JP3425385B2 - Objective lens for optical information recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] [0001] The present invention relates to an optical disk and the like.
Used for detecting information recorded on optical information recording media
It is about a lens. [0002] 2. Description of the Related Art Used for detecting information recorded on an optical disc.
FIG. 6 shows an example of a general optical system used. This optic
In the system, the light emitted from the light source 1 is
It becomes parallel light. This parallel light is converted by the objective lens 3
The light is focused on the information surface on the disc 4 and the information on the optical disc 4 is
The information is read optically. Further, information on the optical disc 4
The light reflected by the surface enters the objective lens 3 again and is
It becomes light and is collected by the collimating lens 2. Focused
The reflected light is reflected by the half mirror 5 and collected on the detection element 6.
Is done. In this way, this optical system can detect optical information
Wear. FIG. 7 shows an example of an optical system other than the above. FIG.
In the optical system of (1), the light emitted from the light source 1
Directly incident on the optical disk 4 by the objective lens 3
It is focused on the information surface. Reflected on the information surface on the optical disc 4
The reflected light enters the objective lens 3 again and is reflected by the half mirror 5.
The light is reflected and collected on the detection element 6. Like this
Thus, optical information can be detected. Generally, the former method (FIG. 6) is
The limited system and the latter method (the one in Fig. 7) are called finite systems.
You. [0005] Considering the miniaturization and weight reduction of the optical disk device,
The optical system is composed of the finite system of FIG.
It is advantageous. [0006] As such a conventional technology of a finite system, for example,
For example, Japanese Patent Publication No. 4-28282, Japanese Patent Application Laid-Open No. 4-143714,
JP-A-4-143715, JP-A-4-163510,
An example is disclosed in Japanese Unexamined Patent Publication No. 8-334686. However, in these conventional techniques,
Is that the wavefront increases when the NA (numerical aperture) of the objective lens increases.
Aberration increases. In particular, the wavefront aberration at the periphery of the lens
It increases sharply and corrects this wavefront aberration well.
There is a problem that can not be done. [0008] SUMMARY OF THE INVENTION The present invention relates to the above-described circumstances.
The surface that constitutes the objective lens,
The aspheric coefficient on the light source side where light is incident
The wavefront aberration by enabling the action of higher-order terms.
To provide an optical system that can satisfactorily correct
The purpose is. [0009] An optical information storage device according to claim 1.
The recording medium objective lens has a positive single lens with the convex surface facing the light source side.
And the surface on the light source side and the optical information recording medium side
Both surfaces are aspherical surfaces and satisfy the following conditions:
It is configured to add.   0.8h₁≤R₁≦ 1.0h₁ 0.13 ≦ | m | ≦ 0.26 0.5 ≦ | R ₁ / R ₂ | ≦ 0.8 0.55 <d / f <0.7 [0010]However, R ₁ : Paraxial radius of curvature on the light source side surface h ₁ : Nearest effective numerical aperture (NA) of lens (ie,
The outermost part of the NA)
Side surface (R ₁ Height of the ray incident on the surface) from the optical axis R₂: Paraxial radius of curvature on the surface on the optical information recording medium side m: imaging magnification d: center thickness of the objective lens f: focal length of the objective lens. [0011] [Action]In the present inventionThe condition is the aspherical surface on the light source side
In the condition to make higher order terms in the coefficient work effectively
is there. Now, R₁Is the upper limit 1.0h₁When bigger than
The effect of higher-order terms is small, and the wavefront aberration at the periphery is sharp.
It becomes difficult to prevent the increase. Also, R
₁Is the lower limit 0.8h₁When smaller, waves at the periphery
Advantageous for correcting surface aberration, but complicated aspherical shape
It is preferable because it becomes disadvantageous in lens production
I don't. [0012]Condition ~By adding
It is for obtaining more preferable performance. [0013]ArticleThe condition is suitable for the objective lens of the present invention.
3 shows the range of the imaging magnification for use. | M | is the upper limit of 0.
When larger than 26, the numerical aperture (NA) on the light source side
Becomes large, and the marginal rays enter the objective lens.
The angle becomes too large, and the wavefront aberration can be corrected well.
It will be difficult. | M | is smaller than the lower limit of 0.13.
Sometimes it is advantageous to correct wavefront aberration, but
The focal length of the object lens increases, and the optical system becomes smaller.
It becomes difficult to mold. The conditions are set so that the wavefront aberration can be satisfactorily corrected.
Is the condition. ｜ R₁/ R₂| Is larger than the upper limit of 0.8
When the threshold is large, the aspherical coefficient
The effect of higher-order terms cannot be made effective,
As a result, the wavefront aberration cannot be satisfactorily corrected.
It becomes. Also, | R₁/ R₂Is smaller than the lower limit of 0.5
Sometimes it is advantageous to activate the action of higher order terms
However, the aspherical shape becomes complicated, which makes
It is unfavorable because it is profitable. The condition is a condition relating to the thickness of the objective lens.
This is a condition for downsizing the lens. d / f
If the upper limit is 0.7 or more, the lens becomes too large
It is not suitable for miniaturization. The lower limit of d / f is 0.5.
Below 5 is advantageous for miniaturizing the lens,
Lens edge is too small,
It is unfavorable because it is beneficial [0016] BEST MODE FOR CARRYING OUT THE INVENTION A pair for an optical information recording medium according to the present invention
One embodiment of the object lens is shown in FIG. According to this embodiment,
The components of the optical system using the objective lens 3 shown in FIG.
Are basically the same as
Numbers give an overall view of the optical system and a detailed description
Is omitted. In this embodiment, the objective lens 3
Used for optical disc 4 as information recording medium
Things. This objective lens 3 is connected to the light source 1 (see FIG. 7).
A positive single lens with a convex surface facing
Both the surface 3a on the optical disk 4 side and the surface 3b on the optical disk 4 are non-spherical
It is composed of planes. The objective lens 3
The optical axis of the optical system using is shown by reference numeral 7 in FIG. An embodiment of the objective lens shown in FIG. 1 will be described below.
Will be described. Meanings of symbols used in description of examples
(Including the above-mentioned ones) and the implementation conditions are shown below. f: focal length of the objective lens NA: numerical aperture m: imaging magnification R₁: Paraxial radius of curvature on the light source side surface R₂: Paraxial radius of curvature on the optical disk side surface d: center thickness of the objective lens N: refractive index of the objective lens at a wavelength of 780 nm WD: Working distance h₁: Light at the periphery of the effective numerical aperture (NA) of the lens
Source-side surface (R₁Height of the light ray incident on the surface
Sa Cover glass thickness: 1.2mm Refractive index of cover glass: 1.55 In each of the following embodiments, the light source side
And the aspherical shape on the optical disk side, the vertex of the surface is the origin
In a rectangular coordinate system in which the optical axis direction is the Z axis, H
The height from the axis is represented by the following equation. [0020] (Equation 1) here, C = 1 / R (where R is R in the present embodiment)₁Also
Is R₂Is equivalent to ) K: conical constant A₁, A₂, A₃, A₄: Aspheric coefficient It is. (Embodiment 1) f = 2.800 NA = 0.574 m = −0.200 R₁= 2.00000 R₂= -3.662536 d = 1.950 N = 1.52249 WD = 1.649 h₁= 2.025 [0022] [Table 1] Numerical values for each condition   h₁= 2.025, R₁= 2.000   | M | = 0.200   ｜ R₁/ R₂| = 0.552   d / f = 0.696 (Embodiment 2) f = 2.657 NA = 0.575 m = −0.222 R₁= 1.90000 R₂= -3.443261 d = 1.85 N = 1.52249 WD = 1.586 h₁= 1.948 [0025] [Table 2] Numerical values for each condition   h₁= 1.948, R₁= 1.900   | M | = 0.222   ｜ R₁/ R₂| = 0.554   d / f = 0.696 (Embodiment 3) f = 3.070 NA = 0.594 m = -0.167 R₁= 2.15000 R₂= -4.20000 d = 2.10 N = 1.52249 WD = 1.779 h₁= 2.214 [0028] [Table 3]Numerical values for each condition   h₁= 2.214, R₁= 2.150   | M | = 0.167   ｜ R₁/ R₂| = 0.512   d / f = 0.684 (Embodiment 4) f = 2.908 NA = 0.600 m = −0.182 R₁= 2.10000 R₂= -3.70000 d = 2.00 N = 1.52249 WD = 1.712 h₁= 2.164 [0031] [Table 4] Numerical values for each condition   h₁= 2.164, R₁= 2.100   | M | = 0.182   ｜ R₁/ R₂| = 0.568   d / f = 0.688 The wavefront aberration diagrams in each of the above embodiments are shown.
2 to 5. In these figures, y is the image plane
In the height direction from the optical axis on the (optical disk surface)
The focal point displacement (mm), the vertical axis is the wavefront displacement, λ
Indicates the light wavelength, and the horizontal axis indicates the optical path length difference. The objective lens according to the present embodiment has an optical
The surface on the disk 4 side is a convex surface, but may be a concave surface. [0035] 【The invention's effect】The present inventionObjective information lens for optical information recording media
Since the lens has the above-described configuration, the
By enabling the action of higher-order terms in
Sharp increase of wavefront aberration in
Good performance can be obtained. In particular, this objective lens
According to the objective lens due to the bending of the optical information recording medium, etc.
Of the wavefront aberration even if the distance between the laser and the optical information recording medium fluctuates.
There is an effect that generation can be suppressed low. This
Optical information recording for more accurate information detection than before
There is an effect that it can be performed from a medium. [0036]The present inventionObjective lens for optical information recording medium according to the present invention
IsFurther, since the condition is satisfied,To effect
In addition, based on the action of the condition
Good wavefront aberration correction, miniaturization of optical system, lens manufacturing
Effects such as easiness can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view schematically showing an objective lens for an optical information recording medium according to one embodiment of the present invention. FIG. 2 is a wavefront aberration diagram according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating a wavefront aberration in the second embodiment of the present invention. FIG. 4 is a wavefront aberration diagram according to a third embodiment of the present invention. FIG. 5 is a wavefront aberration diagram according to a fourth embodiment of the present invention. FIG. 6 is an explanatory diagram showing a conventional infinite optical disk optical system. FIG. 7 is an explanatory diagram showing a conventional finite optical disk optical system. DESCRIPTION OF THE SYMBOLS 1 Light source 2 Collimating lens 3 Objective lens for optical information recording medium 3a Surface on the light source side of objective lens for optical information recording medium 3b Surface on optical information recording medium side of objective lens for optical information recording medium 4 Optical disk ( Optical information recording medium) 5 Half mirror 6 Detector 7 Optical axis

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-152408 (JP, A) JP-A 1-152409 (JP, A) JP-A 1-152410 (JP, A) JP-A-1-152408 167717 (JP, A) JP-A-2-118508 (JP, A) JP-A-2-195316 (JP, A) JP-A-4-107516 (JP, A) JP-A-4-125608 (JP, A) JP-A-8-5909 (JP, A) JP-A-8-136801 (JP, A) JP-A 8-179198 (JP, A) JP-A 8-334686 (JP, A) JP-A 9-54246 JP-A 9-54247 (JP, A) JP-A 9-81953 (JP, A) JP-A 10-26726 (JP, A) JP-A 10-199023 (JP, A) JP-A-61-248014 (JP, A) JP-A-62-54211 (JP, A) JP-A-62-54212 (JP, A) JP-A-63-13011 (JP, A) JP-A-64-25113 (JP, A) JP-A-2-223907 (JP, A) JP-A-57-201210 (JP, A) JP-A-61-70519 (JP, A) 62-36623 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 13/18 G02B 13/00 G11B 7/135

Claims (1)

(57) [Claims] 1. A positive single lens having a convex surface facing the light source side.
And both the light source side surface and the optical information recording medium side surface.
Is made of an aspheric surface and satisfies the following conditions:
And an objective lens for an optical information recording medium.   0.8h₁≤R₁≦ 1.0h₁   0.13 ≦ | m | ≦ 0.26   0.5 ≦ | R₁/ R₂| ≦ 0.8   0.55 <d / f <0.7 However, R₁: Paraxial radius of curvature on the light source side surface h₁: Light at the periphery of the effective numerical aperture (NA) of the lens
Source-side surface (R₁Height of the ray incident on the surface) from the optical axis R₂: Paraxial radius of curvature on the surface on the optical information recording medium side m: imaging magnification d: center thickness of the objective lens f: focal length of the objective lens.