Stabilization of a microwave oscillator to a fabry-perot cavity

We report the stabilization of a microwave oscillator frequency to the free spectral range of a Fabry-Perot cavity. We use a yittrium-iron-garnet (YIG) oscillator operating at 3.61 GHz to modulate an electro-optic modulator to produce sidebands on a laser beam. While the carrier is locked to a cavity mode by the Pound-Drever-Hall scheme, the sidebands are near resonant with the adjacent modes. The phase difference between the beat signals before and after the cavity is detected to produce an error signal, which is fed back to the microwave oscillator to stabilize its frequency. The Allan deviation of the YIG oscillator at 60 s is 8 × 10^-8, which represents an order of magnitude improvement over the free-running case. We discuss possibilities for further improvements and applications of the scheme to relate optical and microwave frequencies.