Optical waveguide element, method of making the same and optical coupler

Abstract

An optical waveguide element includes an optical waveguide formed on a light-transmissive dielectric substrate and having a higher refractive index than the refraction index of the substrate, the optical waveguide including a region having an effective refractive index which varies nonlinearly in a direction in which a light wave is propagated through the optical waveguide. The light wave guided through the optical waveguide enters the region, in which the angles of incidence and reflection of the guided wave at the boundary between the region and the substrate is gradually reduced due to the variation in the effective refractive index. When the angles of incidence and reflection of the guided wave becomes smaller than a critical angle, the guided wave is emitted out of the waveguide. Since the effective refractive index changes nonlinearly with respect to the distance the guided wave is propagated, the light emitted into the substrate tends to converge at a point, and the beam pattern of the emitted light is spread less.