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 vitreous film containing, e.g., 30-90 wt. % of Sn, 1-20 wt. % of P, 0.1-20 wt. % of Pb, 2-30 wt. % of 0 and 5-35 wt. % of F is formed by vapor deposition on a substrate such as glass, metal, plastic or ceramic. A light-absorbing substance can be incorporated in the vitreous film to provide a recording layer for a heat-mode optical recording medium capable of causing decoloration or formation of pits on irradiation with a laser beam.