Abstract: A reflecting diffraction grating is formed by depositing a metal in vacuum on a blazed diffraction grating having a cross section of regular projections and recesses to provide a metal reflecting film, and forming an SiO protective film on the reflecting film by vacuum deposition.

Abstract: A gradient index-type optical device produced by the ion exchange process, comprising: a transparent dielectric body having a refractive index distribution, and a refractive index distribution-adjusting portion disposed on at least a part of the transparent dielectric body. Because of the presence of the refractive-index distribution, the ion-exchange speed therethrough is controlled to provide a controlled refractive index distribution in the transparent dielectric body. As a result, a gradient index-type optical device having a large refractive index factor (g value) without substantial increase in aberration.

Abstract: A gradient index-type optical device is produced by the ion exchange process. First, a transparent dielectric body contacting an ion to be exchanged is provided with a light-absorbing portion containing also an ion to be exchanged and a coloring component at at least a part of the surface thereof. The transparent dielectric is soaked in or caused to contact a molten salt containing an ion providing a refracted index distribution for ion exchange. In the gradient index-transparent dielectric thus produced, the light-absorbing portion can have a refractive index continuous with that of the transparent dielectric body and a thermal expansion coefficient equal to or smaller than that of the transparent dielectric body, so that flare at the boundary and the stress fragility are alleviated. The optical device can also have a good size accuracy.