Wide Wavelength Tuning of Optical Antennas on Graphene
with Nanosecond Response Time
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Abstract
Graphene
is emerging as a broadband optical material which can
be dynamically tuned by electrostatic doping. However, the direct
application of graphene sheets in optoelectronic devices is challenging
due to graphene’s small thickness and the resultant weak interaction
with light. By combining metal and graphene in a hybrid plasmonic
structure, it is possible to enhance graphene–light interaction
and thus achieve in situ control of the optical response. We show
that the effective mode index of the bonding plasmonic mode in metal–insulator–metal
(MIM) waveguides is particularly sensitive to the change in the optical
conductivity of a graphene layer in the gap. By incorporating such
MIM structures in optic antenna designs, we demonstrate an electrically
tunable coupled antenna array on graphene with a large tuning range
(1100 nm, i.e., 250 cm<sup>–1</sup>, nearly 20% of the resonance
frequency) of the antenna resonance wavelength at the mid-infrared
(MIR) region. Our device exhibits a 3 dB cutoff frequency of 30 MHz,
which can be further increased into the gigahertz range. This study
confirms that hybrid metal–graphene structures are promising
elements for high-speed electrically controllable optical and optoelectronic
devices