The transmission of modulated visible or infrared (IR) beams across the atmosphere to produce Broadband communications is known as free-space optics (FSO), sometimes known as free-space photonics (FSP). Laser beams are most employed, however non-lasing sources such as light-emitting diodes (LEDs) or infrared-emitting diodes (IREDs) can also be used.
FSO theory is substantially the same as fibre optic transmission theory. The distinction is that instead of being steered by an optical fibre, the energy beam is collimated and delivered through clear air or space from the source to the destination.
Working of FSO:
Using low-power infrared lasers in the terahertz range, Free Space Optics (FSO) sends invisible, eye-safe light beams from one “telescope” to another. Laser light is focused on extremely sensitive photon detector receivers in Free Space Optics (FSO) systems to transmit light beams. These receivers are telescopic lenses that gather photons and send digital data that may include Internet communications, video images, radio signals, or computer files. Commercially available systems have speeds ranging from 100 megabits per second to 2.5 gigabits per second, with demonstration systems reporting data rates of up to 160 gigabits per second.