THERMAL ANNEALING OF K+-NA+ ION-EXCHANGED WAVE-GUIDES

The process of thermal annealing of K+-Na+ ion-exchanged waveguides in soda lime glass is characterized and compared with a simple theoretical model. The discrepancies between theory and experiments in the case of initially thick guides disappear if the existence of a stress-induced contribution to the refractive index is assumed that is not proportional to the concentration of the doping ions. The results obtained for initially thin guides are exploited for the design of annealed single-mode channel waveguides: 0.4-dB coupling losses with commercial single-mode fibers at λ = 1.321 µm were measured.