The Research For Subcarrier Demultiplexing Technology Based On Microwave Photonic Filter In Radio-over-Fiber Systems

In this thesis, a subcarrier demultiplexing scheme based on a coefficient-switchable microwave photonic filter in radio-over-fiber systems is proposed. And two subcarriers both modulated with data signal are demultiplexed in the experiment.Firstly, the concepts of microwave photonics and the principle of microwave photonic filters are introduced.Then, the operating principle of the microwave photonic filter based on two Mach-Zehnder modulators is analyzed. If two MZMs are driven by the same RF signal, when they are respectively biased at the opposite transmission slopes, the optical output signals in phase inversion will generate negative coefficient microwave photonic filter. When they are both biased at the same transmission slopes, the optical output signals with same phase will generate positive coefficient microwave photonic filter. According to the theoretical analysis, a coefficient-switchable microwave photonic filter with0.6GHzFSR is experimentally demonstrated.And then, the technology of subcarrier multiplexing and demultiplexing in radio-over-fiber systems is analyzed. And a subcarrier demultiplexing scheme based on the above coefficient-switchable microwave photonic iliter in RoF systems is realized experimentally. The 2.4 GHz and 2.7 GHz subcarrier signals both modulated with 100 Mbps on-off keying (OOK) data are transmitted and demultiplexed. The experimental results show that by simply controlling the bias voltages of the two MZMs, eachofthe two subcarriers can be individually selected out with the other one well depressed, meanwhile the data signal can be recovered well.Finally, the summary and future research is given. The proposed scheme is simple, cost-effective and has good practical applicability.