Definition
An early communication device, invented by Alexander Graham Bell in 1880, that transmitted speech on a beam of modulated light. Sound vibrations caused a mirror to flex, which varied the intensity of a reflected light beam; a selenium cell at the receiving end converted the changing light back into electrical signals and then into sound. The photophone is recognized as the conceptual ancestor of modern fiber-optic and free-space optical communication.
Plain English
An old invention that sent voice through the air on a beam of light instead of through wires. It was the first device to carry a conversation using light, long before fiber optics existed.
Context Anchor
Seen mainly in older aviation communication or electronics references, not as a normal modern cockpit control.
Derivation
From the Greek 'phos' (light) and 'phone' (sound or voice). Literally 'light-sound' — a fitting name for a device that turned voice into light and back into voice.
Intuition Check
Do not read photophone as a camera phone or photo device. Here, photo means light, and phone means sound or voice.
Example Sentence 1
The photophone demonstrated as early as 1880 that voice could travel on light, an idea now realized in the fiber-optic data buses found on modern airliners.
Example Sentence 2
Inventors tested the photophone by speaking into a device that changed how much light reached a receiver.