JPWO2008126562A1 - Objective optical element unit for optical pickup device and optical pickup device - Google Patents

Abstract

In order to provide an objective optical element unit and an optical pickup apparatus for an optical pickup apparatus that can appropriately record and / or reproduce information on different optical information recording media at low cost, the first optical element L1 By superimposing the first basic structure and the second basic structure on the optical surface on the light source side, the light beam that has passed through the center of the first basic structure always passes through the center of the second basic structure. Therefore, the residual coma aberration is reduced, and information can be appropriately recorded and / or reproduced regardless of the temperature change.

Description

  The present invention relates to an objective optical element unit and an optical pickup device for an optical pickup device, and more particularly to an objective optical element unit and an optical pickup device for an optical pickup device capable of recording and / or reproducing information on different types of optical disks. .

  In recent years, research on a high-density optical disk system capable of recording and / or reproducing information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm.・ Development is progressing rapidly. As an example, an optical disc that records and reproduces information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4.7 GB). ), Which can record information of about 25 GB per layer and record / reproduce information with specifications of NA 0.65 and light source wavelength 405 nm, so-called With HD DVD (hereinafter referred to as HD), information of about 15 GB per layer can be recorded on an optical disk having a diameter of 12 cm. Hereinafter, in this specification, such an optical disc is referred to as a “high-density optical disc”.

  In addition, considering the reality that DVDs (digital versatile discs) and CDs (compact discs) on which various types of information are recorded are currently being sold, various types of optical discs can be used as much as possible with a single information recording / reproducing device. Therefore, it is desired to appropriately record / reproduce information. Furthermore, considering that the optical pickup device is mounted on a notebook personal computer or the like, it is not only necessary to have compatibility with a plurality of types of optical discs, but it is important to further promote downsizing.

  Here, as a method for appropriately recording / reproducing information while maintaining compatibility with any of a high-density optical disc, a DVD, and a CD, an optical system for a high-density optical disc and an optical system for a DVD Can be selectively switched according to the recording density of the optical disk for recording / reproducing information, but a plurality of optical systems are required, 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, the optical system for the high-density optical disc and the optical system for the DVD / CD are made common in the compatible optical pickup device. It is preferable to reduce the number of optical components constituting the optical pickup device as much as possible. Patent Document 1 discloses an optical pickup device that can realize compatible use of optical disks having different protective substrate thicknesses using a diffraction structure.
JP 2005-158217 A

  However, according to the technique of Patent Document 1, it is possible to provide an optical pickup device that can be used interchangeably with a high-density optical disk and other optical disks. However, as an objective optical element unit, a spherical surface caused by the thickness of the protective substrate of the optical disk. Since a plastic parallel plate on which a diffractive structure for correcting aberration (an optical path difference providing structure for compatibility) is formed and a glass lens are used, there is a problem that the cost is increased. On the other hand, in order to reduce the cost, it is conceivable that the lens is made of plastic, but the characteristic of the plastic becomes a problem. More specifically, since a plastic has a large refractive index change as compared with glass due to a change in temperature, a lens made of plastic may generate a relatively large spherical aberration due to a change in temperature. Such a problem is remarkable particularly in a high-density optical disk used at a high NA.

  Therefore, in the case of providing an optical path difference providing structure for correcting a temperature change in order to correct the spherical aberration caused by the temperature change, the present inventor has a problem as to where the optical path difference providing structure is provided. I found out that For example, when an optical path difference providing structure for interchangeability is provided on one optical surface of a parallel plate and an optical path difference providing structure for correcting temperature change is provided on the other optical surface, the molds for molding the two are different. When decentration occurs, there is a problem that residual coma aberration occurs.

  In addition, even if no eccentricity occurs due to ideal molding, the parallel plate is tilted with respect to the incident light beam so that the photodetector of the optical pickup device does not receive unnecessary reflected light from the parallel plate. A similar problem occurs. That is, when a parallel plate with an optical path difference providing structure for interchangeability provided on one optical surface and an optical path difference providing structure for correcting temperature changes on the other optical surface is tilted, for example, the light beam incident on the center of the diffractive structure However, it shifts while passing through the parallel plate and exits from a position shifted from the center of the optical path difference providing structure, which may cause residual coma as in the case of decentration.

  The present invention has been made in view of the above-mentioned problems found by the present inventors, and is an optical pickup capable of appropriately recording and / or reproducing information on a different optical information recording medium at a low cost. An object of the present invention is to provide an objective optical element unit and an optical pickup device for an apparatus.

The objective optical element unit for an optical pickup device according to claim 1 includes a first light source that emits a first light flux having a wavelength λ1 (nm) and a second light source having a wavelength λ2 (nm) (λ1 <λ2). A first optical disc having a second light source that emits a light beam and an objective optical element unit, wherein the objective optical element unit passes the first light beam through a protective substrate having a thickness t1 and a required numerical aperture is NA1. It is possible to record and / or reproduce information by focusing on the information recording surface, and the second light flux is passed through a protective substrate having a thickness t2 (t1 ≦ t2). Objective optical element for an optical pickup device capable of recording and / or reproducing information by focusing on the information recording surface of the second optical disk having a required numerical aperture of NA2 (NA1 ≧ NA2) A unit,
The objective optical element unit has a first optical element and a second optical element each made of plastic.
The first optical element and the second optical element are arranged side by side in the optical axis direction,
The first optical element has a first optical surface and a second optical surface facing each other, and the first optical surface of the first optical element has a first optical path difference providing structure. ,
The first optical path difference providing structure is a structure in which a first basic structure and a second basic structure are overlapped,
The first foundation structure and the second foundation structure are both structures having a plurality of concentric steps,
The first basic structure and the second basic structure both have power with respect to the second light flux having the wavelength λ2.

  The objective optical element unit for an optical pickup device according to claim 2 is the invention according to claim 1, wherein the first optical path difference providing structure is such that the wavelength λ1 of the first light flux is It is characterized in that it has no power when it is a design wavelength and has power when the wavelength λ1 of the first light beam deviates from the design wavelength.

The objective optical element unit for an optical pickup device according to claim 3 is the invention according to claim 1 or 2, wherein the following formula (1),
| F _{L2 (λ1)} / f _{L1 (λ1)} | ≦ 0.3 (1)
However,
f _{L1 (λ1)} : focal length when the first light beam is incident on the first optical element f _{L2 (λ1)} : focal length when the first light beam is incident on the second optical element It is characterized by satisfying.

  The objective optical element unit for an optical pickup device according to claim 4 is the invention according to any one of claims 1 to 3, wherein the second of the first optical element is used. The optical surface is an optical surface on the second optical element side.

  The objective optical element unit for an optical pickup device according to claim 5 is the invention according to any one of claims 1 to 4, wherein the first optical element is the first optical path. It is a parallel plate which has a difference providing structure, It is characterized by the above-mentioned.

  The objective optical element unit for an optical pickup device according to claim 6 is the invention according to any one of claims 1 to 5, wherein the second optical element has a condensing function. A lens having a spherical or aspherical optical surface.

  The objective optical element unit for an optical pickup device according to claim 7 is the invention according to claim 6, wherein the second optical element does not have the first optical element, and The first light beam emitted from the first light source can be condensed on the information recording surface of the first optical disc through a protective substrate having a thickness of t1, using only the second optical element. .

  The objective optical element unit for an optical pickup device according to claim 8 is the invention according to any one of claims 1 to 7, wherein the optical axis of the first optical element is: The second optical element is inclined with respect to the optical axis.

  The objective optical element unit for an optical pickup device according to claim 9 is the invention according to any one of claims 1 to 8, wherein the first basic structure is the first basic structure. It has a function of correcting spherical aberration that occurs due to a change in environmental temperature with respect to the luminous flux.

  The objective optical element unit for an optical pickup device according to claim 10 is the invention according to any one of claims 1 to 9, wherein the second basic structure is the first optical element unit. Using the wavelength difference between the wavelength λ1 of the light beam and the wavelength λ2 of the second light beam, it is caused by the difference between the thickness t1 of the protective substrate of the first optical disk and the thickness t2 of the protective substrate of the second optical disk. It has a function of correcting the spherical aberration generated in this way.

  The objective optical element unit for an optical pickup device according to claim 11 is the invention according to any one of claims 1 to 10, wherein the first optical path difference providing structure is the first optical path difference providing structure. An image-side numerical aperture (NA) is formed in a range corresponding to NA2 or less on the first optical surface of one optical element.

  The objective optical element unit for an optical pickup device according to claim 12 is the invention according to any one of claims 1 to 11, wherein the first optical element unit is the first optical element unit. The optical surface has a third optical path difference providing structure around the first optical path difference providing structure, and the third optical path difference providing structure has only the first basic structure.

  The objective optical element unit for an optical pickup device according to claim 13 is the optical device according to claim 12, wherein the first optical path difference providing structure and the third optical path difference providing structure are the first optical path difference providing structure. In the first basic structure, the entire first optical surface of the first optical element becomes deeper in the direction of the optical axis as the height from the optical axis increases, and exceeds a certain height. The structure is characterized in that as the height from the optical axis increases, the structure becomes shallower in the optical axis direction.

The objective optical element unit for an optical pickup device according to claim 14 is the invention according to any one of claims 1 to 13, wherein the optical pickup device has a wavelength λ3 (nm). A third light source that emits a third light beam of (λ2 <λ3), and the objective optical element unit has a required numerical aperture of the third light beam through a protective substrate having a thickness of t3 (t2 <t3). By focusing on the information recording surface of the third optical disk with NA3 (NA2> NA3), it is possible to record and / or reproduce information.
The second optical surface of the first optical element has a second optical path difference providing structure,
The second optical path difference providing structure is characterized in that power is given only to the third light flux.

  The objective optical element unit for an optical pickup device according to claim 15 is the invention according to claim 14, wherein the second optical path difference providing structure is configured such that the wavelength λ1 of the first light flux is Using the wavelength difference of the wavelength λ3 of the third light flux, spherical aberration generated due to the difference between the thickness t1 of the protective substrate of the first optical disc and the thickness t3 of the protective substrate of the third optical disc It has a function of correcting.

  The objective optical element unit for an optical pickup device according to claim 16 is the first basic structure of the first optical path difference providing structure according to the invention of claim 14 or 15. Makes the second-order diffracted light quantity of the first light flux that has passed through the first basic structure larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the second light flux becomes any other order The optical path difference providing structure is configured to be larger than the diffracted light amount and to make the first-order diffracted light amount of the third light flux larger than any other order diffracted light amount.

  The objective optical element unit for an optical pickup device according to claim 17 is the second aspect of the first optical path difference providing structure according to any one of claims 14 to 16. In the basic structure, the 0th-order diffracted light quantity of the first light flux that has passed through the second basic structure is made larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the second light flux It is an optical path difference providing structure that makes the amount of diffracted light of any order larger and makes the 0th-order diffracted light of the third light beam larger than any other order of diffracted light.

  The objective optical element unit for an optical pickup device according to claim 18 is the invention according to any one of claims 14 to 17, wherein the second optical path difference providing structure is the second optical path difference providing structure. The 0th-order diffracted light quantity of the first light flux that has passed through the two-optical path difference providing structure is made larger than any other order diffracted light quantity, and the 0th-order diffracted light quantity of the second light flux is made greater than any other order diffracted light quantity. And an optical path difference providing structure that makes the ± 1st-order diffracted light quantity of the third light beam larger than any other order diffracted light quantity.

  The objective optical element unit for an optical pickup device according to claim 19 is the invention according to any one of claims 14 to 18, wherein the second optical path difference providing structure is the first optical path difference providing structure. In the second optical surface of one optical element, an image-side numerical aperture (NA) is formed in a range corresponding to NA3 or less.

The objective optical element unit for an optical pickup device according to claim 20 includes a first light source that emits a first light flux having a wavelength λ1 (nm) and a second light source having a wavelength λ2 (nm) (λ1 <λ2). A first optical disc having a second light source that emits a light beam and an objective optical element unit, wherein the objective optical element unit passes the first light beam through a protective substrate having a thickness t1 and a required numerical aperture is NA1. It is possible to record and / or reproduce information by focusing on the information recording surface, and the second light flux is passed through a protective substrate having a thickness t2 (t1 ≦ t2). Objective optical element for an optical pickup device capable of recording and / or reproducing information by focusing on the information recording surface of the second optical disk having a required numerical aperture of NA2 (NA1 ≧ NA2) A unit
The objective optical element unit has a first optical element and a second optical element each made of plastic.
The first optical element and the second optical element are arranged side by side in the optical axis direction,
The first optical element has a first optical surface and a second optical surface facing each other,
The first optical surface of the first optical element has a concentric first optical path difference providing structure divided by a plurality of concentric steps in the area of NA2 or less, and the first optical path difference The step amount dX of the step of the providing structure satisfies the following conditional expression:
The first optical surface of the first optical element has a third optical path difference providing structure partitioned by a plurality of concentric steps in a region that is larger than the NA2 and less than or equal to the NA1. The step amount dY of the optical path difference providing structure satisfies the following conditional expression.
0.9 · a · λ1 / (n−1) ≦ dX (nm) ≦ 1.1 · a · λ1 / (n−1)
(2)
0.9 · b · λ1 / (n−1) ≦ dY (nm) ≦ 1.1 · b · λ1 / (n−1)
(3)
Here, n represents the refractive index of the first optical element in the first light flux, a represents an integer of 2, 4, 6, 8 or 10, and provides one first optical path difference. Plural types of a may be used in the structure, b represents an integer of 1, 2, 3, 4 or 5, and plural types of b are used in one third optical path difference providing structure. May be.

  The objective optical element unit for an optical pickup device according to claim 21 is the optical device according to claim 20, wherein the value of a of the step amount dX in the first optical path difference providing structure is A plurality of types are used, and the value of a satisfies at least 2 and 8.

  The objective optical element unit for an optical pickup device according to Claim 22 is characterized in that, in the invention according to Claim 21, in the first optical path difference providing structure, the value of a of the step amount dX is a. A plurality of types are used, and the value of a satisfies at least 2 and 8, and further satisfies any of 4, 6, or 10.

  The objective optical element unit for an optical pickup device according to Claim 23 is the invention according to any one of Claims 20 to 22, wherein the third optical path difference providing structure is the step. The value d of the quantity dY is only one type.

  The objective optical element unit for an optical pickup device according to Claim 24 is the invention according to any one of Claims 20 to 23, wherein the third optical path difference providing structure is the step. The value d of the quantity dY is an integer of 2, 3, or 4.

  The objective optical element unit for an optical pickup device according to claim 25, in the invention according to any one of claims 20 to 24, wherein the first optical path difference providing structure is macroscopic. As can be seen from the above, it has a structure that becomes deeper in the optical axis direction as the height from the optical axis increases.

The objective optical element unit for an optical pickup device according to Claim 26 is the invention according to any one of Claims 20 to 25, wherein the first optical path difference providing structure is Is a structure in which the basic structure and the second basic structure are overlaid,
The first basic structure has a structure that becomes deeper in the direction of the optical axis as the height from the optical axis increases,
The second basic structure is a structure having a plurality of four-step small staircase structures.

  The objective optical element unit for an optical pickup device according to claim 27, in the invention according to any one of claims 20 to 26, wherein the third optical path difference providing structure has an optical axis. It is characterized by having a structure that becomes shallower in the optical axis direction as the height from is increased.

An objective optical element unit for an optical pickup device according to claim 28, in the invention according to any one of claims 20 to 27, wherein the optical pickup device has a wavelength λ3 (nm). A third light source that emits a third light beam of (λ2 <λ3), and the objective optical element unit has a required numerical aperture of the third light beam through a protective substrate having a thickness of t3 (t2 <t3). By focusing on the information recording surface of the third optical disk with NA3 (NA2> NA3), it is possible to record and / or reproduce information.
The second optical surface of the first optical element has a second optical path difference providing structure divided by a plurality of concentric steps in the area of NA3 or less,
The step amount dD of the second optical path difference providing structure is expressed by the following conditional expression (4):
0.9 · 5 · λ1 / (n−1) ≦ dD (nm) ≦ 1.1 · 5 · λ1 / (n−1)
(4)
It is characterized by satisfying.

  The objective optical element unit for an optical pickup device according to claim 29 is the invention according to any one of claims 20 to 28, wherein the optical axis of the first optical element is: The second optical element is inclined with respect to the optical axis.

  An optical pickup device according to claim 30 has the objective optical element unit according to any one of claims 1 to 29.

  The optical pickup device according to claim 31 is the invention according to claim 30, wherein the first optical element is disposed on a light source side, and the second optical element is It is arranged on the optical disc side.

  The optical pickup device of the present invention includes a first light source and a second light source, and can further include a third light source. In the optical pickup device of the present invention, the first light beam from the first light source is condensed on the information recording surface of the first optical disk (also referred to as an optical information recording medium, hereinafter the same), and the second light from the second light source is collected. A condensing optical system including an objective optical element unit for condensing the light beam on the information recording surface of the second optical disk, and the condensing optical system converts the third light beam from the third light source into information on the third optical disk; The light may be condensed on the recording surface. The optical pickup device of the present invention has a light receiving element that receives a reflected light beam from the information recording surface of the first optical disk and the second optical disk, and the light receiving element receives the reflected light from the information recording surface of the third optical disk. It may receive light.

  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. When the third optical disk is used, the third optical disk has a protective substrate having a thickness t3 (t2 <t3) and an information recording surface. The first optical disk is preferably a high-density optical disk, and the second optical disk is preferably a DVD. When the third optical disk is used, the third optical disk is preferably a CD, but the present invention is not limited to this. In addition, when t1 <t2 (for example, when the first optical disk is BD and the second optical disk is DVD), when t1 = t2 (for example, the first optical disk is HD and the second optical disk is DVD). It is more difficult to record and / or reproduce three different optical discs with one objective optical element unit, but the present invention makes it possible. 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 the present specification, as an example of a high-density optical disc, a standard optical disc (for example, a BD) in which information is recorded / reproduced by an objective optical element having a NA of 0.85 and a protective substrate has a thickness of about 0.1 mm. : Blu-ray Disc). As another example of a high-density optical disk, information is recorded / reproduced by an objective optical element having an NA of 0.65 to 0.67, and a protective optical disk having a protective substrate thickness of about 0.6 mm (for example, HD DVD: also simply referred to as HD). In addition, the high-density optical disc includes an optical disc having a protective film with a thickness of about several to several tens of nanometers on the information recording surface (in this specification, the protective substrate includes the protective film), and the thickness of the protective substrate. Also included are optical discs with a zero. The high-density optical disk includes a magneto-optical disk in which a blue-violet semiconductor laser or a blue-violet SHG laser is used as a light source for recording / reproducing information.

  Further, in this specification, a DVD refers to a DVD series optical disc in which information is recorded / reproduced by an objective optical element having an NA of about 0.60 to 0.67 and the protective substrate has a thickness of about 0.6 mm. It is a generic name and includes DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. Further, in this specification, a CD is a CD series optical disc in which information is recorded / reproduced by an objective optical element having an NA of about 0.45 to 0.51 and the protective substrate has a thickness of about 1.2 mm. It is a generic name and includes CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW, and the like. As for the recording density, the recording density of the high-density optical disk is the highest, and then decreases in the order of DVD and CD.

Regarding the thicknesses t1, t2, and t3 of the protective substrate, the following conditional expressions (5), (6), (7),
0.0750mm ≦ t1 ≦ 0.1125mm or 0.5mm ≦ t1 ≦ 0.7mm
(5)
0.5mm ≦ t2 ≦ 0.7mm (6)
0.9mm ≦ t3 ≦ 1.3mm (7)
However, the present invention is not limited to this.

  The objective optical element necessary for reproducing and / or recording information on the first optical disk is NA1, and the objective optical necessary for reproducing and / or recording information on the second optical disk is NA1. The image side numerical aperture of the element is NA2 (NA1 ≧ NA2), and the image side numerical aperture of the objective optical element necessary for reproducing and / or recording information on the third optical disk is NA3 (NA2> NA3). . NA1 is preferably 0.8 or more and 0.9 or less, or preferably 0.55 or more and 0.7 or less. NA2 is preferably 0.55 or more and 0.7 or less. NA3 is preferably 0.4 or more and 0.55 or less.

  The first light source emits a first light flux having a wavelength λ1. The second light source emits a second light flux having a wavelength λ2 (λ1 <λ2). When the third light source is used, the third light source emits a third light flux having a wavelength λ3 (λ2 <λ3). In the present specification, the first light source and the second light source are preferably laser light sources. A laser light source may be used when a third light source is used. As the laser light source, a semiconductor laser, silicon laser, SHG laser, or the like can be preferably used. Note that λ1 and λ2 preferably satisfy the following conditional expression (8). In the case of using the third light source, it is preferable that λ3 satisfies the following conditional expression (9).

1.5 × λ1 (nm) <λ2 <1.7 × λ1 (nm) (8)
1.9 × λ1 (nm) <λ3 <2.1 × λ1 (nm) (9)
When BD or HD and DVD are used as the first optical disc and the second 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 380 nm or more and 415 nm or less. In addition, 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. Further, when a CD is used as the third optical disk, the third wavelength λ3 of the third light source is preferably 750 nm or more and 880 nm or less, more preferably 760 nm or more and 820 nm or less.

  Further, the first light source and the second light source may be unitized, and when the third light source is used, the third light source may be unitized in addition to these. The unitization means that the first light source and the second light source are fixedly housed in one package, for example. However, the unitization is not limited to this, and the two light sources are fixed so that the aberration cannot be corrected. Is widely included. 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 amount of light due to the change in the shape and position of the spot on the light receiving element, performs focus detection and track detection, and moves the objective optical element for focusing and tracking based on this detection 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 portions corresponding to the respective light sources.

  The condensing optical system (or an objective optical element unit to be described later) records and / or records information by condensing the first light flux on the information recording surface of the first optical disc via a protective substrate having a thickness t1. It is possible to perform reproduction, and it is possible to record and / or reproduce information by condensing the second light flux on the information recording surface of the second optical disc via a protective substrate having a thickness t2. To do. When the third light source is provided, the condensing optical system condenses the third light beam on the information recording surface of the third optical disc through the protective substrate having a thickness t3, thereby recording and / or recording information. Alternatively, it is possible to perform reproduction.

  The condensing optical system has an objective optical element unit. The condensing optical system may include only the objective optical element unit, but may include a coupling lens such as a collimator lens in addition to the objective optical element unit. The coupling lens is a single lens or a lens group that is disposed between the objective optical element and the light source and changes the divergence angle of the light beam. Further, the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like. May be. In this specification, the objective optical element unit is disposed at a position facing the optical disk in a state where the optical disk is loaded in the optical pickup device, and has a function of condensing the light beam emitted from the light source on the information recording surface of the optical disk. It refers to a unit of optical elements.

  The objective optical element unit of the present invention has a single first optical element and second optical element, respectively. The first optical element and the second optical element are arranged in the optical axis direction, and their positions are relatively fixed. The first optical element and / or the second optical element has a portion extending in the optical axis direction, the extending portion is in contact with the other optical element, and the first optical element and the second optical element The optical element may be bonded to each other to form an objective optical element unit. On the other hand, the objective optical element unit may be formed by fixing the first optical element and the second optical element to a frame separate from the first optical element and the second optical element. Normally, when the objective optical element unit is disposed in the optical pickup device, the first optical element is on the light source side, and the second optical element is on the optical disk side.

Both the first optical element and the second optical element are made of plastic. The plastic may be any plastic that is generally used for optical materials, but is preferably a cyclic olefin resin material. In addition, the refractive index at a temperature of 25 ° C. with respect to a wavelength of 405 nm is in the range of 1.54 to 1.60, and the refractive index change rate with respect to the wavelength of 405 nm accompanying a temperature change within a temperature range of −5 ° C. to 70 ° C. A resin material having dN / dT (° C. ⁻¹ ) in the range of −20 × 10 ^{−5 to} −5 × 10 ⁻⁵ (more preferably −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ) is used. More preferably. Further, when the first optical element and the second optical element are made of plastic, it is preferable that the coupling lens is also a plastic lens. When forming the objective optical element unit by fixing the first optical element and the second optical element to a separate frame from the first optical element and the second optical element, the frame body Is preferably made of plastic.

  The first optical element has a first optical surface and a second optical surface that face each other. It is preferable that the second optical surface is on the second optical element side. Normally, when the objective optical element unit is disposed in the optical pickup device, the first optical surface is on the light source side and the second optical surface is on the optical disc side, but this is not restrictive. The first optical surface has a first optical path difference providing structure. Further, when the third optical disk is used, the second optical surface may have a second optical path difference providing structure. Therefore, the first optical path difference providing structure is provided on the optical surface on the light source side of the first optical element, and the second optical path difference providing structure is provided on the optical surface on the optical disk side of the first optical element. It is preferable that this is the case, but the reverse may be possible.

  The first optical element is preferably a parallel plate element having the first optical path difference providing structure, but is not limited to the plate element, and has an optical surface having a slight refractive power. May be. In particular, the first optical element is preferably a flat element having a first optical path difference providing structure and a second optical path difference providing structure.

  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. In general, the optical path difference providing structure 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 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. A structure called an NPS structure can also be regarded as a kind of optical path difference providing structure, and can also be regarded as a kind of diffraction structure.

  The first optical path difference providing structure is a structure in which the first basic structure and the second basic structure are overlapped. The first basic structure and the second basic structure are both optical path difference providing structures having power with respect to the second light flux. Here, “having power” means that the optical path difference providing structure has the ability to bend the traveling direction of a predetermined light beam by diffraction action. The first optical path difference providing structure has power in the above sense in the reference state (design temperature, design wavelength) at least for the second light flux. It is preferable that the first optical path difference providing structure does not have power with respect to the first light flux in the reference state. The first optical path difference providing structure may or may not have power with respect to the third light flux in the reference state. The first optical path difference providing structure is preferably a ring-shaped structure divided by concentric steps.

  The first optical path difference providing structure is preferably provided in a region where the image-side numerical aperture (NA) of the first optical surface of the first optical element is equal to or less than NA2. Particularly preferred is the case where NA2 is 0.55 or more and 0.7 or less.

  Note that the first optical surface of the first optical element preferably has a third optical path difference providing structure around the first optical path difference providing structure. Preferably, the third optical path difference providing structure is provided in a region where the image-side numerical aperture (NA) of the first optical surface of the first optical element is larger than NA2 and corresponding to NA1 or less. In addition, it is preferable that the 1st optical path difference providing structure and the 3rd optical path difference providing structure are provided continuously. In particular, NA1 is preferably 0.8 or more and 0.9 or less, and NA2 is preferably 0.55 or more and 0.7 or less.

  The third optical path difference providing structure preferably includes only the first basic structure. Accordingly, the third optical path difference providing structure is also an optical path difference providing structure having power with respect to the second light flux. The first base structure in the first optical path difference providing structure and the first base structure in the third optical path difference providing structure are combined, and the region where the first base structure is provided is the entire first optical surface. It is preferably 70% or more, and preferably 90% or more. More preferably, it is provided on the entire surface.

  Hereinafter, the first basic structure will be described in detail. The first basic structure is a structure that corrects spherical aberration that occurs with a change in environmental temperature with respect to the first light flux. When the wavelength of the first light beam changes or the refractive index of the optical element changes as the environmental temperature changes, it is preferable that the structure corrects spherical aberration that occurs with the change. An example of a preferable structure is a so-called NPS structure. As described above, the first basic structure is an optical path difference providing structure having power for at least the second light flux. The first basic structure preferably has no power (transmits the first light beam) with respect to the first light beam when the wavelength λ1 of the first light beam is the design wavelength. However, when the wavelength λ1 of the first light beam deviates from the design wavelength due to a change in temperature, variations in manufacturing the light source, or the like, it is preferable to have power with respect to the first light beam. Since the first basic structure has such a function, it is possible to correct spherical aberration that occurs with a change in temperature.

  When the optical pickup device includes the third light source, the first basic structure has no power with respect to the third light beam when the wavelength λ3 of the third light beam is the design wavelength (third light beam). Is preferably transmitted). However, when the wavelength λ3 of the third light beam deviates from the design wavelength due to a change in temperature, variations in manufacturing the light source, or the like, it is preferable to have power with respect to the third light beam. Therefore, in both the first optical path difference providing structure and the third optical path difference providing structure, when the wavelength λ1 of the first light beam or the wavelength λ3 of the third light beam is the design wavelength, power is applied to the first light beam or the third light beam. However, when the wavelength λ1 of the first light beam or the wavelength λ3 of the third light beam deviates from the design wavelength, it is preferable to have power for the first light beam or the third light beam. Here, “the wavelength deviates from the design wavelength” is preferably within ± 10 nm.

  The first substructure can take various cross-sectional shapes as shown schematically in FIGS. (In addition, the example described in FIGS. 1-4 is a case where a 1st optical element is flat form.) FIG. 1 is a case where it is a sawtooth shape, FIG. It is a case where it is a stepped shape. In addition, FIG. 3 shows a step shape in which the direction of the step is opposite in the middle, that is, the cross-sectional shape including the optical axis is a predetermined height from the optical axis, the optical path length becomes longer as the distance from the optical axis increases. After a predetermined height from the optical axis, a staircase structure in which the optical path length decreases as the distance from the optical axis decreases, or at a predetermined height from the optical axis, the optical path length decreases as the distance from the optical axis decreases. After the height, a case is shown in which the optical path length is increased as the distance from the optical axis increases. Further, FIG. 4 shows a pattern in which the cross-sectional shape including the optical axis is stepped, arranged concentrically, for each predetermined number of level surfaces (in the example shown in FIG. 4, the number of level surfaces is 5), respectively. A case is shown in which the steps are shifted by the height corresponding to the level plane (four steps in the example shown in FIG. 4). Further, the steps of the first basic structure are preferably arranged with a non-periodic interval in the direction perpendicular to the optical axis. In any case, it is preferable that the first basic structure is also a ring-shaped structure separated by concentric steps.

  In particular, the cross-sectional shape including the optical axis of the first basic structure as a whole is obtained by combining the first basic structure in the first optical path difference providing structure and the first basic structure in the third optical path difference providing structure. As shown in 3 (a) or FIG. 5 (b), at a predetermined height from the optical axis, the optical path length increases as the distance from the optical axis increases, and after the predetermined height from the optical axis, the distance from the optical axis increases. A staircase structure that shortens the optical path length is preferable. As another expression, it is preferable that the structure becomes deeper in the direction of the optical axis as the height from the optical axis becomes larger, and becomes shallower in the direction of the optical axis after exceeding a certain height. I can say that.

  For example, the first basic structure of the first optical path difference providing structure is a structure that becomes deeper in the optical axis direction as the height from the optical axis increases, and the first basic structure of the third optical path difference providing structure ( That is, the third optical path difference providing structure itself) may be a structure that becomes shallower in the optical axis direction as the height from the optical axis increases. Further, the first basic structure of the first optical path difference providing structure is such that many regions (for example, 80% or more in area ratio) of the first optical path difference providing structure are in the optical axis direction as the height from the optical axis increases. However, a part of the structure may be shallower in the optical axis direction as the height from the optical axis increases. On the other hand, the first basic structure of the third optical path difference providing structure (that is, the third optical path difference providing structure itself) has many regions (for example, 80% or more in area ratio) of the third optical path difference providing structure. It has a structure that becomes shallower in the direction of the optical axis as the height from the axis increases, but partly has a structure that becomes deeper in the direction of the optical axis as the height from the optical axis increases. Also good.

The first basic structure in the particularly preferred first optical path difference providing structure is such that the second-order diffracted light quantity of the first light beam that has passed through the first basic structure is larger than any other order diffracted light quantity, This is an optical path difference providing structure in which the first-order diffracted light amount is larger than any other order diffracted light amount. Further, when the third optical disk is used, it is preferable that the first basic structure makes the first-order diffracted light amount of the third light flux that has passed through the first basic structure larger than any other order diffracted light amount. By setting the first basic structure to such a structure, it is possible to suppress the fluctuation range of the diffraction efficiency when the wavelength fluctuates, and to obtain an optical element that is easy to manufacture. In this case, the first basic structure is a ring-shaped structure divided by concentric steps, and the step amount dA in the optical axis direction (see, for example, FIG. 5B) is expressed by the following conditional expression (10 ) Is preferably satisfied.
0.9 · 2 · λ1 / (n−1) ≦ dA (nm) ≦ 1.1 · 2 · λ1 / (n−1)
(10)
However, (lambda) 1 represents the wavelength (nm) of a 1st light beam, and n represents the refractive index of the 1st optical element in a 1st light beam.

As an example of the first basic structure in the other first optical path difference providing structure, the 10th-order diffracted light quantity of the first light flux that has passed through the first basic structure is made larger than any other order diffracted light quantity, This is an optical path difference providing structure in which the 6th-order diffracted light quantity of the two light beams is larger than any other order diffracted light quantity. Further, when the third optical disk is used, the first basic structure preferably makes the fifth-order diffracted light quantity of the third light flux that has passed through the first basic structure larger than any other order of diffracted light quantity. Also in this case, the first basic structure is a ring-shaped structure divided by concentric steps, and the step amount dA in the optical axis direction (see, for example, FIG. 5B) is expressed by the following conditional expression ( 10 ′) is preferably satisfied.
0.9 · 10 · λ1 / (n−1) ≦ dA (nm) ≦ 1.1 · 10 · λ1 / (n−1)
(10 ')
However, (lambda) 1 represents the wavelength (nm) of a 1st light beam, and n represents the refractive index of the 1st optical element in a 1st light beam.

In addition, when the optical pickup device is compatible with not only the first and second optical discs but also the third optical disc, the first basic structure in the first optical path difference providing structure includes all areas corresponding to NA2 or less. The structure may be the same, or the structure may be changed with NA3 as a boundary. For example, in an area of NA3 or less, the second-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 is changed to other values. The optical path difference providing structure in which the first order diffracted light quantity of the third light flux is made larger than any other order diffracted light quantity, and the first order is greater than NA3 and less than or equal to NA2. The fifth-order diffracted light amount of the first light beam that has passed through the basic structure is made larger than any other order diffracted light amount, and the third-order diffracted light amount of the second light beam is made larger than any other order diffracted light amount, An optical path difference providing structure that makes the third-order and second-order diffracted light amounts of the third light beam larger than any other order diffracted light amount may be used. Alternatively, in a region of NA3 or less, the second-order diffracted light amount of the first light beam that has passed through the first basic structure is made larger than any other order diffracted light amount, and the first-order diffracted light amount of the second light beam is changed to other values. The optical path difference providing structure in which the first order diffracted light quantity of the third light flux is made larger than any other order diffracted light quantity, and the first order is greater than NA3 and less than or equal to NA2. The 10th-order diffracted light amount of the first light beam that has passed through the basic structure of the second light beam is made larger than any other order diffracted light amount, and the 6th-order diffracted light amount of the second light beam is made larger than any other order diffracted light amount, An optical path difference providing structure that makes the fifth-order diffracted light quantity of the third light beam larger than any other order diffracted light quantity may be used. In this case, the step amount dA of the first foundation structure in the region of NA3 or less satisfies the above-described conditional expression, and the first foundation structure in the region of NA2 and less than NA2 has the step amount dA ′ in the optical axis direction. Is the following conditional expression (11),
0.9 · 5 · λ1 / (n−1) ≦ dA ′ (nm) ≦ 1.1 · 5 · λ1 / (n−1)
(11)
It is preferable to satisfy.

Alternatively, in a region of NA3 or less, the second-order diffracted light amount of the first light beam that has passed through the first basic structure is made larger than any other order diffracted light amount, and the first-order diffracted light amount of the second light beam is changed to other values. The optical path difference providing structure in which the first order diffracted light quantity of the third light flux is made larger than any other order diffracted light quantity, and the first order is greater than NA3 and less than or equal to NA2. The 10th-order diffracted light amount of the first light beam that has passed through the basic structure of the second light beam is made larger than any other order diffracted light amount, and the 6th-order diffracted light amount of the second light beam is made larger than any other order diffracted light amount, An optical path difference providing structure that makes the fifth-order diffracted light quantity of the third light beam larger than any other order diffracted light quantity may be used. In this case, the step amount dA of the first foundation structure in the region of NA3 or less satisfies the above-mentioned conditional expression (10), and the first foundation structure in the region of NA2 and less than NA2 has the step in the optical axis direction. The quantity dA ′ is the following conditional expression (11 ′):
0.9 · 10 · λ1 / (n−1) ≦ dA ′ (nm) ≦ 1.1 · 10 · λ1 / (n−1)
(11 ')
It is preferable to satisfy.

Further, the first basic structure in the third optical path difference providing structure includes an optical path difference providing structure that makes the b-order diffracted light quantity of the first light flux that has passed through the first basic structure larger than any other order diffracted light quantity. When expressed, b can be any integer. Preferably, b is an integer of 1, 2, 3, 4 or 5. More preferably, b is 2, 3, or 4. In this case, the third optical path difference providing structure is a ring-shaped structure divided by concentric steps, and the step amount dY in the optical axis direction preferably satisfies the following conditional expression (3). In addition, it is preferable that all the level differences of the third optical path difference providing structure satisfy the following conditional expression (3).
0.9 · b · λ1 / (n−1) ≦ dY (nm) ≦ 1.1 · b · λ1 / (n−1)
(3)
Where λ1 represents the wavelength (nm) of the first light beam, n represents the refractive index of the first optical element in the first light beam, and b is an integer of 1, 2, 3, 4, 5 Represents. A plurality of types of b may be used in one third optical path difference providing structure.

More preferably, the following conditional expression (3 ′),
0.95 · b · λ1 / (n−1) ≦ dY (nm) ≦ 1.05 · b · λ1 / (n−1)
(3 ')
Is to satisfy.

More preferably, the following conditional expression (3 ″):
dY (nm) = b · λ1 / (n−1) (3 ″)
Is to satisfy.

  It is preferable that the value of b of the step amount dY in the third optical path difference providing structure is only one type. Further, it is preferable that the value of b of the step amount dY is an integer of 2, 3, or 4.

  Here, the principle of correcting the spherical aberration caused by the temperature change by the first basic structure will be described. A line (A) in FIG. 6 shows a case where the temperature of the single lens (for example, the second optical element) of an example having two optical surfaces made of plastic and aspheric is increased from the design reference temperature. This represents the state of the wavefront, the horizontal axis represents the effective radius of the optical surface, and the vertical axis represents the optical path difference. In the single lens, spherical aberration occurs due to the influence of the refractive index change accompanying the temperature rise, and the wavefront changes as shown by the line (A). In particular, when the single lens is made of plastic, the amount of spherical aberration is increased because the refractive index change with temperature change is large.

  The line (B) is a structure that combines the first basic structure (in this case, the first basic structure of the first optical path difference providing structure and the first basic structure of the third optical path difference providing structure). The line (C) is a diagram showing the state of the wavefront transmitted through the first basic structure and the single lens when the temperature rises from the design reference temperature. It is. From the line (B) and the line (C), the wavefront transmitted through the first basic structure and the wavefront of the single lens when the temperature rises from the design reference temperature cancel each other, so that on the information recording surface of the optical disc When viewed macroscopically, the wavefront of the laser beam focused on is a good wavefront with no optical path difference, and it can be understood that the temperature aberration is corrected by the first basic structure.

  Next, the second basic structure will be described in detail. The second basic structure uses the wavelength difference between the wavelength λ1 of the first light beam and the wavelength λ2 of the second light beam, and the thickness t1 of the protective substrate of the first optical disk and the thickness t2 of the protective substrate of the second optical disk. This structure corrects spherical aberration that occurs based on the difference between the two. As described above, the second basic structure is a structure having power with respect to the second light flux. Preferably, the first light flux and the third light flux have no power (transmits the first light flux and the third light flux), and have a power only for the second light flux. The second substructure can also have various cross-sectional shapes as schematically shown in FIGS. The steps of the second basic structure are preferably arranged with a periodic interval in the direction perpendicular to the optical axis. In any case, it is preferable that the second basic structure is also a ring-shaped structure separated by concentric steps.

  Particularly preferably, the second basic structure is a concentric circle having a plurality of patterns in which the cross-sectional shape including the optical axis is a small step shape as shown in FIG. 4 (a), (b) or FIG. 5 (a). The steps are shifted by the number of steps corresponding to each level surface (particularly preferably 4 steps) for each predetermined number of level surfaces (particularly preferably, the number of level surfaces is 5). A structure is preferred.

A particularly preferable second basic structure is such that the 0th-order diffracted light quantity of the first light beam that has passed through the second basic structure is made larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the second light beam is changed to other values. The optical path difference providing structure is larger than the diffracted light quantity of any order. Further, when the third optical disk is used, the second basic structure preferably makes the 0th-order diffracted light quantity of the third light beam larger than any other order diffracted light quantity. As the second basic structure, for example, as described above, a four-step staircase structure as shown in FIG. In this case, it is preferable that the step amount dB in the optical axis direction of the small step and the step amount dC in the optical axis direction of the large step satisfy the following conditional expressions (12) and (13).
0.9 · 2 · λ1 / (n−1) ≦ dB (nm) ≦ 1.1 · 2 · λ1 / (n−1)
(12)
0.9 · 8 · λ1 / (n−1) ≦ dC (nm) ≦ 1.1 · 8 · λ1 / (n−1)
(13)
However, (lambda) 1 represents the wavelength (nm) of a 1st light beam, and n represents the refractive index of the 1st optical element in a 1st light beam.

  In another preferable second basic structure, the 0th-order diffracted light amount of the first light beam that has passed through the second basic structure is made larger than any other order diffracted light amount, and the −1st-order diffracted light amount of the second light beam Is an optical path difference providing structure in which is larger than any other order of diffracted light quantity. Further, when the third optical disk is used, the second basic structure includes a structure in which the second-order diffracted light amount of the third light flux is made larger than any other order diffracted light amount. When the second basic structure is used, the second light flux and / or the third light flux are diverged light or the light beam rather than making all of the first light flux, the second light flux, and the third light flux enter the objective optical element as parallel light. It is preferable to make it enter into an objective optical element as convergent light. In the region of NA3 or less, the 0th-order diffracted light amount of the first light beam that has passed through the second basic structure is made larger than any other order diffracted light amount, and the −1st-order diffracted light amount of the second light beam is A structure in which the amount of diffracted light is larger than any other order and the −2nd order diffracted light amount of the third light flux is larger than any other order of diffracted light amount is preferable. On the other hand, in the region of NA3 or more and NA2 or less, the 0th-order diffracted light amount of the first light beam that has passed through the second basic structure is made larger than any other order of diffracted light amount, and the −1st order of the second light beam. If the structure is such that the diffracted light quantity is larger than any other order diffracted light quantity, the order of the diffracted light quantity in the third light beam is greater than any other order diffracted light quantity.

  By superposing the first basic structure and the second basic structure, for example, a first optical path difference providing structure as shown in FIG. 5C can be obtained. As shown in FIG. 5C, the first optical path difference providing structure is a complex and non-periodic structure without a pattern. However, when viewed macroscopically, the height from the optical axis is It is preferable to have a structure that becomes deeper in the optical axis direction as the size increases.

  In this way, by superimposing the first basic structure and the second basic structure, in the first optical path difference providing structure, the light beam that has passed through the center of the first basic structure is always the second basic structure. Since the residual coma aberration is reduced, information can be recorded and / or reproduced appropriately regardless of temperature changes.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a ring-shaped structure divided by concentric steps, and the step amount dX in the optical axis direction is It is preferable to satisfy the following conditional expression (2). In addition, it is preferable that all the steps of the first optical path difference providing structure satisfy the following conditional expression (2).
0.9 · a · λ1 / (n−1) ≦ dX (nm) ≦ 1.1 · a · λ1 / (n−1)
(2)
However, (lambda) 1 represents the wavelength (nm) of a 1st light beam, n represents the refractive index of the 1st optical element in a 1st light beam, a is an integer in any one of 2, 4, 6, 8, or 10 Represents. A plurality of types of a may be used in one first optical path difference providing structure.

More preferably, the following conditional expression (2 ′):
0.95 · a · λ1 / (n−1) ≦ dX (nm) ≦ 1.05 · a · λ1 / (n−1)
(2 ')
Is to satisfy.

More preferably, the following conditional expression (2 ″)
dX (nm) = a · λ1 / (n−1) (2 ″)
Is to satisfy.

  The value of a of the step amount dX of the first optical path difference providing structure preferably satisfies at least 2 and 8. That is, it is preferable that the first optical path difference providing structure has at least two types of steps. (Here, the “type” is the same type if the value of a is the same, and is considered to be a different type if the value of a is different.) Specifically, for example, the first optical path difference This is a case where all the step amounts of the imparting structure satisfy either the step amount of 2 · λ1 / (n-1) or the step amount of 8 · λ1 / (n-1). Moreover, in addition to 2 and 8, the value of a in dX may further satisfy any of 4, 6, or 10. That is, the first optical path difference providing structure may have three to five types of step amounts. Specifically, for example, all the step amounts of the first optical path difference providing structure include a step amount of 2 · λ1 / (n−1), a step amount of 8 · λ1 / (n−1), and 10 · This is a case where any one of the steps of λ1 / (n−1) is satisfied.

  When the third optical disk is used, it is preferable that the first optical element has a second optical path difference providing structure on the second optical surface. It is preferable that a second optical path difference providing structure is provided on the optical surface of the first optical element on the second optical element side. The second optical path difference providing structure utilizes the wavelength difference between the wavelength λ1 of the first light beam and the wavelength λ3 of the third light beam, and the thickness t1 of the protective substrate of the first optical disk and the thickness of the protective substrate of the third optical disk. A structure that corrects spherical aberration generated based on the difference in t3 is preferable. Preferably, the first light flux and the second light flux have no power (transmits the first light flux and the second light flux) and have a power only for the third light flux. The second optical path difference providing structure can also have various cross-sectional shapes as schematically shown in FIGS. 1 to 4, but preferably has a binary shape shown as D2 in FIG.

In a particularly preferred second optical path difference providing structure, the 0th-order diffracted light amount of the first light beam that has passed through the second optical path difference providing structure is made larger than any other order diffracted light amount, and the 0th-order diffracted light amount of the second light beam is increased. Is made larger than any other order of the diffracted light quantity, and the ± 1st order diffracted light quantity of the third light flux is made larger than any other order of diffracted light quantity. When the second optical path difference providing structure has a binary shape, the step amount dD in the optical axis direction of the step in the binary structure as shown in FIG. 8 preferably satisfies the following conditional expression (4). More preferably, all the steps of the second optical path difference providing structure satisfy the conditional expression (4).
0.9 · 5 · λ1 / (n−1) ≦ dD (nm) ≦ 1.1 · 5 · λ1 / (n−1)
(4)
However, (lambda) 1 represents the wavelength (nm) of a 1st light beam, and n represents the refractive index of the 1st optical element in a 1st light beam.

More preferably, the following conditional expression (4 ′),
0.95 · 5 · λ1 / (n−1) ≦ dD (nm) ≦ 1.05 · 5 · λ1 / (n−1)
(4 ')
Is to satisfy.

More preferably, the following conditional expression (4 ″)
dD (nm) = 5 · λ1 / (n−1) (4 ″)
Is to satisfy.

  Further, the second optical path difference providing structure is preferably a ring-shaped structure divided by concentric steps. In the second optical path difference providing structure, it is preferable that the image side numerical aperture (NA) of the second optical surface of the first optical element is provided in a region corresponding to NA3 or less. NA3 is preferably 0.4 or more and 0.55 or less.

  However, the second basic structure in the first optical path difference providing structure makes the 0th-order diffracted light quantity of the first light beam that has passed through the second basic structure larger than any other order diffracted light quantity, and In the case of an optical path difference providing structure in which the first-order diffracted light amount is made larger than any other order diffracted light amount, and the second-order diffracted light amount of the third light beam is made larger than any other order diffracted light amount. It is preferable not to provide the second optical path difference providing structure.

  Next, the second optical element is preferably a spherical or aspherical lens having a condensing function. Particularly preferred is a single plastic lens consisting only of an aspheric refracting surface. In addition, the lens is preferably optimized for recording and / or reproducing information with respect to the first optical disk using the first light flux. That is, the second optical element is protected with a thickness t1 so that the first optical element can be used for recording and / or reproducing information without using the first optical element. It is preferable that the design is such that light can be condensed on the information recording surface of the first optical disk via the substrate.

The objective optical element unit has a working distance WD3 for the third optical disk expressed by the following equation (14):
0.20 ≦ WD3 (mm) ≦ 0.50 (14)
It is preferable to satisfy.

When the focal length when the first light beam is incident on the first optical element is f _{L1 (λ1)} , and the focal length when the first light beam is incident on the second optical element is f _{L2 (λ1).} And the following equation (1):
| F _{L2 (λ1)} / f _{L1 (λ1)} | ≦ 0.3 (1)
It is preferable to satisfy.

More preferably, the following formula (1 ′):
| F _{L2 (λ1)} / f _{L1 (λ1)} | ≦ 0.05 (1 ′)
Is to satisfy.

If the first optical element is given power so that f _{L2 (λ1)} / f _{L1 (λ1)} exceeds the lower limit of the expression (1), it is easy to suppress spherical aberration deterioration caused by temperature change. There are benefits. On the other hand, if the first optical element has too much power, the working distance WD3 for the third optical disk may be shortened. Therefore, by setting f _{L2 (λ1)} / f _{L1 (λ1)} to be equal to or lower than the upper limit of the equation (1), the working distance WD3 can be set within the range shown in the equation (1).

Further, f _{L1 (λ1)} may be set to ∞. When the first optical element is not provided with refractive power (for example, a parallel plate), it is preferable to install the first optical element in an inclined state, as will be described later.

  When the first optical element has a flat plate shape, the first optical element and the second optical element with the optical axis of the first optical element inclined by a predetermined amount with respect to the optical axis of the second optical element. It is preferable that the optical element is fixed. That is, it is preferable that the first optical element is disposed at an angle. When the first optical element has a flat plate shape, the first optical element is arranged so that the optical axis of the principal ray of the light beam emitted from the light source of the optical pickup device and the normal line of the flat plate are not parallel to each other. It can be said that it is preferable. In addition, it is preferable that the optical axis of the principal ray of the light beam emitted from the light source of the optical pickup device is parallel to the optical axis of the second optical element. With this configuration, the light beam reflected by the first optical element becomes a ghost and can be prevented from adversely affecting the light receiving surface of the photodetector, and more stable recording and / or reproduction can be performed. Preferably, the predetermined amount is greater than 0 degrees and 5 degrees or less. More preferably, it is 0.5 degree or more and 3 degrees or less.

Further, in the objective optical element, it is preferable that the temperature characteristic is improved even if the wavelength characteristic is somewhat sacrificed. In addition, it is preferable to maintain a good balance between wavelength characteristics and temperature characteristics. More preferably, the temperature characteristics when recording and / or reproducing the first optical disk are improved. In order to satisfy such characteristics, the objective optical element has the structure of the present invention, so that the following conditional expressions (15) and (16),
+ 0.00045 ≦ δSAT1 / f (WFEλrms / (° C. mm)) ≦ + 0.0027
(15)
−0.045 ≦ δSAλ / f (WFEλrms / (nm · mm)) ≦ −0.0045
(16)
It is preferable to satisfy.

  However, δSAT1 represents δSA3 / δT of the objective optical element at the time of recording and / or reproduction of the first optical disk at the wavelength used (in this case, there is no wavelength variation accompanying temperature change). The used wavelength refers to the wavelength of a light source used in an optical pickup device having an objective optical element. Preferably, the wavelength used is a wavelength in the range of 400 nm or more and 415 nm or less, and is a wavelength at which recording and / or reproduction of the first optical disc can be performed via the objective optical element. When the use wavelength cannot be set as described above, δSAT1 of the objective optical element and δSAT2 and δSAT3 described later may be obtained using 405 nm as the use wavelength. In other words, δSAT1 indicates the temperature change rate (temperature characteristic) of the third-order spherical aberration of the objective optical element when recording and / or reproducing the first optical disk at the used wavelength (no wavelength variation). Note that WFE indicates that the third-order spherical aberration is expressed by wavefront aberration. Further, δSAλ represents δSA3 / δλ when recording and / or reproducing the first optical disk at the used wavelength under a condition where the environmental temperature is constant. That is, δSAλ indicates the wavelength change rate (wavelength characteristic) of the third-order spherical aberration of the objective optical element when recording and / or reproducing the first optical disk at the used wavelength under the condition where the environmental temperature is constant. The ambient temperature is preferably room temperature. The room temperature is 10 ° C. or more and 40 ° C. or less, and preferably 25 ° C. f indicates the focal length of the objective optical element at the used wavelength (preferably 405 nm) of the first light flux.

More preferably, the following conditional expression (15) ′,
+ 0.00091 ≦ δSAT1 / f (WFEλrms / (° C. mm)) ≦ + 0.0018
(15) '
Is to satisfy.

Preferably, the following conditional expression (16) ′,
−0.032 ≦ δSAλ / f (WFEλrms / (nm · mm)) ≦ −0.0091
(16) '
Is to satisfy.

More preferably, the following conditional expression (16) ″,
−0.015 ≦ δSAλ / f (WFEλrms / (nm · mm)) ≦ −0.011
(16) ''
Is to satisfy.

Furthermore, the objective optical element has the wavelength dependency of the spherical aberration so that the change of the spherical aberration due to the refractive index change accompanying the temperature change of the objective optical element is corrected by the wavelength change of the first wavelength accompanying the temperature change. Is preferred. Preferably, the following conditional expression (17),
0 ≦ δSAT2 / f (WFEλrms / (° C. mm)) ≦ + 0.00136
(17)
Is to satisfy.

  However, δSAT2 represents δSA3 / δT of the objective optical element at the time of recording and / or reproduction of the first optical disk at the wavelength used (wavelength variation with temperature change is 0.05 nm / ° C.) (preferably 405 nm). That is, δSAT2 is a temperature change rate (temperature characteristic of the third-order spherical aberration of the objective optical element at the time of recording and / or reproduction of the first optical disc at the wavelength used (wavelength variation with temperature change is 0.05 nm / ° C.). ).

Further, when the condensing optical system of the optical pickup device has a coupling lens such as a collimator lens, and the coupling lens is a plastic lens, the following conditional expression (18),
0 ≦ δSAT3 / f (WFEλrms / (° C. mm)) ≦ + 0.00091
(18)
It is preferable to satisfy.

  However, δSAT3 includes a coupling lens and an objective optical element when recording and / or reproducing the first optical disk at a wavelength used (wavelength variation with temperature change is 0.05 nm / ° C.) (preferably 405 nm). This represents δSA3 / δT of the entire optical system. That is, δSAT3 is the temperature change rate (temperature characteristics) of the third-order spherical aberration of the entire optical system at the time of recording and / or reproduction of the first optical disk at the wavelength used (wavelength variation with temperature change is 0.05 nm / ° C.). ).

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

  An optical information recording / reproducing apparatus using each of the above-described methods is generally equipped with the following components, but is not limited thereto. An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc These include a transfer means of an optical pickup device having a guide rail or the like for guiding toward the head, a spindle motor for rotating 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, it is possible to provide an objective optical element unit and an optical pickup device for an optical pickup device that can appropriately record and / or reproduce information with respect to different optical information recording media at a low cost.

It is a figure which shows the example of an optical path difference providing structure. It is a figure which shows the example of an optical path difference providing structure. It is a figure which shows the example of an optical path difference providing structure. It is a figure which shows the example of an optical path difference providing structure. It is a figure for demonstrating the 1st optical path difference providing structure. It is a figure for demonstrating the principle which correct | amends the aberration degradation resulting from the temperature change by a 1st basic structure. It is a schematic block diagram of the optical pick-up apparatus concerning this Embodiment. It is sectional drawing of the objective optical element unit OBU concerning this Embodiment. It is sectional drawing which expands and shows a part of objective optical element unit OBU.

Explanation of symbols

AC1 2-axis actuator AC2 1-axis actuator C1 region C2 region C3 region C4 region CL collimating optical system D1 first optical path difference providing structure D2 second optical path difference providing structure HL lens frame L1 first optical element L2 second optical Element LD1 Blue-violet semiconductor laser LD2 Red semiconductor laser LD3 Infrared semiconductor laser LL Laser light M1 Marker M2 Marker ML Mirror OA1 Optical axis OA2 Optical axis OBU Objective optical element unit P1 First prism P2 Second prism P3 Third prism PD Photodetection PL1 Protective substrate PL2 Protective substrate PL3 Protective substrate PU Optical pickup device RL1 Information recording surface RL2 Information recording surface RL3 Information recording surface S1 Optical surface on the light source side S2 Optical surface on the optical disk side SE Sensor optical system STO Aperture

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, an optical pickup device using the objective optical element unit according to the present invention will be described with reference to FIG. FIG. 7 shows a configuration of an optical pickup device PU that can appropriately record and reproduce information on any of a high-density optical disc BD (first optical disc), DVD (second optical disc), and CD (third optical disc). It is a figure shown roughly. The specifications of the BD are the first wavelength (design wavelength) λ1 = 405 nm, the thickness t1 = 0.0875 mm of the protective substrate PL1, the numerical aperture NA1 = 0.85 (hereinafter, this numerical aperture is referred to as NA1), DVD The specifications of the second wavelength (design wavelength) λ2 = 658 nm, the thickness t2 of the protective substrate PL2 = 0.6 mm, and the numerical aperture NA2 = 0.60 (hereinafter, this numerical aperture is referred to as NA2). The specifications are the third wavelength (design wavelength) λ3 = 785 nm, the thickness t3 of the protective substrate PL3 = 1.2 mm, and the numerical aperture NA3 = 0.45 (hereinafter, this numerical aperture is referred to as NA3). However, the combination of the wavelength, the thickness of the protective substrate, and the numerical aperture is not limited to this.

  The optical pickup device PU includes a blue-violet semiconductor laser LD1 (first light source) that emits a first light beam with a wavelength λ1 for BD, and a red semiconductor laser LD2 (second light source) for DVD that emits a second light beam with a wavelength λ2. , An infrared semiconductor laser LD3 (third light source) for emitting a third light beam of wavelength λ3, a light receiving element PD for BD / DVD / CD, an objective optical element unit OBU, a collimating optical system CL, and a biaxial actuator AC1 1-axis actuator AC2, first prism P1, second prism P2, third prism P3, rising mirror ML, sensor optical system for adding astigmatism to the reflected light beam from the information recording surface of each optical disk It consists of SE.

  FIG. 8 is a cross-sectional view of the objective optical element unit OBU according to the present embodiment. The objective optical element unit OBU has a configuration in which a plastic flat first optical element L1 and a second optical element L2 which is a plastic aspherical lens are connected by a plastic lens frame HL. . Although not shown, the optical axis of the first optical element L1 is inclined by 2.5 degrees with respect to the optical axis of the second optical element L2.

  The first optical element L1 has a refractive index of 1.56 in the first light flux having the wavelength λ1, is made of a polyolefin-based plastic having an Abbe number of 50 or more and 60 or less, and the first optical surface S1 on the light source side is: The second optical surface S2 on the optical disc side is divided into a region C1 corresponding to the numerical aperture NA3, and is divided into a region C2 corresponding to the numerical aperture NA2 or lower and a region C3 corresponding to the numerical aperture NA2 or higher and NA1 or lower. And a region C4 corresponding to a numerical aperture NA3 or more and NA1 or less.

  A first optical path difference providing structure D1 is formed in a region C2 of the first optical surface S1 of the first optical element L1. When the first optical path difference providing structure D1 has a cross-sectional shape in the optical axis direction as shown in FIG. 5B, the depth increases in the optical axis direction as the height from the optical axis increases. When the cross-sectional shape in the optical axis direction is taken as shown in FIG. 5A, the second basic structure having a plurality of four-step small staircase structures is overlaid. ).

  The first basic structure is a structure that corrects spherical aberration that occurs with temperature change for the first light flux. This is a so-called NPS structure. Further, the first basic structure of the first optical path difference providing structure makes the second diffracted light amount of the first light beam that has passed through the first basic structure larger than any other order diffracted light amount, and the second light beam. The first order diffracted light amount is made larger than any other order diffracted light amount, and the first order diffracted light amount of the third light beam is made larger than any other order diffracted light amount. It is the optical path difference providing structure which has power with respect to. Further, the first basic structure has no power with respect to the first light flux and the third light flux when the wavelengths of the first light flux and the third light flux are design wavelengths. When the light beam and the third light beam deviate from the design wavelength, the optical path difference providing structure has power with respect to the first light beam and the third light beam. The first basic structure of the first optical path difference providing structure is a concentric ring-shaped structure divided by steps, and the step amount dA in the optical axis direction is about 1.5 μm.

  The second basic structure uses the wavelength difference between the wavelength λ1 of the first light flux and the wavelength λ2 of the second light flux to determine the difference between the thickness t1 of the BD protective substrate and the thickness t2 of the DVD protective substrate. This is a structure for correcting spherical aberration generated based on the above. In the second basic structure, the 0th-order diffracted light quantity of the first light beam that has passed through the second basic structure is made larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the second light beam is set to any other diffracted light quantity. An optical path difference providing structure that is larger than the diffracted light quantity of the order and makes the 0th-order diffracted light quantity of the third light beam larger than any other order diffracted light quantity, and provides an optical path difference that has power only for the second light flux. Structure. The shape of the second foundation structure is a structure having a plurality of four-step small staircase structures as shown in FIG. In this case, the step amount dB in the optical axis direction of the small step in the small step-like structure is about 1.5 μm, and the step amount dC in the optical axis direction of the large step is about 5.7 μm.

  The first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure has three kinds of step amounts of about 1.5 μm, about 5.7 μm, and about 7.1 μm.

  By superimposing the first foundation structure and the second foundation structure, the light beam that has passed through the center of the first foundation structure can always pass through the center of the second foundation structure. Thus, information can be recorded and / or reproduced appropriately regardless of temperature changes.

  Note that a third optical path difference providing structure composed only of the first basic structure is provided in the region C3 of the first optical surface S1. The third optical path difference providing structure makes the fourth-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 diffracted light quantity, and the third-order and second-order diffraction of the second light beam. The amount of light is made larger than any other order diffracted light amount, and the second order diffracted light amount of the third light flux is made larger than any other order diffracted light amount. In this case, the step amount dY in the optical axis direction of the third optical path difference providing structure is about 2.9 μm.

  Note that the first basic structure of the first optical path difference providing structure and the third optical path difference providing structure has a cross-sectional shape including the optical axis at a predetermined height from the optical axis when captured in the entire regions C2 and C3. The step structure is such that the depth increases as the distance from the optical axis increases, and after a predetermined height from the optical axis, the depth decreases as the distance from the optical axis increases.

  Further, a second optical path difference providing structure D2 that is a binary structure is formed in the region C1 of the second optical surface S2 of the first optical element L1. The second optical path difference providing structure D2 utilizes the wavelength difference between the wavelength λ1 of the first light beam and the wavelength λ3 of the third light beam, and the difference between the thickness t1 of the BD protective substrate and the thickness t3 of the CD protective substrate. This is a structure for correcting spherical aberration generated based on the above.

  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 0th-order diffracted light quantity of the second light flux is set to be different. In this structure, the diffracted light amount of the third light beam is made larger than the diffracted light amount of any other order. The step amount dD in the optical axis direction of the step in the binary structure is about 3.6 μm.

  The second optical element is an aspheric lens made of polyolefin plastic having a refractive index of 1.56. The second optical element is designed to be capable of condensing the first light beam on the information recording surface of the BD without using the first optical element.

  FIG. 9 is an enlarged sectional view showing a part of the objective optical element unit OBU. In the objective optical element unit OBU, the optical axis OA1 of the first optical element L1 is inclined at an angle θ = 2.5 ° with respect to the optical axis OA2 of the second optical element L2. Thereby, the possibility that the reflected light from the first optical element L1 is received by the photodetector can be reduced. 9, the center of the first optical surface on the light source side of the first optical element L1 (that is, the optical surface on which the first optical path difference providing structure and the third optical path difference providing structure are provided). A marker M1 is provided at (optical axis position), and a marker M2 is provided at the center (optical axis position) of the second optical element L2. These markers M1 and M2 are used for alignment of the first optical element L1 and the second optical element L2. The marker may be provided by a paint, or may be provided as a concave portion or a convex portion.

  In order not to deteriorate the imaging characteristics of the objective optical element unit OBU even when the first optical element L1 is inclined, for example, a laser beam LL incident in parallel to the optical axis OA2 of the second optical element L2 from the light source side. Is preferably aligned so that it passes through the marker M1, which is the center of the first optical element L1, and further passes through the marker M2, which is the center of the second optical element L2, and travels along the optical axis OA2. . As described above, by using the markers M1 and M2 to place the center of the second optical element L2 and the first optical element L1 on the same optical path in the optical axis OA2 direction, the tilt angle of the first optical element L1. Regardless of the value of θ, coma generated at least as the objective optical element unit OBU (especially for the first light flux and the second light flux) can be reduced.

  When the first optical path difference providing structure and the third optical path difference providing structure are provided not on the light source side surface of the first optical element but on the surface on the optical disk side, It is preferable that the marker is also provided on the surface on the optical disc side and aligned so that the marker and the marker of the second optical element have the same optical path.

  As a method of arranging the marker M1 of the first optical element L1 on the optical axis OA2 of the second optical element L2, the second optical element L2 attached to the lens frame HL is placed on the optical axis OA2 from the left side of the drawing. While observing, the first optical element L1 is arranged on the front side of the second optical element L2, and the first optical element L1 is moved within the lens frame so that both the markers M1 and M2 coincide. Thereby, the state shown in FIG. 9 is achieved, and the imaging characteristics of the objective optical element unit OBU can be ensured.

  In the optical pickup device PU, when information is recorded / reproduced with respect to the BD, a blue-violet laser beam (first beam) having a wavelength λ1 is emitted in a state of a parallel beam from the collimating optical system CL. After the position of the collimating optical system CL is adjusted in the optical axis direction by the uniaxial actuator AC2, the blue-violet semiconductor laser LD1 is caused to emit light. The divergent light beam emitted from the blue-violet semiconductor laser LD1 is reflected by the first prism P1 and then sequentially passes through the second prism P2 and the third prism P3, as shown by the solid line in FIG. Then, it is converted into a parallel light beam by the collimating optical system CL. After that, after being reflected by the rising mirror ML, the beam diameter is regulated by the stop STO, and becomes a condensed spot formed on the information recording surface RL1 by the objective optical element unit OBU via the protective substrate PL1 of the BD. The objective optical element unit OBU performs focusing and tracking by a biaxial actuator AC1 disposed around the objective optical element unit OBU. The first light beam passes through the first optical surface S1 of the first optical element L1, passes through the second optical surface S2, and enters the second optical element L2 in the state of a parallel light beam. All the first light fluxes within the range (that is, the region where C2 and C3 are combined or the region where C1 and C4 are combined) are collected on the information recording surface of the BD by the second optical element L2. Further, when the environmental temperature changes, the spherical aberration can be suppressed by the mechanism described above.

  The reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective optical element unit OBU, then reflected by the rising mirror ML, and becomes a converged light beam when passing through the collimating optical system CL. After that, after passing through the third prism P3, the second prism P2, and the first prism P1 in order, astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the photodetector PD. Information recorded on the BD can be read using the output signal of the photodetector PD.

  Further, when information is recorded / reproduced with respect to the DVD in the optical pickup device PU, the red laser beam (second beam) having the wavelength λ2 is emitted from the collimating optical system CL in a parallel beam state. After the position of the collimating optical system CL is adjusted in the optical axis direction by the uniaxial actuator AC2, the red semiconductor laser LD2 is caused to emit light. The divergent light beam emitted from the red semiconductor laser LD2 is reflected by the second prism P2 and then transmitted through the third prism P3 and parallel by the collimating optical system CL as shown by the broken line in FIG. Converted into luminous flux. After that, after being reflected by the rising mirror ML, it becomes a condensing spot formed on the information recording surface RL2 via the protective substrate PL2 of the DVD by the objective optical unit OBU. The objective optical element unit OBU performs focusing and tracking by a biaxial actuator AC1 disposed around the objective optical element unit OBU. The second light flux is converted into divergent light in the region C2 of the first optical surface S1 of the first optical element L1, and is transmitted in the region C3. The second light flux that has passed through the region C2 and converted into divergent light passes through the second optical surface S2, enters the second optical element as divergent light, and is collected on the information recording surface of the DVD. . On the other hand, the second light beam transmitted through the region C3 is incident on the second optical element as a parallel light beam, and does not form a condensing spot by the second optical element, and becomes a flare on the information recording surface of the DVD. Therefore, the second light flux in the range within NA2 (namely, the C2 region) is condensed on the information recording surface of the DVD, and the second light flux in the range larger than NA2 (namely, the C3 region) becomes flare.

  The reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective optical element unit OBU, then reflected by the rising mirror ML, and becomes a converged light beam when passing through the collimating optical system CL. After that, after passing through the third prism P3, the second prism P2, and the first prism P1 in order, astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the photodetector PD. Information recorded on the DVD can be read using the output signal of the photodetector PD.

  Further, when information is recorded / reproduced with respect to the CD in the optical pickup device PU, an infrared laser beam (third beam) having a wavelength λ3 is emitted from the collimating optical system CL in a state of a parallel beam. In addition, after the position of the collimating optical system CL is adjusted in the optical axis direction by the uniaxial actuator AC2, the infrared semiconductor laser LD3 is caused to emit light. The divergent light beam emitted from the infrared semiconductor laser LD3 is reflected by the third prism P3 and then converted into a parallel light beam by the collimating optical system CL, as depicted by the alternate long and short dash line in FIG. After that, after being reflected by the rising mirror ML, it becomes a condensing spot formed on the information recording surface RL3 via the protective substrate PL3 of the CD by the objective optical element unit OBU. The objective optical unit OBU performs focusing and tracking by a biaxial actuator AC1 arranged in the periphery thereof. The third light flux passes through the first optical surface S1 of the first optical element L1. The third light flux is converted into divergent light in the region C1 of the second optical surface S2 of the first optical element L1, and is transmitted through the region C4. The third light beam that has passed through the region C1 and converted into divergent light is incident on the second optical element as divergent light, and is condensed on the information recording surface of the CD. On the other hand, the third light beam transmitted through the region C4 enters the second optical element as a parallel light beam, and does not form a condensing spot by the second optical element, and becomes a flare on the information recording surface of the CD. Accordingly, the third light flux in the range within NA3 (namely, the C1 region) is collected on the information recording surface of the CD, and the third light flux in the range larger than NA3 (namely, the C4 region) is flare.

  The reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective optical unit OBU, then reflected by the rising mirror ML, and becomes a converged light beam when passing through the collimating optical system CL. After that, after passing through the third prism P3, the second prism P2, and the first prism P1 in order, astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the photodetector PD. Information recorded on the CD can be read using the output signal of the photodetector PD.

In the optical pickup device PU, the spherical aberration when using the BD can be corrected by driving the collimating optical system CL in the optical axis direction by the uniaxial actuator AC2. With such a spherical aberration correction mechanism, wavelength variations due to manufacturing errors of the blue-violet semiconductor laser LD1, refractive index change and refractive index distribution of the objective optical system with temperature change, focus jump between information recording eyebrows of multilayer disks, manufacturing of the protective substrate PL1 It is possible to correct spherical aberration due to thickness variation and thickness distribution due to error. The spherical aberration correction mechanism may correct spherical aberration when using a DVD or CD.
<Example>
Next, examples that can be used in the above-described embodiment will be described. In the following embodiments, as described above, the objective optical element unit is such that the first optical element is a polyolefin-based plastic flat optical element, and the second optical element is also a polyolefin-based plastic aspherical lens. It is.

Tables 1 to 3 show lens data of this example. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed using E (for example, 2.5E−3).

  The optical surface of the objective optical element 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 1.

  Here, X (h) is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, A2i is an aspherical coefficient, and h is a height from the optical axis.

  Further, the optical path length given to the light flux of each wavelength by the optical path difference providing structure is defined by an equation in which the coefficient shown in Table 2 is substituted into the optical path difference function of Formula 2.

  λ is the wavelength of the incident light beam, λB is the manufacturing wavelength (blazed wavelength), dor is the diffraction order, and B2i is the coefficient of the optical path difference function.

  In this example, the coma after alignment is 0λrms for BD, 0.001λrms for DVD, and −0.017λrms for CD, although the first optical element is tilted by 2.5 degrees. And kept low. In addition, a change in the amount of aberration when the environmental temperature changes can be suppressed to a small level.

In this embodiment, since f _{L1 (λ1)} = ∞ and f _{L2 (λ1)} = 2.2, | f _{L2 (λ1)} / f _{L1 (λ1)} | = 0. Further, regarding the temperature characteristics of the objective optical element of the present example, δSAT1 is +0.0037 WFEλrms / ° C., and δSAT2 is +0.0022 WFEλrms / ° C. Further, since f of the objective optical element at the first wavelength is 2.2 mm, δSAT1 / f is +0.0017 WFEλrms / (° C. · mm). δSAT2 / f is +0.001 WFEλrms / (° C. mm). Regarding the wavelength characteristics of the objective optical element of this example, δSAλ is −0.0284 WFEλrms / nm, and δSAλ / f is −0.0129WFEλrms / (nm · mm). When a collimating optical system having lens data shown in Table 4 below is used, δSAT3 is +0.0005 WFEλrms / ° C., and δSAT3 / f is + 0.00023WFEλrms / (° C. mm).

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate.

Claims (31)

A first light source that emits a first light beam having a wavelength of λ1 (nm); a second light source that emits a second light beam of a wavelength of λ2 (nm) (λ1 <λ2); and an objective optical element unit. The optical element unit records and / or reproduces the information by condensing the first light flux on the information recording surface of the first optical disc having the required numerical aperture NA1 through the protective substrate having the thickness t1. In addition, the second light beam is applied to the information recording surface of the second optical disc having a required numerical aperture NA2 (NA1 ≧ NA2) through a protective substrate having a thickness t2 (t1 ≦ t2). An objective optical element unit for an optical pickup device capable of recording and / or reproducing information by condensing,
The objective optical element unit has a first optical element and a second optical element each made of plastic.
The first optical element and the second optical element are arranged side by side in the optical axis direction,
The first optical element has a first optical surface and a second optical surface facing each other, and the first optical surface of the first optical element has a first optical path difference providing structure. ,
The first optical path difference providing structure is a structure in which a first basic structure and a second basic structure are overlapped,
The first foundation structure and the second foundation structure are both structures having a plurality of concentric steps,
An objective optical element unit for an optical pickup device, wherein both the first basic structure and the second basic structure have power with respect to the second light flux having the wavelength λ2.   The first optical path difference providing structure does not have power when the wavelength λ1 of the first light beam is a design wavelength, and has power when the wavelength λ1 of the first light beam deviates from the design wavelength. The objective optical element unit for an optical pickup device according to claim 1, characterized in that: The objective optical element unit for an optical pickup device according to claim 1 or 2, wherein the following expression is satisfied.
| F _{L2 (λ1)} / f _{L1 (λ1)} | ≦ 0.3 (1)
However,
f _{L1 (λ1)} : focal length when the first light beam is incident on the first optical element f _{L2 (λ1)} : focal length when the first light beam is incident on the second optical element   The optical pickup according to any one of claims 1 to 3, wherein the second optical surface of the first optical element is an optical surface on the second optical element side. Objective optical element unit for equipment.   The objective optical element unit for an optical pickup device according to any one of claims 1 to 4, wherein the first optical element is a parallel plate having the first optical path difference providing structure. .   The optical pickup device according to any one of claims 1 to 5, wherein the second optical element is a lens having a spherical or aspherical optical surface having a condensing function. Objective optical element unit.   The second optical element does not include the first optical element, and only the second optical element, and the first light beam emitted from the first light source is transmitted through the protective substrate having a thickness t1. 7. The objective optical element unit for an optical pickup device according to claim 6, wherein the objective optical element unit can be condensed on the information recording surface of the first optical disk.   8. The optical pickup device according to claim 1, wherein the optical axis of the first optical element is inclined with respect to the optical axis of the second optical element. Objective optical element unit.   The first basic structure according to any one of claims 1 to 8, wherein the first basic structure has a function of correcting a spherical aberration caused by a change in an environmental temperature with respect to the first light flux. An objective optical element unit for an optical pickup device according to any one of the above.   The second basic structure utilizes a wavelength difference between the wavelength λ1 of the first light beam and the wavelength λ2 of the second light beam, and the thickness t1 of the protective substrate of the first optical disk and the second optical disk The objective optical system for an optical pickup device according to any one of claims 1 to 9, which has a function of correcting spherical aberration caused by a difference in thickness t2 of the protective substrate. Element unit.   The first optical path difference providing structure is formed in a region corresponding to an image side numerical aperture (NA) equal to or less than the NA2 on the first optical surface of the first optical element. An objective optical element unit for an optical pickup device according to any one of ranges 1 to 10.   The first optical surface of the first optical element has a third optical path difference providing structure around the first optical path difference providing structure, and the third optical path difference providing structure is the first basic structure. The objective optical element unit for an optical pickup device according to any one of claims 1 to 11, wherein the objective optical element unit is an optical pickup unit.   As for the first basic structure of the first optical path difference providing structure and the third optical path difference providing structure, as the height from the optical axis increases in the entire first optical surface of the first optical element. The structure is characterized in that the structure becomes deeper in the direction of the optical axis and becomes shallower in the direction of the optical axis as the height from the optical axis increases when the height exceeds an arbitrary height. 13. An objective optical element unit for an optical pickup device according to item 12. The optical pickup device includes a third light source that emits a third light beam having a wavelength λ3 (nm) (λ2 <λ3), and the objective optical element unit applies the third light beam to a thickness t3 (t2 <t3). ), The information can be recorded and / or reproduced by focusing on the information recording surface of the third optical disk having a required numerical aperture of NA3 (NA2> NA3) through the protective substrate of FIG.
The second optical surface of the first optical element has a second optical path difference providing structure;
The objective optical element unit for an optical pickup device according to any one of claims 1 to 13, wherein the second optical path difference providing structure has power only with respect to the third light flux. .   The second optical path difference providing structure utilizes the wavelength difference between the wavelength λ1 of the first light beam and the wavelength λ3 of the third light beam, and the thickness t1 of the protective substrate of the first optical disk and the third optical disk 15. The objective optical element unit for an optical pickup device according to claim 14, which has a function of correcting spherical aberration that occurs due to a difference in thickness t3 of the protective substrate.   The first basic structure of the first optical path difference providing structure makes the second-order diffracted light amount of the first light flux that has passed through the first basic structure larger than any other order of diffracted light amount, An optical path difference providing structure in which the first-order diffracted light quantity of the two light beams is made larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the third light beam is made larger than any other order diffracted light quantity. 16. The objective optical element unit for an optical pickup device according to claim 14 or 15, characterized in that:   The second basic structure of the first optical path difference providing structure makes the 0th-order diffracted light quantity of the first light beam that has passed through the second basic structure larger than any other order of diffracted light quantity, An optical path difference providing structure in which the first-order diffracted light amount of the two light beams is made larger than any other order diffracted light amount, and the zero-order diffracted light amount of the third light beam is made larger than any other order diffracted light amount. The objective optical element unit for an optical pickup device according to any one of claims 14 to 16, wherein:   The second optical path difference providing structure makes the 0th-order diffracted light amount of the first light beam that has passed through the second optical path difference providing structure larger than any other order of diffracted light amount, and the 0th-order diffracted light amount of the second light beam. The optical path difference providing structure is characterized in that the diffracted light quantity is made larger than any other order diffracted light quantity, and the ± 1st order diffracted light quantity of the third light flux is made larger than any other order diffracted light quantity. An objective optical element unit for an optical pickup device according to any one of items 14 to 17 in the above-mentioned range.   The second optical path difference providing structure is formed in a range in which an image-side numerical aperture (NA) corresponds to NA3 or less on the second optical surface of the first optical element. An objective optical element unit for an optical pickup device according to any one of ranges 14 to 18. A first light source that emits a first light beam having a wavelength of λ1 (nm); a second light source that emits a second light beam of a wavelength of λ2 (nm) (λ1 <λ2); and an objective optical element unit. The optical element unit records and / or reproduces the information by condensing the first light flux on the information recording surface of the first optical disc having the required numerical aperture NA1 through the protective substrate having the thickness t1. In addition, the second light beam is applied to the information recording surface of the second optical disc having a required numerical aperture NA2 (NA1 ≧ NA2) through a protective substrate having a thickness t2 (t1 ≦ t2). An objective optical element unit for an optical pickup device capable of recording and / or reproducing information by condensing,
The objective optical element unit has a first optical element and a second optical element each made of plastic.
The first optical element and the second optical element are arranged side by side in the optical axis direction,
The first optical element has a first optical surface and a second optical surface facing each other,
The first optical surface of the first optical element has a first optical path difference providing structure that is divided by a plurality of concentric steps in an area of NA2 or less. The step amount dX of the step satisfies the following conditional expression:
The first optical surface of the first optical element has a third optical path difference providing structure partitioned by a plurality of concentric steps in a region that is larger than the NA2 and less than or equal to the NA1. An objective optical element unit for an optical pickup device, wherein the step amount dY of the optical path difference providing structure satisfies the following conditional expression:
0.9 · a · λ1 / (n−1) ≦ dX (nm) ≦ 1.1 · a · λ1 / (n−1)
(2)
0.9 · b · λ1 / (n−1) ≦ dY (nm) ≦ 1.1 · b · λ1 / (n−1)
(3)
Here, n represents the refractive index of the first optical element in the first light flux, a represents an integer of 2, 4, 6, 8 or 10, and provides one first optical path difference. Plural types of a may be used in the structure, b represents an integer of 1, 2, 3, 4 or 5, and plural types of b are used in one third optical path difference providing structure. May be.   21. The optical pickup according to claim 20, wherein in the first optical path difference providing structure, a plurality of types of a values of the step amount dX are used, and the value of a satisfies at least 2 and 8. Objective optical element unit for equipment.   In the first optical path difference providing structure, a plurality of types of a values of the step amount dX are used, the value of a satisfies at least 2 and 8, and further satisfies any of 4, 6, or 10. An objective optical element unit for an optical pickup device according to claim 21.   The optical pickup device according to any one of claims 20 to 22, wherein in the third optical path difference providing structure, the value of b of the step amount dY is only one type. Objective optical element unit.   The third optical path difference providing structure according to any one of claims 20 to 23, wherein the value b of the step amount dY is an integer of 2, 3, or 4. An objective optical element unit for the optical pickup device described.   The first optical path difference providing structure has a structure that becomes deeper in the optical axis direction as the height from the optical axis increases as viewed macroscopically. 25. An objective optical element unit for an optical pickup device according to any one of items 24. The first optical path difference providing structure is a structure in which a first basic structure and a second basic structure are overlapped,
The first basic structure has a structure that becomes deeper in the direction of the optical axis as the height from the optical axis increases,
The objective optical element unit for an optical pickup device according to any one of claims 20 to 25, wherein the second basic structure is a structure having a plurality of four-step small staircase structures. .   27. The structure according to any one of claims 20 to 26, wherein the third optical path difference providing structure has a structure that becomes shallower in the optical axis direction as the height from the optical axis increases. An objective optical element unit for the optical pickup device described. The optical pickup device includes a third light source that emits a third light beam having a wavelength λ3 (nm) (λ2 <λ3), and the objective optical element unit applies the third light beam to a thickness t3 (t2 <t3). ), The information can be recorded and / or reproduced by focusing on the information recording surface of the third optical disk having a required numerical aperture of NA3 (NA2> NA3) through the protective substrate of FIG.
The second optical surface of the first optical element has a second optical path difference providing structure divided by a plurality of concentric steps in the area of NA3 or less,
The objective optical element unit for an optical pickup device according to any one of claims 20 to 27, wherein a step amount dD of the second optical path difference providing structure satisfies the following conditional expression.
0.9 · 5 · λ1 / (n−1) ≦ dD (nm) ≦ 1.1 · 5 · λ1 / (n−1)
(4)   29. The optical pickup device according to claim 20, wherein an optical axis of the first optical element is inclined with respect to an optical axis of the second optical element. Objective optical element unit.   An optical pickup device comprising the objective optical element unit according to any one of claims 1 to 29.   31. The optical pickup device according to claim 30, wherein the first optical element is disposed on a light source side, and the second optical element is disposed on an optical disk side.