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

根据该计划，将开发射频（RF）接收机的新概念。RF接收机是各种系统的重要组成部分，为社会带来变革性的好处。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的好处。光子成像接收器使用光学检测和RF信号处理，实现前所未有的功能，从极宽带无线通信到全天候穿透成像。传统的RF接收机受到检测过程的固有非线性的限制，通过该非线性，多个信号混合并生成寄生响应。成像接收器系统的独特能力是使用光学器件来“看到”上变频的RF信号，就像眼睛或相机看到可见光一样：其视场内的RF能量源在图像平面或相机传感器上产生不同的斑点，因此这些斑点可以被单独检测，从而最小化混合。这种方法在速度、复杂性、线性度方面具有优势，并且还增加了新的功能，例如实时测向、跟踪和处理多个信号源。成像接收器系统将在无线网络中提供更大的容量，同时还可以提高性能并降低基础设施成本。同样的使能技术也将为运输和搜索/救援行动带来好处，允许在雾、烟和沙子等遮蔽物中导航。同样，安全检查站将能够在一定距离被动地检查人员和车辆，从而提高安全性和便利性。研究工作将调查的限制，并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列接收器，其使用光调制器中的频率上转换的相干特性来检测射频（RF）信号，并且使用简单的自由空间光学器件来执行阵列元件之间的信号相关，这通常在信号被检测和数字化之后通过计算来执行。光学上变频过程提供了从UHF到毫米波的宽带宽。自由空间光学处理使来自不同来源的信号在检测之前在空间上分离，从而最大限度地减少互调并显著提高无杂散动态范围（SFDR）。它还提供相控阵接收器的阵列增益，但具有同时形成所有波束的优点。已被调制到检测到的RF载波上的数据的恢复通过使用与光电二极管上的上变频信号混频的宽范围可调谐的光学本机振荡器来实现。该技术方法的基础已在被动毫米波成像方面得到证明。本研究计划将探讨在广泛和一般意义上的方法的基本局限性，但将主要集中在扩展超宽带无线通信的方法的效用，通过使频谱复用，通过空分多址增强容量。它还将研究宽带系统中的一个新概念，即尺度不变性，它旨在取代传统的傅立叶（时频）域形式主义，其中用于携带信息的基函数是连续波（CW）载波，一个新的形式主义的基础上不是时间谐波CW载波，而是尺度不变的功能，这是自然适合于应用极宽的带宽。

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.