| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to easily maintain high diffraction efficiency and to effectively suppress flares, etc., even when a grating pitch is small or even when a grating thickness is large by laminating a plurality of diffraction gratings varying in dispersion from each other apart spacings and offsetting the edges of the respective corresponding grating parts from each other in the direction where these grating parts line up. SOLUTION: The diffraction gratings 4, 5 of a first layer and a second layer consisting of materials varying in dispersion from each other are laminated across an air layer air on a substrate 2. A first diffraction grating face 6 is formed at the boundary between the grating parts 4a of the first layer and the air layer air and a second diffraction grating face 7 is formed at the boundary between the air layer air and the grating parts 5a of the second layer. The constitution in which the positions of the grating edge parts 8 of the grating parts 4a, 5a forming the grating pitch of the respective laminated diffraction gratings 4, 5 are offset from each other relatively in the grating pitch direction (A-A' direction), is adopted. The diffraction grating element provides the optical effect as the one diffraction grating element through the entire layer.
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