A new interference mitigation microwave photonic filter structure that can realize a narrow, high-resolution notch with low amplitude and group-delay ripple in the passband, which is tunable, and which is free of coherent interference limitations, is presented. It is based on a multiple double-pass modulation technique that introduces a new concept for superposing the resultant notches in a predetermined manner so as to obtain notch narrowing at the desired frequency while simultaneously flattening of the response in the passband region. The notch frequency can also be tuned. Experimental results demonstrate robust, coherence-free, multitap microwave notch filter operation with narrow notch together with a wide and flat passband, and which is also tunable.
Chan, E. H. W., & Minasian, R. A. (2011). Multiple-tap, tunable microwave photonic interference mitigation filter. Journal of Lightwave Technology, 29(8), 1069-1076. https://doi.org/10.1109/JLT.2011.2114328