| 摘要 |
PURPOSE:To facilitate generating gap intervals and to hold stably a high coupling efficiency, by mounting a volume type diffraction grating or a relief type blazed diffraction grating on an optical waveguide through a low-refractive index layer formed with a prescribed thickness. CONSTITUTION:An optical waveguide 11 having a refractive index nf is formed on a substrate 10 having a refractive index ns, and a low-refractive index gap layer 12 which changes the thickness in accordance with the intensity distribution of an incident light and has a refractive index nh is formed on the optical waveguide 11, and a volume type diffraction grating 13 having a refractive index ng is formed on the layer 12. Respective refractive indexes satisfy the relation of nf>ng>nh. A parallel luminous flux is incident to the diffraction grating 13 from a light source through a lens system 15, and a diffraction angle thetaB is so selected that the propagation constant of a diffracted light is phase-matched to the guided propagation constant in the waveguide 11, and a thickness s(x) of the gap layer 12 is selected properly, thereby coupling about 100% incident light to the waveguide mode light. Thus, the formation of gap intervals is facilitated, and a high coupling efficiency is held stably. |
