Coherence-Free Microwave Photonic Bandpass Filter Using a Frequency-Shifting Recirculating Delay Line

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 Q value of 200 and an SNR improvement of 40.3 dB compared to conventional recirculating delay line structures.