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对在毫米波频率和更高频率下操作的无线通信系统的开发的极大兴趣的主要原因。未来宽带交互服务（1Gb/s）的需求要求应用光纤馈电网络来分配往返于各个基站天线的无线电信号。光纤技术已经发展到可以插入各种商业射频系统的阶段。今天，在无线通信的RF/光子系统的发展过程中有三个主要步骤。第一步是使用光子学来慢慢取代传统的射频元件，比如用来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。光纤的轻质特性及其对其他信号干扰的免疫性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。这一步的目的是消除本地振荡器，混频器，放大器和主机的其他部分通过直接馈入天线通过光纤在毫米波频率的需要。 在这里，它提出了一个阵列的RF调制器/光电探测器直接集成到一个阵列的天线。这种新的射频/光子天线阵列系统，通过适当的空时处理和编码，将形成一个智能天线，可以提高网络的覆盖范围，容量和质量。据设想，大量这样的RF/光子天线元件可以联网在一起成为星形配置，馈入和馈出无线电集线器。 作为发射器，所提出的光电器件作为光电二极管工作，而作为接收器，该器件作为光调制器工作。已经证明，这种双重功能的半导体电吸收调制器和光电二极管在同一设备中的双工操作，可以发生，使用偏置控制作为发送/接收模式控制。对于全双工操作，两个调制器/光电二极管器件需要被纳入每个收发器元件。 我们建议直接驱动共面波导（CPW）馈电缝隙天线通过转换opticalpower到微波功率，反之亦然，使用这些RF调制器/光电探测器。作为发射器，共面波导线连接到光电探测器的有源表面，微波功率从该表面传播到辐射槽。光电探测器通过光纤从下方馈电。当器件用作光调制器时，还可以实现接收功能。单天线的初步结果表明，一个非常好的带宽和辐射方向图可以实现。 应当注意，这些元件可以经由光纤互连，以在天线位置或在远程位置实现求和、混频和其它信号处理功能。在光电子器件的调制、光电探测、自偏置和射频混频等多功能方面取得了一些初步的成果。它们具有高带宽和高功率等特性，是天线应用的理想选择。本文的重点是进一步研究可用于智能天线结构的光电子器件的材料和器件设计。 该方法将为无线通信系统提供更大的带宽容量，提高系统的可靠性，对无线通信系统具有重要意义。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。 我们的团队将为这项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，在科学中最令人兴奋的跨学科领域之一（射频，光子学，信号处理和通信）培养研究生和本科生。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.