JP2009134791A - Optical pickup device and objective optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device and an objective optical element capable of securing magnification of the optimum forward optical system for each of BD and HD while allowing compatibility between BD and HD using the same light beam with one objective optical element. <P>SOLUTION: In the optical pickup device, a condensing optical system includes a correction surface in a region corresponding to a first region of the objective optical element. The correction surface is divided into a plurality of concentric circular regions about the optical axis by level differences. The focal length f1 of the objective optical element for the first light beam during recording and/or reproducing the first optical disk and the focal length f2 of the objective optical element for the first light beam during recording and/or reproducing the second optical disk satisfy a conditional expression (1) of f1<f2. The magnification m11 of the objective optical element for the first light beam during recording and/or reproducing the first optical disk and the magnification m12 of the objective optical element for the first light beam during recording and/or reproducing the second optical disk satisfy a conditional expression (2) of ¾m11-m12¾<0.02. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  Research and development of a high-density optical disk system capable of recording and / or reproducing information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm. Some are progressing rapidly and are already sold as products. As an example of a high-density optical disc, an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity) It is possible to record information of 23 to 27 GB per layer on an optical disc having a diameter of 12 cm, which is the same size as 4, 7 GB), and recording / reproducing information with specifications of NA 0.65 and light source wavelength 405 nm. An optical disk to be used, so-called HD DVD (hereinafter referred to as HD), can record information of 15 to 20 GB per layer on an optical disk having a diameter of 12 cm.

  Here, simply saying that information can be appropriately recorded / reproduced with respect to one of the high-density optical discs is not sufficient as a product of an optical disc player / recorder (optical information recording / reproducing apparatus). At present, based on the reality that optical discs of two standards, BD and HD, are sold together, it is not only possible to record / reproduce information on one high-density optical disc, and the same applies to both high-density optical discs. In addition, making it possible to appropriately record / reproduce information leads to an increase in commercial value as an optical disc player / recorder for high-density optical discs.

Under such circumstances, Patent Document 1 describes a pickup device that enables compatibility between BD and HD with one objective optical element by sorting light beams of the same wavelength using a diffraction effect.
JP 2006-147069 A

  By the way, in recent years, information recording / reproducing apparatuses capable of recording / reproducing information with respect to BD and information recording / reproducing apparatuses capable of recording / reproducing information with respect to HD have been released as products by various companies. In general, in the condensing optical system of the optical pickup device mounted on the HD, the HD optical path magnification is smaller than the BD optical path magnification. This is because the optimal optical path magnification determined by the far-field pattern of the emitted light from the blue-violet semiconductor laser, the numerical aperture and focal length of the objective optical element for each optical disc, the sensor size of the photodetector, etc. is BD and HD. This is because they are different from each other.

  However, since the focal length when using the BD and the focal length when using the HD are almost equal, the objective optical element disclosed in Patent Document 1 can realize the optimum optical path magnification for each of the BD and HD. There is a risk of disappearing. In addition, even if the focal length when using BD and the focal length when using HD are approximately equal, by using objective optical elements having different magnifications when using BD and HD, It is possible to realize an optical pickup device having an optimum outward optical system magnification for each. However, in such a case, it is necessary to provide a coupling lens or the like that can be largely displaced in the direction of the optical axis between the light source and the objective optical element. May cause high.

  In consideration of the above-mentioned problems, the present invention enables compatibility between one objective optical element of BD and HD that uses the same light beam, and provides an optimum optical path magnification for each of BD and HD. An object of the present invention is to provide an optical pickup device and an objective optical element.

The optical pickup device according to claim 1 includes a first light source that emits a first light beam having a wavelength λ1 (380 nm <λ1 <450 nm), and an objective for condensing the first light beam on an information recording surface of an optical disc. A condensing optical system having an optical element; and condensing the first light flux on an information recording surface of a first optical disc having a protective layer having a thickness of t1, and the first light flux has a thickness of t2 (t1 <t2 In an optical pickup device that records and / or reproduces information by focusing on the information recording surface of the second optical disc having a protective layer)
The objective optical element is divided into at least a first region including the optical axis and a second region around the first region, and the first light flux that has passed through the first region is the first optical disc. The first light flux that has been focused on the information recording surface of the second optical disc and used for recording and / or reproducing information and passed through the second area is reflected on the information recording surface of the first optical disc. Collected and used for recording and / or reproducing information,
The condensing optical system has a correction surface in a region corresponding to the first region of the objective optical element, and the correction surface has a plurality of concentric annular zones centering on an optical axis divided by steps. Have
The focal length f1 of the objective optical element of the first light flux during recording and / or reproduction of the first optical disc, and the objective optical element of the first light flux during recording and / or reproduction of the second optical disc The focal length f2 satisfies the following conditional expression (1), the magnification m11 of the objective optical element of the first light flux at the time of recording and / or reproduction of the first optical disk, and the recording of the second optical disk And / or the magnification m12 of the objective optical element of the first light flux during reproduction satisfies the following conditional expression (2).
f1 <f2 (1)
│m11-m12│ <0.02 (2)
However, the signs of m11 and m12 are “positive” when the first light beam is incident on the objective optical element in a finite convergent light state, and the first light beam is infinite parallel light with respect to the objective optical element. The case where the first light beam is incident on the objective optical element in the state of finite divergent light is defined as “negative”.

  According to the present embodiment, by satisfying the expression (1), the outward optical system magnification at the time of recording and / or reproduction of the second optical disc is larger than the outward optical system magnification at the time of recording and / or reproduction of the first optical disc. Therefore, it is possible to realize an optical pickup device having an optimum optical path magnification for each of the first optical disc and the second optical disc. Further, by setting the magnification of the objective optical element of the first light beam and the magnification of the objective optical element of the second light beam so as to satisfy the expression (2), the optical axis direction of the drive system such as the coupling lens is set. Therefore, the optical pickup device can be simplified and downsized.

An optical pickup device according to a second aspect of the present invention is characterized in that, in the first aspect of the invention, the following conditional expression is satisfied.
1.05 × f1 <f2 <1.25 × f1 (3)

  In the optical pickup device according to the present invention, it is preferable that the focal length of the objective optical element satisfies the expression (3). If the lower limit of equation (3) is not exceeded, the outward optical system magnification for each of the first optical disc and the second optical disc can be set to a more optimal value. Further, if the upper limit of the expression (3) is not exceeded, the off-axis characteristics of the objective optical element with respect to the second optical disk can be improved, and the tolerance for the mounting accuracy of the first light source can be relaxed. The production yield can be improved.

An optical pickup device according to a third aspect of the invention according to the first or second aspect satisfies the following conditional expression.
−0.01 <m11 <0.01 (4)
-0.01 <m12 <0.01 (5)

  In the optical pickup device according to the present invention, it is preferable that the magnification of the objective optical element satisfies the expressions (4) and (5). Equations (4) and (5) mean that a substantially parallel light beam is incident on the objective optical element during recording and / or reproduction of the first optical disc and recording and / or reproduction of the second optical disc. To do. Thereby, aberrations that occur when the objective optical element is shifted in the direction perpendicular to the optical axis can be reduced, so that an optical pickup device having excellent tracking characteristics can be provided.

  According to a fourth aspect of the present invention, there is provided the optical pickup device according to any one of the first to third aspects, wherein the first luminous flux that has passed through the plurality of annular zones of the correction surface is recorded on the information on the first optical disc. The first optical disk area that is condensed so that information can be recorded and / or reproduced on the surface and the first luminous flux that has passed through is not condensed on the information recording surface of the second optical disk, and the first optical disk that has passed through. A second light beam is not condensed on the information recording surface of the first optical disc, and the first light beam that has passed through is condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc. And an optical disk area.

  When realizing the compatibility between BD and HD using the diffraction effect, for example, the utilization efficiency of light passing from the light source to the one optical disk through the diffraction structure (the utilization efficiency here is the optical surface on the light source side of the objective optical element) Assuming that the ratio of the amount of light that contributes to the spot on the optical disk) is 40% (theoretically does not exceed 50%) with respect to the amount of light incident on the optical disk, the optical disk passes through the same diffraction structure toward the photodetector. The light utilization efficiency (the utilization efficiency here is the ratio of the amount of light that contributes to the spot on the photodetector with respect to the amount of light incident on the optical surface on the optical disk side of the objective optical element) is 40%. (Utilization efficiency here is the ratio of the amount of light that contributes to the spot on the photodetector with respect to the amount of light incident on the optical surface on the light source side of the objective optical element), and only 16% of light can be used. , Light utilization effect There is a problem in terms of. According to the present embodiment, it is possible to provide an optical pickup device that can be compatible with a single objective optical element of BD and HD that use the same light beam at a low cost and that has a high light utilization efficiency.

  According to a fifth aspect of the present invention, in the optical pickup device according to the fourth aspect, the objective optical element has a ring zone of 3 or more and 10 or less in total of the first region and the second region. It is characterized by.

  According to the present embodiment, it is possible to provide an optical pickup device that is easy to manufacture and that can suppress a reduction in light utilization efficiency due to an effect in the case where the shape of a step is not accurately transferred due to a manufacturing error. it can.

  An optical pickup device according to a sixth aspect of the present invention is the optical recording apparatus according to any one of the first to fifth aspects, wherein the plurality of annular zones has an information recording surface of the first optical disc when the first light flux is incident thereon. N-order diffracted light that is condensed so that information can be recorded and / or reproduced, and m-order diffracted light that is condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc. It is an optical path difference providing structure to be generated.

On the other hand, as in the invention described in claim 6, when realizing the compatibility of BD and HD using the diffraction effect, the side lobe is connected to the objective optical element dedicated to BD or the objective optical element dedicated to HD. Since it can be reduced to the same extent, crosstalk due to the influence of side lobes can be reduced, and an optical pickup device having excellent recording / reproducing characteristics can be provided. In addition, in the region where the reflected light from the pits formed on the recording surface of the optical disc (the zero-order light that is not diffracted) and the reflected diffracted light (± first-order light) overlap, the order of the zero-order light and the ± first-order light Since there is no region where the phase difference is not shifted by half a wavelength, it is possible to prevent a decrease in the effective amount of light that becomes the modulation signal, and it is possible to maintain good jitter. From this point also, the information recording / reproducing characteristics are excellent. Can be maintained.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the objective optical element is a single lens, and the objective optical element has the correction surface. Features.

  The optical pickup device according to claim 8 is the invention according to any one of claims 1 to 6, wherein the objective optical element has a flat plate-like first optical element and a second optical element that is a lens, The first optical element has the correction surface.

  An optical pickup device according to a ninth aspect includes the second light source that emits a second light flux having a wavelength λ2 (630 nm <λ2 <670 nm) in the invention according to any one of the first to eighth aspects, Information is recorded and / or reproduced by condensing two light beams on an information recording surface of a third optical disk having a protective layer having a thickness t3 (t1 <t3).

  According to a tenth aspect of the present invention, there is provided the optical pickup device according to any one of the first to ninth aspects, further comprising a third light source that emits a third light flux having a wavelength λ3 (760 nm <λ3 <820 nm). Information is recorded and / or reproduced by focusing three light beams on an information recording surface of a fourth optical disk having a protective layer having a thickness t4 (t3 <t4).

  An optical pickup device according to an eleventh aspect is the optical pickup device according to the tenth aspect, wherein the optical pickup device condenses the first light flux on information recording surfaces of the first optical disc and the second optical disc. An objective optical element; and a second objective optical element that condenses the second light flux on the information recording surface of the third optical disc and condenses the third light flux on the information recording surface of the fourth optical disc. It is characterized by that.

The objective optical element according to claim 12 is a first light source that emits a first light flux having a wavelength λ1 (380 nm <λ1 <450 nm), and an objective for condensing the first light flux on an information recording surface of an optical disc. A condensing optical system having an optical element; and condensing the first light flux on an information recording surface of a first optical disc having a protective layer having a thickness of t1, and the first light flux has a thickness of t2 (t1 <t2 In the objective optical element for an optical pickup device that records and / or reproduces information by focusing on the information recording surface of the second optical disk having the protective layer of
The objective optical element is divided into at least a first region including the optical axis and a second region around the first region, and the first light flux that has passed through the first region is the first optical disc. The first light flux that has been focused on the information recording surface of the second optical disc and used for recording and / or reproducing information and passed through the second area is reflected on the information recording surface of the first optical disc. Collected and used for recording and / or reproducing information,
The objective optical element has a correction surface in a region corresponding to the first region, and the correction surface has a plurality of concentric annular zones around an optical axis divided by steps.
The focal length f1 of the objective optical element of the first light flux during recording and / or reproduction of the first optical disc, and the objective optical element of the first light flux during recording and / or reproduction of the second optical disc The focal length f2 satisfies the following conditional expression (1), the magnification m11 of the objective optical element of the first light flux at the time of recording and / or reproduction of the first optical disk, and the recording of the second optical disk And / or the magnification m12 of the objective optical element of the first light flux during reproduction satisfies the following conditional expression (2).
f1 <f2 (1)
│m11-m12│ <0.02 (2)
However, the signs of m11 and m12 are “positive” when the first light beam is incident on the objective optical element in a finite convergent light state, and the first light beam is infinite parallel light with respect to the objective optical element. The case where the first light beam is incident on the objective optical element in the state of finite divergent light is defined as “negative”.

The objective optical element described in claim 13 is characterized in that, in the invention described in claim 12, the following conditional expression is satisfied.
1.05 × f1 <f2 <1.25 × f1 (3)

The objective optical element according to claim 14 is characterized in that, in the invention according to claim 12 or 13, the following conditional expression is satisfied.
−0.01 <m11 <0.01 (4)
-0.01 <m12 <0.01 (5)

  The objective optical element according to claim 15 is the information recording apparatus according to any one of claims 12 to 14, wherein the first luminous flux that has passed through the plurality of annular zones of the correction surface is recorded on the information on the first optical disc. The first optical disk area that is condensed so that information can be recorded and / or reproduced on the surface and the first luminous flux that has passed through is not condensed on the information recording surface of the second optical disk, and the first optical disk that has passed through. A second light beam is not condensed on the information recording surface of the first optical disc, and the first light beam that has passed through is condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc. And an optical disk area.

  The objective optical element according to claim 16 is the invention according to claim 15, wherein the objective optical element has a ring zone of 3 or more and 10 or less in total of the first region and the second region. It is characterized by.

  The objective optical element according to claim 17 is the information recording surface of the first optical disc according to any one of claims 12 to 16, wherein the plurality of annular zones have the first optical flux incident thereon. N-order diffracted light that is condensed so that information can be recorded and / or reproduced, and m-order diffracted light that is condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc. It is an optical path difference providing structure to be generated.

  The objective optical element according to claim 18 is the invention according to any one of claims 12 to 17, wherein the objective optical element is a single lens, and the objective optical element has the correction surface. Features.

  The objective optical element according to claim 19 is the invention according to any one of claims 12 to 17, wherein the objective optical element includes a flat plate-like first optical element and a second optical element that is a lens. The first optical element has the correction surface.

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

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

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

  In the BD, information is recorded / reproduced by an objective optical element having an NA of 0.85, and the thickness of the protective substrate is about 0.1 mm. In the HD, information is recorded / reproduced by an objective optical element having an NA of 0.65 to 0.67, and the thickness of the protective substrate is about 0.6 mm. Furthermore, DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective optical element having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm. ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like are included. Further, in this specification, a CD is a CD series optical disc in which information is recorded / reproduced by an objective optical element having an NA of about 0.45 to 0.51 and the protective substrate has a thickness of about 1.2 mm. It is a generic name and includes CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW, and the like. As for the recording density, the recording density of BD is the highest, followed by HD, DVD, and CD in that order.

  In addition, regarding the thicknesses t1, t2, t3, and t4 of the protective substrate, it is preferable to satisfy the following conditional expressions (6), (7), (8), and (9), but is not limited thereto.

0.0750 mm ≦ t1 ≦ 0.1125 mm (6)
0.5mm ≦ t2 ≦ 0.7mm (7)
0.5mm ≦ t3 ≦ 0.7mm (8)
1.0mm ≦ t4 ≦ 1.3mm (9)

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

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

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

  The condensing optical system has an objective optical element. The objective optical element focuses the first light flux on the information recording surface of the first optical disc so that information can be recorded / reproduced, and the first light flux is recorded / reproduced on the information recording surface of the second optical disc. Concentrate as much as possible. The condensing optical system may include only the objective optical element, but may include a coupling lens such as a collimator lens and a beam expander in addition to the objective optical element. The coupling lens is a single lens or a lens group that is disposed between the objective optical element and the light source and changes the divergence angle of the light beam. The beam expander is a lens group that is disposed between the objective optical element and the light source and changes the diameter of the light beam without changing the divergence angle of the light beam. The collimator lens is a kind of coupling lens, and is a lens that changes a light beam incident on the collimator lens into parallel light. A coupling lens such as a collimator lens can also be used as the divergence changing means. Further, the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like. May be. In addition to the objective optical elements for the first optical disk and the second optical disk, the condensing optical system includes a second objective optical element for the third optical disk, a second objective optical element for the fourth optical disk, or a third optical element. You may have the 2nd objective optical element combined with an optical disk and a 4th optical disk. The objective optical element for the first optical disk and the second optical disk may also serve as the objective optical element for the third optical disk and / or the fourth optical disk.

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

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

  The objective optical element necessary for reproducing and / or recording information on the first optical disk is NA1, and the objective optical necessary for reproducing and / or recording information on the second optical disk is NA1. The image-side numerical aperture of the element is NA2 (NA1> NA2), and the image-side numerical aperture of the objective optical element necessary for reproducing and / or recording information on the third optical disk is NA3 (NA2 ≧ NA3), Let NA4 (NA3> NA4) be the image-side numerical aperture of the objective optical element necessary for reproducing and / or recording information on the fourth optical disk. NA1 is preferably 0.8 or more and 0.9 or less. NA2 and NA3 are preferably 0.55 or more and 0.7 or less. NA4 is preferably 0.4 or more and 0.55 or less.

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

  The first light beam that has passed through the first area of the objective optical element is used for recording / reproduction of the first optical disk and the second optical disk, and the first light beam that has passed through the second area is used for recording / reproduction of the first optical disk. However, it is not used for recording / reproduction of the second optical disc. That is, it can be said that the first area is a so-called shared area used for both the first optical disk and the second optical disk, and the second area is a so-called dedicated area used only for the first optical disk. The first area is preferably an area of NA2 or less, and the second area is preferably an area larger than NA2 and NA1 or less. For example, when the first optical disk is a BD and the second optical disk is an HD, the first area is preferably an area having an image-side numerical aperture (NA) of 0.65 or less, and the second area is an image. It is preferable that the side numerical aperture is greater than 0.65 and 0.85 or less.

  The objective optical element may have a compatible optical path difference providing structure that enables use of the third optical disk and / or the fourth optical disk. Further, the objective optical element may have an optical path difference providing structure for correcting the aberration change at the time of temperature change or wavelength change.

  The condensing optical system of the optical pickup device has a correction surface in a region corresponding to the first region of the objective optical element. The correction surface has a plurality of concentric ring zones centered on the optical axis divided by steps. The objective optical element preferably has a correction surface. However, in addition to the objective optical element, the objective optical element may have a correction element, and the correction element may have a correction surface. In this case, the objective optical element and the correction element perform the same movement in the direction orthogonal to the optical axis during tracking. Note that a region corresponding to the outside of the correction surface, that is, a region corresponding to the second region of the objective optical element may be a simple refracting surface.

  Examples of the correction surface are roughly divided into three examples.

  A first example of the correction surface is a case where a plurality of annular zones on the correction surface includes a first optical disk area and a second optical disk area. The first optical disk area condenses the passed first light beam so that information can be recorded / reproduced on the information recording surface of the first optical disk, while the passed first light beam passes the information recording surface of the second optical disk. The region above does not collect light. In the second optical disk area, conversely, the passed first light beam is not collected on the information recording surface of the first optical disk, and the passed first light beam is recorded / recorded on the information recording surface of the second optical disk. It is an area where light is collected so that it can be reproduced. The first optical disk area and the second optical disk area are preferably provided alternately, but the present invention is not limited to this. The most central area including the optical axis may be the first optical disk area or the second optical disk area.

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

  In the first example, it is preferable that both the first optical disk area and the second optical disk area on the correction surface are refracting surfaces. In this case, the first optical disk area passes through the refraction action. The light flux that has been collected is condensed on the information recording surface of the first optical disc, and the light flux that has passed through the second optical disc area is condensed on the information recording surface of the second optical disc. Such a configuration is preferable because a loss of light amount can be reduced when reflected light on the information recording surface of the optical disc passes through the correction surface. In this case, a light receiving element having a relatively low sensitivity can be used as the light receiving element, so that the cost of the optical pickup device can be reduced.

  One of the first optical disk area and the second optical disk area transmits the first light beam (has no power with respect to the first light beam), and the other is the optical disk with respect to the passed first light beam. Aberrations may be corrected (having power with respect to the first light flux) so that information can be recorded / reproduced on the information recording surface. In particular, the objective optical element has a first optical element that is a correction element and a second optical element that is an aspheric lens, and only the aspheric lens protects the first optical disk or the second optical disk. In the case where the aspherical lens has an optical performance capable of condensing the first light beam on the information recording surface via the substrate, it is preferable to adopt the above-described configuration. For example, when the aspherical lens is designed so that only the aspherical lens can focus the first light beam on the information recording surface with respect to the BD, the first optical disk (BD) area of the correction surface is It is preferable that the second optical disc (HD) region transmits one light beam and has a structure that corrects aberration so that the first light beam is condensed on the information recording surface of HD. .

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

  Next, an example of the second correction surface will be described. In this example, the plurality of regions of the correction surface condense the first light beam that has passed through the information recording surface of the first optical disc, and the first light beam that has passed through also be collected on the information recording surface of the second optical disc. This is a case including a light emitting region. The partial region of the correction surface may be an example of the first correction surface described above, and the remaining region may be the region shown in the second example, or all of the plurality of regions of the correction surface may be included. The region may be the region shown in the second example.

  In this second example, the first light flux that has passed through the area remains focused on the information recording surface of the first optical disc to some extent, but is condensed to such an extent that it can be recorded / reproduced. Even on the information recording surface of the second optical disc, although aberration remains to some extent, the light is condensed to such an extent that recording / reproduction is possible.

  In the above case, the first optical disk priority area and the second optical disk priority area may be included in the plurality of areas on the correction surface. The first optical disc priority area concentrates the passed first light flux so that information can be recorded / reproduced on the information recording surface of the first optical disc, and the passed first light flux is the information recording surface of the second optical disc. This is a region where aberration is corrected so that information can be recorded / reproduced on the top, but aberration is reduced on the information recording surface of the first optical disc. On the other hand, in the second optical disc priority area, the passed first light flux is condensed so that information can be recorded / reproduced on the information recording surface of the first optical disc, and the passed first light flux is information on the second optical disc. This is a region where aberration is corrected so that information can be recorded / reproduced on the recording surface, but aberration is reduced on the information recording surface of the second optical disc. The first optical disc priority area and the second optical disc priority area are preferably provided alternately, but the present invention is not limited to this. The most central area including the optical axis may be the first optical disk priority area or the second optical disk priority area.

  In the third example of the correction surface, a plurality of annular zones on the correction surface condense so that information can be recorded and / or reproduced on the information recording surface of the first optical disc when the first light flux enters. This is a case where the optical path difference providing structure generates n-th order diffracted light and m-th order diffracted light that is collected so that information can be recorded and / or reproduced on the information recording surface of the second optical disc. Here, among the diffracted lights emitted from the optical path difference providing structure, it is preferable that the order of the diffracted light with the largest amount of light is n, and the order of the diffracted light with the next largest amount of light is m. The order of diffracted light with a large amount of light may be m, and the order of diffracted light with the next largest amount of light may be n. As combinations of (n, m), combinations of (0, +1), (+1, +2), (+2, +3), (+1, -1), (+2, -2), (+3, -3) Is a preferred example.

  In addition, the optical path difference providing structure in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.

  The optical path difference providing structure preferably has a plurality of concentric annular zones centered on the optical axis. Each annular zone is preferably separated by a step. Further, the optical path difference providing structure is preferably a type of structure in which a step-like pattern having a cross-sectional shape including the optical axis is repeated. A plurality of optical path difference providing structures may be superposed on the same region. “Superimposition” means literally overlapping. In this specification, even if a certain foundation structure and another foundation structure are provided on other optical surfaces, or even if a certain foundation structure and another foundation structure are on the same optical surface, they are different areas. In the case where there is no overlapping region, it is not superposition in this specification.

  Next, details of the configuration of the first and second examples of the correction surface described above will be described below.

  When the objective optical element is composed of a single lens, the objective optical element may have a correction surface. In this case, a step may be provided in the aspherical first region of the single objective lens, thereby dividing the plurality of annular zones, and the second region may be left as a refractive surface. It is preferable that the first optical disk area and the second area in the first area have the same aspheric shape, and the second optical disk area has a different aspheric shape.

  Further, from the viewpoint of facilitating the production of the objective optical element, it is preferable that the number of annular zones including the first region and the second region is 3 or more and 10 or less. When the number of ring zones is 3, as shown in FIG. 1, for example, the center area including the optical axis is the first optical disk area BA1, the surrounding area is the second optical disk area HA, and the surrounding area is the outermost area. An example in which the outer peripheral area (second area) is the first optical disk area BA2 can be considered. As a result of earnest research, the present inventor has made the number of annular zones combining the first region and the second region from the viewpoint of reducing the side rope of the spot and facilitating the manufacture of the objective optical element. Has been found to be preferably 5 or more and 10 or less. More preferably, the number of ring zones is 6 or more and 10 or less. In addition, also when the objective optical element as mentioned later has the 1st optical element by the side of a light source, and the 2nd optical element by the side of an optical disk, the said range of preferable ring zones is applicable.

Next, when performing recording and / or reproduction of the second optical disc, the light flux that has passed through the first optical disc area is prevented so that the light flux that has passed through the first optical disc area does not cover the defocus area. It is preferable that the objective optical element has a flare on the information recording surface of the second optical disc. Specifically, “to flare” means that light that has passed through the first optical disk area on the information recording surface of the second optical disk is distributed in the donut-shaped area. In particular, when the first optical disc is a BD and the second optical disc is an HD, it is preferable that the inner diameter of the donut-shaped region be Φ0.030 mm or more. In the case of a plurality of donut-shaped regions, it is preferable that the smallest diameter among the inner diameters of each donut-shaped region is Φ0.030 mm or more. In order to generate a good flare when the first optical disc is a BD and the second optical disc is an HD, the working distance (WD _BD ) of the objective optical element in the first optical disc (BD); the value of the difference between the working distance of the objective optical element (WD _HD) in the second optical disk _{(HD) (WD BD -WD HD} ), - 0.36 (mm) or more, to 0.17 (mm) or less Is preferred. More preferably, it is -0.10 (mm) or more and 0.15 (mm) or less. From another viewpoint, it is preferable that the following conditional expression (10) is satisfied.
2 ・ f1 ・ NA1 '> 2 ・ f2 ・ NA2' (10)
F1 is the focal length of the first optical disk area of the objective optical element in the first light flux, f2 is the focal distance of the second optical disk area of the objective optical element in the first light flux, and NA1 'is the first optical disk of the objective optical element. The maximum numerical aperture satisfying the sine condition of the area for use and the maximum numerical aperture satisfying the sine condition of the area for the second optical disk of the NA2 ′ optical element is shown. In addition, also when the objective optical element which has the 1st optical element by the side of a light source and the 2nd optical element by the side of an optical disk which are mentioned later is mentioned, the preferable conditions which generate | occur | produce said flare are applicable.

  In order to obtain an appropriate spot diameter, the following conditions are preferably satisfied. The following conditions are not limited to the case where the objective optical element is a single lens, but also when the objective optical element includes the first optical element on the light source side and the second optical element on the optical disk side, Conditions are applicable.

  First, when the region closest to the center including the optical axis is the second optical disc region, it is preferable that the maximum image-side numerical aperture of the first optical disc region is smaller than NA1. The maximum effective diameter of the first optical disk area is preferably smaller than 2 · f1 · NA1. Note that f1 is the focal length of the first optical disk area of the objective optical element in the first light flux, and NA1 is the image-side numerical aperture defined by the standard required for recording and / or reproduction of the first optical disk. Indicates. For example, when the first optical disk is a BD and the second optical disk is an HD, the maximum image-side numerical aperture of the first optical disk area is preferably smaller than 0.85. In addition, it is preferable that the maximum effective diameter of the first optical disk area is smaller than 2 · f1 · 0.85.

  Next, when the area closest to the center including the optical axis is the first optical disk area, the maximum image-side numerical aperture of the second optical disk area is preferably smaller than NA2. Further, it is preferable that the maximum effective diameter of the second optical disk area is smaller than 2 · f2 · NA2. Note that f2 is the focal length of the second optical disk area of the objective optical element in the first light flux, and NA2 is the image-side numerical aperture defined by the standard required for recording and / or reproduction of the second optical disk. Indicates. For example, when the first optical disk is a BD and the second optical disk is an HD, the maximum image-side numerical aperture of the second optical disk area is preferably smaller than 0.65. The maximum effective diameter of the second optical disk area is preferably smaller than 2 · f2 · 0.65.

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

In the case of the configuration in which the first optical disc area and the second optical disc area have different aspherical shapes in ₁ ), the working distance (WD ₁ ) of the objective optical element during recording and / or reproduction of the first optical disc, 2 Design so that the absolute value (| WD ₁ -WD ₂ |) of the difference from the working distance (WD ₂ ) of the objective optical element during recording and / or reproduction of the optical disc is 0.1 (mm) or more. Is preferred.

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

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

  Further, from the viewpoint of reducing the thickness of a single objective optical element, a step is provided on the surface of the optical surface of the objective optical element, and the step is a region on the far side of the region closer to the optical axis with the step as a boundary. It is desirable that the level difference be shorter than the optical path. For example, the example shown in FIG. 3 is an example in which a step for thinning the objective optical element is further provided in the first optical disc area, which is the central area, with respect to the objective optical element shown in FIG. Even when such a step is provided, it is desirable that the spherical aberration and the sine condition are corrected to a necessary level.

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

The sum Δ of the lengths of coding in the optical axis direction of all the steps provided on the optical surface of the objective optical element (sign is a region where the optical path of each step is closer to the optical axis than the region on the far side It is desirable that the following conditional expression (11) is satisfied in the case where it is shortened.
0.1 mm ≦ Δ ≦ 1.0 mm (11)
If it is above the lower limit, the effect of thinning is great, and if it is below the upper limit, the sine condition can be corrected to the required level while reducing the thickness. Note that “the sum of the coding lengths” means that when both a positive length value and a negative length value exist, they are added as they are. For example, if the positive length value is +1 and the negative length value is −0.5, (+1) + (− 0.5) = + 0.5, ie, +0. 5 is “the sum of the lengths of encoding”.

  As shown in FIG. 1, when a single objective optical element is provided with a first optical disk area and a second optical disk area, a large step (for example, a step of 50 μm or more in the optical axis direction) at the boundary between the areas. ) May occur. Such a large step, when the objective optical element is molded using a mold, may become a hindrance when the optical element is removed from the mold, making the objective optical element more difficult to manufacture. Therefore, when a large step (for example, a step of 50 μm or more in the optical axis direction) occurs at the boundary of each region, the inclined surface is inclined with respect to the optical axis at the step portion so that it can be easily removed from the mold. (Taper) is preferably provided. For example, in the case where the intermediate region has a shape that is recessed in the optical axis direction as shown in FIG. 1, as shown in FIG. 4, only the surface SS1 in which the step surface faces the optical axis is inclined. The surface SS2 in which the step surface faces in the direction opposite to the optical axis is not inclined, so that the influence on the optical performance can be minimized, and the loss of light amount due to the taper can be reduced. It is preferable because it can be easily removed from.

  Furthermore, an optical path difference providing structure for the purpose of compatibility with the third optical disk and the fourth optical disk is used for the structure of the correction surface, and an optical path difference for correcting aberration changes that occur when temperature changes or wavelength changes. The providing structure may be overlapped. One preferable example is that an optical path difference providing structure is provided in which a correction surface is provided in the first region of the objective optical element, and only the second region is corrected for a change in aberration caused by a temperature change or a wavelength change. And an optical path difference providing structure in the first optical disc area in the second area and the first area. In the above description, the example in which the optical path difference providing structure is provided on the optical surface on the light source side is described. However, the optical path difference providing structure for the above-described purpose may be provided on the optical surface on the optical disc side. .

  When the objective optical element includes the first optical element on the light source side and the second optical element on the optical disk side, the first optical element may have a correction surface. In this case, the first optical element is preferably a flat plate, and the second optical element is preferably a lens having an aspheric surface. However, the present invention is not limited to this, and the first optical element has an aspheric surface. Also good. As a preferable example, for example, a step is provided in a region corresponding to the first region of the flat plate-like first optical element, thereby dividing the region into a plurality of regions, and a region corresponding to the second region of the first optical element is The configuration is a plane. Furthermore, an optical path difference providing structure for the purpose of compatibility with the third optical disk and the fourth optical disk is used for the structure of the correction surface, and an optical path difference for correcting aberration changes that occur when temperature changes or wavelength changes. The providing structure may be overlapped. One preferred example is that a correction surface is provided in the first region of the first optical element, and aberrations that occur when the temperature changes or the wavelength changes only in the second region of the first optical element and / or the second optical element. In this configuration, an optical path difference providing structure for the purpose of correcting the change is provided.

  When the flat first optical element has a correction surface, the light source side surface of the first optical element may have a correction surface. Preferably, the optical disk side of the first optical element (second optical element) The surface (which can also be said to be a side) has a correction surface. This configuration is preferable because the light beam incident on the optical disk and the light beam reflected from the optical disk can be easily prevented from being off-axis even if they are not exactly the same. Further, correction surfaces may be provided on both surfaces of the first optical element.

  When the correction surface is provided on the flat plate-like first optical element, it is preferable that the plurality of regions of the correction surface have a flat plate portion region and an aspherical region. I can't. Any of the plurality of regions of the correction surface provided in the flat plate-like first optical element may have an aspherical surface.

  When the correction surface of the flat plate-like first optical element has a flat plate portion region and an aspherical region, the flat plate portion region is one of the first optical disc region and the second optical disc region. It is preferable that the aspherical region is the other.

  A preferred example in the case where the first and second correction surfaces are provided on the flat plate-like first optical element will be described with reference to FIG. As shown in FIG. 5, in this example, the objective optical element OE includes a flat plate-shaped first optical element L1, a second optical element L2 that is an aspherical lens, a first optical element L1, and a second optical element. It has a frame HE to hold and fix. The second optical element L2 is designed so as to be able to focus the first light beam on the information recording surface of the BD by itself. A correction surface CS is provided in a region of NA 0.65 or less that is the first region A1 of the first surface S1 of the first optical element L1. A region larger than NA 0.65 that is the second region A2 of the first surface S1 of the first optical element L1 and NA 0.85 or less is a flat surface.

  The correction surface CS is divided into a plurality of regions having a region BA on a plane and a region HA having an aspherical surface by steps. The area BA on the plane and the area HA having the aspherical surface are alternately provided. The area BA on the plane is a first optical disk (BD) area, and the area HA having an aspherical surface is a second optical disk (HD) area. Since the second optical element is designed to be optimized for BD, the first light beam that has passed through the first optical element, that is, the first light beam that has passed through the BD area BA, which is an area on the plane, It is condensed on the information recording surface of the BD by the element. On the other hand, since the first light beam is not condensed on the HD information recording surface only by the second optical element, the first light beam passes through the HD area HA of the first optical element, thereby giving an aberration due to the aspherical shape. Is done. As a result, the first optical element and the second optical element jointly give aberration, so that the first light flux that has passed through the HD region is condensed on the HD information recording surface. Note that the HD region having an aspherical shape has a structure in which the step is directed opposite to the optical axis near the optical axis, and the step is directed toward the optical axis in a region away from the optical axis. . In addition, an aspherical surface having no step is provided in the transition region therebetween.

  That is, when BD recording / reproduction is performed, the light beam that has passed through the BD area BA and the second area A2 in the first area A1 of the first optical element L1 is reflected on the BD information recording surface by the second optical element. The light flux that has been focused on and passed through the HD area HA of the first area A1 of the first optical element L1 is not collected on the information recording surface of the BD. On the other hand, when recording / reproducing HD, the first light flux that has passed through the HD area HA of the first area A1 of the first optical element L1 is condensed on the information recording surface of the HD by the second optical element. Thus, the first light flux that has passed through the BD area BA and the second area of the first area A1 of the first optical element is not condensed on the HD information recording surface.

  Next, the step amount of the step in the first and second examples of the correction surface described above will be described. Examples of the level difference are roughly divided into three types.

The first example is a case where the step amount of the step on the correction surface is a step amount that gives an optical path difference of a times the wavelength λ1 to the first light flux. Note that a is an arbitrary positive integer other than 0. In this case, the step amount d1 can be expressed by the following equation (12).
d1 = a · λ1 / (n−1) (12)
Here, n is the refractive index of the optical element having a correction surface for the light flux with wavelength λ1.

  For example, when the objective optical element is a single lens optimized for BD, when the first light beam is condensed on the information recording surface of the BD, almost no aberration occurs as shown in FIG. Next, when the first light beam is condensed on the HD information recording surface using only the second optical element, a large aberration occurs as shown in FIG. The aberration diagram shown in FIG. 6 is an aberration diagram of only the first region.

  Therefore, as the objective optical element, an objective optical element having a flat plate-like first optical element having a correction surface as shown in FIG. 5 and a second optical element which is a lens optimized for BD is used, and the amount of the step is set. 7 satisfies the expression (11), the aberration in the first region is as shown in FIG. FIG. 7A shows the aberration in BD, and FIG. 7B shows the aberration in HD. In this case, a = 1.

  Note that the step amount need not be equal for all steps on the correction surface. For example, the step in the region near the optical axis of the correction surface may be increased, and the step in the region far from the optical axis of the correction surface may be decreased. Or the reverse may be sufficient. For example, while the amount of the step satisfies the equation (12), a = 2 is set for the step in the region near the optical axis of the correction surface, and a = 1 is set for the step in the region far from the optical axis of the correction surface. In this case, the aberration in the first region is as shown in FIG. FIG. 8A shows the aberration in BD, and FIG. 8B shows the aberration in HD.

The second example is a case where the step amount of the step on the correction surface is a step amount that gives an optical path difference b times the wavelength λ1 to the first light flux. Note that b is 0 or the sum of any positive integer and x. x is an arbitrary value between 0.4 and 0.6. In this case, the step amount d2 can be expressed by the following equation (13).
d1 = b · λ1 / (n−1) (13)

  As the objective optical element, an objective optical element having a flat plate-shaped first optical element having a correction surface as shown in FIG. 5 and a second optical element which is a lens optimized for BD is used, and the step amount is ( When the expression (13) is satisfied, the aberration in the first region is as shown in FIG. FIG. 9A shows the aberration in BD, and FIG. 9B shows the aberration in HD. In this case, b = 1 + 0.5.

A third example is a case where the step amount of the step on the correction surface is a step amount that gives an optical path difference c times the wavelength λ1 to the first light flux. Note that c is 0 or the sum of any positive integer and y. y is an arbitrary value greater than 0 and less than 0.4 or greater than 0.6 and less than 1. In this case, the step amount d3 can be expressed by the following equation (14).
d1 = c · λ1 / (n−1) (14)

  As the objective optical element, an objective optical element having a flat plate-shaped first optical element having a correction surface as shown in FIG. 5 and a second optical element which is a lens optimized for BD is used, and the step amount is ( When the expression (14) is satisfied, the aberration in the first region is as shown in FIG. FIG. 10A shows the aberration in BD, and FIG. 10B shows the aberration in HD. In this case, c = 1 + 0.8.

  Further, the correction surface is not of a type having a first optical disc (BD) region and a second optical disc (HD) region, and a plurality of regions of the correction surface are passed through the first light flux that has passed through any region. 1. Condensed light on the information recording surface of one optical disc (although some aberrations remain) so that it can be recorded / reproduced, and the first light flux that has passed through also on the information recording surface of the second optical disc (some aberrations remain) However, when the light is collected so as to be recorded / reproduced, the aberration in the first region is as shown in FIG. FIG. 11 (a) shows the aberration in BD, and FIG. 11 (b) shows the aberration in HD. In this case, since the same amount of aberration occurs in both BD and HD, the first optical disk priority area and the second optical disk priority area do not exist in this example.

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

As a first example, for example, a third light beam having a wavelength λ3 emitted from a third light source is condensed on the information recording surface of the fourth optical disk by the objective optical element, and the wavelength λ3 is a wavelength λ1. If it is an approximate integer multiple of 1 and an attempt is made to enable compatibility with the fourth optical disk by the diffraction structure, 1) it becomes difficult to make the diffraction angles different between the first light flux of λ1 and the third light flux of λ3, 2) When a special diffraction structure that can make the diffraction angles of the first light flux and the third light flux different is used, there is a problem that the light use efficiency is lowered. Therefore, a fourth optical disk area may be provided in the first area in addition to the first optical disk area and the second optical disk area. For example, as shown in FIG. 12, the fourth optical disk area CD, the first optical disk area BD, the second optical disk area HD, and the second area outside of the fourth optical disk area CD in order from the inner area including the optical axis. An example in which the first optical disk area BD is provided can be considered. Note that the fact that the wavelength λ3 is a substantially integer multiple of the wavelength λ1 means that the following conditional expression (15) is satisfied.
(M−0.2) · λ1 ≦ λ3 ≦ (m + 0.2) · λ1 (15)
Note that m represents an arbitrary positive integer of 2 or more.

  In addition, when the fourth optical disk area as described above is provided, the maximum image-side numerical aperture of the fourth optical disk area is smaller than the numerical aperture that is standard for recording and / or reproduction of the fourth optical disk. It is preferable to do. Therefore, it is preferable that the maximum effective diameter of the fourth optical disk area is smaller than 2 · f4 · NA4. Note that f4 represents the focal length of the fourth optical disk area of the objective optical element in the third light flux, and NA4 represents the image-side numerical aperture defined by the standard required for recording and / or reproduction of the fourth optical disk. For example, when the fourth optical disk is a CD, the maximum image-side numerical aperture of the fourth optical disk area is preferably smaller than 0.45. More preferably, it is 0.43 or less. When the fourth optical disk is a CD, the maximum effective diameter of the fourth optical disk area is preferably smaller than 2 · fCD · 0.45, and more preferably 2 · fCD · 0.43 or less. Note that fCD represents the focal length of the CD-dedicated region of the objective optical element in the CD light flux.

  Further, by providing an optical path difference providing structure in at least one of the fourth optical disk area, the first optical disk area, and the second optical disk area in the first area, the recording of the third optical disk (for example, DVD) is performed. And / or playback may be enabled. For example, as shown in FIG. 13, in order from the inner area including the optical axis, the fourth optical disk area CD, the first optical disk area BD, the second optical disk area HD, and the second area outside thereof. Optical path difference providing structure DVD that enables recording and / or reproduction of the third optical disk in the first optical disk area BD, the fourth optical disk area CD, the inner first optical disk area BD, and the second optical disk area HD. An example of providing the can be considered.

When the objective optical element of the present invention is applied to a hybrid optical disk in which recording layers of a plurality of types of optical disks including the first optical disk and the second optical disk are laminated on one optical disk, the objective optical element of the first optical disk It is preferable that the working distance (WD ₁ ) and the working distance (WD ₂ ) of the objective optical element in the second optical disc are different. When the first optical disc is BD and the second optical disc is HD, that is, when a hybrid optical disc in which BD and HD are laminated is used, it is more preferable to set the value of the difference between these working distances to (WD ₁ −WD ₂ ), preferably 50 μm or more and 250 μm or less. More preferably, it is 100 μm or more and 250 μm or less. An example in which recording layers of a plurality of types of optical disks are stacked on a single optical disk is a hybrid disk in which recording layers of BD / HD / DVDs are stacked on one side as disclosed in JP-A-2007-42254. Can be mentioned.

  As shown in FIG. 14, the single objective optical element OL1 of the present invention for the first optical disc and the second optical disc and the objective optical for another optical disc (for example, the third optical disc and / or the fourth optical disc). A lens unit in which the element OL2 is integrally formed may be used. As shown in FIG. 14, the integrally formed lens unit is a case where the first objective optical element OL1 and the second objective optical element OL2 are fused (for example, the first objective optical element). And a second objective optical element as shown in FIG. 15 or FIG. 16, and a lens unit having a second objective optical element and a second objective optical element. The optical elements may be integrated by molding separately, and then fitting, adhering or engaging with each other.

  FIG. 15 shows an example of a lens unit in which the first objective optical element and the second objective optical element are engaged and integrally formed. The second objective optical element OL2 made of plastic forms an opening HL having a stepped portion ST in the rectangular plate-shaped flange portion FL2, and the flange portion FL1 is held by the stepped portion ST in the opening HL. In this way, the first objective optical element OL1 made of glass or plastic of the present invention is assembled from the optical axis direction and integrated by adhesion or the like, and the first objective optical element OL1 and the second objective optical element are integrated. A lens unit OE in which OL2 is arranged in parallel is formed.

  FIG. 16 shows another example of a lens unit in which the first objective optical element and the second objective optical element are engaged and integrally formed. The second objective optical element OL2 made of plastic forms a notch CT having a stepped portion ST in the rectangular plate-like flange portion FL2, and the flange portion FL1 is held by the stepped portion ST in the notch CT. In this way, the first objective optical element OL1 made of glass or plastic of the present invention is assembled from the direction orthogonal to the optical axis and integrated by adhesion or the like, and the first objective optical element OL1 and the second objective optical are integrated. A lens unit OE in which the elements OL2 are arranged in parallel is formed.

  As shown in FIG. 17, the flange portion FL1 of the first objective optical element OL1 may be supported on the upper surface of the flange portion FL2 without forming the step ST in the opening HL or the notch CT. Alternatively, although not shown, the first objective optical element OL1 made of glass or plastic and the second objective optical element OL2 made of plastic may be integrated by assembling to a holding member which is a separate member. good. In any case, it is preferable that the holding member has an opening, and the objective lens unit is fitted therein.

Incidentally, the focal length f1 of the objective optical element of the first light flux during recording and / or reproduction of the first optical disc and the focal length f2 of the objective optical element of the first light flux during recording and / or reproduction of the second optical disc. Preferably satisfies the following conditional expression (1). Further, it is preferable that the following conditional expression (1) is satisfied both during recording and / or reproduction of the first optical disk and during recording and / or reproduction of the second optical disk. Moreover, it is preferable to satisfy the following conditional expression (2).
f1 <f2 (1)
│m11-m12│ <0.02 (2)
However, the signs of m11 and m12 are “positive” when the first light beam is incident on the objective optical element in a finite convergent light state, and the first light beam is infinite parallel light with respect to the objective optical element. The case where the first light beam is incident on the objective optical element in the state of finite divergent light is defined as “negative”.

Moreover, it is preferable to satisfy the following formula.
1.05 × f1 <f2 <1.25 × f1 (3)

Moreover, it is more preferable when the following formula is satisfied.
1.10 × f1 <f2 <1.20 × f1 (3 ′)

Furthermore, it is more preferable when the following formula is satisfied.
│m11-m12│ <0.01 (2 ')

The magnification of the objective optical element is s ′ /, where s is the distance from the object side principal point of the objective optical element to the object point, and s ′ is the distance from the image side principal point of the objective optical element to the image point. defined by s. Here, s and s ′ are based on the object side principal point and the image side principal point, respectively. That is, when a finite divergent light beam is incident on the objective optical element, the sign of s is “+”, and when a finite convergent light beam is incident on the objective optical element, the sign of s is “−”.

For example, when recording and / or reproducing a first optical disk, the first light beam is incident on the objective optical element as infinite parallel light, and when recording and / or reproducing the second optical disk, the first light beam is incident on the objective optical element. As an example, a preferred embodiment is a mode in which the light is incident. In the case of this aspect, it is preferable to satisfy the following conditional expressions (4) and (5).
−0.01 <m11 <0.01 (4)
-0.01 <m12 <0.01 (5)

  The forward optical system magnification of the condensing optical system is the distance from the object side principal point to the object point in the outward path of the condensing optical system, and the distance from the image side principal point to the image point in the outward path of the condensing optical system. Where S ′ is defined as S ′ / S. Here, S and S ′ are based on the object side principal point and the image side principal point, respectively. Since the condensing optical system is an inverted system, the sign of the forward optical system magnification of the condensing optical system is negative.

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

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

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

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

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

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 18 shows that information can be appropriately recorded and / or reproduced on the first optical disc BD, the second optical disc HD, the third optical disc DVD, and the fourth optical disc CD. It is a figure which shows schematically the structure of optical pick-up apparatus PU1 of this Embodiment. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. The present invention is not limited to the present embodiment.

  The optical pickup device PU1 includes a first objective optical element OL1 for BD / HD, a second objective optical element OL2 for CD / DVD, a dichroic mirror DM having a first reflecting surface RP1 and a second reflecting surface RP2, λ / 4-wavelength plate QWP, coupling lens CL composed of negative lens L1 and positive lens L2, actuator ACT for displacing positive lens L2 in the direction of the optical axis, polarization beam splitter PBS, laser beam with wavelength λ1 = 405 nm (first A semiconductor laser LD1 (first light source) that emits a light beam), a semiconductor laser (second light source) that emits a laser beam (second light beam) having a wavelength λ2 = 650 nm, and a laser beam (third light beam) having a wavelength λ3 = 785 nm. 2 laser, 1 package 2L1P, and sensor lens S, in which a semiconductor laser (third light source) emitting light is housed in a common package , And a light receiving element PD for receiving the light beam reflected from the BD information recording surface RL1, HD information recording surface RL2, DVD information recording surface RL3, CD information recording surface RL4. The actuator ACT that displaces the positive lens L2 in the optical axis direction is mainly used when performing an interlayer jump in a multilayer optical disc having a plurality of information recording surfaces.

  Here, an example of a single lens is shown as the first objective optical element OL1, but instead of this objective optical element, an objective optical element comprising a plurality of optical elements as shown in FIG. 1 is used. May be. As the second objective optical element OL2, a well-known objective optical element for DVD / CD compatibility can be used. As described above, the configuration of the optical pickup device can be simplified if the light beam having the wavelength λ1 is incident on the first objective optical element OL1 and the light beams having the wavelengths λ2 and λ3 are incident on the second objective optical element OL2.

  The optical surface of the first objective optical element OL1 is divided into a first region including the optical axis and a second region around the first region with a numerical aperture NA of 0.65 as a boundary. A correction surface is provided in the first region. The correction surface has a plurality of concentric annular zones centered on the optical axis divided by the steps. In this case, the plurality of annular zones on the correction surface are condensed so that the passed first light beam can be recorded / reproduced on the information recording surface of the BD, and the passed first light beam is recorded on the information record of the second optical disc. The area for the first optical disc that is not condensed on the surface and the first light flux that has passed through are not condensed on the information recording surface of the first optical disc, and the first light flux that has passed through is not recorded on the information recording surface of the second optical disc. And a second optical disc area that collects light so that recording / reproduction can be performed. Alternatively, a diffractive structure that is an optical path difference providing structure may be provided on the correction surface. In this case, when the first light beam is incident on the diffractive structure, the nth-order diffracted light that is condensed so that information can be recorded / reproduced on the information recording surface of the BD, and information recording / recording on the information recording surface of the HD The m-th order diffracted light is collected so that it can be reproduced.

The focal length f1 of the first objective optical element OL1 with one light beam of wavelength λ1 during recording / reproduction of BD and the focal length f2 of the first objective optical element OL1 with one light beam of wavelength λ1 during recording / reproduction of HD. Satisfies the following conditional expression (1). Also, the magnification m11 of the first objective optical element OL1 with one light beam of wavelength λ1 during recording / reproduction of BD and the magnification m12 of the first objective optical element OL1 with one light beam of wavelength λ1 during recording / reproduction of HD. Satisfies the following conditional expression (2).
f1 <f2 (1)
│m11-m12│ <0.02 (2)
However, the signs m11 and m12 are “positive” when the first light beam is incident on the front first objective optical element OL1 in the state of finite convergent light, and the first light beam is incident on the first objective optical element OL1. The case where the light enters in the state of infinite parallel light is defined as “zero”, and the case where the first light beam enters the first objective optical element OL1 in the state of finite divergent light is defined as “negative”.

  A case of recording / reproducing BD will be described. First, after moving the positive lens L2 in the optical axis direction by the actuator ACT to a position where the first light beam emitted from the positive lens L2 becomes a parallel light beam, the blue-violet semiconductor laser LD1 emits light (the positive lens at this time). The position of L2 is the first position). The divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD1 passes through the dichroic prism DP and the polarization beam splitter PBS, and is converted into a parallel light beam by the coupling lens CL, and then λ / 4 wavelength. The linearly polarized light is converted into circularly polarized light by the plate QWP, passes through the first reflecting surface RP1 of the dichroic mirror DM, is reflected by the second reflecting surface RP2, and the diameter of the light beam is regulated by a diaphragm (not shown), and the first objective optical element OL1 As a result, the spot is formed on the information recording surface RL1 of the BD via the protective substrate PL1 having a thickness of 0.1 mm.

  At this time, a part of the light beam that has passed through the first region of the first objective optical element OL1 and the light beam that has passed through the second region are condensed on the information recording surface RL1 of the BD to form a spot.

  The reflected light beam modulated by the information pits on the information recording surface RL1 passes through the first objective optical element OL1 and the diaphragm again, and then is reflected by the second reflecting surface RP1 of the dichroic mirror DM and passes through the first reflecting surface RP2. , Converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, converged by the coupling lens CL, reflected by the polarization beam splitter PBS, and then given astigmatism by the sensor lens SL. It converges on the light receiving surface of the PD. Then, using the output signal of the light receiving element PD, the information recorded on the BD can be read by focusing or tracking the first objective optical element OL1 by an actuator (not shown).

  Next, a case where HD recording / reproduction is performed will be described. First, after the positive lens L2 is moved to the first position by the actuator ACT, the blue-violet semiconductor laser LD1 is caused to emit light. The divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD1 passes through the dichroic prism DP and the polarization beam splitter PBS, and is converted into a parallel light beam by the coupling lens CL, and then λ / 4 wavelength. The linearly polarized light is converted into circularly polarized light by the plate QWP, passes through the first reflecting surface RP1 of the dichroic mirror DM, is reflected by the second reflecting surface RP2, and the diameter of the light beam is regulated by a diaphragm (not shown). Accordingly, the spot is formed on the HD information recording surface RL2 via the protective substrate PL2 having a thickness of 0.6 mm.

  At this time, a light beam that has passed through the first region of the first objective optical element OL1 and is different from the light beam condensed on the BD is condensed on the HD information recording surface RL2 to form a spot. Further, since the light beam that has passed through the second region of the first objective optical element OL1 has a large spherical aberration, it is not condensed on the RL2 on the HD information recording surface but becomes a flare component, so that the aperture corresponding to the aperture of the HD A limiting element is not necessary.

  The reflected light beam modulated by the information pits on the information recording surface RL2 passes through the first objective optical element OL1 and the diaphragm again, and then is reflected by the second reflecting surface RP1 of the dichroic mirror DM and passes through the first reflecting surface RP2. , Converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, converged by the coupling lens CL, reflected by the polarization beam splitter PBS, and then given astigmatism by the sensor lens SL. It converges on the light receiving surface of the PD. Then, using the output signal of the light receiving element PD, the information recorded on the HD can be read by causing the first objective optical element OL1 to be focused or tracked by an actuator (not shown).

  Next, a case where DVD recording / reproduction is performed will be described. First, the positive lens L2 is displaced in the optical axis direction by the actuator ACT so that the second light beam (λ1 = 650 nm) emitted from the red semiconductor laser of the two lasers 1 package 2L1P passes through the positive lens L2 and becomes a parallel light beam. After that (the position of the positive lens L2 at this time is the second position), the red semiconductor laser of the two-laser one package 2L1P is caused to emit light. The divergent light beam of the second light beam (λ1 = 650 nm) emitted from the red laser diode of 2 lasers 1 package 2L1P is reflected by the dichroic prism DP, passes through the polarization beam splitter PBS, and is converted into a parallel light beam by the coupling lens CL. Then, the light is converted from linearly polarized light to circularly polarized light by the λ / 4 wavelength plate QWP, reflected by the first reflecting surface RP1 of the dichroic mirror DM, the light beam diameter is regulated by the diaphragm (not shown), and the second objective optical element OL2 The spot is formed on the information recording surface RL3 of the DVD through the protective substrate PL3 having a thickness of 0.6 mm.

  The reflected light beam modulated by the information pits on the information recording surface RL3 passes through the second objective optical element OL2 and the diaphragm again, and is then reflected by the first reflecting surface RP1 of the dichroic mirror DM, and is reflected by the λ / 4 wavelength plate QWP. After being converted from circularly polarized light into linearly polarized light, converged by the coupling lens CL and reflected by the polarizing beam splitter PBS, astigmatism is given by the sensor lens SL and converges on the light receiving surface of the light receiving element PD. . Then, using the output signal of the light receiving element PD, the information recorded on the DVD can be read by causing the second objective optical element OL2 to be focused or tracked by an actuator (not shown).

  Next, a case where CD recording / reproduction is performed will be described. The positive lens L2 is displaced in the optical axis direction by the actuator ACT so that the third light beam (λ1 = 785 nm) emitted from the infrared laser diode of the two lasers 1 package 2L1P becomes a parallel light beam after passing through the positive lens L2. After (the position of the positive lens L2 at this time is the third position), the infrared laser diode of the two lasers 1 package 2L1P is caused to emit light. Note that the third position of the positive lens L2 is closer to the dichroic mirror DM than the second position. The divergent light beam of the third light beam (λ3 = 785 nm) emitted from the infrared laser diode of 2 laser 1 package 2L1P is reflected by the dichroic prism DP, passes through the polarization beam splitter PBS, and is converted into a parallel light beam by the coupling lens CL. Then, the light is converted from linearly polarized light to circularly polarized light by the λ / 4 wavelength plate QWP, reflected by the first reflecting surface RP1 of the dichroic mirror DM, the light beam diameter thereof is regulated by the diaphragm (not shown), and the second objective optical element OL2 Thus, the spot is formed on the information recording surface RL4 of the CD via the protective substrate PL4 having a thickness of 1.2 mm.

  The reflected light beam modulated by the information pits on the information recording surface RL4 is again transmitted through the second objective optical element OL2 and the aperture, and then reflected by the first reflecting surface RP1 of the dichroic mirror DM, and is reflected by the λ / 4 wavelength plate QWP. After being converted from circularly polarized light into linearly polarized light, converged by the coupling lens CL and reflected by the polarizing beam splitter PBS, astigmatism is given by the sensor lens SL and converges on the light receiving surface of the light receiving element PD. . Then, using the output signal of the light receiving element PD, the information recorded on the CD can be read by causing the second objective optical element OL2 to be focused or tracked by an actuator (not shown).

(Example)
Next, examples that can be used in the above-described embodiment will be described. Each of the following examples is a single lens objective optical element and is made of plastic. The first optical disc is BD, and the second optical disc is HD. The optical path difference providing structure provided in the embodiments described below can be expressed by the following optical path difference function φ (mm).
[Optical path difference function]
φ = λ / λ _B × dor × (B ₂ y ² + B ₄ y ⁴ + B ₆ y ⁶ + B ₈ y ⁸ + B ₁₀ y ¹⁰ )
However,
φ: optical path difference function λ: wavelength of light beam incident on the diffractive structure λ _B : manufacturing wavelength dor: diffraction order of diffracted light used for recording / reproducing with respect to the optical disk y: distances B ₂ , B ₄ , B ₆ from the optical axis , B ₈ , B ₁₀ : Diffraction surface coefficients

The optical surface of the objective optical element is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in the table are substituted into the following aspherical expression.
[Aspherical expression]
^{z = (y 2 / R)} / [1 + √ {1- (K + 1) (y / R) 2}] + A 4 y 4 + A 6 y 6 + A 8 y 8 + A 10 y 10 + A 12 y 12 + A 14 y 14 + A ₁₆ y ¹⁶ + A ₁₈ y ¹⁸ + A ₂₀ y ²⁰
However,
z: Aspherical shape (distance in the direction along the optical axis from the apex of the aspherical surface)
y: distance from the optical axis R: radius of curvature K: conic coefficient _{A 4, A 6, A 8} , A 10, A 12, A 14, A 16, A 18, A 20: aspherical coefficients

In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented using E (for example, 2.5 × E−3).

Example 1
Table 1 shows lens data of Example 1. In Example 1, the optical surface on the object side includes the optical axis with the position of the numerical aperture NA 0.65 corresponding to the effective diameter of the second optical disk (position of height 1.300 mm from the optical axis) as a boundary. The area is divided into one area and a second area around the first area. This first region is provided with a correction surface, and the correction surface has five concentric annular zones centered on the optical axis divided by the steps. In these five annular zones, the center area including the optical axis is the second optical disk dedicated area, and from there toward the outside in the optical axis orthogonal direction, the first optical disk dedicated area, the second optical disk dedicated area, A first optical disk dedicated area and a second optical disk dedicated area are provided. A first optical disc dedicated area as a second area is formed outside the first area.

  In Example 1, the ratio of the focal length f2 of the objective optical element when the second optical disc is used to the focal length f1 of the objective optical element when the first optical disc is used is set to 1.13, so that the BD is used. And an optical pickup device each having an optimum optical path magnification when using HD. In addition, by setting the magnification when using the first optical disk to 0 and setting the magnification when using the second optical disk to 0, an optical pickup device with good tracking characteristics can be realized.

(Example 2)
Table 2 shows lens data of Example 2. In Example 2, the optical surface on the object side includes the optical axis with the numerical aperture NA 0.65 corresponding to the effective diameter of the second optical disc as a boundary (position with a height of 1.205 mm from the optical axis). The area is divided into one area and a second area around the first area. The first area is provided with a correction surface, and the correction surface is focused so that information can be recorded and / or reproduced on the information recording surface of the first optical disc when the first light beam enters. Optical path difference providing structure for generating 0th-order diffracted light (that is, light that is not subjected to diffraction action) and 1st-order diffracted light that is condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc The diffraction structure is formed. A first optical disc dedicated area as a second area is formed outside the first area, and an optical path difference providing structure is not formed in the second area.

In Example 2, the ratio of the focal length f2 of the objective optical element when the second optical disc is used to the focal length f1 of the objective optical element when the first optical disc is used is set to 1.17, so that the BD is used. And an optical pickup device each having an optimum optical path magnification when using HD. In addition, by setting the magnification when using the first optical disk to 0 and setting the magnification when using the second optical disk to 0, an optical pickup device with good tracking characteristics can be realized.
(Example 3)
Table 3 shows lens data of Example 3. In Example 3, the optical surface on the object side includes the optical axis with the position of the numerical aperture NA 0.65 corresponding to the effective diameter of the second optical disc (the position having a height of 1.000 mm from the optical axis) as a boundary. The area is divided into one area and a second area around the first area. The first area is provided with a correction surface, and the correction surface has two concentric ring zones centered on the optical axis divided by the steps. In these two annular zones, the central area including the optical axis is the first optical disk dedicated area, and the outer side in the direction orthogonal to the optical axis is the second optical disk dedicated area. A first optical disc dedicated area as a second area is formed outside the first area.

  In Example 3, the ratio of the focal length f2 of the objective optical element when the second optical disc is used to the focal length f1 of the objective optical element when the first optical disc is used is set to 1.10, so that the BD is used. And an optical pickup device each having an optimum optical path magnification when using HD. In addition, by setting the magnification when using the first optical disk to 0 and setting the magnification when using the second optical disk to 0, an optical pickup device with good tracking characteristics can be realized.

Example 4
Table 4 shows lens data of Example 4. In Example 4, the optical surface on the object side includes the optical axis with the position of the numerical aperture NA 0.65 corresponding to the effective diameter of the second optical disc (the position having a height of 1.000 mm from the optical axis) as a boundary. The area is divided into one area and a second area around the first area. This first region is provided with a correction surface, and the correction surface has five concentric annular zones centered on the optical axis divided by the steps. In these five annular zones, the center area including the optical axis is the second optical disk dedicated area, and from there toward the outside in the optical axis orthogonal direction, the first optical disk dedicated area, the second optical disk dedicated area, A first optical disk dedicated area and a second optical disk dedicated area are provided. A first optical disc dedicated area as a second area is formed outside the first area.

  In Example 4, the ratio of the focal length f2 of the objective optical element when the second optical disc is used to the focal length f1 of the objective optical element when the first optical disc is used is set to 1.10, so that the BD is used. And an optical pickup device each having an optimum optical path magnification when using HD. In addition, by setting the magnification when using the first optical disk to 0 and setting the magnification when using the second optical disk to 0, an optical pickup device with good tracking characteristics can be realized.

(Example 5)
Table 5 shows lens data of Example 5. In Example 4, the optical surface on the object side includes the optical axis with the position of the numerical aperture NA 0.65 corresponding to the effective diameter of the second optical disc (the position having a height of 0.880 mm from the optical axis) as a boundary. The area is divided into one area and a second area around the first area. The first area is provided with a correction surface, and the correction surface has two concentric ring zones centered on the optical axis divided by the steps. In these two annular zones, the central area including the optical axis is the first optical disk dedicated area, and the outer side in the direction orthogonal to the optical axis is the second optical disk dedicated area. A first optical disc dedicated area as a second area is formed outside the first area.

  In Example 5, the ratio of the focal length f2 of the objective optical element when the second optical disk is used to the focal length f1 of the objective optical element when the first optical disk is used is set to 1.06, so that the BD is used. And an optical pickup device each having an optimum optical path magnification when using HD. In addition, by setting the magnification when using the first optical disk to 0 and setting the magnification when using the second optical disk to 0, an optical pickup device with good tracking characteristics can be realized.

It is sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is a figure which shows a part of cross section of an example of the objective optical element which concerns on this invention. It is sectional drawing of another example of the objective optical element which concerns on this invention. FIG. 5A is an aberration diagram when an objective optical element optimized for BD is used. It is an aberration diagram (a)-(b) at the time of using an example of the objective optical element which concerns on this invention. FIG. 6 is aberration diagrams (a) to (b) when another example of the objective optical element according to the present invention is used. FIG. 6 is aberration diagrams (a) to (b) when another example of the objective optical element according to the present invention is used. FIG. 6 is aberration diagrams (a) to (b) when another example of the objective optical element according to the present invention is used. FIG. 6 is aberration diagrams (a) to (b) when another example of the objective optical element according to the present invention is used. It is the schematic at the time of seeing an example of the objective optical element which concerns on this invention from an optical axis direction. It is the schematic at the time of seeing an example of the objective optical element which concerns on this invention from an optical axis direction. It is sectional drawing of an example of the lens unit containing the objective optical element which concerns on this invention. It is a schematic perspective view of an example of the lens unit containing the objective optical element which concerns on this invention. It is a schematic perspective view of an example of the lens unit containing the objective optical element which concerns on this invention. It is a part of sectional drawing of an example of the lens unit containing the objective optical element which concerns on this invention. It is a schematic block diagram of the optical pick-up apparatus using the objective optical element which concerns on this invention.

Explanation of symbols

2L1P 2 laser 1 package A1 1st area A2 2nd area L1 1st optical element L2 2nd optical element BA BD exclusive area HA HD exclusive area OA Optical axis CS Correction surface DM Dichroic mirror HE Frame body OL Objective optical element S1 1st Optical surface S2 Second optical surface PU1 Optical pickup device LD1 Blue-violet semiconductor laser ACT Actuator PBS Polarizing beam splitter PBS
PD light receiving element SL sensor lens CL coupling lens PL1 to PL4 protective substrate RL1 to RL4 information recording surface QWP λ / 4 wavelength plate

Claims (19)

A condensing optical system having a first light source that emits a first light flux having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the first light flux on an information recording surface of an optical disc; The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the information on the second optical disk having the protective layer having the thickness t2 (t1 <t2) is collected. In an optical pickup device that records and / or reproduces information by focusing on a recording surface,
The objective optical element is divided into at least a first region including the optical axis and a second region around the first region, and the first light flux that has passed through the first region is the first optical disc. The first light flux that has been focused on the information recording surface of the second optical disc and used for recording and / or reproducing information and passed through the second area is reflected on the information recording surface of the first optical disc. Collected and used for recording and / or reproducing information,
The condensing optical system has a correction surface in a region corresponding to the first region of the objective optical element, and the correction surface has a plurality of concentric annular zones centering on an optical axis divided by steps. Have
The focal length f1 of the objective optical element of the first light flux during recording and / or reproduction of the first optical disc, and the objective optical element of the first light flux during recording and / or reproduction of the second optical disc The focal length f2 satisfies the following conditional expression (1), the magnification m11 of the objective optical element of the first light flux at the time of recording and / or reproduction of the first optical disk, and the recording of the second optical disk And / or the magnification m12 of the objective optical element of the first light flux during reproduction satisfies the following conditional expression (2).
f1 <f2 (1)
│m11-m12│ <0.02 (2)
However, the signs of m11 and m12 are “positive” when the first light beam is incident on the objective optical element in a finite convergent light state, and the first light beam is infinite parallel light with respect to the objective optical element. The case where the first light beam is incident on the objective optical element in the state of finite divergent light is defined as “negative”. The optical pickup device according to claim 1, wherein the following conditional expression is satisfied.
1.05 × f1 <f2 <1.25 × f1 (3) The optical pickup device according to claim 1, wherein the following conditional expression is satisfied.
−0.01 <m11 <0.01 (4)
-0.01 <m12 <0.01 (5)   The plurality of annular zones on the correction surface condenses the first luminous flux that has passed so that information can be recorded and / or reproduced on the information recording surface of the first optical disc. The area for the first optical disc that is not condensed on the information recording surface of the second optical disc and the first luminous flux that has passed through are not condensed on the information recording surface of the first optical disc, and the first luminous flux that has passed through is The optical pickup device according to claim 1, further comprising a second optical disc area that collects information so that information can be recorded and / or reproduced on an information recording surface of the second optical disc. .   5. The optical pickup device according to claim 4, wherein the objective optical element has a ring zone of 3 or more and 10 or less in total of the first region and the second region.   The plurality of annular zones include an n-order diffracted light that is condensed so that information can be recorded and / or reproduced on an information recording surface of the first optical disc when the first light flux is incident thereon, and the second optical disc The light according to claim 1, wherein the light path difference providing structure generates m-order diffracted light that is condensed so that information can be recorded and / or reproduced on the information recording surface. Pickup device.   The optical pickup device according to claim 1, wherein the objective optical element is a single lens, and the objective optical element has the correction surface.   The objective optical element has a flat plate-like first optical element and a second optical element that is a lens, and the first optical element has the correction surface. The optical pickup device described.   An information recording surface of a third optical disc having a second light source that emits a second light beam having a wavelength λ2 (630 nm <λ2 <670 nm) and having a protective layer having a thickness t3 (t1 <t3). 9. The optical pickup device according to claim 1, wherein information is recorded and / or reproduced by condensing light.   An information recording surface of a fourth optical disc having a third light source that emits a third light beam having a wavelength λ3 (760 nm <λ3 <820 nm) and having a protective layer having a thickness t4 (t3 <t4). 10. The optical pickup device according to claim 1, wherein information is recorded and / or reproduced by condensing light. The optical pickup device is:
The objective optical element that focuses the first light flux on the information recording surfaces of the first optical disc and the second optical disc;
And a second objective optical element for condensing the second light beam on the information recording surface of the third optical disk and condensing the third light beam on the information recording surface of the fourth optical disk. The optical pickup device according to claim 10. A condensing optical system having a first light source that emits a first light flux having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the first light flux on an information recording surface of an optical disc; The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the information on the second optical disk having the protective layer having the thickness t2 (t1 <t2) is collected. In an objective optical element for an optical pickup device that records and / or reproduces information by focusing on a recording surface,
The objective optical element is divided into at least a first region including the optical axis and a second region around the first region, and the first light flux that has passed through the first region is the first optical disc. The first light flux that has been focused on the information recording surface of the second optical disc and used for recording and / or reproducing information and passed through the second area is reflected on the information recording surface of the first optical disc. Collected and used for recording and / or reproducing information,
The objective optical element has a correction surface in a region corresponding to the first region, and the correction surface has a plurality of concentric annular zones around an optical axis divided by steps.
The focal length f1 of the objective optical element of the first light flux during recording and / or reproduction of the first optical disc, and the objective optical element of the first light flux during recording and / or reproduction of the second optical disc The focal length f2 satisfies the following conditional expression (1), the magnification m11 of the objective optical element of the first light flux at the time of recording and / or reproduction of the first optical disk, and the recording of the second optical disk The objective optical element, wherein the magnification m12 of the objective optical element of the first light flux satisfies the following conditional expression (2) during reproduction.
f1 <f2 (1)
│m11-m12│ <0.02 (2)
However, the signs of m11 and m12 are “positive” when the first light beam is incident on the objective optical element in a finite convergent light state, and the first light beam is infinite parallel light with respect to the objective optical element. The case where the first light beam is incident on the objective optical element in the state of finite divergent light is defined as “negative”. The objective optical element according to claim 12, wherein the following conditional expression is satisfied.
1.05 × f1 <f2 <1.25 × f1 (3) The objective optical element according to claim 12, wherein the following conditional expression is satisfied.
−0.01 <m11 <0.01 (4)
-0.01 <m12 <0.01 (5)   The plurality of annular zones on the correction surface condenses the first luminous flux that has passed so that information can be recorded and / or reproduced on the information recording surface of the first optical disc. The area for the first optical disc that is not condensed on the information recording surface of the second optical disc and the first luminous flux that has passed through are not condensed on the information recording surface of the first optical disc, and the first luminous flux that has passed through is The objective optical element according to any one of claims 12 to 14, further comprising a second optical disc region that condenses light so that information can be recorded and / or reproduced on an information recording surface of the second optical disc. .   The objective optical element according to claim 15, wherein the objective optical element has a ring zone of 3 or more and 10 or less in total of the first region and the second region.   The plurality of annular zones include an n-order diffracted light that is condensed so that information can be recorded and / or reproduced on an information recording surface of the first optical disc when the first light flux is incident thereon, and the second optical disc The objective according to any one of claims 12 to 16, which is an optical path difference providing structure that generates m-th order diffracted light so that information can be recorded and / or reproduced on the information recording surface. Optical element.   The objective optical element according to claim 12, wherein the objective optical element is a single lens, and the objective optical element has the correction surface.   The objective optical element has a flat plate-like first optical element and a second optical element that is a lens, and the first optical element has the correction surface. The objective optical element described.