Phase modulation plays a crucial role in various terahertz applications, including radar detection, biomedical imaging, and data communication. Existing terahertz phase shifters typically rely on tuning the resonant effect of metamaterial structures to achieve a narrow bandwidth phase shift. However, the terahertz band offers a wide bandwidth resource, which has great advantages in high longitudinal resolution detection, high-capacity communication, spectral imaging, and so on. Here, we propose and demonstrate an ultrawideband terahertz phase shifting mechanism that utilizes an optical conductivity tunable interface combined with a nonresonant metasurface operating in the total internal reflection geometry. This approach effectively modulates the phase of the reflected terahertz signal in an ultrawideband. To implement this mechanism, we designed a structure consisting of graphene-loaded nonresonant periodic metal microslits arranged in the total internal reflection geometry. By controlling the gate voltage of the graphene within a range of ±5 V, an averaged ∼120° continuous phase shift in the frequency range of 0.4 to 1.2 THz was achieved, with a group delay less than 50 ps. Notably, in the frequency range of 1 to 1.2 THz, the phase modulation exhibited a linear relationship with the driving voltage. Our device demonstrated minimal fluctuations in the reflected amplitude, with a deviation of less than 1 dB and an insertion loss of less than 10 dB. Additionally, the modulation speed of this solid-state device reached the kHz level. Remarkably, the phase modulation bandwidth (Δf/f) achieved approximately 100% of the arithmetic center frequency at 0.8 THz, surpassing the definition of ultrawideband, which typically encompasses 20% of the center frequency. To the best of our knowledge, this is the first and most wideband phase shifter developed for the terahertz regime with the lowest recorded group delay to date.

中文翻译：

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全内反射几何中可调谐导电界面电调制的超宽带固态太赫兹移相器


相位调制在各种太赫兹应用中发挥着至关重要的作用，包括雷达探测、生物医学成像和数据通信。现有的太赫兹移相器通常依赖于调节超材料结构的谐振效应来实现窄带宽相移。然而，太赫兹频段提供了较宽的带宽资源，在高纵向分辨率探测、大容量通信、光谱成像等方面具有巨大优势。在这里，我们提出并演示了一种超宽带太赫兹相移机制，该机制利用光导率可调谐界面与在全内反射几何结构中运行的非谐振超表面相结合。这种方法有效地调制超宽带中反射的太赫兹信号的相位。为了实现这一机制，我们设计了一种由石墨烯负载的非共振周期性金属微缝组成的结构，这些微缝排列在全内反射几何结构中。通过将石墨烯的栅极电压控制在±5 V的范围内，在0.4至1.2 THz的频率范围内实现了平均~120°的连续相移，群延迟小于50 ps。值得注意的是，在1至1.2 THz的频率范围内，相位调制与驱动电压呈现线性关系。我们的设备展示了反射幅度的最小波动，偏差小于 1 dB，插入损耗小于 10 dB。此外，该固态器件的调制速度达到了kHz级别。值得注意的是，相位调制带宽 (Δf/f) 在 0.8 THz 处实现了大约 100% 的算术中心频率，超过了超宽带的定义，超宽带通常包含 20% 的中心频率。 据我们所知，这是第一个也是最宽带的太赫兹移相器，具有迄今为止记录的最低群延迟。