Extraordinary Transmission Research Articles

Nonlinearly tunable extraordinary optical transmission in a hybird metamaterial

Dielectric metamaterials are promising for significantly enhanced optical nonlinearity for their strongly localized Mie-resonant mode. Here, we theoretically and experimentally studied a hybrid metamaterial exhibiting extraordinary optical transmission (EOT) behavior, in which the transmission amplitude and frequency can be modulated. The EOT of the perforated metal sheet with subwavelength aperture is induced with a dielectric cuboid by setting them in a close proximity and exploiting the first-order Mie-resonant mode. The electromagnetic wave is effectively coupled to the subwavelength aperture by properly placing the dielectric cuboid, and the transmission intensity can be enhanced more than 150 times. Meanwhile, we employed the nonlinear effect of the dielectric cuboid to modulate the operation band of the EOT. Hopefully, our work can inspire innovations for the research of light–matter interactions, electromagnetic light switching devices and filter devices.

A theoretical study of broadband extraordinary optical transmission in gold plasmonic square nanohole arrays and its application on refractive index sensor

A theoretical study of broadband extraordinary optical transmission in gold plasmonic square nanohole arrays and its application on refractive index sensor

Single-Step Fabrication of High-Performance Extraordinary Transmission Plasmonic Metasurfaces Employing Ultrafast Lasers.

Plasmonic metasurfaces based on the extraordinary optical transmission (EOT) effect can be designed to efficiently transmit specific spectral bands from the visible to the far-infrared regimes, offering numerous applications in important technological fields such as compact multispectral imaging, biological and chemical sensing, or color displays. However, due to their subwavelength nature, EOT metasurfaces are nowadays fabricated with nano- and micro-lithographic techniques, requiring many processing steps and carrying out in expensive cleanroom environments. In this work, we propose and experimentally demonstrate a novel, single-step process for the rapid fabrication of high-performance mid- and long-wave infrared EOT metasurfaces employing ultrafast direct laser writing. Microhole arrays composing extraordinary transmission metasurfaces were fabricated over an area of 4 mm2 in timescales of units of minutes, employing single pulse ablation of 40 nm thick Au films on dielectric substrates mounted on a high-precision motorized stage. We show how by carefully characterizing the influence of only three key experimental parameters on the processed micro-morphologies (namely, laser pulse energy, scan velocity, and beam shaping slit), we can have on-demand control of the optical characteristics of the extraordinary transmission effect in terms of transmission wavelength, quality factor, and polarization sensitivity of the resonances. To illustrate this concept, a set of EOT metasurfaces having different performances and operating in different spectral regimes has been successfully designed, fabricated, and tested. Comparison between transmittance measurements and numerical simulations has revealed that all the fabricated devices behave as expected, thus demonstrating the high performance, flexibility, and reliability of the proposed fabrication method. We believe that our findings provide the pillars for mass production of EOT metasurfaces with on-demand optical properties and create new research trends toward single-step laser fabrication of metasurfaces with alternative geometries and/or functionalities.

Enhanced extraordinary terahertz transmission through coupling between silicon resonators.

By using Mie resonance coupling effects, low-loss silicon particles as receiving or transmitting antennas can strongly localize the electromagnetic field. Enhanced extraordinary optical transmission (EEOT) is generated by placing two such silicon particles symmetrically on both sides of subwavelength hole arrays in the terahertz (THz) region. When the hole radius r is 17 times smaller than the resonance wavelength λ (r/λ = 0.06), the enhancement factors of the resonator–hole and the resonator–resonator coupling structures are 154- and 629-fold compared to that of the hole-only structure, respectively. The current distribution, magnetic field and Poynting vector are numerically simulated to reveal the mechanism of the proposed structure. Moreover, the Mie resonance coupling and the induced THz EEOT can be tuned in a wide frequency range. Our results provide a reference for the miniaturization of THz systems.

Реализация физических подходов к конструированию функциональных металлодиэлектрических систем на основе опалов в фотонике

The possibilities of practical implementation of physical approaches to the design of metal-dielectric photonic crystal systems based on opals, which allow controlling the propagation of electromagnetic waves, are shown. The implemented approaches are based on the effects of excitation of surface plasmon-polaritons capable of propagating along the metal-dielectric interface in plasmonic-photonic layered heterostructures, and modification of the photonic-energy structure of the nanocomposite as a result of dispersion of silver in the opal matrix. Experimental results are presented indicating the occurrence of extraordinary transmission and absorption of light in plasmonic-photonic heterostructures, as well as the asymmetric shape of curves in the reflection spectra of nanocomposites, which is associated with the Fano resonance.

Physical approaches to the design of functional metal-dielectric systems based on opals in photonics

The possibilities of practical implementation of physical approaches to the design of metal-dielectric photonic crystal systems based on opals, which allow controlling the propagation of electromagnetic waves, are shown. The implemented approaches are based on the effects of excitation of surface plasmon-polaritons capable of propagating along the metal-dielectric interface in plasmonic-photonic layered heterostructures, and modification of the photonic-energy structure of the nanocomposite as a result of dispersion of silver in the opal matrix. Experimental results are presented indicating the occurrence of extraordinary transmission and absorption of light in plasmonic-photonic heterostructures, as well as the asymmetric shape of curves in the reflection spectra of nanocomposites, which is associated with the Fano resonance. Keywords: photonic crystals, opals, surface plasmon-polaritons, metal-dielectric systems, Fano resonance.

Engineering the Optical Response of the Novel Plasmonic Binary Nanohole Array

The phenomenon of extraordinary optical transmission (EOT) due to its advantages has been considered by researchers in various applications, and in recent years, many efforts have been made to engineer these structures to get the best possible response for desired applications. In this work, the optical properties of novel binary gold nanohole arrays are investigated theoretically. We engineered the optical response of the system by adjusting the ratio of contribution of surface plasmon polariton (SPP) to localized surface plasmon resonance (LSPR) through the manipulation of the geometrical properties. The changes in the topology of this nanohole array affected the intensity and the wavelength of transmission peaks. The sensitivity of the optical response to the refractive index was also investigated. The designed structure is a good candidate for use as a polarization-independent optical label-free sensor.

Extraordinary optical transmission in silicon nanoholes

In this work, for the first time, a study was conducted of the existence of Extraordinary Optical Transmission (EOT) in Silicon (Si) thin films with subwavelength holes array and high excess carrier concentration. Typically EOT is studied in opaque perforated metal films. Using Si would bring EOT and its many applications to the silicon photonics realm and the mid-IR range. Since Si thin film is a semi-transparent film in mid-IR, a generalization was proposed of the normalized transmission metric used in literature for EOT studies in opaque films. The plasma dispersion effect was introduced into the studied perforated Si film through either doping or carriers’ generation. Careful consideration for the differences in optical response modeling in both cases was given. Full-wave simulation and analysis showed an enhanced transmission when using Si with excess carriers, mimicking the enhancement reported in perforated metallic films. EOT was found in the mid-IR instead of the visible range which is the case in metallic films. The case of Si with generated excess carriers showed a mid-IR EOT peak reaching 157% around 6.68 µm, while the phosphorus-doped Si case showed a transmission enhancement of 152% around 8.6 µm. The effect of varying the holes’ dimensions and generated carriers’ concentration on the transmission was studied. The analogy of the relation between the fundamental mode cutoff and the EOT peak wavelength in the case of Si to the case of metal such as silver was studied and verified. The perforated Si thin film transmission sensitivity for a change in the refractive index of the holes and surroundings material was investigated. Also, a study of the device potential in sensing the hole and surroundings materials that have almost the same refractive index yet with different absorption fingerprints was performed as well.

Simulation of Solar Cells with Integration of Optical Nanoantennas.

The evolution of nanotechnology has provided a better understanding of light-matter interaction at a subwavelength scale and has led to the development of new devices that can possibly play an important role in future applications. Nanoantennas are an example of such devices, having gained interest in recent years for their application in the field of photovoltaic technology at visible and infrared wavelengths, due to their ability to capture and confine energy of free-propagating waves. This property results from a unique phenomenon called extraordinary optical transmission (EOT) where, due to resonant behavior, light passing through subwavelength apertures in a metal film can be transmitted in greater orders of magnitude than that predicted by classical theories. During this study, 2D and 3D models featuring a metallic nanoantenna array with subwavelength holes coupled to a photovoltaic cell are simulated using a Finite Element Tool. These models present with slight variations between them, such as the position of the nanoantenna within the structure, the holes’ geometry and the type of cell, in order to verify how its optical response is affected. The results demonstrate that the coupling of nanoantennas to solar cells can be advantageous and improve the capture and absorption of radiation. It is concluded that aperture nanoantennas may concentrate radiation, meaning that is possible to tune the electric field peak and adjust absorption on the main layers. This may be important because it might be possible to adjust solar cell performance to the global regions’ solar spectrum by only adjusting the nanoantenna parameters.

Tunable Extraordinary Optical Transmission with Graphene in Terahertz

Tunable extraordinary optical transmission (EOT) with graphene is realized using a novel metallic ring–rod nested structure in the terahertz frequency regime. The generated double-enhanced transmission peaks primarily originate from the excitation of localized surface plasmon resonances (LSPRs). On using graphene, the resonating surface plasmon distribution changes in the reaction plane, which disturbs the generation of LSPRs. By regulating the Fermi energy (Ef) of the graphene to reach a certain level, an adjustment from bimodal EOT to unimodal EOT is obtained. As the Ef of the graphene integrated beneath the rod increases to 0.5 eV, the transmittance of the peak at 2.42 THz decreases to 6%. Moreover, the transmission peak at 1.77 THz virtually disappears due to the Ef increasing to 0.7 eV when the graphene is placed beneath the ring. The significant tuning capabilities of the bimodal EOT indicate its promising application prospects in frequency-selective surfaces, communication, filtering, and radar.

Giant Extra-Ordinary Near Infrared Transmission from Seemingly Opaque Plasmonic Metasurface: Sensing Applications.

In the present study, we report giant extra-ordinary transmission of near infrared (NIR) light, more than 90%, through a seemingly opaque plasmonic metasurface, which consists of two metal nano-slits arrays (MNSAs) with alternate opening arrangements. By using perfect coupling of the plasmonic modes formed between the sharp edges of the upper and lower MNSAs of silver, a giant, wavelength selective transmission could be obtained. The study is accompanied by optimization of electromagnetic (EM) field coupling for different interlayer spacings and lateral overlap between the two MNSAs to understand their significance in light transmission through the metasurface. The interlayer spacing between the MNSAs works as the transmitting channel for light. The optimization of performance with different fill factors and plasmonic metals was performed as well. Because of the excitation of extended surface plasmons (ESPs) generated at both the MNSAs, the metasurface can be used for refractive index (RI) sensing as one of its applications by using a transparent and flexible polymer, such as polydimethylsiloxane (PDMS), as substrate. The maximum sensitivity which could be achieved for the optimal configuration of the metasurface was 1435.71 nm/RIU, with a figure of merit (FOM) of 80 RIU−1 for 90.45% optical transmission of light for the refractive index variation of analyte medium from 1.33 to 1.38 RIU. The present study strengthens the concept of light funneling through subwavelength structures due to plasmons, which are responsible for light transmission through this seemingly opaque metasurface and finds use in highly sensitive, flexible, and cost-effective EOT-based sensors.

Multifunctional Waterborne Acoustic Metagratings: From Extraordinary Transmission to Total and Abnormal Reflection

Wavelength-thick multifunctional metagratings for waterborne sound are highly desirable in various application scenarios, such as human health monitoring and ocean exploration. In this article, we present a class of metagratings with which distinct and switchable wave manipulation functionalities, such as extraordinary transmission, total reflection, and abnormal reflection can be achieved through a single acoustic grating. Simultaneous and high-efficiency control over both reflected and transmitted waves is achieved through a systematic design approach in which wave diffraction theory, effective medium theory, and intelligent optimization algorithms are concurrently utilized. Switching between different functionalities can be achieved simply by changing the operation frequency, or by changing the incident angles. Robust and perfect wave-front manipulation effects are obtained over a wide range of incident angles and operation frequencies. Our work not only provides a design paradigm of planar acoustic devices for multiple manipulation purposes, but also presents a feasible solution for the development of integrated acoustic devices for distinct underwater applications.

Extraordinary transmission in an add-drop filter configuration driven by nonconservative coupling.

We proposed a nonconservative coupling scheme based on the add-drop filter configuration, in which a high Q factor passive microtoroid resonator is indirectly driven by an active unit, thus providing an additional coupling which might be comparable to a mode decay rate. Extraordinary scattering points are predicted when one of the supermodes becomes lossless. Specifically, when the inherent coupling strength is set at half of the mode's total decay rate, controllable transmission peaks can be realized by tuning the nonconservative coupling strength and phase delay. Our theoretic research might find potential application in tunable light steering based on non-Hermitian resonator systems.

Extraordinary transmission of gold-capped sphere arrays in mid-infrared range.

We report an extraordinary transmission (EOT) of gold-capped silica microsphere monolayers in the mid-infrared range of 5-25 μm. The observed transmittance is significantly greater than that of a flat gold film with the same thickness, although the surface of the microsphere monolayer appeared to be completely covered with gold when observing from above. The calculations based on the finite difference time domain method indicate that light passes through the openings between the gold coating on the substrate and that on the microspheres. The EOT-type studied here occurs over the mid-infrared wavelength range, thus indicating that it is not attributable to the resonance of the surface plasmons. This type of EOT is absent in the visible and near infrared wavelength range, where gold does not function as an ideal metal. In addition, spectral modification originating from localized phonon polariton resonance (LPhPR) in silica microsphere is observed. LPhPR can be interpreted based on the analogy of the localized surface plasmon resonance in metallic nanospheres, in the visible or ultraviolet wavelength range.

Fibre-Optic Surface Plasmon Resonance Biosensor for Monoclonal Antibody Titer Quantification.

An extraordinary optical transmission fibre-optic surface plasmon resonance biosensing platform was engineered to improve its portability and sensitivity, and was applied to monitor the concentrations of monoclonal antibodies (Mabs). By refining the fabricating procedure and changing the material of the flow cell and the components of the optical fibre, the biosensor is portable and robust to external interference. After the implementation of an effective template cleaning procedure and precise control during the fabrication process, a consistent sensitivity of 509 ± 5 nm per refractive index unit (nm/RIU) was achieved. The biosensor can detect the Mab with a limit of detection (LOD) of 0.44 µg/mL. The results show that the biosensor is a potential tool for the rapid quantification of Mab titers. The biosensor can be regenerated at least 10 times with 10 mM glycine (pH = 2.5), and consistent signal changes were obtained after regeneration. Moreover, the employment of a spacer arm SM(PEG)2, used for immobilising protein A onto the gold film, was demonstrated to be unable to improve the detecting sensitivity; thus, a simple procedure without the spacer arm could be used to prepare the protein A-based biosensor. Our results demonstrate that the fibre-optic surface plasmon resonance biosensor is competent for the real-time and on-line monitoring of antibody titers in the future as a process analytical technologies (PATs) tool for bioprocess developments and the manufacture of therapeutic antibodies.

Effects of metallic underlayer on SERS performance of a metal film over nanosphere metasurface

Metal film over nanosphere (MFON) metasurfaces have numerous applications, specifically as nanosensors for bio and chemical detection. Additionally, their interesting optical properties have also attracted the attention of many research groups. In this work, we study the influence of the metallic underlayer on the surface-enhanced Raman scattering (SERS) effect of the MFON structure. Two sets of MFON on silicon and mirror substrates were prepared for SERS measurement with rhodamine 6G. Experimental results show that the mirror layer boosts the SERS signal by two to five times. Finite difference time domain simulation was performed to gain insights into this improvement. Numerical results show that metallic underlayer helps to increase the concentration of the electric field at the hot spots. Moreover, it reflects the Raman signal via the extraordinary optical transmission channel of the MFON structure, improving the back-scattered Raman signal collection efficiency. Both of these effects can contribute to the increase of the SERS signal in agreement with the experimental results. More importantly, it provides an additional tool to tailor the optical properties of MFON metasurfaces.

Extraordinary optical characteristics of one-dimensional double anti-PT-symmetric ring optical waveguide networks

In this paper, a unique one-dimensional double anti-PT-symmetric ring optical waveguide network (1D DAPTSROWN) is designed whose refractive index satisfies n(x)=−n∗(−x). The extraordinary optical characteristics of the network are studied by means of the generalized Floquet–Bloch theorem, three-material network equation and generalized eigenfunction method. Due to the physical difference between the anti-PT-symmetric and PT-symmetric optical waveguide networks, the previous method of the PT-symmetric optical waveguide network is not applicable to the anti-PT-symmetric optical waveguide network designed in this paper. Thus, based on the previous method and the network equation, we propose a connection function to identify the extremum mode points in the anti-PT-symmetric optical waveguide network. At the extremum mode point, the optical waveguide network can produce extraordinary ultra-strong transmission, ultra-strong reflection, and ultra-strong photonic localizations. The corresponding calculated values in this paper arrives at 1028, which is much larger than 1012 (the best result reported previously). This shows that the anti-PT-symmetric network may have potential in applications in designing optical filters, optical amplifiers and so on.

Superposition of ε -Near-Zero and Fabry-Perot Transmission Modes

Metamaterials with near-zero permittivity exhibit extraordinary total transmission of waves within the length-independent conduit. However, such an \ensuremath{\epsilon}-near-zero (ENZ) transmission mode demonstrates an intrinsic narrow-band property using low-loss metastructures, e.g., extremely narrow waveguide transition at the cutoff frequency. As the counterpart to the ENZ mode, the Fabry-Perot (FP) mode also has near-zero reflection but depends on the channel length. For application considerations, the phenomenon of superpositioning ENZ and FP modes is analyzed theoretically and numerically to enhance the bandwidth of near-zero reflection within extreme mismatching waveguide transitions. The achieved bandwidth of the ENZ and FP mode cooperation is larger than the sum of two single modes, exhibiting feasible applications in the integrated waveguide structures, such as integrated transmission lines, circuits, and antennas. As an application example of this physical property, a waveguide crossover is proposed and experimentally verified to achieve wideband dual-narrow-channel total transmission within only one dielectric layer with an extremely low profile.

Optical Analysis of Hole Patterned Ag Nanoparticle Structure.

A structure with periodic sub-wavelength nanohole patterns interacts with incident light and causes extraordinary optical transmission (EOT), with metal nanoparticles leading to localized surface plasmon resonance (LSPR) phenomena. To explore the effects of metal nanoparticles (NPs), optical analysis is performed for metal NP layers with periodic hole patterns. Investigation of Ag NP arrangements and comparisons with metal film structures are presented. Ag NP structures with different hole configuration are explored. Also, the effects of increasing light incident angle are investigated for metal NP structures where EOT peak at 460 nm wavelength is observed. Moreover, electric field distributions at each transmittance peak wavelengths and optical noise are analyzed. As a result, optical characteristics of metal NP structures are obtained and differences in resonance at each wavelength are highlighted.

Enhanced broadband extraordinary terahertz transmission through plasmon coupling between metal hemisphere and hole arrays

Enhanced extraordinary optical transmission (EOT) is generated by a gold hole array with a concentric hemisphere in the terahertz (THz) region. By introducing hemispherical particles and using the plasmon coupling effects of surface plasmon polaritons and localized surface plasmon resonances, it can be found that not only the transmission intensity is greatly enhanced to 0.97 and the bandwidth is nine times wider than that of a non-particle in a hole, but also the size of the structure can be significantly reduced. Additionally, optical characteristics of the hemisphere-in-hole structure are thoroughly analyzed by the schematic diagram, transmission spectra, and optical field distribution. In addition, with the diameter of the hemisphere increasing, the transmission peak maintains at a high value and the peak position redshifts correspondingly. Finally, we alter the shapes and sizes of the central particles to verify the influence on the enhanced THz EOT. Our results provide a reference for theoretical understanding and expand the application prospects for many THz plasmonic devices.