Fig. 2: The frequency arrangement of the comb modes.
A red peak Bn in LO beats with the side band modes in the signal (connected by red dashed lines), whose quadrature fluctuation contributes to the overall noise. Therefore, we entangle the side bands (connected by red dashed lines) of the signal to improve the SNR. Similarly, a blue peak An in signal beats with the sideband mode pairs in LO connected by blue dashed lines, which are to be entangled to improve the SNR. Around each peak, there are N such pairs. Here we explicitly label the pairs at the edges.
