Back when 10M ethernet was popular, it was pretty easy to wire up something like this with the transceiver (AUI) port... wire the tx to a laser and the rx to a photodiode (or whatever), ???, profit.
There's lots of commercial equipment in this space too.
https://ronja.twibright.com/
I wanted to build this back in the day
When I studied our dorm was connected to the campus network via a laser uplink (and the Internet, with each room having a public IP address). I still remember the foggy daya when people, you normally did not see, gathered in the bars, because the network went unbearably slow. It was nice days with every CS student having a server rack in their closet. I had a VT520 hooked up to it be able to read emails and IRC chats bed without having to wait for my PC to boot.
Has to be the early to mid 1990's?
I was going to say, sounds like my college experience decades later. Still a very congested laser link, and I had a headless minitower instead of a rack (though I wasn't a CS student).
I dreamed of doing something like this growing up so that my neighbor and I could play StarCraft without the latency of dialup. I wish I knew then that it was that straightforward.