Coupling Of Plasmon Polaritons Research Articles

Polarization dependent exciton-plasmon coupling in PEA2PbI4/Al and its application to perovskite solar cell

This paper reports the strong coupling between Al nanostructure and two-dimensional (2D) layered perovskite PEA2PbI4 (PEPI) films. The high exciton binding energy of 118 meV and long carrier lifetime of 216 ps are characterized from the 2D PEA2PbI4 film, which indicates that the excitons in perovskite are robust and can couple to metal plasmons. The ordinary and extraordinary optical dispersions are revealed from the anisotropic 2D perovskite. The transmission spectra of PEA2PbI4/Al nanoparticle arrays are simulated under different polarization excitations, and the typical anti-crossing behaviors originating from exciton-plasmon strong coupling are demonstrated. We found that compared with transverse magnetic (TM) polarization, transverse electric (TE) polarization excitation is more conducive to the realization of exciton-plasmon coupling with a larger Rabi splitting. Furthermore, the PEA2PbI4/Al nanoparticle arrays are proposed, which present polarization-dependent local electrical field enhancement due to the exciton-local surface plasmon polariton coupling. Additionally, it is noticed that the proposed plasmonic structure increases the photo-generation rate inside the active material with improved current density. Therefore, the 2D proposed plasmonic design increases the power conversion efficiency (PCE) with an enhancement of 3.3% and 1.3% relative to the planar structures for TE and TM polarizations, respectively. This study provides a deeper understanding of polarized exciton-plasmon coupling properties, promoting the development of the field of plasmon and providing guidance for the design and preparation of efficient optoelectronic devices.

Plasmonic red-light-emission enhancement by honeycomb-latticed InGaN/GaN ordered fine nanocolumn arrays

By using ordered fine nanocolumns suitable for high-efficiency red-emission, emission enhancement based on surface plasmon polariton (SPP) coupling was successfully obtained for the honeycomb lattice. This lattice enables us to obtain a longer SPP resonant wavelength in the red region, which could not be attained for the triangular lattice. A 4.8-fold red-emission enhancement was achieved for the honeycomb lattice, demonstrating effective synergy between plasmonic and nanocrystalline effects within the red-emission nanocolumn system. Additionally, a 3.2-fold light-extraction enhancement was attained by changing the emission directionality by introducing plasmonic crystals (PlCs) in addition to metal reflection.

Raman Probing the Local Ultrastrong Coupling of Vibrational Plasmon Polaritons on Metallic Gratings.

Strong coupling of molecular vibrations with light creates polariton states, enabling control over many optical and chemical properties. However, the near-field signatures of strong coupling are difficult to map as most cavities are closed systems. Surface-enhanced Raman microscopy of open metallic gratings under vibrational strong coupling enables the observation of spatial polariton localization in the grating near field, without the need for scanning probe microscopies. The lower polariton is localized at the grating slots, displays a strongly asymmetric line shape, and gives greater plasmon-vibration coupling strength than measured in the far field. Within these slots, the local field strength pushes the system into the ultrastrong coupling regime. Models of strong coupling which explicitly include the spatial distribution of emitters can account for these effects. Such gratings enable exploration of the rich physics of polaritons, its impact on polariton chemistry under flow conditions, and the interplay between near- and far-field properties through vibrational polariton-enhanced Raman scattering.

SPP excitation and coupling mechanism based onmicro/nano fibers.

A hot trend in the development of optoelectronic devices is how to use the principle of surface plasmon resonance to enhance the performance of integrated photonics devices and achieve miniaturization. This paper proposes an accompanying waveguide coupling structure of micro/nano fibers, which consists of two parallel-placed micro/nano fibers (MNFs) coated with a silver film in the waist region and infused with a refractive index matching oil. In the overlapping region, there exists a segment of surface plasmon polaritons (SPPs) coupling area. The excitation and coupling characteristics of SPPs are studied through numerical simulation. Optimal coupling enhancement configuration is obtained by studying variables such as spacing distance, coupling length, and metal film thickness. A comparison is made with the SPP intensity of a single MNF, showing a 220% increase in electric field intensity, demonstrating its excellent coupling effect. By using this coupling structure, exploration of SPPs excitation and coupling mechanisms is enhanced, and structures resembling interferometric devices can be designed, providing new insights for high-performance miniaturized devices.

Digital imaging through terahertz multifrequency programmable metasurface based on BIC

Due to its intense penetration and low photon energy, terahertz (THz) imaging has been widely applied in biomedical imaging, non-destructive testing, and digital holography. The traditional method of exciting THz is through plasmon polariton coupling, which faces low photon signal excitation sustainability and poor polarization coupling efficiency challenges. This paper proposes a multi-channel THz system based on a high Q-factor bound state in the continuum (BIC) cross-polarization. The system is composed of an Al-graphene programmable metasurface. As an application of this programmable metasurface, we manage a field-programmable gate array (FPGA) to independently adjust the transmission properties of sub-arrays by changing the graphene state on the programmable metasurface through computer control. This feature enables our metasurface, which dynamically display characters in multiple channels, and provide a platform for THz multi-band image encryption and transmission. Additionally, we offer a convenient and stable method to generate multi-frequency effects by coupling bright modes that can produce BIC effects with dark modes that are not excited in that polarization state. Compared with traditional excitation methods, this method is more accessible to process due to its simple device structure.

Enhanced Optical Transmission through a Hybrid Bull's Eye Structure Integrated with a Silicon Hemisphere.

In this work, we demonstrate a novel structure that can generate extraordinary optical transmission with a silicon hemisphere placed on a conventional bull's eye structure. There is a single subwavelength aperture surrounded by concentric periodic grooves on a substrate. The extraordinary optical transmission in this work is realized by the coupling of the surface plasmon polaritons in the periodic grooves and the localized electromagnetic field generated by the Mie resonance in the silicon hemisphere. The maximum normalized-to-area transmission peak can reach up to 662 with a decreasing device area and size. The electromagnetic field distribution at different geometry parameters is analyzed to clarify the mechanisms of the work in this paper. Additionally, the use of dielectric material in the aperture can avoid ohmic losses of metal material compared with the conventional one, which may suggest that a wider range of bull's-eye-structure applications is possible.

Stepped metal gratings as an efficient way to design a broadband absorption efficiency and overcome recombination degradation in an organic solar cell

The Stepped stopped Groove Metal nano-grating (SSGMG) and Stepped Through Groove Metal nano-grating (STGMG) with a stepped hole transport layer (HTL) and a coating layer, is investigated as a novel method to obtain high absorption efficiency in a thin film organic solar cell. Enhancement of the electric field inside the gratings due to the near field and far-field coupling of wedge plasmon polaritons would lead to the improvement of the absorption efficiency of the solar cell. The proposed SSGMG model, with a 40 nm thickness of the photoactive layer, shows an absorption efficiency of 73.73% of the incident light in a wavelength range from 350 nm to 800 nm. the results show that the SSGMG model with an effective thickness of 40 nm has improved the absorption efficiency of the thickness-equivalent planar model (without coating layer) up to 133% of its initial value. Moreover, the effect of the incident angle (θ) and polarization angle (α) on the absorption efficiency was evaluated. We have found that SSGMG would lead to better absorption efficiency than STGMG because of its advantages over unpolarized light absorption. Excitation of surface plasmon polaritons inside the photo-active layer would help to reduce the recombination degradation as a result of the reduced thickness of the active layer as well as the enhanced mobility of charge. The designed structures can be used to overcome recombination degradation which is the intrinsic limitation of organic materials.

A one-step, tunable method of selective reactive sputter deposition as a wrinkling approach for silver/polydimethylsiloxane for electrically conductive pliable surfaces

The wrinkle period and morphology of a metal thin film on an elastic substrate is typically controlled by modifying the substrate before carrying out additional metal deposition steps. Herein, we show that a simultaneously selective and reactive sputtering plasma that modifies the surface of a polydimethylsiloxane (PDMS) substrate while not reacting with the metal during the deposition process decreases the wrinkle wavelength and induces additional wrinkling components and features such as ripples or folds. The selective reaction of the nitrogen plasma with PDMS functionalizes the siloxane surface into silicon oxynitride. This hardens the immediate surface of PDMS, with a quadratic increase in the Young’s modulus as a function of the sputtering flow ratio. The increase in the critical strain mismatch and the corresponding presence of folds in the nitrogen-modified wrinkled silver film form a suitable plasmonic platform for surface-enhanced Raman spectroscopy (SERS), yielding an enhancement factor of 4.8 × 105 for detecting lipids. This enhancement is linked to the emergence of electromagnetic hotspots from surface plasmon polariton coupling between the folds/wrinkles, which in turn enables the detection of low concentrations of organics using SERS. Furthermore, when strained, the nitrogen-modified wrinkles enhance electrical conductivity by a factor of 12 compared with unmodified films. Finally, the optical properties of the substrate can be tuned by altering the N2 content. The simple addition of nonreactive nitrogen to silver sputtering enables simultaneous PDMS hardening and growth of the silver film and together provide a new avenue for tuning wrinkling parameters and enhancing the electrical conductivity of pliable surfaces.

High performance mid infrared temperature sensor based on resonance excitation of hybrid Tamm surface states

Theoretical design of mid infrared temperature sensor based on the resonance excitation of hybrid Tamm surface state (HTSS) is presented. An excellent sensing performance is attained by the coupling of graphene plasmon polaritons and hexagonal boron nitride (hBN) phonon polaritons that forms hybrid polariton modes at the interface. In one dimensional ternary photonic crystal (1D TPC), terminated by hBN layer sandwiched between graphene monolayers, the coupling between Bloch surface waves and hybrid polariton modes leads to the formation of HTSS or Tamm plasmon-phonon modes. Employing Kretschmann configuration coupling mechanism, the excitation of the HTSSs at the truncated interface is manifested for transverse magnetic (TM) polarized wave. The structure supports excited HTSS between 7.14μm to 10.34μm that allows astounding control over the sensing ability by varying the number of unit cells and the resonant angles. The sensor has a high detection accuracy of 1010 at room temperature (300K). It is proved that for 50 unit cells and at 49° angle, a high quality factor of 372176, detection limit of 5K and sensitivity of 0.20pm/K is attained with operating range between 280K to 380K. The operating range is widened from 300K to 900K by changing the resonant angle from 49° to 53°. Further, for 30 unit cells and at 53° angle, the temperature sensing ability of the sensor extends from 100K to 900K with a sensitivity of 0.80pm/K and detection limit of 54.16K.

High Birefringence D-Shaped Germanium-Doped Photonic Crystal Fiber Sensor.

In this work, a surface plasmon resonance (SPR) sensor based on a D-shaped germanium-doped photonic crystal fiber (PCF) is proposed. The finite element method (FEM) is introduced to analyze the structure parameters, such as germanium-doped concentration, lattice pitch, and air hole size. In addition, the coupling properties and birefringence properties of PCF are also studied. The computer simulation results indicate that two different surface plasmon polariton (SPP) coupling modes are produced on the polished surface, covered with metal film, when the analyte refractive index (RI) is . Then, with the increase of the RI, the incompleteness of one of the coupling modes will be transformed into the complete coupling. The effect of germanium concentration on the birefringence is also analyzed. It has an optimal wavelength sensitivity of 5600 nm/RIU when the RI is 1.37. This sensor exhibits a maximum birefringence of 1.06 × 10−2 and a resolution of 1.78 × 10−5 RIU with high linearity.

Strong Coupling of Carbon Quantum Dots in Liquid Crystals.

Carbon quantum dots (CDs) have recently received a tremendous amount of interest owing to their attractive optical properties. However, CDs have broad absorption and emission spectra limiting their application ranges. We herein, for the first time, show synthesis of water-soluble red emissive CDs with a very narrow line width (∼75 meV) spectral absorbance and hence demonstrate strong coupling of CDs and plasmon polaritons in liquid crystalline mesophases. The excited state dynamics of CDs has been studied by ultrafast transient absorption spectroscopy, and CDs display very stable and strong photoluminescence emission with a quantum yield of 35.4% and a lifetime of ∼2 ns. More importantly, we compare J-aggregate dyes with CDs in terms of their absorption line width, photostability, and ability to do strong coupling, and we conclude that highly fluorescent CDs have a bright future in the mixed light–matter states for emerging applications in future quantum technologies.

Gold nanoparticles (AuNPs) and graphene oxide heterostructures with gold film coupling for an enhanced sensitivity surface plasmon resonance (SPR) fiber sensor

Scholars in the field of surface plasmon resonance (SPR) sensors have long been devoted into tackling the question of improving sensitivity while maintaining high-level stability and re-usability. Presented in this paper is a highly sensible SPR fiber sensor established on gold nanoparticle (AuNPs)/graphene oxide (GO) heterostructures and Au film coupling enhancement. The local electric field enhancement of the gold nanoparticle/graphene oxide heterostructure and gold film coupling, together with the sensitivity of the sensor, was analyzed using a finite element method. Theoretical results have provided evidence that this structure is efficient in enhancing the surface plasmon polariton (SPP) coupling, the local electric field, and the depth of electric field propagation outwards, while significantly improving the sensitivity of the sensor. Sensors with single- and double-layer gold nanoparticle/graphene oxide and enhanced Au film coupling were prepared with refractive index (RI) sensitivities of 2899.4 nm/RIU and 3436.2 nm/RIU, respectively, 37.92% and 63.46% higher than for conventional gold film sensors. Due to the chemical bonding of graphene oxide, the materials on the sensor have shown considerably robust interconnections, and the performance of the sensor remains almost unaffected after many measurements. Promising stability and reusability have been demonstrated, presenting favorable prospects for practical applications.

Strong Local Field Enhancement of Raman Scattering Observed in Metal-Dielectric Gratings due to Vertical Fabry-Perot Modes of Surface Plasmon Polaritons

The height dependence of Raman light scattering on organic molecules deposited onto thick one-dimensional metal-dielectric gratings is investigated theoretically and experimentally. We observe oscillations of the intensity of Raman light scattering as a function of the height of the metastructure's strips and demonstrate that these oscillations are explicitly associated with a type of Fabry-Perot effect. We show that the intensity of surface-enhanced Raman scattering can be additionally increased by local field enhancement (by an order of magnitude) at resonances of both pump and Stokes as well as anti-Stokes frequency, due to coupling of the surface plasmon polaritons on the top and bottom metal parts of the gratings via the vertical Fabry-Perot resonances over their middle dielectric part. A semianalytical one-mode model to describe the effect qualitatively is proposed. A significant deviation of the dispersion of Fabry-Perot-coupled plasmon polaritons from the surface-plasmon-polariton dispersion just folded into the first Brillouin zone is demonstrated.

Terahertz hybrid plasmonic waveguides with ultra-long propagation lengths based on multilayer graphene-dielectric stacks.

To develop on-chip photonic devices capable of transmitting terahertz signals beyond the propagation distance of millimeter while keeping deep subwavelength field confinement has been a challenging task. Herein, we propose a novel multilayer graphene-based hybrid plasmonic waveguide (MLGHPW) consisting of a cylindrical dielectric waveguide and hyperbolic metamaterials. The device is based on alternating graphene and dielectric layers on a rib substrate, operating in the terahertz range (f = 3 THz). We couple the fundamental dielectric waveguide mode with the fundamental volume plasmon polarition modes originated from the coupling of plasmon polaritons at individual graphene sheets. The resulting hybrid mode shows ultra-low loss compared with the conventional GHPW modes at the comparable mode sizes. The present MLGHPW demonstrated a few millimeters of propagation length while keeping the mode area of 10-3A0, where A0 is the diffraction-limited area, thus possessing a thirty times larger figure of merit (FoM) compared to other GHPWs. The additional degree of freedom (the number of graphene layers) makes the proposed MLGHPW more flexible to control the mode properties. We investigated the geometry and physical parameters of the device and identified optimal FoM. Moreover, we analyzed the crosstalk between waveguides and confirmed the potential to construct compact on-chip terahertz devices. The present design might have the possible extensibility to other graphene-like materials, like silicene, germanen, stanene etc.

Comparison of surface plasmon polariton characteristics of Ag- and Au-based InGaN/GaN nanocolumn plasmonic crystals

We characterized surface plasmon polariton (SPP) coupling in InGaN/GaN nanocolumn (NC) arrays with Ag- and Au-based plasmonic crystals (PlCs). In both the Ag- and Au-based NC-PlCs, the standing wave SPPs enhanced the light emission from the InGaN/GaN NC arrays. The finite-difference time-domain calculations reproduced the general tendency of the experimental results for the photoluminescence enhancement ratio and SPP resonant wavelength. For the Ag-based NC-PlCs, a stronger electric field intensity was obtained, and the SPP resonance could be controlled over a wide range of wavelengths. Therefore, significant emission enhancement in the visible light region can be realized for the Ag-based NC-PlCs.

Sensitivity Enhanced Refractive Index Fiber Sensor Based on Long-Range Surface Plasmon Resonance in SiO2-Au-TiO2 Heterostructure

Long-range surface plasmon resonance (LRSPR), generated from a coupled plasmon polariton in a thin metal slab sandwiched by two dielectrics, has attracted more and more attention due to its merits, such as longer propagation and deeper penetration than conventional single-interface surface plasmon resonance. Many useful applications related to light–medium interaction have been demonstrated based on the LRSPR effect, especially in the sensing area. Here, we propose and demonstrate an LRSPR-based refractive index sensor by using a SiO2-Au-TiO2 heterostructure, in which a D-shaped honeycomb-microstructure optical fiber (MOF) is designed as the silica substrate and then deposited with a gold film and thin-layer titanium dioxide (TiO2). By using the full-vector finite-element method (FEM), this heterostructure is numerically investigated and demonstrated to excite LRSPR without a buffer layer, which is usually necessary in previous LRSPR devices. Through comprehensive discussion about the influence of structural parameters on the resonant wavelength, the excitation of the LRSPR in the proposed heterostructure is revealed to be highly related to the effective refractive index of MOF’s fundamental core mode, which is mainly determined by the MOF’s pitch, the thicknesses of the silica web and the planar-layer silica. Moreover, the thin-layer TiO2 plays an important role in significantly enhancing the resonance and the sensitivity to analyte’s refractive index as well, when it is coated on the top of the Au film rather than between the metal and waveguide. Finally, the proposed LRSPR sensor based on SiO2-Au-TiO2 heterostructure shows an ultra-high wavelength sensitivity of 20,100 nm/RIU and the corresponding minimum resolution is as low as 4.98×10−7 RIU. Thus, the proposed LRSPR device offers considerable potential for sensing applications in biomedical and biochemical areas.

Adiabatic mode transformation in width-graded nano-gratings enabling multiwavelength light localization

We delineate the four principal surface plasmon polariton coupling and interaction mechanisms in subwavelength gratings, and demonstrate their significant roles in shaping the optical response of plasmonic gratings. Within the framework of width-graded metal–insulator-metal nano-gratings, electromagnetic field confinement and wave guiding result in multiwavelength light localization provided conditions of adiabatic mode transformation are satisfied. The field is enhanced further through fine tuning of the groove-width (w), groove-depth (L) and groove-to-groove-separation (d). By juxtaposing the resonance modes of width-graded and non-graded gratings and defining the adiabaticity condition, we demonstrate the criticality of w and d in achieving adiabatic mode transformation among the grooves. We observe that the resonant wavelength of a graded grating corresponds to the properties of a single groove when the grooves are adiabatically coupled. We show that L plays an important function in defining the span of localized wavelengths. Specifically, we show that multiwavelength resonant modes with intensity enhancement exceeding three orders of magnitude are possible with w < 30 nm and 300 nm < d < 900 nm for a range of fixed values of L. This study presents a novel paradigm of deep-subwavelength adiabatically-coupled width-graded gratings—illustrating its versatility in design, hence its viability for applications ranging from surface enhanced Raman spectroscopy to multispectral imaging.

Polarization-Selective Bidirectional Absorption Based on a Bilayer Plasmonic Metasurface.

We propose an alignment-free and polarization-selective bidirectional absorber composed of a one-dimensional bilayer Au grating array buried in a silicon nitride spacer. The absorptivity of the designed structure is more than 95% (77%) under normal forward (backward) TM-polarized light incidence, and is more than 80% (70%) within a forward (backward) incident angle up to 30°. The great bidirectional absorption performance is illustrated by the resonance coupling of the surface plasmon polaritons (SPPs) resonance, the propagating surface plasmon (PSP) resonance and the localized surface plasmon (LSP) resonance under TM-polarized wave illumination. Moreover, the excitation of the Fano-like resonance mode of the proposed metasurface can produce two significantly different peaks in the absorption spectrum under the oblique TM-polarized incidence, which is beneficial for the plasmon-sensing application. Therefore, the proposed bidirectional metasurface absorber can be a candidate in the application of optical camouflage, thermal radiation, solar cells and optical sensing.

Spatially Broadband Coupled-Surface Plasmon Wave Assisted Transmission Effect in Azo-Dye-Doped Liquid Crystal Cell

Active tuning on a plasmonic structure is discussed in this report. We examined the transient transmission effects of an azo-dye-doped liquid crystal cell on a metallic surface grating. The transition between isotropic and nematic phases in liquid crystal generated micro-domains was shown to induce the dynamic scattering of light from a He-Ne laser, thereby allowing transmission through a non-transparent aluminum film overlaying a dielectric grating. Various grating pitches were tested in terms of transmission effects. The patterned gratings include stripe ones and circular forms. Our results indicate that surface plasmon polariton waves are involved in the transmission process. We also demonstrated how momentum diagrams of gratings and Surface Plasmon Polariton (SPP) modes combined with Mie scattering effects could explain the broadband coupling phenomenon. This noteworthy transition process could be applied to the development of spatially broadband surface plasmon polariton coupling devices.

Optical and thermal radiative properties of topological insulator semiconductor multilayers

Topological insulator semiconductors hold unique electronic transport characteristics that allow them behave like graphene at the surface of the nanoscale thin film. Photonic multilayers consisting of alternating layers of topological insulator and layers of its dielectric spacer can be engineered to demonstrate optical and thermal radiative dispersion attributed to electromagnetic metamaterials. This paper presents case studies explain the relationships between material compositions, geometrical factors, spectral functions, and electronic transport mechanisms to the overall visible to far-infrared radiative properties. It shows how topological insulator multilayers could be useful in thermal-photovoltaic components, optoelectronic devices, and radiative coatings. Two multilayer cases are investigated: Bi2Se3-ZnSe, and Bi2Te3-ZnTe. In each, the photon-electron oscillation functions are determined, and spectral dielectric functions are fitted into a modified form of effective medium theory. The spectral and angular radiative properties of different constituent thickness multilayer slabs, reflectance and transmittance, are obtained. The multilayer thin films exhibit good reflection or absorption of visible or infrared wavelength radiation, depending on the tunable constituent film thicknesses and material configurations. Finite-difference time domain simulations demonstrate that these materials could have a negative index of refraction, which results from plasmon polariton coupling between the conductive surface states. The results of these radiative properties indicate that topological insulator multilayers may find their use in solar thermophotovoltaic absorbers, optical band pass filters and sub-diffraction thin film lenses.