Mid-infrared detectors which converter the detected mid-infrared light to the near infrared (NIR) or even visible are of significant interest in free-space communication. Hongjun Liu’s research team demonstrate a high-performance frequency upconversion from 3.4 mu m to 1.064 mu m pumped by 1.55 mu m in gradient metasurface-assisted thin-film lithium niobate waveguide. Based on this new structure of nonlinear waveguide, the phase-matching condition can be free in on-chip frequency conversion and the power of idler can be 24.5 times as high as that of no metasurface waveguide. The efficient upconversion is realized within a wide signal wavelength range from 3.25 mu m to 3.50 mu m. This study is helpful for obtaining the precise and integrated mid-infrared detectors.

（Original research article "Journal of Physics D: Applied Physics Vol. 52, Issue 3, 035101 (2019) https://iopscience.iop.org/article/10.1088/1361-6463/aaebe7"）