A polarization control system includes a light source that generates two light beams with different polarization states and optical frequencies. A polarization state modulator changes the polarization states of the two light beams. Three detector paths generate a first beat signal, a second beat signal, and a third beat signal from the two light beams. An amplitude detector determines the amplitude of the first beat signal at a beat frequency. A phase comparator determines the phase difference between the second and the third beat signals. The system then uses the amplitude and the phase difference to determine how to adjust the polarization state modulator in order to generate the first and the second light beams with the desired polarization states.