Effect of Phase Noise on the Frequency Calibration of a Tunable Laser by Heterodyne Signal Filtering

Using a frequency comb as frequency reference to calibrate the instantaneous frequency of a tuning laser allows high spectral resolution and a wide calibration range. To obtain the instantaneous frequency of the laser under test, a classical method consists in filtering the heterodyne signal between the frequency comb and the tunable laser with a narrow bandpass filter. For free-running femtosecond lasers, the phase noise of the comb lines affects the instantaneous frequency of the heterodyne signal and the envelope of the filtered calibration signal. In this paper, the characteristics of the frequency calibration signal envelope is analyzed by modeling. Three different filters are used to determine the envelope characteristics. Simulation results show that the probability density function (pdf) of the envelope amplitude tend to be a uniform distribution at higher phase noise level. At low tuning speed, the pdf distributions are the same at symmetric frequency positions of the passband of the filter. At high tuning speed, their distributions become different. The standard deviation of the center of mass becomes larger at higher phase noise level and higher tuning speed.