A new structure that can realize widely tunable microwave photonic notch filtering, high free spectral range (FSR), and coherence-free operation simultaneously, is presented. It is based on a Sagnac loop interferometer that comprises an off-loop-center electroabsorption modulator, and a wavelength dependent delay in the Sagnac loop. The structure is simple, and has no coherent interference or phase induced intensity noise limitations. Experimental results demonstrate both continuous and discrete widely tunable notch filters, high frequency and high FSR, and coherence-free low-noise operation with very deep notches in excess of 40 dB.
Chan, E. H. W., & Minasian, R. A. (2008). Widely tunable, high-FSR, coherence-free microwave photonic notch filter. Journal of Lightwave Technology, 26(8), 922-927. https://doi.org/10.1109/JLT.2007.912529