WO2010089933A1

WO2010089933A1 - Objective lens and optical pickup device

Info

Publication number: WO2010089933A1
Application number: PCT/JP2009/070161
Authority: WO
Inventors: 喬則白石
Original assignee: コニカミノルタオプト株式会社
Priority date: 2009-02-06
Filing date: 2009-12-01
Publication date: 2010-08-12
Also published as: JPWO2010089933A1; CN102292770A

Abstract

Disclosed are an optical pickup device that can be used in thin optical disk drives, and that is able to appropriately record/reproduce data for different optical disks, and an objective lens suitable for the same. Since a large paraxial radius of curvature can be maintained in an area for use with a third optical disk, while the paraxial radius of curvature is smaller in an area for use with a first optical disk, it is possible to make the on-axis thickness of an objective lens thinner, while maintaining a longer focal distance for the third optical disk. Thus, an objective lens can be provided that can shorten the CD focal distance, despite being convertible for recording/reproducing data for three different optical disks, making it especially optimal for thin optical disk drives.

Description

Objective lens and optical pickup device

The present invention relates to an optical pickup apparatus capable of recording and / or reproducing information interchangeably for different types of optical discs and an objective lens used therefor.

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) It is possible to record 25 GB of information per layer on an optical disc having a diameter of 12 cm which is the same size as the above.

By the way, simply saying that information can be appropriately recorded / reproduced on such a high-density optical disc, for example, a BD, is sufficient as a product of an optical disc player / recorder (optical information recording / reproducing apparatus). I can't. In light of the reality that DVDs and CDs (compact discs) on which a wide variety of information is recorded are currently being sold, it is not possible to record / reproduce information with respect to BDs. For example, DVDs owned by users, Similarly, it is possible to appropriately record / reproduce information on a CD, which leads to an increase in the commercial value of an optical disc player / recorder for BD. From such a background, the optical pickup device mounted on the optical disc player / recorder for BD can appropriately record / reproduce information while maintaining compatibility with both BD, DVD, and CD. It is desirable to have performance.

As a method for appropriately recording / reproducing information while maintaining compatibility with both BD and DVD, and further with CD, information between BD optical system and DVD or CD optical system is used. Although a method of selectively switching in accordance with the recording density of the optical disk for recording / reproducing the image is conceivable, a plurality of optical systems are required, which is disadvantageous for miniaturization and increases the cost.

Therefore, in order to simplify the configuration of the optical pickup device and reduce the cost, even in an optical pickup device having compatibility, the optical system for BD and the optical system for DVD or CD can be shared. It is preferable to reduce the number of optical components constituting the pickup device as much as possible. And, it is most advantageous to simplify the configuration of the optical pickup device and to reduce the cost to make the objective lens arranged facing the optical disc in common.

Here, Patent Document 1 discloses an objective lens used in an optical pickup device capable of recording / reproducing information with respect to a plurality of optical discs having two or more substrate thicknesses using light of three types of wavelengths. It is disclosed. In the example of Patent Document 1, information is recorded / reproduced with respect to optical disks having only two substrate thicknesses of 0.6 mm and 1.2 mm using light having wavelengths of 405 nm, 657 nm, and 788 nm. Light having a wavelength of 405 nm and wavelength of 657 nm is used for an optical disc having a substrate thickness of 0.6 mm, and light having a wavelength of 788 nm is used for an optical disc having a substrate thickness of 1.2 mm. In such an objective lens, a surface on which laser light is incident on the objective lens is divided into at least three regions in order to support a plurality of types of optical disks. When any of the laser beams having a plurality of wavelengths passes through a corresponding area of the objective lens, the laser light is condensed on the information recording surface of the corresponding optical disk. In Example 1 of Patent Document 1, the objective lens is divided into four regions, and the innermost region of the objective lens is a refractive surface capable of condensing each of three types of wavelengths on each information recording surface of three types of optical disks. The outer region is a refracting surface that allows light of 405 nm wavelength and 788 nm wavelength to be condensed on the information recording surfaces of the two types of optical discs, and the outer region is irradiated with light of 405 nm wavelength and 657 nm wavelength. A diffraction surface that allows light to be condensed on each information recording surface of the two types of optical disks, and a light diffraction surface that allows light of a wavelength of 405 nm to be condensed on the information recording surface of one type of optical disk are provided outside. Further, in Examples 2 and 3, the objective lens is divided into three regions, and the innermost region is made a refracting surface capable of condensing each of the three types of wavelengths on the information recording surfaces of the three types of optical discs. The outer side is a diffractive surface that allows light of 657 nm wavelength and 788 nm wavelength to be condensed on the information recording surfaces of the two types of optical discs, and the outer side is light of wavelengths of 405 nm and 657 nm. Each information recording surface has a diffractive surface capable of condensing light.

Next, Patent Document 2 is used for an optical pickup device capable of recording / reproducing optical disc information of three types of BD, DVD, and CD having different substrate thicknesses using light of three types of wavelengths. An objective lens is disclosed. In the example of Patent Document 2, information is recorded / reproduced with respect to an optical disc having a substrate thickness of 0.0875 mm, 0.6 mm, and 1.2 mm by using light having wavelengths of 405 nm, 658 nm, and 785 nm. In such an objective lens, a surface on which laser light is incident on the objective lens is divided into at least three regions in order to support a plurality of types of optical disks. When any of the laser beams having a plurality of wavelengths passes through a corresponding region of the objective lens, the laser light is distributed using the diffracted light and condensed on the information recording surface of the corresponding optical disc. Specifically, each of the three kinds of light beams that have passed through the innermost region of the objective lens is made a diffractive surface capable of condensing on the information recording surfaces of BD, DVD, and CD, and 405 nm and 658 nm that have passed outside. Can be condensed on the information recording surfaces of BD and DVD, the 785 nm luminous flux that has passed is made a diffractive surface that is not condensed on the information recording surface of the CD, and the 405 nm luminous flux that has passed through the outside is recorded on the BD. It is possible to condense on the surface, and each of the passed 658 nm and 785 nm light fluxes is a surface that is not condensed on the information recording surface of the DVD and CD, and in Examples 1, 2, and 3, the outermost region is a refractive surface, In Examples 4 and 5, the outermost region is a diffractive surface.

JP 2006-40512 A Japanese Patent No. 4033240

Here, in Patent Document 1, in all embodiments, the type of optical disc capable of recording / reproducing information is one having a substrate thickness of 0.6 mm or 1.2 mm. Therefore, the objective lens described in Patent Document 1 cannot record / reproduce information with respect to a BD having a substrate thickness of 0.1 mm.

Further, in the objective lens described in Patent Document 2, the most central region condenses the first light beam that has passed through the BD, condenses the second light beam on the DVD, and condenses the third light beam on the CD. It is an area that can be. In order to cope with optical discs of three types of standards of BD, DVD, and CD in this region, diffractive structures having different diffraction orders are superimposed on the surface on which the laser light is incident on the objective lens. Therefore, there is a high possibility that an annular zone having a narrow pitch width, which is the width of one concavo-convex portion of the diffraction structure, is generated. In Patent Document 2, it is described that even if the annular zone is removed, if the pitch width is 5 μm or less, the optical performance is not greatly affected. There is a possibility that a narrow-width annular zone still remains difficult in actual shape and manufacture. Of course, if such removal is not performed, it will become more difficult to make a real shape and manufacture.

Also, in the case where one objective lens is adapted to optical disks having different substrate thicknesses, and the optical disk on which information is to be recorded / reproduced is a CD, the optical disk substrate thickness of the CD is larger than other optical disks. Therefore, it is necessary to increase the distance from the image side principal point of the objective lens to the image side focal point. Furthermore, when recording / reproducing a CD, the focal length of the objective lens is sufficient to ensure a sufficient amount of working distance (the distance from the position closest to the optical disc on the surface where the laser light exits from the objective lens to the optical disc). Tend to be longer. For example, in all examples of Patent Document 1, when the optical disc is a CD, the focal length of the objective lens is as long as 3.118 mm, and the axial thickness of the objective lens is as thick as 2.3 mm. Furthermore, the effective diameter is as large as 3.9 mm. In Example 3 of Patent Document 2, when the optical disc is a CD, the focal length of the objective lens is as long as 2.43 mm, and the axial thickness of the objective lens is also as thick as 2.37 mm. Also, in the example in which the focal length of the CD is the shortest in Patent Document 2, the focal length is as long as 2.24 mm. That is, in Patent Document 2, the focal length and the working distance in the CD are ensured by increasing the axial thickness of the objective lens.

However, it is difficult to use a thick objective lens as described above for a thin optical disk drive to be mounted on a notebook computer or the like.

Further, as described in Patent Document 2, when the region including the optical axis of the objective lens is used as a common region through which the light flux for BD, DVD, and CD passes, the substrate thickness is smaller than that of other optical discs. There is also a problem that the working distance of thick CDs becomes insufficient and the usability becomes poor.

The present invention takes the above-described problems into consideration, and can be used in a thin optical disk drive while ensuring a sufficient working distance of a CD, and can appropriately store information on different optical disks such as BD, DVD, and CD. An object of the present invention is to provide an optical pickup device capable of recording / reproducing and an objective lens suitable for the optical pickup device.

The objective lens according to claim 1 includes a first light source that emits a first light flux having a wavelength λ1, a second light source that emits a second light flux having a wavelength λ2 (λ1 <λ2), and a wavelength λ3 (λ2 <λ3). A third light source that emits the third light beam and an objective lens, and the objective lens records information on the information recording surface of the first optical disc having a protective layer having a thickness t1. And / or collecting the second light flux so that information can be recorded and / or reproduced on the information recording surface of the second optical disc having a protective layer having a thickness t2 (t1 <t2). Recording and / or reproducing information by concentrating the third light flux on an information recording surface of a third optical disc having a protective layer having a thickness t3 (t2 <t3) so that information can be recorded and / or reproduced. An objective lens for an optical pickup device that performs reproduction The objective lens is a single lens, and at least one optical surface includes a first region including an optical axis, a second region provided outside the first region, and an outside of the second region. And an objective lens for condensing the first luminous flux that has passed through the area so that information can be recorded and / or reproduced on an information recording surface of the first optical disc. And the area of the objective lens that condenses the passed third light beam so that information can be recorded and / or reproduced on the information recording surface of the third optical disc.

When the first optical disk and the third optical disk can be combined to provide a first optical disk capable of condensing the first light flux on the information recording surface of the first optical disk and condensing the third light flux on the information recording surface of the third optical disk. Has a larger substrate thickness than other optical discs, so the distance from the incident surface of the third light beam to the condensing point is long, and the mother aspherical surface of the region through which the light beam condensed on the information recording surface of the third optical disc passes Therefore, the surface shape of the combined area of the first optical disc and the third optical disc tends to be loose. Furthermore, the first optical disk area that can focus the first light flux on the information recording surface of the first optical disk is required to have the most accurate optical performance, and is therefore arranged in the most central area including the optical axis. There are many. Accordingly, the paraxial radius of curvature of the mother aspheric surface in the first region becomes large, the surface shape becomes loose, the focal length of these regions becomes long, and the axial thickness of the objective lens becomes thick. Since the on-axis thickness of the objective lens is thick, it is difficult to use it for a thin optical disk drive.

According to the present invention, the region of the objective lens (the region for the first optical disk) that focuses the passed first light beam so that information can be recorded and / or reproduced on the information recording surface of the first optical disk. The objective lens region (third optical disc region) for condensing the passed third light beam so that information can be recorded and / or reproduced on the information recording surface of the third optical disc is arbitrarily selected. For example, the paraxial radius of curvature of the third optical disc area can be kept large and the paraxial radius of curvature of the first optical disc area can be reduced, so that the focal length of the third optical disc is increased. While maintaining, it is possible to reduce the axial thickness of the objective lens and ensure a long working distance with respect to the third optical disk. This makes it possible to provide an optimum objective lens for a thin optical disk drive, although information recording / reproduction can be made compatible with three different optical disks.

The objective lens described in claim 2 is characterized in that, in the invention described in claim 1, the following expression is satisfied.

0.15 (mm) ≦ WD3 ≦ 0.5 (mm) (1)
However,
WD3: Working distance when using the third optical disk If the working distance of the third optical disk is too long, the deviation ratio increases, and the edge thickness (minimum thickness in the optical axis direction) of the objective lens decreases. There is a problem that it is difficult to ensure a length suitable for manufacturing. In addition, by increasing the working distance in the third optical disc, the focal length for the third light flux is also increased. However, if the working distance is too long, there arises a problem that the change in aberration increases due to a temperature change when the objective lens is a plastic lens. Therefore, with the above-described configuration, the thickness deviation ratio is kept small while ensuring a sufficient working distance in the third optical disc, and the manufacturing can be easily performed. Moreover, even if the objective lens is a plastic lens, It is possible to provide an objective lens with a small change in aberration.

The objective lens according to claim 3 is the invention according to

claim

1 or 2, wherein the paraxial curvature radius of the mother aspheric surface in a certain region and the paraxial curvature of the mother aspheric surface in another region of the region are set. The difference from the radius is 0.1 mm or more and 0.7 mm or less.

According to a fourth aspect of the present invention, there is provided the objective lens according to the third aspect, wherein the third light beam that has passed through the region can be recorded and / or reproduced on the information recording surface of the third optical disc. The paraxial radius of curvature of the mother aspheric surface in the region where light is condensed and the region where light passes through the first light flux so that information can be recorded and / or reproduced on the information recording surface of the first optical disc. The difference from the paraxial radius of curvature of the mother aspherical surface in a region where the second light flux is condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc is 0.1 mm or more; It is 7 mm or less.

When the surface shape of the lens is a surface shape that prioritizes condensing on the third optical disc, the third optical disc has a larger substrate thickness than other optical discs, and therefore condenses from the incident surface of the third light flux. Since the distance to the point is long and the paraxial radius of curvature of the mother aspheric surface in the region through which the light beam condensed on the information recording surface of the third optical disc passes is large, the surface shape also becomes loose. When the difference in paraxial radius of curvature between the areas is small, the area where the light beam condensed on the information recording surface of the third optical disk does not pass (for example, the area for both the first optical disk and the second optical disk, or the area dedicated to the first optical disk) Since the paraxial radius of curvature of the mother aspherical surface becomes larger, the surface shape becomes loose, the focal length of these regions becomes longer, and the axial thickness of the objective lens becomes thicker. For example, in the example of Patent Document 1, the difference in the radius of curvature of the mother aspheric surface in the region through which the light flux for CD passes is as small as 0.0172 mm in Example 1 and 0.0119 mm in Example 2. For this reason, the focal length of the region where the light flux for CD is not condensed becomes long, and the axial thickness of the objective lens is increased accordingly. In Patent Document 2, the radius of curvature of the mother aspherical surface in the region where the light flux for CD is condensed is increased, and the mother aspherical surface in the region where the light flux for CD is condensed and the region where the light flux for CD is not condensed. Therefore, the paraxial curvature radius of the mother aspherical surface in the region where the light flux for CD is not collected is also large. For example, the difference in the radius of curvature is as small as 0.0701 mm in Example 5 at the maximum. For this reason, the focal length of the region where the light flux for CD is not collected is increased, the axial thickness of the objective lens is increased, and the effective diameter of the objective lens is increased accordingly. The axial thickness of the objective lens is at least 2.37 mm in Example 3 as a minimum. Since the on-axis thickness of the objective lens is thick, it is difficult to use it for a thin optical disk drive.

In other words, the configuration according to claim 3 or claim 4 can maintain a large paraxial radius of curvature of the third optical disk area, so that the focal length of the third optical disk can be maintained long. it can. Furthermore, since the paraxial radius of curvature of the first optical disk / second optical disk combined area and the first optical disk dedicated area can be reduced, the axial thickness of the objective lens can be reduced. Therefore, in the region through which the light beam condensed on the information recording surface of the third optical disk passes, the light beam that condenses the third light beam well on the information recording surface of the third optical disk and condenses on the information recording surface of the third optical disk. In the region where the light beam does not pass, the first light beam or the second light beam is preferably focused on the information recording surface of the first optical disk or the second optical disk, and the axial thickness of the objective lens is reduced. it can.

According to a fifth aspect of the present invention, there is provided the objective lens according to any one of the first to fourth aspects, wherein the passed third light beam can be recorded and / or reproduced on the information recording surface of the third optical disc. The first light flux that has been condensed and passed is not condensed so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the second light flux that has passed through is information on the second optical disc. The recording surface is characterized by having a third optical disc dedicated area that is not condensed so that information can be recorded and / or reproduced.

With the above configuration, the paraxial radius of curvature of the third optical disc region can be maintained large, and the paraxial radius of curvature of the first optical disc region can be reduced, so that the focal length of the third optical disc can be maintained long. However, it is possible to reduce the axial thickness of the objective lens. In addition, while providing the first optical disk, second optical disk, and third optical disk combined area corresponding to all of the first optical disk, the second optical disk, and the third optical disk, the focal distance for the third optical disk is extended and a long working distance is secured. When trying to do so, the pitch of the diffractive structure for distributing the light beams becomes very fine, and it becomes difficult to form the objective lens. Therefore, it is not necessary to provide the first optical disk / second optical disk / third optical disk combined area. It is not necessary to provide a diffraction structure with a very fine pitch, and an objective lens that is easy to manufacture can be obtained.

The objective lens described in claim 6 is characterized in that, in the invention described in claim 5, the third optical disk dedicated region is a refractive surface.

By using the refracting surface having no diffractive structure as the third optical disc dedicated area, it is possible to increase the light utilization efficiency and to easily form the objective lens.

The objective lens described in claim 7 is characterized in that, in the invention described in claim 5 or 6, the number of the third optical disc dedicated area is 1 or more and 3 or less.

With the above-described configuration, it is possible to suppress the light loss of the first light beam condensed on the first optical disc and to simplify the structure of the objective lens, so that an objective lens that is easy to manufacture can be obtained.

The objective lens according to an eighth aspect of the present invention is the objective lens according to any one of the first to seventh aspects, wherein the first region records the first luminous flux that has passed through the information recording surface of the first optical disc, and records information. The second light flux that has been condensed so that it can be reproduced and passed is condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc, but the third light flux that has passed therethrough Is an area for both the first optical disk and the second optical disk that is not condensed so that information can be recorded and / or reproduced on the information recording surface of the third optical disk.

With the above configuration, the paraxial radius of curvature of the third optical disc region can be maintained large, and the paraxial radius of curvature of the first optical disc region can be reduced, so that the focal length of the third optical disc can be maintained long. However, it is possible to reduce the axial thickness of the objective lens. In addition, since it is not necessary to provide a first optical disk / second optical disk / third optical disk combined area corresponding to all of the first optical disk, the second optical disk, and the third optical disk, it is not necessary to provide a diffraction structure with a very fine pitch. Therefore, an objective lens that is easy to manufacture can be obtained.

Compared with other optical discs, the region including the optical axis of the objective lens is used as a common region through which the first, second, and third light beams pass and is focused on the first, second, and third optical discs, respectively. As a result, there is a problem that the working distance of a CD having a thick substrate becomes insufficient and the usability becomes poor. Therefore, with the above configuration, the paraxial radius of curvature of the first area can be set to the paraxial radius of curvature similar to that of the first optical disc dedicated area, and the paraxial radius of curvature of the first area can be reduced. It is possible to reduce the axial thickness of the objective lens. This makes it possible to lengthen the CD working distance.

In addition, an optical disk using a light beam having a short wavelength has a high information recording density and a diameter of each information pit is small. Therefore, in an optical disk using a light beam having a short wavelength, the diameter of a focused spot corresponding to each information pit is small. In addition, a highly accurate light collecting characteristic is required. On the other hand, the light beam that has passed through the region near the optical axis has little change in the traveling direction of light due to refraction or diffraction, and can exhibit good light condensing characteristics. Therefore, in the present invention, the aberration characteristic is improved by using the region including the optical axis of the objective lens as a region for condensing the first light beam and the second light beam having a shorter wavelength than the third light beam.

The objective lens according to claim 9 is the objective lens according to claim 8, wherein the first region has a first diffractive structure, and the first diffractive structure passes through the first light flux. The structure is characterized in that 0-order diffracted light (transmitted light) is generated most as compared with other orders of diffracted light.

An objective lens according to a tenth aspect is the objective lens according to any one of the first to ninth aspects, wherein the second region is configured to transmit the third light flux that has passed through the information recording surface of the third optical disc. The first light flux that has been condensed so as to be able to be recorded and / or reproduced is not condensed so that information can be recorded and / or reproduced on the information recording surface of the first optical disc. The second optical disk is an area dedicated to the third optical disk that does not collect the two light beams so that information can be recorded and / or reproduced on the information recording surface of the second optical disk.

With the above configuration, the paraxial radius of curvature of the area for the third optical disc can be maintained large, and the focal length of the third optical disc can be maintained long. Further, it becomes easy to cope with a relatively small image-side numerical aperture when the third optical disc is used, and appropriate information recording / reproduction can be performed. For example, when the third optical disc is a CD, a CD-dedicated area can be provided within the required numerical aperture of the CD, so that recording / reproduction with respect to the CD can be performed appropriately.

An objective lens according to an eleventh aspect is the objective lens according to any one of the first to tenth aspects, wherein the third region causes the first luminous flux that has passed through to the information recording surface of the first optical disc. Condensed so that information can be recorded and / or reproduced, and the second light flux that has passed through is condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc, but has passed. The third optical flux is a first optical disc / second optical disc combined area that does not collect information so that information can be recorded and / or reproduced on an information recording surface of the third optical disc.

With the above configuration, when the first optical disc is a BD and the second optical disc is a DVD, a BD / DVD combined area can be provided within the required numerical aperture of the BD and DVD, so that recording on the BD and DVD can be performed appropriately. / Playback can be performed.

Further, if the third area is a first optical disk / second optical disk combined area, it is possible to prevent a decrease in the utilization efficiency of the first light flux and the second light flux.

An objective lens according to a twelfth aspect is the invention according to any one of the first to eleventh aspects, wherein the objective lens has a fourth region outside the third region, and outside the fourth region. A fifth region, a sixth region outside the fifth region, the sixth region being a region farthest from the optical axis in the objective lens, the first region, the third region And the fifth region condenses the passed first light beam so that information can be recorded and / or reproduced on the information recording surface of the first optical disk, and the passed second light beam is reflected on the second optical disk. The third light flux that is focused on the information recording surface so that information can be recorded and / or reproduced is not condensed on the information recording surface of the third optical disc so that information can be recorded and / or reproduced. 1 optical disc / second optical disc combined area The second region and the fourth region condense the passed third light flux so that information can be recorded and / or reproduced on the information recording surface of the third optical disc, and the passed first light flux is It is possible to record and / or reproduce information on the information recording surface of the second optical disc without condensing the information on the information recording surface of the first optical disc so that information can be recorded and / or reproduced. The sixth area is a third optical disk dedicated area that does not collect light, and the sixth area condenses and passes the first light flux that has passed therethrough so that information can be recorded and / or reproduced on the information recording surface of the first optical disk. The second light flux is not condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the passed third light flux is recorded on the information recording surface of the third optical disc. And / or playback Characterized in that it is a first optical disk dedicated area is not focused as obtain.

With the above configuration, the paraxial radius of curvature of the third optical disc region can be maintained large, and the paraxial radius of curvature of the first optical disc region can be reduced, so that the focal length of the third optical disc can be maintained long. However, it is possible to reduce the axial thickness of the objective lens. In addition, since it is not necessary to provide a first optical disk / second optical disk / third optical disk combined area corresponding to all of the first optical disk, the second optical disk, and the third optical disk, it is not necessary to provide a diffraction structure with a very fine pitch. Therefore, an objective lens that is easy to manufacture can be obtained. Furthermore, it is possible to suppress the light amount loss of the first light beam condensed on the first optical disk and to simplify the structure of the objective lens, so that an objective lens that is easy to manufacture can be obtained. In addition, when the third optical disc is a CD, a CD-dedicated area can be provided within the required numerical aperture of the CD, so that recording / reproduction with respect to the CD can be performed appropriately. Furthermore, when the first optical disc is a BD and the second optical disc is a DVD, a BD / DVD combined area can be provided within the required numerical aperture of the BD and DVD, so that recording / reproduction with respect to the BD and DVD can be performed appropriately. Can be performed. In addition, by using six regions, it is possible to design with a balanced light utilization efficiency for three light beams having different wavelengths.

The objective lens according to claim 13 is the objective lens according to claim 12, wherein the sixth region is a refractive surface.

The area farthest from the optical axis has a large inclination of the surface normal with respect to the optical axis. If a diffractive structure is provided here, the use efficiency of light may be reduced due to vignetting. It is possible to suppress a decrease in use efficiency of

The objective lens according to claim 14 is the objective lens according to any one of claims 1 to 11, wherein the objective lens has a fourth region outside the third region, and the fourth region is the objective lens. The first region and the third region are the regions farthest from the optical axis of the lens, and the first light beam and the third region can record and / or reproduce information on the information recording surface of the first optical disk. The condensed and passed second light beam is condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disk, and the passed third light beam is recorded on the information recording surface of the third optical disk. The first optical disk / second optical disk combined area that does not collect the light so that information can be recorded and / or reproduced, and the second area transmits the passed third light flux to the information recording surface of the third optical disk. Records and / or Collects the first luminous flux that has passed through the information recording surface of the first optical disc so that it can be recorded and / or reproduced, and passes the second luminous flux that has passed through the first optical flux. An area dedicated to the third optical disk that is not focused so that information can be recorded and / or reproduced on the information recording surface of the second optical disk, and the fourth area records the first light flux that has passed through the information recording surface of the first optical disk. The light is condensed so that information can be recorded and / or reproduced on the surface, and the second light flux that has passed therethrough passes without being condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc. The third light flux is an area dedicated to the first optical disc that does not collect the information so that information can be recorded and / or reproduced on the information recording surface of the third optical disc.

According to the above configuration, the same effect as that of the configuration described in claim 13 can be obtained, and the light amount loss of the first light beam condensed on the first optical disc can be further suppressed as compared with the configuration described in claim 13. In addition, since the structure of the objective lens can be made simpler, an objective lens that is easy to manufacture can be obtained.

The objective lens described in claim 15 is characterized in that, in the invention described in claim 14, the fourth region is a refracting surface.

The area farthest from the optical axis has a large slope of the surface normal, so providing a diffractive structure here may reduce the light utilization efficiency due to vignetting, etc. Can be suppressed.

The objective lens according to a sixteenth aspect is the invention according to any one of the first to fifteenth aspects, wherein in the cross section including the optical axis, there is a step between the first region and the second region. The portion where the first region intersects with the first region is located closer to the light source in the optical axis direction than the region where the step and the second region intersect.

With such a shape, the second area is positioned on the optical disc side with respect to the first area so that the third light beam can be recorded and / or reproduced on the information recording surface of the third optical disk. The distance from the light collecting surface to the surface from which the laser light is emitted from the objective lens is shortened, the working distance WD3 can be secured, and an objective lens suitable for an optical pickup device for a thin optical disk drive is obtained. Can do.

The objective lens according to claim 17 is the objective lens according to claim 16, wherein the first region condenses the passed first light beam on the information recording surface of the first optical disc and passes the second light beam. A first optical disk / second optical disk combined area that collects a light beam on the information recording surface of the second optical disk and does not collect the passed third light beam on the information recording surface of the third optical disk; Condenses the passed third light flux on the information recording surface of the third optical disc, and does not concentrate the passed first light flux on the information recording surface of the first optical disc, and passes the passed second light flux. It is a third optical disc dedicated area that does not concentrate on the information recording surface of the second optical disc.

The objective lens described in Item 18 is characterized in that, in the invention described in Items 1-17, the following conditional expression (2) is satisfied.

d / δ ≦ 5 (2)
However,
d: axial thickness of the objective lens δ: minimum thickness in the optical axis direction of the objective lens When the axial thickness of the objective lens is reduced while maintaining the focusing performance of the objective lens, the edge thickness of the objective lens is reduced, The ratio between the minimum thickness in the optical axis direction of the objective lens and the axial thickness of the objective lens, that is, the thickness deviation ratio tends to be small. If the thickness deviation ratio is small, the edge of the objective lens tends to be chipped. Furthermore, when the objective lens is manufactured by plastic injection molding, the passage when the molten plastic is injected into the mold is narrowed, making molding difficult. In the present invention, the thickness deviation ratio is set to 5 or less, a significant reduction in the edge thickness of the objective lens is suppressed, chipping of the edge of the objective lens is prevented, and moldability is improved.

An optical pickup device according to claim 19 has the objective lens according to any one of claims 1 to 18.

The optical pickup device according to the present invention has three light sources: a first light source, a second light source, and a third light source. Furthermore, the optical pickup device of the present invention condenses the first light flux on the information recording surface of the first optical disc, condenses the second light flux on the information recording surface of the second optical disc, and causes the third light flux to be third. It has a condensing optical system for condensing on the information recording surface of the optical disc. The optical pickup device of the present invention includes a light receiving element that receives a reflected light beam from the information recording surface of the first optical disc, the second optical disc, or the third optical disc.

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 of 2 (t1 <t2) and an information recording surface. The third optical disc has a protective substrate having a thickness t3 (t2 <t3) and an information recording surface. The first optical disc is preferably a BD (Blu-ray Disc), the second optical disc is preferably a DVD, and the third optical disc is preferably a CD, but is not limited thereto. The first optical disc, the second optical disc, or the third optical disc may be a multi-layer optical disc having a plurality of information recording surfaces. Incidentally, the thickness of the protective substrate includes the case of 0, and when the protective film having a thickness of several to several tens of μm is applied to the optical disk, the thickness thereof is also included.

BD records and reproduces information with an objective lens with NA of 0.85, and the thickness of the protective substrate is about 0.1 mm. Further, DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67, and the thickness of the protective substrate is about 0.6 mm. DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. In this specification, CD is a generic name for CD-series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.53, and the thickness of the protective substrate is about 1.2 mm. Including CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like. As for the recording density, the recording density of BD is the highest, followed by the order of DVD and CD.

In addition, regarding the thicknesses t1, t2, and t3 of the protective substrate, it is preferable to satisfy the following conditional expressions (3), (4), and (5), but is not limited thereto. The thickness of the protective substrate referred to here is the thickness of the protective substrate provided on the surface of the optical disk. That is, the thickness of the protective substrate from the optical disc surface to the information recording surface closest to the surface.

0.05mm ≦ t1 ≦ 0.1125mm (3)
0.5mm ≦ t2 ≦ 0.7mm (4)
1.0mm ≦ t3 ≦ 1.3mm (5)
In the present specification, the first light source, the second light source, and the third light source are preferably laser light sources. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used. The first wavelength λ1 of the first light beam emitted from the first light source, the second wavelength λ2 (λ2> λ1) of the second light beam emitted from the second light source, and the third of the third light beam emitted from the third light source. The wavelength λ3 (λ3> λ2) preferably satisfies the following conditional expressions (6) and (7).

1.5 × λ1 <λ2 <1.7 × λ1 (6)
1.8 × λ1 <λ3 <2.0 × λ1 (7)
When recording / reproducing information with respect to the first optical disk, it is necessary to make the condensing spot smaller than that of the second optical disk or the third optical disk. For this purpose, the wavelength of the first light beam is the wavelength of the second light beam, It is necessary to make it shorter than the wavelength of the third light beam. In the laser device used for the light source, the wavelength of the emitted light changes due to the temperature change. In addition, it is preferable to satisfy the conditional expressions (6) and (7) in order to suppress the spherical aberration generated with respect to the temperature change and the wavelength change to such an extent that information can be recorded / reproduced on the optical disk.

When BD, DVD, and CD are used as the first optical disc, the second optical disc, and the third optical disc, respectively, the first wavelength λ1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm. The second wavelength λ2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less, and the third wavelength λ3 of the third light source is preferably 750 nm. The thickness is 850 nm or less, more preferably 760 nm or more and 820 nm or less.

Also, at least two of the first light source, the second light source, and the third light source may be unitized. The unitization means that the first light source and the second light source are fixedly housed in one package, for example. In addition to the light source, a light receiving element to be described later may be packaged.

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 light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking 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. A light receiving element may be used (so-called three beam method or the like). The light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.

The condensing optical system used in the optical pickup device has an objective lens. The condensing optical system may include only the objective lens, but the condensing optical system may include a coupling lens such as a collimator lens in addition to the objective lens. The coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam. The collimating lens is a kind of coupling lens, and is a lens that emits light incident on the collimating lens as 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. In this specification, the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk. The objective lens is a single objective lens. Further, the objective lens may be a glass lens, a plastic lens, or a hybrid lens in which a diffractive structure or the like is provided on a glass lens with a photo-curing resin. A plastic lens is the most suitable from the viewpoint of performance and low cost. The objective lens preferably has a refractive surface that is aspheric. The objective lens preferably has an aspherical base surface (also referred to as a mother aspherical surface) on which a diffractive structure is provided. When determining the mother aspheric surface from the objective lens, the envelope surface connecting the most optical disc side portions of the steps of the diffractive structure can be regarded as the mother aspheric surface.

Further, when the objective lens is a glass lens, it is preferable to use a glass material having a glass transition point Tg of 500 ° C. or lower, and more preferably 480 ° C. or lower. By using a glass material having a glass transition point Tg of 500 ° C. or lower, molding at a relatively low temperature is possible, so that the life of the mold can be extended.

Furthermore, since the specific gravity of a glass lens is generally larger than that of a resin lens, if the objective lens is a glass lens, the weight increases and a load is imposed on the actuator that drives the objective lens. Therefore, when the objective lens is a glass lens, it is preferable to use a glass material having a small specific gravity. Specifically, the specific gravity is preferably 3.0 or less, and more preferably 2.75 or less.

Specific examples of such a glass material include Examples 1 to 12 of JP-A No. 2005-306627. For example, in Example 1 of JP-A-2005-306627, the glass transition point Tg is 460 ° C., the specific gravity is 2.58, the refractive index nd is 1.594, and the Abbe number is 59.8.

When the objective lens 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 1.52 to 1.60. The refractive index change rate dN / dT (° C. ⁻¹ ) is −20 × 10 ^{−5 to} −5 × 10 ^{− with} respect to the wavelength of 405 nm accompanying the temperature change within the temperature range of −5 ° C. to 70 ° C. ^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 lens is a plastic lens, the coupling lens is preferably a plastic lens.

Further, the Abbe number of the material constituting the objective lens is preferably 50 or more.

The objective lens is described below. At least one optical surface of the objective lens includes at least a first region, a second region provided outside the first region, and a third region provided outside the second region. Moreover, you may have a 4th area | region further outside the 3rd area | region. The fourth region may be a region farthest from the optical axis. Alternatively, the fourth region may be further provided outside the third region, and the fifth region may be further provided outside the fourth region. Further, a sixth region may be provided outside the fifth region, and the sixth region may be a region farthest from the optical axis. The number of regions is preferably 10 or less, and more preferably 8 or less. The optical surface having the first region, the second region, and the third region is preferably an optical surface on the light source side, and is preferably an optical surface with a smaller radius of curvature.

The first area is preferably an area including the optical axis of the objective lens, but a minute area including the optical axis may be an unused area or a special purpose area, and the surrounding area may be the first area. When there are the first region, the second region, the third region, and other regions, it is preferable that the regions are provided on the same optical surface. As shown in FIG. 1 showing an example divided into three regions, the first region CN, the second region MD, and the third region OT are provided concentrically around the optical axis on the same optical surface. It is preferable that The first region CN, the second region MD, and the third region OT are preferably adjacent to each other, but there may be a slight gap between them.

It should be noted that in the plurality of regions of the objective lens, the region of the objective lens that condenses the passed first light flux so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the passed third light flux. The area of the objective lens that is condensed so that information can be recorded and / or reproduced on the information recording surface of the third optical disc is a different area. In particular, the first area and the second area are neither the first optical disk / third optical disk combined area or the first optical disk / second optical disk / third optical disk combined area. The third area and the area outside of the third area may have a first optical disk / third optical disk combined area or a first optical disk / second optical disk / third optical disk combined area. It is preferable that all the areas are not the first optical disk / third optical disk combined area or the first optical disk / second optical disk / third optical disk combined area. For example, an objective lens having a first optical disk / second optical disk combined area, a third optical disk dedicated area, and a first optical disk dedicated area, a first optical disk dedicated area, a second optical disk / third optical disk combined area, and a first optical disk dedicated A preferable example is an objective lens having a region.

Further, the passed third light beam is condensed so that information can be recorded and / or reproduced on the information recording surface of the third optical disk in a plurality of areas, and the passed first light beam is recorded on the information recording surface of the first optical disk. Only for the third optical disc that does not condense so that information can be recorded and / or reproduced on the surface, and the second light flux that has passed does not converge so that information can be recorded and / or reproduced on the information recording surface of the second optical disc It is preferable to have a region. In addition, the third optical disk dedicated area may be a diffractive surface, but from the viewpoint of ease of manufacture and improvement of light utilization efficiency, the third optical disk dedicated area is preferably a refractive surface.

It should be noted that the number of the third optical disc dedicated area is preferably 1 or more and 3 or less.

The first region condenses the passed first light flux so that information can be recorded and / or reproduced on the information recording surface of the first optical disk, and the passed second light flux is recorded on the information recording medium of the second optical disk. A first optical disc that focuses light so that information can be recorded and / or reproduced on the surface, but does not collect the passed third light beam so that information can be recorded and / or reproduced on the information recording surface of the third optical disc -It is preferable that it is a 2nd optical disk combined area | region. The third area is also preferably a first optical disk / second optical disk combined area.

Further, the second region condenses the passed third light beam so that information can be recorded and / or reproduced on the information recording surface of the third optical disk, and the passed first light beam is applied to the information recording surface of the first optical disk. A third optical disc dedicated area that does not collect light so that information can be recorded and / or reproduced, and does not collect the second light flux that has passed through the information recording surface of the second optical disk so that information can be recorded and / or reproduced. Preferably there is.

For example, when the objective lens has six regions, the first to sixth diffractive structures may be provided in each of the first to sixth regions. The second area, the fourth area, and the sixth area may be refractive surfaces. The first diffractive structure, the second diffractive structure, the third diffractive structure, the fourth diffractive structure, the fifth diffractive structure, and the sixth diffractive structure are respectively the first region, the second region, the third region, and the fourth diffractive structure of the objective lens. It is preferably provided in a region of 70% or more of the area of each of the region, the fifth region, and the sixth region, and more preferably 90% or more. More preferably, the α-th diffractive structure (α is an integer of 1 to 6) is provided on the entire surface of the α-th region. Since the diffractive structure suitable for each region is provided on the entire surface of each region, the light use efficiency can be increased.

Note that the diffractive structure in this specification is a general term for structures that generate diffracted light with respect to a light beam having a certain wavelength. Preferably, the diffractive structure is a general term for a structure having a step and having an effect of converging or diverging a light beam by diffraction for at least a light beam having a certain wavelength. The diffractive structure preferably has a plurality of steps. 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. Further, even if the optical surface of the objective lens has a plurality of annular zones centered on the optical axis and separated by steps, and each of the annular zones is constituted by an individual aspheric surface, The objective lens that is converged or diverged is an objective lens having a diffractive structure. For example, a light beam having a wavelength of λA that has passed through a plurality of annular zones of an objective lens having a structure composed of individual aspheric surfaces for each annular zone is condensed on an information recording surface of an optical disc having a protective substrate having a thickness tA. In addition, when a light beam having a wavelength of λB (λA ≠ λB) that has passed through the plurality of annular zones is condensed on an information recording surface of an optical disc having a protective substrate having a thickness tB (tA ≠ tB), The objective lens converges or diverges the light beam by a diffractive action, and has a diffractive structure.

The diffractive structure preferably has a plurality of concentric annular zones around the optical axis. The diffractive structure can take various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shapes including the optical axis are roughly classified into a blazed structure and a staircase structure.

As shown in FIGS. 2A and 2B, the blazed structure is a sawtooth shape in cross section including the optical axis of an optical element having a diffractive structure. It has an oblique surface that is neither perpendicular nor parallel to the spherical surface. In the example of FIG. 2, it is assumed that the upper side is the light source side and the lower side is the optical disk side, and a diffractive structure is formed on a plane as a mother aspherical surface.

In addition, as shown in FIGS. 2C and 2D, the staircase structure is a structure in which the cross-sectional shape including the optical axis of an optical element having a diffractive structure is a small staircase (referred to as a staircase unit). That is to have more than one. In the present specification, the “X level” means an annular surface corresponding to (or facing) the optical axis vertical direction in one step unit of the staircase structure (hereinafter sometimes referred to as an optical function surface). Is divided by X steps, and is divided into X ring zones. Particularly, a three-level or higher staircase structure has a small step and a large step. In the staircase unit, the smallest step in the optical axis direction is meant, and the “large step” means the largest step in the optical axis direction in one staircase unit.

The diffraction structure shown in FIG. 2 (c) is referred to as a five-level step structure, and the diffraction structure shown in FIG. 2 (d) is referred to as a two-level step structure. The first diffractive structure is a two-level staircase structure, which includes a plurality of concentric ring zones centered on the optical axis, and the cross-sectional shape of the plurality of ring zones including the optical axis of the objective lens is the optical axis. A plurality of step surfaces Pa and Pb extending in parallel with each other, a light source side optical functional surface Pc connecting the light source side ends of adjacent step surfaces Pa and Pb, and optical disc side ends of adjacent step surfaces Pa and Pb. The optical source side optical functional surface Pc and the optical disc side optical functional surface Pd are alternately arranged along the direction intersecting the optical axis.

Also, in the staircase structure, the length of one staircase unit in the direction perpendicular to the optical axis is called a pitch P. The step surface is preferably parallel or substantially parallel to the optical axis, but the optical functional surface may be inclined with respect to the mother aspheric surface as well as when it is parallel to the mother aspheric surface.

The diffractive structure is preferably a structure in which a certain unit shape is periodically repeated. As used herein, “unit shape is periodically repeated” naturally includes shapes in which the same shape is repeated in the same cycle. In addition, the unit shape that is one unit of the cycle has regularity, and the shape in which the cycle gradually increases or decreases gradually is also included in the “unit shape is periodically repeated”. Suppose that

When the diffractive structure has a blaze structure, the sawtooth shape as a unit shape is repeated. As shown in FIG. 2 (a), the same sawtooth shape may be repeated, and as shown in FIG. 2 (b), the shape of the sawtooth shape gradually increases as it proceeds in the direction of the mother aspheric surface. It may be a shape that increases in size or a shape that decreases. Moreover, it is good also as a shape which combined the shape where the magnitude | size of the serrated shape became large gradually and the shape where the magnitude | size of a serrated shape becomes small gradually. However, even when the size of the serrated shape changes gradually, it is preferable that the size of the step amount in the optical axis direction (or the direction of the passing light beam) hardly changes in the serrated shape. In addition, in some areas, the blazed structure has a step opposite to the optical axis (center) side, and in other areas, the blazed structure has a step toward the optical axis (center). It is good also as a shape in which the transition area | region required in order to switch the direction of the level | step difference of a blaze | braze type | mold structure is provided in the meantime. This transition region is a region corresponding to a point that becomes an extreme value of the optical path difference function when the optical path difference added by the diffractive structure is expressed by the optical path difference function. Note that if the optical path difference function has an extreme point, the inclination of the optical path difference function becomes small, so that the annular zone pitch can be widened, and the decrease in transmittance due to the shape error of the diffractive structure can be suppressed.

When the diffractive structure has a staircase structure, there may be a shape or the like in which a 5-level staircase unit as shown in FIG. 2C is repeated. Furthermore, the shape of the staircase gradually increases as it advances in the direction of the mother aspheric surface, or the shape of the staircase gradually decreases. It is preferable that the level difference in the direction of the light beam to be changed hardly changes.

Hereinafter, the first diffraction structure, the third diffraction structure, and the fifth diffraction structure will be described in detail. The first diffractive structure, the third diffractive structure, and the fifth diffractive structure are preferably structures that enable at least compatibility between the first optical disc and the second optical disc. Therefore, the first diffractive structure, the third diffractive structure, and the fifth diffractive structure are different from the first diffractive structure, the third diffractive structure, or the fifth diffractive structure in the first optical disc. It is preferable to correct the spherical aberration caused by the difference between the thickness t1 of the protective substrate and the thickness t2 of the protective substrate of the second optical disk and / or the spherical aberration caused by the difference between the wavelengths of the first light beam and the second light beam.

The first diffractive structure, the third diffractive structure, and the fifth diffractive structure generate the most n-th order diffracted light when the first light beam passes and generate the most m-th order diffracted light when the second light beam passes. Preferred combinations of (n, m) include (0,1), (1, -2), (2,1) and the like. In particular, n = 0 is preferable because the first region can have a small paraxial radius of curvature suitable for the first optical disk, and the axial thickness of the objective lens can be reduced.

Further, in addition to the first diffractive structure, the third diffractive structure, and the fifth diffractive structure, when the second diffractive structure, the fourth diffractive structure, or the sixth diffractive structure is provided, they may be provided on different optical surfaces of the objective lens, It is preferable to provide on the same optical surface. Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing. Each diffraction structure is preferably provided on the light source side surface of the objective lens rather than the surface of the objective lens on the optical disc side.

In addition, as a preferable mode, a mode in which the third light flux that has passed through an area other than the area dedicated to the third optical disk is not used for recording and / or reproduction of the third optical disk can be mentioned. It is preferable that the third light flux that has passed through an area other than the area dedicated to the third optical disk does not contribute to the formation of a focused spot on the information recording surface of the third optical disk. That is, when the objective lens is provided with a diffractive structure in the first optical disc / second optical disc combined area, the third light flux passing through the diffractive structure in the first optical disc / second optical disc combined area is information on the third optical disc. It is preferable to form a flare on the recording surface. As shown in FIG. 3, in the spot formed on the information recording surface of the third optical disc by the third light beam that has passed through the objective lens, the light amount density is high in the order from the optical axis side (or the center of the spot) to the outside. The spot center portion SCN, the spot intermediate portion SMD whose light intensity density is lower than that of the spot center portion, and the spot peripheral portion SOT whose light intensity density is higher than that of the spot intermediate portion and lower than that of the spot center portion. The center portion of the spot is used for recording and / or reproducing information on the optical disc, and the spot intermediate portion and the spot peripheral portion are not used for recording and / or reproducing information on the optical disc. In the above, this spot peripheral part is called flare. However, the spot peripheral portion is also referred to as flare even when a spot has a spot peripheral portion around the center portion of the spot and there is a spot peripheral portion, that is, when a light spot with a large light is formed around the condensed spot. That is, the third light beam that has passed through the diffraction structure of the shared region of the first light beam and the second light beam of the objective lens forms a spot peripheral portion on the information recording surface of the third optical disk.

Also, as a preferable mode of the region farthest from the optical axis, a mode in which the second light beam and the third light beam that have passed through the region are not used for recording and / or reproduction of the second optical disk and the third optical disk can be mentioned. It is preferable that the second light flux and the third light flux that have passed through the same region do not contribute to the formation of a focused spot on the information recording surfaces of the second optical disc and the third optical disc, respectively. That is, it is preferable that the second light flux and the third light flux that pass through a region farthest from the optical axis form a flare on the information recording surfaces of the second optical disc and the third optical disc. In other words, it is preferable that the second light flux and the third light flux that have passed through a region farthest from the optical axis form a spot peripheral portion on the information recording surfaces of the second optical disc and the third optical disc.

When the region farthest from the optical axis has a diffractive structure, the diffractive structure causes spherochromatism (colored spherical surface) generated by slight fluctuations in the wavelength of the first light source with respect to the first light flux that has passed through the diffractive structure. (Aberration) may be corrected. A slight change in wavelength refers to a change within ± 10 nm. For example, when the first light flux changes by ± 5 nm from the wavelength λ1, the diffraction structure compensates for the variation of the spherical aberration of the first light flux that has passed through the diffraction structure, and the wavefront on the information recording surface of the first optical disc It is preferable that the amount of change in aberration be 0.001λ1 rms or more and 0.070λ1 rms or less.

When the objective lens is a plastic lens, the seventh diffractive structure is used as the temperature characteristic correcting structure, the first diffractive structure, the third diffractive structure, the fourth diffractive structure, the fifth diffractive structure, or the sixth diffractive structure. You may use what further piled up. Or you may make it provide a 7th diffractive structure in the 4th area | region and 6th area | region which are refractive surfaces. Specifically, the level difference in the optical axis direction of the seventh diffractive structure gives an optical path difference of about 5 wavelengths of the first wavelength to the first light flux, and about 3 of the second wavelength to the second light flux. A step amount that gives an optical path difference corresponding to the wavelength, or an optical path difference equivalent to approximately two wavelengths of the first wavelength with respect to the first light flux, and an optical path corresponding to approximately one wavelength of the second wavelength with respect to the second light flux. It is preferable that the difference in level is such that it gives a difference, but the present invention is not limited to this.

Further, it is preferable that the difference between the paraxial curvature radius of the mother aspheric surface in a certain region and the paraxial curvature radius of the mother aspheric surface in another region is 0.1 mm or more and 0.7 mm or less. In particular, as shown in FIG. 4, the first area R1 including the optical axis is the first optical disk / second optical disk combined area, and the second area R2 around the outside is the third optical disk dedicated area, When the outer peripheral third region R3 is the first optical disc / second optical disc combined region and the outer peripheral fourth region R4 is the third optical disc dedicated region, the first region R1 and the third region R3 Is located on the same first mother aspheric surface BL1, and the second region R2 and the fourth region R4 are located on the same second mother aspheric surface BL. Here, the position P1 at which the first mother aspherical surface BL1 intersects the optical axis is preferably located closer to the light source than the position P2 at which the second mother aspherical surface BL2 intersects the optical axis. In other words, in the cross section of the objective lens including the optical axis, a step ST exists between the first region R1 and the second region R2, and a point P3 where the step ST and the first region R1 intersect is It can also be said that it is on the light source side in the optical axis direction as compared to the point P4 where the step ST and the second region intersect. Further, since the distance Δ between the positions P1 and P2 can be expressed approximately as a difference in curvature radius between the mother aspheric surfaces BL1 and BL2, it is preferably 0.1 mm to 0.7 mm. It is desirable that the mother aspheric surfaces BL1 and BL2 intersect within the effective diameter.

Further, as shown in FIG. 1, the objective lens OBJ generally has a flange portion FL having a minimum thickness of the objective lens on the outer side in the optical axis orthogonal direction of the region OT farthest from the optical axis. The ratio of the minimum thickness δ in the optical axis direction to the on-axis thickness d of the objective lens OBJ (d / δ: referred to as thickness deviation ratio) is preferably 5 or less.

The objective-side numerical aperture of the objective lens necessary for reproducing and / or recording information on the first optical disk is NA1, and the objective lens necessary for reproducing and / or recording information on the second optical disk The image-side numerical aperture is NA2 (NA1 ≧ NA2), and the image-side numerical aperture of the objective lens necessary for reproducing and / or recording information on the third optical disk is NA3 (NA2> NA3). NA1 is preferably 0.6 or more and 0.9 or less, more preferably 0.75 or more and 0.9 or less. In particular, NA1 is preferably 0.85. NA2 is preferably 0.55 or more and 0.7 or less. In particular, NA2 is preferably 0.60 or 0.65. NA3 is preferably 0.4 or more and 0.55 or less. In particular, NA3 is preferably 0.45 or 0.53.

The outer boundary of the third optical disc dedicated area farthest from the optical axis of the objective lens is 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3) when the third light beam is used. It is preferably formed in a portion corresponding to the range of 1.15 · NA3 or less. More preferably, the outer boundary of the third optical disk dedicated region farthest from the optical axis of the objective lens is formed in a portion corresponding to NA3. Further, the inner boundary of the region used for the second optical disc farthest from the optical axis of the objective lens is 0.9 · NA 2 or more and 1.2 · NA 2 or less (more preferably 0) when the second light beam is used. .95 · NA2 or more and 1.15 · NA2 or less). More preferably, the inner boundary of the region used for the second optical disk farthest from the optical axis of the objective lens is formed in a portion corresponding to NA2.

When the third light flux that has passed through the objective lens is condensed on the information recording surface of the third optical disc, it is preferable that the spherical aberration has at least one discontinuous portion. In that case, the discontinuous portion has a range of 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3 or more and 1.15 · NA 3 or less) when the third light flux is used. It is preferable that it exists in.

In addition, when spherical aberration is continuous and does not have a discontinuous portion and the third light flux that has passed through the objective lens is condensed on the information recording surface of the third optical disc, NA2 It is preferable that the absolute value of the spherical aberration is 0.03 μm or more, and in NA3, the absolute value of the longitudinal spherical aberration is 0.02 μm or less. More preferably, in NA2, the absolute value of longitudinal spherical aberration is 0.08 μm or more, and in NA3, the absolute value of longitudinal spherical aberration is 0.01 μm or less.

Furthermore, it is preferable that the objective lens satisfies the following conditional expression.

1.5 (mm) ≦ φ1 ≦ 3.4 (mm) (8)
1.7 × f3> φ1 (9)
0.7 ≦ d / f3 ≦ 1.42 (mm) (10)
Here, φ1 represents the effective diameter of the surface on which the first light beam enters the objective lens, f3 represents the focal length of the objective lens when the third light beam is used, and d represents the axial thickness of the objective lens.

Preferably, the following conditional expression is satisfied.

2.1 (mm) ≦ φ1 ≦ 2.5 (mm) (8) ′
Also preferably, the following conditional expression is satisfied.

0.9 ≦ d / f3 ≦ 1.1 (mm) (10) ′
Furthermore, it is preferable to satisfy the following formula.

1.4 (mm) ≦ f3 ≦ 2.0 (mm) (11)
By using a small-diameter objective lens that satisfies the formula (8) and satisfying the formula (9), the focal length f3 when using the third optical disc is increased, so that the optical disc on the surface on which the laser beam is emitted from the objective lens is the most. Since the working distance WD3, which is the distance from the close position to the optical disk, can be secured, the objective lens is moved by the actuator or the like to the optical axis in order to optimize the focused spot diameter on the information recording surface of the third optical disk. There is room for displacement along the line. Further, in order to maintain the focal length f3 long and to maintain the optical performance such as the condensing characteristic and to make it applicable to a thin optical disk drive, while satisfying the conditional expressions (8) and (9) The present inventor has found that the object can be achieved by satisfying the expression (10). Note that “1.7” in the equation (9) corresponds to twice the image-side numerical aperture NA of the first optical disc. In the ordinary first optical disk refractive lens, Φ = 1.7 × f is satisfied, but in the present invention, the focal length of the CD is ensured by making Φ smaller than 1.7 × f3. However, an objective lens with a reduced Φ is obtained. In addition, by satisfying the above formula, the focal length of the third optical disc is sufficiently secured, the focal length is prevented from becoming too long, and even if the objective lens is a plastic lens, the change in spherical aberration due to temperature change is reduced. This is preferable because it can be performed.

Furthermore, in order to obtain an objective lens that can be mounted on a thin optical pickup device, it is preferable to satisfy the following expression.

d ≦ 2.0 (mm) (12)
Further, when the focal length of the first light beam of the objective lens is f1 (mm) and the center thickness of the objective lens is d (mm), it is preferable to satisfy the following formula (13).

0.7 ≦ d / f1 ≦ 1.5 (13)
In addition, it is more preferable to satisfy | fill following formula (13) '.

1.0 ≦ d / f1 ≦ 1.3 (13) ′
Furthermore, it is preferable to satisfy the following formula.

0.7 ≦ d / f2 ≦ 1.3 (14)
Here, f2 represents the focal length of the objective lens when the second light beam is used.

By satisfying conditional expressions (13) and (14), the working distance of the CD as the third optical disk can be secured without reducing the pitch of the diffractive structure, and the objective lens can be easily manufactured. Thus, it is possible to maintain high light use efficiency.

Moreover, it is preferable that the following conditional expression is satisfied.

0.9 ≦ φ2 / φ1 ≦ 1.2 (15)
Note that Φ2 represents the effective diameter of the objective lens when the second optical disk is used. By satisfying the above range, the working distance of the CD as the third optical disk is secured at a distance that does not cause a problem in practical use, and even if the objective lens is a plastic lens, for example, the aberration change when the temperature changes It is possible to maintain a level at which no problem occurs when recording and / or reproducing information on an optical disc.

Furthermore, it is preferable to satisfy the following formula.

0.15 (mm) ≦ WD3 ≦ 0.5 (mm) (16)
However, WD3 represents a working distance when the third optical disc is used.

Preferably, the following equation is satisfied.

0.15 (mm) ≦ WD3 ≦ 0.4 (mm) (16) ′
Furthermore, it is preferable to satisfy the following formula.

0.2 (mm) ≦ WD2 ≦ 0.8 (mm) (17)
However, WD2 represents the working distance when the second optical disc is used.

Furthermore, it is preferable to satisfy the following formula.

0.4 (mm) ≦ WD1 ≦ 1.2 (mm) (18)
However, WD1 represents a working distance when the first optical disc is used.

Hereinafter, two types of preferred modes for the number of regions of the objective lens will be described in detail, but the present invention is not limited to the following modes.
(Example 1) Four-region objective lens The first of the preferred embodiments is an embodiment in which the optical surface of the objective lens is divided into four regions. In this aspect, the fourth region is a region farthest from the optical axis in the objective lens. The first area and the third area are areas for both the first optical disk and the second optical disk. The second area is a third optical disk dedicated area. Further, the fourth region condenses the passed first light flux so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the passed second light flux is applied to the information recording surface of the second optical disc. In the first optical disc dedicated area that does not collect the information so that it can be recorded and / or reproduced, and does not collect the passed third light beam on the information recording surface of the third optical disc so that information can be recorded and / or reproduced. is there.

It is preferable that the first area of the objective lens, which is the first optical disk / second optical disk combined area, has the first diffractive structure. The first diffractive structure generates the most n-th order diffracted light when the first light beam passes and generates the most m-th order diffracted light when the second light beam passes. Preferred combinations of (n, m) include (0,1), (1, -2), (2,1) and the like. In particular, n = 0 is preferable because the first region can have a small paraxial radius of curvature suitable for the first optical disk, and the axial thickness of the objective lens can be reduced.

Further, it is preferable that the third region of the objective lens, which is the first optical disc / second optical disc combined region, has a third diffractive structure. The third diffractive structure is preferably the same structure as the first diffractive structure.

The second region of the objective lens, which is the third optical disk dedicated region, is preferably a refracting surface, but a second diffractive structure may be provided. The refracting surface is preferably a surface that does not have a structure that gives an optical path difference to the light beam incident on the objective lens.

The fourth region of the objective lens, which is the first optical disk dedicated region, is preferably a refractive surface, but a fourth diffractive structure may be provided.

Further, the difference between the paraxial curvature radius of the mother aspheric surface in the first region and the third region and the paraxial curvature radius of the mother aspheric surface in the second region may be 0.1 mm or more and 0.7 mm or less. preferable.
(Example 2) Six-region objective lens A second preferred embodiment is an embodiment in which the optical surface of the objective lens is divided into six regions. In this aspect, the sixth region is a region farthest from the optical axis in the objective lens. The first area, the third area, and the fifth area are areas for both the first optical disk and the second optical disk. The second area and the fourth area are areas dedicated to the third optical disc. Furthermore, the sixth area is a first optical disk dedicated area.

Further, it is preferable that the fifth area of the objective lens, which is the first optical disk / second optical disk combined area, has the fifth diffractive structure. The fifth diffractive structure is preferably the same structure as the first diffractive structure and the third diffractive structure.

The second region of the objective lens, which is the third optical disk dedicated region, is preferably a refracting surface, but a second diffractive structure may be provided.

Further, the fourth area of the objective lens, which is the third optical disk dedicated area, is preferably a refractive surface, but a fourth diffractive structure may be provided.

Further, the sixth area of the objective lens, which is the first optical disk dedicated area, is preferably a refractive surface, but a sixth diffractive structure may be provided.

Further, the difference between the paraxial curvature radius of the mother aspheric surface in the first region, the third region, and the fifth region and the paraxial curvature radius of the mother aspheric surface in the second region and the fourth region is 0.1 mm or more, It is preferable that it is 0.7 mm or less.

The first light beam, the second light beam, and the third light beam may be incident on the objective lens as parallel light, or may be incident on the objective lens as divergent light or convergent light. Preferably, the imaging magnification m1 of the objective lens when the first light beam enters the objective lens satisfies the following formula (19).

-0.02 <m1 <0.02 (19)
On the other hand, when the first light flux is incident on the objective lens as diverging light, the imaging magnification m1 of the objective lens when the first light flux is incident on the objective lens preferably satisfies the following expression (19 ′). .

-0.10 <m1 <0.00 (19 ')
In addition, when the second light flux is incident on the objective lens as parallel light or substantially parallel light, the imaging magnification m2 of the objective lens when the second light flux enters the objective lens satisfies the following expression (20). Is preferred.

-0.02 <m2 <0.02 (20)
On the other hand, when the second light beam is incident on the objective lens as diverging light, the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens preferably satisfies the following expression (20 ′). .

-0.10 <m2 <0.00 (20 ')
Further, when the third light beam is incident on the objective lens as parallel light or substantially parallel light, the imaging magnification m3 of the objective lens when the third light beam enters the objective lens satisfies the following expression (21). Is preferred. When the third light flux is parallel light, a problem easily occurs in tracking. However, even if the third light flux is parallel light, the present invention can obtain good tracking characteristics, and can be used for three different optical disks. On the other hand, recording and / or reproduction can be appropriately performed.

-0.02 <m3 <0.02 (21)
On the other hand, when the third light beam is incident on the objective lens as diverging light, the imaging magnification m3 of the objective lens when the third light beam is incident on the objective lens preferably satisfies the following expression (21 ′). .

-0.10 <m3 <0.00 (21 ')
An optical information recording / reproducing apparatus according to the present invention includes 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 disc drive apparatus main body in which the optical pickup device is stored is taken out to the outside.

The optical information recording / reproducing apparatus using each method described above 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 for guiding toward the head, a spindle motor for rotating 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, an optical pickup device that can be used in a thin optical disk drive while ensuring a sufficient working distance of a CD and can appropriately record / reproduce information on different optical disks such as BD, DVD, and CD. And it is possible to provide an objective lens suitable for it.

(A) is the figure which looked at an example of objective-lens OBJ which concerns on this invention from the optical axis direction, (b) is sectional drawing. FIG. 4 is a cross-sectional view schematically showing several examples (a) to (d) of a diffractive structure provided in the objective lens OBJ according to the present invention. It is the figure which showed the shape of the spot by the objective lens which concerns on this invention. It is an expanded sectional view of an example of objective lens OBJ concerning the present invention. It is a figure which shows schematically the structure of the optical pick-up apparatus which concerns on this invention. FIG. 3 is a cross-sectional view of the objective lens of Example 1. FIG. 7A is a diagram showing longitudinal spherical aberration (solid line) and sine condition (dotted line) when using the BD of Example 1, and FIG. 7B is a vertical spherical surface when using DVD of Example 1. FIG. 7C illustrates aberrations (solid line) and sine conditions (dotted line), and FIG. 7C illustrates longitudinal spherical aberration (solid line) and sine conditions (dotted line) when the CD of Example 1 is used. 6 is a cross-sectional view of an objective lens according to Example 2. FIG. FIG. 9A is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when using the BD of Example 2, and FIG. 9B is a longitudinal spherical surface when using the DVD of Example 2. FIG. 9C is a diagram illustrating the aberration (solid line) and the sine condition (dotted line), and FIG. 9C is a diagram illustrating the longitudinal spherical aberration (solid line) and the sine condition (dotted line) when the CD of Example 2 is used. 6 is a cross-sectional view of an objective lens according to Example 3. FIG. FIG. 11A is a diagram showing longitudinal spherical aberration (solid line) and sine condition (dotted line) when using the BD of Example 3, and FIG. 11B is a longitudinal spherical surface when using the DVD of Example 3. FIG. 11C is a diagram showing aberration (solid line) and a sine condition (dotted line), and FIG. 11C is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when using the CD of Example 3. 10 is a cross-sectional view of an objective lens according to Example 4. FIG. FIG. 13A is a diagram showing the longitudinal spherical aberration (solid line) and the sine condition (dotted line) when using the BD of Example 4, and FIG. 13B is the longitudinal spherical surface when using the DVD of Example 4. FIG. 13C shows aberration (solid line) and sine condition (dotted line), and FIG. 13C shows longitudinal spherical aberration (solid line) and sine condition (dotted line) when the CD of Example 4 is used. 10 is a cross-sectional view of an objective lens according to Example 5. FIG. FIG. 15A is a diagram showing longitudinal spherical aberration (solid line) and sine condition (dotted line) when using the BD of Example 5, and FIG. 15B is a longitudinal spherical surface when using the DVD of Example 5. FIG. 15C illustrates aberrations (solid line) and sine conditions (dotted line), and FIG. 15C illustrates longitudinal spherical aberration (solid line) and sine conditions (dotted line) when the CD of Example 5 is used. 10 is a cross-sectional view of an objective lens according to Example 6. FIG. FIG. 17A is a diagram showing longitudinal spherical aberration (solid line) and sine condition (dotted line) when using the BD of Example 6, and FIG. 17B is a longitudinal spherical surface when using the DVD of Example 6. FIG. 17C is a diagram illustrating aberration (solid line) and a sine condition (dotted line), and FIG. 17C is a diagram illustrating longitudinal spherical aberration (solid line) and a sine condition (dotted line) when the CD of Example 6 is used. 10 is a cross-sectional view of an objective lens according to Example 7. FIG. FIG. 19A is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when using the BD of Example 7, and FIG. 19B is a vertical spherical surface when using the DVD of Example 7. FIG. 19C is a diagram showing aberration (solid line) and a sine condition (dotted line), and FIG. 19C is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when the CD of Example 7 is used. 10 is a cross-sectional view of an objective lens according to Example 8. FIG. FIG. 21A is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when using the BD of Example 8, and FIG. 21B is a vertical spherical surface when using the DVD of Example 8. FIG. 21C is a diagram showing aberration (solid line) and a sine condition (dotted line), and FIG. 21C is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when the CD of Example 8 is used. 10 is a cross-sectional view of an objective lens according to Example 9. FIG. FIG. 23A is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when using the BD of Example 9, and FIG. 23B is a vertical spherical surface when using the DVD of Example 9. FIG. 23C is a diagram showing aberration (solid line) and a sine condition (dotted line), and FIG. 23C is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when the CD of Example 9 is used. 10 is a cross-sectional view of an objective lens according to Example 10. FIG. 10 is a cross-sectional view of an objective lens according to Example 11. FIG. FIG. 14 is a sectional view of the objective lens according to Example 12. It is a figure which shows the modification of an objective lens. It is a figure which shows the modification of an objective lens.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 5 is a diagram schematically showing a configuration of the optical pickup device PU1 of the present embodiment that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. Here, the first optical disc is a BD, the second optical disc is a DVD, and the third optical disc is a CD. The present invention is not limited to the present embodiment.

The optical pickup device PU1 emits a laser beam (first beam) having a wavelength λ1 = 405 nm that is emitted when information is recorded / reproduced with respect to the objective lens OBJ, aperture stop ST, collimator lens CL, polarization dichroic prism PPS, and BD. The unit includes a unit MD1, a laser module LM, and the like in which a first semiconductor laser LD1 (first light source) to be emitted and a first light receiving element PD1 that receives a reflected light beam from the information recording surface RL1 of the BD are integrated.

The laser module LM includes a second semiconductor laser EP1 (second light source) that emits a laser beam (second beam) having a wavelength λ2 = 658 nm and is emitted when information is recorded / reproduced with respect to a DVD, and a CD. A third semiconductor laser EP2 (third light source) that emits a laser beam (third beam) having a wavelength λ3 = 785 nm and is reflected from the information recording surface RL2 of the DVD. It has a second light receiving element DS1 that receives the light beam, a third light receiving element DS2 that receives the reflected light beam from the information recording surface RL3 of the CD, and a prism PS.

In the objective lens OBJ of the present embodiment, on the aspheric optical surface on the light source side, a first region (having a diffractive structure) including the optical axis, a second region (refractive surface) around the first region, and a second region around the first region. It has three regions (having a diffractive structure) and a fourth region (refractive surface) farthest from the optical axis around it. The objective lens OBJ satisfies the following formula.

The divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD1 is transmitted through the polarization dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and then straightened by a quarter wavelength plate (not shown). The polarized light is converted into circularly polarized light, the diameter of the light beam is regulated by the stop ST, and is incident on the objective lens OBJ. Here, the first and second optical disk combined areas of the objective lens OBJ and the first optical disk dedicated area (the light flux that has passed through the third optical disk dedicated area is flared to form a spot peripheral portion). Are spots formed on the information recording surface RL1 of the BD through the protective substrate PL1 having a thickness of 0.1 mm.

The reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective lens OBJ and the aperture stop ST, converted from circularly polarized light to linearly polarized light by a quarter wave plate (not shown), and converged by the collimating lens CL. After being transmitted through the polarization dichroic prism PPS, it is converged on the light receiving surface of the first light receiving element PD1. Then, by using the output signal of the first light receiving element PD1 to focus or track the objective lens OBJ by the biaxial actuator AC, it is possible to read information recorded on the BD.

The divergent light beam of the second light beam (λ2 = 658 nm) emitted from the red semiconductor laser EP1 is reflected by the prism PS, then reflected by the polarization dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and is not shown in the figure. The light is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate and enters the objective lens OBJ. Here, the first optical disk / second optical disk combined area of the objective lens OBJ (the light beam that has passed through the first optical disk dedicated area and the third optical disk dedicated area is flared to form a spot peripheral portion). It becomes a spot formed on the information recording surface RL2 of the DVD through the 6 mm protective substrate PL2, and forms the center of the spot.

The reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective lens OBJ and the aperture stop ST, converted from circularly polarized light to linearly polarized light by a quarter wave plate (not shown), and converged by the collimating lens CL. After being reflected by the polarization dichroic prism PPS and then reflected twice in the prism, it is converged on the second light receiving element DS1. The information recorded on the DVD can be read using the output signal of the second light receiving element DS1.

The divergent light beam of the third light beam (λ3 = 785 nm) emitted from the infrared semiconductor laser EP2 is reflected by the prism PS, then reflected by the polarization dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and then shown in the figure. It is converted from linearly polarized light to circularly polarized light by the quarter wave plate that does not, and enters the objective lens OJT. Here, the third optical disk dedicated area of the objective lens OBJ (the light beam that has passed through the first optical disk / second optical disk combined area and the first optical disk dedicated area is flared to form a spot peripheral portion). It becomes a spot formed on the information recording surface RL3 of the CD through the protective substrate PL3 of 2 mm.

The reflected light beam modulated by the information pits on the information recording surface RL3 is again transmitted through the objective lens OBJ and the aperture stop ST, converted from circularly polarized light to linearly polarized light by a quarter wave plate (not shown), and converged by the collimating lens CL. After being reflected by the polarization dichroic prism PPS and then reflected twice in the prism, it is converged on the third light receiving element DS2. The information recorded on the CD can be read using the output signal of the third light receiving element DS2.

(Example)
Examples that can be used in the above-described embodiment will be described below. In the following embodiments, the BD / DVD combined area (the first light flux that has passed is condensed so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that has passed is recorded on the DVD information recording medium. A compatible area of the objective lens that focuses light so that information can be recorded and / or reproduced on the surface, and a dedicated CD area (the third light beam that has passed through can be recorded and / or reproduced on the information recording surface of the CD). And a dedicated area for the objective lens that focuses the first light flux that has passed therethrough so that information can be recorded and / or reproduced on the information recording surface of the BD. Since the objective lens is configured in combination, the BD / DVD combined area, the BD dedicated area, and the CD dedicated area are shown separately in the lens data table. (The same table is used because the shape of the mother aspherical surface of the BD / DVD combined area and the BD exclusive area is the same.) In the following examples, the light source side optical surface of the objective lens is divided into 4 areas or 6 areas. Although it is divided into regions, the optical surface on the optical disc side is not divided and is a common aspherical surface. If the surface on the optical disk side of the objective lens is not a common aspherical surface, the first light beam and the second light beam that have passed through the objective lens may be emitted from the surface on the optical disk side in the CD-dedicated area. Since there is a possibility that the third light flux that has passed through the optical disc side of the BD / DVD combined area may be emitted from the optical disk side optical surface of the BD / DVD combined area and the CD dedicated area. The optical surface of the objective lens is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Formula 1.

Here, X (h) is an axis in the optical axis direction (the light traveling direction is positive), κ is a conic constant, A _i is an i-th order aspheric coefficient, h is a height from the optical axis, and r is The paraxial radius of curvature.

Further, in the case of the embodiment using the diffractive structure, the optical path difference given to the light flux of each wavelength by the diffractive structure is defined by an equation in which the coefficient shown in the table is substituted into the optical path difference function of Formula 2. .

λ is the wavelength of the incident light beam, λB is the normalized wavelength (blazed wavelength), dor is the diffraction order, and C _i is the coefficient of the i-order optical path difference function.
Example 1
Table 1 shows lens data of Example 1. 6 is a cross-sectional view of the objective lens of Example 1. FIG. FIG. 7A is a diagram showing longitudinal spherical aberration (solid line) and sine condition (dotted line) when using the BD of Example 1, and FIG. 7B is a vertical spherical surface when using DVD of Example 1. FIG. 7C illustrates aberrations (solid line) and sine conditions (dotted line), and FIG. 7C illustrates longitudinal spherical aberration (solid line) and sine conditions (dotted line) when the CD of Example 1 is used. In the first embodiment, as shown in the enlarged view of FIG. 6, the first region R1 including the optical axis is a BD / DVD shared region, the second region R2 around the outside is a CD dedicated region, and the outside periphery The third area R3 is a BD / DVD shared area, the outer area surrounding the fourth area R4 is a dedicated CD area, the outer area surrounding the fifth area R5 is a BD / DVD shared area, The sixth region R6 farthest from the optical axis is a BD dedicated region. The paraxial curvature radius of the mother aspheric surface in the BD / DVD common area is 0.948 mm, and the paraxial curvature radius of the mother aspheric surface in the CD dedicated area is 1.347 mm, and the difference is 0.398 mm. In the BD / DVD common area, a (0/1) diffraction structure (the diffraction order is BD is 0th order, DVD is 1st order, the same notation format hereinafter) is formed. The diffractive structure is a five-level staircase type diffractive structure as shown in FIG. 2 (c), which is composed of four steps giving an optical path difference of one step 2λ1. Moreover, in Example 1, each value is as follows.

φ1 = 2.4mm
WD3 = 0.2mm
f3 = 1.70 mm (1.7 × f3 = 2.890 mm)
d = 1.750 mm
d / f3 = 1.029
Uneven thickness ratio (d / dmin) = 3.50

(Example 2)
FIG. 8 is a sectional view of the objective lens of Example 2. FIG. 9A is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when using the BD of Example 2, and FIG. 9B is a longitudinal spherical surface when using the DVD of Example 2. FIG. 9C is a diagram illustrating the aberration (solid line) and the sine condition (dotted line), and FIG. 9C is a diagram illustrating the longitudinal spherical aberration (solid line) and the sine condition (dotted line) when the CD of Example 2 is used. The second embodiment uses the lens data of the first embodiment and has the same number of areas, but the divided positions of the areas are different. The other points are the same as those in the first embodiment including the numerical values of the formulas, and thus the description thereof is omitted.
(Example 3)
FIG. 10 is a sectional view of the objective lens of Example 3. In the third embodiment, unlike the first and second embodiments, the lens has four areas. As shown in the enlarged view of FIG. 10, the first area R1 including the optical axis is used as a BD / DVD shared area, and the surrounding first area R1. The second area R2 is a CD dedicated area, the surrounding third area R3 is a BD / DVD shared area, and the fourth area R4 farthest from the optical axis is the BD dedicated area. FIG. 11A is a diagram showing longitudinal spherical aberration (solid line) and sine condition (dotted line) when using the BD of Example 3, and FIG. 11B is a longitudinal spherical surface when using the DVD of Example 3. FIG. 11C is a diagram showing aberration (solid line) and a sine condition (dotted line), and FIG. 11C is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when using the CD of Example 3. The third embodiment uses the lens data of the first embodiment, but the number of areas and the division positions are different. The other points are the same as those in the first embodiment including the numerical values of the formulas, and thus the description thereof is omitted.
Example 4
Table 2 shows lens data of Example 4. FIG. 12 is a sectional view of the objective lens of Example 4. FIG. 13A is a diagram showing the longitudinal spherical aberration (solid line) and the sine condition (dotted line) when using the BD of Example 4, and FIG. 13B is the longitudinal spherical surface when using the DVD of Example 4. FIG. 13C shows aberration (solid line) and sine condition (dotted line), and FIG. 13C shows longitudinal spherical aberration (solid line) and sine condition (dotted line) when the CD of Example 4 is used. In the fourth embodiment, as shown in the enlarged view of FIG. 12, the first area R1 including the optical axis is a BD / DVD shared area, the second area R2 around the outside is a CD dedicated area, and the outside circumference The third area R3 is a BD / DVD shared area, the outer area surrounding the fourth area R4 is a dedicated CD area, the outer area surrounding the fifth area R5 is a BD / DVD shared area, The sixth region R6 farthest from the optical axis is a BD dedicated region. The paraxial curvature radius of the mother aspheric surface in the BD / DVD common area is 0.955 mm, and the paraxial curvature radius of the mother aspheric surface in the CD dedicated area is 1.342 mm, and the difference is 0.386 mm. In the BD / DVD shared area, a (1 / -2) diffraction structure is formed. The diffractive structure is a seven-level step diffractive structure having six steps. Moreover, in Example 3, each value is as follows.

φ1 = 2.4mm
WD3 = 0.2mm
f3 = 1.71 mm (1.7 × f3 = 2.907 mm)
d = 1.750 mm
d / f3 = 1.024
Uneven thickness ratio = 2.350

(Example 5)
FIG. 14 is a sectional view of the objective lens of Example 5. FIG. 15A is a diagram showing longitudinal spherical aberration (solid line) and sine condition (dotted line) when using the BD of Example 5, and FIG. 15B is a longitudinal spherical surface when using the DVD of Example 5. FIG. 15C illustrates aberrations (solid line) and sine conditions (dotted line), and FIG. 15C illustrates longitudinal spherical aberration (solid line) and sine conditions (dotted line) when the CD of Example 5 is used. The fifth embodiment uses the lens data of the fourth embodiment and has the same number of regions, but the divided positions of the regions are different. The other points are the same as those in the fourth embodiment including the numerical values of the formulas, and thus the description thereof is omitted.
(Example 6)
FIG. 16 is a cross-sectional view of the objective lens according to Example 6. In the sixth embodiment, unlike the fourth and fifth embodiments, the lens has four areas. As shown in the enlarged view of FIG. 16, the first area R1 including the optical axis is a BD / DVD shared area, and the surrounding first area The second area R2 is a CD dedicated area, the surrounding third area R3 is a BD / DVD shared area, and the fourth area R4 farthest from the optical axis is the BD dedicated area. FIG. 17A is a diagram showing longitudinal spherical aberration (solid line) and sine condition (dotted line) when using the BD of Example 6, and FIG. 17B is a longitudinal spherical surface when using the DVD of Example 6. FIG. 17C is a diagram illustrating aberration (solid line) and a sine condition (dotted line), and FIG. 17C is a diagram illustrating longitudinal spherical aberration (solid line) and a sine condition (dotted line) when the CD of Example 6 is used. The sixth embodiment uses the lens data of the fourth embodiment, but the number of areas and the division positions are different. The other points are the same as those in the fourth embodiment including the numerical values of the formulas, and thus the description thereof is omitted.
(Example 7)
Table 3 shows lens data of Example 7. FIG. 18 is a sectional view of the objective lens of Example 7. FIG. 19A is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when using the BD of Example 7, and FIG. 19B is a vertical spherical surface when using the DVD of Example 7. FIG. 19C is a diagram showing aberration (solid line) and a sine condition (dotted line), and FIG. 19C is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when the CD of Example 7 is used. In Example 7, as shown in the enlarged view of FIG. 18, the first region R1 including the optical axis is a BD / DVD shared region, the second region R2 around the outside is a CD-dedicated region, and the outside periphery The third area R3 is a BD / DVD shared area, the outer area surrounding the fourth area R4 is a dedicated CD area, the outer area surrounding the fifth area R5 is a BD / DVD shared area, The sixth region R6 farthest from the optical axis is a BD dedicated region. The paraxial curvature radius of the mother aspheric surface in the BD / DVD common area is 1.504 mm, and the paraxial curvature radius of the mother aspheric surface in the CD dedicated area is 1.339 mm, and the difference is 0.165 mm. A (2/1) diffraction structure is formed in the BD / DVD shared area. The diffractive structure is a blazed diffractive structure as shown in FIG. 2B having a step of 2λ1. Moreover, in Example 7, each value is as follows.

φ1 = 2.4mm
WD3 = 0.2mm
f3 = 1.71 mm (1.7 × f3 = 2.907 mm)
d = 1.750 mm
d / f3 = 1.024
Uneven thickness ratio = 3.624

(Example 8)
FIG. 20 is a cross-sectional view of the objective lens according to the eighth embodiment. FIG. 21A is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when using the BD of Example 8, and FIG. 21B is a vertical spherical surface when using the DVD of Example 8. FIG. 21C is a diagram showing aberration (solid line) and a sine condition (dotted line), and FIG. 21C is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when the CD of Example 8 is used. Example 8 uses the lens data of Example 7 and has the same number of areas, but the division positions of the areas are different. In other respects, the numerical value of the formula is the same as that of the seventh embodiment, and the description thereof is omitted.
Example 9
FIG. 22 is a sectional view of the objective lens according to Example 9. In the ninth embodiment, unlike the seventh and eighth embodiments, the lens has four areas. As shown in the enlarged view of FIG. 22, the first area R1 including the optical axis is a BD / DVD shared area, and the surrounding first area The second area R2 is a CD dedicated area, the surrounding third area R3 is a BD / DVD shared area, and the fourth area R4 farthest from the optical axis is the BD dedicated area. FIG. 23A is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when using the BD of Example 9, and FIG. 23B is a vertical spherical surface when using the DVD of Example 9. FIG. 23C is a diagram showing aberration (solid line) and a sine condition (dotted line), and FIG. 23C is a diagram showing longitudinal spherical aberration (solid line) and a sine condition (dotted line) when the CD of Example 9 is used. The ninth embodiment uses the lens data of the seventh embodiment, but the number of areas and the division positions are different. In other respects, the numerical value of the formula is the same as that of the seventh embodiment, and the description thereof is omitted.
(Example 10)
Table 4 shows lens data of Example 10. FIG. 24 is a cross-sectional view of the objective lens according to the tenth embodiment. In the tenth embodiment, as shown in the enlarged view of FIG. 24, the first region R1 including the optical axis is a BD / DVD shared region, the surrounding second region R2 is a CD dedicated region, and the surrounding third region R3 is a BD / DVD shared area, and the fourth area R4 farthest from the optical axis is a BD dedicated area. The radius of curvature of the mother aspheric surface in the BD / DVD shared area is 0.836 mm, the radius of curvature of the mother aspheric surface in the CD dedicated area is 1.2475 mm, and the difference is 0.4115 mm. A (0/1) diffraction structure is formed in the BD / DVD shared area. Moreover, in Example 10, each value is as follows.

φ1 = 2.15mm
WD3 = 0.2mm
f3 = 1.60 mm (1.7 × f3 = 2.720 mm)
d = 1.490mm
d / f3 = 0.93125
Uneven thickness ratio (d / dmin) = 4.52

Example 11
Table 5 shows lens data of Example 11. FIG. 25 is a cross-sectional view of the objective lens according to the eleventh embodiment. In Example 11, as shown in the enlarged view of FIG. 25, the first region R1 including the optical axis is a BD / DVD shared region, the surrounding second region R2 is a CD dedicated region, and the surrounding third region R3 is a BD / DVD shared area, and the fourth area R4 farthest from the optical axis is a BD dedicated area. The radius of curvature of the mother aspherical surface in the BD / DVD shared area is 0.8721 mm, the radius of curvature of the mother aspherical surface in the CD dedicated area is 1.2513 mm, and the difference is 0.3792 mm. In the BD / DVD shared area, a (1 / -2) diffraction structure is formed. Moreover, in Example 11, each value is as follows.

φ1 = 2.15mm
WD3 = 0.2mm
f3 = 1.55 mm (1.7 × f3 = 2.635 mm)
d = 1.490mm
d / f3 = 0.9613
Uneven thickness ratio (d / dmin) = 3.77

(Example 12)
Table 6 shows lens data of Example 12. FIG. 26 is a cross-sectional view of the objective lens according to the twelfth embodiment. In Example 12, as shown in the enlarged view of FIG. 26, the first region R1 including the optical axis is a BD / DVD shared region, the surrounding second region R2 is a CD dedicated region, and the surrounding third region R3 is a BD / DVD shared area, and the fourth area R4 farthest from the optical axis is a BD dedicated area. The radius of curvature of the mother aspheric surface in the BD / DVD common area is 1.0150 mm, the radius of curvature of the mother aspheric surface in the CD dedicated area is 1.1598 mm, and the difference is 0.1448 mm. A (2/1) diffraction structure is formed in the BD / DVD shared area. Moreover, in Example 12, each value is as follows.

φ1 = 2.15mm
WD3 = 0.2mm
f3 = 1.63 mm (1.7 × f3 = 2.771 mm)
d = 1.490mm
d / f3 = 0.9141
Uneven thickness ratio (d / dmin) = 2.52

FIGS. 27 to 28 are diagrams showing modifications of the objective lens. In the modification of FIG. 27, the region R1 including the optical axis is a BD / DVD shared region (having the diffraction structure of (0/1)), and the surrounding region R2 is a CD-dedicated region (refractive surface). The outer peripheral region R3 is a BD / DVD shared region (having a (0/1) diffraction structure), and the outer peripheral region R4 is a BD dedicated region (refractive surface).

FIG. 28 shows a modification. As one modification, the region R1 including the optical axis is a BD / DVD shared region (having a (1 / -2) diffraction structure), and the outer peripheral region R2 is a CD-dedicated region (refractive surface). The outer peripheral region R3 is a BD / DVD shared region (having a (1 / -2) diffraction structure).

As another modification of FIG. 28, the region R1 including the optical axis is a BD / DVD shared region (having the diffraction structure of (2/1)), and the surrounding region R2 is a CD dedicated region (refractive The outer peripheral region R3 is a BD / DVD shared region (having a (2/1) diffraction structure).

According to the present invention, it is possible to provide an objective lens and an optical pickup device suitable for a thin optical disk drive device.

AC biaxial actuator PPS polarization dichroic prism CL collimating lens LD1 blue-violet semiconductor laser LM laser module OBJ objective lens PL1 protective substrate PL2 protective substrate PL3 protective substrate PU1 optical pickup device RL1 information recording surface RL2 information recording surface RL3 information recording surface CN central region MD peripheral area OT most peripheral area

Claims

A first light source that emits a first light flux with wavelength λ1, a second light source that emits a second light flux with wavelength λ2 (λ1 <λ2), and a third light source that emits a third light flux with wavelength λ3 (λ2 <λ3) And an objective lens, and the objective lens focuses the first light beam on the information recording surface of the first optical disc having a protective layer having a thickness t1 so that information can be recorded and / or reproduced. The second light beam is condensed on the information recording surface of the second optical disc having a protective layer having a thickness t2 (t1 <t2) so that information can be recorded and / or reproduced, and the third light beam has a thickness. For an optical pickup device that records and / or reproduces information by focusing the information on the information recording surface of a third optical disc having a protective layer of t3 (t2 <t3) so that information can be recorded and / or reproduced. In the objective lens,
The objective lens is a single lens,
At least one optical surface has a first region including an optical axis, a second region provided outside the first region, and a third region provided outside the second region,
Of the region, the objective lens region that focuses the passed first light flux so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the passed third light flux is An objective lens, wherein the objective lens is focused on the information recording surface of the third optical disc so that information can be recorded and / or reproduced.
The objective lens according to claim 1, wherein the following expression is satisfied.
0.15 (mm) ≦ WD3 ≦ 0.5 (mm) (1)
However,
WD3: Working distance when using the third optical disc
A difference between a paraxial radius of curvature of a mother aspheric surface in a certain region and a paraxial radius of curvature of a mother aspheric surface in another region is 0.1 mm or more and 0.7 mm or less. The objective lens according to claim 1 or 2.
Among the regions, the paraxial curvature radius of the mother aspheric surface in the region where the passed third light beam is condensed so that information can be recorded and / or reproduced on the information recording surface of the third optical disc, A region where the first light beam is condensed on the information recording surface of the first optical disc so that information can be recorded and / or reproduced, or the second light beam that has passed through the information recording surface of the second optical disc can be recorded and / or recorded. 4. The objective lens according to claim 3, wherein a difference from a paraxial radius of curvature of a mother aspheric surface in a condensing region so that reproduction can be performed is 0.1 mm or more and 0.7 mm or less.
The passed third light beam is condensed on the information recording surface of the third optical disc so that information can be recorded and / or reproduced, and the passed first light beam is recorded on the information recording surface of the first optical disc. And / or a third optical disc dedicated area that does not collect the light so that it can be reproduced and does not collect the passed second light flux on the information recording surface of the second optical disc so that information can be recorded and / or reproduced. The objective lens according to any one of claims 1 to 4, wherein:
6. The objective lens according to claim 5, wherein the third optical disk dedicated area is a refractive surface.
The objective lens according to claim 5 or 6, wherein the number of the third optical disc dedicated area is 1 or more and 3 or less.
The first region condenses the passed first light flux so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the passed second light flux is reflected on the second optical disc. The information recording surface is condensed so that information can be recorded and / or reproduced, but the passed third light beam is condensed so that information can be recorded and / or reproduced on the information recording surface of the third optical disc. The objective lens according to any one of claims 1 to 7, wherein the objective lens is a first optical disk / second optical disk combined area.
The first region has a first diffractive structure;
9. The first diffractive structure is a structure that generates the largest amount of zero-order diffracted light (transmitted light) as compared with diffracted light of other orders when the first light beam passes. Objective lens described in 1.
The second region condenses the passed third light flux so that information can be recorded and / or reproduced on the information recording surface of the third optical disk, and the passed first light flux is information on the first optical disk. The second light flux that has passed is not condensed so that information can be recorded and / or reproduced on the recording surface, and the second light flux that has passed through is not condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc. The objective lens according to any one of claims 1 to 9, wherein the objective lens is an area dedicated to three optical disks.
The third region condenses the passed first light flux so that information can be recorded and / or reproduced on the information recording surface of the first optical disk, and the passed second light flux is reflected on the second optical disk. However, the third light flux that has passed therethrough is collected so that information can be recorded and / or reproduced on the information recording surface of the third optical disc. 11. The objective lens according to claim 1, wherein the objective lens is a first optical disk / second optical disk combined area that does not emit light.
The objective lens has a fourth region outside the third region, has a fifth region outside the fourth region, and has a sixth region outside the fifth region,
The sixth region is a region farthest from the optical axis in the objective lens,
The first region, the third region, and the fifth region condense and pass the first light flux that has passed through the information recording surface of the first optical disc so that information can be recorded and / or reproduced. The second light beam is condensed on the information recording surface of the second optical disk so that information can be recorded and / or reproduced, and the passed third light beam is recorded and / or information on the information recording surface of the third optical disk. It is a first optical disc / second optical disc combined area that does not collect light so that it can be reproduced.
The second region and the fourth region condense the passed third light flux so that information can be recorded and / or reproduced on the information recording surface of the third optical disc, and the passed first light flux is It is possible to record and / or reproduce information on the information recording surface of the second optical disc without condensing the information on the information recording surface of the first optical disc so that information can be recorded and / or reproduced. Is an area dedicated to the third optical disc that does not collect light on
The sixth area condenses the passed first light flux so that information can be recorded and / or reproduced on the information recording surface of the first optical disk, and the passed second light flux is information on the second optical disk. The third light beam that has passed through is not condensed so that information can be recorded and / or reproduced on the recording surface, and the third light flux that has passed therethrough is not condensed so that information can be recorded and / or reproduced on the information recording surface of the third optical disc. The objective lens according to any one of claims 1 to 11, wherein the objective lens is an area dedicated to one optical disk.
The objective lens according to claim 12, wherein the sixth region is a refractive surface.
The objective lens has a fourth region outside the third region,
The fourth region is a region farthest from the optical axis in the objective lens,
The first region and the third region condense the passed first light flux so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the passed second light flux is The information is recorded and / or reproduced on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the passed third light beam can be recorded and / or reproduced on the information recording surface of the third optical disc. The first optical disc / second optical disc combined area that does not collect light,
The second region condenses the passed third light flux so that information can be recorded and / or reproduced on the information recording surface of the third optical disk, and the passed first light flux is information on the first optical disk. The second light flux that has passed is not condensed so that information can be recorded and / or reproduced on the recording surface, and the second light flux that has passed through is not condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc. 3 is an area dedicated to optical discs,
The fourth region condenses the passed first light flux so that information can be recorded and / or reproduced on the information recording surface of the first optical disk, and the passed second light flux is information on the second optical disk. The third light beam that has passed through is not condensed so that information can be recorded and / or reproduced on the recording surface, and the third light flux that has passed therethrough is not condensed so that information can be recorded and / or reproduced on the information recording surface of the third optical disc. The objective lens according to any one of claims 1 to 11, wherein the objective lens is an area dedicated to one optical disk.
The objective lens according to claim 14, wherein the fourth region is a refractive surface.
In the cross section including the optical axis, there is a step between the first region and the second region, and a portion where the step and the first region intersect is compared with a region where the step and the second region intersect. The objective lens according to claim 1, wherein the objective lens is located on the light source side in the optical axis direction.
The first region condenses the passed first light flux on the information recording surface of the first optical disc, condenses the passed second light flux on the information recording surface of the second optical disc, and passes the passed first light flux. A first optical disk / second optical disk combined area that does not collect three light beams on the information recording surface of the third optical disk;
The second region condenses the passed third light flux on the information recording surface of the third optical disc, and passes the first light flux passed without being condensed on the information recording surface of the first optical disc. 17. The objective lens according to claim 16, wherein the objective lens is an area dedicated to a third optical disc that does not collect the second light flux on the information recording surface of the second optical disc.
The objective lens according to any one of claims 1 to 17, wherein the following conditional expression (2) is satisfied.
d / δ ≦ 5 (2)
However,
d: axial thickness of the objective lens δ: minimum thickness of the objective lens in the optical axis direction
An optical pickup device comprising the objective lens according to any one of claims 1 to 18.