The constantly developing world of all-weather laser satellite communication

Using light beams for communication is not a new idea, even outside of Star Trek, Star Wars, and other similar fantasy stories. Scientist and science fiction writer Arthur Clark predicted that beam communication, at that time modern satellite communication was just a dream.

In 1975, the magazine published an article about laser communication or laser communication equipment. The demonstration of optical communication technology occurred in the mid-1990s. For example, the Japan Communications Research Laboratory successfully demonstrated laser communication experiments on the Japanese Engineering Test Satellite VI in 1994, which was the first dedicated laser communication satellite used to demonstrate air to ground laser communication.

The reason for this interest in laser communication is that the optical communication systems we know today have several advantages over the currently used UHF, SHF, and EHF systems, including higher data rates, better signal-to-noise ratios due to higher directionality, no interference, smaller antennas, lower overall power requirements, higher spectrum availability, and narrower beams that are more difficult to intercept and interfere with, And establishing a network does not require coordination from the International Telecommunication Union.

As mentioned earlier, capacity has a major advantage. The spectrum is several thousand times larger than the radio frequency spectrum; Therefore, when the radio frequency ranges from approximately 300 Hz to 300 GHz, the spectrum ranges from approximately 400 to 800 terahertz. The frequency is so high that so many zeros are required, to the extent that optical communication systems are measured in nanometers, with 800 nm being a typical wavelength/frequency. Although the implemented data rate depends on the signal encoding scheme, generally speaking, they may be a thousand times higher than the rate in RF communication.

For many years, satellite laser communication has been a characteristic of the Ministry of National Defense's planning. Those involved in the ill fated transformational satellite communication program believe that it is necessary to connect TSAT's orbital laser satellite network with the global fiber optic network of the defense information system network, which connects the orbital laser ring in space to the ground global laser ring of the global fiber optic network. The solution is to deploy the Earth station in geographically dispersed mild weather locations to avoid the dissipation effects of rain, drizzle, clouds, fog, and dust.

This solution illustrates the drawbacks of known optical communication systems today. These systems have higher pointing accuracy required by satellites, increasing complexity and availability risks, and are noise sources for solar receivers. As mentioned earlier, they are the main interference factors in rain, drizzle, clouds, fog, and dust.

Despite atmospheric barriers, some experiments and systems are using air to ground lasers. Since the beginning of 2022, NASA's laser communication relay demonstration has demonstrated bidirectional laser communication from geostationary orbit.

The drawing board, brass plate, prototype, and initial launch of giant satellite constellations have multiple laser dependent networks. Telesat in Canada, with its constellation of light speed, may be a microcosm of laser communication networks, developing satellite to satellite connections on similar and different orbits. Although the system has been plagued by financial difficulties, design changes and increased investment seem to be putting it back on track. SpaceX's Starlink satellite internet service has launched over 25 satellites, and last year it was confirmed that laser satellites were used to provide internet connectivity to several regions, even though it was only air to air. Low Earth orbit satellites have over 5000 systems and concepts, providing numerous proposals and contract requests for laser terminal manufacturers.

Source: Laser Net