The photophone (also known as a radiophone) is a telecommunications device which allowed for the transmission of both articulated sounds and normal human conversations 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. Both were later to become full associates in the Volta Laboratory Association, created and financed by Bell.
On April 1, 1880, Bell's assistant transmitted the world's first wireless telecommunication to him from the roof of the Franklin School to the window of Bell's laboratory, some 213 metres (700 ft) away.
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', writing that the Photophone was "the greatest invention ever made, greater than the telephone".
The device is similar to fiber-optic communications which came into widespread use during the 1980s.