| 摘要 |
PURPOSE:To make possible the adjustment of a focal length and the compliance thereof with a design value even if the shape of a recess cannot be worked exactly to the design by forming a photosensitive material having the refractive index higher than the refractive index of an optical waveguide onto the surface of the recess in such a manner that the film thickness of the photosensitive material increases gradually from the periphery of the recess toward the center. CONSTITUTION:The geodesic lens is provided with the recess on the surface of a lithium niobate substrate 11 as a geodesic lens part 14, is formed with the optical waveguide 12 by thermal diffusion of titanium near the surface of the substrate and is provided with a thin film 13 of arsenic sulfide on the optical waveguide of the lens part 14. The thin film 13 is made into the rotationally symmetric shape in which the film thickness is largest at the center of the thick film lens and decreases gradually toward the periphery in accordance with the theory of a Luneberg lens. The optical path length is longer and the change component of the equiv. refractive index is larger the nearer the center of the recess and therefore the phase plane of the guided light is more delayed nearer the center. The guided light 15 made incident in parallel with the lens is thus condensed to a focusing point 16. |
