What solutions, if any, are there for visible light transmission (VLC)?
A project from the Czech Repuplic called RONJA gets 10 Mbps through more than a kilometer of open air with ordinary red LEDs. It uses a specialized amplifier design to drive the LED, but if all you want is to modulate an LED at a few 10s of kHz, then just wiring it to an output pin of a microcontroller will work.