An optical low pass filter (OLPF) used in front of the sensor of a CCD camera was designed

according to the birefringent effect of quartz crystal and infrared cut-off optical filter. When a object is imaged on the discrete photoelectric detector at different spatial frequencies

OLPF can reduce the frequency-mixing phenomenon effectively and eliminate the effect of infrared light on color rendition to improve image quality of the CCD camera. Especially

when the objects such as fringes or grates are imaged on the sensor of the CCD camera

it can enhance the image distinction and eliminate the effects of the disturbing fringes of false color. Based on analyzing the operational principle of OLPF and function of IR-CUT optical filter

a special IR-CUT coating is designed to make the CCD camera obtain colored image in daytime and black-white image at night. The coating is deposited on thin quartz crystal sheet with double ion beam sputter technique

the measuring results show that the spectral character and image quality are perfect.