Objective lens and optical head device provided with the same
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United States of America Patent
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Issued Date -
Jan 12, 2006
app pub date -
Jul 8, 2005
filing date -
Jul 9, 2004
priority date (Note) -
Abandoned
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Abstract
An objective lens by which an effective value of spherical aberration with respect to an optical recording medium is reduced and in which a beam spot having a small diameter can be formed on a recording surface of the optical recording medium. An objective lens for an optical head device comprises a refraction surface provided with a middle region and a peripheral region, where, assuming that a distance from an optical axis to an outer peripheral portion of the middle region in a direction crossing the optical axis at right angles is R, there exist in a range of R/3 to 2R/3 from the optical axis, zero regions where the spherical aberration with respect to an optical recording medium turns to zero and/or an increase/decrease region where the spherical aberration with respect to the optical recording medium increases or decreases toward zero.
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