| 摘要 |
PURPOSE:To obtain the lens system of a small size and light weight without generating deterioration of quality by disposing a lens both faces of which are aspherical between a semiconductor laser and an optical disk and constituting the lens system so as to satisfy specific conditions. CONSTITUTION:The light of the semiconductor laser 1 is converged through a beam splitter 2, a lens 3 and cover glass 4 onto the optical disk. Both faces of the lens 3 are mode of aspherical faces r3, r4 and the laser side NA is specified to 0.12 to 0.2 and the disk side to >=0.4. The lens system is so constituted as to satisfy the condition equations I to IV where X: the distance from the tangent plane at the vertex of the aspherical face of a height H from the optical axis, H: the height form the optical axis, C: the curvature at the vertex of the aspherical face, K: coefft. of a circular cone, f: the focal length of the lens, I.O: the distance of the disk pit surface from a laser oscillation surface, r3: the radius of curvature on the light source side, n3: the refractive index of the lens, D, E, F, G: coeffts. |
