Fig. 3: Phase correlation between sub-combs.
From: Agile THz-range spectral multiplication of frequency combs using a multi-wavelength laser
a Optical spectrum of the sub-combs centered at around λ2 and λ3. The large difference in optical linewidth between the tones of the two sub-combs is indicative of the lack of coherence between the sub-combs. b RF spectrum of the photomixed sub-combs. The strongest beatnote features a long-term 3-dB-linewidth of approximately 38 MHz, linked to the absence of coherence between the sub-combs.
