You should be able to use the NRZ generator instead, but your optical output won’t look as good! There was an issue with the rise and fall times of the NRZ pulse generator, which generally does not effect things but here is noticeable. It has been fixed, and will be in the soon to be released update. So at this point I’d recommend staying with the PSK generator. You could write a small MatLab or Scilab component that will convert the M-ary signal to electrical. Or maybe the easiest solution is to upgrade to the latest 12.2.1?