| 摘要 |
<p>A stable tracking error signal not easily affected by uneven distribution of reflected light from an optical disc and unaffected by lens shift is generated. The optical disc drive comprises an objective lens (5) having an aperture radius r0 for focusing a light beam radiated from a light source (1), a polarization hologram substrate (2) for dividing a light beam reflected on an optical disc (6) into a plurality of branch light beams, a light detection substrate (6) on which at least a part of the plurality of branch light beams impinges to produce a signal depending on the quantity of light of individual incident branch light beams, and a shading mask (16) for intercepting a part of the light beam. When an xy coordinate including the x-axis parallel with the radial direction of the optical disc (6) and the y-axis perpendicular to the x-axis is defined on a virtual plane passing the central portion of an objective lens (5) and perpendicular to the optical axis (7), the shading mask (16) intercepts the light beam not to pass through a region on the virtual plane defined by coordinates (x, y) satisfying relations |x|>a, |y|>b, and a<SUP>2</SUP>+b<SUP>2</SUP><R0<SUP>2 </SUP>(a and b are positive real numbers).</p> |
