Aliasing-enabled frequency translation and signal fusion via guided mode resonance in terahertz systems

In terahertz (THz) time-domain spectroscopy, the digital Nyquist limit set by the temporal sampling interval of the recorded waveform can hinder efficient acquisition of high-frequency narrowband resonant features, in addition to the finite analog bandwidth of conventional detectors. Here, we present a THz measurement and sensing framework that intentionally exploits aliasing by combining guided mode resonance (GMR) structures with down-sampling (DS). In this approach, a broadband THz pulse is first converted into a narrowband, long-lived oscillation at a resonance frequency by a GMR structure, which acts as a spectral encoder. Subsequent DS induces controlled aliasing, allowing the encoded high-frequency information to be folded into the low-frequency domain, where it can be recovered within the available digital sampling range. We experimentally verify that the aliased frequency follows a deterministic folding relation in the single-resonance case, demonstrating controllable frequency translation under intentional sub-Nyquist sampling. In a dual-resonance configuration, two distinct resonances are merged into a single low-frequency response, establishing aliasing as a signal fusion mechanism. Graphene-integrated GMR structures further confirm that material-dependent resonance variations are preserved after aliasing, validating the framework for practical sensing. These results establish intentional sub-Nyquist (bandpass) sampling of GMR-encoded resonances as a controllable measurement resource, relaxing the digital sampling-rate requirement for accessing high-frequency narrowband features and providing a scalable strategy for THz spectroscopy and sensing.