OP: A new THz technology: artificial dielectrics

太赫兹波的频率范围从约0.1太赫兹到约5太赫兹（波长从3毫米到0.06毫米），是通信、国土安全、医疗诊断、无损评估、质量控制和环境监测等各种应用的理想选择。事实上，太赫兹领域已成为近年来最令人兴奋的研究前沿之一，甚至在大众文化中也引起了极大的兴趣。与目前可用的技术相比，上述对社会的潜在好处推动了对更通用、更节能的技术的需求，以控制和操纵太赫兹波。因此，这项研究旨在开发一种新的太赫兹技术，该技术基于所谓的人工电介质。人造电介质是一种人造介质，它模仿自然介质的特性，甚至表现出通常在自然界中不可能出现的特性。例如，众所周知的介电性质，折射率，通常具有大于1的值，在人造介质中可以具有小于1的值。这项新技术将类似于超材料的新兴技术，它正在彻底改变光学领域。超材料也是人造的媒介，可以用反直觉的方式控制光的流动。事实上，这项提议的技术提供了许多与超材料相同的有趣可能性。该技术的一个关键优势是能够连续地设计折射率，从而能够实现非均匀介质。相比之下，在超材料中实现电磁特性的连续变化更具挑战性。因此，如果考虑到超材料对光学领域的影响，所提出的研究必将对太赫兹波科学领域的发展产生巨大的影响。该提案还将促进教育推广，包括培训和教育研究生、本科生和大学预科生。这种人工电介质的概念提供了一个有趣的工程平台，向崭露头角的科学家介绍基本的物理现象。这项研究计划的主要目标是开发一种利用人工电介质控制和操纵太赫兹波的新技术。在这个项目的过程中，几个关键的太赫兹波设备将通过这项新技术开发出来。这些人造介电器件将比现有的类似功能器件具有更好的性能，并且将实现目前在太赫兹波范围内无法实现的功能。研究的范围可分为两个主要方向。在一个推力，装置将开发利用人工电介质的均匀版本。这些装置将包括波片和偏振分束器。在另一个推力，装置将开发利用人工电介质的非均匀版本。这些将包括梯度折射率（GRIN）装置，如麦克斯韦鱼眼透镜和吕尼堡透镜。实验工作将使用时域太赫兹系统进行，该系统能够产生和检测由基带太赫兹频谱组成的皮秒脉冲。在这些系统中，发射器和接收器模块是光纤耦合的，以提供必要的自由度，因为光束路径并不总是在视线范围内。重要的是，这种人工介电技术将解决长期存在的问题，实现高折射率梯度，这阻碍了强大的GRIN器件的实际应用。这项工作还将为麦克斯韦鱼眼透镜预测的超分辨率（不受波长限制的完美成像）现象提供更多的线索。这些研究进展将为太赫兹波的控制和操纵提供许多新的组件和能力，对太赫兹领域产生巨大的影响。

Terahertz waves, spanning frequencies ranging from about 0.1 THz to about 5 THz (wavelengths from 3 mm to 0.06 mm), are ideal for a wide variety of applications in communications, homeland security, medical diagnosis, non-destructive evaluation, quality control, and environmental monitoring. In fact, the terahertz field has become one of the most exciting research frontiers in recent years, stimulating a great deal of interest even in the popular culture. The above potential benefits to society have fueled the need for more versatile and energy efficient technologies to control and manipulate terahertz waves, compared to what is currently available. Therefore, this research aims to develop a new terahertz technology based on what are known as artificial dielectrics. Artificial dielectrics are man-made media that mimic the properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. This new technology will be analogous to the emerging technology of metamaterials that is revolutionizing the field of optics. Metamaterials are also man-made media that can control the flow of light even in counter-intuitive ways. In fact, the proposed technology offers many of the same intriguing possibilities as that of metamaterials. A key advantage of the technology is the ability to engineer the refractive index continuously, thereby being able to realize inhomogeneous media. In contrast, continuous variation of the electromagnetic properties is more challenging to achieve in metamaterials. Therefore, if one considers the impact metamaterials has had on the field of optics, the proposed research is bound to have an enormous impact in advancing the field of terahertz-wave sciences. This proposal will also promote educational outreach in terms of training and educating graduate, undergraduate, and pre-college students. This artificial dielectric concept provides an intriguing engineering platform to introduce budding scientists to fundamental physical phenomena.The primary goal of this research program is to develop a new technology for the control and manipulation of terahertz waves utilizing artificial dielectrics. During the course of this project, several key terahertz-wave devices will be developed via this new technology. These artificial- dielectric devices will have far better performance than existing similar functional devices, and will enable capabilities that are currently not available in the terahertz-wave regime. The scope of the research can be divided into two main thrusts. In one thrust, devices will be developed utilizing the homogenous version of the artificial dielectric. These devices will include wave- plates and polarizing beam-splitters. In the other thrust, devices will be developed utilizing the inhomogeneous version of the artificial dielectric. These will include gradient-index (GRIN) devices, such as the Maxwell' fish-eye lens and the Luneburg lens. The experimental work will be carried out using time-domain terahertz systems that are capable of generating and detecting picosecond pulses comprising of a baseband terahertz spectrum. In these systems, the transmitter and receiver modules are fiber coupled to provide the necessary degrees of freedom since beam paths are not always in line-of-sight. Importantly, this artificial-dielectric technology will resolve the long-standing problem of realizing high-index gradients, which has hampered the practical use of powerful GRIN devices. This work will also shed more light into the predicted super-resolution (perfect imaging that is not limited by the wavelength) phenomenon associated with the Maxwell' fish-eye lens. These research developments will have an enormous impact on the terahertz field by providing many new components and capabilities for the control and manipulation of terahertz waves.