I understand this problem you are experiencing and I don’t have a very good answer! From my understanding the “0001” part works fine. It repeats because the defined sequence is only 4 bits long while the simulation lasts for 16 bits. The User Defined Bit Sequence Generator then just repeats the sequence.
As for the problem in the case of “1111” or “1111111111111111” if you prefer and the opposite case, this must be a bug and I don’t think there is an easy fix for it. I have notified the OptiSystem team about, so hopefully we can get a fix out soon in the next release. In the meantime, are the cases “1111” and “0000” absolutely necessary for your simulation?
Damian