MIT Creates Lasers That Whisper in Your Ear

How do you whisper to someone across the room? With lasers, of course. MIT has developed a system using lasers to transmit audio signals directly to the ear, and no one else in the area can hear them. As a nice bonus, the laser won’t burn your skin or eyes should you turn your head at the wrong moment.

The laser system leverages what is known as the photoacoustic effect. That simply means that the absorption of light waves by a material produces sound waves. In this case, the light is absorbed by water molecules in the air, but the researchers learned to very carefully tune the laser to control where the sound appears. It’s essentially a narrow cone of sound.

Making sound with a laser is one thing, but creating specific tones or transmitting a message is much harder. The team evaluated two methods for doing this. First, there’s the laser sweeping technique, which involves altering the wavelength of light to create different sounds. The traditional photoacoustic method uses varying power to encode a message.

Both approaches have their strengths. The laser sweeping technique is the most impressive demonstration of the technology. It can transmit sound up to 2.5 meters away at 60 decibels. That’s equivalent to background noise in a busy restaurant. The photoacoustic approach isn’t as loud, so it won’t work as far away. However, it can produce sound with much higher fidelity.

Currently, this is a fun tech demo. If you need to speak to someone far away, we have these devices called “phones” that make it very easy. However, there might be cases in which such technology is useful. Perhaps you don’t have someone’s phone number, but you want to relay some information quietly. They can’t reply, though. This is a one-way communication system — it’s unlikely the person you’re whispering to has their own talking laser.

It’s also possible this technology could evolve into a warning system that alerts people to danger when they’re out of earshot. The latter application will require more work to extend the range and eliminate interference. The MIT researchers are planning to develop methods to extend the range of the lasers in outdoor settings to make that a reality. The team is shooting for 100 to 500 meters. Success could make this technology a viable commercial product.