The technology uses optical signals to communicate wirelessly over a range of distances.
The first recorded use of an optical signal as a mean of communication goes as far back
as the times of the Ancient Greeks when signals were transmitted over long distances by
using shiny objects to reflect sunlight. Its first modern use, in the form of a device called a
heliograph, was in 1935 when the U.S. and British armies sent Morse code over distances
of tens of miles by using mirrors to create flashes of reflected sunlight.
236 Chapter 9
The early development of optical wireless as a wireless communication technology
goes back to the time of the early development of radio frequency (RF) wireless communication
technology. An optical wireless telephonic device called the photophone was
invented by Alexander Graham Bell in 1880, at about the same time as Marconi and
Edison were demonstrating wireless telephony using radio frequency. The photophone
used lightbeams to transmit voice conversation over distances of a few hundred meters.
Bell considered this invention to be one of his most important inventions. It, however,
had the same limitation as heliograph.
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