IrDA

Light: it's the radiation we can see. The communications potential of light is obvious, and indeed, many of the earliest forms of long-distance communication relied on it: signal fires, semaphore, heliographs. You could say that we still make extensive use of light for communications today, in the form of fiber optics. Early on, some fiber users (such as AT&T) even preferred the term "lightguide," a nice analogy to the long-distance waveguides that Bell Laboratories had experimented with. The comparison between lightguide and waveguide illuminates (heh) an important dichotomy in radiation-based communication. We make wide use of radio frequency in both free-space applications ("radio" as we think of it) and confined applications (like cable television). We also make wide use of light in confined fiber optic systems. That leaves us to wonder about the less-considered fourth option: free-space optical (FSO) communications, the use of modulated light without a confined guide. Well, if I…