Abstract: A method for producing an oxide glass thin film is provided, in which volatilization of additives in a porous film from which the thin film is formed is effectively suppressed, and which the oxide glass film has a desired arrangement of refractive index with a low optical loss. According to this method, glass fine particles mainly containing SiO.sub.2 with a first additive are deposited on a substrate to form a porous thin film. A gas containing a second additive is supplied to a first chamber and heated to a first predetermined temperature profile to provide a heated gas containing an oxide. After disposing the substrate in a second chamber communicated with the first chamber, the substrate is heated to make the deposited porous glass into transparent glass while controlling a temperature in the second chamber according to a second temperature profile.

Abstract: A method of producing an oxide glass thin film includes a process to obtain a transparent glass film, in which volatilization of additives in a porous film deposited is effectively suppressed and which can provide an oxide glass thin film having a desired arrangement of refractive index with a low optical loss. The method is for producing an oxide glass thin film, in which glass fine particles mainly containing SiO.sub.2 with additives are deposited on a substrate to form a porous thin film and then heated to form a transparent glass film. In the method, vapor of oxides of additive components is mixed in an atmosphere in which the porous thin film is heated to form the transparent glass film, whereby stopping the volatilization of the additives in the porous film deposited, preventing diffusion of the additives added to a core layer, and preventing the volatilization of glass transition temperature lowering components of additives (P.sub.2 O.sub.5, B.sub.2 O.sub.3, GeO.sub.2, etc.).