Terahertz Beam Steering Based on Trajectory Deflection in Dielectric-Free Luneburg Lens
Terahertz Beam Steering Based on Trajectory Deflection in Dielectric-Free Luneburg Lens
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DOI：
10.1109/tthz.2020.2983915
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发表时间：
2020-05-01
影响因子：
3.2
通讯作者：
Monnai, Yasuaki
中科院分区：
文献类型：
--
作者：
Sato, Kazuto;Monnai, Yasuaki
太赫兹波的自由空间传输为包括通信和雷达在内的无线应用开辟了巨大的机会，实现了更高的信息容量，更高的空间分辨率，以及比微波更小的孔径。然而，由于较短的波长，它涉及严重的路径损耗。为了补偿路径损耗，通过波束转向的点对点传输是必不可少的。然而，宽带和低损耗波束转向的实现在太赫兹范围内仍然具有挑战性，主要是由于缺乏实用的移相器。为了解决这个问题，我们在这里展示了一种基于无介质Luneburg透镜中轨迹偏转的太赫兹光束转向新方法。它将点激励转换成基于梯度有效折射率的平行导电板内的基横电模式的偏转光束，然后将其发射到自由空间。不存在介电介质有助于降低插入损耗，并且还能够实现有效折射率的外部控制。重要的是，这种方法是由角杠杆辅助的;板倾斜的非常小的变化导致束轨迹的非常大的偏转。我们通过将板倾斜从-25 '改变到+25 '（-0.42度到+0.42度）来展示从-25度到+25度的光束转向，其被转移到60倍大的角度。例如，通过使用压电或MEMS致动器，可以容易地产生这种小的倾斜。由于激发点可以固定，所提出的器件可以很容易地耦合到广泛的芯片源和检测器，提供波导集成。作为一个应用示例，我们实现了高分辨率雷达，它可以识别目标的方向和范围。
Free-space transmission of terahertz waves opens great opportunities for wireless applications including communications and radar, enabling higher information capacity, higher spatial resolution, and yet smaller apertures than using microwaves. Nevertheless, due to the shorter wavelengths, it involves a severe path loss. To compensate for the path loss, point-to-point transmission by beam steering is indispensable. However, the implementation of broadband and low-loss beam steering is still challenging in the terahertz range due mainly to the lack of practical phase shifters. To circumvent this issue, here we demonstrate a novel approach of terahertz beam steering based on trajectory deflection in a dielectric-free Luneburg lens. It converts a point excitation into a deflected beam in the fundamental transverse electric mode inside parallel conducting plates based on graded effective refractive index, which is then launched into free-space. The absence of dielectric medium contributes to reduce the insertion loss and also enables external control of the effective refractive index. Importantly, this approach is assisted by angular leverage; a very little change of the plate tilt results in very large deflection of the beam trajectory. We demonstrate beam steering from -25 degrees to +25 degrees by changing the plate tilt from -25 ' to +25 ' (-0.42 degrees to +0.42 degrees), which is transferred to the 60 times larger angles. Such a small tilt can easily be generated, for example, by using piezo or MEMS actuators. Since the excitation point can be fixed, the proposed device can easily be coupled to a wide range of chip sources and detectors, offering waveguide integration. As an application example, we implement high-resolution radar that identifies both the direction and range toward an object.