Sapphire circular window is one of the basic optical components in optics, usually used as a protective window for electronic sensors or external environment detectors. It is used to separate the environment on both sides, such as separating the inside and outside of the instrument, so that the inside and outside of the instrument are isolated from each other, so as to protect the internal devices. The sapphire circular window does not change the magnification of the system.

Windows are optical glass that have been ground and polished to form two surfaces parallel to each other. They are commonly used as protective devices for electronic sensors, optical lenses, and laser processing heads.