Research On The Linearization Techniques In The Radio-Over-Fiber System

Radio-Over-Fiber (ROF) technology has been widely applied in ultra-wide-band and millimeter waves wireless communication system, which combines the advantages of wireless communication and optical fiber communication. ROF link with high performance can be realized through the use of external modulation. However, signals deteriorate during transmission because of the inherent nonlinearity of the external modulator, which limits the system’s spurious free dynamic range (SFDR). How to further suppress the system’s nonlinearity and increase SFDR becomes an important research direction in ROF technology. First of all, the thesis summarizes research background and research status of ROF technology at home and abroad. The external modulator’s nonlinearity generation principle is analyzed, and the linearization method proposed in recent years is summarized:electric field linearization method and optical field linearization method. The performance parameters of ROF link with the Mach-zehnder modulator as the external modulator is introduced. As an important parameter of ROF link, SFDR becomes the focus research of this thesis.A linearized ROF link based on a polarization modulator was proposed, the theory of restraining third order intermodulation distortion (IMD3) in the link is studied and simulation analysis is presented. The best link gain can be achieved in this technique, at the same time, SFDR can reach to123.6dBHz2/3. Under the condition of the same noise basement, SFDR of the proposed link is increased nearly20dB-Hz2/3than that of the conventional link.Finally, a linearized downconverting radio-over-fiber link based on a polarization modulator in a Sagnac loop was proposed. The thesis describes the modulation method and operating principle of the link in theory, and proceeds simulation analysis. Results show that:IMD3is suppressed effectively and the link’s SFDR is increased by optimizing the three polarization angle and phase angle of the controller, as well as the angle between the polarizer and PBS spindle. Compared with the conventional downconverting ROF link, the proposed link has high linearity and simplified structure.