2D Photonic Crystals Research Articles

Full-space wavefront control enabled by a bilayer metasurface sandwiching 1D photonic crystal.

Metasurfaces, composed of sub-wavelength structures, have a powerful capability to manipulate light propagations. However, metasurfaces usually work either in pure reflection mode or pure transmission mode. Achieving full-space manipulation of light at will in the optical region is still challenging. Here we propose a design method of full-space meta-device containing a bilayer metasurface sandwiching 1D photonic crystal to manipulate the transmitted and reflected wave independently. To provide a proof-of-concept demonstration, a device is proposed to show the light focusing in transmission and a vortex beam in reflection. Meanwhile, a device focusing the reflected light with oblique 45° incidence and the transmitted light with normal incidence is designed to indicate its application potential in augmented reality (AR) application. Our design provides a promising way to enrich the multifunctional meta-devices for potential applications.

A meta-analysis of butterfly structural colors: their color range, distribution and biological production.

Butterfly scales are among the richest natural sources of optical nanostructures, which produce structural color and iridescence. Several recurring nanostructure types have been described, such as ridge multilayers, gyroids and lower lamina thin films. While the optical mechanisms of these nanostructure classes are known, their phylogenetic distributions and functional ranges have not been described in detail. In this Review, we examine a century of research on the biological production of structural colors, including their evolution, development and genetic regulation. We have also created a database of more than 300 optical nanostructures in butterflies and conducted a meta-analysis of the color range, abundance and phylogenetic distribution of each nanostructure class. Butterfly structural colors are ubiquitous in short wavelengths but extremely rare in long wavelengths, especially red. In particular, blue wavelengths (around 450 nm) occur in more clades and are produced by more kinds of nanostructures than other hues. Nanostructure categories differ in prevalence, phylogenetic distribution, color range and brightness. For example, lamina thin films are the least bright; perforated lumen multilayers occur most often but are almost entirely restricted to the family Lycaenidae; and 3D photonic crystals, including gyroids, have the narrowest wavelength range (from about 450 to 550 nm). We discuss the implications of these patterns in terms of nanostructure evolution, physical constraint and relationships to pigmentary color. Finally, we highlight opportunities for future research, such as analyses of subadult and Hesperid structural colors and the identification of genes that directly build the nanostructures, with relevance for biomimetic engineering.

Optical field enhanced nonlinear optical performance of chalcogenide nanocomposite-based 1D photonic crystal

Optical field enhanced nonlinear optical performance of chalcogenide nanocomposite-based 1D photonic crystal

Effect of Aqueous Media over Stability and Optical Performance of Mesoporous 1D Photonic Crystals

Effect of Aqueous Media over Stability and Optical Performance of Mesoporous 1D Photonic Crystals

Genetic Optimization of the Y-Shaped Photonic Crystal NOT Logic Gate

The present paper is devoted to the actual problem of photonic crystal (PhC) logic gate design. The development of components for photonic digital computing systems will provide opportunities for high-efficient information processing. The use of 2D photonic crystals is one of the most promising approaches to designing interference logic gates. Photonic crystal band gap and use of lattice defects are giving opportunities for flexible control of waveguiding light. Interference logic gates of NOT, OR, AND, and XOR types based on the Y-shaped structure are well known. However, known realizations have limited energy efficiency. Earlier, a method for minimizing energy losses at the PhC waveguide bending based on genetic optimization of the PhC waveguide topology was proposed and investigated. In this paper, the genetic algorithm for optimization of the PhC interference logic gate of the NOT type was used. Optimization of the Y-shaped topology allowed for an increase in the energy efficiency of the logic gate to 95%. A description of the developed numerical procedure as well as computer simulation results are presented. The developed procedure includes the possibility of taking into account the limitations of the technology to be used for the realization of a designed 2D PhC structure.

All-optical 8-QAM signal demodulator based on 2D photonic crystals

This paper proposes a novel two-dimensional photonic crystal-based 8-QAM signal demodulator with a unique combination of nonlinear cavities and line defects. It consists of chalcogenide cylinders arranged in a square lattice against an air background. The proposed structure enables 8-QAM signal demodulation in an all-optical environment. Instead of the photoelectric conversion process, the structure converts the communication signal into the corresponding optical logic signal by distinguishing the intensity and phase differences of the incident light. The performances are analyzed and calculated by using the finite difference time-domain method and the plane wave expansion method. Simulation results illustrate that the maximum response time of the demodulator is 1.067 ps, and the minimum light contrast ratio is 4.39 dB.

Degeneration of topological corner, hinge, and surface states in three-dimensional photonic crystals.

The third-order topological insulators based on three-dimensional (3D) photonic crystals (PCs) have hardly been achieved because the nontrivial bandgap in 3D PCs is difficult to form. In this Letter, we elaborately construct 3D Su-Schrieffer-Heeger lattice in which the periodic modulation of refractive index is uniform in three axis directions. The high-order topological PCs are characterized by the nontrivial bulk polarizations and the mirror eigenvalues. Such a structure can achieve topological 1-codimensional surface states, 2-codimensional hinge states, and 3-codimensional corner states. More importantly, it is found for the first time, to the best of our knowledge, that the topological states exhibit a degeneration behavior, i. e., the corner, and hinge state, or corner and surface states coexist at nearly the same frequency, but maintain their own mode properties. The multiple topological states in 3D PCs as well as the degeneration of topological states will open a new window for the study of topological photonics.

Stimuli‐responsive hydrogel microgels on porous silicon one‐dimensional photonic crystals: Tapping the full potential for optical sensor applications

AbstractPorous silicon 1D photonic crystals, namely rugate filters, are covered with a loosely packed hexagonally ordered array of stimuli‐responsive hydrogel microgels, and the optical properties of the resulting hybrid sensor are thoroughly investigated. For this purpose, both rugate filters with and without hydrogel microgel on top are immersed in ethanol/water mixtures possessing different compositions and NaCl solutions. Reflectance spectra of all samples are taken and analyzed concerning the spectral positions and reflectance intensity of the strong peak related to the photonic crystal rugate peak as well as the side bands resulting from Fabry–Pérot interference at the interfaces bordering the porous silicon. For the latter analysis, a Fourier transform is applied to the side bands for calculating the effective optical thickness (EOT). Thereby it can be shown that the spectral position of both the rugate peak and the EOT peak is best suited for monitoring refractive index changes in the immersion medium whereas the swelling and collapse of the stimuli‐responsive hydrogel microgel can be only detected by variations in the amplitude of the rugate peak and the EOT peak. These results are confirmed by simulations using a simple geometrical model and shall serve as guide for developing tailor‐made optical sensors.

Lattice Transformation-Induced Retroreflective Structural Colors.

Retroreflective structural colors can usually be achieved based on interference combined with a total internal reflection mechanism or diffraction of a monolayer hexagonal two-dimensional (2D) colloidal array. Here, a novel retroreflective structural color was generated based on a hexagonal-parallelogram lattice transformation by stretching 3D photonic crystals with nonclosely packed long-range order. Compared to previous retroreflective colors, this new retroreflective color exhibits two unique off/on color switches: (1) a strain-dependent off/on color switch along the stretching direction and (2) a sample horizontal rotation angle-dependent off/on color switch under the fixed strain. These strain-responsive retroreflective colors are ideal candidates for visually sensing kinesio tapes' strain in practical applications and anticounterfeiting. This work reveals a new structural color regulation mechanism and will advance potential applications in anticounterfeiting, sensing, displays, etc.

Disentangled Higher‐Orbital Bands and Chiral Symmetric Topology in Confined Mie Resonance Photonic Crystals

AbstractTopological phases based on tight‐binding models have been extensively studied in recent decades. By mimicking the linear combination of atomic orbitals in tight‐binding models based on the evanescent couplings between resonators in classical waves, numerous experimental demonstrations of topological phases have been successfully conducted. However, in dielectric photonic crystals, the Mie resonances' states decay too slowly as , leading to intrinsically different physics between tight‐binding models and dielectric photonic crystals. Here, a confined Mie resonance photonic crystal is proposed by embedding perfect electric conductors between dielectric rods, creating the chiral symmetric band structure which ideally matches tight‐binding models with nearest‐neighbour couplings. As a consequence, disentangled band structure spanned by higher atomic orbitals is observed. Moreover, the result provides an effective route to achieve a 3D photonic crystal with a complete photonic bandgap and third‐order topology. The implementation offers a versatile platform for studying exotic higher‐orbital bands and achieving tight‐binding‐like 3D topological photonic crystals.

Tri-phase photonic crystal emitter for thermophotovoltaic systems

Thermophotovoltaics (TPVs) are devices that convert thermal radiation into electricity using a low-bandgap photovoltaic (PV) cell. While the theoretical efficiency can approach the Carnot limit, designing a TPV selective emitter that is spectrally matched with the PV cell's bandgap and is stable at high temperatures is critical for achieving high-efficiency systems. Photonic crystal (PhC) emitters can provide excellent spectral control, but prior experimental designs lack the thermal stability required for high-performance TPVs. In this study, a tri-phase PhC emitter design is proposed and optimized. The tri-phase design introduces an additional material in one of the alternating layers of an existing 1D PhC emitter, potentially stabilizing it at high temperatures. BaZrO3 is introduced in the CeO2 layers of a CeO2/MgO PhC emitter. Stanford Stratified Structure Solver (S4) is used to model the emittance of multiple tri-phase PhC variations. The parameter for optimization is the spectral efficiency of the emitter. The structure with the highest spectral efficiency is only 0.02% less efficient than the original design. The structure with the lowest spectral efficiency is only 0.28% less efficient. Therefore, any tri-phase variation can be applied to existing PhC emitters without compromising on their spectral efficiency. Without the need for manufacturing specific parameters, the tri-phase PhC can be an inexpensive emitter for real world applications that may improve thermal stability without compromising on the spectral efficiency, making the practical applications of TPVs feasible.

Tuberculosis biomedical sensor based on on-chip nanocavity 2D photonic crystal with high sensitivity and quality factor

Tuberculosis (TB) stands as one of the most severe and fatal communicable diseases in the universe, in accordance with the World Health Organization (WHO). Before the COVID-19 pandemic, tuberculosis held the highest mortality rate due to an individual infection, surpassing even HIV/AIDS. The identification of the disease at its initial stages plays a crucial role in patient management and has the potential to enhance the chances of survival. This study presents a unique biomedical sensor based on a two-dimensional (2D) photonic crystal, which demonstrates high accuracy in diagnosing and distinguishing between regular and irregular strains of tuberculosis bacteria. The proposed sensor is designed, presented, and evaluated. It can identify different types of tuberculosis with ultra-high-quality factor and adequate sensitivity in comparison with related photonic detection methods. Also, the presented sensor features a simplistic design with a fabrication possibility using current technologies. The presented sensor exhibited an ultra-quality factor of 10731, an extremely small detection limit of 5.87 × 10-6, and a remarkable sensitivity of 1738.7 nm/RIU. A comprehensive overview of non-optical sensing methods is addressed and linked to the current work. A detailed comparative exploration of this study and associated photonic-based literatures are carried out to verify the efficiency and originality of the proposed sensor.

Hofstadter butterfly in optical multilayers

This research focuses on the theoretical examination of the propagation of electromagnetic waves in a multilayer structure in which the refractive index in each medium is modulated by a similar expression of Harper’s potential for the electronic 1D model, or, equivalently, to on-site energies in the Aubry–André model. We applied the transfer matrix approach to different multilayers, with a refractive index modulated by a similar expression of Harper’s potential to obtain the optical transmittance spectra for normal incidence. We calculate the transmittance spectrum as a function of frequency and the Harper model phase for two scenarios in order to search for probable edge states that might arise in this system: first, when the quarter wavelength ratio relates to layer thicknesses through njdj=λ0/4, with nj being the refractive index of the jth layer of the 1D photonic crystal and λ0 is the central wavelength; second, we consider the effects when the thicknesses of the layers are related by d2j=2d2j+1. Besides, to obtain the photonic equivalent for Hofstadter butterfly fractal spectra, we calculate the transmittance spectrum as a function of the periodicity control parameter of the Harper model at the critical point.

Strong Self‐Enhancement of Optical Nonlinearity in a Topological Insulator with Generation of Tamm State

AbstractAs new states of matter currently attracting broad attention in the optics field, topological insulators (TIs) present topologically‐protected conducting surface states surrounding insulating bulk and prominent third‐order optical nonlinearities in an ultrawide frequency range. Optical frequency conversion in TI nanofilms plays a crucial role in TI nonlinear optical functionalities, whose enhancement is in demand for high‐performance devices. Herein, an optical Tamm state is observed between the Sb2Te3 TI nanofilm and 1D photonic crystal (PC) with a self‐enhancement behavior of optical nonlinearity in the TI nanofilm. The experiments demonstrate that there exists a distinct reflection dip in the forbidden band of the PC, which is attributed to the appearance of Tamm state in the TI/PC structure. The wavelength of the TI‐based Tamm state possesses a nearly linear redshift with increasing TI film thickness. The measurements are in excellent agreement with simulation and theoretical calculations. Moreover, a strong third‐harmonic generation reinforcement of 30‐fold is experimentally observed in a 90 nm Sb2Te3 film, which stems from the field enhancement induced by the TI self‐excited Tamm state at the fundamental frequency. This work opens a new door for generation of optical Tamm states and applications of TIs in high‐efficiency nonlinear optical functionalities, especially frequency conversion.

Unsupervised machine learning to classify the confinement of waves in periodic superstructures.

We propose a rigorous method to classify the dimensionality of wave confinement by utilizing unsupervised machine learning to enhance the accuracy of our recently presented scaling method [Phys. Rev. Lett.129, 176401 (2022)10.1103/PhysRevLett.129.176401]. We apply the standard k-means++ algorithm as well as our own model-based algorithm to 3D superlattices of resonant cavities embedded in a 3D inverse woodpile photonic band gap crystal with a range of design parameters. We compare their results against each other and against the direct usage of the scaling method without clustering. Since the clustering algorithms require the set of confinement dimensionalities present in the system as an input, we investigate cluster validity indices (CVIs) as a means to find these values. We conclude that the most accurate outcome is obtained by first applying direct scaling to find the correct set of confinement dimensionalities, and subsequently utilizing our model-based clustering algorithm to refine the results.

Wide-angle high-performance polarizers based on all-elliptical-metamaterial one-dimensional photonic crystals

As a class of all-dielectric metamaterials, elliptical metamaterials (EMMs) with elliptical iso-frequency curves provide a lossless platform to manipulate light with unity efficiency. Herein, we select two kinds of EMMs as the elements to constitute a special class of one-dimensional (1D) photonic crystals (PCs) called all-EMM 1D PCs and realize polarization-sensitive photonic bandgaps (PBGs). Enabled by the polarization-sensitive property of the PBG, we achieve a wide-angle high-performance polarizer. The maximum polarization extinction ratio reaches 1.82 × 104 and the width of the operating angle range reaches 36.07°. Besides, the performance of the polarizer demonstrates robustness against the layer thickness. The all-EMM 1D PCs are 1D nanostructures completely consisting of dielectric thin films, which can be much easily fabricated compared with 2D and 3D nanostructures. Our work provides a lithography-free recipe to design wide-angle high-performance polarizers.

Structuring light beams via nonlinear diffraction in 3D nonlinear photonic crystal

We show that nonlinear diffraction in nonlinear photonic crystal offers a convenient way to generate structured light at new frequencies. To this end we fabricate a 3D nonlinear photonic crystal containing two layers of fork-shaped ferroelectric domain gratings. Illumination of the structure by a fundamental Gaussian beam leads to the generation of two co-propagating second harmonic vortices with opposite topological charges, whose subsequent interference forms Hermite–Gaussian (HG) beams in far field.

A Theoretical Approach for Detecting the Chikungunya Virus Based on 1D Photonic Crystals

In the current study, it is aimed at using defective 1D photonic crystals (PCs) to detect the chikungunya virus in various healthy and diseased blood samples composed of plasma, platelets, red blood cells, and uric acid. The proposed PC structure has 14 periods and consists of repeating SiC and SiO2 layers with a central cavity layer. When blood samples are injected into the cavity layer, the transmittance spectrum is examined theoretically by using a transfer matrix approach to determine how the wavelength of the defect mode changes. The cavity layer is 540 and 648 nm thick, and the work is carried out at different angles of incidence. The performance of the sensor is quantified by computing the sensitivity, figure of merit, quality factor, and limit of detection values of the sensor for various blood samples. The maximum sensitivity is 1205.5 nm RIU−1 and detection limit of the order is 10−6 in this proposed work. A lower value of sensor resolution of 0.01218 is also achieved. Such a high‐performance sensor is suitable for biosensing applications with better sensing capabilities.

Sol-Gel Barium Titanate Nanohole Array as a Nonlinear Metasurface and a Photonic Crystal.

The quest of a nonlinear optical material that can be easily nanostructured over a large surface area is still ongoing. Here,wedemonstrate a nanoimprinted nonlinear barium titanate2D nanohole array that shows the optical properties of a 2D photonic crystal and a metasurface, depending on the direction of the optical axis. The challenge of nanostructuring the inert metal-oxide is resolved by direct soft nanoimprint lithography with sol-gel derived barium titanate enabling critical dimensions of 120 nm with aspect ratios of five. The nanohole array exhibits a photonic bandgap in the infrared range when probed along the slab axis, while lattice resonant states are observed in out-of-plane transmission configuration. The enhanced light-matter interaction from the resonant structure enables to increase in the second-harmonic generation in the near-ultraviolet by a factor of 18 illustrating the potential in the flexible fabrication technique for barium titanate photonicdevices.

Forensic-level security using non-imitable anticounterfeiting films: Humidity-sensitive 1D photonic crystals with UV-tunable color response and their encryption using small aldehydes

Although considerable progress has been made in anticounterfeiting film technologies, developing difficult-to-imitate novel anticounterfeiting films is still challenging. Herein, we report novel photopatternable one-dimensional photonic crystal (1D PC)-based anticounterfeiting films, whose colors can be changed by human breath and which can be encrypted and decrypted using small aldehydes and hydrochloric acid, respectively. A photo-crosslinkable TiO2–copolymer hybrid (Ti70) and primary-amine-containing copolymer (P(AEMA97-co-BPA3)–NH2) were prepared and utilized to fabricate 11-layered 1D PC (TiNH2 PC). In addition, using UV post-treatment with customized photomasks, TiNH2 PCs with hidden photopatterns that showed tunable humidity-responsive bright color contrast could be fabricated. However, after exposure to aldehydes, the TiNH2 PC showed reduced or no color shifts in response to further changes in the relative humidity. This is because the hydrophilicity of the P(AEMA97-co-BPA3)–NH2 layers decreased when they converted to P(AEMA97-co-BPA3)-imine layers under aldehyde exposure. However, the aldehyde-exposed TiNH2 PC could be reversibly recycled to its pristine state by simply immersing it in a hydrochloric acid solution (1 M) for 30 min. These findings provide insights into fabricating various colorimetric sensors as non-imitable anticounterfeiting films with selective encryption/decryption for achieving forensic-level security.