Patent ID: 7911925
Filing Date: 2011-03-22
Classification: G11B

Abstract:
1. An optical pickup, comprising: a light source; a beam shaping element for shaping an elliptical light beam emitted from the light source into a substantially circular light beam; an element for condensing the light beam shaped by the beam shaping element onto an optical information recording medium; a detector for detecting the light beam reflected by the optical information recording medium; a positioning portion for positioning the beam shaping element relative to the light source, wherein if it is assumed that m is a beam shaping magnification of the beam shaping element, L[mm] is a distance from a light source side surface of the beam shaping element to a center position of the positioning portion, α[1/K] is a coefficient of linear expansion of the retaining holder, ΔWA[mλ] is amount of astigmatic aberration caused by the beam shaping element and ΔT[K] is an environmental temperature variation amount, the positioning portion positions the beam shaping element in such a manner as to satisfy the following relational expressions (1) and (2):