LENS UNIT, ELEMENT FOR CORRECTING ABERRATION AND DESIGN METHOD OF ELEMENT FOR CORRECTING ABERRATION

摘要

PROBLEM TO BE SOLVED: To provide a lens unit and an element for correcting aberration for reducing aberration even when ambient temperature or the wavelength of a laser is changed, and to provide a design method of the element for correcting aberration.

SOLUTION: The lens unit comprises a pickup lens 15 made of plastics and elements 14 for correcting aberration disposed on a laser light source side of the pickup lens 15 and having a flat plate shape having a plurality of annular steps. The element for correcting aberration 14 has the plurality of annular steps having such thicknesses that phases are different in wavelength units from each other when light is normally transmitted and such an amount of steps that aberration generated in the pickup lens 15 is reduced when temperature and/or the wavelength is changed.

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