Enhanced Continuous‐Wave Mid‐Infrared Frequency‐Upconversion Imaging Based on Quasi‐Guided‐Mode Metasurfaces

Nonlinear metasurfaces provide a powerful platform for tailored light generation and frequency manipulation. However, nonlocal metasurfaces supporting high‐quality (Q) factor guided‐mode resonances have been recently explored to enhance nonlinear effects, while simultaneously achieving efficient continuous‐wave (CW) operation and flexible spectral degrees of freedom in parametric frequency upconversion under low‐threshold or weak‐light regimes remains a longstanding challenge. Here, we extend the powerful features of nonlocal metasurfaces to CW nonlinear phenomena, demonstrating sum‐frequency generation (SFG)‐based upconversion imaging of a CW 4330 nm mid‐infrared (MIR) signal utilizing a quasi‐guided‐modes (QGMs)‐engineered thin‐film lithium niobate (TFLN) metasurface. Driven by the stable high‐Q characteristics of Brillouin zone folding across a wide wavevector range, this metasurface successfully achieves imaging under low‐intensity illumination. Furthermore, near‐infrared pump wavelength tuning experimentally demonstrates dynamic resonance matching, while theoretical dispersion analysis and broadband simulations reveal the potential for spectrally tunable MIR upconversion, offering a viable pathway for integrated, continuous‐wave infrared detection systems.