Design Of Highly Phase Stabilized RF Optical Fiber Transmission System Based On Lightdomain Compensation

With more and more space exploration and the detection depth constantly deepened, the frequency of the antenna used in space detection tends to be higher. However, the increase of antenna operating frequency has brought a huge challenge in the transmission of millimeter-wave signal. As a supporting technology, interference antenna array requires that each antenna obtains the coherent millimeter-wave signal with low-phase drift from the central station, ensuring that the received heterodyne signal of each antenna can be combined coherently. Therefore, the stable transmission of phase information is crucial. Compared with cable, transmission of millimeter-wave signals over optical fiber has unique advantages, such as small loss, wide bandwidth, etc., especially for long distance transmission. However, the changes of external environment such as temperature and stress probable lead to the change of the refractive index of optical fiber, resulting in phase jitter. So there must be a mechanism to compensate and eliminate the jitter to guarantee the phase stability of the optical fiber transmission system.In the phase-stable system, the control algorithm which affects the stability and precision of the system directly is vital. Thus, the control algorithms of and the key devices used in radio-frequency(RF) phase-stable transfer system over fiber are introduced in this paper. At first, the basic principles of optical devices and three kinds of electro-optic modulation mode are discussed. So is the proportion-integral-differential(PID) controller's principle. As the focus of this paper, PID parameter tuning methods such as Z-N Tuning, CohenKuhn Tuning and Adaptive Fuzzy Parameter Tuning must be summarized in detail, followed by their usage scenario and respective advantages and disadvantages. Based on these studies, the performances of these tuning methods are compared by simulating them in MATLAB at last.This paper designs a high precision digital phase detector. Because the accuracy of the phase detector determines the ability to detect small signal that is small phase difference, it plays a vital role in the accuracy of the stable phase system. After the deep analysis of the phase-detected principle, a high precision digital phase detector is designed, and simulated under Multisim. Finally, we complete the PCB design.In this paper, a new highly stable RF signal optical transmission scheme based on phase detection in electric domain and compensation in optical domain is studied, and its performances are verified through experiments. Firstly, the influence of temperature variation on the optical fiber is analyzed, and the principles of several phase-compensation schemes are presented, as well as their merits and demerits. Besides, this paper makes a research on the technical indices of the current schemes in the experiment. On the basis of the above analysis, the solution of the phase-stable system based on the phase detection of reference signal and optical compensation is finally adopted. Then, as two key techniques of the scheme, high-precision phase detection technique and control-compensation algorithm are discussed. At the same time, the principle of phase detection is analyzed and the designed high-precision phase detector and control algorithms are simulated respectively. Finally, an experimental platform is established in laboratory environment, using the air-condition simulating the outside temperature, to test the system before and after link compensation. In the temperature range of 16 and 28 degrees Celsius, the RF signal transmits 4 kilometers over optical fiber. Experiment results show that at last the phase stability reaches peak to peak 0.17°, with standard deviation 0.021° after compensation.