| 摘要 |
PURPOSE:To realize high optical performance with a small-sized, lightweight aspherical single lens whose core thickness is small without using an aspherical surface term of high order by making a biconvex single lens, which is aspherical on both sides of a light source and an optical disk, satisfy specific requirements. CONSTITUTION:This is the biconvex single lens which has aspherical surfaces on both sides of the light source and optical disk and the requirements shown by inequalities I III are satisfied to obtain a thin type lens. In the inequalities I - III, (d) is the core thickness of the single lens, (f) the focal length of the single lens, r1 the radius of curvature at the peak of the light-source side lens surface, r2 the radius of curvature at the peak of the optical-disk side lens surface, and (n) the refractive index of the lens corresponding to in-use wavelength. Consequently, although the numerical aperture is about 0.5 and the image formation magnification is about -0.3 or large, the small-sized, lightweight objective which is extremely small in core thickness and has practically sufficient optical performance is obtained without using any aspherical surface term of high order. |
