Hybrid Plasmonic Modes Research Articles

Sodium-based plasmonic waveguides with high confinement factors and ultra-low gain thresholds.

The noble metal-based hybrid plasmon mode features low loss and strong field localization, making it widely applicable in the field of nanophotonic devices. However, due to the high loss of noble metals, the gain threshold is unacceptably high, usually larger than 0.1 µm-1. Here we present a hybrid plasmonic waveguide consisting of a SiO2 layer coated Na nanowire and a hexagonal semiconductor nanowire. Based on the high performance of the proposed waveguide, the Purcell factor exceeding 120 and a confinement factor above 90% are achieved, leading to an ultra-low gain threshold of 0.02117 µm-1. In addition, the proposed waveguide exhibits an extremely low cross talk, making it highly suitable for applications in compact photonic integrated devices. The proposed waveguide may contribute to the development of low-threshold nano-lasers and promote other applications in nanophotonics.

Label-Free Detection of DNA Base Mutation and Hybridized DNA by an Electrostatically Modified 3D Plasmonic Array.

Surface-enhanced Raman scattering (SERS) represents a promising avenue for DNA detection as it offers intrinsic chemical insights with high sensitivity compared to conventional methods. However, label-free and quantitative detection of unmodified DNA by SERS remains a major challenge in DNA analysis. To overcome this challenge, we propose a positively charged plasmonic nanosurface for DNA capture and quantitative analysis. Highly sensitive and uniform SERS enhancement was realized by a three-dimensional plasmonic array supporting well-designed hybrid plasmonic modes. Subsequently, the plasmonic array was modified with an electrostatically functionalized PDDA (poly(diene-dimethylammonium-chloride)) self-assembled monolayer in a single step. The effectiveness of the resulting PDDA-SERS substrate was demonstrated by the label-free and quantitative detection of base content and base mutation in hybridized DNA. The PDDA-SERS substrate provides a robust platform for SERS analysis not only of DNA but also of other electronegative analytes.

Substrate-induced hybridization of plasmon modes in the composite nanostructure of nanodisk array/thin film for spectrum modulation

Abstract Hybridization coupling among plasmon modes is an effective approach to manipulate near-field properties thus optical spectral shapes of plasmonic nanostructures. Generally, mode hybridization coupling is achieved by modifying the topography and dimensions of nanostructures themselves, with few concerns about substrate-induced manipulation. Herein, we propose a composite nanostructure consisting of a gold (Au) nanodisk array and a thin Au film supported by a dielectric substrate. In this configuration, both the refractive index of the dielectric substrate and thin gold film’s thickness mediate the interaction of plasmon modes supported by upper and lower interfaces of the composite nanostructure, resulting in two hybridized plasmon modes. We systematically investigate the relationship between optical fields at the top surface of plasmon modes before and after the hybridization coupling. Specifically, the near-field amplitude at the top surface of the unhybridized modes is stronger than that of individual hybridized mode, and lower than the near-field summation of these two hybridized modes. This work not only provides a straightforward strategy for generating two plasmon modes in a nanostructure but also elucidates the variation of the optical field during the hybridization process, which is of crucial significance for applications, such as upconversion enhancement and multi-resonance sensing.

Compact unidirectional waveguide grating emitter with enhanced wavelength sensitivity based on the hybrid plasmonic mode

Waveguide grating antennas are widely adopted in beam-steering devices, typically enabling the beam steering in longitudinal direction within a two-dimensional scanning optical array by changing the input wavelength. However, traditional waveguide grating antennas suffer from limited tuning range due to low dispersion of the gratings. In this paper, a compact silicon grating waveguide antenna array is proposed with enhanced wavelength sensitivity by introducing a periodically modulated hybrid plasmonic mode. The hybrid plasmonic mode is supported by the hybrid plasmonic waveguides (HPWs) composed of silicon waveguides and periodic subwavelength silver strips. In order to convert the guided waves to the radiated waves, a series of silicon emitting segments are deposited above the HPWs. Additionally, the horizontally arranged array of HPWs also acts as a reflector of the downward radiation, resulting in an effective unidirectional emission. Through the optimization of physical parameters, the proposed antenna array achieves a wavelength-length tuning efficiency up to 0.3°/nm within the wavelength range of 1500∼1600 nm, exhibiting a significant improvement compared with traditional ones. Moreover, an average upward emissivity exceeding 80% with a maximum value of 89% within the 100 nm bandwidth is demonstrated through the numerical simulations. The proposed compact antenna array provides an alternative solution in realizing large-scale integrated high-tuning-efficiency optical beam-steering devices.

Enhancing modulation performance by design of hybrid plasmonic optical modulator integrating multi-layer graphene and TiO2 on silicon waveguides

A novel way to enhance modulation performance is through the design of a hybrid plasmonic optical modulator that integrates multi-layer graphene and TiO2 on silicon waveguides. In this article, a design is presented of a proposed modulator based on the use of the two-dimensional finite difference eigenmode solver, the three-dimensional eigenmode expansion solver, and the CHARGE solver. Leveraging inherent graphene properties and utilizing the subwavelength confinement capabilities of hybrid plasmonic waveguides (HPWs), we achieved a modulator design that is both compact and highly efficient. The electrical bandwidth f 3dB is at 460.42 GHz and it reduces energy consumption to 12.17 fJ/bit with a modulator that functions at a wavelength of 1.55 μm. According to our simulation results, our innovation was the optimization of the third dielectric layer’s thickness, setting the stage to achieve greater modulation depths. This synergy between graphene and HPWs not only augments subwavelength confinement, but also optimizes light–graphene interaction, culminating in a markedly enhanced modulation efficiency. As a result, our modulator presents a high extinction ratio and minimized insertion loss. Furthermore, it exhibits polarization insensitivity and a greater bandwidth. Our work sets a new benchmark in optical communication systems, emphasizing the potential for the next generation of chip-scale with high-efficiency optical modulators that significantly outpace conventional graphene-based designs.

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.

Aluminum-based quasi-3D self-aligning plasmonic metasurface with an attenuated substrate effect for high-sensitivity sensing

We propose an aluminum (Al)-based quasi-3D self-aligning plasmonic metasurface theoretically in this paper; it demonstrates a hybrid plasmon mode with narrow bandwidth and high peak-to-dip contrast that can be used for high-sensitivity sensing applications. This metasurface consists of a top Al nanodisk array elevated by a composite array of a dielectric nanopillar and Al nanohole. A moderate bulk refractive index sensitivity of up to 384 nm/RIU and an excellent surface sensitivity are achieved in this work, owing to an enhanced optical field around the top Al nanodisk readily accessing the external environment. High nanopillars here mean the top Al nanodisk is away from the bottom nanoholes, which is equivalent to suspending the top nanodisk into approximately symmetrical surroundings to eliminate adverse substrate effects. This work provides a valuable economic and high-performance sensing strategy for precise biochemical detection.

Hybrid Plasmon Modes at Chiroferrite-Graphene Interface

Hybrid Plasmon Modes at Chiroferrite-Graphene Interface

Improving the performance of ring resonator refractive index sensor through structural modifications

In this work, different types of whispering gallery mode ring resonator structures such as strip, slotted, hybrid plasmonic mode, and subwavelength grating ring resonators are simulated using the finite difference time domain method (FDTD). The proposed devices are modeled to be used as refractive index sensor. The comparative analysis of strip, slotted, hybrid plasmonic mode, and subwavelength grating ring resonators is done in terms of sensitivity, Q factor, and figure of merit (FOM) to find out the most suitable device according to the requirement. Additionally, the effect of waveguide width on sensitivity and Q factor is analyzed. The analysis shows that, compared to other simulated whispering gallery mode ring resonator sensor designs, the subwavelength grating ring resonator produces the best sensitivity of 1012 nm/RIU, and the slotted ring resonator produces the best FOM of 1610.

Coupling and thermosplasmonic properties of asymmetric hexagonal nanoframes

The interaction of light with asymmetric nanostructures leads to the coupling of plasmon modes. Understanding the nature and tunability of these hybridized plasmon modes is essential for both fundamental studies and the development of new applications. Herein, we systematically examine these coupled plasmon modes and heat generated by the asymmetric hexagonal nanoframes dimers (HNDs). Our results show that there are three plasmon bands in the examined wavelength. One of these bands is related to the coupled plasmon modes, which can be actively controlled by changing the height of nanoparticles. These coupled plasmon modes originate from the interaction of dipoles with a minimum splitting energy of 170 meV. Moreover, the thermoplasmonic studies show that the temperature of the asymmetric HNDs strongly depends on the coupling of nanoframes which shows great promise for highly sensitive thermal imaging.

Hybrid dielectric slot-plasmonic ring resonator for Purcell enhancement

We present a computational study of Purcell factor enhancement for a novel hybrid-plasmonic ring resonator using a novel implementation of the body-of-revolution (BOR) finite-difference time-domain (FDTD) method. In this hybrid structure, a dielectric slot ring is surrounded by a metallic ring such that a hybrid plasmonic mode is generated within two thin low-index gaps. The surrounding metallic ring decreases the binding loss for small ring radii, leading to high-quality factors and mode-field confinement. The hybrid resonator shows high quality-factor values above 103 and small mode volumes down to simultaneously, thus providing large Purcell factors (F p > 104). The distributed strong confinement within two gaps renders the proposed resonator useful for multi-emitter applications.

Theoretical Investigation on the Metamaterials Based on the Magnetic Template-Assisted Self-Assembly of Magnetic-Plasmonic Nanoparticles for Adjustable Photonic Responses.

The assembly of artificial nano- or microstructured materials with tunable functionalities and structures, mimicking nature's complexity, holds great potential for numerous novel applications. Despite remarkable progress in synthesizing colloidal molecules with diverse functionalities, most current methods, such as the capillarity-assisted particle assembly method, the ionic assembly method based on ionic interactions, or the field-directed assembly strategy based on dipole-dipole interactions, are confined to focusing on achieving symmetrical molecules. But there have been few examples of fabricating asymmetrical colloidal molecules that could exhibit unprecedented optical properties. Here, we introduce a microfluidic and magnetic template-assisted self-assembly protocol that relies mainly on the magnetic dipole-dipole interactions between magnetized magnetic-plasmonic nanoparticles and the mechanical constraints resulting from the specially designed traps. This novel strategy not only requires no specific chemistry but also enables magnetophoretic control of magnetic-plasmonic nanoparticles during the assembly process. Moreover, the assembled asymmetrical colloidal molecules also exhibit interesting hybridized plasmon modes and produce exotic optical properties due to the strong coupling of the individual nanoparticle. The ability to fabricate asymmetrical colloidal molecules based on the bottom-up method opens up a new direction for the fabrication of novel microscale structures for biosensing, patterning, and delivery applications.

Hybrid Plasmonic Modes for Enhanced Refractive Index Sensing

AbstractCompared to single nanoparticles, strongly coupled plasmonic nanoparticles provide attractive advantages owing to their ability to exhibit multiple resonances with unique spectral features and higher local field intensity. These enhanced plasmonic properties of coupled metal nanoparticles have been used for various applications including realization of strong light‐matter interaction, photocatalysis, and sensing. In this article, the basic physics of hybrid plasmonic modes in coupled metallic nanodimers is reviewed and their potentials for refractive index sensing are assessed. In particular, the spectral line shapes of various modes of hybrid plasmons including bonding and antibonding modes in symmetric nanodimers, Fano resonances in asymmetric nanodimers, charge transfer plasmons in linked nanoparticle dimers, hybrid plasmon modes in nanoshells, gap modes in particle‐on‐mirror configurations, and hybrid magnetoplasmonic modes in heterodimers are overviewed. Beyond the dimeric nanosystems, the potentials of surface lattice resonances in periodic nanoparticle arrays for sensing applications are also showcased. Finally, based on the critical assessment of the recent research on coupled plasmonic modes, the outlook on the future prospects of hybrid plasmon‐based refractometric sensing are discussed. Given their tunable resonances and ultranarrow spectral features, coupled metal nanoparticles are expected to play key roles in developing precise plasmonic nanodevices with extreme sensitivity.

Plasmonic enhanced ultra-thin solar cell: A combined approach using fractal and nano-antenna structure to maximize absorption

In this study, a combined structure is proposed to develop ultra-thin silicon solar cells. This integrated structure consists of silver fractal-like nano-particles and leaky wave nanoantennas. The nano-cuboid pattern embedded inside anti-reflective coating benefits from different optical modes, such as surface plasmons and cavity modes, which trap more light and amplify the electric field in the upper region of the absorber layer. On the bottom side, the hybrid plasmonic mode in the structure of the optical nanoantenna makes it possible to focus and direct the incoming light on the bottom of the absorber layer and increase the optical pathlengths in the ultra-thin film solar cell. The nanoantenna behavior and three-dimensional finite-difference time-domain analysis show that photon absorptions improve significantly at long wavelength lightwaves through this proposed combined structure. The short circuit current enhancement of the solar cell under 1 sun standard illumination is obtained by a factor of 1.94 and 1.80 for TM and TE polarization of incident light, respectively. Due to the acceptable results for different incident angles and polarizations, ultra-thin thickness, and nano-cuboids synthesis feasibility, our structure has the potential to be applied in the design of miniaturized photovoltaic devices.

Symmetry-Breaking Effects of Near-Infrared II Thermoplasmonics of Gold–Silica–Cuprous Selenide Hybrid Nanoshells

This study presents a numerical investigation of the plasmonic and photothermal properties of Au-silica-Cu2–xSe hybrid nanoshells (Cu2–xSe HNSs) consisting of a silica-Cu2–xSe core–shell nanoshell embedded with a spherical Au core at varied core offsets. The plasmon modes in the symmetry-broken Cu2–xSe HNSs are explained by plasmon hybridization theory in combination with charge density distribution. Results unveil that the hybridized plasmon modes in a symmetry-broken Cu2–xSe HNS arise from the interaction of the primitive plasmon modes of the same angular momentum on the Au core and the Cu2–xSe nanoshell. An increase in the core offset redshifts and weakens the near-infrared II (NIR-II) plasmon band corresponding to the low-energy bonding dipolar mode but redshifts and enhances the low-energy bonding quadrupolar mode. At the NIR-II plasmon resonance wavelengths, the temperature increase distribution is uniform on the Au core but inhomogeneous on the Cu2–xSe nanoshell. The variation of the temperature increase with the core offset suggests spectral tunability of NIR-II thermoplasmonic properties in the Cu2–xSe HNSs through varying the core offset. Our work provides a paradigm for rational design of NIR-II plasmonic materials with optimal photothermal performances for in vivo biomedical applications through symmetry breaking.

Wavefront engineering based on hybrid plasmonic mode

Plasmonic lens provided great optical performance through the interaction between light and metallic nanostructure in the past years. However, the wavefront control on the metallic lens was still limited by the fabrication and geometrical design. Here, an unconventional plasmonic lens with sufficient phase modulation was developed as a focusing device; it was constructed using both circular and annular apertures in a silver film. The circular and annular apertures induced localized and cylindrical surface plasmon modes with the incident light, respectively. The propagation phase in these apertures was related to their geometric parameters. These apertures with lower aspect ratios were designed to have the artificial phase from zero to Pi and arranged in concentric arrays to manipulate the wavefront of the lens. The focal length and spot size were determined by the phase distribution on the plasmonic lens. The focal spot with a subwavelength size was obtained by the appropriate manipulation of the phase. We also demonstrated the focusing properties of this plasmonic lens experimentally to validate our design. Owing to the circular symmetry of the circular and annular apertures, this type of plasmonic lens has considerable potential for use as a polarization-insensitive device.

Tunable Hybrid Plasmonic Semiconductor Laser Based on Loss Perturbation

We propose a tunable plasmonic semiconductor laser that exploits loss perturbation as a tuning mechanism. A metal oxide semiconductor (MOS) capacitive structure is added on top of an edge-emitting Fabry-Perot (FP) diode laser, such that a hybrid plasmonic TM mode that overlaps partly with the MOS capacitor and the semiconductor gain region is supported as the lasing mode. We also propose the use of a layer of conductive oxide, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g</i> ., indium tin oxide (ITO), as the semiconductor of the MOS structure, because the epsilon near zero (ENZ) condition can be attained therein under accumulation, thereby producing a very large change in the effective index of the hybrid plasmonic TM mode. The change in the imaginary part of the effective index is used to tune the lasing wavelength - exploiting loss perturbation to achieve laser tuning is paradigm-shifting. The laser proposed operates at telecom wavelengths, requiring an electrical forward bias to pump the active layer, and a gate voltage to drive the MOS tuning capacitor. Simulations yield a tuning range of over 7 nm in the O-band for a 100 μm long FP laser cavity.

Broadband long-wave infrared high-absorption of active materials through hybrid plasmonic resonance modes

Broadband high absorption of long-wavelength infrared light for rough submicron active material films is quite challenging to achieve. Unlike conventional infrared detection units, with over three-layer complex structures, a three-layer metamaterial with mercury cadmium telluride (MCT) film sandwiched between an Au cuboid array and Au mirror is studied through theory and simulations. The results show that propagated/localized surface plasmon resonance simultaneously contribute to broadband absorption under the TM wave of the absorber, while the Fabry–Perot (FP) cavity resonance causes absorption of the TE wave. As surface plasmon resonance concentrates most of the TM wave on the MCT film, 74% of the incident light energy is absorbed by the submicron thickness MCT film within the 8–12 μm waveband, which is approximately 10 times than that of the rough same thickness MCT film. In addition, by replacing the Au mirror with Au grating, the FP cavity along the y-axis direction was destroyed, and the absorber exhibited excellent polarization-sensitive and incident angle-insensitive properties. For the corresponding conceived metamaterial photodetector, as carrier transit time across the gap between Au cuboid is much less than that of other paths, the Au cuboids simultaneously act as microelectrodes to collect photocarriers generated in the gap. Thus the light absorption and photocarrier collection efficiency are hopefully improved simultaneously. Finally, the density of the Au cuboids is increased by adding the same arranged cuboids perpendicular to the original direction on the top surface or by replacing the cuboids with crisscross, which results in broadband polarization-insensitive high absorption by the absorber.

Nanoplasmonic hybrid hotspot in graphene transistor

A field effect transistor based on graphene was introduced to generate a hybrid plasmonic mode. The main reasons to consider graphene in this study are the achievement of high field confinement and the graphene two carrier transport channel near its charge neutrality point. We have observed a nonlinear behavior of the hybrid plasmonic mode near the graphene charge neutrality point because of the existence of the two carrier model. This nonlinear behavior reflects the intrinsic nanoelectronic characteristics of graphene. The proposed nanoelectronic device presents an ultraconfined tunable hybrid hotspot, the mode area of which is ${10}^{5}$ times smaller than the diffraction limited spot area. Moreover, this area is three orders of magnitude smaller than the modal area of the similar metal-based hybrid nanostructure. Such a nanoscale 3D hotspot with plasmonic-photonic character has been reported here. Furthermore, a hybrid structure based on bilayer twisted graphene was numerically investigated which renders ultrahigh confinement and ultralong propagation distance. The proposed nanodevice can be applied to design compact integrated circuits, optical neural networks, and high resolution sensors.

Vertically‐Stacked Discrete Plasmonic Meta‐Gratings for Broadband Space‐Variant Metasurfaces

AbstractReexamining the plasmonic metasurfaces for efficient transmissive nanophotonics devices has recently drawn considerable attention. It attributes to their ease of fabrication and tunability in terms of the excitation of abundant multipoles. Despite recent efforts in developing plasmonic meta‐atoms, meta‐gratings provide an ultimate solution that enables efficient conversion of the polarization in a broadband range, particularly at optical frequencies. In this work, by vertically stacking meta‐gratings whose bandwidths overlap with each other and possess no physical limitation, plasmon mode hybridization is introduced so that highly‐transmissive broadband plasmonic metasurfaces are realized. It is reported that the intra‐coupling in a discrete plasmonic meta‐grating plays a key role in geometric phase‐controlled metasurface design. As a proof of concept, a half‐wave plate using plasmonic meta‐gratings to convert the incident circularly‐polarized light in a wavelength range from 1106 to 1521 nm with a peak efficiency of 50.2% and a gradient metasurface with truncated discrete meta‐grating as building blocks for deflecting the light with a maximum of 32.60% are demonstrated. Finally, the physical picture is explained through the electric field distributions, mode coupling, and energy splitting. The presented framework may provide an optimized way to enhance efficiency and expand the bandwidth for plasmonic systems.