Photophone

This article is about Alexander Graham Bell and Sumner Tainter's optical phone. For the sound-on-film technology, see RCA Photophone.
An image of darkened brass historical plaque with a streak of green corrosion running down it, mounted on the exterior side of a brick building.
A historical plaque on the side of the Franklin School in Washington, D.C. which marks one of the points from which the photophone was demonstrated
A diagram from one of Bell's 1880 papers

The photophone is a telecommunications device that allows transmission of speech on a beam of light. It was invented jointly by Alexander Graham Bell and his assistant Charles Sumner Tainter on February 19, 1880, at Bell's laboratory at 1325 L Street in Washington, D.C.[1][2] Both were later to become full associates in the Volta Laboratory Association, created and financed by Bell.

On June 3, 1880, Bell's assistant transmitted a wireless voice telephone message from the roof of the Franklin School to the window of Bell's laboratory, some 213 meters (about 700 ft.) away.[3][4][5][6]

Bell believed the photophone was his most important invention. Of the 18 patents granted in Bell's name alone, and the 12 he shared with his collaborators, four were for the photophone, which Bell referred to as his "greatest achievement", telling a reporter shortly before his death that the photophone was "the greatest invention [I have] ever made, greater than the telephone".[7][8]

The photophone was a precursor to the fiber-optic communication systems that achieved worldwide popular usage starting in the 1980s.[9][10][11] The master patent for the photophone (U.S. patent 235,199 Apparatus for Signalling and Communicating, called Photophone) was issued in December 1880,[5] many decades before its principles came to have practical applications.

  1. ^ Bruce 1990, pg. 336
  2. ^ Cite error: The named reference SDU was invoked but never defined (see the help page).
  3. ^ Bruce 1990, pg. 338
  4. ^ Carson 2007, pg. 76–78
  5. ^ a b Cite error: The named reference Groth was invoked but never defined (see the help page).
  6. ^ Mims 1982, p. 11.
  7. ^ Cite error: The named reference Phillipson+Neilson was invoked but never defined (see the help page).
  8. ^ Mims 1982, p. 14.
  9. ^ Cite error: The named reference Morgan was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference AmericanScientist-1984.V72.No1 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Gallardo+Mims was invoked but never defined (see the help page).