| 摘要 |
PURPOSE:To decrease the number of lens elements and to reduce the cost, size, and weight of a device by providing a four lens elements, i.e. biconvex lens, concave meniscus lens, biconvex lens, and convex meniscus lens successively from a light source side, and satisfying specific inequalities. CONSTITUTION:Light from a semiconductor laser 1 is converged on the pit surface of a disk through a lens system 3 and cover glass 4 and its reflected light is made incident on a detector 5. Then, NA is set to >=1.0 at the semiconductor laser side and to >=0.4 at the detector side, and four specific inequalities hold, where I0 is the distance from the light source to the disk pit surface and (r) is the radius of curvature. An inequality (1) is for the size and weight reduction of the device and wave aberration compensation, an inequality (e) for the correction of sine condition, an inequality (3) for spherical aberration compensations. Therefore, a collimator system and an objective system are united together and the number of lens elements is decreased to reduce the cost, thereby obtaining the small-sized, lightweight device.
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