JPH11249007A - Lens device having aberration adjusted by step - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lens device which can sealiged by simple machining technology and has aberrations adjusted by providing a step on the lens surface. SOLUTION: This is so constituted that aberrations are adjusted by providing on the surface of the lens 2 the lines of a step (d) symmetrically about a plane (p) containing its optical axis or a plane parallel to the said plane and forming a beltlike area (s) encircled with the lines. The said zone may be in a shape of one of a parallel zone, a pincushion zone, and barrel zone. Further, the said zone may be convex or concave. The said beltlike area and other areas can be made of the same optical material or different kind of optical materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens device for adjusting aberration by a step which can be used in a reading lens optical system for a CD, MD, DVD or the like using a laser diode or the like as a light source.

[0002]

2. Description of the Related Art In a pickup for a CD, MD, or DVD, as shown in FIG. 6, a parallel plane glass 9 (a so-called ass correction plate 9) is provided with a laser diode 8 and a collimator lens 1.
There is a device which is disposed between the first and second optical axes at an angle to a plane perpendicular to the optical axis. Furthermore, proposals for combining with a toric lens have been made, and some of them have been implemented. As an extension of this idea, a method of changing the curvature and the curved surface shape with respect to the orthogonal axis like a toric lens or a cylindrical lens on the lens surface (Japanese Patent Laid-Open No. 8-179198) is used.
It has been proposed to manufacture a rotationally asymmetric lens.

[0003]

In order to manufacture the above-mentioned lens, it is necessary to prepare a rotationally asymmetric complicated mold, and special techniques are required. SUMMARY OF THE INVENTION An object of the present invention is to provide a lens device in which aberration is adjusted by providing a step on a lens surface which can be realized by a simple processing technique.

[0004]

According to the present invention, there is provided a lens comprising:
The lens is configured such that a step line is provided symmetrically on a plane including the optical axis or a plane parallel to the plane on the surface of the lens, and a band-shaped region surrounded by the line is provided to adjust aberration. The shape of the band may be any of a parallel band, a wound band and a barrel band. The band can be either convex or concave. The band-shaped region and the other region can be made of the same optical material or different optical materials.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is an optical path diagram showing an example in which a lens according to the present invention is used as a collimator lens in connection with a laser diode, and FIG. 2 is a sectional view and a front view of the lens showing an embodiment. The lens has surfaces R ₁ and R
₂ (= R ₁ ) and R ₃ , and the surface R ₂ of the lens 2 on the side of the laser diode 1 is a band-shaped depression. A step d described later is provided between R ₁ and R ₂ . In this example, an optical resin material with the same refractive index is molded in a mold, but a thin film is applied to the lens itself in a strip shape by vacuum evaporation or the like, or the film is partially peeled off by etching etc. after attaching to the whole. It is also possible. The effect is the same whether the step is made of the same material as the lens or of a different substance. The same effect can be obtained regardless of whether the step is high or low at the center.

[0006]

EXAMPLE A rotationally symmetric aspheric plastic objective lens (NA = 0.45 f = 3.04 mm, distance between images 25)
mm A band-like step (depth d) is provided at the wavelength λ = 780 nm and n = 1.524). FIG. 2 shows a sectional view and a front view of an embodiment of the lens according to the present invention. The mold for manufacturing this embodiment can be easily manufactured by providing a band in close contact with a normal rotationally symmetric lens mold.

For the measurement of aberration, an aberration coefficient was obtained from the analysis of interference fringes. As shown in FIG. 2, a band having a width of about 1 mm (s = 1 mm) was attached to an effective diameter of about 3 mm, and the aberration was measured while changing the depth d (μm). FIG. 3 shows the relationship between the band depth d and astigmatism. From this figure, it can be seen that an arbitrary astigmatism can be created by changing the depth d.

FIG. 4 shows the measurement results of changes in astigmatism and coma with the horizontal axis representing the deviation (Δs) between the plane p including the optical axis of the lens and the center of the band s. Band width s = 1mm, step d
Is 0.15 μm. Deviation from the center of band s (Δs)
Was measured at points of 0, 0.25 mm, and 0.5 mm.
As is apparent from FIG. 4, no change is observed in the astigmatism, but the coma changes depending on the amount of deviation.

FIG. 5 shows that the aforementioned width s = 1 mm and depth d
(0.2 μm) shows a comparison between an example in which astigmatism is corrected to improve the angle of view characteristics of the objective lens and a case in which such correction or adjustment is not performed. Assuming that the allowable amount of astigmatism is 0.2λ, it can be seen that the usable angle of view is about 3.0 ° before the improvement, and is greatly improved to 4.6 ° after the improvement.

[0010]

Next, an example of using the lens according to the present invention will be described. It is generally said that a laser diode has astigmatism. Therefore, in an optical disk pickup using a laser diode as shown in FIG. 6, in order to correct this aberration, as described above with reference to FIG. A correction plate is additionally used.
By employing a collimator lens or an objective lens whose astigmatism is adjusted according to the present invention, astigmatism equivalent to that of a correction plate can be produced, so that there is no need to add a correction plate. The insertion of the astigmatism correction plate also causes coma at the same time, but the lens according to the present invention does not have such a problem and only the astigmatism of the laser diode can be corrected, so that ideal correction can be performed. .

When a lens is manufactured using a mold or the like, there are many cases where aberrations cannot be completely removed and remain due to the accuracy of the mold. In such a case, by adopting the present method as the last correction, it is possible to provide an almost perfect lens.

The lens according to the invention is suitable for correcting astigmatism of plastic lenses. In a plastic lens or the like used for picking up an optical disc, even if the shape is as designed, astigmatism may occur due to the birefringence of some plastic materials. The amount of astigmatism is predictable because it is substantially constant depending on the material, molding conditions, or polarization state of light. If the astigmatism that cancels out this amount is corrected in advance by a step, a lens having no aberration can be manufactured.

[Brief description of the drawings]

FIG. 1 is an optical path diagram showing an example in which a lens according to the present invention is used as a collimator lens in connection with a laser diode.

FIG. 2 is a cross-sectional and front view of a lens according to the present invention.

FIG. 3 is a graph showing a change in astigmatism when a band depth d is changed.

FIG. 4 is a graph showing changes in astigmatism and coma when the center of the band is shifted from the optical axis.

FIG. 5 is a graph showing a change in astigmatism angle characteristic between a case where a band is not provided and a case where a band is provided.

FIG. 6 is an optical path diagram showing a conventional astigmatism correction technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser diode 2 Collimator lens 8 Laser diode 9 Parallel plane glass (so-called ass correction plate) 10 Collimator lens

Claims (4)

[Claims] 1. A lens device wherein a stepped line is provided symmetrically on a plane including the optical axis or a plane parallel to the plane on the surface of the lens, and a band-shaped region surrounded by the line is provided to adjust aberration. 2. The lens device according to claim 1, wherein the shape of the band is one of a parallel band, a pin-shaped band, and a barrel-shaped band. 3. The lens device according to claim 1, wherein the band is convex or concave. 4. The lens device according to claim 1, wherein the belt-shaped region and the other region are made of the same optical material or different optical materials.