Study On Optical Heterodyne Method And Photodetector In Radio-over-Fiber Systems

As the development of high-speed data service, the bandwidth of the present systems can't satisfy the desire of these applications. In order to improve the capacity of wireless communication system and achieve wideband communication, high frequency transmission band has to be applied. Millimeter-wave communication can provide high capacity bandwidth, however, the attenuation of millimeter-wave in atmospheric propagation is high, and so the transmission distance is limited. On the other hand, the optical communication has high quality transmission, but the mobility is not good. The Radio-over-Fiber systems combine these two systems to solve the problems mentioned above. The RoF systems can realize high capacity wireless communication with advantages of both systems. In RoF systems, the generation of millimeter-wave is a key technique. There are many methods to generate the millimeter-wave and optical heterodyne method is an important one of them. Besides the key techniques, the devices play a significant role in system performance. Photodetector is a crucial device in the base station of the RoF systems, it affects the noise figure and other parameters of the signals.This master's thesis studied on the optical heterodyne method and photodetector in RoF systems, the main job and achievements can be summarized as follows:1. Researched the system architecture, key techniques, key devices and performance parameters of the RoF systems. Analyzed the millimeter-wave generation technique and photodetector specifically.2. Studied the optical heterodyne method of the millimeter-wave generation methods, analyzed the technical characteristics of the current system structure. Applied the OCS into the optical heterodyne method to solve the phase noise problem, researched the system principle and the results proved that this system can eliminate the phase noise aroused by the frequency instability of lasers and simple the system structure.3. A RoF system that uses the three-frequency optical heterodyne method to generate millimeter-wave is studied. Researched the principle and the system structure. An experimental system, which demonstrated the theoretical feasibility of the three-frequency optical heterodyne, is designed.4. Analyzed the principle of balance detection, combined the three-freq-uency optical heterodyne method and balance detection, proved the improvement of SNR by simulation.5. Studied the photodetctor, analyzed the principle, development of the photodetector, and researched the nonlinear of the photodetctor and high power detector specifically.