Hybrid Plasmonic Modes Research Articles

Hybrid plasmonic mode converter: theoretical formulation and design with a graphical approach

The theoretical formulation based on rigorous transmission-line networks is developed for a general mode conversion problem and lays the groundwork for a simpler yet more efficient graphical design approach for hybrid plasmonic mode converters (HPMCs). The concurrence of co- and cross-polarization conversion to and among higher-order photonic and HP modes followed by subsequent power redistributions and losses over the course of the HPMC can lead to performance degradation and largely determines the silicon core thickness. Using gradient ascent of the TM polarization fraction incorporated with modal index contours sets critical perturbation parameters for required transverse structural asymmetry. Polarization reversal estimates are shown to be practically applicable for about 60% of the total device length. The mode conversion efficiency (MCE), insertion loss (IL), and the polarization conversion efficiency of the proposed HPMC (<7×0.4 μm2) at λ0=1550 nm are 90.04%, 0.4691 dB, and 99.96%, respectively. The 85%-bandwidth of the MCE is 135 nm, while the IL stays below 0.5 dB over a 68-nm spectral range.

Highly efficient graphene-on-gap modulator by employing the hybrid plasmonic effect.

We propose a highly efficient graphene-on-gap modulator (GOGM) by employing the hybrid plasmonic effect, whose modulation efficiency (up to 1.23dB/μm after optimization) is ∼12-fold larger than that of the present graphene-on-silicon modulator (∼0.1 dB/μm). The proposed modulator has the advantage of a short modulation length of ∼3.6 μm, a relatively low insertion loss of ∼0.32 dB, and a larger modulation bandwidth of ∼0.48 THz. The physical insight is investigated, showing that both the slow light effect and the overlap between graphene and the mode field contribute. Moreover, an efficient taper coupler has been designed to convert the quasi-transverse electric mode of conventional silicon waveguide to the hybrid plasmonic mode of GOGM, with a high coupling efficiency of 91%. This Letter may promote the design of high-performance on-chip electro-optical modulators.

Near-infrared hybrid plasmonic multiple quantum well nanowire lasers.

The lasing characteristics of hybrid plasmonic AlGaAs/GaAs multiple quantum well (MQW) nanowire (NW) lasers beyond diffraction limit have been investigated by 3D finite-difference time-domain simulations. The results show that the hybrid plasmonic MQW NW has lower threshold gain over a broad diameter range in comparison with its photonic counterpart. Beyond the diffraction limit, the hybrid plasmonic MQW NW has a lowest threshold gain of 788 cm-1 at a diameter of 130 nm, and a cutoff diameter of 80 nm, half that of the photonic lasers. In comparison with the hybrid plasmonic core-shell NWs, the hybrid plasmonic MQW NWs exhibit significantly lower threshold gain, higher Purcell factor, and smaller cutoff diameter, which are attributed to the superior overlap between the hybrid plasmonic modes and gain medium, as well as a stronger optical confinement due to the grating-like effect of MQW structures. Moreover, the hybrid plasmonic MQW NW has a lower threshold gain than that of the core-shell NW over a broad wavelength range. The hybrid plasmonic MQW NW structure is promising for ultrasmall and low-consumption near-infrared nanolasers.

Doped Silicon Nanocrystal Plasmonics

Doped semiconductor nanocrystals represent an exciting new type of plasmonic material with optical resonances in the infrared. Unlike noble metal nanoparticles, the plasmon resonance can be tuned by altering the doping density. Recently, it has been shown that silicon nanocrystals can be doped using phosphorus and boron resulting in highly tunable infrared plasmon resonances. Due to the band structure of silicon, doping with phosphorus contributes light (transverse) and heavy (longitudinal) electrons, while boron contributes light and heavy holes and one would expect two distinct plasmon branches. Here we develop a classical hybridization theory and a full quantum mechanical TDLDA approach for two-component carrier plasmas and show that the interaction between the two plasmon branches results in strongly hybridized plasmon modes. The antibonding mode where the two components move in phase is bright and depends sensitively on the doping densities. The low energy bonding mode with opposite charge alignment ...

Near-field spectral properties of coupled plasmonic nanoparticle arrays

We investigated the grating effect in complex gold dolmen structures, in which multiple plasmon modes are present due to plasmon hybridization, experimentally from both the far field and the near field. In particular, the near-field properties were investigated using photoemission electron microscopy, and it was demonstrated that two hybridized plasmon modes on the dolmen structures could be influenced by the grating effect. For comparison, we also investigated the grating effect in arrays of simple nanoblocks and heptamer structures, which were supposed to support a strong bright plasmon mode and a strong dark plasmon mode, respectively, in the near field. We found that the spectral responses of the two hybridized modes on the dolmen structures as the pitch size changed evolved in a manner similar to that of the bright dipole mode on the nanoblocks, whereas the dark mode on the heptamer structures is less sensitive to the pitch size.

Utilization of hybrid plasmonic modes to investigate surface interactions between nanocubes and polymer substrates

Silver nanocube monolayers deposited on polymer films were heated past the glass transition temperature of the polymer. Surface interactions between the cubes and substrate dictate the depth and rate of incorporation into the polymer. Silver nanocubes support hybrid plasmonic modes that are spatially separated when there is anisotropy in the local refractive index. Using this measure, it becomes possible to monitor the position of the cubes relative to the surface and tune spectral features in the visible spectrum. These spatially resolved plasmonic modes were used to probe the local glass transition temperature of polystyrene (PS), polymethylmethacrylate (PMMA) and polyvinyl chloride (PVC), the glass transition temperature of PS, PMMA, PVC were 103 ± 2, 122 ± 12, 81 ± 2 °C, respectively.

Mid-infrared subwavelength modulator based on grating-assisted coupling of a hybrid plasmonic waveguide mode to a graphene plasmon.

This work reports a mid-infrared modulator based on a hybrid plasmonic waveguide with graphene on a grating in its slot region. The modulator utilizes a graphene plasmon for electro-optic tuning in a more practical and effective way than graphene-plasmon-based waveguide devices studied up to now. The hybrid plasmonic waveguide can be easily and efficiently integrated with input and output photonic waveguides. It supports a hybrid plasmonic waveguide mode and a graphene-plasmon-based waveguide mode. Grating-assisted coupling of the former to the latter in it is demonstrated to work successfully even though the two modes have significantly different propagation constants and losses. Theoretical investigation of the modulator shows that the coupling via the grating of length 5.92 μm generates a deep rejection band at a wavelength of 8.014 μm in the transmission spectrum of the output photonic waveguide of the modulator. With the graphene chemical potential tuned between 0.6 eV and 0.65 eV, the transmission at the wavelength is modulated between -27 dB and -1.8 dB. The subwavelength modulator, which may have a large bandwidth and small energy consumption, is expected to play a key role in free-space communications and sensing requiring mid-infrared integrated photonics.

Novel routes to electromagnetic enhancement and its characterisation in surface- and tip-enhanced Raman scattering.

Quantitative understanding of the electromagnetic component in enhanced Raman spectroscopy is often difficult to achieve on account of the complex substrate structures utilised. We therefore turn to two structurally simple systems amenable to detailed modelling. The first is tip-enhanced Raman scattering under electron scanning tunnelling microscopy control (STM-TERS) where, appealing to understanding developed in the context of photon emission from STM, it is argued that the localised surface plasmon modes driving the Raman enhancement exist in the visible and near-infrared regime only by virtue of significant modification to the optical properties of the tip and sample metals (gold here). This is due to the strong dc field-induced (∼109 V m-1) non-linear corrections to the dielectric function of gold via the third order susceptibility term in the polarisation. Also, sub-5 nm spatial resolution is shown in the modelling. Secondly, we suggest a novel deployment of hybrid plasmonic waveguide modes in surface enhanced Raman scattering (HPWG-SERS). This delivers strong confinement of electromagnetic energy in a ∼10 nm oxide 'gap' between a high-index dielectric material of nanoscale width (a GaAs nanorod and a 100 nm Si slab are considered here) and a metal, yielding a monotonic variation in the Raman enhancement factor as a function of wavelength with no long-wavelength cut-off, both features that contrast with STM-TERS.

Real‐Time Probing Nanopore‐in‐Nanogap Plasmonic Coupling Effect on Silver Supercrystals with Surface‐Enhanced Raman Spectroscopy

Nanopore structures have displayed attractive prospects in diverse important applications such as nanopore‐based biosensors and enhanced spectroscopy. However, on the one hand, the fabrication techniques to obtain sub‐10 nm sized nanopores so far is very limited. On the other hand, the electromagnetic enhancement of nanopores is still relatively low. In this work, using a facile chemical etching strategy on 2D plasmonic Ag nanoparticle supercrystals, fine nanopore arrays with sub‐10 nm pore size have been successfully fabricated and a “nanopore‐in‐nanogap” hybrid plasmon mode has been investigated. An in situ etching and surface‐enhanced Raman spectroscopy (SERS) detection indicate that novel hybrid plasmon structure may create an enhanced electromagnetic coupling and increase SERS signal at ≈10× magnification. The breaking of plasmon bonding dipolar mode and generation of antibonding‐like plasmon mode contribute to this enhanced electromagnetic coupling. The facile etching strategy, as a common approach, may open the doors for the fabrication of nanopores in various compositions for numerous applications.

Hybridized plasmon modes and near-field enhancement of metallic nanoparticle-dimer on a mirror.

For the attractive plasmonic structure consisting of metal nanoparticles (NPs) on a mirror, the coexistence of near-field NP-NP and NP-mirror couplings is numerically studied at normal incidence. By mapping their 3D surface charge distributions directly, we have demonstrated two different kinds of mirror-induced bonding dipole plasmon modes and confirmed the bonding hybridizations of the mirror and the NP-dimer which may offer a much stronger near-field enhancement than that of the isolated NP dimers over a broad wavelength range. Further, it is revealed that the huge near-field enhancement of these two modes exhibit different dependence on the NP-NP and NP-mirror hot spots, while both of their near-field resonance wavelengths can be tuned to the blue exponentially by increasing the NP-NP gaps or the NP-mirror separation. Our results here benifit significantly the fundamental understanding and practical applications of metallic NPs on a mirror in plasmonics.

Waveguide-coupled hybrid plasmonic modulator based on graphene.

In this paper, we propose a low-transmission-loss, high-speed, graphene-based electro-absorption modulator with a hybrid plasmonic waveguide at 1.55 μm. In the proposed device, double-layer graphene is placed on top of the horizontal hybrid plasmonic waveguide to enhance the light-graphene interaction. The adjustment of the in-plane permittivity of the anisotropy graphene causes a significant modulation of the absorption at the operating bandwidth of 0.4 THz, with modulation length of 8.5 μm and modulator footprint of 1.6 μm2. A taper silicon coupler is used for waveguide coupling, and 80% coupling efficiency is achieved. In addition, the modulation potential on a smaller footprint is further shown.

Ag 나노입자와 나노홀 배열구조를 이용한 초박형 단결정 Si 태양전지의 광흡수 증진

We investigated the influences of Ag nanoparticle (NP) arrays and surface nanohole (NH) patterns on the optical characteristics of 10-<TEX>${\mu}m$</TEX>-thick c-Si wafers using finite-difference time-domain (FDTD) simulations. In particular, we comparatively studied the plasmonic effects of both monomer arrays (MA) and heptamer arrays (HA) consisting of identical Ag NPs. HA improved the optical absorption of the c-Si wafers in much wider wavelength range than MA, with the help of hybridized plasmon modes. The light trapping capability of the NH array pattern is superior to that of the Ag plasmonic NPs. We also found that the addition of the Ag HA on the wafers with surface NH patterns further enhanced optical absorption: the expected short-circuit current density was as high as <TEX>$34.96mA/cm^2$</TEX>.

Enhanced Faraday rotation by crystals of core-shell magnetoplasmonic nanoparticles

Collective hybridized plasmon modes, which enable strong magnetooptical coupling and consequent enhanced Faraday effect in three-dimensional periodic assemblies of magnetic dielectric nanoparticles coated with a noble-metal shell, are studied by means of rigorous full electrodynamic calculations using an extension of the layer-multiple-scattering method, in conjunction with the effective-medium approximation. A thorough analysis of relevant photonic dispersion diagrams and transmission spectra provides a consistent explanation of the underlying physical mechanisms to a degree that goes beyond existing interpretation. It is shown that properly designed structures of such composite magnetoplasmonic nanoparticles offer a versatile platform for engineering increased and broadband Faraday rotation.

Design and Analysis of a Compact SOI-Based Aluminum/Highly Doped p-Type Silicon Hybrid Plasmonic Modulator

A silicon-based n-p-n-type hybrid plasmonic modulator operating at telecom wavelength of 1550 nm is theoretically investigated in this paper. The proposed modulator is dependent on the integration of a 1- $\mu\text{m}$ -long n-p-n-type Al/p-Si hybrid plasmonic waveguide with Si waveguides. It is demonstrated that when the p-type silicon is highly doped, it shows metal-like properties which can support the propagation of surface plasmon polariton waves. The simulation results show that the output power of TE (TM) mode decreases from −7.6 dB (−2.5 dB) to −31.5 dB (−7.5 dB) when the Al stack is 0.2 $\mu\text{m}$ high and the carrier concentration in p-Si is set to be $1\times 10^{21} \text{cm}^{-3}$ , which is achieved with a voltage increase from 0 to 1.2 V. Such a plasmonic modulator not only depends on the propagation loss due to electroabsorption effect but takes advantage of the coupling loss raised by modal mismatch as well, which leads to a high modulation efficiency.

Flexible nanofiber-coupled hybrid plasmonic Bragg grating.

We report a hybrid plasmonic Bragg grating composed of a nanofiber coupled with orthogonally oriented metal strips. Numerical simulations are performed to study the transmission and reflection spectra of the grating. It shows that the TM polarization has much stronger Bragg reflection due to the excitation of hybrid plasmonic modes. The dependence of reflection peaks on several key device parameters is analyzed. Light propagation simulation further reveals that both fundamental and first-order TM modes are excited upon Bragg reflection, leading to two separate peaks in the spectrum. We implement the prototype device by attaching a nanofiber onto the surface of an array of sub-micrometer-wide metal strips. The main reflection peak is measured to have a 3-dB bandwidth of 15 nm and out-of-band rejection of more than 30 dB. The effects of nanofiber radius, alignment angle and coupling length on the device performance are also experimentally investigated.

Hybrid Plasmonic Modulators and Filters Based on Electromagnetically Induced Transparency

A hybrid plasmonic modulator based on microdisk resonators enhanced with electro-optic polymers is presented. Modulation is achieved by dynamically controlling an electromagnetically induced transparency window using a push–pull driving configuration. The proposed device combines small footprint, high modulation depths, low insertion losses, and low power consumption. By properly selecting the voltage values and the microdisk radii, modulation at different wavelengths and tunable spectral filtering are achieved.

Tunable Localized Hybrid Plasmon Modes and Fano Resonances in Au Core-Semishell

We present a numerical study of the plasmonic properties of Au core-semishell. Symmetry breaking in semishell results in a dipole–quadrupole Fano resonance without the offset of the Au core. The plasmon hybridization theory is applied to interpret the origin of the localized hybrid plasmon modes and Fano resonances. The multiple hybrid plasmon modes resonance can be excited for the extreme core offset inducing high order dark modes visible. The Fano resonances can be tuned by changing the size of the Au core, the degree of symmetry breaking of the semishell, and the dielectric properties of local environment. The tunability of the plasmon resonances and Fano resonances in Au core-semishell provides potential application for tunable nanophotonic devices, such as filters and sensors.

Hybrid electro-optic plasmonic modulators based on directional coupler switches

By breaking the diffraction limit, plasmonics enable the miniaturization of integrated optical signal processing units in a platform compatible with traditional CMOS technology. In such architectures, modulators and switches are essential elements for fast and low-power optical signal processing. This work presents the design of a CMOS-compatible hybrid plasmonic modulator based on directional couplers enhanced with a layer of electro-optic polymer. The modulator shows very broad operating window with low crosstalk values and very small footprint with respect to similar couplers and switches of the silicon photonics platform.

Lasing Emission from Plasmonic Nanodome Arrays

Plasmonic nano‐dome arrays (PNDA) have been previously studied as chemical and biological sensors. The present study reports large‐area plasmonic lasing from the PNDA structures with liquid‐phase gain materials to provide optical gain. The PDNA structure consists of a 2D array of nanoposts, fabricated inexpensively using a nanoreplica molding process, with silicon dioxide and gold thin‐film coatings to produce the dome‐shaped surface profile. Covered with a dye‐doped solution, the PDNA structures can generate lasing emission when they are optically pumped above the lasing threshold. The lasing emission is enabled by energy coupling from the photoexcited dye molecules to the hybridized plasmon mode supported by the PDNA oscillator. Two PDNA lasers with array periods of 400 and 450 nm are fabricated and characterized. Plasmonic resonant modes of the PDNA lasers are numerically studied to illustrate the underlying lasing mechanism. The emission characteristics, including lasing wavelength, linewidth, threshold, beam divergence, and radiation angle, are presented in the paper. The PNDA laser represents a new path for plasmonic lasing in the near‐infrared region with potential applications that include integrated photonic circuits, optical communications, and high‐performance biosensors.

Hybrid plasmonic gap modes in metal film-coupled dimers and their physical origins revealed by polarization resolved dark field spectroscopy.

Plasmonic gap modes sustained by metal film-coupled nanostructures have recently attracted extensive research attention due to flexible control over their spectral response and significantly enhanced field intensities at the particle-film junction. In this work, by adopting an improved dark field spectroscopy methodology - polarization resolved spectral decomposition and colour decoding - we are able to "visualize" and distinguish unambiguously the spectral and far field radiation properties of the complex plasmonic gap modes in metal film-coupled nanosphere monomers and dimers. Together with full-wave numerical simulation results, it is found that while the monomer-film system supports two hybridized dipole-like plasmon modes having different oscillating orientations and resonance strengths, the scattering spectrum of the dimer-film system features two additional peaks, one strong yet narrow resonant mode corresponding to a bonding dipolar moment and one hybridized higher order resonant mode, both polarized along the dimer axis. In particular, we demonstrate that the polarization dependent scattering radiation of the film-coupled nanosphere dimer can be used to optically distinguish from monomers and concurrently determine the spatial orientation of the dimer with significantly improved accuracy at the single-particle level, illustrating a simple yet highly sensitive plasmon resonance based nanometrology method.