Low insertion loss optical pulse interleaving for ultra-low phase noise photonic microwave generation

We report a 32-times multiplication of optical pulse rate based on a cascaded optical fiber ring interferometer for generating ultra-low noise photonic microwaves. The optical power loss of the interleaver is approximately 0.5 dB, which is the lowest insertion loss for optical pulse interleaving to date. The time delay in each interleaver stage is precisely controlled by measuring the power ratio between the harmonics of the generated microwaves. In addition, the relationship between the phase noise reduction from the continuous-wave shot noise limit and interleaver delay errors is verified experimentally for the first time. Finally, a phase noise level of -173 dBc/Hz for a single multiplication channel at an offset frequency of 2 MHz was measured.