How Laser Communication Works

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:

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.

Laser communications may be a boon for space exploration, but far more earthly pursuits will determine its fate as a commercial technology.

Take, for example, Wall Street's emerging breed of high-speed traders who leverage the power of quantitative analysis, the speed of premium broadband and a multiplicity of microtransactions to pile up earnings one fractional penny at a time. For a business built on "robo-traders," computer algorithms making millisecond trades according to a set of rules, transmission time is money, and lasers are the fastest game in town [sources: Adler; CBS News; Strasburg].

To squeeze the most out of each trade, companies like Spread Networks invested in the best available fiber and cut every kink and curve they could from the data hoses connecting trade capitals like Chicago, New York, London and Tokyo (each extra mile adds about eight microseconds to data round-trips). When that wasn't fast enough, others groups, like McKay Brothers and Tradeworx, cast fiber optics aside in favor of microwaves beamed through the air. Though only a step above radio in terms of power and speed, microwaves travel faster through air than light passes through fiber optics [sources: Adler; Strasburg].

Lasers would potentially post the fastest speeds of all; the speed of light through air is nearly as fast as in a vacuum, and could traverse the 720 miles (1,160 kilometers) separating New York and Chicago in about 3.9 milliseconds -- a round-trip (aka latency) of 7.8 milliseconds, compared to 13.0-14.5 milliseconds for new fiber optic systems and 8.5-9.0 milliseconds for microwave transmitters [source: Adler].

In the security sphere, lasers and other optical communications systems offer more secure communications -- and the means to eavesdrop on them. Quantum cryptography takes advantage of a property of quantum physics -- namely, that a third party cannot detect the quantum state of the photonic encryption key without altering it and, therefore, being detected -- to establish highly secure communications using beams of photons created by attenuated lasers [sources: Grant; Waks et al.]. In fall of 2008, researchers in Vienna began experimenting with a quantum Internet based in part on this principle [source: Castelvecchi]. Unfortunately, lasers have also been used to intercept and spoof such signals in a non-quantum way, thereby circumventing detection. Quantum encryption companies are working to address the problem [sources: Dillow; Lydersen et al.].

In fact, the main drawbacks to laser communications within the atmosphere have to do with interference by rain, fog or pollutants, but given the technology's advantages, these issues are unlikely to stop the forward progress of the technology. So, literally or figuratively, the sky is the limit for laser communications technologies.