Some Studies On Radio Over Fibre And Signal Processing Technologies Based On Microwave Photonics

Microwave photonics, which combines the two worlds of microwave radiofrequency engineering and optoelectronics, makes the microwave photonic systems much more powerful than the traditional electronic systems since the huge bandwidth and low loss characteristics of optical fibre communications. Microwave photonic technology has provided new opportunities for the development of both mobile communications and broadband access network, driving the whole communication and signal processing field to the high-speed and low-cost direction, and also shows great application potential in the fields of electronic engineering, optical communications, public communications, military defense, and medical engineering as well. In this dissertation, we will focus on the main applications of microwave photonics, studying the optical fibre transmission and photonic processing technologies of microwave and RF signals theoretically and experimentally, including the radio over fibre systems, microwave photonic signal processing, and also microwave generation utilizing optical methods.For the radio over fibre (RoF) technology, we firstly present and discuss the basic principle and link structures of the RoF system, then go through several schemes for simplifying the base station, and implement the simplified RoF system with commertial electro-absorption modulator. Furthermore, we study the specific applications of RoF technology in both the distributed antenna systems and multiple-input-multiple-output (MIMO) systems, in which a3×3RoF-based MIMO system is proposed and experimentally demonstrated. The experimental results shows that the RoF-based distributed MIMO system could further improve the signal-to-noise ratio (SNR) and also the spatial correlation characteristics, therefore owns larger channel capacity, smaller power consumption, more uniform distribution, and more flexible system extension compared with the traditional distributed antenna and MIMO systems. For the microwave photonic signal processing technology, we analyze and discuss the microwave photonic filter and its applications in detail, including various single-source microwave photonic filters, multiple-source microwave photonic filters, and cascaded microwave photonic filters based on different structures. A conherence-free single-source microwave photonic filter with switchable positive or negative coefficients based on phase and intensity hybrid modulation is proposed and experimentally demonstrated. And the experimental results shows that the cascaded microwave photonic filter could further optimize the single-passband frequency response, making it frequency-tunable and shape-adjustable. Based on the great compatibility with RoF technology, we further study the subcarrier demultiplexing and also the frequency conversion technologies with different microwave photonic filters in the RoF systems. And for the microwave photonic generation technology, in fact it could be seen as the applications of microwave photonic signal processing technology somehow. In this dissertation, we present and discuss several optical methods for both single-frequency microwave signal and ultra-wideband (UWB) pulse generation in detail. The experimental results shows that based on the microwave photonic filter systems both microwave signals with high frequency and UWB pulses with different orders can be generated flexibly, which have good potential applications in e.g. RoF and UWB over fibre systems.