Low instability, low phase-noise femtosecond optical frequency comb microwave synthesizer

The ability of a frequency comb from a femtosecond mode-locked laser to faithfully reproduce the properties of optical oscillators at microwave frequencies is examined. The fractional frequency instability of the femtosecond comb microwave synthesizer is 2×10^-14/τ, and could improve by at least a factor of 10 upon elimination of excess photodetection noise. Phase-noise levels are also examined. The femtosecond comb frequency synthesizer is compared to other high-performance microwave oscillators and synthesizers and is found to be among the best available. With the realization of predicted improvements in phase-noise and stability for the femtosecond combs and optical frequency standards, the femtosecond comb could eventually synthesize the highest quality microwaves.