node density. The band structure is measured experimentally for all three microwave structures, manufactured by 3D laser printing for metamaterials with refractive index up to . Results agree well with finite-difference-time-domain numerical investigations and a priori calculations of the band gap for the hyperuniform structure: the diamond structure shows gaps but being anisotropic as expected, the stealthy hyperuniform pattern shows an isotropic gap of very similar magnitude, while the amorphous structure does not show a gap at all. Since they are more easily manufactured, prototyping centimeter scaled microwave structures may help optimizing structures in the technologically very interesting region of infrared.

Complete photonic bandgap in a low-index two-dimensional quasicrystalline structure.

A bandgap in the continuum spectrum of photons in addition to its basic physical significance has strong potential for applications. Analogous to semiconductor crystals for electrons, periodic dielectric structures named photonic crystals were proposed to control photon flux propagation. In our search for low refractive index (RI) structures with a photonic bandgap, initial research efforts were focused on photonic crystal design, while aperiodic structures allow lower values of refractive index contrast to sustain a photonic bandgap. Here, we report on a two-dimensional quasicrystalline structure designed as a set of one-dimensional lattices merged into a single binary structure made of two materials with refractive index contrast 2|n1 - n2|/(n1 + n2) = 0.16 and even less in theory. We confirmed the theoretical prediction of bandgap exciting by measuring the radiation suppression of a dipole source placed in the center of the quasicrystalline structure. The full-wave numerical simulations and the experimental study appear to be in good agreement with the theoretical model.

Design of a Neural Network Model for Point-Defect Microcavities in Two-Dimensional Silicon-Based Dielectric Column Photonic Crystals

Currently, circuits are becoming more and more highly integrated, but current electronic chip technology has difficulty in meeting the requirements for increased data transmission speed and capacity because of its characteristics of increased energy loss due to interactions between electronic components. In contrast, photonic technology is a promising solution due to its characteristics of high speed, wide bandwidth, and low interaction. Photonic crystals are materials with an artificial periodic dielectric structure, with photonic bandgap and localization properties that are critical to their performance. Photonic crystals, which use photons as an information transfer medium, allow flexible control of photon propagation, just as electrons are controlled in semiconductors, and the study of multifunctional photonic crystals is important for the construction of integrated optical circuits. This paper proposes a neural network-based model to analyze and predict the optical properties of point defect microcavities in 2D silicon-based dielectric column photonic crystals. By modeling the complex relationship between the structural parameters of the photonic crystal and its optical response, a theoretical approach for the design of 2D silicon dielectric column photonic crystals can be provided.

Polynomial expansion method for full wave three-dimensional analysis of dielectric waveguides and periodic structures

In summary, the utilization of Legendre polynomial expansion in the modal analysis of stratified dielectric layers with doubly periodic permittivity profiles offers a departure from conventional methods. This novel approach, grounded in the analytical projection of Maxwell’s equations onto the Hilbert space defined by Legendre polynomials, results in well-behaved algebraic equations. These equations, in turn, facilitate the derivation of propagation constants and electromagnetic field profiles, circumventing issues related to numerical instability and oscillatory behavior. Moreover, the method's adaptability to extend its application to nonperiodic dielectric waveguides through the periodic repetition concept further underscores its versatility and potential impact in electromagnetic field analysis. Finally, to validate the proposed method, we conducted a comparative analysis of three standard test cases against previously reported results in the literature. The comparison showcased a high level of agreement, affirming the accuracy and efficacy of the presented approach.

Unidirectional Lasing from Mirror-Coupled Dielectric Lattices.

This paper reports how a hybrid system composed of transparent dielectric lattices over a metal mirror can produce high-quality lattice resonances for unidirectional lasing. The enhanced electromagnetic fields are concentrated in the cladding of the periodic dielectric structures and away from the metal. Based on a mirror-image model, we reveal that such high-quality lattice resonances are governed by bound states in the continuum resulting from destructive interference. Using hexagonal arrays of titanium dioxide nanoparticles on a silica-coated silver mirror, we observed lattice resonances with quality factors of up to 2750 in the visible regime. With the lattice resonances as optical feedback and dye solution as the gain medium, we demonstrated unidirectional lasing under optical pumping, where the array size was down to 100 μm × 100 μm. Our scheme can be extended to other spectral regimes to simultaneously achieve strongly enhanced surface fields and high quality factors.

Inverse design in photonic crystals.

Photonic crystals are periodic dielectric structures that possess a wealth of physical characteristics. Owing to the unique way they interact with the light, they provide new degrees of freedom to precisely modulate the electromagnetic fields, and have received extensive research in both academia and industry. At the same time, fueled by the advances in computer science, inverse design strategies are gradually being used to efficiently produce on-demand devices in various domains. As a result, the interdisciplinary area combining photonic crystals and inverse design emerges and flourishes. Here, we review the recent progress for the application of inverse design in photonic crystals. We start with a brief introduction of the background, then mainly discuss the optimizations of various physical properties of photonic crystals, from eigenproperties to response-based properties, and end up with an outlook for the future directions. Throughout the paper, we emphasize some insightful works and their design algorithms, and aim to give a guidance for readers in this emerging field.

Engineering Atomic-Scale Patterning and Resistive Switching in 2D Crystals and Application in Image Processing.

The ultrathin thickness of 2D layered materials affords the control of their properties through defects, surface modification, and electrostatic fields more efficiently compared with bulk architecture. In particular, patterning design, such as moiré superlattice patterns and spatially periodic dielectric structures, are demonstrated to possess the ability to precisely control the local atomic and electronic environment at large scale, thus providing extra degrees of freedom to realize tailored material properties and device functionality. Here,the scalable atomic-scale patterning in superionic cuprous telluride by using the bonding difference at nonequivalent copper sites is reported. Moreover, benefitting from the natural coupling of ordered and disordered sublattices,controllable piezoelectricity-like multilevel switching and bipolar switching with the designed crystal structure and electrical contact is realized, and their application in image enhancement is demonstrated. This work extends the known classes of patternable crystals and atomic switching devices, and ushers in a frontier for image processing with memristors.

Photonic management of silicon nanocylinder arrays to enhance photovoltaic performance

The light–matter interaction of subwavelength and periodic silicon (Si) nanostructures strongly correlates with their geometrical features, resulting in them being highly unsuitable for the practical development of Si-based photovoltaic applications. In this study, the concepts of effective medium and retrieval methods are needed to deal with the subwavelength periodic dielectric structure. Using finite-difference time-domain simulations, we study the interactions of electromagnetic radiation with a square array of dielectric rods parallel to the incident light, and the effective optical properties such as refractive index, permittivity, and permeability are calculated. Furthermore, the electric field distributions are also plotted for a deeper understanding of the energy changes within Si nanocylinder arrays (SiNCAs) under different incident wavelengths of radiation. By employing calculated optimized SiNCAs for the construction of hybrid solar cells, improved cell performances showing a conversion efficiency of 13.79% are demonstrated, with further estimation by electrical chemical measurements for a better understanding of the carrier transition. These are numerically and experimentally interpreted by the involvement of excellent light-trapping effects, delivering a method to design correlated photovoltaic devices.

A Generalized Polymer Precursor Ink Design for 3D Printing of Functional Metal Oxides

HighlightsA facile and generalized design strategy of polymer precursor inks was developed for direct ink writing of metal oxide into submicron 3D architectures.The Maillard reaction between polyethyleneimine and glucose endows the 3D-printed precursors with the excellent shape fidelity during high-temperature pyrolysis.As-printed 3D periodic dielectric structure with woodpile geometry shows a significant light-matter effect in mid-infrared region.

Hexagonal higher-symmetric dielectric periodic structures for planar graded-index lenses

We investigate dispersion properties of a hexagonal dielectric periodic structure that can be used to engineer dielectric graded-index lenses. The connection between the geometry of the hexagonal periodic structure and its symmetries is explained. Furthermore, we demonstrate that a hexagonal structure with increased symmetry is more isotropic than its conventional counterpart. To validate our analysis, we designed, manufactured, and measured a planar Luneburg lens antenna. The antenna has a neat fan-shaped beam from 23 to 31 GHz. The results validate the broadband operation of the periodic structure and could be of interest for the design of cost-effective antennas.

CIRCULAR POLARIZATION IN A $2\mathrm{D}$ PERIODIC ARTIFICIAL ANISOTROPIC DIELECTRIC MEDIUM

The phenomenon of polarization rotation in dielectric periodic structures is quite interesting. A similar structure was used in a sample with a 2D artificial periodic structure, where the plane wave propagation method was applied. Anisotropic dielectric constants were obtained, which were used for polarization rotation, and polarization rotation in an anisotropic medium was studied based on the dielectric permittivity of the effective medium. Those relationships, quantities, and parameters depending on the dielectric medium, dielectric permittivity, and 2D periodic structure have been studied and analyzed, which provide control of the degree of anisotropy, i.e. provide a distinction between fast and slow modes, which in turn provide the best polarization rotation per unit length.

Manipulating multi-spectral slow photons in bilayer inverse opal TiO2@BiVO4 composites for highly enhanced visible light photocatalysis

Manipulation of light has been proved to be a promising strategy to increase light harvesting in solar-to-chemical energy conversion, especially in photocatalysis. Inverse opal (IO) photonic structures are highly promising for light manipulation as their periodic dielectric structures enable them to slow down light and localize it within the structure, thereby improving light harvesting and photocatalytic efficiency. However, slow photons are confined to narrow wavelength ranges and hence limit the amount of energy that can be captured through light manipulation. To address this challenge, we synthesized bilayer IO TiO2@BiVO4 structures that manifested two distinct stop band gap (SBG) peaks, arising from different pore sizes in each layer, with slow photons available at either edge of each SBG. In addition, we achieved precise control over the frequencies of these multi-spectral slow photons through pore size and incidence angle variations, that enabled us to tune their wavelengths to the electronic absorption of the photocatalyst for optimal light utilization in aqueous phase visible light photocatalysis. This first proof of concept involving multi-spectral slow photon utilization enabled us to achieve up to 8.5 times and 2.2 times higher photocatalytic efficiencies than the corresponding non-structured and monolayer IO photocatalysts respectively. Through this work, we have successfully and significantly improved light harvesting efficiency in slow photon-assisted photocatalysis, the principles of which can be extended to other light harvesting applications.

Tuning the infrared resonance of thermal emission from metasurfaces working in near-infrared

We simulated numerically and demonstrated experimentally that the thermal emittance of a metasurface consisting of an array of rectangular metallic meta-atoms patterned on a layered periodic dielectric structure grown on top of a metallic layer can be tuned by changing several parameters. The resonance frequency, designed to be in the near-infrared spectral region, can be tuned by modifying the number of dielectric periods, and the polarization and incidence angle of the incoming radiation. In addition, the absorbance/emittance value at the resonant wavelength can be tuned by modifying the orientation of meta-atoms with respect to the illumination direction.

Morphology dependent excitation of hybrid Tamm-bandedge state in metal coated opal three-dimensional photonic crystal

The optical Tamm state is a type of electromagnetic mode that exists at the interface between a periodic dielectric structure and a metal layer. While optical Tamm states have recently gained attention as a potential replacement for surface plasmon polaritons in various applications, most of these demonstrations have been limited to one-dimensional periodic dielectric structures, such as Bragg mirrors. In this article, we present a detailed study on the existence of optical Tamm states at the interface between a metal layer and opal-like three-dimensional photonic crystal (3D-PhC) structures, with a focus on two types of devices with different cross-sectional morphologies. One device consisted of a corrugated silver layer on self-assembled PS opals, while the second one was realized by self-assembling PS opals on a thin flat gold film. Our experimental and numerical observations revealed a dip in the reflection spectra for both configurations, but a hybrid Tamm-PhC bandedge state was found to exist only between the corrugated metal layer and 3D-PhC. Importantly, the nature of the hybrid Tamm-PhC bandedge states was found to strongly depend on the thickness of the metal layer. In contrast, no mode hybridization was observed at the interface between the flat metal and 3D-PhC, and the reflection dip in this case corresponded to a PhC edge mode. Our demonstration highlights the potential for realizing cost-effective and integrated hybrid plasmonic-photonic crystal structures for sensitive nanophotonic sensors.

Tough and Transparent Photonic Hydrogel Nanocomposites for Display, Sensing, and Actuation Applications

Thermosensitive hydrogels with periodic dielectric structures displaying tunable structural color by temperature stimuli have attracted much research interest recently. However, reported thermosensitive photonic hydrogels either using the poly(N-isopropylacrylamide) (PNIPAM) bulk hydrogel as the responsive matrix or using PNIPAM microgels as the photonic building blocks have poor mechanical strength. Moreover, the expensive and time-consuming preparation process also limits their further application. In this work, a different strategy for preparing PNIPAM-based photonic hydrogel nanocomposite films with strong mechanical strength is proposed by incorporating a PNIPAM microgel film with the polyacrylamide (PAM) hydrogel. The preparation process is simple but efficient, and the obtained nanocomposite films have tunable mechanical strength by changing the crosslinking degree of the PAM hydrogels. More interestingly, the structural color of the nanocomposite films can be retained up to 80 °C (at least), much higher than those of previously reported PNIPAM-based photonic materials. In addition to being thermochromic, the film is sensitive to humidity, and the structural color-changing process is similar to the molting process of cicadas. Furthermore, the nanocomposite films have synchronous shape deformations and color changes and can be used as color-tunable soft actuators. The microgel film-capped photonic hydrogels provide a new strategy for the preparation of thermoresponsive photonic hydrogels and structural color-tunable actuators.

Study of radiation power spectra in the 1-D photonic periodic dielectric structure

We explored the thermal power radiation spectrum ρ (ω, T) of electromagnetic radiation in a 1D photonic periodic structure combining Si and Sio2 with truncated Sio2 media and an absorbing substrate. A theoretical model based on a transfer matrix for both normal and oblique incidence angles together with Kirchhoff’s second rule is used to predict the thermal radiation power spectrum. In order to study the radiation spectra, we used the TE and TM modes with truncation parameters and incidence angles in the mid, left, and right gap frequencies, which correspond to the mid, left, and right mid-gap temperatures. Layers nA&nB are A and B’s indices are considered to be constant and controlled in these modes.

Polaritonic Chern Insulators in Monolayer Semiconductors.

Systems with strong light-matter interaction open up new avenues for studying topological phases of matter. Examples include exciton polaritons, mixed light-matter quasiparticles, where the topology of the polaritonic band structure arises from the collective coupling between matter wave and optical fields strongly confined in periodic dielectric structures. Distinct from light-matter interaction in a uniform environment, the spatially varying nature of the optical fields leads to a fundamental modification of the well-known optical selection rules, which were derived under the plane wave approximation. Here we identify polaritonic Chern insulators by coupling valley excitons in transition metal dichalcogenides to photonic Bloch modes in a dielectric photonic crystal slab. We show that polaritonic Dirac points, which are markers for topological phase transition points, can be constructed from the collective coupling between valley excitons and photonic Dirac cones in the presence of both time-reversal and inversion symmetries. Lifting exciton valley degeneracy by breaking time-reversal symmetry leads to gapped polaritonic bands with nonzero Chern numbers. Through numerical simulations, we predict polaritonic chiral edge states residing inside the topological gaps. Our Letter paves the way for the further study of strong exciton-photon interaction in nanophotonic structures and for exploring polaritonic topological phases and their practical applications in polaritonic devices.