Dual-band asymmetric transmission of linear polarization in bilayered chiralmetamaterialJinhui Shi, Xingchen Liu, Shengwu Yu, Tingting Lv, Zheng Zhu, Hui Feng Ma, and Tie Jun Cui

Citation: Applied Physics Letters 102, 191905 (2013); doi: 10.1063/1.4805075 View online: http://dx.doi.org/10.1063/1.4805075 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/102/19?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Dual-band polarization angle independent 90° polarization rotator using twisted electric-field-coupled resonators Appl. Phys. Lett. 104, 034102 (2014); 10.1063/1.4863227 Cross polarization converter formed by rotated-arm-square chiral metamaterial J. Appl. Phys. 114, 224506 (2013); 10.1063/1.4846096 A frequency-tunable 90°-polarization rotation device using composite chiral metamaterials Appl. Phys. Lett. 103, 101908 (2013); 10.1063/1.4820810 Polarization-insensitive and polarization-controlled dual-band absorption in metamaterials Appl. Phys. Lett. 102, 081122 (2013); 10.1063/1.4794173 Dual-band asymmetry chiral metamaterial based on planar spiral structure Appl. Phys. Lett. 101, 161901 (2012); 10.1063/1.4756901

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 72.10.122.9

On: Tue, 29 Apr 2014 05:44:20

Dual-band asymmetric transmission of linear polarization in bilayeredchiral metamaterial

Jinhui Shi,1,2,a),b) Xingchen Liu,1,a) Shengwu Yu,1 Tingting Lv,1 Zheng Zhu,1 Hui Feng Ma,2

and Tie Jun Cui2,b)

1Key Laboratory of In-Fiber Integrated Optics of Ministry of Education, College of Science,Harbin Engineering University, Harbin 150001, China2State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China

(Received 27 January 2013; accepted 1 May 2013; published online 14 May 2013)

A bilayered chiral metamaterial is proposed and demonstrated to exhibit dual-band asymmetric

transmission of linearly polarized electromagnetic waves in two opposite directions. Simulated and

measured results show that the bilayered chiral metamaterial can achieve cross-polarization conversion

with an efficiency of over 90% for both y- and x-polarized waves. The proposed metasurface

can be regarded as an ultrathin polarization-controlled switch that is easily switched on/off by

changing a linearly polarized wave to its orthogonal component. VC 2013 AIP Publishing LLC.

[http://dx.doi.org/10.1063/1.4805075]

Metamaterials, as a rapidly developing cutting-edge

research field, could be engineered to own unprecedented

electromagnetic properties such as negative refraction and

invisibility cloak, which can offer the possibilities for numer-

ous metadevices.1 Since chirality was regarded as an alterna-

tive route to negative refraction,2,3 many chiral metamaterials

have been proposed to realize negative refractive index.4–8

Besides negative index, artificial chiral metamaterials can

possess giant gyrotropy,9,10 circular dichroism,11–13 and

strong optical activity.14–20 Due to their unique properties,

chiral metamaterials promise to tailor the polarization state of

light and be functionalized as polarization rotators,21,22 circu-

lar polarizers,23,24 and polarization spectrum filters with

ripple-free isolated transmission peaks.25,26 Another remark-

able effect is circular conversion dichroism leading to an

asymmetric transmission (AT) phenomenon, which was dis-

covered in planar chiral metamaterial patterns to show a

directionally asymmetric total transmission from microwave

to optical frequencies.27–29 Subsequently, it was experimen-

tally verified that the AT effect can also be observed in

extrinsically chiral metamaterials, if chirality is associated

with the mutual orientation of the planar metamaterial and

the wave propagation direction.30,31 The AT phenomenon

arises from reversed right-to-left and left-to-right polarization

conversion efficiencies for opposite directions of wave propa-

gation. In contrast to the Faraday effect, the AT effect in chi-

ral metamaterials happens in the absence of a static magnetic

field. More recently, great efforts have been put to achieving

the AT effect for linearly polarized waves.32–36 This phenom-

enon can be explained by the de Hoop reciprocity as revealed

by Jones matrix formulation.32,33 However, although a diode-

like asymmetric transmission of linearly polarized waves

based on combining chirality and electromagnetic wave tun-

neling was reported,36 simple structure, high polarization

conversion efficiency, and multiband operation of the AT

phenomenon are still highly desirable.37,38

In this letter, we propose a dual-band asymmetric trans-

mission for forward and backward propagating linearly

polarized waves in a bilayered chiral metamaterial. The chi-

ral metamaterial is composed of bilayered continuous metal-

lic strips in an orthogonal arrangement and a sandwiched

dielectric spacer layer. Theoretical and experimental results

demonstrate that the bilayered chiral metamaterial is nearly

transparent to incident linearly polarized waves in two sepa-

rated AT bands, where a linearly polarized wave can be com-

pletely converted to its cross-polarization and then totally

transmitted, while the same linearly polarized wave cannot

pass through the metamaterial in the opposite direction. Each

AT band can be switched on/off by changing the polarization

state of the incident wave. A dual-band AT for two orthogo-

nal linearly polarized waves at normal incidence has not

been observed before.

The response of a metamaterial is determined not only by

the behavior of an individual unit cell but also by the spatial

arrangement of meta-molecules involved in an ensemble.

Here, we propose a bilayered stereometamaterial with chirality

to manipulate polarization states of electromagnetic waves.

Each stereo dimer consists of two spatially separated metallic

patterns, which are structurally identical but twisted. Figures

1(a) and 1(b) present a front view and a stereogram of a unit

cell of our model slab, respectively. The chiral metamaterial is

composed of continuous double I-shape (DI) structures only

connected by one arm, developed from the reported fish-scale

metamaterial.34 Introducing a small gap will enhance electro-

magnetic response of the chiral metamaterial. The metallic pat-

terns on both sides of a dielectric layer are identical, but are

rotated relative to each other at an angle of 90� around the zaxis. Obviously, this bilayered metamaterial structure lacks

four-fold rotational symmetry and in addition the mirror sym-

metry in z direction is broken. It is predicted that the bilayered

metamaterial will exhibit an AT effect for a linearly polarized

wave due to chiral property. The metamaterial consists of a

square metamolecule array with a period of a¼ 12 mm, ren-

dering the structure non-diffractive at the normal incidence for

frequencies below 25 GHz. The other geometric parameters of

the metallic strips marked in Fig. 1(a) are the width

a)J. Shi and X. Liu contributed equally to this work.b)Electronic addresses: hrbeusjh@gmail.com and tjcui@seu.edu.cn

0003-6951/2013/102(19)/191905/5/$30.00 VC 2013 AIP Publishing LLC102, 191905-1

APPLIED PHYSICS LETTERS 102, 191905 (2013)

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 72.10.122.9

On: Tue, 29 Apr 2014 05:44:20

w¼ 1.2 mm, the length l1¼ 4.8 mm, l2¼ 11.2 mm and the slit

gap b¼ 0.8 mm. Figure 1(c) depicts a photograph of the fabri-

cated sample. The metamaterial patterns with an overall size

of 388� 296 mm2 were etched from 35 lm copper cladding

on the Rogers RO3003 substrate with a thickness of

t¼ 0.762 mm. Due to the intrinsic non-chirality, the single-

layered DI metamaterial is absolutely inaccessible to achieve

the asymmetric transmission at normal incidence. Fortunately,

our optimized chiral metamaterial can present an AT effect

with unit transmission for linearly polarized waves due to the

near-field coupling of two orthogonal resonators. The bilay-

ered DI chiral metamaterial can obtain a well-engineered AT

effect by simply changing the slit width b, which is more desir-

able for practical applications than previous structures.34–36

Using the commercial software CST MICROWAVE STUDIO,

we study the transmission properties of the chiral metamate-

rial at the normal incidence of linearly polarized waves in

the frequency range of 8–18 GHz, where copper is treated as

a perfectly electric conductor and the lossy dielectric sub-

strate (Rogers RO3003) is assumed to have a relative dielec-

tric permittivity of 3 þ 0.0039i. The calculated results can

be presented in terms of complex transmission coefficients

Tijd in Jones matrix, where tij

d ¼jTijdj. The subscripts i and j

correspond to the polarization states of the transmitted and

incident waves, which could be either x or y linearly polar-

ized waves in our case. The superscript d refers to the for-

ward (f, along -z axis) or backward (b, along þz axis) wave

propagations. The experiments were carried out in an

anechoic chamber using a vector network analyzer (Agilent

N5230C) and two broadband horn antennas. By changing

the orientation of the two horn antennas, all four components

of the wave transmission for different polarizations were

measured.

Figure 2 shows the simulated and measured transmis-

sions in the bilayered chiral metamaterial for the forward and

backward propagating waves. The co-polarization transmis-

sion coefficient txx of x-polarized wave coincides well with tyy

of y-polarized wave since an orthogonal arrangement of two

subwavelength resonators ensures that the whole structure is

isotropic for observations at normal incidence. In contrast to

co-polarization transmission, the cross-polarization coeffi-

cient txy is extremely different from tyx at all frequencies we

consider. The two above conditions indicate the presence of

the AT effect for linearly polarized waves and the absence of

the AT effect for circularly polarized waves in the bilayered

DI chiral metamaterial.35 Most interestedly, there are two

individual pass bands showing strong optical activity in the

thin metamaterial with a total thickness of about k/24, one for

x-to-y polarization rotation and the other for y-to-x polariza-

tion rotation. In Fig. 2(a), the cross-polarization transmission

FIG. 1. (a) The front view of a unit cell in the bilayered chiral metamaterial.

(b) The stereogram of a unit cell. (c) Photograph of the experimental

sample.

FIG. 2. Simulated ((a) and (c)) and

measured ((b) and (d)) transmission

spectra for forward ((a) and (b)) and

backward ((c) and (d)) propagating

waves. The insets indicate wave propa-

gation directions.

191905-2 Shi et al. Appl. Phys. Lett. 102, 191905 (2013)

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 72.10.122.9

On: Tue, 29 Apr 2014 05:44:20

txy reaches a maximum of 0.95 at around 10.79 GHz and both

the co-polarization transmissions txx and tyy are below 0.15.

In this pass band, incident y-polarized wave is almost

completely transmitted to x-polarized wave while incident

x-polarized wave is completely blocked through the metama-

terial slab. Meanwhile, an obvious resonant peak in tyx can be

observed with a maximum larger than 0.93 at around

14.57 GHz, where incident x-polarized wave is almost

completely transmitted to y-polarized wave while incident

y-polarized wave cannot pass through the metamaterial slab.

In addition, txy and tyx interchange with each other shown in

Fig. 2(c) when the propagation direction is reversed. The

measured cross-polarization transmissions in Figs. 2(b) and

2(d) are in good agreement with the simulated ones in Figs.

2(a) and 2(c). Although the discrepancy is caused by the fab-

rication error and random error in experiments, the measured

and simulated co-polarization transmission txx and tyy basi-

cally agree with each other. Prospectively, the bilayered DI

metamaterial can be functionalized as a dual-band polariza-

tion spectral filter for incident unpolarized light sandwiched

between two orthogonal polarizers, underpinned by optical

activity phenomenon. Furthermore, this metasurface can be

regarded as an ultrathin polarization-controlled switch since

each AT pass band is easily switched on/off only by changed

a linearly polarized wave to its orthogonal component

mechanically.

As verified in the previous simulations and experiments,

txx is exactly equal to tyy, which could ensure zero asymmetric

transmission of circular polarization waves for this chiral

metamaterial. The bilayered DI chiral metamaterial could ex-

hibit asymmetric transmission for linearly polarized waves

only. The AT effect of the linearly polarized waves is usually

characterized by a parameter D, which is defined as the differ-

ence between the transmissions in two opposite propagation

directions.32,33 Since the amplitudes of txx and tyy are identical

in the absence of linear anisotropy and jTbyxj

2 ¼ jTfxyj

2due to

the specific asymmetry, the AT parameters for the linear

polarized wave (superscript x or y) are then defined as

Dx ¼ jTfyxj

2 � jTbyxj

2 ¼ jTfyxj

2 � jTfxyj

2;

Dy ¼ jTfxyj

2 � jTbxyj

2 ¼ jTfxyj

2 � jTfyxj

2;(1)

In order to visualize the AT effect, Figure 3 presents the simu-

lated and measured AT parameter D for forward propagating

x- and y- polarized waves according to Eq. (1). In particular,

one can see that both the asymmetry factor curves Dx and Dy

show two opposite peaks locating at about 10.79 and

14.57 GHz in Fig. 3(a). Two values of �0.9/0.9 and 0.87/

�0.87 in the curves Dx and Dy imply that the x/y-polarized

wave in the forward direction is mostly forbidden/allowed at

about 10.79 GHz and allowed/forbidden at 14.57 GHz, respec-

tively. The measured asymmetric transmissions in Fig. 3(b)

agree very well the simulated ones, which are currently 0.95 at

10.80 GHz and 0.89 at 14.67 GHz. It is clearly demonstrated

that two curves of Dx and Dy are exactly contrary to each other

in Fig. 3. The slight amplitude difference may be caused by the

mismatch between the assumed imaginary part of permittivity

and the realistic material parameter. Apparently, the bilayered

DI metamaterial reveals a dual-band one-way transmission for

linearly polarized waves, one for x-polarized wave and the

other for y-polarized wave.

To understand the physical origin of the dual-band AT

effect, we present surface current distributions of both

single-layered and bilayered DI metamaterials at the reso-

nant frequencies. No matter whether the incident waves are

x- or y-polarized, only broad dipole resonances can be

excited in the single-layered DI metamaterial, formed by

weak in-phase surface currents in the insets of Fig. 4(a).

Figures 4(b) and 4(c) show the instantaneous induced surface

current distributions of the front and back layers in the bilay-

ered DI metamaterial for the waves passing through the slab

along the forward direction at resonances I and II marked in

Fig. 2(a). When the DI structures are arranged orthogonally,

dramatic changes happen due to near field coupling in chiral

meta-molecules. In each case, the electric field is concen-

trated strongly in the gaps of the ring resonator. Importantly,

two different modes are excited at resonances I and II shown

in Figs. 4(b) and 4(c), corresponding to the conversions of y-

to-x and x-to-y, respectively. At resonance I, the surface cur-

rents concentrate along the two arms without gaps and they

oscillate in two opposite directions for each layer. At reso-

nance II, the surface currents concentrate along the gap bear-

ing arms and they oscillate in the same direction for each

layer. Compared with the single-layered DI metamaterial,

first, surface currents of both layers can be resonantly excited

at resonances I and II. The amplitudes of the currents in this

case are 6 times stronger than ones excited in the single-

layered DI metamaterial. Second, instantaneous direction of

the current flow in the front layer is contrary to that in the

back layer.

The antisymmetric current distributions lead to a negli-

gible electric response in the xy plane middle between two

layers. Meanwhile, excitation of the antisymmetric current

mode enables the formation of a strong magnetic resonance

in this xy plane. H1 and H2 represent the induced magnetic

FIG. 3. Simulated (a) and measured (b) asymmetric transmission parameter

D. Black solid and red dashed curves correspond, respectively, to asymmet-

ric transmissons of x and y linearly polarized waves in the forward propaga-

tion direction.

191905-3 Shi et al. Appl. Phys. Lett. 102, 191905 (2013)

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 72.10.122.9

On: Tue, 29 Apr 2014 05:44:20

fields excited by antiparallel current pairs in Figs. 4(b) and

4(c). At resonance I, when the incident wave is y-polarized,

the induced magnetic field H2 is along the x-axis and perpen-

dicular to the incident electric field E, thus, there is no

cross-coupling between H2 and the electric field. H2 never

contributes to the polarization rotation. An obvious chiral

property is observed that the induced magnetic field H1 is

along y-axis and parallel to the electric field. The cross-

coupling between the electric and magnetic fields leads to

optical activity and a cross-polarization transmission with

y-to-x polarization conversion. Consequently, the AT effect

at 10.79 GHz occurs. At resonance II, another antisymmetric

current mode is generated by x-polarized illumination, yield-

ing y-oriented H2 and x-oriented H1. The cross-coupling

between the electric field and the induced magnetic field H1

results in a cross-polarization transmission with x-to-y polar-

ization conversion. Therefore, the second AT pass band is

achieved at 14.57 GHz. Within two AT pass bands, the

co-polarization transmissions are mostly suppressed by opti-

mizing the geometrical parameters. Then the transmitted

wave can be mostly converted to its cross polarization after

passing through the chiral metamaterial.

In summary, we have proposed a bilayered chiral meta-

material that is composed of connected I-shape resonators

arranged by a twist angle of 90�. The chiral metamaterial has

been theoretically and experimentally demonstrated to reveal

a dual-band AT effect for two orthogonal linearly polarized

waves, distinct from the metamaterials previously reported

that only show a single-band AT effect for one

polarization.32–36 Strong AT effect of linearly polarized waves

along two opposite propagation directions occurs and the

proposed metamaterial can reveal a perfect polarization con-

version with over 90% conversion efficiency for both x- and

y-polarized waves. Apparently, the AT effect in our metama-

terial can be completely switched on/off by changing a line-

arly polarized wave to its orthogonal state mechanically. It

can also be predicted that the coupling strength provides us a

convenient way to engineer the AT effect occurring at a dif-

ferent frequency only by changing the slit width. Our findings

are beneficial in designing one-way transmission devices and

exploring polarization-controlled devices.

This work was supported by the National Science

Foundation of China under Grant Nos. 61201083, 61275094,

U1231201, in part by the Natural Science Foundation of

Heilongjiang Province in China under Grant No. LC201006,

in part by the China Postdoctoral Science Foundation

under Grant No. 2012M511171, in part by the Special

Foundation for Harbin Young Scientists under Grant No.

2012RFLXG030, in part by the Fundamental Research Funds

for the Central Universities, and in part by the 111 Project

(B13015) to Harbin Engineering University. H. F. Ma and

T. J. Cui acknowledge the support from the National Science

Foundation of China under Grant Nos. 61171024, 61171026,

60990320, and 60990324, National High Tech (863) Projects

under Grant Nos. 2011AA010202 and 2012AA030402, and

the 111 Project under Grant No. 111-2-05.

1N. I. Zheludev and Y. S. Kivshar, Nature Mater. 11, 917 (2012).2S. Tretyakov, I. Nefedov, A. Sihvola, S. Maslovski, and C. Simovski,

J. Electromagn. Waves Appl. 17, 695 (2003).3J. B. Pendry, Science 306, 1353 (2004).4E. Plum, J. Zhou, J. Dong, V. A. Fedotov, T. Koschny, C. M. Soukoulis,

and N. I. Zheludev, Phys. Rev. B 79, 035407 (2009).5S. Zhang, Y. S. Park, J. Li, X. Lu, W. Zhang, and X. Zhang, Phys. Rev.

Lett. 102, 023901 (2009).6J. Zhou, J. Dong, B. Wang, T. Koschny, M. Kafesaki, and C. M.

Soukoulis, Phys. Rev. B 79, 121104 (2009).7R. Zhao, L. Zhang, J. Zhou, T. Koschny, and C. M. Soukoulis, Phys. Rev.

B 83, 035105 (2011).8Z. F. Li, K. B. Alici, H. Caglayan, M. Kafesaki, C. M. Soukoulis, and E.

Ozbay, Opt. Express 20, 6146 (2012).9A. V. Rogacheva, V. A. Fedotov, A. S. Schwanecke, and N. I. Zheludev,

Phys. Rev. Lett. 97, 177401 (2006).10E. Plum, V. A. Fedotov, A. S. Schwanecke, N. I. Zheludev, and Y. Chen,

Appl. Phys. Lett. 90, 223113 (2007).11M. Decker, M. W. Klein, M. Wegener, and S. Linden, Opt. Lett. 32, 856

(2007).12D. H. Kwon, P. L. Werner, and D. H. Werner, Opt. Express 16, 11802

(2008).13S. V. Zhukovsky, A. V. Novitsky, and V. M. Galynsky, Opt. Lett. 34,

1988 (2009).14E. Plum, V. A. Fedotov, and N. I. Zheludev, Appl. Phys. Lett. 93, 191911

(2008).15M. Decker, M. Ruther, C. E. Kriegler, J. Zhou, C. M. Soukoulis, S.

Linden, and M. Wegener, Opt. Lett. 34, 2501 (2009).16Z. Li, K. B. Alici, E. Colak, and E. Ozbay, Appl. Phys. Lett. 98, 161907

(2011).17E. Plum, X.-X. Liu, V. A. Fedotov, Y. Chen, D. P. Tsai, and N. I.

Zheludev, Phys. Rev. Lett. 102, 113902 (2009).18R. Singh, E. Plum, W. L. Zhang, and N. I. Zheludev, Opt. Express 18,

13425 (2010).19M. Decker, R. Zhao, C. M. Soukoulis, S. Linden, and M. Wegener, Opt.

Lett. 35, 1593 (2010).

FIG. 4. Surface current distributions of the single-layered and bilayered DI

metamaterials. (a) Transmission spectra of the single-layered DI metamate-

rial. The insets indicate surface currents for incident x- and y-polarized

waves at transmission dips. (b) and (c) Surface current distributions for for-

ward propagating y- and x-polarized waves at resonances I and II labeled in

Fig. 2(a). The large solid and dashed arrows indicate instantaneous direc-

tions of the current flow. H1 and H2 represent the induced magnetic fields

excited by antiparallel surface current pairs.

191905-4 Shi et al. Appl. Phys. Lett. 102, 191905 (2013)

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 72.10.122.9

On: Tue, 29 Apr 2014 05:44:20

20M. X. Ren, E. Plum, J. J. Xu, and N. I. Zheludev, Nat. Commun. 3, 833

(2012).21Y. Q. Ye and S. L. He, Appl. Phys. Lett. 96, 203501 (2010).22M. Mutlu and E. Ozbay, Appl. Phys. Lett. 100, 051909 (2012).23J. K. Gansel, M. Thiel, M. S. Rill, M. Decker, K. Bade, V. Saile, G.

von Freymann, S. Linden, and M. Wegener, Science 325, 1513

(2009).24Y. Zhao, M. A. Belkin, and A. Al�u, Nat. Commun. 3, 870 (2012).25N. I. Zheludev, E. Plum, and V. A. Fedotov, Appl. Phys. Lett. 99, 171915

(2011).26J. H. Shi, H. F. Ma, W. X. Jiang, and T. J. Cui, Phys. Rev. B 86, 035103

(2012).27V. A. Fedotov, P. L. Mladyonov, S. L. Prosvirnin, A. V. Rogacheva, Y.

Chen, and N. I. Zheludev, Phys. Rev. Lett. 97, 167401 (2006).28R. Singh, E. Plum, C. Menzel, C. Rockstuhl, A. K. Azad, R. A. Cheville,

F. Lederer, W. Zhang, and N. I. Zheludev, Phys. Rev. B 80, 153104

(2009).

29A. S. Schwanecke, V. A. Fedotov, V. V. Khardikov, S. L. Prosvirnin, Y.

Chen, and N. I. Zheludev, Nano Lett. 8, 2940 (2008).30E. Plum, V. A. Fedotov, and N. I. Zheludev, J. Opt. A: Pure Appl. Opt. 11,

074009 (2009).31E. Plum, V. A. Fedotov, and N. I. Zheludev, J. Opt. 13, 024006 (2011).32C. Menzel, C. Helgert, C. Rockstuhl, E. B. Kley, A. T€unnermann, T.

Pertsch, and F. Lederer, Phys. Rev. Lett. 104, 253902 (2010).33C. Huang, Y. J. Feng, J. M. Zhao, Z. B. Wang and T. Jiang, Phys. Rev. B

85, 195131 (2012).34J. Han, H. Q. Li, Y. C. Fan, Z. Y. Wei, C. Wu, Y. Cao, X. Yu, F. Li, and

Z. S. Wang, Appl. Phys. Lett. 98, 151908 (2011).35M. Kang, J. Chen, H. Cui, Y. Li, and H. Wang, Opt. Express 19, 8347 (2011).36M. Mutlu, A. E. Akosman, A. E. Serebryannikov, and E. Ozbay, Phys.

Rev. Lett. 108, 213905 (2012).37J. M. Hao, Y. Yuan, L. X. Ran, T. Jiang, J. A. Kong, C. T. Chan, and

L. Zhou, Phys. Rev. Lett. 99, 063908 (2007).38W. J. Sun, Q. He, J. M. Hao, and L. Zhou, Opt. Lett. 36, 927 (2011).

191905-5 Shi et al. Appl. Phys. Lett. 102, 191905 (2013)

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 72.10.122.9

On: Tue, 29 Apr 2014 05:44:20