DIFFRACTION OPTICAL ELEMENT AND OPTICAL HEAD UNIT

摘要

PROBLEM TO BE SOLVED: To increase the light use efficiency of a CD/DVD compatible optical head unit and to make the head unit small-sized and lightweight by obtaining a wavelength-selective diffraction optical element which has a small decrease in diffraction efficiency even when its grating pitch becomes fine.

SOLUTION: The diffraction optical element is mounted on the optical head unit. This diffraction optical element is equipped with a diffraction grating 12 which has a staircase shape in the cross section and a diffraction grating 13 which has a rectangular shape in the cross section, on one surface of a transparent substrate 11. Then the optical head unit has wavelength selectivity such that one of different-wavelength light beams made incident on the diffraction optical element is diffracted and the light of the other wavelength is transmitted.

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