Multi-functional components with excellent properties of sapphire materials are widely used in bearing and optical fields. It is made of high purity synthetic sapphire (single crystal alumina, Al₂O₃) with high hardness, high light transmittance and resistance to extreme environments. In the bearing, the sapphire optical ring window is not only used as a support structure, but also can realize the transmission or monitoring of optical signals, which is an indispensable key component in precision equipment.