Abstract

Glass waveguides are generally fabricated by ion-exchange process by immersing the glass substrate in a molten salt mixture. These waveguides have the maximum index change at the glass surface, and their index profile depends upon the diffusion time, the melt temperature, the compositions of the glass and the melt, and on any applied electric field. The surface waveguides can be buried by immersing them in pure salt bath and carrying out diffusion in one more step with or without external field. Burying the waveguide under the glass surface reduces the scattering losses arising from the surface irregularities. The buried profile can be tailored to give desired waveguide characteristics by changing the process parameters. Both planar and channel Na⁺-Ag⁺ ion-exchanged buried waveguides have been reported [1-3]. Since the silver melt concentration used in these studies was relatively large (N_Ag ⩾ 0.1 mole fraction), the resultant surface index change was also large (Δn ~ 0.1), giving rise to either multimode waveguides or very shallow single-mode guides, incompatible with single-mode fibers. Moreover, the interdiffusion coefficient under these conditions is concentration dependent, a fact that makes the solution of the diffusion equation more cumbersome.

© 1987 Optical Society of America