JPH04234014A - Aspherical single lens - Google Patents

Abstract

PURPOSE:To obtain the single lens which is constituted of faces formed by using up to the terms of the sixth order at the max. and has >=0.53 numerical aperture (N.A.) by using a lens having a specific aspherical shape. CONSTITUTION:This lens is a biconvex lens, both faces of which are constituted of aspherical faces. The aspherical shape of the J-th face is formed as the shape expressed by equation 1 where h of the aspherical shape is designated as the height from the optical axis; Zj as the distance in the optical axis direction from the tangent plane at the aspherical vertex of the point on the aspherical face at the height h from the optical axis of the J-th face (J is 1 or 2); 1/CJ as the radius of curvature of the J-th face; KJ as the circular conical constant of the J-th face; A2i, j as the aspherical coefft. of the 2i face (i is >=1 integer) of the J-th face and when all the units expressing the length are in mm.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens used in an optical information recording/reproducing optical system.

0002

[Prior Art] Objective lenses used in optical information recording and reproducing optical systems have a numerical aperture (N.A.) of 0.53 to 0.60.
degree is necessary.

[0003]This N. A. As an objective lens that satisfies the above requirements and ensures sufficient resolution and wide field of view for practical use,
No. 200518 is known.

0004

[Problem to be solved by the invention] JP-A-61-2005
No. 18 shown in Examples 4, 5, and 6. A. =0
．． In the No. 6 lens, its aspherical shape uses a 14th order and higher order aspherical coefficient. However, N
．． A. In a lens with a large value, the amount of asphericity on the lens surface becomes large, especially at the peripheral portion. Therefore, it is preferable to form a shape that does not use as high-order aspherical coefficients as possible in order to maintain the shape accuracy of the surface during processing.

[0005] This invention is composed of a surface that uses terms of at most up to the sixth order as an aspherical shape, and has an N. A. The object of the present invention is to provide a single lens having a coefficient of 0.53 or more.

[0006]

[Means for Solving the Problems] The lens of the present invention is characterized by being a double-convex single lens, and both surfaces are aspherical. Regarding the aspherical shape, h is the height from the optical axis, and ZJ is the J-th surface ( J
is the distance in the optical axis direction from the tangential plane of the aspherical surface vertex of the point on the aspherical surface at the height h from the optical axis in 1 or 2), 1/C
J is the radius of curvature of the J-th surface, KJ is the conic coefficient of the J-th surface,
When A2i,J is the 2i-order (i is an integer greater than or equal to 1) aspherical coefficient of the J-th surface, and all lengths are expressed in mm, the aspherical shape of the J-th surface is expressed by the following equation 2. The present invention provides an aspherical single lens that can be used as an aspheric lens.

[0007]

[Math 2]

Furthermore, the lens of the present invention is useful as an objective lens that focuses light that has been made parallel by a collimator lens onto an image plane. Especially 2.5 ×A2,1 ≦
By selecting the condition A2,2≦3.5×A2,1, it is possible to achieve a high numerical aperture, specifically a numerical aperture of 0.53 or more.

[0009]

[Operation] The condition expressed by Equation 2 indicates that the aspherical coefficient of the aspherical surface includes only terms up to the sixth power of the height h from the optical axis, which reduces the difficulty in processing. It can be reduced. Since aspherical coefficients are used only up to the 6th order, aberration correction becomes extremely difficult, but 2.5 × A2,
Difficulties in correcting aberrations can be overcome by selecting aspheric coefficients that satisfy 1≦A2,2≦3.5×A2,1.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the lens of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the state in which the lens of the present invention is used, where L indicates the lens of the present invention and I indicates the image plane, that is, the pit surface of the disk. G is a parallel plane plate corresponding to the protective layer of the disk. Also, as a geometric dimension, WD is the working distance, d
is the center thickness of the lens of the present invention, and t is the thickness of G.

The shape of the lens L is such that h is the height from the optical axis,
ZJ is the height h of the J-th surface (J is 1 or 2) from the optical axis.
The distance in the optical axis direction of the point on the aspheric surface from the tangent plane of the aspheric apex, 1/CJ is the radius of curvature of the J-th surface, KJ is the conic coefficient of the J-th surface, and A2i, J is 2i of the J-th surface. When the following aspherical coefficients (i is an integer of 1 or more) are used, and all lengths are expressed in mm, it is expressed by the following equation 3.

[Math 3]

Examples 1 to 14 are shown in Tables 1 to 14 below.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

[Table 4]

[0018]

[Table 5]

[0019]

[Table 6]

[0020]

[Table 7]

[0021]

[Table 8]

[0022]

[Table 9]

[0023]

[Table 10]

[0024]

[Table 11]

[0025]

[Table 12]

[0026]

[Table 13]

[0027]

[Table 14]

Wavefront aberrations of Examples 1 to 14 are shown in FIGS. 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 , shown in FIGS. 26 and 28. In addition, the changes in axial wavefront aberration with respect to parallel eccentricity of each example are shown in Figs. 3, 5, 7, 9, 11,
13, FIG. 15, FIG. 17, FIG. 19, FIG. 21, FIG. 23, FIG. 25, FIG. 27, and FIG. 29.

As is clear from Tables 1 to 14 and FIGS. 2 to 29, the wavefront aberration RMS value can be improved in the range up to an off-axis image height of 0.10 mm without using high-order aspherical coefficients of 8th order or higher. Aberrations were well corrected to 0.07 λ or less, and a lens with sensitivity to parallel eccentricity was designed such that the wavefront aberration RMS value was 0.10 λ or less for an eccentricity of 10 μm.

[0030]

[Effects of the Invention] As explained above, the lens according to the present invention sufficiently satisfies the specifications as a magneto-optical objective lens without using an aspheric coefficient of order 8 or higher, and reduces the influence of errors in its processing. It has the effect of being able to do it.

[Brief explanation of the drawing]

[Fig. 1] Cross-sectional view showing the usage state of the lens of the present invention

[Figure 2]
Diagram showing wavefront aberration of Example 1

[Figure 3] Diagram showing the sensitivity of parallel eccentricity in Example 1

[Figure 4] Diagram showing wavefront aberration of Example 2

[Figure 5] Diagram showing the sensitivity of parallel eccentricity in Example 2

[Fig. 6] Diagram showing wavefront aberration of Example 3

[Figure 7] Diagram showing the sensitivity of parallel eccentricity in Example 3

[Fig. 8] Diagram showing wavefront aberration of Example 4

[Fig. 9] Diagram showing the sensitivity of parallel eccentricity in Example 4

[Figure 10]
Diagram showing wavefront aberration of Example 5

[Fig. 11] Diagram showing the sensitivity of parallel eccentricity in Example 5

[Fig. 12] Diagram showing wavefront aberration of Example 6

[Fig. 13] Diagram showing the sensitivity of parallel eccentricity in Example 6

FIG. 14 is a diagram showing wavefront aberration of Example 7

FIG. 15 Example 7
Diagram showing the sensitivity of parallel eccentricity of

[Fig. 16] Diagram showing wavefront aberration of Example 8

[Fig. 17] Diagram showing the sensitivity of parallel eccentricity in Example 8

FIG. 18 is a diagram showing wavefront aberration of Example 9

[Figure 19]
Diagram showing the sensitivity of parallel eccentricity in Example 9

FIG. 20 Example 1
Diagram showing wavefront aberration of 0

[Fig. 21] Diagram showing the sensitivity of parallel eccentricity in Example 10

[Fig. 22] Diagram showing wavefront aberration of Example 11

[Figure 23] Diagram showing the sensitivity of parallel eccentricity in Example 11

FIG. 24 is a diagram showing wavefront aberration of Example 12.

[Figure 25] Diagram showing the sensitivity of parallel eccentricity in Example 12

FIG. 26 is a diagram showing wavefront aberration of Example 13

[Fig. 27] Diagram showing the sensitivity of parallel eccentricity in Example 13

FIG. 28 is a diagram showing wavefront aberration of Example 13

[
Figure 29: Diagram showing the sensitivity of parallel eccentricity in Example 14

[Explanation of symbols]

L Lens of the present invention I Image plane G Parallel plane plate WD working distance d Center thickness of the lens of the present invention t G thickness CL Collimator lens

Claims (3)

[Claims] Claim 1: A double-convex single lens, both surfaces of which are aspherical, and for the aspherical shape, h is the height from the optical axis,
ZJ is the height h of the J-th surface (J is 1 or 2) from the optical axis.
The distance in the optical axis direction of the point on the aspheric surface from the tangent plane of the aspheric apex, 1/CJ is the radius of curvature of the J-th surface, KJ is the conic coefficient of the J-th surface, and A2i, J is 2i of the J-th surface. When the aspheric coefficient of
An aspherical single lens characterized by: [Math 1] [Claim 2]Claim 1 wherein the numerical aperture is 0.53 or more.
Aspherical single lens. [Claim 3] 2.5 × A2,1 ≦A2,2 ≦3.
5. The aspherical single lens according to claim 1, which satisfies 5×A2,1.