Nanotube based hybrid plasmon polariton waveguide for propagation loss reduction and enhanced field confinement inside the gap region at the subwavelength scale

We present a comprehensive numerical investigation on the guiding properties of a nanotube based hybrid plasmonic waveguide, which comprises a high-index dielectric nanotube placed above a metallic substrate. It is shown that the incorporation of the nanotube offers additional freedom for tuning the optical performance of the hybrid plasmonic structure when compared to the traditional nanowire based hybrid counterparts, which enables further reduction of the propagation loss and enhanced field confinement inside the gap region, while simultaneously maintaining a subwavelength mode size at appropriate geometries. Systematic geometric parameters mapping considering the size of the nanotube and the dimension of the gap reveals that the tradeoff between the confinement and loss could be further balanced through optimizing key physical parameters. These investigations potentially lay the groundwork for the further applications of nanotube based hybrid structures.     

Photonic bandgap plasmonic waveguides

A type of a plasmonic waveguide has been proposed featuring an "open" design that is easy to manufacture, simple to excite and offers convenient access to a plasmonic mode. Optical properties of photonic bandgap (PBG) plasmonic waveguides are investigated experimentally by leakage radiation microscopy and numerically using the finite element method confirming photonic bandgap guidance in a broad spectral range. Propagation and localization characteristics of a PBG plasmonic waveguide have been discussed as a function of the wavelength of operation, waveguide core size, and the number of ridges in the periodic reflector for fundamental and higher order plasmonic modes of the waveguide.     

The optical transmission characteristics through coupled metallic nanotube arrays

The plasmonic properties in coupled metallic nanotube arrays are investigated theoretically by the finite-difference time-domain (FDTD) method. We calculate the transmission spectra and the electric field distributions. We show that there is a photonic band gap over a wide optical wavelength range and the transmission spectrum depends strongly on the inner radii, the separation distance and the number of the nanotubes. Based on the localized nature of the field distribution, we also clearly show that the presence of local plasmon resonant modes that originate from multipolar plasmon polaritons and a big magnitude of opposing surface charges build up in the gap between adjacent nanotubes.     

Plasmonic Zener tunneling in metal-dielectric waveguide arrays

We elucidate in this Letter plasmonic Zener tunneling (PZT) in metal-dielectric waveguide arrays (MDWAs) by using numerical simulations and theoretical analyses. PZT in MDWAs occurs at the waveguide entrance and wherever the beam completes Bloch oscillations, because the bandgap between the first and second bands is minimal at the center of the first Brillouin zone. This feature significantly differs from that of optical Zener tunneling in dielectric waveguide arrays. The dependence of the simulated tunneling rate on the gradient of the relative permittivity of the dielectric layers correlates with the tunneling theory, thus confirming the occurrence of PZT in MDWAs.     

Terahertz demonstrations of effectively two-dimensional photonic bandgap structures

We demonstrate effectively two-dimensional (2D) terahertz (THz) photonic bandgap (PBG) structures for transverse electromagnetic (TEM) mode propagation within metal parallel plate waveguides (PPWG). The 2D-PBG structures consisting of square arrays of dielectric cylinders were characterized by THz time-domain spectroscopy (THz-TDS). THz photonic bandgaps were observed, as determined by the 160 mum lattice constant, the 65 mum diameter, and the dielectric constant of the cylinders. The experimental measurements were fitted with excellent agreement to 2D theory, confirming that for TEM mode propagation, effectively 2D propagation experiments can be achieved within the bounded space of the PPWG.     

Effects of dielectric core and embedding medium on plasmonic coupling of gold nanoshell arrays

The effects of the dielectric core and the dielectric embedding medium separately on transmission spectra and plasmon resonance properties of gold nanoshell arrays were investigated by using the finite-difference time-domain (FDTD) theory. It is found that when the hollow nanoshell arrays are placed in air, the wide photonic band gap becomes narrower as the core dielectric constant increases. On the contrary, when the nanoshell arrays with dielectric core are placed in the dielectric medium, the photonic band gap becomes wider. Furthermore, increasing core or medium dielectric constant leads to a redshift of the transmission spectra due to the polarization of the dielectric. Based on the electric field distributions, we also clearly show that the plasmon properties of the nanoshell arrays are strongly influenced by the presence of the dielectric.     

二维光子晶体T型波导分支器数值模拟研究

采用平面波展开法和时域有限差分法,对GaAs二维正方晶格光子晶体的色散特性和带隙结构进行了数值模拟研究,并对GaAs二维光子晶体线缺陷构成的T型波导分支器的微波传输特性进行了模拟和优化。数值模拟结果表明,光子晶体填充比对带隙结构有显著地影响。通过在拐角处插入额外的电介质棒对GaAs二维正方光子晶体T型波导分支器进行优化,数值模拟的结果表明,优化的GaAs二维正方光子晶体T型波导分支器在一阶带隙范围内透射系数将提高到0.96以上。     

Compact and broadband waveguide taper based on partial bandgap photonic crystals

Partial bandgap characteristics of parallelogram lattice photonic crystals are proposed to suppress the radiation modes in a compact dielectric waveguide taper so as to obtain high transmittance in a large wavelength range. Band structure of the photonic crystals shows that there exists a partial bandgap, The photonie crystals with partial bandgap are then used as the cladding of a waveguide taper to reduce the radiation loss efficiently. In comparison with the conventional dielectric taper and the complete bandgap photonic crystal taper, the partial bandgap photonic crystal taper has a high transmittance of above 85% with a wide band of 170 nm.     

Optical modes in a plasmonic waveguide with electrically anisotropic metamaterial

We study the optical modes in a plasmonic waveguide with electrically anisotropic metamaterial and dielectric, including symmetric (anti-symmetric) photonic mode and symmetric (anti-symmetric) plasmonic mode. The dispersion curves for these modes are derived, and a graphical method is used to calculate the solution of symmetric photonic mode and anti-symmetric plasmonic mode. By simulation results the conditions of the existence for these modes are deduced in each case.     

Larger complete photonic bandgaps in two-dimensional photonic crystal heterostructure

A two-dimensional photonic crystal heterostructure with a large complete photonic bandgap is presented. It consists of two photonic crystals, whose dielectric configurations are reverse, with triangular lattice of circular columns. The structure retains the ease of fabrication while increasing the maximum quality factor of the gap 2–3 times after optimization. Photonic bandgap properties are calculated using a plane-wave method and the transmission spectra are obtained.     

Plasmonics – the missing link between nanoelectronics and microphotonics

Plasmonics is an exciting new device technology that has recently emerged. It exploits the unique optical properties of metallic nanostructures to enable routing and manipulation of light at the nanoscale. A tremendous synergy can be attained by integrating plasmonic, electronic, and conventional dielectric photonic devices on the same chip and taking advantage of the strengths of each technology. We will provide a perspective on future directions and possibilities for integrating plasmonic devices on a Si chip. PACS 42.82.-m; 42.82.Ds     

FDTD analysis of 12-fold photonic quasi-crystal central pattern localized states

The TM bandgap features of the 2D 12-fold quasi-crystal are examined based on the width of the dielectric strip and pattern central symmetry location within the quasi-crystal. Results indicate that the bandgap properties observed for a particular fill factor is independent of the rotational symmetry center when the dielectric strip is wide, and still observable when the strip width is considerably reduced, confirming the general belief that the bandgap generating properties of the quasi-crystal are a local dielectric effect for the lower frequency band. Thin strips are shown to posses defect states in the bandgap region of the thicker equivalent strips, defect states analogous to intentionally introduced defect states of translational symmetric photonic crystals. We explore the mode profiles of the defect state when the defect is coincidental with the rotational symmetry central pivot point of the quasi-crystal pattern. In addition we show that the rotational center “defect” may be used to enhance the optical guidance of light around a 90° bend in a waveguide implanted in the quasi-crystal.     

光子晶体的制备方法及其应用

光子晶体是一种介电常数不同的、其空间呈周期分布的新型光学材料。由于光子晶体具有光子带隙、光子局域和控制光子态密度等特性,所以它具有广阔的应用前景。简述了光子晶体的主要特征,重点介绍了其制备方法、进展以及实际的和潜在的应用。     

Boxlike filter response based on complementary photonic bandgaps in two-dimensional microresonator arrays

We propose that a boxlike filter response can be obtained by utilizing complementary photonic bandgap properties of the column and row configurations in two-dimensional microresonator arrays. The filters are fabricated using deep-UV lithography in silicon-on-insulator technology. The observed sidelobes reduction is approximately 10 dB, and the usable bandwidth can be as high as 500-750 GHz.     

Mode density inside an omnidirectional mirror is heavily directional but not small

We show that ominidirectional reflection is not a sufficient signature of a photonic bandgap. Although dramatic angular redistribution takes place, the mode density of the electromagnetic field is hardly altered within the ominidirectional reflection range but rather has characteristics typical of a waveguide. The strikingly large polarization anisotropy is due to the huge dielectric contrast but not to a photonic bandgap.     

Effect of Dielectric Constant Contrast and Filling Factor to Photonic Bandgap

The effect of dielectric constant contrast and the filling factor to the photonic bandgap in a 2-D square lattice photonic crystal is discussed. The location, width and number of photonic bandgap can be modulated.     

Photonic bandgap properties of 8-fold symmetric photonic quasicrystals

The bandgap properties of 2D 8-fold symmetric photonic quasicrystals (PQCs) composed of a set of rods are numerically investigated for various fill factors, dielectric constants and propagation angles using the finite difference time domain (FDTD) method. Some interesting properties are found besides the known results: (i) the central frequency of the bandgap shifts to low frequency as r/a increases; (ii) an optimum fill factor to obtain the largest gap width exists, which decreases with increasing dielectric constant; (iii) compared with the behavior for a given fill factor, the variation of bandgap width for the optimum fill factor increases much more significantly with the dielectric constant. Selection guidelines for 8-fold symmetric PQC designs are provided for optimum fill factors and variation of the relative bandgap width at different dielectric constants.     

Understanding plasmon resonances of metal-coated colloidal crystal monolayers

Metal films deposited over two-dimensional colloidal crystals (MFoCC) constitute a low-cost periodic structure with interesting photonic and plasmonic properties. It has previously been shown that this structure exhibits a behaviour similar to the well-known Extraordinary Optical Transmission (EOT) of metallic hole arrays in planar films. Here, we explore the transmission characteristics of AgFoCC by systematic comparison with that of the bare CC. Furthermore with additional reflectivity measurements we evaluate the AgFoCC overall plasmonic response, which, notably, exhibits a strong plasmon absorption band at wavelengths larger than those of the transmitted maximum. By corroborating these results with finite-difference time-domain electromagnetic simulations, we identify a hybrid metal-dielectric propagative mode in the transmission mechanism. On the contrary a strongly localized mode is responsible for the maximum light absorption by this structure. These results shed new light on the current understanding of this highly promising plasmonic structure, being useful for the design of surface-enhanced Raman scattering and enhanced fluorescence substrates.     

Ultrafast photonic crystal optical switching

Photonic crystal, a novel and artificial photonic material with periodic dielectric distribution, possesses photonic bandgap and can control the propagation states of photons. Photonic crystal has been considered to be a promising candidate for the future integrated photonic devices. The properties and the fabrication method of photonic crystal are expounded. The progresses of the study of ultrafast photonic crystal optical switching are discussed in detail.     

异质镜像光子晶体的光子带隙研究

对异质镜像结构光子晶体(ABCCBA)^N进行了研究。首先,利用一维介电体系中处理光传播的方法--传输矩阵法,详细推导了异质镜像光子晶体透射率的计算公式;然后,采用Matlab软件编程仿真并分析了光子带隙形成与镜像周期数目、光子带隙数目与光子晶体薄层厚度、光子带隙位置与入射角大小等的关系。结果表明:光子带隙的形成及变化主要受光子晶体薄层厚度及入射角大小变化的影响。通过改变影响光子晶体光子带隙的参数,可得到不同频段的光子带隙,用来制作高质量反射镜、滤波器和发光二极管等。