The error measurement and control circuitry 130 may be configured to receive a first signal and a second signal. The first signal may include the beat tone combined with the carrier envelope offset provided by the coupler 123 of the beat generator 120. The second signal may include the carrier envelope offset. The first and second signals may be received by the comb error measurement circuitry 140 of the error measurement and control circuitry 130. The carrier envelope offset may be provided from the optical frequency comb using an f-to-2f interferometer, such as may be part of the beat generator circuitry 120.

The comb error measurement circuitry 140, as illustrated, includes mixer circuitry 141. The mixer circuitry 141 may mix the first signal and the second signal. In mixing the first and second signals, a carrier envelope offset may be separated from the beat tone. The separated beat tone signal and carrier envelope offset signal may be provided by the mixer circuitry 141. The beat tone signal may be provided to the beat tone digital phase detector 142. The carrier envelope offset may be provided to the carrier envelope offset digital phase detector 143.

The beat tone digital phase detector 142 may be configured to receive the beat tone and provide a beat tone error signal based on the received beat tone. In some embodiments, the beat tone digital phase detector 142 may use quadrature demodulation to provide the beat tone error signal.