Dielectric Spacer Layer Research Articles

An electrically tunable plasmonic optical modulator with high modulation depth based on graphene-wrapped silver nanowire

We report a systematic study of a graphene-wrapped plasmonic optical modulator with a high modulation depth. The optical modulator consists of a silver (Ag) nanowire as a single mode plasmonic waveguide being wrapped with a graphene monolayer as an electrically controllable absorbing material. While a thin dielectric spacing layer is used to electrically isolate the Ag nanowire from the graphene monolayer, we find it further promotes higher optical absorption by manipulating a strong electric field at its outer surface, where the graphene layer is located. By optimizing the dielectric layer thickness as well as the Ag nanowire radius, a strong optical modulation of 0.46 dB μm−1 with a high-speed characteristic at the operating wavelength of 785 nm is achieved. This design is further implemented at the telecommunication wavelength (1550 nm) with an optimized modulation depth of 1.07 dB μm−1.

Absorption enhancement of a dual-band metamaterial absorber

In this paper, we propose and fabricate a dual-band metamaterial absorber in 6–24THz region. Electric field distribution reveal that the first absorption band is obtained from localized surface plasmon (LSP) modes which are excited both on inside and outside edges of each circular-patterned metal-dielectric stack, while the second absorption band is excited by LSP modes on outside edges of each stack. Measured results indicate that the absorption band width can be tuned by increasing the radius of circular-patterned layers or reducing the thickness of dielectric spacing layers. Moreover, the designed dual-band metamaterial absorber is independent on circular-patterned dielectric layer combinations.

Graphene based surface plasmon resonance gas sensor for terahertz

We report a SPR based gas sensor using doped graphene monolayer employing the ATR technique via modified Otto coupling configuration. The proposed gas sensor is an approach different from the already reported Otto geometry for SP excitation in terahertz frequencies where the air gap has been replaced by a dielectric spacer layer (organic material) of refractive index (nd) 1.44, 1.50 and 1.54 at operating terahertz frequency of 5 THz. The performance of the sensor with respect to key system parameters such as the thickness of the dielectric layer, sensitivity, detection accuracy and FOM are investigated in the paper using angular interrogation via Transfer matrix method. It is observed that with increasing refractive index of spacer dielectric, the proposed gaseous sensor exhibits trade off between sensitivity and detection accuracy. However, the FOM is approximately equal for refractive indices 1.44 and 1.50 of spacer material, which is ~20 % higher than that at nd = 1.54. The FOM for nd = 1.44, increases from 527 (analyte refractive index = 1.00) to 741 RIU−1 (analyte refractive index = 1.10).

A transmissive/absorbing radome with double absorbing band

ABSTRACTA concise transmissive/absorbing radome principle model is presented, which realizes flat‐top wide‐band transmission band and two electromagnetic absorbing wide band located above and beneath the transmission band. Simulation indicates reflection signature of this radome structure could be reduced by over −10 dB out of transmission band. Frequency‐selective characters are achieved by one resistive FSS layer and two metallic FSS layers with nested square element, along with two dielectric spacer layers. An experimental‐demonstration sample plate fabrication and measurement testifies the model preliminarily. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2016–2019, 2016

Actively controllable EIT-like resonance between localized and propagating surface plasmons for optical switching

We theoretically investigate the plasmonic interaction between radiative localized surface plasmon resonances and subradiative propagating surface plasmon modes in a nanostructure consisting of a periodic array of gold nanobars and an optically thick gold film, separated by a silica dielectric spacer layer. A controllable transparency window within the broad dipole resonance profile is observed clearly in the reflectance spectra via tailoring the length of the bar, the periodicity of the nanoparticle array, or the incident angle of applied field, respectively, a classic analog of electromagnetically induced transparency (EIT). We believe that the last excitation configuration is particularly beneficial for the realization of active manipulation of plasmonic optical switching without using coupling/control fields required in the conventional EIT scheme.

Role of the spacer layer in plasmonic antireflection coatings comprised of gold or silver nanoparticles

Metal nanoparticles (NPs) can increase the absorption of light within semiconductors and hence improve the efficiency of solar cells. We experimentally investigate the effect that gold and silver NPs have on the reflectance of silicon wafers. The NPs are fabricated using the low cost, large area technique of thermal dewetting. We show that a dielectric spacer layer between the NPs and the semiconductor is required to achieve a net reduction of reflection. Furthermore, the optimum thickness of the spacer layer is found to be independent of NP size and metal type.

Spectroscopic Characteristics of Three Dimensional Split-Ring Resonator Arrays at Terahertz Frequencies.

In this work, three-dimensional, stacked arrays of subwavelength, square, dual, concentric split ring resonators exhibiting characteristics at the Terahertz frequencies have been designed, simulated, and fabricated through a photolithographic lift-off process and electron beam evaporation metal deposition. Characterization of the split-ring resonator arrays was performed by transmission mode Terahertz time domain spectroscopy. The effects of the split-ring resonator unit cell spatial dimensions on resonant absorption frequencies and relative absorption strength are investigated as well as effects from the addition of a dielectric spacing layer and additional split-ring resonator layer. The split-ring resonator arrays were seen to develop two distinct and switchable LC resonances as well as a dipole resonance by measuring the arrays at 0° and 90° in-plane rotations about the terahertz propagation vector. The dielectric spacing layer served to effectively lower the resonant frequencies of the split-ring resonantors while the dual split-ring resonator array was seen to have a slight modulating effect on the absorption strength at the resonant frequencies compared to that of the passivated array without the second layer.

固体介质间隔层激光标准具性能的影响因素研究

固体介质间隔层激光标准具性能的影响因素研究

Directionally-controlled periodic collimated beams of surface plasmon polaritons on metal film in Ag nanowire/Al2O3/Ag film composite structure.

Plasmonics holds promise for the realization of miniaturized photonic devices and circuits in which light can be confined and controlled at the nanoscale using surface plasmon polaritons (SPPs), surface waves of collective oscillations of electrons at a metal/dielectric interface. However, realizing plasmonic applications fundamentally requires the ability to guide and transfer SPPs in different plasmonic structures. Here the generation and control of periodic collimated SPP-beams are reported in composite structures of silver nanowire on silver film with a dielectric spacer layer between them. It is revealed that the collimated beams on the silver film originate from the interference between film-SPPs generated by two SPP modes on the nanowire. The direction of the collimated beams can be readily tuned by changing the thickness of the dielectric spacer. These findings demonstrate the transfer of nanowire SPPs to film SPPs and offer a new approach to generate nondiffracting SPP-beams, which could facilitate the design and development of complex plasmonic systems for device applications and enable the tailoring of SPP radiation and SPP-matter interactions.

TE polarization broadband absorber based on stacked metal-dielectric grating structure

The broadband absorption effect of stacked metal-dielectric grating structures is studied. Two TE polarization broadband absorbers, which consisted of two or three pairs of vertically cascaded metal-dielectric grating structures, are designed and investigated. The absorbers exhibit near-unity absorbance at multiple adjacent wavelengths and high absorbance over a wide wavelength range. The electric field distributions at multiple adjacent resonant wavelengths are investigated, which can provide a qualitative understanding of such broadband absorption behavior. The mechanism of such broadband absorption effect is attributed to guided mode resonance in different dielectric spacer layers. It is believed that the results may provide useful guidance for the design of TE polarization broadband absorbers.

Distinguishing plasmonic absorption modes by virtue of inversed architectures with tunable atomic-layer-deposited spacer layer

We demonstrated the distinguishing between plasmonic absorption modes by exploiting an inversed architecture with tunable atomic-layer-deposited dielectric spacer layer. The dielectric spacer layer was manipulated between the bottom metal–nanoparticle monolayer and the upper metal film to inspect the contributions of metal nanoparticles and dielectric film in a step-by-step manner. The experimental and simulated differences between the two peak absorption positions (Δf) and between the corresponding half width at half maxima (Δw) confirmed the evolutions of gap plasmon and interference-enhanced local surface plasmon resonance absorption modes in the plasmonic metamaterial absorbers (PMAs), which were useful for understanding the underlying mechanism of amorphous PMAs.

Parallel LC circuit model for multi-band absorption and preliminary design of radiative cooling.

We perform a comprehensive analysis of multi-band absorption by exciting magnetic polaritons in the infrared region. According to the independent properties of the magnetic polaritons, we propose a parallel inductance and capacitance(PLC) circuit model to explain and predict the multi-band resonant absorption peaks, which is fully validated by using the multi-sized structure with identical dielectric spacing layer and the multilayer structure with the same strip width. More importantly, we present the application of the PLC circuit model to preliminarily design a radiative cooling structure realized by merging several close peaks together. This omnidirectional and polarization insensitive structure is a good candidate for radiative cooling application.

Controlled synthesis of multilayered gold nanoshells for enhanced photothermal therapy and SERS detection.

It can be streamlined: A facile and controllable approach for the fabrication of core/shell-structured multilayer gold nanoshells with uniform nanosize, monodispersity, and tunable plasmonic properties has been successfully developed by utilizing an organosilica layer as the dielectric spacer layer.

Optimization of the Rayleigh anomaly of metallic gratings for terahertz sensor applications

The frequency of the Rayleigh anomaly of a metallic grating varies with the refractive index of the surrounding medium. To employ this phenomenon in optical sensors it is essential that the feature, due to the Raleigh anomaly in the sensor’s optical response, is very distinct and stable. We study the reflectance of optical structures consisting of a metallic grating with a thin dielectric film on highly reflective silicon substrates in the terahertz (THz) range between 0.6 and 2 THz. A distinct reflectance peak due to the Rayleigh anomaly can only be observed if a dielectric spacer layer is inserted between the metallic grating and silicon substrate. The dielectric layer between the grating and substrate acts as a Fabry–Pérot resonator with a low quality factor. Thus, the corresponding Fabry–Pérot modes only couple weakly to the Rayleigh anomaly. At the frequency of the Rayleigh anomaly, the combined structure exhibits a distinct peak due to the Rayleigh anomaly, no matter whether there is a Fabry–Pérot low or high reflection band at this frequency. In particular, the reflection background in the vicinity of the frequency of the Rayleigh anomaly is suppressed when the Rayleigh anomaly is in resonance with a Fabry–Pérot low reflection band, whilst the Rayleigh reflectance peak itself is retained. The underlying physics is confirmed by a simple analytic model and by numerical calculations. This approach of optimizing the optical response of metallic gratings is important for the design of THz sensing devices based on Rayleigh anomalies.

Strong coupling between localized and propagating surface plasmon modes in a noncentrosymmetric metallic photonic slab

We have investigated the coupling behaviors between localized and propagating surface plasmon modes in a noncentrosymmetric structure consisting of an L-shaped metal nanoparticle array and a thick metal film, separated by a silica dielectric spacer layer. It is found that surface plasmon modes exhibit hybrid behaviors due to the noncentrosymmetry of the structure. The hybrid surface plasmon modes will interact with different-order localized plasmon modes in the nanoparticle in their spectrally overlapping regions. The strong coupling between the localized and propagating plasmon modes gives rise to the energy anticrossing behavior with large mode splitting. Furthermore, a narrow absorption branch is also observed between two anticrossing absorption branches, which is absent in the centrosymmetric system. The findings hold promise in applications such as photonic and energy conversion systems and the design of novel plasmonic nanodevices.

Broadband infrared metamaterial absorber with visible transparency using ITO as ground plane.

Metamaterials that have broadband absorption at MIR frequencies, and yet, are transmitive at visible frequencies are fabricated using a semi-conducting Indium Tin Oxide (ITO) film as ground plane. The metamaterial absorber consists of an array of uniform aluminum disks separated by a Zinc Sulphide (ZnS) dielectric spacer layer from the ITO ground plane. The metamaterial was fabricated by a simple, cost-effective vapor deposition through a shadow mask. Compared with the usual metal/dielectric/metal tri-layer absorbers, the metal/dielectric/ITO absorber shows a peak absorbance of 98% and >70% over the mid-infrared regime from 4 to 7 μm. The broadband nature arises due to smaller dispersion in the dielectric permittivity of ITO compared to that of plasmonic metals at mid-infrared frequencies.

Engineering optical bistability in a multimaterial loop metasurface

The performance of a multimaterial loop (MML) metasurface integrated with Kerr nonlinear material as the dielectric spacer layer is investigated comprehensively with the finite-difference time-domain method. Optical bistability is obtained by exciting the metasurface with a saw-tooth profile for its amplitude. Based on effects of coupling between the plasmonic loops on the performance of the MML metasurface, it is shown that there is a trade-off between the required input intensity for switching and the extinction ratio of the two states of the switch. Two distinct designs are proposed where in the second design, which has lower coupling, the extinction ratio is increased by a factor of 2 while the required intensity for switching is 13 times higher than that of the first design.

TE polarization selective absorber based on metal-dielectric grating structure for infrared frequencies

The spectrum selective absorption effect in grating-based devices is studied. A TE polarization spectrum selective absorber exhibiting near 100% absorption at the resonant wavelength is investigated for infrared frequencies. A qualitative physical understanding of such perfect selective absorption effect is illustrated by investigating the electric field distributions and time-averaged power loss density. The influences of structure parameters on the absorption spectrum are studied in detail. Based on the study above, two multi-band absorbers with the vertically cascaded metal-dielectric grating structures are designed and investigated. The principle of such perfect absorption effects is attributed to guided mode resonance in different dielectric spacer layers. The designed absorber can be used in sub-diffraction-scale infrared pixels, high quality sensors and thermal emitters.

Improving the mid-infrared energy absorption efficiency by using a dual-band metamaterial absorber

In this paper, a dual-band mid-infrared metamaterial absorber was proposed to improve the energy absorption efficiency. Up to 99% absorption was obtained at 9.03 and 11.83μm in the simulation, and each absorption band can be tuned by the dielectric spacing layer, i.e., the dielectric constant and its thickness. The dual-band absorption mechanism was analyzed, and the quite well absorption performance at large incident angles was also presented. The results of this study can be applied in the field of thermal absorbing and solar energy harvesting.

Improved Broadband Near-Unity Light Transparency of a Metal Layer With Film-Coupled Dual Plasmonic Arrays

We report improved light transparency over a broad bandwidth in a metal-layered structure with two film-coupled subwavelength non-close-packed plasmonic arrays. Through the introduction of dual ultrathin dielectric spacing layers between the metal layer and the double plasmonic disk arrays, coupling of the input and output effects of light is efficiently enhanced through strong near-field localized plasmon resonances between adjacent plasmonic disks and the near-field plasmon cavity mode in the gap between the double plasmonic arrays and the metal layer. A broad bandwidth of 300 nm with near-unity light transmittance (above 90%) in the optical regime is achieved through the localized plasmon resonances and the symmetrical structure used here. The transparency of this structure is polarization independent and incident angle insensitive, and can be tuned by varying the structure parameters and the dielectric environment. In addition, the period of the plasmonic arrays and the thickness of the nanometer-separated plasmonic structure are less than λ /20 and λ/8, respectively. These values suggest that the proposed structure may have potential applications in deep subwavelength optoelectronic devices, including broadband optically transparent electrodes, highly integrated light input and output components, and plasmonic filters.