During this afternoon presentation I mentioned that error floor is not just inherent to HOM (PAM4, DMT, etc), during March 2012 bm meeting I reported error floor on the 25G VCSEL NRZ link see page 9.
In my opinion the error floor in this case was due to non-linear response of the VCSEL and slow turn off.
Obviously HOM links are more sensitive to the electrical impairment specially from driver to OE device interface plus any non-linear behavior, but non these are fundamental. As an example PAM4 results shown from M. Mazzini OFC 2015 see page 11 does not show classic high error floor
Thanks,
Ali Ghiasi
Ghiasi Quantum LLC
