JP2009037715A - Optical pickup apparatus and objective optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device using the same light flux compatible with BD and HD by using objective optical elements and to provide an objective optical element. <P>SOLUTION: In the optical pick up device wherein a light source that emits a light flux of a wavelength of λ1, and the optical pickup device that records and reproduces information by converging the light flux on a first optical disk with a protective layer having a thickness of t1 and converging the light flux on a second optical disk with a protective layer having a thickness of t2 (t1<t2), the objective optical element is made of plastic, and its optical surface is divided into a plurality of concentric regions, and the regions include at least one region for the first optical disk and at least one region for the second optical disk, the light flux passing through the region for the first optical disk is converged on the first optical disk, and not converged on the second optical disk, the light flux passing through the region for the second optical disk is converged on the second optical disk and not converged on the first optical disk, and an optical path difference giving structure is formed in the region for the first optical disk. <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 for different types of optical disks using light beams having the same wavelength.

  In recent years, research and development of high-density optical disc systems that can record and / or reproduce information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm. Development is progressing rapidly. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4, 7 GB) Can record information of 23 to 27 GB per layer on an optical disk with a diameter of 12 cm, which is the same size as the above, and an optical disk that records and reproduces information with specifications of NA 0.65 and light source wavelength 405 nm, so-called With HD DVD (hereinafter referred to as HD), information of 15 to 20 GB per layer can be recorded on an optical disk having a diameter of 12 cm. Such an optical disc is referred to as a high density optical disc in this specification.

  By the way, simply saying that information can be appropriately recorded / reproduced with respect to one high-density optical disc cannot be said to have sufficient value as a product of an optical disc player / recorder (optical information recording / reproducing apparatus). Considering the fact that the software recorded on both high-density optical disks is already on the market, it is possible to record / reproduce information on both high-density optical disks in the same way. This leads to an increase in commercial value as an optical disc player / recorder for optical discs.

  However, for BD and HD, which are high-density optical discs, the thickness of each protective substrate is different even though the wavelength of the light beam used is the same. It is difficult to correct spherical aberration generated based on the above. Therefore, it is more difficult to provide compatibility between BD and HD using a single objective optical element, as compared with compatibility with other optical disks.

On the other hand, Patent Document 1 describes an objective optical element and an optical pickup device that use liquid crystals to give different aberrations during recording / reproduction of BD and HD, and enable compatibility with one objective optical element. ing. Patent Document 2 describes a pickup device that enables BD and HD to be used interchangeably with a single objective optical element by sorting light beams of the same wavelength using a diffraction effect.
JP 2007-26540 A JP 2006-147069 A

  However, since the optical pickup device described in Patent Document 1 requires a liquid crystal, power supply and electrical control are necessary, which complicates the mechanism and increases the cost. It was.

  Further, as in the optical pickup device described in Patent Document 2 above, when realizing the compatible use of BD and HD using the diffraction effect, for example, the light from the light source passing through the diffraction structure to one of the optical disks Utilization efficiency (the utilization efficiency here is the ratio of the amount of light that contributes to the spot on the optical disk with respect to the amount of light incident on the optical surface on the light source side of the objective optical element) is 40% (diffractive distribution using a diffraction structure) (Theoretically does not exceed 50%), the utilization efficiency of light passing from the optical disk through the same diffraction structure toward the photodetector (the utilization efficiency here is the optical surface on the optical disk side of the objective optical element) The ratio of the amount of light that contributes to the spot on the photodetector with respect to the amount of light incident on the light detector is 40%, so the total utilization efficiency (the utilization efficiency here is the light on the light source side of the objective optical element) The ratio of the amount of light that contributes to the spot on the photodetector with respect to the amount of light incident on the surface is only 40% square, and only 16% of light can be used. It can be said that it is extremely difficult.

  On the other hand, there is an attempt to realize compatible use of BD and HD by separately providing a BD refractive surface and an HD refractive surface on the optical surface of the objective optical element. According to such an attempt, since a liquid crystal element or the like is not used, the structure can be simplified and energy can be saved, and since a diffraction structure or the like is not used, there is an advantage that the light use efficiency can be increased.

  By the way, when the objective optical element is molded from plastic, mass production is possible, and there is a merit that a highly accurate surface shape can be created at a low cost. However, since the NA is particularly high according to the BD specification, the allowable range of aberration required for the objective optical element is very narrow, whereas in a plastic objective optical element, for example, the refractive index due to environmental temperature changes There is a problem that the spherical aberration caused by the change and the wavelength change of the light source tends to exceed the allowable range, thereby making it impossible to record / reproduce appropriate information.

  The present invention takes the above-mentioned problems into consideration, enables compatibility between one objective optical element of BD and HD using the same light beam at a low cost without using a complicated mechanism, An object of the present invention is to provide an optical pickup device and an objective optical element that have high utilization efficiency and can suppress a change in spherical aberration even when an environmental temperature change occurs.

The optical pickup device according to claim 1 includes a first light source that emits a first light beam having a wavelength λ1 (380 nm <λ1 <450 nm), and an objective for condensing the first light beam on an information recording surface of an optical disc. A condensing optical system having an optical element;
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an optical pickup device that records and / or reproduces information by focusing on a surface,
The objective optical element is made of plastic, and its optical surface is divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
At least one of the first optical disk areas has an optical path difference providing structure.

  According to the present invention, by forming an optical path difference providing structure in the first optical disk area, most of the light beams that have passed through the first optical disk area form spots on the information recording surface of the first optical disk. In addition, since most of the reflected light from the information recording surface passes through the first optical disk area and is received by the photodetector of the optical pickup device, it is compared with the conventional light beam distribution technique using the diffraction effect. , Far more efficient use of light. In addition, by forming an optical path difference providing structure in at least one area for the first optical disc, various spherical aberrations can be corrected, and information can be recorded / reproduced appropriately. In addition, although the use efficiency of light can be similarly improved by making the said area | region for 2nd optical disks into a refracting surface, you may provide an optical path difference providing structure here.

  According to a second aspect of the present invention, there is provided the optical pickup device according to the first aspect, wherein the optical path difference providing structure corrects a spherical aberration caused by a temperature change.

An optical pickup device according to a third aspect of the invention according to the first or second aspect satisfies the following conditional expression.
+ 0.00045 ≦ δSAT1 / f (WFEλrms / (° C. mm)) ≦ + 0.0027
However, δSAT1 is δSA3 / δT of the objective optical element when performing recording and / or reproduction of the first optical disk at the use wavelength (no wavelength variation) of the first light beam, that is, the use wavelength of the first light beam. This refers to the temperature change rate of the third-order spherical aberration of the objective optical element when recording and / or reproducing the first optical disk (without wavelength variation), and f is the focal point of the objective optical element in the first light flux Refers to distance.

  An optical pickup device according to a fourth aspect of the present invention is the optical pickup device according to any one of the first to third aspects, wherein the wavelength λ1 of the light beam emitted from the first light source is a design wavelength. When the temperature changes from 25 ° C. to 55 ° C., the amount of change in wavefront aberration on the information recording surface of the first optical disk satisfies 0.010λ1 rms to 0.070λ1 rms.

According to a fifth aspect of the present invention, there is provided the optical pickup device according to any one of the first to fourth aspects, wherein the following conditional expression is satisfied.
0 ≦ δSAT2 / f (WFEλrms / (° C. mm)) ≦ + 0.0017
However, δSAT2 is δSA3 / δT of the objective optical element when performing recording and / or reproduction of the first optical disk at a wavelength used for the first light flux (wavelength variation accompanying temperature change is 0.05 nm / ° C.). That is, the temperature change of the third-order spherical aberration of the objective optical element at the time of recording and / or reproduction of the first optical disk at the use wavelength of the first light beam (wavelength variation with temperature change is 0.05 nm / ° C.). Refers to the rate.

The optical pickup device according to claim 6 is the invention according to any one of claims 1 to 5, wherein the condensing optical system of the optical pickup device has a coupling lens,
The coupling lens is a plastic lens;
The following conditional expression is satisfied.
0 ≦ δSAT3 / f (WFEλrms / (° C. mm)) ≦ + 0.0012
However, δSAT3 is the coupling lens and the objective optical element at the time of recording and / or reproducing the first optical disc at the wavelength used for the first light flux (wavelength variation accompanying temperature change is 0.05 nm / ° C.). That is, recording and / or reproduction of the first optical disc at the use wavelength of the first light beam (wavelength variation with temperature change is 0.05 nm / ° C.) of the entire condensing optical system including It indicates the temperature change rate of the third-order spherical aberration of the entire focusing optical system.

  According to a seventh aspect of the present invention, in the invention according to any one of the second to sixth aspects, the optical path difference providing structure includes only the first basic structure that corrects the spherical aberration caused by the temperature change. It is characterized by becoming.

  An optical pickup device according to an eighth aspect is the invention according to the seventh aspect, wherein the first basic structure is an NPS structure.

  An optical pickup device according to a ninth aspect is the invention according to any one of the second to sixth aspects, wherein the optical path difference providing structure corrects a spherical aberration caused by a temperature change of the objective optical element. The first basic structure is superposed on a second basic structure that corrects axial chromatic aberration based on a change in wavelength of a light beam emitted from the first light source.

  According to a tenth aspect of the present invention, in the invention according to the ninth aspect, the first basic structure is an NPS structure, and the second basic structure is a diffractive structure.

An optical pickup device according to an eleventh aspect is the optical pickup apparatus according to the tenth aspect, wherein the NPS structure has a p-th order diffracted light amount of the first light flux that has passed through the NPS structure, as compared to any other order of diffracted light amount. The diffractive structure is a structure that makes the q-order diffracted light amount of the first light beam that has passed through the diffractive structure larger than any other order diffracted light amount, and has the following conditional expression: It is characterized by satisfying.
p ≧ q (1)

  The optical pickup device according to a twelfth aspect is the invention according to the tenth or eleventh aspect, wherein the diffractive structure and the NPS structure both have a step, and a step amount in the optical axis direction of the step of the diffractive structure is small. The step amount of the NPS structure is smaller than the step amount in the optical axis direction.

  The optical pickup device according to a thirteenth aspect is the optical pickup device according to any one of the first to twelfth aspects, wherein the optical path difference providing structure has an optical axis direction distance from a surface vertex when viewed macroscopically. It is characterized in that it gradually increases as it goes in the orthogonal direction and then gradually decreases.

  An optical pickup device according to a fourteenth aspect is characterized in that, in the invention according to any one of the first to thirteenth aspects, the objective optical element is a single ball.

The objective optical element according to claim 15,
A condensing optical system having a first light source that emits a first light flux having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the first light flux on an information recording surface of an optical disc; ,
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an objective optical element used in an optical pickup device that records and / or reproduces information by focusing light on a surface,
The objective optical element is made of plastic, and its optical surface is divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
At least one of the first optical disk areas has an optical path difference providing structure.

  The objective optical element according to claim 16 is characterized in that, in the invention according to claim 15, the optical path difference providing structure corrects a spherical aberration generated due to a temperature change of the objective optical element. .

The objective optical element according to claim 17 is characterized in that, in the invention according to claim 15 or 16, the following conditional expression is satisfied.
+ 0.00045 ≦ δSAT1 / f (WFEλrms / (° C. mm)) ≦ + 0.0027
−0.045 ≦ δSAλ / f (WFEλrms / (nm · mm)) ≦ −0.0045
However, δSAT1 is δSA3 / δT of the objective optical element at the time of recording and / or reproducing the first optical disk at the use wavelength (no wavelength variation) of the first light beam, that is, the use wavelength of the first light beam. The temperature change rate of the third-order spherical aberration of the objective optical element at the time of recording and / or reproducing the first optical disk (without wavelength variation), and δSAλ is the first use wavelength of the first light flux. ΔSA3 / δλ when recording and / or reproducing the optical disk, that is, the wavelength of the third-order spherical aberration of the objective optical element when recording and / or reproducing the first optical disk at the wavelength used by the first light beam It indicates the rate of change, and f indicates the focal length of the objective optical element in the first light flux.

The objective optical element according to claim 18 is characterized in that, in the invention according to any one of claims 15 to 17, the following conditional expression is satisfied.
0 ≦ δSAT2 / f (WFEλrms / (° C. mm)) ≦ + 0.0017
However, δSAT2 is δSA3 / δT of the objective optical element when performing recording and / or reproduction of the first optical disk at a wavelength used for the first light flux (wavelength variation accompanying temperature change is 0.05 nm / ° C.). That is, the temperature change of the third-order spherical aberration of the objective optical element at the time of recording and / or reproduction of the first optical disk at the use wavelength of the first light beam (wavelength variation with temperature change is 0.05 nm / ° C.). Refers to the rate.

  The objective optical element according to claim 19 is the objective optical element according to any one of claims 16 to 18, wherein the optical path difference providing structure is composed only of the first basic structure that corrects the spherical aberration caused by the temperature change. It is characterized by becoming.

The objective optical element described in claim 20 is characterized in that, in the invention described in claim 19, the first basic structure is an NPS structure.

  The objective optical element according to claim 21 is the invention according to any one of claims 16 to 18, wherein the optical path difference providing structure corrects a spherical aberration caused by a temperature change of the objective optical element. The first basic structure is superposed on a second basic structure that corrects axial chromatic aberration based on a change in wavelength of a light beam emitted from the first light source.

  The objective optical element according to claim 22 is characterized in that, in the invention according to claim 21, the first basic structure is an NPS structure and the second basic structure is a diffractive structure.

In the objective optical element according to claim 23, in the invention according to claim 17, the NPS structure is configured such that the p-order diffracted light quantity of the first light beam that has passed through the NPS structure is higher than the diffracted light quantity of any other order. The diffractive structure is a structure that makes the q-order diffracted light amount of the first light beam that has passed through the diffractive structure larger than any other order diffracted light amount, and has the following conditional expression: It is characterized by satisfying.
p ≧ q (1)

  An objective optical element according to a twenty-fourth aspect is the invention according to the twenty-second or twenty-third aspect, wherein the diffractive structure and the NPS structure both have a step, and a step amount in the optical axis direction of the step of the diffractive structure is small. The step amount of the NPS structure is smaller than the step amount in the optical axis direction.

  The objective optical element according to claim 25 is the invention according to any one of claims 15 to 24, wherein the optical path difference providing structure has a distance in the optical axis direction from the surface vertex when viewed macroscopically. It is characterized in that it gradually increases as it goes in the orthogonal direction and then gradually decreases.

  An objective optical element according to a twenty-sixth aspect of the invention according to any one of the fifteenth to twenty-fifth aspects is a single ball.

  The optical pickup device of the present invention records / reproduces information to / from 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 (2), (3), (4), and (5), but is not limited thereto.

0.0750 mm ≦ t1 ≦ 0.1125 mm (2)
0.5mm ≦ t2 ≦ 0.7mm (3)
0.5mm ≦ t3 ≦ 0.7mm (4)
1.0mm ≦ t4 ≦ 1.3mm (5)

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

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

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

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

  In this specification, the objective optical element is disposed at a position facing the optical disk in a state where the optical disk is loaded in the optical pickup device, and has a function of condensing the light beam emitted from the light source on the information recording surface of the optical disk. An optical system having Preferably, the objective optical element is an optical system that is disposed at a position facing the optical disc in the optical pickup device and has a function of condensing a light beam emitted from the light source on the information recording surface of the optical disc, An optical system that can be integrally displaced at least in the optical axis direction by an actuator. The objective optical element may be composed of two or more lenses and optical elements, or may be only a single lens. 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 is a plastic lens. When the objective optical element is a single lens, it becomes a plastic lens. When the objective optical element is composed of a plurality of optical elements, it is preferable that all the optical elements are made of plastic. As the plastic, it is preferable to use a cyclic olefin-based resin material, and among the cyclic olefin-based materials, the refractive index at a temperature of 25 ° C. with respect to a wavelength of 405 nm is in the range of 1.54 to 1.60, and −5 The refractive index change rate dN / dT (° C. ⁻¹ ) with respect to the wavelength of 405 nm accompanying the temperature change in the temperature range from ℃ to 70 ° C. is −20 × 10 ^{−5 to} −5 × 10 ⁻⁵ (more preferably −10 × is more preferable to use a resin material is 10 ^-5 to within the range of -8 × 10 ^-5). When the objective optical element is a plastic lens, the coupling lens is preferably a plastic lens.

  In order to record / reproduce information to / from the second optical disk, NA1 is the image-side numerical aperture of the objective optical element necessary for recording / reproducing information on / from the first optical disk. The required image-side numerical aperture of the objective optical element is NA2 (NA1> NA2), and the image-side numerical aperture of the objective optical element necessary for recording / reproducing information on the third optical disk is NA3 ( NA2 ≧ NA3), and the image-side numerical aperture of the objective optical element necessary for recording / reproducing information with respect to the fourth optical disk is NA4 (NA3> NA4). NA1 is preferably 0.8 or more and 0.9 or less. More preferably, NA1 is 0.85. NA2 and NA3 are preferably 0.55 or more and 0.7 or less. More preferably, NA2 is 0.65 and NA3 is 0.65. NA4 is preferably 0.4 or more and 0.55 or less. More preferably, NA4 is 0.45.

  The objective optical element may be 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, the first area is a so-called shared area (first optical disk area + second optical disk area described later) used for both the first optical disk and the second optical disk, and the second area is the first optical disk. It can be said that this is a so-called dedicated area (first optical disk area to be described later) that is used only for this purpose. 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.

  When the objective optical element is viewed from another viewpoint, the optical surface of the objective optical element is divided into a plurality of concentric areas, and the plurality of areas are at least one first optical disk area and at least one second optical disk area. It can be said that it has. The first light flux that has passed through the first optical disk area is condensed so that information can be recorded / reproduced on the information recording surface of the first optical disk, and is not condensed on the information recording surface of the second optical disk. The first light flux that has passed through the second optical disc area is condensed so that information can be recorded / reproduced on the information recording surface of the second optical disc, and is not condensed on the information recording surface of the first optical disc.

  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.

  Each of the first optical disk area and the second optical disk area may be an aspherical refracting surface, or may be provided with an optical path difference providing structure. The objective optical element preferably has only a first optical disk area and a second optical disk area. In addition, 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. For example, FIG. 1 shows a first optical disk area BA whose center area including the optical axis is an aspheric refracting surface, and a second optical disk area HA having an aspheric refracting surface around it. There is a first optical disk area BA2 which is an aspherical refracting surface. FIG. 2 shows a first optical disk area BA whose center area including the optical axis is an aspherical refracting surface, and a second optical disk area HA having an optical path difference providing structure around the first optical disk area BA. There is a first optical disk area BA2 which is an aspherical refracting surface.

  Further, from the viewpoint of facilitating the production of the objective optical element, it is preferable that the total number of ring zones including the first optical disk area and the second optical disk area is 3 or more and 10 or less. When the number of ring 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 (however, the optical path difference providing structure is omitted) can be considered. As a result of diligent research, the present inventor combined the first optical disk area and the second optical disk area from the viewpoint of reducing the side rope of the spot and facilitating the manufacture of the objective optical element. It has been found that the number of ring zones is preferably 5 or more and 10 or less. More preferably, the number of ring zones is 6 or more and 10 or less. It should be noted that the above-described preferable range of the number of annular zones can also be applied when the objective optical element has a first optical element on the light source side and a second optical element on the optical disk side.

Next, when performing recording / reproduction of the second optical disc, in order to prevent the light flux that has passed through the first optical disc area from falling on the defocus area, the light flux that has passed through the first optical disc area is 2 It is preferable that the objective optical element has a flare on the information recording surface of the optical disc. Specifically, “to flare” means that light that has passed through the first optical disk area on the information recording surface of the second optical disk is distributed in the donut-shaped area. In particular, when the first optical disc is a BD and the second optical disc is an HD, it is preferable that the inner diameter of the donut-shaped region be Φ0.030 mm or more. In the case of a plurality of donut-shaped regions, it is preferable that the smallest diameter among the inner diameters of each donut-shaped region is Φ0.030 mm or more. 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 (6) is satisfied.
2 ・ f1 ・ NA1 '> 2 ・ f2 ・ NA2' (6)
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 indicates the image-side numerical aperture defined by the standard required for recording / reproduction of the first optical disk. . 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 / reproduction of the second optical disk. . 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 disk area and the second optical disk area have different aspherical shapes in ₁ ), the working distance (WD ₁ ) of the objective optical element during recording / reproduction of the first optical disk and the second optical disk It is preferable that the absolute value (| WD ₁ −WD ₂ |) of the difference from the working distance (WD ₂ ) of the objective optical element at the time of recording / reproducing is 0.1 (mm) or more.

  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.

  As a preferred embodiment, an optical path difference providing structure that corrects spherical aberration caused by a temperature change as described later is provided in the first optical disc region, and the above-described method for reducing the level difference in the second optical disc region. What is called an objective optical element provided with the optical path difference providing structure. In this aspect, in recording / reproduction of the first optical disk having a large NA, recording / reproduction can be performed stably even if a temperature change occurs, and since there is no large step on the optical surface, it is easy to manufacture, Furthermore, the loss of light quantity can be reduced and the light quantity can be increased.

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

  Further, from the viewpoint of reducing the thickness of a single objective optical element, a step is provided on the surface of the optical surface of the objective optical element, and the step is a region on the far side of the region closer to the optical axis with the step as a boundary. It is desirable that the level difference be shorter than the optical path. For example, the example shown in FIG. 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. In addition, since the objective optical element is made of plastic, it is preferable that the step be a step that produces a diffractive action that compensates for a change in spherical aberration caused by a change in temperature of the plastic by a change in laser oscillation wavelength accompanying the change in temperature.

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 (7) is satisfied in the case where it is shortened:
0.1 mm ≦ Δ ≦ 1.0 mm (7)
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.

  The objective optical element preferably has an optical path difference providing structure for correcting spherical aberration caused by a temperature change in at least one first optical disc region. Further, the spherical aberration caused by the temperature change is only one of the spherical aberration based on the refractive index change caused by the temperature change of the objective optical element and the spherical aberration based on the wavelength change of the light source based on the temperature change. In both cases, both cases are included.

  It should be noted that the optical path difference providing structure for correcting the spherical aberration caused by the temperature change is preferably provided in all the first optical disk areas, but may be provided only in some of the first optical disk areas. Good. For example, in order to avoid the structure of the first optical disc region closest to the optical axis from becoming complicated, the first optical disc region closest to the optical axis is corrected for spherical aberration caused by a temperature change. The optical path difference providing structure may not be provided. In addition, an optical path difference providing structure for correcting spherical aberration caused by a temperature change may be provided only in the first optical disc region farthest from the optical axis.

  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 NPS structure can also be regarded as a kind of optical path difference providing structure. 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.

It is preferable that the following conditional expression is satisfied.
+ 0.00045 ≦ δSAT1 / f (WFEλrms / (° C. mm)) ≦ + 0.0027
However, δSAT1 is δSA3 / δT of the objective optical element at the time of recording / reproducing the first optical disk at the wavelength used for the first light beam (no wavelength variation), that is, the wavelength used for the first light beam (no wavelength variation). Indicates the temperature change rate of the third-order spherical aberration of the objective optical element when performing recording / reproduction of the first optical disc in f, and f indicates the focal length of the objective optical element in the first light flux.

Moreover, it is preferable to satisfy the following conditional expressions.
−0.045 ≦ δSAλ / f (WFEλrms / (nm · mm)) ≦ −0.0045
However, δSAλ is δSA3 / δλ when recording / reproducing the first optical disk at the used wavelength of the first light beam, that is, the objective optical element when recording / reproducing the first optical disk at the used wavelength of the first light beam. F represents the focal length of the objective optical element in the first light flux.

Furthermore, it is preferable to satisfy the following conditional expression.
0 ≦ δSAT2 / f (WFEλrms / (° C. mm)) ≦ + 0.0017
However, δSAT2 is δSA3 / δT of the objective optical element at the time of recording / reproducing on the first optical disk at the use wavelength of the first light beam (wavelength variation with temperature change is 0.05 nm / ° C.), that is, the first light beam. Is the temperature change rate of the third-order spherical aberration of the objective optical element when recording / reproducing the first optical disc at the wavelength used (wavelength variation with temperature change is 0.05 nm / ° C.).

Moreover, when the condensing optical system of an optical pick-up apparatus has a plastic coupling lens, it is preferable to satisfy the following conditional expressions.
0 ≦ δSAT3 / f (WFEλrms / (° C. mm)) ≦ + 0.0012
However, δSAT3 is a condensing optical system including a coupling lens and an objective optical element for recording / reproducing the first optical disc at the wavelength used for the first light flux (wavelength variation with temperature change is 0.05 nm / ° C.). ΔSA3 / δT of the entire system, that is, the third spherical surface of the entire condensing optical system when recording / reproducing the first optical disk at the wavelength of use of the first light flux (wavelength variation accompanying temperature change is 0.05 nm / ° C.) Refers to the temperature change rate of aberration.

  The optical path difference providing structure may consist of only the first basic structure that corrects the spherical aberration caused by the temperature change, or the first basic structure that corrects the spherical aberration caused by the temperature change. And a second basic structure for correcting axial chromatic aberration based on a change in wavelength of the light beam emitted from the first light source may be superimposed. The first basic structure is preferably an NPS structure, and the second basic structure is preferably a diffractive structure.

  Here, the effect of the NPS structure and the diffraction structure referred to in this specification will be described with reference to FIG. The horizontal axis in FIG. 5 represents the incident height h at the entrance pupil of the objective optical element, and the vertical axis represents the optical path difference between the light beam passing through the optical axis and the light beam passing through the incident height h. The area surrounded by the curve and the horizontal axis can be regarded as the amount of aberration. The optical path difference between a light beam having an aspheric refracting surface and passing through the optical axis and a light beam passing through any incident height h is assumed to be the wavelength x of the light beam incident on the objective optical element at an environmental temperature of 25 ° C. An objective optical element that is 0 (that is, a straight line overlapping the horizontal axis) is considered as a reference. In the aspheric objective optical element, when the environmental temperature is 55 ° C., for example, an optical path difference occurs between the light beam passing through the optical axis and the light beam passing through the incident height h as shown by AS. Aberration corresponding to the area surrounded by AS and the horizontal axis occurs. Next, a plurality of annular zone step structures X optimized for the wavelength x are provided on the aspheric objective optical element. When the ambient temperature is 55 ° C. and the wavelength x is incident on the objective optical element having the step structure X, when the curve DS becomes a smooth curve DS that approaches the horizontal axis as a whole, the step structure X is It is a diffractive structure as used in this specification. By providing the diffractive structure, since the curve indicating the optical path difference approaches the horizontal axis as a whole, the area surrounded by the curve and the horizontal axis is reduced, and it can be seen that the aberration caused by the temperature change is reduced. Next, a plurality of annular zone step structures Y different from those described above, which are optimized for the wavelength x, are provided on the aspheric objective optical element described above. When the ambient temperature is 55 ° C. and the wavelength x is incident on the optical element having the step structure Y, when the curve AS is a curve indicated by intermittent NPS having discontinuous portions, the step structure Y is It is an NPS structure as used in the specification. When the NPS structure and the diffractive structure are combined, a curve indicated by NPS + DS in FIG. 5 is obtained, and the aberration corresponding to the area indicated by hatching is obtained.

  Generally, when an objective optical element is provided with an NPS structure that improves temperature characteristics (aberration deterioration characteristics with respect to temperature changes), wavelength characteristics (aberration deterioration characteristics with respect to wavelength changes of incident light beams) deteriorate. More specifically, the NPS structure that improves the temperature characteristics is such that the spherical aberration becomes under (undercorrected) when the temperature changes to the high temperature side and when the wavelength changes to the long wavelength side. Therefore, although the degree of over-correction (overcorrection) of the spherical aberration that occurs when the temperature changes to the high temperature side is reduced, the degree of under-spherical aberration that occurs when the wavelength changes to the long wavelength side is increased. On the other hand, by providing a diffractive structure on the objective optical element, it is possible to correct axial chromatic aberration, but the wavelength characteristic changes in the opposite direction to that of the NPS structure. That is, the diffractive structure changes in a direction in which the spherical aberration is over when the wavelength is changed to the longer wavelength side. However, the change direction of the spherical aberration that occurs when the wavelength changes is the opposite direction between the NPS structure and the diffractive structure, and it works just to cancel out, so the objective optical element has a structure that superimposes the NPS structure and the diffractive structure. Then, the wavelength characteristic is good.

  Furthermore, by providing the NPS structure and the diffractive structure on the same optical surface, it is possible to reduce the eccentricity error during manufacturing. The optical path difference providing structure is preferably provided on the light source side surface of the objective optical element rather than the surface of the objective optical element on the optical disk side.

The NPS structure is a structure in which the p-order diffracted light amount of the light beam that has passed through the NPS structure is made larger than any other order diffracted light amount. It is preferable that the diffracted light quantity of any order is greater than the order, and the following conditional expression is satisfied.
p ≧ q (1)

  Note that p is preferably 5 or 4. By setting p to 5 or 4, it is possible to suppress a change in diffraction efficiency generated in the NPS structure when the environmental temperature changes and / or when the wavelength changes, and on the other hand, the pitch of the ring zone of the NPS structure is fine. It is preferable because it becomes an objective optical element that can be easily manufactured and can be suppressed. Further, q is preferably 2 or 1. In particular, (p, q) = (5, 2) or (4, 2) is preferable because the diffraction efficiency is increased.

  It is preferable that the step amount in the optical axis direction of the step of the diffractive structure is smaller than the step amount of the NPS structure. Regardless of whether the NPS structure and diffraction are superimposed or only the NPS structure is provided, all the step amounts of the NPS structure are 0.9 · p · λ1 / (n−1) or more, 2.0 · It is preferable to satisfy p · λ1 / (n−1) or less. Note that n is the refractive index of the objective optical element at the wavelength λ1. Moreover, it is preferable that all the steps of the diffractive structure are 0.9 · q · λ1 / (n-1) or more and 2.0 · q · λ1 / (n-1) or less. In particular, the step amount of the NPS structure preferably satisfies 0.9 · p · λ1 / (n−1) or more and 1.1 · p · λ1 / (n−1) or less within NA of 0.45. Further, the step height of the diffractive structure is preferably 0.9 · q · λ1 / (n-1) or more and 1.1 · q · λ1 / (n-1) or less within NA of 0.45.

It is preferable that all the steps in the optical path difference providing structure in which the NPS structure and the diffractive structure are overlapped consist of at least three of dA, dB, dC, and dD shown in the following conditional expressions (8) to (11). Particularly preferably, all the steps are composed of only three of dA, dC, and dD. This configuration can be achieved by overlapping the NPS structure and the diffractive structure so that the position of the step of the NPS structure coincides with the position of the step of the diffractive structure.
0.9 · q · λ1 / (n-1) ≦ dA ≦ 2.0 · q · λ1 / (n-1) (8)
0.9 · p · λ1 / (n−1) ≦ dB ≦ 2.0 · p · λ1 / (n−1) (9)
0.9 · (p−q) · λ1 / (n−1) ≦ dC ≦ 2.0 · (pq) · λ1 / (n−1) (10)
0.9 · (p + q) · λ1 / (n−1) ≦ dD ≦ 2.0 · (p + q) · λ1 / (n−1) (11)
However, n shows the refractive index of the objective optical element in the light beam of λ1.

Further, the level difference amount of the optical path difference providing structure is such that all the level differences within NA of 0.45 are at least two of dA ′, dB ′, dC ′, and dD ′ shown in the following conditional expressions (12) to (15). Preferably it consists of one. Particularly preferably, all the step amounts are only dA ′ and dC ′ within NA of 0.45.
0.9 · q · λ1 / (n−1) ≦ dA ′ ≦ 1.1 · q · λ1 / (n−1)
(12)
0.9 · p · λ1 / (n−1) ≦ dB ′ ≦ 1.1 · p · λ1 / (n−1)
(13)
0.9 · (p−q) · λ1 / (n−1) ≦ dC ′ ≦ 1.1 · (p−q) · λ1 / (n−1) (14)
0.9 · (p + q) · λ1 / (n−1) ≦ dD ′ ≦ 1.1 · (p + q) · λ1 / (n−1) (15)

  Further, the optical path difference providing structure in which the NPS structure and the diffractive structure are superposed can be grasped as follows from the viewpoint of the shape.

  In other words, the optical surface of the objective optical element is divided into a plurality of regions divided by a plurality of concentric boundary steps, and each region divided by the boundary steps has a plurality of concentric in-region steps. It is a way of thinking that it is doing. The boundary step here is a step of the above-mentioned NPS structure, and the in-region step is a step of the diffractive structure. The amount of step in the optical axis direction of the step of the diffractive structure is preferably smaller than the amount of step in the optical axis direction of the step of the NPS structure. Note that the boundary step may be the case where the step of the NPS structure and the step of the diffraction structure overlap.

  In each region, the boundary step is facing away from the optical axis in the region near the optical axis, and the boundary step is facing the optical axis in the region away from the optical axis. Is preferred. In this specification, “the boundary step is facing the opposite side of the optical axis” means that the surface forming the step is the direction opposite to the optical axis (in the direction of the arrow) as shown in FIGS. ). Further, “the boundary step faces the optical axis side” means that the surface constituting the step faces the direction of the optical axis (arrow direction) as shown in FIGS. . That is, the NPS structure is preferably a structure as shown in FIG. Moreover, it is preferable that the number of steps facing the opposite side of the optical axis is equal to the number of steps facing the optical axis.

  Moreover, it is preferable that all the steps in the region face the optical axis side.

  Further, in each region, the step amount of the boundary step is preferably larger than the step amount of the in-region step.

  As a design method of the optical path difference providing structure in which the NPS structure and the diffractive structure are superposed, for example, the design can be performed as follows. First, p, which is the diffraction order of the NPS structure, is determined, and after determining how many regions the optical surface is divided into, the NPS structure is designed based on the aspherical expression using the aspheric coefficient. Can do. Next, the diffraction order q of the diffractive structure is determined, and the diffractive structure is designed using a phase difference function in each region of the NPS structure, thereby obtaining an optical path difference providing structure in which the NPS structure and the diffractive structure are superimposed. be able to. Since the diffractive structure is designed based on the phase difference function, the phase difference of the phase difference function is set so that the pitch of the diffractive structure corresponds to every m · 2π (m is an integer). Accordingly, it can be understood that the pitch of the diffractive structure is periodic. However, when designing the diffractive structure using the optical path difference function in each region of the NPS structure, the step (boundary step) of the NPS structure and the position of the outermost step of the diffractive structure in each region match. It is also possible to perform fine adjustment such as slightly shifting the pitch of the diffractive structure or the NPS structure. In addition, the design method of the optical element of the present invention is not limited to the above, and any optical design method may be used as long as the optical element of the present invention can be obtained as a result.

  In addition, it is preferable that the optical path difference providing structure is macroscopically smaller after the distance in the optical axis direction from the surface apex gradually increases as it goes in the direction orthogonal to the optical axis. In this specification, “when viewed macroscopically, the distance in the optical axis direction from the surface vertex gradually increases as it goes in the direction perpendicular to the optical axis”, as shown in FIG. In the direction perpendicular to the optical axis from P, the shape is such that it gradually becomes farther from the surface vertex as it passes through steps 1, 2, and 3, and gradually passes away from the surface vertex P as it passes through steps 4, 5, and 6 on the contrary. .

  The objective optical element may have a compatible optical path difference providing structure that enables the use of the third optical disk and / or the fourth optical disk.

  Furthermore, an optical path difference providing structure for the purpose of compatibility with the third optical disk or the fourth optical disk may be superimposed on the optical path difference providing structure that reduces the spherical aberration caused by the temperature change. 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 an optical path difference providing structure. 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 the flat plate-like first optical element, thereby dividing it into a plurality of areas, and the area corresponding to the outermost peripheral part of the first optical element is a flat structure. In addition, an optical path difference providing structure for compatibility with the third optical disk and the fourth optical disk, and an optical path difference providing structure for correcting aberration changes that occur when the temperature changes or changes in wavelength are superimposed. May be.

Next, the step amount of the optical path difference providing structure will be described. An example of such a step amount is a step amount that gives an optical path difference 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 (8).
d1 = a · λ1 / (n−1) (8)
Here, n is the refractive index of the optical element having the optical path difference providing structure for the light flux with wavelength λ1.

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

As a first example, for example, a third light beam having a wavelength λ3 emitted from a third light source is condensed on the information recording surface of the fourth optical disk by the objective optical element, and the wavelength λ3 is a wavelength λ1. If it is an approximate integer multiple of 1 and an attempt is made to enable compatibility with the fourth optical disk by the diffraction structure, 1) it becomes difficult to make the diffraction angles different between the first light flux of λ1 and the third light flux of λ3, 2) When a special diffraction structure that can make the diffraction angles of the first light flux and the third light flux different is used, there is a problem that the light use efficiency is lowered. Therefore, a fourth optical disk area may be provided in the second area in addition to the first optical disk area and the second optical disk area. For example, as shown in FIG. 7, the fourth optical disk area CD, the first optical disk area BD, the second optical disk area HD, and the second area outside 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 (9) is satisfied.
(M−0.2) · λ1 ≦ λ3 ≦ (m + 0.2) · λ1 (9)
Note that m represents an arbitrary positive integer of 2 or more.

  Further, when the fourth optical disk area as described above is provided, the maximum image-side numerical aperture of the fourth optical disk area is made smaller than the numerical aperture that is used as a standard for recording / reproducing of the fourth optical disk. Is preferred. 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 / reproducing 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 second area, the recording of the third optical disk (for example, DVD) is performed. / Reproduction may be enabled. For example, as shown in FIG. 8, the fourth optical disk area CD, the first optical disk area BD, the second optical disk area HD, and the second area on the outer side in order from the inner area including the optical axis. An optical path difference providing structure DVD that enables recording / reproduction of the third optical disk is provided in the fourth optical disk area CD, the inner first optical disk area BD, and the second optical disk area HD as the first optical disk area BD. Examples are possible.

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

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

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

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

The first light beam may be incident on the objective optical element as parallel light, or may be incident on the objective optical element as divergent light or convergent light. Preferably, the magnification m1 of the first light beam incident on the objective optical element satisfies the following formula (10).
−0.02 <m1 <0.02 (10)

On the other hand, when the first light flux is incident on the objective optical element as diverging light, the magnification m1 of the first light flux incident on the objective optical element preferably satisfies the following formula (11).
-0.10 <m1 <0.00 (11)

In order to make the sine condition compatible in both recording / reproduction of the first optical disk and recording / reproduction of the second optical disk, it is preferable to satisfy the following conditional expression (12).
m11 <m12 (12)
M11 represents the magnification of the first light beam incident on the objective optical element at the time of recording / reproduction of the first optical disk, and m12 represents the objective optical of the first light beam at the time of recording / reproduction of the second optical disk. The magnification of the incident light beam to the element is shown.

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

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

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

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

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

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

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 13 is a diagram schematically showing a configuration of the optical pickup device PU1 of the present embodiment capable of appropriately recording / reproducing information with respect to the BD as the first optical disc and the HD as the second optical disc. is there. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. The present invention is not limited to the present embodiment.

  The optical pickup device PU1 includes information recording surfaces of an objective optical element OBJ, a λ / 4 wavelength plate QWP, a collimating lens CL, a polarizing prism PBS, a semiconductor laser LD that emits a laser beam (light beam) of 405 nm, and sensor lenses SL and BD. It has a light receiving element PD that receives a reflected light beam from the information recording surface RL2 of RL1 and HD. In the present embodiment, the objective optical element OBJ is a single ball, but two or more optical elements may be used in combination.

  On the optical surface on the light source side of the objective optical element OBJ, a first area AR1 for a circular BD including the optical axis, a second area AR2 for HD in the surrounding ring zone, and a ring shape around the surrounding area. The first regions AR3 for BD are alternately formed. In the first regions AR1 and AR3, an optical path difference providing structure is formed in order to correct spherical aberration that occurs in response to changes in the environmental temperature. The optical axis direction distance gradually increases as it goes in the direction perpendicular to the optical axis, and then gradually decreases.

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

  At this time, the light beam that has passed through the first areas AR1 and AR3 of the objective optical element OBJ is condensed on the information recording surface of the BD to form a spot, but the light beam that has passed through the second area AR2 becomes flare light. , No focused spot is formed on the information recording surface of the BD.

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

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

  At this time, the light beam that has passed through the second area AR2 of the objective optical element OBJ is condensed on the HD information recording surface to form a spot, but the light beam that has passed through the first areas AR1 and AR3 becomes flare light. , No condensing spot is formed on the information recording surface of HD. (In FIG. 1, during HD recording / reproduction, the light beam does not appear to enter the first area AR3, but actually enters the first area AR3.)

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

(Example)
Next, examples that can be used in the above-described embodiment will be described. Example 1 is an objective optical element of a single lens. Table 1 shows lens data of Example 1. In the table, ri represents the radius of curvature, di represents the position in the optical axis direction from the i-th surface to the (i + 1) -th surface, and ni represents the refractive index of each surface. 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). In addition, 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 mathematical formulas obtained by substituting the coefficients shown in Table 1 into Formula 1. FIG. 14 is a cross-sectional view of the objective optical element of Example 1.

  In the first embodiment, the first optical disc is BD, and the second optical disc is HD. The 2-1 surface to the 2-3 surface are areas for the first optical disk, the 2-4 surface is the area for the second optical disk, and the 2-5 surface to the 2-13 surface are areas for the first optical disk. is there. That is, in Example 1, the most central region including the optical axis is the first optical disc region, and the second optical disc region and the second region are sequentially directed from there to the outside in the optical axis orthogonal direction. Although the optical disk area has a three-divided structure, the first optical disk area has a plurality of surfaces divided by predetermined steps, thereby forming an optical path difference providing structure. With this optical path difference providing structure, it is possible to reduce spherical aberration caused by temperature change. Further, this optical path difference providing structure is composed of only the first basic structure, and in this embodiment, the first basic structure is an NPS structure. Further, this NPS structure is an NPS structure that generates the fourth-order diffracted light most when a 405 nm light beam is incident. All the regions have an aspheric shape, and the first optical disc region has a continuous aspheric shape except for a step.

  Here, X (h) is an axis in the optical axis direction (with the light traveling direction being positive), κ is a conical coefficient, Ai is an aspherical coefficient, h is a height from the optical axis, and r is a paraxial radius of curvature. It is.

  Table 2 shows the results of comparative studies conducted by the present inventors for the comparative example in which the optical path difference providing structure is not provided in the first optical disc region and the objective optical element of Example 1. The change in the refractive index of the lens material is -9 x E -05 (/ ° C). According to the results of the comparative study in Table 2, the change in wavefront aberration when the ambient temperature rises by 30 ° C. when using BD is that the third-order spherical aberration of the comparative example is 0.092 λrms when there is no shift in the light source wavelength. On the other hand, the third-order spherical aberration of Example 1 was confirmed to be 0.066 λrms and −0.026 λrms. The value of δSAT1 / f is 0.0016 (WFEλrms / (° C. mm)). Further, when the ambient temperature is increased by 30 ° C. when using the BD, the change in wavefront aberration is such that the third-order spherical aberration of the comparative example is 0.1 when the light source wavelength shift is +1.5 nm (0.05 nm / ° C.). In contrast to 100λrms, the third-order spherical aberration of Example 1 was confirmed to be 0.042λrms and a reduction effect of −0.058λrms. Note that the value of δSAT2 / f is 0.0010 (WFEλrms / (° C. mm)).

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 part of sectional drawing of an example of the objective optical element which concerns on this invention. The horizontal axis shows the light ray height at the entrance pupil of the objective optical element, and the vertical axis shows the difference in the navigation path between the light ray passing through the optical axis and the light ray passing through the light ray height h. It is a schematic block diagram of an optical path difference providing structure. 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 using the objective optical element which concerns on this invention. It is a schematic perspective view of an example of the lens unit using the objective optical element which concerns on this invention. It is a schematic perspective view of an example of the lens unit using the objective optical element which concerns on this invention. It is a part of sectional drawing of an example of the lens unit using the objective optical element which concerns on this invention. It is a figure which shows schematically the structure of the optical pick-up apparatus which concerns on this invention. FIG. 2 is a cross-sectional view of the objective optical element of Example 1, where (a) shows the state when using BD, and (b) shows the state when using HD.

Explanation of symbols

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

Claims (26)

A condensing optical system having a first light source that emits a first light flux having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the first light flux on an information recording surface of an optical disc; ,
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an optical pickup device that records and / or reproduces information by focusing on a surface,
The objective optical element is made of plastic, and its optical surface is divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
At least one area for the first optical disc has an optical path difference providing structure.   The optical pickup device according to claim 1, wherein the optical path difference providing structure corrects spherical aberration caused by a temperature change. The optical pickup device according to claim 1, wherein the following conditional expression is satisfied.
+ 0.00045 ≦ δSAT1 / f (WFEλrms / (° C. mm)) ≦ + 0.0027
However, δSAT1 is δSA3 / δT of the objective optical element when performing recording and / or reproduction of the first optical disk at the use wavelength (no wavelength variation) of the first light beam, that is, the use wavelength of the first light beam. This refers to the temperature change rate of the third-order spherical aberration of the objective optical element when recording and / or reproducing the first optical disk (without wavelength variation), and f is the focal point of the objective optical element in the first light flux Refers to distance.   In the case where the wavelength λ1 of the light beam emitted from the first light source is the design wavelength, the wavefront aberration on the information recording surface of the first optical disk when the environmental temperature changes from 25 ° C. to 55 ° C. 4. The optical pickup device according to claim 1, wherein the change amount satisfies 0.010λ1 rms or more and 0.070λ1 rms or less. The optical pickup device according to claim 1, wherein the following conditional expression is satisfied.
0 ≦ δSAT2 / f (WFEλrms / (° C. mm)) ≦ + 0.0017
However, δSAT2 is δSA3 / δT of the objective optical element when performing recording and / or reproduction of the first optical disk at a wavelength used for the first light flux (wavelength variation accompanying temperature change is 0.05 nm / ° C.). That is, the temperature change of the third-order spherical aberration of the objective optical element at the time of recording and / or reproduction of the first optical disk at the use wavelength of the first light beam (wavelength variation with temperature change is 0.05 nm / ° C.). Refers to the rate. The condensing optical system of the optical pickup device has a coupling lens,
The coupling lens is a plastic lens;
The optical pickup device according to claim 1, wherein the following conditional expression is satisfied.
0 ≦ δSAT3 / f (WFEλrms / (° C. mm)) ≦ + 0.0012
However, δSAT3 is the coupling lens and the objective optical element at the time of recording and / or reproducing the first optical disc at the wavelength used for the first light flux (wavelength variation accompanying temperature change is 0.05 nm / ° C.). That is, recording and / or reproduction of the first optical disc at the use wavelength of the first light beam (wavelength variation with temperature change is 0.05 nm / ° C.) of the entire condensing optical system including It indicates the temperature change rate of the third-order spherical aberration of the entire focusing optical system.   The optical pickup device according to claim 2, wherein the optical path difference providing structure includes only a first basic structure that corrects a spherical aberration caused by a temperature change.   8. The optical pickup device according to claim 7, wherein the first basic structure is an NPS structure.   The optical path difference providing structure includes a first basic structure that corrects spherical aberration caused by a temperature change, and a second basic structure that corrects axial chromatic aberration based on a wavelength change of a light beam emitted from the first light source. The optical pickup device according to claim 2, wherein the optical pickup device is superimposed.   The optical pickup device according to claim 9, wherein the first basic structure is an NPS structure, and the second basic structure is a diffractive structure. The NPS structure is a structure that makes the p-order diffracted light amount of the first light flux that has passed through the NPS structure larger than any other order diffracted light amount,
The diffractive structure is a structure that makes the q-order diffracted light quantity of the first light flux that has passed through the diffractive structure larger than any other order diffracted light quantity, and satisfies the following conditional expression: Item 11. The optical pickup device according to Item 10.
p ≧ q (1)   The diffractive structure and the NPS structure both have a step, and the step amount in the optical axis direction of the step in the diffractive structure is smaller than the step amount in the optical axis direction of the step in the NPS structure. Item 12. The optical pickup device according to Item 10 or 11.   The optical path difference providing structure is characterized in that, when viewed macroscopically, the distance in the optical axis direction from the surface apex gradually increases and then gradually decreases in the direction orthogonal to the optical axis. The optical pick-up apparatus in any one.   The optical pickup device according to claim 1, wherein the objective optical element is a single ball. A condensing optical system having a first light source that emits a first light flux having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the first light flux on an information recording surface of an optical disc; ,
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an objective optical element used in an optical pickup device that records and / or reproduces information by focusing light on a surface,
The objective optical element is made of plastic, and its optical surface is divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
At least one area for the first optical disk has an optical path difference providing structure.   The objective optical element according to claim 15, wherein the optical path difference providing structure corrects spherical aberration caused by a temperature change. The objective optical element according to claim 15, wherein the following conditional expression is satisfied.
+ 0.00045 ≦ δSAT1 / f (WFEλrms / (° C. mm)) ≦ + 0.0027
−0.045 ≦ δSAλ / f (WFEλrms / (nm · mm)) ≦ −0.0045
However, δSAT1 is δSA3 / δT of the objective optical element when recording and / or reproducing the first optical disk at the wavelength used (no wavelength variation) of the first light beam, that is, the wavelength used of the first light beam. The temperature change rate of the third-order spherical aberration of the objective optical element at the time of recording and / or reproducing the first optical disk (without wavelength variation), and δSAλ is the first use wavelength of the first light flux. ΔSA3 / δλ when recording and / or reproducing the optical disk, that is, the wavelength of the third-order spherical aberration of the objective optical element when recording and / or reproducing the first optical disk at the wavelength used by the first light beam It indicates the rate of change, and f indicates the focal length of the objective optical element in the first light flux. The optical pickup device according to claim 15, wherein the following conditional expression is satisfied.
0 ≦ δSAT2 / f (WFEλrms / (° C. mm)) ≦ + 0.0017
However, δSAT2 is δSA3 / δT of the objective optical element when performing recording and / or reproduction of the first optical disk at a wavelength used for the first light flux (wavelength variation accompanying temperature change is 0.05 nm / ° C.). That is, the temperature change of the third-order spherical aberration of the objective optical element at the time of recording and / or reproduction of the first optical disk at the use wavelength of the first light beam (wavelength variation with temperature change is 0.05 nm / ° C.). Refers to the rate.   The optical pickup device according to any one of claims 16 to 18, wherein the optical path difference providing structure comprises only a first basic structure that corrects spherical aberration caused by a temperature change.   The optical pickup device according to claim 19, wherein the first basic structure is an NPS structure.   The optical path difference providing structure includes a first basic structure that corrects spherical aberration caused by a temperature change, and a second basic structure that corrects axial chromatic aberration based on a wavelength change of a light beam emitted from the first light source. The objective optical element according to claim 16, wherein the objective optical element is superposed.   The objective optical element according to claim 21, wherein the first basic structure is an NPS structure, and the second basic structure is a diffractive structure. The NPS structure is a structure that makes the p-order diffracted light amount of the first light flux that has passed through the NPS structure larger than any other order diffracted light amount,
The diffractive structure is a structure that makes the q-order diffracted light quantity of the first light flux that has passed through the diffractive structure larger than any other order diffracted light quantity, and satisfies the following conditional expression: Item 22. The objective optical element according to Item 22.
p ≧ q (1)   The diffractive structure and the NPS structure both have a step, and the step amount in the optical axis direction of the step in the diffractive structure is smaller than the step amount in the optical axis direction of the step in the NPS structure. Item 22. The objective optical element according to Item 22 or 23.   The optical path difference providing structure is characterized in that, when viewed macroscopically, the distance in the optical axis direction from the surface apex gradually increases and then gradually decreases in the direction orthogonal to the optical axis. The objective optical element according to any one of the above.   The objective optical element according to claim 15, wherein the objective optical element is a single ball.

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