In this Letter we report on an all optical-fiber approach to the synthesis of ultralow-noise microwave signals by photodetection of femtosecond laser pulses. We use a cascade of Mach–Zehnder fiber interferometers to realize stable and efficient repetition rate multiplication. This technique increases the signal level of the photodetected microwave signal by close to . That in turn allows us to demonstrate a residual phase-noise level of at and at from a signal. The residual noise floor of the fiber multiplier and photodetection system alone is around at the same offset frequency, which is very close to the fundamental shot-noise floor.
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