Article

Multispectral Plasmon Induced Transparency in Coupled Meta-Atoms

Electrical and Computer Engineering Department, Boston University, Boston, Massachusetts 02215, United States.
Nano Letters (Impact Factor: 13.59). 03/2011; 11(4):1685-9. DOI: 10.1021/nl200197j
Source: PubMed

ABSTRACT

We introduce an approach enabling construction of a scalable metamaterial media supporting multispectral plasmon induced transparency. The composite multilayered media consist of coupled meta-atoms with radiant and subradiant hybridized plasmonic modes interacting through the structural asymmetry. A perturbative model incorporating hybridization and mode coupling is introduced to explain the observed novel spectral features. The proposed scheme is demonstrated experimentally by developing a lift-off-free fabrication scheme that can automatically register multiple metamaterial layers in the transverse plane. This metamaterial which can simultaneously enhance nonlinear processes at multiple frequency domains could open up new possibilities in optical information processing.

Full-text

Available from: Hatice Altug
r
XXXX American Chemical Society
A dx.doi.org/10.1021/nl200197j
|
Nano Lett. XXXX, XXX, 000000
LETTER
pubs.acs.org/NanoLett
Multispectral Plasmon Induced Transparency in Coupled Meta-Atoms
Alp Artar,
Ahmet A. Yanik,
and Hatice Altug*
Electrical and Computer Engineering Department, Boston University, Boston, Massachusetts 02215, United States
b
S Supporting Information
E
lectromagnetically induced transparency (EIT), a spectrally
narrow optical transmission window accompanied with
extreme dispersion, results from quantum interferenc e of multi-
ple excitation pathways through short and long-lived
resonances.
1
Within this spectral window, dramatically slowed
down photons and orders of magnitude enhanced nonlinearities
can enable manipulation of light at few-photon power levels.
2
Historically, EIT has been implemented in laser-driven atomic
quantum systems. However, limited material choices and stringent
requirements to preserve the coherence of excitation pathways in
atomic systems have signicantly constrained the use of EIT
eect.
3
Recent studies have revealed that EIT-like optical re-
sponses can be obtained classically using on-chip plasmonic
and photonic nanoresonators.
420
Much of the research eort
so far f ocused on isolated meta-atoms (either photonic or
plasmonic) showing EIT-like eect at a single resonance. On the
other hand, metamaterial systems supporting EIT-like optical
responses at multiple-spectral windows can simultaneously en-
hance multicolored photonphoton interactions and open up
new possibilities in nonlinear optics and optical information
processing.
2123
In this Letter, we propose and demonstrate a novel approach
based on coupled meta-atoms to construct a homogeneous and
scalable medium supporting multispectral EIT-like eect
(plasmon induced transparency). The proposed structure con-
sists of a two slot antenna based complementary metamaterial
layers with a small gap (dielectric layer thickness) enabling strong
near-eld intera ction in between. Each planar metamaterial layer
has bright (radiant) and dark (subradiant) plasmonic modes
coupled through the structural asymmetry (s 0) in an analogy
to transition-allowed and -forbidden atomic orbitals coupled
through a common excited state.
6
As shown in Figure 1b (blue
curve), isolated meta-atoms on a single-layer metamaterial
exhibit an EIT-like reection
10
with spectral features that are
controlled by the articial atomic orbitals (plasmonic modes).
Once stacked in a multilayered s tructure (Figure 1b, black
curve), presence of s trong near-eld coupling between the
meta-atoms causes splitting of the EIT resonances and leads
to multispectral EIT-like behav ior. The underlying physi cal
principles for this phenomenon are related to plasmonic
hybridization eects
24
and dark-bright mode couplings of the
in-phase and out-phase hybridized states. To explain these
novel spectral features, we introduce a perturbative model
incorporating hybridization and mode coupling. Fur thermore,
we experimentally demonstrate the proposed scheme by
developing a lift-o free fabrication scheme that can simulta-
neously register multiple metamaterial layers in the third
dimension.
In the following, we start by describing the perturbative model
that provides insight into the physical processes involved in these
structures. For the double layered metamaterial, a total Hamil-
tonian can be dened as
H
T
¼
~
H
0
þ
~
H
0
0
þ
~
K þΣ
~
Here,
~
H
0
and
~
H
0
0
are the 2 2 unperturbed Hamiltonians of
the isolated metamaterial layers dened in a basis set consist-
ing of decoupled bright (dipolar) and dark (quadrupole)
modes in the absence of a structural asymmetry (s 6¼ 0).
The weak interactions between the bright and the dark modes
Received: January 18, 2011
Revised: March 4, 2011
ABSTRACT: We introduce an approach enabling construction
of a scalable metamaterial media supporting multispectral
plasmon induced transparency. The composite multilayered
media consist of coupled meta-atoms with radiant and sub-
radiant hybridized plasmonic modes interacting through the
structural asymmetry. A perturbative model incorporating
hybridization and mode coupling is introduced to explain the observed novel spectral features. The proposed scheme is
demonstrated experimentally by developing a lift-o-free fabrication scheme that can automatically register multiple metamaterial
layers in the transverse plane. This metamaterial which can simultaneously enhance nonlinear processes at multi ple frequency
domains could open up new possibilities in optical information processing.
KEYWORDS: Metamaterials, electromagnetically induced transparency, plasmons, plasmon hybridization, Fano resonances,
strong coupling
Page 1
B dx.doi.org/10.1021/nl200197j |Nano Lett. XXXX, XXX, 000–000
Nano Letters
LETTER
are incorp orat ed with the p ertu rbati ve Hami lton ian
~
K,whena
structural asymmetry is introduced (s 6¼ 0). Interactions
between the two metamaterial layers are included through
the strong near-eld coupling Hamiltonian Σ
~
. Accord-
ingly, the total Hamiltonian for the coupled meta-atoms is
given as
H
T
¼
~
H
0
þ
~
H
0
0
þ
~
K þ
~
Σ ¼
j1æ j2æ
Æ1j
Æ2j
H
0
þK Σ
Σ
H
0
0
þK
0
"#
¼
jD
0
æ jQ
0
æ jD
0
0
æ jQ
0
0
æ
ÆD
0
j
ÆQ
0
j
ÆD
0
0
j
ÆQ
0
0
j
E
D
0
k τ
inter,D
χ
0
k
E
Q
0
χτ
inter,Q
τ
inter,D
χ
E
D
0
0
k
0
ðχ
0
Þ
τ
inter,Q
ðk
0
Þ
E
Q
0
0
2
6
6
6
6
4
3
7
7
7
7
5
ð1Þ
where |1æ and |2æ represent the top and bottom metamaterial
layers, respectively. The eigenvalues of the bright (|D
0
æ) and the
dark (|Q
0
æ) modes of the isolated metamaterials are dened as
E
D
0
and E
Q
0
. For clarity, eigenstates and eigenvalues of the second
layer are denoted with primes, even for structurally symmetric
layers. κ and κ
0
are due to the weak intralayer coupling among the
dark and bright modes in each lay er. τ
inter,D
and τ
inter,Q
are the
strong interlayer coupling terms for the bright and dark modes,
respectively. χ and χ
0
are the cross couplings among the bright
and dark modes of dierent layers (interlayer). An important
consideration in our analysis is that χ and χ
0
, the cross couplings
among the bright and dark modes, are weak and can be neglected.
Validity of this assumption will be justied in the following by
benchmarking our analytical relations with numerical simula-
tions and experimental measurements. For a metamaterial
system where the individual layers have identical structural
characteristics , the Hamiltonian terms for both layers are iden-
tical (κ = κ
0
, τ
inter,D/Q
= τ
inter,D
0
/Q
0
, E
D
0
/Q
0
= E
D
0
0
/Q
0
0
). After
a simple rearrangement of the matrix elements and a unitary
transformation, the total Hamiltonian can be rewritten as in
H
T
hyb
¼
^
U½H
T
^
U
¼
jD
þ
æ jD
æ jQ
þ
æ jQ
æ
ÆD
þ
j
ÆD
j
ÆQ
þ
j
ÆQ
j
E
D
0
þΔ
D
þε
D
0 k 0
0 E
D
0
þΔ
D
ε
D
0 k
k
0 E
Q
0
þΔ
Q
þε
Q
0
0 k
0 E
Q
0
þΔ
Q
ε
Q
2
6
6
6
6
4
3
7
7
7
7
5
ð2Þ
in an orthogonal basis set consisting of
jD
(
æ ¼
1
ffiffi
2
p
½jD
0
æ ( jD
0
0
æð3aÞ
jQ
(
æ ¼
1
ffiffi
2
p
½jQ
0
æ ( jQ
0
0
æð3bÞ
Figure 1. (a) Geometry of the multilayered metamaterial. Structure
consists of two Au layers (30 nm thickness) that are separated by a
dielectric (SiN
x
) layer (70 nm thickness). Each layer has a dipole and a
quadrupole slot antenna (all slot antennas have 700 nm length,
100 nm width). The small in-plane separation between the dipolar
and quadrupolar antennas is 50 nm on both sides and periods are
1200 nm on both x and y directions. Parameter s is dened as the ose t
of the dipolar antenna from the geometrical center of the structure.
Blue arrows show the conguration of the incident light. (b) Simu-
lated reection spectra for asymmetric (s 0) single- and double-
layered structures are shown (with an oset for clarity). Multispectral
EIT-like response (in-phase and out-of-phase) is observable with
double-layered metamaterial.
Figure 2. (a) Hybridization scheme for the dipolar mode. (b) Tuning of
the spectra with the dielectric layer thickness is shown for the symmetric
structure (s = 0). As the dielectric layer thickness reduces, splitting of energy
between the hybrid modes increases. Single layer spectrum is shown with the
blue dashed curve. Splitting energies (2ε
D
) are 202, 260, 297 meV and
energy osets (Δ
D
) are 60, 68, 78 meV for gap sizes (dielectric layer
thicknesses) of 90, 70, 50 nm, respectively. (c) Charge distribution at the air/
metal interface (top view), demonstrating the dipolar mode excitation. This
charge distribution is acquired from in-phase state |D
þ
æ of the multilayered
structure; however the out-of-phase state |D
æ andalsothesingle-layered
dipolar state |D
0
æ have the exact same charge distribution (not shown). (d)
Charge distributions of the hybrid dipolar modes acquired from a multi-
layered structure with a dielectric layer thickness of 50 nm (cross-sectional
view) are shown at a position marked with the red dashed line in (c).
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C dx.doi.org/10.1021/nl200197j |Nano Lett. XXXX, XXX, 000–000
Nano Letters
LETTER
diagonalizing the Hamiltonian H
s=0
T
=
~
H
0
þ
~
H
0
0
þ Σ
~
(when
the system is symmetric s = 0) in the strong coupling regime
(|E
D
0
E
D
0
0
| , 2τ
inter,D
and |E
Q
0
E
Q
0
0
| , 2τ
inter,Q
). These hybrid
eigenstate pairs are in-phase (þ) and out-of phase ()super-
positions of the isolated layer eigenmodes of the structurally symmetric
multilayer system (s = 0). The associated energies of the dipolar
hybrid modes are, E
D
(
= E
D
0
þ Δ
D
( ε
D
,wheretheoset term is
Δ
D
= ÆD
0
|τ
inter,D
|D
0
æ and the splitting term is ε
D
= ÆD
0
|τ
inter,D
|D
0
0
æ
(a similar set can be obtained for quadrupole modes). Since o
diagonal terms in the transformed Hamiltonian H
hyb
T
are much
weaker than the diagonal terms, the o-diagonal matrix elements κ
and κ
0
are treated as the elements of the perturbative Hamiltonian
introduced by the structural asymmetry (s 0). Using the trans-
formed Hamiltonian H
hyb
T
, a set of coupled Lorentzian oscillator
relations can be derived in an analogy to atomistic EIT resonances.
Initially, the hybridization of eigenstate pairs in the form of in-phase
(þ) and out-of phase () superpositions of the isolated layer eigen-
modes is shown in Figure 2 for the structurally symmetric multilayer
system (s =0andκ =0)usingnite dierence time-domain (FDTD)
analysis. For a single-layered metamaterial, only the resonance dip
corresponding to the excitation of the dipolar bright mode is observ-
able in the reection spectrum (Figure 2(b), dashed blue curve). For
the double layered metamaterial, two resonance dips appear corre-
sponding to in-phase and out-of-phase hybridized modes due to the
degeneracy breaking as given in eq 3a (solid curves in Figure 2b). The
mode ener gies an d the splitting in between are controlled by the
strength of the interlayer coupling of the metamaterial layers. As
predicted by our Hamiltonian treatment, smaller gaps (dielectric layer
thicknesses) lead to larger energy splittings as this coupling becomes
stronger (Figure 2b). The in-phase and out-of-phase character of these
hybridiz ed states ar e a lso conrmed with FDTD simulations showing
cross-sectional charge distributions of the dipolar modes (Figure 2d).
The in-phase hybrid mode is radiant as a result of its overall dipolar
character. The radiant out-of-phase mode is harder to excite with
respect to the in-phase mode, due to the partial cancellation of the
dipolar moments of the subsequent layers. Nevertheless, resonance dip
corresponding to the out-of-phase mode is still observable due to the
retardation eects (Figure 2b, solid curves). In Figure 2b, resonances
due to hybridized quadrupolar modes are not observable, since any
linear combination of the subradiant quadrupolar modes of the isolated
structures is also subradiant. Structural symmetry must be broken for
the excitation of these quadrupolar hybridized modes.
Breaking the symmetry of the multilayered structure (s 0)
leads to near-eld coupling between the dark and bright modes
(κ 0) and results in the excitation of the dark modes with the
perpendicularly incident light. Indirect excitation of these hybrid
quadrupolar dark modes leads to multispectral EIT-like behavi or
(Figure 3 black curve). Charge distribution of the out-of-phase
(OP) EIT resonance at the top surface (Figure 3a inset),
indicates strong coupling of the external driving eld to this
mode. A simi lar charge distribution is also observed for the in-
phase (IP) EIT resonance (not shown). Cross sectional charge
distributions of the quadrupolar modes (Figure 3b) conrm the
in-phase and out-of-phase mode characters. Full spectral re-
sponse of the multilayered structure can be understood following
our perturbative Hamiltonian approach. Here, a coupled Lor-
entzian oscillator model is derived from the transformed Hamil-
tonian H
hyb
T
in a simi lar way to the EIT concepts in atomic
physics. In our analysis, the following three observations are
employed. (i) Breaking of the structural symmetry (s 0) results
in weak near-eld coupling of the hybridized dark and bright
modes, an eect which can be incorporated to the unperturbative
Hamiltonian (s = 0) with the perturbative terms κ and κ
0
. (ii)
There is no direct coupling between the in-phase and out-of-phase
hybrid modes, due to the large energy dierence in between (D
(
S Q
-
). (iii) Damping rates of the quadrupole (γ
Q
(
) and dipole (γ
D
(
)
hybrid modes are small enough that the condition γ
Q
(
, γ
D
(
, ω
(
is
satised. Here ω
(
are the resonant frequencies of the in-phase and
out-of-phase hybrid pairs (ω
(
= E
D
(
/p E
Q
(
/p).
We can express all hybrid states in the form of |φæ = φ~e
iωt
(where φ
is Q
(
and D
(
) and denote the external driving eld as
~
E
0
e
iωt
.Then,in
agreement with the total Hamiltonian of the system, the following set
of linear equations is obtained for the coupled Lorentzian oscillators
ω ω
þ
þiγ
þ
D
k
þ
00
k
þ
ω ω
þ
δ
þ
þiγ
þ
Q
00
00ω ω
þiγ
D
k
00k
ω ω
δ
þiγ
Q
2
6
6
6
6
4
3
7
7
7
7
5
~
D
þ
~
Q
þ
~
D
~
Q
2
6
6
6
6
4
3
7
7
7
7
5
¼
g
þ
~
E
0
0
g
~
E
0
0
2
6
6
6
6
4
3
7
7
7
7
5
ð4Þ
Figure 3. (a) Asymmetric (s = 150 nm) and symmetri c (s =0nm)
double-layer EIT-like spectra. Two dips seen in the symmetric structures
spectrum corresponds to hybrid dipolar modes as in Figure 2b. Asym-
metric structure shows two EIT-like peaks at dierent spectral positions. A
modelt based on Lorentzian harmonic oscillators is shown for the double-
layered structure (red dashed curve with κ
=12THz,κ
þ
= 23 THz),
25
which traces the calculated spectra very well. A genetic search algorithm
is implemented to extract the parameters using a least-squares sum t.
Calculated group indices for the in-phase and out-of-phase modes are n
g
þ
= 16, n
g
= 9.3. These values can be optimized by adjusting the coupling
terms κ
(
. Inset shows the top view charge distribution at the air/metal
interface for the out-of-phase EIT peak (in-phase EIT peak also shows
the same distribution). Stronger excitation of the quadrupolar mode is
shown. (b) Cross-sectional charge distributions of the quadrupolar
antennas are shown at a position marked with the red dashed line in
the inset. Hybridization of the quadrupolar resonance is shown.
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D dx.doi.org/10.1021/nl200197j |Nano Lett. XXXX, XXX, 000–000
Nano Letters
LETTER
Here κ
(
values are the coupling parameters of the perturbative
term for the in-phase and out-of-phase hybrid pairs, which are
determined by the structural oset s. δ
(
values are the small
detuning of the frequencies of in-phase and out-of-phase hybrid
mode pairs (δ
(
=(E
D
(
E
Q
(
)/p). g
(
values are the geometrical
parameters that dene the coupling eciency of the dipolar hybrid
modes (D
(
)totheexternaleld. Equation 4 represents two
coupled Lorentzian oscillator pairs correspondi ng to in-phase
and out-of-phase hybridized modes of the whole structure. The
external eld (E
0
) drives the bright modes in each meta-atom,
which are subsequently coupled to the dark modes (through κ
(
).
With these equations the amplitudes of the dipolar hybrid states
(D
(
) can be derived as
~
D
(
¼
g
(
~
E
0
ðω ω
(
δ
(
þiγ
(
Q
Þ
ðω ω
(
þiγ
(
D
Þðω ω
(
δ
(
þiγ
(
Q
Þðk
(
Þ
2
ð5Þ
The complex amplitudes of the corresponding modes (given
in eq 5) are directly proportional to the polarizability of the
modes, which governs the spectral characteristics of the plasmo-
nic structure. The overall spectral response is given by the
superposition of these amplitudes. The close agreement between
this analytical derivation and the FDTD analysis conrms the
validity of our perturbative model as shown in Figure 3a (dashed
curve). The physical principles leading to multispectral EIT-like
behavior can be equivalently observed in other structures. As an
example, we implemented our approach with multilayered dol-
men structures,
6
and obtained a clear multispectral EIT-like
behavior (see Supporting Information).
Equation 5 is in close analogy to atomic physics, where the
investigated atomic absorption cross section are given with a
similar formula.
1
This analogy allows us to illustrate multispectral
EIT phenomena in our composite structure with ve-level state
diagram as shown in Figure 4. It is important to note that these
eigenstates are strongl y correlated, since they are a linear
combination of the same basis sets (D
0
,Q
0
) as shown in the
hybridization diagram in Figure 2a.
Experimental verication of this novel phenomenon is demon-
strated using a lift-o free fabrication method that results in
simultaneous patterning of multilayered slot antennas.
26
In our
fabrication scheme, we start with a free-standing membrane, which
is patterned with nanoapertures using e-beam lithography and dry-
etching.
27,28
Subsequent metal deposition on both sides with a
highly directional e-beam evaporation results in multiple stacks that
are automatically registered with respect to each other in the xy-
plane. Similarly, this fabrication scheme can be extended to
fabricate devices with an even larger number of layers.
29
Cross-
sectional scanning electron microscope (SEM) image of the nal
structure shows negligible metal covering at the inner side walls
(inset to Figure 5d). Spectral data collection is done with a Bruker
IFS 66/s Fourier transform infrared (FTIR) spectrometer with a
Hyperion 1000 IR microscope in reection mode. In measure-
ments obtained from the single-layered structure, a clear EIT-like
spectral response is observed at a single frequency (100 THz,
Figure 5c). On the other hand, experimental measurements
obtained from the double-layered structure reveal two EIT peaks
as predicted by the analytical relations (Figure 5d). The length of
the dipolar slot antenna is 700 nm, and its width is 125 nm. The
quadrupolar antenna lengths are 900 nm with a same width of
125 nm. The small in-plane separation between the dipolar and the
quadrupolar antenna is 60 nm. The thicknesses of the deposited
gold lms are 30 nm on both sides with a dielectric layer of 70 nm in
between. A structural asymmetry (s) of 135 nm is introduced to
enable the excitation of hybrid quadrupolar modes.
In conclusion, we presented a method to extend the EIT-like
phenomena to multiple spectral positions by tailoring the near-eld
Figure 4. Coupled three-level system model for multispectral plasmon
induced transparency. Coupled meta-atoms have four states which form
a ve-level system with the continuum.
Figure 5. (a) Illustration of the double-layered structure fabrication on a free-standing membrane. (b) SEM image of an array is shown. Reection
spectra of the symmetric (s = 0) and asymmetric (s 0) for (c) single-layered and (d) double-layered structures are shown. A model t based on
Lorentzian harmonic oscillators is shown for the double-layered asymmetric structures spectrum (red dashed curve with κ
= 9.7 THz, κ
þ
= 27.4
THz).
30
The dipolar slot antenna length is 700 nm and the quadrupolar antenna lengths are 900 nm, all antenna widths are kept at 125 nm. The gap
between the dipolar and quadrupolar antennas is 60 nm. Periods are 1200 nm on both x and y directions. Both Au layers are 30 nm with a 70 nm dielectric
layer in-between. Inset in (d) showsthe cross sectionimage of the double-layered structure. Coverageofthesidewalls due to the metaldeposition is minimal.
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E dx.doi.org/10.1021/nl200197j |Nano Lett. XXXX, XXX, 000–000
Nano Letters
LETTER
coupling of meta-atoms in a multilayered metamaterial system. In
particular, two near-eld interaction mechanisms make this phe-
nomena possible; (i) hybridization of plasmonic resonances (Σ
~
)
and (ii) interaction between the bright and dark antennas (
~
K). The
method is demonstrated experimentally and theoretically with
planar slot antenna based multilayered metamaterial systems. For
experimental demonstration, a lift-o free fabrication scheme that
can simultaneously register multiple metamaterial layers is intro-
duced. The provided analytical investigations are kept general.
Therefore, our method can be easily extended to other antenna
geometries
31
(see Supporting Information) as well as scaled to a
larger number of metamaterial layers.
ASSOCIATED CONTENT
b
S
Supporting Information. Additional information regard-
ing electric eld distributions and enhancements at plasmon
induced reection peaks and multispectral plasmon induced
transparency with nanoparticles. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: altug@bu.edu.
Author Contributions
These authors contributed equally
ACKNOWLEDGMENT
This work is supported in part by NSF CAREER Award
(ECCS-0954790), ONR Young Investigator Award, Massachu-
setts Life Science Center New Investigator Award, NSF Engi-
neering Research Center on Smart Lighting (EEC-0812056),
Boston Univer sity Photonics Center, and Army Research
Laboratory.
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(25) Other used model parameters are, ω
þ
/ω
= 128/57 THz, δ
þ
/
δ
= 0.9/0.8 THz, γ
Q
þ
/γ
Q
= 8.32/6.1 THz, γ
D
þ
/γ
D
= 30.7/
17.7 THz.
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þ
/ω
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þ
/δ
= 14.9/4.8 THz, γ
Q
þ
/γ
Q
= 12.19/4.49 THz, γ
D
þ
/γ
D
= 45.7/11.9 THz.
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  • Source
    • "As an intriguing physical phenomenon, EIT occurs in atomic systems due to the quantum destructive interference between the excitation pathways to the atomic upper level [6], [7]. Tremendous attention has been attracted to study EIT phenomenon and they have been observed in various plasmonic structures, such as symmetry-reduced grating structure [8], coupled resonant systems [9], [10], metamaterials [11]–[13] and metal-insulatormetal (MIM) waveguides [14]–[17]. Among all the nanostructures, the MIM waveguide structures have attracted many researchers' attention due to their deep-sub-wavelength confinement of light [18]–[21]. "
    [Show abstract] [Hide abstract] ABSTRACT: A compact structure is proposed to achieve electromagnetically induced transparency (EIT) response, which consists of a side-coupled cavity and a ring resonator. Novel structures and the transmission characteristics are studied in several different situations. The plasmonic device can be used as a high-sensitivity refractive sensor with a sensitivity of 1200 nm/RIU. In addition, multi-EIT-like peaks appear in the original broadband spectrum by adding another side-coupled cavity or ring resonator, and the physical mechanism is presented. The system paves a new way toward highly integrated optical circuits and networks, particularly for nanosensor, spectral splitter, and nonlinear devices.
    Full-text · Article · Dec 2015 · IEEE Photonics Journal
  • Source
    • "Recently, an analogous behavior of EIT, denoted as phonon-induced transparency (PIT), has been observed in stacked bilayer graphene nanoribbons [9]. Generally, a broken symmetry is used as a prerequisite for plasmonic EIT, since only the asymmetry of the resonators should allow the excitation of the forbidden dark mode7891011. As a result, these structures show polarization dependent response. "
    [Show abstract] [Hide abstract] ABSTRACT: We report the experimental observation and the evidence of the analogue of electromagnetically-induced transparency (EIT) in a symmetric planar metamaterial. This effect has been obtained in the THz range thanks to a destructive Fano-interference between the two first modes of an array of multi-gap split ring resonators deposited on a silicon substrate. This structure is a planar thin film material with four-fold symmetry. Thanks to this property, a polarization-independent transmission has been achieved. The proposed metamaterial is well adapted to variety of slow-light applications in the infrared and optical range.
    Full-text · Article · Mar 2015 · Photonics
  • Source
    • "It has been found that PIT possesses many particular applications, such as slow light [14] [15] [16], sensing [17] [18] [19] [20], and optical switching [21]. Many plasmonic nanostructures have been proposed and demonstrated to realize PIT, such as dipole antennas [22] [23], detuned dipoles [24], split ring resonators [25] [26], and metallic nanoparticles [27]. The spectral response for most nanostructures, however, depends strongly on the polarization of the incident wave, which becomes problematic in potential applications. "
    [Show abstract] [Hide abstract] ABSTRACT: In this article, we demonstrate plasmonic-induced optical transparency (PIT) in a planar metamaterial consisting of a metallic regular triangle (RT) embedded in a ring nanostructure. The interference between the bright dipole mode of the RT and the dark quadrupole mode of the ring leads to the emergence of a transparent window in the visible regime. By combining nanostructures with different degrees of symmetry, the PIT transmission properties of our metamaterial remain stable with respect to the incident polarization, showing polarization-insensitivity to the incident wave. The transmission efficiency of the PIT peak for different polarizations can be maintained at greater than 95.77% with a fluctuation range of 0.01% in our calculation accuracy.
    Full-text · Article · Dec 2014 · Journal of optics
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