A new microwave photonic filter that realizes a high-resolution bandpass filter response with coherence-free operation and without the limitations of phase-induced intensity noise is presented in this paper. It is based on a frequency-shifting recirculating delay line, which can simultaneously achieve a multitap, high-resolution filter and a very large suppression of noise, while also enabling the use of a conventional narrow-linewidth laser source without suffering from coherent interference effects. Experimental results demonstrate a filter value of 200 and an SNR improvement of 40.3 dB compared to conventional recirculating delay line structures.
Pulikkaseril, C., Chan, E. H. W., & Minasian, R. A. (2010). Coherence-free microwave photonic bandpass filter using a frequency-shifting recirculating delay line. Journal of Lightwave Technology, 28(3), 262-269. https://doi.org/10.1109/JLT.2009.2038349