The "Optical Pumps" that repeater the spans are the biggest constraint. See: https://www.popsci.com/google-fastest-internet-cable-atlantic-dunant/ https://www.

The "Optical Pumps" that repeater the spans are the biggest constraint. See: https://www.popsci.com/google-fastest-internet-cable-atlantic-dunant/ https://www.popsci.com/google-fastest-internet-cable-atlanti... Also keep in a mind that fiber itself is theoretically unlimited bandwidth wise. So as the transmission gear on each end that lights the fiber improves so does the available bandwidth each fiber pair can't provide. The other issue is that the cable plant itself has a limited life as well generally around 20 years although that number has gone up recently to 25 or so years. So anything that's fiber not lit for the majority of that 25 year life span is potentially money wasted.