According to theory written in "Optical Electronics" by Yariv, for a amplitude modulation EOM

TransmissionOut/ Input  = sin^2(  pi/2   *    V/Vpi)

If I can properly, obtain my transfer function measurement then I can very well define my V. Hence, I can estimate the fit parameters better. Also, the quality of fit can then be better estimated by seeing if we have this pi/2 factor inside the sin square function or not.

Currently I am using the voltage input to RF circuit, and not the voltage across the EOM electrodes.