JP2009217866A - Optical pickup device and objective optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device and an objective optical element in which compatibility with a BD and an HD using the same light beam with one objective optical element can be performed. <P>SOLUTION: Since the number of apertures NA1 of an image side during using a first optical disk is larger than the number of apertures NA2 of an image side during using a second optical disk, also an effective diameter during using the second optical disk is larger than an effective diameter during using the first optical disk, a difference between focal distance during using the second optical disk and a focal distance during using the first optical disk can be secured largely, thereby, the light beam passing through a region for the first optical disk forms favorable flare for an information recording plane of the second optical disk and the light beam passing through a region for the second optical disk forms favorable flare for an information recording plane of the first optical disk, and thereby, the erroneous detection of recording/reproducing signals can be suppressed. Also, light utilization efficiency can be improved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup device and an objective optical element capable of recording and / or reproducing information interchangeably with respect to different types of optical disks using light beams having the same wavelength.

  In recent years, research and development of high-density optical disc systems that can record and / or reproduce information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm. Development is progressing rapidly. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4.7 GB) Can record information of 23 to 27 GB per layer on an optical disk with a diameter of 12 cm, which is the same size as the above, and an optical disk that records and reproduces information with specifications of NA 0.65 and light source wavelength 405 nm, so-called With HD DVD (hereinafter referred to as HD), information of 15 to 20 GB per layer can be recorded on an optical disk having a diameter of 12 cm. These optical disks are referred to herein as high density optical disks.

  By the way, it can be said that the value of an optical disc player / recorder (optical information recording / reproducing device) as a product is sufficient simply by saying that information can be appropriately recorded / reproduced only on one of these types of high-density optical discs. It is desirable to have a performance capable of appropriately recording / reproducing information while maintaining compatibility with both BD and HD.

  However, BD and HD are generated based on the difference in the thickness of the protective substrate using the wavelength difference because the thickness of each protective substrate is different although the wavelength of the light beam used is the same. It is difficult to correct spherical aberration. Therefore, it is more difficult to provide compatibility between BD and HD using a single objective optical element, as compared with compatibility with other optical disks.

  Under such circumstances, Patent Document 1 discloses an optical head in which an optical surface is concentrically divided into three or more lens surfaces, and an odd-numbered lens surface and an even-numbered lens surface from the center have different focal positions. A lens for is described.

Patent Document 2 describes a pickup device that enables compatibility between BD and HD with a single objective optical element by sorting light beams having the same wavelength using a diffraction effect.
Japanese Patent No. 3435249 JP 2006-147069 A

  Here, the lens described in Patent Document 1 is used for an optical head compatible with CD and LD, and the image side numerical aperture of the LD is larger than the image side numerical aperture of the CD. Further, a lens surface for condensing the light beam on the information recording surface of the LD is disposed outside the lens surface farthest from the optical axis for condensing the light beam on the information recording surface of the CD. However, with such a configuration, since the focal length when using the CD and the focal length when using the LD are close, the light flux that has passed through the lens surface for LD is erroneously detected when using the CD, or when using the LD. There is a possibility that the light flux that has passed through the lens surface for CD is erroneously detected.

  In addition, as in the optical pickup device described in Patent Document 2 above, when realizing the compatibility between BD and HD using a diffraction effect, for example, use of light passing from a light source to one optical disk through a diffraction structure Efficiency (the utilization efficiency here is the ratio of the amount of light that contributes to the spot on the optical disk to the amount of light incident on the optical surface on the light source side of the objective optical element) is 40% (in the case of diffraction distribution using a diffraction structure) (Theoretically does not exceed 50%), the light utilization efficiency from the optical disk to the photodetector through the same diffraction structure (the utilization efficiency here is the optical surface on the optical disk side of the objective optical element) Since the ratio of the amount of light that contributes to the spot on the photodetector with respect to the amount of incident light is 40%, the total utilization efficiency (here, the utilization efficiency is the optical surface on the light source side of the objective optical element) The ratio of the amount of light that contributes to the spot on the photodetector with respect to the amount of incident light is only squared to 40%, and only 16% of the light can be used. You can say that.

  The present invention considers the above-mentioned problems, and collects a light beam having the same wavelength, for example, on a BD and HD information recording surface using a common objective lens without using a complicated mechanism. Enables the recording or reproduction of information, works well for both BD and HD, and / or works well during recording and reproduction, and has a high light utilization efficiency and An object is to provide an objective optical element.

The optical pickup device according to claim 1 includes a first light source that emits a first light beam having a wavelength λ1 (380 nm <λ1 <450 nm), and an objective for condensing the first light beam on an information recording surface of an optical disc. A condensing optical system having an optical element;
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an optical pickup device that records and / or reproduces information by focusing on a surface,
The objective optical element has its optical surface divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
The image-side numerical aperture NA1 when using the first optical disc is larger than the image-side numerical aperture NA2 when using the second optical disc, and the effective diameter when using the second optical disc is effective when using the first optical disc. It is characterized by being larger than the diameter.

  According to the present invention, the required numerical aperture NA1 according to the standard of the first optical disc is larger than the required numerical aperture NA2 according to the standard of the second optical disc, and the effective diameter when using the second optical disc is the first optical disc. Since it is larger than the effective diameter when using one optical disc, it is possible to ensure a large difference between the focal length when using the second optical disc and the focal length when using the first optical disc, so that the information recording surface of the second optical disc can be secured. On the other hand, the light beam that has passed through the first optical disk area forms a good flare, and the light beam that has passed through the second optical disk area forms a good flare with respect to the information recording surface of the first optical disk. Therefore, erroneous detection of the recording / reproducing signal can be suppressed. Further, by using such a configuration, it is possible to increase the light utilization efficiency as compared with an objective optical element that uses the diffraction effect to make the first optical disk and the second optical disk compatible.

  According to a second aspect of the present invention, in the optical pickup device of the first aspect, at least one of the second optical disk areas is more than the first optical disk area farthest from the optical axis of the objective optical element. And further away from the optical axis.

The optical pickup device according to claim 3 is the optical pickup device according to claim 1 or 2, wherein the first optical disc is a BD, and the second optical disc is an HD.
The region closest to the center including the optical axis of the objective optical element is the second optical disc region.

According to a fourth aspect of the present invention, in the invention of the first or second aspect, the first optical disc is a BD, the second optical disc is an HD,
The region closest to the center including the optical axis of the objective optical element is the first optical disc region.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the objective optical element is a single lens.

The optical pickup device according to claim 6 is the invention according to any one of claims 1 to 4, wherein the objective optical element includes a first optical element and a second optical element,
The optical surface of the first optical element is divided into the plurality of concentric regions.

  According to a seventh aspect of the present invention, in the optical pickup device according to any of the first to sixth aspects, the objective optical element includes three or more areas including the first optical disk area and the second optical disk area. It has 10 or less ring-shaped areas.

  An optical pickup device according to an eighth aspect of the present invention is the optical pickup device according to any one of the first to seventh aspects, wherein a working distance of the objective optical element during recording and / or reproduction of the first optical disc and the second optical disc The working distance of the objective optical element during recording and / or reproduction is different.

The optical pickup device according to claim 9 is the invention according to claim 1, the working distance WD ₁ of the objective optical element when the recording and / or reproducing of the first optical disk, the first (2) The working distance WD ₂ of the objective optical element at the time of recording and / or reproducing of the optical disk satisfies the following expression.
(| WD ₁ −WD ₂ |) ≦ 0.1 (mm)

  By satisfying the above configuration, in an optical pickup device that is compatible with one objective lens, the working distance can be close with two optical discs, so that space saving and power saving of the optical pickup device can be achieved.

The objective optical element according to claim 10 includes a first light source that emits a first light flux having a wavelength λ1 (380 nm <λ1 <450 nm), and an objective for condensing the first light flux on an information recording surface of an optical disc. A condensing optical system having an optical element;
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an objective optical element of an optical pickup device that records and / or reproduces information by focusing on a surface,
The objective optical element has its optical surface divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
The image-side numerical aperture NA1 when using the first optical disc is larger than the image-side numerical aperture NA2 when using the second optical disc, and the effective diameter when using the second optical disc is effective when using the first optical disc. It is characterized by being larger than the diameter.

  The objective optical element according to claim 11 is the invention according to claim 10, wherein at least one of the second optical disk areas is more than the first optical disk area farthest from the optical axis of the objective optical element. And further away from the optical axis.

The objective optical element according to claim 12 is the objective optical element according to claim 10 or 11, wherein the first optical disc is a BD and the second optical disc is an HD.
The region closest to the center including the optical axis of the objective optical element is the second optical disc region.

The objective optical element according to claim 13 is the objective optical element according to claim 10 or 11, wherein the first optical disc is a BD and the second optical disc is an HD.
The region closest to the center including the optical axis of the objective optical element is the first optical disc region.

  The objective optical element according to claim 14 is characterized in that, in the invention according to any one of claims 10 to 13, the objective optical element is composed of a single lens.

The objective optical element according to claim 15 is the invention according to any one of claims 10 to 13, wherein the objective optical element includes a first optical element and a second optical element,
The optical surface of the first optical element is divided into the plurality of concentric regions.

  The objective optical element according to claim 16 is the invention according to any one of claims 10 to 15, wherein the objective optical element includes three or more areas including the first optical disk area and the second optical disk area. It has 10 or less ring-shaped areas.

The objective optical element according to claim 17 is the invention according to any one of claims 10 to 16, the working distance WD ₁ of the objective optical element when the recording and / or reproducing of the first optical disk, the first (2) The working distance WD ₂ of the objective optical element at the time of recording and / or reproducing of the optical disk satisfies the following expression.
(| WD ₁ −WD ₂ |) ≦ 0.1 (mm)

  The optical pickup apparatus of the present invention records / reproduces information with respect to at least the first optical disc and the second optical disc. The optical pickup device has at least one first light source. Furthermore, the optical pickup device has a condensing optical system for condensing the first light flux on the information recording surface of the first optical disc and condensing the first light flux on the information recording surface of the second optical disc. The optical pickup device also includes a light receiving element that receives a reflected light beam from the information recording surface of the first optical disc or the second optical disc.

  When the optical pickup device is a device for recording / reproducing the third optical disc and / or the fourth optical disc in addition to the first optical disc and the second optical disc, in addition to the first light source, the second light source and / or You may have a 3rd light source. When the optical pickup device is a device that records / reproduces the third optical disc and / or the fourth optical disc in addition to the first optical disc and the second optical disc, the condensing optical system receives the second light from the second light source. The light beam is condensed on the information recording surface of the third optical disk, and the third light beam from the third light source is condensed on the information recording surface of the fourth optical disk. Further, when the optical pickup device is a device for recording / reproducing the third optical disc and / or the fourth optical disc in addition to the first optical disc and the second optical disc, the information recording surface of the third optical disc or the fourth optical disc A light receiving element that receives the reflected light beam from the light source may be included.

  The first optical disc has a protective substrate having a thickness t1 and an information recording surface. The second optical disc has a protective substrate having a thickness t2 (t1 <t2) and an information recording surface. The first optical disc and the second optical disc have the same wavelength of light flux used for recording / reproduction. The first optical disk is preferably a BD and the second optical disk is preferably an HD, but the present invention is not limited to this. When the third optical disk or the fourth optical disk is used, the third optical disk has a protective substrate having a thickness t3 (t2 ≦ t3) and an information recording surface. The fourth optical disc has a protective substrate having a thickness t4 (t3 <t4) and an information recording surface. The third optical disk is preferably a DVD and the fourth optical disk is preferably a CD, but is not limited thereto. The first optical disc, the second optical disc, the third optical disc, or the fourth optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.

  In the BD, information is recorded / reproduced by an objective optical element having an image-side numerical aperture NA1 = 0.85, and the thickness of the protective substrate is about 0.1 mm. In the HD, information is recorded / reproduced by an objective optical element having an image-side numerical aperture NA2 = 0.65 to 0.67, and the thickness of the protective substrate is about 0.6 mm. Furthermore, a DVD is a DVD series optical disc in which information is recorded / reproduced by an objective optical element having an image-side numerical aperture NA3 = 0.60 to 0.67, and a protective substrate has a thickness of about 0.6 mm. It is a generic name and includes DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. Further, in this specification, CD means that information is recorded / reproduced by an objective optical element having an image-side numerical aperture NA4 of about 0.45 to 0.51, and the thickness of the protective substrate is about 1.2 mm. And a CD-ROM, a CD-Audio, a CD-Video, a CD-R, a CD-RW, and the like. As for the recording density, the recording density of BD is the highest, followed by HD, DVD, and CD in that order.

  In addition, regarding the thicknesses t1, t2, t3, and t4 of the protective substrate, it is preferable to satisfy the following conditional expressions (1), (2), (3), and (4), but is not limited thereto.

0.0750 mm ≦ t1 ≦ 0.1125 mm (1)
0.5mm ≦ t2 ≦ 0.7mm (2)
0.5mm ≦ t3 ≦ 0.7mm (3)
1.0mm ≦ t4 ≦ 1.3mm (4)

  In the present specification, the light source such as the first light source, the second light source or the third light source is preferably a laser light source. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used.

  When BD is used as the first optical disc and HD is used as the second optical disc, the wavelength λ1 of the first light beam emitted from the first light source is preferably 380 nm or more and 450 nm or less. When a DVD is used as the third optical disk and a CD is used as the fourth optical disk, the wavelength λ2 of the second light beam emitted from the second light source is preferably 630 nm or more and 670 nm or less, and is emitted from the third light source. The wavelength λ3 of the third light flux is preferably 760 nm or more and 820 nm or less.

  As the light receiving element, a photodetector such as a photodiode is preferably used. Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the amount of light due to the change in the shape and position of the spot on the light receiving element, performs focus detection and track detection, and moves the objective optical element for focusing and tracking based on this detection I can do it. The light receiving element may comprise a plurality of photodetectors. The light receiving element may have a main photodetector and a sub photodetector. For example, two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. It is good also as a simple light receiving element. The light receiving element may have a plurality of light receiving portions corresponding to the respective light sources.

  The condensing optical system has an objective optical element. The objective optical element focuses the first light flux on the information recording surface of the first optical disc so that information can be recorded / reproduced, and the first light flux is recorded / reproduced on the information recording surface of the second optical disc. Concentrate as much as possible. The condensing optical system may include only the objective optical element, but may include a coupling lens such as a collimator lens and a beam expander in addition to the objective optical element. The coupling lens is a single lens or a lens group that is disposed between the objective optical element and the light source and changes the divergence angle of the light beam. The beam expander is a lens group that is disposed between the objective optical element and the light source and changes the diameter of the light beam without changing the divergence angle of the light beam. The collimating lens is a kind of coupling lens, and is a lens that changes a light beam incident on the collimating lens into parallel light. Further, the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like. May be. The condensing optical system may have an objective optical element for the third optical disk and an objective optical element for the fourth optical disk in addition to the objective optical elements for the first optical disk and the second optical disk. The objective optical element for the first optical disk and the second optical disk may also serve as the objective optical element for the third optical disk and / or the fourth optical disk.

  In this specification, the objective optical element is disposed at a position facing the optical disk in a state where the optical disk is loaded in the optical pickup device, and has a function of condensing the light beam emitted from the light source on the information recording surface of the optical disk. An optical system having Preferably, the objective optical element is an optical system that is disposed at a position facing the optical disc in the optical pickup device and has a function of condensing a light beam emitted from the light source on the information recording surface of the optical disc, An optical system that can be integrally displaced at least in the optical axis direction by an actuator. The objective optical element may be composed of two or more lenses and optical elements, or may be only a single lens. The objective optical element may be a glass lens, a plastic lens, or a hybrid lens in which an optical path difference providing structure or the like is provided on a glass lens with a photocurable resin or the like. When the objective optical element has a plurality of lenses, a glass lens and a plastic lens may be mixed and used. When the objective optical element has a plurality of lenses, it may be a combination of a flat plate optical element having an optical path difference providing structure and an aspheric lens, or a combination of an optical element having a flat plate portion and a swash plate portion and an aspheric lens. There may be. The objective optical element may have an optical path difference providing structure. The objective optical element preferably has an aspheric refractive surface.

When the objective optical element is a plastic lens, it is preferable to use a cyclic olefin-based resin material. Among the cyclic olefin-based materials, the refractive index at a temperature of 25 ° C. with respect to a wavelength of 405 nm is 1.54 to 1.60. The refractive index change rate dN / dT (° C. ⁻¹ ) with respect to the wavelength of 405 nm accompanying the temperature change within the temperature range of −5 ° C. to 70 ° C. is −20 × 10 ^{−5 to} −5 × 10 ^It is more preferable to use a resin material in the range of ⁻⁵ (more preferably −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ). When the objective optical element is a plastic lens, the coupling lens is preferably a plastic lens.

  The standard image side numerical aperture necessary for reproducing / recording information on the first optical disc is NA1, and the standard image side numerical aperture necessary for reproducing / recording information on the second optical disc is used. NA2 (NA1> NA2), NA3 (NA2 ≧ NA3) as the image-side numerical aperture required for reproducing / recording information on the third optical disc, and reproducing information on the fourth optical disc / NA4 (NA3> NA4) is the image-side numerical aperture required for recording. NA1 is preferably 0.8 or more and 0.9 or less. More preferably, NA1 is 0.85. NA2 and NA3 are preferably 0.55 or more and 0.7 or less. More preferably, NA2 is 0.65 and NA3 is 0.65. NA4 is preferably 0.4 or more and 0.55 or less. More preferably, NA4 is 0.45.

  The objective optical element is divided into a first region including at least the optical axis and a second region around the first region. The first region and the second region may have a clear structural difference between the first region and the second region on the optical surface of the objective optical element. On the other hand, the objective optical element may be a convenient area without providing a clear area in terms of configuration.

  The first light beam that has passed through the first area of the objective optical element is used for recording / reproduction of the first optical disk and the second optical disk, and the first light beam that has passed through the second area is used for recording / reproduction of the second optical disk. However, it is not used for recording / reproduction of the first optical disk. That is, the first area is a so-called shared area (first optical disk area + second optical disk area) used for both the first optical disk and the second optical disk, and the second area is used only for the second optical disk. It can be said that this is a so-called dedicated area (second optical disk area).

  When the objective optical element is viewed from another viewpoint, the optical surface of the objective optical element is divided into a plurality of concentric areas, and the plurality of areas are at least one first optical disk area and at least one second optical disk area. It can be said that it has. However, at least one of the second optical disk areas is further away from the optical axis than the first optical disk area farthest from the optical axis of the objective optical element. That is, the effective diameter when using the second optical disk is larger than the effective diameter when using the first optical disk. In this specification, the effective diameter means a diameter of a region through which a light beam used for recording / reproducing of an optical disk passes on the optical surface of the objective optical element. In particular, in an objective optical element that receives parallel light, the effective diameter of the objective optical element may be defined on the optical surface on the parallel light side (light source side) of the objective optical element. The first light flux that has passed through the first optical disk area is condensed so that information can be recorded / reproduced on the information recording surface of the first optical disk, and is not condensed on the information recording surface of the second optical disk. The first light flux that has passed through the second optical disc area is condensed so that information can be recorded / reproduced on the information recording surface of the second optical disc, and is not condensed on the information recording surface of the first optical disc.

  The objective optical element may have a compatible optical path difference providing structure that enables use of the third optical disk and / or the fourth optical disk. Further, the objective optical element may have an optical path difference providing structure for correcting the aberration change at the time of temperature change or wavelength change. In addition, the optical path difference providing structure in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.

  The first optical disk area and the second optical disk area are preferably provided alternately, but the present invention is not limited to this. The most central area including the optical axis may be the first optical disk area or the second optical disk area.

  That is, the first light flux that has passed through the first optical disk area has a very small aberration on the information recording surface of the first optical disk, so that information cannot be recorded / reproduced on the information recording surface of the second optical disk. The aberration is large. On the other hand, the first light flux that has passed through the second optical disk area has a large aberration on the information recording surface of the first optical disk so that information cannot be recorded / reproduced. On the information recording surface of the second optical disk, Aberration is very small.

  Both the first optical disk area and the second optical disk area are preferably refracting surfaces. In this case, the light beam that has passed through the first optical disk area is reflected on the information recording surface of the first optical disk by using the refraction action. And condensing the light beam that has passed through the second optical disk area onto the information recording surface of the second optical disk. Such a configuration is preferable because a loss of light amount can be reduced when reflected light on the information recording surface of the optical disc passes through the correction surface. In this case, a light receiving element having a relatively low sensitivity can be used as the light receiving element, so that the cost of the optical pickup device can be reduced.

  When the objective optical element has a first optical element and a second optical element, and the optical surface of the first optical element is divided into a plurality of concentric areas, the first optical disk area and the second optical disk One of the use areas transmits the first light beam (has no power with respect to the first light beam), and the other records / reproduces information on the information recording surface of the optical disc with respect to the first light beam that has passed. However, it is also possible to adopt a configuration in which the aberration is corrected so that the light can be condensed (having power with respect to the first light flux). In particular, the objective optical element includes a first optical element having a correction surface and a second optical element that is an aspheric lens, and only the aspheric lens protects the first optical disk or the second optical disk. In the case where the aspherical lens has an optical performance capable of condensing the first light beam on the information recording surface via the substrate, it is preferable to adopt the above-described configuration. For example, when the aspherical lens is designed so that the first light beam can be condensed on the information recording surface with respect to the BD with only the aspherical lens, the first optical element (BD) area of the first optical element is The second optical disc (HD) region transmits the first light flux, and has a structure that corrects aberrations so that the first light flux is condensed on the information recording surface of the HD. Is preferred.

  On the other hand, the first optical disc area corrects the aberration so that the first light beam that has passed through is focused on the information recording surface of the first optical disc so that information can be recorded / reproduced. The use area may be configured to correct aberration so that information can be recorded / reproduced on the information recording surface of the second optical disk that has passed. In particular, the objective optical element has a first optical element having a correction surface and a second optical element that is an aspheric lens, and the aspheric lens alone protects both the first optical disk and the second optical disk. In the case where the first light beam cannot be condensed on the information recording surface via the substrate, the above-described configuration is preferable. For example, when the aspherical lens is designed so that the first light beam cannot be condensed with respect to both BD and HD with only the aspherical lens, the area for the first optical disk (BD) of the first optical element is The aberration is corrected so that the first light flux is condensed on the BD information recording surface, and the second optical disc (HD) area is collected on the HD information recording surface with respect to the first light flux. It is preferable to have a structure that corrects aberration so as to emit light.

  When the objective optical element is composed of a single lens, a step may be provided on the aspherical optical surface of the single objective lens, thereby dividing it into a plurality of concentric regions. It is preferable that the first optical disc region has the same aspherical shape, and the second optical disc region has a different aspherical shape. When the objective optical element has a plurality of first optical disk areas, it is preferable that these first optical disk areas have the same aspherical shape, and when the objective optical element has a plurality of second optical disk areas, It is preferable that the second optical disc regions have the same aspherical shape.

  Further, from the viewpoint of facilitating manufacture of the objective optical element, it is preferable that the number of ring-shaped areas including the first optical disk area and the second optical disk area is 3 or more and 10 or less. When the number of ring-shaped areas is 3, for example, as shown in FIG. 3, the center area including the optical axis is the second optical disk area HA1, the surrounding area is the first optical disk area BA, and the surrounding area. An example in which the outermost peripheral area of the second optical disk area HA2 is considered. As a result of diligent research, the present inventor combined the first optical disk area and the second optical disk area from the viewpoint of reducing the side rope of the spot and facilitating the manufacture of the objective optical element. It was found that the number of ring-shaped regions is preferably 5 or more and 10 or less. More preferably, the number of annular zones is 6 or more and 10 or less. Even when the objective optical element includes the first optical element on the light source side and the second optical element on the optical disc side, the above-described range of the preferable number of annular zones can be applied.

Next, when performing recording / reproduction of the second optical disc, in order to prevent the light flux that has passed through the first optical disc area from falling on the defocus area, the light flux that has passed through the first optical disc area is 2 It is preferable that the objective optical element has a flare on the information recording surface of the optical disc. Specifically, “to flare” means that light that has passed through the first optical disk area on the information recording surface of the second optical disk is distributed in the donut-shaped area. In particular, when the first optical disc is a BD and the second optical disc is an HD, it is preferable that the inner diameter of the donut-shaped region be Φ0.030 mm or more. In the case of a plurality of donut-shaped regions, it is preferable that the smallest diameter among the inner diameters of each donut-shaped region is Φ0.030 mm or more. To that end, the following (A)
(F _BD −f _HD ) ≦ −0.15 (mm) (A)
However, it is preferable that the condition (A) is satisfied by the condition “the effective diameter when using the second optical disk is larger than the effective diameter when using the first optical disk” according to claim 1.

Furthermore, in an optical pickup device that is compatible with one objective lens, if the working distance is close between two optical discs, the optical pickup device can save space and power, so the following conditional expression (B) It is desirable to satisfy.
(| WD ₁ −WD ₂ |) ≦ 0.1 (mm) (B)
F1 is the focal length of the first optical disk area of the objective optical element in the first light flux, f2 is the focal distance of the second optical disk area of the objective optical element in the first light flux, and NA1 'is the first optical disk of the objective optical element. The numerical aperture according to the standard of the area for use and the numerical aperture according to the standard of the area for the second optical disc of the NA2 ′ object optical element are shown. It should be noted that even when the objective optical element has the first optical element on the light source side and the second optical element on the optical disk side, the preferable conditions for generating the flare can be applied.

  Next, as a configuration for improving the off-axis characteristics of the objective optical element that is a single lens, 1) change the aspherical shape of the first optical disk area and the second optical disk area, or 2) For example, as shown in FIG. 4, a configuration in which an optical path difference providing structure is provided in the first optical disk area (or the second optical disk area) is conceivable. Here, to improve the off-axis characteristics means that the wavefront aberration becomes 0.1 RMS or less when the light beam enters the objective optical element at an oblique incidence of 0.5 °.

In the case of the configuration in which the first optical disk area and the second optical disk area have different aspherical shapes in ₁ ), the working distance (WD ₁ ) of the objective optical element during recording / reproduction of the first optical disk and the second optical disk It is preferable to make the working distance (WD ₂ ) of the objective optical element different during recording / reproduction.

  On the other hand, in order not to cause a large step on the optical surface, it is preferable to provide an off-axis characteristic by providing an optical path difference providing structure in the second optical disc area as in 2). Depending on other design conditions, the above method 1) or 2) may be used properly.

  Incidentally, on the optical surface on the optical disc side of the single objective optical element, there are a region through which the light beam used for recording / reproduction of the first optical disc passes and a region through which the light beam used for recording / reproduction of the second optical disc passes. An objective optical element that does not overlap is preferable because the loss of light quantity can be reduced. When this viewpoint is emphasized, it is preferable that the number of annular zones of the objective optical element is small. For example, a three-band objective optical element is preferable.

  Further, from the viewpoint of reducing the thickness of a single objective optical element, a step is provided on the surface of the optical surface of the objective optical element, and the step is a region on the far side of the region closer to the optical axis with the step as a boundary. It is desirable that the level difference be shorter than the optical path. For example, the example shown in FIG. 7 is an example in which a step for thinning the objective optical element is further provided in the second optical disc area, which is the central area, with respect to the objective optical element shown in FIG. Even when such a step is provided, it is desirable that the spherical aberration and the sine condition are corrected to a necessary level.

  The step between the first optical disc region and the second optical disc region is not limited to the example shown in FIG. When the objective optical element is made of plastic, it may be a step that produces a diffractive action that compensates for the spherical aberration change caused by the temperature change of the plastic by the change of the laser oscillation wavelength accompanying the temperature change. When the objective optical element is made of glass, the influence of temperature change is small, so that it is easy to obtain a deep step without degrading temperature characteristics.

The sum Δ of the lengths of coding in the optical axis direction of all the steps provided on the optical surface of the objective optical element (sign is a region where the optical path of each step is closer to the optical axis than the region on the far side It is desirable that the following conditional expression (6) is satisfied in the case where it is shortened:
0.1 mm ≦ Δ ≦ 1.0 mm (6)
If it is above the lower limit, the effect of thinning is great, and if it is below the upper limit, the sine condition can be corrected to the required level while reducing the thickness. Note that “the sum of the coding lengths” means that when both a positive length value and a negative length value exist, they are added as they are. For example, if the positive length value is +1 and the negative length value is −0.5, (+1) + (− 0.5) = + 0.5, ie, +0. 5 is “the sum of the lengths of encoding”.

  As shown in FIG. 3, when the first optical disk area and the second optical disk area are provided in a single objective optical element, a large level difference (for example, a level difference of 50 μm or more in the optical axis direction) is provided at the boundary between the areas. ) May occur. Such a large step, when the objective optical element is molded using a mold, may become a hindrance when the optical element is removed from the mold, making the objective optical element more difficult to manufacture. Therefore, when a large step (for example, a step of 50 μm or more in the optical axis direction) occurs at the boundary of each region, the inclined surface is inclined with respect to the optical axis at the step portion so that it can be easily removed from the mold. (Taper) is preferably provided. For example, as shown in FIG. 3, in the case where the middle region is recessed in the optical axis direction, as shown in FIG. 8, only the surface SS1 in which the step surface faces the optical axis is inclined. The surface SS2 in which the step surface faces in the direction opposite to the optical axis is not inclined, so that the influence on the optical performance can be minimized, and the loss of light amount due to the taper can be reduced. It is preferable because it can be easily removed from.

  Furthermore, the optical surface of the objective optical element has an optical path difference providing structure for the purpose of compatibility with the third optical disc and the fourth optical disc, and the purpose is to correct the change in aberration that occurs at the time of temperature change or wavelength change. The optical path difference providing structure may be overlapped. One of the preferred examples is an optical path difference providing structure for correcting an aberration change occurring when the temperature or wavelength changes only in the first optical disk area or only in the second area of the objective optical element. Is provided. In the above description, the example in which the optical path difference providing structure is provided on the optical surface on the light source side is described. However, the optical path difference providing structure for the above-described purpose may be provided on the optical surface on the optical disc side. .

  When the objective optical element has a first optical element and a second optical element, and the first optical element is divided into a plurality of concentric areas, the plurality of areas do not give aberration and an area that gives aberration. It is preferable to have a transparent region (for example, a flat plate region and an aspherical region), but is not limited thereto. A plurality of regions provided in the first optical element may all be regions that give aberration.

  When the first optical element has a region that does not give aberration (for example, a region of a flat plate portion) and a region that gives aberration (for example, a region on an aspherical surface or a swash plate), a region that does not give aberration is It is preferable that one of the first optical disk area and the second optical disk area, and the other area to be given aberration.

  Here, a preferable example of the objective optical element will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a single objective optical element OE. The optical path above the optical axis indicates the optical path when using BD, and the optical axis below the optical axis indicates the optical path when using HD. . Here, the optical surface on the optical disk side of the objective optical element OE is divided into three ring-shaped areas having a second optical disk area AR1, a first optical disk area AR2, and a second optical disk area AR3 with the optical axis as the center. They are arranged in this order in the direction away from the optical axis. Here, the inner diameter (2 · Δ2) of the aperture AP2 when using HD is larger than the inner diameter (2 · Δ1) of the aperture AP1 when using BD, that is, the effective diameter when using HD is when using BD. It is larger than the effective diameter.

  When recording / reproducing BD, the light beam that has passed through the first optical disk area AR2 is condensed on the information recording surface of the BD by the objective optical element OE, and has passed through the second optical disk areas AR1 and AR3. Is not condensed on the information recording surface of the BD. On the other hand, when recording / reproducing the HD, the first light flux that has passed through the second optical disc areas AR1 and AR3 is condensed on the information recording surface of the HD by the objective optical element OE, and the first optical disc area The first light flux that has passed through AR2 is not condensed on the HD information recording surface.

  Note that the following modes can be considered when compatibility with other optical discs as well as the first optical disc and the second optical disc is performed with one objective optical element.

As a first example, for example, a third light beam having a wavelength λ3 emitted from a third light source is condensed on the information recording surface of the fourth optical disk by the objective optical element, and the wavelength λ3 is a wavelength λ1. If it is an approximate integer multiple of 1 and an attempt is made to enable compatibility with the fourth optical disk by the diffraction structure, 1) it becomes difficult to make the diffraction angles different between the first light flux of λ1 and the third light flux of λ3, 2) When a special diffraction structure that can make the diffraction angles of the first light flux and the third light flux different is used, there is a problem that the light use efficiency is lowered. Therefore, a fourth optical disk area may be provided in the second area in addition to the first optical disk area and the second optical disk area. For example, as shown in FIG. 5, the fourth optical disk area CD, the second optical disk area HD, the first optical disk area BD, and the second area outside of the fourth optical disk area CD in order from the inner area including the optical axis. An example in which the second optical disk area HD is provided is conceivable. Note that the fact that the wavelength λ3 is substantially an integral multiple of the wavelength λ1 means that the following conditional expression (7) is satisfied.
(M−0.2) · λ1 ≦ λ3 ≦ (m + 0.2) · λ1 (7)
Note that m represents an arbitrary positive integer of 2 or more.

  Further, by providing an optical path difference providing structure in at least one of the fourth optical disk area, the first optical disk area, and the second optical disk area in the second area, the recording of the third optical disk (for example, DVD) is performed. / Reproduction may be enabled. For example, as shown in FIG. 6, the fourth optical disk area CD, the second optical disk area HD, the first optical disk area BD, and the second area outside of the fourth optical disk area CD in order from the inner area including the optical axis. An example in which the second optical disc area HD is provided, and an optical path difference providing structure DVD that enables recording / reproduction of the third optical disc is provided in the inner second optical disc area HD and the outer second optical disc area HD can be considered. .

  The objective optical element of the present invention can also be applied to a hybrid optical disc in which recording layers of a plurality of types of optical discs including the first optical disc and the second optical disc are laminated on one optical disc. An example in which recording layers of a plurality of types of optical disks are stacked on a single optical disk is a hybrid disk in which recording layers of BD / HD / DVDs are stacked on one side as disclosed in JP-A-2007-42254. Can be mentioned.

  As shown in FIG. 9, the single objective optical element OL1 of the present invention for the first optical disk and the second optical disk and the objective optical element OL2 for other optical disks (for example, the third optical disk / fourth optical disk). Alternatively, a lens unit that is integrally formed may be used. As shown in FIG. 9, the integrally formed lens unit is a case where the first objective optical element OL1 and the second objective optical element OL2 are fused (for example, the first objective optical element). And a second objective optical element as shown in FIG. 10 or FIG. 11 as well as a lens unit having a second objective optical element by integral molding by injection molding). The optical elements may be integrated by molding separately, and then fitting, adhering or engaging with each other.

  FIG. 10 shows an example of a lens unit in which the first objective optical element and the second objective optical element are engaged and integrally formed. The second objective optical element OL2 made of plastic forms an opening HL having a stepped portion ST in the rectangular plate-shaped flange portion FL2, and the flange portion FL1 is held by the stepped portion ST in the opening HL. In this way, the first objective optical element OL1 made of glass or plastic of the present invention is assembled from the optical axis direction and integrated by adhesion or the like, and the first objective optical element OL1 and the second objective optical element are integrated. A lens unit OE in which OL2 is arranged in parallel is formed.

  FIG. 11 shows another example of a lens unit in which the first objective optical element and the second objective optical element are engaged and integrally formed. The second objective optical element OL2 made of plastic forms a notch CT having a stepped portion ST in the rectangular plate-like flange portion FL2, and the flange portion FL1 is held by the stepped portion ST in the notch CT. In this way, the first objective optical element OL1 made of glass or plastic of the present invention is assembled from the direction orthogonal to the optical axis and integrated by adhesion or the like, and the first objective optical element OL1 and the second objective optical are integrated. A lens unit OE in which the elements OL2 are arranged in parallel is formed.

  As shown in FIG. 12, the flange portion FL1 of the first objective optical element OL1 may be supported on the upper surface of the flange portion FL2 without forming the step ST in the opening HL or the notch CT. Alternatively, although not shown, the first objective optical element OL1 made of glass or plastic and the second objective optical element OL2 made of plastic may be integrated by assembling to a holding member which is a separate member. good. In any case, it is preferable that the holding member has an opening, and the objective lens unit is fitted therein.

  The first light beam may be incident on the objective optical element as parallel light, or may be incident on the objective optical element as divergent light or convergent light. Preferably, the magnification m1 of the first light beam incident on the objective optical element satisfies the following formula (8).

−0.02 <m1 <0.02 (8)

  On the other hand, when the first light flux is incident on the objective optical element as diverging light, the magnification m1 of the first light flux incident on the objective optical element preferably satisfies the following formula (9).

  -0.10 <m1 <0.00 (9)

In order to make the sine condition compatible in both recording / reproduction of the first optical disk and recording / reproduction of the second optical disk, it is preferable to satisfy the following conditional expression (10).
m11 <m12 (10)
M11 represents the magnification of the first light beam incident on the objective optical element at the time of recording / reproduction of the first optical disk, and m12 represents the objective optical of the first light beam at the time of recording / reproduction of the second optical disk. The magnification of the incident light beam to the element is shown.

  For example, when recording / reproducing the first optical disk, the first light beam is incident on the objective optical element as infinite parallel light, and when recording / reproducing the second optical disk, the first light beam is incident on the objective optical element as finite convergent light. Is a preferred example.

  The optical information recording / reproducing apparatus has an optical disc drive apparatus having the optical pickup device described above.

  Here, the optical disk drive apparatus provided in the optical information recording / reproducing apparatus will be described. The optical disk drive apparatus can hold an optical disk mounted from the optical information recording / reproducing apparatus main body containing the optical pickup apparatus or the like. There are a system in which only the tray is taken out and a system in which the optical disk drive apparatus main body in which the optical pickup device or the like is stored is taken out.

  An optical information recording / reproducing apparatus using each of the above-described methods is generally equipped with the following components, but is not limited thereto. An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc These include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.

  In addition to these components, the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.

  According to the present invention, with a simple and low-cost configuration, without using a complicated mechanism for BD and HD, it is compatible with one objective optical element of BD and HD that uses the same light beam at low cost. In addition, it is possible to provide an optical pickup device and an objective optical element with high light utilization efficiency.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a diagram schematically showing a configuration of the optical pickup apparatus PU1 of the present embodiment that can appropriately record / reproduce information with respect to the BD as the first optical disc and the HD as the second optical disc. is there. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. The present invention is not limited to the present embodiment.

  The optical pickup device PU1 includes an objective optical element OE, a λ / 4 wavelength plate QWP, a collimating lens CL, a polarizing prism PBS, a semiconductor laser LD (first light source) that emits a 405 nm laser beam (first beam), and a sensor. And a light receiving element PD that receives a reflected light beam from the information recording surface RL1 of the lenses SL and BD and the information recording surface RL2 of the HD. In the drawing, an example having a single objective optical element is shown as the objective optical element OE. However, instead of this objective optical element, an objective optical element composed of a plurality of elements may be used.

  The objective optical element OE has the optical surface shape shown in FIG.

  A case of recording / reproducing BD will be described. First, the divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD is transmitted through the polarization prism PBS, converted into a parallel light beam by the collimator lens CL, and then linearly generated by the λ / 4 wavelength plate QWP. Polarized light is converted into circularly polarized light, its beam diameter is regulated by a diaphragm (not shown), and a spot formed on the information recording surface RL1 of the BD via the protective substrate PL1 having a thickness of 0.0875 mm by the objective optical element OE. Become.

  At this time, the light beam that has passed through the first optical disk area AR2 is condensed on the information recording surface of the BD by the objective optical element OE, and the light beam that has passed through the second optical disk areas AR1 and AR3 is on the information recording surface of the BD. Is not collected.

  The reflected light beam modulated by the information pits on the information recording surface RL1 passes through the objective optical element OE and the aperture again, and then is converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and converged by the collimating lens CL. After being reflected by the polarizing prism PBS, the light is converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, the information recorded on the BD can be read by using the output signal of the light receiving element PD to focus or track the objective optical element OE by the biaxial actuator AC.

  Next, a case where HD recording / reproduction is performed will be described. First, the divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD is transmitted through the polarization prism PBS, converted into a parallel light beam by the collimator lens CL, and then linearly generated by the λ / 4 wavelength plate QWP. Polarized light is converted into circularly polarized light, its beam diameter is regulated by a diaphragm (not shown), and a spot formed on the information recording surface RL2 of the HD via the protective substrate PL2 having a thickness of 0.6 mm by the objective optical element OE Become.

  At this time, the first light flux that has passed through the second optical disk areas AR1 and AR3 is condensed on the information recording surface of the HD by the objective optical element OE, and the first light flux that has passed through the first optical disk area AR2 is It is not condensed on the information recording surface of HD.

  The reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective optical element OE and the aperture, and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and converged by the collimating lens CL. After being reflected by the polarizing prism PBS, the light is converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, by using the output signal of the light receiving element PD, the objective optical element OE is focused or tracked by the biaxial actuator AC, whereby the information recorded on the HD can be read.

It is sectional drawing of an example of the objective optical element OE which concerns on this invention. It is a figure which shows schematically the structure of the optical pick-up apparatus which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is the schematic at the time of seeing an example of the objective optical element which concerns on this invention from an optical axis direction. It is the schematic at the time of seeing an example of the objective optical element which concerns on this invention from an optical axis direction. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is a part of sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the lens unit which concerns on this invention. It is a schematic perspective view of an example of the lens unit which concerns on this invention. It is a schematic perspective view of an example of the lens unit which concerns on this invention. It is a part of sectional drawing of an example of the lens unit which concerns on this invention.

Explanation of symbols

AR2 First optical disk area AR1, AR3 Second optical disk area BA BD area HA HD area OE Objective optical element PU1 Optical pickup device LD Blue-violet semiconductor laser AC Biaxial actuator PBS Polarizing prism CL Collimating lens PL1 Protection substrate PL2 Protection Substrate RL1 Information recording surface RL2 Information recording surface QWP λ / 4 wavelength plate

Claims (17)

A condensing optical system having a first light source that emits a first light flux having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the first light flux on an information recording surface of an optical disc; ,
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an optical pickup device that records and / or reproduces information by focusing on a surface,
The objective optical element has its optical surface divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
The required numerical aperture NA1 according to the standard of the first optical disc is larger than the required numerical aperture NA2 according to the standard of the second optical disc, and the effective diameter when using the second optical disc is effective when using the first optical disc. An optical pickup device having a diameter larger than that of the optical pickup device.   2. The light according to claim 1, wherein at least one of the second optical disc regions is further away from the optical axis than the first optical disc region farthest from the optical axis of the objective optical element. Pickup device. The first optical disc is a BD and the second optical disc is an HD;
3. The optical pickup device according to claim 1, wherein an area closest to the center including the optical axis of the objective optical element is the area for the second optical disk. The first optical disc is a BD and the second optical disc is an HD;
3. The optical pickup device according to claim 1, wherein an area closest to the center including the optical axis of the objective optical element is the area for the first optical disk.   The optical pickup device according to claim 1, wherein the objective optical element is a single lens. The objective optical element has a first optical element and a second optical element,
The optical pickup device according to claim 1, wherein an optical surface of the first optical element is divided into the plurality of concentric regions.   7. The objective optical element according to claim 1, wherein the first optical disk area and the second optical disk area are combined to have a ring-shaped area of 3 or more and 10 or less. Optical pickup device.   The working distance of the objective optical element during recording and / or reproduction of the first optical disc is different from the working distance of the objective optical element during recording and / or reproduction of the second optical disc. The optical pickup device according to any one of 1 to 7. The working distance WD ₁ of the objective optical element at the time of recording and / or reproduction of the first optical disc and the working distance WD ₂ of the objective optical element at the time of recording and / or reproduction of the second optical disc are expressed by the following equations: The optical pickup device according to claim 1, wherein:
(| WD ₁ −WD ₂ |) ≦ 0.1 (mm) A condensing optical system having a first light source that emits a first light flux having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the first light flux on an information recording surface of an optical disc; ,
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an objective optical element of an optical pickup device that records and / or reproduces information by focusing on a surface,
The objective optical element has its optical surface divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
The image-side numerical aperture NA1 when using the first optical disc is larger than the image-side numerical aperture NA2 when using the second optical disc, and the effective diameter when using the second optical disc is effective when using the first optical disc. An objective optical element having a larger diameter.   11. The objective according to claim 10, wherein at least one of the second optical disc regions is further away from the optical axis than the first optical disc region farthest from the optical axis of the objective optical element. Optical element. The first optical disc is a BD and the second optical disc is an HD;
The objective optical element according to claim 10 or 11, wherein an area closest to the center including the optical axis of the objective optical element is the area for the second optical disc. The first optical disc is a BD and the second optical disc is an HD;
The objective optical element according to claim 10 or 11, wherein an area closest to the center including the optical axis of the objective optical element is the first optical disc area.   The objective optical element according to claim 10, wherein the objective optical element is a single lens. The objective optical element has a first optical element and a second optical element,
The objective optical element according to claim 10, wherein an optical surface of the first optical element is divided into the plurality of concentric regions.   16. The objective optical element according to claim 10, wherein the first optical disk area and the second optical disk area are combined to have a ring-shaped area of 3 to 10 in total. Objective optical element. The working distance WD ₁ of the objective optical element at the time of recording and / or reproduction of the first optical disc and the working distance WD ₂ of the objective optical element at the time of recording and / or reproduction of the second optical disc are expressed by the following equations: The objective optical element according to claim 10, wherein the objective optical element is satisfied.
(| WD ₁ −WD ₂ |) ≦ 0.1 (mm)

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