Free-space Optical Communication
Main article: Free space optical communication.
Free Space Optics (FSO) systems are generally employed for 'last mile' communications and can function over distances of several kilometers as long as there is a clear line of sight between the source and the destination, and the optical receiver can reliably decode the transmitted information. IrDA is an example of low-data-rate, short distance free-space optical communications using LEDs.
Other free-space systems can provide high-data-rate, long-range links using small, low-mass, low-power-consumption subsystems.
Read more about this topic: Optical Communication
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