Metallic Slit Arrays Research Articles

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

The transmission of normally incident plane wave through an array of subwavelength metallic slits curved with a single 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 superposition 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.

Analysis and design of concave lens with metallic slit array for terahertz wave band

This paper presents a three-dimensional concave lens constructed from a metallic slit array. The effective refractive index is estimated to be \(0<n<1\). The actual lens requires spacers in the slits. A lens using a low loss dielectric material for the terahertz frequency band is designed. The fast wave effect is enhanced in order to mitigate the slow wave effect of the dielectric material. Full wave analysis results are obtained by ANSYS HFSS and the focusing effect of the three-dimensional concave lens is confirmed in the terahertz frequency band.

Coupling of air/metal and substrate/metal surface plasmon polaritons in Au slit arrays fabricated on quartz substrate

We report on the coupling of the air/metal mode and the substrate/metal mode surface plasmon polaritons in one-dimensional metallic slit arrays fabricated on a dielectric substrate. Anti-crossing is exhibited at an incident angle where the two independent modes can be resonantly excited at a specific wavelength. The size of the anti-crossing gap was measured while changing the metal thickness.

Evolution of surface plasmon resonance with slab thickness in hybrid nano-structures of Au/InGaAs slab waveguide

We report on the evolution of the surface plasmon (SP) and waveguide mode (WM) as the core thickness is varied in InGaAs slab waveguides covered by metallic sub-wavelength slit arrays. By comparing transmission spectrum in the near-infrared region with numerical simulations, transmission dips were assigned to resonant excitations of either SPs or WMs. As the core thickness was smaller than the SP penetration depth, the resonance energy exhibits a blue shift, which scales with the field intrusion into the substrate region. For the core thickness of 400 nm supporting both the WM and SP, effective refractive index of the SP is almost constant due to the field decay within the InGaAs region, which is different to the case of the WM.

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.

금속 슬릿 배열로 구성된 편광 선택 가능한 블레이즈드 회절 격자

본 논문에서는 금속 슬릿 배열로 구성된 편광 선택 가능한 블레이즈드 회절 격자를 제안한다. 마이크로 스케일의 블레이즈드 회절 격자를 디자인 하고 이 구조에 추가적으로 나노스케일의 금속 슬릿 구조를 적용하여 편광 선택기능을 부여하였다. 이 소자에 대하여 사례 연구로 예를 디자인하여 FDTD(Finite Difference Time Domain method)방법을 이용한 전산모사를 통해 성능을 검증해 보았다. 임의의 디자인 사례에 대해 대략 77.61% 의 회절효율과 8.99의 편광선택비가 얻어졌으며 편광선택비를 높이기 위한 또 다른 디자인에서는 64.22%의 회절효율과 81.09의 편광선택비가 얻어졌다. A polarization selective blazed grating employing metal-slit arrays was proposed. Nano-scale metal-slits were applied to the micro-scale blazed grating to give the functionality of polarization selection. Case study was carried out for the proposed structure utilizing numerical FDTD (Finite Difference Time Domain method) simulation. Diffraction efficiency of 77.61% and polarization extinction ratio of 8.99 was achieved with arbitrary parameters and diffraction efficiency of 64.22% and polarization extinction ratio of 81.09 was achieved with other parameters to enhance extinction ratio.

Tunable nonreciprocal terahertz transmission and enhancement based on metal/magneto-optic plasmonic lens

A tunable metal/magneto-optic plasmonic lens for terahertz isolator is demonstrated. Based on the magneto-optical effect of the semiconductor material and non-symmetrical structure, this plasmonic lens has not only the focusing feature but also nonreciprocal transmission property. Moreover, a transmission enhancement through this device greatly larger than that of the ordinary metallic slit arrays is contributed by the extraordinary optical transmission effect of the magneto surface plasmon polaritons. The results show that the proposed isolator has an isolation bandwidth of larger than 0.4THz and the maximum isolation of higher than 110dB, and its operating frequency also can be broadly tuned by changing the external magnetic field or temperature. This low-loss, high isolation, broadband tunable nonreciprocal terahertz transmission mechanism has a great potential for terahertz application systems.

Beam Focusing by Tapered Metallic Nano-Slits

In this study, we discussed the influence of tapered metallic subwavelength slit array with variant width of slits on beam focus properties. In order to analyze the phenomenon, a finite-difference time-domain numerical algorithm and phase matching theory were adopted for computational numerical simulation of the nano-structures. The structures were flanked with the penetrated slits through a metal film coated on a quartz substrate. We found that the phase delay of each slit will grow with the decrease of slit width. Optical transmission of each slit can be adjusted by using an optimum choice of the taper angle, taper slit width and the wavelength of incident light. So by optimizing the slit width of the input and output apertures, the trapezoidal slit array can show focusing property. The focal width and focal intensity can be controlled effectively by regulating the aperture width of slits. These results are very encouraging for further study on nano-optics and the applied planar lenses.

Compact planar lenses based on a pinhole and an array of single mode metallic slits

Plasmonic lenses are based on complex combinations of nanoscale high aspect ratio slits. We show that their design can be greatly simplified, keeping similar performance while releasing technological constraints. The simplified system, called Huygens lens, consists in a central aperture surrounded by several identical single mode slits in a thin gold layer that does not rely anymore on surface plasmons. The focusing behaviour with respect to the position and number of slits is investigated, and we demonstrate the interest of this design to get compact array of lenses.

Chromatic aberration of light focusing in hyperbolic anisotropic metamaterial made of metallic slit array

The dispersion of a hyperbolic anisotropic metamaterial (HAM) and the chromatic aberration of light focusing in this kind of HAM are studied. The HAM is formed by alternately stacking metal and dielectric layers. The rules of materials and filling factors affecting the optical property of HAM are given. The chromatic aberration of light focusing is demonstrated both theoretically and numerically. By comparing the theory with the simulation results, the factors influencing the focal length, including the heat loss of material and low spatial frequency modes, are discussed. The investigation emphasizes the anomalous properties, such as chromatic aberration and low spatial frequency modes influencing focus position, of HAM compared with that in conventional lens. Based on the analysis, the possibility of using HAM to focus light with two different wavelengths at the same point is studied.

Remarkable transmission characteristics of optical waves through modulated double-layered metallic slit arrays

We reveal the distinct wavelength dependence of not only the transmission power but also the phase change in double-layered metallic slit array systems with gradually modulated slit intervals, which are promising structures for achieving novel optical phased-array functions, through finite-difference time-domain simulations. In spite of the structural modifications, the transmittance of the non-periodic system displays waveguide mode resonance for a conventional constant-period array system. By the resonance effect, maximum phase change is achieved with sufficiently high output powers around the transmission peak wavelength, and further enhanced to values much larger than those estimated simply from the optical path.

Focusing Properties of the Visible Light Wave through Plasmonic Lenses with Subwavelength Chirped Slits

Focusing properties of a new kind of plasmonic lenses are investigated in the visible wavelength range through a subwavelength metallic chirped slit arrays which have the same depth but chirped widths. The chirped widths of slits are like a piece-wise-linear distribution which will be approximated by linearly increasing the width of a subwavelength feature and can build up a required phase front for focusing. We analyzed the focusing characteristics of different metallic lenses (silver and gold, respectively) with chirped widths that are obtained by generalizing the relevant phase delay for TE- and TM-polarized incident waves, for different f-numbers of lenses and for different material thickness, respectively. Meanwhile, the comparison of the metallic and dielectric lenses is also presented. The results of calculations show that, the metallic lenses are more sensitive to the polarization of incidence wave than that of dielectric lenses, and can get narrower full-width half-maximum (FWHM) beam width than that of dielectric lenses for TM-polarized incident waves, respectively. No matter which f-number we choose, the FWHM of dielectric lenses are higher than the plasmonic lenses, and the plasmonic lenses can get a higher focal resolution than dielectric lenses do. This kind of plasmonic lenses should have a good potential for applications in photonic and plasmonic integrated devices, sensing, and nano-optical manipulations, etc.

Airy Beam Excitation Using a Subwavelength Metallic Slit Array

A novel method for launching an Airy wave packet based on a metallic slit array with stepped-height is proposed. By appropriately adjusting the amplitude and phase of the transmittance from the metallic slit array, the Airy beam can be launched in a compact area. The method can be used in various applications, such as particle tweezing and trapping, without the need for any optical components or bulky structure.

Modeling Infrared Radiative Properties of Metallic Complex Slit Arrays

Modeling Infrared Radiative Properties of Metallic Complex Slit Arrays

Enhanced in and out-coupling of InGaAs slab waveguides by periodic metal slit arrays

We studied the in- and the out-coupling efficiencies of photons with a thin InGaAs slab covered by periodic gold nano-slit arrays, by measuring transmission and photoluminescence (PL) spectra. While the maximum in-coupled photons into the InGaAs slab waveguide were found at dip positions in transmission spectra, the mostly out-coupled photons were observed as peaks in PL spectra. For different periods of slit arrays and incident angles we discussed spectral positions of transmission dips and efficiency of the in-coupling influenced by the absorption coefficient of InGaAs. In PL spectra we measured overall enhanced PL intensities from the InGaAs slab covered by slit arrays compared to that of a bare InGaAs, where the peak positions are determined by the period of slit arrays as well. Our findings are important for designing semiconductors both as an optically passive waveguide and active light emitter.

Design of extraordinary-optical-transimission refractive-index sensor of subwavelength metallic slit array based on a Fabry-Perot model

The refractive index sensing properties of a period array of subwavelength metallic slits in water environment are investigated. The transmission spectra of the slit array are calculated with a rigorous fully-vectorial method. A simple semi-analytical Fabry-Perot model that can accurately reproduce the rigorous fully-vectorial data is built up. We find that the transmission peak becomes sharpest as it is exactly located at the Rayleigh anomaly position, which is explained based on the resonance condition derived from the model. The method to design the slit array to achieve this sharpest transmission peak is presented. The full width at half-maximum (δλ) of the designed transmission peak can be as low as 0.01 nm, which corresponds to a refractive-index measurement uncertainty (δns) of 2× 10-6 RIU. The influences of array period, slit width and incident angle on the designed sensitivity, δλ, δns and peak transmittance of the sensor are systematically provided.

Optical responses from lossy metallic slit arrays under the excitation of a magnetic polariton

This work numerically investigates optical responses (absorptance, reflectance, and transmittance) of lossy metallic slit arrays at the excitation of a magnetic polariton (MP). The studied wavenumber is between 1.2×103 and 2.5×104 cm−1 for the spectral regions in which aluminum and tungsten are lossy, which do not coincide. The loss of silver is negligible. Optical response spectra clearly specify the resonance modes, excitation frequency, and impacts from loss, as well as other mechanisms. The inductance and capacitance circuit model predicting MP frequency is not always valid, and the best fitting constant varies with material, slit geometry, angle of incidence, and wavelength. Electromagnetic fields in the near field further illustrate the interplay between the incidence and slit arrays.

Metallic slit arrays filled with third-order nonlinear media: Optical Kerr effect and third-harmonic generation

We acknowledge support from the Spanish Ministry of Science and Innovation under Projects No. MAT2008-06609-C02 and No. CSD2007-046-Nanolight.es

A surface plasmon biosensor based on sub-wavelength metal slit arrays

A novel surface plasmon sensor which is constructed with sub-wavelength metal slit arrays deposited on a buffer media layer is proposed. To obtain the maximum resonant transmission, the buffer layer is coated on a glass substrate and the refractive index of the buffer layer is selected close to that of the water environment. Based on rigorous coupled wave analysis, the numerical simulation shows that the resonant transmission is enhanced and the peak mediated by surface plasmon resonance is much sharper due to the buffer layer. Therefore, this surface plasmon sensor with a buffer layer provides an improved measurement precision in biosensing application.

Optical Transmission through Subwavelength Metallic Slit Arrays

Mid-Infrared radiative property of submicron silver slit arrays have been numerically studied with the finite difference time domain method. The slit width varies from 50 nm to 300 nm and a square feature may attach at either or both slit sides. Although the side length of features is one or two orders of magnitude shorter than the wavelength, the attached nanoscale features can modify the transmittance significantly. The transmittance has also been furtherly investigated in detail by looking into electromagnetic fields and Poynting vectors of selected slit geometries. The investigation results show that such change can be attributed to the cavity resonance effect inside the slit arrays. The work is of great importance to the wavelength-selective devices design in optical devices and thermal applications field.