Optical sound transmission

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As Lichttonübertragung refers to the transmission of analog low frequency signals using light . For this purpose, a light source is controlled with the signal to be transmitted in order to obtain a modulated luminous flux which is then picked up by a light-sensitive element. The light can be transmitted freely through the room as well as in light guides or within an encapsulated housing ( optocoupler ). Related, but clearly distinguishable, is the optical tone process used in sound films .

technology

LEDs or glow lamps are usually used as the light source . Due to the thermal inertia of the filament in incandescent lamps, these are only suitable to a limited extent, but the light from an incandescent lamp can be modulated with the help of a Kerr cell . In connection with a Pockels cell , lasers can also serve as a modulated light source. A photo element , for example a photo cell , photo resistor , photo diode or photo transistor , functions as the receiving element . In order to achieve low-distortion transmission, the input signal is usually superimposed with a direct current in order to operate the system at a favorable operating point . To reduce interference, z. B. by encapsulation minimizes the influence of extraneous light.

Applications

The optical sound transmission in this simple form is used for galvanic isolation with the help of optocouplers. The transmission through the free space is of little practical importance, but it is part of many experiment kits. The photophone is an early application of the technology, but there with mechanical modulation of the light source. With the advent of laser and digital technology , the basic principle experienced a renaissance in the form of optical data transmission in fiber optic networks and optical radio relay systems .

Another application is in the form of an infrared hearing aid , with which, above all, radio or television sound is transmitted for better perception for the hard of hearing .

literature

  • Siegfried Wirsum: Mixers and mixer modules. 6th edition, Franzis Verlag, Munich 1986, ISBN 3-7723-3356-7 , pp. 65-72.
  • Peter Welzel, Harald Schummy (ed.): Data transmission. LAN and Internet protocols for IT professions, 4th edition, Friedrich Vieweg & Sohn Verlag, Wiesbaden 2001, ISBN 978-3-528-34369-9 .