Free-Space Optical Communication
Free-space optical communication promises speed, but is difficult to harness, as Chris Edwards discovers.
When NASA dispatched a probe in 2012 to collect data on the rarefied dust and gas cloud around the Moon, the space agency decided on a change in how it would relay the data over 400,000km back to Earth.
Instead of using radio-frequency (RF) transmissions, the team opted to modulate information onto light beams. Telescopes on the ground looked for the blinking signals.
The telescopes coupled the infrared light with a wavelength chosen for its compatibility with telecom networks into fibres to be decoded by electro-optic receivers.
The Lunar Laser Communication Demonstration (LLCD) set a downlink speed record of more than 600Mbit/s, with speeds hitting 20Mbit/s going the other way.
Data rates have spiralled upward since in experiments by a variety of space agencies. In 2023, NASA’s TeraByte Infrared Delivery (TBIRD) delivered 200Gbit/s from low-Earth orbit to ground using light.
Author summary: NASA explores free-space optical communication for faster data transfer.