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Free Space Optics

I read an article on the Finley Engineering blog that talks about new research with free-space optics. For those not familiar with the term, this means communication gear that communicates directly using light without any wires.

The article talks about a Chinese team of scientists that have been able to use light to transmit ultrahigh-definition video signal between high-rise buildings. That’s an interesting feat because light signals in an urban environment must deal with air pollution, vehicle exhausts, and other factors that place small particles in the air that can disrupt a light signal. The scientists have found new ways to compensate for attenuation and scattering due to environmental factors.

If perfected, light transmitters could play some interesting roles. It might make sense to use light transmission in places with unusual terrain constraints. The technology could be used to pop up an instant broadband connection between buildings until a more permanent connection can be built. The technology could provide a quick fix for restoring key broadband connections after disaster recovery. The real promise for the technology is in space. It makes sense to use lasers to communicate between satellites or to communicate between manned outposts.

The technology has been around for a long time. Alexander Bell created a photophone in 1880 that he thought was one of his most important inventions. He demonstrated the use of the technology by transmitting a call about 700 feet between two buildings using a light signal. We all use remote controls that transmit signals using infrared light.

There have been earlier attempts to use the technology in the telecom industry. Back during the telecom boom of the late 1990s, several well-funded start-ups tried to develop working technology using light instead of radio frequency to transmit broadband. The biggest of these was Terabeam that attracted over a half-billion dollars in start-up funding and was backed by AT&T and Lucent. I recall talking to engineers at Terabeam about the technology. Other well-funded start-ups that explored the technology included AirFiber and LightPointe Communications.

But none of the companies could ever overcome the natural problems that occur in ambient outdoor conditions. It turns out the real killer for the technology is fog, which completely cuts off transmissions. But the technology also was never reliable in normal weather due to pollution and airborne particles.

The concept resurfaced again a decade later and was labeled as Li-Fi. The concept with this technology was to transmit data by turning LED diodes on and off extremely quickly as a way to transmit the ones and zeros needed for digital transmission. Scientists have been able to achieve a transmission speed as fast as 224 gigabits per second by simultaneously transmitting separate signals over different frequencies of light.

There were several trials of Li-Fi technology in Europe in 2018 and 2019 at a BMW plant, a school, and at the 2019 Paris airshow.

Free space optics is an attractive technology in environments like busy factories, nuclear power plants, or airports that are already busy with multiple radio frequencies. It’s an interesting way that can be used to pass data between smart cars that avoids all of the issues associated with radio frequencies. The technology is being considered for transmissions within aircraft to reduce interference with existing critical devices.

The idea of using light to transmit data is enticing because the visible light spectrum can carry approximately 10,000 times more bandwidth than the entire radio frequency spectrum. It’s a concept that is attractive to carriers because it could mean making short-length data transmissions without having to own spectrum. I doubt that we have heard the end of free space optics.

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