Design and Fabrication of 940 nm Filter and Research on Its Low Angle Effect

In this study, a 940-nm narrowband filter used for face recognition is designed and examined and a narrowband filter with low angle effect is developed. TiO₂ and SiO₂ are chosen as high and low refractive index materials, respectively. The film system is designed by using the Essential Macleod software and optimized by changing the material of the spacer layer. The film system has 11 layers and a total thickness of 2480.76 nm. The thin film is plated by using the electron beam thermal evaporation deposition technology, and the transmittance spectral characteristics are tested using a Fourier infrared spectrometer. The center wavelength of the finally developed filter is 940 nm. In the cut-off range (200 to 1100 nm), the pass-band transmittance is greater than 80%, average cut-off transmittance is less than 1%, and offset at 0° to 22° passband is 14 nm.