Your router’s fastest port is probably sitting unused.
I've been asked to help connect 2 sites via single mode, and were told that we have to use dwdm and were allocated a specific channel. I've only ever used the "normal" single- or multi-mode ...
10GBASE-Lr 1310-nm SFP+ (LC) for up to 10 km over SMF 10GBASE-Sr 850-nm SFP+ (LC) for up to 300 m over MMF (oM3) 10GBASE-LrM 1310-nm SFP+ (LC) for up to 220 m over MMF (oM2) 1000BASE-LX 1310-nm SFP ...