Light can be used to transmit information just like radio waves can. To transmit information using radio waves the radio energy is modulated, which means the information is superimposed on the radio (RF) energy by varying its power levels. The same can be done with light up to even higher frequencies than RF will allow due to the shorter wavelength. By varying the intensity of the light, it is possible to attach information to the optical energy. The faster we vary the intensity of the light, the more information we can transmit in a shorter time.
This technology is mainly found in fiber-optic data transmission equipment (switches, hubs, etc.) for computer networks.
The whole, enire internet runs on fiber optics, the fiber optics are just on the backbone. Cable/DSL companies have fiber running to an area, like a town maybe, and then use copper TV cable or phone lines to finish the trip to your house. Nowadays, Verizon (and maybe some others) are beginning to roll out FiOS, which will run fiber optics all the way into your house, and yes, it is fast.
Fiber optic cables are utilized using lasers emitting at 1550nm, well into the IR and away from visible. They use 1550nm because there is a minimum in the absorption curve for the glass that comprises the fiber optic cable. Here's an ok chart that shows this, the the minimum in loss in the glass occurring at 1550nm:
The cables also use a phenomenon called "total internal reflection" to keep the light in the cable, but that's not so much laser-related as it is just optics-related.
It's simply very long strands of glass. More precisely, it's a very long strand/tube of glass, that's inside a different kind of glass. Think...corndog, or Twinkie, or something else like that. Light goes into the inner cylinder of glass, and if the strand is done correctly with one kindof glass around the inner cylinder, it won't leave the inner cylinder. It'll bounce off the wall between the 2 kinds of glass, and always stay in the inner cylinder, and travel all the way to the other end. There is always some loss along the way, so there'll be signal amplifiers along the way if it's a very long trip.
That's a terrible description, pictures help, but I'm not at my computer at the moment.