Increasing data transmission to speeds in excess of 1 Gb/s require a more concentrated signal at the target, which for RF systems means transmission antennas larger than a meter to narrow the beam, and higher transmit powers to deliver the same energy per bit to the receiver. The centimeter-long wavelengths of microwaves in high-frequency RF transmission bands, such as Ka-band at 26 GHz, result in widely diffracting beams that spread over hundreds of kilometers on the Earth when transmitted over 39,000 km from a satellite above in geosynchronous orbit (GEO).

RF communications have become a bottleneck for moving data at Internet speeds in space. In both realms, progress in terrestrial optical technology continues to push the limits of what can be done in space. More recently, NASA has been investigating new space-to-space and space-to-ground applications closer to Earth. NASA a late entrant in this game, has lately shown rapid progress, culminating in a recent demonstration of a 622-Mb/s error-free data downlink from the moon to the Earth in 2013. National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) are now deploying their first operational systems, which could pave the way for later commercial suppliers and, in future years, revolutionize communication both across the globe and across the solar system. Although the first laser communication systems were demonstrated in space in the 1990s, it is only recently that the technology, reliability and economics of photonic components have combined with the need for more bandwidth to push these systems more broadly into operation.

The potential for the laser to overcome these issues in space was realized soon after its invention, although its special properties introduced new issues, such as the pointing and tracking of narrow beams over great distances while overcoming cloud cover, turbulence and other hurdles introduced by the atmosphere.

These links rely on radio-frequency (RF) communications, which, while reliable, are orders of magnitude slower in moving data than optical fiber links, and have issues related to antenna footprint, power requirements and limited available spectrum. But for the majority of Earth’s surface, where running fiber is impractical physically or financially, communication satellites in space provide connectivity-to remote ground users and also to mobile platforms such as aircraft, ships and even other satellites. Laser communications through optical fibers move tens of terabits of data every second between cities and across oceans. Posted May 02, 2016 by GoPhotonics Editorial Team

Freespace optical communication