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We describe a means of eliminating undesired surface guiding in titanium-diffused strip waveguides on LiNbO3. Surface guiding for light of the extraordinary polarization, normally produced when the crystal is diffused in dry argon or oxygen, can be eliminated entirely by adding water vapor to the diffusion gases. Infrared absorption measurements show that hydrogen enters crystals diffused in a wet atmosphere. Although the mechanism for the prevention of surface guiding is not fully understood, we suggest that the presence of excess hydrogen reduces lithium mobility.
Jackel et al. (1981) studied this question.