JPWO2013168692A1 - Objective lens and optical pickup device - Google Patents

Abstract

A single objective lens that can be compatible with three types of optical discs, BD / DVD / CD, has high moldability and is compatible with miniaturization, and forms an appropriate spot diameter even when using BD. An objective lens suitable for a compact optical pickup device capable of performing stable information recording / reproduction according to the above, and an optical pickup device equipped with this objective lens are provided. The first optical path difference providing structure in the central area of the objective lens is a structure having a first basic structure (2/1/1) and a second basic structure (1/1/1), and a second optical path difference in the intermediate area. The providing structure is a structure having a fourth basic structure (1/1/1) and a third basic structure (7/4) or (5/3), and the third optical path difference providing structure in the peripheral region is the first A structure having a fifth basic structure that makes the second-order or fourth-order diffracted light quantity of the light beam larger than any other order diffracted light quantity is adopted.

Description

  The present invention relates to an optical pickup apparatus, an objective lens, and an optical information recording / reproducing apparatus capable of recording and / or reproducing (recording / reproducing) information interchangeably with different types of optical disks.

  In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a wavelength 390 such as a blue-violet semiconductor laser is used. A laser light source of ˜420 nm has been put into practical use. When these blue-violet laser light sources are used, when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used, it is possible to record information of 15 to 20 GB on an optical disk having a diameter of 12 cm. When the NA of the objective optical element is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm.

  As an example of an optical disk using the above-described objective lens with NA of 0.85, there is a BD (Blu-ray disk). Since the coma generated due to the tilt (skew) of the optical disk increases, the BD has a thinner protective substrate than the DVD (0.1 mm compared to 0.6 mm for the DVD) and is caused by the skew. The amount of coma is reduced.

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

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

  Therefore, in order to simplify the configuration of the optical pickup device and reduce the cost, even in an optical pickup device having compatibility, the optical system for BD and the optical system for DVD or CD can be shared. It is preferable to reduce the number of optical components constituting the pickup device as much as possible. And, it is most advantageous to simplify the configuration of the optical pickup device and to reduce the cost to make the objective lens arranged facing the optical disc in common. In order to obtain a common objective lens for a plurality of types of optical disks having different recording / reproducing wavelengths, it is necessary to form an optical path difference providing structure such as a diffraction structure having a wavelength dependency of spherical aberration in the objective lens. is there.

  In addition, an objective lens that is commonly used for three types of optical disks of BD, DVD, and CD needs to be able to cope with differences in the required numerical apertures of BD, DVD, and CD. For example, in a BD having a large required numerical aperture, a light beam that has passed through almost the entire area of the effective optical surface of the objective lens is condensed on the information recording surface of the BD. The light beam that has passed through the region near the center of the lens is condensed on the information recording surface of the CD, but the light beam that has passed through the outer region of the lens needs to be blown off as a flare so as not to be collected on the information recording surface of the CD. Therefore, as shown in FIG. 1, the objective lens used in common for the three types of optical disks of BD, DVD, and CD collects light beams for concentric three regions (BD, DVD, and CD) as shown in FIG. Center region CN, BD and intermediate region MD for condensing the luminous flux for DVD, and peripheral region OT for condensing the luminous flux for BD), and each region needs to exhibit different optical performance behavior Comes out. Further, in order to show the behavior of different optical performance, a lens having a different structure that generates different diffraction orders for each region has been considered.

  In Patent Document 1, by defining a relational expression of the optical path difference function in the central region and the peripheral region, spherical aberration when using three types of optical discs is corrected well, and at the same time, spot performance deterioration due to unnecessary diffraction order light is reduced. There are described three types of compatible objective lenses for optical discs that can be avoided and have a sufficient working distance, and an optical information recording / reproducing apparatus equipped with the objective lenses.

JP2011-129239A

  However, the objective lens described in Patent Document 1 is not easy to manufacture because the number of ring zones in the peripheral region is very large and the pitch (ring zone width in the direction perpendicular to the optical axis) is also small. This problem is particularly noticeable when the objective lens is downsized. It has also been found that there is a problem that the spot diameter increases when BD is used. As a result of intensive research on the increase in the BD spot diameter, the present inventor has found that there are the following three causes.

The first cause is that the expected angle of the light source side optical surface is large in the vicinity of the effective diameter of the objective lens when a BD light beam is used. When designed to satisfy the sine condition, the power balance between the light source side optical surface and the disk side optical surface is uniquely determined, and therefore the light source side optical surface expected angle increases near the effective diameter of the light flux with wavelength λ1. Therefore, it becomes difficult for the cutting tool for cutting the die to cut the optical path difference providing structure as designed, and the processing accuracy is lowered.
The second cause is an increase in reflectivity associated with an increase in the incident angle of light on the optical surface because the expected angle of the objective lens is large. As a result, in the vicinity of the effective diameter when the wavelength λ1 is used, that is, in the vicinity of the outer diameter in the peripheral area, the rim intensity is reduced and the amount of transmitted light to the focused spot is reduced. Therefore, a phenomenon that can be referred to as a reverse apodization effect occurs. And an increase in spot diameter when using BD may occur.

  The third cause is the effect of the shadow effect. Here, what is found by the inventor's research on the effect of shadow will be described in detail below. FIG. 2 is a diagram showing a part of a cross-sectional view of an objective lens provided with a blazed optical path difference providing structure as an example. In FIG. 2, on the optical surface S of the objective lens, a serrated annular zone R is formed concentrically along the mother aspherical surface. Here, when a light beam incident on one annular zone R is considered, the light beam LB1 incident on the root side of the sawtooth passes through the annular zone R, exhibits a behavior based on the design, and proceeds in the objective lens. However, the light beam LB2 (indicated by hatching) incident on the leading end side of the saw blade is reflected outside by the inner side surface (step surface) SP after entering the annular zone R, so-called “shadow effect”. Is generated. Due to the effect of the shadow, the light beam LB2 is not condensed on the information recording surface of the optical disc, and the use efficiency of light is reduced accordingly. The effect of the shadow is particularly significant in the high NA region where the light refraction angle is large. In addition, due to mold processing accuracy and transferability problems, a fine shape such as the tip of the serrated ring zone or the vicinity of the root tends to cause a molding error with respect to the design shape, thereby increasing scattered light. Therefore, the use efficiency of light is reduced. That is, when the number of ring zones of the optical path difference providing structure is increased, the light region that does not contribute to light collection increases, and accordingly, the light use efficiency decreases accordingly.

  In the objective lens described in Patent Document 1, the number of annular zones in the peripheral region is very large, and the number of annular zones tends to increase from the optical axis side toward the periphery in the peripheral region. In the vicinity of the effective diameter of the luminous flux at the time of use, the influence of the shadow effect becomes very large, and the rim strength is reduced. As a result, a phenomenon that can be called a reverse apodization effect occurs, and an increase in the spot diameter when BD is used has occurred.

  The present invention has been made in view of the above-described problems, and has improved the moldability of the objective lens, can cope with downsizing, and is stable by forming an appropriate spot diameter even when using a BD. It is an object of the present invention to provide a compatible single objective lens for three types of optical discs of BD / DVD / CD capable of recording / reproducing information, and an optical pickup device equipped with this objective lens.

The objective lens according to claim 1 emits a first light source that emits a first light flux having a first wavelength λ1 (390 nm ≦ λ1 ≦ 415 nm) and a second light flux that has a second wavelength λ2 (630 nm ≦ λ2 ≦ 670 nm). And a third light source that emits a third light beam having a third wavelength λ3 (760 nm ≦ λ3 ≦ 820 nm), and a protective substrate having a thickness t1 using the first light beam. Recording and / or reproducing information, recording and / or reproducing information of a DVD having a protective substrate with a thickness of t2 (t1 <t2) using the second light beam, and using the third light beam An objective lens used in an optical pickup device for recording and / or reproducing information of a CD having a protective substrate having a thickness of t3 (t2 <t3),
The objective lens is a single lens,
The optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region,
The central region has a first optical path difference providing structure,
The intermediate region has a second optical path difference providing structure,
The peripheral region has a third optical path difference providing structure;
The objective lens condenses the first light flux that passes through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that passes through the central region. Are recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the central region is recorded and / or recorded on the information recording surface of the CD. Or collect it so that it can be regenerated,
The objective lens condenses the first light flux passing through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the intermediate area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the intermediate region is recorded and / or recorded on the information recording surface of the CD. Or do not concentrate so that it can be regenerated,
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the peripheral area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the peripheral area is recorded on the information recording surface of the CD. And / or do not collect light for playback
The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
The first basic structure is a blaze-type structure, and the first-order diffracted light quantity of the first light beam that has passed through the first basic structure is made larger than any other order of diffracted light quantity, and passes through the first basic structure. The first-order diffracted light quantity of the second light flux is made larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the third light flux that has passed through the first basic structure is changed to any other order diffracted light quantity. Bigger than
The second basic structure is a blazed structure, and the second-order diffracted light quantity of the first light beam that has passed through the second basic structure is made larger than any other order of diffracted light quantity, and passes through the second basic structure. The first order diffracted light quantity of the second light flux is made larger than any other order diffracted light quantity, and the first diffracted light quantity of the third light flux that has passed through the second basic structure is changed to any other order diffracted light quantity. Bigger than
The second optical path difference providing structure is a structure in which at least a third basic structure and a fourth basic structure are overlapped,
The third basic structure is a blazed structure, and the first-order diffracted light quantity of the first light beam that has passed through the third basic structure is made larger than any other order of diffracted light quantity, and passes through the third basic structure. The first-order diffracted light amount of the second light flux is made larger than any other order diffracted light amount,
The fourth foundation structure is a blazed structure, and the fifth or seventh-order diffracted light quantity of the first light flux that has passed through the fourth basic structure is made larger than any other order of diffracted light quantity, Making the third or fourth order diffracted light quantity of the second light flux that has passed through the structure larger than any other order diffracted light quantity;
The third optical path difference providing structure has at least a fifth basic structure,
The fifth basic structure is a blazed structure, and the second-order or fourth-order diffracted light quantity of the first light beam that has passed through the fifth basic structure is made larger than any other order diffracted light quantity. It is said.

  According to the objective lens of the first aspect, the three types of optical disks of BD / DVD / CD can be used interchangeably with a common objective lens. In addition, since the first and second optical path difference providing structures are formed by superimposing two types of blazed basic structures, the degree of design freedom is 2 as compared with the case where the optical path difference providing structure is formed with a single structure. It becomes possible to freely determine the magnification for the three disks while achieving compatibility. Further, the first basic structure existing in the central region has a (1/1/1) structure (the most first-order diffracted light is generated in any of the first light flux, the second light flux, and the third light flux). Since the basic structure is a (2/1/1) structure (the second-order diffracted light is generated most in the first light beam, and the first-order diffracted light is generated most in the second light beam and the third light beam). In any of the CDs, high diffraction efficiency can be obtained at all three wavelengths while setting the magnification of the objective lens to 0 or almost 0. In addition, since the amount of step of the diffractive structure in the central region does not become too large, it is possible to suppress light loss due to manufacturing errors, to suppress the shadow effect, to ensure high light utilization efficiency, and to maintain the wavelength and temperature. Variations in diffraction efficiency during the change can also be reduced.

  In addition, the third basic structure existing in the intermediate region is a (1/1) structure (most first-order diffracted light is generated in the first and second light beams), and the fourth basic structure is a (5/3) structure ( The 5th-order diffracted light is generated most in the first light beam, the 3rd-order diffracted light is generated most in the second light beam, or the fourth basic structure is the (7/4) structure (the 7th-order diffracted light is most generated in the first light beam). In the second light flux, most of the fourth-order diffracted light is generated), so that it is possible to appropriately control the variation of spherical aberration at the time of temperature change when using BD or DVD. Also, high diffraction efficiency can be obtained when using BD and DVD.

  Furthermore, since the fifth basic structure existing in the peripheral region makes the second-order or fourth-order diffracted light quantity larger than any other order diffracted light quantity when passing the first light flux, the pitch is set as compared with the first-order case. Since the number of ring zones can be reduced, manufacturing can be facilitated and errors can be reduced in both mold processing and resin molding. In the peripheral area, the number of annular zones tends to increase from the optical axis side toward the periphery, and the angle of view of the objective lens increases near the outer diameter in the peripheral area. Decrease, increase in reflectance, etc., especially when the pitch is small, this problem becomes significant and the rim strength decreases, but the pitch of the fifth foundation structure in the peripheral region can be increased. Therefore, it is possible to reduce a decrease in machining accuracy and to prevent a decrease in rim strength. Furthermore, since the number of ring zones decreases, the influence of the shadow effect around the effective diameter can be reduced, and an increase in spot diameter due to a decrease in rim strength can be suppressed. In addition, when the first-order diffracted light quantity is maximized when the first light beam passes, if the objective lens is to be miniaturized, the pitch is inevitably narrowed and cannot be manufactured due to processing accuracy. However, since the pitch can be increased, the objective lens can be reduced in size.

The objective lens according to claim 2 is the invention according to claim 1, wherein the ratio of pupil transmittance in the vicinity of the peripheral area of the intermediate area to the vicinity of the optical axis center of the objective lens in the second light flux. r2 is
r2 ≦ 0.9 (1)
And
When the effective diameter of the objective lens in the second light flux is h2, the imaging magnification in the second light flux is m2, and the focal length in the first light flux is f1,
0.66 ≦ h2 / (2 · f1 · (1-m2)) ≦ 0.75 (2)
It is characterized by satisfying.

  The objective lens of the present invention overlaps two basic structures in the intermediate region, and further, in a certain region, the number of annular zones tends to increase toward the periphery from the optical axis. In the vicinity of the region, the light utilization efficiency is deteriorated. As a result, the ratio r2 of the pupil transmittance in the vicinity of the peripheral region of the intermediate region with respect to the vicinity of the optical axis center of the objective lens in the second light flux is within the range of the expression (1), and a phenomenon that can be called a reverse apodization effect occurs. When using a DVD, the spot diameter may increase. The term “near” in the vicinity of the optical axis center refers to a range of 10% of the effective radius when using a DVD from the optical axis to the direction perpendicular to the optical axis. The vicinity of the peripheral area of the intermediate area refers to a range of 10% of the effective radius when using the DVD with respect to the intermediate area direction from the boundary between the intermediate area and the peripheral area. A range of 10% of the effective radius when using a DVD from the outer diameter of the area to the intermediate area direction.

  The objective lens of the present invention is a BD / DVD / CD compatible objective lens. However, since there are only two optical surfaces, the sine condition cannot be satisfied for all optical disks, and BD, DVD, Since the sine condition is set so that the balance is improved to some extent in all the CDs, there is a possibility that the spot diameter is further increased when the BD is used.

  However, according to the invention described in claim 2, by satisfying a value equal to or higher than the lower limit of the expression (2), the effective diameter of the second light flux when the objective lens is used in DVD is increased, that is, the NA is increased. Since the spot diameter when the DVD is used is narrowed down, the reverse apodization effect when using the DVD can be suppressed. In addition, when the BD is used, an intermediate region having a relatively small amount of transmitted light as compared with the vicinity of the optical axis is widened, so that an apodization effect is produced and the spot diameter of the BD can be reduced. This can be preferably used particularly for a compatible lens for reproduction of three types of optical disks of BD / DVD / CD. Furthermore, by satisfying a value equal to or lower than the upper limit of the formula (2), the spot diameter when using the DVD is not reduced more than necessary. Also, on the DVD side, the error sensitivity of wavefront aberration can be kept small, and stable recording / reproducing characteristics can be obtained.

The objective lens described in claim 3 is the invention described in claim 1 or 2 and is characterized by satisfying the following expression.
1.0 ≦ f1 ≦ 2.2 (3)

  When the focal length f1 when using the BD is within the range of the expression (3), the objective lens becomes relatively small, and therefore the pitch in the vicinity of the outer diameter in the peripheral region becomes even finer, and the problem of the present invention is large. However, such a large problem can be solved by making the second-order or fourth-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity. Further, if the focal length f1 is within the range of the expression (3), the number of ring zones in the central region is increased in order to secure a working distance when using the CD, that is, in order to increase the paraxial power of diffraction. Correspondingly, it is necessary to increase the number of ring zones in the intermediate region. As a result, in the vicinity of the peripheral region of the intermediate region, there is a possibility that the light utilization efficiency will be further reduced and the spot diameter may be increased when using DVD or BD. In this case, formula (2) It can be solved by satisfying. The working distance is a distance in the optical axis direction from the surface of the optical disk to the position closest to the optical disk of the objective lens.

  Furthermore, since the focal length is within the range of the expression (3), the distance from the objective lens to the disk can be reduced, and it can be suitably mounted on a slim type optical pickup device.

An objective lens according to a fourth aspect is the invention according to any one of the first to third aspects, wherein when an effective diameter of the first light flux of the objective lens is h1, the following expression is obtained. It is characterized by satisfying.
1.9 ≦ h1 ≦ 3.0 (4)

  When the objective lens is a small objective lens satisfying the formula (4), the pitch in the vicinity of the outer diameter in the peripheral region becomes even finer, and the problem of the present invention becomes large. This can be solved by making the second-order or fourth-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity. In addition, since the pitch in the vicinity of the intermediate region, particularly the peripheral region of the intermediate region is also small, there is a possibility that the spot diameter increases when using DVD or BD. In this case, satisfying the equation (2) solves the problem. it can.

The objective lens according to claim 5 is the invention according to any one of claims 1 to 4, wherein the i-th basic structure of the objective lens has the following formula φ _i (h) = (C _i2 × h ² + C _i4 × h ⁴ + C _i6 × h ⁶ + C _i8 × h ⁸ + C _i10 × h ¹⁰ ) Miλ / λB _i
(Where h (unit: mm) is the height from the optical axis, C _i2 , C _i4 , C _i6 ... _Are secondary in the optical path difference function (i is a natural number) of the i-th substructure, The fourth-order and sixth-order optical path difference function coefficients, Mi is the diffraction order in the optical path difference function of the i-th basic structure that maximizes the diffraction order of the incident light beam, and λ (unit: mm) is the use of the incident light beam. ΛB _i (unit: mm) represents a manufacturing wavelength in the i-th basic structure, respectively)), and the focal length of the first basic structure is expressed as fD ₁ When defined as (unit: mm), the following equation is satisfied,
−0.40 <f1 / fD ₁ <−0.10 (5)
(However, fD ₁ = −λB ₁ / (2 × C ₁₂ × M1 × λ), and the value of M1 is 1.)
When the effective diameter (diameter) of the second light beam is defined as h2 (unit: mm) and the effective diameter (diameter) of the third light beam is defined as h3 (unit: mm), the following conditional expression (6)
−0.025 <(φ ₅ (h3 / 2) −φ ₅ (h2 / 2)) / (M5 × f1) <0.025 (6)
(However, the value of M5 is 2 or 4.)
It is characterized by satisfying.

  Satisfying the expression (5) is preferable because the chromatic aberration at the time of using the BD does not become too large while ensuring the working distance at the time of using the CD. If the lower limit of Expression (5) is exceeded, the pitch is widened, so that the workability is improved, and the amount of chromatic aberration generated when the first optical disk is used can be suppressed to a level that allows recording and reproduction. Moreover, it is preferable to fall below the upper limit of the formula (5) because a working distance when using a CD can be sufficiently secured.

When the effective diameter (diameter) of the second light beam is defined as h2 (unit: mm) and the effective diameter (diameter) of the third light beam is defined as h3 (unit: mm), the following condition (6)
−0.025 <(φ ₅ (h3 / 2) −φ ₅ (h2 / 2)) / (M5 × f1) <0.025 (6)
(However, the value of M5 is 2 or 4.)
By satisfying the above, the second and third light beams in which unnecessary diffraction orders of the second and third light beams transmitted through the peripheral region are transmitted through the central region while satisfactorily correcting the spherical aberration generated when the environment is changed when the BD is used. Since it is possible to avoid convergence in the vicinity of the image forming position, it is preferable because deterioration of spot performance can be suppressed. Moreover, since the number of steps does not increase too much by making it within the range of the formula (6), manufacturing is easy, and a decrease in light utilization efficiency is suppressed, so that a good spot can be obtained, and the upper limit is set. By lowering, the spherical aberration at the time of temperature change does not become too large.

The objective lens of Claim 6 is invention as described in any one of Claims 1-5, Comprising: The following formula | equation is satisfy | filled.
0.68 ≦ h2 / (2 · f1 · (1-m2)) ≦ 0.74 (2) ′

  The smaller the objective lens, the smaller the pitch of the basic structure, and the lowering of the rim strength when using the BD becomes more significant, that is, the spot diameter increases when using the BD. However, it is preferable to satisfy the formula (2) ′ because the apodization effect at the time of using the BD becomes strong, and even with such an objective lens, it is possible to obtain an appropriate spot diameter for BD recording / reproduction. In addition, since the pitch in the vicinity of the intermediate region, particularly the peripheral region of the intermediate region is also small, there is a possibility that the spot diameter will increase when using the DVD, but it is preferable because it can be solved by satisfying the equation (2) ′.

An objective lens according to a seventh aspect is the invention according to any one of the first to sixth aspects, wherein the thickness of the objective lens on the optical axis is d (mm) as follows: It is characterized by satisfying the formula.
1.0 ≦ d / f1 ≦ 1.5 (7)

  When dealing with a short-wavelength, high-NA optical disk such as BD, the objective lens is likely to generate astigmatism and decent coma, but the above configuration causes astigmatism and It is possible to suppress the occurrence of decentration coma.

  In addition, when the objective lens is thick, the working distance at the time of recording / reproducing of the CD tends to be shortened. Therefore, it is preferable not to exceed the upper limit of Expression (7). Furthermore, by not exceeding the lower limit of Expression (7), it is possible to suppress the occurrence of astigmatism and decentration coma.

The objective lens according to claim 8 is the invention according to any one of claims 1 to 7, wherein at least a step of the first basic structure provided near the optical axis of the central region is light. Facing the opposite direction of the axis,
The second basic structure provided at least near the optical axis of the central region is characterized in that the step is directed in the direction of the optical axis.

  Thereby, in the first optical path difference providing structure in which the first basic structure and the second basic structure are overlapped, the amount of step in the optical axis direction can be further reduced, thereby suppressing the shadow effect and the diffraction efficiency at the time of wavelength variation. It is possible to further suppress the decrease in the above.

The objective lens according to claim 9 is the invention according to any one of claims 1 to 8, and satisfies the following expression when the total number of annular zones in the peripheral region is N3. It is a feature.
5 (mm) ≤ N3 · f1 ≤ 100 (mm) (8)

  By setting the value of equation (8) below the upper limit, it is possible to prevent the pitch from becoming too small, so that it is possible to suppress the effect of shadows, to prevent deterioration of workability, and to reduce the shape error, resulting in diffraction efficiency. Can be prevented. In addition, by setting the range in (8), chromatic aberration can also be reduced.

  An optical pickup device according to a tenth aspect has the objective lens according to any one of the first to ninth aspects.

An optical pickup device according to an eleventh aspect is the optical pickup device according to the tenth aspect, in which at least the coupling lens through which the first light flux and the second light flux pass, and the coupling lens in the optical axis direction. Has an actuator to move to
When the first light beam passes, the coupling lens can be displaced in the optical axis direction by the actuator;
When the second light beam passes, the position of the coupling lens in the optical axis direction is fixed.

  For example, in order to cope with a BD having a plurality of information recording layers, it is conceivable that when a BD is used, the coupling lens is displaced in the optical axis direction so as to correspond to recording / reproduction on each information recording layer. In such a case, the function of displacing the coupling lens in the optical axis direction is indispensable. However, when using a DVD, the coupling lens may be fixed without being displaced in the optical axis direction. is there. The reason is that flare does not occur when using BD, but flare occurs when using DVD. By changing the coupling lens, the flare aberration changes, and as a result, the flare is recorded / reproduced. The reason is that there is a possibility of adversely affecting the driving force, and the reason why it is desired to simplify the control of the coupling lens displacement by the drive. For such a problem, the objective lens of the present invention is used to suppress aberrations caused by changes in temperature and wavelength when using a DVD. As a result, a coupling lens is used when the second light beam passes when using a DVD. Can be recorded / reproduced with respect to the information recording surface of the DVD even when the position in the optical axis direction is fixed (that is, when spherical aberration correction is not performed by the coupling lens). We were able to solve the problem.

  The optical pickup device according to the present invention has at least three light sources: a first light source, a second light source, and a third light source. Furthermore, the optical pickup device of the present invention condenses the first light beam on the information recording surface of the BD, condenses the second light beam on the information recording surface of the DVD, and focuses the third light beam on the information recording surface of the CD. A condensing optical system for condensing the light. The optical pickup device of the present invention includes a light receiving element that receives a reflected light beam from an information recording surface of a BD, DVD, or CD.

  The BD has a protective substrate having a thickness t1 and an information recording surface. The DVD has a protective substrate having a thickness t2 (t1 <t2) and an information recording surface. The CD has a protective substrate having a thickness of t3 (t2 <t3) and an information recording surface. The BD, DVD, or CD may be a multi-layer optical disc having a plurality of information recording surfaces.

  In this specification, the BD means that information is recorded / reproduced by a light beam having a wavelength of 390 to 415 nm, an objective lens having a designed NA of 0.80 to 0.90, and the thickness of the protective substrate is 0.02. It is a generic term for BD series optical discs of up to 0.125 mm, and includes BD having only a single information recording layer, BD having two or more information recording layers, and the like. Further, in this specification, the DVD is a light beam having a wavelength of 630 to 670 nm, and information is recorded / reproduced by an objective lens having a designed NA of 0.550 to 0.70. It is a generic term for DVD series optical discs of about 0.6 mm, and includes DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. Further, in this specification, a CD is a light beam having a wavelength of 760 to 820 nm, information is recorded / reproduced by an objective lens having a designed NA of 0.40 to 0.55, and the thickness of the protective substrate is It is a generic name for CD series optical discs of about 1.2 mm, 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 the order of DVD and CD.

In addition, regarding the thicknesses t1, t2, and t3 of the protective substrate, it is preferable to satisfy the following conditional expressions (9), (10), and (11), but is not limited thereto. The thickness of the protective substrate referred to here is the thickness of the protective substrate provided on the surface of the optical disk. That is, the thickness of the protective substrate from the optical disc surface to the information recording surface closest to the surface.
0.050 mm ≤ t1 ≤ 0.125 mm (9)
0.5mm ≤ t2 ≤ 0.7mm (10)
1.0 mm ≤ t3 ≤ 1.3 mm (11)

In the present specification, the first light source, the second light source, and the third light source are preferably laser light sources.
As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used. The first wavelength λ1 of the first light beam emitted from the first light source, the second wavelength λ2 (λ2> λ1) of the second light beam emitted from the second light source, and the third of the third light beam emitted from the third light source. The wavelength λ3 (λ3> λ2) preferably satisfies the following conditional expressions (12) and (13).
1.5 · λ1 <λ2 <1.7 · λ1 (12)
1.8 · λ1 <λ3 <2.0 · λ1 (13)

  The first wavelength λ1 of the first light source is 390 nm or more and 415 nm or less, the second wavelength λ2 of the second light source is 630 nm or more and 670 nm or less, and the third wavelength λ3 of the third light source is 760 nm or more and 820 nm or less.

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

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

  The condensing optical system has an objective lens. The condensing optical system preferably has a coupling lens such as a collimator in addition to the objective lens. The coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam. The collimator is a type of coupling lens, and is a lens that emits light incident on the collimator as parallel light. In this specification, the objective lens refers to a single lens that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source on the information recording / reproducing surface of the optical disk. . In addition, the single objective lens of the present invention is preferably a plastic lens. A convex lens is preferable. The objective lens preferably has a refractive surface that is aspheric. In the objective lens, the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.

Moreover, it is preferable to use an alicyclic hydrocarbon-based polymer material such as a cyclic olefin-based resin material as the plastic material constituting the objective lens. The resin material has a refractive index of 1.50 to 1.60 at a temperature of 25 ° C. with respect to a wavelength of 405 nm, and a wavelength of 405 nm accompanying a temperature change within a temperature range of −5 ° C. to 70 ° C. The refractive index change rate dN / dT (° C. ⁻¹ ) is -20 × 10 ⁻⁵ to ⁻⁵ × 10 ⁻⁵ (more preferably −10 × 10 ⁻⁵ to ⁻⁸ × 10 ⁻⁵ ). It is more preferable to use a certain resin material. When the objective lens is a plastic lens, it is preferable that the coupling lens is also a plastic lens.

  Some preferred examples of the alicyclic hydrocarbon polymer are shown below.

  A first preferred example includes a polymer block [A] containing a repeating unit [1] represented by the following formula (I), a repeating unit [1] represented by the following formula (I) and the following formula ( II) and / or polymer block [B] containing a repeating unit [3] represented by the following formula (III), and repeating in the block [A] From the block copolymer in which the relationship between the molar fraction a (mol%) of the unit [1] and the molar fraction b (mol%) of the repeating unit [1] in the block [B] is a> b. It is the resin composition which becomes.

(In the formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and R ^{2 to} R ¹² each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, or 1 carbon atom. ˜20 alkoxy groups or halogen groups.)

(In the formula, R ¹³ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)

(In the formula, R ¹⁴ and R ¹⁵ each independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)

  Next, a second preferred example is obtained by addition polymerization of a monomer composition comprising at least an α-olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (IV). A polymer (B) obtained by addition polymerization of a polymer (A), a monomer composition comprising an α-olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (V) ).

[Wherein, n is 0 or 1, m is 0 or an integer of 1 or more, q is 0 or 1, and R ^{1 to} R ¹⁸ , Ra and Rb each independently represent a hydrogen atom or a halogen atom. Or a hydrocarbon group, R ^{15 to} R ¹⁸ may be bonded to each other to form a monocycle or polycycle, and the monocycle or polycycle in parentheses may have a double bond, R ¹⁵ and R ¹⁶ , or R ¹⁷ and R ¹⁸ may form an alkylidene group. ]

[Wherein, R ^{19 to} R ²⁶ each independently represents a hydrogen atom, a halogen atom or a hydrocarbon group. ]

  In order to add further performance to the resin material, the following additives may be added.

(Stabilizer)
It is preferable to add at least one stabilizer selected from a phenol stabilizer, a hindered amine stabilizer, a phosphorus stabilizer, and a sulfur stabilizer. By suitably selecting and adding these stabilizers, for example, it is possible to more highly suppress the white turbidity and the optical characteristic fluctuations such as the refractive index fluctuations when continuously irradiated with light having a short wavelength of 405 nm. .

  As a preferable phenol-based stabilizer, conventionally known ones can be used, for example, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2 , 4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate and the like, and JP-A Nos. 63-179953 and 1-168643. Acrylate compounds described in Japanese Patent Publication No. 1; octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2,2'-methylene-bis (4-methyl-6-tert-butylphenol) ), 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3 5-di-t-butyl-4-hydroxybenzyl) benzene, tetrakis (methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenylpropionate)) methane [ie pentaerythritol Methyl-tetrakis (3- (3,5-di-tert-butyl-4-hydroxyphenylpropionate))], triethylene glycol bis (3- (3-tert-butyl-4-hydroxy-5-methylphenyl) Alkyl-substituted phenolic compounds such as propionate); 6- (4-hydroxy-3,5-di-t-butylanilino) -2,4-bisoctylthio-1,3,5-triazine, 4-bisoctylthio- 1,3,5-triazine, 2-octylthio-4,6-bis- (3,5-di-t-butyl-4-oxyanilino) -1,3,5-to Triazine group-containing phenol compounds such as azine; and the like.

  Preferred hindered amine stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) succinate, bis ( 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis (N-octoxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-benzyloxy-2, 2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-cyclohexyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6) -Pentamethyl-4-piperidyl) 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1-acryloyl-2,2,6 6-tetramethyl-4-piperidyl) 2,2-bis (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1,2,2,6,6-pentamethyl) -4-piperidyl) decandioate, 2,2,6,6-tetramethyl-4-piperidyl methacrylate, 4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy]- 1- [2- (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy) ethyl] -2,2,6,6-tetramethylpiperidine, 2-methyl-2- (2 , 2,6,6-tetramethyl-4-piperidyl) amino-N- (2,2,6,6-tetramethyl-4-piperidyl) propionamide, tetrakis (2,2,6,6-tetramethyl- 4-pipe Jill) 1,2,3,4-butane tetracarboxylate, tetrakis (1,2,2,6,6-pentamethyl-4-piperidyl) 1,2,3,4-butane tetracarboxylate, and the like.

  Further, the preferable phosphorus stabilizer is not particularly limited as long as it is a substance usually used in the general resin industry. For example, triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonyl). Phenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9 Monophosphite compounds such as 1,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; 4,4′-butylidene-bis (3-methyl-6-tert-butylphenyl-di-tridecyl) Phosphite), 4,4 'isopropylidene-bis (phenyl-di-alkyl (C12-C15) phos Aito) and the like diphosphite compounds such as. Among these, monophosphite compounds are preferable, and tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like are particularly preferable.

  Preferred sulfur stabilizers include, for example, dilauryl 3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3- Thiodipropionate, pentaerythritol-tetrakis- (β-lauryl-thio) -propionate, 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane Etc.

  The blending amount of each of these stabilizers is appropriately selected within a range that does not impair the purpose of the present invention, but is usually 0.01 to 2 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based copolymer, Preferably it is 0.01-1 mass part.

(Surfactant)
A surfactant is a compound having a hydrophilic group and a hydrophobic group in the same molecule. The surfactant can prevent white turbidity of the resin composition by adjusting the rate of moisture adhesion to the resin surface and the rate of moisture evaporation from the surface.

  Specific examples of the hydrophilic group of the surfactant include a hydroxy group, a hydroxyalkyl group having 1 or more carbon atoms, a hydroxyl group, a carbonyl group, an ester group, an amino group, an amide group, an ammonium salt, a thiol, a sulfonate, A phosphate, a polyalkylene glycol group, etc. are mentioned. Here, the amino group may be primary, secondary, or tertiary. Specific examples of the hydrophobic group of the surfactant include an alkyl group having 6 or more carbon atoms, a silyl group having an alkyl group having 6 or more carbon atoms, and a fluoroalkyl group having 6 or more carbon atoms. Here, the alkyl group having 6 or more carbon atoms may have an aromatic ring as a substituent. Specific examples of the alkyl group include hexyl, heptyl, octyl, nonyl, decyl, undecenyl, dodecyl, tridecyl, tetradecyl, myristyl, stearyl, lauryl, palmityl, cyclohexyl and the like. Examples of the aromatic ring include a phenyl group. The surfactant only needs to have at least one hydrophilic group and hydrophobic group as described above in the same molecule, and may have two or more groups.

  More specifically, examples of such surfactants include myristyl diethanolamine, 2-hydroxyethyl-2-hydroxydodecylamine, 2-hydroxyethyl-2-hydroxytridecylamine, 2-hydroxyethyl-2- Hydroxytetradecylamine, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, di-2-hydroxyethyl-2-hydroxydodecylamine, alkyl (8-18 carbon atoms) benzyldimethylammonium chloride, ethylene Examples thereof include bisalkyl (carbon number 8 to 18) amide, stearyl diethanolamide, lauryl diethanolamide, myristyl diethanolamide, palmityl diethanolamide, and the like. Among these, amine compounds or amide compounds having a hydroxyalkyl group are preferably used. In the present invention, two or more of these compounds may be used in combination.

  From the viewpoint of effectively suppressing the white turbidity of the molded product accompanying fluctuations in temperature and humidity and maintaining the light transmittance of the molded product high, the surfactant is added to 100 parts by mass of the alicyclic hydrocarbon-based polymer. It is preferable to add 0.01-10 mass parts with respect to it. The addition amount of the surfactant is more preferably 0.05 to 5 parts by mass, and still more preferably 0.3 to 3 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based polymer.

(Plasticizer)
The plasticizer is added as necessary to adjust the melt index of the copolymer.

  Plasticizers include bis (2-ethylhexyl) adipate, bis (2-butoxyethyl) adipate, bis (2-ethylhexyl) azelate, dipropylene glycol dibenzoate, tri-n-butyl citrate, tri-citrate -N-butylacetyl, epoxidized soybean oil, 2-ethylhexyl epoxidized tall oil, chlorinated paraffin, tri-2-ethylhexyl phosphate, tricresyl phosphate, t-butylphenyl phosphate, tri-2-ethylhexyl phosphate Diphenyl, dibutyl phthalate, diisohexyl phthalate, diheptyl phthalate, dinonyl phthalate, diundecyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisodecyl phthalate, ditridecyl phthalate, butylbenzyl phthalate, dicyclophthalate Known materials such as xylyl, di-2-ethylhexyl sebacate, tri-2-ethylhexyl trimellitic acid, Santizer 278, Paraplex G40, Drapex 334F, Plastolein 9720, Mesamol, DNODP-610, HB-40 are applicable. . The selection of the plasticizer and the addition amount are appropriately performed under the condition that the permeability of the copolymer and the resistance to environmental changes are not impaired.

  As these resins, cycloolefin resins are preferably used, and specifically, ZEONEX manufactured by Nippon Zeon, APEL manufactured by Mitsui Chemicals, TOPAS manufactured by TOPAS ADVANCED POLYMERS, ARTON manufactured by JSR, and the like are preferable. Take as an example.

  Further, the Abbe number of the material constituting the objective lens is preferably 35 or more and 80 or less, and more preferably 50 or more and 80 or less.

  The objective lens will be described below. The objective lens of the present invention is a single lens, and at least one optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region. The central region is preferably a region including the optical axis of the objective lens, but a minute region including the optical axis is used as an unused region or a special purpose region, and the surroundings are defined as a central region (also referred to as a central region). Also good. The central region, the intermediate region, and the peripheral region are preferably provided on the same optical surface. As shown in FIG. 1, the central region CN, the intermediate region MD, and the peripheral region OT are preferably provided concentrically around the optical axis on the same optical surface. In addition, a first optical path difference providing structure is provided in the central area of the objective lens, a second optical path difference providing structure is provided in the intermediate area, and a third optical path difference providing structure is provided in the peripheral area. The central region, the intermediate region, and the peripheral region are preferably adjacent to each other, but there may be a slight gap between them.

  The central area of the objective lens can be said to be a BD / DVD / CD shared area used for recording / reproducing BD, DVD, and CD. That is, the objective lens condenses the first light flux passing through the central area so that information can be recorded / reproduced on the information recording surface of the BD, and the second light flux passing through the central area is recorded as information recording on the DVD. The light is condensed so that information can be recorded and / or reproduced on the surface, and the third light flux passing through the central region is condensed so that information can be recorded / reproduced on the information recording surface of the CD. In addition, the first optical path difference providing structure provided in the central region has the BD protective substrate thickness t1 and the DVD protective substrate thickness with respect to the first and second light fluxes passing through the first optical path difference providing structure. It is preferable to correct spherical aberration generated due to the difference in thickness t2 / spherical aberration generated due to the difference in wavelength between the first light beam and the second light beam. Further, the first optical path difference providing structure is different from the thickness t1 of the BD protective substrate and the thickness t3 of the CD protective substrate with respect to the first and third light fluxes that have passed through the first optical path difference providing structure. It is preferable to correct the spherical aberration caused by the difference in the wavelength of the first light beam and the third light beam.

  The intermediate area of the objective lens is used for BD / DVD recording / reproduction, and can be said to be a BD / DVD shared area not used for CD recording / reproduction. That is, the objective lens condenses the first light flux passing through the intermediate area so that information can be recorded / reproduced on the information recording surface of the BD, and the second light flux passing through the intermediate area is recorded as information recording on the DVD. Light is collected so that information can be recorded / reproduced on the surface. On the other hand, the third light flux passing through the intermediate region is not condensed so that information can be recorded / reproduced on the information recording surface of the CD. The third light flux passing through the intermediate region of the objective lens preferably forms a flare on the information recording surface of the CD. As shown in FIG. 3, in the spot formed on the information recording surface of the CD by the third light beam that has passed through the objective lens, the spot center having a high light quantity density in the order from the optical axis side (or the spot center) to the outside. It is preferable to have a portion SCN, a spot intermediate portion SMD whose light intensity density is lower than that of the spot central portion, and a spot peripheral portion SOT whose light intensity density is higher than that of the spot intermediate portion and lower than that of the spot central portion. The center portion of the spot is used for recording / reproducing information on the optical disc, and the middle portion of the spot and the peripheral portion of the spot are not used for recording / reproducing information on the optical disc. In the above, this spot peripheral part is called flare. However, there is no spot middle part around the center part of the spot and there is a spot peripheral part, that is, even when a light spot is formed thinly around the condensing spot, the spot peripheral part may be called a flare. Good. In other words, it can be said that the third light flux that has passed through the intermediate region of the objective lens preferably forms a spot peripheral portion on the information recording surface of the CD.

  The peripheral area of the objective lens is used for BD recording / reproduction, and can be said to be a BD-dedicated area that is not used for DVD / CD recording / reproduction. That is, the objective lens condenses the first light flux passing through the peripheral region so that information can be recorded / reproduced on the information recording surface of the BD. On the other hand, the second light flux that passes through the peripheral area is not condensed so that information can be recorded / reproduced on the information recording surface of the DVD, and the third light flux that passes through the peripheral area does not converge. Do not collect light so that information can be recorded / reproduced on top. The second light flux and the third light flux that pass through the peripheral area of the objective lens preferably form a flare on the information recording surface of DVD and CD. That is, it is preferable that the second light flux and the third light flux that have passed through the peripheral area of the objective lens form a spot peripheral portion on the information recording surface of DVD and CD.

  The first optical path difference providing structure is preferably provided in a region of 70% or more of the area of the central region of the objective lens, and more preferably 90% or more. More preferably, the first optical path difference providing structure is provided on the entire surface of the central region. The second optical path difference providing structure is preferably provided in a region of 70% or more of the area of the intermediate region of the objective lens, and more preferably 90% or more. More preferably, the second optical path difference providing structure is provided on the entire surface of the intermediate region. The third optical path difference providing structure is preferably provided in a region of 70% or more of the area of the peripheral region of the objective lens, and more preferably 90% or more. More preferably, the third optical path difference providing structure is provided on the entire surface of the peripheral region.

  In addition, the optical path difference providing structure in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure of the present invention is preferably 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. When the objective lens provided with the optical path difference providing structure is a single aspherical lens, the incident angle of the light flux to the objective lens differs depending on the height from the optical axis. Each will be slightly different. For example, when the objective lens is a single aspherical convex lens, the step amount increases as the distance from the optical axis increases even with the optical path difference providing structure that provides the same optical path difference.

  In addition, the diffractive structure referred to in this specification is a general term for structures that have a step and have an action of converging or diverging a light beam by diffraction. For example, a plurality of unit shapes are arranged around the optical axis, and a light beam is incident on each unit shape, and the wavefront of the transmitted light is shifted between adjacent annular zones, resulting in new It includes a structure that converges or diverges light by forming a simple wavefront. The diffractive structure preferably has a plurality of steps, and 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. In addition, when the objective lens provided with the diffractive structure is a single aspherical lens, the incident angle of the light beam to the objective lens differs depending on the height from the optical axis, so the step amount of the diffractive structure is slightly different for each annular zone. It will be. For example, when the objective lens is a single lens aspherical convex lens, even if the diffractive structure generates diffracted light of the same diffraction order, the step amount increases as the distance from the optical axis increases.

  By the way, it is preferable that the optical path difference providing structure has a plurality of concentric annular zones centered on the optical axis. In addition, the basic structure of the optical path difference providing structure can generally have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shape including the optical axis is roughly divided into a blazed structure and a staircase structure. Is done.

  As shown in FIGS. 4A and 4B, the blazed structure means that the cross-sectional shape including the optical axis of an optical element having an optical path difference providing structure is a sawtooth shape. Although the expression is sawtooth, a shape in which the apex portion of the sawtooth is rounded is also included in the sawtooth. In the example of FIG. 4, it is assumed that the upper side is the light source side and the lower side is the optical disk side, and the optical path difference providing structure is formed on a flat surface as an aspherical surface. In the blazed structure, the length in the direction perpendicular to the optical axis of one blaze unit is called a pitch P. (See FIGS. 4A and 4B.) The length of the step in the direction parallel to the optical axis of the blaze is referred to as a step amount B. (See Fig. 4 (a))

  In addition, as shown in FIGS. 4C and 4D, the staircase structure has a small staircase shape in cross section including the optical axis of an optical element having an optical path difference providing structure (referred to as a staircase unit). ). In the present specification, “V level” means a ring-shaped surface (hereinafter also referred to as a terrace surface) corresponding to (or facing) the optical axis vertical direction in one step unit of the step structure. In other words, it is divided by V steps and divided into V ring zones. Particularly, a three-level or higher staircase structure has a small step and a large step. For example, the optical path difference providing structure illustrated in FIG. 4C is referred to as a five-level step structure, and the optical path difference providing structure illustrated in FIG. 4D is referred to as a two-level step structure (also referred to as a binary structure). . A two-level staircase structure will be described. A plurality of annular zones including a plurality of concentric annular zones around the optical axis, and a plurality of annular zones including the optical axis of the objective lens have a plurality of stepped surfaces Pa and Pb extending in parallel to the optical axis, The light source side terrace surface Pc for connecting the light source side ends of the adjacent step surfaces Pa and Pb and the optical disk side terrace surface Pd for connecting the optical disk side ends of the adjacent step surfaces Pa and Pb are formed. The surface Pc and the optical disc side terrace surface Pd are alternately arranged along the direction intersecting the optical axis. In the staircase structure, the length of one step unit in the direction perpendicular to the optical axis is referred to as a pitch P (see FIGS. 4C and 4D). The length of the step in the direction parallel to the optical axis of the staircase is referred to as step amounts B1 and B2. In the case of a three-level or higher staircase structure, a large step amount B1 and a small step amount B2 exist (see FIG. 4C).

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

  When the optical path difference providing structure has a blazed structure, the sawtooth shape as a unit shape is repeated. As shown in FIG. 4 (a), the same sawtooth shape may be repeated, and as shown in FIG. 4 (b), the shape of the sawtooth shape gradually increases as it moves away from the optical axis. A shape in which the pitch becomes longer or a shape in which the pitch becomes shorter may be used. In addition, in some areas, the blazed structure has a step opposite to the optical axis (center) side, and in other areas, the blazed structure has a step toward the optical axis (center). It is good also as a shape in which the transition area | region required in order to switch the direction of the level | step difference of a blaze | braze type | mold structure is provided in the meantime. In addition, when it is set as the structure which switches the direction of the level | step difference of a blaze | braze type | mold in this way, it becomes possible to widen an annular zone pitch and it can suppress the transmittance | permeability fall by the manufacturing error of an optical path difference providing structure.

The first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure may be provided on different optical surfaces of the objective lens, but are preferably provided on the same optical surface.
Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing. The first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the light source side surface of the objective lens rather than the optical disk side surface of the objective lens.
The first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the optical surface having the smaller absolute value of the radius of curvature of the objective lens. When the optical path difference providing structure is provided on a surface having a large effective diameter, for example, the minimum annular zone width of the basic structure can be designed wider, and there is an advantage that light amount loss due to a step portion of the annular zone can be suppressed. In addition, there is a merit that the annular structure does not wear when the objective lens is rubbed with a lens cleaner. It is also conceivable to provide the first basic structure and the second basic structure on different optical surfaces without overlapping. Similarly, the third basic structure and the fourth basic structure may be provided on different optical surfaces without overlapping.

Next, the 1st optical path difference providing structure provided in a center area | region is demonstrated. The first optical path difference providing structure is a structure in which at least the first basic structure and the second basic structure are overlapped. The first optical path difference providing structure is preferably a structure in which only the first basic structure and the second basic structure are overlapped.
Since the optical path difference providing structure is made by superimposing two types of blazed basic structures, the design flexibility is doubled and compatibility is achieved compared to the case where the optical path difference providing structure is formed with a single structure. However, the magnification can be freely determined for the three disks.

  The first basic structure is a blazed structure. In addition, the first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and the first-order diffracted light quantity that has passed through the first basic structure. Is made larger than any other order of the diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light quantity. This is called a (1/1/1) structure. Since the diffraction order that maximizes the amount of diffracted light of the first light beam is an odd first order, different paraxial powers can be applied to BD and CD, and correction of relative spherical aberration that occurs between BD and CD is good. It can be done. In addition, since the first-order diffracted light, which is a lower order, is generated when the first light beam is used, the step amount of the first basic structure does not become too large, making the manufacture easy, and suppressing the light amount loss caused by the manufacturing error. This is preferable because it can reduce the diffraction efficiency fluctuation at the time of wavelength fluctuation.

  Moreover, it is preferable that the first foundation structure provided at least near the optical axis in the central region has a step in a direction opposite to the optical axis. “The step is directed in the direction opposite to the optical axis” means a state as shown in FIG. In addition, the first basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis among steps of the (1/1/1) structure. Of all the steps of the first basic structure existing in the central region, it is preferable that at least 50% or more are directed in the direction opposite to the optical axis, more preferably 70% or more, and even more preferably 90% or more. Is in the opposite direction to the optical axis.

  For example, the step of the first basic structure provided near the middle region of the central region may face the direction of the optical axis. That is, as shown in FIG. 6B, the step is directed in the direction opposite to the optical axis when the first basic structure is near the optical axis, but the step of the first basic structure is the optical axis near the intermediate region. It is good also as a shape which faces the direction. However, it is preferable that all the steps of the first basic structure provided in the central region are directed in a direction opposite to the optical axis.

  In this way, the direction of the step of the first basic structure in which the diffraction order of the first light beam is the first order is directed in the direction opposite to the optical axis, so that the three types of optical disks of BD / DVD / CD can be used interchangeably. Even with a thick objective lens having a large axial thickness, a working distance can be further ensured when the CD is used.

The first basic structure is the first basic structure from the viewpoint of securing a sufficient working distance when using a CD even in a thick objective lens having a thick on-axis thickness, which is used for compatibility with three types of optical disks of BD / DVD / CD. It is preferable to have paraxial power with respect to the light beam. Here, “having paraxial power” means that C ₂ h ² is not 0 when the optical path difference function of the first basic structure is expressed by the following equation ( ₂ ).

Further, when the focal length of the first basic structure is defined as fD ₁ (unit: mm), a configuration that satisfies the following formula may be adopted.
−0.40 <f1 / fD ₁ <−0.10 (5)
(However, fD ₁ = −λB ₁ / (2 × C ₁₂ × M1 × λ), the value of M1 is 1)
(ΛB ₁ is the manufacturing wavelength of the first basic structure, C ₁₂ is the second-order optical path difference function coefficient of the first basic structure, and M 1 is the diffraction order of the first basic structure)
The “manufacturing wavelength” is the wavelength of the luminous flux that gives the highest Mi-order diffraction efficiency when passing through the i-th basic structure.

  Satisfying the expression (5) is preferable because the chromatic aberration at the time of using the BD does not become too large while ensuring the working distance at the time of using the CD. If the lower limit of the formula (5) is exceeded, the amount of chromatic aberration generated when the first optical disk is used is sufficiently suppressed, and if it is less than the upper limit of the formula (5), a working distance when using the CD can be secured sufficiently.

  The second basic structure is also a blazed structure. Further, the second basic structure makes the second-order diffracted light quantity of the first light beam that has passed through the second basic structure larger than any other order of diffracted light quantity, and the first-order of the second light beam that has passed through the second basic structure. Is made larger than any other order of the diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the second basic structure is made larger than any other order of diffracted light quantity. This is called a (2/1/1) structure. Since the diffraction order at which the diffracted light quantity of the first light beam is the maximum is an even second order, high diffraction efficiency can be obtained in all of the first to third light beams. In addition, since the second-order diffracted light, which is a lower order, is generated when the first light beam is used, the step amount of the second basic structure does not become too large, making the manufacture easy, and suppressing the light quantity loss caused by the manufacturing error. This is preferable because it can reduce the diffraction efficiency fluctuation at the time of wavelength fluctuation.

  Moreover, it is preferable that the level | step difference of the 2nd foundation structure provided in the vicinity of the optical axis of a center area | region has faced the direction of the optical axis. “The step is directed in the direction of the optical axis” means a state as shown in FIG. The second basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis among steps of the (2/1/1) structure. It is preferable that at least 50% or more of all the steps of the second basic structure existing in the central region face the direction of the optical axis, more preferably 70% or more, more preferably 90% or more. It is facing the direction of.

  For example, in the second basic structure provided near the middle region of the central region, the step may be directed in a direction opposite to the optical axis. That is, as shown in FIG. 6A, the step is directed in the direction of the optical axis when the second foundation structure is near the optical axis, but the step of the second foundation structure is opposite to the optical axis near the intermediate region. It is good also as a shape which faces a direction. However, preferably, the second basic structure provided in the central region is that all the steps are directed in the direction of the optical axis.

  Since the first optical path difference providing structure is a (1/1/1) structure and the second basic structure (2/1/1) are overlapped, the height of the step is Very low. Therefore, it is possible to further reduce manufacturing errors, further reduce the light amount loss, and further suppress the change in diffraction efficiency when the wavelength changes.

  Furthermore, at least near the optical axis of the central region, the first basic structure in which the step is directed in the direction opposite to the optical axis, and at least near the optical axis of the central region, the step is directed in the direction of the optical axis. By superimposing two foundation structures, the height of the step after superposition is higher than when superimposing the steps so that the first and second foundation structures have the same step direction. Accordingly, it is possible to further suppress the shadow effect, to further suppress the light amount loss due to the manufacturing error, and to further suppress the fluctuation of the diffraction efficiency at the time of the wavelength fluctuation.

  Further, not only can the three types of optical discs of BD / DVD / CD be compatible, but also the light usage efficiency that can maintain high light usage efficiency for any of the three types of optical discs of BD / DVD / CD. It is preferable to provide a balanced objective lens. For example, it is preferable to provide an objective lens that has a diffraction efficiency of 80% or more for the wavelength λ1, a diffraction efficiency of 60% or more for the wavelength λ2, and a diffraction efficiency of 50% or more for the wavelength λ3. Furthermore, it is more preferable to provide an objective lens that has a diffraction efficiency of 80% or more for the wavelength λ1, a diffraction efficiency of 70% or more for the wavelength λ2, and a diffraction efficiency of 60% or more for the wavelength λ3. In addition, by orienting the step of the first basic structure in the direction opposite to the optical axis, it is easier to change the aberration in the direction of under (undercorrection) when the wavelength changes to the long wavelength side. .

Viewpoint of the shape and step amount of the first optical path difference providing structure after the first basic structure in which the step is opposite to the optical axis and the second basic structure in which the step is directed toward the optical axis are overlapped Therefore, the first optical path difference providing structure in which the first basic structure having the (1/1/1) structure and the second basic structure having the (2/1/1) structure are overlapped is expressed as follows. be able to. The first optical path difference providing structure provided at least in the vicinity of the optical axis of the central region has both a step facing in the opposite direction to the optical axis and a step facing in the direction of the optical axis. It is preferable that the step amount d11 of the step facing the direction opposite to the axis and the step amount d12 of the step facing the direction of the optical axis satisfy the following conditional expressions (14) and (15). More preferably, the following conditional expressions (14) and (15) are satisfied in all the regions of the central region. If the objective lens provided with the optical path difference providing structure is a single aspherical convex lens, the incident angle of the light flux to the objective lens differs depending on the height from the optical axis, so that the optical path difference providing structure that gives the same optical path difference Even so, in general, as the distance from the optical axis increases, the step amount tends to increase. In the following conditional expression, the upper limit is multiplied by 1.5 because the increase in the level difference is taken into account. Here, n represents the refractive index of the objective lens at the first wavelength λ1.
0.6 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (14)
0.6 · (λ1 / (n-1)) <d12 <1.5 · (2λ1 / (n-1)) (15)

  The first optical path difference providing structure provided “at least in the vicinity of the optical axis of the central region” includes at least a step facing in a direction opposite to the optical axis closest to the optical axis and an optical axis closest to the optical axis. An optical path difference providing structure having both of the steps facing the direction of. Preferably, the optical path difference providing structure has a step existing between at least a half position in the direction orthogonal to the optical axis from the optical axis to the boundary between the central region and the intermediate region.

  Since λ1 is 390 to 415 nm (0.390 to 0.415 μm), when n is 1.50 to 1.60, the conditional expression can be expressed as follows.

0.39 μm <d11 <1.15 μm (16)
0.39 μm <d12 <2.31 μm (17)

  Further, as a method of overlapping the first foundation structure and the second foundation structure, the shape of the foundation structure is finely adjusted so that the positions of all the steps of the second foundation structure and the positions of the steps of the first foundation structure are matched. Alternatively, it is preferable to finely adjust the shape of the foundation structure so that the positions of all the steps of the first foundation structure and the positions of the steps of the second foundation structure are matched.

As described above, when the positions of all the steps of the second foundation structure are matched with the positions of the steps of the first foundation structure, d11 and d12 of the first optical path difference providing structure are the following conditional expressions (14) ′, ( 15) ′ is preferably satisfied. More preferably, the following conditional expressions (14) ′ and (15) ′ are satisfied in all regions of the central region.
0.6 · (λ1 / (n−1)) <d11 <1.5 · (λ1 / (n−1)) (14) ′
0.6 · (λ1 / (n−1)) <d12 <1.5 · (λ1 / (n−1)) (15) ′

  Further, since λ1 is 390 to 415 nm (0.390 to 0.415 μm), when n is 1.50 to 1.60, the conditional expression can be expressed as follows.

0.39 μm <d11 <1.15 μm (16) ′
0.39 μm <d12 <1.15 μm (17) ′

More preferably, the following conditional expressions (14) ″ and (15) ″ are preferably satisfied. More preferably, the following conditional expressions (14) ″ and (15) ″ are satisfied in all the regions of the central region.
0.9 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (14) ''
0.9 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (15) ''

  Further, since λ1 is 390 to 415 nm (0.390 to 0.415 μm), when n is 1.50 to 1.60, the conditional expression can be expressed as follows.

0.59 μm <d11 <1.15 μm (16) ″
0.59 μm <d12 <1.15 μm (17) ″

  Further, in the first basic structure having the (1/1/1) structure, when the wavelength of the incident light beam is changed to be longer, the spherical aberration is changed in the undercorrection direction (under), and (2 / In the second basic structure having the 1/1) structure, when the wavelength of the incident light beam is changed to be longer, it is preferable that the spherical aberration is changed in the undercorrection direction (under). With such a configuration, when the refractive index of the objective lens changes due to an increase in the temperature of the optical pickup device, the refractive index of the objective lens is also utilized by utilizing the fact that the wavelength of the light source increases due to the increase in the environmental temperature. It is possible to correct a change in spherical aberration due to a change in the rate and form an appropriate focused spot on the information recording surface of each optical disc. Thereby, even if the objective lens is made of plastic, it is possible to provide an objective lens that can maintain stable performance even when the temperature changes.

  It is preferable that the paraxial power of the first foundation structure is larger than that of the second foundation structure. That is, it is preferable that the average pitch of the first foundation structure is smaller than the average pitch of the second foundation structure. Thereby, a working distance in the CD can be secured even in an objective lens having a large axial thickness, which is a BD / DVD / CD compatible objective lens. Furthermore, in order to reduce chromatic aberration, to form a good light spot even when the light source causes high-frequency superposition, and to reduce the problem of stray light when the optical disc has a plurality of information recording surfaces, In one optical path difference providing structure, 2 to 5 (particularly preferably 2 to 3) ring zones of the first foundation structure are included in one ring zone closest to the optical axis of the second foundation structure. Is preferred. In this case, the “ring zone” closest to the optical axis of the second foundation structure is described, but in practice, it is usually a “circle” including the optical axis. Accordingly, the “annular zone closest to the optical axis” mentioned here includes a circular shape. Further, in one ring zone of the second foundation structure closest to the intermediate region, 1 to 5 ring zones of the first foundation structure (particularly preferably 2 to 3 pieces) are included in one ring zone of the second foundation structure. ) Is also preferably included. The ratio of the total number of ring zones of the first foundation structure to the second foundation structure in the central region is preferably 1.0 or more and 5.0 or less, more preferably 2.0 or more and 3.0 or less. is there.

  As shown in FIG. 7D, when the first basic structure and the second basic structure are superimposed as they are, a part may protrude as shown by a dotted line, but the width of the protruding part is 5 μm or less. If it is narrow, the projecting portion is shifted in parallel along the optical axis, and eliminating the projecting portion has no significant effect, so that one annular zone of the second foundation structure can have a plurality of the first foundation structure. The zonal is just like that (see the solid line). Therefore, in the example of FIG.7 (d), it handles as the ring zone of three 1st foundation structures on one ring zone of a 2nd foundation structure. When the first foundation structure and the second foundation structure are superimposed as they are, a dent may be eliminated in the same manner even when a dent having a width of 5 μm or less is generated.

Here, if Δλ1 (nm) is the change amount of the first wavelength and ΔWD (μm) is the chromatic aberration of the objective lens caused by the change Δλ of the first wavelength, it is preferable that the following expression is satisfied.
0.3 (μm / nm) ≦ ΔWD / Δλ1 ≦ 0.6 (μm / nm) (18)
The “chromatic aberration” here is a shift in the focus position that occurs when the wavelength of the light beam changes. That is, it is a shift of “position where wavefront aberration is best” that occurs when the wavelength of the light beam changes.

  In order to obtain such a configuration, as described above, in the first optical path difference providing structure, the ring zone of the first foundation structure is 2 to 1 ring zone closest to the optical axis of the second foundation structure. It is preferable to include 5 (particularly preferably 2 to 3). By setting the chromatic aberration to the above-described range, the optical disc has a plurality of information recording surfaces while ensuring a working distance in the CD even in an objective lens having a large axial thickness, which is a BD / DVD / CD compatible objective lens. This is preferable because the problem of stray light can be reduced and the temperature and wavelength characteristics can be improved when using a DVD. Also, the number of ring zones of the first foundation structure superimposed on one ring zone closest to the intermediate region in the second foundation structure is 1-5 overlaps for one ring zone of the second foundation structure. It is preferable that Furthermore, the ratio of the total number of ring zones of the first foundation structure to the second foundation structure in the central region is preferably 1.0 or more and 5.0 or less, more preferably 2.0 or more and 3.0 or less. That is.

  The first basic structure preferably has a negative paraxial diffraction power, so that a working distance when using a CD can be secured even in an objective lens having a large axial thickness such as an objective lens for BD / DVD / CD. The second basic structure preferably has a positive paraxial diffraction power. As described above, since both the first basic structure and the second basic structure have paraxial diffraction power, when using an optical disk having a plurality of information recording surfaces, unnecessary light reflected by the information recording surface that is not a target for recording / reproducing is used. This is preferable because it can be further away from the necessary light.

The minimum pitch of the first optical path difference providing structure is preferably 15 μm or less. From this point of view, the ratio p / f1 between the minimum pitch p of the first optical path difference providing structure and the focal length f1 at the first wavelength λ1 is preferably 0.004 or less. More preferably, it is 10 μm or less.
Moreover, it is preferable that the average pitch of the first optical path difference providing structure is 30 μm or less. More preferably, it is 20 μm or less. By adopting such a configuration, it is possible to obtain an under-wavelength characteristic with a just good level as described above, and the third optical disc generated in the third light flux that has passed through the first optical path difference providing structure. The best focus position of the necessary light used for recording / reproducing information can be separated from the best focus position of unnecessary light not used for recording / reproducing information on the third optical disc, and erroneous detection can be reduced. Become. The average pitch is a value obtained by adding all pitches of the first optical path difference providing structure in the central region and dividing the sum by the number of steps of the first optical path difference providing structure in the central region.

  Here, the objective lens of the present invention preferably has an axial chromatic aberration of 0.9 μm / nm or less. More preferably, the longitudinal chromatic aberration is 0.8 μm / nm or less. If the pitch of the first basic structure is too small, the longitudinal chromatic aberration may be deteriorated. Therefore, the design is made so that the pitch is not such that the longitudinal chromatic aberration is larger than 0.9 μm / nm. It is preferable. From this viewpoint, it is preferable that the ratio p / f1 between the minimum pitch p of the first optical path difference providing structure and the focal length f1 at the first wavelength λ1 is 0.002 or more. On the other hand, in order to ensure a sufficient working distance in CD, it is preferable that the longitudinal chromatic aberration is 0.4 μm / nm or more.

The first best focus position where the light intensity of the spot formed by the third light flux is the strongest by the third light flux passing through the first optical path difference providing structure, and the second strongest light intensity of the spot formed by the third light flux. It is preferable that the best focus position satisfies the following conditional expression (19). Here, the best focus position refers to a position where the beam waist becomes a minimum within a certain defocus range. The first best focus position is the best focus position of the necessary light used for CD recording / reproduction, and the second best focus position is the best of the luminous flux having the largest light quantity among the unnecessary light that is not used for CD recording / reproduction. The focus position.
0.35 ≦ L / f1 ≦ 0.7 (19)
However, L [mm] indicates the distance between the first best focus and the second best focus.

  Several preferable examples of the first optical path difference providing structure described above are shown in FIGS. 7 (a), (b), and (c). In FIG. 7, for convenience, the first optical path difference providing structure ODS1 is shown as being provided in a flat plate shape, but it is usually provided on a single aspherical convex lens. The first basic structure BS1 which is a (1/1/1) diffraction structure is overlapped with the second basic structure BS2 which is a (2/1/1) diffraction structure. In FIG. 7A, the step of the second basic structure BS2 faces the direction of the optical axis OA, and the step of the first basic structure BS1 faces the direction opposite to the optical axis OA. Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1. Next, in FIG.7 (b), the level | step difference of 2nd foundation structure BS2 has faced the direction of optical axis OA, and the level | step difference of 1st foundation structure BS1 has also faced the direction of optical axis OA. Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1. Next, in FIG.7 (c), the level | step difference of 1st foundation structure BS1 has faced the direction opposite to optical axis OA, and the level | step difference of 2nd foundation structure BS2 has also faced the direction opposite to optical axis OA. . Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1.

Furthermore, when the total number of ring zones in the central region is N1, it is preferable that the following expression is satisfied. As a result, it is possible to prevent the working distance of the CD from becoming too short and to suppress the workability from being lowered due to the ring zone pitch becoming too small. Note that the number of steps substantially parallel to the optical axis in the central region may be regarded as the total number of annular zones in the central region.
160 (mm) ≤ N1 · f1 ≤ 210 (mm) (20)

  Next, the second optical path difference providing structure provided in the intermediate region will be described. The second optical path difference providing structure is preferably a structure in which at least two basic structures of a third basic structure and a fourth basic structure are overlapped. More preferably, it is a structure in which only the third foundation structure and the fourth foundation structure are overlapped. Since the optical path difference providing structure is formed by superimposing two types of blazed basic structures, it is possible to secure a greater degree of design freedom than when the optical path difference providing structure is formed with a single structure. This is advantageous in an objective lens having a small diameter.

  The third basic structure is a blazed structure. Further, the first-order diffracted light amount of the first light beam that has passed through the third basic structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the third basic structure is changed to other values. It is made larger than the diffracted light quantity of any order. The fourth basic structure is also a blazed structure. The fifth-order or seventh-order diffracted light quantity of the first light beam that has passed through the fourth basic structure is made larger than any other order diffracted light quantity, and the third-order or fourth-order diffraction of the second light beam that has passed through the fourth basic structure. Make the light intensity larger than any other order of diffracted light. Since the diffraction order of the first light flux that has passed through the third basic structure is the first order that is an odd number, the diffraction power that is different between BD and DVD can be imparted, and relative spherical aberration that occurs with DVD Can be corrected satisfactorily. In addition, since the first-order diffracted light that is a low order is generated, the step amount of the third basic structure does not become too large, the manufacturing becomes easy, the light quantity loss caused by the manufacturing error can be suppressed, and the wavelength change This is preferable because fluctuations in diffraction efficiency can also be reduced. Since the diffraction order at which the diffracted light quantity of the first light beam that has passed through the fourth basic structure is the maximum is the fifth or seventh order, the BD accompanying the temperature change or the like without affecting the spherical aberration correction of the third basic structure. Alternatively, it is possible to flare out the CD while appropriately controlling the fluctuation of the spherical aberration when using the DVD. Also, high diffraction efficiency can be obtained when using BD and DVD.

The fourth basic structure defines φ _i (h) as follows:
φ _i (h) = (C _i2 × h ² + C _i4 × h ⁴ + C _i6 × h ⁶ + C _i8 × h ⁸ + C _i10 × h ¹⁰ ) Miλ / λB _i
(Where h (unit: mm) is the height from the optical axis, C _i2 , C _i4 , C _i6 ... _Are secondary in the optical path difference function (i is a natural number) of the i-th substructure, The fourth-order and sixth-order optical path difference function coefficients, Mi is the diffraction order in the optical path difference function of the i-th basic structure that maximizes the diffraction order of the incident light beam, and λ (unit: mm) is the use of the incident light beam. ΛB _i (unit: mm) represents the manufacturing wavelength of the i-th basic structure, respectively.) Further, the effective diameter (diameter) of the second light flux is h2 (mm), and the effective diameter (diameter) of the first light flux When h1 (mm), the following formula may be satisfied.
−0.05 <(φ ₄ (h2 / 2) −φ ₄ (h1 / 2)) / f1 <0.03
The diffraction order in the optical path difference function of the i-th basic structure that maximizes the diffraction order of the incident light beam is, for example, the first order when the basic structure is (1/1/1), (2/1/1). 1) indicates the second order, (7/4) indicates the seventh order, and (5/3) indicates the fifth order.

Assuming that the diffraction order in which the amount of diffracted light of the first light flux is the maximum is 7th in the fourth basic structure, the third and fourth orders of the third light flux that have passed through the intermediate region are within the above formula. It is possible to suppress the unnecessary diffraction order light having the next high diffraction efficiency from being collected in the vicinity of the spot when the CD is used, and the spherical aberration with respect to the temperature change when using the DVD is also well corrected. As an alternative to the above formula, when the focal length of the fourth basic structure is set to fD ₄ (mm), the same effect as the above formula can be obtained even if the following two formulas are satisfied at the same time. it can.
−0.03 <(φ ₄ (h2 / 2) −φ ₄ (h1 / 2)) / f1 <0
0 <f1 / fD ₄ <0.08
(However, fD ₄ = −λB ₄ / (2 × C ₄₂ × M4 × λ), and the value of M4 is 7 or 5.)

  In addition, since the first optical path difference providing structure and the second optical path difference providing structure have a plurality of diffractive structures superimposed as a compatible basic structure, the magnification of the objective lens is 0 in any of BD, DVD, and CD. Alternatively, high diffraction efficiency can be obtained at all three wavelengths while setting the value to almost zero.

  Further, when the effective diameter of the first light flux is as small as 1.9 to 3.0 mm, the pitch is already sufficiently fine in the second optical path difference providing structure composed of the third basic structure and the fourth basic structure, and the annular zone Since the number is sufficiently large, if another foundation structure is stacked in addition to the third foundation structure and the fourth foundation structure, the pitch will become finer and the number of zones will increase, resulting in manufacturing errors. Problems such as lowering of the diffraction efficiency due to, and lowering of the diffraction efficiency due to the effect of the shadow of the annular zone will increase. In particular, if a structure with a large step amount such as a binary structure of 0/0 / ± 1 is overlapped, the problem of a decrease in diffraction efficiency due to a shadow effect or the like becomes more serious. Therefore, in the second optical path difference providing structure, a structure in which only the third basic structure and the fourth basic structure are overlapped is preferable because the light use efficiency can be increased.

  Further, the second optical path difference providing structure in the intermediate region has a step in which the third basic structure faces in the direction opposite to the optical axis, and the fourth basic structure has a step in which the optical axis direction faces. It is preferable. Therefore, it is preferable that the second optical path difference providing structure has a step that faces in a direction opposite to the optical axis and a step that faces in the direction of the optical axis.

  Furthermore, all the steps of the first foundation structure are directed in the direction opposite to the optical axis, all the steps of the second foundation structure are directed to the direction of the optical axis, and all the steps of the third foundation structure are If the direction is opposite to the optical axis, and all the steps of the fourth basic structure are oriented in the direction of the optical axis, the working distance when using the CD becomes longer, and the axial chromatic aberration of the BD is further increased. It becomes easy to take.

In the third basic structure having the (1/1) structure, when the wavelength of the incident light beam is changed so as to become longer, the spherical aberration changes in the undercorrection (under) direction, and the (7/4) structure (the first) 7th order diffracted light is generated most in one light beam, and 4th order diffracted light is generated most in the second light beam, or (5/3) structure (5th order diffracted light is generated most in the first light beam, and the second light beam is generated. In the fourth basic structure in which the third-order diffracted light is generated most), the spherical aberration is undercorrected (under) or overcorrected (over) when the wavelength of the incident light beam is changed to be longer. It is preferable to change in the direction.
The overcorrection (over) direction and the undercorrection (under) direction referred to here represent spherical aberration in the intermediate region, and the state in which the condensing position shifts to the over side as NA increases in the intermediate region is overcorrected ( The over-correction (under) direction is defined as the converging position shifts to the under side as NA increases. It is not the direction of the focusing position relative to the paraxial focusing position.

  With such a configuration, even in the second optical path difference providing structure, when the refractive index of the objective lens changes due to the temperature increase of the optical pickup device, the wavelength of the light source also increases due to the increase in the environmental temperature. Is used to correct the deterioration of the spherical aberration due to the change in the refractive index of the objective lens, so that a more appropriate condensing spot can be formed on the information recording surface of each optical disc when the environmental temperature changes.

  Since the second optical path difference providing structure includes the third basic structure and the fourth basic structure, in addition to compatibility with BD and DVD, the remaining degree of freedom can be used for CD flare out. Therefore, since the aperture limitation at the time of using the CD can be performed by the second optical path difference providing structure having a simple shape, it is possible to suppress a decrease in light use efficiency due to the shadow effect as compared with the case of adding another basic structure. Further, it is possible to suppress a decrease in light utilization efficiency due to a manufacturing error, and as a result, it is possible to improve the light utilization efficiency. In addition, when the DVD is used, both the temperature characteristic and wavelength characteristic of the DVD can be improved.

  Further, in order to improve the wavelength characteristics when using the DVD, in the second optical path difference providing structure, the ring zone of the third basic structure is 3 to 11 in one ring zone closest to the central region of the fourth basic structure. It is preferable that they are included.

Further, the objective lens of the present invention has two basic structures superimposed in the intermediate region, and further, in a certain region, the number of annular zones tends to increase as it goes from the optical axis toward the periphery. In the vicinity of the peripheral area, the light utilization efficiency is deteriorated. As a result, the ratio r2 of the pupil transmittance in the vicinity of the peripheral region of the intermediate region with respect to the vicinity of the optical axis center of the objective lens in the second light flux is expressed by the following equation: r2 ≦ 0.9 (1)
Therefore, a phenomenon that can be called a reverse apodization effect occurs, and the spot diameter may increase when the DVD is used. The term “near” in the vicinity of the center of the optical axis refers to a range of 10% of the effective diameter when using a DVD from the optical axis to the direction perpendicular to the optical axis. The vicinity of the peripheral area of the intermediate area means a range of 10% of the effective diameter when using the DVD with respect to the intermediate area direction from the boundary between the intermediate area and the peripheral area. The vicinity of the outer diameter of the peripheral area is the peripheral area. The range of 10% of the effective diameter when using a DVD from the outer diameter to the intermediate area direction.

  The objective lens of the present invention is a BD / DVD / CD compatible objective lens. However, since there are only two optical surfaces, the sine condition cannot be satisfied for all optical discs, and the most required specification is required. Is set so that the sine condition is satisfied with a severe BD, there is a possibility that the spot diameter will be further increased when the DVD is used.

For the above problem, the following equation is satisfied when the outer diameter of the intermediate region is h2, the focal length of the first light beam of the objective lens is f1, and the imaging magnification of the second light beam of the objective lens is m2. Is preferred.
0.66 ≦ h2 / (2 · f1 · (1-m2)) ≦ 0.75 (2)
By satisfying a value equal to or greater than the lower limit of the expression (2), the effective diameter of the second light flux when the objective lens is used in DVD is increased, that is, NA is increased, and the spot diameter is reduced when DVD is used. It becomes possible to suppress the reverse apodization effect at the time of use. In addition, when the BD is used, an intermediate region having a relatively small amount of transmitted light as compared with the vicinity of the optical axis is widened, so that an apodization effect is generated, and the spot diameter can be narrowed even for the BD. This can be preferably used particularly for a compatible lens for reproduction of three types of optical disks of BD / DVD / CD. Furthermore, by satisfying a value equal to or lower than the upper limit of the formula (2), the spot diameter when using the DVD is not reduced more than necessary. In addition, it is preferable that r2 is 0.3 or more and 0.9 or less because the degree of the enlargement of the spot diameter due to the decrease in the rim strength does not become too large, and the effect of the expression (2) becomes more remarkable. More preferably, r2 is 0.4 or more and 0.8 or less, and further preferably r2 is 0.5 or more and 0.75 or less.

More preferably, the following expression (2) ′ is satisfied.
0.68 ≦ h2 / (2 · f1 · (1-m2)) ≦ 0.74 (2) ′
The smaller the objective lens, the smaller the pitch of the basic structure, and the lowering of the rim strength when using the BD becomes more significant, that is, the spot diameter increases when using the BD. However, it is preferable to satisfy the formula (2) ′ because the apodization effect when using the BD becomes strong, and even with such an objective lens, a spot diameter suitable for recording / reproducing of the BD can be obtained. In addition, since the pitch in the vicinity of the intermediate region, particularly the peripheral region of the intermediate region is also small, there is a possibility that the spot diameter will increase when using the DVD, but it is preferable because it can be solved by satisfying the equation (2) ′.

Moreover, it is preferable that the objective lens of this invention satisfy | fills Formula (3), when the focal distance in the 1st light beam of an objective lens is set to f1.
1.0 ≦ f1 ≦ 2.2 (3)
When the focal length f1 when using the BD is within the range of the expression (3), the objective lens becomes relatively small, and therefore the pitch in the vicinity of the outer diameter in the peripheral region becomes even finer, and the problem of the present invention is large. However, such a large problem can be solved by making the second-order or fourth-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity. Further, if the focal length f1 is within the range of the expression (3), the number of ring zones in the central region is increased in order to secure a working distance when using the CD, that is, in order to increase the paraxial power of diffraction. Correspondingly, it is necessary to increase the number of ring zones in the intermediate region. As a result, in the vicinity of the peripheral region of the intermediate region, there is a possibility that the light utilization efficiency will be further reduced and the spot diameter may be increased when using DVD or BD. In this case, formula (2) It can be solved by satisfying.
The working distance is a distance in the optical axis direction from the surface of the optical disk to the position closest to the optical disk of the objective lens. Furthermore, since the focal length is within the range of the expression (3), the distance from the objective lens to the disk can be reduced, and it can be suitably mounted on a slim type optical pickup device. Further, when f1 satisfies the following expression (3) ′, the effect of the present invention becomes more remarkable.
1.0 ≦ f1 ≦ 2.0 (3) ′

The objective lens may be designed to satisfy the following formula (11) when the focal length of the second light flux of the objective lens is f2.
0.61 ≦ h2 / (2 · f2 · (1-m2)) ≦ 0.65 (21)
By satisfying formula (11), the effective diameter when using a DVD can be increased, which is preferable.

  Next, the third optical path difference providing structure provided in the peripheral region will be described. The third optical path difference providing structure has at least a fifth basic structure. Although another foundation structure may be superimposed, it is preferably only the fifth foundation structure.

  The fifth basic structure is a blazed structure. In addition, the second-order or fourth-order diffracted light amount of the first light flux that has passed through the fifth basic structure is made larger than any other order diffracted light amount. For this reason, the pitch can be made larger than in the first case, that is, the number of ring zones is reduced, so that the manufacturing can be facilitated and the error can be reduced both in the mold processing and the resin molding. In the peripheral area, the number of annular zones tends to increase from the optical axis side toward the periphery, and the angle of view of the objective lens increases near the outer diameter in the peripheral area. Decrease, increase in reflectance, etc., especially when the pitch is small, this problem becomes significant and the rim strength decreases, but the pitch of the fifth foundation structure in the peripheral region can be increased. Therefore, it is possible to reduce a decrease in machining accuracy and to prevent a decrease in rim strength. Furthermore, since the number of ring zones decreases, the influence of the shadow effect around the effective diameter can be reduced, and an increase in spot diameter due to a decrease in rim strength can be suppressed. In addition, when the first-order diffracted light quantity is maximized when the first light beam passes, if the objective lens is to be miniaturized, the pitch is inevitably narrowed and cannot be manufactured due to processing accuracy. However, since the pitch can be increased, the objective lens can be reduced in size. By making the second-order diffracted light quantity larger than any other order diffracted light quantity, it is possible to further suppress fluctuations in diffraction efficiency during wavelength fluctuations.

Moreover, it is preferable that the i-th basic structure of the objective lens of the present invention can be developed into an optical path difference function of the following form,
φ _i (h) = (C _i2 × h ² + C _i4 × h ⁴ + C _i6 × h ⁶ + C _i8 × h ⁸ + C _i10 × h ¹⁰ ) Miλ / λB _i
(Where h (unit: mm) is the height from the optical axis, C _i2 , C _i4 , C _i6 ... _Are secondary in the optical path difference function (i is a natural number) of the i-th substructure, The fourth-order and sixth-order optical path difference function coefficients, Mi is the diffraction order in the optical path difference function of the i-th basic structure that maximizes the diffraction order of the incident light beam, and λ (unit: mm) is the use of the incident light beam. The wavelength λB _i (unit: mm) indicates the production wavelength in the i-th basic structure.) In that case, it is also preferable that the following conditional expression (6) is satisfied.
−0.025 <(φ ₅ (h3 / 2) −φ ₅ (h2 / 2)) / (M5 × f1) <0.025 (6)
(However, the value of M5 is 2 or 4, h2 is the effective diameter (diameter) (mm) of the second light beam, and h3 is the effective diameter (diameter) (mm) of the third light beam.)
It is characterized by satisfying.

  By satisfying the equation (6), the second and second unwanted light of the third and third beams transmitted through the peripheral region are transmitted through the central region while satisfactorily correcting the spherical aberration generated when the environment is changed when using the BD. Since it is possible to avoid convergence of the third light flux in the vicinity of the imaging position, it is preferable because deterioration of spot performance can be suppressed. Further, it is preferable that the number of steps is not excessively increased by setting the value within the range of the formula (6), which makes it possible to obtain a good spot that is easy to manufacture and suppresses a decrease in light utilization efficiency. By falling below the upper limit, the spherical aberration at the time of temperature change does not become too large.

  Moreover, if all the steps of the first to fifth foundation structures are independently directed in the same direction, high light utilization efficiency can be obtained in any use of BD, DVD, and CD, which is unnecessary. It is preferable because it can prevent light from being dispersed and the spot performance from being deteriorated. Note that the fifth basic structure may face the direction of the optical axis, or may face the direction opposite to the optical axis. In particular, it is preferable that the fifth basic structure is directed toward the optical axis because spherical aberration at the time of temperature change is corrected well.

  Here, the schematic diagram of a preferable objective lens is shown in FIG. It is the figure which showed the upper half from the optical axis among the cross sections of the objective lens containing optical axis OA. Note that FIG. 8 is a schematic diagram to the last, and is not a drawing showing an accurate length ratio or the like based on the embodiment.

  The objective lens in FIG. 8 has a central region CN, an intermediate region MD, and a peripheral region OT. A first optical path difference providing structure ODS1 is provided in the central area, a second optical path difference providing structure ODS2 is provided in the middle area, and a third optical path difference providing structure ODS3 is provided in the peripheral area. .

  The first optical path difference providing structure ODS1 in FIG. 8 is a (2/1/1) blazed structure in which the step is directed toward the optical axis and a (1/1/1) second basic structure BS2. The blazed structure has a structure in which a first basic structure BS1 with a step facing away from the optical axis is superimposed. In FIG. 8, the second foundation structure BS2 has three annular zones, and two annular zones of the first foundation structure BS1 are included on the annular zone (circular shape) closest to the optical axis in the second foundation structure BS2. ing. In addition, three annular zones of the first foundation structure BS1 are included in one annular zone closest to the intermediate region in the second foundation structure BS2.

  The second optical path difference providing structure ODS2 in FIG. 8 is a (7/4) or (5/3) blazed structure, and a fourth basic structure BS4 in which the step is directed toward the optical axis (1/1). ) And a third base structure BS3 in which the level difference faces the direction opposite to the optical axis. In FIG. 8, the fourth foundation structure BS4 is a three-ring zone, and three ring zones of the third foundation structure BS3 are included on the zone closest to the central region in the fourth foundation structure BS4. Further, four annular zones of the third foundation structure BS3 are included in one annular zone closest to the peripheral region in the fourth foundation structure BS4. That is, since the annular density of the annular zone closest to the peripheral region of the intermediate region is high, the shadow effect and the influence of the shaping error are large, and the pupil transmittance is smaller than that near the optical axis.

  The third optical path difference providing structure ODS3 in FIG. 8 is a blazed structure in which the second-order or fourth-order diffracted light quantity is maximized when the first light beam passes, and the sixth base has a step toward the optical axis. It consists only of the structure BS5. Compared to the primary case, the pitch can be widened, so that the moldability of the objective lens can be improved, the size can be reduced, and the rim strength is increased. The diameter can be formed.

  The NA on the image side of the objective lens necessary for reproducing / recording information on the BD is NA1, and the NA on the image side of the objective lens necessary for reproducing / recording information on the DVD is NA2 (NA1 > NA2), and the image side numerical aperture of the objective lens necessary for reproducing / recording information on the CD is NA3 (NA2> NA3). NA1 is preferably 0.8 or more and 0.9 or less. In particular, NA1 is preferably 0.85. NA2 is preferably 0.55 or more and 0.7 or less. In particular, NA2 is preferably 0.60 or 0.65. NA3 is preferably 0.4 or more and 0.55 or less. In particular, NA3 is preferably 0.45 or 0.53.

  The boundary between the central region and the intermediate region of the objective lens is 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3 or more, 1.15 · NA 3) when the third light beam is used. It is preferably formed in a portion corresponding to the following range. More preferably, the boundary between the central region and the intermediate region of the objective lens is formed in a portion corresponding to NA3. Further, the boundary between the intermediate region and the peripheral region of the objective lens is 0.9 · NA 2 or more and 1.2 · NA 2 or less (more preferably 0.95 · NA 2 or more, 1.15) when the second light flux is used. -It is preferably formed in a portion corresponding to the range of NA2 or less. More preferably, the boundary between the intermediate region and the peripheral region of the objective lens is formed in a portion corresponding to NA2.

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

In addition, it is preferable that h1 (mm) is 1.9 or more and 4.0 or less about the effective diameter with respect to the 1st light beam of an objective lens, More preferably, it is satisfy | filling the following formula | equation (4).
1.9 ≦ h1 ≦ 3.0 (4)
When the objective lens is a small objective lens satisfying the formula (4), the pitch in the vicinity of the outer diameter in the peripheral region becomes even finer, and the problem of the present invention becomes large. This can be solved by making the second-order or fourth-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity. In addition, since the pitch in the vicinity of the intermediate region, particularly the peripheral region of the intermediate region is also small, there is a possibility that the spot diameter increases when using DVD or BD. In this case, satisfying the equation (2) solves the problem. it can.

  In addition, when the lens has a small diameter that satisfies Equation (4) and requires a working distance of 0.25 mm or more when using a CD, the pitch of the optical path difference providing structure is reduced, and the number of annular zones is reduced. Although it is desirable to increase the paraxial power of diffraction, for example, by increasing the value, the reverse phenomenon of apodization may occur even more strongly when using a DVD. In such a case, the spot diameter when using the DVD can be reduced by satisfying a value equal to or higher than the lower limit of the above-described formula (2).

Further, in terms of ensuring a sufficient working distance in the third optical disc, the total number N _all of the annular zones formed on the objective lens is preferably 100 or more and 250 or less.

Further, when the total number of ring zones in the peripheral region is N3, it is preferable to satisfy the following expression.
5 (mm) ≤ N3 · f1 ≤ 100 (mm) (8)
By setting the value to be equal to or higher than the lower limit of the formula (8), the spherical aberration generated with respect to the temperature change when using the BD is not excessively increased. On the other hand, by setting the value of equation (8) below the upper limit, it is possible to prevent the pitch from becoming too small, so that the effect of shadows can be suppressed, and the shape error can be reduced by preventing deterioration of workability. Decrease in diffraction efficiency can be prevented. In addition, by setting the range in (8), chromatic aberration can also be reduced. Note that the number of steps substantially parallel to the optical axis in the peripheral region may be regarded as the total number of ring zones in the peripheral region.

The objective lens preferably satisfies the following conditional expression (7).
1.0 ≦ d / f1 ≦ 1.5 (7)
Here, d represents the thickness (mm) on the optical axis of the objective lens, and f represents the focal length of the objective lens in the first light flux.

  When an optical disk with a short wavelength and high NA such as BD is used, there is a problem that astigmatism easily occurs and decentration coma easily occurs in the objective lens, but the lower limit of conditional expression (7) arises. By not exceeding this value, it is possible to suppress the generation of astigmatism and decentration coma.

  In addition, the objective lens tends to be a thick objective lens with a thick on-axis thickness, and the working distance at the time of CD recording / reproduction tends to be shortened. Therefore, the upper limit value of conditional expression (7) may not be exceeded. preferable.

  The working distance (WD3) of the objective optical element when using the third optical disk is preferably 0.15 mm or more and 1.5 mm or less. Preferably, it is 0.25 mm or more and 0.5 mm or less. Next, the working distance (WD2) of the objective optical element when using the second optical disk is preferably 0.2 mm or more and 1.3 mm or less. Furthermore, the working distance (WD1) of the objective optical element when using the first optical disk is preferably 0.25 mm or more and 1.0 mm or less.

The first light beam, the second light beam, and the third light beam may be incident on the objective lens as parallel light, or may be incident on the objective lens as divergent light or convergent light. Even during tracking, in order to prevent coma from occurring, it is preferable that all of the first light beam, the second light beam, and the third light beam be incident on the objective lens as parallel light or substantially parallel light. By using the first optical path difference providing structure of the present invention, all of the first light beam, the second light beam, and the third light beam can be incident on the objective lens as parallel light or substantially parallel light. The effect becomes more remarkable. When the first light flux becomes parallel light or substantially parallel light, it is preferable that the imaging magnification m1 of the objective lens when the first light flux is incident on the objective lens satisfy the following formula (22).
−0.01 <m1 <0.01 (22)

In addition, when the second light beam is incident on the objective lens as parallel light or substantially parallel light, the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens satisfies the following expression (23). Is preferred.
-0.01 <m2 <0.01 (23)

On the other hand, when the second light beam is incident on the objective lens as diverging light, the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens preferably satisfies the following expression (23) ′. .
−0.025 <m2 ≦ −0.01 (23) ′

When the third light beam is incident on the objective lens as a parallel light beam or a substantially parallel light beam, the imaging magnification m3 of the objective lens when the third light beam enters the objective lens satisfies the following expression (24). Is preferred.
−0.01 <m3 <0.01 (24)

On the other hand, when the third light beam is incident on the objective lens as diverging light, the imaging magnification m3 of the objective lens when the third light beam is incident on the objective lens preferably satisfies the following expression (24) ′. .
−0.025 <m3 ≦ −0.01 (24) ′
As a result, the coma generated during tracking falls within a recordable / reproducible range.

  The optical pickup device may include a coupling lens through which at least the first light beam and the second light beam pass, and may include an actuator that moves the coupling lens in the optical axis direction. In particular, when the BD has a plurality of information recording surfaces such as two layers or three layers or more, when recording / reproducing one layer to another layer, the difference in the thickness of the transparent substrate is required. Therefore, spherical aberration generated due to the difference in thickness must be corrected. At that time, it is conceivable to correct the generated spherical aberration by moving the coupling lens in the optical axis direction and changing the magnification of the objective lens. Further, spherical aberration that occurs when the temperature or wavelength changes can be corrected by moving the coupling lens in the optical axis direction and changing the magnification of the objective lens.

  However, even in the case of an optical pickup device that corrects various spherical aberrations by moving the coupling lens in the optical axis direction when using BD, the position of the coupling lens in the optical axis direction is fixed when using DVD. It is preferable.

  The reason is that flare does not occur when using BD, but flare occurs when using DVD. By changing the coupling lens, the flare aberration changes, and as a result, the flare is recorded / reproduced. The reason is that there is a possibility of adversely affecting the driving force, and the reason why it is desired to simplify the control of the displacement of the coupling lens in the drive.

  In order to fix the position of the coupling lens in the optical axis direction when using a DVD, the wavelength of the incident light beam in one of the third basic structure and the fourth basic structure constituting the second optical path difference providing structure of the objective lens. The spherical aberration changes in the direction of undercorrection when it changes to become longer, while the spherical aberration changes in the overcorrection direction when the wavelength of the incident light beam becomes longer in the other direction. The spherical aberration accompanying the temperature change and wavelength change when using the DVD can be recorded and reproduced. As a result, when using the DVD, the coupling lens is moved in the optical axis direction when the second light beam passes. Even when the position is fixed, information can be recorded / reproduced on the information recording surface of the DVD.

  An optical information recording / reproducing apparatus according to the present invention includes an optical disc drive apparatus having the optical pickup device described above.

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

  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, it is possible to cope with downsizing while having high moldability, and it is possible to perform stable information recording / reproduction by forming an appropriate spot diameter even when using a BD. An objective lens suitable for such an optical pickup device and an optical pickup device equipped with this objective lens can be provided.

It is the figure which looked at the single objective lens OL concerning this embodiment in the optical axis direction. It is a figure for demonstrating the effect of a shadow. It is a figure which shows the state which forms the spot which the 3rd light beam which passed the objective lens forms on the information recording surface of a 3rd optical disk. It is an axial direction sectional view showing an example of an optical path difference grant structure, (a) and (b) show an example of a blaze type structure, and (c) and (d) show an example of a step type structure. (A) shows a state in which the step is directed in the direction of the optical axis, and (b) is a diagram showing a state in which the step is directed in a direction opposite to the optical axis. (A) shows a shape in which the step is in the direction of the optical axis in the vicinity of the optical axis, but changes in the middle, and in the vicinity of the intermediate region, the step is in the direction opposite to the optical axis. FIG. 4 is a diagram showing a shape in which a step is directed in the opposite direction to the optical axis in the vicinity of the axis, but is switched in the middle, and the step is directed toward the optical axis in the vicinity of the intermediate region. It is a conceptual diagram of a 1st optical path difference providing structure, (a), (b), (c) shows the example of a preferable 1st optical path difference providing structure, (d) is a 1st foundation structure and a 2nd foundation structure, An example in which is superimposed is shown. It is a schematic diagram of a preferable objective lens. It is a figure which shows schematically the structure of optical pick-up apparatus PU1 of this embodiment which can perform recording and / or reproduction | regeneration of information appropriately with respect to BD, DVD, and CD which are different optical disks. It is a figure showing the spherical aberration and sine condition in Example 1 and 2, (a) is BD, (b) is DVD, (c) is the case of CD. It is a figure showing the spherical aberration and sine condition in Example 3 and 4, (a) is BD, (b) is DVD, (c) is the case of CD. It is a figure showing the spherical aberration and sine condition in Example 5 and 6, (a) is BD, (b) is DVD, (c) is the case of CD. It is a figure showing the spherical aberration and sine condition in Example 7 and 8, (a) is BD, (b) is DVD, (c) is the case of CD.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 9 is a diagram schematically showing a configuration of the optical pickup apparatus PU1 of the present embodiment that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks. The optical pickup device PU1 is a slim type and can be mounted on a thin optical information recording / reproducing device. Here, the first optical disc is a BD, the second optical disc is a DVD, and the third optical disc is a CD. Note that the present invention is not limited to this embodiment.

  The optical pickup device PU1 emits light when recording / reproducing information with respect to the objective lens OL, the λ / 4 wavelength plate QWP, the collimating lens COL, the polarization beam splitter BS, and the dichroic prisms DP and BD, and has a wavelength of λ1 = 405 nm. A first semiconductor laser LD1 (first light source) that emits a laser beam (first beam) and a laser beam (second beam) that is emitted when recording / reproducing information on a DVD and has a wavelength λ2 = 660 nm. The second semiconductor laser LD2 (second light source) that emits and the third semiconductor laser LD3 that emits a laser beam (third beam) having a wavelength λ3 = 785 nm emitted when information is recorded / reproduced with respect to the CD are integrated. A laser unit LDP, a sensor lens SEN, a light receiving element PD as a photodetector, and the like.

  As shown in FIG. 1, in the single objective lens OL according to the present embodiment, a central region CN including the optical axis on the aspherical optical surface on the light source side, an intermediate region MD arranged around the center region CN, and A peripheral region OT disposed around the periphery is formed concentrically with the optical axis as the center. Although not shown, the first optical path difference providing structure already described in detail is formed in the center region CN, and the second optical path difference providing structure already described in detail is formed in the intermediate region MD. In addition, a third optical path difference providing structure is formed in the peripheral region OT. In the present embodiment, the third optical path difference providing structure is a blazed diffractive structure. The objective lens of this embodiment is a plastic lens. The first optical path difference providing structure formed in the center region CN of the objective lens OL is a structure in which the first basic structure and the second basic structure are overlapped, and the first basic structure has passed through the first basic structure. The first order diffracted light amount of the first light beam is made larger than any other order diffracted light amount, and the first order diffracted light amount of the second light beam that has passed through the first basic structure is made larger than any other order diffracted light amount. The first-order diffracted light quantity of the third light beam that has passed through the first basic structure is made larger than any other order of diffracted light quantity, and the second basic structure has a second-order diffracted light quantity that has passed through the second basic structure. Make the diffracted light quantity larger than any other order diffracted light quantity, make the first diffracted light quantity of the second light flux that passed through the second basic structure larger than any other order diffracted light quantity, and pass through the second basic structure The first-order diffracted light quantity of the third light flux To be larger than the amount of light.

  The second optical path difference providing structure formed in the intermediate region MD of the objective lens OL is a structure in which the third basic structure and the fourth basic structure are overlapped, and the third basic structure has passed through the third basic structure. The first order diffracted light quantity of the first light beam is made larger than any other order diffracted light quantity, and the first order diffracted light quantity of the second light beam that has passed through the third basic structure is made larger than any other order diffracted light quantity. The first-order diffracted light amount of the third light beam that has passed through the third basic structure is made larger than any other order of diffracted light amount, and the fourth basic structure is the fifth-order or first-order light beam that has passed through the fourth basic structure. The seventh-order diffracted light amount is made larger than any other order diffracted light amount, and the third-order or fourth-order diffracted light amount of the second light flux that has passed through the fourth basic structure is made larger than any other order diffracted light amount.

  The third optical path difference providing structure formed in the peripheral region OT of the objective lens OL has a fifth basic structure, and the fifth basic structure is the second or fourth order of the first light flux that has passed through the fifth basic structure. Make the amount of diffracted light greater than the amount of diffracted light of any other order.

  The divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD1 passes through the dichroic prism DP, passes through the polarization beam splitter BS, and then passes through the collimating lens COL as shown by the solid line. It becomes parallel light, is converted from linearly polarized light into circularly polarized light by the λ / 4 wavelength plate QWP, the light beam diameter is regulated by a diaphragm (not shown), and enters the objective lens OL. Here, the light beam condensed by the central region, the intermediate region, and the peripheral region of the objective lens OL becomes a spot formed on the information recording surface RL1 of the BD through the protective substrate PL1 having a thickness of 0.1 mm. .

  The reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective lens OL and a diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and by the collimating lens COL. A converged light beam is reflected by the polarization beam splitter BS, and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. The information recorded on the BD can be read by using the output signal of the light receiving element PD to focus or track the objective lens OL by the biaxial actuator AC1. Here, when the wavelength fluctuation occurs in the first light flux or when recording / reproducing of a BD having a plurality of information recording layers, the spherical aberration generated due to the wavelength fluctuation or different information recording layers is changed in magnification. The collimating lens COL as a means is changed in the optical axis direction by the uniaxial actuator AC2, and can be corrected by changing the divergence angle or convergence angle of the light beam incident on the objective optical element OL.

  The divergent light beam of the second light beam (λ2 = 660 nm or 658 nm) emitted from the semiconductor laser LD2 of the laser unit LDP is reflected by the dichroic prism DP and passes through the polarization beam splitter BS and the collimating lens COL as indicated by the dotted line. The λ / 4 wavelength plate QWP converts the linearly polarized light into circularly polarized light and enters the objective lens OL. Here, the light beam condensed by the central region and the intermediate region of the objective lens OL (the light beam that has passed through the peripheral region is flared and forms a spot peripheral part) is passed through the protective substrate PL2 having a thickness of 0.6 mm. Thus, the spot is formed on the information recording surface RL2 of the DVD and forms the center of the spot.

  The reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective lens OL, converted from circularly polarized light to linearly polarized light by the λ / 4 wave plate QWP, and converted into a convergent light beam by the collimator lens COL. The light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. And the information recorded on DVD can be read using the output signal of light receiving element PD. In the present embodiment, since the information can be recorded / reproduced on the DVD even when the coupling lens COL is fixed, the control system of the optical pickup device is simplified.

  The divergent light beam of the third light beam (λ3 = 785 nm) emitted from the semiconductor laser LD3 of the laser unit LDP is reflected by the dichroic prism DP, as shown by the one-dot chain line, and passes through the polarization beam splitter BS and the collimating lens COL. The linearly polarized light is converted into circularly polarized light by the λ / 4 wave plate QWP, and is incident on the objective lens OL. Here, the light beam condensed by the central region of the objective lens OL (the light beam that has passed through the intermediate region and the peripheral region is flared to form a spot peripheral portion) is passed through the protective substrate PL3 having a thickness of 1.2 mm. Thus, the spot is formed on the information recording surface RL3 of the CD.

  The reflected light beam modulated by the information pits on the information recording surface RL3 is transmitted again through the objective lens OL, converted from circularly polarized light to linearly polarized light by the λ / 4 wave plate QWP, and converted into a convergent light beam by the collimating lens COL. The light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. And the information recorded on CD can be read using the output signal of light receiving element PD.

(Example)
Examples that can be used in the above-described embodiments will be described below. In the following (including lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) may be expressed using E (for example, 2.5 × E−3). The optical surface of the objective lens is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Formula 1.

  Here, X (h) is an axis in the optical axis direction (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.

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

[Equation 2]
Φ (h) = Σ (C _2i h ²ⁱ × λ × m / λB)
Here, λ: wavelength used, m: diffraction order, λB: manufacturing wavelength, h: distance in the direction perpendicular to the optical axis from the optical axis. The “manufacturing wavelength” is the wavelength of the luminous flux that gives the highest Mi-order diffraction efficiency when passing through the i-th basic structure.
Further, the pitch P (h) = λB / (Σ (2i × C _2i × h ^2i-1 )).

(Example 1)
Table 1 shows lens data of Example 1. The objective lens of Example 1 is a plastic single lens, and the steps of the first basic structure and the third basic structure are opposite to the optical axis, and the second basic structure, the fourth basic structure, and the fifth basic structure. The level difference of the structure faces the direction of the optical axis. In addition, the first optical path difference providing structure of Example 1 has (1/1/1) of the second basic structure which is a blazed diffraction structure of (2/1/1) in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped. The second optical path difference providing structure is the fourth basic structure, which is a blazed diffraction structure of (5/3), and the third basic structure, which is a blazed diffraction structure of (1/1), in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
The third optical path difference providing structure has a fifth basic structure that makes the second-order diffracted light amount of the first light beam larger than any other order diffracted light amount in the entire peripheral region.

  FIG. 10 shows a diagram of the spherical aberration SA and the sine condition SC in Example 1. In FIG. 10, (a) is a graph when BD is used, (b) is when DVD is used, (c) is a graph when CD is used, and the vertical axis of (a) is the effective luminous flux when BD is used. When the half value (h1 / 2) of the diameter (diameter) is 1.0, the vertical axis of (b) is the half value (h2 / 2) of the effective diameter (diameter) of the luminous flux when using the DVD. The vertical axis of (c) in the case of 1.0 is the distance from the optical axis when the half value (h3 / 2) of the effective diameter (diameter) of the light beam when using the CD is 1.0. Represents.

(Example 2)
Table 2 shows lens data of Example 2. The objective lens of Example 2 is a plastic single lens, and the steps of the first basic structure and the third basic structure are opposite to the optical axis, and the second basic structure, the fourth basic structure, and the fifth basic structure. The level difference of the structure faces the direction of the optical axis. In addition, the first optical path difference providing structure of Example 2 has (1/1/1) of the second basic structure which is a blazed diffraction structure of (2/1/1) in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped. The second optical path difference providing structure is the fourth basic structure, which is a blazed diffraction structure of (5/3), and the third basic structure, which is a blazed diffraction structure of (1/1), in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
The third optical path difference providing structure has a fifth basic structure that makes the fourth-order diffracted light amount of the first light flux larger than any other order diffracted light amount in the entire peripheral region.

  Example 2 is different from Example 1 only in the fifth basic structure. In FIG. 10A of Example 1, the flare light of DVD and CD that has passed through the peripheral region is omitted. The spherical aberration SA and sine condition SC in the second embodiment are the same as those in FIG. 10 in the first embodiment.

(Example 3)
Table 3 shows lens data of Example 3. The objective lens of Example 3 is a plastic single lens, and the steps of the first basic structure and the third basic structure are opposite to the optical axis, and the second basic structure, the fourth basic structure, and the fifth basic structure. The level difference of the structure faces the direction of the optical axis. Further, the first optical path difference providing structure of Example 3 has (1/1/1) of the (2/1/1) blazed diffraction structure of the second basic structure in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped. The second optical path difference providing structure has a (7/4) blazed diffractive structure as a fourth basic structure (7/1) blazed diffractive structure as a third basic structure in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
The third optical path difference providing structure has a fifth basic structure that makes the second-order diffracted light amount of the first light beam larger than any other order diffracted light amount in the entire peripheral region.

  FIG. 11 shows a diagram of spherical aberration SA and sine condition SC in Example 3. In FIG. 11, (a) is a graph when BD is used, (b) is a graph when DVD is used, (c) is a graph when CD is used, and the vertical axis of (a) is the effective luminous flux when BD is used. When the half value (h1 / 2) of the diameter is 1.0, the vertical axis of (b) is when the half value (h2 / 2) of the effective diameter of the luminous flux when using the DVD is 1.0. The vertical axis of (c) represents the distance from the optical axis when the half value (h3 / 2) of the effective diameter of the light beam when using the CD is 1.0.

Example 4
Table 4 shows lens data of Example 4. The objective lens of Example 4 is a plastic single lens, and the steps of the first basic structure and the third basic structure are opposite to the optical axis, and the second basic structure, the fourth basic structure, and the fifth basic structure. The level difference of the structure faces the direction of the optical axis. Further, the first optical path difference providing structure of Example 4 has (1/1/1) of the second basic structure which is a (2/1/1) blazed diffraction structure in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped. The second optical path difference providing structure has a (7/4) blazed diffractive structure as a fourth basic structure (7/1) blazed diffractive structure as a third basic structure in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
The third optical path difference providing structure has a fifth basic structure that makes the fourth-order diffracted light amount of the first light flux larger than any other order diffracted light amount in the entire peripheral region.

  Example 4 is different from Example 3 only in the fifth basic structure. FIG. 11A of Example 3 omits the flare light of the DVD and CD that have passed through the peripheral region. The diagram of the spherical aberration SA and the sine condition SC in the fourth embodiment is the same as FIG. 11 in the third embodiment.

(Example 5)
Table 5 shows lens data of Example 5. The objective lens of Example 5 is a plastic single lens, and the steps of the first basic structure, the third basic structure, and the fifth basic structure are opposite to the optical axis, and the second basic structure and the fourth basic structure. The level difference of the structure faces the direction of the optical axis. Further, the first optical path difference providing structure of Example 5 has (1/1/1) of the second basic structure which is a blazed diffraction structure of (2/1/1) in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped. The second optical path difference providing structure is the fourth basic structure, which is a blazed diffraction structure of (5/3), and the third basic structure, which is a blazed diffraction structure of (1/1), in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
The third optical path difference providing structure has a fifth basic structure that makes the second-order diffracted light amount of the first light beam larger than any other order diffracted light amount in the entire peripheral region.

  FIG. 12 shows a diagram of spherical aberration SA and sine condition SC in Example 5. In FIG. 12, (a) is a graph when BD is used, (b) is when DVD is used, (c) is a graph when CD is used, and the vertical axis of (a) is the effective luminous flux when BD is used. When the half value (h1 / 2) of the diameter is 1.0, the vertical axis of (b) is when the half value (h2 / 2) of the effective diameter of the luminous flux when using the DVD is 1.0. The vertical axis of (c) represents the distance from the optical axis when the half value (h3 / 2) of the effective diameter of the light beam when using the CD is 1.0.

(Example 6)
Table 6 shows lens data of Example 6. The objective lens of Example 6 is a plastic single lens, and the steps of the first basic structure, the third basic structure, and the fifth basic structure are opposite to the optical axis, and the second basic structure and the fourth basic structure. The level difference of the structure faces the direction of the optical axis. In addition, the first optical path difference providing structure of Example 6 has (1/1/1) of the second basic structure which is a (2/1/1) blazed diffraction structure in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped. The second optical path difference providing structure is the fourth basic structure, which is a blazed diffraction structure of (5/3), and the third basic structure, which is a blazed diffraction structure of (1/1), in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
The third optical path difference providing structure has a fifth basic structure that makes the fourth-order diffracted light amount of the first light flux larger than any other order diffracted light amount in the entire peripheral region.

  Example 6 is different from Example 5 only in the fifth basic structure. In FIG. 12A of Example 5, the flare light of the DVD and CD that has passed through the peripheral region is omitted. The spherical aberration SA and the sine condition SC in Example 6 are the same as those in Example 5 shown in FIG.

(Example 7)
Table 7 shows lens data of Example 7. The objective lens of Example 7 is a plastic single lens, and the steps of the first basic structure, the third basic structure, and the fifth basic structure are opposite to the optical axis, and the second basic structure and the fourth basic structure. The level difference of the structure faces the direction of the optical axis. Further, the first optical path difference providing structure of Example 7 has (1/1/1) of the (2/1/1) blazed diffractive structure (2/1/1) in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped. The second optical path difference providing structure has a (7/4) blazed diffractive structure as a fourth basic structure (7/1) blazed diffractive structure as a third basic structure in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
The third optical path difference providing structure has a fifth basic structure that makes the second-order diffracted light amount of the first light beam larger than any other order diffracted light amount in the entire peripheral region.

  FIG. 13 shows a diagram of spherical aberration SA and sine condition SC in Example 3. In FIG. 13, (a) is a graph when BD is used, (b) is when DVD is used, (c) is a graph when CD is used, and the vertical axis of (a) is the effective luminous flux when BD is used. When the half value (h1 / 2) of the diameter is 1.0, the vertical axis of (b) is when the half value (h2 / 2) of the effective diameter of the luminous flux when using the DVD is 1.0. The vertical axis of (c) represents the distance from the optical axis when the half value (h3 / 2) of the effective diameter of the light beam when using the CD is 1.0.

(Example 8)
Table 8 shows lens data of Example 8. The objective lens of Example 8 is a plastic single lens, and the steps of the first basic structure, the third basic structure, and the fifth basic structure are opposite to the optical axis, and the second basic structure and the fourth basic structure. The level difference of the structure faces the direction of the optical axis. In addition, the first optical path difference providing structure of Example 8 has (1/1/1) of the second basic structure which is a (2/1/1) blazed diffraction structure in the entire central region. It is an optical path difference providing structure in which the first basic structure which is a blazed diffraction structure is overlapped. The second optical path difference providing structure has a (7/4) blazed diffractive structure as a fourth basic structure (7/1) blazed diffractive structure as a third basic structure in the entire intermediate region. It is an optical path difference providing structure in which the structures are overlapped.
The third optical path difference providing structure has a fifth basic structure that makes the fourth-order diffracted light amount of the first light flux larger than any other order diffracted light amount in the entire peripheral region.

  Example 8 is different from Example 7 only in the fifth basic structure. In FIG. 13A of Example 7, the flare light of the DVD and CD that has passed through the peripheral region is omitted. The spherical aberration SA and sine condition SC in Example 8 are the same as those in FIG. 13 in Example 7.

  In all of Examples 1 to 8, the spot diameter does not become too large when BD is used, and a favorable spot diameter is formed. Table 9 lists the values of formulas (1) to (8) in each example.

  The present invention is not limited to the embodiments described in the specification, and includes other embodiments and modifications for those skilled in the art from the embodiments and technical ideas described in the present specification. it is obvious. The description and examples are for illustrative purposes only, and the scope of the invention is indicated by the following claims.

AC1 Biaxial actuator B Step amount BS Polarizing beam splitter CN Central region COL Collimating lens DP Dichroic prism LD1 First semiconductor laser or blue-violet semiconductor laser LD2 Second semiconductor laser LD3 Third semiconductor laser LDP Laser unit MD Intermediate region OA Optical axis ODS Optical path difference providing structure OL Objective lens OT Peripheral region P Pitch PD Light receiving element PL1 Protective substrate PL2 Protective substrate PL3 Protective substrate PU1 Optical pickup device QWP λ / 4 wavelength plate RL1 Information recording surface RL2 Information recording surface RL3 Information recording surface SEN Sensor lens

Claims (11)

A first light source that emits a first light beam with a first wavelength λ1 (390 nm ≦ λ1 ≦ 415 nm), a second light source that emits a second light beam with a second wavelength λ2 (630 nm ≦ λ2 ≦ 670 nm), and a third wavelength λ3 A third light source that emits a third light beam (760 nm ≦ λ3 ≦ 820 nm), and recording and / or reproducing information of a BD having a protective substrate with a thickness of t1 using the first light beam, Recording and / or reproducing information of a DVD having a protective substrate having a thickness of t2 (t1 <t2) using the second light flux, and having a thickness of t3 (t2 <t3) using the third light flux. An objective lens used in an optical pickup device for recording and / or reproducing information of a CD having a protective substrate,
The objective lens is a single lens,
The optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region,
The central region has a first optical path difference providing structure,
The intermediate region has a second optical path difference providing structure,
The peripheral region has a third optical path difference providing structure;
The objective lens condenses the first light flux that passes through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that passes through the central region. Are recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the central region is recorded and / or recorded on the information recording surface of the CD. Or collect it so that it can be regenerated,
The objective lens condenses the first light flux passing through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the intermediate area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the intermediate region is recorded and / or recorded on the information recording surface of the CD. Or do not concentrate so that it can be regenerated,
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the peripheral area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the peripheral area is recorded on the information recording surface of the CD. And / or do not collect light for playback
The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
The first basic structure is a blaze-type structure, and the first-order diffracted light quantity of the first light beam that has passed through the first basic structure is made larger than any other order of diffracted light quantity, and passes through the first basic structure. The first-order diffracted light quantity of the second light flux is made larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the third light flux that has passed through the first basic structure is changed to any other order diffracted light quantity. Bigger than
The second basic structure is a blazed structure, and the second-order diffracted light quantity of the first light beam that has passed through the second basic structure is made larger than any other order of diffracted light quantity, and passes through the second basic structure. The first order diffracted light quantity of the second light flux is made larger than any other order diffracted light quantity, and the first diffracted light quantity of the third light flux that has passed through the second basic structure is changed to any other order diffracted light quantity. Bigger than
The second optical path difference providing structure is a structure in which at least a third basic structure and a fourth basic structure are overlapped,
The third basic structure is a blazed structure, and the first-order diffracted light quantity of the first light beam that has passed through the third basic structure is made larger than any other order of diffracted light quantity, and passes through the third basic structure. The first-order diffracted light amount of the second light flux is made larger than any other order diffracted light amount,
The fourth foundation structure is a blazed structure, and the fifth or seventh-order diffracted light quantity of the first light flux that has passed through the fourth basic structure is made larger than any other order of diffracted light quantity, Making the third or fourth order diffracted light quantity of the second light flux that has passed through the structure larger than any other order diffracted light quantity;
The third optical path difference providing structure has at least a fifth basic structure,
The fifth basic structure is a blazed structure, and the second-order or fourth-order diffracted light quantity of the first light beam that has passed through the fifth basic structure is made larger than any other order diffracted light quantity. Objective lens. The ratio r2 of the pupil transmittance in the vicinity of the peripheral region of the intermediate region with respect to the vicinity of the optical axis center of the objective lens in the second light flux,
r2 ≦ 0.9 (1)
And
When the effective diameter of the objective lens in the second light flux is h2, the imaging magnification in the second light flux is m2, and the focal length in the first light flux is f1,
0.66 ≦ h2 / (2 · f1 · (1-m2)) ≦ 0.75 (2)
The objective lens according to claim 1, wherein The objective lens according to claim 1, wherein the following expression is satisfied.
1.0 ≦ f1 ≦ 2.2 (3) The objective lens according to claim 1, wherein the following expression is satisfied when an effective diameter of the objective lens in the first light flux is h1.
1.9 ≦ h1 ≦ 3.0 (4) The i-th basic structure of the objective lens has the following formula φ _i (h) = (C _i2 × h ² + C _i4 × h ⁴ + C _i6 × h ⁶ + C _i8 × h ⁸ + C _i10 × h ¹⁰ ) Miλ / λB _i
(Where h (unit: mm) is the height from the optical axis, C _i2 , C _i4 , C _i6 ... _Are secondary in the optical path difference function (i is a natural number) of the i-th substructure, The fourth-order and sixth-order optical path difference function coefficients, Mi is the diffraction order in the optical path difference function of the i-th basic structure that maximizes the diffraction order of the incident light beam, and λ (unit: mm) is the use of the incident light beam. ΛB _i (unit: mm) represents a manufacturing wavelength in the i-th basic structure, respectively)), and the focal length of the first basic structure is expressed as fD ₁ When defined as (unit: mm), the following equation is satisfied,
−0.40 <f1 / fD ₁ <−0.10 (5)
(However, fD ₁ = −λB ₁ / (2 × C ₁₂ × M1 × λ), and the value of M1 is 1.)
When the effective diameter (diameter) of the second light beam is defined as h2 (unit: mm) and the effective diameter (diameter) of the third light beam is defined as h3 (unit: mm), the following conditional expression (6)
−0.025 <(φ ₅ (h3 / 2) −φ ₅ (h2 / 2)) / (M5 × f1) <0.025 (6)
(However, the value of M5 is 2 or 4.)
The objective lens according to claim 1, wherein: The objective lens according to claim 1, wherein the following expression is satisfied.
0.68 ≦ h2 / (2 · f1 · (1-m2)) ≦ 0.74 (2) ′ The objective lens according to claim 1, wherein when the thickness on the optical axis of the objective lens is d (mm), the following expression is satisfied.
1.0 ≦ d / f1 ≦ 1.5 (7) The first basic structure provided at least near the optical axis of the central region has a step in a direction opposite to the optical axis,
The objective lens according to any one of claims 1 to 7, wherein the second basic structure provided at least in the vicinity of the optical axis of the central region has a step in the direction of the optical axis. The objective lens according to claim 1, wherein the following expression is satisfied when the total number of annular zones in the peripheral region is N3.
5 (mm) ≤ N3 · f1 ≤ 100 (mm) (8)   An optical pickup device comprising the objective lens according to claim 1. A coupling lens through which at least the first luminous flux and the second luminous flux pass, and an actuator for moving the coupling lens in the optical axis direction;
When the first light beam passes, the coupling lens can be displaced in the optical axis direction by the actuator;
The optical pickup device according to claim 10, wherein when the second light beam passes, the coupling lens is fixed in a position in an optical axis direction.

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