Surface Plasmon Waveguide Modes Research Articles

Manipulation of plasmon dephasing time via the coupling between localized surface plasmon resonance and waveguide modes

Manipulation of plasmon dephasing time of the hybrid modes has gained much attention in recent years, which plays critical roles in many important applications of plasmonics. Here, we manipulate the dephasing time of plasmonic field resulting from coupling of the localized surface plasmon (LSP) of the nanosphere array and the waveguide mode supported by the indium tin oxide film with quasi-normal mode-assisted harmonic oscillator model method. It results in the formation of two distinct modes, transverse electric (TE) and transverse magnetic (TM) modes. Such coupling can significantly modify the dynamics of the original plasmonic modes. The dephasing time of the hybrid plasmon modes, encompassing both TE and TM modes, can be extended from 1.25fs to 4.95fs, which is about 2–7 times compared to that of a single localized surface plasmon resonant mode. More importantly, by changing the structural parameters, we can flexibly manipulate either the dephasing time with a fixed wavelength or the resonant wavelength with a fixed dephasing time.

Plasmonic hybridized modes empowered by strong plasmon interaction in the nanograting-dielectric-metal stacked structure

Abstract The coupling between surface plasmon polaritons (SPPs) and waveguide (WG) modes has been widely investigated by using prism-coupled structures and has demonstrated a large number of interesting physical phenomena. However, these conventional structures mainly rely on the angle-dependent total internal reflection excitation. This is not conducive to their further development due to the large volume and the requirement of oblique incidence. In this paper, we theoretically propose a three-layer nanograting-dielectric-metal (NDM) plasmonic structure. Within this structure, a thickness-dependent plasmonic WG (PWG) mode in the middle dielectric cavity strongly couples with SPPs on the top surface, resulting in two new hybridized PWG-SPPs modes. This hybridization coupling phenomenon is analyzed in detail by using plasmonic hybridization and two coupled oscillator models. Besides, a thorough investigation is conducted on the sensing performance of these two PWG-SPPs hybridized modes. The difference in sensing characteristics between these two hybridized modes can be well explained by their coupling strength variation. This NDM plasmonic nanostructure owns unparalleled advantages in the generation and modulation of a variety of new modes, effectively promoting the development of miniaturized optoelectronic devices.

High performance ultra-thin perovskite solar cell by surface plasmon polaritons and waveguide modes

Although perovskite solar cell has been widely studied due to their high-efficiency potential, the design of ultra-thin perovskite solar cells for flexible and less toxic device fabrication has received less attention. The use of ultra-thin perovskite thin layer leads to low-efficiency solar cells due to insufficient absorption of light. In this paper, the optical absorption of the ultra-thin PSC is improved via surface plasmon polaritons and waveguide modes through the using a silver back grating electrode into hole transport free-layer structure. The investigations are based on the FDTD numerical method and the effects of grating dimensions and periodicity on the absorption of the active layer are systematically investigated to achieve the high performance of the structure. Also, the value of the short circuit current density was investigated by changing the dimensions of the grating. In the optimum device with the thickness of the absorber layer of 150 nm, the absorption enhancement of 20% is obtained in the wavelength 300 nm-800 nm compared to the reference flat solar cell. In addition, the design of ultrathin solar cells based on the grating electrode with perovskite thicknesses of 50 nm, 100 nm, and 200 nm is studied. The results provide a way for the design and production ultra-thin, low toxicity, and high performance solar cells.

Efficient second harmonic generation at quasi-bound states in the continuum in hybrid nanostructures of 2D plasmonic array and waveguide

We numerically investigate the second harmonic generation (SHG) in hybrid plasmonic–photonic structures consisting of an array of periodic gold nanodisks covered by a nonlinear dielectric layer. In the designed hybrid systems, symmetry-protected bound states in the continuum (BICs) at normal incidence, and Friedrich–Wintgen BICs due to the coupling between localized surface plasmon resonances (LSPRs) and waveguide modes at oblique incidence, are observed under both transverse-electric (TE) and transverse-magnetic (TM) polarized illuminations. SHG near the BICs is studied, and the dramatically enhanced nonlinear optical response at quasi-BICs is obtained. Such enhancement is ascribed to the enhanced local field due to hybrid modes of LSPRs and photonic modes. The results indicate that hybrid plasmonic-dielectric systems supporting BICs at both TE- and TM-polarized incidences are promising platforms for linear and nonlinear photonic devices.

The impact of plasmonic electrodes on the photocarrier extraction of inverted organic bulk heterojunction solar cells

Nano-patterning the semiconducting photoactive layer/back electrode interface of organic photovoltaic devices is a widely accepted approach to enhance the power conversion efficiency through the exploitation of numerous photonic and plasmonic effects. Yet, nano-patterning the semiconductor/metal interface leads to intertwined effects that impact the optical as well as the electrical characteristic of solar cells. In this work we aim to disentangle the optical and electrical effects of a nano-structured semiconductor/metal interface on the device performance. For this, we use an inverted bulk heterojunction P3HT:PCBM solar cell structure, where the nano-patterned photoactive layer/back electrode interface is realized by patterning the active layer with sinusoidal grating profiles bearing a periodicity of 300 nm or 400 nm through imprint lithography while varying the photoactive layer thickness (LPAL) between 90 and 400 nm. The optical and electrical device characteristics of nano-patterned solar cells are compared to the characteristics of control devices, featuring a planar photoactive layer/back electrode interface. We find that patterned solar cells show for an enhanced photocurrent generation for a LPAL above 284 nm, which is not observed when using thinner active layer thicknesses. Simulating the optical characteristic of planar and patterned devices through a finite-difference time-domain approach proves for an increased light absorption in presence of a patterned electrode interface, originating from the excitation of propagating surface plasmon and dielectric waveguide modes. Evaluation of the external quantum efficiency characteristic and the voltage dependent charge extraction characteristics of fabricated planar and patterned solar cells reveals, however, that the increased photocurrents of patterned devices do not stem from an optical enhancement but from an improved charge carrier extraction efficiency in the space charge limited extraction regime. Presented findings clearly demonstrate that the improved charge extraction efficiency of patterned solar cells is linked to the periodic surface corrugation of the (back) electrode interface.

Generation of symmetry-protected bound states in the continuum in a graphene plasmonic waveguide system for optical switching.

A graphene-involved plasmonic lossy system that allows coupling between surface plasmon polaritons and waveguide modes is proposed. The physical mechanism behind the hybrid resonance modes is investigated carefully through finite element method (FEM) simulations and rigorous coupled wave theory (RCWA). We demonstrate that by introducing an incident angle to break the symmetry of the structure, the bound states in the continuum (BIC) evolve to an observable quasi-BIC with new resonance dips, and the generated signals possess a very high Q-factor. Such transformation is investigated carefully by calculating the band structure of the system and the corresponding Q-factors. The results showed that the calculated results from the band structure are consistent with the simulations. In addition, the hybrid plasmonic system allows for switching modulation due to the tunability of graphene, and the max modulation depth of nearly 100% is reached. The outstanding Q-factor and dynamic tunability of this easy-to-fabricate hybrid structure may be helpful in engineering various plasmonic devices, including tunable optical switches, absorbers, sensors, etc.

Faraday effect in magnetoplasmonic nanostructures with spatial modulation of magnetization.

For the first time, to the best of our knowledge, the properties of the Faraday effect are addressed in a magnetoplasmonic nanostructure with nonuniform spatial distribution of the magnetization. It is shown that the coincidence in period and phase between magnetization modulation and the field of the optical mode provides the resonant enhancement of the Faraday effect. This effect is observed for both the surface plasmon polariton and waveguide modes.

Effects of electron transport layer thickness on light extraction in corrugated OLEDs.

This study reported the effects of electron transport layer (ETL) thickness on light extraction in corrugated organic light-emitting diodes (OLEDs) and each layer in OLEDs exhibited a periodical corrugated structure, which was determined by depositing thin films on a glass substrate with a nanoimprinted blazed grating structure. The insight is that light extraction in corrugated OLEDs significantly depends on the ETL thickness. Varying the ETL thickness changed the distribution of carrier recombination and led to exciton formation and optical interference, thereby resulting in different attribution of optical loss modes in OLEDs, which increased or even decreased light extraction and device efficiency. Trapped light extraction from the surface plasmon polariton (SPP) and waveguide (WG) modes was identified by splitting the light into transverse electric and transverse magnetic emissions. Thus, the contributions from the individual SPP and WG modes to the external quantum efficiency (EQE) were distinctly clarified by comparing the experimental results with the theoretical calculations. At the ETL thickness of 115 nm, the corrugated OLED exhibited a significantly enhanced (1.83-fold) EQE compared to the planar one due to the effective extraction of trapped light from the SPP and WG modes. The EQE was enhanced by 0.5%, wherein 0.39% came from the WG mode and 0.11% came from the SPP mode.

Room-temperature corrugated indium zinc oxide anode to achieve high-efficiency blue phosphorescent organic light-emitting diodes

A corrugated indium zinc oxide thin film was fabricated on a glass substrate at room temperature for use in a blue phosphorescent organic light-emitting device (OLED) to facilitate device efficiency in term of the external quantum efficiency (EQE) of the device, which increased from 28.77% to 34.33% after the fabrication of the aforementioned layer. Furthermore, a remarkably high EQE of 52.51% was achieved through external light extraction by attaching a hemispheric macrolens on the substrate of the device. Consequently, the efficiency of the developed blue phosphorescent OLED became 1.83 times higher than that of a planar counterpart. Moreover, this finding was verified through theoretical analyses, that indicated the underlying light extraction physics was attributed to the efficient extraction of trapped light from the surface plasmon polariton, waveguide, and substrate modes. (submitted to Organic Electronics).

Classical Analogy of Double Electromagnetically Induced Transparencies from Interactions of Surface Plasmon Resonances and Waveguide Modes

Classical Analogy of Double Electromagnetically Induced Transparencies from Interactions of Surface Plasmon Resonances and Waveguide Modes

Systematic Evolution of Resonant Coupling Behavior Between Surface Plasmon Polaritons and Multi-waveguide Modes in Metal-Dielectric Multi-layers

A multi-layer structure consisting of metal and dielectric layers which allows coupling between surface plasmon polaritons and waveguide modes is studied by calculating reflectivity curves of incident light. A wide waveguide structure is employed to ensure SPP resonance with different order waveguide modes when varying coupling layer thicknesses. Multi-hybrid plasmonic waveguide modes (HPWG) are formed in the coupled system. The weight fractions of metal SPP deduced from losses of HPWG modes are calculated for each hybridized mode, which can be considered as a parameter of evaluating coupling strength. Three different evolution stages for hybrid modes are clearly distinguished based on the variation of loss with spacer layer thickness. The interaction between SPP and waveguide experiences a series of change from weak Fano resonance, via strong coupling, finally to weak coupling process. In case of strong coupling regime, the contribution of metal SPP for low order hybrid modes starts to increase and then decreases with decreasing spacer layer thicknesses. Furthermore, difference of resonant behavior for hybrid modes in both weak coupling stages is analyzed in detail.

Plasmonic and photonic enhancement of photovoltaic characteristics of indium-rich InGaN p-n junction solar cells.

In this paper, we demonstrate via Finite-difference time-domain (FDTD) simulations that the performance of indium-rich InxGa1-xN (x = 0.6) p-n junction thin-film solar cells is improved by incorporating an integrated structure of a 2-dimensional (2D) array of ITO nanodiscs on the top surface and a 2D array of Ag nanodiscs in the active layer above the Ag back reflector of the solar cell. The bottom Ag nanodiscs primarily enhance the absorption of longer wavelengths by coupling incident light into surface plasmon resonance (SPR) and waveguide modes. The top ITO nanodiscs enhance the middle wavelengths (400 nm to 800 nm) by coupling the incident light to photonic modes in the active layer. Thus, the integrated structure of nanodisc arrays leads to a very high absorption in the active region in broad spectral range (> 0.85 for wavelengths lying between 350 nm and 800 nm), significantly increasing the short circuit current density (Jsc) and power conversion efficiency (PCE) of the solar cell. In the proposed solar cells, the geometries of the silver and ITO nanodiscs were optimized to obtain the maximum possible values of the Jsc. The highest enhancements in Jsc and PCE of ∼25% and ∼26%, respectively, were obtained in a solar cell containing the integrated structure of ITO and Ag nanodisc arrays. Moreover, the performance of these cells was examined under oblique light incidence and it was observed that the solar cells containing the integrated structure of nanodisc arrays have a significantly larger value of Jsc when compared to the cells having no nanostructures or having only the top ITO nanodisc array or only the bottom Ag nanodisc array.

Tunable Fano resonances and improved sensitivity in waveguide-coupled surface plasmon resonance sensors with a bimetallic layer

A multilayer structure consisting of Au–Ag bimetal and dielectric layers which allows coupling between surface plasmon polaritons and waveguide modes is studied by calculating reflectivity curves of incident light. The coupling results in asymmetric resonance modes, which can be attributed to Fano resonances (FR). The variation trend of FR is investigated in detail by fitting numerical results with an analytic model when changing both waveguide widths and silver thicknesses. It is demonstrated that changing the thickness ratio of Au–Ag bilayers can tune the coupling strength and the line shape of FR. We build the resonant mode diagram according to the different asymmetric line shape which can be depicted by the sign of the fitting Fano constant q. At a critical Ag thickness, the coupling gives rise to a q = 0 symmetrical resonance state (plasma induced transparency). Finally, the best optimized thickness combination (Ag/Au) in the structure is found when the refractive index of the sensing layer medium changes. The sensitivity of the optimized sensor is twice as high as that of the single Au film structure.

Enhanced dielectric waveguide mode from the coupling of surface plasmon polaritons excited by a parallel electron beam

Abstract The coherent, power enhanced and mode selected light radiation from the coupling of surface plasmon polaritons (SPPs) and waveguide modes is presented here. The results of theoretical analysis show that this coupling occurs in the structure of a thin metal film with finite thickness dielectric medium loading excited by free electrons at certain beam energies, referred to as the coupling points. The research of particle-in-cell simulation is also carried out, and results agree well that of theoretical analyses. Because of the coupling, the power intensity of the coherent radiation is extremely enhanced up to 32 times compared with that transformed from SPPs by Cherenkov radiation directly in the infinite medium. And even at the non-coupling points, there is also a 5 times enhancement of the radiation power. The results also show that the main mode of the loading medium is changed from the zero order waveguide mode to the mode whose operating frequency is near to that of asymmetric SPPs mode. Accordingly, the results presented here is of great significance of developing miniature, integratable, high-power-density light radiation sources from visible light to ultra-violet rays at room temperature.

Exploring the Near-Field of Strongly Coupled Waveguide-Plasmon Modes by Plasmon-Induced Photocurrent Generation Using a Gold Nanograting-Loaded Titanium Dioxide Photoelectrode

Near-field spectrum measurement techniques, including near-field scanning optical microscopy, electron energy loss spectroscopy, and multiphoton photoemission electron microscopy, are powerful means to investigate near-field interactions directly on closely spaced metallic nanoparticles or a metallic nanostructure coupled with optical modes, such as whispering gallery mode and waveguide mode, which are called coupled plasmonic systems. In the present study, we have successfully measured the near-field spectra of coupled plasmonic systems using a simple photoelectrochemical measurement based on plasmon-induced water oxidation. Coupling was explored between the localized surface plasmon resonance (LSPR) mode and waveguide mode of periodic gold nanogratings patterned on a thin titanium dioxide waveguide film. It is known that the far-field reflection spectrum of this waveguide-LSPR coupling system shows a complicated shape with multiple peaks, and the coupling has been explored by numerical electromagnetic s...

Observation of Fano line shapes arising from coupling between surface plasmon polariton and waveguide modes

We demonstrate experimentally the generation of narrow Fano line shapes in planar multilayer structures. The Fano line shape originates from coupling between a high loss surface plasmon polariton mode with a low loss planar waveguide mode. The line shape is shown to depend strongly on the structural parameters that govern the position of the waveguide mode and the coupling strength, and to be in good agreement with results of electromagnetic calculations.

Fano resonance and plasmon-induced transparency in waveguide-coupled surface plasmon resonance sensors

A planar multilayer structure that allows coupling between surface plasmon polaritons and waveguide modes is proposed. Calculated reflectivity curves exhibit sharp resonances due to the Fano resonance and plasmon-induced transparency arising from the coupling. Electric field profiles obtained at the resonances demonstrate the hybrid nature of the modes excited. When the Fano resonance is used for sensing, the sensitivity with intensity modulation is enhanced by two orders of magnitude relative to that of conventional surface plasmon resonance sensors.

Dynamically generating a large-area confined optical field with subwavelength feature size.

By using a prism of high refractive index, free-space cylindrical vector beams can be selectively converted into confined optical fields with large area, such as surface plasmon polaritons or waveguide modes, whose interference will produce optical features at the nanometer scale. Due to the polarization sensitivity of these modes, the macroscopic distribution of the confined field can be dynamically manipulated through an electronically driven liquid crystal. Based on these phenomena, a promising maskless interference nanolithography is proposed and experimentally demonstrated.

Phosphorescent transparent organic light-emitting diodes with enhanced outcoupling efficiency: Reduction of surface plasmon losses

In this work, we fabricated nanostructured transparent organic light-emitting diodes (TrOLEDs) using phosphorescent materials and a WO3 layer with various periods of perforation, to improve light extraction. Using these nanostructured TrOLEDs, higher external quantum efficiency (EQE) values were achieved, of 7.8% (bottom emission), and 2.0% (top emission) at 100mA/cm2. Compared to conventional TrOLEDs, these were 28% and 33% higher for bottom and top emission, respectively. In addition, by varying the periods of the nanostructures, we found that the extraction of the trapped surface plasmon mode was mainly responsible for enhancing outcoupling efficiency. When adopting light extraction methods in TrOLEDs, one should consider the influence of the optical clarity of devices. The nanostructured TrOLEDs in this study showed good optical clarity as the total transmittance was consistent with direct transmittance. Photographs of the TrOLEDs also showed neither optical blur nor haziness. Lastly, the total transmittance of the nanostructured TrOLEDs was similar to that of a conventional TrOLED except for two points where light coupling to the surface plasmon mode and waveguide mode occurred.

A marriage of convenience: Hybridization of surface plasmon and dielectric waveguide modes

AbstractPlasmonics has attracted a lot of interest in the past few years because of its unique features, especially for its ability to confine light in extremely small volumes. However, application of plasmonics is restricted by the large propagation loss associated with plasmonic waveguides. On the other hand, dielectric waveguides enjoy low loss, although the mode confinement is relatively weaker. Hybrid plasmonic waveguides (HPWGs), which combine these two guiding mechanisms, allow one to utilize the benefits of both technologies. Over the past few years there have been intense research activities around the world on this new guiding scheme. In this work the operating principle of HPWGs, various HPWG structures proposed by different research groups, and their potentail applications are reviewed.