Nickel-indiffused lithium niobate ridge optical waveguides fabricated by a novel self-aligned process

The fabrication process for the self-aligned technique is illustrated. At first, the patterns of waveguides are transferred onto the LiNbO/sub 3/ substrate by the photolithographic process. Then, the Ni diffusant, the diffusion barrier of Ti, and the PE masks of Si are successively deposited on the substrate by an E-beam evaporation system. By using the lift-off process, the tri-layered structure composed of Ni/Ti/Si is left on the substrate with good adhesion and exact alignment. Putting the sample into the oven, the diffusion process is performed under 800-900/spl deg/C for several hours to drive Ni atoms into the LiNbO/sub 3/ substrate. With the protection of the PE mask formed by the combination of Ti and Si, the regions not protected by the PE mask will be domain-inverted in the molten benzoic acid, and then will be etched in pure HF, completing the fabrication of a Ni:LiNbO/sub 3/ ridge waveguide. It has been proved that Ni diffusion of 300 /spl Aring/ (for a waveguide with extraordinarily polarization at a wavelength of 1.3 /spl mu/m), Ti diffusion barrier of 700 /spl Aring/, and Si PE mask of 3000 /spl Aring/ become the best combination.