JPWO2012063848A1 - Objective lens for optical pickup device, optical pickup device and optical information recording / reproducing device - Google Patents

Abstract

While reducing the cost, it is possible to perform compatibility of the three types of optical discs of BD / DVD / CD with a common objective lens, while improving temperature characteristics and suppressing fluctuations in diffraction efficiency at the time of wavelength change. Provided are an optical pickup device having an objective lens that can be used, an optical information recording / reproducing device, and an objective lens suitable therefor. The first foundation structure and the second foundation structure constituting the first optical path difference providing structure of the objective lens are blazed, and the first foundation structure wheel is placed on one annular zone closest to the optical axis in the second foundation structure. 2 to 5 bands are included.

Description

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

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

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

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

  As a method for appropriately recording / reproducing information while maintaining compatibility with both BD and DVD, and 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 an optical path difference providing structure such as a diffraction structure having a wavelength dependency of spherical aberration in the objective lens. is there.

  Patent Document 1 has an objective lens that has a structure in which two basic structures each of which is a diffractive structure are superimposed, and can be used in common for three types of optical disks, and an optical pickup device equipped with this objective lens Is described.

  Of the three types of optical discs described in Patent Document 1, two types are obviously DVD / CD, but NA = 0.67 corresponding to a wavelength of 405 nm is referred to as referring to the embodiment, that is, HD-DVD. / DVD / CD is an application that emphasizes the compatibility of three types of optical discs. The inventor examined whether or not the embodiment of this application can be applied to the compatibility of three types of optical discs of BD / DVD / CD. The NA of BD is generally 0.85, and HD-DVD It was found that the spherical aberration becomes large due to the change in the refractive index of the objective lens when the temperature changes, because the NA is higher than the NA. Further, an objective lens applied to HD-DVD / DVD / CD as described in Patent Document 1 has a relatively low NA of HD-DVD of 0.65. Therefore, a thin lens with a thin objective lens can be used. As a result, the problem of working distance when using a CD with a thick protective substrate is less likely to occur. On the other hand, the objective lens applied for the compatibility of the three types of optical disks of BD / DVD / CD has a high BD NA of 0.85. Therefore, an objective lens having a thick objective lens is often used. As a result, when the technique described in Patent Document 1 is applied as it is to an objective lens for BD / DVD / CD, there is a problem that a sufficient working distance cannot be secured when a CD having a thick protective substrate is used. is there. Furthermore, in the superposition structure in which the diffraction structures shown in Patent Document 1 are superposed, a structure that generates the third-order diffracted light with HD-DVD and a structure that generates the second-order diffracted light with HD-DVD even with the lowest step amount. They are superposed and the amount of step in the optical axis direction is large. As a result, it has been found that the diffraction efficiency tends to greatly change when the wavelength changes.

Japanese Patent No. 4562645 JP 2009-199707 A

  On the other hand, in Patent Document 2, first-order diffracted light is generated for 405 nm laser light, zero-order diffracted light is generated for 660 nm laser light, and zero-order diffracted light is generated for 790 nm laser light. For the 405 nm laser light, the first order diffracted light for the 660 nm laser light, and the first order for the 790 nm laser light. An objective optical system for an optical pickup device is disclosed in which information is recorded / reproduced so as to be compatible with BD, DVD, and CD by superimposing a second diffractive structure that generates folded light.

  However, in recent years, an optical pickup device for recording / reproducing information with respect to a plurality of information recording surfaces has been developed for BDs and DVDs and is already on the market. When the objective optical system disclosed in Patent Document 2 is used for the optical pickup device, unnecessary light generated from the diffraction structure is used to record / reproduce information when light beams having three different wavelengths pass through the common region. It has been found that there is a risk of focusing on the information recording layer other than the recording layer and generating an error signal.

  Furthermore, when one of a plurality of information recording layers is selected in the BD to form a focused spot, a coupling lens such as a collimator is displaced in the optical axis direction, and the substrate thickness up to the selected information recording layer is determined. The spherical aberration accompanying the change is corrected. Therefore, even when the DVD is used, for example, spherical aberration caused by a change in the refractive index of the objective lens when the environmental temperature changes can be similarly corrected by displacing the coupling lens in the optical axis direction.

  However, in consideration of complicated control of the drive for driving the coupling lens, it may be desirable not to displace the coupling lens when using a DVD. Also, when using a BD, all the luminous flux that has passed through the effective diameter of the objective lens is used to form a converging spot, so that flare light does not naturally occur. On the other hand, when using a DVD, an NA lower than that of the BD is ensured. Therefore, a part of the light flux is made flare light. In such a case, if the coupling lens is displaced in the optical axis direction, flare light is erroneously detected, which may generate an error signal that hinders information recording / reproduction. Therefore, there is a demand for fixing the objective lens when using the DVD. Therefore, there is a problem that it is desired to improve the temperature characteristics and wavelength characteristics of the objective lens when the DVD is used.

  An object of the present invention is to solve the above-mentioned problems. While reducing costs, a working distance when using a CD is ensured so that three types of optical disks of BD / DVD / CD can be compatible. While using a common objective lens, the adverse effect of unnecessary light reflected by layers other than the target layer can be reduced even when using an optical disc having multiple layers, and the temperature and wavelength characteristics when using a DVD are reduced. It is an object of the present invention to provide an optical pickup apparatus, an optical information recording / reproducing apparatus, and an objective lens suitable for the optical pickup apparatus including an objective lens capable of improving and suppressing fluctuations in diffraction efficiency when the wavelength changes.

The objective lens according to claim 1 emits a first light source that emits a first light flux having a first wavelength λ1 (390 nm ≦ λ1 ≦ 415 nm) and a second light flux that has a second wavelength λ2 (630 nm ≦ λ2 ≦ 670 nm). And a third light source that emits a third light beam having a third wavelength λ3 (760 nm ≦ λ3 ≦ 820 nm), and a protective substrate having a thickness t1 using the first light beam. Recording and / or reproducing information, recording and / or reproducing information of a DVD having a protective substrate with a thickness of t2 (t1 <t2) using the second light beam, and using the third light beam An objective lens used in an optical pickup device for recording and / or reproducing information of a CD having a protective substrate having a thickness of t3 (t2 <t3),
The optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region,
The central region has a first optical path difference providing structure,
The objective lens condenses the first light flux that passes through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that passes through the central region. Are recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the central region is recorded and / or recorded on the information recording surface of the CD. Or collect it so that it can be regenerated,
The objective lens condenses the first light flux passing through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the intermediate area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the intermediate region is recorded and / or recorded on the information recording surface of the CD. Or do not concentrate so that it can be regenerated,
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the peripheral area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the peripheral area is recorded on the information recording surface of the CD. And / or do not collect light for playback
The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
The first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and 1 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, making the first 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 second-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 1 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, making the first 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 first foundation structure and the second foundation structure are blazed, and 2 to 5 annular zones of the first foundation structure are included on one annular zone closest to the optical axis in the second foundation structure. It is characterized by that.

  The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped, and the first basic structure is a primary beam of the first light flux that has passed through the first basic structure. The amount of diffracted light is made larger than the amount of diffracted light of any other order, the amount of first order diffracted light of the second light beam that has passed through the first basic structure is made larger than the amount of diffracted light of any other order, and the first basic structure The first-order diffracted light quantity of the third light flux that has passed through the second base structure is made larger than any other order of diffracted light quantity, and the second basic structure reduces the second-order diffracted light quantity of the first light flux that has passed through the second basic structure. The first order diffracted light amount of the second light flux that passed through the second basic structure was made larger than any other order diffracted light amount, and passed through the second basic structure. The amount of the first-order diffracted light of the third light flux is any other order In the first optical path difference providing structure in which at least the first basic structure and the second basic structure are overlapped, it is possible to reduce the step amount in the optical axis direction, thereby reducing the wavelength variation. A decrease in diffraction efficiency can be suppressed.

  In order to deal with a BD having a plurality of information recording layers, it is conceivable that when a BD is used, the coupling lens is displaced in the optical axis direction so as to correspond to recording / reproduction on each information recording layer. In such a case, the function of already displacing the coupling lens in the optical axis direction is indispensable, but when using a DVD, the coupling lens may be fixed without being displaced in the optical axis direction. is there. The reason is that flare does not occur when BD is used, but flare occurs when DVD is used. Therefore, when the coupling lens is displaced, the aberration of the flare changes, and as a result, the flare adversely affects recording / reproduction. The reason for this is that there is a possibility that the control will be given, and the reason for wanting to simplify the control of the coupling lens in the drive. For such a problem, coupled with the effect of superimposing the first foundation structure and the second foundation structure, the first foundation structure and the second foundation structure are blazed, and the light in the second foundation structure is By using an objective lens including 2 to 5 ring zones of the first basic structure on one ring zone closest to the axis, temperature characteristics and wavelength characteristics when using a DVD can be improved. This is preferable because it is not necessary to displace the coupling lens when using the DVD.

  Further, by superimposing 2 to 5 ring zones of the first basic structure on one ring zone closest to the optical axis in the second basic structure, while maintaining compatibility with BD / DVD / CD, A working distance when using a CD can be secured. Further, the present inventor has found that there is an excellent effect that the problem of unnecessary light (light flux reflected by another layer) when using an optical disk having a plurality of layers can be reduced.

  The objective lens according to claim 2 is the objective lens according to claim 1, wherein the step of the first basic structure provided at least in the vicinity of the optical axis of the central region is directed in a direction opposite to the optical axis. In the second basic structure provided at least in the vicinity of the optical axis of the central region, the step is directed in the direction of the optical axis.

  As a result, in the first optical path difference providing structure in which the first basic structure and the second basic structure are overlapped, the level difference in the optical axis direction can be further reduced, thereby further suppressing the decrease in diffraction efficiency when the wavelength varies. it can.

According to a third aspect of the present invention, in the invention according to the first or second aspect, the intermediate region has a second optical path difference providing structure in which at least the third basic structure and the fourth basic structure are overlapped. ,
The third basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the third basic structure larger than any other order of diffracted light quantity, so that 1 of the second light flux that has passed through the third basic structure. Make the next diffracted light quantity larger than any other order diffracted light quantity,
In the fourth basic structure, the second-order diffracted light amount of the first light beam that has passed through the fourth basic structure is made larger than any other order of diffracted light amount, and 1st of the second light beam that has passed through the fourth basic structure. It is characterized in that the next diffracted light quantity is made larger than any other order diffracted light quantity.

  Thereby, in the second optical path difference providing structure in which at least the third basic structure and the fourth basic structure are overlapped, the step amount in the optical axis direction can be reduced, thereby reducing the diffraction efficiency at the time of wavelength variation. Can be suppressed. Further, the orders of the diffracted light having the highest light intensity in the first basic structure and the third basic structure are matched, and the orders of the diffracted light having the highest light intensity in the second basic structure and the fourth basic structure are matched. Therefore, the spherical aberration can be made continuous even when the temperature and the wavelength of the light flux passing through the central region and the intermediate region are changed, and the occurrence of higher order aberrations can be suppressed. In addition, the pupil transmittance distribution is almost flat between the intermediate region and the peripheral region, and it is possible to effectively suppress the spot thickening that occurs when the amount of light changes greatly at the boundary due to abolishment or the like. It is also possible to ensure the degree of freedom in designing the objective lens.

  According to a fourth aspect of the present invention, there is provided the objective lens according to the third aspect, wherein the third foundation structure and the fourth foundation structure are blazed, and one objective lens closest to the central region of the fourth foundation structure is provided. One to three annular zones of the third basic structure are included on the annular zone.

  Thereby, when using a BD having a plurality of information recording layers or when using a DVD, the condensing position of unnecessary light generated by passing through the intermediate region is the information recording layer other than the information recording layer for recording / reproducing information. It can be separated from the information recording device. In addition, the wavelength characteristics when using a DVD can be improved.

  The objective lens according to claim 5 is the objective lens according to claim 3 or 4, wherein the step of the third basic structure provided near the boundary with the central region faces in a direction opposite to the optical axis. The fourth basic structure provided near the boundary with the central region is characterized in that the step is directed in the direction of the optical axis.

  As a result, in the second optical path difference providing structure in which the third basic structure and the fourth basic structure are overlapped, the level difference in the optical axis direction can be further reduced, thereby further suppressing the decrease in diffraction efficiency at the time of wavelength fluctuation. it can.

  The objective lens according to claim 6 is the invention according to any one of claims 3 to 5, wherein the intermediate region is provided with only the third foundation structure and the fourth foundation structure, and other foundations. The structure is not provided.

  The objective lens according to claim 7 is the invention according to any one of claims 1 to 6, wherein one annular zone closest to the intermediate region in the second foundation structure is connected to the annular zone of the first foundation structure. 1 to 5 are included.

An objective lens according to an eighth aspect is characterized in that, in the invention according to any one of the first to seventh aspects, the following expression is satisfied.
160 (mm) ≤ N · f ≤ 210 (mm) (1)
Here, the total number of annular zones in the central region is N, and the focal length of the objective lens in the first light flux is f (mm).

  By setting the value of the expression (1) to be equal to or higher than the lower limit, the working distance of the CD can be secured, and the possibility of scratching due to interference with the optical disk can be reduced. On the other hand, by making the value of the expression (1) equal to or less than the upper limit, it is possible to prevent the pitch from becoming too small. Therefore, it is possible to prevent the workability from being lowered and the shape error to be reduced.

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

The optical pickup device according to claim 10 is the invention according to claim 9,
A coupling lens through which at least the first luminous flux and the second luminous flux pass, and an actuator for moving the coupling lens in the optical axis direction;
When the first light beam passes, the coupling lens can be displaced in the optical axis direction by the actuator;
When the second light beam passes, the coupling lens is fixed in a position in the optical axis direction.

  For example, in order to cope with a BD having a plurality of information recording layers, it is conceivable that when a BD is used, the coupling lens is displaced in the optical axis direction so as to correspond to recording / reproduction on each information recording layer. In such a case, the function of displacing the coupling lens in the optical axis direction is indispensable. However, when using a DVD, the coupling lens may be fixed without being displaced in the optical axis direction. is there. The reason is that flare does not occur when using BD, but flare occurs when using DVD. By changing the coupling lens, the flare aberration changes, and as a result, the flare is recorded / reproduced. The reason is that there is a possibility of adversely affecting the driving force, and the reason why it is desired to simplify the control of the coupling lens displacement by the drive. For such a problem, by using the objective lens of the present invention to improve both the temperature characteristic and the wavelength characteristic when using the DVD, as a result, the coupling occurs when the second light beam passes when using the DVD. Even in a state where the position of the lens in the optical axis direction is fixed, information can be recorded / reproduced with respect to the information recording surface of the DVD, and the above-mentioned problems can be solved.

  An optical information recording / reproducing apparatus according to an eleventh aspect includes the optical pickup apparatus according to the ninth or tenth aspect.

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

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

  In this specification, 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 (2), (3), and (4), 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 (2)
0.5mm ≤ t2 ≤ 0.7mm (3)
1.0mm ≤ t3 ≤ 1.3mm (4)

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 (5) and (6).
1.5 · λ1 <λ2 <1.7 · λ1 (5)
1.8 · λ1 <λ3 <2.0 · λ1 (6)

  The first wavelength λ1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm or more and 415 nm or less, and the second wavelength λ2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably. Is 630 nm or more and 670 nm or less, and the third wavelength λ3 of the third light source is preferably 750 nm or more and 880 nm or less, more preferably 760 nm or more and 820 nm or less.

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

  As the light receiving element, a photodetector such as a photodiode is preferably used. Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking I can do it. The light receiving element may comprise a plurality of photodetectors. The light receiving element may have a main photodetector and a sub photodetector. For example, two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. It is good also as a simple light receiving element. The light receiving element may have a plurality of light receiving 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 of the present invention is preferably a single plastic lens. A convex lens is preferable. The objective lens preferably has a refractive surface that is aspheric. In the objective lens, the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.

Moreover, it is preferable to use an alicyclic hydrocarbon-based polymer material such as a cyclic olefin-based resin material as a plastic material constituting the objective lens. 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, it is preferable that the coupling lens is also a plastic lens.

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

  A first preferred example includes a polymer block [A] containing a repeating unit [1] represented by the following formula (I), a repeating unit [1] represented by the following formula (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 purpose of the present invention, but is usually 0.01 to 2 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based copolymer, Preferably it is 0.01-1 mass part.

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

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

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

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

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

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

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

  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. At least one optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region. The central region is preferably a region including the optical axis of the objective lens, but a minute region including the optical axis is used as an unused region or a special purpose region, and the surroundings are defined as a central region (also referred to as a central region). Also good. The central region, the intermediate region, and the peripheral region are preferably provided on the same optical surface. As shown in FIG. 1, the central region CN, the intermediate region MD, and the peripheral region OT are preferably provided concentrically around the optical axis on the same optical surface. In addition, a first optical path difference providing structure is provided in the central area of the objective lens, 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.

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

  The intermediate area of the objective lens is used for BD / DVD recording / reproduction, and can be said to be a BD / DVD shared area not used for CD recording / reproduction. That is, the objective lens condenses the first light flux passing through the intermediate area so that information can be recorded / reproduced on the information recording surface of the BD, and the second light flux passing through the intermediate area is recorded as information recording on the DVD. Light is collected so that information can be recorded / reproduced on the surface. On the other hand, the third light flux passing through the intermediate region is not condensed so that information can be recorded / reproduced on the information recording surface of the CD. The third light flux passing through the intermediate region of the objective lens preferably forms a flare on the information recording surface of the CD. As shown in FIG. 2, in the spot formed on the information recording surface of the CD by the third light beam that has passed through the objective lens, the spot center having a high light amount density in the order from the optical axis side (or the spot center) to the outside. It is preferable to have a portion SCN, a spot intermediate portion SMD whose light intensity density is lower than that of the spot central portion, and a spot peripheral portion SOT whose light intensity density is higher than that of the spot intermediate portion and lower than that of the spot central portion. The center portion of the spot is used for recording / reproducing information on the optical disc, and the middle portion of the spot and the peripheral portion of the spot are not used for recording / reproducing information on the optical disc. In the above, this spot peripheral part is called flare. However, there is no spot middle part around the center part of the spot and there is a spot peripheral part, that is, even when a light spot is formed thinly around the condensing spot, the spot peripheral part may be called a flare. Good. In other words, it can be said that the third light flux that has passed through the intermediate region of the objective lens preferably forms a spot peripheral portion on the information recording surface of the CD.

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

  The first optical path difference providing structure is preferably provided in a region of 70% or more of the area of the central region of the objective lens, and more preferably 90% or more. More preferably, the first optical path difference providing structure is provided on the entire surface of the central region. The second optical path difference providing structure is preferably provided in a region of 70% or more of the area of the intermediate region of the objective lens, and more preferably 90% or more. More preferably, the second optical path difference providing structure is provided on the entire surface of the intermediate region. 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, 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. 3A and 3B, 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. 3, 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 in the direction perpendicular to the optical axis of one blaze unit is called a pitch P. (See FIGS. 3A and 3B.) 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. 3 (a))

  In addition, as shown in FIGS. 3 (c) and 3 (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). ). In the present specification, “V level” means a ring-shaped surface (hereinafter also referred to as a terrace surface) corresponding to (or facing) the vertical direction of the optical axis in one step unit of the step structure. In other words, it is divided by V steps and divided into V ring zones. Particularly, a three-level or higher staircase structure has a small step and a large step. For example, the optical path difference providing structure illustrated in FIG. 3C is referred to as a five-level staircase structure, and the optical path difference providing structure illustrated in FIG. 3D is referred to as a two-level staircase 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. 3 (a), the same sawtooth shape may be repeated, and as shown in FIG. 3 (b), the shape of the sawtooth shape gradually increases as it moves away from the optical axis. A shape in which the pitch becomes longer or a shape in which the pitch becomes shorter may be used. In addition, in some areas, the blazed structure has a step opposite to the optical axis (center) side, and in other areas, the blazed structure has a step toward the optical axis (center). It is good also as a shape in which the transition area | region required in order to switch the direction of the level | step difference of a blaze | braze type | mold structure is provided in the meantime. In addition, when it is set as the structure which switches the direction of the level | step difference of a blaze | braze type | mold in this way, it becomes possible to widen an annular zone pitch and it can suppress the transmittance | permeability fall by the manufacturing error of an optical path difference providing structure.

  The first optical path difference providing structure 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. It is also conceivable to provide the first basic structure and the second basic structure on different optical surfaces without overlapping. Similarly, the third basic structure and the fourth basic structure may be provided on different optical surfaces without overlapping.

  Next, the 1st optical path difference providing structure provided in a center area | region is demonstrated. The first optical path difference providing structure is a structure in which at least the first basic structure and the second basic structure are overlapped. The first optical path difference providing structure is preferably a structure in which only the first basic structure and the second basic structure are overlapped.

  The first basic structure is a blazed structure. In addition, the first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and the first-order diffracted light quantity that has passed through the first basic structure. Is made larger than any other order of the diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light quantity. This is called a (1/1/1) structure. In particular, if the first-order diffracted light that is low order is generated, the step amount of the first basic structure does not become too large, so that the manufacture is facilitated, and the light quantity loss due to the manufacturing error can be suppressed, and the wavelength It is preferable because fluctuations in diffraction efficiency during fluctuations can be reduced.

  Moreover, it is preferable that the first foundation structure provided at least near the optical axis in the central region has a step in a direction opposite to the optical axis. “The step is directed in the direction opposite to the optical axis” means a state as shown in FIG. In addition, the first basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis among steps of the (1/1/1) structure. Preferably, at least a (1/1/1) structure step existing between the optical axis and the half-position in the direction orthogonal to the optical axis from the optical axis to the boundary between the central region and the intermediate region is the optical axis. Is pointing in the opposite direction.

  For example, as for the 1st foundation structure provided near the middle field of a central field, a level difference may face the direction of an optical axis. That is, as shown in FIG. 5B, the step is directed in the opposite direction to the optical axis when the first foundation structure is near the optical axis, but is switched halfway, and the step of the first foundation structure is near the intermediate region. It is good also as a shape which faces the direction of an optical axis. However, it is preferable that all the steps of the first basic structure provided in the central region are directed in a direction opposite to the optical axis.

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

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

  The second basic structure is also a blazed structure. In the second basic structure, the second-order diffracted light amount of the first light beam that has passed through the second basic structure is made larger than the diffracted light amount of any other order, and the first-order diffraction of the second light beam that has passed through the first basic structure. The light quantity is made larger than any other order of diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light quantity. This is called a (2/1/1) structure. In particular, if low-order second-order diffracted light or first-order diffracted light is generated, the step amount of the second basic structure does not become too large, which facilitates manufacturing and suppresses light loss caused by manufacturing errors. This is preferable because it can reduce the diffraction efficiency fluctuation at the time of wavelength fluctuation.

  Moreover, it is preferable that the level | step difference of the 2nd foundation structure provided in the vicinity of the optical axis of a center area | region has faced the direction of the optical axis. “The level difference faces the direction of the optical axis” means a state as shown in FIG. The second basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis among steps of the (2/1/1) structure. Preferably, at least a half of the optical axis orthogonal direction from the optical axis to the boundary between the central region and the intermediate region and the (2/1/1) structure step existing between the optical axis and the optical axis direction It is suitable.

  For example, in the second basic structure provided near the middle region of the central region, the step may be directed in a direction opposite to the optical axis. That is, as shown in FIG. 5A, the step is directed in the direction of the optical axis when the second foundation structure is near the optical axis, but is switched halfway, and the step of the second foundation structure is located near the optical axis. It is good also as a shape which faces the reverse direction. However, preferably, the second basic structure provided in the central region is that all the steps are directed in the direction of the optical axis.

  When the first optical path difference providing structure is formed by superimposing the first basic structure having the (1/1/1) structure and the second basic structure having the (2/1/1) structure, the height of the step is extremely high. Can be lowered. Therefore, it is possible to further reduce manufacturing errors, further reduce the light amount loss, and further suppress the change in diffraction efficiency when the wavelength changes.

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

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

Viewpoint of the shape and step amount of the first optical path difference providing structure after the first basic structure in which the step is opposite to the optical axis and the second basic structure in which the step is directed toward the optical axis are overlapped Therefore, the first optical path difference providing structure in which the first basic structure having the (1/1/1) structure and the second basic structure having the (2/1/1) structure are overlapped is expressed as follows. be able to. The first optical path difference providing structure provided at least in the vicinity of the optical axis of the central region has both a step facing in the opposite direction to the optical axis and a step facing in the direction of the optical axis. It is preferable that the step amount d11 of the step facing the direction opposite to the axis and the step amount d12 of the step facing the direction of the optical axis satisfy the following conditional expressions (7) and (8). More preferably, the following conditional expressions (7) and (8) are satisfied in all the regions of the central region. If the objective lens provided with the optical path difference providing structure is a single aspherical convex lens, the incident angle of the light flux to the objective lens differs depending on the height from the optical axis, so that the optical path difference providing structure that gives the same optical path difference Even so, in general, as the distance from the optical axis increases, the step amount tends to increase. In the following conditional expression, the upper limit is multiplied by 1.5 because the increase in the level difference is taken into account. Here, n represents the refractive index of the objective lens at the first wavelength λ1.
0.6 · (λ1 / (n−1)) <d11 <1.5 · (λ1 / (n−1)) (7)
0.6 · (λ1 / (n−1)) <d12 <1.5 · (2λ1 / (n−1)) (8)

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

  For example, when λ1 is 390 to 415 nm (0.390 to 0.415 μm) and n is 1.54 to 1.60, the above conditional expression can be expressed as follows.

0.39 μm <d11 <1.15 μm (9)
0.39 μm <d12 <2.31 μm (10)

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

As described above, when the positions of all the steps of the second foundation structure are matched with the positions of the steps of the first foundation structure, d11 and d12 of the first optical path difference providing structure are the following conditional expressions (7) and (8 ) Is preferably satisfied. More preferably, the following conditional expressions (7) and (8) are satisfied in all the regions of the central region.
0.6 · (λ1 / (n−1)) <d11 <1.5 · (λ1 / (n−1)) (7)
0.6 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (8)

  For example, when λ1 is 390 to 415 nm (0.390 to 0.415 μm) and n is 1.54 to 1.60, the above conditional expression can be expressed as follows.

0.39 μm <d11 <1.15 μm (9) ′
0.39 μm <d12 <1.15 μm (10) ′

More preferably, the following conditional expressions (7) ′ and (8) ′ are preferably satisfied. More preferably, the following conditional expressions (7) ′ and (8) ′ are satisfied in all the regions of the central region.
0.9 · (λ1 / (n−1)) <d11 <1.5 · (λ1 / (n−1)) (7) ′
0.9 · (λ1 / (n−1)) <d12 <1.5 · (λ1 / (n−1)) (8) ′

  For example, when λ1 is 390 to 415 nm (0.390 to 0.415 μm) and n is 1.54 to 1.60, the above conditional expression can be expressed as follows.

0.59 μm <d11 <1.15 μm (9) ″
0.59 μm <d12 <1.15 μm (10) ″

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

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

  As shown in FIG. 6D, when the first basic structure and the second basic structure are directly overlapped, a part may protrude as shown by a dotted line, but the width of the protruding part is 5 μm or less. If it is narrow, the projecting portion is shifted in parallel along the optical axis, and eliminating the projecting portion has no significant effect, so that one annular zone of the second foundation structure can have a plurality of the first foundation structure. The zonal is just like that (see the solid line). Therefore, in the example of FIG. 6 (d), it is assumed that three annular zones of the first foundation structure are on one annular zone of the second foundation structure. When the first foundation structure and the second foundation structure are superimposed as they are, a dent may be eliminated in the same manner even when a dent having a width of 5 μm or less is generated.

Here, when Δλ (nm) is the amount of change in the first wavelength and ΔWD (μm) is the chromatic aberration of the objective lens caused by the change Δλ in the first wavelength, it is preferable that the following expression is satisfied.
0.3 (μm / nm) ≦ ΔWD / Δλ ≦ 0.6 (μm / nm) (11)
The “chromatic aberration” here is a shift in the focus position that occurs when the wavelength of the light beam changes. That is, it is a shift of “position where wavefront aberration is best” that occurs when the wavelength of the light beam changes.

  In order to obtain such a configuration, as described above, in the first optical path difference providing structure, two annular zones N1 of the first basic structure are equal to one annular zone closest to the optical axis of the second basic structure. It is preferable that -5 pieces (particularly preferably 2 to 3 pieces) are included. By setting the chromatic aberration to the above-described range, the optical disc has a plurality of information recording surfaces while ensuring a working distance in the CD even in an objective lens having a large axial thickness, which is a BD / DVD / CD compatible objective lens. This is preferable because the problem of stray light can be reduced and the temperature and wavelength characteristics can be improved when using a DVD. In addition, the number N2 of the first foundation structure annular zones superimposed on one annular zone closest to the intermediate region in the second foundation structure is preferably equal to or smaller than N1, for example, 1 to 5 overlapping zones. It should be done. It should be noted that the effects described here are particularly noticeable in an objective lens used for a so-called slim pickup having an effective diameter Φ of 3.2 mm or less.

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

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 (12). Here, the best focus position refers to a position where the beam waist becomes a minimum within a certain defocus range. The first best focus position is the best focus position of the necessary light used for CD recording / reproduction, and the second best focus position is the best of the luminous flux having the largest light quantity among the unnecessary light that is not used for CD recording / reproduction. The focus position.
0.05 ≦ L / f13 ≦ 0.35 (12)
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 (12) ′ is satisfied.
0.10 ≦ L / f13 ≦ 0.25 (12) ′

  Several preferable examples of the first optical path difference providing structure described above are shown in FIGS. 6 (a), (b), and (c). Although FIG. 6 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. 6A, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA. Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1. Next, in FIG. 6B, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 also faces the direction of the optical axis OA. Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1. Next, in FIG.6 (c), the level | step difference of 1st foundation structure BS1 has faced the direction opposite to optical axis OA, and the level | step difference of 2nd foundation structure BS2 has also faced the direction opposite to optical axis OA. . Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1.

Furthermore, when the total number of annular zones in the central region is N and the focal length of the first light flux of the objective lens is f (mm), it is preferable that the following expression is satisfied. As a result, it is possible to prevent the working distance of the CD from becoming too short and to suppress the workability from being lowered due to the ring zone pitch becoming too small. Note that the number of steps substantially parallel to the optical axis in the central region may be regarded as the total number of annular zones in the central region.
160 (mm) ≤ N · f ≤ 210 (mm) (1)

  Next, the second optical path difference providing structure provided in the intermediate region will be described. The second optical path difference providing structure is preferably a structure in which at least two basic structures of a third basic structure and a fourth basic structure are overlapped.

  It is preferable that both the third foundation structure and the fourth foundation structure are blazed structures. Further, the third basic structure makes the first-order diffracted light amount of the first light beam that has passed through the third basic structure larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the third basic structure. Is preferably larger than any other order of diffracted light. In addition, it is preferable that the first-order diffracted light amount of the third light flux that has passed through the third basic structure is larger than any other order diffracted light amount. In addition, the fourth foundation structure makes the second-order diffracted light amount of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light amount, and the first-order of the second light beam that has passed through the fourth foundation structure. Is preferably larger than any other order of diffracted light. Further, the first-order diffracted light amount of the third light flux that has passed through the fourth basic structure is made larger than any other order diffracted light amount. Thereby, in the second optical path difference providing structure in which at least the third basic structure and the fourth basic structure are overlapped, the amount of step in the optical axis direction can be reduced, thereby suppressing the decrease in diffraction efficiency at the time of wavelength variation. Further, the orders of the diffracted light having the highest light intensity in the first basic structure and the third basic structure are matched, and the orders of the diffracted light having the highest light intensity in the second basic structure and the fourth basic structure are matched. Therefore, the spherical aberration can be made continuous even when the temperature and the wavelength change for the light flux passing through the central region and the intermediate region, and as a result, the occurrence of higher order aberrations can be suppressed.

  The second optical path difference providing structure may be a structure in which the fifth basic structure is overlapped in addition to the third and fourth basic structures. However, in order to simplify the structure and suppress a decrease in light utilization efficiency due to manufacturing errors. The second optical path difference providing structure preferably includes only the third basic structure and the fourth basic structure.

  At this time, the fifth basic structure makes the 0th-order diffracted light quantity of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light quantity, and the second light flux that has passed through the fifth basic structure. The 0th-order diffracted light amount is made larger than any other order diffracted light amount, and the G-th order diffracted light amount of the third light flux that has passed through the fifth basic structure is made larger than any other order diffracted light amount. It is preferable. By superimposing such a fifth basic structure, a phase shift occurs between the central region and the intermediate region without adversely affecting the first light beam and the second light beam passing through the intermediate region of the objective lens. Accordingly, it is possible to easily give only the third light flux an effect of forming a flare at a position far from the light spot on the information recording surface of the CD.

  Preferably, G is ± 1. When G is ± 1, the fifth basic structure is preferably a two-level step structure (also referred to as a binary structure) as shown in FIG.

  Further, the third-order diffracted light amount of the first light beam that has passed through the third basic structure is made larger than any other order of diffracted light amount, and the second-order diffracted light amount of the second light beam that has passed through the third basic structure is changed to other values. The diffraction light quantity of any order is made larger (also referred to as (3/2) structure), the second-order diffraction light quantity of the first light beam that has passed through the fourth basic structure is made larger than any other order of diffraction light quantity, The first-order diffracted light amount of the second light beam that has passed through the four basic structures may be made larger than any other order diffracted light amount (also referred to as a (2/1) structure). With such a configuration, the diffraction efficiency in BD can be further increased.

  In addition, even when the 3rd foundation structure and the 4th foundation structure are the combination of the (1/1) structure and the (2/1) structure, it is the combination of the (3/2) structure and the (2/1) structure. Even in this case, the third basic structure provided at least in the middle region at the position closest to the central region has the step in the direction opposite to the optical axis, and at least in the middle region at the position closest to the central region. As for the 4th foundation structure provided, it is preferred that the level | step difference has faced the direction of an optical axis. More preferably, the steps of all the third foundation structures in the intermediate region are directed in the direction opposite to the optical axis, and the steps of all the fourth foundation structures in the intermediate region are directed in the direction of the optical axis. is there.

  In the third basic structure, when the wavelength of the incident light beam changes so as to become longer, the spherical aberration changes in an undercorrected (under) direction, and in the fourth basic structure, the wavelength of the incident light beam becomes longer. If it changes, the spherical aberration may change in the direction of under-correction (under).

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

  On the other hand, when one of the third basic structure and the fourth basic structure is changed so that the wavelength of the incident light beam becomes longer, the spherical aberration changes in the undercorrection (under) direction, and the incident light is incident on the other side. When the wavelength of the luminous flux to be changed is changed to be longer, the spherical aberration may be changed in the overcorrection (over) direction.

  The vertical axis represents the height in the direction perpendicular to the optical axis from the optical axis, the horizontal axis is a coordinate indicating aberration, the left side of the horizontal axis is negative, the right side is positive, and the negative is closer to the objective lens. In the case where the positive is a direction away from the objective lens, overcorrection is a state inclined in the positive direction, and undercorrection is a state inclined in the negative direction. Even if the value of the aberration is negative, if the inclination is inclined in the positive direction, it is regarded as overcorrection. Even if the value of the aberration is positive, if the inclination is in the negative direction, it is regarded as insufficient correction.

  Further, in the optical path difference function of the first foundation structure and the second foundation structure, or the third foundation structure and the fourth foundation structure, a paraxial term (for example, the term of C2 in (Equation 2) or B2 in (Equation 3)) When the graph of the optical path difference function is created by deleting only the term), if the position of the graph (regardless of the slope) is on the negative side, it is considered as undercorrected, and if it is on the positive side, it is considered as overcorrected. May be.

  In the longitudinal spherical aberration diagram, in the third basic structure in the intermediate region, when the wavelength becomes longer, the position of the spherical aberration (the inclination does not matter) becomes the positive side, and in the fourth basic structure, the position of the spherical aberration becomes longer as the wavelength becomes longer. Is preferably on the negative side. By configuring in this way, it becomes possible to reduce the chromatic aberration of the BD (condensation position shift when the wavelength changes).

  In one of the third basic structure and the fourth basic structure, when the wavelength of the incident light beam is changed so as to become longer, the spherical aberration changes in the undercorrection (under) direction. If the spherical aberration is changed in the overcorrection direction when the wavelength is changed to be longer, when the first light beam is condensed on the information recording surface of the BD as the entire objective lens, the first aberration is changed. The amount of change in the third-order spherical aberration when the wavelength of one light beam is changed by +5 nm can be set to −30 mλrms to +50 mλrms, which is preferable. When the first light beam is condensed on the information recording surface of the BD as the entire objective lens, the amount of change in the third-order spherical aberration when the wavelength of the first light beam changes by +5 nm is -10 mλrms or more and +10 mλrms or less. More preferably. When the first light beam is condensed on the information recording surface of the BD as the entire objective lens, the amount of change in the fifth-order spherical aberration when the wavelength of the first light beam changes by +5 nm is −20 mλrms to 20 mλrms. It is preferable that More preferably, it is −10 mλrms or more and +10 mλrms or less.

  With such a configuration, in either one of the third basic structure and the fourth basic structure, if the wavelength of the incident light beam is changed to be longer, the spherical aberration changes in the overcorrection direction. Even if the two-optical path difference providing structure is composed of only the third and fourth basic structures, flare can be easily produced when using the CD. Accordingly, flare out when using a CD can be performed with a simple second optical path difference providing structure, so that a decrease in light utilization efficiency due to a shadow effect is suppressed, and a decrease in light utilization efficiency due to manufacturing errors is also suppressed. As a result, the light utilization efficiency can be improved. This reduces the effect of correcting the temperature characteristics when using BD in the intermediate area, but the temperature characteristics are too poor because both the first basic structure and the second basic structure in the central area are insufficiently corrected at long wavelengths. This can be prevented, and the wavelength characteristic correction effect when using the BD can be increased. In addition, when the DVD is used, both the temperature characteristic and wavelength characteristic of the DVD can be improved.

  When the wavelength of the incident light beam is changed to be longer in the fourth basic structure, the spherical aberration is changed in an undercorrected (under) direction, and the wavelength of the incident light beam is longer in the third basic structure. In this case, it is preferable that the spherical aberration changes in the overcorrected (over) direction because the flare can be easily moved farther when the CD is used.

  Further, in order to improve the wavelength characteristics when using the DVD, in the second optical path difference providing structure, the ring zone of the third basic structure is 1 to 3 in the ring zone closest to the central region of the fourth basic structure. It is preferable that it is contained (particularly preferably 2 to 3). More preferably, in the second optical path difference providing structure, 1 to 5 (particularly preferably 2 to 3) ring zones of the third foundation structure are provided for one ring zone closest to the peripheral region of the fourth foundation structure. It is included.

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

  Here, the schematic diagram of a preferable objective lens is shown in FIG. It is the figure which showed the upper half from the optical axis among the cross sections of the objective lens containing optical axis OA. Note that FIG. 20 is a schematic diagram to the last, and is not a drawing showing an accurate length ratio or the like based on the embodiment.

  The objective lens in FIG. 20 has a central region CN, an intermediate region MD, and a peripheral region OT. A first optical path difference providing structure ODS1 is provided in the central area, a second optical path difference providing structure ODS2 is provided in the middle area, and a third optical path difference providing structure is provided in the peripheral area.

  The first optical path difference providing structure ODS1 in FIG. 20 has a (2/1/1) blazed structure and a second basic structure BS2 in which a step is directed toward the optical axis, and (1/1/1). The blazed structure has a structure in which a first basic structure BS1 with a step facing away from the optical axis is superimposed. In FIG. 20, the second foundation structure BS2 has three annular zones, and four annular zones of the first foundation structure BS1 are included on the annular zone (circular shape) closest to the optical axis in the second foundation structure BS2. ing. In addition, two annular zones of the first foundation structure BS1 are included in one annular zone closest to the intermediate region in the second foundation structure BS2.

  The second optical path difference providing structure ODS2 in FIG. 20 has a (2/1/1) blazed structure and a fourth basic structure BS4 whose level difference faces the optical axis, and (1/1/1). The blazed structure has a structure in which a third basic structure BS3 having a level difference opposite to the optical axis is superimposed. In FIG. 20, the fourth foundation structure BS4 has three annular zones, and three annular zones of the third foundation structure BS3 are included on the annular zone closest to the central region in the fourth foundation structure BS4. Further, one ring zone of the third foundation structure BS3 is included in one ring zone closest to the peripheral region in the fourth foundation structure BS4.

  The third optical path difference providing structure ODS3 in FIG. 20 is composed of only a sixth basic structure BS6 having a (2/1/1) blazed structure in which the step is directed toward the optical axis.

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

Moreover, it is preferable that an objective lens satisfy | fills the following conditional expression (14).
0.8 ≦ d / f ≦ 1.5 (14)
Here, d represents the thickness (mm) on the optical axis of the objective lens, and f represents the focal length of the objective lens in the first light flux.

  When an optical disk with a short wavelength and high NA such as BD is used, there is a problem that astigmatism is likely to occur in the objective lens and decentration coma is likely to occur, but the conditional expression (12) is satisfied. As a result, it is possible to suppress the generation of astigmatism and decentration coma.

  In addition, since the objective lens becomes a thick objective lens with a thick on-axis thickness, the working distance at the time of CD recording / reproduction tends to be shortened, so that the upper limit value of conditional expression (14) may not be exceeded. preferable.

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 beam becomes parallel light or substantially parallel light, it is preferable that the imaging magnification m1 of the objective lens when the first light beam is incident on the objective lens satisfy the following formula (15).
-0.01 <m1 <0.01 (15)

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 enters the objective lens satisfies the following formula (16). Is preferred.
-0.01 <m2 <0.01 (16)

On the other hand, when the second light beam is incident on the objective lens as diverging light, the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens preferably satisfies the following expression (16) ′. .
−0.025 <m2 ≦ −0.01 (16) ′

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 (17). Is preferred.
-0.01 <m3 <0.01 (17)

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 (17) ′. .
−0.025 <m3 ≦ −0.01 (17) ′

  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 0.2 mm or more and 0.5 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 1.3 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 1.0 mm or less.

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

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

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

  In order to fix the position of the coupling lens in the optical axis direction when using a DVD, the wavelength of the incident light beam in one of the third basic structure and the fourth basic structure constituting the second optical path difference providing structure of the objective lens. So that the spherical aberration changes in the direction of insufficient correction, and on the other side, the spherical aberration changes in the direction of overcorrection when the wavelength of the incident light beam changes longer. As a result, both the temperature characteristic and the wavelength characteristic when using the DVD can be improved, and as a result, when using the DVD, the position of the coupling lens in the optical axis direction is fixed when the second light beam passes. However, it is preferable because information can be recorded / reproduced with respect to the information recording surface of the DVD.

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

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

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

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

  According to the present invention, in a thick objective lens having a thick on-axis thickness that is used interchangeably with three types of optical disks of BD / DVD / CD, temperature characteristics are improved while ensuring a working distance when using a CD. It becomes possible to do. Further, when an optical disc having a plurality of information recording surfaces is used, the adverse effect of unnecessary light reflected on the information recording surface that is not a recording / reproducing target on recording / reproducing can be reduced. Furthermore, it is possible to improve the temperature characteristics and wavelength characteristics when using a DVD. Furthermore, it is possible to suppress an increase in the height of the step of the optical path difference providing structure, and accordingly, it is possible to suppress a light amount loss due to a manufacturing error and suppress a fluctuation in diffraction efficiency at the time of a wavelength fluctuation. Is possible. With these effects, recording / reproduction of three types of optical discs of BD / DVD / CD can be performed well with a common objective lens. Further, it is particularly suitable for recording / reproducing information on / from an optical disc having a plurality of information recording layers.

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 an axial direction sectional view showing an example of an optical path difference grant structure, (a) and (b) show an example of a blaze type structure, and (c) and (d) show an example of a step type structure. (A) shows a state in which the step is directed in the direction of the optical axis, and (b) is a diagram showing a state in which the step is directed in a direction opposite to the optical axis. (A) shows a shape in which the step is in the direction of the optical axis in the vicinity of the optical axis, but changes in the middle, and in the vicinity of the intermediate region, the step is in the direction opposite to the optical axis. FIG. 4 is a diagram showing a shape in which a step is directed in the opposite direction to the optical axis in the vicinity of the axis, but is switched in the middle, and the step is directed toward the optical axis in the vicinity of the intermediate region. It is a conceptual diagram of a 1st optical path difference providing structure, (a), (b), (c), (d) shows the 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 record and / or reproduce | regenerate information appropriately with respect to BD, DVD, and CD which are different optical disks. FIG. 4 is a longitudinal spherical aberration diagram of Example 1, wherein (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. FIG. 4 is a longitudinal spherical aberration diagram of Example 2, wherein (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. FIG. 4 is a longitudinal spherical aberration diagram of Example 3, wherein (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. FIG. 6 is a longitudinal spherical aberration diagram of Example 4, wherein (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. FIG. 6 is a longitudinal spherical aberration diagram of Example 5, wherein (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. FIG. 6 is a longitudinal spherical aberration diagram of Example 6, wherein (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. FIG. 10 is a longitudinal spherical aberration diagram of Example 7, wherein (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. FIG. 10 is a longitudinal spherical aberration diagram of Example 8, wherein (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. FIG. 10 is a longitudinal spherical aberration diagram of Example 9, wherein (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. FIG. 10 is a longitudinal spherical aberration diagram of Example 10, where (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. FIG. 10 is a longitudinal spherical aberration diagram of Example 11, wherein (a) shows longitudinal spherical aberration when using BD, and (b) shows longitudinal spherical aberration when using DVD. It is a schematic diagram of a preferable objective lens.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 7 is a diagram schematically showing a configuration of the optical pickup device PU1 of the present embodiment that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. The present invention is not limited to the present embodiment.

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

  As shown in FIG. 1, in the single objective lens OL according to the present embodiment, a central region CN including an optical axis on the aspherical optical surface on the light source side, an intermediate region MD arranged around the central region CN, Further, 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 the present embodiment is a plastic lens. The first optical path difference providing structure formed in the central region CN of the objective lens OL is a structure in which the first basic structure and the second basic structure are overlapped as shown in FIG. The first-order diffracted light amount of the first light beam that has passed through the first basic structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the first basic structure is set to any other order. The first order diffracted light amount of the third light flux that has passed through the first basic structure is made larger than any other order diffracted light amount, and is provided at least near the optical axis of the central region CN. In the basic structure, the step is directed in the direction opposite to the optical axis, and in the second basic structure, the second-order diffracted light quantity of the first light beam that has passed through the second basic structure is greater than the diffracted light quantity of any other order. And the primary of the second light flux that has passed through the second basic structure. The diffracted light larger than the other diffracted light of any order, larger than the third light flux of the first-order diffracted light of other diffraction light amount of any order which has passed through the second basic structure. The first foundation structure and the second foundation structure are blazed, and 2 to 5 ring zones of the first foundation structure are included on one ring zone closest to the optical axis in the second foundation structure. One to five annular zones of the first foundation structure are included in one annular zone closest to the intermediate region in the second foundation structure.

  Further, the second path difference providing structure formed in the intermediate region MD of the objective lens OL is a structure in which the third foundation structure and the fourth foundation structure are overlapped, and the third foundation structure is the third foundation structure. The first-order diffracted light amount of the first light beam that has passed is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the third basic structure is made larger than any other order of diffracted light amount. The fourth basic structure increases the second-order diffracted light quantity of the first light beam that has passed through the fourth basic structure, and increases the second-order diffracted light quantity of any other order so that 1 of the second light flux that has passed through the fourth basic structure. The next diffracted light quantity is made larger than any other order diffracted light quantity. Further, the third foundation structure and the fourth foundation structure are blazed, and 1 to 3 ring zones of the third foundation structure are included on one ring zone that is close to the central region CT in the fourth foundation structure. . An example of the objective lens OL is shown in FIG.

  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.

  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. Correction can be made by changing the divergence angle or convergence angle of the light beam incident on the objective optical element OL by changing the collimating lens COL as means in the optical axis direction.

  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 portion) is recorded on the DVD through the protective substrate PL2. It becomes a spot formed on the surface RL2, 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.

  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 collected 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 and forms a spot peripheral part) is recorded on the CD through the protective substrate PL3. It becomes a spot formed on the surface RL3.

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

(Example)
Examples that can be used in the above-described embodiment 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
The objective lens of Example 1 is a plastic single lens. Table 1 shows lens data. A conceptual diagram of the first optical path difference providing structure of the first embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the first embodiment). In the first optical path difference providing structure of Example 1, the (1/1/1) blaze is added to the second basic structure BS2 that is a (2/1/1) blaze-type diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 1, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 3, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure is 2, and the number of ring zones of the third foundation structure is 3 on the ring zone of the fourth foundation structure closest to the center area in the middle area, and is the most peripheral in the middle area. The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is three. Further, the total number of ring zones in the central region × focal length N · f when using BD is 182.6 mm.

(Example 2)
The objective lens of Example 2 is a plastic single lens. Table 2 shows lens data. A conceptual diagram of the first optical path difference providing structure of Example 2 is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of Example 2). In the first optical path difference providing structure of Example 2, the (1/1/1) blaze is added to the second basic structure BS2 which is a (2/1/1) blazed diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 2, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 2, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure above is 1, and the number of ring zones of the third foundation structure on the ring zone of the fourth foundation structure closest to the center area in the middle area is 2, and the most peripheral area in the middle area The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is two. Further, the total number of ring zones in the central region × focal length N · f when using BD is 200.2 mm.

(Example 3)
The objective lens of Example 3 is a plastic single lens. Table 3 shows lens data. A conceptual diagram of the first optical path difference providing structure of the third embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the third embodiment). In the first optical path difference providing structure of Example 3, the (1/1/1) blaze is added to the second basic structure BS2 that is a (2/1/1) blaze-type diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 3, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 3, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure is 2, and the number of ring zones of the third foundation structure is 3 on the ring zone of the fourth foundation structure closest to the center area in the middle area, and is the most peripheral in the middle area. The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is three. Further, the total number of ring zones in the central region × focal length N · f when using BD is 198.0 mm.

Example 4
The objective lens of Example 4 is a plastic single lens. Table 4 shows the lens data. A conceptual diagram of the first optical path difference providing structure of the fourth embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the fourth embodiment). In the first optical path difference providing structure of Example 4, the (1/1/1) blaze is added to the second basic structure BS2 that is a (2/1/1) blaze-type diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 4, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 2, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure above is 1, and the number of ring zones of the third foundation structure on the ring zone of the fourth foundation structure closest to the center area in the middle area is 2, and the most peripheral area in the middle area The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is two. Further, the total number of ring zones in the central region × focal length N · f when using BD is 206.8 mm.

(Example 5)
The objective lens of Example 5 is a plastic single lens. Table 5 shows lens data. A conceptual diagram of the first optical path difference providing structure of the fifth embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the fifth embodiment). In the first optical path difference providing structure of Example 5, the (1/1/1) blaze is added to the second basic structure BS2 that is a (2/1/1) blaze-type diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 5, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 3, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure above is 1, and the number of ring zones of the third foundation structure on the ring zone of the fourth foundation structure closest to the center area in the middle area is 2, and the most peripheral area in the middle area The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is two. Further, the total number of ring zones in the central region × focal length N · f when using BD is 209.0 mm.

(Example 6)
The objective lens of Example 6 is a plastic single lens. Table 6 shows lens data. A conceptual diagram of the first optical path difference providing structure of Example 6 is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of Example 6). In the first optical path difference providing structure of Example 6, the (1/1/1) blaze is added to the second basic structure BS2 that is a (2/1/1) blaze-type diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 6, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 3, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure is 2, and the number of ring zones of the third foundation structure is 3 on the ring zone of the fourth foundation structure closest to the center area in the middle area, and is the most peripheral in the middle area. The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is five. Further, the total number of ring zones in the central region × focal length N · f when using BD is 167.7 mm.

(Example 7)
The objective lens of Example 7 is a plastic single lens. Table 7 shows the lens data. A conceptual diagram of the first optical path difference providing structure of the seventh embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the seventh embodiment). In the first optical path difference providing structure of Example 7, the (1/1/1) blaze is added to the second basic structure BS2 which is a (2/1/1) blaze-type diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 7, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 3, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure is 2, and the number of ring zones of the third foundation structure is 3 on the ring zone of the fourth foundation structure closest to the center area in the middle area, and is the most peripheral in the middle area. The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is three. Further, the total number of annular zones in the central region × focal length N · f when using BD is 180.0 mm.

(Example 8)
The objective lens of Example 8 is a plastic single lens. Table 8 shows lens data. A conceptual diagram of the first optical path difference providing structure of the eighth embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the eighth embodiment). The first optical path difference providing structure of Example 8 has a (1/1/1) blaze in the second basic structure BS2 that is a (2/1/1) blaze-type diffractive structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 8, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 3, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure is 2, and the number of ring zones of the third foundation structure is 3 on the ring zone of the fourth foundation structure closest to the center area in the middle area, and is the most peripheral in the middle area. The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is five. Further, the total number of ring zones in the central region × focal length N · f when using BD is 167.7 mm.

Example 9
The objective lens of Example 9 is a plastic single lens. Table 9 shows the lens data. A conceptual diagram of the first optical path difference providing structure of the ninth embodiment is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of the ninth embodiment). In the first optical path difference providing structure of Example 9, the (1/1/1) blaze is added to the second basic structure BS2 which is a (2/1/1) blaze-type diffractive structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 9, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 2, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure above is 1, and the number of ring zones of the third foundation structure on the ring zone of the fourth foundation structure closest to the center area in the middle area is 2, and the most peripheral area in the middle area The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is two. Further, the total number of ring zones in the central region × focal length N · f when using BD is 187.1 mm.

(Example 10)
The objective lens of Example 10 is a plastic single lens. Table 10 shows lens data. A conceptual diagram of the first optical path difference providing structure of Example 10 is shown in FIG. 6A (FIG. 6A is a conceptual diagram different from the actual shape of Example 10). In the first optical path difference providing structure of Example 10, the (1/1/1) blaze is added to the second basic structure BS2 which is a (2/1/1) blazed diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 10, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 3, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure above is 2, and the number of ring zones of the third foundation structure on the ring zone of the fourth foundation structure closest to the center area in the intermediate area is 2, and the most peripheral area in the intermediate area The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is two. Further, the total number of ring zones in the central region × focal length N · f when using BD is 174.8 mm.

(Example 11)
The objective lens of Example 11 is a plastic single lens. Table 11 shows the lens data. A conceptual diagram of the first optical path difference providing structure of Example 11 is shown in FIG. 6A (FIG. 6A is different from the actual shape of Example 11 and is merely a conceptual diagram). In the first optical path difference providing structure of Example 11, the (1/1/1) blaze is added to the second basic structure BS2 which is a (2/1/1) blazed diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA.

  In Example 11, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 3, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure above is 2, and the number of ring zones of the third foundation structure on the ring zone of the fourth foundation structure closest to the center area in the intermediate area is 2, and the most peripheral area in the intermediate area The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is two. Further, the total number of ring zones in the central region × focal length N · f when using BD is 170.9 mm.

  Table 12 summarizes the numerical values of the formulas defined in the claims corresponding to the above embodiments.

  8 (a) to 18 (a) are longitudinal spherical aberrations when BD is used in the embodiment, and FIGS. 8 (b) to 18 (b) are longitudinal spherical aberrations when DVD is used in the embodiment. The effective diameter is shown as 1. 8A to 18A, b1 is the 0th-order diffracted light generated in the (1/1/1) structure, and the second-order diffracted light generated in the (2/1/1) structure. b2 is the first order diffracted light generated in the (1/1/1) structure, and b2 is the third order diffracted light generated in the (2/1/1) structure. b3 is the first order diffracted light generated in the (1/1/1) structure, and b2 is the second order diffracted light generated in the (2/1/1) structure. b4 is the first-order diffracted light generated in the (1/1/1) structure, and b1 is the first-order diffracted light generated in the (2/1/1) structure. b5 is the second-order diffracted light generated in the (1/1/1) structure, and b2 is the second-order diffracted light generated in the (2/1/1) structure. Here, information is recorded / reproduced with respect to the BD using b3, and b1, b2, b4, and b5 are all unnecessary light. As is apparent from FIGS. 8A to 18A, since all unnecessary light is collected at a position away from b3, an error signal may be generated even when a BD having a plurality of information recording layers is used. There are few.

  Further, in FIGS. 8B to 18B, d1 is the 0th-order diffracted light generated in the (1/1/1) structure, and the first-order diffracted light generated in the (2/1/1) structure. Shows the effective diameter of CD as 1. d2 is the first-order diffracted light generated in the (1/1/1) structure, and d2 is the second-order diffracted light generated in the (2/1/1) structure. d3 is the first-order diffracted light generated in the (1/1/1) structure, and is the first-order diffracted light generated in the (2/1/1) structure. d4 is the 1st-order diffracted light generated in the (1/1/1) structure and the 0th-order diffracted light generated in the (2/1/1) structure. d5 is the second-order diffracted light generated in the (1/1/1) structure, and is the first-order diffracted light generated in the (2/1/1) structure. Here, information is recorded / reproduced with respect to the DVD using d3, and d1, d2, d4, and d5 are all unnecessary light. As is apparent from FIGS. 8B to 18B, since all unnecessary light is condensed at a position away from d3, an error signal may be generated even when a DVD having a plurality of information recording layers is used. There are few.

  Another embodiment 12 will be described. In the case of the twelfth embodiment, the optical path difference given to the light flux of each wavelength by the diffractive structure is defined by an equation obtained by substituting the coefficient shown in the table into the optical path difference function of Formula 3.

Here, h is the height from the optical axis, λ is the wavelength of the incident light beam, m is the diffraction order, and B _2i is the coefficient of the optical path difference function.

(Example 12)
The objective lens of Example 12 is a plastic single lens. The conceptual diagram of the first optical path difference providing structure of Example 12 is the same as FIG. In the first optical path difference providing structure of Example 12, the (1/1/1) blaze is added to the second basic structure BS2 that is a (2/1/1) blaze-type diffraction structure in the entire central region. The first basic structure BS1, which is a diffractive structure of the mold, is an optical path difference providing structure that is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA. Further, the average pitch of the first foundation structure BS1 is smaller than the average pitch of the second foundation structure BS2, and the number of steps facing the direction opposite to the optical axis of the first foundation structure is the second foundation structure. This is more than the number of steps facing the direction of the optical axis. In the first basic structure BS1 and the second basic structure BS2, when the wavelength of the incident light beam is changed to be longer, the spherical aberration is changed in the direction of insufficient correction.

  Further, the second optical path difference providing structure of Example 12 is an optical path in which only the third basic structure that is the same as the first basic structure and the fourth basic structure that is the same as the second basic structure are overlapped in the entire intermediate region. It has a difference giving structure. The step of the third foundation structure faces in the opposite direction to the optical axis, and the step of the fourth foundation structure faces the optical axis. When the wavelength of the incident light beam is changed to be longer in the third basic structure, the spherical aberration is changed in the overcorrection direction, and the wavelength of the incident light beam is changed to be longer in the fourth basic structure. The spherical aberration changes in the direction of insufficient correction.

  The third optical path difference providing structure of Example 12 is composed of only the sixth basic structure. In the sixth basic structure, the second-order diffracted light amount of the first light beam that has passed through the sixth basic structure is made larger than the diffracted light amount of any other order, and the first-order diffraction of the second light beam that has passed through the sixth basic structure. This is a blaze-type diffractive structure in which the amount of light is made larger than any other order of diffracted light, and the first order diffracted light of the third light beam that has passed through the sixth basic structure is made larger than any other order of diffracted light.

  Table 13 shows lens data of Example 12.

  Regarding the wavelength characteristics of the BD of Example 12, when the light source wavelength fluctuates by +5 nm, the third-order spherical aberration is −1 mλrms and the fifth-order spherical aberration is 1 mλrms.

  In Example 12, the number of ring zones of the first foundation structure on the zone of the second foundation structure closest to the optical axis in the center region is 2, and the zone of the second foundation structure closest to the middle region in the center region The number of ring zones of the first foundation structure above is 2, and the number of ring zones of the third foundation structure on the ring zone of the fourth foundation structure closest to the center area in the intermediate area is 2, and the most peripheral area in the intermediate area The number of zones of the third foundation structure on the zone of the fourth foundation structure close to the region is two.

  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

Furthermore, when one of a plurality of information recording layers is selected in the BD to form a focused spot, a coupling lens such as a collimator is moved in the direction of the optical axis, and the substrate thickness up to the selected information recording layer is determined. The spherical aberration accompanying the change is corrected. Therefore, even when the DVD is used, for example, spherical aberration caused by a change in the refractive index of the objective lens when the environmental temperature changes can be similarly corrected by moving the coupling lens in the optical axis direction.

However, in consideration of complicated control of the drive that drives the coupling lens, it may be desirable not to move the coupling lens when using a DVD. Also, when using a BD, all the luminous flux that has passed through the effective diameter of the objective lens is used to form a converging spot, so that flare light does not naturally occur. On the other hand, when using a DVD, an NA lower than that of the BD is ensured. Therefore, a part of the light flux is made flare light. In such a case, if the coupling lens is moved in the optical axis direction, flare light is erroneously detected, which may generate an error signal that hinders information recording / reproduction. Therefore, there is a demand for fixing the coupling lens when using the DVD. Therefore, there is a problem that it is desired to improve the temperature characteristics and wavelength characteristics of the objective lens when the DVD is used.

The objective lens according to claim 1 emits a first light source that emits a first light flux having a first wavelength λ1 (390 nm ≦ λ1 ≦ 415 nm) and a second light flux that has a second wavelength λ2 (630 nm ≦ λ2 ≦ 670 nm). And a third light source that emits a third light beam having a third wavelength λ3 (760 nm ≦ λ3 ≦ 820 nm), and a protective substrate having a thickness t1 using the first light beam. Recording and / or reproducing information, recording and / or reproducing information of a DVD having a protective substrate with a thickness of t2 (t1 <t2) using the second light beam, and using the third light beam An objective lens used in an optical pickup device for recording and / or reproducing information of a CD having a protective substrate having a thickness of t3 (t2 <t3),
The optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region,
The central region has a first optical path difference providing structure,
The objective lens condenses the first light flux that passes through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that passes through the central region. Are recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the central region is recorded and / or recorded on the information recording surface of the CD. Or collect it so that it can be regenerated,
The objective lens condenses the first light flux passing through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the intermediate area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the intermediate region is recorded and / or recorded on the information recording surface of the CD. Or do not concentrate so that it can be regenerated,
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the peripheral area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the peripheral area is recorded on the information recording surface of the CD. And / or do not collect light for playback
The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
The first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and 1 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, making the first 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 second-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 1 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, making the first 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 first basic structure provided at least near the optical axis of the central region has a step in a direction opposite to the optical axis,
The second basic structure provided at least in the vicinity of the optical axis of the central region has a step facing the direction of the optical axis,
The first foundation structure and the second foundation structure are blazed, and 2 to 5 annular zones of the first foundation structure are included on one annular zone closest to the optical axis in the second foundation structure. It is characterized by that.

In order to deal with a BD having a plurality of information recording layers, it is conceivable that when a BD is used, the coupling lens is moved in the optical axis direction so as to correspond to recording / reproduction on each information recording layer. In such a case, the function of moving the coupling lens in the optical axis direction is indispensable, but when using a DVD, the coupling lens may be fixed without moving in the optical axis direction. is there. The reason is that flare does not occur when BD is used, but flare occurs when DVD is used. Therefore, by moving the coupling lens, the flare aberration changes, and as a result, the flare adversely affects recording / reproduction. The reason for this is that there is a possibility that the control will be given, and the reason for wanting to simplify the control of the coupling lens in the drive. For such a problem, coupled with the effect of superimposing the first foundation structure and the second foundation structure, the first foundation structure and the second foundation structure are blazed, and the light in the second foundation structure is By using an objective lens including 2 to 5 ring zones of the first basic structure on one ring zone closest to the axis, temperature characteristics and wavelength characteristics when using a DVD can be improved. This is preferable because it is not necessary to move the coupling lens when using the DVD.

2. The invention according to claim 1, wherein the first basic structure provided at least in the vicinity of the optical axis of the central region has a step in a direction opposite to the optical axis, and at least in the vicinity of the optical axis of the central region. In the first optical path difference providing structure in which the first basic structure and the second basic structure are overlapped with each other, the second basic structure provided on the first basic structure overlaps the optical axis direction. Can be further reduced, thereby further suppressing a decrease in diffraction efficiency when the wavelength varies .

According to a second aspect of the present invention, there is provided the objective lens according to the first aspect, wherein the first basic structure provided in the central region is such that all steps are directed in a direction opposite to the optical axis, The second basic structure provided in the region is characterized in that all the steps are directed in the direction of the optical axis .

The optical pickup device according to claim 10 is the invention according to claim 9,
A coupling lens through which at least the first light flux and the second light flux pass, and an actuator for moving the coupling lens in the optical axis direction;
When the first light beam passes, the actuator moves the coupling lens in the optical axis direction,
When the second light beam passes, the coupling lens is fixed in a position in the optical axis direction.

For example, in order to support a BD having a plurality of information recording layers, it is conceivable that when a BD is used, the coupling lens is moved in the optical axis direction so as to correspond to recording / reproduction on each information recording layer. In such a case, the function of moving the coupling lens in the optical axis direction is indispensable. However, when using a DVD, the coupling lens may be fixed without moving in the optical axis direction. is there. The reason is that flare does not occur when using BD, but flare occurs when using DVD. By moving the coupling lens, the flare aberration changes, and as a result, the flare is recorded / reproduced. The reason is that there is a possibility of adversely affecting the driving force, and the reason why it is desired to simplify the control of the movement of the coupling lens by the drive. For such a problem, by using the objective lens of the present invention to improve both the temperature characteristic and the wavelength characteristic when using the DVD, as a result, the coupling occurs when the second light beam passes when using the DVD. Even in a state where the position of the lens in the optical axis direction is fixed, information can be recorded / reproduced with respect to the information recording surface of the DVD, and the above-mentioned problems can be solved.

The reason is that flare does not occur when using BD, but flare occurs when using DVD. By moving the coupling lens, the flare aberration changes, and as a result, the flare is recorded / reproduced. The reason for this is that there is a possibility of adversely affecting the drive, and the reason for wanting to simplify the control of the movement of the coupling lens in the drive.

However, in consideration of complicated control of the drive that drives the coupling lens, it may be desirable not to move the coupling lens when using a DVD. Also, when using a BD, all the luminous flux that has passed through the effective diameter of the objective lens is used to form a converging spot, so that flare light does not naturally occur. On the other hand, when using a DVD, an NA lower than that of the BD is ensured. Therefore, a part of the light flux is made flare light. In such a case, if the coupling lens is moved in the optical axis direction, flare light is erroneously detected, which may generate an error signal that hinders information recording / reproduction. Therefore, there is a demand for a pickup device to cause a problem of fixing a coupling lens when using a DVD. For this reason, the objective lens has a problem that it is desired to improve the temperature characteristics and wavelength characteristics of the objective lens when the DVD is used.

An object of the present invention is to solve the above-mentioned problems. While reducing costs, a working distance when using a CD is ensured so that three types of optical disks of BD / DVD / CD can be compatible. While using a common objective lens, the adverse effect of unnecessary light reflected by layers other than the target layer can be reduced even when using an optical disc having multiple layers, and the temperature and wavelength characteristics when using a DVD are reduced. improved, and to provide an objective lens which can suppress a variation of the diffraction efficiency at a wavelength change, and an optical pickup apparatus and optical information recording reproducing equipment with these objective lenses.

The objective lens according to claim 1 emits a first light source that emits a first light flux having a first wavelength λ1 (390 nm ≦ λ1 ≦ 415 nm) and a second light flux that has a second wavelength λ2 (630 nm ≦ λ2 ≦ 670 nm). And a third light source that emits a third light beam having a third wavelength λ3 (760 nm ≦ λ3 ≦ 820 nm), and a protective substrate having a thickness t1 using the first light beam. Recording and / or reproducing information, recording and / or reproducing information of a DVD having a protective substrate with a thickness of t2 (t1 <t2) using the second light beam, and using the third light beam An objective lens used in an optical pickup device for recording and / or reproducing information of a CD having a protective substrate having a thickness of t3 (t2 <t3),
The optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region,
The central region has a first optical path difference providing structure,
The objective lens condenses the first light flux that passes through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that passes through the central region. Are recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the central region is recorded and / or recorded on the information recording surface of the CD. Or collect it so that it can be regenerated,
The objective lens condenses the first light flux passing through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the intermediate area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the intermediate region is recorded and / or recorded on the information recording surface of the CD. Or do not concentrate so that it can be regenerated,
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the peripheral area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the peripheral area is recorded on the information recording surface of the CD. And / or do not collect light for playback
The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
The first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and 1 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, making the first 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 second-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 1 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, making the first 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 first basic structure provided at least near the optical axis of the central region has a step in a direction opposite to the optical axis,
The second basic structure provided at least in the vicinity of the optical axis of the central region has a step facing the direction of the optical axis,
The first foundation structure and the second foundation structure are blazed, and 2 to 5 annular zones of the first foundation structure are included on one annular zone closest to the optical axis in the second foundation structure. Further , it is characterized in that the generated aberration when the wavelength is changed and the generated aberration when the temperature is changed when information is recorded and / or reproduced on the information recording surface of the DVD is reduced .

Claims (11)

A first light source that emits a first light beam with a first wavelength λ1 (390 nm ≦ λ1 ≦ 415 nm), a second light source that emits a second light beam with a second wavelength λ2 (630 nm ≦ λ2 ≦ 670 nm), and a third wavelength λ3 A third light source that emits a third light beam (760 nm ≦ λ3 ≦ 820 nm), and recording and / or reproducing information of a BD having a protective substrate with a thickness of t1 using the first light beam, Recording and / or reproducing information of a DVD having a protective substrate having a thickness of t2 (t1 <t2) using the second light flux, and having a thickness of t3 (t2 <t3) using the third light flux. An objective lens used in an optical pickup device for recording and / or reproducing information of a CD having a protective substrate,
The optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region,
The central region has a first optical path difference providing structure,
The objective lens condenses the first light flux that passes through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux that passes through the central region. Are recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the central region is recorded and / or recorded on the information recording surface of the CD. Or collect it so that it can be regenerated,
The objective lens condenses the first light flux passing through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the intermediate area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the intermediate region is recorded and / or recorded on the information recording surface of the CD. Or do not concentrate so that it can be regenerated,
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passes through the peripheral area. Is recorded on the information recording surface of the DVD so that information can be recorded and / or reproduced, and the third light flux passing through the peripheral area is recorded on the information recording surface of the CD. And / or do not collect light for playback
The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
The first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and 1 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, making the first 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 second-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 1 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, making the first 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 first foundation structure and the second foundation structure are blazed, and 2 to 5 annular zones of the first foundation structure are included on one annular zone closest to the optical axis in the second foundation structure. Objective lens characterized by that. The first basic structure provided at least near the optical axis of the central region has a step in a direction opposite to the optical axis,
2. The objective lens according to claim 1, wherein the step of the second basic structure provided at least near the optical axis of the central region is directed in the direction of the optical axis. The intermediate region has a second optical path difference providing structure in which at least a third basic structure and a fourth basic structure are overlapped,
The third basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the third basic structure larger than any other order of diffracted light quantity, so that 1 of the second light flux that has passed through the third basic structure. Make the next diffracted light quantity larger than any other order diffracted light quantity,
In the fourth basic structure, the second-order diffracted light amount of the first light beam that has passed through the fourth basic structure is made larger than any other order of diffracted light amount, and 1st of the second light beam that has passed through the fourth basic structure. 3. The objective lens according to claim 1, wherein the next diffracted light amount is made larger than any other order diffracted light amount.   The third foundation structure and the fourth foundation structure are blazed, and include one to three ring zones of the third foundation structure on one ring zone closest to the central region in the fourth foundation structure. The objective lens according to claim 3, wherein the objective lens is provided. In the third basic structure provided near the boundary with the central region, the step is directed in the direction opposite to the optical axis,
5. The objective lens according to claim 3, wherein the step of the fourth basic structure provided in the vicinity of the boundary with the central region is directed in the direction of the optical axis.   The said intermediate | middle area | region is provided only with the said 3rd foundation structure and the said 4th foundation structure, The other foundation structure is not provided, The any one of Claims 3 thru | or 5 characterized by the above-mentioned. Objective lens.   The ring zone closest to the intermediate region in the second foundation structure includes 1 to 5 zones of the first foundation structure, according to any one of claims 1 to 6. Objective lens described in 1. The objective lens according to claim 1, wherein the following expression is satisfied.
160 (mm) ≤ N · f ≤ 210 (mm) (1)
Here, the total number of annular zones in the central region is N, and the focal length of the objective lens in the first light flux is f (mm).   An optical pickup device comprising the objective lens according to claim 1. A coupling lens through which at least the first luminous flux and the second luminous flux pass, and an actuator for moving the coupling lens in the optical axis direction;
When the first light beam passes, the coupling lens can be displaced in the optical axis direction by the actuator;
The optical pickup device according to claim 9, wherein when the second light beam passes, the coupling lens is fixed in a position in an optical axis direction.   An optical information recording / reproducing apparatus comprising the optical pickup apparatus according to claim 9.