Photonic Crystal Research Articles

Two-dimensional valley photonic crystal resonant cavities

Introducing defects in photonic crystals is a common method for manipulating and controlling the propagation of electromagnetic waves. By introducing defects in photonic crystal waveguides, the periodicity of the waveguide structure can be disrupted, local modes can be formed, and resonant cavity functions can be achieved. In this study, we designed two groups of two-dimensional valley photonic crystal waveguides, each of which uses different methods to introduce defects and obtained different resonant cavity structures, and designed a resonant cavity sensor. We conducted a detailed theoretical analysis of the resonant cavity through simulation software. In addition, we fabricated the samples and conducted microwave experiments to demonstrate the accuracy of our theoretical research. Our research provides guidance for the application of photonic crystal devices.

High-Q coupled topological edge state in 1D photonic crystal mirror heterostructure for ultrasensitive thermal sensing

This work explores a novel 1D topological photonic crystal (PC) mirror heterostructure for high-performance thermal sensing. The design leverages a unique coupled topological edge state mode (CTES) exhibiting exceptional light confinement at the interface, characterized by a record-high quality (Q) factor. The study investigates the effects of nematic liquid crystal (NLC) integration and temperature variations to enhance functionality. Two NLC defect configurations are explored: complete replacement of silica layers and localized replacement within one topological PC. In both scenarios, the CTES mode exhibits tunability in frequency and Q factor due to the thermo-optic properties of the NLC. This dynamic control offers advantages for various applications beyond thermal sensing, including filtering and switching. The first NLC configuration achieves an outstanding Q factor of 107, surpassing the intrinsic value. Additionally, it demonstrates exceptional thermal sensitivity (−0.12317 nm/°C) and a remarkable figure of merit (1002.48 °C−1). These superior sensing characteristics are attributed to the strong light localization at the interface and the intensified light-matter interaction facilitated by the NLC. The second configuration offers a trade-off between sensitivity and tunability, exhibiting a Q factor in the 106 range, a sensitivity of −0.05853 nm/°C, and a figure of merit of 86.53 °C−1. This study presents a groundbreaking design for 1D topological PC mirror heterostructures with integrated NLC. This platform holds immense promise for developing high-performance, tunable narrowband filters and ultrasensitive thermal sensors, paving the way for advancements in diverse photonic applications.

Electrostatic fence induced assembly of low-concentration colloidal nanospheres to form liquid photonic crystals

Liquid photonic crystals (LPCs) have great application potential in sensors, anti-counterfeiting materials and detection due to their sensitive dynamic responsiveness. Currently, the preparation of LPCs mainly relies on the supersaturation of colloidal nanospheres. However, the supersaturation method usually fails to obtain LPCs based on low-concentration colloidal nanospheres. In turn, the use of high-concentration colloidal nanospheres results in poor mobility of LPCs, which makes them inappropriate for subsequent utilization in responsive systems. In this study, self-assembly of LPCs with vibrant structural colors is achieved through the electrostatic fence effect by introducing an anionic carboxylate-containing polymer as an inducer into the system of low-concentration negatively charged colloidal nanospheres (≥1.25 wt%). It is shown that the anionic carboxylate groups on the inducer molecules and the appropriate molecular chain length are the decisive factors for the inducing effect. The obtained LPCs exhibit a typical non-close-packed structure with a face-centered cubic arrangement of nanospheres. The nearest inter-nanosphere surface distance is 12.10 nm, and the farthest one is as long as 40.30 nm. The LPCs possess good dynamic recovery performance and sensitive optical response characteristics, which are conducive to application in responsive optical sensors directly or after filling.

Dual‐Polarization Huge Photonic Spin Hall Shift and Super‐Subwavelength Detecting Based on Topological Singularities in 1D Photonic Crystals

Dual‐Polarization Huge Photonic Spin Hall Shift and Super‐Subwavelength Detecting Based on Topological Singularities in 1D Photonic Crystals

Facile Preparation of Raspberry-Like SiO2@Polyurea Microspheres with Tunable Wettability and Their Application for Oil-Water Separation.

Raspberry-like microspheres have been widely used as superhydrophobic materials, photonic crystals, drug carriers, etc. Nevertheless, their preparation methods, usually consisting of multiple steps, are generally time- and energy-consuming. Herein raspberry-like SiO2@polyurea microspheres (SiO2@PUM) are readily prepared via a one-step precipitation polymerization of isophorone diisocyanate in a H2O/acetone mixture with the presence of SiO2 particles. The sphere size, surface roughness, and SiO2 content of SiO2@PUM are easily adjustable by varying the experimental conditions. TEM and SEM observations reveal that the final SiO2@PUM exhibits a core-shell structure, with polyurea (PU) in the core and SiO2 particles as the shell. In the process, the SiO2 particles were initially located on the PUM surface as a monolayer. With the reaction proceeding, the monolayer of SiO2 particles became thicker, forming a thicker layer of SiO2 particles on PUM due to the accumulation of SiO2 particles, leading to a multilayer structure of SiO2 particles on the shell of SiO2@PUM. The formation mechanism of the raspberry-like SiO2@PUM was thoroughly discussed and ascribed to electrostatic attraction between the positively charged PU and negatively charged SiO2 particles. Once dried, SiO2@PUM was superhydrophobic and turned hydrophilic if water-wetted. Using a layer of SiO2@PUM, effective separation with good reusability for a variety of oil-water mixtures was achieved regardless of the oil density and types of oil-water emulsions. This work presents a novel protocol for the preparation of raspberry-like microspheres with tunable wettability via a rapid and green process, and the resulting microspheres are highly effective for the separation of diverse types of oil-water mixtures.

Design and fabrication of photonic crystal structures by single pulse laser interference lithography

Photonic crystal (PhC) structures formed by periodic surface nanostructuring have emerged as pivotal elements for controlling light-matter interactions. One important application is reducing losses due to the high surface reflectivity of semiconductor optoelectronic devices, such as enhancing light absorption in photovoltaic cells or improving light extraction in light-emitting diodes (LEDs). Although various methods for fabricating such structures have been documented, the utilization of single pulse laser interference lithography (LIL) using commercial photoresist and its subsequent effective use as an etch mask has not been previously reported. Rapid exposure of photoresists with single nanosecond pulses offers benefits for high throughput patterning and reduces the requirement for a stable optical platform. We have successfully employed single pulse LIL to fabricate antireflective PhC structures on GaAs substrates using a commercial photoresist. Exposure is performed with single 7 ns 355 nm pulses of relatively low energy (<10 mJ). High-quality nanohole arrays of pitch of approximately 365 nm are fabricated and depths up to 400 nm have been etched using inductively coupled plasma (ICP) through the exposed photoresist mask. Reflectivity analyses confirmed that these structures reduce the average reflectance of the GaAs to below 5 % across the 450 nm to 700 nm visible wavelength range. The fabrication of PhC structures using this approach has potential for low-cost wafer-level patterning to provide improved light extraction in LEDs and enhanced light trapping in solar cells.

Up-conversion materials for solid-state lighting

AbstractConventional phosphor-converted white LEDs (WLEDs), using (Stokes) down-conversion light emission, suffer from a red deficiency that increases the Color Temperature towards “cool white light” above 5000 K. The present work describes a phosphor-Up-converted WLED approach that wishes to overcome this issue by achieving white light generation (WLG) through Up-conversion photoluminescence (UCPL), without energy losses due to Stokes shift and excited by a 980 nm LED instead of the more expensive blue LEDs. The UC materials include thin films of lanthanide (Ln)-doped aluminosilicate glass multilayers, alternating (Ln)-doped aluminosilicate and titania films in the form of 1-D photonic crystals and Ln ion-implanted materials. Sol-gel (SG) processing has been used as a low-cost high purity processing method to prepare titania, as well as aluminosilicate films containing Er3+, Tm3+ and Yb3+, for WLG and possible application as WLED materials. The total Ln content varied from a high of 22 mol% to as low as 5.8 mol%. The materials prepared have been characterized by UV-Vis-NIR (using a variable angle specular reflection accessory), plus FTIR and UCPL spectroscopies. The UC light emission was analyzed with the help of CIE chromaticity diagrams. Graphical abstract

Fabrication and optical characterization of porous silicon heterostructure as matrix for sensing organic solvent via resonance peak and Q factor shift

Porous silicon heterostructures with an extensive photonic band gap, featuring a microcavity defect layer, have been successfully fabricated and applied as sensor devices for detecting organic solvent species. These sensors utilize both the resonance peak shift and the inverse Q-factor as sensing parameters. Similar to conventional porous silicon microcavities immersed in various organic solvents, the resonance peak exhibits a linear dependence on the solvent refractive index. However, in the proposed structure, the inverse Q-factor also displays a comparable linear trend with the refractive index, but with greater sensitivity to solvent mixtures. This increased sensitivity arises because the inverse Q-factor deviates from linearity when the prior solvent is not adequately removed from the porous structure before reflectance measurements — a condition not commonly detected by the resonance peak shift. To improve the performance of these sensors, the porous structures were passivated by thermal oxidation. For sensor applications, it is crucial that the contrast in the effective refractive index between the high and low porosity layers of the passivated structures be sufficiently large. Otherwise, when the porous matrix is immersed in solvents, it loses its resonance peak, rendering the structure ineffective for sensor applications.

Two-dimensional photonic crystal acetylcholinesterase hydrogel and organohydrogel sensors for efficient detection of organophosphorus compounds

Sensors capable of detecting organophosphorus (OP) compounds have attracted the most attention owing to severe OP contamination worldwide. Despite many years of research, the developed OP sensors mainly focused on detecting water-soluble OPs in proper environments and the exploration of OP sensors suitable in resource-limited areas is extremely challenging. Here, a simple two-dimensional photonic crystal (2D PC) hydrogel featuring capabilities of effectively quantitative determination of OP compounds is facilely constructed by immobilizing the enzyme acetylcholinesterase (AChE) onto a bovine serum albumin (BSA) protein hydrogel. Owing to the specific interaction between AChE and OP compounds, the OP compounds are easily bound to the hydrogel, triggering volume phase transition and resulting in apparent Debye diffraction ring variations. The resulting hydrogel sensors show a limit of detection (LoD) of 2.23 nM for trichlorfon and 0.07 nM for diethyl methylphosphonate (DMPP), respectively. On the basis of the hydrogel, a responsive organohydrogel is facilely fabricated utilizing a solvent exchange strategy to meet the requirements of applications in harsh environments and detection of the non-water-soluble OP compounds. The organohydrogel sensors, however, demonstrated a LoD of 0.70 μM for trichlorfon and 4.46 μM for DMPP, respectively. This work provides new light on the development of next-generation stable, low-cost, and portable field sensing devices.

Wave patterns of the coupled nonlinear Schrödinger equations in photonic crystal fibers with four-wave mixing

Abstract In this paper, we examine the behavior of modulation instability within photonic crystals. The model employed is the coherent coupled nonlinear Schrödinger equation, incorporating weak birefringence and four-wave mixing, which arises at the edge of the optical mode. The linear analysis is used to derive the modulation instability spectrum. Throughout the modulation instability spectrum, we identify both stable and unstable modes, thereby confirming the breakdown of the plane wave. For certain four-wave mixing parameters, the amplitude of the modulation instability spectrum and its bandwidths expand, creating an opening for localized structures to emerge. Another aspect of this study has been demonstrated in normal and anomalous dispersion regimes where an increasing initial amplitude of the plane wave is fulfilled. Specifically, numerical simulations highlight the occurrence of Benjamin-Feir instability, where wave patterns emerge under the influence of four-wave mixing. Additionally, solitonic waves are generated, demonstrating the presence of Akhmediev breathers and other modulated structures, confirming that photonic crystals with four-wave mixing are conducive to these formations. The findings from this study could inform future research in the development of nonlinear photonic waveguides.

Tunable optical and photovoltaic performance in PTB7-based colored semi-transparent organic solar cells integrated MgF2/WO3 1D-photonic crystals via advanced light management.

This study explores the design, fabrication, and characterization of PTB7-based colored semi-transparent organic solar cells (ST-OSCs) with integrated MgF2/WO3 one-dimensional photonic crystals (1D-PCs). Integrating 1D-PCs enhanced light management by creating tunable photonic band gaps, leading to extraordinary color change and improved photon harvesting. For 1DPC5 - 425 the Average Visible Transmittance (AVT) values were 33.3%, and CIE x, y was 0.43, 0.52, for 1DPC3 - 650 AVT were 25.09% and CIE x, y was 0.23, 0.27, respectively. Thus, extraordinary color changes from blue to yellow could be achieved while keeping transparency. Thereupon, photovoltaic performance showed notable improvements, with Jsc increasing from 7.98mA/cm2 to 9.95mA/cm2 and 10.45mA/cm2 for 1DPC5 - 425 and 1DPC3 - 650, respectively. By 1D-PC integration, power conversion efficiency (PCE) reached from 3.93 to 4.90% and 5.08% for 1DPC5 - 425 and 1DPC3 - 650, respectively. The Color Rendering Index (CRI) indicated successful color tuning and acceptable rendering, with CRI of 52 and 87. The study demonstrates that 1D-PC integration significantly enhances ST-OSCs' optical and photovoltaic properties, paving the way for advanced energy-harvesting applications.

Phase-modulation-induced reconfigurable rotating photonic lattices in atomic vapors.

We propose a method to prepare optically induced rotating hexagonal and honey-comb photonic lattices by employing the phase modulated three-beam interference in atomic vapors with electromagnetically induced transparency. The phase differences among the three beams are dynamically elaborated to synthesize the circular motion (in transverse dimensions) of waveguides in the photonic lattices. Further, we verify this model experimentally in the case of low-speed modulation. A weak Gaussian probe field is sent into the constructed helical photonic lattices to image their structures under electromagnetically induced transparency (EIT). The motion trajectories of the sites on the discretized output patterns exhibit repeated circles, advocating the formation of rotating lattices. By introducing phase modulations to involved beams, we provide a continent way for producing transverse motions in waveguide arrays with reconfigurability in rotational direction, radius, and speed. This work looks forward to promising applications in topological photonics with great popularity.

Calix[6]arene-Functionalized Photonic Hydrogel Biosensor for Naked-Eye Cholesterol Detection Based on Supramolecular Host-Guest Interactions.

Cholesterol (CHO) is an essential constituent of human cellular tissues and a crucial activity indicator for the clinical diagnosis and prevention of various diseases. Abnormal CHO levels can lead to various cardiovascular diseases, including coronary heart disease, cerebral thrombosis, and atherosclerosis. Thus, developing simple and effective methods for CHO detection is of great significance. Herein, a novel calix[6]arene-modified photonic hydrogel biosensor (PAAH@SCX6) was developed for naked-eye monitoring of CHO based on supramolecular host-guest interactions between 4-sulfocalix[6]arene (SCX6) and CHO molecules. This sensor was constructed by embedding Fe3O4 colloidal nanocrystal cluster chains into a poly(acrylamide-co-acrylic acid) smart hydrogel (PAAH), followed by incorporation of plentiful SCX6 units into the PAAH via hydrogen bonding interactions. The specific recognition of SCX6 to CHO leads to the volume expansion of the hydrogel, causing a shift in the photonic band gap and a change in the hydrogel's structural color. The sensor demonstrated a linear detection range of 2.83-5.20 mM, covering the typical CHO levels in the human body. Importantly, the PAAH@SCX6 biosensor showed high selectivity and satisfactory stability, making it highly suitable for practical applications. Such a photonic hydrogel-based biosensor provides a convenient, simple, and efficient strategy for visual CHO detection.

Dimensional resonance of intrinsic stimulated picosecond emission while it induces a photonic crystal and electron population oscillations in heterostructure Al&lt;sub&gt;x&lt;/sub&gt;Ga&lt;sub&gt;1–x&lt;/sub&gt;As–GaAs–Al&lt;sub&gt;x&lt;/sub&gt;Ga&lt;sub&gt;1–x&lt;/sub&gt;As

Powerful picosecond optical pumping of the GaAs heterostructure layer causes the generation of stimulated picosecond emission in it. Due to its high intensity, the emission induces a Bragg grating of the electron population in the active region of the layer, making the latter an active photonic crystal. In the emission field, the inverse population of electrons oscillates with time, which should lead to spatiotemporal modulation of the emission and this population. It has been discovered that if the distance Y between the end of the heterostructure and the center of the active medium and the geometric parameters of the indicated modulation and movement of emission in the photonic crystal satisfy certain conditions, then dimensional resonance occurs - a maximum of modulation of the dependence of the energy of emission emerging from the end on Y and on pump energy appears locally.

A Stable Perovskite Sensitized Photonic Crystal P-N Junction with Enhanced Photoelectrochemical Hydrogen Production.

The slow photon effect in inverse opal photonic crystals represents a promising approach to manipulate the interactions between light and matter through the design of material structures. This study introduces a novel ordered inverse opal photonic crystal (IOPC) sensitized with perovskite quantum dots (PQDs), demonstrating its efficacy for efficient visible-light-driven H2 generation via water splitting. The rational structural design contributes to enhanced light harvesting. The sensitization of the IOPC with PQDs improves optical response performance and enhances photocatalytic H2 generation under visible light irradiation compared to the IOPC alone. The designed photoanode exhibits a photocurrent density of 3.42 mA cm-2 at 1.23 V vs RHE. This work advances the rational design of visible light-responsive photocatalytic heterostructure materials based on wide band gap metal oxides for photoelectrochemical applications.

Tunable Fano-type resonance with quadrature squeezing in a double-cavity-waveguide structure of photonic crystals

We propose an optical approach to realizing Fano-type spectra of quadrature squeezing in a double-cavity-waveguide structure based on photonic crystals (PhCs). In this scheme, a partially transmitting element (PTE) in the waveguide creates the transmission and reflection light, which interferes with the outflow from the intracavity field and subsequently gives rise to Fano-type interference. Meanwhile, a degenerate parametric amplifier (DPA) embedded into the cavity is expected to yield quantum squeezed states in the interference process. After verifying the existence of the Fano resonance, we report that increasing the nonlinear gain of the DPA not only amplifies the transmitted intensity of the output field, but also improves its quadrature squeezing degree. More importantly, we illustrate that, when maintaining the high performance of quadrature squeezing, the linewidths and frequencies of the asymmetrical spectra can be modulated by adjusting the double-cavity coupling strength. This combination of Fano-type spectra and quadrature squeezing is beneficial for optimizing optical communications and signal processing with a low noise level.

Low Loss in a Gas Filled Hollow Core Photonic crystal fiber

The work in this paper focuses on the experimental confirming of the losses in photonic crystal fibers (PCF) on the transmission of Q-switched Nd:YAG laser. First HC-PCF was evacuated to 0.1 mbar then the microstructure fiber (PCF) was filled with He gas &amp; gas. Second the input power and output power of Q-switched Nd:YAG laser was measured in hollow core photonic bandgap fiber (HCPCF). In this work loss was calculated in the hollow core photonic crystal fiber (HCPCF) filled with air then N2, and He gases respectively. It has bean observed that the minimum loss obtained in case of filling (HC-PCF) with He gas and its equal to 15.070 dB/km at operating wavelength (1040-1090) nm.

Dual-band large-area topological edge states and higher-order corner states in a valley Hall photonic crystal

Dual-band large-area topological edge states and higher-order corner states in a valley Hall photonic crystal

Semiconductor Nanoporous Anodic Alumina Photonic Crystals as a Model Photoelectrocatalytic Platform for Solar Light‐Driven Reactions

In this study, nanoporous anodic alumina distributed‐Bragg reflectors (NAA–DBRs) functionalized with tungsten trioxide (WO3) are used as prototype photoelectrocatalysts (PEC) for harnessing the slow photon effect to maximize photon‐to‐electron conversion efficiency under UV–visible–NIR illumination. NAA–DBR structures are structurally engineered by anodization, where their characteristic photonic stopband is precisely tuned along specific positions of the UV–visible spectrum. Subsequent atomic layer deposition is employed to coat the inner surface of these porous structures with WO3 semiconductor layers. Upon the application of overpotential bias, these platforms reveal excellent electron–hole pair separation to boost photoelectrocatalytic reactions. Photoelectrochemical degradation of methylene blue is used as a model reaction to elucidate enhancements associated with structural and optoelectronic arrangements. Notably, precise spectral alignment between the photonic stopband's red edge and the absorbance band of methylene blue enhances the degradation performance through the slow photon effect. Applying an overpotential bias further improves the photodegradation performance through efficient charge separation. These systems outperform comparable structures in this model reaction, achieving a maximum kinetic rate of 13.7 ± 2.0 h−1. The findings create new opportunities to develop high‐performing PEC technologies harnessing light–matter interactions.

Spontaneous parametric downconversion in a laser-poled lithium niobate nonlinear photonic crystal with nanoscale resolution.

Based on quasi-phase-matching (QPM) theory, nonlinear photonic crystals (NPCs) are capable of realizing efficient spontaneous parametric downconversion (SPDC) for the generation of photonic entangled states. However, the traditional electric field poling techniques employed in NPC fabrication often result in non-negligible processing errors of a few hundred nanometers, thus impeding the production of quantum photon pairs as intended. In this work, we investigate the SPDC photon pairs generated in a laser-poled lithium niobate (LN) NPC. By using the recently developed laser poling technique, the processing error of the NPC is substantially reduced to approximately 15 nm. Consequently, the coincidence counts of the generated photon pairs in the experiment reach 83.6% of the designed value. Our result paves the way for on-demand production of high-quality quantum sources, which has potential applications in quantum communications and quantum computations.