Unidirectional manipulation of surface plasmon polariton by dual-nanocavity in a T-shaped waveguide

A structure of two dimensional T-shaped metal-insulator-metal waveguide with dual-nanocavity is proposed. The two nanocavities located at each side of the slit on the lower metallic surface, act as band rejection filters and are capable of stopping the surface plasmon polaritons (SPPs) at the resonant wavelengths. The Fabry-Perot interferometry theory and the Finite-Difference-Time-Domain method are utilized to investigate the proposed waveguide. The numerical results demonstrate the realization of miniaturized photonic devices for effectively switching the SPPs propagation between the left and right waveguides in one direction.     

High extinction ratio metal-insulator-semiconductor waveguide surface plasmon polariton polarizer

The attenuation characteristics of a multilayer metal clad GaAs-AlGaAs optical waveguide polarizer are theoretically investigated. The dispersion relations and field distribution of the multilayer structures are calculated for different geometrical parameters and material properties. The polarizer studied consists of a single mode finite/infinite metal clad GaAs-AlGaAs waveguide with a dielectric (SiO₂/Si₃N₄) buffer layer inserted between the metal and the waveguide.Conventionally, the TM polarized waves are found to exhibit an absorption peak at a particular buffer thickness (called critical buffer thickness).We shall show that the maximum TM absorption can be improved by a multiple factor up to 7 by choosing a buffer layer thicker than its critical value. This corresponds to an extinction ratio of 1470 dB for a polarizer length of 1 mm. Further, thicker buffers reduce the insertion losses and values as low as 0.1 dB can be obtained. The strong TM absorption in these structures is interpreted as resonant coupling of the guided mode to the lossy surface plasmon polariton supported by the thin metal film. Thicker buffer also reduces the TE losses (insertion losses) and hence increases the extinction ratio (ratio of TM to TE losses).This can be achieved by optimizing the buffer and the metal thicknesses. Another equally efficient polarizer can be designed by positioning a dielectric (same as buffer) layer (superstrate layer) above the metal film and then optimizing the buffer, metal and the superstrate thicknesses. We also show that the proposed polarizer with the superstrate layer is highly stable even when exposed to the extreme atmospheric changes.     

Photonic bandgap structures for long-range surface plasmon polaritons

Propagation of long-range surface plasmon polaritons (LR-SPPs) along periodically thickness-modulated metal stripes embedded in dielectric is studied both theoretically and experimentally for light wavelengths in the telecom range. We demonstrate that symmetric (with respect to the film surface) nm-size thickness variations result in the pronounced band gap effect, and obtain very good agreement between measured and simulated (transmission and reflection) spectra. This effect is exploited to realize a compact wavelength add-drop filter with the bandwidth of 20 nm centered at 1550 nm. The possibilities of achieving a full bandgap (in the surface plane) for LR-SPPs are also discussed.     

Analysis of waveguide structure for surface plasmon polariton interference

This paper describes a multi-reflected mode based on a narrow waveguide to enlarge the interferential area of surface plasmon polaritons (SPPs). A reasonable thickness of metal film is coated under the waveguide, the incident angle and the waveguide thickness are optimized in order to effectively increase interferential area. This is a key point for research into the Goos--H\"anchen shift to optimize the waveguide thickness. Finally, the SPP interferential field is simulated with the finite-difference time-domain (FDTD) technique to prove the optimized results, and indicates that not only is the interferential area enlarged, but the high contrast is also maintained. Furthermore, the mode can fabricate some specific interferential patterns by adding some modulating techniques to the waveguide. So the mode has potential application in the fabrication of sub-wavelength patterns.     

Surface plasmon polaritons mediated by surface modes in a metal-based photonic crystal complex structure

A hybrid metal–organic–photonic crystal (PC), a gold film with a SU8 film on its top followed by a three-dimensional (3D) PC, was designed to exercise additional control upon the photon behaviors. Attenuated total reflection measurements demonstrate that the 3D PC plays a crucial role in the formation of significant optical properties of the metal-based hybrid and the reflectivity minimum in its reflectivity curve is, mostly, a result of synergetic action of the coupling of surface plasmon polaritons to surface modes and additional guided modes yielded in the resonant cavity composed of the gold film and the PC.     

Surface plasmon polaritons on square-lattice arrays of three-fold symmetric nanostructures

The influence of the geometry of three-fold symmetric rotor shaped nanostructures arranged as a two-dimensional square-lattice on the excitation of surface plasmon polaritons (SPPs) is studied numerically. We consider SPP-related extrema of the far-field reflectivity R(α) as a function of the polarization angle α of the incident light. In agreement with recent experimental work, it is observed that these extrema shift away from α=0° and α=90°, where they are found for rotationally invariant nanostructures. The polarization angle corresponding to the most efficient SPP excitation is found to be independent of the shape of the individual nanostructures. We further investigate the influence of the shape and size of the nanostructures and discuss consequences for optical near- and far-field properties.     

Surface plasmon polariton scattering by small ellipsoid particles

Scattering of surface plasmon polaritons (SPP’s) by small ellipsoid particles placed near a dielectric–metal interface is theoretically considered. Using the Green’s function formalism and the dipole approximation, we consider the differential and total scattering cross-sections associated with the SPP-to-SPP scattering as well as with the SPP scattering into waves propagating away from the interface, analyzing the influence of system parameters. As an example, scattering cross-sections of differently shaped gold spheroid particles placed near an air–gold interface are evaluated at the light wavelength of 800 nm. It is shown that the differential and total cross-sections depend strongly upon the particle-to-surface distance, the ratio between the major and minor axes and their orientation with respect to both the interface and the direction of SPP incidence. Implications of the obtained results to the design of SPP micro-optical components are also discussed.     

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.     

Hybrid vertical directional coupling between a long range surface plasmon polariton waveguide and a dielectric waveguide

To investigate light coupling between a long range surface plasmon polariton (LRSPP) waveguide and a conventional integrated optical component, a hybrid vertical directional coupler consisting of a LRSPP waveguides and a dielectric waveguide is investigated and fabricated. In the proposed coupler the dielectric waveguide and LRSPP waveguide are vertically configured for dense integration and strong coupling. The characteristics of the even and odd super-modes of the coupler are also analyzed to design the device. The fabricated device exhibits damped sinusoidal behavior along the coupling length due to propagation loss of the LRSPP waveguide. The maximum power transfer of 86% from the LRSPP waveguide to the dielectric waveguide is achieved at the coupling length of 600 μm. The measured characteristics of the device are in relatively good agreement with a theoretical analysis.     

Two surface plasmon resonances effects for light through the perforated metal film

Light transmission through perforated metal film has been reported and some investigations have been made into the physical origin of this phenomenon. We show that the transmission assisted with surface plasmon (SP) through a perforated metal film results from two different SP resonances effects: surface plasmon resonance due to the periodicity at the left air/metal and right metal/air interfaces and localized cavities resonance inside rectangular holes. The fields intensity is localized separately on the left and right metal-air surfaces for structure-factor-induced surface plasmon mode. And for localized cavities resonance mode, standing electromagnetic fields can also be entirely localized inside the nanohole region. The aspect ratio of the rectangular holes can affect the transmission.     

IR surface plasmon (polariton) phase spectroscopy

New experimental evidence is presented which shows that the reliability and the precision of the determination of the optical constants of the metallic and dielectric surfaces can be improved by using the surface electromagnetic wave absorption spectroscopy and SEW phase spectroscopy simultaneously.     

Mass transport on adsorbate multilayers studied by surface plasmon polariton wave excitation

We excited surface-plasmon polariton waves (SPPW) on Cu(111) by coupling a monochromatic optical beam with a xenon multilayer thickness grating on the metal. The SPPW excitation was detected with an angle-resolved oblique-incidence reflectivity difference technique (OI-RD). The amplitude of the resonance OI-RD signal was a quadratic function of the grating modulation depth. By monitoring the decay of the resonance OI-RD signal as a function of time and temperature, we were able to study the mass transport of xenon that plays a key role in the annealing of a “rough” Xe multilayer crystalline film.     

Surface plasmon polariton coupling between a metal nanowire and a metal helix

The transmittance and steady-state electrical field distribution of a silver nanowire–helix system are investigated using the finite-difference time-domain method. In the nanowire–helix system, surface plasmon polaritons are coupled into the helix or squeezed into the space between the nanowire and helix. The transmittance strongly depends on the topologic shapes of the helix, especially the pitch height. Thus, the nanowire–helix system enables the detection of the displacement associated with helical deformation.     

Magneto-optic phase shift in plasmon propagation along garnet/semiconductor-on-insulator structures

This paper discusses the magneto-optic phase shift in garnet/semiconductor-on-insulator plasmonic waveguides. We consider two structures: (1) Y IG/Si/SiO₂ and (2) Y IG/GaInAsP/AlInAs-oxide. A dispersion relation for the plasmon propagation has been derived and the nonreciprocal phase shift of the fundamental TM mode has been determined at wavelengths of 1.55 μm, 1.5 μm and 1.3 μm.     

Tapered dielectric structure in metal as a wavelength-selective surface plasmon polariton focuser

Symmetric tapered dielectric structures in metal have demonstrated applications such as the nanofocusing of surface plasmon polaritons, as well as the waveguiding of V-channel polaritons. Yet the fabrication of smooth-surfaced tapered structure remains an obstacle to most researchers. We have successfully developed a handy method to fabricate metal-sandwiched tapered nanostructures simply with electron beam lithography. Though these structures are slightly different from conventional symmetric V-shaped structures, systematic simulations show that similar functionality of surface plasmon polariton nanofocusing can still be achieved. When parameters are properly selected, wavelength-selective nanofocusing of surface plasmon polaritons can be obtained.     

Propagation length of surface plasmon polaritons excited by a 1D plasmonic grating

The propagation length of surface plasmon polaritons (SPPs) is investigated experimentally using a 1D metallic grating fabricated on a higher refractive index substrate (Gallium Phosphide, GaP). The experimentally measured value propagation length of the SPP (L_SPP) at 785 nm wavelength is 13.33 ± 0.13 μm, which is close to the theoretical value of the L_SPP on an ideal Au-thin film. The SPP resonance observed in far-field measurements confirms the underlying process and the related effects on the L_SPP measured by scanning near field optical microscope (SNOM). Far-field measurements shows that L_SPP is associated with the full width at half maximum (FWHM) of the SPP resonance which in-turn associated with in-plane directional scattering of the SPP.     

表面等离子体激元纳米激光器技术及应用研究进展

传统半导体激光器由于采用光学系统反馈而存在衍射极限,其腔长至少是其发射波长的一半,因此难以实现微小化。基于表面等离子体激元的纳米激光器可以实现深亚波长乃至纳米尺度的激光发射,而且现代微纳加工技术的逐步成熟,也为亚波长乃至纳米量级激光器的研制提供了成熟的技术条件。本文重点综述了国际上已成功实验验证的基于表面等离子体激元的纳米激光器的最新研究进展,综述了表面等离子体激元的基本原理,给出了若干种表面等离子体激元纳米激光器的结构和特点,指出该类激光器现存问题主要表现在激元损耗高及由此引起的制备工艺和电泵浦涉及的技术难题。文中最后展望了纳米激光器的应用和研究前景。     

Manipulating surface plasmon waves by transformation optics:Design examples of a beam squeezer,bend,and omnidirectional absorber

We present several design examples of how to apply transformation optics and curved space under coordinate transformation to manipulating the surface plasmon waves in a controlled manner.We demonstrate in detail the design procedure of the plasmonic wave squeezer,in-plane bend and omnidirectional absorber.We show that the approximation method of modifying only the dielectric material of a dielectric-metal surface of the plasmonic device could lead to acceptable performance,which facilitates the fabrication of the device.The functionality of the proposed plasmonic device is verified using three-dimensional full-wave electromagnetic simulations.Aiming at practical realization,we also show the design of a plasmonic in-plane bend and omnidirectional absorber by an alternative transformation scheme,which results in a simple device structure with a tapered isotropic dielectric cladding layer on the top of the metal surface that can be fabricated with existing nanotechnology.     

降低表面等离子激元寄生吸收损失的途径研究

从纳米Ag颗粒表面等离子激元光学及表面高能电场特性两方面入手,较为系统地研究了周围介质的导电特性对表面等离子激元的影响.通过对复合薄膜紫外-可见-近红外光谱及表面增强拉曼散射光谱的分析,指出绝缘性的Al₂O₃介质薄膜能够起到良好的表面电场定域效果,且不会引入附加的光吸收损失;而导电性的ITO薄膜则会引入表面价电子的溢出损失,加速了表面电场的衰逝,同时引起长波方向上显著的光吸收损失.研究还表明致密的Al₂O₃介质薄膜能够起到良好的屏蔽作用,且纳米Ag颗粒表面等离子激元特性仅受最近邻材料特性的影响.研究结果为在硅基薄膜太阳电池中实现对纳米Ag颗粒的阻挡、寄生光吸收损失的降低以及表面高能电场的利用,提供了一条有效的解决途径.     

The surface plasmon polariton dispersion relations in a nonlinear-metal-nonlinear dielectric structure of arbitrary nonlinearity

The analytic surface plasmon polaritons(SPPs) dispersion relation is studied in a system consisting of a thin metallic film bounded by two sides media of nonlinear dielectric of arbitrary nonlinearity is studied by applying a generalised first integral approach.We consider both asymmetric and symmetric structures.Especially,in the symmetric system,two possible modes can exist:the odd mode and the even mode.The dispersion relations of the two modes are obtained.Due to the nonlinear dielectric,the magnitude of the electric field at the interface appears and alters the dispersion relations.The changes in SPPs dispersion relations depending on film thicknesses and nonlinearity are studied.