Nonlinear metasurfaces have experienced rapid growth recently due to their potential in various applications, including infrared imaging and spectroscopy. However, due to the low conversion efficiencies of metasurfaces, several strategies have been adopted to enhance their performances, including employing resonances at signal or nonlinear emission wavelengths. This strategy results in a narrow operational band of the nonlinear metasurfaces, which has bottlenecked many applications, including nonlinear holography, image encoding, and nonlinear metalenses. Here, we overcome this issue by introducing a new nonlinear imaging platform utilizing a pump beam to enhance signal conversion through four-wave mixing (FWM), whereby the metasurface is resonant at the pump wavelength rather than the signal or nonlinear emissions. As a result, we demonstrate broadband nonlinear imaging for arbitrary objects using metasurfaces. A silicon disk-on-slab metasurface is introduced with an excitable guided-mode resonance at the pump wavelength. This enabled direct conversion of a broad IR image ranging from >1000 to 4000 nm into visible. Importantly, adopting FWM substantially reduces the dependence on high-power signal inputs or resonant features at the signal beam of nonlinear imaging by utilizing the quadratic relationship between the pump beam intensity and the signal conversion efficiency. Our results, therefore, unlock the potential for broadband infrared imaging capabilities with metasurfaces, making a promising advancement for next-generation all-optical infrared imaging techniques with chip-scale photonic devices.

非线性超表面由于其在红外成像和光谱学等各种应用中的潜力，最近经历了快速增长。然而，由于超表面的转换效率较低，因此采用了多种策略来增强其性能，包括在信号或非线性发射波长处采用共振。这种策略导致非线性超表面的操作频带很窄，这成为许多应用的瓶颈，包括非线性全息、图像编码和非线性超透镜。在这里，我们通过引入一种新的非线性成像平台来克服这个问题，该平台利用泵浦光束通过四波混频（FWM）增强信号转换，从而超表面在泵浦波长而不是信号或非线性发射处谐振。因此，我们展示了使用超表面对任意物体进行宽带非线性成像。引入了硅盘板超表面，在泵浦波长处具有可激发的导模谐振。这使得能够将范围从 >1000 到 4000 nm 的宽红外图像直接转换为可见光。重要的是，采用FWM利用泵浦光束强度与信号转换效率之间的二次关系，大大减少了非线性成像对高功率信号输入或信号光束谐振特征的依赖。因此，我们的研究结果释放了超表面宽带红外成像能力的潜力，为具有芯片级光子器件的下一代全光学红外成像技术带来了有希望的进步。