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What is Free-Space Optics?

By Solomon Branch
Updated May 17, 2024
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Free-space Optics (FSO) is a communication technology using the light moving in open spaces to allow transmission of information between points. The term “free space” can refer to any open space, such as air or outer space. Free space optics is typically used in situations where fiber optic cables cannot be laid down, or their cost is too expensive.

Implementing FSO can be done in several ways. Using infrared laser lights is a common mode, as is using light-emitting diodes (LED) in shorter distances with a lower rate of data. Free-space optics is commonly used in communication between spacecraft, and the current range of free-space optical communication is in the low-thousands of miles. With the use of optical telescopes to expand the beams, the distances could reach much further.

On land, the range for free-space optics is only around one to two miles. The quality of the signal is also dependent on the weather and other atmospheric conditions. Light beams that are used in free-space optics is particularly narrow and is also very easy to encrypt, making it a relatively secure form of communication. Using a specific type of laser, a signal can be created that dissipates if it is interrupted in any way.

There are many advantages and disadvantages to free-space optics. The main advantages are that these systems are easy to implement, are secure, they allow for a high bit rate with few errors in the signal, and are free, unlike a radio signal which needs to be licensed. While the signal cannot be interrupted by electromagnetic waves, it is susceptible to interference from atmospheric conditions including rain, fog, and snow. The attenuation they cause, however, can be modulated using a multi-signal device or a higher end device that boosts the signal.

Despite its shortcomings, free-space optics has a wide range of applications. Large college campuses, for example, can use FSO when they need to connect to local area networks (LANs) together without utilizing cables. Large cities often use the technology for the same reason. Besides spacecraft, free-space optics can also be used to help satellites communicate when in groups. It can also be used as a back-up system in case land-based networks fail, or to facilitate fast communication between two fiber optic cable networks. Free-space optics are also a convenient modality to use when setting up a temporary installation, such as a conference, and allows for fiber optic speed without the burden of cables.

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Discussion Comments
By Amphibious54 — On Jun 08, 2011

@parmnparsley- Line of sight obstruction is not as much of a challenge for laser data link systems as it used to be. The systems do still need to be installed with line of sight in mind, but by incorporating redundancy (multiple data paths), things like birds, cranes, and other obstructions will not interrupt data transfers. This redundancy also allows FSO systems to work in places like San Francisco where heavy fog is commonplace.

By parmnparsley — On Jun 06, 2011

@comparables- FSO wireless access points are more technologically advanced than the wireless technology in your router. They are more useful for setting up secured wireless networks on campuses or industrial parks.

The systems involve lasers, scatterers, and receivers attached to towers on building rooftops. The main consideration when designing these systems is maintaining a direct line of sight. In theory, large bandwidths of data transfer can happen as fast as the speed of light, but it all depends on an unhindered path from the laser to the receiver.

By Comparables — On Jun 05, 2011

Is free space optics the technology that is used in my wireless router? I never knew what it was that was being used. I always thought it was a radio frequency that was transmitted from the antenna over a short distance. If this is the case, is it possible to encrypt the signal from my wireless router to my computers?

I have heard about the horrors people go through because their wireless router was not secure. I have also been a victim of identity theft. I have never heard of free space optics until now, but I would be interested to learn more. Thank you wiseGEEK.

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