Terahertz technology is widely regarded as a key enabler for sixth-generation wireless systems and future integrated sensing, communication, and computing platforms. Compared with microwave and millimeter-wave bands, the terahertz band offers much broader bandwidth and finer spatial resolution. These features make it attractive for high-speed wireless links, intelligent sensing, and compact front-end processors. However, terahertz hardware still faces a difficult challenge: it must be fast, broadband, programmable, and simple enough to be integrated into practical systems.
Programmable metasurfaces provide a powerful way to control electromagnetic waves in real time. By changing the state of many subwavelength elements, they can reshape the amplitude, phase, and polarization of incident waves. Existing terahertz programmable metasurfaces usually follow two routes. One route is pixel-level addressing, which offers high spatial freedom but requires complex wiring, power distribution, and timing control as the array becomes larger. The other route is uniform aperture driving, which is easier to implement but provides only limited control freedom and is usually restricted to binary or low-order modulation.
In a new paper published in Light: Science & Applications , a team of scientists led by Professor Lan Wang and Yaxin Zhang from the University of Electronic Science and Technology of China, Professor Taiichi Otsuji from ENSEMBLE3 Center of Excellence, and co-workers have developed a subarray programmable terahertz metasurface for optical logic and high-order amplitude modulation. Instead of controlling each pixel independently or driving the whole aperture as one unit, the team elevates the subarray to the minimum addressable unit. This architecture provides a practical balance between control freedom and engineering complexity.
The metasurface consists of four independently gated subarrays. Each subarray is composed of periodically arranged AlGaN/GaN high electron mobility transistor meta-atoms. When a gate voltage is applied, the carrier density of the two-dimensional electron gas inside the transistor channel is changed. This process tunes the collective resonance of the subarray and therefore controls the transmission amplitude of terahertz waves. In this way, the device achieves broadband transmission modulation from 170 to 260 GHz.
The most important feature of the device is not only that it modulates terahertz waves, but also that it can process information directly at the wavefront. By treating two subarrays as logical inputs and using the remaining subarrays as functional selectors, the metasurface can realize programmable Boolean operations, including AND, OR, and XNOR. Dynamic measurements in a 220 GHz quasi-optical link show real-time Boolean logic operation up to 200 MHz. This means that part of the decision-making process can be moved from the electronic back end to the terahertz front end itself.
The same subarray coding strategy also enables high-order signal modulation. The four subarrays can be divided into two groups and driven by two independent square-wave signals. The weighted transmission contributions from these two groups generate four distinct amplitude levels, realizing PAM-4 directly at the terahertz wavefront. In the 220 GHz quasi-optical link, the team demonstrated stable PAM-4 waveforms and a single-tone modulation response up to 6 GHz.
The scientists summarize the key idea of their work:
“We use the subarray, rather than the individual pixel or the whole aperture, as the basic programmable unit. This gives the metasurface enough degrees of freedom to perform logic operations and high-order modulation, while avoiding the heavy control complexity of pixel-level addressing.”
They further explain:
“The demonstrated platform shows that terahertz metasurfaces can evolve from passive wave-control devices into compact front-end processors. Such devices may support future wireless systems in which communication, sensing, and computing are handled by the same reconfigurable hardware.”
The reported technique opens a promising route toward compact and programmable terahertz front ends. By combining semiconductor active materials, subarray-level coding, and wavefront-level signal processing, the device may provide useful building blocks for future 6G systems, intelligent sensing, short-range high-speed wireless links, and integrated terahertz communication-computing platforms. Further improvements in packaging, parasitic reduction, and driving circuits may push the modulation speed and multilevel coding capability even higher.
Light: Science & Applications
Subarray programmable terahertz metasurface for optical logic and high-order amplitude modulation