Infrared imaging technology is pivotal for various applications including medical diagnostics, food quality control, and environmental monitoring. However, the efficiency of current IR detection methods, such as thermal and semiconductor detectors is hampered by their slow response, low sensitivity, or need for complex handling. Nonlinear nanostructures and metasurfaces offer a promising alternative by converting infrared light into visible light via frequency conversion process [1]. Nowadays silicon photonics has been widely developed with compact size, excellent uniformity, high quality, potentially lower cost and COMS compatibility. Meanwhile, silicon offers superior third-order nonlinearity for converting an IR signal photon to visible by mixing two pump photons based on four-wave mixing (FWM) [2-5]. Here, I will review our recent work on the development of upconversion infrared imaging based on silicon nanostructures and metasurfaces. By choosing the frequency of the two pump photons, upconversion imaging based on FWM can be extended to a broad range of IR spectral region. The adoption of FWM substantially reduces the dependence on high-power signal inputs or resonant features at signal beam of nonlinear imaging by utilising the quadratic relationship between the pump beam intensity and the signal conversion efficiency. Furthermore, by manipulating the nonlinear emission in the Fourier space, we demonstrate the possibility of using nonlinear silicon metasurfaces to retrieve nonlinear signals in the momentum domain to improve the sensitivity and resolution, and generate complex optical functions, such as edge detection, differentiation, image compression, etc.

1. R. Camacho-Morales, et al, Advanced Photonics 3 (3), 036002 (2021)
2.  L. Xu, et al, New Journal of Physics 24 (3), 035002 (2022)
3. Z. Zheng, et al, Opto-Electron. Adv 6 (8), 220174 (2023)
4. G. Sanderson, et al, J. Opt. Accepted
5. Z. Zheng, et al, Light Sci. Appl. Under revision