Fabrication Of Photonic Crystals Research Articles

Ultra-Fast Fabrication of Mechanical-Water-Responsive Color-Changing Photonic Crystals Elastomers and 3D Complex Devices.

The traditional fabrication of opal-structured photonic crystals is constrained by the rate of solvent evaporation, a process that is not only time-consuming but also labor-intensive. This study introduces a paradigm shift by incorporating silica nanoparticles (SiNPs) with high zeta potentials and hydrogen bonding capabilities into an elastomeric matrix, resulting in a novel non-close-packed structure. This innovation circumvents the limitations of conventional methods by enabling the rapid formation of photonic inks (PI) into vibrant and luminous photonic elastomers (PEs) within seconds. These PEs demonstrate remarkable mechanochromic properties, exhibiting dynamic color changes across the visible spectrum in response to tensile and compressive deformations. Furthermore, the presence of hydroxyl groups endows the PEs with superior water-responsiveness, which can be finely tuned through the ink formulation. The elimination of solvent evaporation dependency facilitates the fabrication of macroscopic photonic crystal devices with complex geometries using digital light processing (DLP)-based 3D printing. This approach ensures exceptional optical performance and high customization potential. The resulting PEs hold significant promise for applications in smart wearables, soft robotics, and advanced human-machine interface technologies.

Bio-inspired synergistic humidity-responsive photonic system for security printing and information encryption

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.

3D Printing Photonic Crystals: A Review.

Living organisms in nature possess diverse and vibrant structural colors generated from their intrinsic surface micro/nanostructures. These intricate micro/nanostructures can be harnessed to develop a new generation of colorful materials for various fields such as photonics, information storage, display, and sensing. Recent advancements in the fabrication of photonic crystals have enabled the preparation of structurally colored materials with customized geometries using 3D printing technologies. Here, a comprehensive review of the historical development of fabrication methods for photonic crystals is provided. Diverse 3D printing approaches along with the underlying mechanisms, as well as the regulation methods adopted to generate photonic crystals with structural color, are discussed. This review aims to offer the readers an overview of the state-of-the-art 3D printing techniques for photonic crystals, present a guide and considerations to fabricate photonic crystals leveraging different 3D printing methods.

Moving Meniscus-Assisted Template-Free Optothermofluidic Nanoparticle Patterning and Its Application in Optothermoconvective Particle Trapping.

Moving meniscus-assisted vertical lifting is a commonly employed particle assembly technique to realize large-area particle patterning for the easy fabrication of colloidal photonic crystals and sensors. Though great success has been achieved for large-area patterning, inscribing desired patterns over the target substrate with precise control over the morphology remains a challenge. The target substrates need to be functionalized (physically or chemically) to realize desired patterns, which increases the complexity and limits their applicability to specific particle-liquid combinations. We demonstrate a new approach for the precise patterning of gold nanoparticles (Au NPs, diameter ∼60 nm) over solid substrates by the synergy of light-induced Marangoni flow and vertical lifting process (moving meniscus), without the requirement of photomasks or templates. The core idea relies on the particle accumulation due to light-induced Marangoni flow near the liquid meniscus in contact with a solid surface (due to plasmonic absorption of the particles) and the controlled lifting of the substrate. We present both the simulation and experimental results of the developed patterning technique. Various patterns such as continuous lines, intermittent lines with varying lengths, patterns with continuously varying widths, cross patterns, etc. are successfully inscribed. Dynamic control over the three-dimensional morphology of the deposited patterns is achieved by varying the lifting velocity, laser irradiation time, and lifting direction during the inscription process. Finally, we show the applicability of the developed plasmonically active surface for the large-area parallel manipulation of nonabsorbing microparticles based on optothermoconvective flow. The major advantage of the developed method compared to the existing light-controlled patterning techniques is its ability to inscribe patterns over large distances (up to several centimeters). We expect that the results presented in this paper will benefit different applications requiring precise particle patterning, such as optical elements, sensors, plasmonic substrates, microfluidic master templates, and electronic circuits.

Rapid Fabrication of Large-Grain Opal Films and Photonic Crystal Hydrogel Sensors by a Filter Paper-Enhanced Evaporation Chip.

Developing a rapid fabrication method for crack-free opal films is a significant challenge with broad applications. We developed a microfluidic platform known as the "filter paper-enhanced evaporation microfluidic chip" (FPEE-chip) for the fabrication of photonic crystal and inverse opal hydrogel (IOPH) films. The chip featured a thin channel formed by bonding double-sided adhesive poly(ethylene terephthalate) with a polymethyl methacrylate cover and a glass substrate. This channel was then filled with nanosphere colloids. The water was guided to evaporate rapidly at the surface of the filter paper, allowing the nanospheres to self-assemble and accumulate within the channel under capillary forces. Experimental results confirmed that the self-assembly method based on the FPEE-chip was a rapid platform for producing high-quality opal, with centimeter-sized opal films achievable in less than an hour. Furthermore, the filter paper altered the stress release mechanism of the opal films during drying, resulting in fewer cracks. This platform was proven capable of producing large-grain, crack-free opal films of up to 30 mm2 in size. We also fabricated crack-free IOPH pH sensors that exhibited color and size responsiveness to pH changes. The coefficient of variation of the gray color distribution for crack-free IOPH ranged from 0.03 to 0.07, which was lower than that of cracked IOPH (ranging from 0.07 to 0.14). Additionally, the grayscale peak value in 1 mm2 of the crack-free IOPH was more than twice that of the cracked IOPH at the same pH. The FPEE-chip demonstrated potential as a candidate for developing vision sensors.

High-efficiency fabrication of uniform photonic crystals by a vertical deposition method from multiple glass slides of simple moulds and their application in isomer recognitions

Vertical deposition method is a simple, cheap and common method for fabricating photonic crystals (PCs). However, a majority of PCs are obtained based on the traditional vertical deposition method from one glass slide, the method is low efficiency. Herein, it is proposed to efficiently fabricate uniform PCs by an optimized vertical deposition method from double or multiple glass slides of simple moulds. Amounts of SiO2 spheres, distances of two glass slides of moulds, preparation temperatures and different diameters of SiO2 spheres are investigated for obtaining uniform PCs. And different types of PCs (the bottom-middle-top 3D PCs, bilayer 2D PCs and amorphous PCs) are also fabricated based on the optimized vertical deposition method. The above method is a simple, cheap and high-efficiency way for mass production of uniform PCs. Meanwhile, the chemicals with similar refractive indices (isomers and cis-trans isomers) can be easily distinguished under high humidity based on dynamic reflection spectra of the PCs. For example, the difference in the refractive indices of m-xylene and p-xylene is only 0.002, the difference of desorption balance time of PCs is 263 s. The PCs have potential applications in visual detections, isomer recognitions and monitoring of volatilization rates of trace liquids.

Photon Management Enabled by Opal and Inverse Opal Photonic Crystals: from Photocatalysis to Photoluminescence Regulation.

Light is a promising renewable energy source and can be converted into heat, electricity, and chemical energy. However, the efficiency of light-energy conversion is largely hindered by limited light-absorption coefficients and the low quantum yield of current-generation materials. Photonic crystals (PCs) can adjust the propagation and distribution of photons because of their unique periodic structures, which offers a compelling platform for photon management. The periodicity of materials with an alternating refractive index can be used to manipulate the dispersion of photons to generate the photonic bandgap (PBG), in which light is reflected. The slow photon effect, i. e., photon propagation at a reduced group velocity near the edges of the PBG, is widely regarded as another valuable optical property for manipulating light. Furthermore, multiple light scattering can increase the optical path, which is a vital optical property for PCs. Recently, the light reflected by PBG, the slow photon effect, and multiple light scattering have been exploited to improve light utilization efficiency in photoelectrochemistry, materials chemistry, and biomedicine to enhance light-energy conversion efficiency. In this review, the fabrication of opal or inverse opal PCs and the theory for improving the light utilization efficiency of photocatalysis, solar cells, and photoluminescence regulation are discussed. We envision photon management of opal or inverse opal PCs may provide a promising avenue for light-assisted applications to improve light-energy-conversion efficiency.

Photonic crystal-coupled enhanced steering emission: A prism-free, objective-free, and metal-free loss-less approach for biosensing

Diagnostic assays utilizing fluorescent reporters in the context of low abundance biomarkers for cancer and infectious disease can reach lower limits of detection through efficient collection of emitted photons into an optical sensor. In this work, we present the rational design, fabrication, and application of one-dimensional photonic crystal (PC) grating interfaces to accomplish a cost-effective prism-free, metal-free, and objective-free platform for augmentation of fluorescence emission collection efficiency. Guided mode resonance (GMR) of the PC is engineered to match the laser excitation (532 nm) and emission maximum (580 nm) of the radiating dipoles to arrive at optimized conditions. The photo-plasmonic hybrid nano-engineering using silver nanoparticles presented >110-fold steering fluorescence enhancement enabling placement of the sample between the excitation source and detector that are in a straight line. From the experimental and simulation inferences, we propose a radiating GMR model by scrutinizing the polarized emission properties of the hybrid substrate, in accordance with the radiating plasmon model. The augmented fluorescence intensity realized here with a simple detection instrument provides sub-nanomolar sensitivity to provide a path toward point-of-care scenarios.

Rapid fabrication of tunable structural color patterns by spray-coating.

Structural color, a color generated based on physical principles, has broad applications such as displays, optical sensors, and anti-counterfeiting. Traditional methods for producing structural colors are often complex and time-consuming, whereas spray-coating colloidal self-assembly offers a simple and controllable alternative. However, due to the high-pressure atomization process, colloidal inks often form amorphous photonic structures (APSs), making it challenging to precisely control the assembly of colloidal particles on substrates to achieve ordered structures. By rationally designing the composition of colloidal mixed solutions, controlling particle concentration, and adjusting evaporation temperatures, it is possible to effectively regulate the assembly of colloidal particles and obtain angle-dependent iridescent colors. This work proposes a simple spray-coating process that enables the control of both ordered and disordered structures, with tunable optical properties, suitable for colloidal patterning on various substrates. This method not only simplifies the fabrication of photonic crystals (PCs) but also has broad potential, particularly in anti-counterfeiting, where it enables the creation of hard-to-replicate structured patterns with enhanced security.

Quasi-3D harnessing of visible light in emissive III-V on Si microstructures: Application to multiple-quantum-well color conversion layers

We report on the design, fabrication, and characterization of the first photonic crystal (PhC)-based red multiple-quantum-well (MQW) color converters fully optimized for augmented reality (AR) microdisplays through a quasi-3D light harnessing principle. This principle leverages an aluminum (Al) bottom reflector and a silicon dioxide (SiO2) gap to harness the bottom-emitted light, along with copper (Cu) lateral mirrors and a silicon nitride (SiN) phase-matcher for Bloch-mode replication. These structures were designed using 3D-FDTD simulations. As a proof-of-principle, we fabricated corresponding devices that exhibit promising characteristics, including record light extraction efficiencies over 40 % for 4 μm pixels and directional emission patterns. Time-resolved photoluminescence (TRPL) analyses, along with a four-wave intensity model developed in this work, indicate that there is still room for improvement. We believe that the guidelines established in this study could pave the way for the use of MQW color converters in the next generation of very bright, high-resolution RGB microdisplays for AR glasses and beyond.

Spectral response of sulfonated polystyrene photonic crystals with varying concentrations of ethanol

Modifying polystyrene (PS) spheres through sulfonation is a well-established method to enhance their hydrophilic properties, rendering them valuable in diverse applications. Fabrication of photonic crystals (PCs) with sulfonated polystyrene (SPS) spheres offers an important platform for sensing applications. The hydrophilic nature of such PC platform helps in improving the detection of water content. In the present work, monodispersed SPS spheres were synthesized by adjusting the duration of the sulfonation reaction on the PS spheres created via emulsifier-free emulsion polymerization. PC opal films were fabricated using self-assembled PS and SPS spheres. The opal films were characterized using various techniques, including Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), angle-resolved reflection spectroscopy (ARRS), zeta potential and dynamic light scattering, and the results were compared and analysed. The hydrophilicity of the opal films was investigated using the water contact angle measurement, and it was found to improved by sulfonation. The spectral response of the PC opal films was investigated by monitoring Bragg’s diffraction spectra from the films using UV–VIS spectrometer. As a demonstration of a specific application, the prepared PC opal films were used to measure the water content in ethanol. PS and SPS opal films exhibited a noticeable blue shift in their spectral response when the water content in ethanol was increased to 3.8% and 3.4%, respectively. The added hydrophilicity brought on by the attached sulfonic groups improved the SPS film’s sensitivity to the water in the ethanol. SPS spheres demonstrated an optical response over a significantly more extensive range of the water content in ethanol than PS, which has a limited response range of up to 50%. Sulfonating PS spheres enhances colloidal stability and minimizes the tendency for aggregation in solution. Sulfonation for more than 3 h is found to exhibit reduced mechanical strength. Though the sulfonation induces an increase in surface roughness, the quality of the ordered arrangement of the spheres remained the same in comparison with PS films. By taking advantage of SPS’s hydrophilicity, high reactivity, stability, and the possibility of attaching additional functional groups, the present study opens up new possibilities for sensing water content in ethanol.

A multi-physics simulation study on material optimization for fabrication of 532-nm operating wavelength photonic crystal

A multi-physics simulation study on material optimization for fabrication of 532-nm operating wavelength photonic crystal

Nanoscale multi-beam lithography of photonic crystals with ultrafast laser

Photonic crystals are utilized in many noteworthy applications like optical communications, light flow control, and quantum optics. Photonic crystal with nanoscale structure is important for the manipulation of light propagation in visible and near-infrared range. Herein, we propose a novel multi beam lithography method to fabricate photonic crystal with nanoscale structure without cracking. Using multi-beam ultrafast laser processing and etching, parallel channels with subwavelength gap are obtained in yttrium aluminum garnet crystal. Combining optical simulation based on Debye diffraction, we experimentally show the gap width of parallel channels can be controlled at nanoscale by changing phase holograms. With the superimposed phase hologram designing, functional structures of complicated channel arrays distribution can be created in crystal. Optical gratings of different periods are fabricated, which can diffract incident light in particular ways. This approach can efficiently manufacture nanostructures with controllable gap, and offer an alternative to the fabrication of complex photonic crystal for integrated photonics applications.

Photonic crystals with rainbow colors by centrifugation-assisted assembly of colloidal lignin nanoparticles

Photonic crystals are optical materials that are often fabricated by assembly of particles into periodically arranged structures. However, assembly of lignin nanoparticles has been limited due to lacking methods and incomplete understanding of the interparticle forces and packing mechanisms. Here we show a centrifugation-assisted fabrication of photonic crystals with rainbow structural colors emitted from the structure covering the entire visible spectrum. Our results show that centrifugation is crucial for the formation of lignin photonic crystals, because assembly of lignin nanoparticles without centrifugation assistance leads to the formation of stripe patterns rather than photonic crystals. We further prove that the functions of centrifugation are to classify lignin nanoparticles according to their particle size and produce monodispersed particle layers that display gradient colors from red to violet. The different layers of lignin nanoparticles were assembled in a way that created semi-closed packing structures, which gave rise to coherent scattering. The diameter of the lignin nanoparticles in each color layer is smaller than that predicted by a modified Bragg’s equation. In situ optical microscope images provided additional evidence on the importance of dynamic rearrangement of lignin nanoparticles during their assembly into semi-closed packing structures. The preparation of lignin nanoparticles combined with the methodology for their classification and assembly pave the way for sustainable photonic crystals.

Rapid fabrication of colloidal crystal films by spin coating using polymeric particles synthesized by dispersion polymerization

Rapid fabrication of colloidal photonic crystals was successfully carried out by spin coating using polymeric beads. To this end, monodisperse polystyrene (PS) nanospheres were synthesized by dispersion polymerization using alcohol as a reaction medium to prepare coating solution. Transmission of visible light at a specific wavelength could be observed, which is measured by transmittance spectra of coating samples. The transmission intensity of light at specific wavelength could be controlled by adjusting rotation speed or the concentration of coating solution, while peak wavelength could be adjusted by the size of PS nanospheres. Inorganic inverse opal like macroporous silica or titania films were fabricated by diffusion of silica or titania nanoparticles through colloidal crystal film, followed by calcination for removal of PS nanospheres. As a demonstrative application of inverse opal films, photocatalytic decomposition of organic dye was performed under UV light illumination by immersing the macroporous titania film in aqueous solution. The rate constant of decomposition reaction could be estimated from transient data of the dye concentration.

Multiplexing Linear and Nonlinear Bragg Diffractions through Volume Gratings Fabricated by Femtosecond Laser Writing in Lithium Niobate Crystal

The femtosecond-laser-writing technique provides a flexible method for fabrication of nonlinear photonic crystals in three dimensions, providing structures that enable efficient complex nonlinear wave interactions and modulation for applications including nonlinear holography, nonlinear beam shaping, and waveguide-integrated wavelength conversion. However, the tightly focused laser pulse inevitably causes structural modification and then changes the local refractive index, resulting in additional linear modulation of the interacting waves. Here, we use the same periodic distributions of the refractive index and the second-order nonlinear coefficient for grating arrays engineered in lithium niobate crystals by femtosecond laser writing to achieve polarization-dependent linear and nonlinear Bragg diffractions simultaneously. The experimental results show that the linear and nonlinear diffraction efficiencies range up to 31% and 2.9 × 10−5, respectively, for grating arrays with dimensions of 100 μm (x) × 100 μm (y) × 100 μm (z). This work paves the way toward the realization of the multiplexing of linear and nonlinear optical modulations in a single structure for potential applications that include multidimensional optical data storage and optical coding.

Recent Progress in the Fabrication of Photonic Crystals Based on Porous Anodic Materials

Photonic crystals (PCs) based on porous anodic materials have been proven to be a potent and versatile instrument for the emergence of new technologies with a wide range of applications. Their lower production costs are one of the key advantages, making PC-based systems more widely available and appropriate for industrial manufacturing. The ability to produce well-defined pores on metal oxide and semiconductor surfaces has experienced a major renaissance due to the striking differences in characteristics between porous surfaces and dense oxide layers. In this review, we give a general overview of the progress of PC fabrication based on porous surfaces of anodized aluminum (Al), silicon (Si), and titanium (Ti) using various anodization techniques, and their optical characteristics and applications are discussed. The anodizing conditions have a large influence on the pore geometry of the produced porous surfaces. The review fully focuses on the advancements made in manufacturing anodic aluminum oxide (AAO), porous silicon (pSi), and titanium-dioxide nanotube (TNT) PCs manufactured using self-ordered anodization under varied conditions. Additionally, a critical assessment of the upcoming developments in PC manufacturing and their optical characteristics suitable for various photonic devices is provided.

Deep Subwavelength Anti-Slot Photonic Crystals Fabricated in Monolithic Silicon Photonics Technology

We report the scalable fabrication and characterization of photonic crystal (PhC) nanobeam waveguides incorporating subwavelength-scale dielectric anti-slot unit cells. These anti-slot PhCs were fabricated using deep UV lithography on a monolithic silicon photonics technology. The dielectric band edge mode is characterized by strong field localization in the anti-slot region where the minimum dielectric feature size is approximately 70 nm. This demonstration opens the door to further investigation of subwavelength engineered photonic structures fabricated using commercial foundry processes for integrated photonics applications that benefit from enhanced light-matter interaction.

Laser-Patterned Alumina Mask and Mask-Less Dry Etch of Si for Light Trapping with Photonic Crystal Structures

Ultra-short 230 fs laser pulses of a 515 nm wavelength were tightly focused onto 700 nm focal spots and utilised in opening ∼0.4-1 μm holes in alumina Al2O3 etch masks with a 20-50 nm thickness. Such dielectric masks simplify the fabrication of photonic crystal (PhC) light-trapping patterns for the above-Lambertian performance of high-efficiency solar cells. The conditions of the laser ablation of transparent etch masks and the effects sub-surface Si modifications were revealed by plasma etching, numerical modelling, and minority carrier lifetime measurements. Mask-less patterning of Si is proposed using fs laser direct writing for dry plasma etching of Si.

Cubic-wavelength mode volume photonic crystal nanobeam cavities in a monolithic CMOS platform.

We report on the design, fabrication, and experimental characterization of photonic crystal (PhC) nanobeam cavities with the smallest footprint, largest intrinsic quality factor, and smallest mode volume to be demonstrated to date in a monolithic CMOS platform. Two types of cavities were designed, with opposite spatial mode symmetries. The opposite mode symmetry, combined with evanescent coupling, allows the nanobeam cavities to be used in reflectionless topologies, desirable in complex photonic integrated circuits (PICs). The devices were implemented and fabricated in a 45 nm monolithic electronics-photonics CMOS platform optimized for silicon photonics (GlobalFoundries 45CLO) and do not require any post-processing. Quality factors exceeding 100 000 were measured for both devices, the highest, to the best of our knowledge, among fully cladded PhC nanobeam cavities in any silicon-on-insulator (SOI) platform. Additionally, the ability of the cavities to confine light into small mode volumes, of the order of (λ/n)3, was confirmed experimentally using near-field scanning optical microscopy (NSOM). These types of cavities are an important step toward realizing ultra-low energy active devices required for the next generation of integrated optical links beyond the current microring resonator-based links and other CMOS PICs.