JP2001134978A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device capable of stably recording and reproducing with respect to each of recording layers in the depth direction with simple and inexpensive constitution. SOLUTION: The optical pickup device has a constitution such that, when a first spot by light beams 10 from a first light source 12 is formed in a guide track layer 2 of an information recording medium 1 having the guide track layer 2 and plural recording layers 6 in the depth direction and a second spot by light beams 20 from a second light source 21 is formed in a prescribed position in the depth direction forming plural recording layers 6, a spherical aberration of either one spot becomes nearly zero and, in that state, the spherical aberration is generated in an optical system forming the other spot so as to offset the spherical aberration generating in the other spot.

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 recording or reproducing information on an information recording medium having a guide track layer and a plurality of recording layers in a depth direction.

[0002]

2. Description of the Related Art An example of this type of optical pickup device is disclosed in Japanese Patent Application Laid-Open No. Hei 4-301226. This optical pickup device uses a guide light source and a scanning light source for recording and reproduction. A guide beam from the guide light source is converted into a parallel light beam by a collimator lens, and then a beam combining element, a galvanometer mirror, and an objective lens are used. Is focused on the guide track layer of the information recording medium. Similarly, the scanning beam from the scanning light source is similarly converted into a parallel light beam by a collimator lens, then combined with the guide beam by the beam combining element, and passes through the galvanomirror and the objective lens to the desired information recording medium. Is condensed on a recording layer having a depth of.

As described above, in recording information,
The guide beam is focused on the guide track layer, and while performing focus control and tracking control based on the returned light, the scanning beam is focused on the recording layer having a desired depth to record information, and the desired depth is recorded. In reproducing or erasing information recorded on the recording layer, the scanning beam is focused on the recording layer having a desired depth, and information is reproduced while performing focus control and tracking control based on the returned light. Alternatively, it is erased.

[0004]

By the way, as described above, the guide beam is condensed on the guide track of the information recording medium by the common objective lens, and the scanning beam is shifted in the optical axis direction to a recording layer having a desired depth. When condensing light to
When the condensing position of the scanning beam, that is, the position of the recording layer changes, and the medium thickness between the guide beam spot and the scanning beam spot changes, the guide beam spot or the scanning beam spot changes depending on the change in the medium thickness. Spherical aberration occurs to degrade the recording / reproducing performance, so that stable recording / reproducing cannot be performed for each recording layer in the depth direction.

For this reason, in the above-described optical pickup device, correction elements having different thickness areas are arranged between the guide light source and the collimator lens and in the optical path between the scanning light source and the collimator lens. These correction elements are driven so that a predetermined thickness area is located in the optical path in accordance with the selected depth position of the recording layer, thereby correcting spherical aberration.

However, in this case, since a correction element and a driving mechanism for the correction element are required, the number of parts is increased, the configuration is complicated, and the cost is increased.

The present invention has been made in view of such a conventional problem, and has an easy and inexpensive configuration and can stably record / reproduce information on / from each recording layer in the depth direction. The purpose is to provide.

[0008]

According to a first aspect of the present invention, there is provided a first light source and a second light source which emit light beams having different wavelengths, and the first light source and the second light source. A light source from the first light source, the light beam from the first light source passing through the objective lens, the guide of the information recording medium having a guide track layer and a plurality of recording layers in a depth direction. The light beam from the second light source is condensed on a desired recording layer of the information recording medium through the objective lens while performing focusing control on the track layer and performing tracking control based on the returned light. In the optical pickup device, a first spot by a light beam from the first light source is formed on a guide track layer of the information recording medium, and a first spot is formed at a predetermined position in a depth direction at which the plurality of recording layers are formed. When a second spot is formed by a light beam from the second light source, the spherical aberration of one of the spots is configured to be substantially zero, and the spherical aberration generated in the other spot in that state. In order to cancel out, the optical system forming the other spot is configured to generate spherical aberration.

According to the first aspect of the present invention, the deterioration of the recording / reproducing performance for each recording layer in the depth direction can be reduced without providing a correction element having a different thickness area for correcting spherical aberration and a driving mechanism therefor. Since it can be effectively prevented, it is possible to stably perform recording / reproduction on each recording layer in the depth direction with a simple and inexpensive configuration.

According to a second aspect of the present invention, in the optical pickup device according to the first aspect, the wavelength of the light beam radiated from the first light source is made larger than the wavelength of the light beam radiated from the second light source. Is also set to be long.

According to the second aspect of the present invention, the second wavelength having a short wavelength is used.
Since the light beam from the light source is converged on a desired recording layer, the size of the second spot can be reduced, so that high-density recording / reproduction can be performed.

The invention according to claim 3 is the optical pickup device according to claim 2, wherein the first spot is formed on the guide track layer and the second spot is formed at the predetermined position. The objective lens is configured such that the spherical aberration of the spot formed on the side closer to the objective lens is substantially zero, and the spherical aberration generated on the spot formed on the side farther from the objective lens in that state. A plano-convex spherical lens is provided in the optical system that forms the spot so as to generate a spherical aberration that cancels out.

According to the third aspect of the present invention, by forming the objective lens such that the spherical aberration of the spot formed on the side close to the objective lens is substantially zero, the spot is formed on the side remote from the objective lens. The spherical aberration generated on the over side of the spot can be easily canceled by generating the spherical aberration on the under side using an inexpensive plano-convex spherical lens.

According to a fourth aspect of the present invention, in the optical pickup device according to the second aspect, when the first spot is formed on the guide track layer and the second spot is formed at the predetermined position. The optical system is configured so that the spherical aberration of one of the spots is substantially zero, and the other spot is formed so as to generate a spherical aberration that cancels out the spherical aberration occurring in the other spot in that state. A hologram is provided in the system.

According to the fourth aspect of the present invention, the spherical aberration of the spot formed on the side closer to or far from the objective lens is made substantially zero, so that the spot formed on the side farther or closer to the objective lens is reduced. Spherical aberration occurring on the over side or the under side can be reliably canceled with a simple configuration using a hologram.

The invention according to claim 5 is the invention according to claims 1, 2, 3
In the optical pickup device described in Item 4, the first spot is formed on the guide track layer, and the second spot is formed at a substantially middle position in a depth direction area forming the plurality of recording layers. In some cases, the spherical aberration of one of the spots is substantially zero.

According to the fifth aspect of the present invention, the spherical aberration is corrected with reference to a substantially middle position in the depth direction region where a plurality of recording layers are formed. Recording / reproduction can be performed more stably with respect to the recording layer.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall schematic configuration diagram showing a first embodiment of the present invention. In FIG. 1, an information recording medium 1 has a reflective surface 2 having a groove.
A recording medium 4 such as a photopolymer, a photorefractive crystal, or a photochromic material provided on the reflection surface 2 via a recording / reproducing laser light absorption layer 3; a surface of the recording medium 4 and the reflection surface 2; And a protective layer 5 provided on the other surface of the recording medium 4 and recording information by changing its refractive index and light absorption at different depth positions in the recording medium 4 to form a plurality of recording layers. 6 are formed. In this embodiment, the information recording medium 1 includes a servo laser beam 10 for performing focus control and tracking control from the recording medium 4 side,
The recording / reproducing is performed by irradiating the recording / reproducing laser beam 20 with the desired recording layer. The wavelength of the servo laser beam 10 is longer than the wavelength of the recording / reproducing laser 20.

The servo laser beam 10 is emitted from the light source unit 1
Emitted from 1. The light source unit 11 is provided with a semiconductor laser (first light source) 12, a photodetector 13, and a hologram 14.
Then, the servo laser beam 10 is emitted. The servo laser beam 10 from the light source unit 11 is collimated by a collimator lens 15, then passes through a dichroic prism 16, and passes through an information recording medium 1 through an objective lens 17.
Is condensed on the reflection surface 2.

The servo laser beam 10 reflected by the information recording medium 1 follows a path reverse to the outward path, passes through an objective lens 17, a dichroic prism 16 and a collimator lens 15, and forms the hologram 1 of the light source unit 11.
4 and diffracted, the diffracted light is received by the photodetector 13, a focus error signal is detected by a known beam size method, Foucault method, or the like, and a tracking error signal is detected by a push-pull method or the like.

On the other hand, the recording / reproducing laser beam 20 is emitted from a semiconductor laser (second light source) 21. The laser light emitted from the semiconductor laser 21 is converted into parallel light by a collimator lens 22 and is incident on the polarization beam splitter 23 as P-polarized light, and the laser light transmitted through the polarization beam splitter 23 is passed through a １ ／ wavelength plate 24. After passing through the dichroic prism 16, the laser light is reflected by the dichroic prism 16, and the laser light reflected by the dichroic prism 16 is condensed on a desired information track of the information recording medium 1 by the objective lens 17. .

The recording / reflection on the information recording medium 1
The reproduction laser beam 20 follows a reverse path to the outward path,
Objective lens 17, dichroic prisms 16 and 1
The light is incident on the polarization beam splitter 23 through the 波長 wavelength plate 24. Here, the reflected light from the information recording medium 1 incident on the polarization beam splitter 23 is １ ／ in the forward path and the return path.
Since the light passes through the wavelength plate 24, it becomes S-polarized light, and is reflected by the polarization beam splitter 23. The laser beam reflected by the polarization beam splitter 23 is condensed by a detection lens 25, and at the converging point, a PIN
The light is received by the photodiode 27, and information recorded on a desired recording layer of the information recording medium 1 is reproduced based on the output.

The collimator lens 15 is configured to be drivable in a focus direction by a uniaxial actuator (not shown), and the objective lens 17 is configured to be drivable in a focus direction and a tracking direction with respect to the information recording medium 1 by a biaxial actuator (not shown). I do.

In this way, the collimator lens 15 and the objective lens 17 are driven in the focus direction in accordance with the desired depth position of the recording layer 6 to be recorded / reproduced. Driven in the focusing direction and the tracking direction based on the tracking error signal, the servo laser beam 10 is focused on the reflection surface 2 and the recording / reproducing laser beam 20 is focused on a desired recording layer. Is controlled to follow the track.

Here, for example, the wavelength of the servo laser beam 10 emitted from the semiconductor laser 12 is 780 nm, the focal length of the collimator lens 15 is 14 mm, and the wavelength of the recording / reproducing laser beam 20 emitted from the semiconductor laser 21 is 6
50 nm, the focal length of the collimator lens 22 is 12 m
m, the numerical aperture is 0.138, the focal length of the objective lens 17 is 2.7 mm, and the numerical aperture is 0.52.

In this embodiment, the recording / reproducing laser beam 20 having a wavelength of 650 nm is irradiated by the objective lens 17 from a substantially intermediate position in the depth direction region (thickness) of the recording medium 4, that is, from the surface of the information recording medium 1. When condensing light at the position of the thickness t1, the objective lens 17 is designed with aberration correction using a glass material having a small Abbe number, for example, SF8, so that the spherical aberration of the spot (second spot) becomes zero. .

The collimator lens 15 constituting the optical system of the servo laser beam 10 having a wavelength of 780 nm reflects the recording / reproducing laser beam 20 in a state where the laser beam 20 is focused on the position of the thickness t1 of the information recording medium 1. A plano-convex spherical lens is formed so as to generate spherical aberration that cancels out spherical aberration occurring at a spot (first spot) of the servo laser beam 10 formed on the surface 2.

That is, as shown in FIG. 2A, when the recording / reproducing laser beam 20 having a wavelength of 650 nm is condensed by the objective lens 17 at the position of the thickness t1 of the information recording medium 1, the spot is formed on the spot. When the objective lens 17 is designed by correcting the aberration so as not to cause spherical aberration, when the servo laser beam 10 having a wavelength of 780 nm is incident on the objective lens 17 as shown in FIG. The image point can be made farther by the chromatic aberration of the objective lens 17. For example, if the chromatic aberration is 0.2 μm / nm, 0.2 μm /
nm × (780−650) nm = 26 μm, and the working distance (WD) is shown in FIG.
WD2 is longer than WD1 in (a) (WD2-W
D1 = 26 μm).

Further, as the wavelength becomes longer, the refractive index of the objective lens 17 becomes lower and the lens power becomes weaker. Therefore, as shown in FIG. (SA3) appears on the over side. Assuming that the numerical aperture of the objective lens 17 is 0.52 and the refractive index of the information recording medium 1 is 1.57, the amount of occurrence of this spherical aberration is 0.008λrms level (where λ
Is 780 nm at the wavelength of the servo laser beam 10).

Here, the spherical aberration caused by the thickness of the information recording medium 1 is such that the thickness error with respect to the reference medium thickness is dt, the refractive index of the information recording medium 1 is n, and the numerical aperture of the objective lens 17 is NA. If the wavelength used is λ, the optics 14 (19
85) It is represented by the following equation from pages 219 to 221.

Ω40 = dt / 8 × (n ² −1) / n ³ × NA ⁴ wavefront aberration rms value = ω40 × 0.0745 / λ

FIG. 4 shows that NA = 0.52, n = 1.57,
It shows the relationship between dt when λ = 780 nm and the amount of tertiary spherical aberration (rms value). As can be seen from FIG. 4, the spherical aberration occurs on the over side when dt is thicker than the reference thickness, and conversely, on the negative side where dt is thinner than the reference thickness. It occurs on the under side.

From FIG. 4, in order to correct the spherical aberration of 0.008 λrms generated in the case of FIG. 2B, the medium thickness should be reduced by about 20 μm and the spherical aberration should be moved to the under side. However, in practice, as shown in FIG. 2 (c), the WD maintains the same WD1 as in FIG. 2 (a) and focuses the servo laser beam 10 having a wavelength of 780 nm on the medium thickness t2. In this case, the increase in the medium thickness (t2-t
1) also needs to be considered. This increase in media thickness (t
2−t1), when n = 1.57, from the state of FIG. 2A, t2−t1 = 0.2 μm / nm × (780−65)
0) nm × 1.57 ≒ 41 μm

Accordingly, when viewed from the medium thickness where the spherical aberration is minimized with respect to the servo laser beam 10 having a wavelength of 780 nm, the focal point of the recording / reproducing laser beam 20 having a wavelength of 650 nm converged to a thickness t1. Thickness error dt from dt
= 20 μm + 41 μm = 61 μm, and for this thickness error of 61 μm, the spherical aberration is 0.0
24λrms will occur.

Therefore, in this embodiment, the above-described 0.
In order to cancel the spherical aberration of 024λrms, FIG.
As shown in the partial schematic diagram of FIG. 4D, the collimator lens 15 of the optical system of the servo laser beam 10 having a wavelength of 780 nm is formed of a plano-convex spherical lens.

As described above, when the collimator lens 15 is constituted by a plano-convex spherical lens, the focal length fco is fixed to the above-mentioned 14 mm, and when the refractive index of the glass material is changed, the collimator lens 15 is substantially taken into the objective lens 17. Collimator lens 1
The spherical aberration at the numerical aperture NA _CO of 5 is as shown in FIG. Here, in the case of a spherical lens, when a light beam from a point light source passes through, a light beam passing through the peripheral portion becomes a wavefront that advances more than a light beam passing through the central portion, and spherical aberration occurs on the under side. Accordingly, it is possible to cancel the spherical aberration occurring on the over side due to the thickness error dt in the information recording medium 1.

For this reason, in this embodiment, the collimator lens 15 is made of a glass material (for example, S
F8) to form a plano-convex spherical lens, whereby the recording / reproducing laser beam 20 is applied to the recording medium 4 of the information recording medium 1 with a thickness t substantially at an intermediate position in the depth direction region (thickness) of the recording medium 4.
When the light is condensed without causing spherical aberration at 1, the wavelength 7 condensed on the reflecting surface 2 having a thickness t2 of 41 μm away from the objective lens 17 in the medium from the thickness t1.
This cancels out the above-mentioned spherical aberration of 0.024 λrms which occurs in the spot of the 80 nm servo laser beam 10.

With this configuration, in FIG. 1, the recording / reproducing beam 20 is focused on the recording layer 6 having a thickness t1 of the information recording medium 1 from the recording layer 6 to be recorded / reproduced.
The collimator lens 15 of the servo optical system is moved in the direction of the optical axis in accordance with the depth position of the servo optical system, and the objective lens 17 is moved in the direction of the optical axis in conjunction with the movement of the collimator lens 15 in the information recording medium 1. When the interval between the two spots in the depth direction is changed, the wavefront aberration of the two spots changes as shown in FIG. 6A, and uniform aberration degradation can be maintained in the thickness direction.

That is, the center position where the recording / reproducing spot is formed on the recording layer 6 having a thickness t1 of 41 μm away from the reflecting surface 2 having a thickness t2 where the servo spot is formed and approaching the objective lens 17. In this case, the wavefront aberration of the two spots is minimized, and both spots are equal as the distance between the two spots approaches or separates, that is, as the recording / reproducing spot approaches or separates from the position of the thickness t1 to the reflection surface 2. The wavefront aberration increases.

On the other hand, if the collimator lens 15 is formed as an aspheric surface in order to correct the aberration by the lens alone, as shown in FIG. 6B, the distance between the two spots is 41 μm.
Since the aberration of the spot having the wavelength of 780 nm is deteriorated at the center position of, when the distance between the two spots approaches, the aberration of the spot having the wavelength of 780 nm further worsens.

As described above, according to this embodiment,
When the recording / reproducing laser beam 20 is condensed at a position at a substantially middle thickness t1 of the recording medium 4 of the information recording medium 1 without using a conventional correction element and its driving mechanism,
The objective lens 1 is designed so that no spherical aberration occurs in the spot.
7 and the collimator lens 15 of the servo optical system so as to cancel the spherical aberration generated in the spot of the servo laser beam 10 focused on the reflection surface 2 located at the thickness t2 in that state. Since spherical aberration is generated, the recording / reproducing performance of each recording layer 6 in the depth direction can be effectively suppressed from deteriorating with a simple and inexpensive configuration, and recording / reproducing can be performed stably. Further, since the above-mentioned collimator lens 15 is constituted by a plano-convex spherical lens, the collimator lens 15 itself can be made inexpensive, and the whole can be made more inexpensive.

FIG. 7 is a schematic diagram showing a configuration of a main part of the second embodiment of the present invention. This embodiment is different from the first embodiment in that the information recording medium 31 has a groove layer 32 at a position of a thickness t1 from the surface on the side of the objective lens 17, and the groove layer 32 on the side away from the objective lens 17. A servo laser beam 10 having a wavelength of 780 nm is condensed on the groove layer 32 by the objective lens 17 using a recording medium having a recording medium 34 provided via an absorption layer 33 for servo laser light. The recording / reproducing of information is performed by converging the reproducing laser beam 20 on desired recording layers 35 at different depth positions in the recording medium 34.

In this embodiment, the recording / reproducing laser beam 20 having a wavelength of 650 nm is applied to a substantially middle position of the depth direction region (thickness) of the recording medium 34, that is, the information recording medium 31.
The objective lens 17 is designed by correcting the aberration so that no spherical aberration occurs at the spot when the light is condensed from the surface to the position of the thickness t2.

In this case, the servo laser beam 10 having a wavelength of 780 nm is simply applied to the objective lens 17 made of a glass material.
When the laser beam 20 is incident as a parallel light beam, an image cannot be formed before the spot of the recording / reproducing laser beam 20 having a wavelength of 650 nm. Therefore, in this embodiment, the hologram element 41 is arranged in the optical path between the objective lens 17 and the dichroic prism 16, and the recording / reproducing laser beam 20 having a wavelength of 650 nm passes through the hologram element 41 as zero-order light. Using a light beam, a servo laser beam 1 with a wavelength of 780 nm
0 uses the light flux of the primary light (condensing side) diffracted by the hologram element 41. The hologram element 41 has
A function of limiting the numerical aperture of the primary light having a wavelength of 780 nm diffracted by the hologram element 41 to a small value such as 0.43 is provided. Thus, the wavelength 650
When the recording / reproducing laser beam 20 having a wavelength of 780 nm is focused on the position of the thickness t2 of the information recording medium 31 without causing spherical aberration, the spot of the servo laser beam 10 having a wavelength of 780 nm becomes a groove having a thickness t1. The objective lens 1 has a positive power so as to be formed on the layer 32 and a focused light beam.
Aberration caused by incidence on the recording medium 7 and information recording medium 3
The spherical aberration generated by the thickness t2 of 1 is integrated to generate a spherical aberration that cancels the remaining spherical aberration. Other configurations are the same as in the first embodiment.

With such a configuration, similarly to the first embodiment, the recording / reproducing performance of each recording layer 35 in the depth direction can be effectively suppressed with a simple and inexpensive configuration. Recording / reproduction can be performed stably. Further, in the medium structure according to this embodiment, the groove layer 32 is a recording medium 34 on which a plurality of recording layers 35 are formed.
Is located closer to the objective lens 17 than the groove layer 3
The return light from the servo spot converged on the recording medium 2 is not reflected or scattered by each recording layer 35 of the recording medium 34, so that the quality deterioration of the servo signal can be effectively prevented. Further, by using the hologram element 41, it is possible to form an image of the spot on the long wavelength side closer to the front side (the objective lens side) than the spot on the single wavelength side, thereby correcting spherical aberration and using the same objective lens. Even in this case, the numerical aperture (aperture function) can be easily set independently for the light beam on the long wavelength side.

FIG. 8 is a schematic diagram showing a configuration of a main part of a third embodiment of the present invention. This embodiment is different from the first embodiment in that the collimator lens 15 of the servo optical system is a normal aspherical lens, and the hologram element 41 is arranged in the optical path between the objective lens 17 and the dichroic prism 16. When the hologram element 41 condenses the recording / reproducing laser beam 20 having a wavelength of 650 nm at the position of the thickness t1 of the information recording medium 1 without causing spherical aberration, the hologram element 41 reflects the laser beam 20 on the reflecting surface 2 having the thickness t2. The second embodiment generates spherical aberration that cancels out the spherical aberration occurring in the spot of the servo laser beam 10 formed in the first embodiment. Other configurations are the same as those of the first embodiment.

Therefore, according to this embodiment, the distance between the two spots can be freely set by designing the hologram element 41 without being limited by the dispersion value of the glass material, and the hologram element 41 is fixed to the optical path. Since there is no need to provide a mechanism for taking this into and out of the optical path, a simple and inexpensive configuration can be used to stabilize each recording layer 6 in the depth direction, as in the first embodiment. Recording / reproduction.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications and changes are possible. For example, in the first embodiment, the shape of the collimator lens 15 of the servo optical system is fixed to a plano-convex spherical lens in order to cancel the spherical aberration generated in the spot of the servo laser beam 10, and the spherical aberration is fixed. Is controlled, but conversely, the shape can be changed by fixing the refractive index. That is, when the refractive index is fixed and the lens shape is changed as shown in FIGS. 9A to 9G, the third-order spherical aberration (SA3) is changed according to the shape as shown in FIGS.
Thus, a lens shape having a desired aberration amount can be selected.

In the first embodiment, the objective lens 1
7 was designed by correcting the aberration with respect to the recording / reproducing laser beam 20. Conversely, the servo 7 was designed by correcting the aberration with respect to the servo laser beam 10 to be generated at the spot of the recording / reproducing laser beam 20. It is also possible to configure the recording / reproducing optical system to generate spherical aberration so as to cancel the spherical aberration. In this case, the spot of the recording / reproducing laser beam 20 has a spherical aberration on the under side, so that, for example, the collimator lens 22 of the recording / reproducing optical system has an aspherical shape.
The collimator lens 22 may generate an excessive spherical aberration.

Similarly, also in the second embodiment, the objective lens 17 is designed by correcting the aberration with respect to the servo laser beam 10 to cancel the spherical aberration generated in the spot of the recording / reproducing laser beam 20. As described above, the recording / reproducing optical system may be configured to generate spherical aberration. In this case, the hologram element 41 has a configuration in which a light beam having a wavelength of 780 nm is transmitted as zero-order light and a light beam having a wavelength of 650 nm is diverged as first-order diffracted light.
1 is a wavelength of 650 nm for a spot of a wavelength of 780 nm
The function of setting the interval between spots and correcting spherical aberration may be provided.

Further, in the second and third embodiments, the hologram element 41 is arranged in the optical path between the objective lens 17 and the dichroic prism 16.
It can be arranged in the optical path of the servo laser light 10 between the servo laser beam 10 and the dichroic prism 16. Further, the hologram element 41 may be formed integrally with the objective lens 17 as shown in FIG. 11, for example, so that focus control and tracking control may be performed integrally with the objective lens 17. Further, when the hologram element 41 is used, the spherical aberration for cancellation generated by the servo optical system or the recording / reproducing optical system is changed according to the amount of aberration between the hologram element 41 and the collimator lens of the optical system. It can be made to occur in both.

Further, the present invention can be effectively applied to a case where a phase change thin film or a magneto-optical thin film is used as an information recording medium.

[0052]

As described above, according to the present invention, the first track by the light beam from the first light source is applied to the guide track layer of the information recording medium having the guide track layer and the plurality of recording layers in the depth direction. Is formed, and when the second spot is formed by the light beam from the second light source at a predetermined position in the depth direction at which the plurality of recording layers are formed, the spherical aberration of one of the spots is substantially reduced. In addition, the optical system forming the other spot is configured to generate spherical aberration so as to cancel the spherical aberration generated in the other spot in that state. It is possible to effectively reduce the deterioration of the recording / reproducing performance for each recording layer in the depth direction with a simple and inexpensive configuration without providing a correction element having a different thickness area for correcting aberration and a driving mechanism thereof. You can stop, it is possible to perform stable recording / reproduction on each recording layer.

[Brief description of the drawings]

FIG. 1 is an overall schematic configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the first embodiment.

FIG. 3 is a diagram for explaining third-order spherical aberration generated by the objective lens shown in FIG. 1;

FIG. 4 is a diagram illustrating a relationship between a thickness error of a medium and a third-order spherical aberration amount.

FIG. 5 is a diagram showing a relationship between a refractive index and a spherical aberration in a plano-convex spherical lens.

FIG. 6 is a diagram showing the relationship between the distance between two spots in the depth direction and the wavefront aberration in the information recording medium according to the first embodiment, in comparison with the conventional case.

FIG. 7 is a schematic diagram showing a configuration of a main part of a second embodiment of the present invention.

FIG. 8 is a schematic diagram showing a configuration of a main part of the third embodiment.

FIG. 9 is a diagram showing various lens shapes for describing a modification of the first embodiment.

10 is a diagram showing third-order spherical aberration in various lens shapes shown in FIG.

FIG. 11 is a diagram illustrating a modification of the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Information recording medium 2 Reflecting surface 3 Absorption layer 4 Recording medium 5 Protective layer 6 Recording layer 10 Laser beam for servo 11 Light source unit 12 Semiconductor laser (first light source) 13 Photodetector 14 Hologram 15 Collimator lens 16 Dichroic prism 17 Objective Lens 20 Recording / reproducing laser beam 21 Semiconductor laser (second light source) 22 Collimator lens 23 Polarizing beam splitter 24 Quarter-wave plate 25 Detection lens 26 Pinhole 27 PIN photodiode 31 Information recording medium 32 Groove layer 33 Absorption layer 34 recording medium 35 recording layer 41 hologram element

Continued on the front page F term (reference) 2H049 CA09 CA20 2H087 KA13 LA25 NA01 PA01 PB01 QA07 QA13 QA33 RA46 5D119 AA04 AA38 BA01 BB13 CA09 CA15 DA01 DA05 EA02 EA03 EC01 EC47 FA05 FA08 JA14 JA43

Claims (5)

[Claims] A first light source and a second light source that emit light beams having different wavelengths; and the first light source and the second light source.
A light source from the first light source passes through the objective lens, passes through the objective lens, and has a guide track layer and a plurality of recording layers in the depth direction. A light beam from the second light source is condensed on a desired recording layer of the information recording medium through the objective lens while performing focusing control on the guide track layer and performing tracking control based on the returned light. In the optical pickup device, a first spot by a light beam from the first light source is formed on a guide track layer of the information recording medium, and the first spot is formed at a predetermined position in a depth direction where the plurality of recording layers are formed. 2
When the second spot is formed by the light beam from the light source, the spherical aberration of one of the spots becomes substantially zero, and the spherical aberration generated in the other spot in that state is cancelled. Thus, an optical pickup device is configured to generate spherical aberration in the optical system that forms the other spot. 2. The optical pickup according to claim 1, wherein the wavelength of the light beam emitted from the first light source is set longer than the wavelength of the light beam emitted from the second light source. apparatus. 3. When the first spot is formed on the guide track layer and the second spot is formed at the predetermined position, the spherical aberration of the spot formed on the side closer to the objective lens is reduced. The objective lens is configured to be substantially zero, and in that state, an optical element for forming the spot is formed so as to generate a spherical aberration that cancels a spherical aberration generated in a spot formed on a side remote from the objective lens. 3. The optical pickup device according to claim 2, wherein a plano-convex spherical lens is provided in the system. 4. When the first spot is formed on the guide track layer and the second spot is formed at the predetermined position, the spherical aberration of one of the spots becomes substantially zero. The hologram is provided in an optical system that forms the other spot so as to generate spherical aberration that cancels out spherical aberration that occurs in the other spot in that state. Optical pickup device. 5. The method according to claim 1, wherein the first spot is formed on the guide track layer, and the second spot is formed at a substantially intermediate position in a depth direction area forming the plurality of recording layers. 3. The method according to claim 1, wherein the spherical aberration of one spot is substantially zero.
5. The optical pickup device according to 3 or 4.