Enhanced spatial terahertz modulation based on
graphene metamaterial
Dandan Sun (孙丹丹), Mengqi Wang (王梦奇), Yuanyuan Huang (黄媛媛),
Yixuan Zhou (周译玄), Mei Qi (祁 媚), Man Jiang (江 曼), and Zhaoyu Ren (任兆玉)*
State Key Lab Incubation Base of Photoelectric Technology and Functional Materials, International Collaborative
Center on Photoelectric Technology and Nano Functional Materials, School of Physics, Institute of Photonics &
Photon-Technology, Northwest University, Xi’an 710069, China
*Corresponding author: rzy@nwu.edu.cn
Received November 3, 2016; accepted February 10, 2017; posted online March 8, 2017
The plasmonic mode in graphene metamaterial provides a new approach to manipulate terahertz (THz) waves.
Graphene-based split ring resonator (SRR) metamaterial is proposed with the capacity for modulating trans-
mitted THz waves under normal and oblique incidence. Here, we theoretically demonstrate that the resonant
strength of the dipolar mode can be significantly enhanced by enlarging the arm-width of the SRR and by stack-
ing graphene layers. The principal mechanism of light–matter interaction in graphene metamaterial provides a
dynamical modulation based on the controllable graphene Fermi level. This graphene-based design paves the
way for a myriad of important THz applications, such as optical modulators, absorbers, polarizers, etc.
OCIS codes: 160.3918, 120.7000, 130.4110.
doi: 10.3788/COL201715.051603.
Graphene is a promising two-dimensional (2D) material in
many fields due to its extraordinary mechanical, thermal,
electronic, and optical properties
[1–3]
. Various graphene-
based electronics and photonics devices operating in a pas-
sive or active mechanism have been demonstrated, such as
optical modulators, saturable absorbers, photodetectors,
and polarizer s
[2,4,5]
. Particularly, graphene has shown ad-
vantages in manipulating terahertz (THz) waves thanks
to the controllable interaction between THz waves and
graphene by turning the carrier concentration (i.e., Fermi
energy) through physical or chemical methods
[6]
, which
could provide a splendid platform for the design of
THz devices
[7]
. Nevertheless, the intensity of interaction
between graphene and THz waves is not strong enough
for practical applications due to its nonresonant Drude-
like behavior
[8]
. Artificially constructed material (metama-
terial) can be introduced for enhanced light–matter
interaction. The plasmonic resonance in metamaterials ex-
cited by incident light can be tailored by the structure and
size
[9]
, which plays a crucial role in modulation and
manipulation of electromagnetic waves. Consequently,
the combination of graphene and metamaterial provides
promise for THz applications, which bridges the “THz
gap” between the far infrared field and microwave
region
[10,11]
. Recently, investigations about graphene meta-
material THz devices have been carried out. For instance,
Alaee et al. proposed a perfect absorber by patterning
graphene micro-ribbons on a dielectrics-metal layer
[12]
.
Freitag et al. demonstrated a polarization sensitive gate
tunable photodetector by patterning graphene micro-
ribbons
[13]
. A pioneering work about a modulator based
on a hybrid graphene/metamaterial structure was also
proposed, which can modulate the amplitude of THz
waves up to 90% with normal incidence
[14]
.
Among the THz applications, a THz modulator is one of
the most important devices. Semiconductors were the
most used materials for THz applications, however, there
still exists some problems in these traditional devices, such
as poor modulation depth and strict opera tion tempera-
ture requirements
[15,16]
. Further improvement for the
traditional semiconductors or 2D graphene-based THz
modulators is largely needed for practical applications.
Here, we demonstrate a graphene metamaterial device
as an efficient method to actively modulate THz waves
by patterning split ring resonators (SRRs) arranged on
a lossless substrate (LS). The THz wave transmission
through the graphene metamaterial can be dynamically
modulated by tuning the Fermi level of graphene. We also
investigated the influence of the arm-width of an SRR and
a graphene layers number on the plasmonic modes of the
metamaterial. Our proposed monolayer structure achieves
high modulation depth of up to 85% and 80% under nor-
mal and oblique incidence, respectively. It should be noted
that our design is flexible for highly effective modulation
when the incident THz wave is oblique over a broad range
of angles. Moreover, the modulation depth can be further
enhanced to 99% if stacked graphene layers are used in the
metamaterial structure. Our proposed concept shows
potentials for the development of broadband THz opto-
electronic devices.
Figures
1(a) and 1(b) show the periodic devices arrange-
ment and a single device of the graphene metamaterial,
respectively. Graphene film was patterned to form an open
square ring, as highlighted in the watchet area. The geo-
metric parameters of the unit cell are L ¼ 4 μm (length)
and H ¼ 3 μm (height). The unit SRR resonator consists
of a graphene layer that has a length of a ¼ 2.8 μ m (width
of the square ring), b ¼ 3.6 μm (length of the square ring),
COL 15(5), 051603(2017) CHINESE OPTICS LETTERS May 10, 2017
1671-7694/2017/051603(4) 051603-1 © 2017 Chinese Optics Letters