Hey I actually design OSP fiber optic networks for a living! The ONT/Demarc is not really that active. Most of the work is done by your router with the box just being a pushloc connector to the OSP drop cable.
From there the drops are usually passively split from a distribution fiber that comes from an area splice, which is then split off a core fiber. The core fibers are actively lit by a fiber OLT (usually serving around 5000-10000 customers). You'll recognize these as a big box somewhere on the side of the road.
That box ties into a regional backbone that usually ends up on single mode fibers that are either left over from the dot com bubble, or installed by DOT on highways.
The whole network really only has 3 active routing locations:
- Office (your ISP)
- OLT (your neighborhood/town box)
- Your router
Here's some pictures of the different hardware:
OLT:
Splice Closure:
(These are often connected to the "snow shoe" things you see on comm lines since they can't exceed the bending radius of the fiber for the slack loop)
Service Splitter:
Note: I am talking about PONs here (Passive Optical Networks) which I would say are most common. Especially since you only need and OLT and tons of cable to set them up. AONs (Active Optical Networks) do have a lot more hardware like modems and muxers/demuxers throughout them, but those are way less common for OSP unless it's built on an existing network and they can't put in the insane amount of fibers needed for the much simpler PON.