Microwave photonic filters based on fiber ring structures

Deduced and tested under different structures and parameters of fiber rings, microwave photonic filters based on fiber ring structures were found out to have better performance with asymmetric coupling ratio and when cascaded. Experimental results show that microwave photonic filters based on fiber ring structure with asymmetric coupling ratio present higher extinction ratio than those with symmetric ones. The unstable factors of cascaded IIR filters were also analyzed. The results show that microwave photonic filters based on two cascaded fiber ring structures using low coherence optical source are more stable than those using coherent optical source. Moreover, no matter the microwave photonic filters are constructed with single fiber ring or cascaded fiber rings , the using of broadband optical source gives the system better filtering performance and more stable frequency response.