Sapphire surface polariton splitting due to resonance with magnesium oxide film phonon

Surface polariton spectra of magnesium oxide films (of thickness ranging from 10 to 300 nm) prepared by chemical vapor deposition technique on sapphire substrates have been studied. The splitting of the dispersion curve of the sapphire surface polariton appears near 700 cm⁻¹ due to the resonance interaction of the sapphire substrate surface polariton with the film optical phonon. This splitting is proportional to the square root of the film thickness. Optical constants of ultrathin magnesium oxide films have been obtained from surface polariton spectra measurements. For the thinnest film (10 nm) they appear to be close to the bulk crystal values.     

长程表面等离子体的增强效应

研究了双层金属薄膜构型中构型参数对长程表面等离子体的影响,并发现了衰减全反射激发方法下长程表面等离子体的增强效应.以特征矩阵算法为基础,通过数值计算构型的反射谱,研究构型参数的变化对反射谱的影响.发现由于衰减全反射激发方法中耦合器的存在导致的非对称特性,会使双层金属薄膜构型中的长程表面等离子体拥有本征模式特性以外的有趣特性,如长程模式得到增强而另一支受到抑制,从而使能量更为集中在希望被激发的一支.研究结果对非对称激发构型中的长程表面等离子体研究具有启发意义.     

Enhancing surface plasmon polariton propagation by two-layer dielectric-loaded waveguides on silver surface

We report a study of a two-layer dielectric-loaded surface plasmon polariton waveguide (TDLSPPW) which consisted of two dielectric layers (high-index/low-index) on a silver film. The discontinuity of the electric field at the interfaces resulted in a concentrated field in the low-index region. It efficiently reduced the propagation loss of the surface plasmon polariton mode. The mode fields and corresponding complex propagation constants were calculated by a vector finite-difference method. The propagation properties were measured by a modified near-field optical microscope. It is confirmed that the propagation length of the proposed TDLSPPW was about 1.6 times longer than conventional single-layer SPP waveguides. In addition, a 90^° waveguide turn with 3 μm radius showed that the bending loss was smaller than 2 dB.     

Mode characteristics of silver-coated inverted-wedge silica microdisks

The characteristics of whispering gallery modes(WGM) in silver-coated inverted-wedge silica microdisks are theoretically investigated by using finite element method. Dielectric TE mode always exists in silver-coated inverted-wedge resonators; dielectric TM mode tends to couple with SPP modes; only pure interior surface plasmonic polariton(SPP) mode but not pure exterior SPP mode is observed in contrast to the metal-coated cylindrical and toroidal resonators. The dependence of quality factor of different kinds of WGMs on the radius of the resonator and the thickness of the coated silver layer are systematically analyzed. We find that the quality factors of the hybrid WGMs associated with SPP mode can reach 104. The maximum light intensity enhancement in ambient for a hybrid mode consisting of a dielectric TM mode and an exterior SPP mode can be obtained when a silver film of thickness ~40 nm is deposited. The silver-coated inverted-wedge silica resonators may be widely applied in sensing and surface enhanced Raman scattering.     

Quantum Theory of Surface Polaritons in Semi-Infinite Dielectric Systems

The interaction system of a semi-infinite diatomic dielectric and the electromagnetic field propagating parallelly to the surface is studied. The long-wave optical phonon modes of the semi-infinite dielectric are calculated including the electronic polarizability by a quantum-mechanical theory. Retardation effects are neglected. A quantum field theory method of surface polaritons is developed to calculate the operator describing the interaction between a photon and the phonon polarization fields of the semi-infinite crystal, with explicit inclusion of surface effects. The dispersion relations of the surface phonon-polaritons are derived and discussed. The results are in good agreement with those obtained by the conventional, macroscopic dielectric theory of surface polaritons and experimental ATR (attenuated total reflection) spectra. The dispersion cuwes of polariton leaking modes caused by the interaction between bulk TO mode with surface effect and photons are presented in a graphical form. The k_||-dependence of the electric field strength in each polariton branch is calculated and presented also in a graphical form. We also research the spatial dependence of the field strength in each polariton branch. It is found that these properties are influenced and modulated by the surface phonons because of the interaction between photons and the surface phonon modes of the semi-infinite dielectric system. Hence the divergent nature (diffraction effect) of light propagating along the fib& and waveguides is restrained. We present a method how to use the boundary conditions in the quantum theory, which will be discussed in detail.     

Interaction between localized and propagating surface plasmons: Ag fine particles on Al surface

Samples consisting of Ag fine particles 4nm in size placed near to an Al surface were prepared by depositing Ag-SiO₂ composite films by a rf cosputtering method onto vacuum-evaporated Al films. Angle-scan attenuated total reflection (ATR) measurements were performed over a wide wavelength range (λ=350-630nm) covering the resonance region (λ-410nm) of localized surface plasmon (LSP) in the Ag particles. It was found that the existence of Ag fine particles near to the Al surface led to a deformation of the dispersion curve of the surface plasmon polariton (SPP) propagating on the Al surface, in particular, in the LSP resonance region. The interaction between LSP and SPP was found to become much stronger as the distance between the particles and the surface decreases. The theoretical calculations based on the effective medium theory, which gave an effective dielectric function of the Ag-SiO₂ composite film, reproduced the deformation of the dispersion curve of the SPP. The deformation of the dispersion observed experimentally was qualitatively explained by the behavior of the effective dielectric function of the Ag-SiO₂ composite film.     

Resonant Effects of FPL and SPP for Light Transmitting through Subwavelength Metallic Gratings

A new model is proposed to explain the physical mechanism of the extraordinary transmission enhancement in subwavelength metallic grating. The extraordinary transmission enhancement is described by the co-operation of Fabry-Perot-like (FPL) resonance and the surface plasmon polariton (SPP) resonance. The rigorous coupled-wave analysis (RCWA) and the finite difference time domain (FDTD) method are employed to illustrate the model by calculating the transmission and the field distributions in the subwavelength metallic grating, respectively. And the numerical calculations show that transmission enhancement is achieved when the coupling resonance of the incident light, the surface plasmon polariton mode and the Fabry-Perot-Like mode is happened, which are in good agreement with the proposed model.     

Coupling mode-based nanophotonic circuit device

Coupling mode-based nanophotonic U-shaped circuit devices is proposed. Furthermore, the coupling of TM mode between adjacent air channels on metal and propagation of surface plasmon polariton (SPP) waves was demonstrated. Different output intensities were derived by modifying the U-shaped air channel width, and the binary logical value “1” or “0” is obtained after definition of threshold. A spacial coupling mode theory is used to explain the computational simulation results. The theory and the numerical results are well fitted to each other. The structure can be used to obtain all four binary arrays applying to the highly integrated optical circuit. PACS 02.60.Cb; 42.25.Fx; 42.25.Bs     

MIM结构的SPP模式理论与仿真计算研究

为了进一步明确MIM （Metal-insulator-metal）波导结构的SPP （Surface plasmon polariton）模式特性,建立了MIM结构的SPP模式关系、激发系数和反射系数的理论模型。仿真数值计算结果表明：较大的介质厚度的TM基态模式衰减超过了振荡模式衰减,与传统的介质波导明显不同;TE模式表现为失真的介质光波导模式特性,其传播距离要远大于TM₀;MIM结构中腔的Q值随着长度增加而增大,表明了SPP反射受限;腔的品质因数改变与端面关系密切;MIM波导可以在具有更大Q值下确保光波更好地耦合成需要的SPP模式。     

Zenneck-Sommerfeld type surface polaritons on the quartz crystal

The surface polariton (SP) propagation along the quartz crystal surface in the frequency region 1050–1090 cm^-1 was studied. The propagation length of SP rises from 50 to 105 μm when the frequencies goes down to transverse frequency (where SP is actually Zenneck-Sommerfeld type mode) and drastically decreases for lower frequencies.     

Dual mode near-field scanning optical microscopy for near-field imaging of surface plasmon polariton

In this paper, we theoretically and experimentally demonstrate that metal coated apertured probes are efficient near-field probes on surfaces with high reflectivity for the scattering as well as for the collection mode near-field scanning optical microscopy (NSOM). We show that a blunt apertured metal coated tip is very effective in suppressing image dipoles which affect strongly the signals scattered from frequently used sharp metal tips or gold nanoparticle attached probes. By using a simultaneous collection and scattering mode (dual mode) NSOM we measure the near-field images of surface plasmon polariton (SPP) launched from a slit. The collection mode measures propagating SPP along lateral distance in a long scan range with high signal-to-noise ratio, and the scattering mode measures the polarization resolved near-field of SPP. Comparisons of the measured data obtained in the dual mode enable to easily characterize SPP and to separate the measured near-field into the propagating SPP and the directly transmitted light.     

Polarization detection analysis of dual-channel surface plasmon resonance sensing for silicone oils based on the D-shaped fiber with a central hole

We present and numerically characterize a dual channel surface plasmon resonance (SPR) sensor based on a D-shaped fiber with a central hole for silicone oil detections. The proposed design incorporates two metalized channels to facilitate the simultaneous detection of one group of silicone oils, which can consist of two different species. It has been demonstrated that the p-polarized input light can induce two peaks among surface plasmon resonance places, which come from the coupling between the core-guided mode and the fundamental surface plasmon polariton (SPP) modes at the D-shaped surface and around the central hole surface. However, the s-polarized input light can only induce one peak among surface plasmon resonance places, which comes from the coupling between the core-guided mode and the fundamental SPP mode around the central hole surface. The simulation results show that the characteristic responses of two channels independently correspond to the refractive index variations in the silicone oils with which they are in contact. A maximum sensitivity of 3500 nm/RIU (refractive index unit) and 4400 nm/RIU are achieved for channel A and B, respectively. This kind of sensor structure and polarization related demodulation method is promising in the simultaneous multi-analytes sensing applications in the future.     

Effects of shape of terminus on excitation of surface plasmon modes on metal nanowires

The effects of the shape of a nanowire terminus on the excited surface plasmon polariton （SPP） modes are investigated. The conical terminus and terminus cut at a certain angle are studied. For the first time, the quantitative mode decompositions are carried out to derive the full information about excited SPP modes. It is demonstrated that tuning the shape of the terminus provides an effective method to control the composition of excited SPP modes on metal nanowires. It is especially found that some important patterns, such as the pure TM0 mode and the superposition of TM0 and HE＋1 or HE-1 modes, can be generated by some specific shapes of the terminus, whereas there is no way to produce these patterns using flat-end nanowires.     

Graded-index ridge surface plasmon polaritons waveguide

We propose and analyze a long-range dielectric-loaded surface plasmon polariton （SPP） waveguide based on graded-index ridge over server millimeter distances. Then the influence of the dielectric thickness and the ridge refractive index on propagation length and mode width is discussed and simulated with the finite ele- ment raethod. The result shows that the SPP can propagate as long as 3.42 mm, as well as the mode width keeping as 1.64μm, a better one compared with the fixed refractive index. Considering its nanoscale dimension and outstanding performance, the structure is easily realized when connected with electrodes.     

Guiding light at the nanoscale: numerical optimization of ultrasubwavelength metallic wire plasmonic waveguides

We present a comprehensive numerical analysis of the guiding of a photonic signal in the form of a strongly confined asymmetric surface plasmon polariton (SPP) mode along metallic nanowire waveguides. The proposed approach provides extremely high localization of the SPP mode, nanoscale integration density, and a feasible technological platform. The waveguide performance was studied over a broad range of subwavelength cross sections at a telecommunication wavelength. It was optimized using a conventional figure of merit for data transfer along a straight waveguide and an all-inclusive figure of merit has been introduced.     

Effects of a bar on optical transmission through Z-shaped metallic slit arrays

We investigate the effects of a bar on optical transmission through Z-shaped metallic slit arrays by using the finite-difference time domain (FDTD) method. A new hybrid Fabry-Perot (FP) surface plasmon polariton (SPP) mode emerges when changing the geometric parameters of the bar, and this mode can be viewed as a coupling between FP mode and SPP mode. In addition, an obvious dip appears in a featured area when the bar deviates from the central line, and a small displacement of the bar leads to tremendous change of the dip. These behaviors can be attributed to the phase resonance. In short, the structure is very sensitive to the metal bar. Furthermore, it combines photonic device miniaturization with sensitivity, which is useful for making optical switches.     

Thermally driven sensitive surface phonon polariton modes in thin-film SiC

The results of this work show that significant changes to the spectral properties of thermal emission may be accomplished by taking advantage of surface phonon polariton (SPP) modes that are very sensitive to small refractive index changes. Surface phonon polaritons are interface restricted wave modes that do not usually participate in thermal radiative energy exchange. In this work, the possibility of varying the spectral properties by using a thin-film surface active material, layered between dielectrics, is explored. Unlike surface gratings, the multilayered structure discussed in this work couples the surface modes into radiative modes using subtle changes in refractive index. The proposed multilayer effect is studied by first developing the SPP mode dispersion relation to identify the spectral location of the surface modes. The relationship between SPP coupling and refractive index change is then developed. The fluctuation-dissipation theorem and an impedance boundary condition is used to theoretically show how thermal radiation can excite SPP modes. Results are then presented that show how film thickness and substrate properties act to support SPP modes that are particularly sensitive to changes in refractive index and therefore offers opportunities for dramatic changes to the spectral properties.     

Multiple modes of surface plasmonic polaritons in transversely-truncated metal/dielectric superlattices

The surface plasmonic polariton (SPP) of a transversely-truncated metal/dielectric superlattice (SL) structure has been solved with an approximate method. The effect of inter-layer interfaces in the SL is taken into consideration efficiently in comparison with the effective-medium method. The silver/air and silver/SiO₂ SLs with a shorter period are regarded as two specific examples in numerical calculation. A series of separated SPP modes are found and highly localized at the surface, and the highest-frequency mode is the only one also predicated by the effective-medium method. These results obviously show the effect of inter-layer interfaces in the case of short period, whilst the reliability and limitation of the effective-medium method is presented as well. Because the skin depths of the modes are extremely small, the SLs can be used as ideal surface-wave waveguides.     

Diffraction properties of binary graphene sheet arrays

We theoretically and numerically investigate the diffraction properties of surface plasmon polariton(SPP) in binary graphene sheet arrays. The single SPP band splits into two minibands by alternatively arranging the graphene waveguides with two different chemical potentials. Numerical simulations show that SPP beams in the array split into two different paths due to the different diffraction relation.