Abstract: A pyro-electric type infrared-ray sensor comprises a pyro-electric thin film such as Pb TiO.sub.3, an upper electrode of Al film formed on the upper surface of the pyro-electric thin film, a lower electrode thin film of Al formed on the bottom surface thereof and an organic thin film which covers the upper surface, and the sensor further comprises an infrared light reflection member, at least partially on the surface of the organic thin film.

Abstract: An anti-reflection film to be used for a plastic optical component is excellent in adhesion, durability and optical characteristic as well as be suited for mass-production. The anti-reflection film is a three-layered structure comprising, from the surface of the optical component on which it is formed, a first layer and a second layer which are made of a same dielectric material and a third layer which is a different dielectric material therefrom. Oxygen is introduced when the first layer is formed in order to provide the first layer smaller in refractive index than the second layer. The first and second layers are each made of any of cerium oxide, tantalum pentoxide and hafnium oxide and the third layer is made of silicon dioxide.