Noise Characterization of an Optical Frequency Comb Using Offline Cross-Correlation

Using an offline cross-correlation technique, we have analyzed the noise behavior of a new type of optical frequency comb (OFC), which is carrier envelope offset free by configuration, due to difference frequency generation. In order to evaluate the instrument’s ultimate noise floor, the phase and amplitude noise of a stabilized OFC are measured simultaneously by using two analog-to-digital converters. Carrier recovery and phase detection are done by post-processing, eliminating the need for external phase-locked loops and complex calibration techniques. In order to adapt the measurement noise floor and the number of averages used in cross correlation, an adaptive frequency resolution for noise measurement is applied. Phase noise results are in excellent agreement with the measurements of the fluctuations of the repetition frequency of the OFC obtained from optical signal.