JPH0963108A - Optical pickup device - Google Patents

Abstract

(57) Abstract: Optical recording media having different thicknesses of optically transparent layers are reproduced and / or recorded without aberration. Laser light from a laser diode 11 of a light source is supplied to a condenser lens 14 via a beam splitter 13 and an aberration correction mechanism 16. The condenser lens 14 forms a minute spot on the recording surface of the optical recording medium. As the optical recording medium, optically transparent layers 22A, 22
Optical discs 21A and 21B having different thicknesses of, for example, 1.2 mm and 0.6 mm are used.
When reading the information recorded in 1A, the aberration correction lens 17a of the aberration correction mechanism 16 is switched and selected, and the spherical aberration of the condenser lens 14 due to the optically transparent layer 22A is corrected.
When reading the information recorded on the optical disk 21B,
The aberration correction lens 17b of the aberration correction mechanism 16 is switched and selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for reading a signal recorded on an optical recording medium such as an optical disc having an optically transparent layer having a different thickness on the recording surface side.

[0002]

2. Description of the Related Art In recent years, in order to protect information recorded on a recording layer of an optical recording medium such as an optical disk or information to be recorded from now on, in order to protect information read characteristics from dirt such as dust and dust from the outside, In order to prevent the deterioration of recording characteristics, an optically transparent protective layer is formed on the recording layer by coating.

Therefore, signals are recorded and reproduced through an optical transparent layer such as a protective layer of an optical disk, so that the condenser lens of the optical pickup device is
It is designed so that the optical characteristics are optimized corresponding to the optically transparent layer.

[0004]

By the way, when reproducing a plurality of optical recording media having different thicknesses of the optically transparent layer by one optical pickup device, it is necessary to correspond to the transparent layer having one thickness. If you try to play back an optical recording medium with a transparent layer of the other thickness using the condenser lens of the optical pickup designed to have the optimum optical characteristics, the original reading performance cannot be exhibited, and in extreme cases Cannot read information.

More specifically, for example, in order to provide a so-called compatible machine capable of reproducing optical disks of different formats with an optical transparent layer having a thickness of 1.2 mm and 0.6 mm, one type of optical disk is used. If an optical pickup designed for the thickness of the transparent layer, for example, 1.2 mm, is used to play the other type of optical disk, for example, an optical disk having a transparent layer of 0.6 mm in thickness, the original reading performance is obtained. In some extreme cases, information cannot be read.

That is, the performance deterioration caused by such a difference in the thickness of the optically transparent layer is due to so-called spherical aberration W _40. This spherical aberration W ₄₀ has an aperture ratio of the condenser lens set to NA, When the thickness of the transparent layer is Δt, it can be expressed as W ₄₀ ∝ (NA) ⁴ · Δt.

The present invention has been made in view of the above situation, and an optical pickup capable of correcting aberration when reading information from a plurality of types of optical recording media having optical transparent layers having different thicknesses. The purpose is to provide a device.

[0008]

In order to solve the above-mentioned problems, the present invention provides a condensing lens for forming a minute spot on the recording surface of an optical recording medium via the optically transparent layer. An aberration correction mechanism for switching and selecting aberration correction means for correcting the spherical aberration of the condenser lens according to the thickness of the optically transparent layer of the optical recording medium.

Here, it is preferable that the aberration correction mechanism is arranged on the entrance pupil side of the condenser lens. Further, the condensing lens is designed corresponding to the thickness of the optically transparent layer of one type of optical recording medium of a plurality of types of optical recording medium having optically transparent layers of different thicknesses, It is desirable for the above-mentioned aberration correction mechanism to switch and select the aberration correction means that forms the aberration of the same polarity and the opposite polarity as the spherical aberration caused by the optically transparent layer of another type of optical recording medium.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram schematically showing an example of a configuration to which an embodiment of the present invention is applied. In this embodiment, a plurality of types of optical recording media having different thicknesses of the optically transparent layer on the recording surface side (hereinafter, also referred to as transparent layer thickness), for example, optical disks 21A and 21B are illustrated. In these optical disks 21A and 21B, the thickness of the respective optically transparent layers 22A and 22B is, for example, 1.2.
mm and 0.6 mm are different from each other.

The optical pickup device shown in FIG. 1 includes a laser diode 11 as a light source, a beam splitter 13 for branching reflected light from the surface of the recording surface of the optical recording medium and guiding it to a photodetector 12, and recording on the optical recording medium. A condensing lens 14 that forms a minute spot on the surface, a photodetector 12 that is a photoelectric conversion element that converts a change in reflected light from an information pit or the like on the recording surface of the medium into an electric signal, and converged light and parallel light. A collimator lens 15 for conversion,
At least an aberration correction mechanism 16 for correcting the spherical aberration of the condenser lens 14 is provided.

In the example of FIG. 1, the condenser lens 14
Is an optically transparent layer 22 of each of the optical disks 21A and 21B.
A, 22B, which is the thickness of 1.2 mm and 0.6 mm, is designed in accordance with a transparent layer having an intermediate thickness, for example, 0.8 mm, and the aberration correction mechanism 16 includes each optical transparent layer 22A,
When the recording surface is irradiated with the laser beam via 22B, the spherical aberrations caused by the respective transparent layers are switched to the aberration correction lenses 17a and 17b having the same amount and the opposite polarity aberrations, thereby performing an appropriate aberration correction. I am trying to do it.

The numerical aperture NA of the condenser lens 14 is designed to be the maximum NA among the NAs required in the respective disc systems using the respective optical discs 21A and 21B or the standards. For example, a transparent layer thickness of 1.2
The numerical aperture NA of the condenser lens 14 is 0.5 when the NA required by the system of the optical disc 21A of 0.5 mm is 0.52 and the NA required by the system of the optical disc 21B having the transparent layer thickness of 0.6 mm is 0.6. Is set to 0.6. The numerical aperture NA can also be changed to 0.52 by switching and selecting the aberration correction lens 17a when reading the optical disk 21A having a transparent layer thickness of 1.2 mm. This is because the aberration correction lenses 17a, 17a of the aberration correction mechanism 16 are
This can be realized by designing the aperture diameters of the aberration correction lenses 17a and 17b so that the substantial numerical aperture NA of the condenser lens 14 becomes 0.52 and 0.6, respectively, by switching and selecting b. .

Here, the relationship between the thickness of the optically transparent layer of the optical recording medium and the spherical aberration of the condenser lens is shown in FIG.
A description will be given with reference to the configuration of FIG. 2 excluding the aberration correction mechanism 16 of FIG.

FIG. 2 shows a basic structure of a general optical pickup device, and parts corresponding to those in FIG. 1 are designated by the same reference numerals. In FIG. 2, laser light from the laser diode 11 serving as a light source is reflected by the beam splitter 13 and supplied to the collimator lens 15 to be collimated light, and this collimated light is incident on the condenser lens 14. The condensing lens 14 condenses the light from the aberration correction lens of the aberration correction mechanism 16 and records the light through an optically transparent layer 22 of an optical recording medium, for example, an optical disk 21, a recording surface,
That is, the surface of the recording layer 23 is irradiated. Condensing lens 14
Is also called an objective lens. The reflected light from the recording surface of the optical disc 21 passes through the optically transparent layer 22 and passes through the condenser lens 1
4, the collimator lens 15, and the beam splitter 13 respectively, and the photodetector 1 which is a photoelectric conversion element.
It is incident on 2. In addition to the above, the configuration for so-called focus servo and tracking servo that causes a minute spot formed by the condenser lens 14 to follow the surface wobbling of the optical disc, the track shift due to the disc rotation, and the like will be described in this example. Since it is not necessary, the illustration and description are omitted.

In the optical pickup device having the configuration shown in FIG. 2, when the condenser lens is optimally designed corresponding to the optical transparent layer of the optical disc using a polycarbonate material having a thickness of 1.2 mm, for example, The spherical aberration W ₄₀ on the axis of this condenser lens is expressed as a curve a in FIG. The curve a in FIG. 3 shows the thickness of the optically transparent layer 22 of the optical disk 21 on the horizontal axis and the spherical aberration W ₄₀ on the vertical axis, and is designed corresponding to such a transparent layer thickness of 1.2 mm. When information is read from an optical disk having a transparent layer thickness of 0.6 mm by using the condensing lens, the spherical aberration W ₄₀ that occurs is W ₄₀ ≈0.4λrms, and the information cannot be read. When a condenser lens designed to have a transparent layer thickness of 0.6 mm is used, the axial spherical aberration W ₄₀ is as shown by the curve b in FIG.

FIG. 4 shows the spherical aberration W ₄₀ when a condenser lens designed to have an optically transparent layer having a thickness of 0.9 mm which is an average value of the above 0.6 mm and 1.2 mm is used. ing.

Here, the difference in the thickness of the optically transparent layer when trying to read information from an optical disc of an arbitrary thickness by using a condenser lens designed for the optically transparent layer of a predetermined thickness, When Δt, the spherical aberration W of the condenser lens
₄₀ is W ₄₀ ≈ A × (NA) ⁴ Δt / λ where A is a proportional constant, NA is the numerical aperture of the condenser lens, and λ
Is the wavelength of the laser light of the light source. In order to correct this spherical aberration W ₄₀ , an optical component having the same amount as W ₄₀ but having the opposite polarity is used as the aberration correcting means.

In the example shown in FIG. 1, the thickness of the optically transparent layer when designing the condenser lens 14 is 0.6 mm and 1.2.
The value is set to a value approximately in the middle of mm, for example, 0.8 mm.
The numerical aperture NA of the condenser lens 14 is 0.6.

An optical disk 21 having an optically transparent layer 22A having a thickness of 1.2 mm is formed by using such a condenser lens 14.
When trying to reproduce A, the spherical aberration is 0.212 λrm
s occurs. On the other hand, aberration correction is performed using the aberration correction lens 17a having an aspherical concave lens shape as shown in FIG. The radius of curvature Ra of the aspherical concave surface of the aberration correction lens 17a is 30.7 mm, and the thickness La of the lens center is La.
2 mm, and the condenser lens 1 as shown in FIG.
By inserting the aberration correction lens 17a between the entrance pupil side of No. 4, for example, between the condenser lens 14 and the collimator lens 15, the total aberration can be set to 0.0127 λrms.

An optical disk 21 having an optically transparent layer 22B having a thickness of 0.6 mm is formed by using the condenser lens 14 described above.
When reproducing B, the spherical aberration is -0.1977.
λrms occurs. On the other hand, an aberration correction lens 17b having an aspherical convex lens shape as shown in FIG. 5B is used. The radius of curvature Ra of the aspherical convex surface of this aberration correction lens 17b is 65.4 mm, and the thickness La at the center of the lens is 2.6 mm.
As shown in FIG. 1B, by inserting the aberration correction lens 17b on the entrance pupil side of the condenser lens 14,
The total aberration can be 0.0061 λrms.

By the way, FIG. 1 shows a collimator lens 15
Although an example is shown in which the aberration correction mechanism 16 is arranged at a position where parallel light is used by using, the present invention can be applied to a finite lens system as shown in FIG. 6 that does not use a collimator lens.

In FIG. 6, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and a condenser lens 24 which is an objective lens collects divergent light from the laser diode 11 of the light source to form an optical disc. To form a minute spot on the recording surface. The aberration correction mechanism 2 is provided on the entrance pupil side of the condenser lens 24.
6 is arranged, and the aberration correction mechanism 26 has an optical disc 21 having an optically transparent layer 22A having a thickness of 1.2 mm.
When reproducing A, the aberration correction lens 27a which is a concave lens
Is placed in the optical path, and the optically transparent layer 22 has a thickness of 0.6 mm.
When reproducing the optical disk 21B having B, the aberration correction lens 27b, which is a convex lens, can be switched to be arranged in the optical path.

Next, FIG. 7 shows an optical pickup using a condenser lens 34 designed optimally for the optical disk 21A having an optically transparent layer 22A having a thickness of 1.2 mm, that is, a spherical aberration being minimized. 1 shows an embodiment of an apparatus. In FIG. 7 as well, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and description thereof will be omitted.

In FIG. 7, an aberration correction mechanism 36 is arranged on the entrance pupil side of the condenser lens 34. The aberration correction mechanism 36 is an opening 37a in a plate-like member that moves in the direction of the arrow in the figure. And a correction lens 37b are provided. An optical transparent plate may be fitted in the opening 37a.

The condenser lens 34 has the maximum NA among the numerical apertures NA required by the standards corresponding to the above-mentioned two types of optical discs 21A and 21B or the disc system.
Designed with. For example, an optical disc 2 in which the thickness of the optically transparent layer (hereinafter also referred to as the transparent layer thickness) is 1.2 mm.
Numerical aperture NA required for 1A system is 0.52,
When the NA required by the system of the optical disk 21B having a transparent layer thickness of 0.6 mm is 0.6, the condenser lens 34 of FIG.
Has a numerical aperture NA of 0.6 and is designed to minimize spherical aberration for a transparent layer thickness of 1.2 mm. That is, the optical axis of the optical disc 2 having the spherical aberration on the axis of the condenser lens as shown by the curve a in FIG.
When reading 1A, as shown in FIG. 7A, the aperture 37a of the aberration correction mechanism 36 is switched and selected, so that the aberration is not corrected, but the size of the diameter of the aperture 37a or the like. Has a substantial numerical aperture NA of the condenser lens 34 of 0.
It is designed to be 52. Further, when reading the optical disc 21B having a transparent layer thickness of 0.6 mm, the aberration correction lens 36b is switched and selected in the aberration correction mechanism 36 as shown in FIG. 7B, and the aberration correction lens 37b is selected.
Is designed to form a spherical aberration of about −0.4λrms corresponding to a transparent layer thickness of 0.6 mm of the curve a in FIG. 3 and an aberration of about + 0.4λrms of the opposite polarity with the same amount. ing.

According to the embodiment described above,
With a simple configuration in which the aberration correction means of the aberration correction mechanism is simply switched, a plurality of types, for example, two types of optical disks 21A and 21B having different transparent layer thicknesses can be reproduced using one optical pickup device. A reproducing device compatible with the disk system can be provided at low cost.

Further, since the aberration correcting means of the aberration correcting mechanism is a transparent optical component such as a lens, an opening or a transparent plate, the light amount from the light source onto the disk is not reduced and the output from the light source is effective. Available.

In the example shown in FIG. 7, the aberration correction mechanism 3
Since only one aberration correction lens 37b needs to be used for 6, it is inexpensive. On the other hand, in the example of FIG.
The aberration correction mechanism 16 includes two aberration correction lenses 17a and 17a.
Although b is used, the amount of aberration correction can be small, so that the accuracy of aberration correction can be made high.

The present invention is not limited to the examples of the above-described embodiments, and for example, an optical pickup device for reading recorded information has been described, but a recording / reproducing optical pickup device and a recording / reproducing device. It can also be easily applied to an optical pickup device for use. Also,
It is needless to say that the types of optical discs having different optically transparent layers are not limited to two types and may be three or more types, and various optical recording media other than the optical discs may be used.

[0032]

According to the present invention, an optical recording medium having a plurality of mutually different optically transparent layer thicknesses can be reproduced and / or recorded by one optical pickup device, and the aberration correction mechanism can be used. By switching and selecting the aberration correction means such as the aberration correction lens, it is possible to inexpensively supply the compatible optical pickup device.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an example of an embodiment of an optical pickup device according to the present invention.

FIG. 2 is a diagram showing a schematic configuration of an example of a general optical pickup device.

FIG. 3 is a diagram showing an example of axial aberration of a condenser lens.

FIG. 4 is a diagram showing another example of the axial aberration of the condenser lens.

FIG. 5 is a diagram showing a specific example of an aberration correction lens that serves as aberration correction means.

FIG. 6 is a diagram showing a schematic configuration of another example of the embodiment of the optical pickup device according to the present invention.

FIG. 7 is a diagram showing a schematic configuration of still another example of the embodiment of the optical pickup device according to the present invention.

[Explanation of symbols]

11 laser diode 12 photodetector 13 beam splitter 14, 24, 34 condenser lens 15 collimator lens 16, 26, 36 aberration correction mechanism 17a, 17b, 27a, 27b, 37b aberration correction lens 37a aperture 21A, 21B optical disk 22A, 22B optical Transparent layer 23A, 23B recording layer

Claims (5)

[Claims] 1. An optical pickup device in which light from a light source is applied to a recording surface through an optically transparent layer of an optical recording medium, and the reflected light is received by a light receiving means, on the recording surface of the optical recording medium. A condenser lens for forming a minute spot through the optically transparent layer, and an aberration correction means for correcting the spherical aberration of the condenser lens in the thickness of the optically transparent layer of the optical recording medium. An optical pickup device comprising: an aberration correction mechanism that is switched and selected according to the selection. 2. The optical pickup device according to claim 1, wherein the aberration correction mechanism is arranged on the entrance pupil side of the condenser lens. 3. The condensing lens is designed to correspond to the thickness of the optically transparent layer of one type of optical recording medium of a plurality of types of optical recording media having optically transparent layers of different thicknesses. The aberration correction mechanism is configured to switch and select an aberration correction means that forms an aberration of an opposite polarity with the same amount as a spherical aberration caused by an optically transparent layer of another type of optical recording medium. 1. The optical pickup device described in 1. 4. The condenser lens is designed to correspond to an intermediate value of thicknesses of a plurality of types of optical recording media having a plurality of optically transparent layers having different thicknesses, and the aberration correction is performed. 2. The optical pickup device according to claim 1, wherein the mechanism switches and selects an aberration correction means that forms an aberration of the same polarity as that of the spherical aberration generated by the optically transparent layer of each type of optical recording medium but has an opposite polarity. . 5. The condensing lens has a maximum numerical aperture out of the numerical apertures required for a plurality of types of optical recording media having optical transparent layers having a plurality of mutually different thicknesses, The optical pickup device according to claim 1, wherein the aberration correction means of the aberration correction mechanism has an aperture that realizes a numerical aperture required for each of the types of optical recording media.