Abstract Metasurfaces composed of subwavelength optical antennas offer fruitful functionalities to manipulate the amplitude, phase and polarization of light. Sufficient phase tunability of metasurfaces has significant potential for dynamic beam steering, hologram and flat optics exhibiting tunable focusing. Here, we demonstrate a graphene based metasurface that gives rise to more than 330° smooth and continuous phase modulation at mid-infrared spectrum. The phase modulator model introduces multiple resonances including Split-Ring-resonator (SRR) resonance and inductance-capacitance (LC) resonance, leading to the outstanding sensitivity of the metasurface to tiny change of surrounding electromagnetic environment. Through adjusting the Fermi level of the monolayer graphene beneath the resonators, both scattered amplitude and phase can be efficiently modulated, so that the electrically programmable metasurface enables nearly arbitrary manipulation of scattered wavefront. Electro-optically tunable focusing and beam steering are numerally realized by constructing one dimensional discrete array element. The phased array design achieves an average efficiency up to 22% within 60° steering range. The reflective focusing lens with focal lengths of 10 μm, 15 μm and 20 μm are successfully demonstrated, respectively. The proposed metasurface has promising potential in optoelectronic applications such as imaging, sensing and focusing.

中文翻译：

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基于石墨烯的活性超表面具有超过 330° 的相位可调性，可在中红外光谱下运行

摘要 由亚波长光学天线组成的超表面提供了丰富的功能来操纵光的振幅、相位和偏振。超表面足够的相位可调性对于动态光束控制、全息图和呈现可调聚焦的平面光学具有巨大的潜力。在这里，我们展示了一种基于石墨烯的超表面，可以在中红外光谱中产生超过 330° 的平滑和连续相位调制。相位调制器模型引入了多个谐振，包括分裂环谐振器 (SRR) 谐振和电感电容 (LC) 谐振，导致超表面对周围电磁环境的微小变化具有出色的灵敏度。通过调整谐振器下方单层石墨烯的费米能级，散射振幅和相位都可以有效调制，因此电可编程超表面几乎可以任意操纵散射波前。电光可调聚焦和光束控制是通过构造一维离散阵列元件在数字上实现的。相控阵设计在 60° 转向范围内实现了高达 22% 的平均效率。分别成功演示了焦距为10 μm、15 μm和20 μm的反射聚焦透镜。所提出的超表面在成像、传感和聚焦等光电应用中具有广阔的潜力。电光可调聚焦和光束控制是通过构造一维离散阵列元件在数字上实现的。相控阵设计在 60° 转向范围内实现了高达 22% 的平均效率。分别成功演示了焦距为10 μm、15 μm和20 μm的反射聚焦透镜。所提出的超表面在成像、传感和聚焦等光电应用中具有广阔的潜力。电光可调聚焦和光束控制是通过构造一维离散阵列元件在数字上实现的。相控阵设计在 60° 转向范围内实现了高达 22% 的平均效率。分别成功演示了焦距为10 μm、15 μm和20 μm的反射聚焦透镜。所提出的超表面在成像、传感和聚焦等光电应用中具有广阔的潜力。