A Theoretical Model for Recirculating Frequency-Shifted Fiber Loop Supporting Ultra-Large Number of Circulations

In this work, the dynamics of signal evolution in the recirculating frequency shifted fiber loop (RFSFL) is investigated and a theoretical model is proposed. The numerical simulation based on this model reveals that a precise balance between the in-loop gain and the injected pulse power is essential for large number of circulations with flat signal envelope. Physical experiments are conducted under such guidance, where the achieved number of circulations is increased by an order compared with previous record to 1250. For the first time to our knowledge, stepped-frequency continuous wave (SFCW) microwave signal reaching 100 GHz bandwidth is generated in a RFSFL-based photonic microwave synthesizer. This work provides propellant to applications where ultrabroad-bandwidth and high linearity SFCW waveforms are required.