Optical transmission through subwavelength slit apertures in metallic films

Transmission of polarized light through subwavelength slit apertures is studied in visible and near infrared range wavelengths. We examine the roles played by the slit apertures, such as length, depth, period and number of slits. The experiment results, including dispersion curves, demonstrate among other things that the surface plasmon polariton and Fabry-Perot waveguide modes collectively dictate the transmission properties of subwavelength slit arrays and that as they approach each other, not only large gaps are formed but also mode interconversion occurs. These findings are discussed and compared to theoretical predictions.     

Controlling the phase delay of light transmitted through double-layer metallic subwavelength slit arrays

We demonstrate that the phase of light transmitted through double-layer subwavelength metallic slit arrays can be controlled through lateral shift of the two layers. Our samples consist of two aluminum layers, each of which contains an array of subwavelength slits. The two layers are placed in sufficient proximity to allow coupling of the evanescent fields at resonance. By changing the lateral shift between the layers from zero to half the period, the phase of the transmitted electromagnetic field is increased by pi, while the transmitted intensity remains high. Such a controllable phase delay could open new capabilities for nanophotonic devices that cannot be achieved with single-layer structures.     

Enhanced optical transmission through double-layer gold slit arrays

We investigate the relationship between the transmission and the layer distance of double-layer gold slit arrays by using the finite-difference time-domain method.The results show that the transmission properties can be influenced strongly by layer distance.We attribute the two types of resonant modes to surface plasmon resonance and the localised waveguide resonance.We find that the localised waveguide transmission peak redshifts and becomes broader with increasing layer distance D.We also describe and explain the splitting,shift,and degeneration of the surface plasmon resonant transmission peak theoretically.In addition,to clarify the physical mechanism of the transmission behaviours,we analyse the distributions of electric field and total energy for the three transmission peaks with distance D=45 nm for the double-layer system.Light transporting behaviours are mostly concentrated in the region of the slits as well as the interspaces of the two layers,and for different resonant wavelengths the electric field and energy distributions are different.It is expected that the results obtained here will be helpful for designing subwavelength metallic grating devices.     

The extraordinary optical transmission through double-layer gold slit arrays

We present the numerical investigation of the optical transmission through a periodic gold nano-slit structure composed with two non-identical layers, and compare it with that of double-layer structure with two identical layers. The optical enhancement is attributed to the surface Plasmon resonance collaborated with the localized waveguide resonance. It is shown that the transmission behaviors are strongly dependent on the layer separation and lateral displacement between the two single metallic gratings. Especially, it is found that extraordinary transmission exists even if the slit of one layer shifts laterally over that of the other one to the situation that no light can propagate directly when layer separation D = 0. When the slit widths of two layers are not equal, the surface plasmon resonance peak alternately decreases and increases twice, and the localized waveguide resonance peak appears at a longer wavelength as the lateral displacement varies for a non-zero layer separation, which differs from the situation with two identical layers. These transmission properties of the structures show promise for applications in optical devices.     

Enhanced infrared transmission through subwavelength coaxial metallic arrays

We report the observation of enhanced near-infrared transmission through arrays of subwavelength coaxial metallic structures compared with that through comparable diameter hole arrays as a result of localized electromagnetic modes supported by the complex coaxial unit cell. Polarization and angle-dependent transmission measurements clearly demonstrate the coupling between this localized mode and delocalized surface plasmon modes. A generalized, multiple discrete states Fano line shape provides a good fit to the experimental results.     

太赫兹波段下金属狭缝的透射增强特性研究

用太赫兹时域光谱技术研究了具有不同宽度的金属狭缝透射光谱特征. 实验结果显示在实验测量有效光谱范围(02 THz—26 THz)内,当狭缝宽度小到一定程度,在频谱中出现了共振增强,具有明显的带通带阻现象,并在理论上分析了这种共振透射现象的原因. 关键词： 表面等离子体 太赫兹脉冲 时域光谱技术 金属狭缝     

二维亚波长金属小孔阵列的透射光增强效应

对金属薄膜上的二维亚波长小孔阵列的光透射增强现象进行了数值模拟，结果显示不仅实际金属薄膜上的小孔阵列结构具有透射增强效应，理想导体薄膜的相同结构也具有透射增强效应，但没有实际金属薄膜的增强明显-通过分析指出，这种小孔阵列的光透射增强效应是一种复杂的波导耦合效应-与金属薄膜上的表面电流一样，表面等离激元波具有将入射光能量从金属表面向小孔转移的作用，但不是透射增强的本质原因- 关键词： 表面电流 共振耦合 透射增强 表面等离激元     

Role of propagating slit mode in enhanced transmission through slit arrays in a metallic films

The mechanisms responsible for enhanced transmission of electromagnetic wave through an array of subwavelength slits in a metallic film are analyzed. Theoretical model of the enhanced transmission which takes into account the penetration of electromagnetic field into real metal is developed. Semi-analytical model based on Fabry–Perot formula is considered. Comparison of theoretical model, semi-analytical model and results of numerical simulation of Maxwell equations in time-dependent form (FDTD method) for silver with various geometric parameters is presented. The roles of surface plasmons and plasmon localized along slits are studied.     

金属亚波长狭缝中凹槽对其透过特性的影响

利用时域有限差分方法,研究了单个二维金属亚波长狭缝中空气凹槽的结构、位置等参数变化对其透过特性的影响. 整个缝槽结构可以类比为LC振荡环路,凹槽结构变化时,不同程度地改变振荡电路的电感和电容,从而使共振透射峰出现移动. 凹槽位置变化时,电路的驱动源改变,从而改变缝槽结构中的电磁场分布,使得共振透射峰出现分裂. 利用LC共振原理分析了凹槽各个参数变化时共振透射峰的变化情况. 关键词： 表面等离子体 透射率 LC振荡')" href="#">LC振荡     

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.     

微型腔单一亚波长金属狭缝的光波透射

利用时域有限差分法模拟了厚金属层上单一亚波长狭缝内壁刻有一微型腔结构光波传输,结果发现在特定波长发生异常的增强透射。结合透射峰值对应波长近场分布,利用麦克斯韦方程组和波导理论对增强透射进行解释,认为光波在微型腔和狭缝中形成共振腔模起了重要作用:在狭缝内形成纵模,可以形成透射峰;在腔内形成不同的腔模也可以形成透射模。     

Enhanced millimeter-wave transmission through subwavelength hole arrays

We explore, both experimentally and theoretically, the existence in the millimeter-wave range of the phenomenon of extraordinary light transmission through arrays of subwavelength holes. We have measured the transmission spectra of several samples made on aluminum wafers by use of an AB Millimetre quasi-optical vector network analyzer in the wavelength range 4.2-6.5 mm. Clear signals of the existence of resonant light transmission at wavelengths close to the period of the array appear in the spectra.     

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.     

Investigation on the transmission of subwavelength metallic cavity arrays

Numerical investigation of the optical transmission through the one-dimensional subwavelength metallic cavity arrays (SMCA) is presented. Based on the finite-difference time-domain technique, we discuss the influence of the structural parameters on the transmission spectrum. The transmission peaks are attributed to the Fabry-Perot resonance; and the transmission dips are attributed to the surface plasmon resonance. For the SMCA with two cavities in one unit, the redshift of the transmission peak with increasing the distance between the two cavities originates from the depression of the coupling strength. These results obtained here will be helpful to design the plasmonic frequency-selecting device.     

Terahertz transmission properties of thin, subwavelength metallic hole arrays

We present experimental results of the transmission magnitude and phase change of terahertz pulses through thin metallic films patterned with subwavelength hole arrays on silicon wafers. Terahertz time-domain spectroscopy measurements reveal a sharp phase peak centered on the surface plasmon resonance. Correspondingly, and consistent with the Kramers-Kronig relations, the measured transmission magnitude has the shape of the derivative of this peak. In addition, we determine that the aperture shape has a notable effect on the transmission properties of two-dimensional hole arrays.     

Transmission of light through coaxial and non-coaxial double-layer gold slit arrays

We investigate numerically the transmittance of light through gold double-layer structures with periodic coaxial and non-coaxial slits. We attribute the enhanced optical transmission to the surface plasmon resonance collaborating with the localized waveguide resonance. The transmission spectra and the surface electric fields are used to characterize the resonances of both types. For the coaxial system, with the increase of the slit width of the second layer, the resonance peak values of both types increase sharply at first until the two layers have the same slit width and then decrease dramatically; additionally, the center of the localized waveguide resonance peak shifts to shorter wavelength noticeably, but the surface plasmon peak center moves negligibly. As regards the non-coaxial structure, it shows a similar behavior of the localized waveguide resonance peak to that of the coaxial one; however, the surface plasmon resonance peak behaves in a different way. These results may be associated with the surface plasmon coupling modes and the Fabry–Perot cavity modes in the double-layer structure.     

Light transmission through metallic slit with a bar

The transmission characteristics of a metallic slit with a bar are investigated by using the two-dimensional finite difference time-domain method. It is found that the introduction of a bar enriches the transmission spectrum. As the bar locates at the center of the electric (magnetic) field antinodes, the transmission peaks have longer (shorter) wavelengths in comparison with the corresponding resonant peaks of the single slit. It is true for both the fundamental mode and second order mode. The proposed mode in a previous paper [Y. Wang, Y. Wang, Y. Zhang, S. Liu, Opt. Express 17 (2009) 5014] can well explain the above phenomenon. The increase in ability to accumulate charge or decrease in the length of current flow dominates when the bar lies at different positions, which results in a redshift or blueshift of transmission peaks. Moreover, it is also found that the transmission spectrum of the studied structure can be tuned by adjusting the length and width of the bar. It is expected that our results may be utilized to control the electromagnetic wave in subwavelength optics.     

Resonant terahertz transmission in subwavelength metallic hole arrays of sub-skin-depth thickness

We study surface-plasmon-enhanced terahertz transmission through subwavelength metallic hole arrays of sub-skin-depth thickness. Dynamic evolution of surface-plasmon resonance in terms of array thickness is characterized by use of terahertz time-domain spectroscopy in the frequency range 0.1-4.5 THz. A critical thickness of lead array film is observed, above which surface-plasmon coupling of terahertz pulses begins and is enhanced rapidly as the array thickness is increased toward the skin depth. The experimental results indicate that high-efficiency extraordinary terahertz transmission can be achieved at an array thickness of only one third of skin depth.     

Theory of extraordinary optical transmission through subwavelength hole arrays

We present a fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films. Good agreement is obtained with experimental data. An analytical minimal model is also developed, which conclusively shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metal-dielectric interface. Different regimes of tunneling (resonant through a "surface plasmon molecule," or sequential through two isolated surface plasmons) are found depending on the geometrical parameters defining the system.     

Multiple paths to enhance optical transmission through a single subwavelength slit

In this Letter, we explore transmission properties of a single subwavelength slit flanked by a finite array of grooves made on a thick metallic film. We identify three main mechanisms that can enhance optical transmission: groove cavity mode excitation (controlled by the depth of the grooves), in-phase groove reemission (controlled by the period of the groove array), and slit waveguide mode (controlled by the thickness of the metal film). By tuning these geometrical parameters, enhancements of transmission of light by up to 2 orders of magnitude can be achieved when all three mechanisms coincide. Experimental verification of these findings is also shown for structured silver films fabricated by focused-ion-beam milling.