| 摘要 |
PROBLEM TO BE SOLVED: To provide a reflective diffraction element having high diffraction efficiency. SOLUTION: The element has such a structure that has a layered structure 6 composed of a diffraction grating layer 2 comprising a lamellar grating and a uniform layer 4 having a uniform refractive index, as a periodical unit, and a plurality of the above layered structures 6 are stacked in a depth direction. In the diffraction grating layer 2, a duty ratio of the lamellar grating is set in such a manner that propagation constants in a depth direction in different modes are degenerated so that the optical thickness of the diffraction grating layer 2 can be defined. The optical thicknesses of the diffraction grating layer 2 and the uniform layer 4 are approximately a quarter wavelength of the center wavelength of the incident light. COPYRIGHT: (C)2007,JPO&INPIT
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