Soon after, he tested the photophone, another talking machine that used a beam of sunlight to carry voices from one place to another. Although he had high hopes for the future of his photophone, it depended on a constant source of sunlight and proved to be impractical. Not until the invention of lasers and optical fibers did Bell's dream come true. In the mid-1970s, researchers began pumping pulses of laser light through thin glass fibers to move information.
Light is actually a sequence of vibrations.
Scientists discovered how to vary these patterns of vibrations and convey information. When a conversation occurs over a telephone system that uses optical fibers, the vibrations of your voice are converted to the pattern of the laser. At the other end, these variations are turned back into sound. Because lasers can be modulated with highly complex patterns much greater quantities of information can be transmitted. Stringing electrical cables or optical fiber cables from place to place is very expensive.