Ina,
if you compare layout2 and the Data2 QPSK, you might notice the difference is only that the input to the MZ is CW.
So based on this notice, I have replaced the input of MZ of the data2 by a combination of output of Data1 and another CW laser.
you will find that in the attached project for you. another important point based on this notice is that, the higher the power of the CW laser, the higher the Q factor of Data2.
I think this would help you the problem. just try to adjust the CW laser power to have acceptable Q factor for Data1 and Data2.
I think also the same Scenario will be used to add Data3 as well.
It is an interesting example
please update me on the progress if there is anything else we can help.
thanks
Mohamed