Optical-fiber pulse rate multiplier for ultralow phase-noise signal generation

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 18 dB. That in turn allows us to demonstrate a residual phase-noise level of -118 dBc/Hz at 1 Hz and -160 dBc/Hz at 10 MHz from a 12 GHz signal. The residual noise floor of the fiber multiplier and photodetection system alone is around -164 dBc/Hz at the same offset frequency, which is very close to the fundamental shot-noise floor.