Friday, June 03, 2016

Talking on sunshine: Alexander Bell transmits voice via light modulation on June 3, 1880

What did Alexander Graham Bell think his greatest invention to be? If you believed him to say the telephone, you would be wrong. Bell considered the photophone his greatest invention.

On June 3, 1880 (four years after he patented the telephone and four years after Custer's "Last Stand"), a wireless voice message was transmitted via light modulation about 700 feet.

On Aug 28, 1880, Bell filed his patent application for what would become US Patent 235199. On August 30, 1880, the New York Times ridiculed the utility of the photophone.


About 100 years later US Patent 4002897 (assigned to Bell Labs) noted the following:

Almost 100 years ago, Alexander Graham Bell invented a completely optical communication system including apparatus which he named "photophone". The system was fairly simple, utilizing a transmitter for converting human voice signal waves into correspondingly power-modulated optical signals. These optical signals were detected by a (remote) receiver for converting the optical signals into audible acoustic signals which were a faithful representation of the original human voice signals. Several of the patents issued on this system include U.S. Pat. No. 235,199, (Dec. 7, 1880) to A. G. Bell; U.S. Pat. No. 235,496 (Dec. 14, 1880) to A. G. Bell and S. Tainter, and U.S. Pat. No. 241,909, (May 24, 1881) to A. G. Bell and S. Tainter. In addition, a paper on this subject was published by A. G. Bell in Philosophical Magazine, Vol. 11 (Series 5), pp. 510-528 (1881), entitled "Upon the Production of Sound by Radiant Energy." Such an optical communication system relied upon a rather intense source of light, which then could be provided only by sunlight, a relatively unreliable source, and upon transmission of the light through the air, a relatively unreliable transmission path. With the advent in recent years of intense optical laser sources and of optical fibers, the possibility of a reliable optical communication system is thus more realistic. Such a system includes at one end a transmitter feeding an optical fiber. The optical fiber would ordinarily bring the optical signal to a repeater which then feeds an amplified optical signal to another optical fiber, ultimately bringing the optical signal to an opto-acoustic receiver. The receiver then converts the optical signal into an audible acoustic signal for delivery to a receiving human ear.


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