Periodic Dielectric Structures Research Articles

Direct femtosecond laser printing of silk fibroin periodic structure with lower mid-infrared reflectivity

Periodic dielectric structures offer an efficient way to control light propagation at micro- and nanoscale, also presenting low losses. Among many techniques that can produce such structures, femtosecond Laser-Induced Forward Transfer (fs-LIFT) is a promising one due to its relatively simple implementation and ability to process broad classes of materials, preserving their integrity. In particular, Silk fibroin (SF), a natural biopolymer, can be processed by fs-LIFT to print well-ordered periodic arrays of microstructures. Due to its high transparency, biocompatibility, and high possibilities of functionalization, SF is a suitable material for photonics. In this work, a 2D lattice of hemi-elliptical SF microdroplets was fabricated via fs-LIFT, and finite-element (FEM) simulations were carried out to study their response to electromagnetic radiation in the near to mid-infrared spectral region, considering the influence of the substrate. The simulation results indicated a decrease in reflectivity which was corroborated with experimental results. In addition, coating the fabricated structures with a higher index dielectric material was shown to enhance the decrease in reflectivity in the mid-infrared spectral region. These results demonstrate a straightforward way to print ordered arrays of SF microstructures in a relatively large area, with potential application as controllable reflectivity coating for the near to mid-infrared spectral region.

Nanoporous Anodic Alumina Photonic Crystals for Sunlight Harvesting Applications: A Perspective

Nanoporous anodic alumina (NAA) fabricated by anodization of aluminum is a versatile platform material with tailorable geometric, optical, and chemical features for specific light‐based technologies and applications. Recent advances in anodization technology have enabled a new generation of NAA‐based photonic crystals (PCs)—periodic dielectric nanoporous structures that selectively allow, forbid, and confine the flow of incoming electromagnetic waves of specific wavelengths across their structure. NAA–PCs provide exciting new opportunities to engineer light–matter interactions with versatility across the broad spectrum, from UV to IR. But despite these fundamental advances, demonstrations of sunlight‐harvesting technologies based on NAA–PCs are still limited. Herein, an up‐to‐date summary of recent advances in NAA–PC technology is provided, and proof‐of‐concept demonstrations and future pathways to propel this versatile platform material across sunlight‐harvesting technologies such as photocatalysis, photoelectrocatalysis, photothermal energy conversion, and solar cells are discussed.

Research Progress on the Design of Structural Color Materials Based on 3D Printing

AbstractThe structural color is produced by the reflection of light through a periodic dielectric structure with photonic bandgap. Because of its special visual effects, researchers in many fields begin to pay attention to photonic crystals with structural colors. This review focuses on the combination of 3D printing technology and photonic crystal structural color materials, summarizes the influence factors of structural color rendering mechanism and the evaluation of color performance, and summarizes the research of structural color materials in simulation. Finally, the challenges faced by structural color materials are summarized, and the future development trend of structural color materials is prospected.

Methods to Tune the Optical Response of Porous Photonic Crystal Structures

Photonic crystals are periodic dielectric structures which selectively tune the wavelengths of light propagating through the material1 2. The highly ordered, repeating structural lattice induces a photonic bandgap or stopband which inhibits or partially attenuates certain frequencies of light, similar to the electronic bandgap with forbidden energies present in semiconductor materials3. These forbidden frequencies are blocked in transmission and reflected from the material surface. The inherent sensitivity of this photonic response to repeating lattice size dimensions and the magnitude of the refractive index contrast between the constituent materials allows for tailored optical behaviour by adjusting the photonic crystal structural parameters or environment4 5.A range of interesting applications using both the photonic bandgap and material porosity have emerged, predicated on the ability to accurately forecast the wavelength position of the photonic response. Colorimetric sensors6 7, photocatalysts8 9 and solar cells10 are prime examples of these types of applications; the porosity of the photonic crystal facilitates greater material infiltration and reactions, while the photonic bandgap acts to enhance the optical component of the process. Critically, the use of these structures is tied to our ability to predict and interpret the signature optical response.Here, we examine several techniques which can be used modify the photonic bandgap/stopband for photonic crystal structures. For TiO2 and SnO2 inverse opal photonic crystals, we explore how solvent infiltration into the highly porous network red-shifts the observed photonic response. Using solvents with different refractive indices, we apply the shifted photonic stopband data to determine the fill fraction of solid material comprising the photonic crystal network. We also examine functionalization of artificial opal and inverse opal photonic crystals with metal films. We detail the emergence of a consistent photonic stopband blue-shift with increasing metal content and propose a reduction in the effective refractive index of the entire photonic crystal introduced by the specific properties of the metal film. Importantly, the effects investigated here are broadly applicable to a range of realistic operating conditions across many disciplines where an understanding of the photonic stopband is paramount to the application. References Yablonovitch, E., Inhibited Spontaneous Emission in Solid-State Physics and Electronics. Physical Review Letters 1987, 58 (20), 2059-2062.John, S., Strong localization of photons in certain disordered dielectric superlattices. Physical Review Letters 1987, 58 (23), 2486-2489.Joannopoulos, J. D.; Villeneuve, P. R.; Fan, S., Photonic crystals: putting a new twist on light. Nature 1997, 386 (6621), 143-149.Blanford, C. F.; Schroden, R. C.; Al-Daous, M.; Stein, A., Tuning Solvent-Dependent Color Changes of Three-Dimensionally Ordered Macroporous (3DOM) Materials Through Compositional and Geometric Modifications. Advanced Materials 2001, 13 (1), 26-29.Aguirre, C. I.; Reguera, E.; Stein, A., Tunable Colors in Opals and Inverse Opal Photonic Crystals. Advanced Functional Materials 2010, 20 (16), 2565-2578.Zhang, Y.; Qiu, J.; Hu, R.; Li, P.; Gao, L.; Heng, L.; Tang, B. Z.; Jiang, L., A visual and organic vapor sensitive photonic crystal sensor consisting of polymer-infiltrated SiO2 inverse opal. Physical Chemistry Chemical Physics 2015, 17 (15), 9651-9658.Li, H.; Chang, L.; Wang, J.; Yang, L.; Song, Y., A colorful oil-sensitive carbon inverse opal. Journal of Materials Chemistry 2008, 18 (42), 5098-5103.Chen, J. I. L.; von Freymann, G.; Choi, S. Y.; Kitaev, V.; Ozin, G. A., Amplified Photochemistry with Slow Photons. Advanced Materials 2006, 18 (14), 1915-1919.Collins, G.; Lonergan, A.; McNulty, D.; Glynn, C.; Buckley, D.; Hu, C.; O'Dwyer, C., Semiconducting Metal Oxide Photonic Crystal Plasmonic Photocatalysts. Advanced Materials Interfaces 2020, 7 (8), 1901805.Liu, L.; Karuturi, S. K.; Su, L. T.; Tok, A. I. Y., TiO2 inverse-opal electrode fabricated by atomic layer deposition for dye-sensitized solar cell applications. Energy & Environmental Science 2011, 4 (1), 209-215. Figure 1 SEM images and optical transmission spectra for (a) TiO2 and (b) SnO2 inverse opals. In each case the wavelength position of the photonic stopband is red-shifted significantly when a solvent infiltrates the porous photonic crystal network. SEM images and optical transmission spectra for (c) artificial polystyrene opals coated with a gold film and (d) TiO2 inverse opals coated with a copper film. Metal film incorporation into the photonic crystal network acts to consistent blue-shift the observed photonic stopband. Figure 1

High-Q refractive index sensors based on all-dielectric metasurfaces.

Possessing fantastic abilities to freely manipulate electromagnetic waves on an ultrathin platform, metasurfaces have aroused intense interest in the academic circle. In this work, we present a high-sensitivity refractive index sensor excited by the guided mode of a two-dimensional periodic TiO2 dielectric grating structure. Numerical simulation results show that the optimized nanosensor can excite guided-mode resonance with an ultra-narrow linewidth of 0.19 nm. When the thickness of the biological layer is 20 nm, the sensitivity, Q factor, and FOM values of the nanosensor can reach 82.29 nm RIU−1, 3207.9, and 433.1, respectively. In addition, the device shows insensitivity to polarization and good tolerance to the angle of incident light. This demonstrates that the utilization of low-loss all-dielectric metasurfaces is an effective way to achieve ultra-sensitive biosensor detection.

Waveguide Characteristics Near the Second Bragg Condition

We show that in an optical waveguide with no material losses at wavelengths near the second-order Bragg condition, there exists two pairs of modes. One pair has identical propagation constants but have different attenuation coefficients, while a second pair with identical propagation constants (different from the first pair) and have different attenuation coefficients. The four attenuation coefficients may have either a positive value, representing power leaking out of a waveguide mode or a negative value, representing power from an external source leaking into a mode. Moreover, a mode with a positive (negative) attenuation before the second Bragg condition, has a negative (positive) attenuation after the second Bragg condition. Radiation near the second-order Bragg condition of a periodic waveguide typically occurs at an angle perpendicular or nearly perpendicular to the propagation direction of the waveguide because the scattering centers have a period equal to or close to the period of the longitudinal propagation constant of the mode. In this paper, stable numerical solutions for the modes of periodic dielectric structures are developed using Floquet-Bloch theory. One primary focus in this paper illustrates a unique method of analyzing such modes using eigenvectors forming a Hilbert space, allowing for expansion of arbitrary vectors and their derivatives used for calculations such as that involving group velocities. The dimension of the vector space is determined by the number of space harmonics used in the solution of the Floquet-Bloch equations. The accuracy of the numerical solutions is affected by the number of space harmonics; as that number is increased, the number of waveguide partitions must be increased to maintain a given accuracy.

Promoting the Performance of 2D Material Photodetectors by Dielectric Engineering.

Low light absorption and limited carrier lifetime are two limiting factors hampering the further breakthrough of the performance of 2D materials (2DMs)-based photodetectors. This study proposes an ingenious dielectric engineering strategy toward boosting the photosensitivity. Periodic dielectric structures (PDSs), including SiO2 /h-BN, SiO2 /Al2 O3 , and SiO2 /SrTiO3 (STO), are exploited to couple with 2D photosensitive channels (denoted as PDS-2DMs). The responsivity, external quantum efficiency, and detectivity of an optimized SiO2 /STO(300nm) -WSe2 photodetector reach 89081 A W-1 , 2.7 × 107 %, and 1.8 × 1013 Jones, respectively. These performance metrics are orders of magnitude higher than a pristine WSe2 photodetector, enabling reliable sub-1 pW weak light detection. Based on systematic characterizations and first-principle calculations, such dramatic performance improvement is associated with the promoted direct bandgap transition, reduced exciton binding energy, and PDS-induced periodic intramolecular built-in electric field across the atomically thin channels, which efficiently separates the photoexcited electron-hole pairs. More inspiringly, this strategy is also successfully exploited to 2D WS2 photodetectors, demonstrating broad applicability. As a whole, this work promises an exceptional avenue to ameliorate 2DM photodetectors and opens up a new horizon "dielectric optoelectronics," simultaneously highlighting the role of dielectric environment during analyzing the fundamentals of 2DM devices.

Two-Dimensional Glide-Symmetric Dielectric Structures for Planar Graded-Index Lens Antennas

In this letter, we propose and study a 2-D glide-symmetric dielectric periodic structure. We demonstrate that glide symmetry broadens the bandwidth of operation and achieves lower effective refractive indices when compared to non-glide configurations. These two properties are beneficial for producing graded-index lens antennas. To demonstrate the potential of the proposed unit cell, we designed a Luneburg lens operating in the K- and K <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\text {a}\!$</tex-math></inline-formula> -bands. The lens was manufactured with conventional additive manufacturing and it has a potential use for future wireless communications given its low-cost and low-profile.

Ultrafast Nonlinear Pulse Propagation Dynamics in Metal–Dielectric Periodic Photonic Architectures

Abstract1D metal–dielectric (MD) periodic structures take advantage of large refractive index contrast between metal and dielectrics to invoke extremely high nonlinear ultrafast responses of metal. These structures are also special due to their extremely high laser damage threshold. The Bragg‐like 1D MD structure (Ag/SiO2)4 enables strong optical field confinement with much enhanced nonlinear features as compared to simple metal or single (Ag/SiO2)1 structure. In the present work, the ultrafast nonlinear optical responses of the above structures are investigated via femtosecond broadband optical pump–probe technique. The enhanced nonlinear optical absorption is of reverse saturation of absorption nature, resulted due to free‐carrier absorption and excited‐state absorption processes. The spectral nonlinearities are closely related to the pump‐induced modification of the metal's dielectric functions, which are qualitatively visualized by transfer matrix and two‐temperature models. The ultrafast temporal evolution of nonlinear absorption clearly demonstrates enhanced optical nonlinearity, disentangled by the electron–electron and electron–phonon dynamic interactions at picosecond time scales. A phenomenological pulse propagation model is employed that incorporates the experimentally obtained nonlinear absorption coefficients and different nonlinear effects exhibited by the system. The findings of these new optical materials can possibly pave the way for promising applications in ultrafast photonics.

All-optical tunable high-order Gaussian beam splitter based on a periodic dielectric atomic structure.

Beam splitting of high-order Gaussian (HOG) beams increases the channel capacity and improves the processing speed of the incoming information. Here a novel all-optical tunable multi-port HOG beam splitter under a periodic dielectric atomic structure is proposed and demonstrated. The original HOG beam is replicated in the output beams. A distinguishable five-port output beam is observed in the experiment, which is beneficial for high-speed optical communications. By tuning the optical properties of this periodic dielectric structure, the spatial position and intensity distribution of each output port are precisely controllable. The splitting ratio δ can be finely adjusted in the range 0 - 4.8. This work provides a new approach for multi-port HOG beam splitters and the basis for all-optical communication.

Core/shell colloidal nanoparticles based multifunctional and robust photonic paper via drop-casting self-assembly for reversible mechanochromic and writing

Photonic crystals film that possesses periodic dielectric structure have shown great prospect in developing environmentally friendly paper alternatives due to the unique properties of dye free and non-photobleaching, but their practical application is limited by the weak interaction between colloidal particles. Although some progress has been obtained, it is still a challenge to develop photonic paper with the desired mechanical and optical properties. Herein, multifunctional hard core/soft shell nanoparticles with controlled size are fabricated by semi-continuous seed emulsion polymerization method. Compared with convention colloidal particles, these core/shell nanoparticles can facile self-assemble into large-scale dense ordered structure film via dried at room temperature due to the relatively low glass transition temperature (Tg) of the shell layers. The facile fabrication route enables the continuous high-through put production of the photonic papers. The as-formed papers not only possess the capacity to solvent (water/ethanol) rewritable and multicolor painting, but also can rapidly reversible mechanochromic. Moreover, due to the good compatibility of core/shell interface, these photonic films possess excellent mechanical properties, demonstrating that this multifunctional film makes the fabrication of novel robust rewritable papers possible and enables visual monitoring of deformation degree.

Novel Bloch wave excitation platform based on few-layer photonic crystal deposited on D-shaped optical fiber

With the goal of ultimate control over the light propagation, photonic crystals currently represent the primary building blocks for novel nanophotonic devices. Bloch surface waves (BSWs) in periodic dielectric multilayer structures with a surface defect is a well-known phenomenon, which implies new opportunities for controlling the light propagation and has many applications in the physical and biological science. However, most of the reported structures based on BSWs require depositing a large number of alternating layers or exploiting a large refractive index (RI) contrast between the materials constituting the multilayer structure, thereby increasing the complexity and costs of manufacturing. The combination of fiber–optic-based platforms with nanotechnology is opening the opportunity for the development of high-performance photonic devices that enhance the light-matter interaction in a strong way compared to other optical platforms. Here, we report a BSW-supporting platform that uses geometrically modified commercial optical fibers such as D-shaped optical fibers, where a few-layer structure is deposited on its flat surface using metal oxides with a moderate difference in RI. In this novel fiber optic platform, BSWs are excited through the evanescent field of the core-guided fundamental mode, which indicates that the structure proposed here can be used as a sensing probe, along with other intrinsic properties of fiber optic sensors, as lightness, multiplexing capacity and easiness of integration in an optical network. As a demonstration, fiber optic BSW excitation is shown to be suitable for measuring RI variations. The designed structure is easy to manufacture and could be adapted to a wide range of applications in the fields of telecommunications, environment, health, and material characterization.

Periodic structure of different dielectric layers for dielectric laser accelerators.

In this paper, a periodic structure of different dielectric layers is proposed and investigated for relativistic electron acceleration. The periodic dielectric structure provides an accelerating electric field inside the structure. Results show that the electron beam can experience a strong electric force in one direction during propagation in the structure, leading to the acceleration gradient increasing by more than double in comparison with dual-grating structures. Acceleration gradient enhancement occurs without increasing the electric field much inside the structure; therefore, the maximum achievable acceleration gradient and acceleration factor are increased by more than 100%, reaching 0.7. Thereby, by using the proposed structure GV/m, the acceleration gradient can be achieved with a wide electron channel. Also, the required input laser fluence is reduced for the same acceleration gradient. Acceleration gradient and acceleration factor optimization is done corresponding to structure parameters. Our work shows that the proposed structure helps to make dielectric laser accelerators more efficient.

A Multi-Bandgap Periodic Structure Device Acting as Multiplexer or Demultiplexer of Electromagnetic Signals

In this work, a device capable of acting as a multiplexer (MUX) and demultiplexer (DEMUX) for electromagnetic waves in gigahertz range is designed and modeled numerically. The device is based on optimized dielectric periodic structures. It can combine signals of different central frequencies injected at its input ports to a single output port, thus acting as a MUX. Reciprocally, the device can separate mixed signals of different frequencies to specific output ports, acting as a DEMUX. To this aim, specific imperfections are introduced into the periodic structure. The design and analysis of the device are performed using the finite-difference time-domain method (FDTD). Transfer functions between pairs of input and output ports are calculated and used to define the design metrics

Millimetre‐wave design and verification of a meta‐surface dielectric window made of polytetrafluoroethylene in Ka‐ and Q‐band

A periodic dielectric meta-surface structure was designed to extend the output window operating bandwidth of a wideband mode gyrotron travelling wave tube. The equivalent permittivity of the meta-surface matching layer can be adjusted arbitrarily by changing the lattice dimensions. The fabricated meta-surface dielectric window demonstrated a relative bandwidth of 53.9% with a reflection below in the Ka- and Q-band.

Single-source formulation for the analysis of electromagnetic penetrable objects

Modified global surface impedance (MGSI) formulation, a fast and efficient single-source integral equation for analyzing penetrable objects including plasmonic circuits and dielectric periodic structures, is proposed. Using the equivalence principle, a single-source formulation for the exterior region of the desired problem is constructed. Then the assumed equivalent source (surface electric current) is written as the sum of two surface electric currents, one related to the other based on the global surface impedance (GSI) model. Thus, the conventional surface integral equation (SIE) for the exterior problem will be modified by this new single-source formulation. The interior problem is also formulated using the GSI model resulting in our proposed MGSI formulation. MGSI eliminates the need for equivalent magnetic current in the SIE formulation. It also helps one to formulate the interior and exterior problems independently. Moreover, in our approach material property does not affect the problem convergence behavior, while the convergence behavior of the conventional SIE deteriorates for a plasmonic structure and also for a dielectric object with high contrast to its surrounding medium. The accuracy and efficiency of the proposed formulation are demonstrated by comparing its results with the conventional SIE in solving several two-dimensional examples.

Photonic band gap phenomenon in a metal–dielectric periodic structure

We study the photonic band structure of a metal–dielectric periodic structure. The metallic component is described by the Drude model; therefore, the electric permittivity is frequency dependent, i.e., dispersive. Rather than solving a nonlinear eigenvalue problem for the band structure of the material, we follow a time-dependent formulation described in Raman and Fan (Phys Rev Lett 104:087401, 2010) which leads to a linear eigenvalue problem. At issue is the question of completeness of the eigenfunctions, which is claimed but not proven in Raman and Fan (2010). We establish completeness in one dimension. We further describe the existence of accumulation points in the spectrum that lead to an infinite family of ‘zero group velocity’ waves. Numerical calculations illustrate some of the main ideas of this work.

Metastructures for the Giant Enhancement of Raman Scattering in the Near Infrared Spectral Range

The properties of periodic dielectric structures coated with a thick metal layer, which allow enhancing an inelastic light scattering signal by more than eight orders of magnitude at a laser pump wavelength of 1064 nm, have been studied. It has been shown that the giant resonance enhancement of the Raman signal in the near infrared range is ensured by additionally enhanced plasma resonance and by geometrical resonance between the sizes of the dielectric structure and the wavelength of laser radiation. The dependence of the enhancement factor of the Raman scattering on the height of columns in periodic dielectric structures, as well as the dependence of the enhancement factor on the thickness of the metallic coating, has been studied. New resonance modes have been revealed, for which the height of dielectric columns is 1/4, 1/2, and 3/4 of the wavelength of laser radiation. It has been shown that record high enhancement factors of the Raman scattering can be reached in the near infrared range, which is also due to a high Q factor of plasma waves in metals at these frequencies.

Nonlinear Optics in Dielectric Guided-Mode Resonant Structures and Resonant Metasurfaces.

Nonlinear optics is an important area of photonics research for realizing active optical functionalities such as light emission, frequency conversion, and ultrafast optical switching for applications in optical communication, material processing, precision measurements, spectroscopic sensing and label-free biological imaging. An emerging topic in nonlinear optics research is to realize high efficiency optical functionalities in ultra-small, sub-wavelength length scale structures by leveraging interesting optical resonances in surface relief metasurfaces. Such artificial surfaces can be engineered to support high quality factor resonances for enhanced nonlinear optical interaction by leveraging interesting physical mechanisms. The aim of this review article is to give an overview of the emerging field of nonlinear optics in dielectric based sub-wavelength periodic structures to realize efficient harmonic generators, wavelength mixers, optical switches etc. Dielectric metasurfaces support the realization of high quality-factor resonances with electric field concentrated either inside or in the vicinity of the dielectric media, while at the same time operate at high optical intensities without damage. The periodic dielectric structures considered here are broadly classified into guided-mode resonant structures and resonant metasurfaces. The basic physical mechanisms behind guided-mode resonances, electromagnetically-induced transparency like resonances and bound-states in continuum resonances in periodic photonic structures are discussed. Various nonlinear optical processes studied in such structures with example implementations are also reviewed. Finally, some future directions of interest in terms of realizing large-area metasurfaces, techniques for enhancing the efficiency of the nonlinear processes, heterogenous integration, and extension to non-conventional wavelength ranges in the ultra-violet and infrared region are discussed.

Perturbation theories for symmetry-protected bound states in the continuum on two-dimensional periodic structures

On dielectric periodic structures with a reflection symmetry in a periodic direction, there can be antisymmetric standing waves (ASWs) that are symmetry-protected bound states in the continuum (BICs). The BICs have found many applications, mainly because they give rise to resonant modes of extremely large quality-factors ($Q$-factors). The ASWs are robust to symmetric perturbations of the structure, but they become resonant modes if the perturbation is non-symmetric. The $Q$-factor of a resonant mode on a perturbed structure is typically $O(1/\delta^2)$ where $\delta$ is the amplitude of the perturbation, but special perturbations can produce resonant modes with larger $Q$-factors. For two-dimensional (2D) periodic structures with a 1D periodicity, we derive conditions on the perturbation profile such that the $Q$-factors are $O(1/\delta^4)$ or $O(1/\delta^6)$. For the unperturbed structure, an ASW is surrounded by resonant modes with a nonzero Bloch wave vector. For 2D periodic structures, the $Q$-factors of nearby resonant modes are typically $O(1/\beta^2)$, where $\beta$ is the Bloch wavenumber. We show that the $Q$-factors can be $O(1/\beta^6)$ if the ASW satisfies a simple condition.