Narrow Results

Surface plasmon and evanescent wave sensors are attractive for chemical and biological sensing applications. They can work in aqueous media and when used in conjunction with the appropriate surface chemistry they can have high specificity and high sensitivity. However, most surface plasmon sensors are relatively complex as they are based on the use of attenuated total internal reflection to excite surface plasmon resonance in a thin gold film and require light to be incident at the appropriate angle and polarization. Other surface plasmon and optical affinity sensors have used the evanescent waves in planar waveguides to interact with the environment. These devices are sensitive but, have strict optical coupling requirements and are difficult to fabricate. In optical fiber evanescent wave sensors the interaction with the surrounding environment is usually obtained by tapering an optical fiber, which significantly weakens the structure, or by just utilizing the end of the optical fiber. In this paper, in-line optical fiber structures are presented that are mechanically robust, and provide a large interaction length for high sensitivity. They are compatible with standard chemistries for optical affinity sensing of biological compounds.

This study presents the design and analysis of a novel surface plasmon resonance sensor based on D-type photonic crystal fiber. The analyte channel in the sensor comprises an open ring with a thin gold film deposited on the channel, inducing the surface plasmon resonance effect to enhance the resonance effect and improve the spectral sensitivity of the sensor. The proposed design eliminates the need to introduce liquid into the analyte channel. Upon inserting the sensor into the vessel, the analyte automatically flows into the liquid channel. Simulations illustrate the capability of the proposed sensor to detect low refractive indices spanning from $1.15$ to $1.26$, exhibiting a remarkable spectral sensitivity of up to 9000nm/RIU. The surface plasmon resonance sensor presented in this study emerges as a competitive candidate for applications requiring low refractive index detection. It is all because of its promising sensing results, wide refractive index sensing range, and simple, compact fiber design.

We consider the quantum field theory approach to graphene. The model consists of the photon field in the bulk, i.e., in (3+1) dimensions, and a spinor field on a brane, i.e., in (2+1) dimensions. Integrating out the spinor field, an effective action appears, from which one has modified Maxwell equations accounting for the response of graphene. Within this model, one has the known one-loop polarization tensor allowing to investigate specific questions. Here, we consider the surface plasmons which may travel along graphene, with finite chemical potential or finite temperature.

Using the recently developed polarization tensor in $(2+1)$ dimensions for the electronic excitations of graphene, we investigate the influence of temperature on the surface plasmons on graphene. We consider nonzero mass gap, but zero chemical potential. Plasmons may exist for both polarizations, transverse electric (TE) and transverse magnetic (TM), of the electromagnetic field. For TE, the momentum region, where the dispersion function is real, appears bounded from below, whereas for TM it is bounded from above. We discuss the similarities of these features with those found previously in the case with nonzero chemical potential, but zero temperature.

Surface plasmons supported by various metallic nanostructures have given rise to several significant breakthroughs in the field of integrated photonic devices due to its ability to effectively confine and enhance optical field in subwavelength volume. In particular, the demand to actively control optical responses of plasmonic systems becomes urgent for the miniaturization of signal processing devices, surface-enhanced Raman scattering (SERS) substrates and biochemical sensors. In this paper, we systematically investigate the plasmon modes as well as their interaction in a layered nanostructure composed of a periodically-arranged radiative nanoring and a metallic ground plane, as well as a thin insulating spacer. A tunable transparent peak on the background of the broadband plasmon resonance emerges in the reflection spectrum as changing the periodicity of nanoparticle array, a plasmonic analogue of electromagnetically induced transparency (EIT). Owing to the structural symmetry of the rings, we demonstrate a new scheme of controlling the interference between localized and delocalized plasmons by means of incident polarization and believe that the proposed metasurface may find applications in optical switching if the polarization-controlled components are introduced.

The entanglement of two distant quantum dots coupled to metallic waveguide has been investigated theoretically in the presence of the flip-flop interaction with the analytic solutions of eigenvalue equations of the system. High entanglement of two quantum dots could be achieved by adjusting the direct-coupling strength of two quantum dots, the coupling strength of quantum dots with surface plasmon along metallic waveguide, the group velocity of surface plasmon and detuning. The discussed system with the flip-flop interaction provides us with a rich way to realize the quantum device for quantum information processing, such as quantum communication and quantum computation.

Two-dimensional material-based photodetectors (PDs) show great potential owing to unique optoelectronic characteristics and attract much attention in research. However, poor absorption of two-dimensional material remains a vital restriction. Responsivity improvement by applying Au nanoparticles (NPs) through surface plasmon (SP) is studied both in theory and simulation. The effect of size and NPs distribution density is analyzed concerning absorption promotion and fabrication feasibility. Both absorption spectrum and inner electric field are studied. A novel face-to-face PD is proposed that performs better in visible range. The results can be helpful in two-dimensional material PD design and fabrication where high responsivity is required.

The application of the subwavelength planar structure to control the propagation direction of surface plasmon polaritons (SPPs) has attracted many interests in recent years. However, the traditional unidirectional transmission devices of SPPs are limited by the low extinction ratio, narrow working band and the incapability of controlling the transmission directions. In this study, a novel SPPs unidirectional transmission device based on metallic aperture arrays of the right triangle (RT) is proposed and demonstrated by numerical simulations (finite-difference time-domain method). The maximum extinction ratio of the unidirectional transmission device can reach upto 33 dB under the irradiation of linearly polarized light, and the device possesses a wide operating band ($\sim 300$ nm) while the extinction ratio is greater than 10 dB. Moreover, the transmission direction of SPPs can be flexibly controlled by tuning the polarization of the incident beam. This broadband, polarization-mediated and high extinction ratio unidirectional transmission device shows great potential in the compact plasmonic devices.

Simple dimensional analysis of typical nonlinear optical phenomena in metal nanoparticles indicates that qualitatively new effects may be expected in nonlinear optics of surface plasmon polaritons. It appears that some of these effects are similar to well-known effects of quantum gravitational theory.

A mode separation approach in the nanoring resonator by a cascaded slot cavity is proposed and numerically investigated using the finite-difference time-domain (FDTD) method. With the cascaded slot cavity, the specified modes in the nanoring can be separated to realize a wide free spectral range (FSR) or single channel filtering, which provides a free degree to the plasmonic filters design. Simulation results also demonstrate that the full-width at half-maximum (FWHM) of the single channel filter obtained from the cascaded slot cavity can be effectively reduced to meet various requirements.

The transmission characteristics and electromagnetic responses of orthogonal-coupled slot cavities system are investigated with finite difference time domain (FDTD) method. Results show the electromagnetically induced transparency (EIT)-like transmission can be realized in the proposed structure due to the destructive interference between the horizontal cavity (bright mode) and the vertical cavity (dark mode). Moreover, trapped resonance modes in the horizontal cavity can be selective whether to be induced in vertical cavity or not depending on their relative position. Consequently, EIT-like transmission can be obtained in visible and near-infrared range, simultaneously or individually. The corresponding physical mechanisms are discussed in terms of counter profiles of fields |Hz| and coupled mode theory. Influences of the geometrical parameters on EIT-like transmission are also investigated to generate transparency windows with different shape.

In this work, Ag nanoparticles were deposited on quartz glass substrates by magnetron sputtering method, and the morphology was characterized by SEM. Ag nanoparticle surface plasmon resonance characteristics were observed by transmittance measurement. The experimental results demonstrated an increase in particle size that was correlated to an increase in sputtering time and a plasmon resonance absorption peak redshift. This phenomenon was partially explained by Mie scattering model. The differences between our theoretical analysis and experimental results show that both the shape of and the spacing between nanoparticles are key parameters affecting plasmon resonance peak location.

Metal nanoparticles have the ability to localize and strongly enhance the incident electromagnetic field due to the surface plasmon polariton. The coupling between AuNPs and ZnO thin films affects their emission properties. In this study, we prepared the ZnO/Al₂O₃/AuNPs multilayer films, and investigated the effect of spacer layer on enhancement and quenching of photoluminescence by surface plasmon. The emission intensities of the thin films vary when Al₂O₃ space layer with different thickness was embedded in the ZnO/Au films, consistent with theoretical predictions. The photoluminescence modulation is also made via controlling the polarization of the excitation source. The photoluminescence anisotropy of these systems shows that enhanced photoluminescence can be achieved through coupling of the emission from ZnO with the surface plasmon resonance of AuNPs.

We investigate theoretically and numerically the tunable plasmon-induced transparency (PIT) phenomenon in graphene-sheet system in infrared range. We show that when surface plasmon polaritons (SPPs) propagate along a monolayer graphene sheet with two detuned side-coupled resonators, the PIT-like transmission spectra of SPPs appear. Thanks to the tunable permittivity of graphene by bias voltages, the resonant wavelength of side-coupled resonators can be changed. So the transmission spectra can be tuned dynamically and the tunable PIT phenomenon is achieved. Numerical simulation by finite element method is conducted to verify our design.

A cylindrical graphene plasmon waveguide (CGPW) which consists of two rolled graphene ribbons, a dielectric core and a dielectric interlayer is proposed. An analytical model for the single-mode condition and cutoff frequency of high-order graphene surface plasmon (GSP) modes is presented and verified by finite element method (FEM) simulations. Single-mode operation region of CGPW is identified in the frequency–radius space. By varying the separation between two graphene sheets and the Fermi level of graphene, a large tunability of the mode behavior is also demonstrated. The proposed structure may provide a new freedom to manipulate GSPs, and would lead to novel applications in optics.

We propose a metal–insulator–metal (MIM) structure which consists of a $\pi$-shaped resonator and a surface plasmon polariton (SPP) waveguide. The finite element method (FEM) is employed in the simulation. The results show that this structure forms an optical pressure sensor. The transmission spectra have a redshift with increasing pressure, and the relation between the wavelength shift and the pressure is linear. The nanoscale pressure sensor shows a high sensitivity and may have potential applications in biological and biomedical engineering.

We investigate numerically the optical properties through gold split-ring resonator (SRR) with inner cross dimer array by using the finite difference time domain (FDTD) method. The dependence of the geometrical parameters on the optical properties of SRR with inner cross dimer array is studied. The study covers the change of transmission spectra with the metallic cross arm length, width of air slits, width of SRRs and environmental dielectric constants. The spatial distributions of the electric and magnetic fields are also discussed to further understand more basic physical mechanisms behind some dip and peak.

We theoretically report a strong light–matter interaction in a sandwich structure composed of hybridized inorganic–organic perovskite nanowires, silica (SiO₂) films and a silver (Ag) film. Surface plasmon effectively enhances the strong exciton–photon coupling strength of perovskite nanowires, which depends on reduction of effective mode volume and local field enhancement. By calculation, we find that the thicknesses of SiO₂ and Ag films can affect the coupling strength. With the suitable thickness of SiO₂ (5 nm) and Ag (30 nm) films, Rabi splitting can reach 319 meV, while without an Ag film Rabi splitting is only 270 meV. Furthermore, Rabi splitting shows a negative correlation with SiO₂ film thickness within a limited range. Still, it has a nonlinear relation with Ag film thickness because the imaginary part of the effective index for the hybridized mode shows a nonlinear relation with Ag film thickness. Our structure provides suitable parameters for the experiment and has potential application in nano-lasers.

This paper investigates the enhanced photoluminescence of CsPbX₃ by the localized surface plasmon (LSP) of Ag nanoparticles. The Ag nanoparticles with different sizes were obtained by annealing Ag thin films at different temperatures. Then the Ag/PMMA/perovskite structure was fabricated to realize the exciton-LSP coupling effect, and enhancement was found for wavelength-tunable CsPbX₃ films. When the Ag film is heated to 200^∘C, the maximum enhancement factor of LSP is 6.03. The LSP coupling effect induces the slight blue shift of the fluorescence emission center which is caused by the limitation of electron free trajectories under the LSP resonance frequency of Ag nanoparticles. As the gap between nanoparticles decreases, the absorption cross-section increases, and the scattering rate of electrons on the surface of metal nanoparticles greatly exceeds the internal scattering rate, causing the LSP resonance frequency to shift to the blue region, resulting in a blue shift of the PL spectrum.

Low efficiency of Terahertz (THz) radiation and radiation power have limited the development of THz Science and Technology. Thus, with the aims of achieving greater photoconductive current and improving radiation characteristics of THz photoconductive antenna (PCA), this study utilized Extraordinary Optical Transmission (EOT) of light passing through various subwavelength metal structures to control and restrain the light wave in subwavelength scale. Furthermore, by grooving the grating electrode structure, the influence of metal grating’s EOT on the transmission field of PCA were investigated and analyzed. Simulation results show that the effect of local electric field enhancement is significant. When the incident power is 0.1W, the peak value of the local electric field reaches $7.04\times 10^7$V/m. In addition, comparing to the grating electrode with no groove structure in which the field intensity was less than $4.28\times 10^6$V/m, the local electric field increased by 16.4 times, respectively. Correspondingly, the photocurrent intensity of the improved photoconductive plasmonic structure is increased by 72.3 times. In conclusion, the improved plasma photoconductive structure was shown to obviously enhance the transmission field strength of semiconductor materials and the current of the PCA, and accordingly, to improve the THz radiation capability.