photophone

Alexander Graham Bell, in early 1880, invented the photophone, a system utilizing mir-

rors to focus modulated sunlight onto a selenium cell. He was successful in transmitting voice over a distance of 700 feet on sunny days, and was granted four patents for the invention. Although it was clearly impractical, Bell nonetheless felt the photophone to be his greatest achievement. During World War II, the Nazi military experimented with similar but more advanced systems in tank warfare applications, but the technology remained impractical. Contemporary free space optics (FSO) transmission systems do not use mirrors and selenium cells, but undoubtedly have conceptual roots in the photophone. Bell later renamed the photophone the radiophone. See also FSO.

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