Researchers at the Massachusetts Institute of Technology have developed a way to encrypt and transmit sound using a laser beam directly to a person's ear - so that only the person can hear the message.
Scientists have figured out how to use a laser to transmit sound - be it music or speech - to a person at the opposite end of the room, without any receiving equipment. The development, described in Optics Letters, represents a potential breakthrough for the future of audio and communications equipment.
“Our system can be used at some distance to transmit information directly to the human ear,” says Charles M. Wynn, a researcher at the Massachusetts Institute of Technology (MIT). "This is the first system to use lasers that are absolutely safe for eyes and skin to localize the sound signal to a specific person in any environment."
In their work, the MIT team describes the process of creating two different ways of transmitting tones, music and recorded speech using a laser.
Both techniques are based on the so-called photoacoustic effect - the formation of sound waves as a result of the absorption of light by a material. In the case of MIT research, this material was water vapor in air.
For one method developed, the researchers "scanned" a laser beam at the speed of sound, changing the length of the sweeps to encrypt the different audible pitches of sound.
This technique allowed them to transmit sound to a person more than two meters away at a volume of 60 decibels - about this level the music in a restaurant plays. There was no interference between the sound source and the target.
For another method, specialists encrypted the audio message by changing the power of the laser beam. Scientists say this technique has helped produce a quieter yet clearer sound.
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While the idea of using a laser to send a message to a friend through a room filled with people sounds tempting, the MIT team has much more important plans for this technology.
They are confident that further research will increase the transmission distance, which could make this technique useful in dangerous situations such as mass shooting: for example, the authorities could transmit instructions directly to people so that no one else can hear them.
“We hope this will eventually become an industrial technology,” says Ryan M. Schullenberger. "There are many exciting opportunities, and we want to develop communications technology that is useful."
Vladimir Guillen