Ultralow phase noise microwave generation with an Er: Fiber-based optical frequency divider

We present an optical frequency divider based on a 200 MHz repetition rate Er:fiber mode-locked laser that, when locked to a stable optical frequency reference, generates microwave signals with absolute phase noise that is equal to or better than cryogenic microwave oscillators. At 1 Hz offset from a 10 GHz carrier, the phase noise is below ?100 dBc=Hz, limited by the optical reference. For offset frequencies >10 kHz, the phase noise is shot noise limited at ?145 dBc=Hz. An analysis of the contribution of the residual noise from the Er:fiber optical frequency divider is also presented.