They do a splitter in datacenters to the NSA so I presume that is similar many fiber optic wires. From what I understand is that the submarine has to stay there to collect the data. So I presume they split it and have a cable they connect to it that routes it right to the sub. However I think Hawaii is a big NSA station because a lot of those international lines right through near there. I wonder if they could split the stream and run a whole cable back to Hawaii with it.
https://en.wikipedia.org/wiki/Room_641A
https://www.washingtonpost.com/business/economy/the-nsa-slid...
https://wikileaks.org/spyfiles/files/0/55_201110-ISS-IAD-T1-...