Efficient coupling between annealed K/sup +/-Na/sup +/ ion-exchanged channel waveguides and 10/125 single-mode fibers at λ=1.321 μm

The process of thermal annealing of K/sup +/-Na/sup +/ ion-exchanged channel waveguides has been studied with the aim of optimizing their coupling efficiency with commercial single-mode fibers at /spl lambda/=1.321 /spl mu/m. Waveguides obtained in soda-lime glass slides, with mask apertures ranging between 13.4 and 2.6 /spl mu/m, were characterized before the annealing by combining nearfield measurements and an etching procedure. The experimental results were successfully compared with a theoretical model based on the variational principle. The refractive index distribution of K/sup +/-Na/sup +/ ion-exchanged channel waveguides supporting one or a low number of modes was given: compared to the corresponding slab case, the refractive index step /spl Delta/n/sub o/ remained constant, while the waveguide depth was lower. The thermal annealing process of the channels was then performed and modeled by means of the standard diffusion theory. As a result, the channel fabrication parameters for optimum guide-fiber coupling could be predicted: 0.23-dB mode mismatch losses were measured between the optimized channel and a commercial 10/125 single-mode fiber, at /spl lambda/=1.321 /spl mu/m.