One-way transmission through the subwavelength slit in nonsymmetric metallic gratings

Abstract

An approach for obtaining one-way transmission in the beaming regime is suggested that is based on the directional radiation of surface plasmons in nonsymmetric metallic gratings with a single slit. In contrast to the various nonsymmetric one-way diffraction gratings that have recently been proposed, the possibility of obtaining of narrow beams is demonstrated. Strong directional selectivity can appear a wide range of the observation angles, while the angle of incidence is retained. © 2010 Optical Society of America OCIS codes: 050.2770, 240.6690.Achieving optical isolation has been the focus of interest for a long time. Within the passive framework, it can be obtained using anisotropic [1,2] or nonlinear [3] materials. Recently, several grating structures have been proposed for freely propagating waves, which enable the realization of the regimes with strong directional selectivity, that are not the same but similar in some features to the conventional isolation [4][5][6]. They all only contain isotropic constituents, and therefore no transformation of the initially linear polarization of the incident wave occurs.In particular, it has been shown for the branched slit metallic gratings with different periods of the front-and back-side interfaces (nonsymmetric gratings) at normal incidence, θ ¼ 0, that higher-order transmittance can be either zero or nonzero, depending on whether the larger-period or smaller-period interface is illuminated [4]. In contrast to the slit gratings, in those based on the photonic crystals with nonisotropic dispersion, the zero order cannot be coupled to a Floquet-Bloch wave in the vicinity of θ ¼ 0, so transmittance is zero in one direction and nonzero in the opposite direction, while θ is retained. Furthermore, a similar effect can be obtained at θ ≠ 0 in case of isotropic dispersion with the effective index of refraction as 0 < n eff < 1, for example, in the gratings containing low-permittivity layers [6], and in the photonic crystal gratings [5]. If only zero order is coupled to a wave propagating inside a grating, the interfaces are isolated from each other in the sense that the numbers of higher diffraction orders, which contribute to transmission and reflection, are determined only by the period of the corresponding interfaces. The common features of the approaches in [4][5][6] are that at least one higher order is propagating and that they operate with wide beams.At the same time, beaming is known to be obtainable in metallic gratings with slits, owing to surface plasmons [7][8][9][10][11]. For example, a plane or corrugated interface between a Drude metal and dielectric medium can support surface plasmons [12]. Since the skin depth of the plane metallic surfaces in the microwave regime approaches zero, they cannot be supported. Pendry et al. theoretically showed that the metallic surfaces, which can be thought of as perfect electric conductors in microwave regime, can support surface-plasmon-like waves, known as designer surface plasmons, when the surface has subwavelength hol...

Visible-frequency asymmetric transmission devices incorporating a hyperbolic metamaterial

“…A symmetric transmission using reciprocal electromagnetic devices has recently become a thriving research topic owing to potential applications in integrated photonic systems for communications and information processing [1][2][3][4][5][6][7][8][9][10][11][12] , such as, directionally-sensitive beam splitting 2,3 , multiplexing 4 and optical interconnection 7,8 . This Lorentz-reciprocal effect is characterized by the high contrast between forward and reverse transmission under illumination from anti-parallel directions.…”

“…Though reciprocal asymmetric transmission devices cannot be used for functions attainable only with non-reciprocal-active devices, such as optical isolation [13][14][15][16] , they have unique advantages such as small footprint, broad asymmetric transmission bandwidth and passive operation. Asymmetric transmission can be achieved through the use of artificial structures, such as, nonsymmetric gratings [2][3][4][5][6]11,12 , photonic crystals 7,8 and split-ring resonators 1,9,10 which break spatial inversion symmetry. Nevertheless, fabrication and alignment challenges associated with the intrinsic complexity of such approaches have not so far enabled structures with an efficient asymmetric transmission response at visible frequencies.…”

Experimental validation of strong directional selectivity in nonsymmetric metallic gratings with a subwavelength slit

“…At the same time, the transmission mechanism studied in Ref. 17 can be interpreted as an extension of that suggested earlier for the gratings based on the two-dimensional photonic crystals 19 and gratings containing solid metallic or wire slabs with the effective index of refraction 0 Ͻ n Ͻ 1. 20 However, for the mechanism in Ref.…”

“…17 In fact, this mechanism exploits the effect of isolation, which manifests itself in such structures in that the transmission process can be separated into three relatively independent steps, i.e., coupling in, transmission through the hole, and coupling out. 18 In particular, this means that since the surface plasmon appearance depends on corrugation parameters, the exit interface is mainly responsible for the beaming into the exit half-space, while the input interface might just slightly affect the field topology.…”

“…20 However, for the mechanism in Ref. 17, surface plasmons are necessary, rather than specific dispersion features of the waves propagating in the structure/ material, on which the unidirectional gratings in Refs. 19 and 20 are based.…”