In the past, radio-frequency signals were commonly used for low-speed wireless electronic systems, and optical signals were used for high-speed wired communication systems. However, as the emergence of new millimeter-wave technology, which is capable of providing multi-gigabit transmission over a wireless radio-frequency channel, the borderline between radio-frequency and optical transport systems becomes blurred. As a result, there are ample opportunities to design and develop next-generation broadband systems by combining the advantages of these two technologies to overcome inherent limitations of various broadband end-to-end interconnects, such as signal generation, transportation, data recovery, and synchronization. For the transmission distances of a few centimeters to thousands of kilometers, the integration of radio-frequency electronics and photonics to build radio-over-fiber systems ushers in a new era of research opportunity for the upcoming very-high-throughput broadband services.
Recent developments in radio-over-fiber systems have garnered momentum to be recognized as the most promising solution for the backhaul transmission of multi-gigabit wireless access networks, especially for the license-free, very-high-throughput 60-GHz band. Adopting radio-over-fiber systems in local-access or in-building networks can greatly extend 60-GHz signal reach by using ultra-low loss optical fibers. However, systems operating at such high frequency are difficult to generate in an old fashion way. In this dissertation, several novel techniques of homodyne and heterodyne optical-carrier suppressions for radio-over-fiber systems are investigated and various system architectures are designed to overcome these limitations of 60-GHz wireless access networks, bringing the dream of delivering multi-gigabit wireless services of any content, at anytime and anywhere closer to the reality.
In addition to the advantages for the access networks, extremely high spectral efficiency, which is the most important parameter for long-haul networks, can be achieved by radio-over-fiber signal generation. As a result, the transmission performance of spectrally efficient radio-over-fiber signaling technique, including orthogonal frequency division multiplexing and orthogonal wavelength division multiplexing, is broadly and deeply investigated in this research as well. On the other hand, radio-over-fiber is also used for the frequency synchronization that can resolve the performance limitation of wireless interconnect systems for off-chip high-performance-computing transmission. A novel wireless interconnect system assisted by a new carrier-over-fiber technique is proposed and analyzed in this dissertation.
In conclusion, multiple advantageous facets of radio-over-fiber systems can be found in various levels of networking systems. The rapid development of new applications using radio-over-fiber technology developed in this research will revolutionize the conventional wisdom of broadband optical and wireless digital communications.