Free Space Optical Communications

Key Takeaways

Free space optical communications (FSOC) uses modulated laser or LED beams to wirelessly transmit data through free space.
It offers high bandwidth, low latency, and secure transmission—ideal for space, air, sea, and land applications.
FSOC systems vary by type (coherent/incoherent), range, platform, and architecture. Despite benefits, FSOC faces challenges like signal alignment and weather interference.
Avantier provides custom optical solutions for reliable, high-performance FSOC systems.

No longer is data transfer limited to radio waves or wire. Free space optical communication (FSOC) enables almost instantaneous data transfer in space, in the air, on the surface of the sea, and between fixed locations on land. This method of data transfer can provide far more bandwidth than radio frequency (RF) wireless communication, and is difficult to jam or intercept. It relies not on cables or radio stations, but on optical transmitters and receivers.

What is Free Space Optical Communication?

Free space optical communication is a set of optical techniques that enables the wireless transmission of information. A modulated narrow laser beam carries the digital data from transmitter to receiver through free space, without reliance on optical fibers.

Why Free-Space Optical Communications?

Wireless communication systems used to be limited to radio waves, a cumbersome and easily-intercepted method that left much to be desired. Where high bandwidth was required, optical fiber could be laid. Free space optical communication brings the benefits of an optical connection to stations connected wirelessly by line of sight, and promises high speed connections unlimited by cables. Benefits of free space optical communication include:

High data rates
Low latency
Secure data transmission

Types of Free-Space Optical Communications

There are two main types of free space optical communications; coherent and non coherent.

Coherent FSOC systems are used over long distances and with high data rates. They are based on laser, and may require the integration of state-of-the-art modulation techniques and adaptive optics. Space based laser communication is one example of a coherent FSO system.
Incoherent FSOC systems use LEDS to relay data over a short distance. They are not capable of the high data rates produced by laser communication but may be suitable when lower data rates. Visible light communication (VLC) is a type of FSO that uses visible light; IRC uses infrared light.

Free space optical communications can also be categorized by architecture, by platform, or by range. When categorizing by range, FSOC systems can be divided into short-range (for indoor and urban use, within a few hundred meters), medium-range (for distances up to three kilometers), or long-range (for distances of more than several kilometers). If categorizing by platform, one may divide FSOC systems into terrestrial, airborne, and satellite systems.

There are four principal types of architecture used in designing FSOC systems: point-to-point, mesh, point-to-multipoint or ring.

Point-to-point (single beam) — this is the simplest of configurations, where a single transmitter sends an optical signal to a single receiver. The benefit of this architecture is ease of use; the downside is that adverse conditions may cause data loss or signal deterioration.
Mesh— a more complex but also more foolproof configuration, consisting of multiple transmitters and multiple receivers working together.
Point-to-Multipoint (star)— a hub and spoke configuration, where one transmitter sends a signal to multiple receivers.
Ring—- a circular or ring shaped configuration for data transmission that has redundancy built in.

Applications

A fourth way of categorizing FSOC is by its applications. Short range FCOS systems using micro-optics and lenses may be used for intra-machine communications. A long-range FSOC system can used to bring high speed internet to rural areas or disaster locations. It can provide secure, reliable communication for military and defense applications, both on land and in the water.

It can also be used to provide fast reliable space communication. For more information on FSOC in space, see our comprehensive knowledge base article on space-based laser communication.

Challenges of Free-Space Optical Communication

In spite of its promise, FSOC faces significant challenges. Alignment between receiver and transmitter can be difficult to achieve. For instance, in space optical communication, an optical ground station must be in line of sight with the space station in order to set up an optical link. Atmospheric turbulence can lead to data loss, and weather-induced signal degradation can significantly impair performance. When designing an FSOC system, it is important to note that some wavelengths of light are less prone to weather interference than others.

Free-Space Optical Communication at Avantier

Avantier is a premium producer of custom optics for free space optical communication, and our design and engineering team is experienced in surmounting the challenges facing FSOC to produce high performance, reliable optical performance for optical communication applications. Contact us today if you’d like to find out more or to schedule an initial consult.

References

A. Al-Gailani et al., “A Survey of Free Space Optics (FSO) Communication Systems, Links, and Networks,” in IEEE Access, vol. 9, pp. 7353-7373, 2021, doi: 10.1109/ACCESS.2020.3048049.

Alimi & Monteiro. Revolutionizing Free-Space Optics: A Survey of Enabling Technologies, Challenges, Trends, and Prospects of Beyond 5G Free-Space Optical (FSO) Communication Systems. Sensors 2024, 24(24), 8036;

Walsh, S.M., Karpathakis, S.F.E., McCann, A.S. et al. Demonstration of 100 Gbps coherent free-space optical communications at LEO tracking rates. Sci Rep 12, 18345 (2022).

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