Search

In the last two decades, photonic crystals and structures that are based on them (photonic structures) have been examined and have been widely utilized in various optical applications. In this article, a theoretical and numerical model for the propagation of electromagnetic waves in multilayer dielectric structures is developed. The propagation of ultra-short light pulses in multilayer media and microresonators is investigated, and the energy reflection and transmission coefficients depending on the parameters of the environment and duration of the optical pulse are calculated. A method for calculating the transmission and reflection spectra of one-dimensional photonic crystal based on FDTD modeling with the emission of ultra-short optical pulses is proposed. To calculate the transmission and reflection spectrum of a one-dimensional photonic crystal and to simulate the propagation of ultra-short light pulses, in multilayer dielectric structures and microresonators, based on the numerical solution of Maxwell's equations with the finite difference approximation in the space-time domain, is performed.

Mechanochromic photonic crystals are attractive due to their force-dependent structural colors; however, showing unrecordable color and unsatisfied performances, which significantly limits their development and expansion toward advanced applications. Here, a thermal-responsive mechanochromic photonic crystal with a multicolor recordability-erasability was fabricated by combining non-close-packing mechanochromic photonic crystals and phase-change materials. Multicolor recordability is realized by pressing thermal-responsive mechanochromic photonic crystals to obtain target colors over the phase-change temperature followed by fixing the target colors and deformed configuration at room temperature. The stable recorded color can be erased and reconfigured by simply heating and similar color-recording procedures respectively due to the thermoswitchable on-off mechanochromism of thermal-responsive mechanochromic photonic crystals along with solid-gel phase transition. These thermal-responsive mechanochromic photonic crystals are ideal rewritable papers for ink-freely achieving multicolor patterns with high resolution, difficult for conventional photonic papers. This work offers a perspective for designing color-recordable/erasable and other stimulus-switchable materials with advanced applications. Mechanochromic photonic crystals are extremely attractive due to their force-dependent structural colors yet are limited by unrecordable color and unsatisfactory performances. Here, the authors report a thermal-responsive mechanochromic photonic crystal with multicolor recordability-erasability. [ABSTRACT FROM AUTHOR]

[Display omitted] • A convenient, panchromatic adjustable, re-writable photonic paper was prepared. • Photonic paper exhibited excellent pH, temperature, ionic strength, and ethanol responsive properties. • Photonic paper had fast wetting capability and strong reconfigurability. • A time–temperature dependent optical anti-counterfeiting system was constructed. Multi-responsive re-writable photonic paper (MRPP) with inverse opal structure was prepared by introducing [poly(hydroxyethyl methacrylate)-poly(dimethylamino ethyl methacrylate)-poly(N-isopropyl acrylamide)] (PHEMA-PDMAEMA-PNIPAM) multi-responsive gel (MRH) into silica (SiO 2) photonic crystal (PC) template. First, monomers such as HEMA, DMAEMA, and NIPAM were filled into the SiO 2 PC template. Then, MRPP with dynamic responsive color change capability was prepared by ultraviolet (UV) curing and hydrofluoric (HF) etching. MRPP has temperature, pH, ionic strength, and ethanol concertration responsiveness, fast wetting capability (∼1.4 s), strong re-writability (∼600 cycles), and the ability to use inorganic salt solution as an environmental-friendly ink to achieve panchromatic adjustment. Based on the multiple responsiveness of MRPP and its difference in solvent volatility, a time–temperature dependent optical anti-counterfeiting system with higher security level and fast identification of encryption was successfully constructed. The excellent performance of MRPP indicates its great application value in the field of re-writable photonic paper as well as information security. [ABSTRACT FROM AUTHOR]

Printable colloidal photonic crystals (CPCs) with unique photonic bandgaps and elaborate shapes have attracted significant interest due to their characteristics, such as simplicity of fabrication, adjustable structural colors, photobleaching resistance, and stimulus‐responsiveness. In this review, strategies for printing CPC patterns, including direct use of CPCs as inks, region‐selective modification on responsive (solvent, force, and temperature) CPC papers, and printing combined with lithography, are first summarized. Second, based on the advantages of CPC printing technology, their applications in color displays, coatings, sensors, anticounterfeiting labels, and information storage, are discussed in detail. Finally, the current challenges and outlook regarding CPC printing technology are proposed. [ABSTRACT FROM AUTHOR]

In this paper, our novel epitaxial nanowire‐based surface‐emitting lasers and self‐powered, wavelength distinguishable photodetectors in the ultraviolet are reviewed, and their potentially applications to portable sensing and imaging systems for extended environment awareness are discussed. [ABSTRACT FROM AUTHOR]

Constructing photonic crystals with core-shell structured nanoparticles is an important means for applications such as secure communication, anti-counterfeiting marking, and structural color camouflage. Nonetheless, the precise synthesis technology for core-shell structured nanoparticles at the hundred-nanometer scale faces significant challenges. This paper proposes a controlled synthesis method for core-shell structured nanoparticles using a template method. By using 100 nm diameter silica nanospheres as templates and coating them with a ferroferric oxide shell layer, SiO2@Fe3O4 core-shell structured nanoparticles with regular morphology and good uniformity can be obtained. The study experimentally investigated the effects of feed amount, modifiers, temperature, and feed order on the coating effect, systematically optimizing the preparation process. Centrifugal driving technology was used to achieve structural colors in the visible wavelength range. Additionally, the method successfully created well-defined and uniform core-shell structured nanoparticles using 200 nm diameter silica nanospheres as templates, demonstrating that this controllable synthesis method can effectively produce core-shell structured nanoparticles over a wide range of particle sizes. The template method proposed in this paper can significantly improve morphological regularity and size uniformity while effectively reducing the preparation cost of core-shell structured nanoparticles. [ABSTRACT FROM AUTHOR]

The ever‐increasing complexity of environmental pollutants urgently warrants the development of new detection technologies. Sensors based on the optical properties of hydrogels enabling fast and easy in situ detection are attracting increasing attention. In this paper, the data from 138 papers about different optical hydrogels (OHs) are extracted for statistical analysis. The detection performance and potential of various types of OHs in different environmental pollutant detection scenarios were evaluated and compared to those obtained using the standard detection method. Based on this analysis, the target recognition and sensing mechanisms of two main types of OHs are reviewed and discussed: photonic crystal hydrogels (PCHs) and fluorescent hydrogels (FHs). For PCHs, the environmental stimulus response, target receptors, inverse opal structures, and molecular imprinting techniques related to PCHs are reviewed and summarized. Furthermore, the different types of fluorophores (i.e., compound probes, biomacromolecules, quantum dots, and luminescent microbes) of FHs are discussed. Finally, the potential academic research directions to address the challenges of applying and developing OHs in environmental sensing are proposed, including the fusion of various OHs, introduction of the latest technologies in various fields to the construction of OHs, and development of multifunctional sensor arrays. [ABSTRACT FROM AUTHOR]

Photonic crystal ring resonators (PCRR) as momentous candidates for future photonic crystal integrated circuits (PCICs) draw worldwide attention. In this paper, different configurations are proposed based on single, parallel, and serial PCRRs. To be precise, the different coupling lengths and alignments have been discussed in double and triple PCRRs in parallel and serial configurations to achieve the highest efficiency concerning the desired applications such as an add-drop filter (ADF) and a power splitter. Moreover, in the achieved optimum double and triple PCRRs, the effect of coupling radius change has been discussed. [ABSTRACT FROM AUTHOR]

The study of optical topological insulators (PTIs) has revealed intriguing optical properties that diversify the ways in which light can be manipulated, offering significant potential for a wide range of applications. This paper presents a machine learning (ML)-based approach for the reverse design of optical PTIs. Using finite element methods, the paper addresses the challenge of computing the band structure of a dual-band model, enabling the construction of a dataset suitable for ML training. With the goal of maximizing dual-band bandgaps, the study employs the random forest algorithm to predict target parameters and further designs topological edge states. Leveraging these boundary state patterns, two different optical PTI beam splitters are devised, and their transmission coefficients and losses are computed. The results demonstrate that optical devices designed using topological boundary states exhibit enhanced stability and robustness. This approach offers a reliable solution for applications in fields such as optical communication and optical sensing. [ABSTRACT FROM AUTHOR]

This paper introduces a "photonic crystal fibre (PCF)"–based "surface plasmon sensor" that can measure the amount of glucose in urine. The sensor incorporates TiO2 and gold as plasmonic materials, arranged in layered configurations to enhance performance. The finite element approach is used to simulate the proposed sensor for measuring the amount of glucose in urine. A thin coating of analyte layer is coated over TiO2 layer of photonic crystal fibre (PCF) to enable external sensing. The sensing capacity is investigated for the four different glucose concentration levels—2.5gm/dl, 5gm/dl, 10gm/dl and 20gm/dl—whose equivalent refractive index (RI) is 1.338, 1.341, 1.346 and 1.358 respectively. A perfectly matched layer (PML) serves as the boundary condition for the topmost layer of the PCF. By varying the geometrical parameters, an optimized structural design is obtained which achieves a wavelength sensitivity of 4583.33 nm/RIU and amplitude sensitivity of 219.065 RIU−1 respectively. Experimental validation for different urine samples demonstrated better accuracy and sensitivity than the available methods. [ABSTRACT FROM AUTHOR]

In the paper, a circularly polarized (CP) frequency beam-scanning antenna based on photonic crystal (PC) is proposed, which possesses the characteristics of eliminating open-stopband (OSB). In the microwave field, the PC is typically constructed by embedding the air or metal column into the material. However, it is difficult for the PC with perfect magnetic conductor walls to accomplish the degeneracy of eigenmodes at the Γ point. Additionally, antennas based on the PC with perfect electric conductor walls exhibit a narrow scanning angle. The proposed unit based on 1D PC possesses perfect electric and magnetic conductor walls. The unit can not only eliminate OSB but also has a wide scanning range. In addition, the unit breaks into the original symmetrical field distributions of 1D PC. Based on the perturbation theory, leaky-wave slots can be designed to generate electromagnetic waves with the CP characteristics. And a CP antenna based on the unit is designed. The antenna can achieve a 70° beam-scanning within the entire operating band (7.6–9.2 GHz), and the variation of the realized gains is below 1.0 dBi around the broadside frequency. Simultaneously, the antenna is fabricated and measured. The measured results are in accordance with the simulation, which validates the success of the design. [ABSTRACT FROM AUTHOR]

Biomedical silk protein optics has become the subject of intensive research aimed at solving the challenges associated with traditional medical devices in terms of biocompatibility and performance balance. With its significant potential for biomedical applications in the field of drug storage and wound monitoring, it is dedicated to reducing the perturbation of neighbouring tissues. The transparency and biocompatibility of silk proteins make them ideal materials in the field of optical device fabrication, effectively overcoming the challenges posed by conventional materials. In this paper, we explore in detail the complex aspects of the design, synthesis and application related to biomedical silk protein optical devices and comprehensively analyse the potential use of silk protein-centric microstructures (e.g., micropillars, microneedles, and photonic crystals) in the development of optical devices. This review also offers insights into the challenges of applying silk protein optical devices in healthcare and their future trends, aiming to provide a comprehensive overview of the advances, potential impacts and emerging research directions in the field of biomedical silk protein optical devices. [ABSTRACT FROM AUTHOR]

This paper seeks to progress the field of topological photonic crystals (TPC) as a promising tool in face of construction flaws. In particular, the structure can be used as a novel temperature sensor. In this regard, the considered TPC structure comprising two different PC designs named PC1 and PC2. PC1 is designed from a stack of multilayers containing Silicon (Si) and Silicon dioxide (SiO2), while layers of SiO2 and composite layer named hyperbolic metamaterial (HMM) are considered in designing PC2. The HMM layer is engineered using subwavelength layers of Si and Bismuth Germinate, or BGO ( Bi 4 Ge 3 O 12 ). The mainstay of our suggested temperature sensor is mainly based on the emergence of some resonant modes inside the transmittance spectrum that provide the stability in the presence of the geometrical changes. Meanwhile, our theoretical framework has been introduced in the vicinity of transfer matrix method (TMM), effective medium theory (EMT) and the thermo-optic characteristics of the considered materials. The numerical findings have extensively introduced the role of some topological parameters such as layers' thicknesses, filling ratio through HMM layers and the periodicity of HMM on the stability or the topological features of the introduced sensor. Meanwhile, the numerical results reveal that the considered design provides some topological edge states (TESs) of a promising robustness and stability against certain disturbances or geometrical changes in the constituent materials. In addition, our sensing tool offers a relatively high sensitivity of 0.27 nm/°C. [ABSTRACT FROM AUTHOR]

In this paper, an attempt has been made to investigate a one-dimensional photonic crystal containing N-doped germanium semiconductor as a nonlinear defect layer with an intensity-dependent refractive index, silica (SiO2) and zinc selenide (ZnSe) as crystal cells. Bistability of the TE polarization of the transmission spectrum due to the nonlinear property of the defect layer is investigated by the transfer matrix method (TMM). The refractive index of the germanium nonlinear semiconductor layer is simultaneously depending on the doping density and the intensity of the irradiated light. The changes in both factors are investigated. The impact on the transmission spectrum of the bistability threshold due to the change in the thickness of the defect layer, the thickness of other layers of crystal cells, and the angle of incident light are investigated. The nonlinear effect caused by light intensity as well as doped density effect on the germanium nonlinear semiconductor medium is used simultaneously. As a result, the nonlinear effect caused by the light intensity to create bistability is more than the doping density. [ABSTRACT FROM AUTHOR]

This paper proposes a unique configuration for an all-optical D Flip Flop (D-FF) utilizing a quasi-square ring resonator (RR) and T-Splitter, as well as NOT and OR logic gates within a 2-dimensional square lattice photonic crystal (PC) structure. The components realizing the all-optical D-FF comprise of optical waveguides in a 2D square lattice PC of 45 × 23 silicon (Si) rods in a silica (SiO2) substrate. The utilization of these specific materials has facilitated the fabrication process of the design, diverging from alternative approaches that employ an air substrate, a method inherently unattainable in fabrication. The configuration underwent examination and simulation utilizing both plane-wave expansion (PWE) and finite-difference time-domain (FDTD) methodologies. The simulation outcomes demonstrate that the designed waveguides and RR effectively execute the operational principles of the D-FF by guiding light as intended. The suggested configuration holds promise as a logic block within all-optical arithmetic logic units (ALUs) designed for digital computing optical circuits. The design underwent optimization for operation within the C-band spectrum, particularly at 1550 nm. The outcomes reveal a distinct differentiation between logic states '1' and '0', enhancing robust decision-making on the receiver side and minimizing logic errors in the photonic decision circuit. The D-FF displays a contrast ratio (CR) of 4.77 dB, a stabilization time of 0.66 psec, and a footprint of 21 μm × 12 μm. [ABSTRACT FROM AUTHOR]

The emergences of silicon-based photonic crystal (PhC) waveguides and two-dimensional (2D) PhC line-defect optical cavities have revolutionized the field of integrated photonics. In this paper, we design and fabricate a high-quality (high-Q) 2D silicon-based PhC optical cavity with integrated waveguides. We employ the 2D finite-difference time-domain (FDTD) method to simulate the cavity, considering two different thicknesses: 0.5 μm and 0.25 μm. By optimizing the line-defect and air-slot widths for the integrated PhC waveguides, we are able to achieve remarkable Q-factors for the PhC optical cavity. With a silicon thickness of 0.5 μm, the high-Q achieves an impressively high value of 8.01 × 106, while at a silicon thickness of 0.25 μm, it achieves 1.91 × 107. This research highlights the importance of design optimization and fabrication techniques in achieving high-Q optical devices using PhC and silicon-based structures. [ABSTRACT FROM AUTHOR]

Twisted moiré photonic crystal is an optical analog of twisted graphene or twisted transition metal dichalcogenide bilayers. In this paper, we report the fabrication of twisted moiré photonic crystals and randomized moiré photonic crystals and their use in enhanced extraction of light in light-emitting diodes (LEDs). Fractional diffraction orders from randomized moiré photonic crystals are more uniform than those from moiré photonic crystals. Extraction efficiencies of 76.5%, 77.8% and 79.5% into glass substrate are predicted in simulations of LED patterned with twisted moiré photonic crystals, defect-containing photonic crystals and random moiré photonic crystals, respectively, at 584 nm. Extraction efficiencies of optically pumped LEDs with 2D perovskite (BA)2(MA) n −1PbnI3 n +1 of n = 3 and (5-(2′-pyridyl)-tetrazolato)(3-CF3−5-(2′-pyridyl)pyrazolato) platinum(II) (PtD) have been measured. [ABSTRACT FROM AUTHOR]

This document discusses the significance of one-dimensional (1D) and two-dimensional (2D) nanomaterials in sensor technology. These materials offer advantages such as a high surface-to-volume ratio, quantum confinement effects, mechanical flexibility, versatile synthesis methods, and multifunctional capabilities. The document presents a collection of 11 papers that explore various aspects of nanomaterials in sensing applications, including synthesis, characterization, and application. The studies cover topics such as surface functionalization, defect engineering, and the applications of nanomaterials in gas sensing, biosensing, and environmental monitoring. The document emphasizes the need for continued research and interdisciplinary collaboration to further advance the development of nanomaterial-based sensors. [Extracted from the article]

We propose and investigate a novel coherent laser array design based on laterally coupled photonic crystal surface-emitting lasers (PCSELs). As a new type of semiconductor laser technology, PCSELs have field confinement in a planar cavity and laser beam emission in the surface normal direction. By engineering lateral couplings between PCSELs with heterostructure photonic crystal designs, we can achieve coherent operations from an array of PCSELs. In this paper, we demonstrate coherent operation from a passively coupled PCSEL array design. We fabricated PCSEL array devices on a GaAs-based quantum well heterostructure at a target wavelength of 1040 nm. Experimental results show that the 2-by-2 PCSEL arrays have spectral linewidth of 0.14–0.22 nm. Beam combining performance was characterized by self-interference experiments. Similar coherency between the PCSEL array and single PCSEL device was observed. Our compact PCSEL array designs by passive lateral coupling have potential applications in fields of on-chip photonic computing, quantum, and information processing. [ABSTRACT FROM AUTHOR]

Designing efficient narrow-band near-infrared photodetectors integrated on silicon for telecommunications remains a significant challenge in silicon photonics. This paper proposes a novel silicon-based hot-electron photodetector employing Tamm plasmons (Si-based TP-HE PD) for narrow-band near-infrared photodetection. The device combines a one-dimensional photonic crystal (1DPC) structure, an Au layer, and a silicon substrate with a back electrode. Simulation results show that the absorption of the TP device with a back electrode is 1.5 times higher than without a back electrode, due to increased absorption from multiple reflections between the back electrode and the 1DPC structure. Experimentally, the responsivity of the fabricated device reaches 0.195 mA/W at a wavelength of 1400 nm. A phenomenological model was developed to analyze the photoelectric conversion mechanism, revealing reasonable agreement between the theoretically calculated and experimentally measured internal quantum efficiencies. Additional experiments and simulations demonstrate the tunability of the resonance wavelength from 1200 nm to 1700 nm by adjusting structural parameters. The Si-based TP-HE PD shows potential for silicon-based optoelectronic applications, offering the advantages of a simple structure, low cost, and compatibility with silicon photonic integrated circuits. This work represents the first demonstration of a silicon-based hot electron NIR photodetector utilizing Tamm plasmons. [ABSTRACT FROM AUTHOR]

This paper addresses the inverse scattering problem for Maxwell's equations in three-dimensional anisotropic periodic media. We study a new imaging functional for the fast and robust reconstruction of the shape of anisotropic periodic scatterers from boundary measurements of the scattered field. The implementation of this imaging functional is simple and avoids the need to solve an ill-posed problem. The resolution and stability analysis of the imaging functional is investigated. Results from our numerical study indicate that this imaging functional is more stable than that of the factorization method and more accurate than that of the orthogonality sampling method in reconstructing periodic scatterers. [ABSTRACT FROM AUTHOR]

Silicon photonic waveguide resonators, such as microring resonators, photonic crystal waveguide cavities, and Fabry–Perot resonators based on the distributed Bragg reflectors, are key device components for silicon-based photonic integrated circuits (Si-PIC). For the Si-PIC with high integration density, the device footprints of the conventional photonic waveguide resonators need to be more compact. Inverse design, which is operated by the design expectation and different from the conventional design methods, has been investigated for reducing the photonic device components nowadays. In this paper, we inversely designed the silicon photonic waveguide reflectors for two target wavelengths: one is 1310 nm and the other is 1550 nm. The silicon photonic waveguide reflectors have reflectance of 0.99993 and 0.9955 for the wavelength of 1310 nm and 1550 nm each with 5-μm-long reflectors. Also, we theoretically investigated Fabry–Perot resonators based on the inversely designed photonic waveguide reflectors. Q factors of the Fabry–Perot resonators have been calculated to be 1.3 × 105 for the wavelength of 1310 nm and 2583 for the wavelength of 1550 nm. We have expected that the inversely designed photonic waveguide reflectors and their applications for the Fabry–Perot resonators can be utilized for compact passive/active device components such as wavelength filters, modulators, and external cavity lasers. [ABSTRACT FROM AUTHOR]

For realizing an all optical photonic crystal (PhC)-based Arithmetic Logic Unit (ALU), one needs an optical 4 to 1 digital multiplexer. This device is a logic circuit in which by using two control ports one can connect four input lines to the output port. In this paper we used nonlinear ring resonators combined with optical waveguides to realize an optical digital multiplexer inside two dimensional PhC structure. The final structure was simulated using finite difference time domain method. The simulation results show that the maximum time delay of the final structure is about 3 ps. [ABSTRACT FROM AUTHOR]

In this paper, a novel silicon nanoparticle-based sensor has been investigated. Bloch surface wave excitation in a one-dimensional photonic crystal using a silicon nanoparticle on the top defect layer is examined on various parameters. This paper compares the confinement of Bloch surface wave using with and without silicon nanoparticles. The confinement of surface waves is modified by varying the size of the silicon nanoparticle. The structural parameters are optimized for an 850 nm (nm) central wavelength. At the central wavelength of 850 nm, the confinement of surface waves gets modified by varying the size of the silicon nanoparticle. The proposed novel silicon nanoparticle-based sensor was investigated and its efficacy in terms of sensitivity, quality factor, and Figure of merit was evaluated. The sensitivity is demonstrated to be 148.88 Degree/Refractive index unit (RIU), with a quality factor of 10,146.83 nm and a figure of merit (FOM) of 1777.24 per Refractive index unit (RIU− 1) for sensors with a silicon nanoparticle-based multilayer structure. [ABSTRACT FROM AUTHOR]

In this paper, the dispersion characteristics of slotted photonic crystal waveguides (SPCWs) have been estimated for any arbitrary set of structural parameters using machine learning-based artificial neural network (ANN). The machine learning-based technique yields faster solutions of the three-dimensional eigenvalue equations, which otherwise require substantial time using the conventional plane wave expansion (PWE)-based numerical simulations. Most importantly, the novel contribution of the work lies in estimating the structural parameters of the SPCWs from the given specifications of the dispersion characteristics through an inverse computation. A simple feed-forward neural network has been employed for both the forward and inverse estimations. The computation performances using both the ANN model and PWE simulations are analyzed and compared. The research offers significant implications for the field of photonics. By employing machine learning techniques, particularly ANNs, researchers and engineers can swiftly and efficiently analyze the dispersion properties of SPCWs, facilitating rapid prototyping and optimization of photonic devices. Additionally, the capability to infer structural parameters from desired dispersion characteristics streamlines the design process, potentially leading to the development of customized waveguides tailored to specific applications. [ABSTRACT FROM AUTHOR]

A novel terahertz polarization isolator using a two-dimensional square lattice tellurium rod array is numerically investigated at the interesting band of 0.22 THz in this short paper. The isolator is designed by inserting six hexagonal tellurium rods into a fully polarized photonic crystals waveguide with high efficiency of −0.34 dB. The TE and TM photonic band gaps of the 7 × 16 tellurium photonic crystals are computed based on the plane wave expansion method, which happen to coincide at the normalized frequency domain from 0.3859(a/λ) to 0.4033(a/λ), corresponding to the frequency domain from 0.2152 to 0.2249 THz. The operating bandwidth of the tellurium photonic crystals waveguide covers 0.2146 to 0.2247 THz, calculated by the finite element method. The six hexagonal tellurium rods with smaller circumradii of 0.16a serve to isolate transverse electric waves and turn a blind eye to transverse magnetic waves. The polarization isolation function and external characteristic curves of the envisaged structure are numerically simulated, which achieves the highest isolation of −33.49 dB at the central frequency of 0.2104 THz and the maximum reflection efficiency of 98.95 percent at the frequency of 0.2141 THz. The designed isolator with a unique function and high performance provides a promising approach for implementing fully polarized THz devices for future 6G communication systems. [ABSTRACT FROM AUTHOR]

Bioinspired structural color represents a burgeoning field that draws upon principles, strategies, and concepts derived from biological systems to inspire the design of novel technologies or products featuring reversible color changing mechanisms, with significant potential applications for camouflage, sensors, anticounterfeiting, etc. This mini-review focuses specifically on the research progress of bioinspired structural color in the realm of camouflage. Firstly, it discusses fundamental mechanisms of coloration in biological systems, encompassing pigmentation, structural coloration, fluorescence, and bioluminescence. Subsequently, it delineates three modulation strategies—namely, photonic crystals, film interference, and plasmonic modulation—that contribute to the development of bioinspired structural color materials or devices. Moreover, the review critically assesses the integration of bioinspired structural color materials with environmental contexts, with a particular emphasis on their application in camouflage. Finally, the paper outlines persisting challenges and suggests future development trends in the camouflage field via bioinspired structural color. [ABSTRACT FROM AUTHOR]

In this paper, we study the nonlinear optical bistability (OB) in a symmetrical multilayer structure. This multilayer structure is constructed by embedding a nonlinear three-dimensional Dirac semimetal (3D DSM) into a Fabry–Perot cavity composed of one-dimensional photonic crystals. The OB phenomenon stems from the third order nonlinear conductivity of 3D DSM. The local field of resonance mode could enhance the nonlinearity and reduce the thresholds of OB. This structure achieves the tunability of OB due to the fact that the transmittance could be modulated by the Fermi energy. It is found that the OB threshold and threshold width could be remarkably reduced by increasing the Fermi energy of the 3D DSM. Besides, we also found that the OB curve depends heavily on the angle of incidence of the incident light, the structural parameters of the Fabry–Perot cavity, and the position of the 3D DSM inside the cavity. After parameter optimization, we obtained OB with a threshold of 10 6   V / m . We believe this simple multilayer structure could provide a reference idea for realizing low-threshold and tunable all-optical switching devices. [ABSTRACT FROM AUTHOR]

Responsive photonic crystal hydrogel sensors are renowned for their colorimetric sensing ability and can be utilized in many fields such as medical diagnosis, environmental detection, food safety, and industrial production. Previously, our group invented responsive photonic nanochains (RPNCs), which improve the response speed of photonic crystal hydrogel sensors by at least 2 to 3 orders of magnitude. However, RPNCs are dispersed in a liquid medium, which needs a magnetic field to orient them for the generation of structural colors. In addition, during repeated use, the process of cleaning and redispersing can cause entanglement, breakage, and a loss of RPNCs, resulting in poor stability. Moreover, when mixing with the samples in liquid, the RPNCs may lead to the contamination of the samples being tested. In this paper, we incorporate one-dimensional oriented RPNCs with agarose gel film to prepare heterogeneous hydrogel films. Thanks to the non-responsive and porous nature of the agarose gel, the protons diffuse freely in the gel, which facilitates the fast response of the RPNCs. Furthermore, the "frozen" RPNCs in agarose gel not only enable the display of structural colors without the need for a magnet but also improve the cycling stability and long-term durability of the sensor, and will not contaminate the samples. This work paves the way for the application of photonic crystal sensors. [ABSTRACT FROM AUTHOR]

In this paper, we designed and investigated a reduction-based method to synthesize controllably monodisperse superparamagnetic nano Fe3O4 colloidal clusters for magnetically responsive photonic crystals. It was shown that the addition of ascorbic acid (VC) to the system could synthesize monodisperse superparamagnetic nano Fe3O4 and avoided the generation of γ-Fe2O3 impurities, while the particle size and saturation magnetization intensity of nano Fe3O4 gradually decreased with the increase of VC dosage. Nano Fe3O4 could be rapidly assembled into photonic crystal dot matrix structures under a magnetic field, demonstrating tunability to various diffraction wavelengths. The nano Fe3O4 modified by polyvinylpyrrolidone (PVP) and silicon coated could be stably dispersed in a variety of organic solvents and thus diffracted different wavelengths under a magnetic field. This is expected to be applied in various scenarios in the field of optical color development. [ABSTRACT FROM AUTHOR]

Breast cancer is the most prevalent cancer in females in a large number of countries around the world. One in every twenty females gets confirmed to have breast cancer during their lifetime, though the number varies significantly by country. There are various conventional methods to spot the breast cancer cells, such as magnetic resonance imaging, X-ray mammography, biopsies, and ultrasound. The early identification of cancer cells helps to save many human lives. This paper investigates tumor detection in a breast phantom using a Photonic crystal (PhC) based hourglass terahertz patch antenna. This paper designed four different antenna structures: conventional hourglass patch antenna (with and without breast phantom) and PhC-based hourglass patch antenna (with and without breast phantom). The proposed PhC antenna models and the breast phantom are designed using the CST studio suite and analyzed the various antenna parameters. The observed S11 parameter for the proposed structures is − 21.50, − 25.34, − 33.78 and − 50.32 dB. The proposed antenna resonated in THz frequency, which does not affect human health and is safer due to non-ionizing characteristics. The suggested PhC structure is tiny, less expensive, lightweight, environmentally benign, and can be utilized as a primary screening technique for people with breast cancer, especially in resource-limited areas. [ABSTRACT FROM AUTHOR]

Inspired by the emerging field of twistronics, moiré photonic structures have attracted great interest. In this paper, we introduce the concept of the moiré Kagome lattice (MKL), which arises from the overlapping of a Kagome lattice at a commensurable angle of 38.211°. MKL exhibits a significantly broader main photonic bandgap (PBG) when compared to the traditional Kagome lattice. Through numerical simulations, we delved into the adjustable properties of the PBG of MKL by varying lattice parameters, including filling factors and materials. Meanwhile, we also observed the presence of photonic flatbands within the MKL structure. Specifically, the emergence of a super flat isolated flatband aids in achieving single-mode omnidirectional lasers and enhancing the omnidirectional electromagnetic interaction of materials, thereby expanding the applications of moiré photonic crystals. [ABSTRACT FROM AUTHOR]

In the present paper, the reflection and transmission properties of a one-dimensional photonic crystal made of alternate layers of isotropic dielectric medium and electro-optic nanocomposite structurally chiral medium (NSCM) are investigated. The electro-optic NSCM is a nanocomposite medium consisting structurally chiral material (SCM) where the silver nanoparticles are randomly dispersed inside it. The numerical results show three kinds of photonic bandgap in this structure, including traditional Bragg gap, circular Bragg gap and plasmonic absorption bandgap, which is due to the plasmonic resonance and absorption of the silver nanoparticles. The effect of the external low-frequency electric field is investigated on the reflection and transmission spectra of the structure. It is shown that the impact of the applied voltage depends on the value of the tilt angle and the maximum changes are experienced for the case of χ = 90 ∘ . Also, the results show that the width of the traditional and circular Bragg gaps is sensitive to the applied voltage; however, the variation of the circular Bragg gap is more noticeable. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In optical processing systems, multiplexer is used to design optical devices such as arithmetic logic unit (ALU) and shift register (SR). Through this paper, we investigate the application of nonlinear photonic crystal ring resonator (PhCRR) based on nonlinear Kerr effect for realizing an all optical 2 × 1 multiplexer. The structure consists of two PhCRRs and five optical waveguides using hexagonal lattice silicon (Si) rods with a background of air. Performance of all optical 2 × 1 multiplexer is replicated with the help of finite difference time domain (FDTD) procedure at a wavelength of 1571 nm, and simulations presented an ultra-compact optical structure with ultra-fast switching speed. [ABSTRACT FROM AUTHOR]

This paper presents a time- and cost-effective method for the large-area fabrication of photonic crystals with nanometer-scale features on the GaN material. The proposed technique utilizes e-beam lithography and double hard mask layers to enable the high aspect ratio etching of the nanoscale features. The double hard mask layer, which is a photoresist, platinum (Pt) and SiO2, is very strong against plasma etching, making it an effective barrier layer to protect the underlying material during the etching process. The fabricated photonic crystal exhibits a high aspect ratio and excellent uniformity over a large area. This technique can be used for the time-effective production of photonic crystals for various applications such as optical sensing, spectroscopy, and telecommunications. The method presented in this paper can also be extended to other material systems beyond GaN. The proposed approach provides a promising route to achieve the large-area fabrication of nanometer-scale structures with high aspect ratios using e-beam lithography. [ABSTRACT FROM AUTHOR]

Photonic crystals are artificial structures with a spatial periodicity of dielectric permittivity on the wavelength scale. This feature results in a spectral region over which no light can propagate within such a material, known as the photonic band gap (PBG). It leads to a unique interaction between light and matter. A photonic crystal can redirect, concentrate, or even trap incident light. Different materials (dielectrics, semiconductors, metals, polymers, etc.) and 1D, 2D, and 3D architectures (layers, inverse opal, woodpile, etc.) of photonic crystals enable great flexibility in designing the optical response of the material. This opens an extensive range of applications, including photovoltaics. Photonic crystals can be used as anti-reflective and light-trapping surfaces, back reflectors, spectrum splitters, absorption enhancers, radiation coolers, or electron transport layers. This paper presents an overview of the developments and trends in designing photonic structures for different photovoltaic applications. [ABSTRACT FROM AUTHOR]

The use of polymer microspheres is becoming increasingly widespread. Along with their most common applications, they are beginning to be used in the synthesis of photonic crystals, microstructure analysis and multiplexed diagnostics for disease control purposes. This paper presents a simple mathematical model that allows us to study the transport mechanisms involved in the deformation of an elastic microchannel under the flow stream of a power-law fluid. In particular, we analyze the momentum transfer to a non-Newtonian fluid (Polydimethylsiloxane, PDMS) due to the deformation of the elastic ceiling of a rectangular microchannel. Hooke's law is used to represent the stress–deformation relationship of the PDMS channel ceiling. Stop-flow lithography is modeled, and the pressure exerted by the deformed PDMS ceiling on the fluid when the microchannel returns to its original form is taken into account. It is found that the response time of the elastic ceiling deformation increases with the channel width and length and decreases with the channel height independently of the power-law exponent of the injected fluid. However, an increase in the power-law exponent beyond unity causes an increase in the wall-deformation response time and the maximum deformation of the channel height compared to a Newtonian fluid. [ABSTRACT FROM AUTHOR]

In this paper, we present the structural and photoluminescence (PL) spectra of 2D-MoS2 and we report a theoretical investigation of the influence of Ag- and Au-doping on the transmission in 2D-MoS2 photonic crystal structure (PCS). A finite-difference time-domain (FDTD) technique and plane wave expansion method (PWE) have been introduced and adapted for periodic and aperiodic structures to extract the PC-bandgap and study the behavior of the transmission spectrum. The impact of the size of defects, the Ag- and Au-doping on the 2D-PC band structure and transmission spectrum has been visualized under the inclusion of the distribution of electromagnetic fields and the associated field maps. It has been shown that the Au-doping changes significantly the 2D-MoS2 PCS and as a result the transmission spectrum increases considerably. We can predict that 2D-MoS2 PC doped with Au is more convenient than doped with Ag in most applications involving optical transmission and waveguides for optoelectronics devices. [ABSTRACT FROM AUTHOR]

In this paper, we design and simulate a two-dimensional photonic crystal-based high speed logical encoder for optical computing application. The encoder consists of a ring resonator, four waveguides and two reflectors arranged in a hexagonal lattice platform. The optical encoder works on the interference effect which guides the propagation of light in the desired path. The light behavior is simulated with four different logic states. The Plane Wave Expansion (PWE) method is used to analyze the band gap and Finite Difference Time Domain (FDTD) analyzes the performance characteristics of the encoder, such as bit rate, delay time, and contrast ratio. The proposed structure has a footprint area of 143.84 µm2. The small compact size structure with simple defect paths reduces the encoder delay time, which in turn increase the data bit rate. The response time of the proposed encoder is 0.119 ps and bit rate is 8.403 Tbps. The encoder is designed with very low output power in "0" logic state and high output power in "1" logic state leading to high contrast ratio of 22.57 dB. Therefore, highly efficient 4 × 2 optical encoder is suitable to build in optical integrated circuits. [ABSTRACT FROM AUTHOR]

Micro-gyroscopes based on the Coriolis principle are widely employed in inertial navigation, motion control, and vibration analysis applications. Conventional micro-gyroscopes often exhibit limitations, including elevated noise levels and suboptimal performance metrics. Conversely, the advent of cavity optomechanical system technology heralds an innovative approach to micro-gyroscope development. This method enhances the device's capabilities, offering elevated sensitivity, augmented precision, and superior resolution. This paper presents our main contributions which include a novel dual-frame optomechanical gyroscope, a unique photonic crystal cavity design, and advanced numerical simulation and optimization methods. The proposed design utilizes an optical cavity formed between dual oscillating frames, whereby input rotation induces a measurable phase shift via optomechanical coupling. Actuation of the frames is achieved electrostatically via an interdigitated comb-drive design. Through theoretical modeling based on cavity optomechanics and finite element simulation, the operating principle and performance parameters are evaluated in detail. The results indicate an expected angular rate sensitivity of 22.8 mV/°/s and an angle random walk of 7.1 × 10−5 °/h1/2, representing superior precision to existing micro-electromechanical systems gyroscopes of comparable scale. Detailed analysis of the optomechanical transduction mechanism suggests this dual-frame approach could enable angular vibration detection with resolution exceeding state-of-the-art solutions. [ABSTRACT FROM AUTHOR]

Presented in this paper is an experimental and numerical study of directiondependent asymmetry of resonant optical characteristics inherent to metal - multilayerdielectric (MMD) nanostructure, which has much in common with the Tamm plasmonic configuration. We demonstrate that when a MMD structure is illuminated from opposite sides, there is a noticeable asymmetry of the forward/backward reflection resonances, contrasting with the strictly symmetrical transmission resonances indicating classical optical reciprocity. Comparative measurements were carried out on a metal film and a quasi-periodic dielectric structure, which are identical to the corresponding parameters of the MMD structure. Directional asymmetry of reflection and transmission is briefly discussed for a modified MMD structure with the Kerr nonlinearity. [ABSTRACT FROM AUTHOR]

Twisted photonic crystals are photonic analogs of twisted monolayer materials such as graphene and their optical property studies are still in their infancy. This paper reports optical properties of twisted single-layer 2D+ moiré photonic crystals where there is a weak modulation in z direction, and bilayer moiré-overlapping-moiré photonic crystals. In weak-coupling bilayer moiré-overlapping-moiré photonic crystals, the light source is less localized with an increasing twist angle, similar to the results reported by the Harvard research group in References 37 and 38 on twisted bilayer photonic crystals, although there is a gradient pattern in the former case. In a strong-coupling case, however, the light source is tightly localized in AA-stacked region in bilayer PhCs with a large twist angle. For single-layer 2D+ moiré photonic crystals, the light source in Ex polarization can be localized and forms resonance modes when the single-layer 2D+ moiré photonic crystal is integrated on a glass substrate. This study leads to a potential application of 2D+ moiré photonic crystal in future on-chip optoelectronic integration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bioinspired photonic system responds dynamically to humidity changes. • Scalable production of multicolor photonic papers at room temperature. • Hygroscopic active ink enables precise regional humidity response. • Color shifts from red to IR, green to golden, blue to green and UV to blue under humid conditions for encrypted printing. • Multilevel humidity responsiveness achieved by regulating ink pH. The proliferation of counterfeiting necessitates an urgent need for enhanced technique to safeguard the authenticity of sensitive items. Inspired by the elytra of Tmesisternus isabellae beetles, we designed a new synergistic humidity responsive photonic system (SHRPS) for security printing based on high quality photonic paper and active ink. The photonic paper itself is not sensitive to humidity; only the targeted areas activated by the active ink exhibit humidity responsiveness. We investigated factors influencing humidity responsiveness, including monomer composition, pH of active ink, and treatment period. We found the optimal monomer mixture contains 40% acrylic acid, and the active ink pH is 13. We also applied a scalable method to fabricate photonic paper, successfully overcome the challenge of large-scale fabrication of photonic crystals at room temperature. By integrating the perfect pair of SHRPS and inkjet printer, concealed information with various sizes and resolutions can be printed, invisible in ambient humidity and revealed by blowing air, presenting various humidity responsive ability of SHRPS for multilevel information encryption, which opens a new window for security printing system. [ABSTRACT FROM AUTHOR]

Understanding the dispersive properties of photonic crystals is a fundamental and well-studied problem. However, the introduction of singular permittivities and damping complicates the otherwise straightforward theory. In this paper, we study photonic crystals with a Drude–Lorentz model for the permittivity, motivated by halide perovskites. We demonstrate how the introduction of singularities and damping affects the spectral band structure and show how to interpret the notion of a "band gap" in this setting. We study a one-dimensional model for which we present explicit solutions. [ABSTRACT FROM AUTHOR]

This paper introduces a highly sensitive biosensor based on a plasmonic nanostructure-enhanced resonance effect. The sensor exploits a hexagonal photonic crystal composed of plasmonic nano-cylinders, including a graphene nano-cylinder as a defect, which can considerably increase the concentration of electric fields. This amplification enables the detection of tiny variations in refractive indices linked to a laser source for plasmonic excitation. Each defect consists of a hollow metallic cylinder surrounded by graphene, all within a metallic matrix. During the sensing process, surface plasmon polaritons interact with the core-guided modes of the patterns, which are subsequently filled with the analytes to be measured. The nano-cylinders' width is optimized to take advantage of their unique optical properties in nanoscale confinement, resulting in high sensitivity. The sensor achieves an impressive sensitivity of 17,750 nm/RIU (refractive index unit) and a FoM of 2218 (RIU−1) for n = 1.456 at the optimum value of ΔR = (Rout − Rin) = 200 nm. These metallic cylindrical channels exhibit distinct responses to different analytes across a wide range of ΔR, enabling simultaneous detection of various types of biomolecules. These exceptional properties make the sensor suitable for a broad range of applications, including real-time chemical and biological sensing. Furthermore, it offers the potential to create compact devices for measuring different refractive indices. [ABSTRACT FROM AUTHOR]

The cylindrical surface with Bragg-enhanced Fresnel reflectivity constructed from non-close-packed photonic crystals (NPCs) was designed for spectral selectivity and optical gain, which broke through the limitations of traditional Fresnel curved mirror with lowest central reflectivity and inability to perform spectral selectivity, and was conducive to expending the application of Fresnel mirror in the fields of signal transmission, optical measurement and instrument design. [Display omitted] According to the Fresnel theory, the reflectivity intensity of spherical and cylindrical convex surfaces decreases from their edge to center, and it is noteworthy and interesting for optical gain to study the enhancement of center reflectance. In this paper, a polydimethylsiloxane (PDMS) − encapsulated cylindrical non-closed-packed photonic crystals (NPCs) composite with Bragg-enhanced Fresnel reflectance was designed for spectral selectivity and optical gain. Theoretically and experimentally, the periodically ordered structure of NPCs achieved high-reflection of light in photonic bandgap and high-transmission in other bands, which enhanced Fresnel reflectivity of the convex center to specific bands. Furtherly, the cylindrical NPCs hydrogel with stretchability was applied for the dynamic tuning of optical signals. The reflection peak of the PDMS-encapsulated cylindrical NPCs composite blue-shifted from 608 nm to 413 nm with 50 % tensile strain and achieved a rapid transition of structural color from orange to blue-violet in 60 cycles. The new kind of photonic crystals composite for optical gain and spectral selection broke through the limitations of traditional Fresnel curved mirrors with the lowest central reflectivity and inability to perform spectral selectivity, and have great significance and application prospects in fields of signal transmission, optical measurement, and instrument design. [ABSTRACT FROM AUTHOR]

In this paper, we have designed and simulated all-optical logic gates with multi-functionalities based on two-dimensional photonic crystals. All-optical logic gates such as AND, OR, XOR, NOR and NAND are designed, simulated and optimized at 1550 nm wavelength. The operations of the proposed logic gates are based on the phenomenon of interference of optical waves and resonance in the cavity and analyzed with performance parameters such as contrast ratio, transmittance ratio and insertion loss. Based on the identical scheme of photonic crystal structure, multi-functionalities can be realized through tuning refractive index induced by applying voltage or manipulating the initial phase of the input optical wave signals. As a result, the proposed all-optical logic gates with multi-functionalities may contribute to the design of advanced photonic integrated devices. [ABSTRACT FROM AUTHOR]

Photonic crystals (PhCs) have gained attention for their ability to control and manipulate light at the nanoscale. They have led to advancements in optical communications, sensing and detection, and the development of novel optical devices. Specific examples include photonic crystal fibers for high-speed data transmission, ultrasensitive sensors for medical diagnostics, and compact wavelength filters and splitters. The articles in this Special Issue explore various applications and advancements in PhCs, offering valuable insights and possibilities for the future of optical devices. [Extracted from the article]