| 摘要 |
A tracking error signal is generated with stability without being easily affected by a distribution fluctuation of light reflected from an optical disc or by a lens shift. An optical disc drive according to the present invention includes: an objective lens 5 with an aperture radius r0 for converging a light beam emitted from a light source 1; a polarizing hologram substrate 2 for dividing the beam reflected from the optical disc 6 into branched light beams; a photodetector substrate 6, on which at least some of the light beams are incident to generate signals representing the intensities of the light beams; and a shielding mask 16 for cutting off the beam partially. If xy coordinates are defined on a virtual plane, passing the center of the lens 5 and intersecting with the optical axis 7 at right angles, such that an x-axis is parallel to the disc radial direction and a y-axis crosses the x-axis at right angles, the shielding mask 16 prevents the beam from passing through areas of the virtual plane defined by coordinates (x, y) satisfying |x|>a, |y|>b and a2+b2<r02 (where a and b are positive real numbers).
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