Photonic Crystal Structure Research Articles

Photonic crystal with magnified resonant peak for biosensing applications

A theoretically and numerically photonic crystal structure with parity-time symmetry is investigated to realize the design of a biomedical sensor for biosensing applications. The transmittance spectra of the structure are investigated, and various performance parameters are evaluated. Different structure parameters such as the unit cell number, the thickness of the sample layer, macroscopic Lorentz oscillation intensity in the PT-symmetry unit cell, the porosity of gallium nitride, and incident angle are theoretically and numerically investigated. To improve the performance of the device, an optimization technique is used. The relatively high sensitivities of 496 nm RIU (the change in the resonant peak wavelength per refractive index unit) and 1002142%/RIU (the change in the transmittance of the resonant peak per refractive index unit) are achieved. The proposed device can be a relatively high-precision detection device for biosensing applications.

Amplification of near field radiation at surfaces of pure dielectric domain with anti-reflection films and photonic crystal structures

With chemical stability under high temperatures, dielectric materials can be idealized thermal emitters for different energy applications. However, dielectric materials do not support surface waves at near-infrared ranges for longer-distance thermal photon tunneling, which limits their applications in near-field thermal radiation. It is demonstrated in this study that thermal field amplification at near-infrared wavelengths at dielectric surfaces could be achieved through asymmetric Fabry–Perot resonance with anti-reflection coatings or 1D photonic crystal type structures. ⩾100 nm near-infrared thermal photon tunneling can be achieved when these thin film structures are added to the emitter and the collector surfaces. Among these two thin film structures, 1D photonic crystal type periodic structures constructed with the same high refractive index material as the emitter/collector material allow near-field thermal photon tunneling at large parallel wavenumbers. Moreover, the field amplification can be increased by adding more 1D photonic crystal layers to achieve even longer distances near field thermal photon tunneling.

Design of wavelength division multiplexing devices based on tunable edge states of valley photonic crystals.

Wavelength division multiplexing (WDM) devices are key photonic integrated circuit (PIC) elements. Conventional WDM devices based on silicon waveguides and photonic crystals have limited transmittance due to the high loss introduced by the strong backward scattering from defects. In addition, it is challenging to reduce the footprint of those devices. Here we theoretically demonstrate a WDM device in the telecommunication range based on all-dielectric silicon topological valley photonic crystal (VPC) structures. We tune its effective refractive index by tuning the physical parameters of the lattice in the silicon substrate, which can continuously tune the operating wavelength range of the topological edge states, which allows the designing of WDM devices with different channels. The WDM device has two channels (1475 nm-1530 nm and 1583 nm-1637 nm), with contrast ratios of 29.6 dB and 35.3 dB, respectively. We demonstrated highly efficient devices for multiplexing and demultiplexing in a WDM system. The principle of manipulating the working bandwidth of the topological edge states can be generally applied in designing different integratable photonic devices. Thus, it will find broad applications.

High-performance chiral all-optical OR logic gate based on topological edge states of valley photonic crystal

For all-optical communication and information processing, it is necessary to develop all-optical logic gates based on photonic structures that can directly perform logic operations. All-optical logic gates have been demonstrated based on conventional waveguides and interferometry, as well as photonic crystal structures. Nonetheless, any defects in those structures will introduce high scattering loss, which compromises the fidelity and contrast ratio of the information process. Based on the spin-valley locking effect that can achieve defect-immune unidirectional transmission of topological edge states in valley photonic crystals (VPCs), we propose a high-performance all-optical logic OR gate based on a VPC structure. By tuning the working bandwidth of the two input channels, we prevent interference between the two channels to achieve a stable and high-fidelity output. The transmittance of both channels is higher than 0.8, and a high contrast ratio of 28.8 dB is achieved. Moreover, the chirality of the logic gate originated from the spin-valley locking effect allows using different circularly polarized light as inputs, representing “1” or “0”, which is highly desired in quantum computing. The device’s footprint is 18 μm × 12 μm, allowing high-density on-chip integration. In addition, this design can be experimentally fabricated using current nanofabrication techniques and will have potential applications in optical communication, information processing, and quantum computing.

Исследование спектроскопических свойств фотонных кристаллов и наноструктур

The paper proposes substantiation of dependence of dielectric permittivity, polariton dispersion and light group velocity in the sodium uranyl acetate on the wavelength. Many bands were found in the uranyl compounds transmission and absorption spectra. It was indicated that the polariton waves group velocity was decreasing anomalously in vicinity of the resonant absorption frequencies, i.e., the light was effectively stopped. This led to abnormal increase in the efficiency between the light interaction processes and the matter. Optical properties of the one-dimensional photonic crystal film formed by electrochemical etching of aluminum foil were studied. Experimental data on the transmission and reflection spectra in the region of first, second and third stop bands of the anode photonic aluminum oxide crystal were compared with theoretical dependence obtained from the known dispersion relation. Refractive indices of the first and second layers of various thin photonic crystal films, structure period and effective refractive index of the structures were theoretically calculated. Possibility of controlling position of the stop bands of one-dimensional photonic crystals in accordance with the Wulff --- Bragg’s relation was established. The studied photonic crystals could be used in experimental setups to register the light combined scattering spectra of dielectric media in the low-frequencies region

Design, Preparation and Characterization of Mid-infrared Low-emissivity Film

The rapid development of infrared detection technology requires that military targets have mid-infrared stealth performance. In this paper, a mid-infrared low-emissivity film based on one-dimensional photonic crystal structure was designed and prepared. The results showed that its reflectivity properties are improved and total thickness is reduced by optimizing the construction parameters. The thickness and refractive index of the prepared Ge film and ZnSe film were tested using IR ellipsometer. After the test results were brought into the designed structure, mid-infrared low-emissivity films with emissivity of 0.032, 0.068, 0.146, 0.203 and 0.366 were prepared by vacuum evaporation. The infrared reflectivity of the mid-infrared low-emissivity films was tested using Fourier spectrometer, and the test results are in good agreement with calculated results.

Highly Directive Leaky-Wave Radiation in 2-D Dielectric Photonic Crystals

A comparative study of the directive radiation obtained from two kinds of 2-D photonic crystal structures excited by an electric source is presented in this letter. These structures consist of a stack of periodic chains of dielectric cylinders in free space or of circular voids in dielectric media. On the basis of an in-depth description of the physical phenomena underlying the Bloch transverse-electric modal field configurations of such structures, a set of design rules to achieve highly directive leaky-wave radiation is obtained. An analysis of the two types of structures shows that it is preferable to consider holey lattices to achieve more directive radiation, obtained by the excitation of a weakly attenuated fundamental leaky mode. Indeed, radiators consisting of an integer number of periodic chains of voids drilled in a dielectric medium over a metal plate show directivity at broadside approximately 6 dB higher than in the dielectric cylinder case. This class of holey lattices can be used to design highly directive leaky-wave antennas, with significant advantages of easy manufacturing, design simplicity, and low complexity.

Anodizing aluminum in a viscous electrolyte to produce one-dimensional photonic crystals

In the paper, the possibility to produce anodic aluminum oxide (AAO) featuring one-dimensional photonic crystal along the normal to the surface is shown. The AAO structure is represented by alternating layers of different porosity and is formed in a viscous electrolyte based on sulfuric acid and ethylene glycol at the periodically varying from high (1.8 mA/cm2) to low (0.4 mA/cm2) current density with a rectangular pulse shape. The pore sizes and interpore distance, pore density and porosity, thickness and period of the AAO structure have been determined. The specular reflection spectra features for single layers that make up the AAO structure and for one-dimensional photonic crystals structures consisting of 165 periods have been studied. An increase in the porosity of the upper layers of the structure due to chemical etching of the pores during the oxide growth is noted. It is shown that the invariance of the spectral position of the photonic band gap for AAO structures is achieved by a 0.1 % decrease in charge at each subsequent anodizing cycle during their formation, which leads to a decrease in the period of the structure in the lower layers, compensating for the increase in the upper layers porosity. The reflection spectra have been analyzed for the incidence angles of 10° and 30° and used to calculate the period of the structure and the effective refractive index. The effective refractive index of the single layers that make up the AAO structure is calculated using the optical Fabry–Perot oscillations. For AAO with the properties of one-dimensional photonic crystal, a green color is observed at normal light incidence, and an iridescent color is observed when the angle changes. AAO can be used as a decorative coating on the housings of electronic devices (tablets, laptops, phones, etc.) and when creating design objects made of aluminum and its alloys.

Eight-channel C-Band demultiplexer based on one-dimensional photonic crystals defected with lithium niobate

We propose an eight-channel Dense Wavelength Division Demultiplexer (DWDM) device based on one-dimensional photonic crystal (1-D PC) structures defected with lithium niobate (LiNbO3) thin films. The demultiplexer operates in the C-band window (1460–1560 nm), which belongs to the ITU grid for DWDM applications. The desired output wavelength is achieved by applying the proper external electric field to the LiNbO3 layer at various temperatures. The transfer matrix method (TMM) is used to simulate the transmittance spectrum. Efficient output channels with transmittances of about 90% are attained. An excellent quality factor of 30919 and a very small line width of 0.05 nm are exceptional values acquired by the output channels. A very small channel spacing of 0.182 nm is attained without compromising the crosstalk, which reaches a minimum value of −34 dB. The astounding characteristics of the eight channels reveal that the proposed demultiplexer could be a potentially efficient device for DWDM networks.

Influence of photonic crystals on the performance parameters of GeSn vertical-structure photodiodes

In recent years, use of photonic crystals has been recognized as a viable approach to resolve the contradiction between operating speed and light absorption in vertical-structure photodiodes. In this paper, we present a photonic crystal that enhances the responsivity of a GeSn pin photodiode in the near-infrared region of the spectrum. Additionally, the effects of this photonic crystal on the most important properties of the GeSn photodiodes are studied. Based on measurement and analysis of the device’s dark current, responsivity, and speed characteristics, the photonic crystal structure reduces the dark current by approximately 57%, increases the responsivity at 1550 nm and 1650 nm by factors of 2.4 and 3.9, respectively, and increases the 3dB bandwidth at 1550 nm by a factor of approximately 2.6. These results demonstrate that photonic crystals have good application value for solution of the contradiction between the light absorption and operating speed characteristics of high-speed photodiodes.

Simulation of Boosting Efficiency of GaAs Absorption Layers with KNbO3 Scatterers for Solar Cells

In this work, gallium arsenide (GaAs), which has an adjustable band gap and low cost, was adopted as an absorption layer in which KNbO3, having good dielectric, photoelectric, and piezoelectric properties, served as a scattering element for the improvement in absorption efficiency of solar cells. Benefited by the high absorption efficiency of KNbO3, the utilization of the ultraviolet and infrared bands for solar cells can be strengthened. In addition, the ferroelectric and photovoltaic characteristics of KNbO3 enable the realization of decreased thickness of solar cells. Based on the simulation of the shape, width, and period of the scattering element, the effect of the thickness of the scattering element on the absorption efficiency, quantum efficiency, and total efficiency of absorption efficiency was comprehensively simulated. The results show that the absorption layer delivers the optimal performance when using a hexagonal KNbO3 scattering element. The absorption efficiency of the GaAs absorption layer with KNbO3 as the scattering element is increased by 28.42% compared with that of a GaAs absorption layer with empty holes. In addition, the quantum efficiency is maintained above 98% and the total efficiency is 91.59%. At the same time, the efficiency of such an absorption layer is still above 90% when the angle ranges from 0 to 70°. This work provides theoretical guidance for the rational design of solar cells based on photonic crystal structures.

Generation of Tamm Plasmon Resonances for Light Confinement Applications in Narrowband Gradient-Index Filters Based on Nanoporous Anodic Alumina.

Gold-coated gradient-index filters based on nanoporous anodic alumina (Au-coated NAA-GIFs) were used as model platforms to elucidate how Tamm plasmons can be tailored by engineering the geometric features of the plasmonic and photonic components of these hybrid structures. NAA-GIFs with well-resolved, intense photonic stopbands at two positions of the visible spectrum were fabricated through sinusoidal pulse anodization. These model photonic crystals were used to assess how the quality of Tamm plasmon resonances can be enhanced by tuning the features of the dielectric mirror and the thickness of the porous gold coating layer. It is found that the highest value of the quality factor of Tamm resonance (Q Tamm = 237) is obtained for 11 nm of gold on a dielectric mirror with low porosity corresponding to the resonant spectral position of λTamm of ∼698 nm. Our analysis indicates that Tamm resonances in as-produced Au-coated NAA-GIFs are weak due to the constrained range of wavelengths (narrow bands) at which these photonic crystal structures reflect light. However, after broadening of their photonic stopband upon pore widening, Tamm resonances become better resolved, with higher intensity. It is also observed that the quality of light confinement worsens progressively with the thickness of the porous gold coating layer after a critical value. In contrast to conventional surface plasmon resonance systems, this hybrid Tamm porous system does not require complex coupling systems and provides a nanoporous structure that can be readily tailored for a range of photonic technologies such as sensing and lasing.

Monolithically integrated photonic crystal surface emitters on silicon with a vortex beam by using bound states in the continuum.

Optical resonant cavities with high quality factor (Q-factor) are widely used in science and technology for their capabilities of strong confinement of light and enhanced light-matter interaction. The 2D photonic crystal structure with bound states in the continuum (BICs) is a novel concept for resonators with ultra-compact device size, which can be used to generate surface emitting vortex beams based on symmetry-protected BICs at the Γ point. Here, to the best of our knowledge, we demonstrate the first photonic crystal surface emitter with a vortex beam by using BICs monolithically grown on CMOS-compatible silicon substrate. The fabricated quantum-dot BICs-based surface emitter operates at 1.3 µm under room temperature (RT) with a low continuous wave (CW) optically pumped condition. We also reveal the BIC's amplified spontaneous emission with the property of a polarization vortex beam, which is promising to provide a novel degree of freedom in classical and quantum realms.

Remarkable enhancement of photoluminescence and photoresponse due to photonic crystal structures based on GeSiSn/Si multiple quantum wells

The GeSiSn/Si structures surface with multiple quantum wells (MQWs) was modified by developing photonic crystals (PCs) to increase the photoluminescence and photoresponse near 2 μm. The structural parameters of GeSiSn/Si MQWs obtained by molecular-beam epitaxy were optimized, and PCs were formed. They consisted of a periodic cylindrical hole array. Numerical simulation methods were used to optimize the hole depth, which makes it possible to effectively excite quasi-guided modes and not affect the active layer including GeSiSn/Si MQWs. The increase of the photoluminescence (PL) signal related to vacancy complexes was observed for all samples with the PC structure. The maximum PL amplification of about 5 times at the wavelength near 2 μm was demonstrated. The annealing of PC structures with GeSiSn/Si MQWs resulted in the appearance of PL associated with interband optical transitions. The PL enhancement was observed by almost an order of magnitude in the narrow wavelength range with the PL maximum near 1.8 μm. Based on Ge0.84Si0·076Sn0·084/Si MQWs p-i-n photodiodes with the PC, the photoresponse increase was shown in the wide wavelength range up to 1.8 μm.

Highly boosted trace-amount terahertz vibrational absorption spectroscopy based on defect one-dimensional photonic crystal.

Although terahertz (THz) spectroscopy demonstrates great application prospects in the fields of fingerprint sensing and detection, traditional sensing schemes face unavoidable limitations in the analysis of trace-amount samples. In this Letter, a novel, to the best of our knowledge, absorption spectroscopy enhancement strategy based on a defect one-dimensional photonic crystal (1D-PC) structure is proposed to achieve strong wideband terahertz wave-matter interactions for trace-amount samples. Based on the Fabry-Pérot resonance effect, the local electric field in a thin-film sample can be boosted by changing the length of the photonic crystal defect cavity, so that the wideband signal of the sample fingerprint can be greatly enhanced. This method exhibits a great absorption enhancement factor, of about 55 times, in a wide terahertz frequency range, facilitating the identification of different samples, such as thin α-lactose films. The investigation reported in this Letter provides a new research idea for enhancing the wide terahertz absorption spectroscopy of trace samples.

Butterfly-Inspired Tri-State Photonic Crystal Composite Film for Multilevel Information Encryption and Anti-Counterfeiting.

Counterfeiting is a worldwide issue and has long troubled legitimate businesses, while nowadays anti-counterfeiting materials and technology are still insufficient to combat the escalating counterfeit behaviors. Inspired by hindwing structure of Troides magellanus, a new kind of anti-counterfeiting material taking advantage of both physical and chemical structures to display multiple optical states is prepared. The chemical units (luminescent lanthanide) are blended with physical units (monodispersed colloidal particles) and mediating molecules, which are then assembled into a photonic crystal structure at room temperature in less than 10s through a new assembly technique called molecule-mediated shear-induced assembly technique (MSAT). The as-prepared photonic crystal films feature three unique optical states, each displaying structural, fluorescent, and phosphorescent color under different lighting conditions, which integrates colors from both physical and chemical origins. Furthermore, by incorporating different luminescent materials into different parts of the photonic crystal pattern, a high-level information encryption system is designed to be capable of carrying three distinct types of information. Thanks to this powerful tool of MSAT, it is now possible to assemble different-sized, even irregular non-spherical units with monodispersed spherical units into high-quality photonic crystal films, which provides easy access to incorporating new features into photonic crystal systems.

Photonic Crystal Enhanced Fluorescence: A Review on Design Strategies and Applications.

Nanoscale fluorescence emitters are efficient for measuring biomolecular interactions, but their utility for applications requiring single-unit observations is constrained by the need for large numerical aperture objectives, fluorescence intermittency, and poor photon collection efficiency resulting from omnidirectional emission. Photonic crystal (PC) structures hold promise to address the aforementioned challenges in fluorescence enhancement. In this review, we provide a broad overview of PCs by explaining their structures, design strategies, fabrication techniques, and sensing principles. Furthermore, we discuss recent applications of PC-enhanced fluorescence-based biosensors incorporated with emerging technologies, including nucleic acids sensing, protein detection, and steroid monitoring. Finally, we discuss current challenges associated with PC-enhanced fluorescence and provide an outlook for fluorescence enhancement with photonic-plasmonics coupling and their promise for point-of-care biosensing as well monitoring analytes of biological and environmental relevance. The review presents the transdisciplinary applications of PCs in the broad arena of fluorescence spectroscopy with broad applications in photo-plasmonics, life science research, materials chemistry, cancer diagnostics, and internet of things.

Deep reactive ion etching of cylindrical nanopores in silicon for photonic crystals

Periodic arrays of deep nanopores etched in silicon by deep reactive ion etching are desirable structures for photonic crystals and other nanostructures for silicon nanophotonics. Previous studies focused on realizing as deep as possible nanopores with as high as possible aspect ratios. The resulting nanopores suffered from structural imperfections of the nanopores, such as mask undercut, uneven and large scallops, depth dependent pore radii and tapering. Therefore, our present focus is to realize nanopores that have as cylindrical as possible shapes, in order to obtain a better comparison of nanophotonic observations with theory and simulations. To this end in our 2-step Bosch process we have improved the mask undercut, the uneven scallops, pore widening and positive tapering by optimizing a plethora of parameters such as the etch step time, capacitively coupled plasma (ion energy) and pressure. To add further degrees of control, we implemented a 3-step DREM (deposit, remove, etch, multistep) process. Optimization of the etching process results in cylindrical nanopores with a diameter in the range between 280 and 500 nm and a depth around 7 μm, corresponding to high depth-to-diameter aspect ratios between 14 and 25, that are very well suited for the realization of silicon nanophotonic structures.

Quasi-guided modes resulting from the band folding effect in a photonic crystal slab for enhanced interactions of matters with free-space radiations.

We elucidate that guided modes supported by a regular photonic crystal slab structure composed of a square lattice of air holes in a silicon slab will transition into quasi-guided (leaky) modes when the radius of every second column of air holes is changed slightly. This intentional geometric perturbation will lead to a doubling of the period in one direction and the corresponding shrinkage of the first Brillouin zone. Because of the translational symmetry in the k-space, leaky waves inheriting the spatial dispersion of the original guided modes, which do not interact with external radiation, will appear with the dispersion curves above the light cone. Our results show that ultrahigh Q-factor resonances with large operating bandwidth can be achieved. Interestingly, the perturbation in only one direction of the photonic lattice will lead to an in-plane wave number-dependent resonance characteristic in both directions. Our numerical results demonstrate a local enhancement of the electric field magnitude by the order of 102, which is even more significant than those in most plasmonic structures. These quasi-guided modes with superior properties will provide a new platform for efficient light-matter interactions.

AIE-doped Poly(Ionic Liquid) Photonic Spheres for the Discrimination of Psychoactive Substances.

Drugs of abuse has drawn intense attention due to increasing concerns to public health and safety. The construction of a sensing platform with the capability to identify them remains a big challenge because of the limitations of synthetic complexity, sensing scope and receptor extendibility. Here a kind of poly(ionic liquid) (PIL) photonic crystal spheres doped with aggregation-induced emission (AIE) luminogens was developed. As diverse noncovalent interactions involve in PIL moieties, the single sphere shows different binding affinity to a broad range of psychoactive substances. Furthermore, the dual-channel signals arising from photonic crystal structures and sensitive AIE-luminogens provide high-dimensional information for discriminative detection of targets, even for molecules with slight structural differences. More importantly, such single sphere sensing platform could be flexibly customized through ion-exchange, showing great extendibility to fabricate high-efficiency/high-throughput sensing arrays without tedious synthesis.