WO2013114662A1

WO2013114662A1 - Objective lens for optical pickup device, and optical pickup device

Info

Publication number: WO2013114662A1
Application number: PCT/JP2012/073785
Authority: WO
Inventors: 中塚雄三
Original assignee: コニカミノルタ株式会社
Priority date: 2012-02-03
Filing date: 2012-09-18
Publication date: 2013-08-08

Abstract

Provided is an optical pickup device equipped with an objective lens that can combine off-axis characteristics and is easy to adjust at assembly time while making it possible to exchange three types of optical discs, i.e., BD/DVD/CD, by using a common objective lens. Also provided is an objective lens suitable for the optical pickup device. A first optical path difference imparting structure provided in the center region of the objective lens features at least a first substructure and a second substructure stacked one atop the other, and a second optical path difference imparting structure provided in the center region features at least a third substructure and a fourth substructure stacked one atop the other. When a DVD is being used, a second light beam enters the objective lens as a convergent beam.

Description

Objective lens for optical pickup device and optical pickup device

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

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, it is possible to record 15 to 20 GB of information on an optical disk having a diameter of 12 cm when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used. 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.

BD (Blu-ray Disc) is an example of an optical disc that uses an NA 0.85 objective lens as described above. Since the coma generated due to the tilt (skew) of the optical disk increases, the BD has a thinner protective substrate (0.1 mm with respect to 0.6 mm of DVD) than the case of the DVD cage, and is caused by skew. The amount of coma is reduced.

By the way, simply saying that information can be recorded / reproduced appropriately with respect to a BD cannot be said to be sufficient as a product of an optical disc player / recorder (optical information recording / reproducing apparatus). 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.

By the way, in the case where an objective lens is provided with an optical path difference providing structure to achieve compatibility, for example, if an attempt is made to improve the off-axis characteristics of a BD, the off-axis characteristics of the DVD are lowered. When the off-axis characteristic of the DVD is lowered, the lens tilt sensitivity is lowered, so that adjustment such as tilting the objective lens to cancel the residual coma aberration becomes difficult. On the other hand, if it is attempted to improve the off-axis characteristics of a DVD, the BD off-axis characteristics deteriorate. Thus, since there is a trade-off relationship between the off-axis characteristics of the BD and the off-axis characteristics of the DVD, it is difficult to achieve both.

Here, Patent Document 1 discloses an objective lens in which a diffractive structure is provided in a common region through which light beams condensed on three optical disks pass and a finite light beam is incident. However, as described in paragraph [0011] of Patent Document 1, such conventional technology uses light incident on the objective lens as a finite light beam in order to eliminate the drawbacks of the diffractive structure (to correct spherical aberration). There is no mention of the problem of off-axis characteristics as described above.

JP 2006-252602 A

The present invention is intended to solve the above-described problems, and enables compatibility of three types of optical discs of BD / DVD / CD with a common objective lens while achieving both off-axis characteristics. An object of the present invention is to provide an optical pickup device including an objective lens that can be easily adjusted during assembly, and an objective lens suitable for the optical pickup device.

The objective lens according to claim 1, wherein a first light source that emits a first light beam having a first wavelength λ1, a second light source that emits a second light beam having a second wavelength λ2 (λ2> λ1), and a third wavelength. a third light source that emits a third light beam having a wavelength of λ3 (λ3> λ2), and recording and / or reproducing information on a first optical disk having a protective substrate with a thickness of t1 using the first light beam. Recording and / or reproducing information on the second optical disc having a protective substrate having a thickness t2 (t1 <t2) using the second light flux, and a thickness t3 (t2 <t) using the third light flux. an objective lens used in an optical pickup device for recording and / or reproducing information of a third optical disc having a protective substrate at 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 intermediate region has a second optical path difference providing structure,
The objective lens condenses the first light flux that passes through the central area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the central area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the central region is condensed on the information recording surface of the third optical disc. Condensing so that information can be recorded and / or reproduced,
The objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the intermediate area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the intermediate region is condensed on the information recording surface of the third optical disc. Without collecting light so that information can be recorded and / or reproduced.
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the peripheral area. The second light flux is not condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc, and the third light flux passing through the peripheral region is used as the information recording surface of the third optical disc. Do not concentrate so that information can be recorded and / or reproduced
The 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 A-order diffracted light quantity of the first light flux that has passed through the first basic structure larger than any other order diffracted light quantity, and B of the second light flux that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The first basic structure is a blaze-type structure;
The second basic structure makes the D-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and the E of the second light beam that has passed through the second basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the F-order diffracted light quantity of the third light flux that has passed through the second basic structure larger than any other order diffracted light quantity,
The second optical path difference providing structure is a structure in which at least a third basic structure and a fourth basic structure are overlapped,
The third basic structure makes the G-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, so that the H of the second light beam that has passed through the third basic structure. Make the next diffracted light quantity larger than any other order diffracted light quantity,
The third basic structure is a blazed structure;
In the fourth basic structure, the first-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 the second light beam J that has passed through the fourth basic structure has J Make the next diffracted light quantity larger than any other order diffracted light quantity,
The fourth basic structure is a blazed structure.
When the second optical disk is used, the second light beam is incident on the objective lens in a convergent light state.

The present inventor has found a method for solving the problems of the prior art by a novel approach. First, the inventor paid attention to the advantage of configuring an optical path difference providing structure by superimposing a plurality of basic structures. More specifically, in order to perform recording / reproduction of information interchangeably with optical discs having different specifications using a common objective lens, the information is caused by the transparent substrate thickness of the optical disc and the wavelength difference of the light beam used. Although the spherical aberration must be canceled, the spherical aberration can be canceled by providing a predetermined optical path difference in the optical path difference providing structure. However, in the case of the optical path difference providing structure having a single structure, there is a problem that the usable optical system magnification is limited. On the other hand, when the optical path difference providing structure is formed by superimposing a plurality of basic structures, the degree of freedom of the optical path difference that can be set increases, so that the third-order spherical aberration generated thereby can be controlled. That is, the optical system magnification is not limited, and the magnification can be interchanged while ensuring the degree of design freedom. The present inventor pays attention to such characteristics and uses the optical path difference providing structure in which a plurality of basic structures are superposed to reduce the limitation on the optical system magnification. It has been found that the off-axis characteristics of the can be improved. However, when the first light beam is incident, since it has a high NA, the influence on coma aberration and the like is large, and therefore it can be said that it is preferable to enter a parallel light beam, a substantially parallel light beam, or the like on the objective lens. On the other hand, since the NA is relatively low when the second light beam is incident, there is no significant problem even if the convergent light beam is incident on the objective lens, and the off-axis characteristics can be improved thereby. In other words, when the DVD is used, the second light beam is incident on the objective lens in the state of convergent light, thereby improving the off-axis characteristics when using the DVD while maintaining the off-axis characteristics when using the BD. This makes it easier to adjust the coma aberration due to the lens tilt especially when the second light beam is incident.

The objective lens described in claim 2 is characterized in that, in the invention described in claim 1, the following expression is satisfied.
0 <m2 <0.16 (1)
However, m2 represents the magnification of the objective lens when the second light beam is incident on the objective lens.

By satisfying the range of formula (1), off-axis characteristics when using a DVD can be improved more effectively.

According to a third aspect of the present invention, there is provided the objective lens according to the first or second aspect, wherein A = G = 1, B = H = 1, C = 1, D = I = 2, E = J = 1, F. = 1.

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 amount of the third light beam that has passed through the first light beam is larger than any other order diffracted light amount, the first basic structure is a blazed structure, and the second basic structure is the second basic structure The second-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 second basic structure is greater than any other order of diffracted light amount. And pass through the second foundation structure By making the first order diffracted light quantity of the third light beam larger than any other order diffracted light quantity, the second foundation structure is a blazed structure, so that at least the first foundation structure and the second foundation structure It has been found that in the first optical path difference providing structure in which the two are stacked, the amount of step in the optical axis direction can be reduced, thereby suppressing the decrease in diffraction efficiency when the wavelength varies.

Further, the second optical path difference providing structure is a structure in which at least a third basic structure and a fourth basic structure are overlapped, and the third basic structure is one of the first light flux that has passed through the third basic structure. The next diffracted light quantity is made larger than any other order diffracted light quantity, and the first diffracted light quantity of the second light flux that has passed through the third basic structure is made larger than any other order diffracted light quantity, The basic structure is a blazed structure, and the fourth basic structure makes the second diffracted light quantity of the first light flux that has passed through the fourth basic structure larger than the diffracted light quantity of any other order. By making the first-order diffracted light quantity of the second light flux that has passed through the structure larger than any other order diffracted light quantity, the fourth base structure is a blazed structure, so that at least the third base structure and the The above 4th superposed with 4 basic structures In the optical path difference providing structure, it is possible to reduce the step difference amount in the optical axis direction, whereby it was found that a reduction in the diffraction efficiency at the time of wavelength variation can be suppressed.

Here, when referring to “first-order diffracted light” in the claims, the diffraction direction is not limited, so the actual diffracted light is a concept including both + 1st-order diffracted light and −1st-order diffracted light. is there. However, it is assumed that the signs (±) of the diffracted lights generated for the first light flux, the second light flux, and the third light flux in the same portion of the same basic structure match.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the working distance when using the second optical disc is equal to or greater than the working distance when using the third optical disc. And

If the second light beam is incident on the objective lens in the state of convergent light, the working distance may be shortened. However, if at least the working distance when using the second optical disk is greater than or equal to the working distance when using the third optical disk, it can be said that there is no particular problem in actual use.

The objective lens according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 4, the working distance when the second optical disk is used is 0.25 mm or more.

Therefore, it can be said that there is no problem in actual use.

The objective lens according to claim 6 is generated when the objective lens is shifted by 0.2 mm in the direction perpendicular to the optical axis when the second optical disk is used in the invention according to any one of claims 1 to 5. Aberration is characterized by being below the Marechal limit (0.07λrms).

Since the second light flux is in the state of convergent light, wavefront aberration occurs when the objective lens is shifted in the direction perpendicular to the optical axis, but the amount of wavefront aberration generated when shifted by 0.2 mm is below the Marshall limit. Therefore, it can be said that there is no problem in practical use.

According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the third light beam is incident on the objective lens in a parallel light state when the third optical disk is used. It is characterized by becoming.

The objective lens according to claim 8 is the invention according to any one of claims 1 to 6, wherein when the third optical disk is used, the third light beam is incident on the objective lens in a state of convergent light or divergent light. It is designed to do this. As a result, it is possible to improve off-axis characteristics when using the third optical disk and lengthen the working distance when using the third optical disk while maintaining the off-axis characteristics when using the first optical disk.

The objective lens according to claim 9 is the third-order coma aberration generated when the second light flux having an angle of view of 0.5 degrees is incident on the objective lens in the invention according to any one of claims 1 to 8. DVD-CM3 is characterized by being 40 mλrms or less.

This can improve off-axis characteristics when using a DVD. Preferably, the DVD-CM3 is 10 mλrms or less.

An objective lens according to a tenth aspect is the third-order coma aberration generated when the first light flux having an angle of view of 0.5 degrees is incident on the objective lens in the invention according to any one of the first to ninth aspects. The sum of the BD-CM3 and the third-order coma aberration DVD-CM3 generated when the second light flux having an angle of view of 0.5 degrees is incident on the objective lens is 40 mλrms or less.

This ensures a good balance between off-axis characteristics when using BD and off-axis characteristics when using DVD. Preferably, (BD−CM3 + DVD−CM3) is 10 mλrms or less.

An optical pickup device according to an eleventh aspect includes the objective lens according to any one of the first to tenth aspects.

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.

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. Further, 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 to 440 nm, more preferably 390 nm to 415 nm, and the second wavelength λ2 of the second light source is preferably 570 nm to 680 nm, 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.

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

As the light receiving element, a photodetector such as a photodiode is preferably used. Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking I can do it. The light receiving element may comprise a plurality of photodetectors. The light receiving element may have a main photodetector and a sub photodetector. For example, two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. 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 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. The resin material has a refractive index within a range of 1.50 to 1.60 at a temperature of 25 ° C. with respect to a wavelength of 405 nm, and a wavelength of 405 nm according to 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.

(Wherein 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, a carbon number of 1 ˜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.)

(Wherein 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). Polymer (B) obtained by addition polymerization of polymer (A) and 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 the preferred 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-tert-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris ( , 5-di-t-butyl-4-hydroxybenzyl) benzene, tetrakis (methylene-3- (3 ', 5'-di-t-butyl-4'-hydroxyphenylpropionate)) methane [ie pentaerythris Limethyl-tetrakis (3- (3,5-di-tert-butyl-4-hydroxyphenylpropionate))], triethylene glycol bis (3- (3-tert-butyl-4-hydroxy-5-methylphenyl) ) Propionate) and other alkyl-substituted phenolic compounds; 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- Triazine group-containing phenol compounds such as triazine; 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-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-tert-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-pi Lysyl) 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)) Fight) 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 amount of each of these stabilizers is appropriately selected within a range not to 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, The amount is preferably 0.01 to 1 part by mass.

(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 a surfactant 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. On the other hand, it is preferable to add 0.01 to 10 parts by mass. The addition amount of the surfactant is more preferably 0.05 to 5 parts by mass, 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, tricitrate 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, butyl benzyl phthalate, dicyclyl phthalate Known materials such as hexyl, di-2-ethylhexyl sebacate, tri-2-ethylhexyl trimellitic acid, Santizer 278, Paraplex G40, Drapex 334F, Plastolein 9720, Mesamol, DNODP-610, HB-40, etc. are applicable. . The selection of the plasticizer and the addition amount are appropriately performed under the condition that the permeability of the copolymer and the resistance to environmental changes are not impaired.

As these resins, cycloolefin resins are preferably used. Specifically, ZEONEX manufactured by Nippon Zeon Co., Ltd., APEL manufactured by Mitsui Chemicals, Inc., TOPAS® ADVANCED® POLYMERS manufactured by TOPAS, and JSR manufactured by ARTON are preferable. Take as an example.

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

The objective lens is 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 / reproduction of BD (an example of the first optical disk), DVD (an example of the second optical disk), and CD (an example of the third optical disk). 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 region of the objective lens is used for BD recording / reproduction, and can be said to be a BD-dedicated region 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 referred to 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 a function 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.

Incidentally, it is preferable that the optical path difference providing structure has a plurality of concentric annular zones with the optical axis as the center. In addition, 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 blaze-type structure means that the cross-sectional shape including the optical axis of the optical element having the 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). . A two-level staircase structure is described below. A plurality of annular zones including a plurality of concentric annular zones around the optical axis, and a plurality of annular zones including the optical axis of the objective lens have a plurality of stepped surfaces Pa and Pb extending in parallel to the optical axis, The light source side terrace surface Pc for connecting the light source side ends of the adjacent step surfaces Pa and Pb and the optical disk side terrace surface Pd for connecting the optical disk side ends of the adjacent step surfaces Pa and Pb are formed. The surface Pc and the optical disc side terrace surface Pd are alternately arranged along the direction intersecting the optical axis.

In the staircase structure, the length in the direction perpendicular to the optical axis of one step unit is referred to as a pitch P.
(See FIGS. 3C and 3D) The length of the step in the direction parallel to the optical axis of the staircase is referred to as step amounts B1 and B2. In the case of a three-level or higher staircase structure, a large step amount B1 and a small step amount B2 exist. (See Fig. 3 (c))

The optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated. 「“ The unit shape is periodically repeated ”here 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.

When the optical path difference providing structure has a staircase structure, there may be a shape in which a 5-level stair unit as shown in FIG. Furthermore, it may be a shape in which the pitch of the staircase unit gradually increases as it moves away from the optical axis, or a shape in which the pitch of the staircase unit gradually decreases.

The first optical path difference providing structure and the second optical path difference providing structure may be provided on different optical surfaces of the objective lens, respectively, but are preferably provided on the same optical surface. Furthermore, also when providing a 3rd optical path difference providing structure, it is preferable to provide in the same optical surface as a 1st optical path difference providing structure and a 2nd optical path difference providing structure. Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing. In addition, the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the light source side surface of the objective lens rather than the surface of the objective lens on the optical disk side. In other words, the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the optical surface having the smaller absolute value of the radius of curvature of the objective lens.

Next, the first optical path difference providing structure provided in the central region will be described. 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 blaze type structure. In addition, the first basic structure makes the A-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and B of the second light flux that has passed through the first basic structure. The diffracted light amount is made larger than any other order diffracted light amount, and the C 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. This is called an (A / B / C) structure. A is preferably an odd number, and particularly preferably A = B = C = 1. 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 the diffraction efficiency fluctuation at the time of fluctuation can be reduced.

Further, it is preferable that the first basic structure provided at least in the vicinity of 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. (The shape as shown in FIG. 4B is also a blazed structure.) Further, the first basic structure provided “at least in the vicinity of the optical axis in the central region” is a step difference in the (A / B / C) structure. Of these, it is the level difference closest to the optical axis. Preferably, at least a step of the (A / B / C) structure existing between the optical axis and the half of the optical axis orthogonal direction from the optical axis to the boundary between the central region and the intermediate region and the optical axis is the optical axis. Is pointing in the opposite direction.

For example, in the first basic structure provided near the middle region of the central region, the step may be directed in the direction of the 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.

As described above, the direction of the step of the first basic structure in which the diffraction order of the first light flux is the A 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 B 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 blaze type structure. The second basic structure makes the D-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order diffracted light amount, and the E-order diffraction of the second light beam that has passed through the first basic structure. The light quantity is made larger than any other order of diffracted light quantity, and the F-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 (D / E / F) structure. It is preferable that D is an even number, and it is preferable that D = 2 and E = F = 1. 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.

Further, it is preferable that the step of the second basic structure provided at least in the vicinity of the optical axis in the central region is directed in the direction of the optical axis. “The level difference faces the direction of the optical axis” means a state as shown in FIG. (The shape as shown in FIG. 4A is also a blazed structure.) Further, the second basic structure provided “at least in the vicinity of the optical axis in the central region” is a level difference of the (D / E / F) structure. Of these, it is the level difference closest to the optical axis. 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 a step of the (D / E / F) structure 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 superposing the first basic structure having the (A / B / C) structure and the second basic structure having the (D / E / F) 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 also possible to provide a balanced objective lens. For example, it is possible to provide an objective lens having a diffraction efficiency of 80% or more for the wavelength λ1, a diffraction efficiency of 60% or more for the wavelength λ2, and a diffraction efficiency of 50% or more for the wavelength λ3. Furthermore, it is possible to provide an objective lens having a diffraction efficiency of 80% or more for the wavelength λ1, a diffraction efficiency of 70% or more for the wavelength λ2, and a diffraction efficiency of 60% or more for the wavelength λ3. 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 (A / B / C) structure and the second basic structure having the (D / E / F) structure are overlapped is expressed as follows. be able to. As an example, when A = B = C = 1, D = 2, and E = F = 1, the first optical path difference providing structure provided at least near the optical axis in the central region is opposite to the optical axis. Both the step facing the direction of the optical axis and the step facing the direction of the optical axis, the step amount d11 of the step facing the direction opposite to the optical axis, and the direction of the optical axis The step amount d12 of the step preferably satisfies 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)

Furthermore, as a method of overlapping the first foundation structure and the second foundation structure, the pitches of the first foundation structure and the second foundation structure are matched, the positions of all the steps of the second foundation structure, and the steps of the first foundation structure. It is preferable to match the positions of all the steps of the first foundation structure with the positions of the steps of the second foundation structure.

As described above, when all the steps of the second foundation structure and the steps of the first foundation structure are combined and overlapped, d11 and d12 of the first optical path difference providing structure are the following conditional expressions (11) , (12) is preferably satisfied. More preferably, the following conditional expressions (11) and (12) are satisfied in all the regions of the central region.
0.6 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (11)
0.6 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (12)

0.39 μm <d11 <1.15 μm (13)
0.39 μm <d12 <1.15 μm (14)

More preferably, the following conditional expressions (15) and (16) are preferably satisfied. More preferably, the following conditional expressions (15) and (16) ′ are satisfied in all the regions of the central region.
0.9 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (15)
0.9 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (16)

0.59 μm <d11 <1.15 μm (17)
0.59 μm <d12 <1.15 μm (18)

Further, in the first basic structure having the (A / B / C) 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 (D / In the second basic structure which is the E / F) structure, when the wavelength of the incident light beam is changed to be longer, it is preferable that the spherical aberration is changed in an undercorrected 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 contribution rate of the first foundation structure is dominant compared to the second foundation structure. From the viewpoint of making the contribution ratio of the first foundation structure dominant as compared with the second foundation structure, it is preferable that the average pitch of the first foundation structure is smaller than the average pitch of the second foundation structure. It should be noted that the axial chromatic aberration is reduced while ensuring a working distance in the CD, a good light spot is formed even when the light source causes high frequency superposition, and the optical disc has a plurality of information recording surfaces. In order to reduce the problem of stray light, in the first optical path difference providing structure, there are 2 to 5 ring zones of the first foundation structure (particularly preferable) for one ring zone closest to the optical axis of the second foundation structure. 2 to 3) are preferably included. More preferably, in the entire first 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 of the second foundation structure. That is. That is, the average pitch of the first foundation structure is preferably 1/5 or more and 1/2 or less (particularly preferably 1/3 or more and 1/2 or less) of the average pitch of the second foundation structure.

Further, it is preferable that the longitudinal chromatic aberration of the objective lens is 0.3 μm / nm or more and 0.6 μm / nm or less. In order to obtain such a configuration, as described above, in the first optical path difference providing structure, the ring zone of the first foundation structure is 2 to 1 ring zone closest to the optical axis of the second foundation structure. It is preferable to include 5 (particularly preferably 2 to 3). It is preferable to set the axial chromatic aberration in the above-mentioned range because the problem of stray light can be reduced when the optical disc has a plurality of information recording surfaces while ensuring the working distance in the CD.

The first best focus position where the light intensity of the spot formed by the third light flux is the strongest by the third light flux passing through the first optical path difference providing structure, and the second strongest light intensity of the spot formed by the third light flux. It is preferable that the best focus position satisfies the following conditional expression (19). Here, the best focus position refers to a position where the beam waist becomes a minimum within a certain defocus range. The first best focus position is the best focus position of the necessary light used for recording / reproduction of the third CD, and the second best focus position of the unnecessary light that is not used for recording / reproduction of the CD is the light flux having the largest amount of light. Best focus position.
0.05 ≦ L / f13 ≦ 0.35 (19)
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 (20) is satisfied.
0.10 ≦ L / f13 ≦ 0.25 (20)

A preferred example of the first optical path difference providing structure described above is shown in FIGS. 6 (a), 6 (b) and 6 (c). 6 (a), 6 (b), and 6 (c), the first optical path difference providing structure ODS1 is shown as a flat plate for convenience, but it is provided on a single aspherical convex lens. May be. A first foundation structure BS1 having an (A / B / C) structure is overlaid on a second foundation structure BS2 having a (D / E / F) 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 BS faces the direction opposite to the optical axis OA. Further, the pitches of the first foundation structure BS1 and the second foundation structure BS2 are matched, and it can be seen that the positions of all the steps of the second foundation structure and the positions of the steps of the first foundation structure match. In this example, as an example, when A = B = C = 1, D = 2, and E = F = 1, d1 = λ1 / (n−1) and d2 = λ1 / (n−1) ). In this example, if λ1 = 405 nm (0.405 μm) and n = 1.5592, d1 = d2 = 0.72 μm. 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 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.

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 basic structure and the fourth basic structure are blazed structures. Further, the G-order diffracted light quantity of the first light beam that has passed through the third basic structure is made larger than any other order diffracted light quantity, and the H-order diffracted light quantity of the second light beam that has passed through the third basic structure is changed to other values. The fourth diffracted light quantity is made larger than the diffracted light quantity of any order (also referred to as a (G / H) structure), and the fourth basic structure converts the I-order diffracted light quantity of the first light flux that has passed through the fourth basic structure into any other order. It is preferable that the J-order diffracted light amount of the second light flux that has passed through the fourth basic structure be larger than any other order diffracted light amount (also referred to as (I / J) structure). It is preferable that A = G, B = I, D = I, and E = J, and it is particularly preferable that G = 1, H = 1, I = 2, and J = 1. 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 even when the temperature and the wavelength are changed.

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 Kth-order diffracted light amount of the third light beam passing 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, K is ± 1. When K 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. When it changes, the spherical aberration may change in the direction of insufficient correction.

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 overcorrection (over) and undercorrection (under) will be described with reference to FIG. In FIG. 7, the vertical axis represents the height in the direction perpendicular to the optical axis from the optical axis, and the horizontal axis represents the aberration. The left side of the horizontal axis is negative and the right side is positive. Negative is a direction approaching the objective lens, and positive is a direction away from the objective lens. At this time, overcorrection is a state inclined in the positive direction as shown in FIG. 7B, and undercorrection is a state inclined in the negative direction as shown in A in FIG. Although the aberration value is positive in B of FIG. 7, even if the aberration value is negative, if the inclination is inclined in the positive direction as shown in B, it is regarded as overcorrection. Further, although the aberration value is negative in A of FIG. 7, even if the aberration value is positive, if the inclination is inclined in the negative direction as in A, it is regarded as insufficient correction.

Further, only the paraxial term (for example, the term B2 in (Equation 2)) is deleted from the optical path difference function of the first basic structure and the second basic structure, or the third basic structure and the fourth basic structure. When creating a graph of a function, if the position of the graph (inclination is irrelevant) is on the negative side, it may be regarded as undercorrected, and if it is on the positive side, it may be considered overcorrected.

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 (the shift of the condensing position 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 of the third-order spherical aberration when the wavelength of one light beam changes 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 or more and 20 mλrms or less. 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.

In the second optical path difference providing structure, 1 to 3 (particularly preferably 2 to 3) ring zones of the third foundation structure are included in one ring zone closest to the central region of the fourth foundation structure. It is preferable. More preferably, in the entire second optical path difference providing structure, 1 to 3 (particularly preferably 2 to 3) ring zones of the third foundation structure are included in one ring zone of the fourth foundation structure. That is. That is, the average pitch of the third foundation structure is preferably equal to or less than 1/2 (particularly preferably, 1/3 or more, 1/2 or less) of the fourth foundation structure.

When providing the third optical path difference providing structure in the peripheral structure, it is possible to provide an arbitrary optical path difference providing structure. 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.

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 flux 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 (21).
0.8 ≦ d / f ≦ 1.5 (21)
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 dealing with an optical disk with a short wavelength and a high NA such as BD, there arises a problem that astigmatism is likely to occur in the objective lens, and decentration coma is likely to occur, but the conditional expression (21) is satisfied. As a result, it is possible to suppress the generation of astigmatism and decentration coma.

In addition, since the objective lens has a thick on-axis thickness, the working distance at the time of CD recording / reproduction tends to be short, so the upper limit of conditional expression (21) 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 flux becomes parallel light or substantially parallel light, it is preferable that the imaging magnification m1 of the objective lens when the first light flux is incident on the objective lens satisfy the following formula (22).
-0.01 <m1 <0.01 (22)

The second light beam is incident on the objective lens as a convergent light beam. The imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens preferably satisfies the following formula (1).
0 <m2 <0.16 (1)
More preferably, the following formula is satisfied.
0 <m2 <0.07 (1) ′
More preferably, the following expression is satisfied.
0.01 ≦ m2 <0.07 (1) ″

The third light beam is preferably incident on the objective lens as a parallel light beam. The imaging magnification m3 of the objective lens when the third light beam enters the objective lens preferably satisfies the following formula (23).
-0.01 <m3 <0.01 (23)

On the other hand, the third light beam may be incident on the objective lens as a divergent light beam or a convergent light beam. The imaging magnification m3 of the objective lens when the third light beam enters the objective lens as a divergent light beam preferably satisfies the following formula (23) ′, and when the third light beam enters the objective lens as a convergent light beam: It is preferable that the imaging magnification m3 of the objective lens satisfies the following formula (23) ″.
−0.025 ≦ m3 ≦ −0.01 (23) ′
0.01 ≦ m3 ≦ 0.025 (23) ″

Also, the working distance (WD) of the objective optical element when using the third optical disk is preferably 0.25 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 disk is preferably 0.25 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. Further, the working distance when using the second optical disk is preferably equal to or greater than the working distance when using the third optical disk.

In the optical pickup device, the coupling lens may have 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 recording medium, the reason why it is desirable to always keep the initial position of the coupling lens to discriminate the type of DVD, or simply moving the coupling lens by the drive. For example, there is a reason for wanting to reduce the cost of firmware for this.

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 above-described optical pickup apparatus.

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.

The optical information recording / reproducing apparatus using each method described above 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. 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. It is also possible to provide an objective lens with balanced light utilization efficiency that can maintain high light utilization efficiency for any of the three types of optical disks of BD / DVD / CD. With these effects, recording / reproduction of three types of optical discs of BD / DVD / CD can be performed well with a common objective lens.

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) thru | or (c) show the preferable example of a 1st optical path difference providing structure, (d) is the example which superimposed the 1st foundation structure and the 2nd foundation structure. Indicates. It is a figure which shows whether an aberration is under (undercorrection) or over (overcorrection). 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. It is sectional drawing of the objective lens of a comparative example. It is a graph which shows the off-axis characteristic in the objective lens of a comparative example. It is a figure which shows the 3rd-order coma aberration with respect to the lens tilt at the time of DVD use in a comparative example. It is a figure which shows the 3rd-order coma aberration with respect to the lens tilt at the time of DVD use in a comparative example. FIG. 3 is a cross-sectional view of the objective lens of Example 1. 6 is a graph showing off-axis characteristics in the objective lens of Example 1. FIG. 6 is a diagram illustrating third-order coma aberration with respect to lens tilt when using a DVD in Example 1. FIG. 6 is a diagram illustrating third-order coma aberration with respect to lens tilt when using a DVD in Example 1. 6 is a cross-sectional view of an objective lens according to Example 2. FIG. 6 is a graph showing off-axis characteristics in the objective lens of Example 2. FIG. 6 is a diagram illustrating third-order coma aberration with respect to lens tilt when using a DVD in Example 2. FIG. 6 is a diagram illustrating third-order coma aberration with respect to lens tilt when using a DVD in Example 2. 6 is a cross-sectional view of an objective lens according to Example 3. FIG. 10 is a graph showing off-axis characteristics in the objective lens of Example 3. FIG. 10 is a diagram illustrating third-order coma aberration with respect to lens tilt when using a DVD in Example 3. FIG. 10 is a diagram illustrating third-order coma aberration with respect to lens tilt when using a DVD in Example 3. 10 is a cross-sectional view of an objective lens according to Example 4. FIG. 10 is a graph showing off-axis characteristics in the objective lens of Example 4. It is a figure which shows the 3rd-order coma aberration with respect to the lens tilt at the time of DVD use in Example 4. FIG. It is a figure which shows the 3rd-order coma aberration with respect to the lens tilt at the time of DVD use in Example 4. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 8 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 overlaid as shown in FIG. The structure is such that 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 different. The first order diffracted light amount of the third light beam 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 first basic structure, the step is directed in the direction opposite to the optical axis, and the second basic structure converts the second-order diffracted light amount of the first light beam that has passed through the second basic structure to any other order. The second light flux that is larger than the diffracted light quantity and passes through the second basic structure. The first order diffracted light amount is made larger than any other order diffracted light amount, and the first order diffracted light amount of the third light beam that has passed through the second basic structure is made larger than any other order diffracted light amount, and at least the center The second foundation structure provided in the vicinity of the optical axis of the region CN has a step in the direction of the optical axis, and the first and second foundation structures have changed so that the wavelength of the incident light beam becomes longer. In this case, it is preferable that the spherical aberration changes in the direction of insufficient correction.

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, passes through the polarization beam splitter BS and the collimating lens COL, as indicated by the dotted line, and λ The / 4 wavelength plate QWP converts the linearly polarized light into circularly polarized light and enters the objective lens OL in the form of a convergent light beam. 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 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 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. It is converted from linearly polarized light into circularly polarized light by the λ / 4 wave plate QWP, and enters the objective lens OL in a state of a parallel light beam, a divergent light beam, or a convergent light beam. 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 passes through the objective lens OL again, is converted from circularly polarized light to linearly polarized light by the λ / 4 wave plate QWP, and is converged by the collimating lens COL, The light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. And the information recorded on CD can be read using the output signal of light receiving element PD.

(Example)
Examples that can be used in the above-described embodiment will be described below. In the following (including the 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. .

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.

(Comparative example)
The objective lens of the comparative example is a plastic single lens. In the comparative example, parallel light is incident when the DVD is used (m2 = 0). FIG. 9 is a cross-sectional view of a comparative objective lens. The first optical path difference providing structure of the comparative example has a (1/1/1) blaze type in the second basic structure BS2 that is a (2/1/1) blaze type diffraction structure in the entire central region. The optical path difference providing structure is formed by overlapping the first basic structure BS1 which is a diffractive structure. The second optical path difference providing structure has a structure in which 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. The peripheral region has a (2/1/1) blazed diffraction structure as a third optical path difference providing structure. Table 1 shows lens data of the comparative example. FIG. 10 is a graph showing the third-order coma aberration when using a BD and the third-order coma aberration when using a DVD when a light beam tilted with respect to the optical axis is incident as off-axis characteristics in the objective lens of the comparative example. FIG. 11 is a diagram showing the third-order coma aberration with respect to the lens tilt when using the DVD, and FIG. 12 is a diagram showing the third-order coma aberration with respect to the lens shift when using the DVD. In FIG. 10, the third-order coma aberration BD-CM3 generated when the first light flux having an angle of view of 0.5 degrees is incident on the objective lens, and the second light flux having an angle of view of 0.5 degrees is applied to the objective lens. The value of the third-order coma aberration DVD-CM3 generated when the light is incident is given as a reference. In FIG. 11, the value of the third-order coma aberration DVD-CM3 generated when the second light beam is incident on the objective lens with a lens tilt of 0.5 degrees is given as a reference. In FIG. 12, the value of the third-order coma aberration DVD-CM3 generated when the second light beam is incident on the objective lens when the lens shift is 0.2 mm in the direction orthogonal to the optical axis is referred to.

(Example 1)
The objective lens of Example 1 is a plastic single lens. In Example 1, convergent light is incident when a DVD is used (m2 = 0.16). FIG. 13 is a cross-sectional view of the objective lens of Example 1. FIG. 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. The second optical path difference providing structure has a structure in which 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. The peripheral region has a (2/1/1) blazed diffraction structure as a third optical path difference providing structure. Table 2 shows lens data of Example 1. FIG. 14 is a graph showing the third-order coma aberration when using a BD and the third-order coma aberration when using a DVD when a light beam tilted with respect to the optical axis is incident as off-axis characteristics in the objective lens of Example 1. FIG. 15 is a diagram showing the third-order coma aberration with respect to the lens tilt when using the DVD, and FIG. 16 is a diagram showing the third-order coma aberration with respect to the lens shift when using the DVD. In FIG. 14, the third-order coma aberration BD-CM3 generated when the first light flux having an angle of view of 0.5 degrees is incident on the objective lens, and the second light flux having an angle of view of 0.5 degrees is incident on the objective lens. The value of the third-order coma aberration DVD-CM3 generated at the time of being applied is given as a reference. In FIG. 15, the value of the third-order coma aberration DVD-CM3 generated when the second light beam is incident on the objective lens with a lens tilt of 0.5 degrees is given as a reference. In FIG. 16, the value of the third-order coma aberration DVD-CM3 generated when the second light beam is incident on the objective lens when the lens shift is 0.2 mm in the direction orthogonal to the optical axis is referred to.

(Example 2)
The objective lens of Example 2 is a plastic single lens. In Example 2, convergent light is incident when a DVD is used (m2 = 0.06). FIG. 17 is a cross-sectional view of the objective lens 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. The second optical path difference providing structure has a structure in which 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. The peripheral region has a (2/1/1) blazed diffraction structure as a third optical path difference providing structure. Table 3 shows lens data of Example 2. FIG. 18 is a graph showing the third-order coma aberration when using a BD and the third-order coma aberration when using a DVD when a light beam tilted with respect to the optical axis is incident as off-axis characteristics in the objective lens of Example 2. FIG. 19 is a diagram showing the third-order coma aberration with respect to the lens tilt when using the DVD, and FIG. 20 is a diagram showing the third-order coma aberration with respect to the lens shift when using the DVD. In FIG. 18, the third-order coma aberration BD-CM3 generated when the first light flux with an angle of view of 0.5 degrees is incident on the objective lens, and the second light flux with an angle of view of 0.5 degrees is applied to the objective lens. The value of the third-order coma aberration DVD-CM3 generated when the light is incident is given as a reference. In FIG. 19, the value of the third-order coma aberration DVD-CM3 generated when the second light beam is incident on the objective lens with a lens tilt of 0.5 degrees is given as a reference. In FIG. 20, the value of the third-order coma aberration DVD-CM3 generated when the second light flux is made incident on the objective lens when the lens shift is 0.2 mm in the optical axis orthogonal direction is given as a reference.

(Example 3)
The objective lens of Example 3 is a plastic single lens. In Example 3, convergent light is incident when a DVD is used (m2 = 0.05). Further, convergent light is incident when the CD is used (m3 = 0.02). FIG. 21 is a sectional view of the objective lens of Example 3. FIG. 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. The second optical path difference providing structure has a structure in which 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. The peripheral region has a (2/1/1) blazed diffraction structure as a third optical path difference providing structure. Table 4 shows lens data of Example 3. FIG. 22 is a graph showing the third-order coma aberration when using a BD and the third-order coma aberration when using a DVD when a light beam tilted with respect to the optical axis is incident as off-axis characteristics in the objective lens of Example 3. FIG. 23 is a diagram showing the third-order coma aberration with respect to the lens tilt when using the DVD, and FIG. 24 is a diagram showing the third-order coma aberration with respect to the lens shift when using the DVD. In FIG. 22, the third-order coma aberration BD-CM3 generated when the first light flux with an angle of view of 0.5 degrees is incident on the objective lens, and the second light flux with an angle of view of 0.5 degrees is applied to the objective lens. The value of the third-order coma aberration DVD-CM3 generated when the light is incident is given as a reference. In FIG. 23, the value of the third-order coma aberration DVD-CM3 generated when the second light beam is incident on the objective lens with a lens tilt of 0.5 degrees is given as a reference. In FIG. 24, the value of the third-order coma aberration DVD-CM3 generated when the second light beam is incident on the objective lens when the lens shift is 0.2 mm in the direction orthogonal to the optical axis is referred to.

(Example 4)
The objective lens of Example 4 is a plastic single lens. In Example 4, convergent light is incident when using a DVD (m2 = 0.05). Further, divergent light is made incident when the CD is used (m3 = −0.01). FIG. 25 is a cross-sectional view of the objective lens according to Example 4. 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. The second optical path difference providing structure has a structure in which 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. The peripheral region has a (2/1/1) blazed diffraction structure as a third optical path difference providing structure. Table 5 shows lens data of Example 4.
FIG. 26 is a graph showing the third-order coma aberration when using a BD and the third-order coma aberration when using a DVD when a light beam tilted with respect to the optical axis is incident as off-axis characteristics in the objective lens of Example 4. FIG. 27 is a diagram showing the third-order coma aberration with respect to the lens tilt when using the DVD, and FIG. 28 is a diagram showing the third-order coma aberration with respect to the lens shift when using the DVD. In FIG. 26, the third-order coma aberration BD-CM3 generated when the first light flux having an angle of view of 0.5 degrees is incident on the objective lens, and the second light flux having an angle of view of 0.5 degrees is applied to the objective lens. The value of the third-order coma aberration DVD-CM3 generated when the light is incident is given as a reference. In FIG. 27, the value of the third-order coma aberration DVD-CM3 generated when the second light beam is incident on the objective lens with a lens tilt of 0.5 degrees is given as a reference. In FIG. 28, the value of the third-order coma aberration DVD-CM3 generated when the second light beam is incident on the objective lens when the lens shift is 0.2 mm in the direction orthogonal to the optical axis is referred to.

As apparent from a comparison between FIG. 10 and FIG. 14, the off-axis characteristics when using the DVD of Example 1 are improved compared to the comparative example (in the comparative example, the DVD-CM3 is 50 mλrms, whereas In Example 1, DVD-CM3 is 39 mλrms). 11 and 15, it is clear that the lens tilt characteristic when using the DVD of Example 1 is improved compared to the comparative example, so that adjustment during assembly is easy. In contrast, the comparative example cannot be adjusted no matter how much the objective lens is tilted. Further, as is apparent from a comparison between FIG. 10 and FIGS. 18, 22, and 26, the off-axis characteristics when using DVDs in Examples 2 to 4 are particularly preferably compatible with the off-axis characteristics when using BD. (BD-CM3 + DVD-CM3 is 2mλrms or less). 11 and FIGS. 19, 23, and 27, it is clear that the lens tilt characteristics when using DVDs of Examples 2 to 4 are improved compared to the comparative example, so that adjustment during assembly is easy. It is. In addition, Examples 2 to 4 are excellent because third-order coma aberration does not occur even when a lens shift occurs as shown in FIGS.

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

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

Claims

A first light source that emits a first light flux with a first wavelength λ1, a second light source that emits a second light flux with a second wavelength λ2 (λ2> λ1), and a third light flux with a third wavelength λ3 (λ3> λ2) And recording and / or reproducing information on a first optical disc having a protective substrate with a thickness of t1 using the first light flux, and using the second light flux to obtain a thickness. Records and / or reproduces information on the second optical disk having the protective substrate t2 (t1 <t2), and uses the third light flux to have the third optical disk having the protective substrate having the thickness t3 (t2 <t3) An objective lens used in an optical pickup device that records and / or reproduces information of
The optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region,
The central region has a first optical path difference providing structure,
The intermediate region has a second optical path difference providing structure,
The objective lens condenses the first light flux that passes through the central area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the central area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the central region is condensed on the information recording surface of the third optical disc. Condensing so that information can be recorded and / or reproduced,
The objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the intermediate area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the intermediate region is condensed on the information recording surface of the third optical disc. Without collecting light so that information can be recorded and / or reproduced.
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the peripheral area. The second light flux is not condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc, and the third light flux passing through the peripheral region is used as the information recording surface of the third optical disc. Do not concentrate so that information can be recorded and / or reproduced
The 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 A-order diffracted light quantity of the first light flux that has passed through the first basic structure larger than any other order diffracted light quantity, and B of the second light flux that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The first basic structure is a blaze-type structure;
The second basic structure makes the D-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and the E of the second light beam that has passed through the second basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the F-order diffracted light quantity of the third light flux that has passed through the second basic structure larger than any other order diffracted light quantity,
The second optical path difference providing structure is a structure in which at least a third basic structure and a fourth basic structure are overlapped,
The third basic structure makes the G-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, so that the H of the second light beam that has passed through the third basic structure. Make the next diffracted light quantity larger than any other order diffracted light quantity,
The third basic structure is a blazed structure;
In the fourth basic structure, the first-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 the second light beam J that has passed through the fourth basic structure has J Make the next diffracted light quantity larger than any other order diffracted light quantity,
The fourth basic structure is a blazed structure.
2. The objective lens according to claim 1, wherein the second light beam is incident on the objective lens in a convergent light state when the second optical disk is used.
The objective lens according to claim 1, wherein the following expression is satisfied.
0 <m2 <0.16 (1)
However, m2 represents the magnification of the objective lens when the second light beam is incident on the objective lens.
3. The objective lens according to claim 1, wherein A = G = 1, B = H = 1, C = 1, D = I = 2, E = J = 1, and F = 1.
The objective lens according to any one of claims 1 to 3, wherein a working distance when the second optical disk is used is equal to or greater than a working distance when the third optical disk is used.
The objective lens according to any one of claims 1 to 4, wherein a working distance when the second optical disc is used is 0.25 mm or more.
6. The aberration generated when the objective lens is shifted by 0.2 mm in the direction perpendicular to the optical axis when using the second optical disc is less than the Marshall limit (0.07 λrms). The objective lens of any one of Claims 1.
The objective lens according to any one of claims 1 to 6, wherein, when the third optical disk is used, the third light beam is incident on the objective lens in a parallel light state.
The third light beam according to any one of claims 1 to 6, wherein when the third optical disk is used, the third light beam is incident on the objective lens in a state of convergent light or divergent light. Objective lens.
9. The third-order coma aberration DVD-CM3 generated when the second light flux having an angle of view of 0.5 degrees is incident on the objective lens is 40 mλrms or less. Objective lens described in 1.
Third-order coma aberration BD-CM3 generated when the first light beam having an angle of view of 0.5 degrees is incident on the objective lens, and the second light beam having an angle of view of 0.5 degrees is incident on the objective lens. The objective lens according to any one of claims 1 to 9, wherein a total of the third-order coma aberration DVD-CM3 generated at the time is 40 mλrms or less.
An optical pickup device comprising the objective lens according to any one of claims 1 to 10.