The configuration with SB2 resonant in both recycling cavities is considered here.

Once the modulation frequency is chosen, the optimal Schnupp asymmetry is the one that maximizes the power of SB2 inside the signal recycling cavity, since this corresponds to the maximum amplitude of SRCL signal that can be extracted from SB2.

Using a Finesse simulation, the Schnupp asymmetry has been scanned, for each choice of modulation frequencies below 110 MHz. The results are summarized in the following plots:

In summary a comparison of the different behavior of SB2 for all modulation frequencies is given in the following plot:

The optimal asymmetries are:

However, the optimal asymmetry depends also on the choice of SRM and PRM transmissivities, as clear from the following plots:

Also the losses in the arm cavities play a role, since they are directly connected to the michelson interferometer reflectivity.