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.     

Transmission through metallic array slits curved with perpendicular waveguides

The transmission of normally incident plane wave through an array of subwavelength metallic slits curved with perpendicular waveguides has been explored. Two-dimensional electromagnetic fields inside and near the metal film are simulated by the finite-difference time-domain (FDTD) method. The perpendicular waveguides in the middle of slits affect the modes of slits in two different manners: commonly, the extended length of the waveguides leads to the increase of the resonant wavelength; shifting the waveguides location along the vertical slits, red or blue shift of resonant wavelengths can be achieved, however to some confirmed length of the perpendicular waveguides, there is the only one resonant wavelength. In addition, a new explanation model is proposed in which the resonance is ascribed to three reasons: the Fabry-Perot cavity theory, the surface current flow, and the surface charges. All the calculated results are well explained by our proposed model.     

Waveguide resonance of subwavelength metallic slits

The transmission characteristics of a metallic film with subwavelength periodic slits are investigated by using the two-dimensional finite-difference time-domain method (2D-FDTD). Two models are constructed to show the dependance of the transmission spectrum on the slit structure. A sandwiched structure is used to exhibit the contribution of the metallic wall inside slits to the extraordinary high transmission. And a filled slit structure is employed to reflect the relation between the average refractive index inside the slits and the transmission spectrum of the structure. The transmission characteristics of two structures can be explained well with the waveguide resonance theory.     

Role of surface plasmon polaritons in anomalous transmission of an electromagnetic wave through two arrays with subwavelength slits

The anomalously large transmission of an electromagnetic wave through structures consisting of two periodic arrays of subwavelength slits in films has been investigated. The conditions ensuring zero transmittance of this system have been determined. The role of surface plasmon polaritons in transmission anomalies has been analyzed. An analysis of the systems consisting of three arrays of slits has revealed specific features of the transmittance that are independent of the number of slits. It has been demonstrated that, at a wavelength corresponding to the excitation of a surface plasmon polariton in the gap between two periodic arrays of subwavelength slits, the transmittance is zero (i.e., transmission is suppressed). The investigation has been carried out using numerical simulations with the Fourier modal method.     

Light Transmission of a Thin Metal Screen with an Infinite Array of Periodic Nanoslits

Optics and Spectroscopy - A rational method for calculating the transmission of light by a thin metal screen with an infinite periodic array of subwavelength slits is proposed. The calculation...     

Optical transmission through double-layer metallic subwavelength slit arrays

We present measurements of transmission of infrared radiation through double-layer metallic grating structures. Each metal layer contains an array of subwavelength slits and supports transmission resonance in the absence of the other layer. The two metal layers are fabricated in close proximity to allow coupling of the evanescent field on individual layers. The transmission of the double layer is found to be surprisingly large at particular wavelengths, even when no direct line of sight exists through the structure as a result of the lateral shifts between the two layers. We perform numerical simulations using rigorous coupled wave analysis to explain the strong dependence of the peak transmission on the lateral shift between the metal layers.     

Transmission through array of subwavelength metallic slits curved with a single step or mutli-step

The transmission of normally incident plane wave through an array of subwavelength metallic slits curved with a sin- gle step or mutli-step has been explored theoretically. The transmission spectrum is simulated by using the finite-difference time-domain method. The influences of surface plasmon polaritons make the end of finite long sub-wavelength metallic slit behaves as magnetic-reflecting barrier. The electromagnetic fields in the subwavelength metallic slits are the superpo- sition of standing wave and traveling wave. The standing electromagnetic oscillation behaves like LC oscillating circuit to decide the resonance wavelength. Therefore, the parameters of adding step may change the LC circuit and influence the transmission wavelength. A new explanation model is proposed in which the resonant wavelength is decided by four factors： the changed length for electric field, the changed length for magnetic field, the effective coefficient of capacitance, and the effective coefficient of inductance. The effect of adding step is presented to analyze the interaction of two steps in slit with mutli-step. This explanation model has been proved by the transmission through arrayed subwavelength metallic slits curved with two steps and fractal steps. All calculated results are well explained by our proposed model.     

Enhanced light transmission through a single subwavelength aperture

The optical transmission through a subwavelength aperture in a metal film is strongly enhanced when the incident light is resonant with surface plasmons at the corrugated metal surface surrounding the aperture. Conversely, the aperture acts as a novel probe of the surface plasmons, yielding useful insights for optimizing the transmission enhancement. For the optimal corrugation geometry, a set of concentric circular grooves, three times more light is transmitted through the central subwavelength aperture than directly impinges upon it. This effect is useful in the fabrication of near-field optical devices with extremely high optical throughput.     

Enhanced transmission through periodic arrays of subwavelength holes: the role of localized waveguide resonances

By using the rigid full-vectorial three-dimensional finite-difference time-domain method, we show that the enhanced transmission through a metallic film with a periodic array of subwavelength holes results from two different resonances: (i) localized waveguide resonances where each air hole can be considered as a section of metallic waveguide with both ends open to free space, forming a low-quality-factor resonator, and (ii) well-recognized surface plasmon resonances due to the periodicity. These two different resonances can be characterized from electromagnetic band structures in the structured metal film. In addition, we show that the shape effect in the enhanced transmission through the Au film with subwavelength holes is attributed to the localized waveguide resonance.     

Surface-plasmon-assisted resonant tunneling of light through a periodically corrugated thin metal film

We present experimental results and a numerical model confirming that surface plasmons can resonantly enhance light transmission through a corrugated metal film. A new interpretation in terms of plasmon-assisted light tunneling is given to recent experiments on light penetration through periodic subwavelength holes in a thin metal film. We designed a narrow-band filter suitable for applications in optical communication by optimizing the film and the grating parameters.     

Anomalous transmission of electromagnetic wave through periodic arrays of subwavelength slits arranged on thin metal films

We study the optical properties of periodic structures, each of which consists of arrays of subwavelength slits in thick films that are placed directly against a continuous thin film. We find that the transmittance of the entire system including the thin film is higher than the transmittance of the isolated thin film alone. Our investigations are performed through numerical simulations with the Fourier modal method.     

Enhancement of spatial coherence by surface plasmons

We report on a method to generate a stationary interference pattern from two independent optical sources, each illuminating a single slit in Young's interference experiment. The pattern arises as a result of the action of surface plasmons traveling between subwavelength slits milled in a metal film. The visibility of the interference pattern can be manipulated by tuning the wavelength of one of the optical sources.     

Optical transmission through metal/dielectric multilayer films perforated with periodic subwavelength slits

The transmission of p-polarized plane wave through Ag/SiO₂ multilayer films perforated with periodic subwavelength air slits is investigated by using the finite-difference time-domain (FDTD) method. The results show that the optical transmission property is mediated by the interference among the propagating coupled-SPP modes along the lateral direction inside the SiO₂ layers and the conditions of Fabry-Pérot-like resonance along the longitudinal direction together. When some geometric parameters are suitably initialized, the high transmission peaks can split into more peaks as the functional layer (metal/dielectric/metal sandwich stack) number increases, and the wavelength of the same-order transmission peak exhibits a red shift as the grating period increases.     

Extraordinary Transmission through Metallic Grating with Subwavelength Slits for S-Polarization Illumination

Based on the rigorous coupled-wave analysis algorithm, we have systematically analysed the effect of the geometrical parameters of a dielectric film coated metallic grating with subwavelength slits on extraordinary optical transmission for s-polarization illumination. Results show that the dielectric film which sustains a waveguide electromagnetic mode on the top of the metallic lamellar grating can strongly enhance the transmittance, the positions of the transmission peaks are mainly determined by the period of the metallic grating, the thickness and refractive index of the dielectric film. This structure shows potential applications in excellent polarizers or polarization-isotropic devices at infrared spectral range by appropriately choosing the geometrical parameters.     

单一亚波长孔径增强透射效应的传输线模型

为了研究亚波长孔径的增强透射效应,把传输线理论引入到了单一亚波长金属孔径的增强光学透射效应中。把金属孔径看成传输线,将电流在传输线上的传输和类Fabry-Pérot腔联系起来;把孔径的出射面看成是传输线的输出端,将出射面的电流看成是一种局域的衰逝电流,电流经传输线在传输线的输出端以天线辐射的形式辐射电磁波。解释了孔径透射的近场分布问题、孔径增强透射峰的位置问题和透射峰位置随金属板厚度的红移问题,得到了与其它理论和实验一致的结果,对开发基于增强透射的亚波长元件具有重要的参考价值。     

High-optical-throughput individual nanoscale aperture in a multilayered metallic film

The optical transmission of an individual subwavelength aperture in a multilayered metal film is shown to be enhanced compared with that of a homogeneous metal film. The enhancement effect is due to the light coupling to surface plasmon excitation facilitated by a film periodicity. The sensitivity of the transmission to the dielectric filling of the aperture is also shown. The latter effect can be used to switch and control the transmittance. Devices based on enhanced transmission through nanosized apertures can find applications in high-density optical and magneto-optical data storage, high-resolution microscopy, and photolithography, where nanoscale light sources with high-optical-power throughput are required, as well as in sensor applications.     

Plasmon-assisted two-slit transmission: Young's experiment revisited

We present an experimental and theoretical study of the optical transmission of a thin metal screen perforated by two subwavelength slits, separated by many optical wavelengths. The total intensity of the far-field double-slit pattern is shown to be reduced or enhanced as a function of the wavelength of the incident light beam. This modulation is attributed to an interference phenomenon at each of the slits, instead of at the detector. The interference arises as a consequence of the excitation of surface plasmons propagating from one slit to the other.     

Extraordinary THz transmission through subwavelength semiconductor slits under antiparallel external magnetic fields

We theoretically study the resonant transmission of electromagnetic waves at the THz frequencies through subwavelength semiconductor slits under external static magnetic fields. The dispersion relations of the surface plasmon polaritons (SPPs) inside a subwavelength slit are analytically derived. It is found that the SPPs propagating along one direction and its reverse are symmetric when parallel external magnetic fields are applied, but are asymmetric when antiparallel external magnetic fields are applied. The transmission properties of periodic subwavelength semiconductor slit arrays with the antiparallel magnetic fields in each unit cell are investigated by the mode expansion technique. The two significant transmission characteristics are observed: (i) The resonant peaks are redshifted with increasing external magnetic fields; (ii) The transmissions in the two opposite directions through the slit arrays are asymmetric. The origin of the transmission asymmetry is reasonably explained by the magnetic-field induced asymmetric SPP propagation losses.     

Plasmon mechanism of light transmission through a metal film or a plasma layer

It is shown that a smooth metal film (or a plasma layer) can be made transparent for an electromagnetic wave when two identical subwavelength diffraction gratings are placed on both sides of the film. The electromagnetic wave transmission through the metal film is caused by excitation of evanescent surface waves (plasmons) and their transformation into propagating waves at the gratings. A model which is developed analytically shows that the problem of the wave transmission is physically equivalent to the problem of excitation of two coupled resonators of evanescent waves which are formed at the two film surfaces.     

Optical transmission resonances tuned by external static magnetic field in an n-doped semiconductor grating with subwavelength slits

Transmission behavior of light through a grating consisting of n-doped semiconductor with subwavelength slits under the application of external static magnetic fields is investigated. As dielectric constant of n-doped semiconductor can be substantially altered by applied magnetic field, in the Voigt configuration and for TM-polarized illumination, two transmission resonance peaks associated with localized waveguide modes of slits are significantly shifted toward the lower frequency regime with the increase of the applied magnetic field. These characteristics can be assigned to a reduction of effective plasma frequency of n-doped semiconductor under the applied magnetic field. Our findings may provide possibility for achieving tunable transmission resonance spectrum.