Beam-Scanning Planar Lens Based on Metal–Dielectric–Metal Waveguide Arrays

Under specific illumination conditions, periodic arrays of metal–dielectric–metal (MDM) waveguides act as uniform optical phased-array antenna where the phase of the radiating optical wave can be controlled by modifying the refractive index distribution of the dielectric material. Based on this property, we propose a planar gradient index MDM-based lens which can transform spherical waves of the transverse-magnetic surface plasmon polariton waves to plane waves with specific beam deflections by adjusting the refractive index configurations. Using numerical simulations based on two-dimensional finite-difference time-domain method, it is confirmed that beam focusing and splitting with multiple dflection angles can also be achieved.     

Fano Resonance in a Gear-Shaped Nanocavity of the Metal–Insulator–Metal Waveguide

The filter function of the metal–insulator–metal (MIM) waveguide with a gear-shaped nanocavity is investigated using the finite-difference time-domain method. Since the gear breaks the symmetric distribution of the resonance, Fano resonance occurs in the gear-shaped nanocavity. Fano resonance strongly depends on the structural parameters of the gear. Compared to the MIM waveguide with a disk-shaped nanocavity, the MIM waveguide with a gear-shaped nanocavity allows for a much more sensitive detection of small refractive index changes of the filled media inside the nanocavity, which reveals a potential sensor application of the MIM waveguide with a gear-shaped nanocavity.     

Plasmonic Photonic Bloch Oscillations in Composite Metal–Insulator–Metal Waveguide Structure

This study proposes the time-evolved plasmonic photonic Bloch oscillations (PBOs) in a composite metal–insulator–metal (CMIM) waveguide structure. This device contains two kinds of MIM waveguide with different thickness of the insulator gaps. The time-resolved plasmonic PBO motion in this CMIM waveguide can be observed by introducing a linearly graded dielectric material. The ray trajectory results from the Hamiltonian optics are consistent with the finite-difference time-domain simulation results.     

Location-Dependent Local Field Enhancement Along the Surface of the Metal–Dielectric Core–Shell Nanostructure

A theoretical study based on quasi-static approximation is performed to investigate the location-dependent local field enhancement around the dielectric shell-coated gold nanosphere. Our calculation results show that the local field distribution near a gold nanoparticle can be altered greatly by coating with a dielectric shell. Because of the polarizability of the dielectric shell, increasing azimuth angle along the inner surface leads to the increase of the local field, which is opposite to that of the outer surface. Furthermore, the location-dependent local field enhancement and resonance frequency at both the inner and outer surfaces can also be modulated by varying the shell thickness and shell dielectric constant. These calculation results about the location-dependent local field enhancement show the potential of dielectric-coated metallic nanostructure for single-molecule detection based on surface-enhanced Raman scattering and surface enhanced fluorescence.     

Characteristics of Symmetric Surface Plasmon Polariton Mode in Glass–Metal–Glass Waveguide

The propagation characteristics of symmetric surface plasmon polariton mode in a glass–metal–glass waveguide are presented. Gallium lanthanum sulfide has been taken as the glass and silver (Ag) has been used as the metal. The analysis has been done both numerically and analytically. A two-dimensional finite-difference time-domain-based simulation model has been developed in order to analyze the propagation characteristics numerically. The obtained results using numerical and analytical methods have been compared and a very good agreement has been found.     

A High-Performance Refractive Index Sensor Based on Hybrid Resonance Modes in a Square Nanocavity Coupled with Metal–Insulator–Metal Plasmonic Waveguide

Plasmonics - We present one of the simplest nanoscale systems for a high-performance refractive index (RI) sensor. We investigate analytically and numerically the transmission response of the...     

Frequency-Dependent Polarization Properties of Local Electric Field in Gold–Dielectric Multi-Nanoshells

The polarization properties of the local electric field in the gold–dielectric–gold multilayer nanoshells are investigated by theoretical calculation based on the quasi-static approximation. The calculation results show that the complete polarized incident light does not only stimulate the same directional polarized local electric field. The polarized angle of the local field may changes from 0° to 90° as the wavelength and location are changed. The distributions of local field polarization are different in dielectric layer or gold shell and display different features in different plasmonic hybridization mode. As the incident wavelength is increased, the hot spot of polarizing angle moves monotonously in the middle dielectric shell, whereas moves nonmonotonously in the gold shell and surrounding environment. In the gold shell, the gap between hot spots of polarizing angle may occur at the resonance frequency. However, the hot spots of polarizing angle always occur at the resonance frequencies in the surrounding environment. These interesting results show that the single-molecule detection based on metal nanostructure induced surface-enhanced Raman scattering and surface enhanced fluorescence could be optimized by adjusting the incident light polarization and frequency.     

Characteristics of Quantum Plasmonic Waves Guided by a Symmetric Metal–Gap–Dielectric Nano-system

Plasmonics - The guiding properties of a symmetric conductor–gap–dielectric system consists of a metal film symmetrically surrounded by media of two dielectrics, and is theoretically...     

Localized Surface Plasmon Resonance and Refractive Index Sensitivity of Metal–Dielectric–Metal Multilayered Nanostructures

The localized surface plasmon resonances of multilayered nanostructures are studied using finite difference time domain simulations and plasmon hybridization method. Concentric metal–dielectric–metal (MDM) structure with metal core and nanoshell separated by a thin dielectric layer exhibits a strong coupling between the core and nanoshell plasmon resonance modes. The coupled resonance mode wavelengths show dependence on the dielectric layer thickness and composition of core and outer layer metal. The aluminum-based MDM structures show lower plasmon wavelength compared with Ag- and Au-based MDM nanostructures. The calculated refractive index sensitivity (RIS) factor is in the order Ag–Air–Ag>Au–Air–Au>Al–Air–Al for monometallic multilayered nanostructures. Bimetallic multilayered nanostructures support strong and tunable plasmon resonance wavelengths as well as high RIS factor of 510 nm/refractive index unit (RIU) and 470 nm/RIU for Al–Air–Au and Ag-Air-Au, respectively. The MDM structures not only exhibit higher index sensitivity but also cover a wide ultraviolet–near-infrared wavelengths, making these structures very promising for index sensing, biomolecule sensing, and surface-enhanced Raman spectroscopy.     

Buried Effects of Surface Plasmon Resonance Modes for Periodic Metal–Dielectric Nanostructures Consisting of Coupled Spherical Metal Nanoparticles with Cylindrical Pore Filled with a Dielectric

We numerically investigate the buried effects of surface plasmon resonance (SPR) modes for the periodic silver-shell nanopearl dimer (PSSND) array and their solid counterparts with different buried depths in a silica substrate by means of finite element method with three-dimensional calculations. The investigated PSSND array is an important novel geometry for plasmonic metal nanoparticles (MNPs), combining the highly attractive nanoscale optical properties of both metallic nanoshell and cylindrical pore filled with a dielectric. Numerical results for SPR modes corresponding to the effects of different illumination wavelengths, absorption spectra, pore–dielectric, electric field components and total field distribution, charge density distribution, and the model of the induced local field or an applied field of the PSSND array are reported as well. It can be found that the buried MNPs with cylindrical pore filled with a dielectric in a substrate exhibit tunable SPR modes corresponding to the bonding and antibonding modes that are not observed for their solid counterparts.     

Dispersion and Field Distribution of SPP Waves at the Interface of a Metal and Nonlinear Magnetic Material

We study the properties of surface plasmon polaritons at an interface between a metal and a strongly nonlinear magnetic cladding, characterized by permeability $\mu=\mu_\textrm{l}+\mu_{\textrm{nl}} H^2$ . It is observed that the dispersion of modes has a significant dependance on the incident power. The incident power can be adjusted to control the propagation length. In addition, the structure shows strong confinement of the modes at the interface.     

Multiple Surface Plasmon Resonances in a Metal–Insulator–Metal Structure Assembled Via Silver–Copper Nanoparticle Arrays

The Ag–Cu nanoparticle arrays, prepared using the electrochemical deposition method, were assembled into the metal–insulator–metal (MIM) structure with polyvinyl alcohol acting as insulating layer, the transmission spectrum of the MIM structure was observed to support the multiple surface plasmon resonances in the wavelength range 1,000 to 2,600 nm. The multiple peaks were formed due to the superposition and coupling of the surface plasmon resonance of nanoparticles with various sizes in the metal layers. The newly found MIM structure in which multiple resonances exist has a potential application in multiband-pass filters and optical magnetic metamaterials at the resonance wavelength.     

Five-Band Terahertz Perfect Absorber Based on Metal Layer–Coupled Dielectric Metamaterial

Plasmonics - A five-band tunable ideal terahertz metamaterial absorber based on subwavelength range is proposed. It consists of a reflective layer, a dielectric layer, and an absorbing layer...     

Design of a High-Resolution Metal–Insulator–Metal Plasmonic Refractive Index Sensor Based on a Ring-Shaped Si Resonator

In this paper, a high-resolution refractive index sensor is proposed based on a novel metal–insulator–metal plasmonic topology. The structure is based on a Si nano-ring located inside a circular cavity. It acts as an optical notch filter with a quality factor equal to 269. The proposed filter topology is numerically simulated using the finite difference time domain method. It is shown that the proposed filter can also act as a refractive index sensor with a sensitivity of 636 nm/RIU and a fairly high figure of merit (FoM) equal to 211.3 RIU⁻¹. It is shown that the sensor can easily detect a refractive index change of ± 0.001 for dielectrics whose refractive index is between 1 and 1.2. For the refractive index range of 1.33 to 1.52, the maximum FoM of the sensor is 191 RIU⁻¹. The simplicity of the design and its high resolution are the two main features of the proposed sensor which make it a good candidate for biomedical applications.

     

The Ideal Free Distribution in a Predator–Prey Model with Multifactor Taxis

Biophysics - The concept of an ideal free distribution (IFD) is analyzed for the predator–prey system in an inhomogeneous ring-shaped habitat. Diffusion–reaction–advection...     

Nonlocality-Induced Negative Refraction and Subwavelength Imaging by Parabolic Dispersions in Metal–Dielectric Multilayered Structures with Effective Zero Permittivity

We investigate metal–dielectric multilayered structures with an effectively zero permittivity. Nonlocality induced by the surface plasmons in such structures can produce intriguing dispersions characterized by two crossing branches of parabolas. We obtain the critical conditions to set the two branches of parabolas apart, and reverse the direction of group velocity such that the system becomes capable of negative refraction as well as subwavelength imaging. Such phenomena theoretically exist in the quasistatic limit.