Shortwave Infrared Upconversion Imaging with Tunable Dual-Resonance Microcavity

Shortwave infrared (SWIR) imaging is widely employed in light detection and ranging, biomedical imaging, industrial inspection, and night vision. However, current InGaAs-based SWIR cameras remain expensive due to their complex fabrication and cooling requirements. Here, we report a cost-effective alternative using a standard silicon camera, augmented by upconversion from NaYF₄:Er@NaYF₄ core-shell nanoparticles in a tunable, dual-resonance Fabry-Pérot cavity. A spatially varying cavity length allows spectral tunability, and the dual-resonance design enhances infrared absorption and visible emission simultaneously, resulting in up to 10⁴-fold increase in upconversion intensity over a broad range of excitation wavelengths (1530-1570 nm). This enhancement enables imaging at 1550 nm with sub-10 μm spatial resolution, comparable to InGaAs-based systems, but at a significantly lower cost. We further demonstrate the potential of this platform for silicon wafer alignment and low-visibility imaging. This work introduces a scalable, cost-effective approach for SWIR imaging by leveraging mature silicon technologies and cavity-enhanced photon upconversion.