I don't have much time to research or do this myself at the moment, but considering the cost of Free Space Optic (FSO) links, I was wondering if anyone knows of- or is keen to explore the possibility of hacking cheap NIC's or Fiber media converters to communicate through some LED's and lenses, or laser diodes.
The projects that I do know of only offer low bandwidth:
Koruza (http://irnas.eu/UsefulSource/koruza/koruza1.xml) (This is actually an SFC hack)
..can't remember the others now
Some relevant searches:
Other keywords: Visible light communication (VLC), Terrestrial laser communications, Li-Fi / LiFi, Optical Wireless Communications