Metasurfaces for Spatio-temporal Light Modulation

对于外行观众来说，光调制器可能是他们从未听说过的最重要的发明。时间调制是编码和传送信息的基础，也就是互联网，其中波束的特性在时间上迅速改变。第二种调制方式是空间光调制，其中光束的空间分布被改变。这种调制形式在消费产品中不太常见，但将成为未来系统的基本主力，例如用于增强现实的全息显示器或用于遥感的光束扫描，例如自动车辆扫描前方的路径。到目前为止，没有设备或平台可以同时提供这两种形式的调制。光调制器或者是快速的，但仅限于单个光通道(即使该通道可能通过巧妙的编码方案承载多个信号通道)，或者可以具有高空间分辨率，但是很慢，即在赫兹-千赫范围内。在该方案中，我们提出了一类新的光调制器--时空光调制器，这是一个可以同时提供空间和时间调制的单一平台。为此，我们的项目将解决三个关键的原则证明演示。首先，我们将演示包含epsilon-近零材料的基础平台、高效超曲面。这是一个由天线阵列和透明导电氧化物组成的系统，这种材料几乎为零。通过动态调节透明导电氧化物的性质，我们改变了系统的光学响应，为我们提供了一种调制机制。我们将展示该平台具有非常高的运行效率，超过了当前可调变形表面的技术水平。接下来，我们展示了这个系统可以作为空间光调制器，通过在我们的元表面上创建一个像素阵列。最后，但最重要的是，我们将在我们的超表面平台中展示时间调制，达到GHz速度。仅这些演示中的每一个都将是技术上的一大进步，但我们的目标是通过提供的创新亚表面设计和对epsilon近零材料的理解的最新进展，解锁所有这三个。

For a lay audience, an optical modulator might be the most important invention they have never heard of. Temporal modulation, where the properties of the beam change rapidly in time is fundamental for encoding and conveying information, i.e. the internet. A second modulation style is spatial light modulation, where the spatial distribution of a beam is modified. This form of modulation is less common in consumer products, but will be a fundamental workhorse of future systems, e.g. holographic displays for augmented reality or scanning of optical beams for remote sensing, such as an autonomous vehicle scanning the path ahead.To date, no device or platform can provide both forms of modulation. Optical modulators are either fast, but limited to a single optical channel (even though this channel might carry multiple signal channels, through clever encoding schemes) or can feature high spatial resolution, but are 'slow', i.e. in the Hz-kHz regime. In this proposal, we present a new class of optical modulators - the spatio-temporal light modulator, a single platform that can provide both spatial and temporal modulation. To this end, our project will address three key proof-of-principle demonstrations. First, we will demonstrate the fundamental platform, high-efficiency metasurfaces incorporating epsilon-near-zero materials. This is a system consisting of an array of antennas, coupled with a transparent conductive oxide, the epsilon-near-zero material. By dynamically tuning the properties of the transparent conductive oxide, we modify the optical response of the system, providing us with a modulation mechanism. We will show that this platform features very high operating efficiency beyond the current state of the art of tunable metasurfaces. Next, we show that this system can act as a spatial light modulator, by creating a pixel array in our metasurfaces. And last but most definitely not least we will show temporal modulation in our metasurfaces platform, reaching GHz speeds.Each of these demonstrations alone would be a step-change in technology, yet we aim to unlock all three, through the innovative metasurfaces design presented and the recent advances in the understanding of epsilon-near-zero materials.