# High-efficiency infrared upconversion imaging with nonlinear silicon metasurfaces empowered by quasi-bound states in the continuum

## TL;DR

This paper demonstrates high-efficiency infrared to visible upconversion imaging using silicon metasurfaces with quasi-bound states in the continuum, enabling high-resolution thermal imaging with enhanced nonlinear conversion.

## Contribution

It introduces a novel silicon metasurface design supporting high-Q resonances for efficient third-harmonic generation, advancing infrared imaging technology.

## Key findings

- Achieved a third-harmonic generation efficiency of 3×10^{-5} at 10 GW/cm^2
- Enabled high-fidelity infrared image upconversion with ~6 μm resolution
- Demonstrated CMOS-compatible metasurfaces for practical infrared sensing

## Abstract

Infrared imaging is indispensable for its ability to penetrate obscurants and visualize thermal signatures, yet its practical use is hindered by the intrinsic limitations of conventional detectors. Nonlinear upconversion, which converts infrared light into the visible band, offers a promising pathway to address these challenges. Here, we demonstrate high-efficiency infrared upconversion imaging using nonlinear silicon metasurfaces. By strategically breaking in-plane symmetry, the metasurface supports a high-$Q$ quasi-bound states in the continuum resonance, leading to strongly enhanced third-harmonic generation (THG) with a conversion efficiency of $3\times10^{-5}$ at a pump intensity of 10 GW/cm$^{2}$. Through this THG process, the metasurface enables high-fidelity upconversion of arbitrary infrared images into the visible range, achieving a spatial resolution of $\sim 6$ $\upmu$m as verified using a resolution target and various customized patterns. This work establishes a robust platform for efficient nonlinear conversion and imaging, highlighting the potential of CMOS-compatible silicon metasurfaces for high-performance infrared sensing applications with reduced system complexity.