Two-dimensional Metallic Photonic Crystals Research Articles

Towards Perfect Ultra-Broadband Absorbers, Ultra-Narrow Waveguides, and Ultra-Small Cavities at Optical Frequencies.

In this study, we design ultra-broadband optical absorbers, ultra-narrow optical waveguides, and ultra-small optical cavities comprising two-dimensional metallic photonic crystals that tolerate fabrication imperfections such as position and radius disorderings. The absorbers containing gold rods show an absorption amplitude of more than 90% under 54% position disordering at nm. The absorbers containing silver rods show an absorptance of more than 90% under 54% position disordering at nm. B-type straight waveguides that contain four rows of silver rods exposed to air reveal normalized transmittances of 75% and 76% under 32% position and 60% radius disorderings, respectively. B-type L-shaped waveguides containing four rows of silver rods show 76% and 90% normalized transmittances under 32% position and 40% radius disorderings, respectively. B-type cavities containing two rings of silver rods reveal 70% and 80% normalized quality factors under 32% position and 60% radius disorderings, respectively.

Plasmon-Induced Transparency for Tunable Atom Trapping in a Chiral Metamaterial Structure.

Plasmon-induced transparency (PIT), usually observed in plasmonic metamaterial structure, remains an attractive topic for research due to its unique optical properties. However, there is almost no research on using the interaction of plasmonic metamaterial and high refractive index dielectric to realize PIT. Here, we report a novel nanophotonics system that makes it possible to realize PIT based on guided-mode resonance and numerically demonstrate its transmission and reflection characteristics by finite element method simulations. The system is composed of a high refractive-index dielectric material and a two-dimensional metallic photonic crystal with 4-fold asymmetric holes. The interaction mechanism of the proposed structure is analyzed by the coupled-mode theory, and the effects of the parameters on PIT are investigated in detail. In addition, we first consider this PIT phenomenon of such fields on atom trapping (87Rb), and the results show that a stable 3D atom trapping with a tunable range of position of about ~17 nm is achieved. Our work provides a novel, efficient way to realize PIT, and it further broadens the application of plasmonic metamaterial systems.

Strong coupling between hybrid plasmonic–photonic resonances and excitons in metallic photonic crystal–monolayer WS2 nanostructures

Nanostructures, supporting hybrid plasmonic–photonic modes that combine the advantages of the electromagnetic field enhancement of the localized plasmon resonances (LSPRs) and the higher quality factor of the photonic resonances, have served as flexible and efficient platforms for engineering strong light–matter interactions. Here, we demonstrate theoretically that the two-dimensional metallic photonic crystals (PhCs) as a class of hybrid plasmonic–photonic lattices play an active role in light–matter interaction. The metallic PhCs are composed of optical waveguides strongly coupled to periodically arranged metallic nanodisks, and this coupling gives rise to the formation of waveguide–plasmon polaritons. By combining two-dimensional semiconducting materials (WS2) and the metallic PhCs, we prove strong coupling between waveguide–plasmon modes and excitons at room temperature. The strong coupling includes three types of resonances: guided modes excited by diffractive gratings, LSPRs on individual nanodisks, and WS2 excitons. Using coupled oscillator models, we show that the mode composition and coupling strength between polaritons can be controlled effectively by tuning the geometrical factor of the lattice, and thus reveal the LSPR-mediated energy transfer process. Our reports are not only of fundamental interest but could also be useful for practical applications based on monolayer semiconductors.

Определение электрофизических параметров металлических фотонных кристаллов в СВЧ и оптическом диапазонах.

Original methods for determining the effective electrophysical parameters of two-dimensional metallic photonic crystals, applicable in a wide frequency range from radio to visible ranges are researched. In contrast to the currently widespread analytical approaches to describing such parameters, the subject of this article is the methods that can be used both for the rigorous numerical analysis and for the direct practical application. It is shown that in the radio and infrared ranges in the first allowed zone of photonic crystals the determination of their effective dielectric constant can be carried out either on the basis of studying the intrinsic resonance properties of spatially limited structures or by studying the processes of reflection and refraction at their boundaries. In the visible range metallic photonic crystals exhibit properties that are largely similar to those of solid metals. However, photonic crystals have significantly lower heat losses and a positive effective dielectric constant <1. ​​This makes them promising for creating various devices for converting optical radiation. Determination of the effective electrophysical parameters at these frequencies is possible on the basis of a direct comparison of the amplitude-phase distributions of the field in photonic crystals and continuous media.

Broadband selective solar absorber based on dielectric-filled anti-reflection coated film-coupled two-dimensional metallic photonic crystals

We propose and numerically demonstrate a highly efficient solar absorber based on dielectric-filled anti-reflection coated film-coupled two-dimensional metallic photonic crystals. The proposed solar absorber has a polarization-independent high absorptivity above 95% in the range of 0.33–1.45 µm with insensitivity to incident angle of light as large as 50°. In the range beyond 2.2 µm, the thermal emissivity of this structure is below 20%, which shows its strong absorption selectivity. The efficient light harvesting property of the proposed solar absorber can be attributed to the anti-reflection mode, cavity resonance and coupled surface plasmon polaritons.

Reconfigurable coupler-based metallic photonic crystal lens and nematic liquid crystal

In this paper, a new design for a lens built around a two-dimensional (2D) metallic photonic crystal (PhC) platform with negative refractive index is proposed. The proposed lens has been composed of a silver layer with a triangular array of circular air holes. A three-dimensional geometric study performed with the aid of 2D finite element method results in focusing the light rays with intensity and FWHM of 10.5 and 1.7 μm, respectively. The suggested lens is used to efficiently couple the light from a planar waveguide with a large spot size area into another PhC waveguide with a subwavelength spot size area. Additionally, filling the drilled holes in the proposed lens with nematic liquid crystal allows obtaining a reconfigurable lens with significant wave FWHM shaping with extinction ratios of about 8 dB. The proposed reconfigurable lens is used to couple two different waveguides with different coupling ratios.

Tuning photonic bands in plasma metallic photonic crystals

Introducing plasma in the background provides additional degrees of freedom for tuning dispersion curves of photonic crystals. 2D photonic crystals in triangular lattice arrangements offer more global bandgap regions and thus are of more interest for various applications. The dispersion characteristics of a two-dimensional plasma metallic photonic crystal (PMPC) in square as well as triangular lattice arrangements have been analyzed in this paper using the orthogonal finite difference time domain method. The dispersion characteristics of PMPCs for the range of r/a ratios and plasma frequencies for triangular lattice configuration have been analyzed. On introducing plasma in the background, the photonic bands of PMPC are shifted towards higher normalized frequencies. This shift is more for lower bands and increases with plasma frequency. The cut-off frequency was observed for both TE and TM polarizations in PMPC and showed strong dependence on r/a ratio as well as plasma frequency. Photonic bandgaps of PMPC may be tuned by controlling plasma parameters, giving opportunity for utilizing these PMPC structures for various applications such as fine-tuning cavities for enhanced light-matter interaction, plasmonic waveguides, and Gyrotron cavities.

Tuning the flow of light in two-dimensional metallic photonic crystals based on Faraday effect

In this paper, we investigate the tunability of two-dimensional metallic photonic crystals by an external magnetic field. Our theoretical analysis is based on the frequency-dependent plane wave expansion method. The numerical results show that the external magnetic field has a pronounced effect on the permittivity of the metals. Therefore, the photonic band structures can be strongly tuned and controlled by adjusting the external magnetic field. Our structure is a good candidate for many applications such as filters, optical switches and modulators.

Femtosecond laser direct writing of large-area two-dimensional metallic photonic crystal structures on tungsten surfaces.

Metallic photonic crystals (MPCs) and metamaterials operating in the visible spectrum are required for high-temperature nanophotonics, but they are often difficult to construct. This study demonstrates a new approach to directly write two-dimensional (2D) MPCs on tungsten surfaces through the cylindrical focusing of two collinear femtosecond laser beams with certain temporal delays and orthogonal linear polarizations. Results are physically attributed to the laser-induced transient crossed temperature grating patterns and tempo-spatial thermal correlations. Optical properties of the fabricated MPCs are characterized. Such a simple and efficient technique can be used to fabricate large-area, 2D microstructures on metal surfaces for potential applications.

Nanoimprinted superlattice metallic photonic crystal as ultraselective solar absorber

A two-dimensional superlattice metallic photonic crystal (PhC) and its fabrication by nanoimprint lithography on tantalum substrates are presented. The superior tailoring capacity of the superlattice PhC geometry is used to achieve spectrally selective solar absorption optimized for high-temperature and high-efficiency solar-energy-conversion applications. The scalable fabrication route by nanoimprint lithography allows for a high-throughput and high-resolution replication of this complex pattern over large areas. Despite the high fill factor, the pattern of polygonal cavities is accurately replicated into a resist that hardens under ultraviolet radiation over an area of 10 mm2. In this way, cavities of 905 nm and 340 nm width are achieved with a period of 1 μm. After pattern transfer into tantalum via a deep reactive ion-etching process, the achieved cavities are 2.2 μm deep, separated by 85–95 nm wide ridges with vertical sidewalls. The room-temperature reflectance spectra of the fabricated samples show excellent agreement with simulated results, with a high spectral absorptance approaching blackbody absorption in the range from 300 to 1900 nm and a steep cutoff. The calculated solar absorptivity of this superlattice PhC is 96% and its thermal transfer efficiency is 82.8% at an operating temperature of 1500 K and an irradiance of 1000 kW/m2.

Global optimization of omnidirectional wavelength selective emitters/absorbers based on dielectric-filled anti-reflection coated two-dimensional metallic photonic crystals.

We report the design of dielectric-filled anti-reflection coated (ARC) two-dimensional (2D) metallic photonic crystals (MPhCs) capable of omnidirectional, polarization insensitive, wavelength selective emission/absorption. Using non-linear global optimization methods, optimized hafnium oxide (HfO2)-filled ARC 2D Tantalum (Ta) PhC designs exhibiting up to 26% improvement in emittance/absorptance at wavelengths λ below a cutoff wavelength λc over the unfilled 2D TaPhCs are demonstrated. The optimized designs possess high hemispherically average emittance/absorptance εH of 0.86 at λ < λc and low εH of 0.12 at λ > λc.

Beam shaping in two-dimensional metallic photonic crystals

We study light beam propagation in periodic metallic nanostructures—metallic photonic crystals (MPhCs). In particular, we consider a two-dimensional rhombic array of metallic cylinders embedded in air and explore its ability to tailor spatial propagation of light beams. We show that the structure supports self-collimated propagation and negative (anomalous) diffraction. In this later case, flat lensing is observed, leading to the focusing of beams behind the MPhCs. Moreover, the anisotropic attenuation of light provided by the structure enables spatial filtering of noisy beams.

Defect mode properties of two-dimensional plasma-filled defective metallic photonic crystal

This paper studies the frequency and amplitude properties of a defect mode which is only in a plasma-filled metallic photonic crystal with defect layer. Results show that the frequency almost has no change and the amplitude declines gradually with the growth of the number of the layers. The frequency of the defect mode not only can be modulated by filling ratio but also can be tuned by plasma density without modifying the structure. The amplitude can be modified by plasma angular frequency as well. These characteristics provide a foundation to design tunable filters, high power millimeter devices.

同轴波导中二维金属光子晶体的电磁特性

同轴波导中二维金属光子晶体的电磁特性

Finite element method analysis of band gap and transmission of two-dimensional metallic photonic crystals at terahertz frequencies

Photonic band gap and transmission characteristics of 2D metallic photonic crystals at THz frequencies have been investigated using finite element method (FEM). Photonic crystals composed of metallic rods in air, in square and triangular lattice arrangements, are considered for transverse electric and transverse magnetic polarizations. The modes and band gap characteristics of metallic photonic crystal structure are investigated by solving the eigenvalue problem over a unit cell of the lattice using periodic boundary conditions. A photonic band gap diagram of dielectric photonic crystal in square lattice array is also considered and compared with well-known plane wave expansion results verifying our FEM approach. The photonic band gap designs for both dielectric and metallic photonic crystals are consistent with previous studies obtained by different methods. Perfect match is obtained between photonic band gap diagrams and transmission spectra of corresponding lattice structure.

Controlling the self-collimation characteristics of a near-infrared two-dimensional metallic photonic crystal

Self-collimation characteristics of the two-dimensional square-lattice photonic crystal (PC) consisting of metal rods immersed in silicon are studied by the finite-difference time-domain method. The Drude dispersion model is adopted to describe the metal rod, and the self-collimation behaviours of the near-infrared light through the PC are studied. The frequency region and the tolerance of incident angle for the self-collimation behaviour can be controlled by changing the shape of the metal rods.

Effect of a magnetic field on a two-dimensional metallic photonic crystal

We study the effect of a static magnetic field on the band structure of a two-dimensional metallic photonic crystal (MPC). The band structure of the MPC has been calculated using the transfer matrix method. It is found that the position of the photonic band gap and the band edges of the MPC depends on the polarization of the incident light and intensity of the applied magnetic field. In our calculations we consider linearly polarized light as well as right- and left-circularly polarized light. In the case of right-circularly polarized light it is found that as the intensity of the magnetic field increases the width of the band gap of the crystal decreases. At a certain magnetic field strength the band gap disappears altogether. In other words there is a transition from a metallic photonic band gap material to a transparent dielectric material. This is an interesting effect which is similar to the metal-insulator transition that occurs in semiconductors. On the other hand, for left-circularly and linear polarized light the band edges shift to the higher energy and the band gap increases in the presence of a magnetic field. This implies that the MPC switches from a transparent state to reflecting states due to the application of the magnetic field. This is an interesting effect which might be used to make photonic switches.

Extraordinary resonance transmission of two-dimensional terahertz metallic photonic crystals without defect

In this paper, we have demonstrated a kind of extraordinary transmission in the photonic first pass band of two-dimensional terahertz metallic photonic crystals: in the regime of low-middle metal filling radio, resonances among the metallic cylinders lead to sharp and high resonance peaks of Lorentz type, layer dependency of the peak numbers. The effect of positional disorders of metallic cylinders has been investigated as well. Based on a simple model proposed in this paper, we can intuitively understand the extraordinary transmission and roughly estimate resonance frequencies. Our results agree qualitatively with the experimental data reported in Appl. Phys. Lett. 65, 645.

THz wave propagation in two-dimensional metallic photonic crystal with mechanically tunable photonic-bands

Transmission and dispersion relation of THz waves in two-dimensional photonic crystal (PC) composed of metal rods are studied by using finite-difference time-domain simulation and THz time-domain spectroscopy measurement. The PC is embedded in a parallel metal plate waveguide with an air gap between the PC and one of the plates. The photonic-band-gap well-defined at small air gap narrows systematically with opening the air gap and disappears when the air gap is 2 ~ 3 times the rod height, where the two-dimensional nature of PC is destroyed. The mechanical tunability of photonic band structure would be useful in functional THz device.

Dependency of the photonic band gaps in two-dimensional metallic photonic crystals on the shapes and orientations of rods

Photonic bands in two types of two-dimensional metallic photonic crystals (2-D MPCs), which are composed of dielectric rods embedded into a metallic background (type I MPCs) and metallic rods in a dielectric background (type II MPCs), are investigated theoretically using a method based on the frequency-dependent plane-wave expansion method. We discuss the maximization of the normalized gap width as a function of the rod shapes and orientations. In addition, we study the effect of dielectric constants of the rods and the background on the width of the photonic band gap. Four different shapes of rods-square, circular, diamond, and rectangular-are considered. The numerical results show that the type I MPCs have a higher normalized gap width than the type II MPCs. We observe that the rotation of the noncircular rods in the type I MPCs leads to a slight variation, less than 10%, in the normalized values of the gap width in the two lattice structures. However, rotating the metallic square rods arranged in a square lattice results in doubling of the normalized gap width. The normalized gap width can be tailored by changing the dielectric constant of the rods (background) in type I (type II) MPCs.