| 摘要 |
PURPOSE:To substantially increase the threshold value of an optical damage and to improve the coupling efficiency in the input and output stage of guided light by injecting protons to the surface of a lithium niobate crystal substrate or lithium tantalate crystal substrate. CONSTITUTION:The y plane or x plane of the lithium niobate crystal substrate 1 is first polished flat, then the surface is subjected to ordinary ultrasonic cleaning by acetone followed by pure water. The surface is dried by blowing gaseous nitrogen to form a thermally diffused Ti layer. A proton exchange layer 13 is formed in the diffused layer 11 and a thin Au film is deposited by evaporation only to the region where surface acoustic waves and the guide light act on each other. On the other hand, the thin Au film is deposited by evaporation on the rear side of the substrate as well and while a voltage 12 is impressed thereto, the thin film is subjected to an annealing treatment. As a result, an optical waveguide layer 31 which is shallower in the depth of diffusion than in the optical coupling section and has the high density of the protons on the substrate surface is formed. The refractive index near the surface is decreased when the surface of the waveguide 31 is subjected to the laser annealing treatment by a laser 15. A low refractive index layer 16 is thus formed and finally a comb-shaped electrode 14 is formed. |
