UCLA engineers shrink powerful terahertz systems onto a single semiconductor chip

High-frequency waves classified as terahertz occupy a relatively underused region of the electromagnetic spectrum between infrared light and microwaves. Researchers have long recognized its unique potential for applications including ultrafast wireless communication, security screening, remote sensing and medical imaging.

As technologies push toward higher operating frequencies and data rates, photonics-based terahertz systems, which use light at superspeed to generate and process terahertz signals, have emerged as a promising alternative to conventional electronic technologies because of their superior bandwidth and power efficiency. However, today's terahertz optoelectronic systems, which are electronic systems that control light, remain bulky, complex and difficult to scale for widespread use. They typically rely on multiple separate components - including lasers, amplifiers, modulators, sources and detectors - that must be individually made, aligned and interconnected, limiting use outside specialized laboratory settings.

Now, a UCLA-led research team has demonstrated a way to integrate these functions onto a single semiconductor chip compatible with modern photonic technologies. The breakthrough, published in Nature Communications, paves the way for compact, scalable terahertz systems for next-generation communication, imaging and sensing applications.

By adapting terahertz generation and detection to be compatible with photonic integrated circuits, the researchers from the UCLA Samueli School of Engineering demonstrate a path toward shrinking laboratory-scale terahertz systems into compact, mass-producible chips - much like electronic integrated circuits transformed computers from refrigerator-sized machines into modern microprocessors.

"Terahertz optoelectronic systems have been bulky, expensive, power-hungry and difficult to scale for widespread use," said study leader Mona Jarrahi, a professor of electrical and computer engineering and holder of UCLA Samueli's Northrop Grumman Chair in Electrical Engineering. "By demonstrating that many of these functions can be integrated onto a single chip using proven industry-standard fabrication platforms, our study opens the door to practical, scalable terahertz technologies for real-world applications."

Earlier approaches to single-chip optoelectronic terahertz systems primarily relied on specialized materials and fabrication techniques incompatible with standard photonic chip technology.

The team's breakthrough focused instead on quantum well semiconductor structures - extremely thin layers of material engineered to control light - tailored to simultaneously generate, detect, modulate and amplify terahertz signals on a single shared chip platform.

Quantum wells are already widely used in photonic integrated circuits. The researchers' key innovation was demonstrating that these structures could also support terahertz signal generation and detection through a process called gain-enhanced interband photomixing, in which two laser beams combine to generate signals at a desired wavelength.

Using quantum well substrates in photonic integrated circuits, the team demonstrated highly efficient terahertz generation and highly sensitive terahertz detection relative to existing photomixer-based, or light interference-based, terahertz technologies.

At UCLA, Jarrahi is also a member of the California NanoSystems Institute and faculty director of the Semiconductor Hub at UCLA Samueli, a $125 million, industry-backed initiative that aims to accelerate research and workforce development in AI-powered chip technologies.

Other authors on the paper include UCLA electrical and computer engineering doctoral students Yifan Zhao, Shahid-E-Zumrat and Szu-An Tsao - all members of Jarrahi's research group, the Terahertz Electronics Lab. The study was funded by the U.S. Office of Naval Research, the U.S. Department of Energy and the Institution of Engineering and Technology Harvey Prize.