Photonic Imaging Receiver for Ultra-wideband Radio-frequency Communications and Sensing

根据该计划，将开发射频（RF）接收器的新概念。射频接收器是为社会带来变革性效益的各种系统中的重要组成部分。也许最突出的是无线宽带互联网连接。增强无线网络的容量将加速家庭、学校、医院、企业和政府之间的全球连接带来的好处。光子成像接收器使用光学检测和处理射频信号，实现前所未有的能力，从极宽带无线通信到全天候干扰穿透成像。传统的射频接收器受到检测过程固有非线性的限制，多个信号混合并产生杂散响应。成像接收器系统的独特功能是使用光学来“看到”上转换的射频信号，就像眼睛或相机看到可见光一样：其视场内的射频能量源在图像平面或相机传感器上产生不同的斑点，因此这些斑点可以单独检测，最大限度地减少混合。这种方法在速度、复杂性、线性度方面具有优势，并且还增加了实时测向、跟踪和多信号源处理等新功能。该成像接收系统将在无线网络中提供更大的容量，同时提高性能并降低基础设施成本。同样的使能技术也将在运输和搜索/救援行动中发挥作用，允许在雾、烟和沙子等遮挡物中进行导航。同样，安全检查站将能够在一定距离内被动地检查人员和车辆，从而提高安全性和便利性。研究工作将调查限制和优化这种成像接收器系统的性能潜力。光子成像接收器是一种新型的相控阵接收器，它利用光调制器中频率上变频的相干特性来检测射频（RF）信号，并利用简单的自由空间光学来执行阵列元素之间的信号相关性，而传统上，这种相关性是在信号被检测和数字化后进行计算的。光上转换过程提供从UHF到毫米波的宽带宽。自由空间光处理使来自不同源的信号在检测之前进行空间分离，最大限度地减少互调并显着提高无杂散动态范围（SFDR）。它也提供了相控阵接收机的阵列增益，但具有同时形成所有波束的优点。通过使用与光电二极管上转换信号混合的可广泛调谐的光学本地振荡器，可以恢复已调制到检测射频载波上的数据。在无源毫米波成像的背景下，验证了该技术方法的基础。该研究计划将从广义和一般意义上探索该方法的基本局限性，但主要侧重于将该方法的效用扩展到超宽带无线通信，通过空间分多址实现频谱重用来增强容量。它还将研究宽带系统中的一个新概念，即尺度不变性，它试图用一种新的形式取代传统的傅立叶（时频）域形式，其中用于携带信息的基函数是连续波（CW）载波，而不是基于时谐CW载波，而是基于尺度不变函数，这自然适合于极宽带宽的应用。

A new concept in radio frequency (RF) receivers will be developed under this program. RF receivers are a vital component in a variety of systems that are yielding transformative benefits for society. Perhaps most prominent is wireless broadband internet connectivity. Enhancing the capacity of wireless networks will accelerate the benefits of worldwide connectivity among households, schools, hospitals, businesses, and governments. The photonic imaging receiver uses optical detection and processing of RF signals to enable unprecedented capabilities, from extremely broadband wireless communications to all-weather obscurant-penetrating imaging. Conventional RF receivers are limited by the intrinsic nonlinearity of the detection process, by which multiple signals mix and generate spurious responses. The unique capability of the imaging receiver system is the use of optics to"see" upconverted RF signals much like the eye or a camera sees visible light: sources of RF energy within its field of view produce distinct spots on an image plane or camera sensor, whereupon these spots can be detected separately, minimizing intermixing. This approach affords advantages in speed, complexity, linearity, and also adds new capabilities such as real-time direction finding, tracking, and processing of multiple signal sources. The imaging receiver system will offer increased capacity in wireless networks, while also improving performance and reducing infrastructure cost. The same enabling technology will also provide benefits in transportation and search/rescue operations, allowing navigation in obscurants like fog, smoke, and sand. Likewise, security checkpoints will be able to screen persons and vehicles passively at a distance, enhancing both security and convenience. The research effort will investigate the limits and optimize the performance potential of such imaging receiver systems. The photonic imaging receiver is a novel type of phased array receiver that uses the coherent properties of frequency upconversion in optical modulators to detect radio-frequency (RF) signals, and simple free-space optics to perform signal correlations between array elements, which are conventionally performed computationally after signals are detected and digitized. The optical upconversion process offers broad bandwidth, from UHF to millimeter-wave. Free-space optical processing enables signals coming from different sources to be spatially separated prior to detection, minimizing intermodulation and dramatically improving spur-free dynamic range (SFDR). It also provides the array gain of a phased array receiver, but with the advantage of forming all beams simultaneously. The recovery of data that has been modulated onto detected RF carriers is enabled by the use of a widely tunable optical local oscillator that is mixed with the upconverted signal on a photodiode. The foundation of the technical approach has been proven in the context of passive millimeter-wave imaging. This research program will explore the fundamental limitations of the approach in a broad and general sense, but will primarily focus on extending the utility of the approach toward ultra-wideband wireless communications, enhancing capacity by enabling spectrum reuse through spatial division multiple access. It will also investigate a novel concept in wideband systems, namely scale invariance, which seeks to replace conventional Fourier (time-frequency) domain formalism, in which the basis functions used for carrying information are continuous-wave (CW) carriers, with a new formalism based not on time-harmonic CW carriers but rather scale-invariant functions, which are naturally suited to applications with extremely broad bandwidth.