Interference suppression and tunability enhancement for OFC-based simultaneous microwave down-conversion and filtering

Optical frequency comb (OFC) offers a promising platform for accomplishing simultaneous microwave down-conversion and filtering. However, microwave input needs to be restricted within a Nyquist zone to avoid the interferences generated from broadband RF signals and tightly spaced local oscillators. Here, we propose and demonstrate a novel method to suppress these interferences. With the assistance of two dispersion elements and a tunable delay interferometer (DI), we realize flexible configuration of the transfer functions of all beat tones. Thus, we can suppress the interferences by shifting the corresponding transfer functions outside the baseband, and the frequency tunability of this scheme is also enhanced. A filter and down-converter with pass band tunable from 5.5 GHz to 14.5 GHz and the interference suppression ratio exceeding 18 dB for broadband microwave input covering 4 Nyquist zones was achieved in our experiments.