| 摘要 |
<P>PROBLEM TO BE SOLVED: To obtain a diffraction element which is capable of controlling diffraction efficiency such as approximately fixing wavelength dependency of diffraction efficiency, and to obtain an optical head unit with a high degree of freedom in design and high light utilization efficiency by packaging the diffraction element in the optical head unit. <P>SOLUTION: A diffraction element is provided which comprises cyclic projections and recesses formed on a transparent substrate. In the diffraction element, each projection includes an optical multilayer film disposed in parallel with a transparent substrate surface, and at least each recess is filled with a filler of which the refraction factor is different from that of the transparent substrate. In the diffraction element, the projection is the optical multilayer film having a cyclic structure of high refraction factor layers (H layers) and low refraction factor layers (L layers). A difference between an arithmetic average value of the refraction factors of the optical multilayer films and a refraction factor of the fillers filling the recesses is 0.12 or less and a primary diffraction efficiency in light within a wavelength range from 350 nm to 900 nm is 35% or more. <P>COPYRIGHT: (C)2013,JPO&INPIT |
