Since we measured the electrical signal we sent to OPO's EOM(see the last attached picture of elog), we can have a precise estimation for modulation depth. According to the specification(you can find it in our wiki page), the modulation depth has a linear relationship with the peak voltage. It crosses points (0, 0) and (1, 6.5), see attached figure 1 and 2. Since the curve is straight, two points is enough to know the function. Then we use the relationship between Vp and dBm, Vp = 10^((P(dBm)-10)/20). In the end, we get the function of power(dBm) and modulation depth. Since now we are sending signal of 12.6dBm, we get the modulation depth should be 0.15.

However, in the simulation of Finesse, we assume modulation depth of 0.3. So we need to do simulation again to have a more resonable error signal estimation.