We present an optical frequency divider based on a $200\mathrm{MHz}$ 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 $1\mathrm{Hz}$ offset from a $10\mathrm{GHz}$ carrier, the phase noise is below $-100\mathrm{dBc}/\mathrm{Hz}$ , limited by the optical reference. For offset frequencies $>10\mathrm{kHz}$ , the phase noise is shot noise limited at $-145\mathrm{dBc}/\mathrm{Hz}$ . An analysis of the contribution of the residual noise from the Er:fiber optical frequency divider is also presented.