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Fast, Secure, Wireless Communication for a Connected World

 

Wireless transmission of information through the air using lasers

 

Much more bandwidth than radio-based wireless communication

 

Enables fast, affordable internet that can reach rural areas or disaster sites

 

Enables highly-secure communication for defense applications

Fast, global communication is critical in our increasingly-connected world. The World Bank has declared that broadband internet access is a basic necessity for economic and human development, not a luxury.1 It opens up opportunities for education, employment, healthcare access, and government transparency and accountability that would be otherwise lost. Free-space optical (FSO) communication involves using lasers to transmit data from one location to another, whether it is from a satellite to a telescope-like ground station, one satellite to another, or between different locations on the ground (Figure 1). According to Global Market Insights, the FSO market will likely grow at a rate of over 35% in each of the next five years, skyrocketing from $200 million to $2 billion by 2027.2 In addition to fast internet access that can reach areas without optical fiber connections, FSO provides the means for highly-secure communications for defense applications that are difficult to intercept.

General process for free-space optical communication.
Figure 1: General process for free-space optical communication.

High-Speed Internet: A Modern Basic Necessity

The World Bank estimates that 80% of the population of advanced economies have broadband high-speed internet access, while only 35% of the population in developing countries have broadband access.1 "Broadband" here is defined as internet faster than dial-up. FSO communication offers the potential for better wireless communication for groups that already have broadband internet access, as well as those that do not. Optical communication provides bandwidth increases of 10 – 100X compared to radio frequency (RF) wireless communication and requires less input power.3 The costs associated with setting up ground-based radio stations to receive FSO signals are also significantly less than installing new optical fiber connections because of the associated labor and digging costs. In some cases, it is also cheaper to use FSO communication from one location on the ground to another than to install optical fiber cables.

Current commercially-available FSO networks feature typical data rates ranging from 100 Mbps to 10 Gbps, while high-end prototypes report capacities as high as 160 Gbps.4 Many different companies are establishing networks of satellites that will facilitate high-speed, FSO-enabled communications (Figure 2). FSO communication offers a practical solution for creating global, broadband wireless connectivity.5

Networks of satellites have already been deployed to facilitate high-speed, free-space optical communication to ground-based receivers.
Figure 2: Networks of satellites have already been deployed to facilitate high-speed, free-space optical communication to ground-based receivers.

Secure FSO Communication for Defense

FSO communication is highly-advantageous for defense applications because of its increased level of security compared to RF or other wireless communication. FSO laser transmissions can be encrypted, are invisible or narrow-band, cannot be deciphered using RF meters or spectrum analyzers, propagate along a line-of-sight path which is difficult to intercept, and a matching FSO receiver is needed to collect the information.4 The receivers for FSO communication can also be designed to be mobile and easy to use, allowing them to be easily deployed in the field for defense applications. This facilitates fast, high-bandwidth, secure communication that can save lives.

Considerations for Optical Components Used in FSO

Optical systems designed to receive FSO signals must be highly-sensitive, as atmospheric absorption, dispersion, the large distances between the transmitter and receiver, and scintillation make the ratio between the outgoing and incoming signal very large (Figure 3). Scintillation refers to rapid variations in the received signal because of the structure of the atmosphere through which the light propagates.6

WeatherWavelength, λAttenuation in dB at L Distance
1 km10 km100 km
Conditions microns      
Clear weather (at sea level) 0.53, 1.06 0.06 0.6 6
10.6 0.54 5.4 54
C02 absorption 0.53, 1.06 - - -
10.6 0.25 2.5 25
Haze
(Density: 0.1 mg/m3)
0.53, 1.06 1.4 14 140
10.6 0.66 6.6 66
Light fog
(Size: 0.5-10μ; density: 0.5 mg/m3; visability: ~2 km)
0.53, 1.06 0.1-5 1-50 10-500
10.6 .9 9 90
Fog
(Size: 0.5-10μ; density: 1 mg/m3; visability: ~0.5 km)
0.53, 1.06 0.2-10 2-100 20-1000
10.6 1.9 19 190
Rain 5mm/hr 0.53, 1.06 1.6 16 160
Rain 25mm/hr 0.53, 1.06 4.2 42 420
Rain 75mm/hr 0.53, 1.06 0.7 7 70
Light rain (Size: 1000μ; density: 50 mg/m3) 10.6 1.6 16 160
Light Snow 0.53, 1.06 1.9 19 190
Heavy Snow 0.53, 1.06 6.9 69 690
Figure 3: Table showing the attenuation of FSO communications in different weather conditions such as fog and rain.7

The pointing accuracy and stability of the optical systems used for FSO are also critical. The narrow beam divergence inherent to laser-based communication (about 10X less than RF signals) makes pointing accuracy more important for FSO compared to traditional RF communications.8 Pointing accuracy requirements may typically be on the order of several hundred µrad, so extra gimbals or other steering mechanisms may be needed.9 Tight mechanical tolerancing in the optomechanical assembly design can help prevent movement of internal lens elements, which in turn improves pointing accuracy. The unwanted movement of lens elements inside the assembly can be described by roll, decenter, and the coupling of these effects from one element to another (Figure 4). More information can be found in our Tips for Designing Manufacturable Lenses and Assemblies Application Note. The algorithms used in FSO systems are also carefully tailored to better locate and receive the faint, narrow signals.

A. Roll motion of a lens element. B. Coupled roll motion. C. Decenter motion of a lens element. D. Coupled decenter motion.
Figure 4: A. Roll motion of a lens element. B. Coupled roll motion. C. Decenter motion of a lens element. D. Coupled decenter motion.

References

  1. The World Bank. (2019). Connecting for Inclusion: Broadband Access for All. World Bank. https://www.worldbank.org/en/topic/digitaldevelopment/brief/connecting-for-inclusion-broadband-access-for-all .
  2. Global Market Insights. (November 2021). Free Space Optics (FSO) Communication Market Size By Platform (Terrestrial, Satellite, Airborne), By Application (Mobile Backhaul, Enterprise Connectivity, Disaster Recovery, Defense, Satellite), COVID-19 Impact Analysis, Regional Outlook, Growth Potential, Competitive Market Share & Forecast, 2021 – 2027. Global Market Insights. https://www.gminsights.com/industry-analysis/free-space-optics-fso-communication-market .
  3. NASA. (2021). Laser Communications Relay Demonstration (LCRD). Space Technology Mission Directorate. https://www.nasa.gov/mission_pages/tdm/lcrd/index.html .
  4. fSONA. (2003). FSO Guide. fSONA Optical Wireless. http://www.fsona.com/technology.php?sec=fso_guide.
  5. Majumdar, A. (October 2019). Optical Wireless Communications for Broadband Global Internet Connectivity (1st ed.). Elsevier.
  6. National Oceanic and Atmospheric Administration. (2022). Satellite Communications. Space Weather Prediction Center. https://www.swpc.noaa.gov/impacts/satellite-communications.
  7. Raible, D. E. (2011). Free Space Optical Communications with High Intensity Laser Power Beaming. ETD Archive.. https://engagedscholarship.csuohio.edu/etdarchive/251.
  8. Kaushal, H. and Kaddoum, G. (2015). Free Space Optical Communication: Challenges and Mitigation Techniques. IEEE Communications Surveys & Tutorials, 19(1), 57 - 96. DOI: 10.1109/COMST.2016.2603518.
  9. Hall, S. (May 2020). A Survey of Free Space Optical Communications in Satellites. Georgia Institute of Technology. https://www.ssdl.gatech.edu/sites/default/files/ssdl-files/papers/mastersProjects/Hall_Stephen_8900.pdf.
  10. CableFree (2022). Free Space Optics (FSO). CableFree 10+ Gigabit Wireless Networks. https://www.cablefree.net/cablefree-free-space-optics-fso/.

FAQs

FAQ  Can obstructions like fog and vapor in the air interfere with free-space optical (FSO) communications?
Yes, while FSO communications are generally unaffected by rain or light snow, fog and vapor can interfere with FSO communication. The laser light can be absorbed or scattered by the small water droplets in the air, lowering bandwidth or even blocking the signal. Because of this, FSO may not be the best communication solution in foggy areas.10
FAQ  Does Edmund Optics® manufacture FSO systems?

No, but Edmund Optics does manufacture optical components like the ones used in FSO systems.

Technical Resources

Application Notes

Technical information and application examples including theoretical explanations, equations, graphical illustrations, and much more.

Beam Quality and Strehl Ratio
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Gaussian Beam Propagation
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Roughness of Diamond Turned Off-Axis Parabolic Mirrors
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Ultrafast Dispersion
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Key Parameters of a Laser System
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Videos

Informative corporate or instructional videos ranging from simple tips to application-based demonstrations of product advantages.

Introduction to Laser Optics Lab 
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Metrology at Edmund Optics: Measuring as a Key Component of Manufacturing 
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Single Point Diamond Turning: EO Build-to-Print Manufacturing 
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Free-Space Optical Communication – TRENDING IN OPTICS: EPISODE 6 
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Technical Calculators

Technical calculators based on commonly used and referenced equations in the Optics, Imaging and Photonics industries.

Gaussian Beams Calculator
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