A non-reflecting metamaterial slab under the finite-embedded coordinate transformation

doi:10.1364/OE.18.014093

« Show journal navigation

A non-reflecting metamaterial slab under the finite-embedded coordinate transformation

Il-Min Lee, Seung-Yeol Lee, Kyoung-Youm Kim, and Byoungho Lee »View Author Affiliations

Optics Express, Vol. 18, Issue 13, pp. 14093-14106 (2010)
http://dx.doi.org/10.1364/OE.18.014093

View Full Text Article

Acrobat PDF (2047 KB)

Journal Search
Article Lookup

Article Tools

Citations

Alert me when this article is cited
Export Citation/Save

Article Navigation

▸ Article Outline
– Abstract
1. Introduction
2. Derivation of the governing equation
3. Two-dimensional examples
4. Extended example: an extended two-dimensional case
5. Conclusion
– References and links

Article Tools
Full Text
Article Info
References
Cited By
Figures
Metrics
Download PDF

Viewing Equations in the
HTML Article

Optimal Viewing Recommendations

Full Text
Article Info
References (18)
Cited By
Figures (5)
Metrics

Abstract

Under the restrictions that the mapping functions of transformation are defined in extended two-dimensional (2D) forms and the incident waves are 2D propagating fields, the conditions for non-reflecting boundaries in a finite-embedded coordinate transformation metamaterial slab are derived. By exploring several examples, including some reported in the literatures and some novel ones developed in this study, we show that our approach can be efficiently used to determine the condition for a finite-embedded coordinate transformed metamaterial slab to be non-reflecting.

1. Introduction

Coordinate transformation optics (hereafter referred to as transformation optics) is a recently introduced concept of tailoring electromagnetic waves to achieve certain desirable characteristics via the use of specially designed metamaterials [1

J. B. Pendry, D. Schurig, and D. R. Smith, “Controlling electromagnetic fields,” Science 312(5781), 1780–1782 (2006). [CrossRef] [PubMed]

]. The technique is based on the form-invariance of Maxwell’s equations under smooth and differentiable coordinate transformations [2

A. Ward and J. Pendry, “Refraction and geometry in Maxwell's equations,” J. Mod. Opt. 43, 773–793 (1996). [CrossRef]

]. The mathematically defined transformations are cast into corresponding changes of constitutive material parameters and consequently, of electromagnetic entities, such as electromagnetic fields, currents, and charge distributions. The invisibility cloak has been proposed [1

J. B. Pendry, D. Schurig, and D. R. Smith, “Controlling electromagnetic fields,” Science 312(5781), 1780–1782 (2006). [CrossRef] [PubMed]

] as an innovative example of these, and many related experimental [3

D. Schurig, J. J. Mock, B. J. Justice, S. A. Cummer, J. B. Pendry, A. F. Starr, and D. R. Smith, “Metamaterial electromagnetic cloak at microwave frequencies,” Science 314(5801), 977–980 (2006). [CrossRef] [PubMed]

] and theoretical studies have been proposed. In addition to cloaking devices, including the carpet cloak [4

J. S. Li and J. B. Pendry, “Hiding under the carpet: a new strategy for cloaking,” Phys. Rev. Lett. 101(20), 203901 (2008). [CrossRef] [PubMed]

], acoustic cloak [5

S. A. Cummer, B. I. Popa, D. Schurig, D. R. Smith, J. Pendry, M. Rahm, and A. Starr, “Scattering theory derivation of a 3D acoustic cloaking shell,” Phys. Rev. Lett. 100(2), 024301 (2008). [CrossRef] [PubMed]

], matter wave cloak [6

S. Zhang, D. A. Genov, C. Sun, and X. Zhang, “Cloaking of matter waves,” Phys. Rev. Lett. 100(12), 123002 (2008). [CrossRef] [PubMed]

] and an anti-cloak [7

H. Y. Chen, X. D. Luo, H. R. Ma, and C. T. Chan, “The anti-cloak,” Opt. Express 16(19), 14603–14608 (2008). [CrossRef] [PubMed]

], other interesting concepts of coordinate transformation optics such as adaptive beam bends and beam expanders [8

M. Rahm, D. A. Roberts, J. B. Pendry, and D. R. Smith, “Transformation-optical design of adaptive beam bends and beam expanders,” Opt. Express 16(15), 11555–11567 (2008). [CrossRef] [PubMed]

], field concentrators [9

M. Rahm, D. Schurig, D. Roberts, S. Cummer, D. Smith, and J. Pendry, “Design of electromagnetic cloaks and concentrators using form-invariant coordinate transformations of Maxwell’s equations,” Photonics Nanostruct. Fundam. Appl. 6(1), 87–95 (2008). [CrossRef]

], source transformation devices [10

N. Kundtz, D. A. Roberts, J. Allen, S. Cummer, and D. R. Smith, “Optical source transformations,” Opt. Express 16(26), 21215–21222 (2008). [CrossRef] [PubMed]

] and illusion optical devices [11

Y. Lai, J. Ng, H. Y. Chen, D. Z. Han, J. J. Xiao, Z. Q. Zhang, and C. T. Chan, “Illusion optics: the optical transformation of an object into another object,” Phys. Rev. Lett. 102(25), 253902 (2009). [CrossRef] [PubMed]

] have been reported as well.

From a topological view point, transformation optics can be categorized into two types. In the first type of transformation, the spatial domain of the transformation is ideally localized within a finite space: in other words, the interaction of light waves with the transformed region is designed to occur near localized objects. The invisibility cloak (free space), carpet cloak (ground mirror) or illusion optics (other objects) are such examples. Therefore, the properties of outgoing light waves from such transformed media, at least in ideal cases, recover those of their original states. In contrast, the other type of transformation optical device has been proposed, i.e. finite-embedded coordinate transformation optical devices [12

M. Rahm, S. A. Cummer, D. Schurig, J. B. Pendry, and D. R. Smith, “Optical design of reflectionless complex media by finite embedded coordinate transformations,” Phys. Rev. Lett. 100(6), 063903 (2008). [CrossRef] [PubMed]

]. In this type of transformation, the metrics of space are not necessarily recovered into those of the original space. In many cases, the main objective of transformed optical media is to modify the outgoing wavefronts. The beam shifter, divider [12

] and expander [8

M. Rahm, D. A. Roberts, J. B. Pendry, and D. R. Smith, “Transformation-optical design of adaptive beam bends and beam expanders,” Opt. Express 16(15), 11555–11567 (2008). [CrossRef] [PubMed]

] are examples of this type.

The concept of finite-embedded coordinate transformation optics has stimulated some interest in the reflection conditions at the interfaces between transformed and untransformed media. Due to some slight vagueness in the non-reflecting condition between these media suggested in the original introductory paper [12

], the issue of the necessary and/or sufficient conditions for finite-embedded media to be transparent has been discussed [8

M. Rahm, D. A. Roberts, J. B. Pendry, and D. R. Smith, “Transformation-optical design of adaptive beam bends and beam expanders,” Opt. Express 16(15), 11555–11567 (2008). [CrossRef] [PubMed]

,13

W. Yan, M. Yan, and M. Qiu, “Necessary and sufficient conditions for reflectionless transformation media in an isotropic and homogenous background,” arXiv:0806.3231v1 (2008).

–17

I. Gallina, G. Castaldi, V. Galdi, A. Alù, and N. Engheta, “General class of metamaterial transformation slabs,” Phys. Rev. B 81(12), 125124 (2010). [CrossRef]

]. The non-reflecting condition derived in Ref [13

W. Yan, M. Yan, and M. Qiu, “Necessary and sufficient conditions for reflectionless transformation media in an isotropic and homogenous background,” arXiv:0806.3231v1 (2008).

]. covers three-dimensionally (3D) transformed media with non-planar boundaries. The derived condition given in Eq. (11) in Ref. [13

W. Yan, M. Yan, and M. Qiu, “Necessary and sufficient conditions for reflectionless transformation media in an isotropic and homogenous background,” arXiv:0806.3231v1 (2008).

]. states that if the boundary coordinate in the transformed medium can be expressed as the rotation of the original space with a constant displacement vector added, the boundary is non-reflecting. However, in this report we will show that a non-reflecting coordinate transformed boundary can exist for a skewed-and-expanded transformation (see Section 3.2 and Fig. 4 ) which cannot be covered by Eq. (11) in Ref. [13

W. Yan, M. Yan, and M. Qiu, “Necessary and sufficient conditions for reflectionless transformation media in an isotropic and homogenous background,” arXiv:0806.3231v1 (2008).

]. Another general study on the boundary conditions for generalized transformed media was also reported [14

L. Bergamin, “Electromagnetic fields and boundary conditions at the interface of generalized transformation media,” Phys. Rev. A 80(6), 063835 (2009). [CrossRef]

]. Although our study is restricted to more specific cases of extended two-dimensional (2D) problems, we provide more explicit conditions and illustrative examples throughout this paper which were not addressed in Ref. [14

L. Bergamin, “Electromagnetic fields and boundary conditions at the interface of generalized transformation media,” Phys. Rev. A 80(6), 063835 (2009). [CrossRef]

]. Recently, studies on the mapping method that can make the 2D transformation optical slab transparent in a general way have been reported [15

I.-M. Lee, “Study on the transmission characteristics of the optical waves in photonic metamaterials,” PhD Dissertation (School of Electrical Engineering, Seoul National University, Seoul, Korea, 2009).

–17

I. Gallina, G. Castaldi, V. Galdi, A. Alù, and N. Engheta, “General class of metamaterial transformation slabs,” Phys. Rev. B 81(12), 125124 (2010). [CrossRef]

]. However, the discussions concerning this are limited only to cases of 2D transformed media and cannot deal with extended 2D cases which are treated in our paper (see Section 4 and Fig. 5 ).

Fig. 4 Field distributions for the skewed-and-expanded coordinate transformation.

Fig. 5 Numerical results for the example of the 2D beam expander without any reflection. The normalized field distribution at

z = 0

plane is depicted in (a). The results in (b) show the material parameters (

\bar{\bar{m}}

) along the line

y = 5 λ

In this work, the non-reflecting boundary conditions of a finite-embedded coordinate transformed metamaterial slab will be explored. For the sake of simplicity, we imposed two restrictions in our study. The first one is that the mapping functions of the coordinate transformation,

x'

and

y'

are not z-dependent: only

z'

can be x-, y- and z-dependent. This is more general than the 2D transformations treated in Refs. [15

–17

I. Gallina, G. Castaldi, V. Galdi, A. Alù, and N. Engheta, “General class of metamaterial transformation slabs,” Phys. Rev. B 81(12), 125124 (2010). [CrossRef]

]. As will be seen in this study, this is not a straightforward extension of the 2D case and care must be taken in deriving the non-reflecting condition. We also assume that the incident field is defined in 2D conventions, i.e., we exclude conical incidence. With this assumption, the dispersion relation in the transformed media can be given in a very simple form. The governing equations which make transformed media transparent are presented, along with details of the derivation procedure. Several examples, including known mapping functions in several literatures as well as some novel ones, will be discussed with numerical implementations. A discussion of the design of some novel transformation optical devices is also presented.

2. Derivation of the governing equation

In this section, we start with the basics of the coordinate transformation in a Cartesian coordinate system and derive an equation which describes the non-reflecting boundaries in 2D finite-embedded coordinate transformation media (CTM). Let us consider a coordinate transformation in a Cartesian coordinate system, which maps the points in the original space (or the virtual space)

(x, y, z)

to those in the physical space (or the transformed space)

(x', y', z')

as follows:

(x', y', z') = (F (x, y, z), G (x, y, z), H (x, y, z)),

(1)

where F, G, and H are the mapping functions of the coordinate transformation. We further assume that the mapping functions in Eq. (1) can have inverse transformations.

Now let us consider the case where this CTM is finitely embedded as in Fig. 1 . We assume that the material parameters in the original space can be different from those of the surrounding media in the physical space. As depicted in Fig. 1, the transformed medium (region II) fills a finite-extent (along x’-direction) of the physical space and the material parameters of both sides of the transformed medium (region I and III) can also be different.

Fig. 1 Geometrical representation of a finite-embedded coordinate transformation.

For the sake of simplicity, we further assume that the mapping functions in Eq. (1) are defined in a sort of extended 2D convention such that

F (x, y, z) = F (x, y), G (x, y, z) = G (x, y), H (x, y, z) = h (x, y) z .

(2)

This means that the mapping functions

x'

and

y'

are not z-dependent but

z'

can be x- and y-dependent by the scale factor

h (x, y)

: this is the reason why we refer to this mapping as extended 2D case.

From the form-invariance of Maxwell’s equations, the material tensors in virtual space

\bar{\bar{m}}

can be re-expressed in the physical space as

\bar{\bar{m}}'

with the following relation [1

J. B. Pendry, D. Schurig, and D. R. Smith, “Controlling electromagnetic fields,” Science 312(5781), 1780–1782 (2006). [CrossRef] [PubMed]

{\bar{\bar{m}}}^{i' j'} = A_{i}^{i'} A_{j}^{j'} {\bar{\bar{m}}}^{i j} / \det (A_{i}^{i'}),

(3)

where

\bar{\bar{m}}

and

\bar{\bar{m}}'

denote either the permittivity or the permeability tensor and

A_{i}^{i'}

is the element of the transformation Jacobian matrix defined as

A_{i}^{i'} = \partial x^{i'} / \partial x^{i} .

(4)

Throughout this paper, we assume that the material in the virtual space is isotropic and homogeneous so that the material parameters in the original space can be expressed as

\bar{\bar{ε}} = ε_{0} ε_{r}

and

\bar{\bar{μ}} = μ_{0} μ_{r}

. Under this condition, the material tensor in transformed space can be defined as

\bar{\bar{ε}} = ε_{0} ε_{r} \bar{\bar{m}}'

and

\bar{\bar{μ}} = μ_{0} μ_{r} \bar{\bar{m}}'

with

\bar{\bar{m}}' = A A^{t} / \det (A)

where A is the Jacobian matrix and the superscript t denotes the matrix transpose.

Now suppose that the material tensor

\bar{\bar{m}}'

can be expressed as

\bar{\bar{m}}' = [\begin{matrix} a & b & c \\ b & d & e \\ c & e & f \end{matrix}]

(5)

and its inverse matrix

{(\bar{\bar{m}}')}^{- 1}

is given as

{(\bar{\bar{m}}')}^{- 1} = \frac{1}{Δ} [\begin{matrix} (d f - e^{2}) & - (b f - c e) & (b e - c d) \\ - (b f - c e) & (a f - c^{2}) & - (a e - b c) \\ (b e - c d) & - (a e - b c) & (a d - b^{2}) \end{matrix}] = \frac{1}{Δ} [Δ_{j i}],

(6)

where

Δ_{i j}

is the matrix cofactor and Δ is the determinant of

\bar{\bar{m}}'

given as

Δ = a d f - a e^{2} - b^{2} f - c^{2} d + 2 b c e

(7)

from the coordinate transformation results shown in Eq. (1). Substituting Eq. (5) into Maxwell’s equations with time dependency of

\exp (- j ω t)

gives the following wave equation in a matrix form:

\frac{k_{0}^{2}}{Δ^{2}} S E + k_{0}^{2} n^{2} E = 0,

(8)

where E is a column vector of

(E_{x}, E_{y}, E_{z})

, n is the refractive index of the original material,

n_{I I}^{2} = ε_{I I} μ_{I I}

, and

k_{0}

is the free-space wavenumber. The system matrix S in Eq. (8) is given as

S = {[\begin{matrix} Δ_{12} κ_{z} - Δ_{13} κ_{y} & - Δ_{11} κ_{z} + Δ_{13} κ_{x, I I} & Δ_{11} κ_{y} - Δ_{12} κ_{x, I I} \\ Δ_{22} κ_{z} - Δ_{23} κ_{y} & - Δ_{12} κ_{z} + Δ_{23} κ_{x, I I} & Δ_{12} κ_{y} - Δ_{22} κ_{x, I I} \\ Δ_{23} κ_{z} - Δ_{33} κ_{y} & - Δ_{13} κ_{z} + Δ_{33} κ_{x, I I} & Δ_{13} κ_{y} - Δ_{23} κ_{x, I I} \end{matrix}]}^{2},

(9)

where

κ_{i} = k_{i} / k_{0}

and we drop the prime notations in subscripts for simplicity. From the condition that Eq. (8) has a non-trivial solution, the determinant of

(S / Δ^{2} + n^{2} I)

, where I is the identity matrix, should be zero. Therefore, we arrive at the following dispersion relation for this transformed media

n_{I I}^{2} {(- Δ n_{I I}^{2} + a κ_{x, I I}^{2} + d κ_{y}^{2} + f κ_{z}^{2} + 2 b κ_{x, I I} κ_{y} + 2 c κ_{z} κ_{x, I I} + 2 e κ_{y} κ_{z})}^{2} / Δ^{2} = 0.

(10)

For simplicity, we assume that the incident plane wave arising from region I has

k_{z} = 0

. Under this assumption and for a non-zero n, the dispersion relation in Eq. (10) can be expressed with cofactor elements as:

Δ_{33} {(Δ_{22} κ_{x, I I} - Δ_{12} κ_{y})}^{2} = Δ_{22} n_{I I}^{2} Δ^{2} + Δ_{22} {(Δ_{23} κ_{x, I I} - Δ_{13} κ_{y})}^{2} - Δ_{33} (Δ_{11} Δ_{22} - Δ_{12}^{2}) κ_{y}^{2} .

(11)

In general, the transformed medium in region II is inhomogeneous and anisotropic and thus, cannot be approximated efficiently using simple models such as a stair-case approximation. Therefore, we restrict our analysis to those cases in which the variations in the material parameters in the transformed space are smooth and differentiable. Furthermore, since our interest is to attempt to determine conditions that make this finite slab of CTM non-reflecting, multiple reflections can be ignored. As a consequence, we can consider the reflections at each interface (

x' = d_{1}'

and

x' = d_{2}'

) separately as if they were single interfaces. In addition, when we obtain the non-reflecting condition at the first boundary (

x' = d_{1}'

), the condition required for reflectance of the second boundary (

x' = d_{2}'

) to be zero can be obtained very easily, i.e., we can adopt the condition obtained at the first boundary with an appropriate change in material parameters from I to III.

From an analysis of eigenvalues and eigenvectors of this transformed media under the assumption of a plane monochromatic wave, it is apparent that the TE- and TM-polarized fields are eigen-bases of this transformed material. Therefore, we can decompose the problem into TE- and TM-polarized cases. Now let us consider the reflectance of the TM-polarized plane monochromatic wave [

E = (E_{x}, E_{y}, 0)

and

H = (0, 0, H_{z})

] incident on the first boundary. The magnetic field components in the immediate vicinity of the first boundary are readily expressed as

H_{z, I} = \exp [j (k_{x, I} x + k_{y} y)] + r \exp [j (- k_{x, I} x + k_{y} y)],

(12)

H_{z, I I} = t \exp [j (k_{x, I I} x + k_{y} y)],

(13)

where r and t are complex coefficients of the reflectance and the transmittance, respectively. From Maxwell’s equations, the tangential electric field in region I can be easily obtained as

E_{y, I} = \frac{k_{x, I}}{k_{0} ε_{I}} {\exp [j (k_{x, I} x + k_{y} y)] - r \exp [j (- k_{x, I} x + k_{y} y)]} .

(14)

The tangential electric field in region II can be obtained similarly with the material parameters given in Eq. (5) as

E_{y, I I} = \frac{Δ_{22} k_{x, I I} - Δ_{12} k_{y}}{k_{0} ε_{I I} Δ} t \exp [j (k_{x, I I} x + k_{y} y)] .

(15)

From the continuity of the tangential components of the electromagnetic field at the boundary, we have

r = \frac{Δ ε_{I I} κ_{x, I} - ε_{I} (Δ_{22} κ_{x, I I} - Δ_{12} κ_{y})}{Δ ε_{I I} κ_{x, I} + ε_{I} (Δ_{22} κ_{x, I I} - Δ_{12} κ_{y})},

(16)

t = \frac{2 Δ ε_{I I} κ_{x, I}}{Δ ε_{I I} κ_{x, I} + ε_{I} (Δ_{22} κ_{x, I I} - Δ_{12} κ_{y})} .

(17)

Therefore, to make r zero, we have

Δ ε_{I I} κ_{x, I} = ε_{I} (Δ_{22} κ_{x, I I} - Δ_{12} κ_{y}) .

(18)

To make the medium non-reflecting for all incidence angles (i.e. for arbitrary values of

k_{y}

), Eq. (18) should be satisfied for the arbitrary values of

k_{y}

. Considering Eqs. (11) and (18), we find that such conditions can be fulfilled only if the following condition is satisfied by the coordinate transformation (see the Appendix):

(A_{x}^{x'} A_{y}^{z'} - A_{y}^{x'} A_{x}^{z'}) (A_{x}^{x'} A_{x}^{z'} + A_{y}^{x'} A_{y}^{z'}) = 0.

(19)

When Eq. (19) is satisfied, the condition for which the extended 2D finite embedded coordinate medium is non-reflecting can be obtained as (see the Appendix):

Δ_{22}^{2} μ_{I I}^{2} = Δ_{33} μ_{I}^{2},

(20)

which can be expressed in Jacobian elements as

{(A_{z}^{z'})}^{2} {[{(A_{x}^{x'})}^{2} + {(A_{y}^{x'})}^{2}]}^{2} μ_{I I}^{2} = {(A_{x}^{x'} A_{y}^{y'} - A_{y}^{x'} A_{x}^{y'})}^{4} μ_{I}^{2},

(21)

and further simplified in an alternate form as

(A_{z}^{z'}) [{(A_{x}^{x'})}^{2} + {(A_{y}^{x'})}^{2}] = \pm ρ {(A_{x}^{x'} A_{y}^{y'} - A_{y}^{x'} A_{x}^{y'})}^{2},

(22)

where

ρ = μ_{I} / μ_{I I}

The condition for the second interface can be readily obtained by changing

μ_{I}

in Eq. (20) with

μ_{I I I}

Δ_{22}^{2} μ_{I I}^{2} = Δ_{33} μ_{I I I}^{2} .

(23)

Let us consider the case

μ_{I}^{2} \neq μ_{I I I}^{2}

. Even for this case, we can still generally say that the boundaries can be made non-reflecting when the mapping function at each boundary satisfies the conditions in Eq. (20) or (23) separately and the mapping functions in between change smoothly. Under this condition, and from the duality for the TE-polarized case, we have the following form for the condition for the non-reflecting boundary:

{(A_{z}^{z'}) [{(A_{x}^{x'})}^{2} + {(A_{y}^{x'})}^{2}] |}_{i} = \pm {ρ_{i} {(A_{x}^{x'} A_{y}^{y'} - A_{y}^{x'} A_{x}^{y'})}^{2} |}_{i} .

(24)

where

ρ_{i} = ε_{i} / ε_{I I}

for TE- and

ρ_{i} = μ_{i} / μ_{I I}

for TM-mode light waves and i denotes either I or III and we used the notation

|_{i}

to denote the left and the right boundaries.

In fact, the solution sets that satisfy Eq. (20) are not identical to those satisfying Eq. (18): in squaring Eq. (18), another set of solutions is introduced. In fact, this latter set of solutions makes the denominator of Eq. (16) or (17) zero, which physically means that these solutions are those for the excitation of the waveguide mode propagating along the y-direction with a propagation constant

k_{y}

satisfying the squared form of Eq. (18). In practical situations, the excited waveguide modes under the condition of Eq. (21) are surface modes (formed only when the two media (I and II) have opposite signs for permittivity or permeability) which can be excited by the incidence of evanescent waves. Therefore, if we exclude this specific case of surface wave excitation that requires both opposite signs and the incidence of evanescent waves, the conditions in Eq. (24) can be regarded as necessary and sufficient conditions for a non-reflecting boundary. Otherwise, these conditions become necessary ones to make the finite-embedded CTM non-reflecting.

In Eq. (24), the ±sign means that the signs of the material parameters between the transformed and the background media can be freely selectable. However, as stated above, choosing opposite signs can result in the excitation of the surface waves at the interface, and if it is not inevitable, selecting the same sign as the surrounding media [i.e., choosing + in Eq. (24)] is recommended.

Equation (24) can be used as a guideline for the design of a planar finite-embedded CTM interface. Since the differential equation given in Eq. (24) is quite general, providing a general solution is difficult. Instead, we will explore several simple test solutions and show the utility and validity of the derived conditions in the next sections.

3. Two-dimensional examples

The simplest example satisfying Eq. (19) is the case where the transformation is totally 2D:

A_{x}^{z'} = A_{y}^{z'} = 0.

(25)

For this case, we can assume that the mapping functions given in Eq. (1) can be expressed in the following forms:

x' (x, y) = A (x) + B (y) + F (x) G (y) + c_{1},

(26)

y' (x, y) = C (x) + D (y) + H (x) K (y) + c_{2},

(27)

z' (x, y) = c_{3} z,

(28)

where

c_{i}

(

i = 1, 2, 3

) are constants.

By substituting Eqs. (26)–(28) into (24) we have

{c_{3} [{(A_{x} + F_{x} G)}^{2} + {(B_{y} + F G_{y})}^{2}] |}_{i} = {\pm ρ_{i} {[(A_{x} + F_{x} G) (D_{y} + H K_{y}) - (B_{y} + F G_{y}) (C_{x} + H_{x} K)]}^{2} |}_{i},

(29)

where

|_{i}

denotes the left and right boundaries and the subscript η means the partial derivative with respect to the variable η, i.e.,

X_{η} = \partial X (x, y) / \partial η

for

η = x

or y. In the following sub-sections, we consider several examples for the mapping functions given in Eqs. (26)–(28).

3.1. Beam shifter and beam expander

The beam shifter and expander based on coordinate transformation optics are shown schematically in Fig. 2 .

Fig. 2 Geometrical representation of (a) beam shifter and (b) beam expander.

The mapping function of the beam shifter in its simple form can be found in Ref. [12

], and it is given as follows:

x' = x, y' = y + \tan θ x, z' = c_{3} z,

(30)

where the upper and lower limits in the transformed region are ignored, for the simplicity of the discussion.

By comparing the conventions given in Eqs. (26)–(28), we can set

A (x) = x, F (x) = 1, C (x) = x \tan θ, D (y) = y, K (y) = 1,

(31)

with all other functions not specified in Eq. (31) being zero. Substituting these in Eq. (29) gives

c_{3} = \pm ρ_{i} .

(32)

For the case of

c_{3} = 1

, this result supports the widely-known fact that if the impedance of the medium in the virtual space for the given polarization is matched to those of the background media in the physical space, the shift transformation causes no reflection at the boundary [12

Let us turn our attention to the beam expander. The simplest form of the mapping function for the beam expander can be given as [8

M. Rahm, D. A. Roberts, J. B. Pendry, and D. R. Smith, “Transformation-optical design of adaptive beam bends and beam expanders,” Opt. Express 16(15), 11555–11567 (2008). [CrossRef] [PubMed]

]

x' = x, y' = m (x) y, z' = c_{3} z,

(33)

where the magnification coefficient

m (x)

is assumed to have a value of 1 at the first boundary (x = 0) and a constant value M at the second boundary (x = d). In a simple implementation, the x-dependent magnification coefficient can be defined in a linear function of x as follows:

m (x) = (M - 1) (x - d) / d + M,

(34)

where d is the x-directional thickness of the transformed region.

From Eqs. (26)–(28), we can set:

A (x) = x, F (x) = 1, H (x) = m (x), K (y) = y,

(35)

with other functions that are not specified being zero. Substituting these in Eq. (29) gives

c_{3} = \pm ρ_{i} {[m (x_{i})]}^{2} .

(36)

From the definition that

c_{3}

is a constant, the above result implies that, if the square of the magnification factor

m (x)

at the boundaries becomes different from

\pm c_{3} / ρ_{i}

, the coordinate expansion in the transversal direction (along y-direction) will cause reflection. Therefore, to make the interfaces non-reflecting, regions I and III should be filled with material that can satisfy Eq. (36).

3.2. Rotated and skewed-and-expanded transformation

Now let us consider another example in which the mapping functions in Eqs. (26)–(28) have the form of the combined characteristics of the longitudinal and transversal expansions. We will examine a simple mapping function given as

x' = α x + β y, y' = χ x + δ y, z' = z,

(37)

where α, β, χ, and δ are all non-zero constants. From the conventions in Eqs. (26)–(28), we have the following:

A (x) = α x, B (y) = β y, C (x) = χ x, D (y) = δ y,

(38)

with the other functions and constants not specified being zero. From the condition of Eq. (29) we have

(α^{2} + β^{2}) = {(α δ - β χ)}^{2},

(39)

where we assumed that the impedances of media I, II, and III are matched and

\pm ρ

is dropped for the sake of simplicity.

Initially, consider the case in which

δ = α

and

χ = - β

. For this case, Eq. (39) can be expressed as

(α^{2} + β^{2}) = {(α^{2} + β^{2})}^{2} .

(40)

Therefore, from the assumption of non-zero constants, we have

(α^{2} + β^{2}) = 1

. This condition can be generally satisfied by setting

α = \cos θ

and

β = \sin θ

. Hence the mapping in Eq. (37) can be expressed as

x' = \cos θ x + \sin θ y, y' = - \sin θ x + \cos θ y, z' = z,

(41)

which corresponds to the 2D rotation of the coordinates. Actually, the rotation of the coordinates does not change the material parameter in Eq. (5) because

\bar{\bar{m}}'

for this transformation is a unit diagonal matrix.

However, Eq. (39) can be satisfied in various other ways than

δ = α

and

χ = - β

. For example, by choosing the values of the constants in Eq. (39) as

α = 3

β = 4

χ = 1

, and

δ = 3

, this gives the mapping of

x' = 3 x + 4 y, y' = x + 3 y, z' = z,

(42)

and a metric tensor of

\bar{\bar{m}}' = [\begin{matrix} 5 & 3 & 0 \\ 3 & 2 & 0 \\ 0 & 0 & 0.2 \end{matrix}],

(43)

which satisfies Eq. (39).

This coordinate transformation given in Eq. (42) maps the geometrical grids of the virtual space in the Cartesian coordinates into skewed and expanded ones as presented in Fig. 3 . In Fig. 3, the dotted and circled lines correspond to lines that are parallel to the x-axis and y-axis before the transformation, respectively, and the thin grid lines denote the grid lines in the

x'

y'

coordinates.

Fig. 3 Transformed geometrical grid made by the skewed and expanded transformation given by Eq. (42).

In Fig. 4, we present the electric field distributions obtained from a commercial software program based on the finite element method [18

“Comsol multiphysics” (Comsol AB), <http://www.comsol.com>.

]. In this figure, the field radiated from a point (line) source propagates through a finite coordinate transformed slab which satisfies the condition of Eq. (39) by the mapping function in Eq. (42) without reflections. In this calculation, the thickness of the coordinate transformed slab is

4 λ

, where λ is the free-space wavelength.

3.3. Further examples

Some interesting discussions on the non-reflecting condition of the finite-embedded CTM has been reported [17

I. Gallina, G. Castaldi, V. Galdi, A. Alù, and N. Engheta, “General class of metamaterial transformation slabs,” Phys. Rev. B 81(12), 125124 (2010). [CrossRef]

]. In that study, the following mapping function was considered:

x' = a u (x), y' = y / u_{x} (x) + v (x), z' = z,

(44)

which can be expressed using the conventions in Eqs. (26)-(28) as

A (x) = a u (x), C (x) = v (x), H (x) = 1 / u_{x} (x), K (y) = y,

(45)

in which the other functions and constants are all zero. In this case, using the newly-derived condition of Eq. (29), we can obtain the following condition for a non-reflecting boundary:

{(a u_{x})}^{2} = {(a u_{x} / u_{x})}^{2},

(46)

which corresponds to

u_{x} = \pm 1,

(47)

and this coincides well with the results reported in Ref. [17

I. Gallina, G. Castaldi, V. Galdi, A. Alù, and N. Engheta, “General class of metamaterial transformation slabs,” Phys. Rev. B 81(12), 125124 (2010). [CrossRef]

Let us consider another example similar to Eq. (44) with the following form of transformation:

x' = a u_{x} (x), y' = y / u (x) + v (x), z' = z,

(48)

which can be expressed using the conventions in Eqs. (26)-(28) as

A (x) = a u_{x} (x), C (x) = v (x), H (x) = 1 / u (x), K (y) = y

(49)

with other functions and constants being zero. Using the condition in Eq. (29), we have the condition of the non-reflecting boundary as

{(a u_{x x})}^{2} = {(a u_{x x} / u)}^{2},

(50)

which corresponds to

u = \pm 1

(51)

at the boundaries. From the mapping functions in Eqs. (44) and (48), it can be found that mapping functions which enable transparency can have various other forms than that introduced in Ref. [12

4. Extended example: an extended two-dimensional case

4.1. Non-reflecting beam expander

Now let us consider more complicated cases which satisfy Eq. (19). What we examine is the case in which the mapping functions are given as

x' = x, y' = m (x) y, z' = c (x) z .

(52)

This satisfies Eq. (19) for

A_{y}^{z'} = A_{y}^{x'} = 0

. The mapping functions in Eq. (52) correspond to the case in which the scaling of the axes is applied simultaneously in two tangential directions. For this case, the material tensor

\bar{\bar{m}}'

is given as

\bar{\bar{m}}' = \frac{1}{c m} [\begin{matrix} 1 & m_{x} y & c_{x} z \\ m_{x} y & {(m_{x} y)}^{2} + m^{2} & m_{x} y c_{x} z \\ c_{x} z & m_{x} y c_{x} z & {(c_{x} z)}^{2} + c^{2} \end{matrix}] .

(53)

If we assume that

k_{z} = 0

, Eq. (22) is applicable to this case, and we arrive at the following condition for the non-reflecting boundaries:

c (x) = \pm ρ_{i} {[m (x)]}^{2} .

(54)

The electric field distributions and the corresponding values of the material parameters are shown in Fig. 5.

The results presented in Eq. (54) and in Fig. 5 are contradictory to conventional knowledge on coordinate-transformation-based beam expander. Until now, it was generally believed that a non-reflecting beam expander cannot be produced except for the case where the indices of the surrounding media are selected so as to match the square value of the magnification factor

m (x)

at the boundaries (See the related discussions in Ref. [8

M. Rahm, D. A. Roberts, J. B. Pendry, and D. R. Smith, “Transformation-optical design of adaptive beam bends and beam expanders,” Opt. Express 16(15), 11555–11567 (2008). [CrossRef] [PubMed]

].). However, as evidenced by Eq. (54), this is not true if we restrict the magnification to be applied in only one of the transversal directions (along the direction of y-axis in this case) and ignore the conical incidences (

k_{z, I} = 0

In Fig. 5, we assume that all the untransformed media are free-space (

ρ = 1

) and the x-dependent magnification factor is a linear function given in Eq. (34) with the thickness of the slab d of 2λ and the magnification factor at the second interface M of 1.5. The calculated field distribution shows that the slab for the beam expander expands the beam, with almost no reflection, at the interfaces. The small observable ripples in the field distribution at the left-side of the CMT slab are due to numerical errors and the non-optimized nature of the gradient along the x-direction in the scale function

m (x)

. If the material parameters of the transformed region in the x-direction are carefully designed to implement adiabatic variation over a sufficiently long width, the ripples can be decreased. However, the results clearly show that the proposed method can be readily applied to the design of non-reflecting CTM.

5. Conclusion

A general method is proposed to create a non-reflecting finite-embedded coordinate transformed slab, when the mapping function is defined in extended 2D conventions under the condition of

k_{z} = 0

. A governing equation that can be used as the determining equation or as a guideline for the design is also proposed. To verify our approach and demonstrate the validity of our strategy, we explored several examples and discussed their topological meanings. We hope that our approach and the discussions contained in this report will be helpful in designing or understanding finite-embedded coordinate transformed media. We also hope that the approach introduced in this study can serve as a guideline or a starting point for investigations of more general cases such as conical incidences or full 3D mapping functions.

Appendices

Appendix

Here we show that Eq. (19) is a necessary condition for a slab of finite-embedded coordinate transformation to be non-reflecting under the constraint of the extended 2D mapping functions given in Eq. (2).

Let us start from the condition which makes the reflectance r zero in Eq. (18):

Δ ε_{I I} κ_{x, I} = ε_{I} (Δ_{22} κ_{x, I I} - Δ_{12} κ_{y}) .

(A1)

To make the interface non-reflecting, Eq. (A1) should be held for arbitrary values of

κ_{y}

. For this objective, we square both sides of Eq. (A1) and eliminate all

κ_{x, I}

and

κ_{x, I I}

dependencies by using the dispersion relations for media I and II. The dispersion relation for medium I is expressed as

κ_{x, I}^{2} = n_{I}^{2} - κ_{y}^{2},

(A2)

and that for medium II is expressed as Eq. (11), which can be re-expressed as

{[(Δ_{22} Δ_{33} - Δ_{23}^{2}) κ_{x, I I} + (Δ_{23} Δ_{13} - Δ_{12} Δ_{33}) κ_{y}]}^{2} = Δ^{2} [(Δ_{22} Δ_{33} - Δ_{23}^{2}) n_{I I}^{2} - Δ_{33} κ_{y}^{2}] .

(A3)

For any real-valued coordinate transformation

a = [{(A_{x}^{x'})}^{2} + {(A_{y}^{x'})}^{2} + {(A_{z}^{x'})}^{2}] / \det (A)

cannot be zero. Therefore, we have

Δ_{22} Δ_{33} - Δ_{23}^{2} = a Δ \neq 0

. If we assume that the coordinate transformation can be complex-valued, and hence admit those cases of

Δ_{22} Δ_{33} - Δ_{23}^{2} = 0

, Eq. (A3) can be expressed as

[{(Δ_{23} Δ_{13} - Δ_{12} Δ_{33})}^{2} + Δ^{2} Δ_{33}] κ_{y}^{2} = 0.

(A4)

Let us examine Eq. (A4) further. When

{(Δ_{23} Δ_{13} - Δ_{12} Δ_{33})}^{2} + Δ^{2} Δ_{33} = 0

κ_{y}

cannot be determined. Otherwise, we have

κ_{y} = 0

. All these cases are contrary to the claim that Eq. (A1) holds regardless of

κ_{y}

. Therefore, we discard the case where

Δ_{22} Δ_{33} - Δ_{23}^{2}

is zero. Therefore, we can express

κ_{x, I I}

as a function of

κ_{y}

κ_{x, I I} = \frac{1}{Δ_{22} Δ_{33} - Δ_{23}^{2}} {- (Δ_{23} Δ_{13} - Δ_{12} Δ_{33}) κ_{y} \pm Δ {[(Δ_{22} Δ_{33} - Δ_{23}^{2}) n_{I I}^{2} - Δ_{33} κ_{y}^{2}]}^{1 / 2}} .

(A5)

When we substitute Eqs. (A2) and (A5) into Eq. (A1) and, after performing some arithmetic manipulations, we have

\begin{array}{l} {(Δ_{22} Δ_{33} - Δ_{23}^{2})}^{2} Δ^{2} ε_{I I}^{2} (n_{I}^{2} - κ_{y}^{2}) \\ = ε_{I}^{2} {Δ_{23} (Δ_{12} Δ_{23} - Δ_{22} Δ_{13}) κ_{y} \pm Δ Δ_{22} {[(Δ_{22} Δ_{33} - Δ_{23}^{2}) n_{I I}^{2} - Δ_{33} κ_{y}^{2}]}^{1 / 2}}^{2} . \end{array}

(A6)

For the sake of simplicity, we take a simplified from of Eq. (A6) by adopting proper substitutions in the coefficients:

A - B κ_{y}^{2} = {[C κ_{y} \pm {(D + E κ_{y}^{2})}^{1 / 2}]}^{2},

(A7)

which can be expressed as

A - D - (B + C^{2} - E) κ_{y}^{2} = \pm 2 C κ_{y} {(D + E κ_{y}^{2})}^{1 / 2} .

(A8)

We square both sides of Eq. (A8) to obtain

{(A - D)}^{2} - 2 [(A - D) (B + C^{2} + E) + 2 C^{2} D] κ_{y}^{2} + [{(B + C^{2} + E)}^{2} - 4 C^{2} E] κ_{y}^{4} = 0.

(A9)

This should be held for arbitrary values of

κ_{y}

. Therefore, we have the following set of equations that should be satisfied simultaneously:

A - D = 0,

(A10)

C D = 0,

(A11)

{(B + C^{2} + E)}^{2} - 4 C^{2} E = 0.

(A12)

Before solving the above coupled equations, let us first examine Eq. (A11). From this equation, we can find that either C or D should be zero. By comparing Eqs. (A6) and (A7), we can find that Eq. (A11) can be re-expressed in a more explicit form as

Δ_{23} (Δ_{12} Δ_{23} - Δ_{22} Δ_{13}) = 0 or Δ_{22}^{2} (Δ_{22} Δ_{33} - Δ_{23}^{2}) = 0,

(A13)

where the two equations correspond to the conditions that

C = 0

D = 0

, in the order of appearance.

Let us consider the latter case first. As we examined before,

Δ_{22} Δ_{33} - Δ_{23}^{2}

is not zero. Then if

Δ_{22} = 0

, all

κ_{x, I I}

dependent terms in the dispersion relation of Eq. (A3) vanish, i.e., the value of

κ_{x, I I}

is undetermined. Therefore we can also discard this case. Therefore, to satisfy Eq. (A11), we find that

C = 0

. With this result, we further find from Eqs. (A10) and (A12) that

A = D

and

B = - E

By comparing Eqs. (A6) and (A7) once again and using the results of

A = D

and

B = - E

, we have following conditions:

(Δ_{22} Δ_{33} - Δ_{23}^{2}) ε_{I I}^{2} n_{I}^{2} = Δ_{22}^{2} ε_{I}^{2} n_{I I}^{2},

(A14)

{(Δ_{22} Δ_{33} - Δ_{23}^{2})}^{2} ε_{I I}^{2} = Δ_{22}^{2} Δ_{33} ε_{I}^{2} .

(A15)

Equations (A14) and (A15) can be further simplified by combining them as

Δ_{33} n_{I}^{2} = (Δ_{22} Δ_{33} - Δ_{23}^{2}) n_{I I}^{2} .

(A16)

As a final step, we substitute Eq. (A16) into Eq. (A14) to obtain the form of

Δ_{33} μ_{I}^{2} = Δ_{22}^{2} μ_{I I}^{2} .

(A17)

Now, let us consider the condition of

C = 0

in more detail. As we examined in Eq. (A13), this corresponds to the case

Δ_{23} (Δ_{12} Δ_{23} - Δ_{22} Δ_{13}) = 0

. This condition can be expressed using the Jacobian elements of the coordinate transformation:

(A_{x}^{x'} A_{y}^{z'} - A_{y}^{x'} A_{x}^{z'}) (A_{x}^{x'} A_{x}^{z'} + A_{y}^{x'} A_{y}^{z'}) = 0.

(A18)

With Eq. (A18), we derive Eq. (19). Equation (A18) is a necessary condition for the boundary of an extended 2D finite embedded coordinate medium to be non-reflecting. As a result, Eqs. (A17) and (A18) are necessary and sufficient conditions for an extended 2D finite embedded coordinate medium to be non-reflecting.

Acknowledgment

The authors wish to acknowledge the support of the National Research Foundation and the Ministry of Education, Science and Technology of Korea through the Creative Research Initiative Program (Active Plasmonics Application Systems).

References and links

1.	J. B. Pendry, D. Schurig, and D. R. Smith, “Controlling electromagnetic fields,” Science 312(5781), 1780–1782 (2006). [CrossRef] [PubMed]
2.	A. Ward and J. Pendry, “Refraction and geometry in Maxwell's equations,” J. Mod. Opt. 43, 773–793 (1996). [CrossRef]
3.	D. Schurig, J. J. Mock, B. J. Justice, S. A. Cummer, J. B. Pendry, A. F. Starr, and D. R. Smith, “Metamaterial electromagnetic cloak at microwave frequencies,” Science 314(5801), 977–980 (2006). [CrossRef] [PubMed]
4.	J. S. Li and J. B. Pendry, “Hiding under the carpet: a new strategy for cloaking,” Phys. Rev. Lett. 101(20), 203901 (2008). [CrossRef] [PubMed]
5.	S. A. Cummer, B. I. Popa, D. Schurig, D. R. Smith, J. Pendry, M. Rahm, and A. Starr, “Scattering theory derivation of a 3D acoustic cloaking shell,” Phys. Rev. Lett. 100(2), 024301 (2008). [CrossRef] [PubMed]
6.	S. Zhang, D. A. Genov, C. Sun, and X. Zhang, “Cloaking of matter waves,” Phys. Rev. Lett. 100(12), 123002 (2008). [CrossRef] [PubMed]
7.	H. Y. Chen, X. D. Luo, H. R. Ma, and C. T. Chan, “The anti-cloak,” Opt. Express 16(19), 14603–14608 (2008). [CrossRef] [PubMed]
8.	M. Rahm, D. A. Roberts, J. B. Pendry, and D. R. Smith, “Transformation-optical design of adaptive beam bends and beam expanders,” Opt. Express 16(15), 11555–11567 (2008). [CrossRef] [PubMed]
9.	M. Rahm, D. Schurig, D. Roberts, S. Cummer, D. Smith, and J. Pendry, “Design of electromagnetic cloaks and concentrators using form-invariant coordinate transformations of Maxwell’s equations,” Photonics Nanostruct. Fundam. Appl. 6(1), 87–95 (2008). [CrossRef]
10.	N. Kundtz, D. A. Roberts, J. Allen, S. Cummer, and D. R. Smith, “Optical source transformations,” Opt. Express 16(26), 21215–21222 (2008). [CrossRef] [PubMed]
11.	Y. Lai, J. Ng, H. Y. Chen, D. Z. Han, J. J. Xiao, Z. Q. Zhang, and C. T. Chan, “Illusion optics: the optical transformation of an object into another object,” Phys. Rev. Lett. 102(25), 253902 (2009). [CrossRef] [PubMed]
12.	M. Rahm, S. A. Cummer, D. Schurig, J. B. Pendry, and D. R. Smith, “Optical design of reflectionless complex media by finite embedded coordinate transformations,” Phys. Rev. Lett. 100(6), 063903 (2008). [CrossRef] [PubMed]
13.	W. Yan, M. Yan, and M. Qiu, “Necessary and sufficient conditions for reflectionless transformation media in an isotropic and homogenous background,” arXiv:0806.3231v1 (2008).
14.	L. Bergamin, “Electromagnetic fields and boundary conditions at the interface of generalized transformation media,” Phys. Rev. A 80(6), 063835 (2009). [CrossRef]
15.	I.-M. Lee, “Study on the transmission characteristics of the optical waves in photonic metamaterials,” PhD Dissertation (School of Electrical Engineering, Seoul National University, Seoul, Korea, 2009).
16.	P. Zhang, Y. Jin, and S. He, “Inverse transformation optics and reflection analysis for two-dimensional finite embedded coordinate transformation,” arXiv:0906.2038v2 (2009).
17.	I. Gallina, G. Castaldi, V. Galdi, A. Alù, and N. Engheta, “General class of metamaterial transformation slabs,” Phys. Rev. B 81(12), 125124 (2010). [CrossRef]
18.	“Comsol multiphysics” (Comsol AB), <http://www.comsol.com>.

OCIS Codes
(230.0230) Optical devices : Optical devices
(160.3918) Materials : Metamaterials
(070.7345) Fourier optics and signal processing : Wave propagation

ToC Category:
Physical Optics

History
Original Manuscript: May 17, 2010
Revised Manuscript: June 7, 2010
Manuscript Accepted: June 9, 2010
Published: June 15, 2010

Citation
Il-Min Lee, Seung-Yeol Lee, Kyoung-Youm Kim, and Byoungho Lee, "A non-reflecting metamaterial slab under the finite-embedded coordinate transformation," Opt. Express 18, 14093-14106 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-13-14093

Sort: Author | Year | Journal | Reset

References

J. B. Pendry, D. Schurig, and D. R. Smith, “Controlling electromagnetic fields,” Science 312(5781), 1780–1782 (2006). [CrossRef] [PubMed]
A. Ward and J. Pendry, “Refraction and geometry in Maxwell's equations,” J. Mod. Opt. 43, 773–793 (1996). [CrossRef]
D. Schurig, J. J. Mock, B. J. Justice, S. A. Cummer, J. B. Pendry, A. F. Starr, and D. R. Smith, “Metamaterial electromagnetic cloak at microwave frequencies,” Science 314(5801), 977–980 (2006). [CrossRef] [PubMed]
J. S. Li and J. B. Pendry, “Hiding under the carpet: a new strategy for cloaking,” Phys. Rev. Lett. 101(20), 203901 (2008). [CrossRef] [PubMed]
S. A. Cummer, B. I. Popa, D. Schurig, D. R. Smith, J. Pendry, M. Rahm, and A. Starr, “Scattering theory derivation of a 3D acoustic cloaking shell,” Phys. Rev. Lett. 100(2), 024301 (2008). [CrossRef] [PubMed]
S. Zhang, D. A. Genov, C. Sun, and X. Zhang, “Cloaking of matter waves,” Phys. Rev. Lett. 100(12), 123002 (2008). [CrossRef] [PubMed]
H. Y. Chen, X. D. Luo, H. R. Ma, and C. T. Chan, “The anti-cloak,” Opt. Express 16(19), 14603–14608 (2008). [CrossRef] [PubMed]
M. Rahm, D. A. Roberts, J. B. Pendry, and D. R. Smith, “Transformation-optical design of adaptive beam bends and beam expanders,” Opt. Express 16(15), 11555–11567 (2008). [CrossRef] [PubMed]
M. Rahm, D. Schurig, D. Roberts, S. Cummer, D. Smith, and J. Pendry, “Design of electromagnetic cloaks and concentrators using form-invariant coordinate transformations of Maxwell’s equations,” Photonics Nanostruct. Fundam. Appl. 6(1), 87–95 (2008). [CrossRef]
N. Kundtz, D. A. Roberts, J. Allen, S. Cummer, and D. R. Smith, “Optical source transformations,” Opt. Express 16(26), 21215–21222 (2008). [CrossRef] [PubMed]
Y. Lai, J. Ng, H. Y. Chen, D. Z. Han, J. J. Xiao, Z. Q. Zhang, and C. T. Chan, “Illusion optics: the optical transformation of an object into another object,” Phys. Rev. Lett. 102(25), 253902 (2009). [CrossRef] [PubMed]
M. Rahm, S. A. Cummer, D. Schurig, J. B. Pendry, and D. R. Smith, “Optical design of reflectionless complex media by finite embedded coordinate transformations,” Phys. Rev. Lett. 100(6), 063903 (2008). [CrossRef] [PubMed]
W. Yan, M. Yan, and M. Qiu, “Necessary and sufficient conditions for reflectionless transformation media in an isotropic and homogenous background,” arXiv:0806.3231v1 (2008).
L. Bergamin, “Electromagnetic fields and boundary conditions at the interface of generalized transformation media,” Phys. Rev. A 80(6), 063835 (2009). [CrossRef]
I.-M. Lee, “Study on the transmission characteristics of the optical waves in photonic metamaterials,” PhD Dissertation (School of Electrical Engineering, Seoul National University, Seoul, Korea, 2009).
P. Zhang, Y. Jin, and S. He, “Inverse transformation optics and reflection analysis for two-dimensional finite embedded coordinate transformation,” arXiv:0906.2038v2 (2009).
I. Gallina, G. Castaldi, V. Galdi, A. Alù, and N. Engheta, “General class of metamaterial transformation slabs,” Phys. Rev. B 81(12), 125124 (2010). [CrossRef]
“Comsol multiphysics” (Comsol AB), < http://www.comsol.com >.

J. Mod. Opt.

A. Ward and J. Pendry, “Refraction and geometry in Maxwell's equations,” J. Mod. Opt. 43, 773–793 (1996). [CrossRef]

Opt. Express

Photonics Nanostruct. Fundam. Appl.

M. Rahm, D. Schurig, D. Roberts, S. Cummer, D. Smith, and J. Pendry, “Design of electromagnetic cloaks and concentrators using form-invariant coordinate transformations of Maxwell’s equations,” Photonics Nanostruct. Fundam. Appl. 6(1), 87–95 (2008). [CrossRef]

Phys. Rev. A

L. Bergamin, “Electromagnetic fields and boundary conditions at the interface of generalized transformation media,” Phys. Rev. A 80(6), 063835 (2009). [CrossRef]

Phys. Rev. B

I. Gallina, G. Castaldi, V. Galdi, A. Alù, and N. Engheta, “General class of metamaterial transformation slabs,” Phys. Rev. B 81(12), 125124 (2010). [CrossRef]

Phys. Rev. Lett.

Y. Lai, J. Ng, H. Y. Chen, D. Z. Han, J. J. Xiao, Z. Q. Zhang, and C. T. Chan, “Illusion optics: the optical transformation of an object into another object,” Phys. Rev. Lett. 102(25), 253902 (2009). [CrossRef] [PubMed]
M. Rahm, S. A. Cummer, D. Schurig, J. B. Pendry, and D. R. Smith, “Optical design of reflectionless complex media by finite embedded coordinate transformations,” Phys. Rev. Lett. 100(6), 063903 (2008). [CrossRef] [PubMed]
J. S. Li and J. B. Pendry, “Hiding under the carpet: a new strategy for cloaking,” Phys. Rev. Lett. 101(20), 203901 (2008). [CrossRef] [PubMed]
S. A. Cummer, B. I. Popa, D. Schurig, D. R. Smith, J. Pendry, M. Rahm, and A. Starr, “Scattering theory derivation of a 3D acoustic cloaking shell,” Phys. Rev. Lett. 100(2), 024301 (2008). [CrossRef] [PubMed]
S. Zhang, D. A. Genov, C. Sun, and X. Zhang, “Cloaking of matter waves,” Phys. Rev. Lett. 100(12), 123002 (2008). [CrossRef] [PubMed]

Science

D. Schurig, J. J. Mock, B. J. Justice, S. A. Cummer, J. B. Pendry, A. F. Starr, and D. R. Smith, “Metamaterial electromagnetic cloak at microwave frequencies,” Science 314(5801), 977–980 (2006). [CrossRef] [PubMed]
J. B. Pendry, D. Schurig, and D. R. Smith, “Controlling electromagnetic fields,” Science 312(5781), 1780–1782 (2006). [CrossRef] [PubMed]

Other

“Comsol multiphysics” (Comsol AB), < http://www.comsol.com >.
I.-M. Lee, “Study on the transmission characteristics of the optical waves in photonic metamaterials,” PhD Dissertation (School of Electrical Engineering, Seoul National University, Seoul, Korea, 2009).
P. Zhang, Y. Jin, and S. He, “Inverse transformation optics and reflection analysis for two-dimensional finite embedded coordinate transformation,” arXiv:0906.2038v2 (2009).
W. Yan, M. Yan, and M. Qiu, “Necessary and sufficient conditions for reflectionless transformation media in an isotropic and homogenous background,” arXiv:0806.3231v1 (2008).

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Click here to see a list of articles that cite this paper