Research On Optical Methods For Processing Microwave And Radio-Over-Fiber Techniques

This topic belongs to the interdiscipline that crosses microwave wireless communication and fiber communication. Nowadays, the signals transmitted in the backbone network——fiber communication are digital baseband signals. Along with that the wireless terminals are increasing, in order to simplify base stations and decrease the cost on devices, we learn and investigate how to transmit microwave signals through the fiber communication systems. By the analysis on three different structures and configurations of baseband signals transmission, interfrequency signals transmission and radiofrequency signals transmission, we describe the relation between subcarrier frequency and base station simpilification. Due to the rapid development of opti-electronic devices, optical devices are much better than electronic devices on the performance like response speed. We adopt to simplify the modules and analyze the principles of Fiber Bragg Gratings and Mach-Zehnder Modulators based on Li Nb O3.Also we derive the principle of optical carrier suppression transmission.Two kinds of non-linear devices are choosed to multiply the microwave frequency, namely, phase modulators and electro-absorption modulators. In the method of phase modulators, we get a 40 GHz microwave of-80 d Bm W with a input 20 GHz microwave of 0d Bm W, whose optical carrier is 1550 nm. Different results comes when the phase modulator is substituted by a electro-absorption modulator that many high-order harmonics appear. In the output of photonic detecter, a 40 GHz microwave of-50 d Bm W is obtained. Obviously electro-absorption modulators are reasonable to be used to generate higher-frequency microwave signals.Real radio-over-fiber systems must take the optical amplifiers and fibers into consideration. In this article, we make a verification module firstly. Due to the standards in IEEE 802.11 b and 802.11 g, a radio-over-fiber system which can transmit the mixed signals(analog signals and digital signals) synchronously is designed. By observing the receipt signals and origin signals, we can find that digital signals are transmitted efficiently. Moreover, phase modulation on microwave sub-carrier is combined with a Mach-Zehnder Modulator to achieve the transmission of 1Gbit/s digital signals. In the simulation results, the bit error rate is lower than 10-42, which indicates an available radio-over-fiber system.