Ultra-High-Capacity Optical Communications and Networking: "Smart RF/Photonic Antennas" for Ultra-High Capacity Wireless Communications

目前，对无线系统中更大带宽和容量的需求是导致人们对工作在毫米波和更高频率的无线通信系统发展的极大兴趣的主要原因。未来宽带交互业务(1 Gb/S)的需求要求应用光纤馈送网络将无线电信号分配到各个基站的天线和从天线发送出去。光纤技术已经到了考虑插入各种商业射频系统的阶段。今天，在无线通信的RF/光子学系统的发展中有三个主要步骤。第一步是使用光子学慢慢取代传统的射频组件，例如用于连接天线和电子设备的同轴电缆。与同轴电缆相比，光纤为宽带射频通信系统提供了更理想的介质。光纤的轻质特性和对其他信号干扰的免疫力使其在未来射频分配系统的发展中非常关键。第二步，也是更具挑战性的一步，是光子学和射频无线电路的无缝集成。这一步的挑战是将光子学和射频电路作为互补系统，并将它们融合在一起。最后，第三步是发展光耦合天线。在这一步骤中，目的是通过直接通过毫米波频率的光纤馈电天线来消除对本地振荡器、混频器、放大器和许多其他部件的需要。本文提出将射频调制器/光电探测器阵列直接集成到天线阵列中。这种新的射频/光子天线阵列系统，经过适当的空时处理和编码，将形成一个可以提高网络覆盖、容量和质量的iosmart天线。据设想，大量这样的射频/光子天线元件可以联网在一起，形成星形结构，馈入和馈出无线电集线器。作为发射器，所提出的光电设备作为光电二极管运行，而作为接收器，该设备作为光调制器运行。已经证明，在使用偏置控制作为发送/接收模式控制的情况下，可以在同一器件中实现半导体电吸收调制器和光电二极管的双重功能以进行双工操作。对于全双工操作，需要在每个收发器元件中集成两个调制器/光电二极管器件。我们提出通过将光功率转换为微波功率来直接驱动共面波导馈电的缝隙天线，反之亦然。作为发射机，共面波导线连接到光电探测器的有源面，微波功率从该表面传播到辐射缝隙。光电探测器通过光纤从下方馈入。当器件起到光调制器的作用时，也可以实现接收功能。对单个天线的初步结果表明，该天线可以获得很好的带宽和辐射方向图。应当注意，这些元件可以通过光纤互连，以在天线站点或远程站点实现求和、混频和其他信号处理功能。在光电器件的调制、光探测、自偏置和射频混频等多功能领域已经取得了一些初步成果。它们已经显示出高带宽和高功率等特性，这些特性是天线应用所希望的。这里的主要重点是进一步研究可以集成到智能天线体系结构中的光电子元件的材料和器件设计。通过提供更高的系统带宽容量和提高系统的可靠性，该方法将对无线通信系统产生重大影响。它可能导致一种新型的长距离宽带网络基础设施，支持光信号的透明传输。我们的团队是为这项拟议的研究提供四个关键要素的专业知识。我们的项目将提供一个很好的机会，在最令人兴奋的科学交叉学科领域(射频、光子学、信号处理和通信)培训研究生和本科生。不同机构的研究人员之间的互动将得到小组成员之间存在的密切合作的帮助。

The need for more bandwidth and capacity in wireless systems currently is the main culprit for thegreat interest in the development of wireless communications systems operating at millimeter wavefrequencies and higher. The future needs of broad-band interactive services (1Gb/s) demand theapplication of optical fiber feed networks for distribution of the radio signals to and from the antennas atthe various base stations. Fiber-optic technologies have reached the stage where insertions into variouscommercial RF systems are being considered. Today, there are three main steps in the evolution ofRF/Photonics systems for wireless communications. The first step has been in the direction of usingphotonics to slowly replace conventional RF components, such as, the coax that is used to interconnectthe antenna to the electronics. Optical fibers, in contrast to coaxial cable, provide a more ideal medium forbroadband RF communication systems. The light weight property of fibers, and its immunity from othersignal interference make them very critical in the development of future RF distribution systems. Thesecond, and more challenging step, is in the seamless integration of photonics and RF wireless circuits.The challenge in this step is to use photonics and RF circuits as complementary systems and blend themtogether. Finally, the third step is towards the development of optically coupled antennas. In this step theaim is to eliminate the need of local oscillators, mixers, amplifiers and a host of other parts by directlyfeeding an antenna through a fiber at millimeter wave frequencies. Here, it is proposed that an array of RF modulator/photodetectors be integrated directly to an arrayof antennas. This new RF/photonic antenna array system, with the appropriate space-time processing andcoding, will form a iosmart antennaln that can enhance network coverage, capacity, and quality. It isenvisioned that a large number of such RF/Photonic antenna elements could be networked together into astar configuration, feeding in and out of a radio hub. As a transmitter, the proposed optoelectronic device operates as a photodiode, while as a receiverthe device operates as an optical modulator. It has already been demonstrated that this dual function of asemiconductor electroabsorption modulator and photodiode in the same device for duplex operation, canoccur, using bias control as a transmit/receive mode control. For full duplex operation, twomodulator/photodiode devices need to be incorporated in the each transceiver element. We propose to directly drive a coplanar waveguide (CPW)-fed slot antenna by converting opticalpower into microwave power and vice versa using these RF modulator/photodetectors. As a transmitter,the CPW line is connected to the active surface of the photodetector, from which the microwave powerpropagates to feed the radiating slot. The photodetector is fed via an optical fiber from beneath. When thedevice functions as an optical modulator, the receive function can also be achieved. Preliminary resultsfor a single antenna show that a very good bandwidth and radiation patterns can be achieved. It should be noted that these elements can be interconnected via the fiber to achieve summation,mixing and other signal processing functions, at the antenna site or at a remote site. Some preliminaryresults have been achieved in the area of multiple functionality for the optoelectronic components, such asmodulation, photodetection, self-biasing and RF frequency mixing. They have shown properties, such ashigh bandwidth and high power, that are desirable for the antenna applications. A main emphasis here isto further investigate the material and device designs for the optoelectronic component that canincorporate into the smart antenna architecture. The proposed approach will have significant impacts on wireless communication systems byproviding higher system bandwidth capacity and enhancing their reliability. It may lead to a new type oflong distance, broadband network infrastructure that supports transparent transport of optical signals. Our team is formed to provide the expertise in the four key elements for this proposed research.Our project will provide a good opportunity to train graduate and undergraduate students in one of themost exciting interdisciplinary areas in science (RF, photonics, signal processing and communications).The interactions between the researchers at the different institutions will be aided by the closecollaboration that exists between the members of the group.