Plasmon Modes Research Articles

Plasmonic structure assisted all-optical tunable fiber laser

In this paper, we proposed and demonstrated a tunable fiber laser using all-optical plasmonic modulation, where the localized surface plasmon resonance effect of gold nanobipyramids (GNBPs) and polarization maintaining thin-cladding photonic crystal fiber were utilized to realize tunable output wavelength controlled by the 980 nm pump light. The laser achieves a tunability of 2.21 nm in C-band, with a side mode suppression ratio of 27 dB and the peak intensity can also be tuned continuously. The proposed tunable laser shows an average power fluctuation of less than 1 dB and the output wavelength and the power intensity both exhibit high stability. Therefore, the proposed plasmonic structure assisted all-optical tunable laser has advantages such as compact structure, good reproducibility, continuous tuning, and simple operation, which indicates great potential in future all-optical applications.

Long-range, short-wavelength, and ultrafast heat conduction driven by three plasmon modes supported by graphene

Long-range, short-wavelength, and ultrafast heat conduction driven by three plasmon modes supported by graphene

Resonance mechanisms of coupled-particle plasmonic nano-antennas to maximize UV fluorescence enhancement of biological molecules

We investigated several geometric parameters such as the height, width and length, and the contribution of different plasmonic modes on the enhancement factors of aluminum (Al) bowtie nano-antennas (BNAs) on tryptophan’s native fluorescence in the ultraviolet (UV) to visible range. The highest fluorescence enhancement was produced by the tallest BNAs. Analysis revealed that, in tall BNAs illuminated at normal incidence, phase retardation amplified quadrupole resonances which were exploited to obtain high excitation enhancement. The optimized oxide-free Al BNA predicted 331 × excitation enhancement, 74 x radiative enhancement, 993 × fluorescence net enhancement and the optimized oxidized Al BNA predicted 128 × excitation enhancement, 142 × radiative enhancement and 461 × fluorescence net enhancement. These enhancement factors are the largest reported for simulated UV plasmonic structures in literature using tryptophan as the model molecule. The effect of length and width on the different plasmonic modes were also studied and explained in depth. An oxide layer dampened the excitation enhancement but has negligible effect on emission enhancements. The numerical study conducted in this manuscript sheds light to light–matter interaction in the UV frequency range.

Selective Nitridation of Ceramic Open Cell Foams for Efficient Photothermal Heating

AbstractThis study presents the synthesis of ceramic open cell foams as a new platform for photothermal energy conversion based on the inert structural ceramic alumina and the plasmonic transition metal nitride TiN. TiO2 precursor grains inside the mixed ceramic matrix are converted to TiN via the molten salt synthesis route. Photothermal measurements using an 850 nm LED as a light source show that the ceramic foams with only ≈5% TiN in the alumina matrix showed a 34% increased efficiency in converting light to heat compared to flat ceramic discs of the same composition. The TiN content in the flat discs does not affect the heat conversion efficiency, indicating that the available surface area and the material's ability to trap and direct light to the plasmonic nanostructures are the most important parameters for its photothermal activity. These results show the feasibility of synthesizing mixed ceramics based on inert materials like alumina and transition metal nitrides. Applications in solar heating, water evaporation, and related use cases of photothermal energy conversion can be realized with improved performance over 2D materials. Particularly processes that are based on continuous flow like solar thermal heating or photothermal catalysis will benefit from this new material platform.

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.

Plasmon-Assisted Si-ITO Integrated Electro-Optical Rib-Shape Modulator

An integrated plasmonic indium-tin-oxide (ITO)-based silicon electro-optical modulator has been designed, fabricated, and characterized. A sandwich structure shows a 40 GHz bandwidth at the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-2$</tex-math></inline-formula> dB level and an extinction ratio of about 1.8 dB. The device is fabricated on a silicon-on-insulator wafer. A silicon waveguide is excluded from the electric circuit. Instead, an ITO layer is used both as a bottom electrical contact and as an electric field-sensitive medium. As a gate oxide, we used a silicon dioxide layer capped with a gold top electrode to form a capacitor. The dielectric rib inside the ITO-Au capacitor forms a coupling interface between the TE photonic and plasmonic modes.

Optical readout and actuation of plasmonic nano-optomechanical drum resonators

We demonstrate optical readout and actuation of nanomechanical motion using plasmonic fields in a nanoscale gap waveguide. The top gold layer of the waveguide is free to vibrate like a drumhead, and patterned with an optical grating to facilitate efficient coupling to free-space radiation. The change of the plasmonic gap mode with the top layer position couples the plasmonic resonance to the mechanical displacement of the drum. We characterize optical and mechanical resonances of the system, and demonstrate sensing of nanomechanical vibrations with ∼10−14 m/Hz sensitivity. The mechanical resonators are actuated through plasmonic forces. Quantifying their magnitude shows that plasmonic forces can significantly exceed pure radiation pressure, indicating that their nature is dominated by a photothermoelastic effect. This work opens avenues to the use of plasmonic readout and control in nanomechanical sensing applications.

Coupling Nd3+:Y2O3 fluorescent submicron particles to linear plasmonic chains

We report on the fabrication and optical characterization of a new hybrid material consisting of Nd3+ doped Y2O3 submicron particles associated with linear chains of plasmonic nanostructures. By drop-casting deposition, single Nd3+ doped Y2O3 polycrystalline particles are dispersed and located in the vicinities of plasmonic chains of silver nanoparticles formed on the surface a LiNbO3 substrate. The interaction between the plasmonic modes of the chain with the fluorescent yttria submicron particles is analyzed by micro-luminescence experiments. Orthogonal polarization configurations of the excitation radiation, namely, perpendicular and parallel to plasmonic chain axis, are employed to study the effect of the longitudinal and transverse chain plasmonic modes on the luminescence of the particles. A remarkable dependence of the emission intensity of the Nd3+:Y2O3 submicron particles on the excitation polarization is observed, showing the capability of plasmonic chains to modulate the emission of fluorescent submicron particles in contact with the chain. Numerical simulations evidence a different distribution of the excitation radiation field within the Nd3+:Y2O3 particle depending on the type of excited plasmonic mode, longitudinal or transversal, of the chain, and hence, the ability of plasmonic chains for controlling the emission of Rare Earth doped submicron particles.

Advanced mid-infrared plasmonic waveguides for on-chip integrated photonics

Long-wave infrared (LWIR, 8–14 µm) photonics is a rapidly growing research field within the mid-IR with applications in molecular spectroscopy and optical free-space communication. LWIR applications are often addressed using rather bulky tabletop-sized free-space optical systems, preventing advanced photonic applications, such as rapid-time-scale experiments. Here, device miniaturization into photonic integrated circuits (PICs) with maintained optical capabilities is key to revolutionize mid-IR photonics. Subwavelength mode confinement in plasmonic structures enabled such miniaturization approaches in the visible-to-near-IR spectral range. However, adopting plasmonics for the LWIR needs suitable low-loss and -dispersion materials with compatible integration strategies to existing mid-IR technology. In this paper, we further unlock the field of LWIR/mid-IR PICs by combining photolithographic patterning of organic polymers with dielectric-loaded surface plasmon polariton (DLSPP) waveguides. In particular, polyethylene shows favorable optical properties, including low refractive index and broad transparency between ∼2 μm and 200 µm. We investigate the whole value chain, including design, fabrication, and characterization of polyethylene-based DLSPP waveguides and demonstrate their first-time plasmonic operation and mode guiding capabilities along S-bend structures. Low bending losses of ∼1.3 dB and straight-section propagation lengths of ∼1 mm, pave the way for unprecedented complex on-chip mid-IR photonic devices. Moreover, DLSPPs allow full control of the mode parameters (propagation length and guiding capabilities) for precisely addressing advanced sensing and telecommunication applications with chip-scale devices.

Gain-assisted magnetoplasmonic switching in metal–dielectric–metal plasmonic waveguides

Optical switches in metal–dielectric–metal (MIM) structures attracted much interest for chip-scale plasmonic modulator merging nanoelectronics and ultrafast photonics. The absorption switches employed gain modulations; thus, their switching speed is limited to the sub-gigahertz range because of the spontaneous lifetime of the transition. In this paper, we theoretically predicted that the function of the absorption switches is achieved employing magnetic field reversal and constant gain instead of gain modulations. We investigated analytically and numerically transmission in the presence of both gain and gyration and revealed that the transmission shift by the external magnetic field is maximized at a resonance value of gain. The switching speed can reach the THz range thanks to the large optical bandwidth in the MIM stub structures and the advanced magnetization switching technology. The MIM structure with combined gain and magnetoplasmonic properties enhances interaction between light and magnetic field on nanoscale and enables the device footprint down to the deep subwavelength scale λ2/50.

Reshaping plasmon modes by film interference

Reshaping plasmon modes by film interference

Absorption enhancement of ultra-thin film Solar Cell using Fabry-Perot and plasmonic modes

In this paper, we investigate the photonic and plasmonic modes in order to enhance the absorption of ultrathin film Si Solar Cells. The simulations based on FEM show that these mechanisms enhance the absorption of the cell significantly. In order to investigate the plasmonic effects and use the amazing optical properties of localized surface plasmons (LSPs), multiple Au nanoparticles (NPs) with different radii have been used on the front surface of the Cell. Simulations show that the use of Au NPs with radii of 25, 50, and 75 nm simultaneously on the front surface of the Cell, increases the absorption dramatically. It is observed that multiple Au NPs with configuration illustrated in Case 5, enhance the absorption significantly due to the excitation of the multiple plasmonic modes in UV and Visible regions. In order to enhance the absorption in near-IR, we use Cu NPs on the backside of the cell. The highest average absorption of 84.7%, short-circuit current density of 36.7 (mA/cm2), and efficiency of 30.1% is achieved, with an increase of 177.7%, 178%, and 178.7% compared to Case 1, respectively. These methods promise the performance improvement of ultra-thin film solar cells and increase their application potential in Solar energy harvesting.

Thermal dynamics of gold nanoshell dimers under femtosecond laser pulse irradiation: A numerical approach.

We present a numerical investigation of the photothermal response of gold nanoshell (AuNS) dimers when subjected to femtosecond laser pulse irradiation. The time-varying temperature fields for core-shell AuNS dimers are quantified by implementing finite element modeling, integrating the electromagnetic and thermal dual-physics simulations. Given the ultrafast nature of laser pulses, we employ a two-temperature model to accurately portray the energy transfer from excited electrons to the lattice system, a process typically completed post pulse-termination. The temporal analysis of the temperature in the AuNS and the surrounding medium, together with the spatial temperature distribution under different separation distances, elucidates the processes that drive the AuNS dimers' transient temperature distribution and heat dissipation. We report on the critical effects of geometrical parameters on the photothermal response, demonstrating that thinner shells maximize the total deposited energy per unit volume, resulting in increased temperature fields, while decreasing separation distances result in excessive field amplification due to plasmonic modes' production. Our robust numerical approach, enabling simulations with tunable material properties and configurations, may help design nanomaterials with desired features for photothermal cancer treatment and imaging.

Origin of plasmonic Fano resonance in metal-hole/split-ring-resonator metamaterials disclosed by temporal coupled-mode theory.

In plasmonic Fano resonance, the interaction between a discrete plasmonic mode and a continuum of plasmonic mode gives rise to an asymmetric line shape in the scattering or absorption spectrum, enabling a wide range of applications such as sensing, switching, and slow light devices. Here, we establish a theoretical solution in the framework of temporal coupled-mode theory (TCMT) to study the three-dimensional (3D) and two-dimensional (2D) Fano resonances induced by strong coupling between metal hole (MH) and split ring resonator (SRR) array. We first separately analyze the transmission spectra of the MH array and SRR array under different polarized light excitation. We further investigate the electromagnetic field and charge density distribution corresponding to the resonant modes at the peak or valley wavelength of the transmission spectrum and figure out the electric/magnetic dipole feature of these resonance modes. We then establish a theoretical solution by TCMT for Fano resonances arising from the coupling of these modes. The calculated transmission spectrum is closely matching with the numerically simulated transmission spectrum for these Fano resonances in the MH-SRR array, which effectively elucidates that the asymmetry of the Fano resonances is caused by the coupling between bright and dark plasmonic modes involved in the two structures. Our results can help to understand the profound physics in such coupled plasmonic systems.

Identification of dark axisymmetric plasma modes in partially gated two-dimensional electron gas disk

We investigate the dark axisymmetric plasmon spectrum for partially gated two-dimensional gas of the disk shape. The extension of the central gate spot provides a change in plasmon dispersion from the root to a linear dependence on the wave vector. Intriguingly, the interaction between neighboring modes occurs because of stepwise change in carrier screening across the circumference of the gate. This behavior is unexpected when changing from a fully screened to unscreened two-dimensional gas by increasing the dielectric width under the gate [A.L.Fetter, Phys.Rev.B 33, 5221 (1986)]. Our results provide the accurate identification of axisymmetric plasmon modes recently observed in experiment and, in addition, pave the way for feedback plasmon resonator study.

Air-silica core microstructured optical fiber-based SPR sensor for temperature and refractive index measurement

We propose an air-silica core microstructured optical fiber-based surface plasmon resonance (SPR) sensor to simultaneously measure temperature and refractive index (RI). The sensing channel is formed by coating the outside of the fiber with a gold film and a polydimethylsiloxane (PDMS) layer as a temperature sensing medium, and then being immersed into the liquid analyte. The plasmon mode can penetrate through the PDMS layer and then into the analyte, therefore both the temperature and the analyte RI changings can lead to the variations of SPR spectra that will be measured. Our numerical results demonstrate that the proposed sensor can support two resonance peaks in the x-polarized core mode and one resonance peak in the y-polarized core mode, therefore providing two detection approaches, peak-based and polarization-based approaches. By measuring the two peaks in the x-polarized core mode, for the peak-based approach, the temperature coefficients are −2.077 nm/°C and −2.723 nm/°C, and the RI coefficients are 1252 nm/RIU and 1931 nm/RIU, respectively. While by measuring the second peak in x-polarized core mode and the peak in y-polarized core mode, for the polarization-based approach, the temperature coefficients are −2.723 nm/°C and −3.401 nm/°C, and the RI coefficients are 1931 nm/RIU and 2973 nm/RIU, respectively.

Si3N4-plasmonic ferroelectric MZIR modulator for 112-Gbaud PAM-4 transmission in the O-band.

This paper presents a simulation-based analysis on the performance of plasmonic ferroelectric Mach-Zehnder in a ring (MZIR) versus symmetric Mach-Zehnder modulators (MZMs) on Si3N4 targeting O-band operation. The detailed investigation reveals the tradeoff between Au and Ag legacy noble metals providing lower modulator losses and CMOS compatible Cu featuring low cost. The numerical models also show that by opting for the MZIR layout there is a reduction in the Vπ x L product of 46% for Ag, 39% for Au and 30% for Cu versus MZMs. Time-domain simulations verify the successful generation of 112 Gbaud PAM-4 Signals from both MZIRs and MZMs for as low as 2 × 1.3 Vpp and 5µm long plasmonic phase shifters (PSs) with MZIRs providing a ΔQ signal improvement over MZMs of 2.9, 2.4, and 1.3 for Ag, Au, and Cu metals respectively. To the best of our knowledge, this is the first theoretical demonstration of such a low-loss, low-voltage, high-speed, and CMOS compatible plasmonic modulator on Si3N4, in the O-band.

Super-Radiant SERS Enhancement by Plasmonic Particle Gratings.

Despite recent developments, surface-enhanced Raman spectroscopy (SERS) applications face challenges in achieving both high sensitivity and uniform Raman signals over a large area. Using the directional self-assembly of plasmonic nanoparticles in lattice structures, we show how one can increase the SERS signal 43-fold over randomly aligned gold nanoparticles without relying on the photoluminescence of Rhodamine 6G. For this study, we have chosen the lattice constant for an off-resonant case that matches the lattice resonance and super-radiant plasmon mode along the particle chain. Supported by electromagnetic simulations, we systematically analyze the radiative components of the plasmon modes by varying the particle size while keeping the lattice periodicity constant. We perform polarization-dependent SERS measurements and compare them with other standard SERS excitation wavelengths. Using the self-assembled plasmonic particle lattice, we have developed an effective SERS substrate that provides a significantly higher signal with 73% less surface coverage. This colloidal approach enables the cost-effective and scalable fabrication of highly sensitive, uniform, and polarization-dependent SERS substrates.

Enhanced Asymmetric Light‐Plasmon Coupling in Graphene Nanoribbons for High‐Efficiency Transmissive Infrared Modulation

AbstractGraphene plasmonic modulators can manipulate the mid‐infrared light in transmission mode, which is currently challenging for traditional liquid crystal and digital micromirror devices, opening up a new avenue for infrared scene projection, infrared optical communication, and hyper spectra imaging. Nevertheless, their efficiencies are not high enough due to the single‐layer atomic thickness and low free carrier density of graphene. Here, it is demonstrated that the modulation efficiency can be significantly improved by enhancing the asymmetric light‐plasmon coupling. A general theoretical model is established to describe the modulation behaviors of the modulator, revealing the critical role of the asymmetric coupling rate. By using dielectric environment engineering and graphene structure design experimentally to enhance the asymmetric coupling rate from 0.45×1012 to 7.05×1012 s−1, the modulation efficiency has been improved from 4% to 41% at 1530 cm−1, while maintaining the bandwidth as large as 230 cm−1. The modulator outperforms previous transmission‐type graphene plasmonic modulators in both efficiency and bandwidth, presenting great potential in next‐generation infrared integrated photonics platforms.

Designing a perfect surface plasmon resonance absorber based on graphene and hexagonal boron nitride photonic crystal nanorods

In this work, absorbers in the terahertz region based on one-dimensional photonic crystal nanorods coated with phosphorene, phosphorene-graphene, and phosphorene–hexagonal boron nitride layers were designed. On addition of a graphene layer to the structure, strong localized surface plasmon resonance was observed in two different plasmonic modes via two significant peaks at wavelengths of 10.09 μm and 12.47 μm. The absorption of the structure was affected by the presence of an antireflection layer, and the two modes showed an absorption rate of 99% at wavelengths of 9.72 μm and 9.86 μm, increasing the absorption band to 0.54 μm full width at half maximum. By our changing the dielectric environment with a higher refractive index, better localization and greater absorption occurred. Furthermore, a perfect absorber with two absorption peaks at wavelengths of 11.39 μm and 14.02 μm with 99% and 97% absorption and full width at half maximum of 0.35 μm and 1.1 μm, respectively, was created. Finally, a perfect absorber with an absorption bandwidth of 2.1 μm was obtained in the structure in which hexagonal boron nitride had been placed as a spacer between the monolayers of phosphorene.