Comparison of the sensitivity of extraordinary transmittance peaks with the surrounding media for hole and slit arrays

In this paper we compare the sensitivity of the Extraordinary Transmittance (ET) peak position with the surrounding media for two types of metallic structures: arrays of holes and arrays of slits recorded in Au films. Both types of array were fabricated using Interference Lithography (IL) with a period of 700 nm and an Au thickness of 150 nm. The transmission spectra measurements were performed at normal incidence using a spectrophotometer. The results show that an array of slits presents a higher sensitivity for the surrounding media than the array of holes. Theoretical TE and TM simulations of the transmission spectra for the slit arrays agree very well with the experimental results, confirming the better sensitivity of the slit arrays.     

Transmission enhancement by conversion of evanescent waves into propagating waves

The convolution between spatial modes of two different parts of an optical system can convert evanescent waves into propagating waves. This principle is applied to different optical systems for analyzing various effects in transmission enhancements experiments. We discuss here the differences between the present principle which is related to broadening of resonances and the near-field optical microscopy based on a tunneling effect by a tip detector. The present analysis is applied in particular to two systems: a) transmission enhancement in one slit by coupling the transmitted radiation with transversal Fabry–Pérot electromagnetic (EM) modes, and b) transmission enhancement by coupling between a metallic film with arrays of holes and surface plasmons (SP). The present approach gives more information on transmission enhancement phenomena than that obtained by conventional treatments and can also solve certain disagreements between different theories. The differences between the present process of converting evanescent waves into propagating waves, and that related to the new development of getting a super-resolution by an hyperlens are discussed. PACS 41.20.Jb; 73.20.Mf; 42.79.Dj     

Waveguide properties of single subwavelength holes demonstrated with radially and azimuthally polarized light

We investigate the transmission of focused beams through single subwavelength holes in a silver film. We use radially and azimuthally polarized light to excite higher-order waveguide modes as well as to match the radial symmetry of the aperture geometry. Remarkably, the transmission properties can be described by a classical waveguide model even for thicknesses of the silver film as thin as a quarter of a wavelength. PACS  42.25.Bs; 42.25.Ja; 42.79.Gn     

Optimization of photonic crystal $60^{\circ}$ waveguide bends for broadband and slow-light transmission

We present results on broadband transmission through photonic crystal waveguide bends optimized for slow-light modes. Theoretical analysis and topology optimization are complemented by experimental verification of designs fabricated in SOI material. PACS  42.82.Et; 42.79.Gn; 42.70.Qs     

Experimental studies of extraordinary light transmission through periodic arrays of subwavelength square and rectangular holes in metal films

We fabricate a series of periodic arrays of subwavelength square and rectangular air holes on gold films, and measure the transmission spectra of these metallic nanostructures. By changing some geometrical and physical parameters, such as array period, air hole size and shape, and the incident light polarization, we verify that both global surface plasmon resonance and localized waveguide mode resonance are influential on enhancing the transmission of light through nanostructured metal films. These two resonances induce different behaviours of transmission peak shift. The transmission through the rectangular air-hole structures exhibits an obvious polarization effect dependent on the morphology. Numerical simulations are also made by a plane-wave transfer-matrix method and in good consistency with the experimental results.     

Ultrasonic transmission through multiple-sublattice subwavelength holes arrays

The ultrasonic transmission through plates perforated with 2 × 2 or 3 × 3 square array of subwavelength holes per unit cell are studied by numerical simulations. Calculations are obtained by means of a theoretical model under the rigid-solid assumption. It is demonstrated that when the inter-hole distance within the unit cell is reduced, new transmission dips appear resulting from Wood anomalies that have influence on the second and the third order Fabry-Perot peak. When the inter-hole distance within the unit cell is reduced, the transmission spectrum of the multiple-sublattice holes arrays tends to the transmission spectrum of a plate perforated with only one hole in the unit cell.     

Dual resonance in a long-period waveguide grating

We fabricated a specially designed polymer long-periodwaveguide grating to demonstrate the phenomenon of dual resonance arising from light coupling between the core mode and a low-ordercladding mode of the waveguide. By varying the temperature of the grating, we observed the onset and the evolution of the dual-resonancewavelengths. The separation between the dual-resonancewavelengths was varied by ∼110 nm with a temperature variation of ∼10 °C. The experimental results are explained well by the simulation results. PACS 42.79.Dj; 42.79.Gn     

Nanofabrication of a space-variant optical transmission filter

A space-variant optical transmission filter is demonstrated for which a simplified process is used to tailor the spatial response of the filter across the surface of a single wafer. A multilayer stack, of alternating high or low refractive index dielectric materials, was used to produce a narrow transmission notch in the center of a wide stop band. Subsequent patterning and etching of arrays of holes through the volume of the dielectric stack was performed to control the fill factor of the dielectric in the layers. The position of the transmission notch within the reflection spectrum was varied across the device surface by adjusting the hole diameter of the hole arrays. Experimental and numerical simulation were used to confirm the space-variant transmission characteristics of a single-wafer sample with two zones of different hole diameter arrays in the 1550 nm wavelength regime.     

Finite-depth and intrinsic losses in vertically etched two-dimensional photonic crystals

We address the issue of out-of-plane losses in two-dimensional (2D) photonic crystals (PC) etched through a GaAs monomode waveguide clad with standard GaAlAs alloys. We correlate experimental transmission of PCs with two kinds of loss simulation results. The first kind is 2D and introduces an ad hoc imaginary index in the air holes to account for the losses [see (Benisty et al. Appl. Phys. Lett. 76, 532, 2000)]. The second kind is a novel exact three-dimensional calculation inspired by grating-Fourier analysis that provides quantitatively unprecedented agreement with experimental measurements taking into account hole depth as a limiting parameter. We conclude that, in revision to the conclusions of the above reference, the experimental losses are not the intrinsic ones, being larger by a factor of 5 to 10 due to insufficient hole depth. The transition occurs at a critical etch depth shown to be here around 700 nm. We thus predict, for holes deeper than 700 nm, much improved crystals with very low transmission losses and microresonators with ultra-high quality factors.     

周期排列的H-空气槽光学特性研究

利用电子束直写系统和反应离子束刻蚀的方法制作了周期性排列H-形空气槽.样品的参量：金膜的厚度为120 nm,石英基底的厚度0.8 mm（其中有5 nm厚的铬层）,样品是由30×30个单个H-形周期排列形成的,总体尺寸为40×40 μm2.每个H-形之间的周期为1.1 μm,H-形的臂长均为500 nm,空气槽的宽度为120 nm.然后用实验的方法测量了在近红外波段的透过曲线,在近红外波段1.6 μm处的透过率约为16.3%,用传输矩阵的方法对H-形空气槽结构进行了理论模拟,实验与理论模拟结果吻合较好.随后研究了当入射光的偏振方向与H-形结构的长轴之间的夹角分别为0°、30°、45°、60°和90°时透过曲线的变化情况.通过实验和理论表明,表面等离子体在这种特殊的结构中仍然存在,并且在光的增强透过起着决定性的作用.     

Experimental study of transmission enhancement of evanescent waves through silver films assisted by surface plasmon excitation

In this paper, we investigated an essential precursor of superlensing: enhancing the transmission of evanescent waves assisted by excitation of surface plasmon. Using natural roughness as a well characterized grating, the transmission of evanescent waves is studied through silver thin films of increasing thickness. Measurements and calculations are performed in the wavelength range of 514.5 nm to 351.1 nm where the real part of the permittivity of silver is negative. Pronounced peaks due to surface-plasmon excitations are observed in the transmission spectra. We found the transmission of evanescent waves rapidly grows with the film thickness up to about 50 nm, after which it decays as loss becomes significant. As the permittivity of a silver slab approaches -1, we experimentally observed a broadening of surface plasmon bandwidth. Our study indicates a pathway to access the deep subwavelength features by metamaterial superlens. PACS 42.79-e; 42.30.Wb; 78.20.Ci; 78.66.Bz     

Investigation of the guided-mode characteristics of hollow-core photonic band-gap fibre with interstitial holes

This paper investigates the guided-mode characteristics of hollow-core photonic band-gap fibre (HC-PBGF) with interstitial holes fabricated by an improved twice stack-and-draw technique at visible wavelengths. Based on the simulation model with interstitial holes, the influence of glass interstitial apexes on photonic band-gaps is discussed. The existing forms of guided-mode in part band gaps are shown by using the full-vector plane-wave method. In the experiment, the observed transmission spectrum corresponds to the part band gaps obtained by simulation. The fundamental and second-order guided-modes with mixture of yellow and green light are observed through choosing appropriate fibre length and adjusting coupling device. The loss mechanism of guided-modes in HC-PBGF is also discussed.     

金膜上亚波长小孔阵列表面等离激元颜色滤波器偏振性质

金属薄膜上制备的表面等离激元颜色滤波器具有很强的颜色可调性. 在200 nm厚的金膜上, 通过聚焦离子束刻蚀, 制备一系列周期逐渐变化的圆形、方形、矩形亚波长尺寸小孔方阵列表面等离激元颜色滤波器, 改变入射光的偏振方向, 观察其超透射滤波现象. 研究发现: 对于矩形小孔阵列, 其透射光颜色随入射光偏振方向的变化而改变; 而对于圆形、方形的小孔阵列, 其透射光颜色对入射光的偏振方向并不敏感. 分析表明, 对于金膜上刻蚀的小孔结构, 虽然结构的周期性导致的表面等离激元极化子会对透射光的颜色变化产生一定影响, 但是随小孔形状变化的局域表面等离激元共振才是影响透射光颜色的决定性因素. 如果入射光没有在小孔中激发出局域表面等离激元, 则表面等离激元极化子对透射光的影响也会消失. 根据不同形状小孔周期结构透射光颜色随入射光的偏振变化特点, 制备出了包含两种小孔形状的复合周期结构. 随着入射光偏振方向的改变, 该结构会显示出不同的颜色图案. 关键词： 表面等离激元极化子 局域表面等离激元 颜色滤波器 亚波长小孔阵列     

The extraordinary optical transmission characters of the metallic film with rectangular hole arrays

The metallic films perforated with a periodic array of air holes show extraordinary optical transmission properties. In this paper the influence of the incident light's polarization direction and the arrays’ period on the transmission through the rectangular hole arrays immersed in a metallic film is studied by utilizing the finite-difference time-domain method. The results show that the intensities and number of the transmission peaks can be adjusted by changing the incident light's polarization direction, while the intensities can keep constant for some particular frequencies. The transmission peak's wavelength can be easily controlled by altering the lattice period parallel to the electric field for the rectangular holes. These results maybe provide reference for the design of multiple-wavelength resonance devices.     

基于椭圆孔包层和微型双孔纤芯的新型高双折射光子晶体光纤

设计了一种新型高双折射光子晶体光纤,即其包层引入椭圆形空气孔,且以三角晶格方式周期排列,纤芯引入亚波长尺寸(~0.16 μm)的微型双孔结构阵列.采用全矢量有限元法和各向异性完美匹配层边界条件分析了该型光子晶体光纤的双折射特性和色散特性,详细介绍了该光子晶体光纤在不同的椭圆率、椭圆归一化面积、微型双孔孔径、两小孔之间间距的情况下双折射和限制损耗随波长的变化曲线.模拟结果表明,通过同时在包层和纤芯引入非对称性,获得了较高的双折射(~10^-3量级)和极低(~10^-4 dB/km)的限制损耗.提供了一种新的光子晶体光纤设计方法,即通过同时在包层和纤芯引入新结构来同时获得高双折射和低损耗.     

Theory of extraordinary transmission of light through quasiperiodic arrays of subwavelength holes

By using a theoretical formalism able to work in both real and k spaces, the physical origin of the phenomenon of extraordinary transmission of light through quasiperiodic arrays of holes is revealed. Long-range order present in a quasiperiodic array selects the wave vector(s) of the surface electromagnetic mode(s) that allows an efficient transmission of light through subwavelength holes.     

Origin of superenhanced light transmission through two-dimensional subwavelength rectangular hole arrays

Superenhanced light transmission through subwavelength rectangular hole arrays have been reported and some investigations have been made into the physical origin of this phenomenon [K.J. Klein Koerkamp et al., Phys. Rev. Lett. 92, 183901 (2004)]. In our current work, by performing FDTD (finite difference in the time domain) numerical simulations, we demonstrate that mechanism that is different from surface plasmon polaritons set up by the periodicity at the in-plane metal surfaces may account for this superenhanced light transmission. We suggest that for arrays of rectangular holes with small enough width in comparison to the wavelength of the incident light, standing electromagnetic fields can be set up inside the cavity by the surface plasmons on the hole walls with its intensity being substantially enhanced inside the cavity. So resonant cavity-enhanced light transmission is predominant and responsible for its superenhanced light transmission. Rectangular holes behave as Fabry-Pérot resonance cavities except that the frequency of their fundamental modes is restricted by their TM cutoff frequency. However we believe that both localized surface plasmon modes and surface plasmon polaritons set up by the periodicity at the in-plane metal surfaces have their shares in extraordinary optical transmission of rectangular hole arrays especially when the width of the rectangular hole is not small enough and the metal film is not thick enough.     

Wire network behavior in superconducting Nb films with diluted triangular arrays of holes

We present results of transport measurements on superconducting Nb films with diluted triangular arrays (honeycomb and kagomé) of holes. The patterned films have large disk-shaped interstitial regions even when the edge-to-edge separations between nearest neighboring holes are comparable to the coherence length. Changes in the field interval of two consecutive minima in the field dependent resistance R(H) curves are observed. In the low field region, fine structures in the R(H) and T(c)(H) curves are identified in both arrays. Comparison of experimental data with calculation results reveals that these structures observed in honeycomb and kagomé hole arrays resemble those in wire networks with triangular and T(3) symmetries, respectively. The findings suggest that even in these specified periodic hole arrays with very large interstitial regions, the low field fine structures are determined by the connectivity of the nanostructures.     

Transmission of an obliquely incident beam of light through small apertures in a metal film

We recently found that the intensity of the electric near field of a triangular aperture in a metal film is strongly localized at one edge of the aperture for incident light polarized perpendicular to this edge. Previous numerical calculations of the near field of a triangular aperture in a planar metal film, using the field susceptibility technique, yielded a nearly quantitative agreement with the experiments. Using this numerical technique, we have investigated the influence of an obliquely incident plane wave on the near field of small circular and triangular apertures. An interpretation of the numerical results leads to a deeper understanding of the way in which light transmission through the aperture is excited. The data suggest that after excitation of currents in the metal film by the incident light, a scattering of these currents by the aperture generates the near field of the aperture. We found that the excitation of small apertures (size <100 nm) is due to a tangential magnetic field whereas the perpendicular electric field plays no role. The excitation of a small aperture can thus be described exclusively by a magnetic polarizability. We found that for thin metal films an interference of the scattered field with the field transmitted through the metal film changes the near field pattern. PACS 41.20.-q; 42.79.Ag; 68.37.Uv; 78.67.-n     

Rapid dendritic growth and solute trapping within undercooled ternary Ni-5%Cu-5%Mo alloy

In this report, we present experimental results of transmittance through nanohole arrays created onto Au films on glass substrates. 110-nm-thick Au films with arrays of nanoholes were fabricated by using self-assembled polystyrene spheres, of which the diameters were reduced to designed values on site by dry etching, as a template. Transmission spectra of the nanostructured Au films show strong enhancement (more than 45%) in a wide range from 300 nm to 1600 nm, the measurement wavelength range. Besides a peak observed at around 500 nm in all spectra, a wider peak on the longer wavelength side was observed, which shifted to longer wavelength when periodicities of the hole arrays were increased.