How Laser Communication Works

The Next Best Thing to Being There

The goal of communications technologies is to convey information quickly, completely and accurately. If you've ever had dinner with a boor, then you know how little information a wall of noise can contain; if you've ever played the game telephone, you've experienced how meaning can be mangled when poorly relayed.

Historically, long-distance communications have multiplied these difficulties. Transmission -- by drum, bonfire, smoke, flag or light -- first required translation into a necessarily simple code. Telegraph cables and Morse code made complex transmission possible but expensive, again enforcing the virtue of brevity.

Modern electronic communication requires a sending device that can encode any data into a transmittable form and a receiver that can distinguish between the message (signal) and its surrounding line static (noise). Information theory, a mathematical model pioneered by U.S. engineer Claude Shannon in 1948, provided the framework that ultimately solved this problem and made technologies like the cell phone, the Internet and the modem possible [source: National Geographic].

In principle, laser communication systems resemble the modems that we have used in our homes since the rise of the Internet. Modem stands for MODulation-DEModulation, a process in which digital information is converted to analog for transmission, then back again. Early acoustic modems used sound waves for transmission over phone lines. Optical modems move from sound to a higher-frequency part of the spectrum, light.

It's not an entirely novel concept. Audiovisual devices with optical audio, such as many DVD players, use a modem-like device called a transmission module to convert digital signals to LED or laser light, which then travels along fiber optic cable to a destination component such as a television or audio receiver. There a light reception module converts the light back into a digital electrical signal suitable for speakers or headphones.

NASA's proof-of-concept Lunar Laser Communication Demonstration (LLCD), developed by MIT's Lincoln Laboratory, uses a similar system, but dispenses with the fiber in favor of laser transmission through air and space (sometimes called free-space optical communication, or FSO). LLCD uses three components:

  1. A modem module (MM)
  2. An optical module (OM), which sends and receives modulated laser beams via a 4-inch (10-centimeter) telescope
  3. A controller electronics (CE) module that ties the first two together. The CE also ties the LLCD to the orbiter, NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE), and performs vital tasks like sequencing, stabilization, and relaying commands and telemetry [sources: Britannica; NASA; NASA].

With the experiment's success, the future of laser communications just got a bit brighter, but is there a market for such technology outside of the space agency? You bet there is.