Optical thin film products are functional materials that precisely control optical properties such as light reflection, transmission, absorption, and polarization, by forming extremely thin films, on the order of nanometers, in single or multiple layers on the surface of substrates such as glass or plastic. With a multi-layer film structure, it is possible to selectively transmit or reflect light within specific wavelength bands, realizing a wide range of functions such as low reflection, high reflection, bandpass, and UV/IR cut. Main processing methods include vacuum deposition (PVD), sputtering, and chemical vapor deposition (CVD), among others, and the optimization of film-forming materials and process conditions determines the quality. They have become an indispensable elemental technology in a wide range of fields where advanced optical performance is required, such as camera lenses, displays, projectors, optical communication components, medical devices, solar cells, and semiconductor manufacturing equipment.