Process for producing low-loss embedded waveguide

DETAILED DESCRIPTION An object of the present invention is to provide a novel process for producing a low-loss waveguide by a simple ion exchange process, thereby to overcome the above-described problems of the conventional processes.
Other objects and effects of the present invention will be apparent from the following description.
The present invention provides a process for producing a low-loss embedded waveguide, which comprises: a first ion exchange step in which a glass substrate containing a monovalent ion and capable of undergoing ion exchange is subjected to thermal ion exchange through an ion exchange-control film provided on the substrate and having a predetermined waveguide pattern formed therein, by immersing the substrate in a first molten salt containing a first monovalent ion capable of changing the refractive index of the substrate; an etching step in which the ion exchange-control film is removed form the substrate by etching; an electric field-applying annealing step in which an electric field is applied to the substrate at substantially right angles to the substrate at a temperature near the temperature at which the first ion exchange step was conducted, provided that the side of the substrate which had the ion exchange-control film is used as a positive potential side; and a second ion exchange step in which the resulting glass substrate is subjected to thermal ion exchange by immersing the substrate in a second molten salt containing a second monovalent ion capable of changing the refractive index of the substrate in a manner contrary to the first monovalent ion.