WO2013084558A1

WO2013084558A1 - Objective lens for optical pickup device, optical pickup device and optical information recording and reproducing device

Info

Publication number: WO2013084558A1
Application number: PCT/JP2012/073430
Authority: WO
Inventors: 井上寿志
Original assignee: コニカミノルタ株式会社
Priority date: 2011-12-09
Filing date: 2012-09-13
Publication date: 2013-06-13

Abstract

Provided are an objective lens for an optical pickup device, an optical pickup device using the same, and an optical information recording and reproducing device which allow three types of optical disks including BD, DVD and CD to be replaceable by means of a common objective lens with no restriction on optical magnification while allowing for greater design freedom, high efficiency, and excellent manufacturability. A second optical path difference giving structure provided on the intermediate region of an objective lens is a step-like structure wherein the number of steps for each annular zone is identical. The second optical path difference giving structure sets the amount of zero-order diffracted light of a first luminous flux that passed through said second optical path difference giving structure to be greater than the amount of any order diffracted light and sets the amount of first-order diffracted light of a second luminous flux that passed through said second optical path difference giving structure to be greater than the amount of any order diffracted light. Further, said second optical path difference giving structure sets the amount of first-order diffracted light of a third luminous flux that passed through said second optical path difference giving structure to be greater than the amount of any order diffracted light.

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 a diffractive structure having a wavelength dependency of spherical aberration in the objective lens.

Patent Document 1 describes an objective lens that has a step-like diffractive structure and can be used in common for three types of optical disks. Patent Document 2 superimposes two basic structures that are diffractive structures. An objective lens that can be used in common with three types of optical discs and an optical pickup device equipped with this objective lens are described.

By the way, to compensate for spherical aberration for three different disc thicknesses, and to satisfy each temperature, temperature characteristics to correct spherical aberration caused by refractive index change when environmental temperature changes are satisfied. It can be said that a minimum of three degrees of freedom are necessary to achieve this. However, in the case of the combination of the diffraction orders of Patent Document 1, since compatibility is realized with “refractive surface + diffractive surface + finite light”, it is impossible to realize BD / DVD / CD compatibility with infinite light. Become. Furthermore, in the case of a slim type (for example, an effective diameter Φ for BD of 2.7 mm or less), in the case of a BD / DVD / CD compatible lens, the CD needs to have diverging light incident in order to increase the working distance of the CD. In that case, since the effective diameter is larger than the infinite light incidence even with the same NA, there is a problem that the diffraction efficiency of the BD is lowered.

On the other hand, in Example 1 disclosed in Patent Document 2, the optical surface of the objective lens has a central region for condensing a BD / DVD / CD light beam, and a BD / DVD light beam around the central region. And a peripheral region that collects a BD light beam around the intermediate region, and the intermediate region is a second structure in which three diffraction structures (basic structures) are superimposed. An optical path difference providing structure is provided. However, when the three diffractive structures are superposed in this manner, the shape of the second optical path difference providing structure becomes complicated, and the annular zone width becomes small, which makes it difficult to manufacture. On the other hand, Example 4 disclosed in Patent Document 2 has the same problem as Patent Document 1.

JP 2009-245575 A JP 2011-96350 A

The present invention has been made to solve the above-mentioned problems, and enables the compatibility of three types of optical discs of BD / DVD / CD with a common objective lens while limiting the optical system magnification. An objective lens for an optical pickup device having excellent design flexibility, high efficiency, and excellent manufacturability, and an optical pickup device and an optical information recording / reproducing device using the objective lens And

The objective lens according to claim 1, wherein a first light source that emits a first light beam having a first wavelength λ1, a second light source that emits a second light beam having a second wavelength λ2 (λ2> λ1), and a third wavelength. a third light source that emits a third light beam having a wavelength of λ3 (λ3> λ2), and recording and / or reproducing information on a first optical disk having a protective substrate with a thickness of t1 using the first light beam. Recording and / or reproducing information on the second optical disc having a protective substrate having a thickness t2 (t1 <t2) using the second light flux, and a thickness t3 (t2 <t) using the third light flux. an objective lens used in an optical pickup device for recording and / or reproducing information of a third optical disc having a protective substrate at t3),
The optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region,
The central region has a first optical path difference providing structure,
The intermediate region has a second optical path difference providing structure,
The objective lens condenses the first light flux that passes through the central area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the central area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the central region is condensed on the information recording surface of the third optical disc. Condensing so that information can be recorded and / or reproduced,
The objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the intermediate area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the intermediate region is condensed on the information recording surface of the third optical disc. Without collecting light so that information can be recorded and / or reproduced.
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the peripheral area. The second light flux is not condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc, and the third light flux passing through the peripheral region is used as the information recording surface of the third optical disc. Do not concentrate so that information can be recorded and / or reproduced
The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
The first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and 1 of the second light flux that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, making the first order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The second basic structure makes the second-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and 1 of the second light beam that has passed through the second basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, making the first order diffracted light quantity of the third light flux that has passed through the second basic structure larger than any other order diffracted light quantity,
The second optical path difference providing structure is a staircase structure having a plurality of small staircase structures having the same number of steps, and the second optical path difference providing structure is a first light flux that has passed through the second optical path difference providing structure. Making the 0th-order diffracted light quantity larger than any other order diffracted light quantity, and making the first-order diffracted light quantity of the second light flux that has passed through the second optical path difference providing structure larger than any other order diffracted light quantity; The first-order diffracted light amount of the third light beam that has passed through the second optical path difference providing structure is made larger than any other order diffracted light amount.

As a result of diligent research, the present inventor has found an example in which the second optical path difference providing structure is compatible with the first optical path difference providing structure even when the second optical path difference providing structure is a simple step structure having the same number of steps in each zone. did.
That is, the second optical path difference providing structure makes the 0th-order diffracted light quantity of the first light beam that has passed through the second optical path difference providing structure larger than any other order diffracted light quantity, and passed through the second optical path difference providing structure. The first order diffracted light amount of the second light beam is made larger than any other order diffracted light amount, and the first order diffracted light amount of the third light beam that has passed through the second optical path difference providing structure is made higher than any other order diffracted light amount. When it is increased (this is referred to as a (0/1/1) structure), as shown in FIG. 1, the optical path difference function shown in [Equation 1] of the first and second light fluxes of the objective lens is shown. However, it has been found that the central region and the middle region are continuous. As a result, the influence of spherical aberration can be reduced when a wavelength change occurs.

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

Also, since the imaging magnification of the objective lens is set to 0 for light beams having three different wavelengths, that is, infinite parallel light can be used, the efficiency when using a BD or DVD can be increased. In addition, since the second optical path difference providing structure is a simple staircase structure having a plurality of small staircase structures having the same number of steps, the zone width can be widened to increase the light utilization efficiency. This makes it easy to manufacture a mold for forming the objective lens, and suppresses efficiency reduction due to manufacturing errors as much as possible. Furthermore, according to the present invention, it is possible to reduce the positional deviation in the optical axis direction of the wavefront aberration best position when the first light beam undergoes a wavelength change of 1 nm. That is, chromatic aberration when using the first optical disk can be reduced.

The objective lens according to claim 2 is characterized in that, in the invention according to claim 1, in the second optical path difference providing structure, the small step type structure has two steps (binary structure).

According to a third aspect of the present invention, there is provided the objective lens according to the second aspect, wherein the height of each step of the two-step structure of the two steps is h (μm), and the step is directed in the optical axis direction. The following expression is satisfied, when the case is positive and the case where the step is opposite to the optical axis is negative.
-1.0 ≦ h ≦ -0.6 (A)
0.6 ≦ h ≦ 1.0 (B)

According to a fourth aspect of the present invention, there is provided the objective lens according to the first aspect, wherein the second optical path difference providing structure has three steps of the small step type structure.

According to a fifth aspect of the present invention, in the invention according to the fourth aspect, the height per step of the three-step small structure of the three steps is h (μm), and the step is directed in the optical axis direction. The following expression is satisfied, when the case is positive and the case where the step is opposite to the optical axis is negative.
-1.2 ≦ h ≦ -0.7 (C)
2.7 ≦ h ≦ 4.4 (D)

With the configuration according to claim 4 or claim 5, the height of one step can be reduced, and the efficiency of BD and DVD can be increased. However, the number of steps may be less than 3 at the boundary of the region.

The objective lens according to claim 6 is the objective according to claim 1, wherein the second optical path difference providing structure has four steps in the small step type structure. lens.

According to a seventh aspect of the invention, there is provided the objective lens according to the sixth aspect of the invention, wherein the height of one step of the four-step structure of the four steps is h (μm), and the step is directed in the optical axis direction. The following expression is satisfied, when the case is positive and the case where the step is opposite to the optical axis is negative.
-3.4 ≦ h ≦ -2.0 (E)
1.4 ≦ h ≦ 2.3 (F)

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 the third optical path difference providing structure is a blaze type. The structure is characterized in that the second-order diffracted light amount of the first light flux that has passed through the third optical path difference providing structure is made larger than any other order diffracted light amount.

Thereby, the temperature characteristic can be satisfied by using the diffraction power of the third optical path difference providing structure, and the optical path difference function of the objective lens is continuous in the intermediate region and the peripheral region. When this occurs, the influence of spherical aberration can be reduced. Moreover, when the second light flux passes through the peripheral area and becomes flare light, it can be separated from the main light that passes through the intermediate area and is condensed on the information recording surface of the second optical disk, thereby suppressing the generation of an error signal. it can.

The objective lens according to claim 9 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 the third optical path difference providing structure includes a plurality of optical path difference providing structures. A staircase structure having a small staircase structure, wherein the 0th-order diffracted light quantity of the first light beam that has passed through the third optical path difference providing structure is made larger than any other order diffracted light quantity.

Thereby, the temperature characteristic can be satisfied by using the diffraction power of the third optical path difference providing structure, and the optical path difference function of the objective lens is continuous in the intermediate region and the peripheral region. When this occurs, the influence of spherical aberration can be reduced.

An objective lens according to a tenth aspect is the invention according to the ninth aspect, wherein the third optical path difference providing structure has a two-step (binary structure) structure of the small staircase structure.

An objective lens according to an eleventh aspect is the invention according to the tenth aspect, wherein a height of one step of the two-step structure of the two steps is set to h (μm), and the step has an optical axis direction. It is characterized in that the following equation is satisfied when the direction is facing positive and the step is facing the opposite direction to the optical axis.
-1.0 ≦ h ≦ -0.6 (G)
0.6 ≦ h ≦ 1.0 (H)

The objective lens according to a twelfth aspect is the invention according to the ninth aspect, wherein the third optical path difference providing structure has three steps of the small staircase structure.

The objective lens described in claim 13 is the invention described in claim 12, wherein the height per step of the three-step small structure of the three steps is h (μm), and the step is in the optical axis direction. It is characterized in that the following equation is satisfied when the direction is facing positive and the step is facing the opposite direction to the optical axis.
-1.2 ≦ h ≦ -0.7 (I)
2.7 ≦ h ≦ 4.4 (J)

The objective lens according to claim 14 is characterized in that, in the invention according to any one of claims 1 to 7, the peripheral region is a refractive surface.

This can increase the light utilization efficiency.

An objective lens according to a fifteenth aspect of the present invention is the objective lens according to any one of the first to fourteenth aspects, wherein an effective diameter for recording and / or reproducing information on the first optical disc is φ1 (mm ), The following expression is satisfied.
1.8 ≦ φ1 ≦ 4.0 (1)

Thereby, it can be widely applied from a thin optical pickup device called a so-called slim type to an optical pickup device called a half-height type. Furthermore, it is more preferable when the following formula is satisfied.
2.0 ≦ φ1 ≦ 4.0 (1 ')

The objective lens described in claim 16 satisfies the following expression when the working distance of the third optical disc is CW (mm) in the invention described in any one of claims 1-15. Features.
CW ≧ 0.2 (2)

According to the present invention, the working distance when using the third optical disk can be secured so as to satisfy the expression (2).

The objective lens according to claim 17 is the objective lens according to any one of claims 1 to 16, wherein the main light of the third light flux condensed on the information recording surface of the third optical disc and the flare light of the third light flux. When the distance is x (μm), the following expression is satisfied.
| X | ≧ 5 (3)

According to the present invention, since the expression (3) can be satisfied, flare light, which is a light beam outside the effective diameter of the third light beam, can be separated from the main light, so that an error signal can be prevented from being generated.

The objective lens described in Item 18 satisfies the following expression when the annular zone width of the second optical path difference providing structure is L (μm) in the invention described in any one of Items 1-17. It is characterized by that.
2 ≦ | L | ≦ 12 (4)

According to the present invention, the zone width can be widened so as to satisfy the expression (4), so that the ease of manufacturing the objective lens is increased.

The objective lens according to claim 19 satisfies the following expression, where Δ (mm) is a positional deviation in the optical axis direction of the wavefront aberration best position when the first light beam undergoes a wavelength change of 1 nm. The objective lens according to any one of claims 1 to 18, wherein:
1.9 × 10 ⁻⁴ ≦ Δ / f ≦ 2.5 × 10 ⁻⁴ (6)

By determining the optical axis position Δ of the wavefront aberration best when the first light beam causes a wavelength change of 1 nm within a range satisfying the expression (6), the influence of the spherical aberration when the wavelength change occurs can be reduced. . For example, when a light source with mode hopping and poor monochromaticity is used, it is possible to reduce the deviation of the optical axis position.

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 (7), (8), and (9), 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 (7)
0.5mm ≤ t2 ≤ 0.7mm (8)
1.0mm ≤ t3 ≤ 1.3mm (9)

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 (10) and (11) （.

1.5 · λ1 <λ2 <1.7 · λ1 (10)
1.8 · λ1 <λ3 <2.0 · λ1 (11)
When BD, DVD, and CD are used as the first optical disc, the second optical disc, and the third optical disc, respectively, the first wavelength λ1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm. The second wavelength λ2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less, and the third wavelength λ3 of the third light source is preferably 415 nm or less. It is 750 nm or more and 880 nm or less, More preferably, it is 760 nm or more and 820 nm or less.

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

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

The condensing optical system has an objective lens. The condensing optical system preferably has a coupling lens such as a collimator in addition to the objective lens. The coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam. The collimator is a type of coupling lens, and is a lens that emits light incident on the collimator as parallel light. In this specification, the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk. The objective lens may be composed of two or more lenses and / or optical elements, or may be composed of a single lens, but is preferably an objective lens composed of a single convex lens. . The objective lens may be a glass lens or a plastic lens, or an optical path difference providing structure is provided on the glass lens with a photo-curing resin, a UV-curing resin, or a thermosetting resin. Although it may be a hybrid lens, it is preferably a plastic lens. When the objective lens has a plurality of lenses, a glass lens and a plastic lens may be mixed and used. When the objective lens includes a plurality of lenses, it may be a combination of a flat optical element having an optical path difference providing structure and an aspherical lens (which may or may not have an optical path difference providing structure). The objective lens preferably has a refractive surface that is aspheric. In the objective lens, the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.

When the objective lens is a glass lens, it is preferable to use a glass material having a glass transition point Tg of 500 ° C. or lower, more preferably 400 ° C. or lower. By using a glass material having a glass transition point Tg of 500 ° C. or lower, molding at a relatively low temperature is possible, so that the life of the mold can be extended. Examples of such a glass material having a low glass transition point Tg include K-PG325 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.

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

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

Moreover, it is preferable to use an alicyclic hydrocarbon-based polymer material such as a cyclic olefin-based resin material as a plastic material constituting the objective lens. The resin material has a refractive index within a range of 1.50 to 1.60 at a temperature of 25 ° C. with respect to a wavelength of 405 nm, and a wavelength of 405 nm according to a temperature change within a temperature range of −5 ° C. to 70 ° C. The refractive index change rate dN / dT (° C. ⁻¹ ) with respect to the range of −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. 2, 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 the spherical aberration that occurs due to the difference between t3 and the spherical aberration that occurs 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. 3, in the spot formed on the information recording surface of the third optical disc by the third light beam that has passed through the objective lens, the light amount density is high in the order from the optical axis side (or the center of the spot) 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. 4A and 4B, 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. 4, it is assumed that the upper side is the light source side and the lower side is the optical disk side, and the optical path difference providing structure is formed on a 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. 4A and 4B.) The length of the step in the direction parallel to the optical axis of the blaze is referred to as a step amount B. (See Fig. 4 (a))

Further, as shown in FIGS. 4C and 4D, the staircase structure has a plurality of small staircase structures in which the cross-sectional shape including the optical axis of the optical element having the optical path difference providing structure has the same number of steps. (Sometimes referred to as a staircase unit). In the present specification, “V step” refers to 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 staircase structure. In other words, it is divided by V steps and divided into V ring zones. Particularly, a stepped structure having three or more steps has a small step and a large step.

For example, the optical path difference providing structure illustrated in FIG. 4C is referred to as a five-step staircase structure, and the optical path difference providing structure illustrated in FIG. 4D is referred to as a two-step staircase structure (also referred to as a binary structure). . A two-step staircase structure will be described below. A plurality of annular zones including a plurality of concentric annular zones around the optical axis, and a plurality of annular zones including the optical axis of the objective lens have a plurality of stepped surfaces Pa and Pb extending in parallel to the optical axis, The light source side terrace surface Pc for connecting the light source side ends of the adjacent step surfaces Pa and Pb and the optical disk side terrace surface Pd for connecting the optical disk side ends of the adjacent step surfaces Pa and Pb are formed. The surface Pc and the optical disc side terrace surface Pd are alternately arranged along the direction intersecting the optical axis.

In the staircase structure, the length in the direction perpendicular to the optical axis of one step unit is referred to as a pitch P.
(See FIGS. 4C and 4D) The length of the step in the direction parallel to the optical axis of the staircase is referred to as step amounts B1 and B2. In the case of a stepped structure having three or more steps, a large step amount B1 and a small step amount B2 exist. (Refer to FIG. 4 (c)) In the stepped structure, the zone width is indicated by L1 to L7 in FIGS. 4 (c) and 4 (d), and the direction perpendicular to the optical axis between the steps. The width of

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

When the optical path difference providing structure has a staircase structure, there may be a shape in which a 5-step stair unit as shown in FIG. 4C is repeated. Furthermore, it may be a shape in which the pitch of the staircase unit gradually increases as it moves away from the optical axis, or a shape in which the pitch of the staircase unit gradually decreases.

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

Next, the first optical path difference providing structure provided in the central region will be described. The first optical path difference providing structure is a structure in which at least the first basic structure and the second basic structure are overlapped.

The first basic structure is preferably a blazed structure. In addition, the first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and the first-order diffracted light quantity that has passed through the first basic structure. Is made larger than any other order of the diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light quantity. At this time, the step amount of the first basic structure that generates low-order diffracted light does not become excessively large, so that the manufacturing becomes easy, the light quantity loss caused by the manufacturing error can be suppressed, and the diffraction efficiency at the time of wavelength variation It is preferable because fluctuations can be reduced.

Further, at least the first basic structure provided in the vicinity of the optical axis in the central region has a step in the direction opposite to the optical axis. “The step is directed in the direction opposite to the optical axis” means a state as shown in FIG. The first basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis. Preferably, at least a half step in the direction perpendicular to the optical axis from the optical axis to the boundary between the central region and the intermediate region and the step existing between the optical axes are directed in the opposite direction to the optical axis. It is.

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

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

The first basic structure is the first basic structure from the viewpoint of securing a sufficient working distance when using a CD even in a thick objective lens having a thick on-axis thickness, which is used for compatibility with three types of optical disks of BD / DVD / CD. It is preferable to have paraxial power with respect to the light beam. Here, “having paraxial power” means that C ₂ is not 0 when the optical path difference function of the first basic structure is expressed by the following equation (1).

Also, the second basic structure is preferably a blazed structure. In the second basic structure, the second-order diffracted light amount of the first light beam that has passed through the second basic structure is made larger than the diffracted light amount of any other order, and the first-order diffraction of the second light beam that has passed through the first basic structure. The light quantity is made larger than any other order of diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order of diffracted light quantity. At this time, the step amount of the second basic structure that generates low-order diffracted light does not become excessively large, which facilitates manufacturing, reduces the light amount loss due to manufacturing errors, and increases the diffraction efficiency when the wavelength varies. It is preferable because fluctuations can be reduced.

In the second basic structure provided at least near the optical axis in the central region, the level difference faces the direction of the optical axis. “The step is directed in the direction of the optical axis” means a state as shown in FIG. In addition, the second basic structure provided “at least in the vicinity of the optical axis of the central region” refers to a step at least closest to the optical axis. Preferably, a step existing between at least half of the optical axis orthogonal direction from the optical axis to the boundary between the central region and the intermediate region faces the direction of the optical axis.

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.

In this way, the first basic structure in which odd-order diffracted light is generated with respect to the first light flux and the step is directed in the direction opposite to the optical axis at least in the vicinity of the optical axis of the central region, and the first light flux The first basic structure and the second basic structure are generated by superimposing the second basic structures that generate even-order diffracted light with respect to each other and have a step facing the direction of the optical axis at least in the vicinity of the optical axis in the central region. Compared to the case where the steps are overlapped so that the direction of the steps is the same, it is possible to suppress the height of the steps after being overlapped from being increased, and accordingly, the light quantity loss due to manufacturing errors can be suppressed. In addition to this, it is possible to suppress fluctuations in diffraction efficiency during wavelength fluctuations. In addition, since the diffraction power can be adjusted by superimposing the first basic structure and the second basic structure, the working distance of the CD can be increased.

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

The first optical path difference providing structure provided at least in the vicinity of the optical axis of the central region has both a step facing in the opposite direction to the optical axis and a step facing in the direction of the optical axis. It is preferable that the step amount d11 of the step facing the direction opposite to the axis and the step amount d12 of the step facing the direction of the optical axis satisfy the following conditional expressions (12) and (13). More preferably, the following conditional expressions (12) and (13) 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)) (12)
0.6 · (λ1 / (n-1)) <d12 <1.5 · (2λ1 / (n-1)) (13)

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

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

0.39 μm <d11 <1.15 μm (14)
0.39 μm <d12 <2.31 μm (15)

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

As described above, when all the steps of the second foundation structure and the steps of the first foundation structure are aligned and overlapped, d11 and d12 of the first optical path difference providing structure are the following conditional expressions (16) , (17) is preferably satisfied. More preferably, the following conditional expressions (16) and (17) are satisfied in all the regions of the central region.
0.6 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (16)
0.6 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (17)

0.39 μm <d11 <1.15 μm (18)
0.39 μm <d12 <1.15 μm (19)

More preferably, the following conditional expressions (20) and (21) are preferably satisfied. More preferably, the following conditional expressions (20) and (21) are satisfied in all the regions of the central region.
0.9 · (λ1 / (n-1)) <d11 <1.5 · (λ1 / (n-1)) (20)
0.9 · (λ1 / (n-1)) <d12 <1.5 · (λ1 / (n-1)) (21)

0.59 μm <d11 <1.15 μm (22)
0.59 μm <d12 <1.15 μm (23)

In addition, by adopting a first optical path difference providing structure in which the first basic structure and the second basic structure are overlapped, the first basic structure underperforms aberration (undercorrection) when the wavelength increases (wavelength characteristics). On the other hand, the 2nd basic structure allows the aberration to be over-corrected (overcorrection) when the wavelength becomes long (over-wavelength characteristic is over), so that the wavelength characteristic becomes too large or over. Therefore, it is possible to obtain an under-wavelength characteristic with a just good level. The “under right wavelength characteristic of a good level” preferably has an absolute value of λrms of 150 or less. Thereby, even if the objective lens is made of plastic, it is preferable from the viewpoint that it becomes possible to suppress the aberration change at the time of the temperature change.

On the other hand, from the viewpoint of securing the WD of the CD, it is preferable that the contribution rate of the first foundation structure is dominant in the paraxial power compared to the second foundation structure. Thereby, it is preferable that the average pitch of a 1st foundation structure is small compared with the average pitch of a 2nd foundation structure. In another expression, it can be said that the pitch between the steps facing the direction opposite to the optical axis is smaller than the pitch between the steps facing the direction of the optical axis. In the first optical path difference providing structure, It can be said that the number of steps facing in the direction opposite to the optical axis is larger than the number of steps facing in the direction of the optical axis. In addition, it is preferable that the average pitch of a 1st foundation structure is 1/4 or less of the average pitch of a 2nd foundation structure. More preferably, it is 1/6 or less. It is preferable that the average pitch of the first foundation structure is 1/4 or less (preferably 1/6 or less) of the average pitch of the second foundation structure. In another expression, in the first optical path difference providing structure in the central region, the number of steps facing the direction opposite to the optical axis is four times or more than the number of steps facing the direction of the optical axis. Can be said to be preferable. More preferably, it is 6 times or more.

Further, it is preferable that the minimum pitch of the first optical path difference providing structure is 15 μm or less. From this point of view, the ratio p / f1 between the minimum pitch p of the first optical path difference providing structure and the focal length f1 at the first wavelength λ1 is preferably 0.004 or less. More preferably, it is 10 μm or less. Moreover, it is preferable that the average pitch of the first optical path difference providing structure is 30 μm or less. More preferably, it is 20 μm or less. With such a configuration, the WD of the CD can be secured, and the best necessary light used for recording / reproducing information that is generated in all the first to third light fluxes that have passed through the first optical path difference providing structure. The focus position can be separated from the generation position of unnecessary light by the first optical path difference providing structure, and erroneous detection can be reduced. The average pitch is a value obtained by adding all pitches of the first optical path difference providing structure in the central region and dividing the sum by the number of steps of the first optical path difference providing structure in the central region.

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

The first best focus position where the light intensity of the spot formed by the third light flux is the strongest by the third light flux passing through the first optical path difference providing structure, and the second strongest light intensity of the spot formed by the third light flux. It is preferable that the best focus position satisfies the following conditional expression (24). 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 ≦ 0.8 (24)
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 (24) ′ is satisfied.
0.50 ≦ L / f13 ≦ 0.75 (24) ′

A preferred example of the first optical path difference providing structure described above is shown in FIG. Although FIG. 7 shows the first optical path difference providing structure ODS1 as a flat plate for convenience, it may be provided on a single aspherical convex lens. The first foundation structure BS1 is overlaid on the second foundation structure BS2. 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 pitches of the first foundation structure BS1 and the second foundation structure BS2 are matched, and it can be seen that the positions of all the steps of the second foundation structure and the positions of the steps of the first foundation structure match. In this example, 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 is a staircase structure having a plurality of small staircase structures having the same number of steps, and the second optical path difference providing structure is the 0th order of the first light flux that has passed through the second optical path difference providing structure. The diffracted light quantity is made larger than any other order diffracted light quantity, the first-order diffracted light quantity of the second light flux that has passed through the second optical path difference providing structure is made larger than any other order diffracted light quantity, and the second optical path difference The first-order diffracted light quantity of the third light flux that has passed through the providing structure is made larger than any other order diffracted light quantity.

In the second optical path difference providing structure, the small staircase structure is preferably 2 steps (binary structure), 3 steps or 4 steps. Particularly preferred is a three-step process.

In the case of a two-step small staircase structure, the height in the optical axis direction per step is h (μm), and the step is facing the optical axis direction (as shown in FIG. 5A). It is preferable that the following expression is satisfied when the positive and step differences are opposite to the optical axis (as in FIG. 5B).
-1.0 ≦ h ≦ -0.6 (A)
0.6 ≦ h ≦ 1.0 (B)

In the case of a three-step small staircase structure, the height per step is set to h (μm), the case where the step is facing the optical axis, and the step is facing the direction opposite to the optical axis. When negative, it is preferable to satisfy the following formula. At this time, −1.2 ≦ h ≦ −0.7 is a preferable range of the small step value of each step of the small step structure, and 2.7 ≦ h ≦ 4.4 is a preferable range of the large step value of the small step structure. is there. It is preferable that a large step of the small staircase structure is a step facing the optical axis direction, and a small step of each step of the small staircase structure is a step facing the direction opposite to the optical axis.
-1.2 ≦ h ≦ -0.7 (C)
2.7 ≦ h ≦ 4.4 (D)

The small step h in the three-step small staircase structure is 0.9 · 1.09 · λ1 / (n-1) or more and 1.5 · 1.09 · λ1 / (n-1) or less. It is preferable that Note that λ1 is the wavelength of the first light source, and n is the refractive index of the material constituting the objective lens at the wavelength λ1.

In the case of a four-step small staircase structure, the height per step is set to h (μm), the case where the step is facing the optical axis direction, and the step is facing the direction opposite to the optical axis. When negative, it is preferable to satisfy the following formula.
-3.4 ≦ h ≦ -2.0 (E)
1.4 ≦ h ≦ 2.3 (F)

When the annular zone width of the second optical path difference providing structure is L (μm), it is preferable that the minimum annular zone width of the second optical path difference providing structure satisfies the following expression (4). More preferably, all the zone widths of the second optical path difference providing structure satisfy the following expression.
2 ≦ | L | ≦ 12 (4)

The peripheral region may be a refractive surface or a third optical path difference providing structure. When the third optical path difference providing structure is provided in the peripheral region, an arbitrary optical path difference providing structure can be provided. For example, the third optical path difference providing structure may be a blazed structure or a staircase structure.

When the third optical path difference providing structure is a blazed structure, it is preferable to make the second-order diffracted light quantity of the first light beam that has passed through the third optical path difference-providing structure larger than any other order of diffracted light quantity. At this time, the first-order diffracted light amount of the second light beam that has passed through the third optical path difference providing structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the third light beam that has passed through the third optical path difference-providing structure. It is preferable to make the amount of diffracted light larger than the amount of diffracted light of any other order.

When the third optical path difference providing structure is a stepped structure having a plurality of small staircase structures, the 0th-order diffracted light amount of the first light beam that has passed through the third optical path difference providing structure is diffracted in any other order. It is preferable to make it larger than the amount of light. At this time, the first-order diffracted light amount of the second light beam that has passed through the third optical path difference providing structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the third light beam that has passed through the third optical path difference-providing structure. It is preferable to make the amount of diffracted light larger than the amount of diffracted light of any other order. (This type of optical path difference providing structure may be referred to as a 0/1/1 structure.)

When the third optical path difference providing structure is a 0/1/1 structure, it is preferable that the third optical path difference providing structure has a two-step structure (binary structure) or one of three steps.

If the small staircase structure of the third optical path difference providing structure is 2 steps, the height per step of the small staircase structure is h (μm), and the step is positive, the step It is preferable that the following expression is satisfied, when the case where is oriented in the direction opposite to the optical axis is negative.
-1.0 ≦ h ≦ -0.6 (G)
0.6 ≦ h ≦ 1.0 (H)

In addition, when the small staircase structure of the third optical path difference providing structure is 3 steps, the height per step of the small staircase structure is set to h (μm), and the case where the step is facing the optical axis direction is correct. It is preferable that the following expression is satisfied when the step is in a direction opposite to the optical axis and negative.
-1.2 ≦ h ≦ -0.7 (I)
2.7 ≦ h ≦ 4.4 (J)

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.

In addition, when the effective diameter with respect to the 1st light beam of an objective lens is set to (phi) 1 (mm), it is preferable to satisfy | fill the following formula | equation.
1.8 ≦ φ1 ≦ 4.0 (1)
More preferably, the following expression is satisfied.
2.0 ≦ φ ≦ 3.0 (1 ′)

The objective lens preferably satisfies the following conditional expression (5).
1.0 ≦ d / f ≦ 1.5 (5)
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. More preferably, 1.0 ≦ d / f ≦ 1.2.

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 (5) is satisfied. As a result, it is possible to suppress the generation of astigmatism and decentration coma.

In addition, satisfying conditional expression (5) 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 beam becomes parallel light or substantially parallel light, it is preferable that the imaging magnification m1 of the objective lens when the first light beam is incident on the objective lens satisfy the following formula (26).
-0.01 <m1 <0.01 (26)

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 (27). Is preferred.
-0.01 <m2 <0.01 (27)

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 (27) ′. .
−0.025 <m2 ≦ −0.01 (27) ′

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 is incident on the objective lens satisfies the following expression (28). Is preferred.
-0.01 <m3 <0.01 (28)

On the other hand, when the third light beam is incident on the objective lens as diverging light, the imaging magnification m3 of the objective lens when the third light beam is incident on the objective lens preferably satisfies the following expression (28) ′. .
−0.025 <m3 ≦ −0.01 (28) ′

Also, the working distance (WD) of the objective optical element when using the third optical disk is preferably 0.2 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.

When the distance between the main light of the third light beam condensed on the information recording surface of the third optical disk and the light beam (flare light) outside the effective diameter of the third light beam is x (μm), it is preferable that the following expression is satisfied. . At this time, as shown in FIG. 39, x (μm) indicates the distance in the optical axis direction between the portion farthest from the optical axis of the main light and the portion closest to the optical axis of the flare light.
| X | ≧ 5 (3)

Further, if the positional deviation in the optical axis direction of the wavefront aberration best position when the wavelength of the first light beam changes by 1 nm is Δ (mm), it is preferable to satisfy the following formula (6). The wavefront aberration best position here refers to the position in the optical axis direction where the total wavefront aberration such as longitudinal chromatic aberration and chromatic spherical aberration is minimized when the wavelength of the first light beam changes by 1 nm.
1.9 × 10 ⁻⁴ ≦ Δ / f ≦ 2.5 × 10 ⁻⁴ (6)
In addition, it is more preferable to satisfy the formula.
1.95 × 10 ⁻⁴ ≦ Δ / f ≦ 2.05 × 10 ⁻⁴ (6 ′)

The optical pickup device preferably includes a coupling lens through which at least the first light beam and the second light beam pass, and an actuator that moves the coupling lens in the optical axis direction. Further, when the first light beam passes, the coupling lens can be displaced in the optical axis direction by an actuator, and when the second light beam passes, the coupling lens is fixed in the position in the optical axis direction. It is preferable.

For example, in order to deal with a first optical disc having a plurality of information recording layers, when the first optical disc is used, the coupling lens is displaced in the optical axis direction so as to correspond to recording / reproduction on each information recording layer. Can be considered. In such a case, the function of already displacing the coupling lens in the optical axis direction is indispensable, but when using the second optical disc, the coupling lens is desired to be fixed without being displaced in the optical axis direction. There is a case. The reason for this is that flare does not occur when the first optical disc is used, but flare occurs when the second optical disc is used. Therefore, by changing the coupling lens, the flare aberration changes, and as a result, the flare is changed. May cause adverse effects on recording / playback, the reason for always keeping the initial position of the coupling lens to determine the type of the second optical disk, or simply the drive For example, the cost of firmware for displacing the coupling lens may be reduced as much as possible.

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 discs of BD / DVD / CD, deterioration of chromatic aberration is suppressed while ensuring a working distance when using a CD. It becomes possible. Furthermore, it is possible to suppress an increase in the height of the step of the optical path difference providing structure, and accordingly, it is possible to suppress a light amount loss due to a manufacturing error and suppress a fluctuation in diffraction efficiency at the time of a wavelength fluctuation. Is possible. It is also possible to provide an objective lens with balanced light utilization efficiency that can maintain high light utilization efficiency for any of the three types of optical disks of BD / DVD / CD. In addition, it is possible to suppress the aberration that occurs when the temperature of the optical pickup device rises, and when the objective lens is made of plastic, an objective lens that can maintain stable performance even when the temperature changes is provided. Is possible. With these effects, recording / reproduction of three types of optical discs of BD / DVD / CD can be performed well with a common objective lens. Furthermore, by making the effective diameter small, the focal length is shortened, and an objective lens suitable for a slim type optical pickup device can be provided.

It is a figure which shows the optical path difference function as an example. It is the figure which looked at the single objective lens OL concerning this Embodiment in the optical axis direction. It is a figure which shows the state which forms the spot which the 3rd light beam which passed the objective lens forms on the information recording surface of a 3rd optical disk. It is an axial direction sectional view showing an example of an optical path difference grant structure, (a) and (b) show an example of a blaze type structure, and (c) and (d) show an example of a step type structure. (A) shows a state in which the step is directed in the direction of the optical axis, and (b) is a diagram showing a state in which the step is directed in a direction opposite to the optical axis. (A) shows a shape in which the step is in the direction of the optical axis in the vicinity of the optical axis, but changes in the middle, and in the vicinity of the intermediate region, the step is in the direction opposite to the optical axis. FIG. 4 is a diagram showing a shape in which a step is directed in the opposite direction to the optical axis in the vicinity of the axis, but is switched in the middle, and the step is directed toward the optical axis in the vicinity of the intermediate region. It is a conceptual diagram of 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. It is a conceptual sectional view at the time of providing the 1st optical path difference providing structure, the 2nd optical path difference providing structure, and the 3rd optical path difference providing structure of Example 1 in a flat plate element. 6 is a graph showing an optical path difference function when using the BD of Example 1. In Example 1, it is a vertical spherical aberration figure at the time of BD use in a reference wavelength (405 nm). In Example 1, it is a longitudinal spherical aberration figure at the time of BD use in the case of changing to +5 nm long wavelength side with respect to a reference wavelength. FIG. 4 is a longitudinal spherical aberration diagram when the CD is used in Example 1. It is a conceptual sectional view at the time of providing the 1st optical path difference providing structure of Example 2, the 2nd optical path difference providing structure, and the 3rd optical path difference providing structure in a flat plate element. 6 is a graph showing an optical path difference function when using a BD of Example 2. In Example 2, it is a longitudinal spherical aberration figure at the time of BD use in a reference wavelength (405 nm). In Example 2, it is a vertical spherical aberration figure at the time of BD use in the case of changing to +5 nm long wavelength side with respect to a reference wavelength. FIG. 6 is a longitudinal spherical aberration diagram when the CD is used in Example 2. It is a conceptual sectional view at the time of providing the 1st optical path difference providing structure of Example 3, the 2nd optical path difference providing structure, and the 3rd optical path difference providing structure in a flat plate element. 10 is a graph showing an optical path difference function when using a BD of Example 3. In Example 3, it is a longitudinal spherical aberration figure at the time of BD use in a reference wavelength (405 nm). In Example 3, it is a vertical spherical aberration figure at the time of BD use in the case of changing to +5 nm long wavelength side with respect to a reference wavelength. FIG. 6 is a longitudinal spherical aberration diagram when the CD is used in Example 3. It is a conceptual sectional view at the time of providing the 1st optical path difference providing structure of Example 4 and the 2nd optical path difference providing structure in a flat plate element. It is a graph which shows the optical path difference function at the time of BD use of Example 4. In Example 4, it is a vertical spherical aberration figure at the time of BD use in a reference | standard wavelength (405 nm). In Example 4, it is a vertical spherical aberration figure at the time of BD use in the case of changing to +5 nm long wavelength side with respect to a reference wavelength. FIG. 6 is a longitudinal spherical aberration diagram when the CD is used in Example 4. It is a conceptual sectional view at the time of providing the 1st optical path difference providing structure of Example 5, the 2nd optical path difference providing structure, and the 3rd optical path difference providing structure in a flat plate element. 10 is a graph showing an optical path difference function when using a BD of Example 5. In Example 5, it is a vertical spherical aberration figure at the time of BD use in a reference wavelength (405 nm). In Example 5, it is a vertical spherical aberration figure at the time of BD use in the case of changing to +5 nm long wavelength side with respect to a reference wavelength. FIG. 10 is a longitudinal spherical aberration diagram when the CD is used in Example 5. It is a conceptual sectional view at the time of providing the 1st optical path difference providing structure of Example 6, the 2nd optical path difference providing structure, and the 3rd optical path difference providing structure in a flat plate element. 10 is a graph showing an optical path difference function when using a BD of Example 6. In Example 6, it is a vertical spherical aberration figure at the time of BD use in a reference wavelength (405 nm). In Example 6, it is a vertical spherical aberration figure at the time of BD use in the case of changing to +5 nm long wavelength side with respect to a reference wavelength. FIG. 10 is a longitudinal spherical aberration diagram when the CD is used in Example 6. It is an example of a longitudinal spherical aberration diagram when using a CD, and is a diagram for explaining a distance between main light and flare light. It is a shape figure before superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 1. FIG. It is a shape figure after superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 1. FIG. It is a shape figure before superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 2. FIG. It is a shape figure after superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 2. FIG. It is a shape figure before superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 3. It is a shape figure after superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 3. It is a shape figure before superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 4. It is a shape figure after superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 4. It is a shape figure before superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 5. FIG. It is a shape figure after superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 5. FIG. It is a shape figure before superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 6. It is a shape figure after superimposing the 1st foundation structure and the 2nd foundation structure about the 1st optical path difference providing structure of the central field in Example 6.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 8 is a diagram schematically showing a configuration of the optical pickup device PU1 of the present embodiment that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks. The optical pickup device PU1 is a slim type and can be mounted on a thin optical information recording / reproducing device. Here, the first optical disc is a BD, the second optical disc is a DVD, and the third optical disc is a CD. 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. 2, in the single objective lens OL according to the present embodiment, a central region CN including the optical axis on the aspherical optical surface on the light source side, an intermediate region MD arranged around the 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. Further, a third optical path difference providing structure or a refracting surface is formed in the peripheral region OT. 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 -1st 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 first basic structure, the step is directed in the direction opposite to the optical axis (that is, has negative power), and the second basic structure is the second-order diffracted light amount of the first light flux that has passed through the second basic structure. Is larger than any other order of diffracted light, and the second substructure is The first-order diffracted light amount of the second light beam that has passed is made larger than any other order diffracted light amount, and the first-order diffracted light amount of the third light beam that has passed through the second basic structure is made larger than any other order diffracted light amount. Enlarge.

In the second optical path difference providing structure, the 0th-order diffracted light quantity of the first light flux that has passed through the second optical path difference providing structure is made larger than any other order diffracted light quantity, and the second optical path difference providing structure passes through the second optical path difference providing structure. The first order diffracted light amount of the light beam is made larger than any other order diffracted light amount, and the first order diffracted light amount of the third light beam that has passed through the optical path difference providing structure is made larger than any other order diffracted light amount.

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

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

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

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

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

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

(Example)
Examples that can be used in the above-described 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). Further, 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 obtained by substituting the coefficients shown in Table 2 into Formula 2.

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 obtained by substituting the coefficient shown in the table into the optical path difference function of the above equation (1). Is done.

Example 1
The objective lens of Example 1 is a plastic single lens, and has an effective diameter φ1 = 2 mm. The first optical path difference providing structure of Example 1 is (1, 1, 1) in the second basic structure BS2 that is a blazed diffraction structure (2, 1, 1) in the entire central region. This is an optical path difference providing structure in which the first basic structure BS1 which is a blazed diffraction structure is overlapped. The second optical path difference providing structure is a three-step staircase type diffraction structure of (0, 1, 1). The third optical path difference structure is a (2, 1, 1) blazed diffraction structure.

Table 1 shows the lens data of Example 1. WD in the table means working distance.

Furthermore, the actual shape of the objective lens was designed based on the lens data of Example 1. The actual shape data are shown in Tables 2A to 2C. By substituting the data shown in Table 2A, Table 2B, and Table 2C (continuous) into the mathematical formula shown in Equation 3, the actual shape data of each annular zone is obtained.

H represents the height from the optical axis in the direction perpendicular to the optical axis. Furthermore, FIG. 9 shows a conceptual cross-sectional view when the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure of Example 1 are provided in a flat plate element. The central region where the first optical path difference providing structure is provided is CN, the intermediate region where the second optical path difference providing structure is provided is the region indicated by MD, and the periphery where the third optical path difference providing structure is provided The region is a region indicated by OT.

FIG. 10 is a graph showing the optical path difference function when the BD is used, with the phase difference on the vertical axis and the height from the optical axis on the horizontal axis, and the optical path difference function is continuous between regions. I understand. FIG. 11 is a longitudinal spherical aberration diagram when using BD at the reference wavelength (405 nm), and FIG. 12 is a longitudinal spherical aberration diagram when using BD when the wavelength is changed to the +5 nm long wavelength side with respect to the reference wavelength. The vertical axis of the graph is 1 when the effective diameter φ1 of the BD is 2.0 mm. FIG. 13 is a vertical spherical aberration diagram when using a CD, showing main light and flare light generated within ± 0.1 mm, and the vertical axis of the graph shows the effective diameter of BD φ1 = 2.0 mm. 1 is assumed. Flares that occur in the dedicated area occur outside the range of -0.01mm to 0.01mm.

In Example 1, the working distance CW when using a CD is 0.2 mm, the distance between the main light and the flare light condensed on the information recording surface of the CD is x = 5 μm, and the second optical path difference providing ring The minimum value of the band width L (μm) is 3.42 μm. Further, d / f = 1.0 where d (mm) is the thickness of the objective lens on the optical axis, and f (mm) is the focal length of the objective lens in the first light flux. When the change in the optical axis position of the wavefront aberration best when the first light beam undergoes a wavelength change of 1 nm is Δ (mm), Δ / f = 2.5 × 10 ⁻⁴ mm.

(Example 2)
The objective lens of Example 2 is a plastic single lens, and has an effective diameter φ1 = 2.4 mm. The first optical path difference providing structure of Example 1 is (1, 1, 1) in the second basic structure BS2 that is a blazed diffraction structure (2, 1, 1) in the entire central region. This is an optical path difference providing structure in which the first basic structure BS1 which is a blazed diffraction structure is overlapped. The second optical path difference providing structure is a three-step staircase type diffraction structure of (0, 1, 1). The third optical path difference structure is a (2, 1, 1) blazed diffraction structure.

Table 3 shows the lens data of Example 2.

Furthermore, the actual shape of the objective lens was designed based on the lens data of Example 2. The actual shape data are shown in Tables 4A to 4B. By substituting the data shown in Table 4A and Table 4B (continuous) into the mathematical formula shown in Formula 3, the actual shape data of each annular zone is obtained.

H represents the height from the optical axis in the direction perpendicular to the optical axis. Furthermore, FIG. 14 shows a conceptual cross-sectional view in the case where the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure of Example 2 are provided in a flat plate element. The central region where the first optical path difference providing structure is provided is CN, the intermediate region where the second optical path difference providing structure is provided is the region indicated by MD, and the periphery where the third optical path difference providing structure is provided The region is a region indicated by OT.

FIG. 15 is a graph showing the optical path difference function when the BD is used with the phase difference on the vertical axis and the height from the optical axis on the horizontal axis. The optical path difference function is continuous between regions. I understand. FIG. 16 is a longitudinal spherical aberration diagram when using BD at the reference wavelength (405 nm), and FIG. 17 is a longitudinal spherical aberration diagram when using BD when the wavelength changes to the +5 nm long wavelength side with respect to the reference wavelength. The vertical axis of the graph is 1 when the effective diameter of the BD φ1 = 2.4 mm. FIG. 18 is a longitudinal spherical aberration diagram when using a CD, showing main light and flare light generated within ± 0.1 mm, and the vertical axis of the graph shows the effective diameter φ1 = 2.4 mm of BD. 1 is assumed.

In Example 2, the working distance CW at the time of using the CD is 0.2 mm, the distance x between the main light and the flare light condensed on the information recording surface of the CD is 10 μm, and the second optical path difference providing ring The minimum value of the band width L (μm) is 6.84 μm. Further, d / f = 1.0 where d (mm) is the thickness of the objective lens on the optical axis, and f (mm) is the focal length of the objective lens in the first light flux. Further, Δ / f = 2.2 × 10 ⁻⁴ mm, where Δ (mm) is the change in the optical axis position of the wavefront aberration best when the first light beam undergoes a wavelength change of 1 nm.

(Example 3)
The objective lens of Example 3 is a plastic single lens, and has an effective diameter φ1 = 2.4 mm. The first optical path difference providing structure of Example 1 is (1, 1, 1) in the second basic structure BS2 that is a blazed diffraction structure (2, 1, 1) in the entire central region. This is an optical path difference providing structure in which the first basic structure BS1 which is a blazed diffraction structure is overlapped. The second optical path difference providing structure is a three-step staircase type diffraction structure of (0, 1, 1). The third optical path difference structure is a two-step staircase type diffraction structure of (0, 1, 1).

Table 5 shows the lens data of Example 3.

Furthermore, the actual shape of the objective lens was designed based on the lens data of Example 3. The actual shape data are shown in Tables 6A to 6B. By substituting the data shown in Table 6A and Table 6B (continuous) into the mathematical formula shown in Formula 3, the actual shape data of each annular zone can be obtained.

H represents the height from the optical axis in the direction perpendicular to the optical axis. Further, FIG. 19 shows a conceptual cross-sectional view in the case where the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure of Example 3 are provided in the flat plate element. The central region where the first optical path difference providing structure is provided is CN, the intermediate region where the second optical path difference providing structure is provided is the region indicated by MD, and the periphery where the third optical path difference providing structure is provided The region is a region indicated by OT.

FIG. 20 is a graph showing the optical path difference function when the BD is used with the phase difference on the vertical axis and the height from the optical axis on the horizontal axis. The optical path difference function is continuous between regions. I understand. FIG. 21 is a longitudinal spherical aberration diagram when using BD at the reference wavelength (405 nm), and FIG. 22 is a longitudinal spherical aberration diagram when using BD when the wavelength changes to the +5 nm long wavelength side with respect to the reference wavelength. The vertical axis of the graph is 1 when the effective diameter of the BD φ1 = 2.4 mm. FIG. 23 is a longitudinal spherical aberration diagram when using a CD, and shows main light and flare light generated within ± 0.1 mm. The vertical axis of the graph shows the effective diameter of BD φ1 = 2.4 mm. 1 is assumed.

In Example 3, the working distance when using a CD is CW = 0.2 mm, the distance between the main light and the flare light condensed on the information recording surface of the CD is x = 10 μm, and the second optical path difference providing ring The minimum value of the band width L (μm) is 6.96 μm. Further, d / f = 1.0 where d (mm) is the thickness of the objective lens on the optical axis, and f (mm) is the focal length of the objective lens in the first light flux. Further, Δ / f = 2.2 × 10 ⁻⁴ mm, where Δ (mm) is the change in the optical axis position of the wavefront aberration best when the first light beam undergoes a wavelength change of 1 nm.

(Example 4)
The objective lens of Example 4 is a plastic single lens, and has an effective diameter φ1 = 2.4 mm. The first optical path difference providing structure of Example 1 is (1, 1, 1) in the second basic structure BS2 that is a blazed diffraction structure (2, 1, 1) in the entire central region. This is an optical path difference providing structure in which the first basic structure BS1 which is a blazed diffraction structure is overlapped. The second optical path difference providing structure is a three-step staircase type diffraction structure of (0, 1, 1). The peripheral region is a refractive surface.

Table 7 shows the lens data of Example 4.

Furthermore, the actual shape of the objective lens was designed based on the lens data of Example 4. The actual shape data is shown in Table 8. By substituting the data shown in Table 8 into the equation shown in Equation 3, actual shape data of each annular zone can be obtained.

H represents the height from the optical axis in the direction perpendicular to the optical axis. Furthermore, FIG. 24 shows a conceptual cross-sectional view when the first optical path difference providing structure and the second optical path difference providing structure of Example 4 are provided in the flat plate element. The central region provided with the first optical path difference providing structure is CN, the intermediate region provided with the second optical path difference providing structure is the region indicated by MD, and the peripheral region without the optical path difference providing structure is OT. This is the indicated area.

FIG. 25 is a graph showing the optical path difference function when the BD is used with the phase difference on the vertical axis and the height from the optical axis on the horizontal axis, and the optical path difference function is continuous between regions. I understand. FIG. 26 is a longitudinal spherical aberration diagram when using BD at the reference wavelength (405 nm), and FIG. 27 is a longitudinal spherical aberration diagram when using BD when the wavelength is changed to +5 nm long wavelength side with respect to the reference wavelength. The vertical axis of the graph is 1 when the effective diameter of the BD φ1 = 2.4 mm. FIG. 28 is a longitudinal spherical aberration diagram when using a CD, showing main light and flare light generated within ± 0.1 mm, and the vertical axis of the graph shows the effective diameter of BD φ1 = 2.4 mm. 1 is assumed.

In Example 4, the working distance when using a CD is CW = 0.2 mm, the distance between the main light and the flare light condensed on the information recording surface of the CD is 10 μm, and the second optical path difference providing ring The minimum value of the band width L (μm) is 6.88 μm. Further, d / f = 1.0 where d (mm) is the thickness of the objective lens on the optical axis, and f (mm) is the focal length of the objective lens in the first light flux. Further, Δ / f = 2.2 × 10 ⁻⁴ mm, where Δ (mm) is the change in the optical axis position of the wavefront aberration best when the first light beam undergoes a wavelength change of 1 nm.

(Example 5)
The objective lens of Example 5 is a plastic single lens, and has an effective diameter φ1 = 3.0 mm. The first optical path difference providing structure of Example 1 is (1, 1, 1) in the second basic structure BS2 that is a blazed diffraction structure (2, 1, 1) in the entire central region. This is an optical path difference providing structure in which the first basic structure BS1 which is a blazed diffraction structure is overlapped. The second optical path difference providing structure is a three-step staircase type diffraction structure of (0, 1, 1). The third optical path difference structure is a (0, 1, 1) blazed diffraction structure.

Table 9 shows the lens data of Example 5.

Furthermore, the actual shape of the objective lens was designed based on the lens data of Example 5. The actual shape data are shown in Tables 10A to 10B. By substituting the data shown in Table 10A and Table 10B (continuous) into the mathematical formula shown in Formula 3, the actual shape data of each annular zone is obtained.

H represents the height from the optical axis in the direction perpendicular to the optical axis. Furthermore, FIG. 29 shows a conceptual cross-sectional view when the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure of Example 5 are provided in the flat plate element. The central region where the first optical path difference providing structure is provided is CN, the intermediate region where the second optical path difference providing structure is provided is the region indicated by MD, and the periphery where the third optical path difference providing structure is provided The region is a region indicated by OT.

FIG. 30 is a graph showing the optical path difference function when the BD is used with the phase difference on the vertical axis and the height from the optical axis on the horizontal axis, and the optical path difference function is continuous between regions. I understand. FIG. 31 is a longitudinal spherical aberration diagram when using BD at the reference wavelength (405 nm), and FIG. 32 is a longitudinal spherical aberration diagram when using BD when the wavelength changes to the +5 nm long wavelength side with respect to the reference wavelength. The vertical axis of the graph assumes that the effective diameter of the BD φ1 = 3.0 mm is 1. FIG. 33 is a longitudinal spherical aberration diagram when using a CD, showing main light and flare light generated within ± 0.1 mm, and the vertical axis of the graph shows the effective diameter of BD φ1 = 3.0 mm. 1 is assumed.

In Example 5, the working distance CW when using the CD is 0.2 mm, the distance x between the main light and the flare light condensed on the information recording surface of the CD is 11 μm, and the second optical path difference providing ring The minimum value of the band width L (μm) is 8.44 μm. Further, d / f = 1.2, where d (mm) is the thickness of the objective lens on the optical axis, and f (mm) is the focal length of the objective lens in the first light flux. Further, Δ / f = 1.9 × 10 ⁻⁴ mm, where Δ (mm) is the change in the optical axis position of the wavefront aberration best when the first light beam undergoes a wavelength change of 1 nm.

(Example 6)
The objective lens of Example 6 is a plastic single lens, and has an effective diameter φ1 = 3.74 mm. The first optical path difference providing structure of Example 1 is (1, 1, 1) in the second basic structure BS2 that is a blazed diffraction structure (2, 1, 1) in the entire central region. This is an optical path difference providing structure in which the first basic structure BS1 which is a blazed diffraction structure is overlapped. The second optical path difference providing structure is a three-step staircase type diffraction structure of (0, 1, 1). The third optical path difference structure is a (0, 1, 1) blazed diffraction structure.

Table 11 shows lens data of Example 6.

Furthermore, the actual shape of the objective lens was designed based on the lens data of Example 6. The actual shape data is shown in Tables 12A to 12B. By substituting the data shown in Table 12A and Table 12B (continuous) into the mathematical formula shown in Formula 3, the actual shape data of each annular zone can be obtained.

H represents the height from the optical axis in the direction perpendicular to the optical axis. Furthermore, FIG. 34 shows a conceptual cross-sectional view in the case where the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure of Example 6 are provided in the flat plate element. The central region where the first optical path difference providing structure is provided is CN, the intermediate region where the second optical path difference providing structure is provided is the region indicated by MD, and the periphery where the third optical path difference providing structure is provided The region is a region indicated by OT.

FIG. 35 is a graph showing the optical path difference function when the BD is used with the phase difference on the vertical axis and the height from the optical axis on the horizontal axis, and the optical path difference function is continuous between regions. I understand. FIG. 36 is a longitudinal spherical aberration diagram when using BD at the reference wavelength (405 nm), and FIG. 37 is a longitudinal spherical aberration diagram when using BD when the wavelength changes to the +5 nm long wavelength side with respect to the reference wavelength. The vertical axis of the graph assumes that the effective diameter of the BD φ1 = 3.74 mm. FIG. 38 is a longitudinal spherical aberration diagram when using a CD, showing main light and flare light generated within ± 0.1 mm, and the vertical axis of the graph shows the effective diameter of BD φ1 = 3.74 mm. 1 is assumed.

In Example 6, the working distance CW when using the CD = 0.36 mm, the distance x = 13 μm between the main light and the flare light focused on the information recording surface of the CD, and the second optical path difference providing ring The minimum value of the band width L (μm) is 9.14 μm. Further, d / f = 1.2, where d (mm) is the thickness of the objective lens on the optical axis, and f (mm) is the focal length of the objective lens in the first light flux. Further, Δ / f = 2.0 × 10 ⁻⁴ mm where Δ (mm) is the change in the optical axis position of the wavefront aberration best when the first light beam undergoes a wavelength change of 1 nm.

In addition, regarding the first optical path difference providing structure in the central region of each of Examples 1 to 6, the shape diagrams before and after the first basic structure and the second basic structure are superimposed are described as FIGS. 40 to 51. To do.

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

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

Claims

A first light source that emits a first light flux with a first wavelength λ1, a second light source that emits a second light flux with a second wavelength λ2 (λ2> λ1), and a third light flux with a third wavelength λ3 (λ3> λ2) And recording and / or reproducing information on a first optical disc having a protective substrate with a thickness of t1 using the first light flux, and using the second light flux to obtain a thickness. Records and / or reproduces information on the second optical disk having the protective substrate t2 (t1 <t2), and uses the third light flux to have the third optical disk having the protective substrate having the thickness t3 (t2 <t3) An objective lens used in an optical pickup device that records and / or reproduces information of
The optical surface of the objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region,
The central region has a first optical path difference providing structure,
The intermediate region has a second optical path difference providing structure,
The objective lens condenses the first light flux that passes through the central area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the central area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the central region is condensed on the information recording surface of the third optical disc. Condensing so that information can be recorded and / or reproduced,
The objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the intermediate area. Two light beams are condensed on the information recording surface of the second optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the intermediate region is condensed on the information recording surface of the third optical disc. Without collecting light so that information can be recorded and / or reproduced.
The objective lens condenses the first light flux passing through the peripheral area so that information can be recorded and / or reproduced on the information recording surface of the first optical disc, and the objective lens passes through the peripheral area. The second light flux is not condensed so that information can be recorded and / or reproduced on the information recording surface of the second optical disc, and the third light flux passing through the peripheral region is used as the information recording surface of the third optical disc. Do not concentrate so that information can be recorded and / or reproduced
The first optical path difference providing structure is a structure in which at least a first basic structure and a second basic structure are overlapped,
The first basic structure makes the first-order diffracted light quantity of the first light beam that has passed through the first basic structure larger than any other order of diffracted light quantity, and 1 of the second light flux that has passed through the first basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, making the first order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order diffracted light quantity,
The second basic structure makes the second-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and 1 of the second light beam that has passed through the second basic structure. Making the next diffracted light quantity larger than any other order diffracted light quantity, making the first order diffracted light quantity of the third light flux that has passed through the second basic structure larger than any other order diffracted light quantity,
The second optical path difference providing structure is a staircase structure having a plurality of small staircase structures having the same number of steps, and the second optical path difference providing structure is a first light flux that has passed through the second optical path difference providing structure. Making the 0th-order diffracted light quantity larger than any other order diffracted light quantity, and making the first-order diffracted light quantity of the second light flux that has passed through the second optical path difference providing structure larger than any other order diffracted light quantity; An objective lens, wherein the first-order diffracted light amount of the third light flux that has passed through the second optical path difference providing structure is made larger than any other order diffracted light amount.
2. The objective lens according to claim 1, wherein the second optical path difference providing structure is such that the small staircase structure has two steps (binary structure).
The height per step of the two-step structure of the two steps is h (μm), and the case where the step is facing the optical axis direction is positive, and the case where the step is facing the direction opposite to the optical axis is negative. The objective lens according to claim 2, wherein:
-1.0 ≦ h ≦ -0.6 (A)
0.6 ≦ h ≦ 1.0 (B)
2. The objective lens according to claim 1, wherein the second optical path difference providing structure has three steps of the small staircase structure.
The height per step of the three-step structure of the three steps is h (μm), and the case where the step is facing the optical axis direction is positive, and the case where the step is facing the direction opposite to the optical axis is negative. The objective lens according to claim 4, wherein:
-1.2 ≦ h ≦ -0.7 (C)
2.7 ≦ h ≦ 4.4 (D)
2. The objective lens according to claim 1, wherein the second optical path difference providing structure includes the small staircase structure having four steps.
The height per step of the four-step small structure of the four steps is h (μm), and the case where the step is facing the optical axis direction is positive, and the case where the step is facing the opposite direction to the optical axis is negative. The objective lens according to claim 6, wherein:
-3.4 ≦ h ≦ -2.0 (E)
1.4 ≦ h ≦ 2.3 (F)
The peripheral region has a third optical path difference providing structure, and the third optical path difference providing structure is a blazed structure, and a second-order diffracted light quantity of the first light beam that has passed through the third optical path difference providing structure. The objective lens according to any one of claims 1 to 7, wherein the objective lens is made larger than any other order of diffracted light quantity.
The peripheral region has a third optical path difference providing structure, and the third optical path difference providing structure is a stepped structure having a plurality of small staircase structures, and passes through the third optical path difference providing structure. The objective lens according to any one of claims 1 to 7, wherein the 0th-order diffracted light amount of one light beam is made larger than any other order diffracted light amount.
10. The objective lens according to claim 9, wherein the third optical path difference providing structure is such that the small staircase structure has two steps (binary structure).
The height per step of the two-step structure of the two steps is h (μm), and the case where the step is facing the optical axis direction is positive, and the case where the step is facing the direction opposite to the optical axis is negative. The objective lens according to claim 10, wherein:
-1.0 ≦ h ≦ -0.6 (G)
0.6 ≦ h ≦ 1.0 (H)
The objective lens according to claim 9, wherein the third optical path difference providing structure is such that the small staircase structure has three steps.
The height per step of the three-step structure of the three steps is h (μm), and the case where the step is facing the optical axis direction is positive, and the case where the step is facing the direction opposite to the optical axis is negative. The objective lens according to claim 12, wherein:
-1.2 ≦ h ≦ -0.7 (I)
2.7 ≦ h ≦ 4.4 (J)
The objective lens according to any one of claims 1 to 7, wherein the peripheral region is a refractive surface.
15. The following expression is satisfied when an effective diameter when recording and / or reproducing information on the first optical disc is φ1 (mm): Objective lens.
1.8 ≦ φ1 ≦ 4.0 (1)
The objective lens according to claim 1, wherein when the working distance of the third optical disk is CW (mm), the following expression is satisfied.
CW ≧ 0.2 (2)
2. The following equation is satisfied, where x (μm) is a distance between the main light of the third light beam condensed on the information recording surface of the third optical disk and the flare light of the third light beam. The objective lens according to any one of 1 to 16.
| X | ≧ 5 (3)
The minimum ring width of the second optical path difference providing structure satisfies the following expression, where L (μm) is the ring width of the second optical path difference providing structure: The objective lens according to any one of 17.
2 ≦ | L | ≦ 12 (4)
The following equation is satisfied, where Δ (mm) is a positional deviation in the optical axis direction of the wavefront aberration best position when the first light beam has a wavelength change of 1 nm. Objective lens according to the above.
1.9 × 10 −4 ≦ Δ / f ≦ 2.5 × 10 −4 (6)
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.