Photonic Band Gap Crystals Research Articles

Expanding momentum bandgaps in photonic time crystals through resonances

Expanding momentum bandgaps in photonic time crystals through resonances

Adjusting the opening and closing of the bandgaps of plasma photonic crystals

Closing or opening the first two photonic bandgaps (PBGs) of plasma photonic crystals (PPCs) by adjusting the plasma parameters are studied. We first calculated the impedance of the band structure of one-dimensional PPCs and found that in the presence of plasma, the impedance under two certain frequencies can match that of the air. We have verified through simulation that when the two PBG frequencies and two impedance-matched frequencies are equal to each other, the two PBGs can be closed simultaneously under the same plasma density. On the other hand, a more common situation is that we need two plasma densities to, respectively, close the two PBGs located near different impedance-matched frequencies. At this point, by adjusting the plasma density, the PBGs can be closed in segments, that is, we can choose to close or open the corresponding PBGs at different plasma densities.

A semi-definite optimization method for maximizing the shared band gap of topological photonic crystals

Topological photonic crystals (PCs) can support robust edge modes to transport electromagnetic energy in an efficient manner. Such edge modes are the eigenmodes of the PDE operator for a joint optical structure formed by connecting together two photonic crystals with distinct topological invariants, and the corresponding eigenfrequencies are located in the shared band gap of two individual photonic crystals. This work is concerned with maximizing the shared band gap of two photonic crystals with different topological features in order to increase the bandwidth of the edge modes. We develop a semi-definite optimization framework for the underlying optimal design problem, which enables efficient update of dielectric functions at each time step while respecting symmetry constraints and, when necessary, the constraints on topological invariants. At each iteration, we perform sensitivity analysis of the band gap function and the topological invariant constraint function to linearize the optimization problem and solve a convex semi-definite programming (SDP) problem efficiently. Numerical examples show that the proposed algorithm is superior in generating optimized optical structures with robust edge modes.

Exploiting the Bragg Mirror Effect of TiO2 Nanotube Photonic Crystals for Promoting Photoelectrochemical Water Splitting.

Exploiting the Bragg mirror effect of photonic crystal photoelectrode is desperately desired for photoelectrochemical water splitting. Herein, a novel TiO2 nanotube photonic crystal bi-layer structure consisting of a top nanotube layer and a bottom nanotube photonic crystal layer is presented. In this architecture, the photonic bandgap of bottom TiO2 nanotube photonic crystals can be precisely adjusted by modulating the anodization parameters. When the photonic bandgap of bottom TiO2 nanotube photonic crystals overlaps with the electronic bandgap of TiO2, the bottom TiO2 nanotube photonic crystal layer will act as a Bragg mirror, leading to the boosted ultraviolet light absorption of the top TiO2 nanotube layer. Benefiting from the promoted UV light absorption, the TiO2 NT-115-NTPC yields a photocurrent density of 1.4 mA/cm2 at 0.22 V vs. Ag/AgCl with a Faradic efficiency of 100%, nearly two times higher than that of conventional TiO2 nanotube arrays. Furthermore, incident photon-to-current conversion efficiency is also promoted within ultraviolet light region. This research offers an effective strategy for improving the performance of photoelectrochemical water splitting through intensifying the light-matter interaction.

Printing of 3D photonic crystals in titania with complete bandgap across the visible spectrum.

A photonic bandgap is a range of wavelengths wherein light is forbidden from entering a photonic crystal, similar to the electronic bandgap in semiconductors. Fabricating photonic crystals with a complete photonic bandgap in the visible spectrum presents at least two important challenges: achieving a material refractive index > ~2 and a three-dimensional patterning resolution better than ~280 nm (lattice constant of 400 nm). Here we show an approach to overcome such limitations using additive manufacturing, thus realizing high-quality, high-refractive index photonic crystals with size-tunable bandgaps across the visible spectrum. We develop a titanium ion-doped resin (Ti-Nano) for high-resolution printing by two-photon polymerization lithography. After printing, the structures are heat-treated in air to induce lattice shrinkage and produce titania nanostructures. We attain three-dimensional photonic crystals with patterning resolution as high as 180 nm and refractive index of 2.4-2.6. Optical characterization reveals ~100% reflectance within the photonic crystal bandgap in the visible range. Finally, we show capabilities in defining local defects and demonstrate proof-of-principle applications in spectrally selective perfect reflectors and chiral light discriminators.

Chiral Polymer‐Organic Molecule Composite with Circularly Polarized Thermally Activated Delayed Fluorescence and Room‐Temperature Phosphorescence by Bridging Effect of Hydrogen Bond

AbstractCircularly polarized luminescence is essential to chiral and photonic science, but achieving circularly polarized thermally activated delayed fluorescence (CP‐TADF) and circularly polarized room‐temperature phosphorescence (CP‐RTP) simultaneously remains a great challenge. This is because it is difficult to satisfy simultaneously the stable triplet exciton, appropriate energy gap, and the regular chiral environment. Herein, a simple strategy is reported to construct a persistent photoluminescent system, which can achieve TADF and RTP simultaneously by suppressing the non‐radiative transition decay of the triplet exciton through intermolecular hydrogen bonding between acridine flavin (AF) and rigid polymer network. The persistent photoluminescent composite exhibited ultra‐long lifetimes and high quantum yields. Then, a rarely multi‐circularly polarized photoluminescence system containing CP‐TADF and CP‐RTP is constructed by the co‐assembly of cellulose nanocrystals, polyvinyl alcohol, and AF. By utilizing the cholesteric structure, photonic band gap of chiral photonic crystals, and the stabilization mechanism of triplet exciton by intermolecular hydrogen bonding between the light emitter and rigid polymer, chiral photoluminescent films exhibited rare optical properties simultaneously: multi‐circularly polarized photoluminescence emission, high and tunable dissymmetric factor, significant quantum yield, and ultralong lifetimes, which are not reported before and broaden the perspective for multi‐circularly polarized luminescence.

Strongly Inhibited Spontaneous Emission of PbS Quantum Dots Covalently Bound to 3D Silicon Photonic Band Gap Crystals.

We present an optical study of the spontaneous emission of lead sulfide (PbS) nanocrystal quantum dots in 3D photonic band gap crystals made from silicon. The nanocrystals emit in the near-infrared range to be compatible with 3D silicon nanophotonics. The nanocrystals are covalently bound to polymer brush layers that are grafted from the Si-air interfaces inside the nanostructure by using surface-initiated atom transfer radical polymerization. The presence and position of the quantum dots were previously characterized by synchrotron X-ray fluorescence tomography. We report both continuous wave emission spectra and time-resolved, time-correlated single photon counting. In time-resolved measurements, we observe that the total emission rate greatly increases when the quantum dots are transferred from suspension to the silicon nanostructures, likely due to quenching (or increased nonradiative decay) that is tentatively attributed to the presence of Cu catalysts during the synthesis. In this regime, continuous wave emission spectra are known to be proportional to the radiative rate and thus to the local density of states. In spectra normalized to those taken on flat silicon outside the crystals, we observe a broad and deep stop band that we attribute to a 3D photonic band gap with a relative bandwidth of up to 26%. The shapes of the relative emission spectra match well with the theoretical density of states spectra calculated with plane-wave expansion. The observed inhibition is 4-30 times, similar to previously reported record inhibitions, yet for coincidental reasons. Our results are relevant to applications in photochemistry, sensing, photovoltaics, and efficient miniature light sources.

Non-utopian optical properties computed of a tomographically reconstructed real photonic nanostructure.

State-of-the-art computational methods combined with common idealized structural models provide an incomplete understanding of experimental observations on real nanostructures, since manufacturing introduces unavoidable deviations from the design. We propose to close this knowledge gap by using the real structure of a manufactured nanostructure as input in computations to obtain a realistic comparison with measurements on the same nanostructure. We demonstrate this approach on the structure of a real inverse woodpile photonic bandgap crystal made from silicon, as previously obtained by synchrotron X-ray imaging. A 2D part of the dataset is selected and processed into a computational mesh suitable for a Discontinuous Galerkin Finite Element Method (DGFEM) to compute broadband optical transmission. We compare this to the transmission of a utopian crystal: a hypothetical model crystal with the same filling fraction where all pores are taken to be identical and circular. The shapes of the nanopores in the real crystal differ in a complex way from utopian pores due to scallops, tapering, or roughness. Hence, the transmission spectrum is complex with significant frequency speckle both outside and inside the main gap. The utopian model provides only limited understanding of the spectrum: while it accurately predicts low frequency finite-size fringes and the lower band edge, the upper band edge is off, it completely misses the presence of speckle, the domination of speckle above the gap, and possible Anderson localized states in the gap. Moreover, unlike experiments where one can only probe from the outside of a real crystal, the use of a numerical method allows us to study all fields everywhere. While at low frequencies the effect of the pore shapes is minimal on the fields, major differences occur at higher frequencies including the gap such as high-field states localized deep inside the real crystal. We conclude that using only external measurements and utopian models may give an erroneous picture of the fields and the local density of states (LDOS) inside a real crystal, while this is remedied by our new approach.

Bioinspired photonic crystal structures from Papilio Ulysses butterfly wings for versatile laser applications

Photonic crystals found within the wing of a Papilio Ulysses butterfly have demonstrated their efficacy in facilitating laser processes, particularly as a scattering material for imaging and illumination applications. This study delves into the investigation of the photonic crystal's band gap within the butterfly's wing, aiming to realize blue band-edge lasing using a newly developed gain medium comprising diphenylaminofluorene-based chromophores featuring a donor-acceptor-donor (D-A-D) motif. The versatility of the fabricated sample is highlighted, as it can function as both a single-mode laser and a random laser, with the operational mode determined by adjusting the excitation power and the direction of the pump source. Specifically, it exhibits a threshold of 2.5 μJ for random laser operation and 7.6 μJ for single-mode laser operation. The unique architectural elements found in the butterfly's wing, including the ridges on the wing scale and the photonic crystal within the scales, play distinct roles in enabling random laser and single-mode laser actions, respectively. This distinctive butterfly wing architecture holds promise for inspiring the development of future photoelectronic circuits requiring a hybrid design that incorporates both single-mode and comb-mode laser functionalities.

Arbitrary Polarization Conversion by the Photonic Band Gap of the One-Dimensional Photonic Crystal

Arbitrary Polarization Conversion by the Photonic Band Gap of the One-Dimensional Photonic Crystal

Multilevel Information Encryption Mediated by Reconfigurable Thermal Emission in Smart Bilayer Material

AbstractSmart thermal emission, which is response to external stimuli, has provided an unparalleled approach to exploiting optical devices that allows for tunable photon radiance. Here, an approach of implementing information encryptions using a smart thermal emission material that exhibits non‐volatile, multifunctional, and on‐chip‐integrable properties is reported. The smart material is a bilayer structure, consisting of a tungsten (W)‐doped vanadium dioxide (VO2) thin film layer and a self‐assembled polystyrene (PS) microsphere layer. Significant differences between the phase transition temperatures of differently doped VO2 films enable reconfigurable thermal emission in response to heat. Levels of information recorded by the patterning of these VO2 films are thus encrypted thermo‐radiatively. Additionally, the structural color of PS layer, as a result of photonic crystal bandgap effect, shades the encoded patterns from visible observation, and provides an anti‐counterfeiting function. Notable observation angle independence and device‐friendly encoding processes are also demonstrated. Based on these thermo‐tunable emission characteristics, the concept of multilevel data encryption via infrared radiation detection, temperature dependence, and visible anti‐counterfeiting, is realized by the smart bilayer material.

High-g-factor phase-matched second harmonic generation near photonic bandgap of polar cholesteric liquid crystals

ABSTRACT The discovery of polar liquid crystals, such as ferroelectric and helielectric liquid crystals, provides fascinating platforms for designing and modulating polarisation structures that generate strong second harmonic generation. Here, we report that the helielectric nematics, i.e. the polar cholesteric liquid crystals, realise an unprecedented phase-matching condition for the second harmonic generation in the photonic bandgap. Like the circular dichroism in the linear optical regime, the phase-matched second harmonic generation generated in a helielectric nematic medium exhibits a circular polarisation selectivity in the nonlinear optical regime. The maximum g-factor for the second harmonic generation is over ~ 1.95.

Frequency encoded tristate Pauli X-gate using SOA assisted photonic band gap crystal

The quantum optical tristate Pauli-X gate can broadly be used due to its very fast speed of operation up to THz order, very fast information processing rate, and a wide domain of application. This Pauli X-gate is also important as it can undergo inversion operation. In this proposed scheme, the quantum tristate Pauli-X logic gate has been constructed by a closely packed square lattice of 2D air photonic band gap crystal (PhCs) composed of GaAsInP-dopped rods. The photonic band gap crystal-based tristate Pauli-X gate is performed also as an all-optical reversible quantum logic gate which has the character of low-powered output, very fast speed and a densely packed design structure. This photonic crystal-based structure is also verified by simulation experiment that this proposed scheme performs as the path of two input signals are cross-exchanged to one another at the output, retaining the path of the other input signal same. In this paper, the frequency encoding technique is used in all the designs to establish the logic of all-optical tristate Pauli X-gate towards the need of obtaining a three-input-three-output inversion system. The frequency encoding technique and the photonic crystal-based three Semiconductor Optical Amplifiers (pc-SOAs) are used here in all the schemes to establish the logic of the tristate Pauli-X gate scheme. Tristate Pauli-X gates have been designed and analyzed by Finite-Difference Time-Domain (FDTD) and Plane Wave Expansion (PWE) techniques. The Plane Wave Expansion (PWE) technique is used here in each system for determining the frequency range of band gap structure of transverse electric (TE) mode in the units of μm-1. All of these devices perform within the frequency range 0.629818≤ω2πc≤0.888037 and 1.17551≤ω2πc ≤ 1.34921 μm-1. The wafer dimension of each photonic band gap crystal-based device is 19.20 μm (length) × 16.20 μm (width) providing a very fast response time and very fast information handling (bit rate) capacity, which is found good for these THz Photonic crystal devices. Simulation results show that the proposed gate provides a response period of 0.291 ps and a bit rate of 3.44 Tbps, operating with a low input power of 3.45 mW. The reversible gate exhibits a response period of 0.289 ps and a bit rate of 3.46 Tbps, operating also with a low input power of 2.70 mW. Additionally, the alternative Pauli-X gate demonstrates a response time of 0.291 ps and a bit rate of 3.44 Tbps, operating with a low input power of 2.83 mW.

Manipulation of random laser by the bandgap in three-dimensional SiO2 photonic crystals

Photonic crystals (PCs) are artificial structures with different dielectric constants that are arranged periodically in space and can control the propagation of electromagnetic waves of specific frequencies. The photonic bandgap can tune the photon state density, which is beneficial for the generation of random lasers (RLs). In this paper, a thin film of PMMA-doped DCJTB is spun-coated on a silicon dioxide (SiO2)PC to produce an RL. The PC is fabricated by a convenient dip-coating method with variable PBGs by changing the diameter of SiO2 nanospheres. By changing the position of the PBG gap, the RL emission peak can be effectively manipulated with an emission wavelength of up to 16 nm. By adding Au nanoparticles, the lasing performance is improved due to the surface plasmon resonance effect and strong photon scattering, where the emission intensity is increased by 191.9 %, and the threshold is decreased by 37.8 %. The imaging results show that the RL has low spatial coherence, which has a good application in speckle-free imaging. This study provides an effective method to produce a low threshold, high-quality RL with convenient manipulation of lasing properties, which opens the door for expanding its application in optoelectronic devices and speckle-free imaging.

The Determination of the Sensitivity of Refractive Index Sensors

A new approach to determining the sensitivity of refractive index sensors is proposed. It has been shown that relative and absolute sensitivity show different results, and also, for the first time, it is demonstrated that relative sensitivity has advantages over absolute sensitivity. In addition, the influence of the relative width of the photonic band gap and the difference in the refractive indices of the layers on the sensitivity are examined and the corresponding dependences of these parameters are obtained. We propose these parameters as a convenient tool for optimizing the sensitivity of sensors based on defective photonic crystals. Finally, results are obtained regarding the behavior of the defect mode at the center of the photonic band gap of one-dimensional photonic crystals.

Tunable wide-angle high-efficiency polarization selectivity based on a one-dimensional photonic crystal containing elliptical metamaterials

Recently, researchers achieved wide-angle high-efficiency polarization selectivity based on polarization-sensitive photonic bandgaps in one-dimensional photonic crystals containing elliptical metamaterials. However, wide-angle high-efficiency polarization selectivity can only operate at fixed wavelengths (around band edges), which intensively limits the practical applications. To overcome this limitation, we construct a one-dimensional photonic crystal containing phase-change-material-based elliptical metamaterials. The position of the polarization-sensitive photonic bandgap can be flexibly controlled by the crystallization rate of the phase change material. Empowered by the wavelength-tunable polarization-sensitive photonic bandgap, we achieve wavelength-tunable wide-angle high-efficiency polarization selectivity. As the crystallization rate increases from 0 % to 100 %, the operating wavelength of polarization selectivity can be flexibly tuned from 1440 to 1796 nm. Meanwhile, the operating angular width remains larger than 50° and the optimal polarization extinction ratio remains on the order of 104. Our work provides a viable route to designing tunable high-performance polarizers.

Alternative scheme for implementation of 3 qubit Fredkin gate with photonic bandgap crystal

Alternative scheme for implementation of 3 qubit Fredkin gate with photonic bandgap crystal

Genetic Optimization of the Y-Shaped Photonic Crystal NOT Logic Gate

The present paper is devoted to the actual problem of photonic crystal (PhC) logic gate design. The development of components for photonic digital computing systems will provide opportunities for high-efficient information processing. The use of 2D photonic crystals is one of the most promising approaches to designing interference logic gates. Photonic crystal band gap and use of lattice defects are giving opportunities for flexible control of waveguiding light. Interference logic gates of NOT, OR, AND, and XOR types based on the Y-shaped structure are well known. However, known realizations have limited energy efficiency. Earlier, a method for minimizing energy losses at the PhC waveguide bending based on genetic optimization of the PhC waveguide topology was proposed and investigated. In this paper, the genetic algorithm for optimization of the PhC interference logic gate of the NOT type was used. Optimization of the Y-shaped topology allowed for an increase in the energy efficiency of the logic gate to 95%. A description of the developed numerical procedure as well as computer simulation results are presented. The developed procedure includes the possibility of taking into account the limitations of the technology to be used for the realization of a designed 2D PhC structure.

Versatile Double Bandgap Photonic Crystals of High Color Saturation.

Double bandgap photonic crystals (PCs) exhibit significant potential for applications in various color display-related fields. However, they show low color saturation and inadequate color modulation capabilities. This study presents a viable approach to the fabrication of double bandgap photonic inks diffracting typical secondary colors and other composite colors by simply mixing two photonic nanochains (PNCs) of different primary colors as pigments in an appropriate percentage following the conventional RGB color matching method. In this approach, the PNCs are magnetically responsive and display three primary colors that can be synthesized by combining hydrogen bond-guided and magnetic field (H)-assisted template polymerization. The as-prepared double bandgap photonic inks present high color saturation due to the fixed and narrow full-width at half-maxima of the parent PNCs with a suitable chain length. Furthermore, they can be used to easily produce a flexible double bandgap PC film by embedding the PNCs into a gel, such as polyacrylamide, facilitating fast steady display performance without the requirement of an external magnetic field. This research not only presents the unique advantages of PNCs in constructing multi-bandgap PCs but also establishes the feasibility of utilizing PNCs in practical applications within the fields of anti-counterfeiting and flexible wearable devices.

Unsupervised machine learning to classify the confinement of waves in periodic superstructures.

We propose a rigorous method to classify the dimensionality of wave confinement by utilizing unsupervised machine learning to enhance the accuracy of our recently presented scaling method [Phys. Rev. Lett.129, 176401 (2022)10.1103/PhysRevLett.129.176401]. We apply the standard k-means++ algorithm as well as our own model-based algorithm to 3D superlattices of resonant cavities embedded in a 3D inverse woodpile photonic band gap crystal with a range of design parameters. We compare their results against each other and against the direct usage of the scaling method without clustering. Since the clustering algorithms require the set of confinement dimensionalities present in the system as an input, we investigate cluster validity indices (CVIs) as a means to find these values. We conclude that the most accurate outcome is obtained by first applying direct scaling to find the correct set of confinement dimensionalities, and subsequently utilizing our model-based clustering algorithm to refine the results.