| 摘要 |
PROBLEM TO BE SOLVED: To generate a side beam, having proper balance, in which aberrations are controlled by providing a diffraction element, in which proper corrections are added to a pattern shape, in an optical pickup device which has the diffraction element and a beam shaping means and uses a differential push-pull method as a track signal generating means. SOLUTION: In the optical pickup device which is provided with a semiconductor laser 1, a diffraction element 3 diffracting a beam emitted by the semiconductor laser, a beam-shaping means 4 for enlarging the diameter of the beam, and an objective lens 7 for condensing the beam on an optical recording medium 8, the diffraction element, which forms a pattern, in accordance with formula (1) ϕ(x,y)=α.y+σ(x,y)...(1) where higher order correction term σ(x, y) which is not less than the first order is added to a first order phase transfer function α.y in an orthogonal coordinate (x, y) system, which forms y axis in the diffraction separating direction, is used as the diffraction element 3. Thus, aberration is restrained to be minimum, and a side beam having proper balance is obtained. |
