Large-tap microwave photonics filter based on recirculating frequency shifting loop

A novel large-tap and tunable microwave photonics (MWPs) filter based on a recirculating frequency shifting loop has been proposed and experimentally demonstrated. To improve the Q-factor value of the MWP filter, we used a simple recirculation loop to economically generate a large-tone optical frequency comb in this scheme. In addition, the cumulative effect in loop structure, which affects the characteristics of the generated taps significantly, is analyzed to predict the performance of the proposed filter. In experiments, we realized a 70-tap filter at 4.5 GHz with the Q-factor value exceeding 70. Also, a filter with center frequency tunable from 1 to 8 GHz is demonstrated.