Fig. 6: Characterization of the linearity of laser frequency modulation.

The first row shows the recorded waveform of the electrical signal used to drive the phase shifter, together with its deviation to a perfect triangular waveform (induced by an RF amplifier) defined as Deviation 1. Because of the periodicity of the signal, Deviation 1 is fully represented within one modulation period, which is obtained by averaging it over multiple modulation periods to have a better accuracy. The periodic waveform of Deviation 1 is thus obtained by duplicating it over multiple modulation periods in time, as shown in the shaded region. The second row shows the waveform of laser frequency modulation retrieved with STFT from the recorded laser beat note. Deviation 2 shows its difference from a perfect triangular function, normalized by the peak-peak amplitude. The last row plots the difference between Deviation 2 and Deviation 1.