Engineers have long focused their efforts on confining signal-carrying photons to chips. Every photon that escapes, they reasoned, is information lost. But one group of researchers has stood that paradigm on its head.
By deliberately “leaking” photons into the air, they created, not the feared amorphous blob of light, but a super-antenna—one that broadcasts data through a spherical radiation field at rates roughly 100× faster than home Wi-Fi.
“The idea behind this work grew out of a very practical question: how can we get terahertz signals off a chip and into open space in a simple, efficient way?” said Ranjan Singh, professor of electrical engineering at the University of Notre Dame. “Existing approaches usually rely on bulky external components or carefully shaped tapers to guide the signal outward, which adds complexity and limits real-world use, especially when trying to send signals straight up from a chip.”
The research, published in Nature Photonics, was led by Singh with Wenhao Wang, an assistant professor at Westlake University and the paper’s first author. The project was a collaboration between the University of Notre Dame, Nanyang Technological University in Singapore, and the University of Lille in France.
Terahertz waves are ideal for both communication and sensing: they can carry huge amounts of data, and their short wavelengths allow them to pick up on details longer waves miss. In short, they can “see” at high resolution and “talk” at very rapid rates. However, terahertz waves have proven finicky and difficult to control.
Singh’s lab had the innovative idea of controlling the terahertz waves through geometry. They etched a silicon chip with rows of tiny triangular holes—one large and one small in each repeating unit. By changing the arrangement of these triangles, the researchers controlled the behavior of the terahertz light, allowing it to be trapped in some areas and leak into free space in others.
The light that escaped through the triangular holes—referred to as a “leaky wave”—organized itself into a cone-shaped beam. Resembling a megaphone in both its form and function, it concentrated and strengthened electromagnetic signals. Rather than create a standard antenna’s narrow, one-directional beam, the team used another pattern of triangular holes to create a near sphere of usable signal.
“Many previous terahertz systems work only by adding layers of complexity, large antenna arrays, mechanical beam steering, or highly customized components,” said Singh. “What makes this work different is that it achieves wide coverage, high speed, and multi-link capability without making the system more complicated.”
The chip can also handle multiple wireless links at once, sending different terahertz signals in different directions at very high data rates (20+ gigabits per second per link). Even more impressively, the same chip can send and receive signals at the same time, supporting uncompressed HD video streaming and ultra-fast data transmission.
Overall, this work shows a powerful new way to build compact, steerable, high-speed terahertz systems on a chip. These ideas could play an important role in future technologies—from 6G wireless networks, to terahertz Wi-Fi, remote sensing, and advanced detection and ranging systems.
Funding for the research came from Singapore’s National Research Foundation and France’s Agence Nationale de la Recherche.
—Karla Cruise, Notre Dame Engineering