After removing the Hg1-xCdxTe infrared focal plane device substrate, the response bandwidth can be extended to the visible light band, which can significantly reduce the size and weight of the system in the application of hyperspectral imaging, and miniaturize the photoelectric detection system. Miniaturization has important practical value. The determination of the optical constants of HgCdTe materials in the visible near-infrared region is of great significance for the performance of HgCdTe devices in this response band. The ellipsometric spectra of different compositions of HgCdTe materials were measured and their optical constants in the band from 400 to 1600 nm were fitted. The obtained optical constants were verified by using the reflectance spectra. Using these measured values, and using ZnS and YF3 as the high and low refractive index anti-reflective coating materials respectively, HgCdTe focal plane devices responding to different widths of back-incident near-infrared light have been designed. Spectroscopic AR coatings have an average transmission rate in the range of the response band of more than 90%.