Interesting, now we need an Arduino to support RFC 1149: IP over Avian Carriers - Wikipedia.
It should be noted that it is likely almost all of the internet traffic these days after it leaves your house likely is transmitted optically over fiber optic lines during at least one step of the journey. Note, you could presumably get more bandwidth by splitting the bits into separate channels that are sent by light at different frequencies, but it will increase the cost of the transmitters and receivers. A quick google shows that you can get low end ethernet converters for about $50 each. Figure maybe $200 if you have to get ethernet sheilds as well. So it likely isn't cost effective....