Vol. 27, No.

12 | 10 Jun 2019 | OPTICS EXPRESS 16624

All-dielectric metamaterial analogue of

electromagnetically induced transparency and
its sensing application in terahertz range
TIAN MA,1,5 QIUPING HUANG,2,3 HONGCHUAN HE,4 YI ZHAO,2 XIAOXIA LIN,2
1,2,3,4,6
AND YALIN LU
1
National Synchrotron Radiation Laboratory, University of Science and Technology of China,
Hefei,Anhui, 230026, China
2
Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and
Technology of China, Hefei, Anhui, 230026, China
3
Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and
Technology of China, Hefei, Hefei 230026, China
4
Department of Materials Science and Engineering, University of Science and Technology of China,
Hefei 230026, China
5
tianma@ustc.edu.cn
6
yllu@ustc.edu.cn

Abstract: A novel electromagnetically induced transparency (EIT) all-dielectric metamaterial

is proposed, fabricated, and characterized. The unit cell of the proposed metamaterial
comprises of two asymmetric split ring resonators (a-SRRs) positioned with a mirror
symmetry. The asymmetric nature of a-SRRs results from the length difference of two arcs.
Optical properties of the fabricated metamaterial are investigated numerically using finite
difference method, as well as experimentally using a terahertz time-domain spectroscopy. The
results confirm that the proposed metamaterial exhibits an EIT transparent window in the
frequency range around 0.78THz with a Q-factor of ~75.7 and a time-delay up to ~28.9ps.
Theoretical investigations show that EIT effects in our metamaterial are achieved by
hybridizing two bright modes in the same unit cell, which are aroused by the excitation of
magnetic moments. We also confirm that the proposed metamaterial has great potential for
sensing applications with high sensitivity and high figure of merit (FOM), which guarantees
potential applications in in situ chemical and biological sensing.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

1. Introduction
The concept of electromagnetically induced transparency (EIT) was originally used to
demonstrate the elimination of absorption within a narrow spectral band due to quantum
interference when light propagates through an originally opaque medium [1]. Accompanied
with the transparency feature, extreme dispersion of the EIT effects can significantly reduce the
group velocity of light and offer promising applications in slow-light and nonlinear devices [2–
5]. However, quantum EIT requires complicated experimental conditions, such as stable laser
pumping and low temperature environment, which observably obstruct its implementations in
practical applications.
Recently, various EIT-analogue optical systems, for instance coupled microresonators
[6,7], optical waveguide [8–10], and metamaterials [11–13], have been drawn great attention
owing to their EIT-like behaviors which are similar to that of the quantum EIT system. These
optical systems are more convenient for practical applications as they are all free from the
stringent requirements of the experimental environment for quantum optics. Among these
optical systems, metamaterial analogues of EIT have attracted great attention as they can easily
realize EIT effects in the whole spectral range from microwave to ultraviolet [14–17] by
defining a properly tailored geometry for the unit cell. Owing to their high transparency and

#364080 https://doi.org/10.1364/OE.27.016624
Journal © 2019 Received 2 Apr 2019; revised 16 May 2019; accepted 17 May 2019; published 29 May 2019
 Vol. 27, No. 12 | 10 Jun 2019 | OPTICS EXPRESS 16625

enhanced nonlinear properties, they have shown great potential in designing novel devices,
such as optical modulators [18–20], optical buffers [21,22], and highly sensitive sensors [23–
25].
Generally, EIT effects in these metamaterial analogues are realized by two approaches,
‘bright-dark’ model and ‘bright-bright’ model. The first one typically involves a narrow band
‘bright’ mode resonator, which can be efficiently coupled to the incident wave directly, and a
broadband ‘dark’ mode resonator, which is not access to the incident wave but can be activated
by the ‘bright’ mode resonator via near field coupling. When these two resonances are excited
in close proximity in both the special and frequency domains, the Fano-type interference
between them results in a narrow transmission or reflection window, and then EIT effects can
be achieved [26–30]. The second approach has been rarely studied and reported. In this
approach, two bright modes with comparable Q-factors are placed close to each other, and the
frequency detuning and hybridization between them result in EIT effects [31–33]. Comparing
to the former one, the second approach is much easier to be realized as both two bright modes
can be directly excited by the incident wave.
However, most of these reported metamaterial analogues of EIT are realized based on
plasmonic effects, which are limited by the large non-radiative ohmic loss on the metal surface.
As a consequence, those plasmonic metamaterial analogues of EIT generally feature reduced
Q-factor and modulation range [34]. Recently developed all-dielectric metamaterials offer a
potential solution to this issue [35]. Multipoles with minimal absorption losses, including
electric dipoles, magnetic dipoles, toroidal dipoles, and higher order Mie resonators, are excited
in these high-refractive-index dielectric nanorenonators, and EIT effects can be realized based
on the coupling between these nanorenonators. Moreover, these all-dielectric metamaterial
analogues are significantly efficient when compared with their metallic counterparts [36–38].
For instance, in [36], authors reported a classical analogue of EIT using all-dielectric
silicon-based metasurfaces. Based on coherent interaction between radiative and non-radiative
resonators combined with the reduction of absorption loss, sharp EIT-like resonances with
Q-factor up to ~483 was accomplished in the near-infrared regime.
In this paper, we propose a novel silicon-based metamaterial for EIT effects at terahertz
frequencies. The unit cell of the proposed metamaterial consists of two asymmetric split ring
resonators (a-SRR) whose asymmetric nature comes from the different lengths of their arcs.
We demonstrate theoretically and then confirm experimentally that the proposed metamaterial
can exhibit an EIT resonance with high transmittances, as well as large group delays, at
frequencies around 0.78THz. Via numerical simulations, we show that the EIT transparent
window in this system is aroused by the interaction between two bright modes, which are
caused by the excitation of magnetic moments simultaneous in the same unit cell. We also
confirm that, owing to the narrow linewidth of EIT resonance, the proposed metamaterial is
promising for optical sensing applications with high sensitivity and figure-of-merit (FoM).
2. Design and characterization
Before the sample fabrication, we characterized optical properties of materials we prepared,
including intrinsic silicon and polydimethylsiloxane (PDMS), using a standard terahertz
time-domain spectroscopy (THz-TDS). The tested silicon sample is a ~100μm-thick silicon
wafer, while the tested PDMS sample is a ~30μm-thick PDMS layer which is spin-coated on a
silicon wafer with a 20mm × 20mm through hole at its center. The experimental results are
shown in Fig. 1. We note that the measured refractive index is much higher that what was
reported in [39] ( nPDMS  1.31 at 0.8THz). This is because that the spin-coated PDMS layer
had been baked at 120°C in an oven for 15min for the solidification.
As schematically demonstrated in Fig. 2(a), the unit cell of the proposed all-dielectric EIT
metamaterial consists of two asymmetric split-ring resonators (a-SRRs) which are made of
intrinsic silicon. The asymmetric nature of a-SRRs is resulted from the length difference of two
d = 100μ m arcs, as the long arc spans α =160° and the short arc spans β =120°. To describe
 Vol. 27, No. 12 | 10 Jun 2019 | OPTICS EXPRESS 16626

the degree of asymmetry of a-SRRs, we define an asymmetric parameter

η = (α -β ) / (α +β ) ×100%, and for the proposed metamaterial η =14.3%. Meanwhile, the pair
of SRRs in the unit cell is of mirror symmetry about the x-z plane, with the spacing between
two SRRs is d = 50μ m. The SRRs are with height of h = 100 μ m, outer radius of
R1 = 75μ m, and inner radius of R2 = 37.5μ m. The periods of the unit cell in x- and y-
directions are Px = 400 μ m and Py = 250 μ m, respectively. The silicon SRRs are posted on a
PDMS substrate with a thickness of t = 30μ m. The electromagnetic field excites the sample at
normal incidence, with its electric field component parallel to the y-axis.

Fig. 1. Complex refractive index measured in the terahertz regime of (a) – (b) intrinsic silicon
and (c) – (d) PDMS.

Fig. 2 (a) Schematic of the all-dielectric metamaterial composed of two asymmetric split ring
resonators. Inset: top view of the unit cell. All dimensions shown here are h = 100 μ m,
t = 30 μ m, Px = 400μ m, Py = 400 μ m, R1 = 75μ m, R2 = 75μ m, α = 160°,
and β = 120°. (b) Microscopy of the fabricated sample. Bars refer to 500μm. (c) Transmission
spectra and (d) corresponding group delay of the proposed metamaterial.
 Vol. 27, No. 12 | 10 Jun 2019 | OPTICS EXPRESS 16627

To characterize the optical properties of the proposed metamaterial, we firstly numerically

simulated the transmission of the proposed metamaterial using a commercially available finite
difference frequency-domain software package CST Microwave Studio. The simulated field
transmission spectrum, and corresponding group delay which is retrieved from the complex
transmission as t g = −∂ϕ (ω ) / ∂ω where ϕ (ω ) is the phase shift of the transmitted THz
wave, are plotted as solid red lines in Fig. 1(c) and (d), respectively. In these simulations, the Si
resonators (ε Si = 11.7) are sitting on a PDMS substrate ( (ε PDMS = 1.69). A distinct EIT-like
peak can be observed at the frequency of 0.78THz. The linewidth (Δω ) of EIT resonances is
evaluated by using a second moment method [40], which can be given by

 ( ω − ω0 ) T ( ω ) d ω ,
2 2

Δω 2 = 4 (1)
 T (ω ) d ω
2

where ωc is the spectral position of EIT peak and T ( ω) is the field transmission. To
investigate the influence of material absorption, we performed simulations with different
silicon material absorptions which were measured by the loss tangent. Although the curve
shape has been changed, we find out that the material absorption would not effect on the
spectral position and Q-factor of the EIT transparent peak. Based on simulation results we
evaluated linewidths of simulated EIT peaks which are ~10.3GHz for both the low-loss silicon
( tan δ = 0.001 ) and the high-loss silicon (tan δ = 0.01). The corresponding Q-factor, which
can be defined as Q = ωc / Δω , is ~75.7. Furthermore, the group delay at the EIT resonant
frequency reaches to 28.9ps and 18.3ps, respectively, leading to the potential of slow-light
applications.
The designed metamaterial was fabricated by starting with a 100μm-thick intrinsic silicon
wafer. A PDMS layer with a thickness of ~30μm was spin-coated on the back surface of the
silicon wafer and was used as the substrate. The designed structure was patterned using the
standard optical lithography followed by the deep reactive-ion etching with a Bosch process.
The optical microscopy of the fabricated sample is shown in Fig. 2(b). Experimental
measurements of THz transmission were performed in a dry gas pumped environment using the
standard photoconductive-antenna based terahertz-time-domain spectroscopy (THz-TDS)
system. During the measurements, the sample was illuminated by a normal-incident THz wave
with the electric field oriented parallel to the split arrangement of SRRs. The experimentally
measured transmittance and group delay were plotted as solid red lines in Fig. 2(c) and (d). A
transmission peak with the transmittance of 63% can be observed at 0.773THz with a Q-factor
of ~54.1. THz wave with central frequency of 0.773THz is delayed maximally by 11.7ps when
propagating through the metamaterial device with a thickness of ~130μm (including the silicon
posts and PDMS substrate), which corresponds to a propagating distance of ~3.5mm in free
space. Although the material absorption of silicon, as shown by Fig. 1(b), is approximately
similar to that of the low-loss silicon we used in simulations in the frequency range from
0.6THz to 0.9THz, experimental measurements show good agreement with numerical
simulations for high-loss silicon. This phenomenon predicts that the material absorption has
been increased due to the fabrication process. Inconsistencies in the shape of transmission
curve and the Q-factor of EIT peak can be attributed to the distortion of the fabricated sample as
the PDMS substrate is very flexible, which would introduce scattering losses and break
coherence between the resonators.
3. Discussion
Firstly, we would like to investigate the physics behand the EIT-like behavior of the proposed
metamaterial. In follow simulations, we use the low-loss silicon as the resonator material to
reduce the influence of the material absorptions on electromagnetic responses. As
schematically shown in Fig. 2(a), each unit cell of the proposed metamaterial can be regard as a
 Vol. 27, No. 12 | 10 Jun 2019 | OPTICS EXPRESS 16628

combination of a long-arc SRR subresonator and short-arc SRR subresonator which are placed
fact-to-face. The EIT window of the proposed metamaterial is due to the interaction between
these two subresonators. In Fig. 3(a), we provide the transmission spectrum of the

Fig. 3. (a) Simulated transmission curves of Short SRR (blue solid line), long SRR (red solid
line), and a-SRR (black solid line) metamaterials. The dashed magenta line refers the
analytically fitted data using the two-oscillator model [Eq. (3)]. (b) Scattered power of the five
major multipoles of the proposed metamaterial, including electric dipole (P), magnetic dipole
(M), electric quadrupole Qe, and magnetic quadrupole Qm. Spatial distribution of (c)-(e) electric
field and (f)-(h) magnetic field in the x-0-z plane bisecting the metamaterial at dip 1 (0.77THz),
peak (0.78THz) and dip 2 (0.80THz), respectively.

Fig. 4. Vector plots of magnetic fields at (a) Dip 1 0.77THz, (b) EIT peak 0.78THz, (c) Dip 2
0.80THz and (d) 0.776THz where the intensity of magnetic field is magnified by 5 times.

proposed a-SRR metamaterial (solid black line), which is superimposed with that of its two
subresonators: short-SRRs (solid blue line) and long-SRRs (solid red line). It can be clearly
observed that two transmission dips occurring at 0.77THz and 0.80THz inherit from the
resonances associated with each individual subresonator, and the EIT peak appearing at
0.78THz is produced by the interaction between them. This behavior is further analyzed by
simulating the spatial distribution of electric and magnetic fields at two transmission dips (dip 1
at 0.77THz and dip 2 at 0.80THz) and the transmission peak (at 0.78THz), respectively. The
simulation results are depicted in Fig. 3(c) and (d). At transmission dips, two subresonators are
excited successively. The induced electric field concentrates on top and bottom parts of
 Vol. 27, No. 12 | 10 Jun 2019 | OPTICS EXPRESS 16629

subresonators and circulates anticlockwise in the x-z plane, which predicts the formation of
displacement current loops. The appearance of current loops can be expected for the excitation
of magnetic moments which concentrate on central parts of subresonators. At the EIT
transparency peak, two subresonators are simultaneously excited. But the induced magnetic
moments in two subresonators, which are clearly depicted by vertical plots of magnetic field as
shown in Fig. 4, are excited in opposite direction, and their interactions with the incident wave
are clearly suppressed. This proves that the EIT transparency window of the proposed
metamaterial is a consequence of the interaction between magnetic moments excited in two
subresonators.
The electric and magnetic fields at resonant frequencies appear due to Mie-type modes, and
the interaction between these modes results the EIT transparence window of the proposed
metamaterial. To analyze the role of these modes in forming the EIT response, we calculate
their relative strength in terms of the scattered electromagnetic power in the far-field zone. The
multipole moments including electric dipole P, magnetic dipole m, electric quadrupole Qe, and
magnetic quadrupole Qm, are calculated based in the density of induced displacement currents
[38,41]. The calculation results are shown in Fig. 3(b). We note that excitations of magnetic
dipole in two subresonators dominates all other standard multipoles at frequencies around two
transmission dips. At frequencies around 0.78THz where the EIT peak appears, the excitation
of magnetic dipole is strongly suppressed. Aside from magnetic dipole, other multipoles,
including P, Qe and Qm, are also excited, which contributes to widening the EIT peak and
suppressing its Q factor due to radiating losses. We also note that the component-wise
contributions of the induced dipole moments are oriented along the corresponding excitation
fields. To be specific, P is excited along the y-axis, while m is parallel to the x-axis.
Furthermore, we also study qualitatively the response of the proposed metamaterial by
applying the coupled harmonic oscillator model, which can be described as [33,42]:
xa ( t ) + γ a xa ( t ) + ωa xa ( t ) + Ω2 xb ( t ) = ca E

(2)
xb ( t ) + γ b xb ( t ) + ωb xb ( t ) + Ω 2 xa ( t ) = cb E


Here, long arc subresonators and short arc subresonators are described as particles a and b,
respectively. ( ωa , ωb ) and ( γ a , γ b ) are resonance angular frequencies and damping strengths,
and Ω refers to the coupling coefficient between two subresonators. ca and cb are the
coupling efficiency between the individual subresonator and the indicant THz wave
E = E0 exp ( iωt ) respectively. The effective susceptibility χ eff of the EIT structure, which is
proportional to the ratio of the polarization ( P ) of the particles to the strength of incident
electric field (E), can be obtained by solving the displacement vectors of two SRRs from Eq.
(2):
P ca xa + cb xb
χ eff = =
ε0 E ε0 E
 ca2 (ω 2 − ωb2 ) + cb2 (ω 2 − ωa2 ) + ca cb Ω
= K × 4
 Ω − (ω 2 − ωa2 + iωγ a )(ω 2 − ωb2 + iωγ b ) (3)

ca2γ b + cb2γ a 
iω 
Ω 4 − (ω 2 − ωa2 + iωγ a )(ω 2 − ωb2 + iωγ b ) 

where K is a proportionality factor. According to the Kramers-Kronig relations, the

transmission coefficient can be given by T = 1- A where A = Im ( χ eff ) is the absorption
losses in the sample. In our fitting, ωa and ωb are set as 2π × 0.77 ×1012 rad / s and
2π × 0.80 × 1012 rad / s, respectively; the loss factors of two SRRs are obtained from the
 Vol. 27, No. 12 | 10 Jun 2019 | OPTICS EXPRESS 16630

linewidth of simulated transmission curve, and calculated as 5.61×1011rad / s and

7.91×1011rad / s. The dashed magenta line in Fig. 2(a) demonstrates the analytically modeled
transmission spectra using Eq. (3). Although there are minor differences in amplitude and
bandwidths for the spectra in Fig. 1(c), the analyzed model shows very good agreements with
the simulated results.
As demonstrated above, the EIT resonance of the proposed metamaterial is resulted from
the interaction between two subresonators. Thus, the coupling coefficient, Ω, plays an
important role in forming a high-Q-factor EIT resonance. We characterize the spectral response
of the proposed metamaterial with respect to the spacing between two SRRs d which is changed
by shifting two subresonators simultaneously. As schematically demonstrated in Fig. 5(c), with
a larger spacing between two SRRs, the spacing between long-arc and short-arc subresonators,
as well as the coupling distance these two subresonators, is reduced. In Fig. 5(a), we show
transmission spectra of metamaterial with different spacing between two SRRs which increases
from 110μm to 150μm. The enlarging of coupling distance leads to redshifts of EIT resonant
frequency. The local distributions of magnetic field as EIT resonant frequencies, as shown in
Fig. 5(b), help further understand the physics behand the formation of EIT peak and its
response to the variation of subresonator spacing. A weak localization of magnetic field at the
long arc resonators can be observed for larger subresonator spacing. The coupling coefficient
Ω , which evaluate the strength of coupling between two subresonators, is extracted from the
analytical fit using the fitting model descripted by Eq. (2) – (3) to simulated transmission
spectra of metamaterials with different SRRs spacing. For comparison, we also retrieved
Q-factors of numerically simulated and analytically modeled EIT peaks using Eq. (1), as
depicted in Fig. 5(d). In addition, we also studied transmission spectrum evolution in terms of
arc length. In Fig. 5, we present electromagnetic response of the proposed metamaterial with
different lengths of short-arc-subresonators, which varies from β = 70° to β = 140°.
Clearly, with shorter lengths of short-arc-subresonators, EIT peaks are broadened and
localizations of magnetic field in long-arc-subresonators are restrained, which provide
weakening the coupling between two subresonators, and decreasing of Q-factor. As shown in
Fig. 5(d) and 6(d), we can easily conclude that Q-factor of EIT peak is inversely proportional to
Ω, which agree with results shown in [11].

Fig. 5. (a) Numerically simulated (solid black lines) and analytically modeled (dashed blue
lines) transmission spectra for the proposed metamaterial with different spacing between two
SRRs. (b) Local H-field maps for the unit cell with varying SRRs spacing. (c) Schematic
 Vol. 27, No. 12 | 10 Jun 2019 | OPTICS EXPRESS 16631

showing the variation of the SRRs spacing. The dashed lines show original positions of
subresonators in the proposed metamaterial with d = 150μm. (d) Extracted coupling
coefficient and Q factor as a function of the SRRs spacing.

Due to their narrow linewidth, one potential application the EIT effects of the proposed
metamaterial is the THz sensing. As a demonstration, we study the proposed a-SRR
metamaterial with different background refractive indices. The simulated transmittance spectra
with background refractive indices varying from 1.0 to 1.4 are presented in Fig. 7. One can
clearly observe a substantial shift of the EIT peak position is realized by small refractive index
changes. The EIT peak position keeps moving to lower frequencies till the surround refractive
index reaches to 1.4. By fitting the shift of the EIT peak position, we obtain the sensitivity of
the proposed metamaterial, which is measured by the shift of resonance per
refractive-index-unit (RIU) changes, as S = 231GHz / RIU . Besides the sensitivity, the
sensing performance of the proposed metamaterial can also be characterized by the
figure-of-merit (FoM), which can be defined by the sensitivity (S) and the linewidth of the
resonance ( Δω ) as FoM = S / Δω . When the background refractive indices vary from 1.0 to
1.4, the average linewidth of EIT resonances is about 18.2GHz, leading to a FoM of 12.7. With
such a high sensitivity and high FoM, the proposed metamaterial can be used as a THz sensor
for identifying various gaseous and aerosol analytes or measuring the concentration of dust
particles in the air.

Fig. 6. (a) Numerically simulated (solid black lines) and analytically modeled (dashed blue
lines) transmission spectra for the proposed metamaterial with different lengths of
short-arc-subresonator. (b) Local H-field maps for the unit cell with varying length of
short-arc-subresonator. (c) Schematic showing the variation of the subresonator spacing. (d)
Extracted coupling coefficient and Q factor as a function of length of short-arc-subresonator.

Finally, we would like to compare EIT-resonant and sensing performances of the proposed
metamaterial with other types of metamaterial-based sensing devices. The Q-factor and FoM of
our metamaterial is comparable to the best records of plasmonic EIT metamaterials [30–33],
but is not as large as that exhibited by dielectric EIT metamaterials working in the visible and
infrared range [36–38]. We should claim that the sensing performance of our metamaterial can
be further improved via optimizing its structure. In Fig. 8(a), we demonstrate a sample that the
metamaterial with an optimized structure can exhibit an EIT peak with a linewidth of 3.5GHz
and a Q-factor of ~270. We also investigate its sensing capacity by simulating its transmission
spectra with different surround refractive index. When the surround refractive index varies
 Vol. 27, No. 12 | 10 Jun 2019 | OPTICS EXPRESS 16632

from 1.0 to 1.4, the EIT resonant frequency shifts from 0.94THz to 0.85THz, resulting a
sensitivity of 226GHz/RIU. The relevant FoM can reaches to ~64.7 when the surround
refractive index is 1.0.

Fig. 7. (a) Simulated transmittance spectra of the proposed metamaterial when the background
refractive indices varying from 1.0 to 1.4. (b) The spectral position of the EIT peak as a function
of the background refractive index. The linear fit (solid black line) reveals the sensitivity as
S = 231GHz / RIU.

Fig. 8. (a) Simulated transmission spectrum of the EIT metamaterial with an optimized structure.
Its structural parameters are as follows: h = 100μm, t = 30μm, Px = 320μm,
Py = 320μm, R1 = 60μm, R2 = 40μm, α = 160°, and β = 140°. (b) Simulated
transmittance spectra of the optimized metamaterial when the background refractive indices
varying from 1.0 to 1.4. Inset: The spectral position of the EIT peak as a function of the
background refractive index.

4. Conclusion
A dielectric metamaterial analogue of EIT is for applications in the terahertz frequency range.
The unit cell of the proposed EIT metamaterial consists of two a-SRRs positioned in a mirror
symmetry. The asymmetric nature of SRRs results from the different lengths of individual arcs,
as the long arcs span α = 160° while the short arcs span β = 120°. Simulation results
revealed that the proposed metamaterial exhibited an EIT-like transmittance window with a
Q-factor of ~75.7 in the frequency range around 0.780THz. Based on the proposed
metamaterial structure, we fabricated a sample comprising of silicon resonators and PDMS
substrate by using standard lithography followed by reactive-ion-itching. Transmittances of the
fabricated sample was characterized by standard THz-TDS system with dry-gas pumping. We
observed an EIT resonance peaked at 0.773THz, featuring a Q-factor of ~54.1. The location
 Vol. 27, No. 12 | 10 Jun 2019 | OPTICS EXPRESS 16633

and Q-factor of the measured EIT resonance are in good agreement with theoretical predictions.
We also confirmed that our metamaterial can be used as an optical sensor for monitoring the
background refractive indices. Its sensitivity and FoM reach to 231GHz/RIU and ~12.7,
respectively, and can be further improved by optimizing its structure. The high sensitivity and
FoM of the proposed metamaterial guarantee its potential applications in in situ chemical and
biological detection.
Funding
National Natural Science Foundation of China (51627901 and 11704373), the National Key
Research and Development Program of China, the Bureau of Facility Support and Budget,
CAS, the Ministry of Science and Technology (2016YFA0401004, 2017YFA0402904), the
Chinese Universities Scientific Fund (WK2340000071, WK2310000076), and Anhui Initiative
in Quantum Information Technologies (AHY100000).
Acknowledgments
The device fabrication in this work was partially carried out at the USTC Center for Micro and
Nanoscale Research and Fabrication.
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