From OLT to ONT, and everything in between, is handled by non-ethernet/non-IP protocols over which you can tunnel whatever higher level protocol you want.
Technically that can continue to whatever hosts PPPoE gateway. Ultimately, OLT is "root node", and ONTs are "leaf nodes" of a passive optical network tree. What is distributed over it is less of interest to it. But that's why you often have ONTs called "media converters" - though they aren't exactly that. A typical ONT also includes xPON MAC component as well as all management functions necessary to login into xPON network, establish session, etc. and demux transported protocol to whatever is delivered on the other side (nearly always ethernet)
Technically that can continue to whatever hosts PPPoE gateway. Ultimately, OLT is "root node", and ONTs are "leaf nodes" of a passive optical network tree. What is distributed over it is less of interest to it. But that's why you often have ONTs called "media converters" - though they aren't exactly that. A typical ONT also includes xPON MAC component as well as all management functions necessary to login into xPON network, establish session, etc. and demux transported protocol to whatever is delivered on the other side (nearly always ethernet)