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Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 1 — Jan. 5, 2009
  • pp: 278–292
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Isolation and one-way effects in diffraction on dielectric gratings with plasmonic inserts

A.E. Serebryannikov and Ekmel Ozbay  »View Author Affiliations


Optics Express, Vol. 17, Issue 1, pp. 278-292 (2009)
http://dx.doi.org/10.1364/OE.17.000278


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Abstract

Diffraction of plane waves on dielectric gratings with planar plasmonic inserts is studied with the emphasis put on the anomalous selectivity of diffraction orders. It is shown that some formally propagating orders can be suppressed within a wide frequency range. The effect of suppression is more general than the isolation effect observed earlier in zero-permittivity and (near-)zero-index slabs and sensitive to the frequency dependent peculiarities of the field distribution within the plasmonic layer. It is required that the real part of the permittivity of this layer is positive less than unity. The wideband features of the suppression effect, i.e., one-way transmission and diffraction-free reflection are demonstrated. Narrowband selectivity effects are also studied. The structures suggested can be used for extending the potential of technologies that are based on multibeam operation and field transformation.

© 2009 Optical Society of America

1. Introduction

Recently, it has been demonstrated that the planar slabs of a matched-index metamaterial having a zero index of refraction can transform the cylindrical waves generated by an embedded line source or external curvilinear wave fronts into planar wave fronts [1

1. R.W. Ziolkowski, “Propagation in and scattering from a matched metamaterial having a zero index of refraction,” Phys. Rev. E 70, 046608 (2004). [CrossRef]

]. A similar transformation can be realized by using epsilon-near-zero materials [2

2. A. Alu, M. G. Silveirinha, A. Salandrino, and N. Engheta, “Epsilon-near-zero metamaterials and electromagnetic sources: Tailoring the radiation phase pattern,” Phys. Rev. B 75, 155410 (2007). [CrossRef]

]. The wave fronts can be transformed in such a way that two regions of space with a rather complex boundary shape can be isolated and the phase pattern in one region can be tailored, while being independent of the excitation shape in the other region. This effect is connected with the fact that the phase variation within an epsilon-near-zero material is small and completely disappears at zero permittivity.

Materials with near-zero permittivity, ε ≈ 0, exist in nature at terahertz frequencies (polar dielectrics) and at the visible and ultraviolet (noble metals). They are necessarily dispersive and their permittivities are often well described in the framework of Drude or Drude-Lorentz models. According to [6

6. J. B. Pendry, A. J. Holden, W. J. Stewart, and I. Youngs, “Extremely low frequency plasmons in metallic mesostructures,” Phys. Rev. Lett. 76, 4773–4776 (1996). [CrossRef] [PubMed]

], Drude-type dispersion can be scaled down to microwave frequencies in arrays of thin metallic wires. Correspondingly, the operation regimes with 0<Reε<1 can be obtained within a wide frequency range. For example, periodic arrays of silver rods have been suggested in [7

7. B. T. Schwartz and R. Piestun, “Total external reflection from metamaterials with ultralow refractive index,” J. Opt. Soc. Am. B 20, 2448–2453 (2003). [CrossRef]

] for obtaining a metamaterial for wavelengths from 0.5 μm to 1.5 μm. Other performances of epsilon-near-zero and matched zero-index metamaterials have been considered, for example, in [2

2. A. Alu, M. G. Silveirinha, A. Salandrino, and N. Engheta, “Epsilon-near-zero metamaterials and electromagnetic sources: Tailoring the radiation phase pattern,” Phys. Rev. B 75, 155410 (2007). [CrossRef]

,8

8. S. Enoch, G. Tayeb, P. Sabouroux, N. Guerin, and P. Vincent, “A metamaterial for directive emission,” Phys. Rev. Lett. 89, 213902 (2002). [CrossRef] [PubMed]

,9

9. M. Silverihna and N. Engheta, “Design of matched zero-index metamaterials using non-magnetic inclusions in epsilon-near-zero media,” Phys. Rev. B 75, 075119 (2007). [CrossRef]

]. In the context of our present interest, we should also mention those metamaterials that have been designed to operate at optical or microwave frequencies in the negative-index regime, but also show the ranges with 0<Reε<1, e.g., see [10

10. R.W. Ziolkowski and C.-Y. Cheng, “Lumped element models of double negative metamaterial-based transmission lines,” Radio Sci. 39, RS2017 (2004). [CrossRef]

]–[14

14. W. J. Padilla, M. T. Aronsson, C. Highstrete, M. Lee, A. J. Taylor, and R. D. Averitt, “Electrically resonant terahertz metamaterials,” Phys. Rev. B 75, 041102 (2007). [CrossRef]

].

It is noteworthy that thin metallic films with corrugated interfaces have been studied by many research groups, by putting the emphasis on the anomalous transmission effects, which appear due to surface plasmon polaritons and hence correspond to Reε<0, or to narrowband transmission effects at Reε>0, e.g., see [15

15. B. Baumeier, T. A. Leskova, and A. A. Maradudin, “Transmission through thin metal film with periodically and randomly corrugated surfaces,” J. Opt. A 8, S191–S207 (2006). [CrossRef]

]–[17

17. M. M. Dvoynenko, I. I. Samoylenko, and J.-K. Wang, “Suppressed light transmission through corrugated metal films at normal incidence,” J. Opt. Soc. Am A 23, 2315–2319 (2006). [CrossRef]

]. A combined structure, which consists of a thin non-corrugated metallic film and periodically located dielectric pillars, has been studied in [18

18. N. Bonod, S. Enoch, L. Li, E. Popov, and M. Neviere, “Resonant optical transmission through thin metallic films with and without holes,” Opt. Express 11, 482–490 (2003). [CrossRef] [PubMed]

]. Some interesting diffraction effects have been observed in the relief gratings, which are obtained by introducing periodic corrugations on the interface between an air half-space and a half-space that is made of a negative-phase-velocity (negative-index) material [19

19. R. A. Depine, A. Lakhtakia, and D. R. Smith, “Enhanced diffraction by a rectangular grating made of a negative phase-velocity (or negative index) material,” Phys. Lett. A 337, 155–160 (2005). [CrossRef]

,20

20. R. A. Depine, M. E. Inchaussandague, and A. Lakhtakia, “Vector theory of diffraction by gratings made of a uniaxial dielectric-magnetic material exhibiting negative refraction,” J. Opt. Soc. Am. B 23, 514–528 (2006). [CrossRef]

].

In the present paper, we study diffraction on three-layer gratings, which consist of the inner non-corrugated plasmonic layer and the outer corrugated dielectric layers, while the permittivity of the plasmonic layer is smaller than unity but positive. In some theoretical performances, one of the dielectric layers is removed, in turn leading to two-layer gratings. It will be shown here that the isolation effect can appear within a wide range of Reε varying in line with the Drude model, i.e., the (near-)zero phase variation is not a necessary condition. For the structures considered, this leads to the appearance of several anomalous diffraction effects, which manifest themselves in the wideband suppression of some propagating diffraction orders and, hence, can be characterized in terms of the diffraction order selectivity. In particular, we will demonstrate that the one-way transmission can be achieved within a wide frequency range. It is distinguished from the recently suggested performances, in which this effect is narrowband. On the other hand, it is distinguished from a transmission that is associated with surface plasmon polaritons at negative Reε, which is a rather narrowband effect. In fact, the used plasmonic materials can be the same as those in [15

15. B. Baumeier, T. A. Leskova, and A. A. Maradudin, “Transmission through thin metal film with periodically and randomly corrugated surfaces,” J. Opt. A 8, S191–S207 (2006). [CrossRef]

]–[18

18. N. Bonod, S. Enoch, L. Li, E. Popov, and M. Neviere, “Resonant optical transmission through thin metallic films with and without holes,” Opt. Express 11, 482–490 (2003). [CrossRef] [PubMed]

], but correspond in most cases to another frequency range. In our case, plasmonic layers have flat interfaces, so that the regions, which are mainly responsible for the isolation and diffraction effects, are different. This feature distinguishes the suggested gratings from the two-layer gratings considered in [3

3. A. E. Serebryannikov, T. Magath, K. Schuenemann, and O.Y. Vasylchenko, “Scattering of s-polarized plane waves by finite-thickness periodic structures made of ultralow-permittivity metamaterials,” Phys. Rev. B 73, 115111 (2006). [CrossRef]

] but makes them similar to some of those in [18

18. N. Bonod, S. Enoch, L. Li, E. Popov, and M. Neviere, “Resonant optical transmission through thin metallic films with and without holes,” Opt. Express 11, 482–490 (2003). [CrossRef] [PubMed]

]. Note that the considered isolation mechanism differs from that occurring due to the reflection-free edge modes in gyromagnetic and gyroelectric crystals [21

21. Z. Wang, J. D. Chong, J. D. Joannopoulos, and M. Soljacic, “Reflection-free one-way edge modes in gyromagnetic photonic crystals,” Phys. Rev. Lett. 100, 013905 (2008). [CrossRef] [PubMed]

,22

22. F. D. M. Haldane and S. Raghu, “Possible realization of directional optical waveguides in photonic crystals with broken time-reversal symmetry,” arXiv:cond-mat/0503588 (2008).

], since no anisotropic material is required in our case. All effects studied in this paper are in accordance with the reciprocity theorem. To numerically solve the diffraction problem, we use a flexible and efficient self-made solver, which is based on the fast coupled-integral-equations technique [23

23. T. Magath and A. E. Serebryannikov, “Fast iterative, coupled-integral-equation technique for inhomogeneous profiled and periodic slabs,” J. Opt. Soc. Am. A 22, 2405–2418 (2005). [CrossRef]

].

2. Theoretical background

General geometry of the suggested structures is shown in Fig. 1. The planar plasmonic layer is sandwiched between two dielectric layers, at least one of which has a periodically corrugated interface. The upper (front-side) and lower (back-side) interfaces are assumed to be set by

f1(x)/h=A+Bcos(2πxM1/L+ϕ1)andf2(x)/h=C+Dcos(2πxM2/L+ϕ2),
(1)

respectively, where h is the total thickness. We refer to the structure shown in Fig. 1 as a DU structure (Double corrugations, Upper interface determines the period of the whole structure). In this case, M 2/M 1 is an integer larger than unity. Correspondingly, M 1/M 2 is an integer larger than unity for a DL structure (Double corrugations, Lower Interface). If D=0, then we obtain a U structure. In turn, L structures correspond to B=0. The upper and lower dielectric layers are assumed to be made of dielectrics with ε=ε U and ε=ε L, respectively. The permittivity of the plasmonic insert (a<y<b) satisfies the Drude model, i.e., it is given by εi(ω) = 1−ω 2 p/[ω(ω+)], where ωp and γ mean plasma and collision frequencies. It is assumed that A + B ≤ 1, CD ≥ 0, C + Da/h, and ABb/h.

Consideration is restricted to the case of TM polarization. We assume that the plane wave is incident on a grating, as shown in Fig. 1. The electric fields in the upper (y>h) and lower (y<0) half-spaces are presented as follows:

Ezxy=Ezixy+n=ρnexp(iαnx+iβny)
(2)

and

Ezxy=n=τnexp(iαnxiβny),
(3)

where βn = [k 2-a 2 n], Im αn = α 0 + 2πnζ/L, ζ = min{M 1,M 2}, α 0 = ksinθ, k=ω/c is free-space wave number, θ is angle of incidence, L is fundamental grating period, ρn and τn are amplitudes of the nth-order reflected and transmitted beams (Bragg waves). In turn, the incident wave is given by Eiz(x,y) = E 0exp(i α 0 xi β 0 y), where β 0 = k cosθ. The intensities of the nth-order reflected and transmitted beams (diffraction efficiencies) are given by

rn=ρnρn*Reβn/Wandtn=τnτn*Reβn/W,
(4)

where W means the energy of the incident wave and asterisk means complex conjugate. On the other hand, W=R+T+A where R, T, and A are reflectance, transmittance, and absorptance, respectively.

Fig. 1. Three-layer grating with plasmonic insert, which is illuminated by a TM polarized plane wave.

In agreement with the general theory of diffraction gratings [24

24. R. Petit, Ed., Electromagnetic theory of gratings (Springer, Berlin Heidelberg New York, 1980).

], the nth-order beams are propagating if k>kn where kn = 2πn∣/(1±∣sinθ∣)L. In the latter formula, signs + and − correspond to sgn n ≠ sgn θ and sgn n = sgn θ, respectively. The nth-order reflected beams diffract at the angles ψn, which can be obtained from the equation sin ψn = sin θ + 2πnζ/kL. It is assumed that the angles ψn and θ are measured from the positive-value part of the y axis in the clockwise and counter-clockwise directions, respectively. The angles of diffraction of the nth-order transmitted beams ψ^n are measured from the negative-value part of the y axis in the counter-clockwise direction, i.e., ψ^n = ψn.

The reciprocity conditions for the 0th-order beams, i.e., t L 0 = t U 0 and t DL 0 = t DU 0 are satisfied for any kL, provided that ϕ1 and ϕ2 in Eq. (1) are chosen in such a manner that a pair of L and U structures, or a pair of DL and DU structures, corresponds in fact to the same structure but the directions of illumination are opposite. These conditions are rather important for our study. Similar conditions for r L 0 and r U 0, and r DL 0 and r DU 0 exist only if k<k ±1. These conditions are unimportant for our purposes, since at least the ±1 st and ±2 nd orders should be propagating in order to illustrate the basic effects expected. Throughout this paper, we take ζ =1 and ωpL/ck ±2 Lθ=0 = 4π. In case of ωpL/c = 4π and θ = 0, which corresponds to most of the presented numerical results, the ±2 nd orders become propagating and Reε i passes through zero nearly simultaneously, while kL is raising. In Fig. 2, the dependences of ψn on kL and those of Reεi, Imεi, and ∣εi∣ on kL are shown, which correspond to the considered range of variation of the problem parameters.

Fig. 2. Diffraction angle in degrees for the orders n=1, 2, and 3 at θ=0 − plot (a), and permittivity of the plasmonic insert at ωpL/c=4π and γ/ωp=0.01 − plot (b).

3. Numerical results and discussion

3.1 Basic effects

Figure 3 shows tn and rn vs kL in the cases U and L, which correspond to the same structure being illuminated from the opposite sides. In Figs. 3(a) and 3(b), it is illuminated from the side of corrugated interface (U case). In Figs. 3(d) and 3(e), illumination is performed from the side of the flat dielectric layer (L case). One of the main effects is demonstrated in Fig. 3(a). It manifests itself in that the ±2 nd-order transmitted beams are suppressed within a wide kL-range (4π<kL<17.2), where they are formally propagating. Therefore, the free-space wave number, starting from which the ± nth-order beams actually contribute to T, T ±n, in case of n = ±2 is substantially larger than k ±2 and ωp/c. At the same time, T ±1 and T 0 are located in the vicinity of k=ωp/c, so that t 0 and t ±1 contribute to T within most of the range 0< Reεi<1. The corrugations affect the transmitted far field, but the actual periodicity cannot be recognized by using the transmission results. From the comparison with Fig. 2(b), it is clearly seen that the range with T=t 0+t -1+t 1 corresponds to 0< Reεi <0.5. One can refer to this effect as the partial translation, or the partial isolation.

The observed effect of the suppression of the propagating orders is similar in some sense to that detected for the gratings made of zero-ε materials, where higher propagating orders in the transmission were suppressed, while the 0th order remained strongly contributive [3

3. A. E. Serebryannikov, T. Magath, K. Schuenemann, and O.Y. Vasylchenko, “Scattering of s-polarized plane waves by finite-thickness periodic structures made of ultralow-permittivity metamaterials,” Phys. Rev. B 73, 115111 (2006). [CrossRef]

]. However, since Reεi>0 and t ±1 ≠ 0, this effect is even closer to that observed in two-dimensional dielectric and metallic photonic crystals with corrugated interfaces, where one or several propagating orders have been suppressed within a wide range of kL-variation that is adjacent to an edge of a band gap [5

5. A. E. Serebryannikov, T. Magath, and K. Schuenemann, “Bragg transmittance of s-polarized waves through finite-thickness photonic crystals with a periodically corrugated interface,” Phys. Rev. E 74, 066607 (2006). [CrossRef]

]. In our case, the transmitted far field is affected by the upper-side corrugations only due to the ±1 st orders, so that the transmission is characterized by wideband selectivity with respect to diffraction orders. In Fig. 3(b), one can see that all the propagating orders contribute to R at 4π<kL<17.2. In particular, R ±2 = k ±2 and, therefore, R ±2 T ±2. Owing to the narrowband diffraction effects, Rr 0 at kL=11.9 and kL=14.8, T= t -1+t 1 at kL = 14.88 and kL = 16.45, and T=t 0 at kL=15 and kL=16.55.

Fig. 3. Transmittance (a,d), reflectance (b,e), and the geometry of grating within a period (c,f) in cases U (a)-(c) and L (d)-(f); A=0.8, B=0.2, C=D=0, ϕ 1=0 in U case, and A=1, B=0, C=D=0.2, ϕ 1=0 in L case; M 1=1, ε U=ε L=2.1, a/h=0.4, b/h=0.6, ωpL/c=4π, γ/ωp=0.01, and θ=0; solid line −n=0, dashed line − n = ±1, dash-dotted line − n = ±2 , dotted line (∑) − sum of all propagating orders; filled circles − k ±2 L and k ±3 L.

Now consider Figs. 3(d) and 3(e). In Fig. 3(d), t ±2 ≠ 0 at 4π<kL<17.2. This occurs due to the effect of the lower (corrugated) interface. The strong difference in the values of t L ±2 and t U ±2 results in the one-way transmission effect, which is similar to that observed in metallic gratings with the multiple branched slits and different periods at different interfaces [4

4. M. J. Lockyear, A. P. Hibbins, K. R. White, and J. R. Sambles, “One-way diffraction grating,” Phys. Rev. E 74, 056611 (2006). [CrossRef]

]. However, in our case this effect is wideband. Furthermore, at kL=16.45 the situation occurs when T Ut -1 + t 1 ≈ 0.41 and T Lt -2 + t 2 ≈ 0.77. Hence, all beams, that actually contribute to the transmission, can show different values of ψ ±n, depending on the side of incidence (ψ ±1 = ±22.5° and ψ ±2 = ±49.8°). The presence of the contributing ±2nd-order transmitted beams enables a substantial increase of T in the L case at ωpL/c<kL<15. For example, T L=0.63 and T U=0.08 at kL=14, where Reεi ≈ 0.2. It is seen in Fig. 3(e), that the corrugations do not affect the reflected far field, except for the narrow ranges with t ±1 < 0.025 arising in the vicinity of kL=16.5 and kL=17.7. As a result, the isolation of two regions, i.e., y/h>0.6 and y/h<0.4, from each other takes place, manifesting itself in that the topological features of the lower corrugated layer are not translated through the plasmonic layer. This effect is, in fact, a counterpart of the isolation effect, which has been studied in [2

2. A. Alu, M. G. Silveirinha, A. Salandrino, and N. Engheta, “Epsilon-near-zero metamaterials and electromagnetic sources: Tailoring the radiation phase pattern,” Phys. Rev. B 75, 155410 (2007). [CrossRef]

] in the transmission through a near-zero index slab with a non-flat front-side interface. In Fig. 3(e), we again obtain R ±2 T ±2, but now also R ±1 T ±1. It is noteworthy that the L structure can be reflection-free. For example, W=T+A at kL= 15.

Fig. 4. Transmittance (a,c), reflectance (d,e), and the geometry of grating within a period (c,f) in cases DU (a)–(c) and DL (d)–(f); A=0.8, B=0.2, C=D=0.0833, ϕ 1=0, ϕ 2=π, M 1=1, M 2=2 in DU case, and A=1-B, B=0.0833, C=D=0.2, ϕ 1= ϕ 2=0, M 1=2, M 2=1 in DL case; ε U=ε L=2.1, a/h=0.4, b/h=0.6, ωpL/c=4π, γ/ωp=0.01, and θ=0; solid line − n=0, dashed line − n =±1, dash-dotted line − n = ±2 , dotted line (∑) − sum of all propagating orders; filled circles show k ±2 L and k ±3 L.

To better understand the mechanism leading to the order selectivity, we consider near-field patterns (in units of ∣Ez∣) within a single grating period, i.e., at 0<x<L and 0<y<h. Several examples are shown in Fig. 5, which correspond to the typical behaviors of tn and rn in Figs. 3 and 4. First, we compare Figs. 5(a) and 5(b) corresponding to the two cases (L and DL), which only differ in the shape of the upper-side interface. Three typical regions can be recognized in each figure. Within the lower region (0<y/h<0.4), the field patterns are nearly the same. Four maxima of ∣Ez(x,y)∣ occur at y=0 within the period, which can be associated with the ±2 nd orders. Indeed, Tt -2 + t 2 at kL=16.45 in Figs. 3(d) and 4(d). In the upper region (0.6<y/h<1), ∣Ez(x,y)∣ in Figs. 5(a) and 5(b) is completely different, that indicates the effect exerted by the upper interface. Four maxima occur at y=const at least within a part of the upper region in Fig. 5(b). In this case, Rr 0 + r -2 + r 2 , see Fig. 4(e). Since the field topology at y<0.4 is not affected by the shape of the upper layer, the middle region (0.4<y/h<0.6) isolates the two others.

Fig. 5. Electric field pattern within a grating period at the parameters from Figs. 3(d), 3(e) – plot (a), from Figs. 4(d), 4(e) – plot (b), from Figs. 3(a), 3(b) – plots (c) and (d), and from Figs. 4(a) and 4(b) – plot (e); kL=16.45 in plots (a)–(c) and kL=16 in plots (d) and (e).

Figures 5(d) and 5(e) show a field pattern in the U and DU cases, when t 0 ≠ 0 but the ±1 st orders dominate in T and the 0th order dominates in R. It is seen that the field topologies differ only within the lower region due to the shape of the lower interface. Again, the plasmonic layer reduces the periodicity, while the role of the upper and lower regions depends on the presence of corrugations. From the presented results, it follows that the structures suggested can provide one with a powerful tool for controlling the number of beams actually contributing to the transmission and reflection and the topology of the near field. One can use the following condition for U-case transmission. If

Reεi<1andk±p/(Reεi)1/2<k<k±(p+1)/(Reεi)1/2,
(5)

the field features, which correspond to the orders with ∣n∣=0,1,…p, can be translated to the lower half-space (partial translation), while those corresponding to ∣n∣= p+1, p+2,… cannot be translated (partial isolation). If the condition k < k ±1/(Reεi)1/2 is satisfied, i.e., p=0 and k 0=0 in Eq. (5), no periodic feature can appear within the plasmonic layer. Therefore, the effect of the upper corrugated interface on the transmitted far field would be reduced, so that the condition Reεi=0 is not necessary for achieving the total isolation (T Ut 0). This case corresponds to the wave front flattening [1

1. R.W. Ziolkowski, “Propagation in and scattering from a matched metamaterial having a zero index of refraction,” Phys. Rev. E 70, 046608 (2004). [CrossRef]

,2

2. A. Alu, M. G. Silveirinha, A. Salandrino, and N. Engheta, “Epsilon-near-zero metamaterials and electromagnetic sources: Tailoring the radiation phase pattern,” Phys. Rev. B 75, 155410 (2007). [CrossRef]

], which can be considered as a special case of the periodicity reduction. To obtain Eq. (5), it has been assumed that Imεi=0.

It can be shown that such a kL range always exists near any ω=ωp that all the higher orders are evanescent within the plasmonic layer, provided that 0<Reεi<1 and Imεi=0. Indeed, k ±n/(Reεi)1/2 = ∞ at Reεi=0 and is decreased with raising Reεi tending to k ±n at Reεi=1. All the higher orders (∣n∣>0) are evanescent if

ωp/c<k<k±12+(ωp/c)2.
(6)

The total isolation is always a wideband effect, because the all materials with Reεi<1 are necessarily dispersive. The band width is determined by the values of dReεi/ and can be relatively large for the typical parameters of the Drude model. In particular, this explains why k ±1< ωp/c< T ±1. Correspondingly, the range of achievable values of the ±1 st-order diffraction angles is limited by

ψ±1<sin1[2π/(k±1L)2+(ωpL/c)2].

For example, ∣ψ±1∣ < 26.5° at ωpL/c=4π and kL=(k±1L)2+(ωpL/c)2=14.05. A rather strong contribution of the higher orders to T at kL<14.05 in Figs. 3 and 4 can be explained by the fact that the thickness of the plasmonic region is not large enough.

3.2 Parametric Study

Fig. 6. Reflectance in DL case at the same parameters and notations as in Fig. 4(e), except for a/h=0.55, b/h=0.75 – plot (a), and except for ωpL/c=5π – plot (b); and electric field pattern within a grating period at kL=16.25 and remaining parameters from plot (b) – plot (c).

Figure 6(c) shows a field pattern for the case of r 0 ≈ 0 from Fig. 6(b). The field topology within the upper region is nearly the same as in the DL case in Fig. 5(b). This does not remain true with respect to the middle and lower regions. Contrary to Fig. 5, the field at the middle region tends to lose the periodic features. Here, the behavior of ∣Ez∣ is completely consistent with Eq. (5). Indeed, k ±1 L/(Reεi)1/2 =24.5 at kL=16.25, where Reεi=0.066 if ωpL/c =5π. This corresponds to p=0 in Eq. (5). The dominance of the ±2 nd orders in T is a pure diffraction effect, which appears due to peculiar wave processes within the lower region.

Fig. 7. Reflectance at the parameters from Fig. 3(e) except for θ=π/6 – plot (a), and at the parameters from Fig. 4(e) except θ=π/6 – plot (b); solid line – n=0, dashed line – n=−1, dash-dotted line – n=−2, thin solid line – n=−4, dotted line – sum of all propagating orders; filled circles − k -3 L and k -4 L.
Fig. 8. Transmittance at the same parameters and notations as shown in Fig. 4(a), except for a/h=0.3, b/h=0.7, A=0.85, and B=0.15 – plot (a); reflectance at the same parameters and notations as in Fig. 4(d), except for a/h=0.3, b/h=0.7, and C=D=0.15 – plot (b); electric field pattern within a grating period at kL= 15.8 and the remaining parameters from plot (a) – plot (c), and at kL=16 and the remaining parameters from plot (b) – plot (d).

Fig. 9. Transmittance (a,b) and reflectance (c) in cases U (a) and L (b,c) at A =0.7, B=0.1, C=0.2, D=0, ϕ 1=0 in U case, and A=0.8,B=0, C=0.3, D=0.1, ϕ 2=0 in L case; M 1=1, εUL=2.1, a/h=0.4, b/h=0.6, ωpL/c=4π, γ/ωp=0.01, and θ=0; solid line − n=0, dashed line − n = ±1, dash-dotted line − n = ±2, dotted line (∑) − sum of all propagating orders; filled circles − k ±2 L and k ±3 L.
Fig. 10. Same as Fig. 9 but for a/h=0.3, b/h=0.1, and A=0.75 and B=0.05 in plot (a), and C=0.25 and D=0.05 in plots (c) and (d).

In the L case in Fig. 9(b), note the peak of T>0.2, which appears at kL= 11.08 in the surface-plasmon regime (Resεi ≈ −0.29). For larger thicknesses of the dielectric layers, this effect has been observed in DU and DL cases only (compare with Figs. 3 and 4). In the comparison with Figs. 3(a) and 3 (d), both narrowband and wideband one-way transmission effects become weaker. No principal difference appears in the reflected far field, see Fig. 9(c).

In Fig. 10, the kL-dependences of tn and rn are presented for the structures, which differ from those in Fig. 9 in that they have a thicker plasmonic layer and less deep corrugations with period L. As was expected, the suppression of the ±1 st orders at kL<14 in the U case in Fig. 10(a) is more pronounced than Fig. 9(a). A comparison with [5

5. A. E. Serebryannikov, T. Magath, and K. Schuenemann, “Bragg transmittance of s-polarized waves through finite-thickness photonic crystals with a periodically corrugated interface,” Phys. Rev. E 74, 066607 (2006). [CrossRef]

] gives one an idea of how to explain a similar effect in metallic photonic crystals with the grating-like corrugations. The used modifications of the layer thicknesses result in a stronger wideband contribution of t 0 than in Fig. 9. The ±2 nd orders are suppressed even at those kL values, at which they contribute to T in the U case in Figs. 9(a) and 3(a). Furthermore, the wideband weakening of the contribution of t ±2 to T occurs even in L case [compare Figs. 9(b) and 10(b)]. These examples show that the effect of the corrugations in producing the higher transmitted orders is weakening with a decreasing corrugation depth in both the U and L cases. The contribution of the higher orders to R also becomes weaker [compare Figs. 9(c) and 10(c)].

In Fig. 11, tn and rn vs kL and near-field patterns are presented for the structures, which differ from those in Fig. 4 in that the dielectric layers with the corrugations of period L are simply removed now. In fact, these structures show period L/2. However, for the sake of convenience, the same notations are kept as above, i.e., we assume here that t2n+1 ≡ 0 . In Fig. 11(a), all the propagating orders contribute to T. Figure 11(b) demonstrates the wideband suppression of r ±2 due to the isolation effect. A comparison of Figs. 11(b) and 3(e) shows that the absence of the upper dielectric layer and the changing of the periodicity of the whole structure do not affect the appearance of this effect.

Fig. 11. Transmittance and reflectance for the same parameters and notations as in Fig. 4, except for ε U=1 in plots (a) and (b), and ε L=1 in plots (d) and (e), and electric field pattern at kL=16 and the same remaining parameters as in plots (a), (b) – plot (c), and at kL=13.5 and the same remaining parameters as in plots (d), (e) – plot (f).

Figure 11(c) shows the near-field pattern, which corresponds to kL=16 in Figs. 11(a) and 11(b). Since there are no upper-side corrugations and k ±2 L/(Reεi)1/2 =20.3 where Reεi=0.383 at kL=16, the ±2 nd orders do not contribute to the field within most part of the plasmonic layer, as well as above it. At the same time, the lower dielectric layer is thick enough in order to transform the field features seen within the plasmonic layer, which are associated with the 0th order, to those of the ±2 nd orders at y=0.

Fig. 12. Second-order transmittance 12 for parameters from Figs. 3(a)–3(c), except for γ=0 –plot (a), and from Figs. 11(d)–11(f), except for γ=0 – plot (b); solid line – P=300 and Q=600, dashed line – P=200 and Q=400, and dash-dotted line – P=50 and Q=100; energy balance Ω is shown for all three sets of P and Q by dotted lines, the most upper line corresponds to P=50 and the lowest line does to P=300.

Finally, we demonstrate how strong suppression of formally propagating orders can typically be in the structures considered, and compare it with the achievable numerical accuracy, see Fig. 12. It is seen that t 2<10-3 at least at kL<16. The strength of suppression can be varied due to a proper choice of the grating parameters. The solid and dashed lines in Fig. 12 almost coincide, so that the used number of discretization points over x and y, P and Q [23

23. T. Magath and A. E. Serebryannikov, “Fast iterative, coupled-integral-equation technique for inhomogeneous profiled and periodic slabs,” J. Opt. Soc. Am. A 22, 2405–2418 (2005). [CrossRef]

], is large enough. In addition, the energy balance Ω is presented in Fig. 12, showing that t 2>Ω can be obtained by increasing P and Ω. It is important that a rather good convergence of t 2 is achieved even if Q can further be decreased by appropriately increasing P and Q. It is noteworthy that at least P=300 and Q=600 were used in all examples presented in Figs. 2–11.

4. Conclusions

For example, for the three-layer structure with the upper corrugated interface (U case), the highest transmitted order is determined by the highest order supported by the plasmonic layer. If the wave is incident on the same structure from the opposite side (L case), it is determined by the lower-side corrugations. Either partial or total isolation can be obtained in the transmission, depending on number of the orders, which are allowed to propagate within the plasmonic layer. As a result, wideband one-way transmission can be realized. In other words, transmission can be substantially different when the structure is illuminated from the different sides. A similar narrowband effect can be obtained, in which diffraction orders contributing to the transmission and reflection are different. An anomalous manifestation of the isolation effect in the L case concerns the fact that the reflected field is not affected by the lower-side corrugations and, therefore, takes on no periodic feature, even if some higher orders within the plasmonic layer might be propagating.

Acknowledgments

This work is supported by the European Union under the projects EU-METAMORPHOSE, EU-PHOREMOST, EU-PHOME, and EU-ECONAM, and by TUBITAK under the Projects Numbers 105E066, 105A005, 106E198, and 106A017. One of the authors (A.S.) thanks TUBITAK for partial support of this work in the framework of the Visiting Scientists Fellowship Program. One of the authors (E.O.) acknowledges partial support from the Turkish Academy of Sciences.

References and links

1.

R.W. Ziolkowski, “Propagation in and scattering from a matched metamaterial having a zero index of refraction,” Phys. Rev. E 70, 046608 (2004). [CrossRef]

2.

A. Alu, M. G. Silveirinha, A. Salandrino, and N. Engheta, “Epsilon-near-zero metamaterials and electromagnetic sources: Tailoring the radiation phase pattern,” Phys. Rev. B 75, 155410 (2007). [CrossRef]

3.

A. E. Serebryannikov, T. Magath, K. Schuenemann, and O.Y. Vasylchenko, “Scattering of s-polarized plane waves by finite-thickness periodic structures made of ultralow-permittivity metamaterials,” Phys. Rev. B 73, 115111 (2006). [CrossRef]

4.

M. J. Lockyear, A. P. Hibbins, K. R. White, and J. R. Sambles, “One-way diffraction grating,” Phys. Rev. E 74, 056611 (2006). [CrossRef]

5.

A. E. Serebryannikov, T. Magath, and K. Schuenemann, “Bragg transmittance of s-polarized waves through finite-thickness photonic crystals with a periodically corrugated interface,” Phys. Rev. E 74, 066607 (2006). [CrossRef]

6.

J. B. Pendry, A. J. Holden, W. J. Stewart, and I. Youngs, “Extremely low frequency plasmons in metallic mesostructures,” Phys. Rev. Lett. 76, 4773–4776 (1996). [CrossRef] [PubMed]

7.

B. T. Schwartz and R. Piestun, “Total external reflection from metamaterials with ultralow refractive index,” J. Opt. Soc. Am. B 20, 2448–2453 (2003). [CrossRef]

8.

S. Enoch, G. Tayeb, P. Sabouroux, N. Guerin, and P. Vincent, “A metamaterial for directive emission,” Phys. Rev. Lett. 89, 213902 (2002). [CrossRef] [PubMed]

9.

M. Silverihna and N. Engheta, “Design of matched zero-index metamaterials using non-magnetic inclusions in epsilon-near-zero media,” Phys. Rev. B 75, 075119 (2007). [CrossRef]

10.

R.W. Ziolkowski and C.-Y. Cheng, “Lumped element models of double negative metamaterial-based transmission lines,” Radio Sci. 39, RS2017 (2004). [CrossRef]

11.

N. Katsarakis, G. Konstantinidis, A. Kostopoulos, R. S. Penciu, T. F. Gundogdu, M. Kafesaki, E. N. Economou, Th. Koschny, and C. M. Soukoulis, “Magnetic response of split-ring resonators in the far-infrared frequency regime,” Opt. Lett. 30, 1348–1350 (2005). [CrossRef] [PubMed]

12.

L. Jylhä, I. Kolmakov, S. Maslovski, and S. Tretyakov, “Modeling of isotropic backward-wave materials composed of resonant spheres,” J. Appl. Phys. 99, 043102 (2006). [CrossRef]

13.

K. Guven, A. O. Cakmak, M. D. Caliskan, T. F. Gundogdu, M. Kafesaki, C. M. Soukoulis, and E. Ozbay, “Bilayer metamaterial: analysis of left-handed transmission and retrieval of effective medium parameters,” J. Opt. A 9, S361–S365 (2007). [CrossRef]

14.

W. J. Padilla, M. T. Aronsson, C. Highstrete, M. Lee, A. J. Taylor, and R. D. Averitt, “Electrically resonant terahertz metamaterials,” Phys. Rev. B 75, 041102 (2007). [CrossRef]

15.

B. Baumeier, T. A. Leskova, and A. A. Maradudin, “Transmission through thin metal film with periodically and randomly corrugated surfaces,” J. Opt. A 8, S191–S207 (2006). [CrossRef]

16.

I. R. Hooper and J. R. Sambles, “Coupled surface plasmon polaritons on thin metal slabs corrugated on both surfaces,” Phys. Rev. B 70, 045421 (2004). [CrossRef]

17.

M. M. Dvoynenko, I. I. Samoylenko, and J.-K. Wang, “Suppressed light transmission through corrugated metal films at normal incidence,” J. Opt. Soc. Am A 23, 2315–2319 (2006). [CrossRef]

18.

N. Bonod, S. Enoch, L. Li, E. Popov, and M. Neviere, “Resonant optical transmission through thin metallic films with and without holes,” Opt. Express 11, 482–490 (2003). [CrossRef] [PubMed]

19.

R. A. Depine, A. Lakhtakia, and D. R. Smith, “Enhanced diffraction by a rectangular grating made of a negative phase-velocity (or negative index) material,” Phys. Lett. A 337, 155–160 (2005). [CrossRef]

20.

R. A. Depine, M. E. Inchaussandague, and A. Lakhtakia, “Vector theory of diffraction by gratings made of a uniaxial dielectric-magnetic material exhibiting negative refraction,” J. Opt. Soc. Am. B 23, 514–528 (2006). [CrossRef]

21.

Z. Wang, J. D. Chong, J. D. Joannopoulos, and M. Soljacic, “Reflection-free one-way edge modes in gyromagnetic photonic crystals,” Phys. Rev. Lett. 100, 013905 (2008). [CrossRef] [PubMed]

22.

F. D. M. Haldane and S. Raghu, “Possible realization of directional optical waveguides in photonic crystals with broken time-reversal symmetry,” arXiv:cond-mat/0503588 (2008).

23.

T. Magath and A. E. Serebryannikov, “Fast iterative, coupled-integral-equation technique for inhomogeneous profiled and periodic slabs,” J. Opt. Soc. Am. A 22, 2405–2418 (2005). [CrossRef]

24.

R. Petit, Ed., Electromagnetic theory of gratings (Springer, Berlin Heidelberg New York, 1980).

OCIS Codes
(050.1960) Diffraction and gratings : Diffraction theory
(050.1970) Diffraction and gratings : Diffractive optics
(120.7000) Instrumentation, measurement, and metrology : Transmission
(160.3900) Materials : Metals
(160.4670) Materials : Optical materials

ToC Category:
Diffraction and Gratings

History
Original Manuscript: October 13, 2008
Revised Manuscript: November 17, 2008
Manuscript Accepted: November 21, 2008
Published: January 2, 2009

Citation
A. E. Serebryannikov and Ekmel Ozbay, "Isolation and one-way effects in diffraction on dielectric gratings with plasmonic inserts," Opt. Express 17, 278-292 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-1-278


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References

  1. R.W. Ziolkowski, "Propagation in and scattering from a matched metamaterial having a zero index of refraction," Phys. Rev. E 70, 046608 (2004). [CrossRef]
  2. A. Alu, M. G. Silveirinha, A. Salandrino, and N. Engheta, "Epsilon-near-zero metamaterials and electromagnetic sources: Tailoring the radiation phase pattern," Phys. Rev. B 75, 155410 (2007). [CrossRef]
  3. A. E. Serebryannikov, T. Magath, K. Schuenemann, and O.Y. Vasylchenko, "Scattering of s-polarized plane waves by finite-thickness periodic structures made of ultralow-permittivity metamaterials," Phys. Rev. B 73, 115111 (2006). [CrossRef]
  4. M. J. Lockyear, A. P. Hibbins, K. R. White, and J. R. Sambles, "One-way diffraction grating," Phys. Rev. E 74, 056611 (2006). [CrossRef]
  5. A. E. Serebryannikov, T. Magath, and K. Schuenemann, "Bragg transmittance of s-polarized waves through finite-thickness photonic crystals with a periodically corrugated interface," Phys. Rev. E 74, 066607 (2006). [CrossRef]
  6. J. B. Pendry, A. J. Holden, W. J. Stewart, and I. Youngs, "Extremely low frequency plasmons in metallic mesostructures," Phys. Rev. Lett. 76, 4773-4776 (1996). [CrossRef] [PubMed]
  7. B. T. Schwartz and R. Piestun, "Total external reflection from metamaterials with ultralow refractive index," J. Opt. Soc. Am. B 20, 2448-2453 (2003). [CrossRef]
  8. S. Enoch, G. Tayeb, P. Sabouroux, N. Guerin, and P. Vincent, "A metamaterial for directive emission," Phys. Rev. Lett. 89, 213902 (2002). [CrossRef] [PubMed]
  9. M. Silverihna and N. Engheta, "Design of matched zero-index metamaterials using non-magnetic inclusions in epsilon-near-zero media," Phys. Rev. B 75, 075119 (2007). [CrossRef]
  10. R. W. Ziolkowski and C.-Y. Cheng, "Lumped element models of double negative metamaterial-based transmission lines," Radio Sci. 39, RS2017 (2004). [CrossRef]
  11. N. Katsarakis, G. Konstantinidis, A. Kostopoulos, R. S. Penciu, T. F. Gundogdu, M. Kafesaki, E. N. Economou, Th. Koschny, and C. M. Soukoulis, "Magnetic response of split-ring resonators in the far-infrared frequency regime," Opt. Lett. 30, 1348-1350 (2005). [CrossRef] [PubMed]
  12. L. Jylhä, I. Kolmakov, S. Maslovski, and S. Tretyakov, "Modeling of isotropic backward-wave materials composed of resonant spheres," J. Appl. Phys. 99, 043102 (2006). [CrossRef]
  13. K. Guven, A. O. Cakmak, M. D. Caliskan, T. F. Gundogdu, M. Kafesaki, C. M. Soukoulis, and E. Ozbay, "Bilayer metamaterial: analysis of left-handed transmission and retrieval of effective medium parameters," J. Opt. A 9, S361-S365 (2007). [CrossRef]
  14. W. J. Padilla, M. T. Aronsson, C. Highstrete, M. Lee, A. J. Taylor, and R. D. Averitt, "Electrically resonant terahertz metamaterials," Phys. Rev. B 75, 041102 (2007). [CrossRef]
  15. B. Baumeier, T. A. Leskova, and A. A. Maradudin, "Transmission through thin metal film with periodically and randomly corrugated surfaces," J. Opt. A 8, S191-S207 (2006). [CrossRef]
  16. I. R. Hooper and J. R. Sambles, "Coupled surface plasmon polaritons on thin metal slabs corrugated on both surfaces," Phys. Rev. B 70, 045421 (2004). [CrossRef]
  17. M. M. Dvoynenko, I. I. Samoylenko, and J.-K. Wang, "Suppressed light transmission through corrugated metal films at normal incidence," J. Opt. Soc. Am A 23, 2315-2319 (2006). [CrossRef]
  18. N. Bonod, S. Enoch, L. Li, E. Popov, and M. Neviere, "Resonant optical transmission through thin metallic films with and without holes," Opt. Express 11, 482-490 (2003). [CrossRef] [PubMed]
  19. R. A. Depine, A. Lakhtakia, and D. R. Smith, "Enhanced diffraction by a rectangular grating made of a negative phase-velocity (or negative index) material," Phys. Lett. A 337, 155-160 (2005). [CrossRef]
  20. R. A. Depine, M. E. Inchaussandague, and A. Lakhtakia, "Vector theory of diffraction by gratings made of a uniaxial dielectric-magnetic material exhibiting negative refraction," J. Opt. Soc. Am. B 23, 514-528 (2006). [CrossRef]
  21. Z. Wang, J. D. Chong, J. D. Joannopoulos, and M. Soljacic, "Reflection-free one-way edge modes in gyromagnetic photonic crystals," Phys. Rev. Lett. 100, 013905 (2008). [CrossRef] [PubMed]
  22. F. D. M. Haldane and S. Raghu, "Possible realization of directional optical waveguides in photonic crystals with broken time-reversal symmetry," arXiv:cond-mat/0503588 (2008).
  23. T. Magath and A. E. Serebryannikov, "Fast iterative, coupled-integral-equation technique for inhomogeneous profiled and periodic slabs," J. Opt. Soc. Am. A 22, 2405-2418 (2005). [CrossRef]
  24. R. Petit, Ed., Electromagnetic theory of gratings (Springer, Berlin Heidelberg New York, 1980).

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