WO2012090852A1

WO2012090852A1 - Objective lens for optical pickup device, optical pickup device, and optical information record/play device

Info

Publication number: WO2012090852A1
Application number: PCT/JP2011/079791
Authority: WO
Inventors: 小嶋俊之
Original assignee: コニカミノルタオプト株式会社
Priority date: 2010-12-28
Filing date: 2011-12-22
Publication date: 2012-07-05
Also published as: JPWO2012090852A1

Abstract

Provided are an optical pickup device and an optical information record/play device which are provided with an objective lens, whereby it is possible to carry out exchanges among three types of optical discs, BD/DVD/CD, with a common objective lens, and an objective lens which is optimal thereto. Enlarging the blaze wavelength λb(2λ) in a base structure of a second light path difference application structure with respect to the blaze wavelength λb(3λ) in a base structure of a first light path difference application structure increases usage efficiency of the light of a second light beam which passes through a central region, and maintains a proper spot diameter whereat said second light beam collects on the information recording face of a second optical disc.

Description

Objective lens for optical pickup device, optical pickup device and optical information recording / reproducing device

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

In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a wavelength 390 such as a blue-violet semiconductor laser is used. A laser light source of ˜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.

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

International Publication No. 08/146675 Pamphlet

By the way, in the objective lens described in the example of Patent Document 1, the blaze wavelength (design wavelength) in the central region, which is a common region used for both BD / DVD / CD, and the BD / DVD are used. However, the blaze wavelength (design wavelength) in the intermediate region, which is a region that is not used for CD, is equal to 395 nm. As a result of diligent research by the present inventors, a phenomenon that the spot diameter is larger than the design value can occur when a focused spot is formed on the information recording surface of a DVD using such an objective lens. There was found. If this is left unattended, an error signal may be generated when the DVD is used.

An object of the present invention is to solve the above-described problems, and a condensing spot having an appropriate size can be obtained when using a DVD, and the compatibility of three types of optical discs of BD / DVD / CD is common. It is an object of the present invention to provide an optical pickup apparatus, an optical information recording / reproducing apparatus, and an objective lens suitable for the optical pickup apparatus including an objective lens that can be performed with the objective lens.

The objective lens according to claim 1, a first light source that emits a first light flux having a first wavelength λ1, a second light source that emits a second light flux having a second wavelength λ2 (λ1 <λ2), and a third wavelength. a third light source that emits a third light beam of λ3 (λ2 <λ3), and records and / or reproduces 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 objective lens is a single lens made of plastic,
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 has at least a first basic structure,
The first basic structure makes the A-order diffracted light amount of the first light beam that has passed through the first basic structure larger than any other order of diffracted light amount, and B of the second light beam that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, making the C-order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The second optical path difference providing structure has at least a third basic structure,
The third basic structure makes the A-order diffracted light amount of the A-th beam that has passed through the third basic structure larger than any other order diffracted light amount, and B of the second light beam that has passed through the third basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the third basic structure larger than any other order diffracted light quantity,
In the case of | A | · λ1> | B | · λ2, the blazed wavelength λb (3λ) in the first basic structure is larger than the blazed wavelength λb (2λ) in the third basic structure,
In the case of | A | · λ1 <| B | · λ2, the blazed wavelength λb (3λ) in the first basic structure is smaller than the blazed wavelength λb (2λ) in the third basic structure. To do.

As a result of diligent research, the inventor has found that the optical path difference providing structure provided to realize compatibility in the central region and the intermediate region of the objective lens used in common for the first light beam and the second light beam is separated from the optical axis. Accordingly, the diffraction pitch of the optical path difference providing structure formed in an aspherical surface is usually narrower. Therefore, the diffraction pitch is narrower in the intermediate region than in the central region, and the influence of the shadow of the step or the fine shape. Due to the manufacturing error resulting from the difficulty in forming the optical path difference providing structure with high precision, the light utilization efficiency of the intermediate region is lower than that in the central region. It has been found that the light utilization efficiency at the most periphery of the focused spot is reduced, and this is the cause of increasing the spot diameter. However, how to increase the light use efficiency around the condensing spot when using a DVD remains a problem.

Therefore, the present inventor paid attention to the blazed wavelength of the basic structure, which is an optical path difference providing structure, in solving such a problem. The blazed wavelength is a wavelength at which the diffraction efficiency is highest in the structure. Specifically, in the case of | A | · λ1> | B | · λ2, the blazed wavelength λb (3λ) in the first basic structure is larger than the blazed wavelength λb (2λ) in the third basic structure, In the case of | A | · λ1 <| B | · λ2, the blazed wavelength λb (3λ) in the first basic structure is made smaller than the blazed wavelength λb (2λ) in the third basic structure. The following effects can be obtained. That is, the second optical path difference providing structure is designed to give priority to the second light flux, and the use efficiency of the light of the second light flux that passes through the intermediate region is increased, and the periphery of the spot that is focused on the information recording surface of the second optical disc such as a DVD As a result, the spot diameter of the condensing spot on the information recording surface of the second optical disc can be set to an appropriate size without increasing. In addition, with the structure of this invention, the utilization efficiency of the light of the 1st light beam which passes an intermediate | middle area | region may fall. However, since the peripheral region outside the intermediate region is a region dedicated to the first light flux, the utilization efficiency of light passing through the peripheral region can be increased. As a result, the efficiency of the spot focused on the information recording surface of the first optical disc such as BD is reduced in the intermediate region, but the peripheral efficiency can be kept high. Therefore, there is no problem that the diameter of the focused spot on the information recording surface of the first optical disc is increased, and an appropriate focused spot diameter can be maintained.

Further, both the first basic structure and the third basic structure make the A-order diffracted light quantity of the first light beam larger than any other order diffracted light quantity, and the B-order diffracted light quantity of the second light beam becomes any other diffracted light quantity. Since the diffracted light amount of the third light beam is larger than the diffracted light amount of the third order, and the diffracted light amount of the third light beam is larger than any other order of diffracted light amount, Spherical aberration can be continuous, and higher order aberrations can be prevented.

The objective lens of claim 2 is the invention of claim 1,
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 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 the third basic structure and the fourth basic structure are overlapped,
The fourth foundation structure makes the D-order diffracted light quantity of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light quantity, and the E of the second light flux that has passed through the fourth foundation structure. The next diffracted light amount is made larger than any other order diffracted light amount, and the F-order diffracted light amount of the third light beam that has passed through the fourth basic structure is made larger than any other order diffracted light amount. To do.

The first optical path difference providing structure is formed by superimposing two types of structures, a first basic structure and a second basic structure, and the second optical path difference providing structure is composed of two types of structures, a third basic structure and a fourth basic structure. Compared to the case where the optical path difference providing structure is formed with a single structure such as a staircase type by overlapping the structure, it is possible to secure a large degree of design freedom, which is particularly advantageous for an objective lens having a small effective diameter. is there.

The objective lens described in claim 3 is characterized in that, in the invention described in claim 1 or 2, the first basic structure is a blazed structure, and the second basic structure is a blazed structure. Thereby, the utilization efficiency of light can be improved.

The objective lens according to claim 4 is the invention according to claim 2 or 3, wherein A, B, C, D, E, and F are respectively
| A | = 1
| B | = 1
| C | = 1
| D | = 2
| E | = 1
| F | = 1
It is characterized by satisfying.

Here, as the basic structure to be interchanged, 1/1/1 (the most primary diffracted light is generated in any of the first light beam, the second light beam, and the third light beam) is defined as the first and third basic structures. 2/1/1 (the second-order diffracted light is generated most in the first light beam, and the first-order diffracted light is generated most in the second light beam and the third light beam) Selected. The reason for this is that, due to the use of a blazed structure with a low step amount (height in the optical axis direction of the step), fluctuations in diffraction efficiency at the time of wavelength change can be prevented, resulting in shadow effects and manufacturing errors. A decrease in light utilization efficiency can be suppressed, and secondly, all three wavelengths have high diffraction efficiency.

The objective lens according to claim 5 is characterized in that, in the invention according to any one of claims 2 to 4, the blazed wavelength in the second basic structure is equal to the blazed wavelength in the fourth basic structure. To do.

According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the light use efficiency of the second light flux changes discontinuously at the boundary between the intermediate region and the central region. The light use efficiency of the second light flux in the intermediate region across the boundary is higher than the light use efficiency of the second light flux in the central region.

The objective lens according to claim 7 is the objective lens according to any one of claims 1 to 6, wherein the blazed wavelength λb (3λ) is 405 to 510 nm, and the blazed wavelength λb (2λ) is 450 to 550 nm.

The objective lens according to claim 8 is the objective lens according to any one of claims 1 to 7, wherein the peripheral region has a third optical path difference providing structure, and a blazed wavelength λb in the third optical path difference providing structure. (1λ) is 385 to 425 nm.

By setting the blazed wavelength in the third optical path difference providing structure within the above range, the efficiency of the peripheral part of the focused spot when using the first optical disk can be increased, so that the spot becomes thicker when using the first optical disk. And an appropriate spot diameter can be obtained.

The objective lens according to claim 9 is the invention according to any one of claims 1 to 8, wherein the first basic structure provided in the central region is such that all steps are directed in a direction opposite to the optical axis. It is characterized by.

The objective lens according to claim 10 is the invention according to any one of claims 2 to 9, wherein in the second basic structure provided in the central region, all the steps are directed in the direction of the optical axis. It is characterized by.

The objective lens according to claim 11 is the invention according to any one of claims 1 to 10, wherein the first optical path difference providing structure provided at least in the vicinity of the optical axis of the central region is an optical axis. It has both a step facing in the opposite direction and a step facing in the direction of the optical axis,
The step amount d11 of the step facing the direction opposite to the optical axis and the step amount d12 of the step facing the direction of the optical axis satisfy the following conditional expressions (2) and (3). It is characterized by.
0.6 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (3)
0.6 · (λ1 / (n-1)) <d12 <1.5 · (2λ1 / (n-1)) (4)
Here, n represents the refractive index of the objective lens at λ1.

The objective lens according to claim 12 is characterized in that, in the invention according to claim 11, the conditional expressions (2) and (3) are satisfied in all regions of the central region.

The objective lens described in claim 13 is characterized in that, in the invention described in claim 11 or 12, the following conditional expression is satisfied.
0.9 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (2) "
0.9 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (3) "

The objective lens according to claim 14 is characterized in that, in the invention according to claim 13, the conditional expressions (2) "and (3)" are satisfied in all regions of the central region.

The objective lens according to claim 15 is the invention according to any one of claims 11 to 14, wherein, in the central region, the number of steps facing the direction opposite to the optical axis is equal to that of the optical axis. It is characterized by being larger than the number of steps facing the direction.

An objective lens according to a sixteenth aspect is characterized in that, in the invention according to any one of the first to fifteenth aspects, the following conditional expression is satisfied.
0.8 ≦ d / f ≦ 1.5 (4)
However, 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.

The objective lens according to claim 17 is the invention according to any one of claims 1 to 16, wherein the second optical path difference providing structure is formed by overlapping a fifth basic structure in addition to the third basic structure. The fifth basic structure has a zero-order diffracted light amount of the first light flux that has passed through the fifth basic structure larger than any other order diffracted light amount, and has passed through the fifth basic structure. The 0th-order diffracted light quantity of the second light flux is made larger than any other order diffracted light quantity, and the G-order diffracted light quantity of the third light flux that has passed through the fifth basic structure is made higher than any other order diffracted light quantity. It is also characterized by a structure that increases the size.

The objective lens according to claim 18 is characterized in that, in the invention according to any one of claims 1 to 16, the second optical path difference providing structure comprises only the third basic structure and the fourth basic structure. And

The objective lens according to claim 19 is characterized in that, in the invention according to any one of claims 1 to 18, the following conditional expressions (5), (6), and (7) are satisfied.
-0.01 <m1 <0.01 (5)
-0.01 <m2 <0.01 (6)
-0.01 <m3 <0.01 (7)
However, m1 represents the magnification of the objective lens when the first light beam is incident on the objective lens, m2 represents the magnification of the objective lens when the second light beam is incident on the objective lens, m3 represents the magnification of the objective lens when the third light beam is incident on the objective lens.

An optical pickup device according to claim 20 has the objective lens according to any one of claims 1 to 19.

An optical information recording / reproducing device according to claim 21 has the optical pickup device according to claim 20.

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

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

In this specification, BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00 mm. It is a generic term for a BD series optical disc of about 125 mm, and includes a BD having only a single information recording layer, a BD having two or more information recording layers, and the like. 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 (8), (9), and (10), 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 (8)
0.5mm ≤ t2 ≤ 0.7mm (9)
1.0 mm ≤ t3 ≤ 1.3 mm (10)

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 (11) and (12).
1.5 · λ1 <λ2 <1.7 · λ1 (11)
1.8 · λ1 <λ3 <2.0 · λ1 (12)

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. A light receiving element may be used. The light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.

The condensing optical system has an objective lens. The condensing optical system preferably has a coupling lens such as a collimator in addition to the objective lens. The coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam. The collimator is a type of coupling lens, and is a lens that emits light incident on the collimator as parallel light. In this specification, the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk. The objective lens 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 1.54 to 1.60 at a temperature of 25 ° C. with respect to a wavelength of 405 nm, and a wavelength of 405 nm associated with a temperature change within a temperature range of −5 ° C. to 70 ° C. The refractive index change rate dN / dT (° C. ⁻¹ ) is -20 × 10 ^{−5 to} −5 × 10 ⁻⁵ (more preferably −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ). It is more preferable to use a certain resin material. When the objective lens is a plastic lens, it is preferable that the coupling lens is also a plastic lens.

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

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

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

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

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

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

In addition, the optical path difference providing structure 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). .

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 structure 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. In the present invention, the blazed structure shown in FIG.

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 has at least a first basic structure, and is preferably a structure in which a second basic structure is further overlapped. However, the first optical path difference providing structure may be formed by the first basic structure alone. The first optical path difference providing structure is preferably a structure in which only the first basic structure and the second basic structure are overlapped.

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

In the first basic structure, the step may be directed in the direction of the optical axis or in the direction opposite to the optical axis. Moreover, the direction of the level | step difference of a 1st foundation structure may be changed in the middle of the center area | region like Fig.5 (a), (b). FIG. 5A shows an example in which the step is directed toward the optical axis at a position close to the optical axis, but the direction of the step is changed halfway, and the step is directed in the opposite direction to the optical axis at a position far from the optical axis. It is. FIG. 5B shows an example in which the step is opposite to the optical axis at a position close to the optical axis, but the direction of the step is changed halfway, and the step is directed to the optical axis at a position far from the optical axis. It is. Moreover, although it is desirable that the direction of the step of the first foundation structure matches the direction of the step of the third foundation structure, it does not need to match. “The step is directed in the direction of the optical axis” means a state as shown in FIG. 4A, and “the step is directed in the direction opposite to the optical axis” is shown in FIG. 4B. Say like the state. However, preferably, the first basic structure provided in the central region is that all the steps are directed in a direction opposite to the optical axis.

CD is used even in thick objective lenses with a large on-axis thickness that are used interchangeably with three types of optical discs of BD / DVD / CD by directing the step of the first basic structure in the direction opposite to the optical axis. Sometimes it is possible to ensure a sufficient working distance.

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 ).

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

In the second basic structure, the step may be directed in the direction of the optical axis or in the direction opposite to the optical axis. In addition, as shown in FIGS. 5A and 5B, the direction of the steps of the second foundation structure may be switched in the middle of the central region. Moreover, although it is desirable that the direction of the step of the second foundation structure matches the direction of the step of the fourth foundation structure, it does not need to match.

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.

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

Further, not only can the three types of optical discs of BD / DVD / CD be compatible, but also the light usage efficiency that can maintain high light usage efficiency for any of the three types of optical discs of BD / DVD / CD. It is preferable to provide a balanced objective lens. For example, the objective lens preferably has a diffraction efficiency of 80% or more for the wavelength λ1, a diffraction efficiency of 60% or more for the wavelength λ2, and a diffraction efficiency of 50% or more for the wavelength λ3. Furthermore, it is preferable that the objective lens has a diffraction efficiency of 80% or more for the wavelength λ1, a diffraction efficiency of 70% or more for the wavelength λ2, and a diffraction efficiency of 60% or more for the wavelength λ3.

When the objective lens is made of plastic, in order to maintain stable performance even when the temperature changes, both the third-order spherical aberration and the fifth-order spherical aberration that occur in the objective lens when the wavelength becomes longer are both under. (Insufficient correction) is preferable.

A more preferable first optical path providing structure includes a first basic structure in which | A |, | B |, and | C | are 1, 1, 1 (also referred to as 1/1/1 structure), and | D | , | E |, | F | are superimposed on a second basic structure of 2, 1, 1 (also referred to as 2/1/1 structure), respectively. With such a first optical path difference providing structure, the height of the step can be very low. Therefore, it is possible to further reduce manufacturing errors, further reduce the light amount loss, and further suppress the change in diffraction efficiency when the wavelength changes.

From the viewpoint of the shape and step amount of the first optical path difference providing structure after the first basic structure and the second basic structure are overlaid, | A |, | B |, | C | The first optical path difference providing structure in which the first basic structure that is 1 and the second basic structure in which | D |, | E |, and | F | Can be expressed in The first optical path difference providing structure provided at least in the vicinity of the optical axis of the central region has both a step facing in the opposite direction to the optical axis and a step facing in the direction of the optical axis. The step amount d11 of the step facing the direction opposite to the axis and the step amount d12 of the step facing the direction of the optical axis preferably satisfy the following conditional expressions (2) and (3). More preferably, the following conditional expressions (2) and (3) 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)) (2)
0.6 · (λ1 / (n-1)) <d12 <1.5 · (2λ1 / (n-1)) (3)

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 perpendicular 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 (13)
0.39 μm <d12 <2.31 μm (14)

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

As described above, when the positions of all the steps of the second foundation structure are matched with the positions of the steps of the first foundation structure, d11 and d12 of the first optical path difference providing structure are the following conditional expressions (2) ′, ( 3) It is preferable to satisfy '. More preferably, the following conditional expressions (2) ′ and (3) ′ are satisfied in all regions of the central region.
0.6 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (2) '
0.6 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (3) '

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

More preferably, the following conditional expressions (2) "and (3)" are preferably satisfied. More preferably, the following conditional expressions (2) ″ and (3) ″ are satisfied in all the regions of the central region.
0.9 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (2) "
0.9 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (3) "

0.59 μm <d11 <1.15 μm (13) ”
0.59 μm <d12 <1.15 μm (14) ”

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

It is preferable that the absolute value of the paraxial power of the first foundation structure is larger than that of the second foundation structure. That is, it is preferable that the average pitch of the first foundation structure is smaller than the average pitch of the second foundation structure. Thereby, a working distance in the CD can be secured even in an objective lens having a large axial thickness, which is a BD / DVD / CD compatible objective lens. Furthermore, in order to reduce chromatic aberration, to form a good light spot even when the light source causes high-frequency superposition, and to reduce the problem of stray light when the optical disc has a plurality of information recording surfaces, In one optical path difference providing structure, 2 to 6 (particularly preferably 2 to 3) ring zones of the first foundation structure are included in one ring zone closest to the optical axis of the second foundation structure. Is preferred. In this case, the “ring zone” closest to the optical axis of the second foundation structure is described, but in practice, it is usually a “circle” including the optical axis. Accordingly, the “annular zone closest to the optical axis” mentioned here includes a circular shape. Further, in one ring zone of the second foundation structure closest to the intermediate region, 1 to 5 ring zones of the first foundation structure (particularly preferably 2 to 3 rings) are included in one ring zone of the second foundation structure. ) Is included.

If the first basic structure and the second basic structure are superimposed as they are, a convex portion with a narrow width may protrude, but if the width of the protruding portion is as narrow as 5 μm or less, the protruding portion is along the optical axis. Even if the projecting portion is eliminated, there is no significant effect, and thus, a plurality of zones of the first foundation structure can be placed exactly on one zone of the second foundation structure. When the first foundation structure and the second foundation structure are superimposed as they are, a dent may be eliminated in the same manner even when a dent having a width of 5 μm or less is generated.

Here, if Δλ (nm) is the wavelength change amount of the first wavelength and ΔWD (μm) is the chromatic aberration of the objective lens caused by the change Δλ of the first wavelength, the following equation is satisfied. The “chromatic aberration” here is a shift in the focus position that occurs when the wavelength of the light beam changes. That is, it is a shift of “position where wavefront aberration is minimized” that occurs when the wavelength of the light beam changes.
0.3 (μm / nm) ≦ ΔWD / Δλ ≦ 0.6 (μm / nm) (15)

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 6 (particularly preferably 2 to 3). By setting the chromatic aberration to the above-described range, the optical disc has a plurality of information recording surfaces while ensuring a working distance in the CD even in an objective lens having a large axial thickness, which is a BD / DVD / CD compatible objective lens. This is preferable because the problem of stray light can be reduced and the temperature and wavelength characteristics can be improved when using a DVD. In addition, the number N2 of the first foundation structure annular zones superimposed on one annular zone closest to the intermediate region in the second foundation structure is preferably equal to or smaller than N1, for example, 1 to 5 overlapping zones. It should be done.

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

The first best focus position where the light intensity of the spot formed by the third light flux is the strongest by the third light flux passing through the first optical path difference providing structure, and the second strongest light intensity of the spot formed by the third light flux. It is preferable that the best focus position satisfies the following conditional expression (16). Here, the best focus position refers to a position where the beam waist becomes a minimum within a certain defocus range. The first best focus position is the best focus position of the necessary light used for recording / reproduction of the third optical disc, and the second best focus position is the largest amount of unnecessary light that is not used for recording / reproduction of the third optical disc. This is the best focus position for many luminous fluxes.
0.05 ≦ L / f13 ≦ 0.35 (16)
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 (15) ′ is satisfied.
0.10 ≦ L / f13 ≦ 0.25 (16) ′

A preferred example of the first optical path difference providing structure described above is shown in FIG. Although FIG. 6 shows the first optical path difference providing structure ODS1 as a flat plate for convenience, it may be provided on a single aspherical convex lens. | D |, | E |, | F | are 2, 1, 1, respectively, and the second basic structure BS2 is | A |, | B |, | C | A certain first basic structure BS1 is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS faces the direction opposite to the optical axis OA. Further, the steps of the first foundation structure BS1 and the second foundation structure BS2 are matched, and the positions of all the steps of the second foundation structure are matched with the positions of the steps of the first foundation structure, but this is not restrictive. In this example, 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.

Next, the second optical path difference providing structure provided in the intermediate region will be described. The second optical path difference providing structure has at least a third basic structure, and is preferably a structure in which a fourth basic structure is further overlapped. However, the second optical path difference providing structure may be formed by the third basic structure alone.

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

In both the first basic structure and the third basic structure, the A-order diffracted light amount of the first light beam is made larger than any other order diffracted light amount, and the B-order diffracted light amount of the second light beam is set to any other order. By changing the blazed wavelength λb between the first basic structure and the third basic structure by making it larger than the diffracted light quantity and making the C-order diffracted light quantity of the third light beam larger than any other order diffracted light quantity. It becomes easy to increase the light use efficiency in the intermediate region. Further, it is preferable because the phase difference generated in the optical path difference providing structure can be substantially equal between the central region and the intermediate region, and the phase shift can be reduced between the central region and the intermediate region. Furthermore, spherical aberration can be continuous in the central region and the intermediate region even during temperature changes and wavelength fluctuations, and generation of higher order aberrations can be prevented. That is, it is preferable that the first foundation structure and the third foundation structure are the same structure, and the second foundation structure and the fourth foundation structure are the same structure. That is, it is desirable that the first optical path difference providing structure and the second optical path difference providing structure are the same structure. However, the pitch may be different between the first optical path difference providing structure and the second optical path difference providing structure.

In addition, it is preferable that a 3rd foundation structure and a 4th foundation structure are blaze | braze type | mold structures. Further, the third basic structure makes the first-order diffracted light quantity of the first light flux that has passed through the third basic structure larger than any other order of diffracted light quantity, and the first-order diffracted light quantity of the second light flux that has passed through the third basic structure Is preferably larger than any other order of diffracted light. In addition, it is preferable that the first-order diffracted light amount of the third light flux that has passed through the third basic structure is larger than any other order diffracted light amount. In addition, the fourth foundation structure makes the second-order diffracted light amount of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light amount, and the first-order of the second light beam that has passed through the fourth foundation structure. Is preferably larger than any other order of diffracted light. Further, the first-order diffracted light amount of the third light flux that has passed through the fourth basic structure is made larger than any other order diffracted light amount. Thereby, in the second optical path difference providing structure in which at least the third basic structure and the fourth basic structure are overlapped, the amount of step in the optical axis direction can be reduced, thereby suppressing the decrease in diffraction efficiency at the time of wavelength variation.

In summary, A, B, C, D, E, and F are respectively
| A | = 1
| B | = 1
| C | = 1
| D | = 2
| E | = 1
| F | = 1
It is preferable to satisfy.

In the case of | A | · λ1> | B | · λ2, the blazed wavelength λb (3λ) in the first basic structure is set to be larger than the blazed wavelength λb (2λ) in the third basic structure. On the other hand, in the case of | A | · λ1 <| B | · λ2, the blazed wavelength λb (3λ) in the first basic structure is made smaller than the blazed wavelength λb (2λ) in the third basic structure. .

With the above configuration, the second optical path difference providing structure can be designed with priority on the second light flux. As a result, the utilization efficiency of the light of the second light flux passing through the intermediate region can be increased, and the efficiency around the spot focused on the information recording surface of the second optical disk such as a DVD can be increased. Thus, the spot diameter of the focused spot on the information recording surface can be made appropriate without increasing.
The light use efficiency of the second light flux changes discontinuously at the boundary between the intermediate area and the central area, and the light use efficiency of the second light flux in the intermediate area across the boundary changes the light use efficiency of the second light flux in the central area. It is preferable to make it higher than the utilization efficiency. FIG. 8A is shown as an example. In FIG. 8 (a), when using the DVD as the second optical disk, the diffraction efficiency of the second light flux (the one-dot chain line) changes discontinuously at the boundary between the central region and the intermediate region. The diffraction efficiency of the second light beam just before the boundary of the intermediate region is higher than the diffraction efficiency of the second light beam just before the boundary of the central region. More preferably, the light use efficiency of the second light flux changes discontinuously at the boundary between the intermediate area and the central area, and the average value of the light use efficiency of the second light flux in the intermediate area is calculated as the second light flux in the central area. Is equal to or higher than the average value of the light utilization efficiency.

The blazed wavelength is a wavelength at which the diffraction efficiency is highest in a certain diffractive structure. In a diffractive structure in which a light beam having a different wavelength passes, depending on which wavelength the blazed wavelength is determined, The diffraction efficiency can be set arbitrarily. The blazed wavelength λb (3λ) is preferably λ1 ≦ λb (3λ) <λ2. More preferably, λb (3λ) is 405 to 510 nm. The blazed wavelength λb (2λ) is preferably λ1 <λb (2λ) ≦ λ2. More preferably, λb (2λ) is 450 to 550 nm.

In addition, the blazed wavelength in the second basic structure may be the same as or different from the blazed wavelength in the fourth basic structure.

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

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

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

In addition, when the second optical path difference providing structure has such a fifth basic structure in addition to the third basic structure, the first optical path difference providing structure has a first difference as compared with the case where the second optical path difference providing structure does not have the fifth basic structure. The decrease in the light utilization efficiency of the second optical path difference providing structure with respect to the optical path difference providing structure becomes larger, and the problem that the condensed spot becomes thicker when using the second optical disc becomes larger. Therefore, since the subject of this invention becomes a big aspect, the effect of this invention also becomes a big thing.

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. More preferably, P is 2 or less. The blazed wavelength λb (1λ) in the sixth basic structure is preferably 385 to 425 nm.

The numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the first optical disc is NA1, and the numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the second optical disc. Is NA2 (NA1> NA2), and the image-side numerical aperture of the objective lens necessary for reproducing / recording information on the third optical disk is NA3 (NA2> NA3). NA1 is preferably 0.75 or more and 0.9 or less, and more preferably 0.8 or more and 0.9 or less. In particular, NA1 is preferably 0.85. NA2 is preferably 0.55 or more and 0.7 or less. In particular, NA2 is preferably 0.60 or 0.65. NA3 is preferably 0.4 or more and 0.55 or less. In particular, NA3 is preferably 0.45 or 0.53.

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

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

The objective lens preferably satisfies the following conditional expression (4).
0.8 ≦ d / f ≦ 1.5 (4)
Here, d represents the thickness (mm) on the optical axis of the objective lens, and f represents the focal length of the objective lens in the first light flux.

When an optical disk with a short wavelength and high NA such as BD is used, there is a problem that astigmatism is likely to occur in the objective lens and decentration coma is likely to occur, but the conditional expression (4) is satisfied. As a result, it is possible to suppress the generation of astigmatism and decentration coma.

Also, satisfying conditional expression (4) results in a thick objective lens with a thick on-axis objective lens, so that the working distance during CD recording / playback tends to be short. By providing the objective lens with the first optical path difference providing structure of the invention, a working distance in CD recording / reproduction can be sufficiently ensured, so that the effect of the present invention becomes more remarkable.

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 (5).
-0.01 <m1 <0.01 (5)

In addition, when the second light beam is incident on the objective lens as parallel light or substantially parallel light, the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens satisfies the following expression (6). Is preferred.
-0.01 <m2 <0.01 (6)

On the other hand, when the second light beam is incident on the objective lens as diverging light, the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens preferably satisfies the following expression (6) ′. .
−0.025 <m2 ≦ −0.01 (6) ′

When the third light beam is incident on the objective lens as a parallel light beam or a substantially parallel light beam, the imaging magnification m3 of the objective lens when the third light beam enters the objective lens satisfies the following formula (7). Is preferred.
-0.01 <m3 <0.01 (7)

On the other hand, when the third light beam is incident on the objective lens as diverging light, it is preferable that the imaging magnification m3 of the objective lens when the third light beam enters the objective lens satisfies the following expression (7) ′. .
−0.025 <m3 ≦ −0.01 (7) ′

Also, the working distance (WD) of the objective optical element when using the third optical disk is preferably 0.15 mm or more and 1.5 mm or less. Preferably, it is 0.3 mm or more and 0.9 mm or less. Next, the WD of the objective optical element when using the second optical disc is preferably 0.2 mm or more and 1.3 mm or less. Furthermore, the WD of the objective optical element when using the first optical disk is preferably 0.25 mm or more and 1.0 mm or less.

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 or the like and to suppress a variation in diffraction efficiency at the time of a wavelength variation. 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 where the step is directed in the direction of the optical axis, and (b) is a diagram showing a state where the step is directed in the 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. (A), (b), (c) is a conceptual diagram of the 1st optical path difference providing structure. It is a figure which shows schematically the structure of optical pick-up apparatus PU1 of this Embodiment which can record and / or reproduce | regenerate information appropriately with respect to BD, DVD, and CD which are different optical disks. (A), (b) is a figure which compares and shows an Example and a comparative example by taking diffraction efficiency on a vertical axis | shaft and taking a pupil radius on a horizontal axis.

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

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

As shown in FIG. 1, in the single objective lens OL according to the present embodiment, a central region CN including an optical axis on the aspherical optical surface on the light source side, an intermediate region MD arranged around the central region CN, Further, a peripheral region OT disposed around the periphery is formed concentrically with the optical axis as the center. Although not shown, the first optical path difference providing structure already described in detail is formed in the center region CN, and the second optical path difference providing structure already described in detail is formed in the intermediate region MD. In addition, a third optical path difference providing structure is formed in the peripheral region OT. In the present embodiment, the third optical path difference providing structure is a blazed diffractive structure. The objective lens of the present embodiment is a plastic lens. The first optical path difference providing structure formed in the central region CN of the objective lens OL is a structure in which the first basic structure and the second basic structure are overlapped as shown in FIG. The first-order diffracted light amount of the first light beam that has passed through the first basic structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the first basic structure is set to any other order. The first order diffracted light amount of the third light flux that has passed through the first basic structure is made larger than any other order diffracted light amount, and is provided at least near the optical axis of the central region CN. In the basic structure, the step is directed in the direction opposite to the optical axis. In the second basic structure, the second-order diffracted light quantity of the first light flux that has passed through the second basic structure is more than the diffracted light quantity of any other order. And the primary of the second light flux that has passed through the second basic structure. The diffracted light larger than the other diffracted light of any order, larger than the third light flux of the first-order diffracted light of other diffraction light amount of any order which has passed through the second basic structure. The blazed wavelength λb (3λ) in the first basic structure of the first optical path difference providing structure is smaller than the blazed wavelength λb (2λ) in the third basic structure of the second optical path difference providing structure.

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. The converged light beam is reflected by the polarization beam splitter BS, and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. The information recorded on the BD can be read by using the output signal of the light receiving element PD to focus or track the objective lens OL by the biaxial actuator AC1. Here, when the wavelength fluctuation occurs in the first light flux or when recording / reproducing of a BD having a plurality of information recording layers, the spherical aberration generated due to the wavelength fluctuation or different information recording layers is changed in magnification. Correction can be made by changing the divergence angle or convergence angle of the light beam incident on the objective optical element OL by changing the collimating lens COL as means in the optical axis direction.

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

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

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

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

(Example)
Examples that can be used in the above-described embodiment will be described below. In the following (including 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, λ is the wavelength of the incident light beam, λB is the manufacturing wavelength (blazed wavelength), dor is the diffraction order, and B _2i is the coefficient of the optical path difference function.

Example 1
The objective lens of Example 1 is a plastic single lens. FIG. 6 shows a conceptual diagram of the first optical path difference providing structure of the first embodiment (FIG. 6 is a conceptual diagram different from the actual shape of the first embodiment). The first optical path difference providing structure of Example 1 is a 1/1/1 blaze-type diffractive structure in the second basic structure BS2, which is a 2/1/1 blaze-type diffractive structure, in the entire central region. This is an optical path difference providing structure in which the first basic structure BS1 is overlapped. Further, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA. Since λ1 = 405 nm and λ2 = 660 nm, | A | · λ1 is 405 and | B | · λ2 is 660. Therefore, | A | · λ1 <| B | · λ2. Here, the blazed wavelength λb (3λ) of the first basic structure in the first optical path difference providing structure in the central region is set to 470 nm, the blazed wavelength 385 nm of the second basic structure, and the second optical path difference providing structure in the intermediate region in the second optical path difference providing structure. The blazed wavelength λb (2λ) of the three basic structures was set to 530 nm, and the blazed wavelength of the fourth basic structure was set to 385 nm. Therefore, the blazed wavelength λb (3λ) in the first basic structure is smaller than the blazed wavelength λb (2λ) in the third basic structure. The blazed wavelength λb (1λ) of the sixth basic structure in the third optical path difference providing structure in the peripheral region is 405 nm.

In addition, the second optical path difference providing structure of Example 1 also has a 1/1/1 blaze type structure in the fourth basic structure BS4 that is a 2/1/1 blaze type diffraction structure in the entire intermediate region. This is a structure in which the third basic structure BS3 which is a diffraction structure is overlapped. The step of the third foundation structure faces in the direction opposite to the optical axis, and the step of the fourth foundation structure faces in the direction of the optical axis.

The third optical path difference providing structure of Example 1 is composed of only the sixth basic structure. In the sixth basic structure, the second-order diffracted light amount of the first light beam that has passed through the sixth basic structure is made larger than the diffracted light amount of any other order, and the first-order diffraction of the second light beam that has passed through the sixth basic structure. This is a blaze-type diffractive structure in which the amount of light is made larger than any other order of diffracted light, and the first order diffracted light of the third light beam that has passed through the sixth basic structure is made larger than any other order of diffracted light.

Table 1 shows the lens data of Example 1.

FIG. 8 is a diagram showing the diffraction efficiency on the vertical axis and the pupil radius on the horizontal axis, and shows the result of the simulation performed by the present inventor. FIG. 8B shows the same specifications as in Example 1, but the blazed wavelength λb (3λ) of the first basic structure in the first optical path difference providing structure in the central region is 470 nm, and the second basic structure is blazed. It is a simulation result of a comparative example with a wavelength of 385 nm, a blazed wavelength λb (2λ) of the third basic structure in the second optical path difference providing structure in the intermediate region = 470 nm, and a blazed wavelength of 385 nm of the fourth basic structure. Obviously, the diffraction efficiency at the time of using the DVD in the intermediate region is gradually lower than that in the central region, so that a phenomenon that the spot diameter becomes thick may occur.

On the other hand, in the case of Example 1 in which λb (3λ) <λb (2λ), as shown in FIG. The light use efficiency in the light changes discontinuously, and the light use efficiency in the DVD use light in the intermediate region across the boundary is higher than the light use efficiency in the DVD use light in the central region. The phenomenon that the diameter increases can be suppressed. On the other hand, in the intermediate region, the diffraction efficiency when using the DVD exceeds the diffraction efficiency when using the BD. As a result, the diffraction efficiency of the intermediate region is low for BD, but the diffraction efficiency of the peripheral region is high. There is no.

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 (λ1 <λ2), and a third light flux with a third wavelength λ3 (λ2 <λ3) 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 objective lens is a single lens made of plastic,
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 has at least a first basic structure,
The first basic structure makes the A-order diffracted light amount of the first light beam that has passed through the first basic structure larger than any other order of diffracted light amount, and B of the second light beam that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, making the C-order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The second optical path difference providing structure has at least a third basic structure,
The third basic structure makes the A-order diffracted light amount of the A-th beam that has passed through the third basic structure larger than any other order diffracted light amount, and B of the second light beam that has passed through the third basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, and making the C-order diffracted light quantity of the third light flux that has passed through the third basic structure larger than any other order diffracted light quantity,
In the case of | A | · λ1> | B | · λ2, the blazed wavelength λb (3λ) in the first basic structure is larger than the blazed wavelength λb (2λ) in the third basic structure,
In the case of | A | · λ1 <| B | · λ2, the blazed wavelength λb (3λ) in the first basic structure is smaller than the blazed wavelength λb (2λ) in the third basic structure. Objective lens.
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 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 the third basic structure and the fourth basic structure are overlapped,
The fourth foundation structure makes the D-order diffracted light quantity of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light quantity, and the E of the second light flux that has passed through the fourth foundation structure. The next diffracted light amount is made larger than any other order diffracted light amount, and the F-order diffracted light amount of the third light beam that has passed through the fourth basic structure is made larger than any other order diffracted light amount. The objective lens according to claim 1.
3. The objective lens according to claim 1, wherein the first basic structure is a blazed structure, and the second basic structure is a blazed structure.
A, B, C, D, E, and F are respectively
| A | = 1
| B | = 1
| C | = 1
| D | = 2
| E | = 1
| F | = 1
The objective lens according to claim 2, wherein:
The objective lens according to any one of claims 2 to 4, wherein the blazed wavelength in the second basic structure is equal to the blazed wavelength in the fourth basic structure.
The light utilization efficiency of the second light flux changes discontinuously at the boundary between the intermediate area and the central area, and the light utilization efficiency of the second light flux in the intermediate area across the boundary is the center area. The objective lens according to claim 1, wherein the use efficiency of the light of the second light flux is higher than that of the objective lens according to claim 1.
7. The objective according to claim 1, wherein the blazed wavelength λb (3λ) is 405 to 510 nm, and the blazed wavelength λb (2λ) is 450 to 550 nm. lens.
8. The peripheral region according to claim 1, wherein the peripheral region has a third optical path difference providing structure, and a blazed wavelength λb (1λ) in the third optical path difference providing structure is 385 to 425 nm. The objective lens described in the item.
The objective lens according to any one of claims 1 to 8, wherein in the first basic structure provided in the central region, all steps are directed in a direction opposite to the optical axis.
The objective lens according to any one of claims 2 to 9, wherein in the second basic structure provided in the central region, all the steps are directed in the direction of the optical axis.
The first optical path difference providing structure provided at least in the vicinity of the optical axis of the central region has both a step that faces the direction opposite to the optical axis and a step that faces the direction of the optical axis. ,
The step amount d11 of the step facing the direction opposite to the optical axis and the step amount d12 of the step facing the direction of the optical axis satisfy the following conditional expressions (2) and (3). The objective lens according to claim 1, wherein:
0.6 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (3)
0.6 · (λ1 / (n-1)) <d12 <1.5 · (2λ1 / (n-1)) (4)
Here, n represents the refractive index of the objective lens at λ1.
The objective lens according to claim 11, wherein the conditional expressions (2) and (3) are satisfied in all regions of the central region.
The objective lens according to claim 11, wherein the following conditional expression is satisfied.
0.9 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (2) "
0.9 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (3) "
The objective lens according to claim 13, wherein the conditional expressions (2) "and (3)" are satisfied in all the regions of the central region.
15. The number of steps in the central region facing in the direction opposite to the optical axis is greater than the number of steps in the direction of the optical axis. The objective lens according to claim 1.
The objective lens according to claim 1, wherein the following conditional expression is satisfied.
0.8 ≦ d / f ≦ 1.5 (4)
However, 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.
The second optical path difference providing structure is a structure in which a fifth basic structure is overlaid in addition to the third basic structure,
The fifth basic structure makes the 0th-order diffracted light quantity of the first light beam 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 quantity is made larger than any other order diffracted light quantity, and the G-order diffracted light quantity of the third light flux that has passed through the fifth basic structure is made larger than any other order diffracted light quantity. The objective lens according to any one of claims 1 to 16, wherein the objective lens is.
The objective lens according to any one of claims 2 to 16, wherein the second optical path difference providing structure includes only the third basic structure and the fourth basic structure.
The objective lens according to claim 1, wherein the following conditional expressions (5), (6), and (7) are satisfied.
-0.01 <m1 <0.01 (5)
-0.01 <m2 <0.01 (6)
-0.01 <m3 <0.01 (7)
However, m1 represents the magnification of the objective lens when the first light beam is incident on the objective lens, m2 represents the magnification of the objective lens when the second light beam is incident on the objective lens, m3 represents the magnification of the objective lens when the third light beam is incident on the objective lens.
An optical pickup device comprising the objective lens according to any one of claims 1 to 19.
An optical information recording / reproducing apparatus comprising the optical pickup apparatus according to claim 20.