Researchers at MIT's Lincoln Laboratory apparently managed to find a way to send secret messages directly into a person's ear sans the need for the recipient to use a special communication equipment.
An operator simply has to point a laser at someone from a distance. That person hears the transmitted audio but others in the same area do not.
They developed laser systems that can transmit tones, music, and recorded speech at a conversational volume to specific people who do not need to wear any special equipment.
How It Works
In a study published in the journal Optics Letters on Friday, the researchers described two different methods to transmit audio messages through a laser.
Both use the so-called photoacoustic effect, which occurs when sound waves are formed as a result of a material absorbing light. Researchers used water vapor in the air as the material.
"A laser transmits the message, which is encoded upon a modulated laser beam and sent directly to the receiver's ear via the photoacoustic effect," the researchers wrote in their study.
One of the methods involve sweeping a laser beam at the speed of sound and changing the length of the sweeps to encode different audible pitches.
This technique can transmit sound to a person more than 8.2 feet away at 60 decibels, the volume of background music or conversation in restaurants. The recipient of the message can hear the sound without anyone else hearing it.
The researchers are working on improving the method so it could work over longer distances.
The other method involves encoding audio message by adjusting the power of the laser beam. Researchers said this produces quieter but clearer results.
The technology may provide a new way for people to communicate secretly. Audio messages may be exchanged across a crowded place without other people hearing them.
Once transmission distance is scaled up, the technology may have important military applications. It may help soldiers exchange covert messages in the battlefield. It can also be used in dangerous situations such as during a mass shooting, when specific people can be covertly warned of an active shooter.