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New technology uses lasers to transmit audible messages to specific people
by Staff Writers
Washington DC (SPX) Jan 24, 2019

Ryan M. Sullenberger and Charles M. Wynn developed a way to use eye- and skin-safe laser light to transmit a highly targeted audible message to a person without any type of receiver equipment.

Researchers have demonstrated that a laser can transmit an audible message to a person without any type of receiver equipment. The ability to send highly targeted audio signals over the air could be used to communicate across noisy rooms or warn individuals of a dangerous situation such as an active shooter.

In The Optical Society (OSA) journal Optics Letters, researchers from the Massachusetts Institute of Technology's Lincoln Laboratory report using two different laser-based methods to transmit various tones, music and recorded speech at a conversational volume.

"Our system can be used from some distance away to beam information directly to someone's ear," said research team leader Charles M. Wynn. "It is the first system that uses lasers that are fully safe for the eyes and skin to localize an audible signal to a particular person in any setting."

Creating sound from air
The new approaches are based on the photoacoustic effect, which occurs when a material forms sound waves after absorbing light. In this case, the researchers used water vapor in the air to absorb light and create sound.

"This can work even in relatively dry conditions because there is almost always a little water in the air, especially around people," said Wynn. "We found that we don't need a lot of water if we use a laser wavelength that is very strongly absorbed by water. This was key because the stronger absorption leads to more sound."

One of the new sound transmission methods grew from a technique called dynamic photoacoustic spectroscopy (DPAS), which the researchers previously developed for chemical detection. In the earlier work, they discovered that scanning, or sweeping, a laser beam at the speed of sound could improve chemical detection.

"The speed of sound is a very special speed at which to work," said Ryan M. Sullenberger, first author of the paper. "In this new paper, we show that sweeping a laser beam at the speed of sound at a wavelength absorbed by water can be used as an efficient way to create sound."

For the DPAS-related approach, the researchers change the length of the laser sweeps to encode different frequencies, or audible pitches, in the light. One unique aspect of this laser sweeping technique is that the signal can only be heard at a certain distance from the transmitter. This means that a message could be sent to an individual, rather than everyone who crosses the beam of light. It also opens the possibility of targeting a message to multiple individuals.

Laboratory tests
In the lab, the researchers showed that commercially available equipment could transmit sound to a person more than 2.5 meters away at 60 decibels using the laser sweeping technique. They believe that the system could be easily scaled up to longer distances. They also tested a traditional photoacoustic method that doesn't require sweeping the laser and encodes the audio message by modulating the power of the laser beam.

"There are tradeoffs between the two techniques," said Sullenberger. "The traditional photoacoustics method provides sound with higher fidelity, whereas the laser sweeping provides sound with louder audio."

Next, the researchers plan to demonstrate the methods outdoors at longer ranges. "We hope that this will eventually become a commercial technology," said Sullenberger. "There are a lot of exciting possibilities, and we want to develop the communication technology in ways that are useful."

Research Report: "Photoacoustic communications: delivering audible signals via absorption of light by atmospheric H2O,"


Related Links
The Optical Society
Space Technology News - Applications and Research


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TECH SPACE
Raytheon contracts Elbit Systems for Two Color Laser System
Washington (UPI) Jan 4, 2019
Raytheon has been awarded a contract to Elbit Systems of America for the Two Color Laser System, a surveillance system element onboard military aircraft. Financial terms of the deal were not disclosed in a news release on Elbit Systems' website, but the U.S. subsidiary of the Israeli company said the contract would be carried out in 2019. The Two Color Laser System serves the Multi-Spectral Targeting System, Elbit Systems said. The system, also known as the TCLS, has smaller size, weight ... read more

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