Studies On Vector Signal Transmission And Optical D/A Converter In ROF System

With the development of the technique of the wireless access networks, Radio over Fiber technology (ROF), which can provide ultra-wide bandwidth to transmit radio signals over a long distance, is attracting more and more people's attention. According to the different ways to transmit radio signals, ROF technology can be divided into two subcategories: analog ROF technology and digital ROF technology, therefore, my research work described in this thesis can also be classified into two parts.In the first part, we mainly focus on developing a new analog ROF system architecture which is especially suitable to transmit vector signals predominately employed in wireless communication systems. In order to simplify system architecture and provide the immunity to radio frequency power degradation problem introduced by chromatic dispersion, we try to transmit vector signals employing optical carrier suppressed modulation (OCS) scheme. By giving detailed theoretical analyses to OCS scheme and its characteristics under the influence of chromatic dispersion introduced by optical fiber, we obtain the transmission functions of the dispersive systems employing direct OCS modulation scheme and optical up-conversion OCS modulation scheme respectively. Then, we develop and demonstrate two new system architectures to transmit vector signals. These two analog ROF system architectures complement each other and have the merits of simple structure, low cost of construction, reliable and flexible services.The second part mainly describes the research work about the optical digital-to-analog converter, which is a very important module in digital ROF system. After carefully analyzing the typical system architecture of optical digital-to-analog converter, we find that the noise and the nonlinearity of the photodetector are two main factors which limit the sample rate and resolution of the system. Then we obtain several expressions which describe the relationships among resolution, sample rate, characteristics of optical sources and photodetector. With the help of these results, we propose a new way to design optical digital-to-analog converter. In such way, we can largely reduce the system's cost, however, keep the system's performance at an acceptable level.