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 slowly elevating a refractive index of an optical waveguide provided on the cavity toward a center of lens from a surroundings thereof.

CONSTITUTION: The optical waveguide 13 of arsenic sulfide provided on the cavity has the refractive index distribution so as to give the same effective refractive index distribution to that of a Luneburg lens for the waveguide light 15 transmitting the lens part 14. The refractive index distribution is rotation symmetry distribution in which the refractive index distribution shows the max. value at the center of the lens, and generally reduces according to approaching to the surroundings of the lens. Therefore, the optical waveguide 13 has a converging effect for the waveguide light 15, thereby displaying the effect of the lens. By the reason that the waveguide light passing the cavity part spreads the geodetic lens having different lengths respectively due to the positions of the different incident lights and by the reason of changing the refractive index of the optical waveguide itself composed of arsenic sulfide provided on the cavity part, as the optical path is long, and the change of the effective refractive index is large according to approaching to the center of the cavity, the phase surface of the waveguide light is late according to approaching to the center of the cavity, thereby gathering the waveguide light 15 incidenting to the lens in parallel, to the focusing point 16.