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° to +25° by changing the plate tilt from –25′ to +25′ (–0.42° to +0.42°), 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.

中文翻译：

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基于无介质Luneburg透镜轨迹偏转的太赫兹光束转向

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遇，与使用微波相比，能够实现更高的信息容量、更高的空间分辨率和更小的孔径。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，通过波束控制进行点对点传输是必不可少的。然而，由于缺乏实用的移相器，在太赫兹范围内实现宽带和低损耗波束控制仍然具有挑战性。为了避免这个问题，我们在这里展示了一种基于无电介质 Luneburg 透镜中的轨迹偏转的太赫兹光束转向的新方法。它基于梯度有效折射率将点激发转换为平行导电板内基本横向电模式的偏转光束，然后发射到自由空间。没有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，这种方法得到了角度杠杆的帮助；板倾斜的非常小的变化会导致光束轨迹的非常大的偏转。我们通过将板倾斜度从 –25' 更改为 +25'（–0.42° 到 +0.42°）来演示从 –25° 到 +25° 的光束控制，将其转移到 60 倍大的角度。例如，通过使用压电或 MEMS 执行器，可以很容易地产生这种小倾斜。由于激励点可以固定，所提出的设备可以很容易地耦合到各种芯片源和检测器，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，可以识别物体的方向和距离。