JP5093634B2 - Objective lens for optical pickup device and optical pickup device - Google Patents

Description

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

  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 ˜415 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 further with CD, information between BD optical system and DVD or CD optical system is used. Although a method of selectively switching according to the recording density of the optical disc to be recorded / reproduced is conceivable, it requires a plurality of optical systems, 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 a diffractive structure having a wavelength dependency of spherical aberration in the objective lens.

  In Patent Document 1, the first to third recording densities differ in the central region by changing the combination of the diffractive structures of the central region and the intermediate region among the regions where the optical surface is divided into three. There is disclosed an objective lens that realizes compatibility of optical discs and, in the middle region, achieves compatibility of compatibility between the first and second optical discs and flare out of unnecessary light when using the third optical disc for restricting the aperture. . In Patent Document 2, a common diffractive structure is used in the central region and the intermediate region among the regions where the optical surface is divided into three, but another diffractive structure is superimposed only on the central region. In the middle area, compatibility of three different optical discs is realized, and in the middle area, compatibility of two different optical discs and flare out of unnecessary light when using the remaining optical discs for aperture limitation are achieved. An objective lens is disclosed.

JP2009-93782A JP 2010-55732 A

  Here, according to the objective lens of Patent Document 1, a diffractive structure in which the order of the diffracted light having the highest light intensity is different between the central region and the intermediate region is employed. When this occurs, since the spherical aberration becomes discontinuous, high-order aberrations occur, and there is a possibility that an appropriate focused spot cannot be formed. Further, according to the objective lens of Patent Document 2, since a structure that is not in the middle region is superimposed on the central region, high-order aberrations occur when a temperature change or a light source wavelength change occurs. The problem of end up occurs. Further, in order to make the two different types of optical disks BD and DVD compatible, when the first wavelength light beam is incident, the second-order diffracted light is generated as the strongest diffracted light, and when the second wavelength light beam is incident. Since only one diffractive structure that generates first-order diffracted light is used as the strongest diffracted light, the power of diffraction is determined according to the wavelength, wavelength characteristics (spherical aberration that occurs when the wavelength of the light source changes), and temperature characteristics. (Spherical aberration that occurs when the environmental temperature changes) is also uniquely determined, making it difficult to adjust the balance and reducing the degree of freedom in designing the objective lens. Further, in the central region, a binary type diffractive structure (0th order diffracted light is generated as the strongest diffracted light when the first wavelength light beam is incident, and as the strongest diffracted light when the second wavelength light beam is incident. When 0th order diffracted light is generated and a light beam of the third wavelength is incident, the first order diffracted light is generated as the strongest diffracted light. For this reason, there are problems that the wavelength dependency of the diffraction efficiency is increased, the moldability is lowered, and the diffraction efficiency due to a manufacturing error is lowered.

  An object of the present invention is to solve the above-mentioned problems. For example, it is possible to perform compatibility of three types of optical disks of BD / DVD / CD with a common objective lens, and suppress high-order aberrations. An object of the present invention is to provide an objective lens capable of improving moldability and an optical pickup device using the objective lens.

The objective lens according to claim 1, wherein a first light source that emits a first light flux having a first wavelength λ1 (nm) and a second light flux that emits a second light flux having a second wavelength λ2 (nm) (λ2> λ1). A first optical disc having a light source and a third light source that emits a third light beam having a third wavelength λ3 (nm) (λ3> λ2), and having a protective substrate having a thickness t1 using the first light beam. Information is recorded and / or reproduced, information is recorded and / or reproduced on a second optical disc having a protective substrate having a thickness t2 (t1 <t2) using the second light flux, and the third light flux is reflected on the third light flux. An objective lens used in an optical pickup device for recording and / or reproducing information on a third optical disk having a protective substrate having a thickness of t3 (t2 <t3).
The objective lens is a single ball,
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 objective lens condenses the first light flux that passes through the central area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the central area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the central region is condensed on the information recording surface of the third optical disc. Condensing so that information can be recorded and / or reproduced,
The objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the intermediate area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the intermediate region is condensed on the information recording surface of the third optical disc. Without collecting light so that information can be recorded and / or reproduced.
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 first optical disc, and the objective lens passes through the peripheral area. The second light flux is not condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc, and the third light flux passing through the peripheral region is used as the information recording surface of the third optical disc. Do not concentrate so that information can be recorded and / or reproduced
The central region has a first optical path difference providing structure in which a first basic structure that is a blazed structure and a second basic structure that is a blazed structure are overlapped,
The intermediate region has a second optical path difference providing structure in which a third basic structure that is a blazed structure and a fourth basic structure that is a blazed structure are overlapped,
The first basic structure makes the A-order diffracted light quantity of the first light flux that has passed through the first basic structure larger than any other order diffracted light quantity, and B of the second light flux that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The second basic structure makes the D-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and the E of the second light beam that has passed through the second basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the F-order diffracted light quantity of the third light flux that has passed through the second basic structure larger than any other order diffracted light quantity,
The third basic structure makes the A-order diffracted light quantity of the first light flux that has passed through the third basic structure larger than any other order of diffracted light quantity, and B of the second light flux that has passed through the third basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the third basic structure larger than any other order diffracted light quantity,
The fourth foundation structure makes the D-order diffracted light quantity of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light quantity, and the E of the second light flux that has passed through the fourth foundation structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the F-order diffracted light quantity of the third light flux that has passed through the fourth basic structure larger than any other order diffracted light quantity,
A, B, C, D, E, and F are respectively
| A | = 1
| B | = 1
| C | = 1
| D | = 2
| E | = 1
| F | = 1
The filling,
The pitch of the first foundation structure, the second foundation structure, the third foundation structure, and the fourth foundation structure is a positive sign when the step of the foundation structure faces the direction opposite to the optical axis, If the step of the foundation structure is facing the direction of the optical axis,
The pitch P2 at the position closest to the boundary of the second foundation structure and the pitch P4 at the position closest to the boundary of the fourth foundation structure across the boundary between the central area and the intermediate area are: In consideration of the sign, the following expression (1) is satisfied.
P4-P2> 0 (1)
However,
When the optical path difference function defining the basic structure is represented by Φ (h) = Σ (C _2i h ²ⁱ × λ × m / λB),
Pitch P (h) = λB / (Σ (2i × C _2i × h ^2i-1 )).
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” referred to here is the wavelength of the light beam that has the highest m-th order diffraction efficiency when passing through the basic structure.

  Hereinafter, the present invention will be described. For convenience, the first optical disk will be described as BD, the second optical disk as DVD, and the third optical disk as CD. By matching the orders of diffracted light with the highest light intensity in the first basic structure and the third basic structure, and matching the orders of diffracted light with the highest light intensity in the second basic structure and the fourth basic structure, Spherical aberration can be made continuous for the light flux passing through the intermediate region and the intermediate region, and as a result, it is preferable because high-order aberrations can be suppressed even during temperature and wavelength changes. However, there still remains a problem of how to perform flare out when using a CD without superimposing a basic structure for performing flare out when using a CD in the central region or intermediate region.

First, as a compatible basic structure, the present inventor makes 1/1/1 (the first-order diffracted light is generated most in any of the first light beam, the second light beam, and the third light beam). The second and fourth foundations have a three-basic structure and 2/1/1 (the second-order diffracted light is most generated in the first light beam, and the first-order diffracted light is most generated in the second and third light beams). The combination to be structured was selected. The reason for this is that, due to the use of a blazed structure with a low level difference (height in the optical axis direction of the level difference), it is possible to prevent a decrease in efficiency when the wavelength or temperature changes, and this is due to shadow effects and manufacturing errors. A decrease in light utilization efficiency can be suppressed, and secondly, it has high diffraction efficiency for all three wavelengths. Further, in these two basic structures, the relationship between the pitch of the central region side and the pitch of the intermediate region side and the pitch of the intermediate region side with respect to the boundary and the relationship between the direction of the step are defined as a certain relationship. It was discovered that under-spherical aberration can be given to the light beam that has passed through the intermediate region when using an optical disc, and that flare can be produced without superimposing any other basic structure. That is, the BD / DVD / CD compatibility in the central region is as follows: (a) over spherical aberration caused by the mother aspherical surface of the objective lens that is a convex lens; (b) under spherical aberration of the 1/1/1 basic structure; c) In the case of performing by adding the under spherical aberration of the 2/1/1 basic structure, the pitch P2 at the position closest to the boundary of the second basic structure across the boundary between the central region and the intermediate region, and When the pitch P4 at the position closest to the boundary of the fourth basic structure satisfies P4-P2> 0, the power of the intermediate region (fourth basic structure) is increased in the central region (the fourth basic structure) in the vicinity of the boundary between the central region and the intermediate region. Since the power in the vicinity of the boundary of the second basic structure) is larger than that in the vicinity of the boundary in the central region, the spherical aberration correction effect is large in the vicinity of the boundary in the intermediate region (the spherical aberration in (c) is large). Become. Therefore, in the vicinity of the boundary of the intermediate region , the effect of the under spherical aberration of (c) is increased , and flare can be produced when the CD is used.

  Magnitude relationship between the pitch P2 at the position closest to the boundary of the second foundation structure on the central region side and the pitch P4 at the position closest to the boundary of the fourth foundation structure on the intermediate region side that causes an under spherical aberration when using CD And a combination of the relationship of the direction of the step will be described. 16, 17, and 18 are graphs in which the vertical axis indicates the pitch P (mm) and the horizontal axis indicates the height h (mm) from the optical axis, and the left side of the boundary BN is the central region. The right side represents the intermediate area. Here, for convenience, the second basic structure and the fourth basic structure are referred to as (2/1/1) diffraction structures. In addition, when the sign of the pitch is negative (−), it indicates that the level difference of the basic structure faces the optical axis side, and when the sign of the pitch is positive (+), it indicates that the level difference of the basic structure is light. Indicates that it is facing away from the axis.

  The inventor divides the focal length f1 of the objective lens in the first light flux into a predetermined range, and the pitch P2 closest to the boundary of the second base structure on the center region side and the boundary of the fourth base structure on the intermediate region side The combination of the magnitude relationship with the pitch P4 at the closest position to the height and the relationship in the direction of the step was examined. FIG. 18 shows a pitch at a position closest to the boundary of the second base structure on the central region side that can cause an under spherical aberration when using a CD when the focal length f1 is as short as 1.0 to 1.8 mm. An example of a combination of the magnitude relationship between P2 and the pitch P4 at the position closest to the boundary of the fourth foundation structure on the intermediate region side and the orientation relationship of the steps is shown. More specifically, in the case of FIG. 18, in the (2/1/1) diffraction structure, | P2 | <| P4 | and the sign of the pitch is positive. Accordingly, in the (2/1/1) diffraction structure, [pitch P4 at the position closest to the boundary of the fourth foundation structure in the middle area of the encoding] − [closest to the boundary of the second foundation structure in the middle area of the encoding) Position pitch P2] = P4-P2> 0. That is, the expression (1) is satisfied.

  FIG. 17 shows the second basic structure on the central region side that can cause under spherical aberration when using a CD when the focal length f1 of the objective lens in the first light flux is relatively short, 1.2 to 2.5 mm. An example of a combination of the magnitude relationship between the pitch P2 at the position closest to the boundary and the pitch P4 at the position closest to the boundary of the fourth basic structure on the intermediate region side and the relationship in the direction of the step is shown. More specifically, in the (2/1/1) diffraction structure shown in FIG. 17, | P2 |> | P4 | and the sign of the pitch is negative. Accordingly, in the (2/1/1) diffraction structure, [pitch P4 at the position closest to the boundary of the fourth foundation structure in the middle area of the encoding] − [closest to the boundary of the second foundation structure in the middle area of the encoding) Position pitch P2] = (− | P4 |) − (− | P2 |)> 0. That is, the expression (1) is satisfied.

  FIG. 16 shows the second basic structure on the central region side that can cause an under spherical aberration when using a CD when the focal length f1 of the objective lens in the first light flux is relatively long, 2.0 to 3.5 mm. The combination of the magnitude relationship between the pitch P2 at the position closest to the boundary and the pitch P4 at the position closest to the boundary of the fourth basic structure on the intermediate region side and the relationship in the direction of the step is shown. More specifically, in the (2/1/1) diffraction structure shown in FIG. 16, | P2 |> | P4 |, and the sign of the pitch is negative. Accordingly, in the (2/1/1) diffraction structure, [pitch P4 at the position closest to the boundary of the fourth foundation structure in the middle area of the encoding] − [closest to the boundary of the second foundation structure in the middle area of the encoding) Position pitch P2] = (− | P4 |) − (− | P2 |)> 0. That is, the expression (1) is satisfied. That is, it can be seen that under spherical aberration can be generated when the CD is used by satisfying Expression (1) regardless of the size of the focal length f1.

  Thus, the sign of the pitch closest to the boundary changes with respect to the focal length, and this uses the paraxial power of the 2/1/1 structure in order to ensure a working distance when using a CD. This is because the shorter the focal length, the smaller the positive paraxial power.

  Furthermore, since the flare at the time of using the CD can be set under due to the configuration of the present invention described above, it is possible to suppress the possibility that the objective lens will collide when the optical disk is first accessed. Further, when the temperature of the BD changes, spherical aberration due to a change in the refractive index of the material can be corrected by a diffraction effect due to a change in wavelength, and the temperature characteristics of the BD can be improved.

  In other words, according to the present invention, three different types of optical disks can be used interchangeably, and an objective that can appropriately form a focused spot on the third optical disk by flaring the third light flux that has passed through the intermediate region. Design flexibility to design an objective lens with good temperature characteristics in BD by superimposing 1/1/1 and 2/1/1 basic structures in the central and intermediate areas while being a lens Can be increased. By using the same diffraction order basic structure of 1/1/1 and 2/1/1 in both the central region and the intermediate region, the spherical aberration becomes discontinuous when the temperature or the wavelength of the light source changes. It is possible to suppress the occurrence of higher order spherical aberration. Furthermore, it is not necessary to superimpose a diffractive structure or the like for flaring the third light flux in the intermediate region, so that molding is easy and manufacturability is improved, and as a result, light utilization efficiency can be increased.

Objective lens according to claim 2 is the invention according to claim 1, wherein the second basis of the width of the closest annular zone to the boundary of the structure Delta] T2, the closest annular zone to the boundary of the fourth basic structure The width of the zone of the first foundation structure, the second foundation structure, the third foundation structure and the fourth foundation structure is set so that the width of the zone of the foundation structure is opposite to the optical axis. The following expression is satisfied when the sign is positive, and when the difference in level of the basic structure is in the direction of the optical axis, the sign is negative.
ΔT4-ΔT2> 0 (2)

  If the condition of claim 1 is satisfied, further, the difference between the pitch of the second foundation structure on the side of the central region and the pitch of the fourth foundation structure on the side of the intermediate region across the boundary between the central region and the intermediate region is large, Further, when the annular zones of the second foundation structure and the fourth foundation structure on both sides of the boundary have an ideal shape, the difference in pitch appears in the difference in the annular zone width. (The ideal shape here refers to one in which the difference in phase applied at the start position and end position of one ring zone is an integer multiple of 2π or a value close thereto. In the case of overlapping shapes, usually, if the difference in step position of each diffraction structure is slight, the molding process becomes difficult, so the design is changed to match one step position with the other, or Since the design is changed so that it is set to the intermediate position, it may not be an ideal shape.) Thus, when the difference in pitch appears in the difference in the annular zone width, the above equation (2) is Will meet. In other words, if Expression (2) is satisfied, Expression (1) is always satisfied, but even if Expression (1) is satisfied, Expression (2) may not be satisfied.

  Equation (2) will be described in more detail below.

  The width ΔT2 of the annular zone closest to the boundary of the second foundation structure on the central region side and the width of the annular zone ΔT4 closest to the boundary of the fourth foundation structure on the intermediate region side, which causes an under spherical aberration when using CD. A combination of the magnitude relationship and the step direction relationship will be described. FIG. 1 is a diagram schematically showing cross sections in the optical axis direction of the second foundation structure and the fourth foundation structure. Here, for convenience, the second basic structure and the fourth basic structure are referred to as (2/1/1) diffraction structures. Also, BN is defined as the boundary between the central region and the intermediate region, the width of the annular zone closest to the boundary of the second foundation structure is | ΔT2 |, and the width of the annular zone closest to the boundary of the fourth foundation structure is | ΔT4 | To do. Further, the sign of the pitch is negative (−) when the level difference of the base structure faces the optical axis side (lower side in FIG. 1), and the level difference of the base structure faces the opposite side (upper side in FIG. 1). The sign of the pitch is positive (+).

  The inventor divides the focal length f1 of the objective lens in the first light flux into a predetermined range, and the width of the annular zone ΔT2 closest to the boundary of the second foundation structure on the center region side and the fourth foundation structure on the intermediate region side. The combination of the magnitude relationship with the width ΔT4 of the annular zone closest to the boundary and the relationship of the direction of the step was examined. FIG. 1A is closest to the boundary of the second substructure on the central region side, which can cause under spherical aberration when using a CD when the focal length f1 is as short as 1.0 to 1.8 mm. A combination of the magnitude relationship between the zone width ΔT2 and the zone width ΔT4 closest to the boundary of the fourth base structure on the intermediate region side and the relationship of the step direction is shown. More specifically, in the (2/1/1) diffraction structure shown in FIG. 1A, | ΔT2 | <| ΔT4 | and the sign of the pitch is positive. Therefore, in the (2/1/1) diffraction structure, [the zone width ΔT4 closest to the boundary of the fourth substructure in the middle region of the encoding] − [mostly the boundary of the second substructure in the central region of the encoding] Close ring width [Delta] T2] = [Delta] T4- [Delta] T2> 0. That is, the expression (2) is satisfied. Incidentally, the expression (1) is also satisfied.

  FIG. 1 (b) shows the second in the central region, which can cause an under spherical aberration when using the CD when the focal length f1 of the objective lens in the first light flux is relatively short, 1.2 to 2.5 mm. The figure shows a combination of the magnitude relationship between the width ΔT2 of the annular zone closest to the boundary of the foundation structure and the width ΔT4 of the annular zone closest to the boundary of the fourth foundation structure on the intermediate region side, and the relationship of the direction of the step. More specifically, in the (2/1/1) diffraction structure shown in FIG. 1B, | ΔT2 |> | ΔT4 | and the sign of the pitch is negative. Therefore, in the (2/1/1) diffraction structure, [the zone width ΔT4 closest to the boundary of the fourth substructure in the middle region of the encoding] − [mostly the boundary of the second substructure in the central region of the encoding] The width of the near annular zone ΔT2] = (− | ΔT4 |) − (− | ΔT2 |)> 0. That is, the expression (2) is satisfied. Further, the expression (1) is also satisfied.

  FIG. 1 (c) shows the second in the central region that can cause an under spherical aberration when using a CD when the focal length f1 of the objective lens in the first light flux is relatively long, 2.0 to 3.5 mm. The figure shows a combination of the magnitude relationship between the width ΔT2 of the annular zone closest to the boundary of the foundation structure and the width ΔT4 of the annular zone closest to the boundary of the fourth foundation structure on the intermediate region side, and the relationship of the direction of the step. More specifically, in the (2/1/1) diffraction structure shown in FIG. 1C, | ΔT2 |> | ΔT4 |, and the sign of the pitch is negative. Therefore, in the (2/1/1) diffraction structure, [the zone width ΔT4 closest to the boundary of the fourth substructure in the middle region of the encoding] − [mostly the boundary of the second substructure in the central region of the encoding] The width of the near annular zone ΔT2] = (− | ΔT4 |) − (− | ΔT2 |)> 0. That is, the expression (2) is satisfied. The expression (1) is also satisfied. That is, it can be understood that under spherical aberration can be generated when the CD is used by satisfying the expression (2) regardless of the size of the focal length f1.

  As described above, the sign of the width ΔT (also the pitch P) of the annular zone closest to the boundary changes with respect to the focal length. This is a 2/1/1 structure in order to ensure a working distance when using the CD. This is because the positive paraxial power becomes smaller as the focal length becomes shorter.

  By satisfying the expression (2), the diffractive powers of the second basic structure and the fourth basic structure are greatly changed, so that flare on the information recording surface of the CD can be skipped.

The objective lens described in claim 3 is characterized in that, in the invention described in claim 1 or 2, the step at the position closest to the boundary of the second basic structure faces the direction of the optical axis.
An objective lens according to a fourth aspect is the invention according to any one of the first to third aspects, wherein a step at a position closest to the boundary of the second foundation structure and a boundary closest to the boundary of the fourth foundation structure are provided. It is characterized in that the step at the close position faces the same direction.
The objective lens according to claim 5 is the invention according to any one of claims 1 to 4 , wherein the pitch P1 at a position closest to the boundary of the first foundation structure and the most of the third foundation structure are The pitch P3 at a position close to the boundary satisfies the following expression (3) in consideration of its sign.
P3-P1> 0 (3)

  According to the present invention, since the flare out when using the third optical disk is performed by changing the respective diffraction powers of the overlapping basic structure, the amount of individual power change can be reduced. That is, in order to perform under flare when using the third optical disk, not only the power of the 2/1/1 structure is changed, but also the power of the 1/1/1 structure is changed to perform flare 2/1. / 1 structure, 1/1/1 structure, under-flare when using the third optical disc can be made while keeping the power change amount small. For this reason, the amount of aberration discontinuity is small when the wavelength or temperature changes, and the occurrence of high-order aberrations can be suppressed.

BD / DVD / CD compatibility in the central region is as follows: (a) Over spherical aberration caused by the mother aspheric surface of the objective lens that is a convex lens, (b) Under spherical aberration of the first basic structure in the central region, (c) When performing by adding the under spherical aberration of the second basic structure in the central region, the pitch P2 at the position closest to the boundary of the second basic structure across the boundary between the central region and the intermediate region, and When the pitch P4 closest to the boundary of the four foundation structures satisfies P4-P2> 0, the power of the middle area (fourth foundation structure) in the vicinity of the boundary between the middle area and the middle area is increased to the middle area (second foundation). greater than the power in the vicinity of the boundary structure), further, P3-P1> by satisfying 0, the power of the intermediate region (third basic structure) near the boundary of the central region and the intermediate region is a central region (the first To become larger than the power in the vicinity of the boundary between the foundation structure), than the vicinity of the border of the central area, is greater spherical aberration correction effect near the boundary of the intermediate region ((b), the spherical aberration of the (c) is large) It will be. Therefore, in the intermediate region, the under spherical aberration of (b) and (c) becomes larger, and flare can be produced when the CD is used.

  Regarding this relationship, from the same viewpoint as in claim 2, there is a large difference between the pitch of the first foundation structure on the central region side and the third foundation structure on the intermediate region side across the boundary between the central region and the intermediate region, The following description is based on the case where the annular zones of the first foundation structure and the third foundation structure on both sides of the boundary have an ideal shape and the difference in pitch appears in the difference in the annular zone width.

  FIG. 2 is a diagram schematically showing cross sections in the optical axis direction of the first foundation structure and the third foundation structure. Here, for convenience, the first basic structure and the third basic structure are referred to as (1/1/1) diffraction structures. Also, BN is the boundary between the central region and the intermediate region, the width of the annular zone closest to the boundary of the first foundation structure is | ΔT1 |, and the width of the annular zone closest to the boundary of the third foundation structure is | ΔT3 | To do. Further, the sign of the pitch is negative (−) when the level difference of the foundation structure faces the optical axis side (lower side in FIG. 2), and the level difference of the foundation structure faces the opposite side (upper side in FIG. 2). The sign of the pitch is positive (+).

  The inventor divides the focal length f1 of the objective lens in the first light flux into a predetermined range, and the width of the annular zone ΔT1 closest to the boundary of the first foundation structure on the central region side and the third foundation structure on the intermediate region side. The combination of the magnitude relationship with the width ΔT3 of the annular zone closest to the boundary and the relationship of the direction of the step was examined. FIG. 2A shows an under spherical aberration when a CD is used in cooperation with the relationship of the equation (1) or (2) when the focal length f1 is as short as 1.0 to 1.8 mm. The magnitude relationship between the width ΔT1 of the annular zone closest to the boundary of the first foundation structure on the central region side and the width ΔT3 of the annular zone closest to the boundary of the third foundation structure on the intermediate region side, and the direction of the step Shows a combination with a relationship. More specifically, in the (1/1/1) diffraction structure shown in FIG. 2A, | ΔT1 | <| ΔT3 |, and the sign of the pitch is positive. Therefore, in the (1/1/1) diffractive structure, [the zone width ΔT3 closest to the boundary of the third basic structure in the middle region of the encoding] − [most in the boundary of the first basic structure in the central region of the encoding] The width of the close annular zone ΔT1] = ΔT3−ΔT1> 0. Note that equation (3) is also satisfied.

  FIG. 2B shows the use of a CD in cooperation with the relationship of the formula (1) or (2) when the focal length f1 of the objective lens in the first light flux is relatively short as 1.2 to 2.5 mm. The width of the annular zone ΔT1 closest to the boundary of the first basic structure on the center region side and the width of the annular zone ΔT3 closest to the boundary of the third basic structure on the intermediate region side that can sometimes cause an under spherical aberration The combination of the relationship and the relationship of the direction of the step is shown. More specifically, in the (1/1/1) diffraction structure shown in FIG. 2B, | ΔT1 | <| ΔT3 |, and the sign of the pitch is positive. Therefore, in the (1/1/1) diffractive structure, [the zone width ΔT3 closest to the boundary of the third basic structure in the middle region of the encoding] − [most in the boundary of the first basic structure in the central region of the encoding] The width of the close annular zone ΔT1] = ΔT3−ΔT1> 0. Further, the expression (3) is also satisfied.

  FIG. 2 (c) shows that the CD is used in cooperation with the relationship of the formula (1) or (2) when the focal length f1 of the objective lens in the first light flux is relatively long, 2.0 to 3.5 mm. The width of the annular zone ΔT1 closest to the boundary of the first basic structure on the center region side and the width of the annular zone ΔT3 closest to the boundary of the third basic structure on the intermediate region side that can sometimes cause an under spherical aberration The combination of the relationship and the relationship of the direction of the step is shown. More specifically, in the (1/1/1) diffraction structure shown in FIG. 2 (c), | ΔT1 |> | ΔT3 | and the sign of the pitch is negative. Therefore, in the (1/1/1) diffractive structure, [the zone width ΔT3 closest to the boundary of the third basic structure in the middle region of the encoding] − [most in the boundary of the first basic structure in the central region of the encoding] The width of the close annular zone ΔT1] = (− | ΔT3 |) − (− | ΔT1 |)> 0. Further, the expression (3) is also satisfied. That is, it can be seen that, by satisfying the above relationship regardless of the focal length f1, the under spherical aberration can be generated when the CD is used in cooperation with the relationship of the equation (1) or (2). .

  As described above, the sign of the width ΔT of the annular zone closest to the boundary (similarly, the pitch P) also changes with respect to the focal length. This is a 1/1/1 structure in order to ensure a working distance when using a CD. This is because the positive paraxial power becomes smaller as the focal length becomes shorter.

The objective lens according to a sixth aspect is the invention according to any one of the first to fifth aspects , wherein the pitch P1 of the position closest to the boundary of the first foundation structure is the closest to the boundary of the third foundation structure. The pitch P3 at the closest position, the pitch P2 at the position closest to the boundary of the second foundation structure, and the pitch P4 at the position closest to the boundary of the fourth foundation structure are as follows. The expression (4) is satisfied.
| P3-P1 | <| P4-P2 | (4)

  Since the (1/1/1) diffractive structure usually has a diffractive power to ensure the working distance of the third optical disk, the pitch is generally finer, so the (2/1/1) diffractive structure with a larger pitch It is possible to perform flare out when using the third optical disc without degrading the moldability by mainly using the change in diffraction power.

According to a seventh aspect of the invention, there is provided the objective lens according to any one of the first to sixth aspects, wherein the third light flux that has passed through the second optical path difference providing structure is undercoated on the information recording surface of the third optical disc. The spherical aberration is generated.

  In this way, since the same basic structure is superimposed on the central area and the intermediate area, an under spherical aberration can be generated on the information recording surface of the third optical disk. Spherical aberration is reduced.

  Here, the generation of under spherical aberration on the information recording surface of the third optical disk means that the third light flux that has passed through the second optical path difference providing structure as shown in the longitudinal spherical aberration diagram of FIG. Means that there is an aberration on the underside. (+ Indicates the direction away from the objective lens.) FIG. 3A is a diagram showing over.

The objective lens according to claim 8 is the objective lens according to any one of claims 1 to 7 , wherein the steps closest to the boundary of the first foundation structure and the third foundation structure are each directed in the direction of the optical axis. and are the faces a step closer the direction of the respective optical axis in the most the boundary of the second basic structure and the fourth basic structure, the pitch P1 most position close to the boundary of the first basic structure, the first The pitch P3 at the position closest to the boundary of the three foundation structures, the pitch P2 at the position closest to the boundary of the second foundation structure, and the pitch P4 of the position closest to the boundary of the fourth foundation structure are: Considering the sign, the following expressions (5) and (6) are satisfied.
P1 <P3 <0 (5)
P2 <P4 <0 (6)

  The case where the expressions (5) and (6) are satisfied is, for example, a case as shown in FIGS. 1 (c) and 2 (c).

The objective lens according to claim 9 is characterized in that, in the invention according to claim 8, when the focal length of the objective lens in the first light flux is f1 (mm), the following expression (7) is satisfied. And
2.0 ≦ f1 ≦ 3.5 (7)

The objective lens according to claim 10 is the invention according to any one of claims 1 to 7 , wherein the steps closest to the boundary of the first foundation structure and the third foundation structure are in directions opposite to the optical axis, respectively. the faces, stepped closest to the boundary of the second basic structure and the fourth basic structure are each directed toward the optical axis, the pitch P1 of the position closest to the boundary of the first basic structure, A pitch P3 at a position closest to the boundary of the third foundation structure, a pitch P2 at a position closest to the boundary of the second foundation structure, and a pitch P4 at a position closest to the boundary of the fourth foundation structure are: Considering the sign, the following expressions (8) and (9) are satisfied.
P3>P1> 0 (8)
P2 <P4 <0 (9)

  The case where the expressions (8) and (9) are satisfied is, for example, a case as shown in FIGS. 1 (b) and 2 (b). The first foundation structure and the third foundation structure are overlapped so that the direction of the steps of the first foundation structure and the third foundation structure is different from the direction of the steps of the second foundation structure and the fourth foundation structure, Compared to the case where the second foundation structure and the fourth foundation structure are overlapped so that the steps have the same direction, the height of the step after the overlapping can be suppressed, and accordingly, manufacturing errors, etc. Therefore, it is possible to suppress the loss of light amount due to the above-mentioned, and to suppress the fluctuation of the diffraction efficiency at the time of the wavelength fluctuation.

Objective lens of claim 11, characterized in the invention of claim 10, when the focal length of the objective lens in the first light flux and f1 (mm), that satisfy the following equation (10) And
1.5 ≦ f1 ≦ 2.5 (10)

An objective lens according to a twelfth aspect is the invention according to any one of the first to seventh aspects, wherein the steps closest to the boundary of the first basic structure and the third basic structure are respectively opposite to the optical axis. the faces, the are most step closer to the boundary face the direction of the optical axis and opposite each of the second basic structure and the fourth basic structure, the pitch of the position closest to the boundary of the first basic structure P1, a pitch P3 at a position closest to the boundary of the third foundation structure, a pitch P2 at a position closest to the boundary of the second foundation structure, and a pitch at a position closest to the boundary of the fourth foundation structure P4 is characterized by satisfying the following expressions (11) and (12) in consideration of the sign.
P3>P1> 0 (11)
P4>P2> 0 (12)

  The case where the expressions (11) and (12) are satisfied is, for example, a case as shown in FIGS. 1 (a) and 2 (a).

The objective lens according to claim 11 satisfies the following expression (13) when the focal length of the objective lens in the first light flux is f1 (mm) in the invention according to claim 10. And
1.0 ≦ f1 ≦ 1.8 (13)

An objective lens according to a fourteenth aspect is the invention according to any one of the first to thirteenth aspects, wherein the paraxial power in the third light flux of the first basic structure is PW1, and the third basic structure is the third basic structure. When the paraxial power in the luminous flux is PW2, the paraxial power in the third luminous flux of the third basic structure is PW3, and the paraxial power in the third luminous flux of the fourth basic structure is PW4, the following (14 ) Is satisfied.
1.0 <(PW1 / PW3) / (PW2 / PW4) <1.5 (14)

  Flare out when using the third optical disk is made by making the power of the diffractive structure different between the common area and the intermediate area, but that alone makes the spherical aberration discontinuous within the effective diameter of the first optical disk and the second optical disk. End up. Therefore, it is desirable to flare out by changing the paraxial power so that the spherical aberration becomes continuous.

  Here, when paraxial power is used as a substitute for power, the value of (PW1 / PW3) and the value of (PW2 / PW4) are made different (that is, (PW1 / PW3) / (PW2 / PW4) is set to 1.0. The distance between the center region and the intermediate region becomes discontinuous so that the spherical aberration becomes discontinuous, and flare can be performed when the third optical disk is used. More specifically, when the expression (14) is satisfied, as shown in FIG. 3A, the longitudinal spherical aberration diagram when using the CD is under the outside of the numerical aperture. Thereby, favorable aperture restriction can be performed when the third optical disk is used.

The objective lens described in claim 15 is characterized in that, in the invention described in any one of claims 1 to 14 , the following expression (15) is satisfied.
0.8 ≦ d / f1 ≦ 1.5 (15)
However, d represents the thickness (mm) on the optical axis of the objective lens, and f1 represents the focal length (mm) of the objective lens in the first light flux.

  Along with the slimming down of the optical pickup device, a reduction in the diameter of the objective lens is required. When dealing with a short-wavelength, high-NA optical disk such as BD, the objective lens tends to generate astigmatism and decent coma, but it satisfies the conditional expression (15). As a result, it is possible to suppress the generation of astigmatism and decentration coma. In addition, the smaller the objective lens, the smaller the pitch of the foundation structure and the more difficult the molding becomes. However, if the value of equation (15) is equal to or greater than the lower limit, the pitch of the foundation structure does not become too small, and The ease of manufacturing is increased. Further, when the intermediate region is underflared with CD as in the present invention, the over-spherical aberration generated in the mother aspherical surface of the objective lens that is a convex lens is larger than in the case where the flare is not made, so the curvature of the lens is gentle. Become. This makes it possible to make the lens thinner, so that an objective lens suitable for a slim pickup can be obtained.

The objective lens according to claim 16 is the invention according to any one of claims 1 to 15 , wherein the central region has a first optical path difference providing structure in which only the first basic structure and the second basic structure are overlapped. The intermediate region has only a second optical path difference providing structure in which only the third basic structure and the fourth basic structure are overlapped.

  Thereby, it is possible to provide an objective lens having an optical path difference providing structure that has a simple shape, has a relatively small step and has improved manufacturability. Therefore, fluctuations in diffraction efficiency can be suppressed even when the wavelength is changed or the temperature is changed, and a decrease in light utilization efficiency due to manufacturing errors and shadow effects can be suppressed.

The objective lens according to claim 17 is the invention according to any one of claims 1 to 16 , wherein a magnification of the objective lens in the first light flux is m1, a magnification of the objective lens in the second light flux is m2, When the magnification of the objective lens in the third light flux is m3, the following expressions (16) to (18) are satisfied.
−0.003 ≦ m1 ≦ 0.003 (16)
−0.003 ≦ m2 ≦ 0.003 (17)
−0.003 ≦ m3 ≦ 0.003 (18)
However, the magnification of the objective lens is a magnification that minimizes the spherical aberration in the case where the corresponding optical disk has only one layer, and in the case where there are a plurality of layers, in the protective substrate having a thickness tm. This is the magnification at which the third-order spherical aberration is minimized, and satisfies the following.
tmin ≦ tm ≦ tmax
tmin: thickness of the protective substrate with the thinnest protective substrate tmax: thickness of the protective substrate with the thickest protective substrate

The objective lens according to claim 18 is the invention according to any one of claims 1 to 16 , wherein the magnification of the objective lens in the first light flux is m1, the magnification of the objective lens in the second light flux is m2, When the magnification of the objective lens in the third light flux is m3, the following expressions (19), (20), and (21) are satisfied.
−0.003 ≦ m1 ≦ 0.003 (19)
−0.03 ≦ m2 <−0.003 (20)
−0.03 ≦ m3 <−0.003 (21)
However, the magnification of the objective lens is a magnification that minimizes the spherical aberration in the case where the corresponding optical disk has only one layer, and in the case where there are a plurality of layers, in the protective substrate having a thickness tm. This is the magnification at which the third-order spherical aberration is minimized, and satisfies the following.
tmin ≦ tm ≦ tmax
tmin: thickness of the protective substrate with the thinnest protective substrate tmax: thickness of the protective substrate with the thickest protective substrate

  When the expressions (19), (20), and (21) are satisfied, it is possible to secure a long working distance in the third optical disc, and accordingly, the annular zone width of the objective lens can be widened, which is easy to manufacture and uses light. An objective lens with high efficiency can be obtained.

The objective lens according to claim 19 , wherein a first light source that emits a first light beam having a first wavelength λ1 (nm) and a second light beam that emits a second light beam having a second wavelength λ2 (nm) (λ2> λ1). A first optical disc having a light source and a third light source that emits a third light beam having a third wavelength λ3 (nm) (λ3> λ2), and having a protective substrate having a thickness t1 using the first light beam. Information is recorded and / or reproduced, information is recorded and / or reproduced on a second optical disc having a protective substrate having a thickness t2 (t1 <t2) using the second light flux, and the third light flux is reflected on the third light flux. An objective lens used in an optical pickup device for recording and / or reproducing information on a third optical disk having a protective substrate having a thickness of t3 (t2 <t3).
The objective lens is a single ball,
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 objective lens condenses the first light flux that passes through the central area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the central area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the central region is condensed on the information recording surface of the third optical disc. Condensing so that information can be recorded and / or reproduced,
The objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the intermediate area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the intermediate region is condensed on the information recording surface of the third optical disc. Without collecting light so that information can be recorded and / or reproduced.
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 first optical disc, and the objective lens passes through the peripheral area. The second light flux is not condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc, and the third light flux passing through the peripheral region is used as the information recording surface of the third optical disc. Do not concentrate so that information can be recorded and / or reproduced
The central region has a first optical path difference providing structure in which a first basic structure that is a blazed structure and a second basic structure that is a blazed structure are overlapped,
The intermediate region has a second optical path difference providing structure in which a third basic structure that is a blazed structure and a fourth basic structure that is a blazed structure are overlapped,
The first basic structure makes the A-order diffracted light quantity of the first light flux that has passed through the first basic structure larger than any other order diffracted light quantity, and B of the second light flux that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The second basic structure makes the D-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and the E of the second light beam that has passed through the second basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the F-order diffracted light quantity of the third light flux that has passed through the second basic structure larger than any other order diffracted light quantity,
The third basic structure makes the A-order diffracted light quantity of the first light flux that has passed through the third basic structure larger than any other order of diffracted light quantity, and B of the second light flux that has passed through the third basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the third basic structure larger than any other order diffracted light quantity,
The fourth foundation structure makes the D-order diffracted light quantity of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light quantity, and the E of the second light flux that has passed through the fourth foundation structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the F-order diffracted light quantity of the third light flux that has passed through the fourth basic structure larger than any other order diffracted light quantity,
A, B, C, D, E, and F are respectively
| A | = 1
| B | = 1
| C | = 1
| D | = 2
| E | = 1
| F | = 1
The filling,
Wherein across the boundary between the central region and the intermediate region, and the second based on the width of the closest annular zone to the boundary of the structure Delta] T2, the width of the closest annular zone to the boundary of the fourth basic structure .DELTA.T4,
The width of the annular zone of the first foundation structure, the second foundation structure, the third foundation structure and the fourth foundation structure is positive when the level difference of the foundation structure faces the direction opposite to the optical axis. When the sign is a sign and the step of the foundation structure faces the direction of the optical axis, the following expression is satisfied when the sign is negative.
ΔT4-ΔT2> 0 (2)
The objective lens according to claim 20 is characterized in that, in the invention according to claim 19, a step at a position closest to the boundary of the second basic structure faces the direction of the optical axis.
The objective lens according to claim 21 is the invention according to claim 19 or 20, wherein the objective lens has a step at a position closest to the boundary of the second foundation structure and a position closest to the boundary of the fourth foundation structure. The step is directed in the same direction.

The optical pickup device according to claim 22, characterized by having an objective lens according to any one of claims 1 to 21.

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

  The first optical disc has a protective substrate having a thickness t1 and an information recording surface. The second optical disc has a protective substrate having a thickness t2 (t1 <t2) and an information recording surface. The third optical disc has a protective substrate having a thickness t3 (t2 <t3) and an information recording surface. The first optical disc is preferably a BD, the second optical disc is a DVD, and the third optical disc is preferably a CD, but is not limited thereto. The first optical disc, the second optical disc, or the third optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.

  In this specification, BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00 mm. It is a generic term for a BD series optical disc of about 125 mm, and includes a BD having only a single information recording layer, a BD having two or more information recording layers, and the like. Furthermore, in this specification, DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm. Including DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. In this specification, CD is a general term for CD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.51 and the thickness of the protective substrate is about 1.2 mm. Including CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW, and the like. As for the recording density, the recording density of BD is the highest, followed by the order of DVD and CD.

  In addition, regarding the thicknesses t1, t2, and t3 of the protective substrate, it is preferable to satisfy the following conditional expressions (22), (23), and (24), 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 (22)
0.5mm ≤ t2 ≤ 0.7mm (23)
1.0mm ≤ t3 ≤ 1.3mm (24)

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 (25) and (26).
1.5 · λ1 <λ2 <1.7 · λ1 (25)
1.8 · λ1 <λ3 <2.0 · λ1 (26)

  When BD, DVD, and CD are used as the first optical disc, the second optical disc, and the third optical disc, respectively, the first wavelength λ1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm. The second wavelength λ2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less, and the third wavelength λ3 of the third light source is preferably 415 nm or less. It is 750 nm or more and 880 nm or less, More preferably, it is 760 nm or more and 820 nm or less.

  If the laser light source is a type that performs high-frequency superimposition, there is a risk of occurrence of crosstalk or the like. However, by setting the axial chromatic aberration to 0.9 μm / nm or less, the laser light source that performs such high-frequency superimposition. However, it is preferable because the occurrence of crosstalk and the like can be prevented. If a laser light source (preferably all three light sources with different wavelengths) having a full width at half maximum of the emitted light beam (full width at half maximum of the peak value) of 0.5 nm or more (preferably all three light sources having different wavelengths) is used, crosstalk, etc. Although the problem becomes larger, it is preferable to set the longitudinal chromatic aberration to 0.9 μm / nm or less because it can be used without problems.

  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. In addition to the light source, a light receiving element to be described later may be packaged.

  As the light receiving element, a photodetector such as a photodiode is preferably used. Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking I can do it. The light receiving element may comprise a plurality of photodetectors. The light receiving element may have a main photodetector and a sub photodetector. For example, two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. A light receiving element may be used. 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 an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk. The objective lens may be composed of two or more lenses and / or optical elements, or may be composed of a single lens, but is preferably an objective lens composed of a single convex lens. . The objective lens may be a glass lens or a plastic lens, or an optical path difference providing structure is provided on the glass lens with a photo-curing resin, a UV-curing resin, or a thermosetting resin. A hybrid lens may also be used. When the objective lens has a plurality of lenses, a glass lens and a plastic lens may be mixed and used. When the objective lens includes a plurality of lenses, it may be a combination of a flat optical element having an optical path difference providing structure and an aspherical lens (which may or may not have an optical path difference providing structure). 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, when using an objective lens as a glass lens, it is preferable to use the glass material whose glass transition point Tg is 500 degrees C or less, More preferably, it is 400 degrees C or less. By using a glass material having a glass transition point Tg of 500 ° C. or lower, molding at a relatively low temperature is possible, so that the life of the mold can be extended. Examples of such a glass material having a low glass transition point Tg include K-PG325 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.

  By the way, since the specific gravity of a glass lens is generally larger than that of a resin lens, if the objective lens is a glass lens, the weight increases and a load is imposed on the actuator that drives the objective lens. Therefore, when the objective lens is a glass lens, it is preferable to use a glass material having a small specific gravity. Specifically, the specific gravity is preferably 4.0 or less, more preferably the specific gravity is 3.0 or less.

In addition, one of the important physical property values when molding and manufacturing a glass lens is the linear expansion coefficient a. Even if a material having a Tg of 400 ° C. or lower is selected, the temperature difference from room temperature is still larger than that of a plastic material. When lens molding is performed using a glass material having a large linear expansion coefficient a, cracks are likely to occur when the temperature is lowered. The linear expansion coefficient a of the glass material is preferably 200 (10 ⁻⁷ / K) or less, more preferably 120 (10 ⁻⁷ / K) or less.

When the objective lens is a plastic lens, it is preferable to use an alicyclic hydrocarbon polymer material such as a cyclic olefin resin material. Further, the resin material has a refractive index within a range of 1.54 to 1.60 at a temperature of 25 ° C. with respect to a wavelength of 405 nm, and a wavelength of 405 nm associated with 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, the coupling lens is preferably 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 (1) 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 , R ^a and R ^b are each independently a hydrogen atom, 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 Alternatively, 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 object of the present invention. 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 Xylyl, di-2-ethylhexyl sebacate, tri-2-ethylhexyl trimellitic acid, Santizer 278, Paraplex G40, Drapex 334F, Plastolein 9720, Mesamoll, DNODP-610, HB-40, etc. 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.

  Moreover, it is preferable that the Abbe number of the material which comprises an objective lens is 50 or more.

  The objective lens will be described below.

When φ1 is an effective diameter (mm) of the objective lens when the first optical disk is used, an objective lens satisfying the following formula is preferably used for a so-called slim type optical pickup device. However, it may be used for other optical pickup devices.
1.9 ≦ φ1 ≦ 3.0 (27)

From the viewpoint of ensuring a working distance in the third optical disc such as a CD, it is preferable to satisfy the following expression.
2.0 ≦ φ1 ≦ 3.0 (27) ′

  Furthermore, 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. 4, 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, and a second optical path difference providing structure is provided in the intermediate area. The peripheral region may be a refracting surface, or a third optical path difference providing structure may be provided in the peripheral region. 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.

  It can be said that the central area of the objective lens is a shared area of the first, second, and third optical disks used for recording / reproduction of the first optical disk, the second optical disk, and the third optical disk. That is, the objective lens condenses the first light flux that passes through the central area so that information can be recorded / reproduced on the information recording surface of the first optical disc, and the second light flux that passes through the central area becomes the second light flux. Information is recorded and / or reproduced on the information recording surface of the optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the central area can be recorded / reproduced on the information recording surface of the third optical disc. Condensed to In addition, the first optical path difference providing structure provided in the central region has the thickness t1 of the protective substrate of the first optical disc and the second optical disc 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 the thickness t2 of the protective substrate / spherical aberration generated due to the difference between the wavelengths of the first light flux and the second light flux. Further, the first optical path difference providing structure has a thickness t1 of the protective substrate of the first optical disc and a thickness of the protective substrate of the third optical disc with respect to the first light beam and the third light beam that have passed through the first optical path difference providing structure. It is preferable to correct spherical aberration generated due to the difference between t3 and spherical aberration generated due to the difference between the wavelengths of the first and third light beams.

  The intermediate area of the objective lens is used for recording / reproduction of the first optical disk and the second optical disk, and can be said to be the first and second optical disk shared areas not used for recording / reproduction of the third optical disk. That is, the objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded / reproduced on the information recording surface of the first optical disc, and the second light flux that passes through the intermediate area becomes the second light flux. The light is condensed on the information recording surface of the optical disc so that information can be recorded / reproduced. 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 third optical disk. The third light flux passing through the intermediate region of the objective lens preferably forms a flare on the information recording surface of the third optical disc. As shown in FIG. 5, in the spot formed on the information recording surface of the third optical disk by the third light flux that has passed through the objective lens, the spot having a high light density in the order from the optical axis side (or the center of the spot) to the outside. It is preferable to have a central 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. That is, 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 third optical disc.

  The peripheral area of the objective lens is used for recording / reproduction of the first optical disk, and can be said to be an area dedicated to the first optical disk that is not used for recording / reproduction of the second optical disk and the third optical disk. 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 first optical disc. 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 second optical disc, and the third light flux that passes through the peripheral area does not converge. The light is not condensed so that information can be recorded / reproduced on the information recording surface. 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 surfaces of the second optical disc and the third optical disc. 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 surfaces of the second optical disc and the third optical disc.

  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. When the peripheral region has the third optical path difference providing structure, 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-lens aspherical convex lens, even if it is an optical path difference providing structure that provides the same optical path difference, generally the distance from the optical axis tends to increase. In addition, when a plurality of basic structures are stacked, the functions can be individually provided by the number of overlapping.

  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 aspherical convex lens, even if it is a diffractive structure that generates diffracted light of the same diffraction order, generally, the distance from the optical axis tends to increase.

  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. 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 shapes including the optical axis are roughly classified into a blazed structure and a staircase structure.

  As shown in FIGS. 6A and 6B, 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. In the example of FIG. 6, it is assumed that the upper side is the light source side and the lower side is the optical disc side, and the optical path difference providing structure is formed on a plane as a mother aspherical surface. In the blazed structure, the length of one blaze unit in the direction perpendicular to the optical axis is referred to as a pitch width P (see FIGS. 6A and 6B). 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. 6A).

  In addition, as shown in FIGS. 6 (c) and 6 (d), the staircase structure has a cross-sectional shape including an optical axis of an optical element having an optical path difference providing structure (referred to as a staircase unit). ).

  For example, the optical path difference providing structure illustrated in FIG. 6C is referred to as a five-level step structure, and the optical path difference providing structure illustrated in FIG. 6D is referred to as a two-level step structure (also referred to as a binary structure). .

  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. 6 (a), the same serrated shape may be repeated, and as shown in FIG. 6 (b), the serrated 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 and the second optical path difference providing structure may be provided on different optical surfaces of the objective lens, respectively, but are preferably provided on the same optical surface. Furthermore, also when providing a 3rd optical path difference providing structure, it is preferable to provide in the same optical surface as a 1st optical path difference providing structure and a 2nd optical path difference providing structure. Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing. In addition, 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 surface of the objective lens on the optical disk side. In other words, 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.

  Next, the 1st optical path difference providing structure provided in a center area | region is demonstrated. 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.

    The first basic structure is preferably a blaze-type optical path difference providing structure. Further, the first basic structure makes the A-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order diffracted light quantity, and the B-order of the second light flux that has passed through the first basic structure. Is made larger than any other order of diffracted light, and the C-th order diffracted light of the third light beam that has passed through the first basic structure is made larger than any other order of diffracted light. However, | A | = 1, | B | = 1, and | C | = 1. As a result, the step amount of the first basic structure does not become excessively large, which facilitates manufacturing, suppresses light loss due to manufacturing errors, and also reduces diffraction efficiency fluctuations during wavelength fluctuations. preferable.

  In addition, the first basic structure may have a level difference in the direction of the optical axis or in the direction opposite to the optical axis. Moreover, the direction of the level | step difference of a 1st foundation structure may be changed in the middle of the center area | region like FIG.14 (b). FIG. 14B shows an example in which the step is opposite to the optical axis at a position close to the optical axis, but the direction of the step is changed halfway, and the step is directed toward the optical axis at a position far from the optical axis. It is. Further, the direction of the step of the first foundation structure may or may not coincide with the direction of the step of the third foundation structure. “The step is directed in the direction of the optical axis” means a state as shown in FIG. 7A, and “the step is directed in the direction opposite to the optical axis” is shown in FIG. 7B. Say like the state.

  However, even in a thick objective lens with a large on-axis thickness, which is used for compatibility with three types of optical disks of BD / DVD / CD, by directing the step of the first basic structure in the direction opposite to the optical axis, It is possible to ensure a sufficient working distance when using a CD.

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 is not 0 when the optical path difference function of the first basic structure is expressed by the following equation ( ₂ ).

    The second basic structure is also preferably a blaze-type optical path difference providing structure. The second basic structure makes the D-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order diffracted light amount, and the E-order diffraction of the second light beam that has passed through the second basic structure. The amount of light is made larger than the diffracted light amount of any other order, and the F-order diffracted light amount of the third light flux that has passed through the second basic structure is made larger than the diffracted light amount of any other order. However, | D | = 2, | E | = 1, and | F | = 1. As a result, the step amount of the second basic structure does not become excessively large, which facilitates manufacturing, can suppress light loss due to manufacturing errors, and can also reduce diffraction efficiency fluctuations during wavelength fluctuations. preferable.

  Further, the step of the second basic structure may face the direction of the optical axis, or may face the direction opposite to the optical axis. In addition, as shown in FIGS. 14A and 14B, the direction of the steps of the second foundation structure may be switched in the middle of the central region. Further, the direction of the step of the second foundation structure may or may not coincide with the direction of the step of the fourth foundation structure.

  Compared to the case where the first foundation structure and the second foundation structure are overlapped so that the direction of the steps is the same by overlapping the first foundation structure and the second foundation structure so that the direction of the steps is different. As a result, it is possible to suppress the height of the height difference after superimposing, and accordingly, it is possible to suppress the loss of light amount due to manufacturing errors, etc., and to suppress the fluctuation of diffraction efficiency at the time of wavelength fluctuation. Is possible.

  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 also possible to provide a balanced objective lens. For example, it is possible to provide an objective lens having 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 possible to provide an objective lens having 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. By changing the aberration in the direction of under (undercorrection) when the wavelength changes to the long wavelength side, it becomes possible to suppress the aberration that occurs when the temperature of the optical pickup device rises. When it is made of plastic, it is possible to provide an objective lens that can maintain stable performance even when the temperature changes.

  When the objective lens is made of plastic, in order to maintain stable performance even when the temperature changes, both the third-order spherical aberration and the fifth-order spherical aberration that occur in the objective lens when the wavelength becomes longer are both under. (Insufficient correction) is preferable. If the third-order spherical aberration is under, it is possible to correct the spherical aberration caused by the refractive index change of the material at the time of temperature change by the diffraction effect due to the wavelength change, and the third-order spherical aberration and the fifth-order spherical aberration have the same sign. Then, it becomes possible to correct the spherical aberration (third order and fifth order) at the time of wavelength change by changing the magnification.

  The first optical path providing structure of the present invention can make the height of the step 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.

  Moreover, it is preferable that the minimum zone width | variety of a 1st optical path difference providing structure is 15 micrometers or less. From this viewpoint, it is preferable that the ratio bw / f1 between the minimum annular zone width bw of the first optical path difference providing structure and the focal length f1 at the first wavelength λ1 is 0.004 or less. More preferably, it is 10 μm or less. Moreover, it is preferable that the average ring zone width | variety of a 1st optical path difference providing structure will be 30 micrometers 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 annular zone width is a value obtained by adding all the annular zone widths 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.

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 (28). 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 recording / reproduction of the third optical disc, and the second best focus position is the largest amount of unnecessary light that is not used for recording / reproduction of the third optical disc. This is the best focus position for many luminous fluxes.
0.05 ≦ L / f13 ≦ 0.35 (28)
However, f13 [mm] indicates the focal length of the third light flux that passes through the first optical path difference providing structure and forms the first best focus, and L [mm] indicates the first best focus and the second best focus. Refers to the distance between.

More preferably, the following conditional expression (28) ′ is satisfied.
0.25 ≦ L / f13 ≦ 0.35 (28) ′

  Several preferable examples of the first optical path difference providing structure described above are shown in FIGS. 8A, 8B, and 8C. Although FIG. 8 shows the first optical path difference providing structure ODS1 as a flat plate for convenience, it may be 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. 8A, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS faces the direction opposite to the optical axis OA. Further, the pitches of the first foundation structure BS1 and the second foundation structure BS2 are matched, and it can be seen that the positions of all the steps of the second foundation structure and the positions of the steps of the first foundation structure match. FIG. 8A also applies when the structure of FIG. 1B is overlapped with the structure of FIG. 2B. Next, in FIG.8 (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 BS has also faced the direction of optical axis OA. Further, the pitches of the first foundation structure BS1 and the second foundation structure BS2 are matched, and it can be seen that the positions of all the steps of the second foundation structure and the positions of the steps of the first foundation structure match. FIG. 8B also applies when the structure of FIG. 1C is overlapped with the structure of FIG. Next, in FIG.8 (c), the level | step difference of 2nd foundation structure BS2 has faced the direction opposite to optical axis OA, and the level | step difference of 2nd foundation structure BS has also faced the direction opposite to optical axis OA. . Further, the pitches of the first foundation structure BS1 and the second foundation structure BS2 are matched, and it can be seen that the positions of all the steps of the second foundation structure and the positions of the steps of the first foundation structure match. This FIG. 8C also applies when the structure of FIG. 1A and the structure of FIG.

  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 only two basic structures of the third basic structure and the fourth basic structure are overlapped.

    The third basic structure makes the A-order diffracted light amount of the first light beam that has passed through the third basic structure larger than any other order diffracted light amount, and the B-order diffraction of the second light beam that has passed through the third basic structure. The light quantity is made larger than any other order of diffracted light quantity, and the C-order diffracted light quantity of the third light flux that has passed through the third basic structure is made larger than any other order of diffracted light quantity. However, | A | = 1, | B | = 1, and | C | = 1. Further, the fourth basic structure makes the C-order diffracted light amount of the first light beam that has passed through the fourth basic structure larger than any other order of diffracted light amount, and the D-order of the second light beam that has passed through the fourth basic structure. Is made larger than any other order of diffracted light, and the F-order diffracted light of the third light beam that has passed through the fourth basic structure is made larger than any other order of diffracted light. However, | D | = 2, | E | = 1, and | F | = 1.

  Further, the steps of the third foundation structure and the fourth foundation structure may face the direction of the optical axis, or may face the direction opposite to the optical axis. Further, as shown in FIGS. 14A and 14B, the direction of the steps of the third foundation structure and / or the fourth foundation structure may be changed in the middle of the central region.

  If a structure with a large step, such as a binary structure of 0/0 / ± 1 is superimposed on the second optical path difference providing structure as the third basic structure for flare out, the diffraction efficiency is reduced due to manufacturing errors. In addition, the problem of a decrease in diffraction efficiency due to the shadow effect or the like becomes serious. Therefore, in the second optical path difference providing structure, a structure in which only the structures other than the third basic structure and the fourth basic structure are overlapped is preferable because the light use efficiency can be increased. In particular, when the effective diameter of the first light flux is as small as 1.9 mm to 3.0 mm, the zone width is already sufficiently narrow in the second optical path difference providing structure composed of the third basic structure and the fourth basic structure, Since the number of ring zones is sufficiently large, if another foundation structure is stacked in addition to the third foundation structure and the fourth foundation structure, the ring zone width will be further reduced and the number of ring zones will be increased. For this reason, problems such as a decrease in diffraction efficiency due to manufacturing errors and a decrease in diffraction efficiency due to the effect of shadows in the zonal zone become serious.

  When the third optical path difference providing structure is provided in the peripheral region, an arbitrary optical path difference providing structure can be provided. The third optical path difference providing structure preferably has a fifth basic structure. In the fifth basic structure, the P-order diffracted light amount of the first light beam that has passed through the fifth basic structure is made larger than any other order diffracted light amount, and the Q-order diffraction of the second light beam that has passed through the fifth basic structure. The light quantity is made larger than any other order diffracted light quantity, and the R-order diffracted light quantity of the third light flux that has passed through the fifth basic structure is made larger than any other order diffracted light quantity. Note that P is preferably 5 or less in order to suppress fluctuations in diffraction efficiency during wavelength fluctuations. More preferably, P is 2 or less.

  The numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the first optical disc is NA1, and the numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the second optical disc. Is NA2 (NA1> NA2), and the image-side numerical aperture of the objective lens necessary for reproducing / recording information on the third optical disk is NA3 (NA2> NA3). NA1 is preferably 0.75 or more and 0.9 or less, and more 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 flux that has passed through the objective lens is condensed on the information recording surface of the third optical disc, it is preferable that the spherical aberration has at least one discontinuous portion. In that case, the discontinuous portion has a range of 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3 or more and 1.15 · NA 3 or less) when the third light flux is used. It is preferable that it exists in.

The objective lens preferably satisfies the following conditional expression (15).
0.8 ≦ d / f1 ≦ 1.5 (15)
However, d represents the thickness (mm) on the optical axis of the objective lens, and f1 represents the focal length of the objective lens in the first light flux.

  When dealing with a short-wavelength, high-NA optical disk such as BD, the objective lens tends to generate astigmatism and decent coma, but it satisfies the conditional expression (15). As a result, it is possible to suppress the generation of astigmatism and decentration coma.

  Also, satisfying conditional expression (15) results in a thick objective lens with a thick on-axis objective lens, so that the working distance during CD recording / playback tends to be short. By providing the objective lens with the first optical path difference providing structure of the invention, a working distance in CD recording / reproduction can be sufficiently ensured, so that the effect of the present invention becomes more remarkable.

  Furthermore, in terms of ensuring a sufficient working distance in the third optical disc, the number of ring zones RN formed on the objective lens is preferably 150 or more and 250 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 (16).
−0.003 ≦ m1 ≦ 0.003 (16)

  When the optical disk has a plurality of layers, the magnification of the objective lens is different in each layer (the incident angle of light to the objective lens is different), so that the maximum value of | m1 | It is preferable to satisfy (16) in the thickness of the protective substrate between the layers. With this configuration, coma aberration during tracking can be reduced in all layers.

Further, 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 (17). Is preferred.
−0.003 ≦ m2 ≦ 0.003 (17)

  When the optical disk has a plurality of layers, the magnification of the objective lens is different in each layer (the incident angle of light to the objective lens is different), so that the maximum value of | m2 | It is preferable to satisfy (17) in the thickness of the protective substrate between the layers. With this configuration, coma aberration during tracking can be reduced in all layers.

On the other hand, when the second light flux is incident on the objective lens as diverging light, it is preferable that the imaging magnification m2 of the objective lens when the second light flux is incident on the objective lens satisfy the following expression (20).
−0.02 ≦ m2 <−0.003 (20)

  Since compatibility is achieved by both diffraction and change in magnification, the wavelength dependence of diffraction can be reduced, and a diffractive structure with a wide zone width can be obtained.

Further, 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 (18). Is preferred.
−0.003 ≦ <m3 ≦ 0.003 (18)

  When the optical disk has a plurality of layers, the magnification of the objective lens is different in each layer (the incident angle of light to the objective lens is different), so that the maximum value of | m3 | It is preferable to satisfy (18) in the thickness of the protective substrate between the layers. With this configuration, coma aberration during tracking can be reduced in all layers.

On the other hand, when the third light beam is incident on the objective lens as diverging light, the imaging magnification m3 of the objective lens when the third light beam is incident on the objective lens preferably satisfies the following expression (21) ′. .
−0.02 ≦ m3 <−0.003 (21) ′

  Since compatibility is achieved by both diffraction and change in magnification, the wavelength dependency of diffraction is reduced, and a diffractive structure having a wide ring width can be obtained. Furthermore, although the working distance (WD) becomes shorter as the optical disc becomes thicker, the WD can be extended by (21) ', and an objective lens suitable for a slim pickup with a short focal length can be obtained.

  In addition, the working distance (WD) 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 0.19 mm or more and 0.7 mm or less. Next, the WD of the objective optical element when using the second optical disc is preferably 0.2 mm or more and 0.7 mm or less. Furthermore, the WD of the objective optical element when using the first optical disk is preferably 0.25 mm or more and 0.7 mm or less.

  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, in a thick objective lens having a thick on-axis thickness that is used for compatibility with three types of optical disks of BD / DVD / CD, the effective diameter can be reduced while ensuring a working distance when using a CD. Can be achieved. By making the effective diameter small, the focal length can be shortened and an objective lens suitable for a slim type optical pickup apparatus can be provided. Also, by reducing the level difference of the optical path difference providing structure, it becomes possible to suppress the light amount loss due to the shadow effect and the manufacturing error, and it can be applied to any of the three types of optical discs of BD / DVD / CD. It is also possible to provide an objective lens with a balanced light utilization efficiency that can maintain a high light utilization efficiency.

It is the figure which showed typically the optical axis direction cross section of the 2nd foundation structure and the 4th foundation structure, (a) is a (2/1/1) diffraction structure, | ΔT2 | <| ΔT4 |, sign of pitch (B) is a (2/1/1) diffraction structure, | ΔT2 |> | ΔT4 |, and (c) is a (2/1/1) diffraction structure when the sign of the pitch is negative. , | ΔT2 |> | ΔT4 |, the case where the sign of the pitch is negative. It is the figure which showed typically the optical axis direction cross section of the 1st foundation structure and the 3rd foundation structure, (a) is a (1/1/1) diffraction structure, | ΔT1 | <| ΔT3 |, sign of pitch (B) is a (1/1/1) diffraction structure, | ΔT1 | <| ΔT3 |, and (c) is a (1/1/1) diffraction structure when the sign of the pitch is positive. , | ΔT1 |> | ΔT3 |, the case where the sign of the pitch is negative. (A) shows an example of over spherical aberration, and (b) shows an example of under spherical aberration. It is the figure which looked at the single objective lens OL concerning this embodiment in the optical axis direction. 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 axial direction sectional drawing which shows the example of an optical path difference providing structure, Comprising: (a), (b) shows the example of a blazed type structure, (c), (d) shows the 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. It is a conceptual diagram of a 1st optical path difference providing structure, Comprising: (a), (b), (c) is a figure which shows the preferable example of a 1st optical path difference providing structure. 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. FIG. 6 is a longitudinal spherical aberration diagram when the CD of Example 1 is used. FIG. 6 is a longitudinal spherical aberration diagram when the CD of Example 2 is used. FIG. 6 is a longitudinal spherical aberration diagram when the CD of Example 3 is used. FIG. 6 is a longitudinal spherical aberration diagram when the CD of Example 4 is used. (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. FIG. 10 is a longitudinal spherical aberration diagram when the CD of Example 5 is used. It is a figure which shows the pitch of each foundation structure in Example 1. FIG. It is a figure which shows the pitch of each foundation structure in Example 2. FIG. It is a figure which shows the pitch of each foundation structure in Example 4. FIG.

  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. 2, 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 -1st order diffracted light amount of the first light beam is made larger than any other order diffracted light amount, and the -1st 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 diffracted light amount of the third light beam that has passed through the first basic structure is made larger than any other order of diffracted light amount, and the second basic structure has the first light beam that has passed through the second basic structure. The second-order diffracted light amount is made larger than any other order diffracted light amount, the first-order diffracted light amount of the second light beam that has passed through the second basic structure is made larger than any other order diffracted light amount, and the second base The amount of the first-order diffracted light of the third light beam that has passed through the structure is any other order Larger than the diffracted 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 -1st order diffracted light amount of the first light beam is made larger than any other order diffracted light amount, and the -1st order diffracted light amount of the second light beam that has passed through the third basic structure is made larger than any other order diffracted light amount. 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 has the first light beam that has passed through the fourth basic structure. The second-order diffracted light amount is made larger than any other order diffracted light amount, the first-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, and the fourth base The amount of the first-order diffracted light of the third light beam that has passed through the structure is any other order Larger than the diffracted light.

Pitch P1 closest to the boundary of the first foundation structure, pitch P3 closest to the boundary of the third foundation structure, and pitch P2 closest to the boundary of the second foundation structure across the boundary between the central area and the intermediate area of the objective lens , And the pitch P4 closest to the boundary of the fourth foundation structure satisfies the following expressions (1) and (3).
P3-P1> 0 (3)
P4-P2> 0 (1)

  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) 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 / 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 passes through the objective lens OL again, is converted from circularly polarized light to linearly polarized light by the λ / 4 wave plate QWP, and is converged 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.
Further, the pitch P (h) = λB / (Σ (2i × C _2i × h ^2i-1 )).

Example 1
Table 1 shows lens data of Example 1. In this embodiment, the steps of the first foundation structure and the third foundation structure are directed in the direction opposite to the optical axis, and the steps of the second foundation structure and the fourth foundation structure are oriented in the direction of the optical axis. is there. The focal length of BD is 2.2 mm, which is a relatively short value here. FIG. 16 shows the pitch of each foundation structure. In FIG. 16, the vertical axis indicates the pitch P (mm), and the horizontal axis indicates the height from the optical axis, with the boundary BN as the boundary, the left side indicates the central region, and the right side indicates the intermediate region. P1, P2, P3, and P4 are pitch values of the first foundation structure, the second foundation structure, the third foundation structure, and the fourth foundation structure that are closest to the boundary BN. Referring to FIG. 16, P1 and P3 are positive values, the absolute value of P3 is larger than P1, P2 and P4 are negative values, and the absolute value of P2 is larger than P4. I understand. Therefore, as shown in Table 6 described later, it can be seen that P4-P2> 0 and P3-P1> 0. FIG. 10 is a longitudinal spherical aberration diagram when the CD is used in Example 1. As shown in FIG. 10, spherical aberration is generated on the under side on the information recording surface of the CD outside the intermediate area, and it can be seen that appropriate flare can be obtained.

(Example 2)
Table 2 shows lens data of Example 2. In this embodiment, the steps of the first foundation structure and the third foundation structure are directed in the direction opposite to the optical axis, and the steps of the second foundation structure and the fourth foundation structure are oriented in the direction of the optical axis. is there. The focal length of BD is a relatively short value of 1.77 mm. FIG. 17 shows the pitch of each foundation structure. Referring to FIG. 17, P1 and P3 are positive values, the absolute value of P3 is larger than P1, P2 and P4 are negative values, and the absolute value of P2 is larger than P4. I understand. Therefore, as shown in Table 6 described later, it can be seen that P4-P2> 0 and P3-P1> 0. FIG. 11 is a longitudinal spherical aberration diagram when the CD is used in Example 2. As shown in FIG. 11, spherical aberration is generated on the under side on the information recording surface of the CD outside the intermediate region, and it can be seen that appropriate flare can be obtained.

(Example 3)
Table 3 shows lens data of Example 3. In this embodiment, the steps of the first foundation structure and the third foundation structure are directed in the direction opposite to the optical axis, and the steps of the second foundation structure and the fourth foundation structure are oriented in the direction of the optical axis. is there. The focal length of BD is a relatively short value of 1.77 mm. As shown in Table 6 to be described later, P4-P2> 0 and P3-P1> 0. FIG. 12 is a longitudinal spherical aberration diagram when the CD is used in Example 3. As shown in FIG. 12, spherical aberration is generated on the under side on the information recording surface of the CD outside the intermediate region, and it can be seen that appropriate flare can be obtained.

Example 4
Table 4 shows lens data of Example 4. In this embodiment, the steps of the first foundation structure and the third foundation structure are directed in the direction opposite to the optical axis, and the steps of the second foundation structure and the fourth foundation structure are also directed in the direction opposite to the optical axis. This is an example. The focal length of BD is 1.41 mm, which is a very short value. FIG. 18 shows the pitch of each foundation structure. Referring to FIG. 18, P1 and P3 are positive values, the absolute value of P3 is larger than P1, P2 and P4 are positive values, and the absolute value of P4 is larger than P2. I understand. Therefore, as shown in Table 6 described later, it can be seen that P4-P2> 0 and P3-P1> 0. FIG. 13 is a longitudinal spherical aberration diagram of Example 4 when using a CD. As shown in FIG. 13, spherical aberration is generated on the under side on the information recording surface of the CD outside the intermediate region, and it can be seen that appropriate flare can be obtained.

(Example 5)
Table 5 shows lens data of Example 5. In this example, the focal length of the BD is 1.41 mm, which is a very short value. However, the steps of the first basic structure and the third basic structure are directed in the opposite direction to the optical axis. This is an exceptional example in which the steps of the two foundation structures and the fourth foundation structure are oriented in the direction of the optical axis. As shown in Table 6 to be described later, P4-P2> 0 and P3-P1> 0. FIG. 15 is a longitudinal spherical aberration diagram when the CD is used in Example 5. As shown in FIG. 15, spherical aberration is generated on the under side on the information recording surface of the CD outside the intermediate region, and it can be seen that appropriate flare can be obtained.

  Table 6 summarizes the values of the conditional expressions described in the claims. In any of the examples, it can be seen that the aberration change at the time of temperature change in the BD is small.

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

AC1 Biaxial actuator 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 OL Objective lens OT Peripheral region 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 (22)

A first light source that emits a first light flux having a first wavelength λ1 (nm), a second light source that emits a second light flux having a second wavelength λ2 (nm) (λ2> λ1), and a third wavelength λ3 (nm) A third light source that emits a third light beam of (λ3> λ2), and recording and / or reproducing information of a first optical disk having a protective substrate with a thickness of t1 using the first light beam, Information is recorded and / or reproduced on the second optical disc having the protective substrate having a thickness t2 (t1 <t2) using the second light flux, and the thickness t3 (t2 <t3) using the third light flux. An objective lens used in an optical pickup device for recording and / or reproducing information on a third optical disk having a protective substrate of
The objective lens is a single ball,
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 objective lens condenses the first light flux that passes through the central area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the central area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the central region is condensed on the information recording surface of the third optical disc. Condensing so that information can be recorded and / or reproduced,
The objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the intermediate area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the intermediate region is condensed on the information recording surface of the third optical disc. Without collecting light so that information can be recorded and / or reproduced.
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 first optical disc, and the objective lens passes through the peripheral area. The second light flux is not condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc, and the third light flux passing through the peripheral region is used as the information recording surface of the third optical disc. Do not concentrate so that information can be recorded and / or reproduced
The central region has a first optical path difference providing structure in which a first basic structure that is a blazed structure and a second basic structure that is a blazed structure are overlapped,
The intermediate region has a second optical path difference providing structure in which a third basic structure that is a blazed structure and a fourth basic structure that is a blazed structure are overlapped,
The first basic structure makes the A-order diffracted light quantity of the first light flux that has passed through the first basic structure larger than any other order diffracted light quantity, and B of the second light flux that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The second basic structure makes the D-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and the E of the second light beam that has passed through the second basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the F-order diffracted light quantity of the third light flux that has passed through the second basic structure larger than any other order diffracted light quantity,
The third basic structure makes the A-order diffracted light quantity of the first light flux that has passed through the third basic structure larger than any other order of diffracted light quantity, and B of the second light flux that has passed through the third basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the third basic structure larger than any other order diffracted light quantity,
The fourth foundation structure makes the D-order diffracted light quantity of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light quantity, and the E of the second light flux that has passed through the fourth foundation structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the F-order diffracted light quantity of the third light flux that has passed through the fourth basic structure larger than any other order diffracted light quantity,
A, B, C, D, E, and F are respectively
| A | = 1
| B | = 1
| C | = 1
| D | = 2
| E | = 1
| F | = 1
The filling,
The pitch of the first foundation structure, the second foundation structure, the third foundation structure, and the fourth foundation structure is a positive sign when the step of the foundation structure faces the direction opposite to the optical axis, If the step of the foundation structure is facing the direction of the optical axis,
The pitch P2 at the position closest to the boundary of the second foundation structure and the pitch P4 at the position closest to the boundary of the fourth foundation structure across the boundary between the central area and the intermediate area are: An objective lens characterized by satisfying the following expression (1) in consideration of the sign:
P4-P2> 0 (1)
However,
When the optical path difference function defining the basic structure is represented by Φ (h) = Σ (C _2i h ²ⁱ × λ × m / λB),
Pitch P (h) = λB / (Σ (2i × C _2i × h ^2i-1 )).
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 width of the closest annular zone to the boundary of the second basic structure Delta] T2, the width of the closest annular zone to the boundary of the fourth basic structure and .DELTA.T4,
The width of the annular zone of the first foundation structure, the second foundation structure, the third foundation structure and the fourth foundation structure is positive when the level difference of the foundation structure faces the direction opposite to the optical axis. 2. The objective lens according to claim 1, wherein the following expression is satisfied when a sign is used and when the step of the basic structure faces the direction of the optical axis, the sign is a negative sign.
ΔT4-ΔT2> 0 (2) 3. The objective lens according to claim 1, wherein a step at a position closest to the boundary of the second foundation structure faces an optical axis. 4. 4. The step according to claim 1, wherein a step at a position closest to the boundary of the second foundation structure and a step at a position closest to the boundary of the fourth foundation structure are directed in the same direction. The objective lens according to claim 1. The pitch P1 at the position closest to the boundary of the first foundation structure and the pitch P3 at the position closest to the boundary of the third foundation structure satisfy the following expression (3) in consideration of the sign. The objective lens according to any one of claims 1 to 4, wherein the objective lens is provided.
P3-P1> 0 (3) A pitch P1 at a position closest to the boundary of the first foundation structure, a pitch P3 at a position closest to the boundary of the third foundation structure, a pitch P2 at a position closest to the boundary of the second foundation structure, and pitch P4 position closest to the boundary of the fourth basic structure, in consideration of the sign, according to any one of claims 1 to 5, characterized by satisfying the following formula (4) Objective lens.
| P3-P1 | <| P4-P2 | (4) The second the third light flux which has passed through the optical path difference providing structure according to any one of claims 1 to 6, characterized in that to generate the spherical aberration of the under the information recording surface of the third optical disc Objective lens. The steps closest to the boundary of the first foundation structure and the third foundation structure are respectively directed toward the optical axis, and the steps closest to the boundary of the second foundation structure and the fourth foundation structure are respectively light. faces the direction of the axis, the pitch P1 of the position closest to the boundary of the first basic structure, the pitch P3 of the position closest to the boundary of the third basic structure, the most the boundary of the second basic structure The pitch P2 at the closest position and the pitch P4 at the position closest to the boundary of the fourth foundation structure satisfy the following expressions (5) and (6) in consideration of the sign thereof. Item 8. The objective lens according to any one of Items 1 to 7 .
P1 <P3 <0 (5)
P2 <P4 <0 (6) The objective lens according to claim 8 , wherein the following expression (7) is satisfied when a focal length of the objective lens in the first light flux is f1 (mm).
2.0 ≦ f1 ≦ 3.5 (7) The steps closest to the boundary of the first foundation structure and the third foundation structure are directed in opposite directions to the optical axis, respectively, and the step closest to the boundary of the second foundation structure and the fourth foundation structure is faces the direction of the optical axis, respectively, the pitch P1 most position close to the boundary of the first basic structure, the third position closest to the boundary of the substructure pitch P3, most the of the second basic structure The pitch P2 at the position close to the boundary and the pitch P4 at the position closest to the boundary of the fourth foundation structure satisfy the following equations (8) and (9) in consideration of the sign. The objective lens according to any one of claims 1 to 7 .
P3>P1> 0 (8)
P2 <P4 <0 (9) The first is a focal length of the objective lens in the light beam was f1 (mm), the objective lens according to claim 10, characterized by satisfying the following equation (10).
1.5 ≦ f1 ≦ 2.5 (10) The steps closest to the boundary of the first foundation structure and the third foundation structure are directed in opposite directions to the optical axis, respectively, and the step closest to the boundary of the second foundation structure and the fourth foundation structure is faces the direction of the optical axis opposite each pitch P1 position closest to the boundary of the first basic structure, the pitch P3 of the position closest to the boundary of the third basic structure, the second basic structure The pitch P2 at the position closest to the boundary and the pitch P4 at the position closest to the boundary of the fourth foundation structure satisfy the following expressions (11) and (12) in consideration of the sign. The objective lens according to any one of claims 1 to 7 , wherein
P3>P1> 0 (11)
P4>P2> 0 (12) The objective lens according to claim 12 , wherein the following expression (13) is satisfied when a focal length of the objective lens in the first light flux is f1 (mm).
1.0 ≦ f1 ≦ 1.8 (13) The paraxial power of the third light flux of the first basic structure is PW1, the paraxial power of the third light flux of the second basic structure is PW2, and the paraxial power of the third light flux of the third basic structure is PW3. The objective lens according to any one of claims 1 to 13 , wherein the following expression (14) is satisfied when a paraxial power in the third light flux of the fourth basic structure is PW4. .
1.0 <(PW1 / PW3) / (PW2 / PW4) <1.5 (14) (15) below the objective lens according to any one of claims 1 to 14, characterized in that satisfies the equation.
0.8 ≦ d / f1 ≦ 1.5 (15)
However, d represents the thickness (mm) on the optical axis of the objective lens, and f1 represents the focal length (mm) of the objective lens in the first light flux. The central region has only the first optical path difference providing structure in which only the first basic structure and the second basic structure are overlapped, and the intermediate region overlaps only the third basic structure and the fourth basic structure. objective lens according to any one of claims 1 to 15, characterized in that it has only the second optical path difference providing structure. When the magnification of the objective lens in the first light flux is m1, the magnification of the objective lens in the second light flux is m2, and the magnification of the objective lens in the third light flux is m3, the following (16) to (18 ) objective lens according to any one of claims 1 to 16, characterized in that satisfies the equation.
−0.003 ≦ m1 ≦ 0.003 (16)
−0.003 ≦ m2 ≦ 0.003 (17)
−0.003 ≦ m3 ≦ 0.003 (18)
However, the magnification of the objective lens is a magnification that minimizes the spherical aberration in the case where the corresponding optical disk has only one layer, and in the case where there are a plurality of layers, in the protective substrate having a thickness tm. This is the magnification at which the third-order spherical aberration is minimized, and satisfies the following.
tmin ≦ tm ≦ tmax
tmin: thickness of the protective substrate with the thinnest protective substrate tmax: thickness of the protective substrate with the thickest protective substrate When the magnification of the objective lens in the first light flux is m1, the magnification of the objective lens in the second light flux is m2, and the magnification of the objective lens in the third light flux is m3, the following (19) (20) (21) the objective lens described in any one of claims 1 to 16, characterized in that satisfies the equation.
−0.003 ≦ m1 ≦ 0.003 (19)
−0.03 ≦ m2 <−0.003 (20)
−0.03 ≦ m3 <−0.003 (21)
However, the magnification of the objective lens is a magnification that minimizes the spherical aberration in the case where the corresponding optical disk has only one layer, and in the case where there are a plurality of layers, in the protective substrate having a thickness tm. This is the magnification at which the third-order spherical aberration is minimized, and satisfies the following.
tmin ≦ tm ≦ tmax
tmin: protective substrate thickness of the thinnest protective substrate tmax: protective substrate thickness of the thickest protective substrate layer A first light source that emits a first light flux having a first wavelength λ1 (nm), a second light source that emits a second light flux having a second wavelength λ2 (nm) (λ2> λ1), and a third wavelength λ3 (nm) A third light source that emits a third light beam of (λ3> λ2), and recording and / or reproducing information of a first optical disk having a protective substrate with a thickness of t1 using the first light beam, Information is recorded and / or reproduced on the second optical disc having the protective substrate having a thickness t2 (t1 <t2) using the second light flux, and the thickness t3 (t2 <t3) using the third light flux. An objective lens used in an optical pickup device for recording and / or reproducing information on a third optical disk having a protective substrate of
The objective lens is a single ball,
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 objective lens condenses the first light flux that passes through the central area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the central area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the central region is condensed on the information recording surface of the third optical disc. Condensing so that information can be recorded and / or reproduced,
The objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the intermediate area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the intermediate region is condensed on the information recording surface of the third optical disc. Without collecting light so that information can be recorded and / or reproduced.
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 first optical disc, and the objective lens passes through the peripheral area. The second light flux is not condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc, and the third light flux passing through the peripheral region is used as the information recording surface of the third optical disc. Do not concentrate so that information can be recorded and / or reproduced
The central region has a first optical path difference providing structure in which a first basic structure that is a blazed structure and a second basic structure that is a blazed structure are overlapped,
The intermediate region has a second optical path difference providing structure in which a third basic structure that is a blazed structure and a fourth basic structure that is a blazed structure are overlapped,
The first basic structure makes the A-order diffracted light quantity of the first light flux that has passed through the first basic structure larger than any other order diffracted light quantity, and B of the second light flux that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The second basic structure makes the D-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and the E of the second light beam that has passed through the second basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the F-order diffracted light quantity of the third light flux that has passed through the second basic structure larger than any other order diffracted light quantity,
The third basic structure makes the A-order diffracted light quantity of the first light flux that has passed through the third basic structure larger than any other order of diffracted light quantity, and B of the second light flux that has passed through the third basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the third basic structure larger than any other order diffracted light quantity,
The fourth foundation structure makes the D-order diffracted light quantity of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light quantity, and the E of the second light flux that has passed through the fourth foundation structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the F-order diffracted light quantity of the third light flux that has passed through the fourth basic structure larger than any other order diffracted light quantity,
A, B, C, D, E, and F are respectively
| A | = 1
| B | = 1
| C | = 1
| D | = 2
| E | = 1
| F | = 1
The filling,
Wherein across the boundary between the central region and the intermediate region, and the second based on the width of the closest annular zone to the boundary of the structure Delta] T2, the width of the closest annular zone to the boundary of the fourth basic structure .DELTA.T4,
The width of the annular zone of the first foundation structure, the second foundation structure, the third foundation structure and the fourth foundation structure is positive when the level difference of the foundation structure faces the direction opposite to the optical axis. When the sign is a negative sign when the level difference of the foundation structure faces the direction of the optical axis,
An objective lens characterized by satisfying the following expression:
ΔT4-ΔT2> 0 (2) The objective lens according to claim 19, wherein a step at a position closest to the boundary of the second foundation structure faces the direction of the optical axis. 21. The step at a position closest to the boundary of the second foundation structure and the step at a position closest to the boundary of the fourth foundation structure are directed in the same direction. Objective lens. An optical pickup device comprising the objective lens according to any one of claims 1 to 21 .