CN102292770A

CN102292770A - Objective lens and optical pickup device

Info

Publication number: CN102292770A
Application number: CN200980155236XA
Authority: CN
Inventors: 白石乔则
Original assignee: Konica Minolta Opto Inc
Current assignee: Konica Minolta Opto Inc
Priority date: 2009-02-06
Filing date: 2009-12-01
Publication date: 2011-12-21
Also published as: WO2010089933A1; JPWO2010089933A1

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

Technical Field

The present invention relates to an optical pickup device capable of recording and/or reproducing information interchangeably with different types of optical discs, and an objective optical element used in the optical pickup device.

Background

In recent years, research and development of a high-density optical disc system capable of recording and/or reproducing information with a violet semiconductor laser having a wavelength of about 400nm (hereinafter, "recording and/or reproducing" is referred to as "recording/reproducing") have been rapidly advanced. For example, an optical Disc for recording/reproducing information with NA0.85 and a light source wavelength of 405nm, so-called Blu-ray Disc (hereinafter referred to as BD), can record 25GB of information per layer on an optical Disc having a diameter of 12cm and the same size as a DVD (NA 0.6, light source wavelength of 650nm, and storage capacity of 4.7 GB).

However, only when information is recorded and reproduced accurately on such a high-density optical disc, for example, a BD, the value of the optical disc reproducing/recording machine (optical information recording/reproducing apparatus) is insufficient. Considering the current situation that DVDs and CDs (compact discs) on which various information is recorded are sold, it is not enough to record/reproduce information only on BDs, and it is a necessary way to improve the product value of BD optical disc players/recorders to realize information recording/reproducing on DVDs and CDs held by users in the same manner. In view of this background, it is desired that an optical pickup device mounted in a BD optical disc player/recorder has a capability of recording/reproducing information with certainty while maintaining compatibility with any of BD, DVD, and CD.

As a method for realizing the appropriate recording/reproduction of information while maintaining compatibility with any of BD, DVD and CD, there is considered a method of selectively switching the optical system for BD and the optical system for DVD and CD depending on the recording density of the optical disc on which information is recorded/reproduced.

Therefore, in order to simplify the structure of the optical pickup device and to achieve low cost, it is preferable to use a BD optical system and DVD and CD optical systems in combination in an optical pickup device having compatibility, and to reduce the number of optical components constituting the optical pickup device as much as possible. However, it is most advantageous to simplify the structure of the optical pickup device and to reduce the cost to make the objective lens arranged opposite to the optical disc common.

In contrast, patent document 1 discloses an objective lens used in an optical pickup device capable of recording/reproducing information on/from a plurality of types of optical discs having thicknesses of 2 or more substrates by using light of 3 types of wavelengths. In the example of patent document 1, optical discs of 0.6mm, 1.2mm and only 2 substrate thicknesses are recorded/reproduced by using light having wavelengths of 405nm, 657nm and 788 nm. Light having a wavelength of 405nm and 657nm was used for an optical disk having a substrate thickness of 0.6mm, and light having a wavelength of 788nm was used for an optical disk having a substrate thickness of 1.2 mm. In order to correspond to a plurality of types of optical discs, the objective lens is configured such that the incident surface of the laser beam on the objective lens is divided into at least 3 regions. When any one of the laser beams with the plurality of wavelengths passes through the corresponding region of the objective lens, the laser beam is condensed on the corresponding information recording surface of the optical disc. In example 1 of patent document 1, the objective lens is divided into 4 regions, and the innermost region of the objective lens is a refractive surface capable of condensing light of 3 wavelengths on the information recording surfaces of 3 types of optical discs, respectively; the outer region of the refractive surface is a refractive surface capable of condensing light with a wavelength of 405nm and a wavelength of 788nm on each information recording surface of 2 kinds of optical disks; the outside of the refraction surface is a diffraction surface which can focus the light with 405nm wavelength and 657nm wavelength on each information recording surface of 2 kinds of optical discs; the outside of the diffraction surface is made to be a diffraction surface capable of condensing light with a wavelength of 405nm on the information recording surface of 1 type of optical disk. In examples 2 and 3, the objective lens was divided into 3 regions, and the innermost region was made to be a refractive surface capable of condensing light of 3 wavelengths on the information recording surfaces of 3 types of optical discs, respectively; the outer region of the refraction surface is a diffraction surface capable of condensing light with 657nm wavelength and 788nm wavelength on each information recording surface of 2 kinds of optical disks; the outer region of the diffraction surface was set to a diffraction surface capable of condensing light having a wavelength of 405nm and a wavelength of 657nm on each information recording surface of 2 kinds of optical disks.

Patent document 2 discloses an objective lens used in an optical pickup device capable of recording and reproducing information on/from 3 types of optical discs of 3 standards, such as BD, DVD, and CD, having different substrate thicknesses by using 3 types of wavelengths of light. In the example of patent document 2, information is recorded/reproduced on/from an optical disc having substrate thicknesses of 0.0875mm, 0.6mm, and 1.2mm by using light having wavelengths of 405nm, 658nm, and 785 nm. In order to correspond to a plurality of types of optical discs, the surface of the objective lens on which the laser beam is incident is divided into at least 3 regions. When any of the laser beams of the plural wavelengths is made to pass through the region corresponding to the objective lens, the laser beam is distributed and condensed on the information recording surface of the corresponding optical disk by diffracted light. Specifically, the innermost area of the objective lens is a diffraction surface which can make the 3 light beams passing through respectively condense on the information recording surfaces of BD, DVD and CD; outside the diffraction surface, the diffraction surface can make the passed 405nm and 658nm light beam condense on the BD and DVD information recording surface, and does not make the passed 785nm light beam condense on the CD; the outside of the diffraction surface is a surface capable of condensing the passed 405nm light beam on the information recording surface of BD and not condensing the passed 658nm and 785nm light beams on the information recording surfaces of DVD and CD; in examples 1, 2 and 3, the outermost region was defined as a refractive surface, and in examples 4 and 5, the outermost region was defined as a diffractive surface.

Prior art documents

Patent document

Patent document 1: japanese unexamined patent publication No. 2006-40512

Patent document 2: japanese patent No. 4033240

Disclosure of Invention

Problems to be solved by the invention

In all the examples of patent document 1, the type of optical disc on which information recording/reproduction can be performed is an optical disc having a substrate thickness of 0.6mm or 1.2 mm. Therefore, the objective lens described in patent document 1 cannot record/reproduce information on/from a BD having a substrate thickness of 0.1 mm.

The objective lens described in patent document 2 has a region in which the 1 st beam, the 2 nd beam, and the 3 rd beam can be focused on the BD, the DVD, and the CD, respectively, in the center area. In order to correspond to 3 types of optical discs of BD, DVD, and CD, diffraction structures having different diffraction orders are superimposed on the surface of the objective lens on which the laser beam is incident. Therefore, a zone having a narrow pitch, which is the width of 1 irregularity in the diffraction structure, is likely to occur. Although patent document 2 describes that removal of the zone does not have a great influence on the optical performance if the pitch width is 5 μm or less, even if the zone having a pitch width of 5 μm or less is removed, there is a possibility that a zone having a narrow width which is difficult to form and manufacture in practice remains. Needless to say, if the removal is not performed, it is more difficult to form the shape and manufacture the product.

In the case of optical discs having different substrate thicknesses, respectively, one objective lens is used, and when the optical disc for information recording/reproduction is a CD, the substrate thickness of the optical disc is larger than that of other optical discs, so that the distance from the image side principal point of the objective lens to the image side focal point must be increased. In addition, in order to secure a sufficient working distance (distance from the optical disc to the position closest to the optical disc on the surface from which the laser beam is emitted from the objective lens) during recording/reproduction of a CD, the focal length of the objective lens tends to be long. For example, in all the examples of patent document 1, when the optical disc is a CD, the focal length of the objective lens is 3.118mm, and the on-axis thickness of the objective lens is 2.3 mm. The effective diameter is also 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 also increased to 2.43mm, and the on-axis thickness of the objective lens is also increased to 2.37 mm. In patent document 2, in an embodiment in which the focal length of the CD is the shortest, the focal length is also as long as 2.24 mm. That is, in patent document 2, the focal length and the working distance in CD are secured by increasing the on-axis thickness of the objective lens.

However, the objective lens having such a large thickness is difficult to be used in a thin optical disc drive device mounted in a notebook computer or the like.

Further, as described in patent document 2, if the area including the optical axis of the objective lens is a general area through which the beam for BD, DVD, and CD passes, the working distance of the CD having a thick substrate is somewhat insufficient compared with other optical discs, which is inconvenient in use and has a problem.

In view of the above problems, it is an object of the present invention to provide an optical pickup device that can be used in a thin optical disk drive device while sufficiently securing a working distance of a CD and that can record and reproduce information on and from different optical disks such as BD, DVD, and CD with certainty, and an objective lens suitable for use in the optical pickup device.

Means for solving the problems

The objective lens according to claim 1 is an objective lens for an optical pickup device having a1 st light source for emitting a1 st light beam having a wavelength λ 1, a2 nd light source for emitting a2 nd light beam having a wavelength λ 2(λ 1 < λ 2), a3 rd light source for emitting a3 rd light beam having a wavelength λ 3(λ 2 < λ 3), and an objective lens, wherein the objective lens condenses the 1 st light beam on an information recording surface of a1 st optical disc having a protective layer having a thickness t1 so as to enable information recording and/or reproduction, condenses the 2 nd light beam on an information recording surface of a2 nd optical disc having a protective layer having a thickness t2(t1 < t2) so as to enable information recording and/or reproduction, and condenses the 3 rd light beam on an information recording surface of a3 rd optical disc having a protective layer having a thickness t3(t2 < t3) so as to enable information recording and/or reproduction, the objective lens is a single lens, and at least one optical surface has a1 st area including an optical axis, a2 nd area provided outside the 1 st area, and a3 rd area provided outside the 2 nd area, and the area of the objective lens in which the 1 st light beam that has passed therethrough is condensed on the information recording surface of the 1 st optical disc so as to be able to record and/or reproduce information is different from the area of the objective lens in which the 3 rd light beam that has passed therethrough is condensed on the information recording surface of the 3 rd optical disc so as to be able to record and/or reproduce information.

When a1 st optical disc and a3 rd optical disc serving area are provided, which can condense a1 st light beam on an information recording surface of a1 st optical disc and condense a3 rd light beam on an information recording surface of a3 rd optical disc, since the 3 rd optical disc has a larger substrate thickness than other optical discs, a distance from an incident surface of the 3 rd light beam to a condensing point is long, and a paraxial curvature radius of a parent aspherical surface of an area through which the light beam condensed on the 3 rd optical disc information recording surface passes needs to be increased, and thus, the surface shapes of the 1 st optical disc and the 3 rd optical disc serving area are easily flattened. Further, since the 1 st optical disc area for condensing the 1 st light beam on the 1 st disc information recording surface is required to have the highest precision of optical performance, it is often disposed in the center area including the optical axis. Thus, the paraxial radius of curvature of the parent aspherical surface of the region 1 is increased, the surface shape becomes flat, the focal length of these regions is also increased, and in short, the thickness on the axis of the objective lens is increased. The on-axis thickness of the objective lens becomes thick, which makes it difficult to use the objective lens in a thin optical disc drive apparatus.

According to the present invention, since the objective lens region (1 st disc region) for converging the 1 st light beam passing therethrough to the information recording surface of the 1 st disc so as to be able to perform information recording and/or reproduction and the objective lens region (3 rd disc region) for converging the 3 rd light beam passing therethrough to the information recording surface of the 3 rd disc so as to be able to perform information recording and/or reproduction can be independently designed, for example, the paraxial radius of curvature of the 3 rd disc region can be maintained large and the paraxial radius of curvature of the 1 st disc region can be reduced, so that the focal distance in the case of the 3 rd disc can be maintained long, the thickness of the objective lens on the axis can be reduced, and the working distance for the 3 rd disc can be ensured long. Thus, it is possible to provide an objective lens which is optimum for a thin optical disc drive device and which can record/reproduce information in and from three different optical discs in a compatible manner.

The objective lens according to claim 2 is the objective lens according to claim 1, wherein the following expression is satisfied:

0.15(mm)≤WD3≤0.5(mm) (1)，

wherein,

WD 3: working distance of the 3 rd optical disc in use

If the working distance is excessively increased in the case of the 3 rd disc, the cross-sectional area ratio of the objective lens is increased, the thickness of the edge (the minimum thickness in the optical axis direction) is decreased, and it is difficult to ensure an appropriate length in manufacturing, which is problematic. In addition, since the working distance when the 3 rd disc is increased, the focal length for the 3 rd beam is also increased. However, if the working distance is too long, the aberration change increases with a temperature change when the objective lens is a plastic lens, which causes a problem. In contrast, with the above configuration, while a sufficient working distance is ensured in the case of the 3 rd disc, the cross section is suppressed from being small, the manufacturing is easy, and even if the objective lens is a plastic lens, the objective lens with a small aberration change in temperature change can be provided.

The objective lens according to claim 3 is the invention according to claim 1 or 2, wherein a difference between a paraxial radius of curvature of the parent aspheric surface in a certain region and a paraxial radius of curvature of the parent aspheric surface in another region is 0.1mm or more and 0.7mm or less.

The objective lens according to claim 4 is the invention according to claim 3, wherein in the region, a difference between a paraxial curvature radius of a parent aspherical surface of a region on the information recording surface of the 3 rd optical disc, through which the 3 rd light beam passes, and a paraxial curvature radius of a parent aspherical surface of a region on the information recording surface of the 1 st optical disc, through which the 1 st light beam passes, and a region on the information recording surface of the 1 st optical disc, through which the 2 nd light beam passes, and a region on the information recording surface of the 2 nd optical disc, through which the 2 nd light beam passes, is capable of recording and/or reproducing information, is 0.1mm to 0.7 mm.

When the surface shape of the lens is configured to be a surface shape that preferentially condenses light on the 3 rd optical disc, the 3 rd optical disc is thicker than the other optical discs, so that the distance from the incident surface of the 3 rd light beam to the condensing point is long, and the paraxial curvature radius of the parent aspheric surface of the region through which the light beam condensed on the 3 rd optical disc information recording surface passes is large, so that the surface shape is flat. When the difference in paraxial curvature radius between the regions is small, the paraxial curvature radius of the parent aspherical surface of the region through which the light beam condensed on the information recording surface of the 3 rd optical disc does not pass (for example, the 1 st optical disc, the 2 nd optical disc serving region, and the 1 st optical disc dedicated region) is also large, so that the surface shape becomes flat, the focal length of these regions becomes long, and in short, the thickness on the axis of the objective lens becomes thick. For example, in the example of patent document 1, the difference in the curvature radius of the parent aspheric surface in the region through which the CD light beam passes is 0.0172mm in example 1 and 0.0119mm smaller in example 2. Therefore, the focal length of the region not collecting the CD light beam becomes longer, and the axial thickness of the objective lens becomes larger. In patent document 2, the curvature radius of the parent aspheric surface of the region where the CD light flux is condensed is increased, and the difference between the curvature radii of the parent aspheric surface of the region where the CD light flux is condensed and the region where the CD light flux is not condensed is decreased, so that the curvature radius of the parent aspheric surface of the region where the CD light flux is not condensed is also increased. For example, the difference in the radius of curvature is at most a small value of 0.0701mm in example 5. Therefore, the focal length of the region not collecting the CD light beam becomes longer, the thickness on the objective lens axis becomes thicker, and the effective diameter of the objective lens becomes larger. The smallest thickness on the objective axis is also up to 2.37mm in example 3. The increased thickness of the objective lens axis makes it difficult to use a thin type optical disc drive apparatus.

That is, by configuring the above-mentioned structures of items 3 and 4, the paraxial radius of curvature of the 3 rd disc region can be maintained large, and therefore the focal length in the case of a long 3 rd disc can be maintained. Further, the paraxial radius of curvature of the 1 st optical disc, the 2 nd optical disc serving area, and the 1 st optical disc dedicated area can be reduced, and therefore the thickness of the objective lens can be reduced on the axis. Therefore, the on-axis thickness of the objective lens can be reduced while favorably converging the 3 rd light beam on the information recording surface of the 3 rd optical disc in the region where the light beam converged on the 3 rd optical disc information recording surface passes and favorably converging the 1 st light beam or the 2 nd light beam on the information recording surface of the 1 st optical disc or the 2 nd optical disc in the region where the light beam converged on the 3 rd optical disc information recording surface does not pass.

The objective lens according to claim 5 is the invention according to any one of claims 1 to 4, and is characterized by having a3 rd disc-dedicated area in which the 3 rd light beam that has passed through is condensed on an information recording surface of the 3 rd disc so as to enable information recording and/or reproduction, the 1 st light beam that has passed through is condensed on an information recording surface of the 1 st disc so as not to enable information recording and/or reproduction, and the 2 nd light beam that has passed through is condensed on an information recording surface of the 2 nd disc so as not to enable information recording and/or reproduction.

With the above configuration, the paraxial radius of curvature of the 3 rd disc region can be maintained large, and the paraxial radius of curvature of the 1 st disc region can be reduced, so that the on-axis thickness of the objective lens can be reduced while maintaining the focal length of the 3 rd disc long. Further, if it is desired to extend the focal length for the 3 rd optical disc and secure a long working distance while setting the 3 rd optical disc and the 2 nd optical disc and the 3 rd optical disc compatible area for the 1 st optical disc, the 2 nd optical disc and the 3 rd optical disc corresponding to all of the 1 st optical disc, the pitch of the diffraction structure for separating the light beams becomes very fine, and it is difficult to form the objective lens.

The objective lens according to claim 6 is the invention according to claim 5, wherein the 3 rd optical disc specific area is a refractive surface.

By making the 3 rd optical disc-dedicated area a refractive surface having no diffractive structure, light use efficiency can be improved, and the objective lens can be easily molded.

The objective lens according to claim 7 is the objective lens according to claim 5 or 6, wherein the number of the 3 rd optical disc specific areas is 1 to 3.

With the above configuration, the loss of the light quantity of the 1 st light beam condensed on the 1 st optical disc can be suppressed, and the objective lens can be easily manufactured because the objective lens structure can be simplified.

The objective lens according to claim 8 is the invention according to any one of claims 1 to 7, wherein the 1 st area is a1 st optical disc/2 nd optical disc shared area in which the 1 st light beam that has passed therethrough is condensed on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, the 2 nd light beam that has passed therethrough is condensed on the information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction, and the 3 rd light beam that has passed therethrough is condensed on the information recording surface of the 3 rd optical disc so as not to enable information recording and/or reproduction.

With the above configuration, the paraxial radius of curvature of the 3 rd disc region can be maintained large, and the paraxial radius of curvature of the 1 st disc region can be reduced, so that the on-axis thickness of the objective lens can be reduced while maintaining the focal length of the 3 rd disc long. Further, since it is not necessary to provide the 1 st disc, 2 nd disc, and 3 rd disc compatible area for the 1 st disc, 2 nd disc, and 3 rd disc, it is not necessary to provide a diffraction structure having a very fine pitch, and an objective lens that can be easily manufactured can be obtained.

If the region including the optical axis of the objective lens is used as a general region where the 1 st, 2 nd and 3 rd light beams pass through and are condensed on the 1 st, 2 nd and 3 rd optical discs, respectively, the working distance of a CD having a thick substrate is slightly insufficient compared with other optical discs, which is inconvenient in use and has a problem. In contrast, with the above configuration, the paraxial radius of curvature in the 1 st region can be made the same as the paraxial radius of curvature in the 1 st optical disc dedicated region, and the paraxial radius of curvature in the 1 st region can be made small, so that the thickness of the objective lens on the axis can be made small. In this way, the working distance of the CD can be increased.

Further, since an optical disc using a short-wavelength light beam has a high information recording density and a small diameter of each information groove, the diameter of a light converging spot is small for each information groove on the optical disc using a short-wavelength light beam, and a high-precision light converging characteristic is generally required. In contrast, the light beam passing through the region closer to the optical axis undergoes refraction and diffraction, and the change in the traveling direction of the light is small, thereby exhibiting excellent light condensing characteristics. In the present invention, the region including the optical axis of the objective lens is set as the region for collecting the 1 st light beam and the 2 nd light beam which are shorter than the 3 rd light beam, thereby improving the aberration characteristic.

The objective lens according to claim 9 is the invention according to claim 8, wherein the 1 st region has a1 st diffraction structure, and the 1 st diffraction structure is a structure in which 0 th order diffracted light (transmitted light) generated when the 1 st beam passes through is larger than any other order diffracted light.

The objective lens according to claim 10 is the invention according to any one of claims 1 to 9, wherein the 2 nd area is a3 rd optical disc dedicated area for condensing the 3 rd light beam passing therethrough on the information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction, condensing the 1 st light beam not passing therethrough on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, and condensing the 2 nd light beam not passing therethrough on the information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction.

With the above configuration, the paraxial radius of curvature of the 3 rd disc region can be maintained large, and the focal length of the 3 rd disc can be maintained long. In addition, it is easy to make the image-side numerical aperture smaller in accordance with the use of the 3 rd optical disc, and it is possible to perform appropriate information recording/reproduction. For example, when the 3 rd optical disc is a CD, the CD-dedicated area can be set within the necessary numerical aperture of the CD, and thus the CD can be recorded/reproduced appropriately.

The objective lens according to claim 11 is the invention according to any one of claims 1 to 10, wherein the 3 rd region is a1 st disc/2 nd disc compatible region in which the 1 st light beam that has passed therethrough is condensed on the information recording surface of the 1 st disc so as to enable information recording and/or reproduction, the 2 nd light beam that has passed therethrough is condensed on the information recording surface of the 2 nd disc so as to enable information recording and/or reproduction, and the 3 rd light beam that has passed therethrough is condensed on the information recording surface of the 3 rd disc so as not to enable information recording and/or reproduction.

With the above configuration, when the 1 st optical disc is a BD and the 2 nd optical disc is a DVD, the BD/DVD dual-purpose area can be set in the necessary numerical apertures of the BD and the DVD, and thus, the BD and the DVD can be recorded/reproduced appropriately.

Further, when the 3 rd area is the 1 st disc and the 2 nd disc serving area, the use efficiency of the 1 st light beam and the 2 nd light beam can be prevented from being lowered.

The objective lens according to claim 12 is the invention according to any one of claims 1 to 11, wherein the objective lens includes a 4 th area outside the 3 rd area, a 5 th area outside the 4 th area, a 6 th area outside the 5 th area, the 6 th area being an area farthest from an optical axis on the objective lens, the 1 st area, the 3 rd area, and the 5 th area being areas where the 1 st light beam that has passed therethrough is condensed on an information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, the 2 nd light beam that has passed therethrough is condensed on an information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction, and the 3 rd light beam that has not passed therethrough is condensed on an information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction, the 2 nd area and the 4 th area are areas dedicated to the 3 rd optical disc in which the 3 rd light beam that has passed through is condensed on the information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction, the 1 st light beam that has passed through is condensed on the information recording surface of the 1 st optical disc so as not to enable information recording and/or reproduction, and the 2 nd light beam that has passed through is condensed on the information recording surface of the 2 nd optical disc so as not to enable information recording and/or reproduction, the 6 th area is an area dedicated to the 3 rd optical disc in which the 1 st light beam that has passed through is condensed on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, the 2 nd light beam that has passed through is condensed on the information recording surface of the 2 nd optical disc so as not to enable information recording and/or reproduction, and the 3 rd light beam that has passed through is condensed on the information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction A disc specific area.

With the above configuration, the paraxial radius of curvature of the 3 rd disc region can be maintained large, and the paraxial radius of curvature of the 1 st disc region can be reduced, so that the on-axis thickness of the objective lens can be reduced while maintaining the focal length of the 3 rd disc long. Further, since it is not necessary to provide the 1 st disc, 2 nd disc, and 3 rd disc compatible area for the 1 st disc, 2 nd disc, and 3 rd disc, it is not necessary to provide a diffraction structure having a very fine pitch, and an objective lens that can be easily manufactured can be obtained. Further, the objective lens structure can be simplified while suppressing loss of the light quantity of the 1 st light beam condensed on the 1 st optical disc, and therefore, an objective lens that is easy to manufacture can be obtained. In addition, when the 3 rd optical disc is a CD, since the CD-dedicated area can be set within the necessary numerical aperture of the CD, the CD can be recorded/reproduced appropriately. Further, when the 1 st disc is a BD and the 2 nd disc is a DVD, the BD/DVD dual-purpose area can be set in the necessary numerical apertures of the BD and the DVD, and thus, the BD and the DVD can be recorded/reproduced appropriately. Further, by dividing the light beam into 6 regions, it is possible to design the light utilization efficiency balance of 3 light beams having different wavelengths.

The objective lens according to claim 13 is the invention according to claim 12, wherein the 6 th region is a refractive surface.

Since the inclination of the area farthest from the optical axis with respect to the surface normal line of the optical axis is large, if a diffraction structure is provided on the upper surface, the light use efficiency may be reduced due to the food light or the like, and the reduction of the light use efficiency can be suppressed by using the diffraction structure as a refraction surface.

The objective lens according to claim 14 is the invention according to any one of claims 1 to 11, wherein the objective lens includes a 4 th region outside the 3 rd region, the 4 th region being a region of the objective lens farthest from the optical axis, the 1 st region and the 3 rd region being a region shared by the 1 st optical disc and the 2 nd optical disc, the 1 st optical beam passing therethrough being condensed on an information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, the 2 nd optical beam passing therethrough being condensed on an information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction, the 3 rd optical beam not passing therethrough being condensed on an information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction, the 2 nd region being a region shared by the 1 st optical disc and the 2 nd optical disc so as to enable information recording and/or reproduction, the 3 rd optical beam passing therethrough being condensed on an information recording surface of the 3 rd optical disc, And a3 rd disc-dedicated area which is focused on the information recording surface of the 1 st disc so as not to allow the 1 st light beam to pass therethrough for information recording and/or reproduction, and is focused on the information recording surface of the 2 nd disc so as not to allow the 2 nd light beam to pass therethrough for information recording and/or reproduction, and the 4 th area is a1 st disc-dedicated area which is focused on the information recording surface of the 1 st disc so as to allow the 1 st light beam to pass therethrough for information recording and/or reproduction, is focused on the information recording surface of the 2 nd disc so as not to allow the 2 nd light beam to pass therethrough for information recording and/or reproduction, and is focused on the information recording surface of the 3 rd disc so as not to allow the 3 rd light beam to pass therethrough for information recording and/or reproduction.

With the above configuration, the same effects as those of the configuration described in item 13 can be obtained, and also, compared with the configuration described in item 13, the loss of the light quantity of the 1 st light flux condensed on the 1 st optical disc can be further suppressed, and the configuration of the objective lens can be simplified, so that an objective lens that is easy to manufacture can be obtained.

The objective lens according to claim 15 is the invention according to claim 14, wherein the 4 th region is a refractive surface.

Since the inclination of the surface normal is large in the region farthest from the optical axis, if a diffraction structure is provided on the surface, the light use efficiency may be reduced by the food light or the like, and the reduction of the light use efficiency can be suppressed by using the diffraction structure as a refraction surface.

The objective lens according to claim 16 is the invention according to any one of claims 1 to 15, wherein, in a cross section including the optical axis, a height difference is provided between the 1 st region and the 2 nd region, and a portion where the height difference intersects with the 1 st region is located on a light source side in the optical axis direction than a portion where the height difference intersects with the 2 nd region.

With such a configuration, the 2 nd area is located on the optical disk side of the 1 st area, and the distance from the surface on which the 3 rd light beam is condensed to the information recording surface of the 3 rd optical disk so as to be able to record and/or reproduce information to the surface from which the laser beam is emitted from the objective lens is shortened, whereby the working distance WD3 can be secured, and the objective lens suitable for the optical pickup device for a thin optical disk drive device can be obtained.

The objective lens according to claim 17 is the invention according to claim 16, wherein the 1 st area is a1 st disc/2 nd disc shared area for focusing the 1 st light beam passing therethrough on the information recording surface of the 1 st disc, focusing the 2 nd light beam passing therethrough on the information recording surface of the 2 nd disc, and not focusing the 3 rd light beam passing therethrough on the information recording surface of the 3 rd disc, and the 2 nd area is a3 rd disc dedicated area for focusing the 3 rd light beam passing therethrough on the information recording surface of the 3 rd disc, not focusing the 1 st light beam passing therethrough on the information recording surface of the 1 st disc, and not focusing the 2 nd light beam passing therethrough on the information recording surface of the 2 nd disc.

The objective lens according to claim 18 is the invention according to any one of claims 1 to 17, wherein the following conditional expression (2) is satisfied:

d/δ≤5 (2)

wherein,

d: on-axis thickness of the objective lens

δ: minimum thickness of the objective lens in the optical axis direction

When the thickness of the objective lens on the axis is reduced while maintaining the condensing performance of the objective lens, the edge thickness of the objective lens is reduced, and the ratio of the minimum thickness of the objective lens in the optical axis direction to the thickness of the objective lens on the axis, that is, the cross-sectional ratio tends to be reduced. When the cross-sectional ratio is reduced, the edge of the objective lens is easily damaged. In addition, when the objective lens is manufactured by plastic injection molding, a flow path is narrow when molten plastic is injected into a mold, and molding is difficult. In the present invention, the cross section ratio is set to 5 or less, thereby suppressing a large decrease in the thickness of the edge of the objective lens, preventing the edge of the objective lens from being damaged, and improving the moldability.

The optical pickup device according to claim 19, further comprising the objective lens according to any one of items 1 to 18.

The optical pickup device of the present invention includes 3 light sources, i.e., a1 st light source, a2 nd light source, and a3 rd light source. The optical pickup device of the present invention includes a condensing optical system for condensing the 1 st light beam on the information recording surface of the 1 st optical disc, condensing the 2 nd light beam on the information recording surface of the 2 nd optical disc, and condensing the 3 rd light beam on the information recording surface of the 3 rd optical disc. The optical pickup device of the present invention further includes a light receiving element for receiving a light beam reflected from the information recording surface of the 1 st, 2 nd or 3 rd optical disk.

The 1 st optical disc has a protective substrate with a thickness t1 and an information recording surface. The 2 nd optical disc has a protective substrate with a thickness of t2(t1 < t2) and an information recording surface. The 3 rd optical disc has a protective substrate with a thickness of t3(t2 < t3) and an information recording surface. Preferably, the 1 st Disc is a BD (Blu-ray Disc), the 2 nd Disc is a DVD, and the 3 rd Disc is a CD, but not limited thereto. The 1 st, 2 nd or 3 rd optical disc may be a multilayer optical disc having a plurality of information recording surfaces. The thickness of the protective substrate also includes 0, and the thickness of the protective film is also included when the protective film is coated on an optical disk to a thickness of several tens of μm.

The BD is subjected to information recording/reproduction by an objective lens of NA0.85, and the protective substrate thickness is about 0.1 mm. DVDs are generic terms for DVD-series optical disks having a protective substrate thickness of about 0.6mm, which are recorded/reproduced with an objective lens having an NA of about 0.60 to 0.67, and include DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. In the present specification, CD is a generic term 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 a protective substrate is about 1.2mm, and includes CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like. The recording density is the highest of those of the BD, and is reduced in the order of DVD and C.

The thicknesses t1, t2, and t3 of the protecting substrates preferably satisfy the following conditional formulae (3), (4), and (5), but are not limited thereto. The thickness of the protective substrate referred to herein 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 surface of the optical disk to the information recording surface closest to the surface is referred to.

0.05mm≤t1≤0.1125mm (3)

0.5mm≤t2≤0.7mm (4)

1.0mm≤t3≤1.3mm (5)

In the present specification, the 1 st light source, the 2 nd light source, and the 3 rd 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. Preferably, the 1 st wavelength 1 of the 1 st light beam emitted from the 1 st light source, the 2 nd wavelength 2(λ 2 > λ 1) of the 2 nd light beam emitted from the 2 nd light source, and the 3 rd wavelength 3(λ 3 > λ 2) of the 3 rd light beam emitted from the 3 rd light source satisfy 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 on/from the 1 st optical disc, the light converging spot must be reduced compared with the 2 nd and 3 rd optical discs, and therefore, the wavelength of the 1 st light beam must be made shorter than the wavelength of the 2 nd and 3 rd light beams. A laser device for a light source, wherein the wavelength of light emitted from the laser device changes with temperature change. Therefore, in order to suppress the spherical aberration generated due to the temperature change and the wavelength change to such an extent that the information recording/reproduction on/from the optical disc can be performed, it is preferable that the conditional expressions (6) and (7) are satisfied.

When the 1 st, 2 nd, and 3 rd optical discs are BD, DVD, and CD, respectively, the 1 st wavelength λ 1 of the 1 st light source is preferably 350nm to 440nm, more preferably 390nm to 420nm, the 2 nd wavelength λ 2 of the 2 nd light source is preferably 570nm to 680nm, more preferably 630nm to 670nm, and the 3 rd wavelength λ 3 of the 3 rd light source is preferably 750nm to 850nm, more preferably 760nm to 820 nm.

In addition, at least 2 light sources among the 1 st light source, the 2 nd light source, and the 3 rd light source may be unitized. The unitization means that, for example, the 1 st light source and the 2 nd light source are fixedly housed in the 1 st package. Further, the light receiving element 1 described later may be integrated with a light source.

As the light receiving element, a photodetector such as a photodiode can be preferably used. The light reflected on the information recording surface of the optical disk is incident on a light receiving element, and a read signal of the information recorded on each optical disk can be obtained by using an output signal of the light receiving element. Further, the change in the shape of the spot or the change in the amount of light due to the change in the position of the spot on the light receiving element is detected, and focusing and tracking can be performed by moving the objective lens based on the detection. The light receiving element may be constituted by a plurality of photodetectors. The light receiving element may include a main photodetector and a sub photodetector. For example, the following light receiving element may be constituted: two (2) sub-photodetectors are provided on both sides of a photodetector that receives main light for information recording/reproduction, and sub-light for tracking adjustment (so-called 3-beam method) is received by the 2 sub-photodetectors. The light receiving element may be provided with a plurality of light receiving elements corresponding to the respective light sources.

A condensing optical system used in an optical pickup device is provided with an objective lens. The condensing optical system may be only the objective lens, but preferably the condensing optical system includes a coupling lens such as a collimator lens in addition to the objective lens. The coupling lens means a single lens or a lens group that changes a beam divergence angle disposed between the objective lens and the light source. The collimator lens is a kind of coupling lens, and is a lens that converts light incident on the collimator lens into parallel light and emits the parallel light. The condensing optical system may further include an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main beam for information recording and reproduction and two sub-beams for tracking and the like. In the present specification, the objective lens is an optical system which is disposed at a position facing an optical disc in an optical pickup device and has a function of condensing a light beam emitted from a light source on an information recording surface of the optical disc. The objective lens is a single objective lens. The objective lens may be a glass lens, a plastic lens, or a hybrid lens having a diffractive structure or the like formed of a photocurable resin or the like on a glass lens, but a plastic lens is most suitable from the viewpoint of ease of molding and low cost. Further, the refractive surface of the objective lens is preferably an aspherical surface. It is also preferable that the base surface of the objective lens provided with the diffractive structure (also called a mother aspherical surface) is aspherical. When the parent aspherical surface is determined from the objective lens, the peripherical surface connecting the disk side portions of the diffraction structure height difference can be used as the parent aspherical surface.

When the objective lens is a glass lens, a glass material having a glass transition point Tg of 500 ℃ or lower, more preferably 480 ℃ or lower is preferably used. By using a glass material having a glass transition point Tg of 500 ℃ or lower, molding at a relatively low temperature is possible, and the life of the mold can be prolonged.

In general, since a glass lens has a higher specific gravity than a resin lens, if the objective lens is made of a glass lens, the weight of the objective lens becomes large, and the load on an actuator for driving the objective lens becomes large. Therefore, when the objective lens is a glass lens, a glass material having a small specific gravity is preferably used. Specifically, the specific gravity is preferably 3.0 or less, and more preferably 2.75 or less.

Examples of such a glass material include examples 1 to 12 of Japanese patent laid-open No. 2005-306627. For example, in example 1 of Japanese patent laid-open No. 2005-306627, the glass transition point Tg was 460 ℃, the specific gravity was 2.58, the refractive index nd was 1.594, and the Abbe number was 59.8.

When the objective lens is a plastic lens, it is preferable to use a cycloolefin resin material, and it is further preferable to use a cycloolefin resin having a refractive index change dN/dT (DEG C) at a wavelength of 405nm with a temperature change in a temperature range of-5 ℃ to 70 ℃ at a refractive index of 1.52 to 1.60 at a wavelength of 405nm at a temperature of 25 ℃ and a refractive index change at a wavelength of 405nm with a temperature change^-1) at-20X 10^-5to-5X 10^-5(more preferably at-10X 10^-5to-8X 10^-5) A resin material within the range. When the objective lens is a plastic lens, it is preferable that the coupling lens is also a plastic lens.

Preferably, the abbe number of the material constituting the objective lens is 50 or more.

The objective lens will be described below. At least one optical surface of the objective lens includes at least a1 st region, a2 nd region disposed outside the 1 st region, and a3 rd region disposed outside the 2 nd region. The region 4 may be further provided outside the region 3. The 4 th region may be a region farthest from the optical axis. Further, the optical element may further include a 4 th region outside the 3 rd region and a 5 th region outside the 4 th region. Further, a 6 th region may be provided outside the 5 th region, and the 6 th region may be a region farthest from the optical axis. The number of domains is preferably 10 or less, more preferably 8 or less. The optical surface provided with the 1 st region, the 2 nd region, and the 3 rd region is preferably a light source side optical surface, and is preferably one optical surface having a small radius of curvature.

The 1 st region is preferably a region including the optical axis of the objective lens, but a minute region including the optical axis may be an unused region or a special-purpose region, and the periphery thereof may be the 1 st region. When there are the 1 st region, the 2 nd region, the 3 rd region, and the other regions, these regions are preferably provided on the same optical surface. As shown in fig. 1 showing an example of division into 3 regions, the 1 st region CN, the 2 nd region MD, and the 3 rd region OT are preferably provided on the same optical surface and are concentric circles around the optical axis. The 1 st region CN, the 2 nd region MD, and the 3 rd region OT are preferably adjacent to each other, but may have a slight gap therebetween.

Among the plurality of regions of the objective lens, the objective lens region for converging the 1 st light beam passing therethrough on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction and the objective lens region for converging the 3 rd light beam passing therethrough on the information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction are different regions. In particular, neither the 1 st area nor the 2 nd area is the 1 st disc 3 rd disc compatible area or the 1 st disc 2 nd disc 3 rd disc compatible area. The 3 rd area and the area outside the area may have a1 st disc 3 rd disc compatible area or a1 st disc 2 nd disc 3 rd disc compatible area, but basically, it is preferable that the area of the objective lens is not the 1 st disc 3 rd disc compatible area or the 1 st disc 2 nd disc 3 rd disc compatible area. Preferred examples include: an objective lens having a1 st disc, a2 nd disc compatible area, a3 rd disc exclusive area, and a1 st disc exclusive area; an objective lens having a1 st disc-dedicated area, a2 nd disc 3 rd disc-shared area, and a1 st disc-dedicated area.

Preferably, the plurality of areas include an objective lens area for converging the 3 rd light beam passing therethrough on the information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction, an objective lens area for converging the 1 st light beam not passing therethrough on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, and an area dedicated to the 3 rd optical disc so as to converge the 2 nd light beam not passing therethrough on the information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction. The area dedicated to the 3 rd optical disc may be a diffraction surface, but from the viewpoint of ease of manufacturing and improvement in light use efficiency, the area dedicated to the 3 rd optical disc is preferably a refraction surface.

The number of areas dedicated to the 3 rd disc is preferably 1 to 3.

The 1 st area is preferably a1 st optical disc and 2 nd optical disc shared area in which the 1 st light beam that has passed through is condensed on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, and the 2 nd light beam that has passed through is condensed on the information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction, but the 3 rd light beam that has passed through is condensed on the information recording surface of the 3 rd optical disc so as not to enable information recording and/or reproduction. Preferably, the 3 rd area is also the 1 st disc and 2 nd disc compatible area.

The 2 nd area is preferably an area dedicated to the 3 rd optical disc, in which the 3 rd light beam that has passed through is condensed on the information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction, the 1 st light beam that has not passed through is condensed on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, and the 2 nd light beam that has passed through is condensed on the information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction.

For example, when the objective lens has 6 regions, the 1 st to 6 th diffraction structures may be provided in the 1 st to 6 th regions, respectively. The 2 nd, 4 th and 6 th regions may be refractive surfaces. The 1 st, 2 nd, 3 rd, 4 th, 5 th and 6 th diffractive structures are preferably provided in regions of 70% or more, more preferably 90% or more, of the area of each of the 1 st, 2 nd, 3 rd, 4 th, 5 th and 6 th regions of the objective lens. More preferably, the α -th diffraction structure (α is an integer of 1 to 6) is provided on the entire α -th region. By providing an appropriate diffraction structure for each region over the entire surface of each region, the light use efficiency can be improved.

The term "diffraction structure" as used herein refers to a general term for a structure that diffracts light at least in a certain wavelength. The diffraction structure is a general term for a structure having a difference in height and having a function of converging or diverging a light beam of at least a certain wavelength by diffraction. Preferably, the diffractive structure is provided with a plurality of step-ups. The step may be disposed at periodic intervals in the optical axis perpendicular direction, or may be disposed at non-periodic intervals in the optical axis perpendicular direction. In addition, even if the optical surface of the objective lens has a plurality of zones divided by the step with the optical axis as the center and each zone is constituted by an aspherical surface, the objective lens which converges or diverges the light beam by the diffraction action is an objective lens having a diffraction structure. For example, when an objective lens having a structure in which each zone is formed by an aspherical surface is used, and a λ a wavelength light beam passing through a plurality of zones is focused on an information recording surface of an optical disc having a protective substrate with a thickness tA, and a λ B (λ a ≠ λ B) wavelength light beam passing through the same plurality of zones is focused on an information recording surface of an optical disc having a protective substrate with a thickness tB (tA ≠ tB), the objective lens has a diffraction structure in which the light beam is converged or diverged by a diffraction action.

Preferably, the diffraction structure has a plurality of annular zones concentric with the optical axis. The diffraction structure may have various cross-sectional shapes (cross-sectional shapes of the surface including the optical axis), and the cross-sectional shapes including the optical axis are roughly classified into a flame-type structure and a stepped structure.

As shown in fig. 2(a) and (b), the optical element having a diffraction structure has a sawtooth-like cross section including the optical axis, and the diffraction structure is not perpendicular to or parallel to the aspherical surface but has an inclined surface. In the example of fig. 2, the upper side is the light source side, the lower side is the disk side, and a diffraction structure is formed on a plane which is a base aspheric surface.

As shown in fig. 2(c) and (d), the step structure has a cross-sectional shape including the optical axis of the optical element having a diffraction structure, and a plurality of small steps (referred to as step units) are provided. In the present specification, "X-step" means a stepped structure in which an annular surface (hereinafter, also referred to as an optical functional surface) corresponding to (facing) the direction perpendicular to the optical axis is divided into X annular surfaces by a step in 1 step unit of the stepped structure, and in particular, 3 or more steps, wherein the stepped structure has a small step and a large step, the small step means the smallest step in the optical axis direction in 1 step unit, and the large step means the largest step in the optical axis direction in 1 step unit.

The diffraction structure shown in fig. 2(c) is referred to as a 5-step structure, and the diffraction structure shown in fig. 2(d) is referred to as a 2-step structure. The 1 st diffraction structure is a 2-step structure including a plurality of annular zones concentric with an optical axis, the objective lens including a cross-sectional shape of the plurality of annular zones of the optical axis is formed by a plurality of height difference surfaces Pa and Pb extending parallel to the optical axis, a light source side optical function surface Pc connecting side ends of adjacent height difference surfaces Pa and Pb with each other, and a disc side optical function surface Pd connecting side ends of adjacent height difference surfaces Pa and Pb with each other, and the light source side optical function surface Pc and the disc side optical function surface Pd are alternately arranged in a direction perpendicular to the optical axis.

In the step structure, the length of 1 step unit in the direction perpendicular to the optical axis is referred to as pitch P. The height difference surface is preferably parallel or slightly parallel to the optical axis, but the optical function surface may be not only parallel to the parent aspherical surface but also inclined with respect to the parent aspherical surface.

Preferably, the diffraction structure is a structure in which a unit shape is periodically repeated. The term "unit shape is repeated periodically" as used herein, and naturally includes a shape in which the same shape is repeated at the same period. The unit shape of 1 unit of the cycle is a shape in which the cycle is regularly gradually lengthened and gradually shortened, and also belongs to the "unit shape is periodically repeated".

When the diffraction structure has a flame-type structure, the unit-shaped zigzag structure is repeated. The same zigzag shape may be repeated as shown in fig. 2(a), or the size of the zigzag shape may be gradually increased or decreased as it goes forward in the direction of the parent aspherical surface as shown in fig. 2 (b). A combination shape in which a shape in which the size of the saw-tooth shape is gradually increased and a shape in which the size of the saw-tooth shape is gradually decreased may be formed. However, even when the size of the sawtooth shape gradually changes, it is preferable that the size of the step difference in the optical axis direction (or the direction in which the light beam passes) is almost constant in the sawtooth shape. In addition to this, the following shape can be formed: in some regions, the height difference of the flame type structure is in a shape facing the opposite direction of the optical axis (center), in other regions, the height difference of the flame type structure is in a shape facing the optical axis (center), and a transition region necessary for switching the height difference direction of the flame type structure is provided therebetween. When the optical path difference added by the diffraction structure is expressed by the optical path difference function, the transition region is a region corresponding to an extreme point of the optical path difference function. When the optical path difference function is at an extreme point, the slope of the optical path difference function is small, the zone pitch can be widened, and the decrease in transmittance due to the shape error of the diffraction structure can be suppressed.

When the diffraction structure has a step-like structure, the diffraction structure may have a shape in which 5 steps are repeated as shown in fig. 2 (c). Further, the shape may be such that the step size gradually increases and the step size gradually decreases as going forward in the parent aspheric surface direction, but it is preferable that the amount of height difference in the optical axis direction (or the direction in which light passes) hardly changes.

The 1 st, 3 rd and 5 th diffraction structures are described in detail below. The 1 st, 3 rd and 5 th diffraction structures are preferably structures for making at least the 1 st and 2 nd optical discs interchangeable. Therefore, it is preferable that the 1 st, 3 rd and 5 th diffraction structures correct spherical aberration generated due to the difference between the thickness t1 of the protective substrate of the 1 st optical disc and the thickness t2 of the protective substrate of the 2 nd optical disc and/or spherical aberration generated due to the difference between the wavelengths of the 1 st and 2 nd optical beams with respect to the 1 st and 2 nd optical beams passing through the 1 st, 3 rd or 5 th diffraction structures.

The 1 st, 3 rd and 5 th diffractive structures generate n-th order diffracted light at most when the 1 st beam passes through them, and generate m-th order diffracted light at most when the 2 nd beam passes through them. Preferable combinations of (n, m) include (0, 1), (1, -2), (2, 1), and the like. In particular, when n is 0, the 1 st region can be made to have a small paraxial radius of curvature suitable for the 1 st optical disc, and the thickness on the objective lens axis can be reduced, which is preferable.

When the 2 nd diffraction structure, the 4 th diffraction structure, or the 6 th diffraction structure is provided in addition to the 1 st diffraction structure, the 3 rd diffraction structure, or the 5 th diffraction structure, the diffraction structures may be provided on different optical surfaces of the objective lens, but it is preferable that the diffraction structures are provided on the same optical surface. It is preferable to provide the optical surface on the same optical surface because an eccentricity error can be reduced during manufacturing. Further, it is preferable that each diffractive structure is provided on the light source side surface of the objective lens, compared to the optical disk side surface of the objective lens.

Preferably, the 3 rd light beam passing through the area other than the 3 rd disc specific area is not used for recording and/or reproducing the 3 rd disc. It is preferable that the 3 rd light beam passing through the area outside the 3 rd optical disc specific area does not contribute to formation of a flare spot on the 3 rd optical disc information recording surface. That is, when the 1 st optical disc, the 2 nd optical disc serving area, is provided with the diffraction structure, the 3 rd optical beam passing through the 1 st optical disc, the 2 nd optical disc serving area, and the diffraction structure is preferably made to form flare on the information recording surface of the 3 rd optical disc by the objective lens. As shown in fig. 3, the 3 rd light beam passing through the objective lens forms a spot on the information recording surface of the 3 rd optical disc, and has a spot center SCN having a high light intensity, a spot middle SMD having a lower light intensity than the spot center, and a spot peripheral SOT having a higher light intensity than the spot middle but lower than the spot center, in order from the optical axis (or the spot center) outward. The spot center portion is used for recording and/or reproducing information on/from the optical disc, and the spot intermediate portion and the spot peripheral portion are not used for recording and/or reproducing information on/from the optical disc. The periphery of the spot is called flare. In the type in which the spot central portion is not present around the spot central portion and the spot peripheral portion is present, that is, when a large spot is formed around the focused spot with a light beam, the spot peripheral portion is also referred to as flare. That is, the 3 rd light beam passing through the 1 st light beam and the 2 nd light beam common region diffraction structure of the objective lens forms a spot peripheral portion on the information recording surface of the 3 rd optical disc.

A preferable mode of the area farthest from the optical axis is a mode in which the 2 nd light beam and the 3 rd light beam that have passed through the same area are not used for recording and/or reproduction on and/or from the 2 nd optical disc and the 3 rd optical disc. It is preferable that the 2 nd and 3 rd light beams passing through the same area do not contribute to formation of a spot on the information recording surface of the 2 nd and 3 rd optical discs, respectively. That is, it is preferable that the 2 nd and 3 rd light beams passing through the area farthest from the optical axis form flare spots on the information recording surfaces of the 2 nd and 3 rd optical discs. In other words, it is preferable that the 2 nd and 3 rd light beams passing through the area farthest from the optical axis form the spot peripheral portions on the 2 nd and 3 rd optical disc information recording surfaces.

When the region farthest from the optical axis has a diffractive structure, the diffractive structure can correct chromatic spherical aberration generated by slight variation in the wavelength of the 1 st light source for the 1 st light beam passing through the diffractive structure. A slight variation in wavelength is a variation within. + -. 10 nm. Preferably, for example, when the 1 st light beam changes by ± 5nm from the wavelength 1, the diffraction structure compensates for the spherical aberration variation of the 1 st light beam passing through the diffraction structure so that the amount of change in the wavefront aberration on the 1 st disc information recording surface is not less than 0.001 λ 1rms and not more than 0.070 λ 1 rms.

When the objective lens is a plastic lens, a structure in which a 7 th diffraction structure is further superimposed on a1 st diffraction structure, a3 rd diffraction structure, a 4 th diffraction structure, a 5 th diffraction structure, or a 6 th diffraction structure as a structure for correcting temperature characteristics can be used. The 7 th diffractive structure may be provided in the 4 th region and the 6 th region which are refractive surfaces. Specifically, the difference in height in the optical axis direction of the 7 th diffractive structure is not limited to the difference in optical path length of approximately 5 wavelength components of the 1 st wavelength for the 1 st light beam and approximately 3 wavelength components of the 2 nd wavelength for the 2 nd light beam, or the difference in optical path length of approximately 2 wavelength components of the 1 st wavelength for the 1 st light beam and approximately 1 wavelength component of the 2 nd wavelength for the 2 nd light beam.

Preferably, the difference between the paraxial radius of curvature of the parent aspheric surface in a certain region and the paraxial radius of curvature of the parent aspheric surface in another region is 0.1mm to 0.7 mm. In particular, as shown in fig. 4, when the 1 st region R1 including the optical axis is the 1 st disc 2 nd disc compatible region, the 2 nd region R2 around the outer side thereof is the 3 rd disc dedicated region, the 3 rd region R3 around the outer side thereof is the 1 st disc 2 nd disc compatible region, and the 4 th region R4 around the outer side thereof is the 3 rd disc dedicated region, the 1 st region R1 and the 3 rd region R3 are located on the same 1 st mother aspherical surface BL1, and the 2 nd region R2 and the 4 th region R4 are located on the same 2 nd mother aspherical surface BL. Here, it is preferable that a position P1 where the 1 st parent aspherical surface BL1 intersects the optical axis be located on the light source side than a position P2 where the 2 nd parent aspherical surface BL2 intersects the optical axis. In other words, it can be said that, in the cross section of the objective lens including the optical axis, there is a level difference ST between the 1 ST region R1 and the 2 nd region R2, and a point P3 at which the level difference ST intersects with the 1 ST region R1 is located on the light source side in the optical axis direction than a point P4 at which the level difference ST intersects with the 2 nd region. The distance Δ between the positions P1 and P2 can be expressed approximately as the difference between the radii of curvature of the parent aspherical surfaces BL1 and BL2, and is preferably 0.1mm to 0.7 mm. It is also preferable that the parent aspherical surfaces BL1 and BL2 intersect each other in the effective diameter.

As shown in fig. 1, the objective lens OBJ is generally provided with a rim portion FL having a minimum objective lens thickness on the outer side in the optical axis perpendicular direction of a region OT farthest from the optical axis, and the ratio (d/δ, referred to as a cross-sectional ratio) of the minimum optical axis thickness δ of the rim portion FL to the on-axis thickness d of the objective lens OBJ is preferably 5 or less.

The numerical aperture on the object side necessary for reproducing and/or recording information from/on the 1 st optical disc is NA1, the numerical aperture on the object side necessary for reproducing and/or recording information from/on the 2 nd optical disc is NA2(NA1 ≧ NA2), and the numerical aperture on the object side necessary for reproducing and/or recording information from/on the 3 rd optical disc is NA3(NA2 > NA 3). NA1 is preferably 0.6 to 0.9, more preferably 0.75 to 0.9. Particularly preferably NA1 is 0.85. Preferably, NA2 is 0.55 to 0.7. Particularly preferred is an NA2 of 0.60 or 0.65. Further, NA3 is preferably 0.4 to 0.55. Particularly preferred is a NA3 of 0.45 or 0.53.

Preferably, the boundary outside the 3 rd disc-dedicated area where the objective lens is farthest from the optical axis is formed in a portion corresponding to a range of 0.9NA3 or more and 1.2NA3 or less (more preferably 0.95NA3 or more and 1.15NA3 or less) when the 3 rd beam is used, and more preferably, the boundary outside the 3 rd disc-dedicated area where the objective lens is farthest from the optical axis is formed in a portion corresponding to NA 3. Preferably, the boundary inside the 2 nd disc area where the objective lens is farthest from the optical axis is a portion corresponding to a range of 0.9NA2 or more and 1.2NA2 or less (more preferably 0.95NA2 or more and 1.15NA2 or less) when the 2 nd beam is used. More preferably, the boundary inside the 2 nd optical disc area where the objective lens is farthest from the optical axis is formed in a portion corresponding to NA 2.

Preferably, when the 3 rd light beam passing through the objective lens is condensed on the information recording surface of the 3 rd optical disc, the spherical aberration has at least 1 discontinuity. In this case, the discontinuity is preferably present in a range of 0.9NA3 or more and 1.2NA3 or less (more preferably 0.95NA3 or more and 1.15NA3 or less) when the 3 rd beam is used.

When the spherical aberration is continuous and there is no discontinuity, or when the 3 rd light beam passing through the objective lens is condensed on the information recording surface of the 3 rd optical disc, the absolute value of the longitudinal spherical aberration of NA2 is preferably 0.03 μm or more and the absolute value of the longitudinal spherical aberration of NA3 is preferably 0.02 μm or less. More preferably, the absolute value of the longitudinal spherical aberration of NA2 is 0.08 μm or more and the absolute value of the longitudinal spherical aberration of NA3 is 0.01 μm or less.

Further, the objective lens preferably 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)

where φ 1 represents the effective diameter of the 1 st beam at the entrance surface of the objective lens, f3 represents the focal length of the objective lens when the 3 rd beam is in use, and d represents the on-axis thickness of the objective lens.

The following conditional expressions are preferably satisfied:

2.1(mm)≤φ1≤2.5(mm) (8)’。

in addition, the following conditional expressions are preferably satisfied:

0.9≤d/f3≤1.1(mm) (10)’。

further preferably satisfies the following formula:

1.4(mm)≤f3≤2.0(mm) (11)。

by configuring the small-diameter objective lens satisfying the expression (8) and satisfying the expression (9), the working distance WD3, which is the distance from the position closest to the optical disc on the laser light emission objective lens surface to the optical disc, can be ensured by extending the focal distance f3 when the 3 rd optical disc is used, and therefore, a margin is created when the objective lens is displaced along the optical axis by an actuator or the like in order to optimize the focused spot on the information recording surface of the 3 rd optical disc. The present inventors have also found that satisfying conditional expressions (8) and (9) and satisfying conditional expression (10) can achieve optical performance such as light collection characteristics while maintaining long focal length f3, and can be applied to a thin optical disc drive apparatus. "1.7" in the expression (9) corresponds to 2 times the image-side numerical aperture NA of the 1 st optical disc. In general, the refractive lens for the 1 st optical disc satisfies Φ of 1.7 × f, but in the present invention, Φ is made smaller than 1.7 × f3, thereby obtaining an objective lens with reduced Φ while ensuring a focal length of a CD. Further, satisfying the above formula is preferable because it is possible to reduce the change in spherical aberration due to temperature change even when the objective lens is a material lens while sufficiently securing the focal distance in the case of the 3 rd optical disc, and suppressing the focal distance from being excessively long.

In order to configure an objective lens that can be mounted on a thin optical pickup device, it is preferable to satisfy the following equation:

d≤2.0(mm) (12)。

further, when the focal length of the objective lens at the 1 st beam is f1(mm) and the center thickness of the objective lens is d (mm), the following formula (13) is preferably satisfied:

0.7≤d/f1≤1.5 (13)。

more preferably satisfies the following formula (13)':

1.0≤d/f1≤1.3 (13)’。

more preferably, the following formula is satisfied:

0.7≤d/f2≤1.3 (14)。

where f2 denotes the objective lens focal length when the 2 nd beam is used.

By satisfying the conditional expressions (13) and (14), the working distance of the CD as the 3 rd optical disc can be secured without reducing the diffraction structure pitch, the objective lens can be easily manufactured, and high light use efficiency can be maintained.

In addition, the following conditional expressions are preferably satisfied:

0.9≤φ2/φ1≤1.2 (15)。

2 denotes an effective diameter of the objective lens when the 2 nd optical disc is used. By satisfying the above range, it is possible to ensure that the working distance of the CD as the 3 rd optical disc is of a level that is practically free from problems, and to maintain the aberration variation level when the temperature is changed even when the objective lens is a plastic lens, for example, to a level that is free from problems in recording and/or reproducing information on the optical disc.

Further preferably satisfies the following formula:

0.15(mm)≤WD3≤0.5(mm) (16)，

where WD3 denotes the working distance of the 3 rd optical disc in use.

Preferably, the following formula is satisfied:

0.15(mm)≤WD≤0.4(mm) (16)’。

further preferably satisfies the following formula:

0.2(mm)≤WD2≤0.8(mm) (17)，

where WD2 denotes the working distance of the 2 nd disc in use.

Further preferably satisfies the following formula:

0.4(mm)≤WD1≤1.2(mm) (18)，

where WD1 denotes the working distance of the 1 st optical disc in use.

The preferred embodiment of the number of 2 objective lens regions will be described in detail below, but the present invention is not limited to the following embodiment.

[ example 1] 4-zone Objective lens

The 1 st preferred embodiment is a method in which the optical surface of the objective lens is divided into 4 regions. In this embodiment, the 4 th region is a region most distant from the optical axis on the objective lens. The 1 st area and the 3 rd area are the 1 st disc and the 2 nd disc used areas. The 2 nd area is a3 rd disc dedicated area. The 4 th area is an area dedicated to the 1 st optical disc, and is configured to focus the 1 st light beam that has passed through the area on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, focus the 2 nd light beam that has passed through the area on the information recording surface of the 2 nd optical disc so as not to enable information recording and/or reproduction, and focus the 3 rd light beam that has passed through the area on the information recording surface of the 3 rd optical disc so as not to enable information recording and/or reproduction.

Preferably, the 1 st area of the objective lens in the 1 st optical disc/2 nd optical disc compatible area has a1 st diffractive structure. The 1 st diffractive structure generates n-th order diffracted light at most when the 1 st beam passes through the structure, and generates m-th order diffracted light at most when the 2 nd beam passes through the structure. Preferable combinations of (n, m) include (0, 1), (1, -2), (2, 1), and the like. In particular, when n is 0, the 1 st region can be made to have a small paraxial radius of curvature suitable for the 1 st optical disc, and the thickness on the objective lens axis can be reduced, which is preferable.

Preferably, the 3 rd area of the objective lens in the 1 st optical disc and the 2 nd optical disc serving area has a3 rd diffraction structure. Preferably, the 3 rd diffractive structure is the same as the 1 st diffractive structure.

Further, the 2 nd area of the objective lens of the 3 rd disc-dedicated area is preferably a refractive surface, but a2 nd diffraction structure may be provided. The refractive surface is preferably a surface having a structure that does not give an optical path difference to the light beam incident on the objective lens.

The 4 th area of the objective lens in the 1 st optical disc dedicated area is preferably a refractive surface, but a 4 th diffraction structure may be provided.

Preferably, the difference between the paraxial radius of curvature of the parent aspheric surface in the 1 st region and the 3 rd region and the paraxial radius of curvature of the parent aspheric surface in the 2 nd region is 0.1mm to 0.7 mm.

[ example 2] 6-zone Objective lens

The 2 nd preferred embodiment is a method in which the optical surface of the objective lens is divided into 6 regions. In this embodiment, the 6 th region is a region most distant from the optical axis on the objective lens. The 1 st, 3 rd and 5 th areas are the 1 st, 2 nd and dual-purpose areas of the optical disc. The 2 nd area and the 4 th area are areas dedicated to the 3 rd disc. The 6 th area is a1 st disc specific area.

Preferably, the 5 th area of the objective lens in the 1 st optical disc and the 2 nd optical disc compatible area has a 5 th diffraction structure. Preferably, the 5 th diffractive structure is the same as the 1 st and 3 rd diffractive structures.

Further, the 2 nd area of the objective lens of the 3 rd disc-dedicated area is preferably a refractive surface, but a2 nd diffraction structure may be provided.

The 4 th area of the objective lens in the 3 rd disc-dedicated area is preferably a refractive surface, but a 4 th diffraction structure may be provided.

The objective lens 6 th area of the 1 st optical disc specific area is preferably a refractive surface, but a 6 th diffractive structure may be provided.

Preferably, the difference between the paraxial radius of curvature of the parent aspheric surfaces of the 1 st, 3 rd and 5 th regions and the paraxial radius of curvature of the parent aspheric surfaces of the 2 nd and 4 th regions is 0.1mm to 0.7 mm.

The 1 st, 2 nd and 3 rd beams 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 1 st light beam is incident on the objective lens satisfies the following formula (19):

-0.02＜m1＜0.02 (19)。

conversely, when the 1 st light beam enters the objective lens as divergent light, the imaging magnification m1 of the objective lens when the 1 st light beam enters the objective lens preferably satisfies the following expression (19'):

-0.10＜m1＜0.00 (19’)。

when the 2 nd beam is made incident on the objective lens as parallel light or substantially parallel light, it is preferable that the imaging magnification m2 of the objective lens when the 2 nd beam is made incident on the objective lens satisfies the following formula (20):

-0.02＜m2＜0.02 (20)。

conversely, when the 2 nd light beam is incident on the objective lens as divergent light, it is preferable that the imaging magnification m2 of the objective lens when the 2 nd light beam is incident on the objective lens satisfies the following expression (20'):

-0.10＜m2＜0.00 (20’)。

when the 3 rd beam is made incident on the objective lens as parallel light or substantially parallel light, it is preferable that the imaging magnification m3 of the objective lens when the 3 rd beam is made incident on the objective lens satisfies the following expression (21). When the 3 rd light beam is parallel light, problems are likely to occur during tracking, but the present invention can obtain good tracking characteristics even when the 3 rd light beam is parallel light, and can record and/or reproduce information on 3 different types of optical discs with certainty.

-0.02＜m3＜0.02 (21)。

Conversely, when the 3 rd light beam is incident on the objective lens as divergent light, it is preferable that the imaging magnification m3 of the objective lens when the 3 rd light beam is incident on the objective lens satisfies the following expression (21'):

-0.10＜m3＜0.00 (21’)。

the optical information recording/reproducing apparatus of the present invention is provided with an optical disk drive apparatus, and the optical pickup apparatus.

In the optical disk drive device provided in the optical information recording/reproducing device, the optical disk drive device is configured in the following manner: only a disc capable of supporting an optical disc is loaded and taken out to the outside from an optical information recording and reproducing apparatus main body housing an optical pickup device and the like; taken out together with the optical disk drive apparatus main body in which the optical pickup apparatus and the like are housed.

The optical information recording and reproducing device according to each of the above-described embodiments is generally provided with the following components, but is not limited thereto: an optical pickup device housed in a case or the like; a drive source of an optical pickup device such as an index motor for moving the optical pickup device together with the housing toward the inner periphery or the outer periphery of the optical disk; an optical pickup device transfer means including a guide rail for guiding the optical pickup device housing to the inner periphery or the outer periphery of the optical disc; and a spindle motor for rotating and picking up the optical disk.

In the former method, in addition to the above-described components, a tray on which an optical disk is mounted and supported and a loading mechanism for sliding the tray are provided, and in the latter method, the tray and the loading mechanism are not provided, and it is preferable that the components are provided in a drawer corresponding to a base which is capable of being drawn out.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide an optical pickup device that can be used in a thin optical disk drive device while securing a sufficient working distance of a CD and that can record and reproduce information on and from optical disks such as BD, DVD, and CD with certainty, and an objective lens suitable for use in the optical pickup device.

Drawings

FIG. 1: (a) an example of the objective lens OBJ of the present invention is shown as viewed from the optical axis direction, and (b) is a cross-sectional view thereof.

FIG. 2: schematic cross-sectional views of some examples (a) to (d) of the diffraction structure provided on the objective lens OBJ of the present invention.

FIG. 3: the shape of the light-gathering spot gathered by the objective lens is schematic.

FIG. 4: an enlarged cross-sectional view of an example of the objective lens OBJ of the present invention.

FIG. 5: the structure of the optical pickup device of the present invention is schematically illustrated.

FIG. 6: example 1 cross-sectional view of an objective lens.

FIG. 7: (a) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of using the BD in example 1 are shown, (b) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of using the DVD in example 1, and (c) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of using the CD in example 1 are shown.

FIG. 8: example 2 cross-sectional view of an objective lens.

FIG. 9: (a) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of BD use in example 2 are shown, (b) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of DVD use in example 2 are shown, and (c) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of CD use in example 2 are shown.

FIG. 10: example 3 cross-sectional view of objective lens.

FIG. 11: (a) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of BD use in example 3 are shown, (b) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of DVD use in example 3, and (c) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of CD use in example 3 are shown.

FIG. 12: example 4 cross-sectional view of objective lens.

FIG. 13: (a) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of BD use in example 4 are shown, (b) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of DVD use in example 4 are shown, and (c) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of CD use in example 4 are shown.

FIG. 14: example 5 cross-sectional view of objective lens.

FIG. 15: (a) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of BD use in example 5 are shown, (b) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of DVD use in example 5 are shown, and (c) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of CD use in example 5 are shown.

FIG. 16: example 6 cross-sectional view of objective lens.

FIG. 17: (a) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of BD use in example 6 are shown, (b) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of DVD use in example 6 are shown, and (c) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of CD use in example 6 are shown.

FIG. 18: example 7 cross-sectional view of an objective lens.

FIG. 19: (a) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of BD use in example 7 are shown, (b) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of DVD use in example 7 are shown, and (c) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of CD use in example 7 are shown.

FIG. 20: example 8 cross-sectional view of objective lens.

FIG. 21: (a) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of BD use in example 8 are shown, (b) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of DVD use in example 8 are shown, and (c) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of CD use in example 8 are shown.

FIG. 22: example 9 cross-sectional view of an objective lens.

FIG. 23: (a) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of BD use in example 9 are shown, (b) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of DVD use in example 9 are shown, and (c) the longitudinal spherical aberration (solid line) and the sine condition (broken line) in the case of CD use in example 9 are shown.

FIG. 24: example 10 cross-sectional view of objective lens.

FIG. 25: example 11 cross-sectional view of an objective lens.

FIG. 26: example 12 cross-sectional view of objective lens.

FIG. 27 is a schematic view showing: the deformation of the objective lens is illustrated schematically.

FIG. 28: the deformation of the objective lens is illustrated schematically.

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings. Fig. 5 is a schematic configuration diagram of an optical pickup device PU1 according to the present embodiment that can record and/or reproduce information on and/or from a BD, DVD, or CD with certainty. The optical pickup device PU1 can be mounted on an optical information recording/reproducing device. Here, the 1 st disc is a BD, the 2 nd disc is a DVD, and the 3 rd disc is a CD. The present invention is not limited to the present embodiment.

The optical pickup PU1 includes an objective lens OBJ, an aperture stop ST, a collimator lens CL, a polarization dichroic prism PPS, a unit MD1 in which a1 ST semiconductor laser LD1 (1 ST light source) emitting light at a wavelength λ 1 of 405nm (1 ST light beam) when recording/reproducing information on/from a BD, a1 ST light receiving element PD1 receiving a light beam reflected by a BD information recording surface RL1, and a laser module LM are integrated.

The laser module LM includes a2 nd semiconductor laser EP1 (2 nd light source) that emits light when recording/reproducing information on/from a DVD and emits a laser beam (2 nd light beam) having a wavelength λ 2 of 658nm, a3 rd semiconductor laser EP2 (3 rd light source) that emits light when recording/reproducing information on/from a CD and emits a laser beam (3 rd light beam) having a wavelength λ 3 of 785nm, a2 nd light receiving element DS1 that receives a light beam reflected from a DVD information recording surface RL2, a3 rd light receiving element DS2 that receives a light beam reflected from a CD information recording surface RL3, and a prism PS.

The objective lens OBJ of the present embodiment has, on the light source side aspheric optical surface, a1 st region (having a diffractive structure) including the optical axis, a2 nd region (refractive surface) around the first region, a3 rd region (having a diffractive structure) around the first region, and a 4 th region (refractive surface) around the first region, which is farthest from the optical axis. The objective OBJ satisfies the following formula:

1.5(mm)≤φ1≤3.4(mm) (8)

1.7×f3＞φ1 (9)

0.7≤d/f3≤1.42(mm) (10)

where φ 1 represents the effective diameter of the 1 st beam on the objective lens entrance surface, f3 represents the objective lens focal length when the 3 rd beam is used, and d represents the on-axis objective lens thickness.

The 1 st beam (λ) emitted from the blue-violet semiconductor laser LD1₁405nm), the beam passes through the polarization dichroic prism PPS, is converted into parallel light by the collimator lens CL, is converted from linear polarization into circular polarization by a λ/4 wave plate not shown, has a beam diameter regulated by the stop ST, and is incident on the objective optical element OBJ. The light beam condensed by the objective lens OBJ in the 1 st optical disk 2-purpose area and the 1 st optical disk dedicated area (the light beam passing through the 3 rd optical disk dedicated area is flare-formed to form a spot peripheral portion) is made to form a spot on the information recording surface RL1 of the BD via a protective substrate PL1 having a thickness of 0.1 mm.

The reflected light beam modulated by the information groove on the information recording surface RL1 passes through the objective lens OBJ and the stop ST again, is converted from circular polarization to linear polarization by a λ/4 plate not shown, is converted into a converging light beam by the collimator lens CL, passes through the polarization dichroic prism PPS, and is converged on the light receiving surface of the 1 ST light receiving element PD 1. Then, the objective optical element OBJ is focused and tracked by the 2-axis actuator AC using the output signal of the 1 st photodetector PD1, and information recorded on the BD can be read.

The 2 nd beam (λ 2 ═ 658nm) emitted from the red semiconductor laser beam EP1 is a divergent beam, reflected by the prism PS, reflected by the polarization dichroic prism PPS, changed into a parallel beam by the collimator lens CL, then changed from linear polarization to circular polarization by a λ/4 wave plate (not shown), and incident on the objective lens OBJ. The objective lens OBJ 1 st optical disk and 2 nd optical disk serving area (the light beam passing through the 1 st optical disk dedicated area and the 3 rd optical disk dedicated area is flare-formed to form a spot peripheral portion) light beam is spot-formed on the information recording surface RL2 of the DVD through the protective substrate PL2 having a thickness of 0.6mm to form a spot central portion.

The reflected light beam modulated by the information groove on the information recording surface RL2 passes through the objective lens OBJ and the stop ST again, is converted from circular polarization to linear polarization by a λ/4 plate not shown, is converted into a converging light beam by the collimator lens CL, is reflected by the polarization dichroic prism PPS, is reflected 2 times inside the prism, and is then collected by the 2 nd light receiving element DS 1. The information recorded on the DVD can be read by the output signal of the 2 nd photodetector DS 1.

A3 rd beam (λ 3 ═ 785nm) diverging beam emitted from the infrared semiconductor laser beam EP2 is reflected by the prism PS, reflected by the polarization dichroic prism PPS, converted into a parallel beam by the collimator lens CL, converted from linear polarization into circular polarization by a λ/4 wave plate (not shown), and incident on the objective lens OJT. The light beam of the objective lens OBJ 3 rd optical disk dedicated area (the light beam passing through the 1 st optical disk 2 nd optical disk dedicated area and the 1 st optical disk dedicated area is flare-formed to form a spot peripheral portion) is made to form a spot on the information recording surface RL3 of the CD via a protective substrate PL3 having a thickness of 1.2 mm.

The reflected light beam modulated by the information groove on the information recording surface RL3 passes through the objective lens OBJ and the stop ST again, is converted from circular polarization to linear polarization by a λ/4 plate not shown, is converted into a converging light beam by the collimator lens CL, is reflected by the polarization dichroic prism PPS, is reflected 2 times inside the prism, and is then collected by the 3 rd light receiving element DS 2. The information recorded on the CD can be read by the output signal of the 3 rd photo detector DS 2.

Examples

Examples that can be used in the above-described embodiments are explained below. In the following embodiments, since the objective lens is configured by combining a BD/DVD dual-purpose area (an interchangeable area of the objective lens for converging the 1 st light beam passing therethrough to the information recording surface of the BD so as to enable information recording and/or reproduction and converging the 2 nd light beam passing therethrough to the information recording surface of the DVD so as to enable information recording and/or reproduction), a CD dedicated area (a dedicated area of the objective lens for converging the 3 rd light beam passing therethrough to the information recording surface of the CD so as to enable information recording and/or reproduction), and a BD dedicated area (a dedicated area of the objective lens for converging the 1 st light beam passing therethrough to the information recording surface of the BD so as to enable information recording and/or reproduction), the BD/DVD dual-purpose area, the BD dedicated area, and the CD dedicated area are divided into the BD/DVD area, the BD dedicated area, and the CD dedicated area in the lens data table (the shapes of the mother aspherical surfaces of the BD/DVD dual-purpose area, so the same table is used). In the following examples, the objective light source side optical surface is divided into 4 regions or 6 regions, and the optical surface on the optical disk side is not divided and is a common aspherical surface. When the disk-side surface of the objective lens is not made to be a common aspherical surface, there is a possibility that the 1 st and 2 nd light beams passing through the objective lens may be emitted from the disk-side surface of the CD-dedicated area and the 3 rd light beam passing through the objective lens may be emitted from the disk-side surface of the BD/DVD dual-purpose area. The objective optical surface is formed as an aspherical surface axially symmetric about the optical axis, and the aspherical surface is defined by numerical expressions in which the coefficients shown in the table are represented by numerical expressions 1.

[ teaching 1]

Where X (h) is the axis in the optical axis direction (positive in the light traveling direction), κ is the cone constant, and A_iIs the i-th order aspheric coefficient, h is the height from the optical axis, and r is the paraxial radius of curvature.

In the case of the embodiment using the diffraction structure, the optical path difference given to each wavelength beam by the diffraction structure is defined by substituting the numerical expression of the coefficients shown in the table into the optical path difference function of the numerical expression 2.

[ number 2]

λ is the incident beam wavelength, λ B is the normalized wavelength (flame wavelength), dor is the diffraction order, C_iIs the i-th order optical path difference function coefficient.

Example 1

Table 1 shows lens data of example 1. FIG. 6 is a sectional view of an objective lens of example 1. Fig. 7(a) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of using the BD of example 1, fig. 7(b) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of using the DVD of example 1, and fig. 7(c) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of using the CD of example 1. In embodiment 1, as shown in the enlarged view of fig. 6, the 1 st region R1 including the optical axis is a BD/DVD common region, the 2 nd region R2 around the outer side thereof is a CD dedicated region, the 3 rd region R3 around the outer side thereof is a BD/DVD common region, the 4 th region R4 around the outer side thereof is a CD dedicated region, the 5 th region R5 around the outer side thereof is a BD/DVD common region, and the 6 th region R6 around the outer side thereof farthest from the optical axis is a BD dedicated region. The paraxial curvature radius of the mother aspheric surface of the BD/DVD shared area is 0.948mm, the paraxial curvature radius of the mother aspheric surface of the CD dedicated area is 1.347mm, and the difference between the two is 0.398 mm. A diffraction structure (0/1) (0 for BD and 1 for DVD. the same description below) is formed in the BD/DVD common area. The diffraction structure is a 5-step diffraction structure as shown in fig. 2(c), and is composed of 4 steps each of which gives a2 λ 1 optical path difference by 1 step. The values for example 1 are as follows:

φ1＝2.4mm

WD3＝0.2mm

f3＝1.70mm(1.7×f3＝2.890mm)

d＝1.750mm

d/f3＝1.029

cross-sectional ratio (d/dmin) 3.50

Example 2

FIG. 8 is a sectional view of an objective lens of example 2. Fig. 9(a) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of BD use in example 2, fig. 9(b) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of DVD use in example 2, and fig. 9(c) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of CD use in example 2. Example 2 employs the lens data of example 1, having the same number of regions but different region division positions. Other points, including the numerical values of the formulae, are the same as those in example 1, and the description thereof is omitted.

Example 3

FIG. 10 is a sectional view of an objective lens of example 3. Embodiment 3 is different from

embodiments

1 and 2 and is a 4-zone lens, and as shown in the enlarged view of fig. 10, the 1 st zone R1 including the optical axis is a BD/DVD common zone, the 2 nd zone R2 around the outer side thereof is a CD dedicated zone, the 3 rd zone R3 around the outer side thereof is a BD/DVD common zone, and the 4 th zone R4 around the outer side thereof, which is farthest from the optical axis, is a BD dedicated zone. Fig. 11(a) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of BD use in example 3, fig. 11(b) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of DVD use in example 3, and fig. 11(c) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of CD use in example 3. In example 3, the lens data of example 1 was used, but the number of regions and the division positions were different. Other points, including the numerical values of the formulae, are the same as those in example 1, and the description thereof is omitted.

Example 4

The lens data of example 4 are shown in table 2. FIG. 12 is a sectional view of an objective lens of example 4. Fig. 13(a) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of BD use in example 4, fig. 13(b) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of DVD use in example 4, and fig. 13(c) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of CD use in example 4. In embodiment 4, as shown in the enlarged view of fig. 12, the 1 st region R1 including the optical axis is a BD/DVD common region, the 2 nd region R2 around the outer side thereof is a CD dedicated region, the 3 rd region R3 around the outer side thereof is a BD/DVD common region, the 4 th region R4 around the outer side thereof is a CD dedicated region, the 5 th region R5 around the outer side thereof is a BD/DVD common region, and the 6 th region R6 around the outer side thereof farthest from the optical axis is a BD dedicated region. The paraxial radius of curvature of the mother aspheric surface of the BD/DVD common region is 0.955mm, the paraxial radius of curvature of the mother aspheric surface of the CD dedicated region is 1.342mm, and the difference between the two is 0.386 mm. A (1/-2) diffraction structure is formed on the BD/DVD common area. The diffraction structure is a 7-step diffraction structure and is composed of 6 steps. The values for example 3 are as follows:

φ1＝2.4mm

WD3＝0.2mm

f3＝1.71mm(1.7×f3＝2.907mm)

d＝1.750mm

d/f3＝1.023

cross section ratio of 2.350

Example 5

FIG. 14 is a sectional view of an objective lens of example 5. Fig. 15(a) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sine condition (broken line) when used at B D in example 5, fig. 15(b) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sine condition (broken line) when used in DVD in example 5, and fig. 15(c) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sine condition (broken line) when used in CD in example 5. Example 5 employs the lens data of example 4, having the same number of regions but different region division positions. Other points, including the numerical values of the formulae, are the same as those in example 4, and the description thereof is omitted.

Example 6

FIG. 16 is a sectional view of an objective lens of example 6. Embodiment 6 is different from embodiments 4 and 5 and is a 4-zone lens, and as shown in the enlarged view of fig. 16, the 1 st zone R1 including the optical axis is a BD/DVD common zone, the 2 nd zone R2 around the outer side thereof is a CD dedicated zone, the 3 rd zone R3 around the outer side thereof is a BD/DVD common zone, and the 4 th zone R4 around the outer side thereof, which is farthest from the optical axis, is a BD dedicated zone. Fig. 17(a) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of using the BD of example 6, fig. 17(b) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of using the DVD of example 6, and fig. 17(c) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of using the CD of example 6. In example 6, the lens data of example 4 was used, but the number of regions and the division positions were different. Other points, including the numerical values of the formulae, are the same as those in example 4, and the description thereof is omitted.

Example 7

The lens data of example 7 are shown in table 3. FIG. 18 is a sectional view of an objective lens of example 7. Fig. 19(a) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of BD use in example 7, fig. 19(b) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of DVD use in example 7, and fig. 19(c) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of CD use in example 7. In embodiment 7, as shown in the enlarged view of fig. 18, the 1 st region R1 including the optical axis is a BD/DVD common region, the 2 nd region R2 around the outer side thereof is a CD dedicated region, the 3 rd region R3 around the outer side thereof is a BD/DVD common region, the 4 th region R4 around the outer side thereof is a CD dedicated region, the 5 th region R5 around the outer side thereof is a BD/DVD common region, and the 6 th region R6 around the outer side thereof farthest from the optical axis is a BD dedicated region. The paraxial curvature radius of the mother aspheric surface of the BD/DVD shared area is 1.504mm, the paraxial curvature radius of the mother aspheric surface of the CD dedicated area is 1.339mm, and the difference between the two is 0.165 mm. A diffraction structure is formed (2/1) on the BD/DVD common area. This diffraction structure is a flame type diffraction structure as shown in FIG. 2(b), and has a level difference of 2 λ 1. The values for example 7 are as follows:

φ1＝2.4mm

WD3＝0.2mm

f3＝1.71mm(1.7×f3＝2.907mm)

d＝1.750mm

d/f3＝1.023

cross section ratio of 3.624

Example 8

FIG. 20 is a sectional view of an objective lens of example 8. Fig. 21(a) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of using the BD of example 8, fig. 21(b) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of using the DVD of example 8, and fig. 21(c) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of using the CD of example 8. Example 8 employs the lens data of example 7, having the same number of regions but different region division positions. Other points, including the numerical values of the formulae, are the same as those in example 7, and the description thereof is omitted.

Example 9

FIG. 22 is a sectional view of an objective lens of example 9. Embodiment 9 is different from embodiments 7 and 8 and is a 4-zone lens, and as shown in the enlarged view of fig. 22, the 1 st zone R1 including the optical axis is a BD/DVD shared zone, the 2 nd zone R2 around the zone is a CD dedicated zone, the 3 rd zone R3 around the zone is a BD/DVD shared zone, and the 4 th zone R4 around the zone farthest from the optical axis is a BD dedicated zone. Fig. 23(a) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of BD use in example 9, fig. 23(b) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of DVD use in example 9, and fig. 23(c) is a schematic diagram of the longitudinal spherical aberration (solid line) and the sinusoidal condition (broken line) in the case of CD use in example 9. In example 9, the lens data of example 7 was used, but the number of regions and the division positions were different. Other points, including the numerical values of the formulae, are the same as those in example 7, and the description thereof is omitted.

Example 10

The lens data of example 10 are shown in table 4. FIG. 24 is a sectional view of an objective lens of example 10. In embodiment 10, as shown in the enlarged view of fig. 24, the 1 st area R1 including the optical axis is a BD/DVD shared area, the 2 nd area R2 around the area is a CD dedicated area, the 3 rd area R3 around the area is a BD/DVD shared area, and the 4 th area R4 around the area farthest from the optical axis is a BD dedicated area. The paraxial curvature radius of the mother aspheric surface of the BD/DVD shared area is 0.836mm, the paraxial curvature radius of the mother aspheric surface of the CD dedicated area is 1.2475mm, and the difference between the two is 0.4115 mm. A diffraction structure is formed (0/1) on the BD/DVD common area. The values for example 10 are as follows:

φ1＝2.15mm

WD3＝0.2mm

f3＝1.60mm(1.7×f3＝2.720mm)

d＝1.490mm

d/f3 cross-sectional ratio (d/dmin) of 0.9 to 4.52

Example 11

The lens data of example 11 are shown in table 5. FIG. 25 is a sectional view of an objective lens of example 11. In example 11, as shown in the enlarged view of fig. 25, the 1 st region R1 including the optical axis is a BD/DVD shared region, the 2 nd region R2 around the region is a CD dedicated region, the 3 rd region R3 around the region is a BD/DVD shared region, and the 4 th region R4 around the region farthest from the optical axis is a BD dedicated region. The paraxial curvature radius of the mother aspheric surface of the BD/DVD shared area is 0.8721mm, the paraxial curvature radius of the mother aspheric surface of the CD dedicated area is 1.2513mm, and the difference between the paraxial curvature radius and the paraxial curvature radius is 0.3792 mm. A (1/-2) diffraction structure is formed on the BD/DVD common area. The values for example 11 are as follows:

φ1＝2.15mm

WD3＝0.2mm

f3＝1.55mm(1.7×f3＝2.635mm)

d＝1.490mm

d/f3 is 0, cross section ratio (d/dmin) is 3.77

Example 12

The lens data of example 12 are shown in table 6. FIG. 26 is a sectional view of an objective lens of example 12. In embodiment 12, as shown in the enlarged view of fig. 26, the 1 st area R1 including the optical axis is a BD/DVD shared area, the 2 nd area R2 around the area is a CD dedicated area, the 3 rd area R3 around the area is a BD/DVD shared area, and the 4 th area R4 around the area farthest from the optical axis is a BD dedicated area. The paraxial curvature radius of the mother aspheric surface of the BD/DVD shared area is 1.0150mm, the paraxial curvature radius of the mother aspheric surface of the CD dedicated area is 1.1598mm, and the difference between the paraxial curvature radius and the paraxial curvature radius is 0.1448 mm. A diffraction structure is formed (2/1) on the BD/DVD common area. The values for example 12 are as follows:

φ1＝2.15mm

WD3＝0.2mm

f3＝1.63mm(1.7×f3＝2.771mm)

d＝1.490mm

d/f3 is 0, cross section ratio (d/dmin) is 2.52

Fig. 27 to 28 are schematic diagrams illustrating modifications of the objective lens. The region R1 including the optical axis in the modification of fig. 27 is a BD/DVD common region (having a (0/1) diffraction structure), the region R2 around the outer side thereof is a CD dedicated region (refractive surface), the region R3 around the outer side thereof is a BD/DVD common region (having a (0/1) diffraction structure), and the region R4 around the outer side thereof is a BD dedicated region (refractive surface).

Fig. 28 shows a modification. As a modification, the region R1 including the optical axis is a BD/DVD common region (having a (1/-2) diffraction structure), the region R2 around the outer side thereof is a CD dedicated region (refractive surface), and the region R3 around the outer side thereof is a BD/DVD common region (having a (1/-2) diffraction structure).

In another modification of fig. 28, the region R1 including the optical axis is a BD/DVD common region (having a (2/1) diffraction structure), the region R2 around the outer side thereof is a CD dedicated region (refractive surface), and the region R3 around the outer side thereof is a BD/DVD common region (having a (2/1) diffraction structure).

Industrial applicability of the invention

According to the present invention, an objective lens and an optical pickup device suitable for a thin optical disc drive device can be provided.

Description of the symbols

AC two-shaft transmission device

PPS polarization dichroism 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 pick-up device

RL1 information recording surface

RL2 information recording surface

RL3 information recording surface

CN Central area

MD peripheral region

OT most peripheral area

Claims

1. An objective lens for an optical pickup device having a1 st light source for emitting a1 st light beam having a wavelength λ 1, a2 nd light source for emitting a2 nd light beam having a wavelength λ 2(λ 1 < λ 2), a3 rd light source for emitting a3 rd light beam having a wavelength λ 3(λ 2 < λ 3), and an objective lens, wherein the objective lens condenses the 1 st light beam on an information recording surface of a1 st optical disc having a protective layer having a thickness t1 so as to enable information recording and/or reproduction, condenses the 2 nd light beam on an information recording surface of a2 nd optical disc having a protective layer having a thickness t2(t1 < t2) so as to enable information recording and/or reproduction, and condenses the 3 rd light beam on an information recording surface of a3 rd optical disc having a protective layer having a thickness t3(t2 < t3) so as to enable information recording and/or reproduction, the objective lens is characterized in that,

the objective lens is a single lens and,

at least one optical surface has a1 st region including an optical axis, a2 nd region disposed outside the 1 st region, and a3 rd region disposed outside the 2 nd region,

in the region, a region of the objective lens through which the 1 st light beam passes is condensed on the information recording surface of the 1 st optical disc so as to be capable of information recording and/or reproduction, and a region of the objective lens through which the 3 rd light beam passes is condensed on the information recording surface of the 3 rd optical disc so as to be capable of information recording and/or reproduction are different regions.

2. The objective lens according to claim 1, wherein the following equation is satisfied:

0.15(mm)≤WD3≤0.5(mm) (1)，

wherein,

WD 3: working distance of the 3 rd disc in use.

3. The objective lens according to claim 1 or 2, wherein a difference between a paraxial radius of curvature of the parent aspheric surface in a certain region and a paraxial radius of curvature of the parent aspheric surface in another region is 0.1mm or more and 0.7mm or less.

4. The objective lens according to claim 3, wherein in the region, a difference between a paraxial curvature radius of a parent aspherical surface of a region in which the 3 rd light beam passing therethrough is condensed on the information recording surface of the 3 rd optical disc so as to be capable of recording and/or reproducing information and a paraxial curvature radius of a parent aspherical surface of a region in which the 1 st light beam passing therethrough is condensed on the information recording surface of the 1 st optical disc so as to be capable of recording and/or reproducing information or a paraxial curvature radius of a region in which the 2 nd light beam passing therethrough is condensed on the information recording surface of the 2 nd optical disc so as to be capable of recording and/or reproducing information is 0.1mm or more and 0.7mm or less.

5. The objective lens according to any one of claims 1 to 4, comprising a3 rd disc-dedicated area for condensing the 3 rd light beam passing therethrough on an information recording surface of the 3 rd disc so as to enable information recording and/or reproduction, condensing the 1 st light beam not passing therethrough on the information recording surface of the 1 st disc so as to enable information recording and/or reproduction, and condensing the 2 nd light beam not passing therethrough on the information recording surface of the 2 nd disc so as to enable information recording and/or reproduction.

6. The objective lens of claim 5, wherein the 3 rd optical disc specific area is a refractive surface.

7. The objective lens of claim 5 or 6, wherein the number of the 3 rd optical disc-dedicated areas is 1 to 3.

8. The objective lens according to any one of claims 1 to 7, wherein the 1 st area is a1 st optical disc/2 nd optical disc dual-purpose area in which the 1 st light beam that has passed therethrough is condensed on an information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, the 2 nd light beam that has passed therethrough is condensed on an information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction, and the 3 rd light beam that has passed therethrough is condensed on an information recording surface of the 3 rd optical disc so as not to enable information recording and/or reproduction.

9. The objective of claim 8,

the 1 st region has a1 st diffractive configuration,

the 1 st diffractive structure is a structure in which 0 th order diffracted light (transmitted light) generated when the 1 st beam passes through is larger than any other order diffracted light.

10. The objective lens according to any one of claims 1 to 9, wherein the 2 nd area is a3 rd optical disc-dedicated area in which the 3 rd light beam that has passed therethrough is condensed on an information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction, the 1 st light beam that has passed therethrough is condensed on an information recording surface of the 1 st optical disc so as not to enable information recording and/or reproduction, and the 2 nd light beam that has passed therethrough is condensed on an information recording surface of the 2 nd optical disc so as not to enable information recording and/or reproduction.

11. The objective lens according to any one of claims 1 to 10, wherein the 3 rd region is a1 st optical disc/2 nd optical disc dual-purpose region in which the 1 st light beam that has passed therethrough is condensed on an information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, the 2 nd light beam that has passed therethrough is condensed on an information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction, and the 3 rd light beam that has passed therethrough is condensed on an information recording surface of the 3 rd optical disc so as not to enable information recording and/or reproduction.

12. The objective of any one of claims 1 to 11,

the objective lens is provided with a 4 th area outside the 3 rd area, a 5 th area outside the 4 th area, and a 6 th area outside the 5 th area,

the 6 th region is a region on the objective lens farthest from the optical axis,

the 1 st area, the 3 rd area, and the 5 th area are areas for the 1 st optical disc and the 2 nd optical disc, respectively, which focus the 1 st light beam passing therethrough on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, focus the 2 nd light beam passing therethrough on the information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction, and focus the 3 rd light beam not passing therethrough on the information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction,

the 2 nd area and the 4 th area are areas dedicated to the 3 rd optical disc in which the 3 rd light beam that has passed through is condensed on the information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction, the 1 st light beam that has passed through is condensed on the information recording surface of the 1 st optical disc so as not to enable information recording and/or reproduction, and the 2 nd light beam that has passed through is condensed on the information recording surface of the 2 nd optical disc so as not to enable information recording and/or reproduction,

the 6 th area is an area dedicated to the 1 st optical disc, and is configured to focus the 1 st light beam that has passed therethrough on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, focus the 2 nd light beam that has passed therethrough on the information recording surface of the 2 nd optical disc so as not to enable information recording and/or reproduction, and focus the 3 rd light beam that has passed therethrough on the information recording surface of the 3 rd optical disc so as not to enable information recording and/or reproduction.

13. The objective lens according to claim 12, wherein the 6 th region is a refractive surface.

14. The objective of any one of claims 1 to 11,

the objective lens is provided with a 4 th area outside the 3 rd area,

the 4 th region is a region farthest from the optical axis on the objective lens,

the 1 st area and the 3 rd area are areas for the 1 st optical disc and the 2 nd optical disc, respectively, in which the 1 st light beam that has passed therethrough is condensed on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, the 2 nd light beam that has passed therethrough is condensed on the information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction, and the 3 rd light beam that has passed therethrough is condensed on the information recording surface of the 3 rd optical disc so as not to enable information recording and/or reproduction,

the 2 nd area is an area dedicated to the 3 rd optical disc in which the 3 rd light beam that has passed through is condensed on the information recording surface of the 3 rd optical disc so as to enable information recording and/or reproduction, the 1 st light beam that has passed through is condensed on the information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, and the 2 nd light beam that has passed through is condensed on the information recording surface of the 2 nd optical disc so as to enable information recording and/or reproduction,

the 4 th area is an area dedicated to the 1 st optical disc, and is configured to focus the 1 st light beam that has passed therethrough on an information recording surface of the 1 st optical disc so as to enable information recording and/or reproduction, focus the 2 nd light beam that has passed therethrough on an information recording surface of the 2 nd optical disc so as not to enable information recording and/or reproduction, and focus the 3 rd light beam that has passed therethrough on an information recording surface of the 3 rd optical disc so as not to enable information recording and/or reproduction.

15. The objective lens according to claim 14, wherein the 4 th region is a refractive surface.

16. The objective lens according to any one of claims 1 to 15, wherein, in a cross section including the optical axis, there is a height difference between the 1 st region and the 2 nd region, and a portion where the height difference intersects the 1 st region is located on a light source side in the optical axis direction than a portion where the height difference intersects the 2 nd region.

17. The objective of claim 16,

the 1 st area is a1 st optical disc/2 nd optical disc shared area in which the 1 st light beam passing therethrough is condensed on the information recording surface of the 1 st optical disc, the 2 nd light beam passing therethrough is condensed on the information recording surface of the 2 nd optical disc, and the 3 rd light beam passing therethrough is not condensed on the information recording surface of the 3 rd optical disc,

the 2 nd area is a3 rd disc-dedicated area for condensing the 3 rd light beam passing therethrough on the information recording surface of the 3 rd disc, for not condensing the 1 st light beam passing therethrough on the information recording surface of the 1 st disc, and for not condensing the 2 nd light beam passing therethrough on the information recording surface of the 2 nd disc.

18. The objective lens according to any one of claims 1 to 17, wherein the following conditional formula (2) is satisfied:

d/δ≤5 (2)

wherein,

d: on-axis thickness of the objective lens

δ: a minimum thickness of the objective lens in an optical axis direction.

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