Research On Phsae Stabilized Transmission Of Microwave Signals Over Optical Fiber Link

In order to meet the application requirements of areas such as deep space science, fundamental physics measurement and electronic warfare, microwave frequency reference signal with high stability, low noise and large regional distribution has been an active field of research. Benefitting from the small transmission loss, anti-electromagnetic interference and easy winding and the low price, the optical fiber has become the preferred medium of large regional distribution of microwave signals. However, the external environment (such as temperature, strain, vibration, etc.) can provoke variations of the optical fiber transmission delay, leading to the phase drift and the increased phase noise of the transferred microwave signal over the optical fiber. Therefore, it is necessary for optical fiber to real time compensate transmission delay to obtain a stable transmission of microwave signal.In this thesis, the effects of optical fiber link on stability of microwave signal transmission are analyzed. Moreover, the basic compensation principle of microwave signal has been presented. In addition, the method of describing signal frequency stability is given.Based on the phase conjugation during phase stabilized transmission of microwave signal over optical fiber link, passive compensation scheme for microwave signal is researched. Non-dynamic phase tracking technology is adopted without any phase tunable parts in the method. By round transmitting of detected signal, which is one-half frequency of signal to be transferred, phase noise induced by optical fiber is obtained in the scheme. Then, signal phase to be transmitted is reversely pre-biased by phase conjugation so that the phases of transferred signal always remain stable.based on the electrical domain compensation during phase stabilized transmission of microwave signal over optical fiber link, the phase error signal is obtained by designing the demodulation module, the phase locking and tracking algorithm are adopted, then the phase shift of the electric phase shifter from the transmitting end is feedback regulated, achieving the goal of pre-compensating phase distortion for the signal to be transmitted. Phase noise introduced by environmental factors is reduced in the transmission process of microwave signal over fiber link. In our experiments that the 2.45GHz microwave signal is transmitted, respectively over 25km and 40km optical link, the results show that RMS phase jitter of recovered the signal was less than 0.035rad and 0.06rad within the time duration of 30 min.