Locking laser frequency of up to 40 GHz offset to a reference with a 10 GHz electro-optic modulator.

We demonstrate a method to lock a laser frequency of up to 40 GHz offset to a reference using a 10 GHz waveguide-type electro-optic modulator (EOM). Offsetting is provided by the EOM sidebands, and first- to fourth-order sidebands are generated by changing the power of the EOM's driving radio frequency. By scanning the driving frequency across the 10 GHz bandwidth, the output laser frequency can be set at any point in an 80 GHz range (from -40 to 40 GHz) by locking a sideband to the reference. This method provides simple, stable, and low-cost generation of phase-coherent laser pairs separated by tens of GHz.