Objective lens for optical pickup

A pickup and objective lens technology, which is applied in the field of objective lenses, can solve the problems of difficult metal model processing, easy wear, and increased production costs, and achieve the effects of suppressing the reduction of optical performance of the objective lens, low manufacturing cost, and simple processing

Inactive Publication Date: 2004-01-14
ASAHI KOGAKU KOGYO KK
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0005] The diffractive lens structure has multiple regions, so metal models are difficult to machine
Also, due to the small width of these areas in the peripheral area of ​​the lens surface, fine cutting tools must be used
However, such delicate cutting tools are subject to wear and tear, so they must be replaced frequently
Therefore, if the above structure is adopted, the production cost will increase

Method used

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  • Objective lens for optical pickup
  • Objective lens for optical pickup
  • Objective lens for optical pickup

Examples

Experimental program
Comparison scheme
Effect test

no. 1 example

[0140] According to the first embodiment of the invention, C=-0.998, δ=0.1912, λ=660 nm, n=1.54044, λ′=668 nm and n′=1.54015. at this time

[0141] N=δ / (λ(n'-1) / ((n-1) / λ')-1)

[0142] =0.1912 / (660(1.54015-1) / ((1.54044-1)668)-1

[0143] =-15.36218 That is to say, when the optical path difference is Nλ, the wavefront aberration formed by the step S will introduce the required value when the temperature changes. However, if the optical path difference formed by the step S includes a fractional part, aberrations will be generated in the reference state (before temperature rise). Therefore, in the reference state, the optical path difference at the step S should be an integer. In this way, the actual height difference at the step S is the value after the decimal part is rounded off, for example, N=-15.

[0144] The step S should be formed so that the optical path of the light passing through the peripheral area of ​​the step S is 15λ longer than the optical path of the light ...

no. 1 approach

[0155] figure 2 It is a schematic diagram showing the objective lens 10 and the cover film D of the optical disc. Note that in the lens arranged in this embodiment, the step S adopts the same magnification ratio as other parts, so the height of the step S cannot be represented as a visible step in the diagram.

[0156] The structural parameters are shown in Table 1. In Table 1 and the tables of other embodiments, f represents the focal length, NA represents the numerical aperture, λ represents the design wavelength, r represents the radius of curvature of the lens surface (unit: mm), and d represents the distance between adjacent surfaces on the optical axis (unit: mm), and n is the refractive index at the design wavelength. , surface numbers #1 and #2 represent the first surface 11 and the second surface 12 of the objective lens 10, respectively, and surface numbers #3 and #4 represent the two coating surfaces D of the optical disc, respectively.

[0157] f=3.30m...

no. 2 approach

[0168] Figure 6 It is a schematic diagram of the objective lens 10 and the optical disc coating D, and the structural parameters are shown in Table 3.

[0169] f=3.00mm NA=0.60λ=660nm

the surface

r

d

n

1

1.9000

1.8000

1.54044

2

-7.3800

1.6230

-

3

∞

0.6000

1.57961

4

∞

-

-

[0170] The first surface 11 is divided into a central region and a peripheral region by a boundary having a height hx with respect to the optical axis. The central area is lower than the peripheral area. These regions may be aspherical surfaces with different shapes but with rotational symmetry, and steps S are formed between the regions (ie, there is a height difference). The second surface 12 is also a rotationally symmetrical aspheric surface without steps.

[0171] Effective radius hmax, boundary height hx, paraxial ...

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Abstract

An objective lens for an optical pickup has a single lens element. One surface of the objective lens is divided into a central area and a peripheral area, and a step providing a level difference along a direction of the optical axis is formed at a boundary therebetween. The step provides a phase shift between light passing through the central area and the peripheral area. The level difference is formed such that a thickness on the peripheral area side is greater than a thickness on the central area side at the boundary. In one case, the objective lens satisfies a condition: 0.83 < hx / hmax < 0.97, where hx is a radius of the boundary, and hmax is an effective radius defining a numerical aperture of the surface formed with the step.

Description

technical field [0001] The invention relates to an objective lens for an optical pickup in an optical disc drive. Background technique [0002] In optical pickups, plastic objective lenses are often used to reduce manufacturing costs. However, the change in refractive index with temperature and the linear expansion coefficient of plastic objectives are larger than those of glass lenses. Therefore, the optical performance of plastic lenses will be greatly reduced due to temperature changes. [0003] For low NA (numerical aperture) objectives used for relatively low data density optical discs, this degradation in performance is within acceptable limits. However, for high NA objectives of relatively high data density optical discs (eg, DVD: Digital Versatile Disc), this performance degradation due to temperature changes exceeds the allowable range, so the optical performance degradation must be checked. compensate. [0004] In Japanese Patent Provisional Publication HEI-11-...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G02B3/08G02B7/02G11B7/135
CPCG02B7/028G11B7/1374G02B3/08G11B7/13922
Inventor 是枝大辅丸山晃一
Owner ASAHI KOGAKU KOGYO KK
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