| 摘要 |
PROBLEM TO BE SOLVED: To make diffraction characteristics different depending on the direction of incident light by alternately arranging the divisions of a diffraction grating having different refractive indices between two materials having different refraction indices. SOLUTION: A diffraction grating alternately arranging divisions having a refractive index N1 and a refractive index N2 (N1>N2) with a pitch Λ is provided between a material 1 and a material 2 having mutually different refractive indices of N1 and N2 and the pitch is set in a proper range for the wavelength to constitute this directional diffraction grating. When wavelength to be used here is made to λ, the pitch satisfy the relation of the formula. Since the refractive index of the diffraction grating is larger than the refractive index of air, the case of diffracting only in an upward path is generated. When the refractive index of the outer medium is larger than the refractive index of the diffraction grating, the case of diffracting only in a return path is generated. By properly setting the pitch, the diffracted light can be produced only in the direction where the refractive index of the outgoing side of the diffraction grating is larger than the refractive index of the incident side. |
