Subarray programmable terahertz metasurface for optical logic and high-order amplitude modulation

Integrated terahertz (THz) communication-sensing-computing systems require reconfigurable platforms that can simultaneously support logic operations and signal modulation. Here, we propose a subarray programmable THz metasurface that elevates the subarray to the minimum addressable unit. Within each subarray, a high electron mobility transistor (HEMT) serves as the active material; collective resonance tuning of the two-dimensional electron gas (2DEG) enables broadband control of array-level resonances and transmission amplitude. Using spatial domain combinatorial coding across subarrays, the device maps Boolean logic over a wide bandwidth and directly realizes four-level pulse amplitude modulation (PAM-4) at the wavefront. In a 220 GHz quasi-optical link, dynamic measurements demonstrate real-time Boolean functions up to 200 MHz and stable PAM-4, while a single-tone modulation reaches 6 GHz. This subarray-level gating strategy integrates optical logic and high-order amplitude modulation on the same hardware without increasing addressing complexity, providing a scalable route to compact, reconfigurable THz front ends for future communications and intelligent sensing.