PURPOSE: To set to a design value of the titled lens adjusting a focal distance, without enabling to work to a shape of a cavity as shown by the design, by providing a cavity on the surface of the electroconductive substrate, and then forming the optical waveguide composed of the optical sensitive material having a uniform thickness on the substrate, and by slowly increasing an irradiating amount of the light toward the center of the cavity from the surroundings thereof.

CONSTITUTION: The cavity h' is formed by cutting on a part of the surface of the lithium niobate substrate 11 followed by polishing, and then by vapor-depositing arsenic sulfide on the substrate, to form the optical waveguides 12, 13 having a prescribed thickness, and composed of arsenic sulfide. The UV ray 15 is irradiated to arsenic sulfide 13 provided on the cavity h' through the mask 14 for exposing the light, having a distribution in which the transmittance of the UV ray is the max. at the center of the lens and gradually reduces according to approaching to the surroundings of the lens. The distribution of the refractive index of the optical waveguide 13 has a rotation symmetry in which the refractive index is max. at the center of the lens and reduced according to approaching to the surroundings of the lens. Accordingly, the optical waveguide converging effect for the waveguide light, thereby displaying the lens effect.