| 摘要 |
PURPOSE:To reduce the size and weight of a device by setting NA to >=0.1 at a semiconductor laser side and to >=0.4 at a disk side, and satisfying a specific conditional equation. CONSTITUTION:Light from a semiconductor laser 1 is converted on a disk pit surface through an aspherical lens 3 and cover glass 3 and its reflected light is made incident on a detector 5. The distance X from the optical axis of a lens for this optical disk to a contact plane at the peak of the aspherical surface at height H is as shown by the equation I, and specific conditional inequalities II hold, where K is a conic coefficient K, 10 is the distance from the laser 1 to the pit surface, and (r) is the radius of curvature. An equality (1) is for the size reduction of the device and the compensation of sine condition, an inequality (2) is for the compensation of sine condition and a spherical aberration, and inequalities (3) and (4) are for the balancing of the spherical aberrations of the 3rd surface r3 and the 4th surface r4. In this case, H is the height from the optical axis, (f) the focal length of the lens for the disk, n3 the refractive index of a single lens, and D, E, F, and G coefficients of terms proportional to the incidence height raised to the 4th power, the 6th power, the 8th power, and the 10th power. Consequently, the device is reduced in size and weight.
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