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

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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.