Multispectral Broadband Light Transparency of a Seamless Metal Film Coated with Plasmonic Crystals

Broadband light transparency of metallic structures has long been pursued due to the potential applications in the optoelectronic communications, flat panel displays, and clean solar energy. Considerable efforts have been made on the multiband electromagnetic wave transparency of plasmonic metamolecules. However, far less work has been focused on the multispectral light transparency of a seamless metal film. Here, we for the first time propose a seamless metal film structure coated by double conventional plasmonic crystals and demonstrate the observed multispectral broadband light transparency behavior. A maximum transmittance larger than 92 % is achieved. The average transmittance of the whole spectral range from 550 to 1,100 nm is exceeding 45.8 %, suggesting the achievement of an ultra-broadband semi-transparent window. Particularly, the transparency features are highly scalable by tuning the structural parameters. Plasmonic resonances and the metallic particle–film plasmonic interactions are responsible for the observed optical transparency properties. These findings and merits make the proposed structure a good candidate for numerous potential applications, including the optoelectronic components, transparent displayers, and light harvesting.     

Narrowband Light Total Antireflection and Absorption in Metal Film–Array Structures by Plasmonic Near-Field Coupling

We study the cooperative effects between plasmon gap modes and optical cavity modes of a novel triple-layer structure consisting of double continuous gold films separated by a gold nanosphere array. Narrowband near-perfect antireflection of optical field is achieved for the first time due to the strong near-field light–matter interaction within the deep sub-wavelength gaps between adjacent nanospheres combined with the spatial field confinement effects of the optical cavity built by the double gold films. The coexistence cooperation of near-field dipole plasmon resonances and spatial optical field confinement presents more efficient light modification than that of the individual subsystem and may open a new approach to manage light flow. By varying the period of nanosphere array, the diameter of nanospheres, and the distance between the array and the film, optical behaviors of the proposed structure can be tuned in a wide range. High environmental sensitivity and large figure of merit factor are obtained using this structure as the detecting substrate. Furthermore, ultra-compact structure and high conduction suggest the proposed structure being a good candidate for potential applications in highly integrated optoelectronic devices, such as plasmonic filters and sensors.     

High Optical Transmission in a Hybrid Plasmonic-Optical Structure with a Continuous Metal Film

Metals are naturally opaque for electromagnetic (EM) waves below violet frequency due to the Coulomb screening effect. In this letter, we demonstrate high optical transparency of a seamless continuous metal film by sandwiching it in a hybrid plasmonic-optical structure. The proposed structure consists of a plasmonic array and an optical cavity, which exhibits magnetic plasmon (MP) resonance and optical Fabry-Perot (FP) resonance, respectively. An optical transparency of 84% in the near-IR regime is achieved making use of interaction between the plasmonic and optical modes. Furthermore, spectral tunability of the high transparency is demonstrated and robustness under oblique incidence is examined. This work may give insights into plasmonic-optical interactions and may be a potential candidate for transparent electrodes.     

Tunable Extraordinary Optical Transmission in a Metal Film Perforated with Two-Level Subwavelength Cylindrical Holes

We propose a novel plasmonic metal structure composed of a silver film perforated with a two-dimensional square array of two-level cylindrical holes on a silica substrate. The transmission properties of this structure are theoretically calculated by the finite-difference time-domain (FDTD) method. Double-enhanced transmission peaks are achieved in the visible and infrared regions, which mainly originate from the excitation of localized surface plasmon resonances (LSPRs), the hybridization of plasmon modes, and the optical cavity mode formed in the holes. The enhanced transmission behaviors can be effectively tailored by changing the geometrical parameters and dielectric materials filled in the holes. These findings indicate that our proposed structure has potential applications in highly integrated optoelectronic devices.     

Metallic Nanowire Array–Polymer Hybrid Film for Surface Plasmon Resonance Sensitivity Enhancement and Spectral Range Enlargement

In this paper, the coupling interaction is investigated between a metallic nanowire array and a metal film under the Kretschmann condition. The plasmonic multilayer is composed of a metallic nanowire array embedded in a polymer layer positioned above a metal film, exploiting the classical surface plasmon resonance (SPR) configuration. We analyze the influence of various structural parameters of the metallic nanowire array on the SPR spectrum of thin metal film. The results show that the coupling interactions of nanowires with the metal film can greatly affect SPR resonance wavelength and increase SPR sensitivity. The coupling strength of metallic nanowire array and metal film also impacts resonance wavelength, which can be used to adjust SPR range but have little effect on its sensitivity. The results are confirmed using a dipole coupling resonance model of metallic nanowire. We demonstrated that this nanostructured hybrid structure can be used for high sensitivity SPR monitoring in a large spectral range, which is important for advanced SPR measurement including fiber-optic SPR sensing technology.     

Retarded Charge–Carrier Recombination in Photoelectrochemical Cells from Plasmon‐Induced Resonance Energy Transfer

N‐type metal oxides such as hematite (α‐Fe₂O₃) and bismuth vanadate (BiVO₄) are promising candidate materials for efficient photoelectrochemical water splitting; however, their short minority carrier diffusion length and restricted carrier lifetime result in undesired rapid charge recombination. Herein, a 2D arranged globular Au nanosphere (NS) monolayer array with a highly ordered hexagonal hole pattern (hereafter, Au array) is introduced onto the surface of photoanodes comprised of metal oxide films via a facile drying and transfer‐printing process. Through plasmon‐induced resonance energy transfer, the Au array provides a strong electromagnetic field in the near‐surface area of the metal oxide film. The near‐field coupling interaction and amplification of the electromagnetic field suppress the charge recombination with long‐lived photogenerated holes and simultaneously enhance the light harvesting and charge transfer efficiencies. Consequently, an over 3.3‐fold higher photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) is achieved for the Au array/α‐Fe₂O₃. Furthermore, the high versatility of this transfer printing of Au arrays is demonstrated by introducing it on the molybdenum‐doped BiVO₄ film, resulting in 1.5‐fold higher photocurrent density at 1.23 V versus RHE. The tailored metal film design can provide a potential strategy for the versatile application in various light‐mediated energy conversion and optoelectronic devices.     

Tunnel Light Through a Continuous Optically Thick Metal Film Utilizing Higher Order Magnetic Plasmon Resonance

In this letter, we investigate the extraordinary optical transmission behavior of a flat continuous metal film sandwiched by magnetic plasmonic structures. A new mechanism by utilizing higher order magnetic plasmon resonance is proposed to enhance the transmission. Numerical simulation results show that 80 % electromagnetic energy can be transmitted through the middle 50-nm-thick continuous gold film in near-infrared regime. The excitation of the second-order magnetic plasmons and the propagating surface plasmons, as well as the interaction between them accounts for such a high transmission. The interaction of magnetic plasmons and surface plasmons leads to new hybrid modes, and the coupled oscillator model is introduced to analyze this hybridization. This work extends the application range of higher order magnetic plasmons and may have potential in transparent electrode and electromagnetic energy transfer applications.     

Tunable Plasmonically Induced Transparency with Asymmetric Multi-rectangle Resonators

Plasmonically induced transparency (PIT) effect in a metal–insulator–metal waveguide coupled to asymmetric multi-rectangle resonators is investigated numerically. By adjusting parameters of resonators, we cannot only realize single, double, or treble PIT peaks in the compact structure, but also induce an off-to-on PIT optical response. Numerical simulation by finite element method was conducted to verify our designs. This proposed structure, hence has potential applications for ultra-compact optoelectronic devices at communication band.

     

Laser‐Generated Nanocrystals in Perovskite: Universal Embedding of Ligand‐Free and Sub‐10 nm Nanocrystals in Solution‐Processed Metal Halide Perovskite Films for Effectively Modulated Optoelectronic Performance

Regulating the chemical/physical features of solution processed metal halide perovskite films by integrating sub‐10 nm nanocrystals is a highly promising strategy to advance their outstanding optoelectronic performance. However, significant challenges remain for the universal embedding of the well‐defined nanocrystals in the film matrix. By generating nanocrystals in desired solvents via pulsed laser irradiation in liquid, the authors demonstrate the effective decoration of sub‐10 nm nanocrystals in perovskite films for enhanced optoelectronic performance. It is believed that this improved performance is due to the modification of the widely adopted “antisolvent” to a novel “anti‐colloidal‐solution” (ACS). Exemplified by a typical ACS; carbon dots in chlorobenzene, its encouraging superiority in regulating, not only the films morphology, but also the electronic structure, is demonstrated. This results in perovskite solar cells with a champion efficiency of 21.41% as well as a pronounced stability over 5000 h in relative humidity of 40%. The capability of nanocrystal embedding for boosted photovoltaic performance is further exploited by employing other laser generated ACSs. Such a strategy may open up a route to regulating hybrid perovskite film performance via nanocrystal embedding for photovoltaics or even beyond optoelectronic applications.     

Tunable Slow Light in Graphene Metamaterial in a Broad Terahertz Range

A graphene-based metamaterial with tunable electromagnetically induced transparency is numerically studied in this paper. The proposed structure consists of a graphene layer composed of H shape between two cut wires, by breaking symmetry can control EIT-like effects and by increasing the asymmetry in the structure has strong coupling between elements. It is important that the peak frequency of transmission window can be dynamically controlled over a broad frequency range by varying the chemical potential of graphene layer. The results show that high refractive index sensitivity and figure of merit can be achieved in asymmetrical structures which is good for sensing applications. We calculated the group delay and the results show we can control the group velocity by varying the S parameter in asymmetrical structure. The characteristics of our system indicate important potential applications in integrated optical circuits such as optical storage, ultrafast plasmonic switches, high performance filters, and slow-light devices.     

Free-Space Plasmonic Filter with Dual-Resonance Wavelength Using Asymmetric T-Shaped Metallic Array

In this study, we propose a plasmonic free-space filter with dual resonance wavelength by using an asymmetric T-shaped array. The structure under the T-shaped structure forms two metal/insulator/metal cavities with different cavity length. Each cavity supports a specific resonance wavelength. A notch filter for second harmonic generation Nd:YAG laser is also proposed. The filter offers two resonance dips and low sideband. In addition, the filter properties are based on the localized surface plasmon. Therefore, the angle tolerance is extremely high. This makes the proposed structure easy to align. The proposed structure can be used in dual wavelength biosensing detection and dual wavelength thermal emission applications.     

Optimization of Optoelectronic Plasmonic Structures

We discuss the interplay between surface plasmon polaritons (SPPs) and localized shape resonances (LSRs) in a plasmonic structure working as a photo-coupler for a GaAs quantum well photodetector. For a targeted electronic inter-subband transition inside the quantum well, maximum photon absorption is found by compromising two effects: the mode overlapping with incident light and the lifetime of the resonant photons. Under the optimal conditions, the LSR mediates the coupling between the incident light and plasmonic structure while the SPP provides long-lived resonance which is limited ultimately by metal loss. The present work provides insight to the design of plasmonic photo-couplers in semiconductor optoelectronic applications.     

Ultra-thin Semiconductor/Metal Resonant Superabsorbers

The design of thin-film semiconductor absorbers is a long-sought-after goal of crucial importance for optoelectronic devices. We propose a new strategy that achieves multi-band optical absorption in an ultra-thin semiconductor-insulator-metal nanostructure. The whole thickness of the absorber is just 60 nm, which is less than λ/12. The ultra-thin semiconductor resonators are used as the photonic coupling elements. The plasmonic metal layer with the thickness about 15 nm simultaneously acts as the transmission cancel layer and the plasmon source for resonant coupling with the optical near-field energy. The combined semiconductor resonators and the thin metal film produce strong electromagnetic field coupling and confinement effects, which mainly contribute to the efficient light trapping for the multi-band strong light absorption. The semiconductors such as Si, GaAs, and Ge are confirmed with the capability to show high light absorption via this simple hybrid metal-semiconductor resonant system. These features pave new insight on ultra-thin semiconductor absorbers and hold potential applications for optoelectronics such as nonlinear optics, hot-electron excitation and extraction, and the related devices.

     

Plasmonic Enhanced Optoelectronic Devices

Plasmonic metal nanostructures have recently attracted extensive research and developed into a promise approach for enhancing the performance of various optoelectronic devices. This brief article reviews recent research advances on the plasmonic enhanced optoelectronic devices and highlights a variety of strategies of incorporating plasmonic nanostructures into different optoelectronics such as solar cells, light-emitting diode, and multicolor photodetector, etc. In addition, the benefits of using various plasmonic metal nanostructures are discussed and the resulting enhancement mechanisms are displayed and summarized.     

Design of Plasmonic Comb-Like Filters Using Loop-Based Resonators

A subwavelength plasmonic comb-like filter is proposed by using dual symmetric slot cavities which are placed between two parallel metal–insulator–metal (MIM) structure waveguides. The structure can be considered as a resonance loop which consists of slot cavity resonators and MIM waveguide resonators. The reflective wavelength range and channel spacing are determined by the lengths of slot cavities and MIM waveguides, respectively. Three, four, and five reflective channels with high reflection are achieved in a small wavelength range. Higher channel count can be available by increasing the length or the real part of effective index of MIM waveguides. Such a device can find applications in various optical systems such as wavelength demultiplexing components.     

High-extinction-ratio and low-insertion-loss Plasmonic Filter with Coherent Coupled Nano-cavity Array in a MIM Waveguide

In this paper, a novel plasmonic filter with very high extinction ratio and low insertion loss is proposed based on the coherent coupled nano-cavity array in a metal–insulator–metal (MIM) waveguide. The coherent coupling interactions among nano-cavities are investigated with an analytical model which is derived based on the temporal coupled-mode theory and transfer-matrix method. The destructive interference of the surface plasmon polaritons coupled from the nano-cavities at the resonant wavelength is achieved by suitably designing the period of the cavity array, which may be used for increasing the extinction ratio of the filter based on the nano-cavity array in the MIM waveguide. A plasmonic filter with an extinction ratio higher than 60 dB and an insertion loss less than 1.0 dB is obtained by applying the destructive interference in the design of a six-rectangular-cavity array in an Ag–air–Ag waveguide. And the correctness of the design for the filter is verified by the results obtained with the finite-difference time-domain simulation technique. This work may provide useful schemes and approaches for realization of various wavelength-sensitive devices in plasmonic integrated circuits.     

A Super Lens System for Demagnification Imaging Beyond the Diffraction Limit

A super lens system is proposed to achieve subdiffraction limit demagnification imaging. The super lens system consists of a hyperlens with planar input and output surfaces, a metal superlens, and a plasmonic reflector. By employing the hyperlens to transform evanescent waves into propagating waves and employing the metal superlens and the plasmonic reflector to amplify evanescent waves, the super lens system can produce a subdiffraction limit image with relatively high electric field intensity. The reduction factor of the super lens system depends on the geometric parameters of the hyperlens. Simulation results show that an image with a half-pitch resolution of about one tenth the operating wavelength and a reduction factor of about 2.2 can be produced by the super lens system. The proposed super lens system has potential applications in nanolithography.     

Optimized Electroless Silver Coating for Optical and Plasmonic Applications

Electroless metal deposition is a simple and convenient technique to fabricate metallic films and to provide isotropic metal functionalization of 3D structures with complex geometries. In this work, we describe the synthesis of silver coatings by means of a modified Tollens reaction and their use as optical coating. The chemical composition of the metallization bath is here addressed to optimize the metal coating deposition. The synthesis parameters have been tailored in order to deposit very smooth films which were characterized by scanning electron microscopy, atomic force microscopy, and optical spectroscopy. 2D diffraction gratings and sinusoidal plasmonic gratings were produced with the proposed method. Optical characterization confirmed the plasmonic activities of the resultant structures, proving the efficiency of the described method for optical applications. Thermal annealing was found to improve the surface roughness of the coating and therefore the optical properties of the plasmonic gratings.     

Multilayer Hybrid Plasmonic Nano Patch Antenna

This is the first report of a hybrid plasmonic nano patch antenna having metal insulator metal (HMIM) multilayer configuration. It is designed in a footprint area of 1.7 × 1.175 μm² to resonate at 1.55 μm wavelength. The proposed antenna is inset fed by an HMIM plasmonic waveguide for achieving proper impedance matching. It is observed, through electromagnetic numerical simulation, that the proposed plasmonic nano patch antenna emits a directional beam with a bandwidth, gain, and efficiency of 0.194 μm, 8.3 dB, and 96% respectively, which are significantly higher than previously reported designs. Since inset-fed antennas are suitable for developing high-gain antenna array, hence further, we examined antenna performance by designing antenna array. The proposed antenna is practically realizable and can be fabricated using standard semiconductor fabrication process. Moreover, it could be used for numerous chip scale applications such as wireless interconnects energy harvesting, photoemission, photo detection, scattering, heat transfer, spectroscopy, and optical sensing.

     

A Three-Dimensional Plasmonic Nanostructure with Extraordinary Optical Transmission

We report a 3D plasmonic nanostructure having an extraordinary optical transmission due to localized surface plasmon (LSP) coupling between nanoholes and nanodisks. The nanostructure contains a free-standing gold nanohole array (NHA) film above a cavity and an array of nanodisks at the bottom of the cavity that is aligned with the NHA. For the device, the LSP-mediated resonance position was dependent on the hole and nanodisk diameter as well as the separation distance. Also, the effect of LSP coupling between each hole and corresponding nanodisk became negligible for cavities deeper than 200 nm as observed as a disappearance of the LSP resonance. The greatest LSP resonance transmission and the highest electric field intensity were observed for the structure with the shallowest cavity. In addition, the structure had high surface plasmon resonance sensitivity and may have potential for surface-enhanced Raman spectroscopy and optical trapping applications.