"Fiber optic cables are replacing copper wiring to increase the speed of digital information transmission. These cables are bundles of extremely pure glass threads that have been coated in two layers of reflective plastic. A light source -- typically a laser -- switches on and off rapidly at one end of the cable to transmit digital data. The light travels through the glass strands and continuously reflects off of the inside of the mirrored plastic coatings in a process known as total internal reflection. Systems based on fiber optics can transmit billions of bits of data per second, and they can even carry multiple signals along the same fiber by using lasers of different colors."
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