'Curving' light beams could enable terahertz comms

Scientists know that in the near future they’ll need to transition to much higher communication frequencies than what current systems rely on, but before that can happen there are a number of quite literal obstacles standing in the way. Now, researchers from Brown University and Rice University say they’ve come one step closer to getting around these solid obstacles, including walls, furniture and even people.

Current systems rely on microwave radiation to carry data, but it’s become clear that the future standard for transmitting data will make use of terahertz waves, which have as much as 100 times the data-carrying capacity of microwaves. One longstanding issue has been that, unlike microwaves, terahertz signals can be blocked by most solid objects, making a direct line of sight between transmitter and receiver a logistical requirement.

“Most people probably use a Wi-Fi base station that fills the room with wireless signals,” said Daniel Mittleman, a professor in Brown’s School of Engineering. “No matter where they move, they maintain the link.

“At the higher frequencies that we’re talking about here, you won’t be able to do that anymore. Instead, it’s going to be a directional beam. If you move around, that beam is going to have to follow you in order to maintain the link, and if you move outside of the beam or something blocks that link, then you’re not getting any signal.”

In the new study, Mittleman and his colleagues introduced the concept of self-accelerating beams. These are special configurations of electromagnetic waves that naturally bend or curve to one side as they move through space. The beams have previously been studied at optical frequencies but are now being explored for terahertz communication.

Using this idea as a jumping off point, the researchers engineered transmitters with carefully designed patterns so that the system can manipulate the strength, intensity and timing of the electromagnetic waves that are produced. With this ability to manipulate the light, the researchers make the waves work together more effectively to maintain the signal when a solid object blocks a portion of the beam.

Essentially, the light beam adjusts to the blockage by shuffling data along the patterns the researchers engineered into the transmitter. When one pattern is blocked, the data transfers to the next one, and then the next one if that is blocked. This keeps the signal link fully intact. Without this level of control, when the beam is blocked, the system can’t make any adjustments, so no signal gets through.

This effectively makes the signal bend around objects as long as the transmitter is not completely blocked. If it is completely blocked, another way of getting the data to the receiver will be needed.

“Curving a beam doesn’t solve all possible blockage problems, but what it does is solve some of them and it solves them in a way that’s better than what others have tried,” said Hichem Guerboukha, who led the study as a postdoctoral researcher at Brown and is now an assistant professor at the University of Missouri–Kansas City.

The researchers validated their findings through extensive simulations and experiments navigating around obstacles to maintain communication links with high reliability and integrity, with their results published in the journal Communications Engineering. The work builds on a previous study from the team that showed terahertz data links can be bounced off walls in a room without dropping too much data.

“This is the world’s first curved data link; a critical milestone in realising the 6G vision of high data rate and high reliability,” said Edward Knightly, a professor of electrical and computer engineering at Rice University.

By using these curved beams, the researchers hope to one day make wireless networks more reliable, even in crowded or obstructed environments. This could lead to faster and more stable internet connections in places like offices or cities where obstacles are common. Before getting to that point, however, there’s much more basic research to be done and plenty of challenges to overcome as terahertz communication technology is still in its infancy.

“One of the key questions that everybody asks us is how much can you curve and how far away,” Mittleman said. “We’ve done rough estimations of these things, but we haven’t really quantified it yet, so we hope to map it out.”

Illustration by the Mittleman Group.