ABSTRACT A near‐infrared (IR) optical modulator based on a silicon photonic crystal (PhC) waveguide structure is introduced. To control the light modulation process, Vanadium dioxide (VO 2 ) nanorods are inserted into the central defect of the PhC waveguide. The full vectorial finite element method (FVFEM) is employed to perform the bandgap analysis, numerical modelling, and the light propagation characteristics inside the proposed PhC structures. Several configurations of VO 2 nanorods are studied to obtain the lowest insertion loss ( IL ) and the highest extinction ratio ( ER ). The obtained results reveal that the presented modulator achieves a low IL of 1.94 dB and a large ER of 10.5 dB by adding a rectangular array of VO 2 nanorods in the central defect of the PhC waveguide. The results obtained are promising compared to those reported in the literature. Thus, the suggested modulator can be a good candidate for integrated photonic applications and optical communications.

Mechanically tunable structural color hydrogel with MXene/PEDOT:PSS conductive networks for dual-channel information encoding.

Barium fluoride (BaF2) scintillators have garnered widespread application in high-energy physics, due to their ultrafast scintillation component peaking at 220 nm. Nevertheless, their slow scintillation component with much higher light yield limits their performance in ultrafast detection scenarios. While existing methods like rare-earth ion doping or pressure control can partially suppress the slow component, the fast component should be enhanced to further improve the performance. In this study, we propose a photonic crystal structure composed of multilayer close-packed SiO2 nanospheres to selectively enhance the fast component of BaF2 scintillators by selectively coupling with the fast component via surface lattice resonances and diffraction effects. A periodicity of 200 nm and 7 layers of SiO2 nanospheres are designed and fabricated, leading to an average enhancement ratio of 1.59 (maximum 1.79) for the fast component, without affecting the slow component. Compared with our previous work on selectively enhancing the fast component of BaF2 using photonic crystal structures, the multilayer nanosphere structure proposed in this paper effectively improves the coupling efficiency between scintillation light and the nanostructure by the increased structural thickness, thus achieving a better selective enhancement effect.

ABSTRACT Tin‐based perovskites are widely used in near‐infrared (NIR) photodetectors owing to their excellent optoelectronic properties and environmental friendliness. However, their performance is severely limited by high defect densities and pronounced instability. Herein, we report the successful fabrication of high‐performance NIR photodetectors based on an inverse opal (IO) photonic crystal structure of formamidinium tin iodide (FASnI 3 ) perovskite. This structural design significantly reduces the defect density of the Sn‐based perovskite functional layer and markedly enhances its stability. Notably, a bifunctional organic additive, 1,4‐butanediammonium iodide (BDADI), plays a key role in enabling the formation of perovskite IO structures by effectively regulating the colloidal chemistry and crystallization kinetics of FASnI 3 . The resulting ordered BDADI‐modified FASnI 3 (FASnI 3 ‐BDADI) IO architecture not only enhances light harvesting via slow‐photon effects but also facilitates efficient carrier transport. As a result, the IO photodetector achieves record‐breaking responsivity (5.90 A·W −1 ) and a champion detectivity (1.06 × 10 14 Jones) at 808 nm, along with excellent unencapsulated stability attributed to the lotus effect of photonic crystal. Leveraging its superior performance and stability, we demonstrate, for the first time, the application of such high‐performance NIR perovskite photodetectors in interference‐resistant image transmission over a distance of up to 30 m.

This paper presents a hybrid wavelength-division multiplexing (WDM) and polarization-division demultiplexing (PDM) device using silicon rods in the honeycomb-lattice photonic crystal structure. The device consists of a directional coupler to split the TE and TM polarizations and channel drop filters that drop the resonant channel wavelengths for both polarizations. The coupling length of the directional coupler is optimized such that only TE-polarized light is coupled to the waveguide, which is placed parallel to the input waveguide, thus separating it from the TM-polarized light. The parameters of the nanocavities in the channel drop filters are optimized to achieve resonant wavelengths in the C-band wavelength range. The period of the rods in the y direction (ayn) is discretely chirped within each cavity channel section to minimize losses and improve efficiency. The proposed WDM -PDM device has been simulated using the finite-difference time-domain (FDTD) solver, achieving a minimum insertion loss and a linewidth of 0.50dB and 1.60nm, respectively. The footprint of the proposed device is 37.00µm×44.63µm. The fabrication tolerance study for over-etch and under-etch conditions is performed, and the rate of the resonance wavelength shift of <2.65 is achieved.

Abstract In this paper, we propose a GaAs photonic crystal line-defect waveguide structure and numerically demonstrate the efficiency of the sum-frequency generation (SFG) and difference-frequency generation (DFG) via phase matching. A sum-frequency conversion efficiency of 83.569% W −1 and a difference-frequency conversion efficiency of 14.870% W −1 are obtained in our photonic crystal structure. Moreover, the effect of group velocity on nonlinearity enhancement is investigated. This work shows that the photonic crystal phase-matching scheme is an effective approach to improve the nonlinear conversion efficiency, offering a promising strategy for the integration of nonlinear photonic devices.

Previous studies have considered the iridescent feathers of the peafowl as a classic example of structural coloration. The structural color is primarily attributed to a two-dimensional (2D) photonic crystal structure composed of melanin rods and air channels embedded in a keratin matrix. While previous optical models have successfully explained spectral tuning via geometric parameters such as lattice constants and cortex thickness, the potential contribution of auxiliary pigments to these complex hues has been largely overlooked. In this study, we combined high-sensitivity UPLC-MS and transcriptome analysis to elucidate the biochemical and genetic mechanisms underlying peafowl coloration. We identified trace amounts of the Xanthophyll lutein (one of the carotenoids) in iridescent train feathers, challenging the purely structural paradigm. Transcriptome analysis revealed significant differences in the expression of the melanin-related gene ASIP between iridescent and non-iridescent feather follicles. Furthermore, we observed significant expression differences in the carotenoid deposition-related gene GSTA2, correlating with the presence of lutein in iridescent regions. We conclude that while melanin provides the structural foundation for iridescence, lutein acts as an indispensable conditional modulator. The coordinated differential expression of melanin synthesis (ASIP) and carotenoid deposition (GSTA2) genes constitutes the genetic basis for the vibrant iridescent coloration of peafowl feathers.

All-optical nonlinear activation function based on the two-dimensional photonic crystal structure through modulating the signal light

Bionic meta microneedle photonic crystal patch for advanced wound care.

InGaN-based micro-light-emitting diodes (micro-LEDs) are emerging to revolutionize the display and lighting technologies, particularly for their excellent robustness, high brightness, high efficiency and small pixel size. Despite the success of blue LEDs, long-wavelength emission, particularly the red emission, has been a challenge for InGaN-based micro-LEDs. Overcoming the low quantum efficiency, color instability, and broad emission in the red wavelength regime are among the most urgent and critical problems that inhibit the commercial implementation of micro-LED technology. In this work, we utilize a nanowire photonic crystal (PhC) structure to reform the radiation behavior of red-emitting InGaN micro-LEDs. Through detailed optimization on the PhC design and device fabrication, we demonstrate red-emitting micro-LEDs with a peak wavelength at 617 nm and a full-width-at-half-maximum (FWHM) of 5 nm, which is about one order of magnitude narrower than previous reported values and is paramount for achieving high color purity. The chromaticity property is highly stable with varying injection currents due to the coupling of emission to photonic band edge mode. A high external quantum efficiency of over 10% was measured from micro-LEDs with a size of 1 µm2. This work provides a vital strategy for high-performance red-emitting micro-LEDs and a potential pathway for full-color micro-LED technology by using all III-nitride semiconductors.

Objectives . Identification of the propagation patterns of surface waves in inhomogeneous and nonlinear crystal structures using mathematical models is an important fundamental problem in condensed matter physics, specifically waveguide optics. Models of waveguide structures used to establish an exact analytical solution are of particular significance. The aim of this work is to carry out a theoretical study of transversely polarized surface electric waves propagating along a photonic crystal with a certain refractive index profile. Methods . The methods of mathematical physics, analysis, differential equations, and theory of special functions, as well as physical models of waveguide optics, were used in this study. Results . A generalized hyperbolic permittivity profile was proposed to describe the spatially inhomogeneous distribution of the optical properties of a photonic crystal. This profile has a wide range of possibilities for varying its shape, allowing it to be used for a wide range of problems not limited to waveguide optics. An exact analytical solution of the wave equation with the selected permittivity profile was found in terms of the Whittaker function. Frequent cases of the generalized profile for which exact analytical solutions were indicated were also considered. These are expressed through the Whittaker and Macdonald functions. The study also describes surface transverse electric waves, where the field is localized near the surface of the photonic crystal and decreases with distance from it. The solution obtained also describes waveguide modes in which the field decreases with distance from the surface of the photonic crystal with oscillations. New features of surface wave localization were established. These were caused by a change in the parameters of the generalized hyperbolic profile modeling the dependence of the permittivity. It was also established that the maximum intensity of the surface wave is located in the photonic crystal. Conclusions . The results of the description of the characteristics of surface waves obtained expand the theoretical concepts of waveguide optics. They can be useful in predicting the optical properties of various photonic crystal structures, as well as in designing various waveguide structures with the required dispersion-optical characteristics.

In this study, a double-lattice photonic crystal structure was designed to achieve deep ultraviolet lasing without the use of any Distributed Bragg Reflector (DBR), which is called a photonic-crystal surface-emitting laser (PCSEL). The plane wave expansion (PWE) method was used to study the influence of various structural parameters on the resonant wavelength. Utilizing the random forest algorithm, we determined that the importance of the lattice constant to the resonant wavelength is 95.24%. Furthermore, we realized the reverse design of double-lattice photonic crystals from the target wavelength to optimal structural parameters through a radial basis function (RBF) network algorithm. Comparative analysis of the extreme learning machine (ELM) and back propagation (BP) algorithms demonstrated that RBF-based performance was notably superior to the training outcomes of other algorithms. The mean absolute error (MAE) of the lattice constant of the test set in the training results was 0.7610 nm, root mean square error (RMSE) was 1.143×10-3 nm, and mean absolute relative error (MARE) was 5.489×10-3. We verified the reliability of the algorithm and designed 13 groups of photonic crystals with different epitaxial structures. The mean square error (MSE) was 0.6188 nm2 compared with that of the plane wave expansion method. This work demonstrates applicability across various wavebands and epitaxial structures in GaN-based devices, providing a novel approach for the rapid iteration of deep ultraviolet PCSELs.

This paper proposes a novel photonic crystal fiber-based 1 × 3 optical drop multiplexer design. According to numerical simulations, optical signals can be injected on the left core and divided into another core at various distances to separate the optical signals in a photonic crystal fiber structure. Throughout the length of the fiber, the innovative design controls the direction of light transmission between layers by alternating between multiple air-hole positions using pure silica layers. The optical systemic communications industry cannot function without wavelength multiplexers/demultiplexers. They function as a data combiner/separator. By employing an optical add-drop multiplexer, it becomes possible to add or remove signals from a stream of multiplexed signals without the need to be concerned about any potential interference with the existing signals, even when they are traveling at varying on-axis distances. This study provides findings about small optical drop multiplexers for fiber-to-the-home applications employing photonic crystal fiber at wavelengths of 0.85, 1.45, and 1.2 µm.

Abstract One-dimensional (1D) photonic crystals (PCs) with two defect layers (DLs) have unique properties of localization of light and multimode low-threshold laser generation, they can also be used as highly sensitive optical sensors. This study investigates the distribution of light in 1D PCs with two DLs at the exceptional points of degeneracy, where defect modes (DMs) merge in the reflection spectrum. The four most significant types of symmetry in such structures are considered, and an unusual distribution of the field at DMs in the PC structure with different symmetry properties around the first and second DLs is shown. Unlike previous works, we demonstrate for the first time four important methods for achieving merging of DMs in 1D PCs with two DLs: merging due to changes in the symmetry of the PC, merging with an increase in the number of unit cells in the middle, merging by altering the thickness of the defects in the PC, and merging by varying the angle and polarization type of the incident light. Additionally, the transmission of light through the 1D PC with two DLs is investigated for the first time under varying angles and types of polarization of incident light. The novelty of this work also lies in the fact that we show the possibility of changing the number of DMs within the photonic bandgaps depending on the s - or p -waves (TE and TM polarizations) incident on the structure at large angles. Such versatility can be further used for the development of tunable optical sensors, filters, and other devices, based on the PCs.

This research introduces a photonic sensor designed to detect gamma-ray radiation, utilizing a one-dimensional regular ternary annular photonic crystal (1D APhC) structure. The sensor consists of alternating layers of porous silicon, silicon dioxide, and polyvinyl alcohol (PVA) polymer, which is doped with crystal violet and carbol fuchsine dyes. Exposure to varying levels of gamma-ray radiation alters the refractive index of the doped polymer, resulting in a shift in the photonic bandgap (PBG). The analysis of this dosimeter emphasizes how the intensity and position of the left band edge of the PBG are affected. Theoretical investigations are performed using Bruggeman’s effective medium equation and the transfer matrix method (TMM). The study examines the impact of gamma-ray radiation intensity, ranging from 0 to 70 Gy, on the refractive index of the polymer. Furthermore, it explores how critical parameters, such as the movement of the left and right band edges, PBG width, and sensor sensitivity, are influenced by structural modifications. Under optimized conditions, the sensor achieves a sensitivity of 200.8351 nm/RIU in detecting gamma-ray radiation exposure from 0 to 70 Gy. This highly sensitive dosimeter design holds significant potential for various scientific applications, facilitating accurate detection of gamma-ray radiation.

A polarization beam splitter (PBS) is a key device for controlling the polarization state of light in photonic integrated circuits (PICs). In this paper, a compact TM-pass/TE-divide PBS based on thin-film lithium niobate (TFLN) and a photonic crystal-multimode interference (PhC-MMI) is proposed. This device achieves different polarization propagation characteristics by etching photonic crystals in the multimode region of the MMI. It is able to separate the two polarization modes of TE and TM, thus realizing the function of polarization beam splitting. The length of the structure proposed in this paper is 243µm. The simulation results at the center wavelength of 1550nm show that the extinction ratio of the TE(TM) polarization mode is 27.7dB (26.3dB), and the insertion loss is 0.78dB (0.83dB). This design has the advantages of high extinction ratio and low crosstalk. In addition, the device adopts a photonic crystal structure, making it free from the inherent TE/TM mode length dependency of traditional MMI devices. It is expected to become an indispensable component in future TFLN PICs.

This study developed a light extraction enhancement method for gallium nitride (GaN) scintillators by integrating microsphere self-assembly technology with filter cathode vacuum arc deposition (FCVA) deposition technology. As a representative third-generation wide-bandgap semiconductor, GaN exhibits excellent radiation resistance and superior optical properties, with its 8-inch wafer fabrication capability providing a critical foundation for large-area imaging applications. To address the light extraction limitations imposed by the high refractive index of GaN, we designed a photonic crystal structure: an array of polystyrene microspheres with a 600-nanometer periodicity, combined with a conformal TiO2 layer deposited via FCVA. Experimental results demonstrate significant enhancement: after angular integration, the integrated spectral intensity of the yellow emission band increased by 197% (100 nm TiO2) and 136% (50 nm TiO2), while the near-band-edge emission integrated spectral intensity increased by 83% (100 nm TiO2) and 70% (50 nm TiO2). This performance enhancement stems from the synergistic effect between the optical localization effect of the PS microsphere array and the high refractive index (∼2.4) of TiO2. The FCVA technique, characterized by its high deposition rate (∼10 nm/min) and substantial ion flux, enables rapid fabrication of TiO2 conformal layers with exceptional large-area uniformity, meeting industrial production requirements. This work establishes a significant technical approach for improving light extraction efficiency in GaN materials, demonstrating promising potential for large-area imaging and related applications.

To boost light harvesting in perovskite thin-film solar cells, we introduce a dual photonic crystal (PhC) architecture that significantly enhances light trapping and device performance. A one-dimensional photonic crystal (1D-PhC), implemented as a distributed Bragg reflector composed of alternating dielectric layers, functions as a highly reflective and low-loss back mirror. Complementarily, a two-dimensional photonic crystal (2D-PhC) pattern is embedded in a flexible poly-dimethylsiloxane substrate replacing conventional glass, effectively minimizing front-surface reflection. The geometries of both photonic structures are carefully optimized to promote efficient photon diffraction and prolong the optical path within the absorber layer, thereby maximizing light absorption. This hybrid PhC configuration enables superior light trapping and enhances the optical field confinement in the active perovskite layer. In addition, interface engineering is employed to reduce carrier recombination losses, further boosting overall device performance. Numerical simulations, conducted using the rigorous coupled wave analysis method via SYNOPSYS RSoft CAD tools, demonstrate a notable improvement in the short-circuit current density (Jsc), which increases from 21.3 mA/cm2 in the planar structure to 39.6 mA/cm2, an enhancement of 85%. Correspondingly, the power conversion efficiency rises from 15.8% to 26.1%, representing a substantial 65% relative improvement. These results underscore the potential of photonic crystal integration for next-generation high-efficiency perovskite solar cells.

Thin-film lithium niobate (TFLN) electro-optic modulators (EOMs) offer distinct advantages, including high speed, broad bandwidth, and low power consumption. However, their large size hinders the density of integration, which trades off with the half-wave voltage. Photonic crystal (PC) structures can effectively reduce the device footprint via the slow-light effect; however, they experience significant losses due to fabrication defects and sharp corners. Here, we theoretically demonstrate an ultracompact Mach–Zehnder interferometer (MZI) EOM based on a TFLN valley photonic crystal (VPC) structure. The design can achieve a high forward transmittance (&gt;0.8) due to defect-immune unidirectional propagation in the VPC, enabled by the unique spin-valley locking effect. The EOM, with a small footprint of 21 μm × 17 μm, achieves an extinction ratio of 16.13 dB and a modulation depth of 80%. The design can be experimentally fabricated using current nanofabrication techniques, making it suitable for broad applications in optical communications.

The influence of the photonic-crystal structure of synthetic opal on the fluorescence spectrum of the laser dye Rhodamine 6G is investigated. Suppression of fluorescence in the stop-band region and a blue shift of the spectrum are observed.