Huixian Zhou, Jierong Cheng, Fei Fan, Xianghui Wang, Shengjiang Chang,
Graphene has attracted widespread
attention in dynamic optoelectronic devices due to its tunable electrical and
optical properties. But different modulation capabilities of the graphene-based
designs at different frequencies are less studied. We study the electrical
tunability of transmissive metalenses based on graphene when working at three
frequencies 0.3, 1.25, and 2 THz, respectively. The constitutive
meta-atoms are composed of graphene patches and metallic gratings for efficient
phase shift in the orthogonal polarization. Although the conductivity of
graphene is tunable at all the frequencies, responses of meta-atoms show weak
and strong dependence on the Fermi level at the low and high frequencies,
respectively. Therefore, the focal length of the metalens is not electrically
tunable at 0.3 THz. In contrast, the metalenses designed at 1.25 and
2 THz show electrically adjustable focal lengths, and the tuning range of
the focal length increases with frequency. The research here provides clear guidance
for the design of graphene metalenses with different electrical tunabilities
for a variety of application scenarios.
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