Optical communication, also known as optical telecommunication, is the remote communication that uses light to convey information. It can be done visually or through the use of electronic devices. The earliest basic forms of optical communication go back several millennia, while the oldest electrical device created to do so was the photophone, invented in 1880.
An optical communication system uses a transmitter, which encodes a message in an optical signal, a channel, which carries the signal to its destination, and a receiver, which reproduces the message of the received optical signal. When electronic equipment is not used, the "receiver" is a person who visually observes and interprets a signal, which may be simple (such as the presence of a beacon) or complex (such as lights using colour coding or a Morse code). sequence).
Optical communication in free space has been deployed in space, while terrestrial forms are naturally limited by geography, climate and the availability of light. This article provides a basic introduction to the different forms of optical communication. Visual techniques such as smoke signals, lights, hydraulic telegraphs, boat flags and traffic lights were the first forms of optical communication. Hydraulic telegraph semaphores date back to the 4th century BC Greece. Emergency flares are still used by navigators in emergency situations, while headlights and navigation lights are used to communicate navigation hazards.
The heliograph uses a mirror to reflect sunlight to a distant observer. When a pointer tilts the mirror to reflect sunlight, the distant observer sees flashes of light that can be used to transmit a preset signaling code. Naval ships often use signal lamps and Morse code in a similar way.
Aviation pilots often use projected visual slope indicator light (VASI) systems to land safely, especially at night. Military aircraft landing on an aircraft carrier use a similar system to land properly on a transport platform. The colored light system communicates the height of the airplane in relation to a standard landing glide path. In addition, airport control towers still use Aldis lamps to transmit instructions to aircraft whose radios have failed.
At present, a variety of electronic systems transmit and receive lightly transported information pulsed by light. Fiber optic communication cables are now used to send the vast majority of electronic data and long distance telephone calls that are not transmitted by radio, land-based or satellite. Optical free space communications are also used every day in various applications.
