Afaik common sfp transceivers or media converters use IR LED's. They can handle a speed of 100 mbps and are rather cheap. Of course this is not the same kind of IR LED you use in a TV remote control. The Ronja project uses IR LED's for 10 mbps data links over several hundred meters:
http://ronja.twibright.com/
So how can this be done? All I could find up to now are encoders/decoders which are integrated in the ethernet chip.
I found some cheap IR transceivers from Vishay which support a couple of mbps, though, still well below 100 mbps. There is also UFIR and GigaIR which support bandwiths of 100 or 1000 mbps. But I could not find any commercial device supporting these specifications.
100 mbps on a distance of 1 m (but more likely only some centimeters). I know that this is possible because fiber optic media converters/ sfp transceivers easily support this. There are also lots of publications on visible light communication or free space optics which achieve these data rates. But except media converters or sfp transceivers they don't have ethernet as an input. In the end I would need something like a fiber optic media converter with two ethernet connections.
The dataflow would be: pc1 --> ethernet1 --> led --> photodiode --> ethernet2 --> pc2