Wideband reconfigurable signal generation based on recirculating frequency-shifting using an optoelectronic loop

A novel photonic-assisted reconfigurable wideband signal generator for linearly frequency-modulated (LFM) signals generation is proposed and experimentally demonstrated. A frequency-shifting recirculating optoelectronic (FSRO) loop is employed to shift and stitch a seed signal repeatedly in the time and the frequency domains through feedback modulation. After experiencing multiple recirculation, a time duration and bandwidth extended LFM signal with a quadratically varying phase of no phase discontinuity is generated. By simply changing loop parameters, the time duration, the bandwidth and the central frequency of the generated LFM signals are adjustable. Although the phase noise will deteriorate during the recirculation, the generated LFM signals with an increased time bandwidth product (TBWP) are still suitable for practical radar applications. A proof-of-concept experiment is carried out. The generation of LFM signals in C and X bands with a TBWP increased by a maximum factor of 196 are achieved. Microwave imaging of rotational targets based on the generated LFM signal is also demonstrated.