Two-step thermal ion exchange process for single-mode waveguides embedded in glass

Abstract

High-capacity fiber optic transmission systems with single­mode fibers (SMFs) require single-mode optical devices. Various works have been carried out to make single-mode waveguides in glass by ion exchange (I/E) processes. These procedures may be thermal I/E, electric field-assisted I/E as well as one-step I/E and two-step I/E processes. The one-step I/E process [1,2], in general, cannot provide embedded waveguides and therefore is less attractive from the point of view of practical applications. One the other hand, by using a two-step electric field-assisted I/E process[3], one can fabricate embedded single-mode waveguides. However, for electric field-assisted I/E processes, a special experimental set-up is necessary where plus- and minus-potential molten salts are kept isolated from each other. While the two-step thermal I/E process with only the K ion[4] seems to be straightforward and the waveguide structure is not an embedded type but an inverted ridge guide.