JP2005353261A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device mounted with an objective optical element for appropriately recording and/or reproducing information on and/or from four kinds of disks having different recording density including high-density optical disks of two types of standards, DVDs and CDs, having different thicknesses in a protective substrate. <P>SOLUTION: An objective optical element OBJ1 specialized for a first optical disk and that OBJ2 specialized for a second optical disk are separately arranged. As a result, even if the thickness in the protective substrate differs, information can be appropriately recorded and/or reproduced to and/or from any of the optical disks by performing an optimum objective optical element design. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup device capable of recording and / or reproducing information on different types of optical information recording media.

  In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a blue-violet semiconductor laser, Laser light sources with wavelengths of 400 to 420 nm, such as blue SHG lasers that perform wavelength conversion of infrared semiconductor lasers using harmonics, are being put into practical use.

  When these blue-violet laser light sources are used, when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used, it is possible to record information of 15 to 20 GB on an optical disk having a diameter of 12 cm. When the NA of the objective lens is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm. Hereinafter, in this specification, an optical disk and a magneto-optical disk using a blue-violet laser light source are collectively referred to as a “high density optical disk”.

  By the way, two standards are currently proposed as high-density optical disks. One is a Blu-ray Disc (hereinafter abbreviated as BD) using an objective lens with NA of 0.85 and a protective substrate thickness of 0.1 mm, and the other is using an objective lens with NA of 0.65 to 0.67. This is an HD DVD (hereinafter abbreviated as HD) having a protective substrate thickness of 0.6 mm. In view of the possibility that these two standard high-density optical discs will be distributed in the market in the future, a high-density optical disc player / recorder capable of recording / reproducing on any high-density optical disc is desired.

  On the other hand, it cannot be said that the value as a product of an optical disk player / recorder is sufficient just to be able to record / reproduce information only on a high density optical disk. In light of the reality that DVDs and CDs (compact discs) on which a wide variety of information is recorded are currently being sold, it is not possible to record / reproduce information on high-density optical discs. Similarly, it is possible to appropriately record / reproduce information on DVDs and CDs as well, increasing the commercial value as an optical disc player / recorder for high-density optical discs. From such a background, an optical pickup device mounted on an optical disc player / recorder for high density optical discs can record / reproduce information appropriately for both high density optical discs, DVDs, and even CDs. It is desirable to have

  Here, Patent Documents 1 and 2 below describe bifocal objective lenses that can perform recording / reproduction compatible with two types of optical disks having different protective substrate thicknesses and the same light source wavelength. The bifocal objective lens disclosed in Patent Documents 1 and 2 records / reproduces optical discs having different protective substrate thicknesses by distributing the amount of incident light flux to two focal points by a diffractive structure formed on the lens surface. Is what you do. Patent Document 3 below has a diffractive structure as a phase structure, an objective optical system that can be used in common for high-density optical discs and conventional DVDs and CDs, and an optical pickup equipped with the objective optical system. An apparatus is described.

JP-A-9-179020 Japanese Patent Laid-Open No. 9-120027 European publication No. 1304689

  However, the bifocal objective lenses disclosed in Patent Documents 1 and 2 described above are DVDs with NA of 0.6 and compact discs (hereinafter referred to as CDs) with NA of about 0.65 as optical disks to be recorded / reproduced. Therefore, four types of optical discs including those for recording / reproducing with respect to BD and HD with large NA are not supported.

  In addition, since the objective optical system described in Patent Document 3 has a large difference in magnification when information is recorded / reproduced on each optical disk, the optical pickup apparatus has a common optical component other than the objective optical system. It is difficult to use a light source module or the like in which a plurality of types of light sources are integrated, and there is a problem that the configuration of the optical pickup device cannot be simplified and the cost can not be reduced. In particular, since the magnification at the time of recording / reproducing information on a CD is large, coma aberration during lens tracking becomes large, which is a problem.

  The present invention has been made in view of these problems. Information recording is performed on four types of discs having different recording densities, including high-density optical discs of two standards having different protective substrate thicknesses, DVD and CD. An object of the present invention is to provide an optical pickup device equipped with an objective optical element that can appropriately perform reproduction.

  In this specification, an optical disk (also referred to as an optical information recording medium) that uses a blue-violet semiconductor laser or a blue-violet SHG laser as a light source for recording / reproducing information is generally referred to as a “high-density optical disk”, and NA0 Information is recorded / reproduced by an objective optical system of .85, an optical disc (eg, BD) having a protective substrate thickness of about 0.1 mm, and information is recorded by an objective optical system of NA 0.65 to 0.67. / It is assumed that an optical disc (for example, HD) of a standard that performs reproduction and has a protective substrate thickness of about 0.6 mm is also included. In addition to the optical disk having such a protective substrate on the information recording surface, the optical disk having a protective film with a thickness of several to several tens of nm on the information recording surface, the thickness of the protective substrate or the protective film It also includes an optical disc with 0. In this specification, the high-density optical disk includes a magneto-optical disk that uses a blue-violet semiconductor laser or a blue-violet SHG laser as a light source for recording / reproducing information.

  Here, “the thickness of the protective substrate of the optical information recording medium is the same” means a large-capacity optical recording medium that succeeds the DVD, and is an HD DVD standard (HD DVD standard) having high compatibility with the DVD standard. The difference in thickness from the DVD protective layer within the range complying with the above) is included.

  In this specification, DVD is a general term for DVD series optical discs such as DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, and DVD + RW. , CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW, etc.

The optical pickup device according to claim 1 is a first optical information recording medium having a first protective substrate thickness t1 and a second protective substrate thickness t2 (t2 ≠ t1) using a light beam having a wavelength λ1. In an optical pickup device that only reproduces information from an optical information recording medium and / or records information,
A first light source that emits a first light flux of wavelength λ1,
A first objective optical element and a second objective optical element provided separately from each other;
When reproducing information from the first optical information recording medium and / or recording information, a first protective substrate is formed by using one of the first and second objective optical elements for the first light flux. By condensing on the information recording surface via
When reproducing information from and / or recording information from the second optical information recording medium, a second protective substrate is used by using the first light beam as the other of the first and second objective optical elements. Configured to be focused on the information recording surface via
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1 (1)
It is characterized by satisfying.

When information is reproduced and / or recorded on both the first optical information recording medium and the second optical information recording medium having different protective substrate thicknesses using one objective optical element, one optical information recording is performed. When the spherical aberration is corrected for the medium, spherical aberration occurs in the other optical information recording medium due to the difference in the thickness of the protective substrate. For example, when spherical aberration correction is performed on one optical information recording medium, the third-order spherical aberration W40 in the other optical information recording medium is
^{_{W40 = {Δt (n λ 2}} -1) / (8n λ 2)} · NA 4 (1)
It is represented by Where Δt: substrate thickness difference between optical information recording media, nλ: refractive index of optical information recording medium substrate at wavelength λ, NA: numerical aperture of objective optical element (also referred to as objective lens). When the difference in the thickness of the protective substrate between the two types of optical information recording media is large as in the condition given by the equation (1), this spherical aberration becomes large and becomes a problem. In contrast, conventionally, spherical aberration caused by the difference in the thickness of the protective substrate is corrected by using diffraction for the objective optical element or making the conjugate length variable.

  In the case where information is reproduced and / or recorded on both the first optical information recording medium and the second optical information recording medium having different protective substrate thicknesses using one objective optical element, the objective optical element is conventionally used. The spherical aberration due to the difference in the thickness of the protective substrate is corrected by using diffraction or making the conjugate length variable. However, when recording and / or reproducing information to and from the first optical information recording medium and the second optical information recording medium, both media are used when light beams having the same wavelength are allowed to pass through the same diffraction structure. Since it becomes impossible to simultaneously increase the diffraction efficiency with respect to time, only one of the efficiency increases. For example, when the efficiency is balanced by two diffraction orders, each efficiency cannot be increased. In addition, in the case of dealing with each optical information recording medium by correcting the spherical aberration caused by the difference in thickness of the protective substrate with the conjugate length of the objective optical element being variable, the protective substrate thicknesses of two types of optical information recording media are used. When the difference is large as in the condition in the equation (1), in order to ensure a working distance (hereinafter referred to as WD) when recording and / or reproducing information on an optical information recording medium having a thicker protective substrate thickness. This is not desirable because the conjugate length of the objective optical element required for this is reduced. Therefore, in the present invention, the objective optical element dedicated to the first optical information recording medium and the objective optical element dedicated to the second optical information recording medium are separated from each other. By designing an objective optical element, information can be appropriately recorded and / or reproduced on any optical information recording medium.

The optical pickup device according to claim 2, wherein the first optical information recording medium having the first protective substrate thickness t1 and the first optical information recording medium using the first light flux having the wavelength λ1 and the second light flux having the wavelength λ2 (λ1 ≠ λ2) The second optical information recording medium having a protective substrate thickness t2 (t2 ≠ t1) and the third optical information recording having a third protective substrate thickness t3 are different in recording density from the first and second information recording media. In an optical pickup device that reproduces information on a medium and / or records information, a first light source that emits a first light beam and a second light source that emits a second light beam are provided separately from each other. An optical path that includes an objective optical element and a second objective optical element, and passes through the first light beam emitted from the first light source before entering the first or second objective optical element; and the second light source. The second light beam emitted from the first or second objective The optical path that passes through before entering the optical element is at least partially in common, and when reproducing information and / or recording information from the first optical information recording medium, the first light flux is used as the first light beam. And one of the second objective optical elements is condensed on the information recording surface via the first protective substrate to reproduce information from the second optical information recording medium and / or When recording is performed, the first light beam is condensed on the information recording surface via the second protective substrate using the other of the first and second objective optical elements, and When reproducing information from and / or recording information from the third optical information recording medium, the third light beam is emitted from one of the first and second objective optical elements. Condensing light onto the information recording surface via a protective substrate The first protective substrate thickness t1 and the second protective substrate thickness t2 are configured as follows:
2.5 <t2 / t1 (1)
Therefore, a more compact optical pickup device can be provided as compared with the case where the optical path of the light beam from the first light source and the path of the light beam from the second light source are configured completely independently. . In particular, the first and second light sources that emit the first light beam and the second light beam, respectively, in the direction perpendicular to the information recording surface of the optical information recording medium, even when trying to realize the maximum compactness when the optical paths are independent. However, in the case of this configuration, such a problem does not occur.

The optical pickup device according to claim 3 is a first optical information recording medium having a first protective substrate thickness t1 and at least a first light flux having a wavelength λ1 and a second light flux having a wavelength λ2 (λ1 ≠ λ2). The second optical information recording medium having a protective substrate thickness t2 (t2 ≠ t1) and the third optical information recording having a third protective substrate thickness t3 are different in recording density from the first and second information recording media. In an optical pickup device for reproducing information on a medium and / or recording information,
A first light source that emits a first luminous flux;
A second light source that emits a second light flux;
A first objective optical element and a second objective optical element provided separately from each other;
When reproducing information from the first optical information recording medium and / or recording information, the first protective substrate is formed by using one of the first and second objective optical elements as the first light flux. By condensing on the information recording surface via
When reproducing information from the second optical information recording medium and / or recording information recording, the second light beam is used as the second light beam by using the other one of the first and second objective optical elements. It is performed by condensing on the information recording surface through a protective substrate,
When reproducing information from and / or recording information from the third optical information recording medium, the third light beam is used as the third light beam by using one of the first and second objective optical elements. Configured to be focused on the information recording surface through a protective substrate,
Either one of the first objective optical element and the second objective optical element has a phase structure on at least one optical surface and is made of plastic,
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1 (1)
In addition to the above-mentioned two types of optical information recording media, information recording and / or reproduction on at least three types of optical information recording media can be performed with high light utilization efficiency, low aberration, and high quality. It is possible to do.

  In other words, the objective optical element used for the first optical information recording medium and the objective optical element used for the second optical information recording medium are separated, so that even when the protective substrate thickness is different, it is optimal. In addition to making it possible to appropriately record and / or reproduce information on both the first and second optical information recording media by designing the objective optical element, for example, the first and second optical information recording media A second optical information recording medium having a recording density different from that of the second optical information recording medium and having the third protective substrate thickness t3 is also emitted from the light source and is longer than the first wavelength λ1. Since information can be recorded and / or reproduced using a light beam with wavelength λ2, information can be recorded and / or reproduced on three types of optical information information recording media. For example, if t1 = 0.085 to 0.1 mm, λ1 = 400 to 420 nm, t2 = 0.6 mm, and λ2 = 640 to 670 nm, it is possible to support not only BD and HD but also DVD, and the specification can be improved. . Alternatively, if t2 = 1.2 mm and λ2 = 780 to 800 nm, it is possible to reproduce and / or record information on CD as well as BD and HD.

The optical pickup device according to claim 4 uses the first light flux of wavelength λ1, the second light flux of λ2 (λ1 ≠ λ2), and the third light flux of λ3 (λ1 ≠ λ3 and λ2 ≠ λ3). The recording density is different from the first optical information recording medium having the protective substrate thickness t1, the second optical information recording medium having the second protective substrate thickness t2 (t2 ≠ t1), and the first and second optical information recording media. , Reproduction of information and / or information of the fourth optical information recording medium having the third protective substrate thickness t3 and the fourth optical information recording medium having the fourth protective substrate thickness t4 (t4 ≠ t1 and t4 ≠ t2). In an optical pickup device that performs recording,
A first light source that emits a first light flux having the wavelength λ1;
A second light source that emits a second light flux having the wavelength λ2.
A third light source that emits a third light flux having the wavelength λ3;
A first objective optical element and a second objective optical element provided separately from each other;
An optical path through which the first light beam emitted from the first light source enters the first or second objective optical element, and a second light beam emitted from the second light source is the first or second objective. At least partly in common with the optical path that passes through before entering the optical element,
When reproducing information from the first optical information recording medium and / or recording information, the first protective substrate is formed using one of the first and second objective elements with the first light flux. Through the condensing on the information recording surface,
When reproducing information from and / or recording information from the second optical information recording medium, a second protective substrate is used by using the first light beam as the other of the first and second objective optical elements. By condensing on the information recording surface via
When reproducing information from the third optical information recording medium and / or recording information, the second light beam is used as the third light beam by using one of the first and second objective optical elements. It is performed by condensing on the information recording surface through a protective substrate,
In the case of reproducing information from the fourth optical information recording medium and / or recording information, the third light beam is used as the fourth light beam by using one of the first and second objective optical elements. Constructed by focusing on the information recording surface through a protective substrate,
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1
Compared with an optical pickup device using three light sources in the case where the optical path of the light beam from the first light source and the path of the light beam from the second light source are configured completely independently, Furthermore, a compact optical pickup device can be provided. In particular, the first and second light sources that emit the first light beam and the second light beam, respectively, in the direction perpendicular to the information recording surface of the optical information recording medium, even when trying to realize the maximum compactness when the optical paths are independent. However, in the case of this configuration, such a problem does not occur.

The optical pickup device according to claim 5 uses the first light flux of at least wavelength λ1, the second light flux of λ2 (λ1 ≠ λ2), and the third light flux of λ3 (λ1 ≠ λ3 and λ2 ≠ λ3). The recording density is different from the first optical information recording medium having the protective substrate thickness t1, the second optical information recording medium having the second protective substrate thickness t2 (t2 ≠ t1), and the first and second optical information recording media. , Reproduction of information and / or information of the fourth optical information recording medium having the third protective substrate thickness t3 and the fourth optical information recording medium having the fourth protective substrate thickness t4 (t4 ≠ t1 and t4 ≠ t2). In an optical pickup device that performs recording,
A first light source that emits a first light flux having the wavelength λ1;
A second light source that emits a second light flux having the wavelength λ2.
A third light source that emits a third light flux having the wavelength λ3;
In the case of having a first objective optical element and a second objective optical element which are provided separately from each other and performing information reproduction and / or information recording from the first optical information recording medium, One light beam is condensed on the information recording surface via the first protective substrate using one of the first and second objective elements,
When reproducing information from and / or recording information from the second optical information recording medium, a second protective substrate is used by using the first light beam as the other of the first and second objective optical elements. By condensing on the information recording surface via
When reproducing information from the third optical information recording medium and / or recording information, the second light beam is used as the third light beam by using one of the first and second objective optical elements. It is performed by condensing on the information recording surface through a protective substrate,
In the case of reproducing information from the fourth optical information recording medium and / or recording information, the third light beam is used as the fourth light beam by using one of the first and second objective optical elements. The first objective optical element and the second objective optical element have a phase structure on at least one optical surface and are made of plastic. Consists of
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1
In addition to the above-mentioned two types of optical information recording media, information recording and / or reproduction on at least three types of optical information recording media can be performed with high light utilization efficiency, low aberration, and high quality. It is possible to do.

  That is, the objective optical element used for the first optical information recording medium and the objective optical element used for the second optical information recording medium are separated from each other. In addition to making it possible to appropriately record and / or reproduce information on both the first and second optical information recording media by performing an optimum objective optical element design, for example, the first optical information recording medium And a third optical information recording medium having a recording density different from that of the second optical information recording medium and having the third protective substrate thickness t3 and a fourth optical information recording medium having the fourth protective substrate thickness t4. Information can be recorded and / or reproduced using a light beam having a second wavelength λ2 and a light beam having a third wavelength λ3 that are emitted from the light source and are longer than the first wavelength λ1. For optical information recording media And thus capable of performing recording and / or reproducing information. For example, when t3 = 0.6 mm, λ2 = 640 to 670 nm, t4 = 1.2 mm, and λ3 = 780 to 800 nm, it is possible to reproduce and / or record not only BD and HD but also CD information. Here, regarding the reproduction of the fourth optical information recording medium, there may be a configuration using a light beam having a wavelength of λ2. Further, by combining the first objective optical element and the second objective optical element so as to correspond to the fourth optical information recording medium in addition to the first to third optical information recording media, four types of optical information recording media can be used. Information can be recorded and / or reproduced in a compatible manner.

  According to a sixth aspect of the present invention, in the optical pickup device according to the fourth or fifth aspect, one of the first and second objective optical elements reproduces information from the first optical information recording medium and / or information. The other is used for reproducing information and / or recording information from the second to fourth optical information recording media, but is not limited to this. There is no.

  An optical pickup device according to a seventh aspect is the invention according to any one of the first to sixth aspects, wherein when reproducing information from the first or second optical information recording medium and / or recording information, Objective optical element driving means for movably arranging the first or second objective optical element in an optical path of the first light beam emitted from the first light source toward the first or second optical information recording medium. Therefore, the optical path of the light beam from the first light source can be switched by the objective optical element driving means.

An optical pickup device according to an eighth aspect of the present invention is the optical pickup apparatus according to the seventh aspect, wherein the objective optical element driving means holds the first and second objective optical elements and their optical axes are on the same circumference. A lens holder that is rotatable with respect to a central axis that is held so as to be positioned at the center of the lens holder, and a driving unit that rotationally drives a support shaft provided on the central axis of the lens holder at an edge of the lens holder,
When reproducing information from the first optical information recording medium and / or recording information, the first objective optical element held by the first rotating operation of the lens holder by the driving means is placed in the optical path. Placed in
When reproducing information from the second optical information recording medium and / or recording information, the second objective optical element held by the second rotating operation of the lens holder by the driving means is placed in the optical path. It is made to arrange in.

An optical pickup device according to a ninth aspect is the invention according to any one of the first to sixth aspects, wherein the information is reproduced from the first and second optical information recording media and / or the information is recorded. The first and second objective optical elements are fixedly arranged, and the incident first light beams arranged in the optical path through which the first light beam emitted from the first light source passes are different from each other. A beam splitter that splits in two directions,
The beam splitter is configured to cause a part of the first light beam emitted from the separated first light source to be incident on the first objective optical element, and to allow a part of the first light beam to be incident on the second objective optical element. Therefore, the optical path can be switched with a simple configuration.

  According to a tenth aspect of the present invention, in the invention according to the ninth aspect, the beam splitter is a polarization beam splitter that separates the incident light beam into two different directions according to a change direction component of the incident light beam. To do.

  According to an eleventh aspect of the present invention, in the invention according to the ninth aspect, the beam splitter is a half mirror that separates the incident light flux into transmitted light and reflected light.

  According to a twelfth aspect of the present invention, in the optical pickup device according to any one of the ninth to eleventh aspects, a λ / 4 wavelength plate is disposed in an optical path between the first light source and the beam splitter. It is characterized by.

  An optical pickup device according to a thirteenth aspect is the invention according to any one of the fourth to twelfth aspects, wherein the first to third light sources are configured as one packaged light source unit. And

  An optical pickup device according to a fourteenth aspect is the invention according to any one of the fourth to twelfth aspects, wherein the second and third light sources are configured as one packaged light source unit. And

An optical pickup device according to a fifteenth aspect is the optical pickup device according to the twelfth or thirteenth aspect, wherein the first and the fourth optical information recording media are reproduced and / or recorded with the first and fourth optical information recording media. Positions where the second objective optical element is fixedly disposed and the first light beam emitted from the first light source and the second and third light beams emitted from the packaged second and third light sources are incident And a wavelength selection element that selectively transmits or reflects the incident first light flux and the second to third light fluxes, and the first to third light fluxes that have passed or reflected through the wavelength selection element. A collimator that is arranged at the incident position and converts the incident light beam into parallel light;
A beam expander that changes a light beam system of at least one of the first to third light beams that has passed through the collimator and a position at which the first to third light beams that have passed through the beam expander are incident together. The ¼ wavelength plate and the first to third light beams are disposed at a position where the first light beam and the third light beam are incident, and a part of the first light beam is transmitted and a part of the first light beam is reflected. Has a half mirror having the property of transmitting or reflecting,
A part of the first light beam transmitted through the half mirror is incident on the first objective optical element, and a part of the reflected first light beam is incident on the second objective optical element while being transmitted through the half mirror or The reflected second and third light beams are configured to be incident on the first objective optical element or the second objective optical element.

  According to a sixteenth aspect of the present invention, in the invention according to any one of the first to fifteenth aspects, at least one of the first and second objective optical elements is made of plastic and has a phase structure. It is the single optical element which has these.

  An optical pickup device according to a seventeenth aspect is the invention according to any one of the first to fifteenth aspects, wherein at least one of the first and second objective optical elements includes a first optical element and a second optical element. And at least one of the first and second optical elements is an optical element having a phase structure made of plastic.

An optical pickup device according to an eighteenth aspect is the invention according to any one of the first to fifteenth aspects, wherein at least one of the first and second objective optical elements includes a first optical element and a second optical element. One of the first and second optical elements is an optical element made of plastic, and the other is an optical element having a phase structure.
An optical pickup device according to a nineteenth aspect is the invention according to the first to fifteenth aspects, wherein one of the first and second objective optical elements is constituted by a glass lens.

The optical pickup device according to claim 20, wherein the first light flux of at least wavelength λ1 (400 nm ≦ λ1 ≦ 420 nm), the second light flux of λ2 (640 nm ≦ λ2 ≦ 670 nm), and the third light flux of λ3 (780 nm ≦ λ3 ≦ 800 nm). Using a light beam, a first optical information recording medium having a first protective substrate thickness t1, a second optical information recording medium having a second protective substrate thickness t2 (t2 ≠ t1), the first and second optical information The recording density is different from the recording medium, and the third optical information recording medium having the third protective substrate thickness t3 and the fourth optical information recording medium having the fourth protective substrate thickness t4 (t4 ≠ t1 and t4 ≠ t2). In an optical pickup device for reproducing information and / or recording information,
A first light source that emits a first light flux having the wavelength λ1;
A second light source that emits a second light flux having the wavelength λ2.
A third light source that emits a third light flux having the wavelength λ3;
A first objective optical element and a second objective optical element provided separately from each other;
In the case of reproducing information from the first optical information recording medium and / or recording information, the first light beam is used as the first objective optical element among the first and second objective elements. By condensing on the information recording surface through the protective substrate of
In the case of reproducing information from the second optical information recording medium and / or recording information, the first luminous flux is used as the second objective optical element out of the first and second objective optical elements. By condensing on the information recording surface through the protective substrate of 2,
In the case of reproducing information from the third optical information recording medium and / or recording information, the second light beam is used as the third light beam by using a second objective optical element among the first and second objective optical elements. By condensing on the information recording surface through the protective substrate of
When reproducing information from the fourth optical information recording medium and / or recording information, the third light beam is used as the fourth light beam by using the second objective optical element among the first and second objective optical elements. By condensing on the information recording surface through the protective substrate of
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1 (1)
While satisfying
The second objective optical element is a part of the first to third light beams, and a first region through which a central light beam portion including an optical axis passes, and an intermediate light beam portion outside the central light beam portion pass through. A second region to
When reproducing information from the second optical information recording medium and / or recording information, the first light flux passing through the first and second areas is placed on the information recording surface of the second optical information recording medium. Focused,
When reproducing information from the third optical information recording medium and / or recording information, the second light flux passing through the first area and the second area is used as the information recording surface of the third optical information recording medium. Focused on the top,
When reproducing information from the fourth optical information recording medium and / or recording information, the third light beam passing through the first area is condensed on the information recording surface of the fourth optical information recording medium. It is characterized by that.

According to the optical pickup device of the present invention, the objective optical element for the first optical information recording medium and the objective optical element for the second optical information recording medium are separated from each other. In addition to making it possible to appropriately record and / or reproduce information on both the first and second optical information recording media by performing an optimum objective optical element design, for example, the first optical information recording medium And a third optical information recording medium having a recording density different from that of the second optical information recording medium and having the third protective substrate thickness t3 and a fourth optical information recording medium having the fourth protective substrate thickness t4. Information can be recorded and / or reproduced using a light beam having a second wavelength λ2 and a light beam having a third wavelength λ3 that are emitted from the light source and are longer than the first wavelength λ1. Optical information recording medium And thus capable of performing recording and / or reproducing information for. In particular, the first objective optical element is used for the first optical information recording medium, and the second objective optical element is used for the three types of optical information recording media of the second to fourth optical information recording media. It is possible to ensure high working quality with high light utilization efficiency and low aberration while ensuring a working distance.

  The optical pickup device according to claim 21 is the optical pickup device according to claim 20, wherein the second objective optical element forms a first diffractive structure in the first region and a second diffractive structure in the second region. The first light beam is incident as convergent light on the second objective optical element, and the third light beam is incident as divergent light.

  According to a twenty-second aspect of the present invention, in the invention according to the twenty-first aspect, the second objective optical element is a tenth-order beam for each of the first to third light beams incident on the first diffractive structure. , Diffracted as sixth-order light and fifth-order light, and diffracted as fifth-order light and third-order light, respectively, with respect to the first and second light beams incident on the second diffractive structure. .

  In an optical pickup device according to a twenty-third aspect, in the invention according to the twenty-first aspect, the second objective optical element is a secondary light for each of the first to third light beams incident on the first diffractive structure. The first and second light beams diffracted as primary light and primary light and incident on the second diffractive structure are diffracted as secondary light and primary light, respectively. .

  An optical pickup device according to a twenty-fourth aspect is the invention according to any one of the twenty-second to twenty-third aspects, wherein at least one of the first and second objective optical elements has a diffractive structure made of a plastic material. It is the single optical element which has.

  An optical pickup device according to a twenty-fifth aspect is the invention according to any one of the twenty-second to twenty-third aspects, wherein at least one of the first and second objective optical elements includes a first optical element and a second optical element. And at least one of the first and second optical elements is an optical element having a diffractive structure made of plastic.

  An optical pickup device according to a twenty-sixth aspect is the invention according to any one of the twentieth to twenty-fifth aspects, wherein one of the first and second objective optical elements is constituted by a glass lens.

  When the objective optical element is made to correspond to three types of optical information recording media or four types of optical information recording media, at least one objective optical element is compatible with two types of optical information recording media or three types of optical information recording media. It is desirable to have sex. In order to provide compatibility at that time, it is desirable that the objective optical element has a phase structure.

  Here, the phase structure formed on the optical surface of the objective optical element has, for example, chromatic aberration caused by a wavelength difference between different wavelengths such as the first wavelength λ1 and the second wavelength λ2, and / or the first optical information recording medium. This is a structure for correcting spherical aberration caused by different thicknesses such as the protective substrate and the protective substrate of the second optical information recording medium. The chromatic aberration here refers to a difference in paraxial image point position caused by a wavelength difference and / or spherical aberration caused by a wavelength difference.

  The phase structure described above may be either a diffractive structure or an optical path difference providing structure. As schematically shown in FIG. 1, the diffractive structure includes a plurality of annular zones 100 and has a sawtooth shape in cross section including the optical axis, or a step 101 as schematically shown in FIG. Are formed of a plurality of annular zones 102 having the same effective diameter, and the cross-sectional shape including the optical axis is a staircase shape, or a staircase structure is formed inside as schematically shown in FIG. 4 or a plurality of annular zones 105 in which the direction of the step 104 is changed in the middle of the effective diameter as shown schematically in FIG. Some are in shape. As shown in FIG. 4, the optical path difference providing structure is composed of a plurality of annular zones 105 in which the direction of the step 104 is changed in the middle of the effective diameter, and the cross-sectional shape including the optical axis is a staircase shape. There is. Therefore, the structure schematically shown in FIG. 4 may be a diffractive structure or an optical path difference providing structure. 1 to 4 schematically show the case where each phase structure is formed on a plane, but each phase structure may be formed on a spherical surface or an aspherical surface.

  Further, in this specification, the “objective optical element” is an optical pickup device that is arranged at a position facing the optical disk, and emits light beams having different wavelengths emitted from a light source, and information on optical disks having different recording densities. An optical system including at least a condensing element having a function of condensing on a recording surface. The objective optical system may be composed of only the condensing element. In such a case, a phase structure is formed on the optical surface of the condensing element.

  Further, when there is an optical element that is integrated with the above-described condensing element and performs tracking and focusing by an actuator, an optical system composed of the optical element and the condensing element is an objective optical element. When the objective optical element is composed of a plurality of optical elements in this way, a phase structure may be formed on the optical surface of the light condensing element. In order to reduce this, it is preferable to form a phase structure on the optical surface of the optical element other than the light condensing element.

Moreover, the above-mentioned condensing element may be a plastic lens or a glass lens. When the condensing element is a plastic lens, it is preferable to use a cyclic olefin-based plastic material. Among the cyclic olefin-based materials, the refractive index N ₄₀₅ at a temperature of 25 ° C. for a wavelength of 405 nm is 1.54 to 1.60. The refractive index change rate dN ₄₀₅ / dT (° C. ⁻¹ ) with respect to the wavelength of 405 nm accompanying the temperature change within the temperature range of −5 ° C. to 70 ° C. is −10 × 10 ^{−5 to} −8 ×. More preferably, plastic materials that are in the range of 10 ⁻⁵ are used.

  Further, when the condensing element is a glass lens, when a glass material having a glass transition point Tg of 400 ° C. or lower is used, molding at a relatively low temperature is possible, so that the life of the mold can be extended. . Examples of such a glass material having a low glass transition point Tg include K-PG325 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.

  By the way, since the specific gravity of the glass lens is generally larger than that of the plastic lens, if the condensing element is made of a glass lens, the weight is increased and a load is imposed on the actuator that drives the objective optical system. Therefore, when the condensing element is a glass lens, it is preferable to use a glass material having a small specific gravity. Specifically, the specific gravity is preferably 3.0 or less, and more preferably 2.8 or less.

Further, as a material for the above-described light collecting element, a material in which particles having a diameter of 30 nm or less are dispersed in a plastic material may be used. By uniformly mixing an inorganic material whose refractive index increases as the temperature rises with a plastic material whose refractive index increases as the temperature rises, it becomes possible to cancel the temperature dependence of both refractive indices. In addition, it is possible to suppress temperature dependency as a lens by homogeneously mixing an inorganic material, for example, silica fine particles, whose refractive index increase accompanying the temperature increase is smaller than that of the plastic material.
Thereby, it is possible to obtain an optical material having a small refractive index change accompanying a temperature change (hereinafter referred to as “athermal resin”) while maintaining the moldability of the plastic material.

  Here, the temperature change of the refractive index of the condensing element will be described. The rate of change of the refractive index with respect to the temperature change is expressed by A in the following formula (Equation 1) by differentiating the refractive index n with the temperature T based on the Lorentz-Lorenz formula.

但し、ｎはレーザ光源の波長に対する前記集光素子の屈折率であり、αは集光素子の線膨張係数であり、［Ｒ］は集光素子の分子屈折力である。

However, n is the refractive index of the said condensing element with respect to the wavelength of a laser light source, (alpha) is a linear expansion coefficient of a condensing element, and [R] is the molecular refractive power of a condensing element.

In the case of a general plastic material, since the contribution of the second term is smaller than that of the first term, the second term can be almost ignored. For example, in the case of acrylic resin (PMMA), the linear expansion coefficient α is 7 × 10 ^{−5, and if} it is substituted into the above equation, A = −12 × 10 ⁻⁵ , which substantially matches the actual measurement value. Here, in the athermal resin, by dispersing in a fine particle plastic material having a diameter of 30 nm or less, the contribution of the second term of the above formula is substantially increased, and the change due to the linear expansion of the first term is canceled out. I am letting. Specifically, it is preferable to suppress the refractive index change rate with respect to the temperature change, which was conventionally about −12 × 10 ⁻⁵ , to an absolute value of less than 10 × 10 ⁻⁵ . More preferably, it is preferably less than 8 × 10 ⁻⁵ , and more preferably less than 6 × 10 ⁻⁵ , in order to reduce the change in spherical aberration accompanying the temperature change of the condensing element.

For example, by dispersing fine particles of niobium oxide (Nb ₂ O ₅ ) in acrylic resin (PMMA), the dependency of the refractive index change on the temperature change can be eliminated. The plastic material used as the base material has a volume ratio of 80 and niobium oxide in a ratio of about 20, and these are uniformly mixed. There is a problem that the fine particles are likely to aggregate, but a technique of applying a charge to the particle surface to disperse the particles is also known, and a necessary dispersion state can be generated.

  This volume ratio can be appropriately increased or decreased in order to control the rate of change in refractive index with respect to temperature change, and a plurality of types of nano-sized inorganic particles can be blended and dispersed.

  The volume ratio is 80:20 in the above example, but can be appropriately adjusted between 90:10 and 60:40. If the volume ratio is smaller than 90:10, the effect of suppressing the change in refractive index is reduced. Conversely, if the volume ratio exceeds 60:40, a problem occurs in the moldability of the athermal resin, which is not preferable.

  The fine particles are preferably inorganic and more preferably oxides. And it is preferable that it is an oxide which the oxidation state is saturated and does not oxidize any more. It is preferable to be an inorganic substance in order to keep the reaction with a plastic material which is a high molecular organic compound low, and because it is an oxide, it deteriorates transmittance and wavefront aberration due to long-term irradiation of a blue-violet laser. Can be prevented. In particular, oxidation is likely to be accelerated under the severe condition of being irradiated with a blue-violet laser at a high temperature. However, with such an inorganic oxide, it is possible to prevent transmittance deterioration and wavefront aberration deterioration due to oxidation. .

  When the diameter of the fine particles dispersed in the plastic material is large, the incident light beam is easily scattered and the transmittance of the condensing element is lowered. In a high-density optical disc, the output of a blue-violet laser used for recording / reproducing information is not sufficiently high. If the transmittance of the condensing element to the blue-violet laser beam is low, the recording speed is increased, and the multilayer disc It is disadvantageous in terms of response. Accordingly, the diameter of the fine particles dispersed in the plastic material is preferably 20 nm or less, and more preferably 10 to 15 nm or less in order to prevent a decrease in the transmittance of the light collecting element.

  According to the present invention, it is possible to provide an optical pickup device capable of appropriately recording and / or reproducing information on, for example, all high-density DVDs and conventional DVDs and CDs.

(First embodiment)
Hereinafter, the present invention will be described in more detail with reference to the drawings. In the present embodiment, the recording densities (ρ1 to ρ4) of the first optical disc to the fourth optical disc are ρ4 <ρ3 <ρ2 <ρ1, and information is recorded on the first optical disc to the 34th disc. The magnification of the objective optical system OBJ1 or OBJ2 at the time of reproduction is set as the first magnification M1 to the fourth magnification M4. However, the combination of wavelength, protective layer thickness, numerical aperture, recording density, and magnification is not limited to this.

  FIG. 5 shows a first embodiment in which information can be recorded / reproduced on all of a high-density optical disc (first optical disc or second optical disc), a conventional DVD (third optical disc), and a CD (fourth optical disc). It is a schematic sectional drawing of the optical pick-up apparatus concerning a form.

  Further, FIG. 6 is a perspective view of an objective lens actuator device used in the optical pickup device of the present embodiment. First, an objective lens actuator device that is an objective optical element driving means will be described. The objective lens actuator device 10 shown in FIG. 6 is arranged in the optical pickup device of FIG. 5, and an objective optical element OBJ1 that condenses laser light from a semiconductor laser, which will be described later, on information recording surfaces of different optical disks. (First objective optical element), OBJ2 (second objective optical element), a lens holder 13 that holds the optical axes of these objective optical elements OBJ1 and OBJ2 on the same circumference 13A, and this lens holder 13 And a lens holder 13 along the support shaft 14. The chassis 15 holds the lens holder 13 along the support shaft 14 so as to be rotatable through a support shaft 14 provided at the position of the center axis of the circumference 13A. And a focusing actuator (not shown) that reciprocates in the selected direction, and the lens holder 13 is urged to rotate to move each of the objective optical elements OBJ1 and OBJ2. And a tracking actuator 20 for Me-decided. The objective lens actuator device 10 is provided with an operation control circuit (not shown) that controls the operation of each actuator.

  The objective optical elements OBJ1 and OBJ2 are respectively provided in holes penetrating the flat plate surface of the disk-shaped lens holder 13, and are disposed at equal distances from the center of the lens holder 13. The lens holder 13 is rotatably engaged with an upper end portion of a support shaft 14 erected from the chassis 15 at the center thereof, and a focusing actuator (not shown) is disposed below the support shaft 14. It is installed.

  In other words, the focusing actuator includes an electromagnetic solenoid composed of a permanent magnet provided at the lower end portion of the support shaft 14 and a coil provided therearound, and by adjusting the current flowing through the coil, the support shaft 14 and the lens. The holder 13 is urged to reciprocate in minute units in the direction along the support shaft 14 (vertical direction in FIG. 6) to adjust the focal length.

  Further, as described above, the lens holder 13 is given a first rotation operation or a second rotation operation around the support shaft 14 having an axis parallel to the optical axis by the tracking actuator 20 which is a driving means. The The tracking actuator 20 includes a pair of tracking coils 21 </ b> A and 21 </ b> B that are symmetrically provided on the edge of the lens holder 13 with the support shaft 14 interposed therebetween, and a support on the chassis 15 that is close to the edge of the lens holder 13. There are two pairs of magnets 22A, 22B, 23A, and 23B provided at symmetrical positions with the shaft 14 in between.

  When the tracking coils 21A and 21B are individually opposed to one pair of magnets 22A and 22B, the magnets 22A and 22B are arranged so that the objective optical element OBJ1 is on the optical path of the laser light reflected by the reflecting mirror 16. The positions of the magnets 23A and 23B are set so that the objective lens OBJ2 is on the optical path of the laser beam when the positions of the magnets 23A and 23B are individually opposed.

  Further, the lens holder 13 described above has a stopper (not shown) that limits the rotation range so that the tracking coil 21A and the magnet 22B or magnet 23B and the tracking coil 21B and the magnet 22A or magnet 23A do not face each other. Is provided.

  Further, the tracking actuator 20 is arranged so that the tangential direction of the outer periphery of the circular lens holder 13 is orthogonal to the tangential direction of the track of the optical disk, and the lens holder 13 is biased to rotate in minute units. This is for correcting the deviation of the irradiation position with respect to the track of the laser beam. Therefore, in order to perform this tracking operation, for example, it is necessary to slightly bias the lens holder 13 while keeping the tracking coils 21A and 21B facing the magnets 22A and 22B.

  In order to perform such tracking operation, each tracking coil 21A, 21B is equipped with an iron piece on the inside thereof, and this iron piece is attracted to each magnet so that a delicate repulsive force is generated between these magnets. In addition, the operation control circuit controls the flow of current through the tracking coils 21A and 21B.

  Next, the optical pickup device main body will be described. In the present embodiment, when information is recorded and / or reproduced on the information recording surfaces of the four types of optical discs OD, the lens holder 13 of the objective lens actuator mechanism 10 is rotated, and the objective as shown in FIG. The optical element OBJ1 or the objective optical element OBJ2 is inserted into the optical path. In the present embodiment, the first semiconductor laser LD1 and the second semiconductor laser LD2 are attached to the same substrate and constitute a single unit called a so-called two-laser one package 2L1P.

[When recording and / or reproducing information with respect to the first optical disc OD1 or the second optical disc OD2]
First, a light beam emitted from a first semiconductor laser LD1 (wavelength λ1 = 400 nm to 420 nm) as a first light source is corrected in beam shape by a beam shaper BS, passes through a dichroic prism DP that is a wavelength selection element, and then collimated. After being converted into a parallel light beam by COL, a polarization beam splitter (a light beam having a first polarization direction component out of an incident light beam is emitted in a certain direction, and a second polarization component different from the first polarization direction component is changed to another beam. It passes through the PBS (which has a characteristic of emitting light in the direction) and enters a beam expander EXP having optical elements L1 and L2. The beam expander EXP in which at least one (preferably the optical element L1) is movable in the optical axis direction has a function of changing (in this case, expanding) the luminous flux diameter of the parallel luminous flux and correcting chromatic aberration and spherical aberration. In particular, a diffractive structure (diffraction ring zone) is formed on the optical surface of the other optical element L2 of the beam expander EXP, whereby chromatic aberration correction is performed on the light beam emitted from the first semiconductor laser LD1. ing. The diffractive structure for correcting chromatic aberration may be provided not only in the optical element L2 but also in another optical element (collimator COL). Note that the chromatic aberration correction function can be achieved not only by the diffraction structure but also by a phase structure, multi-level, and the like.

  By providing the beam expander EXP in this manner, chromatic aberration correction and spherical aberration correction can be performed. Further, for example, in the case of a type in which a high-density DVD has two information recording surfaces, the optical element L1 is provided. The information recording surface can be selected by moving in the optical axis direction. The chromatic aberration correcting optical element and the means for suppressing the spherical aberration may be the objective optical element OBJ1 (OBJ2) provided with a diffractive structure or the like instead of the beam expander EXP.

  In FIG. 5, the light beam that has passed through the beam expander EXP passes through the quarter-wave plate QWP and the aperture stop AP, and the objective optical element OBJ1 or OBJ2 that is an objective optical element having only a refracting surface causes the first optical disc OD1. The information is recorded on the information recording surface via a protective substrate (thickness t1 = 0.085 to 0.1 mm) or via the protective substrate (thickness t2 = 0.55 to 0.65 mm) of the second optical disk OD2. The light is condensed on the recording surface to form a condensing spot.

  The light beam modulated and reflected by the information pits on the information recording surface is again transmitted through the objective optical element OBJ1 or OBJ2, the aperture AP, the quarter wave plate QWP, and the beam expander EXP, and reflected by the polarization beam splitter PBS. Since the astigmatism is given by the cylindrical lens CY1, and passes through the sensor lens SL1 and enters the light receiving surface of the photodetector PD, information is recorded on the first optical disc OD1 or the second optical disc OD2 using the output signal. A read signal of the recorded information is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the focusing actuator (not shown) and the tracking actuator 20 of the objective lens actuator mechanism 10 image the light flux from the first semiconductor laser LD1 on the information recording surface of the first optical disc OD1 or the second optical disc OD2. Thus, the objective optical element OBJ1 or OBJ2 is moved integrally.

[When recording and / or reproducing information on the third optical disc OD3]
In FIG. 5, the light beam emitted from the second semiconductor laser LD2 (wavelength λ2 = 640 nm to 670 nm) as the second light source has its beam shape corrected by the beam shaper BS, passes through the dichroic prism DP, and is parallel by the collimator COL. After being converted into a light beam, the light passes through the polarization beam splitter PBS and enters a beam expander EXP having optical elements L1 and L2.

  The light beam that has passed through the beam expander EXP passes through the quarter-wave plate QWP and the aperture AP, and is protected by the protective substrate (thickness) of the third optical disk OD3 by the objective optical element OBJ1 or OBJ2, which is an objective optical element having only a refractive surface. Through a distance t3 = 0.55 to 0.65 mm), the light is focused on the information recording surface to form a focused spot.

  The light beam modulated and reflected by the information pits on the information recording surface is again transmitted through the objective optical element OBJ1 or OBJ2, the aperture AP, the quarter wave plate QWP, and the beam expander EXP, and reflected by the polarization beam splitter PBS. Astigmatism is given by the cylindrical lens CY1, passes through the sensor lens SL1, and enters the light receiving surface of the photodetector PD. Therefore, the information recorded on the third optical disc OD3 is read using the output signal. A signal is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the objective optical element is formed so that the focusing actuator (not shown) and the tracking actuator 20 of the objective lens actuator mechanism 10 form an image of the light beam from the second semiconductor laser LD2 on the information recording surface of the third optical disk OD3. OBJ1 or OBJ2 is moved together.

[When recording and / or reproducing information on the fourth optical disc OD4]
The light beam emitted from the third semiconductor laser LD3 (wavelength λ3 = 750 nm to 820 nm) as the third light source is reflected by the dichroic prism DP, becomes a parallel light beam with its beam diameter being reduced by the collimator COL, and the polarization beam splitter PBS is It passes through and enters a beam expander EXP having optical elements L1 and L2.

  The light beam that has passed through the beam expander EXP passes through the quarter-wave plate QWP and the aperture AP, and is protected by the objective optical element OBJ1 or OBJ2, which is an objective optical element having only a refracting surface. Is condensed on the information recording surface through a distance t4 = 1.2 mm) to form a condensed spot.

  The light beam modulated and reflected by the information pits on the information recording surface is again transmitted through the objective optical element OBJ1 or OBJ2, the aperture AP, the quarter wave plate QWP, and the beam expander EXP, and reflected by the polarization beam splitter PBS. Astigmatism is given by the cylindrical lens CY1, passes through the sensor lens SL1, and enters the light receiving surface of the photodetector PD. Therefore, the information recorded on the fourth optical disc OD4 is read using the output signal. A signal is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the objective optical element is arranged such that the focusing actuator (not shown) and the tracking actuator 20 of the objective lens actuator mechanism 10 image the light beam from the third semiconductor laser LD3 on the information recording surface of the fourth optical disk OD4. OBJ1 or OBJ2 is moved together.

(Second Embodiment)
FIG. 7 is a schematic configuration diagram of an optical pickup device according to the second embodiment. In the present embodiment, the first semiconductor laser LD1, the second semiconductor laser LD2, and the third semiconductor laser LD3 are attached to the same substrate, and constitute a single unit called a so-called three-laser one package 3L1P.

  The light beams emitted from the first semiconductor laser LD1, the second semiconductor laser LD2, and the third semiconductor laser LD3 are corrected in beam shape by the beam shaper BS, become parallel light beams while reducing the light beam diameter by the collimator COL, and are polarized beams. The light passes through the splitter PBS and enters a beam expander EXP having optical elements L1 and L2.

  The light beam that has passed through the beam expander EXP passes through the quarter-wave plate QWP and the stop AP, and is transmitted through the first to fourth optical discs OD1 to OD1-4 by the objective optical element OBJ1 or OBJ2 that is an objective optical element having only a refractive surface. The light is condensed on the information recording surface via any of the protective substrates to form a light condensing spot.

  The light beam modulated and reflected by the information pits on the information recording surface is again transmitted through the objective optical element OBJ1 or OBJ2, the aperture AP, the quarter-wave plate QWP, and the beam expander EXP, and reflected by the polarization beam splitter PBS. Since the astigmatism is given by the cylindrical lens CY1, it passes through the sensor lens SL1 and is incident on the light receiving surface of the photodetector PD, so that any one of the first to fourth optical discs OD1 to OD4 is used by using the output signal. A read signal of the recorded information is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the focusing actuator (not shown) of the objective lens actuator mechanism 10 and the tracking actuator 20 link the light beam from the third semiconductor laser LD3 onto any one of the information recording surfaces of the first to fourth optical disks OD1 to OD1-4. The objective optical element OBJ1 or OBJ2 is moved integrally so as to form an image.

  In the embodiment described above, one objective optical element is mechanically inserted into the optical path by moving the lens holder 13 holding the two objective optical elements OBJ1 and OBJ2. However, the present invention is not limited to such an embodiment. For example, the position of the objective optical elements OBJ1 and OBJ2 is fixed, and a movable mirror or movable prism is used to change the optical path so that the light beam is directed to one of the objective optical elements according to the optical disk to be used. In addition to a configuration in which an optical path is changed by using a polarization action such as a polarization beam splitter without using it, two optical systems directed from two light sources to two objective optical elements may be provided independently. Here, “fixed” means “moves in the optical axis direction for focusing but does not move in the direction perpendicular to the optical axis”. Further, the objective optical elements OBJ1 and OBJ2 are not necessarily separate from each other. For example, when the objective optical elements OBJ1 and OBJ2 are formed from a plastic resin, an optical element in which the objective optical elements OBJ1 and OBJ2 are arranged in parallel can be integrally formed.

(Third embodiment)
9 and 10 below show examples of the configuration of the pickup device when the position of the objective optical element described above is fixedly arranged. In FIG. 9, the optical path is separated by a half mirror HMR as a beam splitter, and the light beam is guided to the first objective optical element OBJ3 and the second objective optical element OBJ4 which are fixedly arranged so that the optical axes are parallel to each other. 1 shows a configuration for recording and / or reproducing information on each disc.

  In FIG. 9, a semiconductor laser L1 as a first light source for BD or HD is provided, while a semiconductor laser L2 as a second light source for DVD / CD and a semiconductor laser L3 as a third light source are provided in one package. A light source unit 2L1P is provided.

[When recording and / or reproducing information with respect to the first optical disc OD1 or the second optical disc OD2]
First, a light beam emitted from a first semiconductor laser L1 (wavelength λ1 = 400 nm to 420 nm) as a first light source passes through a first polarization beam splitter PBS1 and a dichroic prism DP, and is converted into a parallel light beam by a collimator COL. , And enters a beam expander EXP having a plurality of optical elements.

  The light beam that has passed through the beam expander EXP passes through a quarter-wave plate QWP and a stop AP (not shown), and part of the light beam is transmitted and reflected in part by the half mirror HMR.

  The half mirror HMR here has a configuration in which most of the incident light beam is separated into transmitted light and reflected light with respect to the light beam with wavelength λ1, and most of the incident light beam is transmitted or reflected with respect to the light beams with wavelengths λ2 and λ3 ( FIG. 9 shows the characteristic of reflection).

  When recording or reproducing information with respect to the first optical disc OD1, a part of the light beam transmitted by the half mirror HMR is reflected by the bending mirror MR, and the traveling direction of the light is changed to change the second objective optical element. The light is incident on OBJ4, and a condensed spot is formed on the information recording surface via the protective substrate (thickness t1 = 0.085 to 0.1 mm) of the first optical disc OD1.

  On the other hand, when recording or reproducing information on the second optical disk OD2, a part of the light beam reflected by the half mirror HMR is incident on the first objective optical element OBJ3 to protect the second optical disk OD2. A condensing spot is formed on the information recording surface through a substrate (thickness t2 = 0.55 to 0.65 mm).

  Then, the light beam modulated and reflected by the information pits on the information recording surface is transmitted again through the objective optical element OBJ3 or OBJ4 and the aperture AP, reflected by the half mirror HMR, or reflected by the reflection mirror MR and transmitted through the half mirror HMR. Then, it passes through the quarter-wave plate QWP, the beam expander EXP, the collimator COL, and the dichroic prism DP, is reflected by the first polarization beam splitter PBS1, and is incident on the light receiving surface of the first photodetector PD1. A read signal of information recorded on the first optical disc OD1 or the second optical disc OD2 is obtained using the output signal.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape of the spot and a change in position on the first photodetector PD1. Based on this detection, a focusing actuator and a tracking actuator (not shown) of the objective lens actuator mechanism form an image of the light beam from the first semiconductor laser L1 on the information recording surface of the first optical disk OD1 or the second optical disk OD2. The objective optical element OBJ3 or OBJ4 is moved together.

[When recording and / or reproducing information on the third optical disc OD3]
The light beam emitted from the second semiconductor laser L2 (wavelength λ2 = 640 nm to 670 nm) as the second light source passes through the second polarization beam splitter PBS2, is reflected by the dichroic prism DP, and is collimated by the collimator COL. After that, it enters the beam expander EXP.

  The light beam that has passed through the beam expander EXP passes through the quarter-wave plate QWP, is mostly reflected by the half mirror HMR, is incident on the first objective optical element OBJ3, and is a protective substrate (thickness) of the third optical disk OD3. Through a distance t3 = 0.55 to 0.65 mm), the light is condensed on the information recording surface to form a condensed spot.

  The light beam modulated and reflected by the information pits on the information recording surface is transmitted again through the first objective optical element OBJ3 and the aperture AP, and is reflected by the half mirror HMR, and is reflected by the quarter-wave plate QWP, beam expander EXP, collimator. Since it passes through the COL, is reflected by the dichroic prism DP, is reflected by the second polarization beam splitter PBS2, and is incident on the light receiving surface of the second photodetector PD2, information is output to the third optical disc OD3 using the output signal. A read signal of the recorded information is obtained.

  Further, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the second photodetector PD2. Based on this detection, the first objective optical element so that the focusing actuator and the tracking actuator (not shown) of the objective lens actuator mechanism form an image of the light beam from the second semiconductor laser L2 on the information recording surface of the third optical disk OD3. The OBJ 3 is moved together.

[When recording and / or reproducing information on the fourth optical disc OD4]
The light beam emitted from the third semiconductor laser L3 (wavelength λ3 = 750 nm to 820 nm) as the third light source passes through the second polarization beam splitter PBS2 and is reflected by the dichroic prism DP, and the beam diameter is reduced by the collimator COL. However, it becomes a parallel light beam and enters the beam expander EXP.

  The light beam that has passed through the beam expander EXP passes through the quarter-wave plate QWP and the aperture AP, and is mostly reflected by the half mirror HMR and incident on the first objective optical element OBJ3 to protect the fourth optical disk OD4. The light is condensed on the information recording surface through a substrate (thickness t4 = 1.2 mm) to form a condensed spot.

  The light beam modulated and reflected by the information pits on the information recording surface is again transmitted through the first objective optical element OBJ3, reflected by the half mirror HMR, and transmitted through the quarter-wave plate QWP, the beam expander EXP, and the collimator COL. Then, since it is reflected by the dichroic prism DP, reflected by the second polarization beam splitter PBS2, and incident on the light receiving surface of the second photodetector PD2, information recorded on the fourth optical disc OD4 is recorded using the output signal. Is obtained.

  Further, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the second photodetector PD2. Based on this detection, the first objective optical element so that the focusing actuator and tracking actuator (not shown) of the objective lens actuator mechanism image the light beam from the third semiconductor laser L3 on the information recording surface of the fourth optical disk OD4. The OBJ 3 is moved together.

  The beam expander EXP here is composed of a plurality of optical elements, and at least one optical element is movable in the optical axis direction to change (enlarge in this case) the light beam diameter of the parallel light beam from the collimator COL. It has become. However, the beam expander EXP may have a function of correcting chromatic aberration and spherical aberration as another function. The chromatic aberration here is chromatic aberration (including spherical chromatic aberration) caused by wavelength variation. The spherical aberration is at least one of spherical aberration caused by a difference in thickness of the protective substrate between the disks and spherical aberration caused by temperature variation. Point to one.

  Further, these aberration corrections are not necessarily limited to the configuration in which the beam expander EXP is movable by a plurality of optical elements, and may be performed by forming a plurality of step structures on at least one of the optical surfaces. . The step structure here includes a broader concept than the above-described “phase structure”, and produces a diffractive structure and a phase difference for reducing the aberration by causing a diffractive action on the incident light beam. Phase structure to reduce these aberrations, or both of these structures are configured on different optical surfaces, or they are superimposed on the same optical surface, and have wavelength selectivity Any of the step-like step structures is included in the category. Of course, the beam expander EXP here is composed of a plurality of optical elements, but may be a single optical element.

  Further, such a step structure is not limited to the beam expander EXP but may be provided in another optical element (collimator COL) or the like, and of course, may be provided in the objective optical element OBJ3 (OBJ4).

  By providing the beam expander EXP in this manner, chromatic aberration correction and spherical aberration correction can be performed. Further, for example, in the case of a type in which a high-density DVD has two information recording surfaces, optical on the light source side The information recording surface can be selected by moving the element in the optical axis direction. In this figure, the photodetectors PD1 and PD2 are provided separately, but these photodetectors are configured by one sensor that is used in common for each light flux from the first to third light sources. You may do it. In that case, the illustrated photodetectors PD1 and PD2 can be omitted.

  Further, in this figure, one collimator COL is used for three wavelengths, but this is used for the first optical disk OD1 (for example, BD) and the third and fourth optical disks OD3, OD4 (for example, for DVD / CD). ) May be used.

  In this figure, a half mirror HMR is used to change the traveling direction of the light beam incident on the objective optical elements OBJ3 and OBJ4. This is a preferable configuration for reducing the number of elements of the optical system, but is not necessarily limited thereto.

  In other words, the beam splitter used here may have any configuration that can be changed in a plurality of traveling directions so that the incident light beam can be guided to each objective optical element, and selectively transmits the incident light beam such as a half mirror. However, it is not limited to the one that is reflected, but for example, a polarization beam splitter is configured to separate a first polarization direction component of an incident light beam and a second polarization direction component having a polarization direction component different from the first polarization direction component. Also good. In that case, in the configuration of the optical system as shown in FIG. 9, the first polarization beam splitter PBS1 needs to be a half mirror.

  FIG. 10 omits the half mirror HMR as the beam splitter in FIG. 9, and guides the light beam to the first position for guiding the light beam to the first objective optical element OBJ3 and the light beam to the second objective optical element OBJ4. FIG. 9 shows a configuration for recording and / or reproducing information on each optical disc by moving it to and from the second position. Since the other configurations are the same as those in FIG. 9, detailed description thereof is omitted. .

  In the above embodiment, the first light source (for example, the semiconductor laser L1) and the second light source (for example, the semiconductor lasers L2 and L3) share a part of the optical path of the light flux from each light source. There is no need to stack light sources in the direction of the optical axis, and the degree of freedom in layout is improved.

Next, examples suitable for the above-described embodiment will be described. In the following examples, NA1 = 0.85 to 0.9, NA2 = 0.65 to 0.67, NA3 = 0.60 to 0.67, and NA4 = 0.45. 0.53. Further, HWL is a blazed wavelength of the diffraction grating (for example, a design wavelength of the diffractive structure HOE). In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented by using E (for example, 2.5E-3).

  The optical surface of the objective optical system is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Formula 2.

Here, X (h) is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, A _2i 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 diffractive structure is defined by a mathematical formula in which the coefficient shown in Table 1 is substituted into the optical path difference function of Formula 3.

Ｂ_2iは光路差関数の係数である。

B _2i is a coefficient of the optical path difference function.

(Example A)
In Example A, the first objective optical element is shared by HD (second optical disk) and DVD (third optical disk), and the second objective optical element is BD (first optical disk) and CD (first optical disk). (Fourth optical disc) shared.

Examples 1 to 6 of the first objective optical element in Example A will be described.
(Examples 1-4)
The first objective optical element is composed of a plastic single lens L1, and the light source side surface S1 has a sawtooth diffraction structure as shown in FIG. 1 (hereinafter, this diffraction structure is referred to as “diffractive structure DOE”). ) Is formed, and a diffraction structure DOE having a structure in which a plurality of annular zones formed with an optical axis as a center is formed, and a light beam having a first wavelength λ1 = 405 nm and a second wavelength λ2 are formed by this phase structure. = 655 nm luminous flux has the highest diffraction efficiency in the orders shown in Table 1 below in each example. The optical disk side surface S2 of the single lens L1 is aspheric.

  Next, details of the first objective optical element will be described. The single lens L1 is a plastic lens having a refractive index nd at d-line of 1.5435 and an Abbe number νd of 56.7, a refractive index with respect to λ1 = 405 nm is 1.5601, and a refractive index with respect to λ2 = 655 nm. Is 1.54073. Tables 2 to 5 show lens data of each example.

  The optical surface S1 on the semiconductor laser light source side of the single lens L1 is composed of one region because the NA used for both optical disks is the same NA2, but the wavelength of the light beam used is the first wavelength λ1 and the second wavelength. Therefore, in the NA2 region through which the first light beam from the first semiconductor laser passes and the NA2 region through which the second light beam from the second semiconductor laser passes, the NA2 for the second light beam is different. Since the area becomes larger, the first area AREA1 including the optical axis corresponding to the NA2 area of the first light flux and the second area AREA2 corresponding to the area from the NA2 of the first light flux to the NA2 of the second light flux. They may be divided and provided with different phase structures.

  The diffractive structure DOE ensures compatibility for recording and / or reproducing information to and from the optical disc corresponding to the first light flux having the first wavelength λ1 and the second light flux having the second wavelength λ2. In addition, this structure is also a structure for suppressing the chromatic aberration of the objective optical element in the blue-violet region and the spherical aberration change accompanying the temperature change, which are particularly problematic when the single lens L1 is formed of a plastic lens.

  In the diffractive structure DOE, the height d of the step closest to the optical axis is designed so that the diffraction efficiency of the desired order diffracted light is 100% with respect to the wavelength of 400 nm to 420 nm. When the first light beam is incident on the diffractive structure DOE in which the step depth is set in this way, diffracted light is generated with a diffraction efficiency of 95% or more, and sufficient diffraction efficiency is obtained. Thus, chromatic aberration can be corrected.

  For example, if the height of the step is designed so that the diffraction efficiency of + 2nd order diffracted light is 100% with respect to a wavelength of 400 nm, when the first light beam is incident, + 2nd order diffracted light is generated with a diffraction efficiency of about 97%, It is possible to sort the diffraction efficiency such that when the second light beam is incident, + 1st order diffracted light is generated with a diffraction efficiency of about 94%. For other diffraction order pairs, similar efficiency distribution is possible, and practically sufficient diffraction efficiency can be obtained for each pair. Further, by optimizing with respect to the first wavelength λ1, a configuration in which the diffraction efficiency of the second light flux is emphasized may be adopted.

  Further, as the diffractive structure DOE, in the blue-violet region, when the wavelength of the incident light beam becomes longer, the spherical aberration changes in the direction of insufficient correction, and when the wavelength of the incident light beam becomes shorter, the spherical aberration becomes the overcorrection direction. Objective optical element that is a plastic lens with a high NA by canceling the spherical aberration change that occurs in the condensing element in accordance with the environmental temperature change It is possible to widen the usable temperature range.

  By using the diffractive structure DOE as described above, the magnifications M2 and M3 of the respective light beams can be set to 0 while corresponding to two types of optical disks with one objective optical element. Setting all the imaging magnifications to 0 is very preferable because it solves the coma aberration problem caused by lens shift caused by tracking when recording / reproducing information on the second and third optical disks. It is a configuration. In this embodiment, the optical surface S1 is the diffractive structure DOE, but the diffractive structure DOE may be provided on the optical surface S2.

(Example 5)
The first objective optical element is composed of a plastic single lens L1, and both the light source side surface S1 and the optical disk side surface S2 are aspherical surfaces. Details of the objective optical element will be described. The single lens L1 is a plastic lens having a refractive index nd at d-line of 1.5435 and an Abbe number νd of 56.7, a refractive index with respect to λ1 = 405 nm is 1.5601, and a refractive index with respect to λ2 = 655 nm. Is 1.54073. Table 6 shows lens data of Example 5.

(Example 6)
The first objective optical element is composed of a plastic single lens L1, and the optical surface S1 on the side of the semiconductor laser light source is composed of one area because the NA used for both optical disks is the same NA2. A diffractive structure HOE, which is a structure in which a plurality of annular zones in which step structures as shown in (c) and (d) are formed, is arranged around the optical axis is formed, and the first wavelength is formed by this phase structure. The light beam having λ1 = 405 nm is transmitted without being diffracted as 0th order light, and the light beam having the second wavelength λ2 = 655 nm is diffracted in the + 1st order direction. The optical disk side surface S2 of the single lens L1 is aspheric.

  Next, details of the first objective optical element will be described. The single lens L1 is a plastic lens having a refractive index nd at d-line of 1.5435 and an Abbe number νd of 56.7, a refractive index with respect to λ1 = 405 nm is 1.5601, and a refractive index with respect to λ2 = 655 nm. Is 1.54073. Table 7 shows lens data of Example 6.

  As shown in FIGS. 3C and 3D, the optical surface S1 of the single lens L1 on the side of the semiconductor laser light source is arranged with a plurality of annular zones in which a staircase structure is formed around the optical axis. A diffractive structure HOE, which is a structured structure, is formed.

In the diffraction structure HOE1 formed in the first area AREA1, the depth D of the staircase structure formed in each annular zone is
D · (N1-1) / λ1 = 2 · q (2)
The number of divisions P in each annular zone is set to 5. However, λ1 represents the wavelength of the laser beam emitted from the first emission point EP1 in units of micron (here, λ1 = 0.405 μm), N1 is a medium refractive index with respect to the wavelength λ1, and q is a natural number. It is.

  When the first light flux having the first wavelength λ1 is incident on the step structure in which the depth D in the optical axis direction is set in this way, an optical path difference of 2 × λ1 (μm) is generated between the adjacent step structures. The first light beam is transmitted without being diffracted because no substantial phase difference is given (referred to as “0th-order diffracted light” in this specification).

  On the other hand, when a second light flux having a second wavelength λ2 (here, λ2 = 0.655 μm) is incident on the staircase structure, {2 × λ1 / (N1-1) × ( N2-1) / λ2} × λ2 = {2 × 0.405 / (1.56011-1) × (1.54073-1) /0.655} × λ2 = 1.194 · λ2 (μm) A difference occurs. Since the number of divisions P in each annular zone is set to 5, an optical path difference corresponding to one wavelength of the second wavelength λ2 occurs between adjacent annular zones ((1.194-1) × 5≈ 1) The second light beam is diffracted in the + 1st order direction (+ 1st order diffracted light). The diffraction efficiency of the + 1st order diffracted light of the second light flux at this time is about 87%, but the amount of light is sufficient for recording / reproducing information with respect to the DVD.

  By using the diffractive structure HOE as described above, it is possible to set the magnifications M2 and M3 of the respective light beams to 0 while corresponding to two types of optical disks with one objective optical system. Setting all the imaging magnifications to 0 is very preferable because it solves the coma aberration problem caused by lens shift caused by tracking when recording / reproducing information on the second and third optical disks. It is a configuration. In this embodiment, the optical surface S1 of the single lens L1 on the semiconductor laser light source side is the diffractive structure HOE. However, the diffractive structure HOE may be provided on the optical disc side optical surface S2.

In Example A, Examples 1 and 2 of the second objective optical element that can be used in combination with the first objective optical element described above will be described.
(Example 1)
The second objective optical element is composed of a plastic single lens L1, and its light source side surface S1 corresponds to the first area AREA1 including the optical axis corresponding to the area in NA3 and the area from NA3 to NA1. The first region AREA1 is divided into a plurality of second regions AREA2, and a plurality of sawtooth diffraction structures as shown in FIG. 1 (hereinafter referred to as “diffractive structures DOE”) are formed. A diffractive structure DOE having a structure in which an annular zone is arranged around the optical axis is formed. By this phase structure, a light beam having a first wavelength λ1 = 405 nm is converted into a secondary light, and a third wavelength λ3 = 785 nm. The light beam is diffracted as primary light. The second area AREA2 has an aspherical shape different from the aspherical shape that is the base of the first area AREA1. The optical disk side surface S2 of the single lens L1 is aspheric.

  Next, details of the second objective optical element will be described. The single lens L1 is a plastic lens having a refractive index nd at d-line of 1.5435 and an Abbe number νd of 56.7, a refractive index with respect to λ1 = 405 nm is 1.5601, and a refractive index with respect to λ3 = 785 nm. Is 1.5372. Table 8 shows lens data of Example 1.

  The second area AREA2 of the semiconductor laser light source side optical surface S1 of the single lens L1 does not have a phase structure, but a phase structure different from the first area AREA1 may be provided here.

  The diffractive structure DOE ensures compatibility for recording and / or reproducing information to and from the optical disc corresponding to the light beam having the first wavelength λ1 and the light beam having the third wavelength λ3, and a single lens. A structure for suppressing the chromatic aberration of the objective optical system in the blue-violet region and the change of spherical aberration due to the temperature change, which are particularly problematic when L1 is formed of a plastic lens, can also be used.

  In the diffractive structure DOE, the height d1 of the step closest to the optical axis is designed so that the diffraction efficiency of diffracted light of a desired order is 100% with respect to a wavelength of 400 nm to 420 nm. When the first light beam enters the diffractive structure DOE1 in which the depth of the step is set in this way, diffracted light is generated with a diffraction efficiency of 95% or more, and sufficient diffraction efficiency is obtained. Thus, chromatic aberration can be corrected.

  For example, if the height of the step is designed so that the diffraction efficiency is 100% with respect to a wavelength of 400 nm, when the first light beam is incident, + 2nd order diffracted light is generated with a diffraction efficiency of about 97%, and the second light beam is generated. When incident, it is possible to sort the diffraction efficiency that + 1st order diffracted light is generated with a diffraction efficiency of about 94%. Alternatively, a configuration in which the diffraction efficiency of the first light flux is emphasized by optimizing the first wavelength λ1 may be adopted.

  Further, in the diffractive structure DOE, in the blue-violet region, when the wavelength of the incident light beam becomes longer, the spherical aberration changes in the direction of insufficient correction, and when the wavelength of the incident light beam becomes shorter, the spherical aberration becomes the overcorrection direction. If the spherical aberration has a wavelength dependency that changes to the temperature of the objective optical element, which is a plastic lens with a high NA, by canceling the spherical aberration change that occurs in the single lens with the environmental temperature change, The range can be expanded.

  The width of each annular zone of the diffractive structure DOE provided on the optical surface S1 of the single lens L1 on the semiconductor laser light source side is diffracted with a finite magnification (here, M4 = −0.166) with respect to the third light flux. It is set so that spherical aberration in the direction of insufficient correction is added to the + 1st order diffracted light by the action. The additional amount of spherical aberration due to the diffractive structure DOE and the spherical aberration in the overcorrected direction caused by the difference in thickness between the BD protective substrate and the CD protective substrate cancel each other, so that the diffractive structure DOE and the CD protective substrate The third light flux that has passed through forms a good spot on the information recording surface of the CD. In this embodiment, the optical surface S1 is the diffractive structure DOE. However, the diffractive structure DOE may be provided on the optical surface S2.

(Example 2)
The second objective optical element includes an L1 lens made of plastic and an L2 lens made of glass material. In the L1 lens, a diffractive structure HOE having a structure in which a plurality of annular zones in which step structures as shown in FIGS. 3C and 3D are formed is arranged around the optical axis is formed on the disk side surface S2. With this phase structure, the light beam having the first wavelength λ1 = 405 nm is transmitted as 0th order light without being diffracted, and the light beam having the second wavelength λ3 = 780 nm is diffracted in the + 1st order direction. Although omitted in the present embodiment, an annular structure as shown in FIGS. 2 and 4 may be provided on the light source side surface S1 of the L1 lens. This ring zone structure transmits the light beam having the first wavelength λ1 = 405 nm and the light beam having the second wavelength λ3 = 780 nm without being diffracted in the design standard state, but the wavelength error of the semiconductor laser or the use of the optical pickup device When the wavelength deviates from the design, such as a change in the wavelength of the semiconductor laser due to a temperature rise, the annular structure acts to correct the aberration caused by the wavelength difference or temperature difference. The surface shape serving as the base of the optical surface S1 is a flat plate shape, and the surface shape serving as the base of the optical surface S2 is a concave spherical surface. Here, the base surface may be other than a flat surface or a spherical surface. For example, an aspherical surface is advantageous because it increases the degree of freedom in correcting off-axis aberrations and controlling higher-order aberrations.

  On the other hand, the L2 lens is a double-sided aspherical lens made of glass made of glass mold or the like, and the L2 lens alone has the smallest spherical aberration with respect to the combination of the finite magnification determined by the concave spherical surface of the L1 lens and the BD protective substrate. It is designed to be. When the first magnification M1 with respect to the first light flux and the fourth magnification M4 with respect to the third light flux are set to the same 0 as in the present embodiment, the objective is different depending on the thickness of the protective substrate for the BD and the protective substrate for the CD. The spherical aberration of the third light flux that has passed through the optical element and the CD protective substrate is in an overcorrected direction without the phase structure. In this embodiment, the spherical aberration in the overcorrected direction generated due to the difference in the thickness of the protective substrate for the BD and the protective substrate for the CD by setting the magnification for the third light flux to a finite magnification. To cancel out spherical aberration.

  Next, details of the second objective optical element will be described. The L1 lens is a plastic lens having a refractive index nd of 1.5087 at the d-line and an Abbe number νd of 56.3, a refractive index of 1.52403 for λ1 = 405 nm, and a refractive index of 1 for λ3 = 780 nm. .50261. The L2 lens is a glass mold lens having a refractive index nd of 1.61544 at the d-line and an Abbe number νd of 60.0. Table 9 shows lens data of Example 2.

  When the L1 lens and the L2 lens are integrated, it is common to use a separate lens frame. However, a flange portion formed integrally with the optical function portion is provided around the optical function portion of the L1 lens (the region of the L1 lens through which the first light beam passes), and a part of the flange portion and the L2 lens are connected to each other. It is also possible to have an integrated structure by joining by fusion bonding or adhesion.

  As shown in FIG. 8, the optical surface S2 on the optical disk side of the L1 lens is divided into a first area AREA3 including an optical axis corresponding to the area in NA3, and a second area AREA4 corresponding to the area from NA3 to NA1. In the first area AREA3, as shown in FIGS. 3C and 3D, a plurality of annular zones having a staircase structure formed therein are arranged around the optical axis. A diffraction structure HOE is formed.

In the diffraction structure HOE formed in the third area AREA3, the depth D (μm) of the staircase structure formed in each annular zone is
D · (N1-1) / λ1 = 1 · q (3)
The number of divisions P in each annular zone is set to 2. Here, λ1 represents the wavelength of the laser beam emitted from the light emitting point EP1 in units of micron (here, λ1 = 0.405 μm), N1 is a medium refractive index of the L1 lens with respect to the wavelength λ1, and q is a natural number. It is.

  When the first light flux having the first wavelength λ1 is incident on the staircase structure in which the depth D in the optical axis direction is set in this way, an optical path difference of 1 × λ1 (μm) is generated between the adjacent staircase structures. However, since the first light beam is not substantially given a phase difference, the first light beam is transmitted without being diffracted as zero-order diffracted light.

  On the other hand, when a third light beam having a third wavelength λ3 (here, λ3 = 0.780 μm) is incident on the staircase structure, {1 × λ1 / (N1-1) × ( N3-1) / λ3} × λ3 = {1 × 0.405 / (1.52403-1) × (1.502661-1) /0.780} × λ3 = 0.498 · λ3 (μm) A difference occurs. Since the number P of divisions in each annular zone is set to 2, the third light beam is diffracted in the ± 1st order direction with substantially the same diffraction efficiency (+ 1st order diffracted light and −1st order diffracted light). In this embodiment, information is recorded / reproduced with respect to the CD using the + 1st order diffracted light, and the diffraction efficiency of the + 1st order diffracted light of the second light flux at this time is slightly over 40%. Further, the −1st order diffracted light becomes flare light.

  Here, in order to increase the diffraction efficiency of the + 1st order diffracted light, for example, the inclination of the surface parallel to the staircase-shaped optical axis and the surface not parallel to the optical axis is optimized, or the surface of the surface not parallel to the optical axis is It can be improved by slightly changing the shape from that which is desirable in terms of wavefront aberration. It is also possible to increase the efficiency by changing the medium dispersion of the material constituting the L1 lens and changing the number of divisions P of the staircase shape.

  Further, here, the optical surface S1 on the light source side of the L1 lens has a first area AREA1 including an optical axis corresponding to the area in NA3 and a second area corresponding to the area from NA3 to NA1, as shown in FIG. It may be divided into areas AREA2, and the degree of freedom in design can be increased by adopting a structure in which a plurality of annular zones each having a different phase function are arranged around the optical axis.

  The width of each annular zone of the diffractive structure HOE provided on the optical surface S2 on the optical disc side of the L1 lens adds spherical aberration in the direction of insufficient correction to the + 1st order diffracted light due to diffractive action when the third light beam is incident. Is set to be. The additional amount of spherical aberration due to the diffractive structure HOE and the spherical aberration in the overcorrected direction caused by the difference in thickness between the BD protective substrate and the CD protective substrate cancel each other, so that the diffractive structure HOE and the CD protective substrate The third light flux that has passed through forms a good spot on the information recording surface of the CD.

  By using the diffractive structure HOE as described above, the magnifications M1 and M4 of the respective light beams can be made zero while corresponding to two types of optical disks with one objective optical system. Setting all the imaging magnifications to 0 is very preferable because it solves the coma aberration problem caused by lens shift caused by tracking when recording / reproducing information on the first optical disc and the fourth optical disc. It is a configuration. In this embodiment, the diffractive structure HOE is provided in the L1 lens. However, at least one diffractive structure HOE may be provided in the L2 lens.

  Further, the first area AREA1 and the second area AREA2 of the semiconductor laser light source side optical surface S1 of the L1 lens and the fourth area AREA4 of the optical surface S2 on the optical disk side have a plurality of rings having a sawtooth cross section including the optical axis. A diffraction structure composed of a band (hereinafter, this diffraction structure is referred to as “diffraction structure DOE”) may be formed. The diffractive structure DOE is a structure for suppressing chromatic aberration of the objective optical element.

  In the diffractive structure DOE, the height d1 of the step closest to the optical axis is designed so that the diffraction efficiency of diffracted light of a desired order is 100% with respect to a wavelength of 400 nm to 420 nm. When the first light beam is incident on the diffractive structure DOE in which the step depth is set in this way, diffracted light is generated with a diffraction efficiency of 95% or more, and sufficient diffraction efficiency is obtained. Thus, chromatic aberration can be corrected.

  In the second objective optical element in this embodiment, such a diffractive structure DOE is not provided, but these diffractive structures DOE may be provided on the optical surface of the L2 lens. In this case, the diffractive structure DOE may be a single diffractive structure DOE with the entire optical surface in which the diffractive structure DOE is provided by the L2 lens as one region, or the optical surface in which the diffractive structure DOE is provided by the L2 lens is the optical axis. As the two concentric regions centered on each other, different diffractive structures DOE may be provided in each region. The diffraction efficiencies in the respective regions at this time may be such that the diffraction efficiencies are distributed to the first light flux and the third light flux in the region where the first light flux and the third light flux are transmitted in common. Alternatively, a configuration in which the diffraction efficiency of the first light flux is emphasized by optimizing the first wavelength λ1 may be adopted.

  In the L1 lens of the present embodiment, the diffractive structure HOE is formed on the optical surface S2 on the disk side. On the contrary, the diffractive structure HOE may be formed on the optical surface S1.

(Example B)
In Example B, the first objective optical element is shared by HD (second optical disk) and CD (fourth optical disk), and the second objective optical element is BD (first optical disk) and DVD (first optical disk). (Third optical disc) shared.

Examples 1 to 4 of the first objective optical element in Example B will be described.
(Examples 1-2)
The first objective optical element is composed of a plastic single lens L1, and the light source side surface S1 has a sawtooth diffraction structure as shown in FIG. 1 (hereinafter, this diffraction structure is referred to as “diffractive structure DOE”). ) Is formed, and a diffraction structure DOE having a structure in which a plurality of annular zones formed with an optical axis as a center is formed. By this phase structure, a light beam having a first wavelength λ1 = 405 nm is converted into a secondary light. 3 has a wavelength λ3 = 785 nm and is diffracted as primary light. The optical disk side surface S2 of the single lens L1 is aspheric.

  Next, details of the objective optical element will be described. The single lens L1 is a plastic lens having a refractive index nd at d-line of 1.5435 and an Abbe number νd of 56.7, a refractive index with respect to λ1 = 405 nm is 1.5601, and a refractive index with respect to λ3 = 785 nm. Is 1.5372. Table 10 shows the lens data of Example 1, and Table 11 shows the lens data of Example 2.

  The optical surface S1 on the semiconductor laser light source side of the single lens L1 is composed of one region, but corresponds to the first region AREA1 including the optical axis corresponding to the region in NA3, and the regions from NA3 to NA2. The second region AREA2 may be divided and a different phase structure may be provided for each.

  The diffractive structure DOE ensures compatibility for recording and / or reproducing information to and from the optical disc corresponding to the light beam having the first wavelength λ1 and the light beam having the third wavelength λ3, and a single lens. It is also a structure for suppressing the chromatic aberration of the objective optical system in the blue-violet region and the spherical aberration change accompanying the temperature change, which are particularly problematic when L1 is formed of a plastic lens.

  In the diffractive structure DOE, the height d1 of the step closest to the optical axis is designed so that the diffraction efficiency of diffracted light of a desired order is 100% with respect to a wavelength of 400 nm to 420 nm. When the first light beam enters the diffractive structure DOE1 in which the depth of the step is set in this way, diffracted light is generated with a diffraction efficiency of 95% or more, and sufficient diffraction efficiency is obtained. Thus, chromatic aberration can be corrected.

  For example, if the height of the step is designed so that the diffraction efficiency is 100% with respect to a wavelength of 400 nm, when the first light beam is incident, + 2nd order diffracted light is generated with a diffraction efficiency of about 97%, and the second light beam is generated. When incident, it is possible to sort the diffraction efficiency that + 1st order diffracted light is generated with a diffraction efficiency of about 94%. Alternatively, a configuration in which the diffraction efficiency of the first light flux is emphasized by optimizing the first wavelength λ1 may be adopted.

  Furthermore, in the diffractive structure DOE, in the blue-violet region, when the wavelength of the incident light beam becomes longer, the spherical aberration changes in the direction of insufficient correction, and when the wavelength of the incident light beam becomes shorter, the spherical aberration becomes the overcorrection direction. It has the wavelength dependence of spherical aberration that changes to Accordingly, the usable temperature range of the objective optical element, which is a high NA plastic lens, is expanded by canceling out the spherical aberration change generated in the light condensing element in accordance with the environmental temperature change.

  The width of each annular zone of the diffractive structure DOE provided with the optical surface S1 on the semiconductor laser light source side of the single lens L1 is a spherical surface in the direction of insufficient correction with respect to the + 1st order diffracted light due to the diffractive action when the third light beam is incident. The aberration is set to be added. The additional amount of spherical aberration due to the diffractive structure DOE and the spherical aberration in the overcorrected direction caused by the difference in thickness between the BD protective substrate and the CD protective substrate cancel each other, so that the diffractive structure DOE and the CD protective substrate The third light flux that has passed through forms a good spot on the information recording surface of the CD.

  By using the diffractive structure DOE as described above, it is possible to set the magnifications M2 and M4 of the respective light beams to 0 while corresponding to two types of optical disks with one objective optical system. Setting all the imaging magnifications to 0 is very preferable because it solves the coma aberration problem caused by lens shift caused by tracking when information is recorded / reproduced with respect to the first optical disc and the second optical disc. It is a configuration. In this embodiment, the optical surface S1 is the diffractive structure DOE. However, the diffractive structure DOE may be provided on the optical surface S2.

(Example 3)
The first objective optical element is composed of a plastic single lens L1, and both the light source side surface S1 and the optical disk side surface S2 are aspherical surfaces.

  Next, details of the first objective optical element will be described. The single lens L1 is a plastic lens having a refractive index nd at d-line of 1.5435 and an Abbe number νd of 56.7, a refractive index with respect to λ1 = 405 nm is 1.5601, and a refractive index with respect to λ3 = 785 nm. Is 1.5372. Table 12 shows lens data of Example 3.

  The single lens L1 is designed so that the spherical aberration is minimized with respect to a combination of the lens M1 = 0 and the protective substrate of HD with a single lens. Therefore, as in the present embodiment, when the second magnification M2 for the first light flux and the fourth magnification M4 for the third light flux are the same 0, the difference in thickness between the HD protective substrate and the CD protective substrate As a result, the spherical aberration of the third light beam that has passed through the objective optical element and the CD protective substrate becomes an overcorrected direction. In this embodiment, the spherical aberration in the overcorrected direction generated due to the difference in thickness between the HD protective substrate and the CD protective substrate by setting the spherical aberration overcorrection of the third light flux to a finite magnification. To cancel out spherical aberration.

(Example 4)
The first objective optical element is composed of a plastic single lens L1, and the optical surface S1 on the side of the semiconductor laser light source has a first area AREA1 including an optical axis corresponding to the area in NA3, and NA3 to NA2. The AREA1 is divided into a second area AREA2 corresponding to this area, and a plurality of annular zones in which a staircase structure as shown in FIGS. 3C and 3D is formed are arranged around the optical axis. A diffraction structure HOE is formed, and the light beam having the first wavelength λ1 = 405 nm is transmitted without being diffracted as the 0th order light, and the light beam having the third wavelength λ3 = 785 nm is +1. Diffracted in the following direction. The optical disk side surface S2 of the single lens L1 is aspheric. The second area AREA2 of the optical surface S1 on the semiconductor laser light source side is a flat surface, but another phase structure may be provided here.

  Next, details of the objective optical element will be described. The single lens L1 is a plastic lens having a refractive index nd at d-line of 1.5435 and an Abbe number νd of 56.7, a refractive index with respect to λ1 = 405 nm is 1.5601, and a refractive index with respect to λ3 = 785 nm. Is 1.5372. Table 13 shows lens data of Example 4.

  As shown in FIG. 8, the optical surface S1 of the single lens L1 on the semiconductor laser light source side includes a first area AREA1 including an optical axis corresponding to the area in NA3, and a second area corresponding to areas from NA3 to NA2. The first area AREA1 is divided into a plurality of zones with a staircase structure formed therein as shown in FIGS. 3C and 3D, with the optical axis as the center. A diffractive structure HOE which is an arrayed structure is formed.

In the diffraction structure HOE formed in the third area AREA1, the depth D of the staircase structure formed in each annular zone is
D · (N1-1) / λ1 = 1 · q (4)
The number of divisions P in each annular zone is set to 2. Here, λ1 represents the wavelength of the laser beam emitted from the light emitting point EP1 in units of micron (here, λ1 = 0.405 μm), N1 is a medium refractive index of the L1 lens with respect to the wavelength λ1, and q is a natural number. It is.

  When the first light flux having the first wavelength λ1 is incident on the staircase structure in which the depth D in the optical axis direction is set in this way, an optical path difference of 1 × λ1 (μm) is generated between the adjacent staircase structures. However, since the first light beam is not substantially given a phase difference, the first light beam is transmitted without being diffracted as zero-order diffracted light.

  On the other hand, when a third light beam having a third wavelength λ3 (here, λ3 = 0.785 μm) is incident on the staircase structure, {1 × λ1 / (N1-1) × ( N3-1) / λ3} × λ3 = {1 × 0.405 / (1.5601-1) × (1.53722-1) /0.785} × λ3 = 0.495 · λ3 (μm) A difference occurs. Since the number P of divisions in each annular zone is set to 2, the third light beam is diffracted in the ± 1st order direction with substantially the same diffraction efficiency (+ 1st order diffracted light and −1st order diffracted light). In this embodiment, information is recorded / reproduced with respect to the CD using the + 1st order diffracted light, and the diffraction efficiency of the + 1st order diffracted light of the first light flux at this time is slightly over 40%. Further, the −1st order diffracted light becomes flare light.

  Here, in order to increase the diffraction efficiency of the + 1st order diffracted light, for example, the inclination of the surface parallel to the staircase-shaped optical axis and the surface not parallel to the optical axis is optimized, or the surface of the surface not parallel to the optical axis is It can be improved by slightly changing the shape from that which is desirable in terms of wavefront aberration. It is also possible to increase the efficiency by changing the medium dispersion of the material constituting the L1 lens and changing the number of divisions P of the staircase shape.

Examples 1-2 of the second objective optical element that can be used in combination with the first objective optical element described above in Example B will be described.
Example 1
The second objective optical element is composed of two plastic lenses, and consists of an L1 lens and an L2 lens from the light source side. The L1 lens is provided with a diffractive phase structure on both sides thereof, and a plurality of annular zones having a staircase structure as shown in FIG. 3 are arranged around the optical axis on the light source side surface S1. A diffraction structure HOE which is a structure is formed. By this phase structure, a light beam having the first wavelength λ1 = 405 nm is transmitted without being diffracted as zero-order light, and a light beam having the second wavelength λ2 = 655 nm is transmitted by the + 1st order. Diffracted in the direction. An annular zone structure as shown in FIGS. 2 and 4 is provided on the optical disc side surface S2 of the L1 lens. In the design reference state, this ring zone structure transmits the light beam having the first wavelength λ1 = 405 nm and the light beam having the second wavelength λ2 = 655 nm without being diffracted, but the wavelength error of the semiconductor laser or the use of the optical pickup device When the wavelength or refractive index deviates from the design, such as semiconductor laser wavelength change or lens refractive index change due to temperature rise at the time, the ring zone structure acts to correct the aberration caused by the above wavelength difference or temperature difference. To do. The surface shape serving as the base of these optical surfaces S1 and S2 is an aspherical shape. The L2 lens is a double-sided aspheric lens made of a plastic lens.

  Next, details of the second objective optical element will be described. The L1 lens is a plastic lens having a refractive index nd at d-line of 1.5091 and an Abbe number νd of 56.4, a refractive index of 1.52469 for λ1 = 405 nm, and a refractive index of 1 for λ2 = 655 nm. .50650. L2 is a plastic lens having a refractive index nd of 1.5435 at the d-line and an Abbe number νd of 56.7. Each of the optical function parts (the region of the L1 lens and the L2 lens through which the first light beam passes) has a flange part formed integrally with the optical function part, and part of the flange parts are Are integrated by joining. In the case where the L1 lens and the L2 lens are integrated, they may be integrated via a separate lens frame. Table 14 shows lens data of Example 1.

  As shown in FIG. 8, the optical surface S1 of the L1 lens on the semiconductor laser light source side includes a first area AREA1 including an optical axis corresponding to the area in NA2, and a second area AREA2 corresponding to the area from NA2 to NA1. In the first area AREA1, as shown in FIGS. 3A and 3B, a plurality of annular zones having a staircase structure formed therein are arranged around the optical axis. A diffraction structure HOE1 which is a diffraction structure (hereinafter, this diffraction structure is referred to as “diffraction structure HOE”) is formed.

In the diffraction structure HOE1 formed in the first area AREA1, the depth D1 (μm) of the staircase structure formed in each annular zone is
D1 · (N1-1) / λ1 = 2 · q (5)
The number of divisions P in each annular zone is set to 5. Where λ1 represents the wavelength of the laser beam emitted from the first light emitting point EP1 in units of micron (here, λ1 = 0.405 μm), and N1 is the medium refractive index of the L1 lens with respect to the wavelength λ1. q is a natural number.

  When the first light flux having the first wavelength λ1 is incident on the staircase structure in which the depth D1 in the optical axis direction is set in this way, an optical path difference of 2 × λ1 (μm) is generated between the adjacent staircase structures. The first light beam is transmitted as it is as the 0th-order diffracted light without being diffracted because the phase difference is not substantially given.

  On the other hand, when a second light flux having a second wavelength λ2 (here, λ2 = 0.655 μm) is incident on the staircase structure, {2 × λ1 / (N1-1) × ( N2-1) / λ2} × λ2 = {2 × 0.405 / (1.524669-1) × (1.50650-1) /0.655} × λ2 = 1.194 · λ2 (μm) A difference occurs. Since the number of divisions P in each annular zone is set to 5, an optical path difference corresponding to one wavelength of the second wavelength λ2 occurs between adjacent annular zones ((1.194-1) × 5≈ 1) The second light beam is diffracted in the + 1st order direction (+ 1st order diffracted light). The diffraction efficiency of the + 1st order diffracted light of the second light flux at this time is about 87%, but the amount of light is sufficient for recording / reproducing information with respect to the DVD.

The optical surface S2 on the optical disc side of the L1 lens is an annular structure provided on an aspheric surface composed of one region, and the step D2 (μm) between the annular zones is
D2 · (N1-1) / λ1 = 5 (6)
Is set to When a second light flux having a second wavelength λ2 (here, λ2 = 0.655 μm) is incident on the step, (5 × λ1 / (N1-1) · (N2-1) between adjacent annular zones. ) / Λ2) × λ2 (μm). N2 is the medium refractive index of the L1 lens with respect to the wavelength λ2. Since the ratio of λ2 / (N2-1) and λ1 / (N1-1) is approximately 5: 3 for the second wavelength λ2, there is an optical path difference of approximately 3 × λ2 (μm) between adjacent staircase structures. Similarly to the first light beam, the second light beam is transmitted without being diffracted and transmitted as the 0th-order diffracted light similarly to the first light beam.

  However, when the semiconductor laser of the first wavelength λ1 is changed from the original 0.405 μm to, for example, λ1 ′ = 0.410 μm, the medium refractive index of the L1 lens with respect to 0.410 μm is 1.524. The optical path difference between adjacent annular zones is 5 × 0.405 / (1.52469-1) × (1.524-1) /0.410) × λ1 ′ = 4.933 · λ1 ′ (μm). Become. Aberrations due to wavelength fluctuations are corrected by canceling out aberrations caused by this optical path difference and aberrations occurring in the entire objective optical element system.

  Here, the optical surface S2 on the optical disk side of the L1 lens is, as shown in FIG. 8, a third area AREA3 including an optical axis corresponding to the area in NA2, and a fourth area corresponding to the area from NA2 to NA1. It may be divided into areas AREA4, and the degree of freedom in design can be increased by adopting a structure in which a plurality of annular zones having different phase functions are arranged around the optical axis.

  The second objective optical element is a combination of an L1 lens and an L2 lens having no phase structure, and is designed so that the spherical aberration is minimized with respect to the combination of the first wavelength λ1, the magnification M1 = 0 and the protective substrate of BD. Has been. Therefore, as in the present embodiment, when the first magnification M1 for the first light flux and the second magnification M3 for the second light flux are set to the same 0, the difference in thickness between the protective substrate for BD and the protective substrate for DVD As a result, the spherical aberration of the second light flux that has passed through the objective optical element and the DVD protective substrate becomes overcorrected without a phase structure.

  The width of each annular zone of the diffractive structure HOE1 provided with the optical surface S1 on the semiconductor laser light source side of the L1 lens is such that when the second light beam is incident, spherical aberration in the direction of insufficient correction with respect to the + 1st order diffracted light is caused by the diffractive action It is set to be added. The added amount of spherical aberration due to the diffractive structure HOE1 and the spherical aberration in the overcorrected direction caused by the difference in thickness between the protective substrate of the BD and the protective substrate of the DVD cancel each other, so that the diffractive structure HOE1 and the protective substrate of the DVD The second light flux that has passed through forms a good spot on the information recording surface of the DVD.

  By using the diffractive structure HOE as described above, it is possible to set the magnifications M1 and M3 of the respective light beams to 0 while corresponding to two types of optical disks with one objective optical element. Setting all the imaging magnifications to 0 is very preferable because it solves the coma aberration problem caused by lens shift caused by tracking when recording / reproducing information on the first optical disc and the third optical disc. It is a configuration. In this embodiment, the L1 lens is a diffractive structure HOE, but at least one diffractive structure HOE may be provided on the L2 lens.

  Furthermore, in the second area AREA2 of the optical surface S1 on the semiconductor laser light source side of the L1 lens and the optical surface S2 on the optical disc side, a diffractive structure (hereinafter, referred to as a cross-sectional shape including an optical axis) is composed of a plurality of annular bands having a sawtooth shape. This diffractive structure may be referred to as a “diffractive structure DOE”). The diffractive structure DOE is a structure for suppressing the chromatic aberration of the objective optical system in the blue-violet region and the spherical aberration change accompanying the temperature change, which are particularly problematic when the L2 lens is formed of a plastic lens.

  In the diffractive structure DOE, the height d1 of the step closest to the optical axis is designed so that the diffraction efficiency of diffracted light of a desired order is 100% with respect to a wavelength of 400 nm to 420 nm. When the first light beam enters the diffractive structure DOE1 in which the depth of the step is set in this way, diffracted light is generated with a diffraction efficiency of 95% or more, and sufficient diffraction efficiency is obtained. Thus, chromatic aberration can be corrected.

  In the objective optical element of the present embodiment, such a diffractive structure DOE is not provided, but these diffractive structures DOE may be provided on the optical surface of the L2 lens in addition to the second area AREA2. In this case, the diffractive structure DOE may be a single diffractive structure DOE with the entire optical surface provided with the diffractive structure DOE at L2 as one region, or the optical surface provided with the diffractive structure DOE with the L2 lens as the optical axis. As two concentric circular regions at the center, different diffractive structures DOE may be provided in the respective regions. The diffraction efficiencies in the respective regions at this time may be such that the diffraction efficiencies are distributed to the first light flux and the second light flux in a region where the first light flux and the second light flux are transmitted in common. (For example, if the height of the step is designed so that the diffraction efficiency is 100% with respect to the wavelength of 400 nm [the refractive index of the L lens with respect to the wavelength of 400 nm is 1.5273], when the first light beam is incident, +2 next time It is possible to sort the diffraction efficiency such that when the folded light is generated with a diffraction efficiency of 96.8% and the second light beam is incident, the + 1st order diffracted light is generated with a diffraction efficiency of 93.9%. By optimizing with respect to λ1, a configuration in which the diffraction efficiency of the first light beam is emphasized may be adopted.

  Further, in the diffractive structure DOE, in the blue-violet region, when the wavelength of the incident light beam becomes longer, the spherical aberration changes in the direction of insufficient correction, and when the wavelength of the incident light beam becomes shorter, the spherical aberration becomes the overcorrection direction. It has the wavelength dependence of spherical aberration that changes to Accordingly, the usable temperature range of the objective optical element, which is a high NA plastic lens, is expanded by canceling out the spherical aberration change generated in the light condensing element in accordance with the environmental temperature change.

  In the L1 lens of the present embodiment, the diffractive structure HOE is formed on the optical surface S1 on the semiconductor laser light source side, and the annular zone structure is formed on the optical surface S2 on the optical disc side. An annular zone may be formed on the surface S1, and a diffractive structure HOE may be formed on the optical surface S2.

(Example 2)
The second objective optical element includes an L1 lens made of plastic and an L2 lens made of glass material. The L1 lens is provided with a diffractive phase structure on both sides thereof, and a plurality of annular zones having a staircase structure as shown in FIG. 3 are arranged around the optical axis on the light source side surface S1. A diffraction structure HOE which is a structure is formed. By this phase structure, a light beam having the first wavelength λ1 = 405 nm is transmitted without being diffracted as zero-order light, and a light beam having the second wavelength λ2 = 655 nm is transmitted by the + 1st order. Diffracted in the direction. An annular zone structure as shown in FIGS. 2 and 4 is provided on the optical disc side surface S2 of the L1 lens. In the design reference state, this ring zone structure transmits the light beam having the first wavelength λ1 = 405 nm and the light beam having the second wavelength λ2 = 655 nm without being diffracted, but the wavelength error of the semiconductor laser or the use of the optical pickup device When the wavelength deviates from the design, such as a change in the wavelength of the semiconductor laser due to a temperature rise, the annular structure acts to correct the aberration caused by the wavelength difference or temperature difference. The surface shape serving as the base of these optical surfaces S1 and S2 is a flat plate shape.

  The L2 lens is a glass double-sided aspheric lens made of glass mold or the like, and the objective optical element is a single L2 lens so that the spherical aberration is minimized with respect to the combination of the magnification M1 = 0 and the protective substrate of BD. Designed to. Therefore, as in this embodiment, when the first magnification M1 for the first light flux and the third magnification M3 for the second light flux are set to the same 0, the difference in thickness between the protective substrate for BD and the protective substrate for DVD As a result, the spherical aberration of the second light flux that has passed through the objective optical element and the DVD protective substrate becomes overcorrected without a phase structure.

  Next, details of the second objective optical element will be described. The L1 lens is a plastic lens having a refractive index nd at d-line of 1.5091 and an Abbe number νd of 56.4, a refractive index of 1.52469 for λ1 = 405 nm, and a refractive index of 1 for λ2 = 655 nm. .50650. The L2 lens is a glass lens having a refractive index nd of d line of 1.68893 and an Abbe number νd of 31.1. Table 15 shows lens data of Example 2.

  When the L1 lens and the L2 lens are integrated, it is common to use a separate lens frame. However, a flange portion formed integrally with the optical function portion is provided around the optical function portion of the L1 lens (the region of the L1 lens through which the first light beam passes), and a part of the flange portion and the L2 lens are connected to each other. It is also possible to have an integrated structure by joining by fusion bonding or adhesion.

  As shown in FIG. 8, the optical surface S1 of the L1 lens on the semiconductor laser light source side includes a first area AREA1 including an optical axis corresponding to the area in NA2, and a second area AREA2 corresponding to the area from NA2 to NA1. In the first area AREA1, as shown in FIGS. 3A and 3B, a plurality of annular zones having a staircase structure formed therein are arranged around the optical axis. A diffraction structure HOE1 which is a diffraction structure (hereinafter, this diffraction structure is referred to as “diffraction structure HOE”) is formed.

In the diffraction structure HOE1 formed in the first area AREA1, the depth D1 (μm) of the staircase structure formed in each annular zone is
D1 · (N1-1) / λ1 = 2 · q (6)
The number of divisions P in each annular zone is set to 5. Where λ1 represents the wavelength of the laser beam emitted from the first light emitting point EP1 in units of micron (here, λ1 = 0.405 μm), and N1 is the medium refractive index of the L1 lens with respect to the wavelength λ1. q is a natural number.

  When the first light flux having the first wavelength λ1 is incident on the staircase structure in which the depth D1 in the optical axis direction is set in this way, an optical path difference of 2 × λ1 (μm) is generated between the adjacent staircase structures. However, since the first light beam is not substantially given a phase difference, it is transmitted as it is as the 0th-order diffracted light without being diffracted.

  On the other hand, when a second light flux having a second wavelength λ2 (here, λ2 = 0.655 μm) is incident on the staircase structure, {2 × λ1 / (N1-1) × ( N2-1) / λ2} × λ2 = {2 × 0.405 / (1.524669-1) × (1.50650-1) /0.655} × λ2 = 1.194 · λ2 (μm) A difference occurs. Since the number of divisions P in each annular zone is set to 5, an optical path difference corresponding to one wavelength of the second wavelength λ2 occurs between adjacent annular zones ((1.194-1) × 5≈ 1) The second light beam is diffracted in the + 1st order direction (+ 1st order diffracted light). The diffraction efficiency of the + 1st order diffracted light of the second light flux at this time is about 87%, but the amount of light is sufficient for recording / reproducing information with respect to the DVD.

The optical surface S2 on the optical disc side of the L1 lens is an annular structure provided on an aspheric surface composed of one region, and the step D2 (μm) between the annular zones is
D2 · (N1-1) / λ1 = 5 (7)
Is set to When a second light flux having a second wavelength λ2 (here, λ2 = 0.655 μm) is incident on the step, (5 × λ1 / (N1-1) · (N2-1) between adjacent annular zones. ) / Λ2) × λ2 (μm). N2 is the medium refractive index of the L1 lens with respect to the wavelength λ2. Since the ratio of λ2 / (N2-1) and λ1 / (N1-1) is approximately 5: 3 for the second wavelength λ2, there is an optical path difference of approximately 3 × λ2 (μm) between adjacent staircase structures. Similarly to the first light beam, the second light beam is transmitted without being diffracted and transmitted as the 0th-order diffracted light similarly to the first light beam.

  However, when the semiconductor laser of the first wavelength λ1 is changed from the original 0.405 μm to, for example, λ1 ′ = 0.410 μm, the medium refractive index of the L1 lens with respect to 0.410 μm is 1.524. The optical path difference between adjacent annular zones is 5 × 0.405 / (1.52469-1) × (1.524-1) /0.410) × λ1 ′ = 4.933 · λ1 ′ (μm). Become. Aberrations due to wavelength fluctuations are corrected by canceling out aberrations caused by this optical path difference and aberrations occurring in the entire objective optical element system.

  Here, the optical surface S2 on the optical disk side of the L1 lens is, as shown in FIG. 8, a third area AREA3 including an optical axis corresponding to the area in NA2, and a fourth area corresponding to the area from NA2 to NA1. It may be divided into areas AREA4, and the degree of freedom in design can be increased by adopting a structure in which a plurality of annular zones having different phase functions are arranged around the optical axis.

  The width of each annular zone of the diffractive structure HOE1 provided on the optical surface S1 on the semiconductor laser light source side of the L1 lens is the spherical aberration in the direction of insufficient correction with respect to the + 1st order diffracted light due to the diffractive action when the second light beam is incident. Is set to be added. The added amount of spherical aberration due to the diffractive structure HOE1 and the spherical aberration in the overcorrected direction caused by the difference in thickness between the protective substrate of the BD and the protective substrate of the DVD cancel each other, so that the diffractive structure HOE1 and the protective substrate of the DVD The second light flux that has passed through forms a good spot on the information recording surface of the DVD.

  Thus, by using the diffractive structure HOE, it is possible to set the magnifications M1 and M3 of the respective light beams to 0 while corresponding to two types of optical disks with one objective optical system. Setting all the imaging magnifications to 0 is very preferable because it solves the coma aberration problem caused by lens shift caused by tracking when information is recorded / reproduced with respect to the first optical disc and the second optical disc. It is a configuration. In this embodiment, the L1 lens is a diffractive structure HOE, but at least one diffractive structure HOE may be provided on the L2 lens.

  Further, the second area AREA2 of the semiconductor laser light source side optical surface S1 of the L1 lens and the optical surface S2 of the optical disk side have a diffraction structure (hereinafter referred to as a plurality of annular zones having a sawtooth cross section including the optical axis). This diffractive structure may be referred to as a “diffractive structure DOE”). The diffractive structure DOE is a structure for suppressing chromatic aberration of the objective optical system.

  In the diffractive structure DOE, the height d1 of the step closest to the optical axis is designed so that the diffraction efficiency of diffracted light of a desired order is 100% with respect to a wavelength of 400 nm to 420 nm. When the first light beam enters the diffractive structure DOE1 in which the depth of the step is set in this way, diffracted light is generated with a diffraction efficiency of 95% or more, and sufficient diffraction efficiency is obtained. Thus, chromatic aberration can be corrected.

  In the second objective optical element in this embodiment, such a diffractive structure DOE is not provided, but these diffractive structures DOE may be provided on the optical surface of the L2 lens in addition to the second area AREA2. In this case, the diffractive structure DOE may be a single diffractive structure DOE with the entire optical surface in which the diffractive structure DOE is provided by the L2 lens as one region, or the optical surface in which the diffractive structure DOE is provided by the L2 lens is the optical axis. As the two concentric regions centered on each other, different diffractive structures DOE may be provided in each region. The diffraction efficiencies in the respective regions at this time may be such that the diffraction efficiencies are distributed to the first light flux and the second light flux in a region where the first light flux and the second light flux are transmitted in common. (For example, if the height of the step is designed so that the diffraction efficiency is 100% with respect to the wavelength of 400 nm [the refractive index of the L1 lens with respect to the wavelength of 400 nm is 1.5273], when the first light beam is incident, +2 next time It is possible to sort the diffraction efficiency such that when the folded light is generated with a diffraction efficiency of 96.8% and the second light beam is incident, the + 1st order diffracted light is generated with a diffraction efficiency of 93.9%. By optimizing with respect to λ1, a configuration in which the diffraction efficiency of the first light beam is emphasized may be adopted.

  Furthermore, in the diffractive structure DOE, in the blue-violet region, when the wavelength of the incident light beam becomes longer, the spherical aberration changes in the direction of insufficient correction, and when the wavelength of the incident light beam becomes shorter, the spherical aberration becomes the overcorrection direction. It has the wavelength dependence of spherical aberration that changes to Accordingly, the usable temperature range of the objective optical element, which is a high NA plastic lens, is expanded by canceling out the spherical aberration change generated in the light condensing element in accordance with the environmental temperature change.

  In the L1 lens of the present embodiment, the diffractive structure HOE is formed on the optical surface S1 on the semiconductor laser light source side, and the annular zone structure is formed on the optical surface S2 on the optical disc side. An annular zone may be formed on the surface S1, and a diffractive structure HOE may be formed on the optical surface S2.

(Example C)
In Example C, the first objective optical element is dedicated to BD (first optical disk), and the second objective optical element is HD (second optical disk), DVD (third optical disk), and CD (third optical disk). (Fourth optical disc) shared.

  An example of the first objective optical element in Example C will be described. The first objective optical element is composed of a single lens L1 made of a glass material, and both surfaces of the light source side surface S1 and the optical disk side surface S2 are aspherical surfaces. The refractive index nd at the d-line is 1.6935, the Abbe number νd is 53.2, and the refractive index with respect to λ1 = 405 nm is 1.71157. Table 16 shows lens data of Example 1.

In Embodiment C, Embodiments 1 and 2 of the second objective optical element that can be used in combination with the first objective optical element described above will be described.
(Example 1)

  The second objective optical element is an L1 lens made of plastic.

  The L1 lens has a diffractive structure DOE1 and a diffractive structure DOE2 each having a structure in which a plurality of annular zones in which a stepped structure having a sawtooth cross section as shown in FIG. Is provided. The light source side surface S1 is composed of two regions centered on the optical axis, and in the inner region corresponding to the region of the numerical aperture NA3 when using the CD, the light beam having the first wavelength λ1 = 407 nm by the diffractive structure DOE1 is The light beam diffracted as the 10th-order light and having the second wavelength λ2 = 655 nm is diffracted as the 6th-order light, and the light beam having the third wavelength λ3 = 785 nm is diffracted as the fifth-order light. On the other hand, in the outer region of NA3, the light beam having the first wavelength λ1 = 407 nm is diffracted as fifth-order light by the diffractive structure DOE2 different from the inner region, and the light beam having the second wavelength λ2 = 655 nm is Diffracted as third-order light. Each of the surface shape serving as the base of the light source side surface S1 and the surface shape serving as the base of the optical disc side surface S2 is an aspherical shape including two regions. By providing two regions, off-axis characteristics are improved particularly when a CD is used. The light beam incident on the L1 lens is incident on the light beam having the wavelength λ1 and the light beam on the wavelength λ2 as convergent light, and the light beam having the wavelength λ3 is incident as divergent light. Table 17 shows lens data of Example 1.

  The first area AREA1 and the second area AREA2 of the semiconductor laser light source side optical surface S1 of the L1 lens have a diffractive structure (hereinafter, this diffractive structure is composed of a plurality of annular zones having a sawtooth cross section including the optical axis). A diffractive structure DOE1 and a diffractive structure DOE2 are formed.

The diffractive structure DOE1 and the diffractive structure DOE2 are structures for recording and / or reproducing information using light beams having three different wavelengths, and are particularly problematic when the L1 lens is formed of a plastic lens. This is a structure for suppressing the chromatic aberration of the objective optical system OBJ in the blue-violet region and the spherical aberration change accompanying the temperature change.

  In the diffractive structure DOE1, the height d1 of the step closest to the optical axis is designed so that the diffraction efficiency of a desired order of diffracted light is 100% with respect to a wavelength of 400 nm to 420 nm. When the first light beam enters the diffractive structure DOE1 in which the depth of the step is set in this way, diffracted light is generated with a diffraction efficiency of 95% or more, and sufficient diffraction efficiency is obtained. Thus, chromatic aberration can be corrected.

  In the diffractive structure DOE2, the height d1 of the step closest to the optical axis is, for example, that the diffraction efficiency of diffracted light of a desired order is 100 with respect to a wavelength of 407 nm (the refractive index of the L1 lens with respect to the wavelength of 407 nm is 1.559806). It is designed to be%. When the first light beam enters the diffractive structure DOE1 in which the step depth is set in this way, the + 5th order diffracted light enters the second light beam and the + 3rd order diffracted light has a diffraction efficiency close to 100%. Therefore, sufficient diffraction efficiency can be obtained in any wavelength region, and even when chromatic aberration is corrected in the blue-violet region, chromatic aberration correction in the wavelength region of the second light flux does not become excessive. Here, the diffraction efficiency is distributed to the first light flux and the second light flux. However, by optimizing the first wavelength λ1, the diffraction efficiency of the first light flux may be emphasized.

  In the objective optical element in the present embodiment, such a diffractive structure DOE is not provided on the optical disc side optical surface S2, but these diffractive structures DOE may be provided on the optical surface S2. In this case, the diffractive structure DOE may be a single diffractive structure DOE with the entire optical surface in which the diffractive structure DOE is provided by the L1 lens as one region, and the optical surface in which the diffractive structure DOE is provided by the L1 lens As the two or three concentric regions centered on each other, different diffractive structures DOE may be provided in each region. The diffraction efficiencies in the respective regions at this time may be such that the diffraction efficiencies are distributed to the first light flux and the third light flux in the region where the first light flux and the third light flux are transmitted in common. In the region where the second light flux is transmitted in common, the diffraction efficiency may be assigned to the first light flux and the second light flux. Further, by optimizing with respect to the first wavelength λ1, a configuration in which the diffraction efficiency of the first light flux is emphasized may be adopted.

  Further, in the diffractive structures DOE1 and DOE2, in the blue-violet region, when the wavelength of the incident light beam becomes longer, the spherical aberration changes in the direction of insufficient correction, and when the wavelength of the incident light beam becomes shorter, the spherical aberration is corrected. It has the wavelength dependence of spherical aberration that changes in the excess direction. Accordingly, the usable temperature range of the objective optical element, which is a high NA plastic lens, is expanded by canceling out the spherical aberration change generated in the light condensing element in accordance with the environmental temperature change.

In Example C, Example 2 of the second objective optical element that can be used in combination with the above first objective optical element will be described.
(Example 2)

  The second objective optical element is an L1 lens made of plastic.

  The L1 lens has a diffractive structure DOE1 and a diffractive structure DOE2 each having a structure in which a plurality of annular zones in which a stepped structure having a sawtooth cross section as shown in FIG. Is provided. The light source side surface S1 is composed of two regions centered on the optical axis, and in the inner region corresponding to the region of the numerical aperture NA3 when using the CD, the light beam having the first wavelength λ1 = 407 nm by the diffractive structure DOE1 is The light beam having the second wavelength λ2 = 655 nm is diffracted as the primary light, and the light beam having the third wavelength λ3 = 785 nm is diffracted as the primary light. On the other hand, in the outer region of NA3, the light beam having the first wavelength λ1 = 407 nm is diffracted as secondary light by the same diffraction structure DOE1 as the inner region, and the light beam having the second wavelength λ2 = 655 nm is 1 Diffracted as next light. The surface shape serving as the base of the light source side surface S1 and the surface shape serving as the base of the optical disk side surface S2 are the same aspherical shape in each of the two regions. As for the light beam incident on the L1 lens, the light beam with wavelength λ1 is incident as convergent light, the light beam with wavelength λ2 is incident as parallel light, and the light beam with wavelength λ3 is incident as divergent light. Table 20 shows lens data of Example 2.

  The first area AREA1 and the second area AREA2 of the semiconductor laser light source side optical surface S1 of the L1 lens have a diffractive structure (hereinafter, this diffractive structure is composed of a plurality of annular zones having a sawtooth cross section including the optical axis). A diffractive structure DOE1 which is “diffractive structure DOE”) is formed.

  The diffractive structure DOE1 is a structure for recording and / or reproducing information using light beams of three different wavelengths, and is particularly problematic when the L1 lens is formed of a plastic lens. This is a structure for suppressing the chromatic aberration of the objective optical system OBJ and the spherical aberration change accompanying the temperature change.

  In the diffractive structure DOE1, the height d1 of the step closest to the optical axis is designed so that the diffraction efficiency of the desired order diffracted light is 100% with respect to the wavelength of 400 nm to 420 nm. When the first light beam enters the diffractive structure DOE1 in which the step depth is set as described above, diffracted light is generated with a diffraction efficiency of 95% or more, and when the second light beam is incident, the diffracted light is 90%. When the third light flux is generated with the above diffraction efficiency, the diffracted light is generated with a diffraction efficiency of 95% or more, and sufficient diffraction efficiency can be obtained, and chromatic aberration can be corrected in the blue-violet region.

  In the objective optical element in the present embodiment, such a diffractive structure DOE is not provided on the optical disc side optical surface S2, but these diffractive structures DOE may be provided on the optical surface S2. In this case, the diffractive structure DOE may be provided with two different diffractive structures DOE with the entire optical surface provided with the diffractive structure DOE with the L1 lens as two regions, or the optical surface provided with the diffractive structure DOE with the L1 lens. As a concentric two or three regions centered on the optical axis, different diffractive structures DOE may be provided in each region. The diffraction efficiencies in the respective regions at this time may be such that the diffraction efficiencies are distributed to the first light flux and the third light flux in the region where the first light flux and the third light flux are transmitted in common. In the region where the second light flux is transmitted in common, the diffraction efficiency may be assigned to the first light flux and the second light flux. Further, by optimizing with respect to the first wavelength λ1, a configuration in which the diffraction efficiency of the first light flux is emphasized may be adopted.

  Further, in the diffractive structure DOE1, in the blue-violet region, when the wavelength of the incident light beam becomes longer, the spherical aberration changes in the direction of insufficient correction, and when the wavelength of the incident light beam becomes shorter, the spherical aberration becomes the overcorrection direction. It has the wavelength dependence of spherical aberration that changes to Accordingly, the usable temperature range of the objective optical element, which is a high NA plastic lens, is expanded by canceling out the spherical aberration change generated in the light condensing element in accordance with the environmental temperature change.

(Example D)
In Example D, the first objective optical element is dedicated to HD (second optical disk), and the second objective optical element is BD (first optical disk), DVD (third optical disk), and CD (third optical disk). (Fourth optical disc) shared.

Example 1 of the first objective optical element in Example D will be described.
(Example 1)
The first objective optical element is composed of a single lens L1 made of plastic material, and both surfaces of the light source side surface S1 and the optical disk side surface S2 are aspherical surfaces. The refractive index for λ1 = 407 nm is 1.543. Table 18 shows lens data of Example 1.

In Example D, Example 1 of the second objective optical element that can be used in combination with the first objective optical element described above will be described.
(Example 1)
The second objective optical element includes an L1 lens made of plastic and an L2 lens made of glass material.

  The L1 lens is provided with a diffractive phase structure on both sides thereof, and step structures as shown in FIGS. 3A to 3D are formed on both sides of the light source side surface S1 and the optical disk side surface S2. A diffractive structure HOE having a structure in which a plurality of annular zones are arranged around the optical axis is formed. By this phase structure, a light beam having the first wavelength λ1 = 408 nm is transmitted without being diffracted as zero-order light, The light beam having the second wavelength λ2 = 658 nm and the third wavelength λ3 = 785 nm is diffracted in the + 1st order direction. The surface shape serving as the base of the light source side surface S1 is an aspherical surface, and the surface shape serving as the base of the optical disk side surface S2 is a flat plate shape.

  The L2 lens is a glass double-sided aspheric lens made of glass mold or the like, and the objective optical element is a single L2 lens so that the spherical aberration is minimized with respect to the combination of the magnification M1 = 0 and the protective substrate of BD. Designed. Therefore, when the second magnification M2 with respect to the first light flux, the third magnification M3 with respect to the second light flux, and the fourth magnification M4 with respect to the third light flux are set to the same 0 as in the present embodiment, the protective substrate of the BD and the DVD The second optical flux transmitted through the objective optical element and the DVD protective substrate, the objective optical element and the CD protective substrate, and the difference between the thickness of the protective substrate of the optical disc and the thickness of the protective substrate of the BD and the protective substrate of the CD. The spherical aberration of the third light beam becomes overcorrected without the phase structure.

  Next, details of the second objective optical element will be described. The L1 lens is a plastic lens having a refractive index nd at the d-line of 1.5091 and an Abbe number νd of 56.4, a refractive index of 1.52424 for λ1 = 408 nm, and a refractive index of 1 for λ2 = 658 nm. The refractive index for .50642 and λ3 = 785 nm is 1.50324. The L2 lens is a glass lens having a refractive index nd of 1.6935 at the d-line and an Abbe number νd of 53.2. When the L1 lens and the L2 lens are integrated, it is common to use a separate lens frame. However, a flange portion formed integrally with the optical function portion is provided around the optical function portion of the L1 lens (the region of the L1 lens through which the first light beam passes), and a part of the flange portion and the L2 lens are connected to each other. It is also possible to have an integrated structure by joining by fusion bonding or adhesion. Table 19 shows lens data of Example 1.

  As shown in FIG. 8, the optical surface S1 of the L1 lens on the semiconductor laser light source side includes a first area AREA1 including an optical axis corresponding to the area in NA2, and a second area AREA2 corresponding to the area from NA2 to NA1. In the first area AREA1, as shown in FIGS. 3A and 3B, a plurality of annular zones having a staircase structure formed therein are arranged around the optical axis. A diffraction structure HOE1 which is a diffraction structure (hereinafter, this diffraction structure is referred to as “diffraction structure HOE”) is formed.

In the diffraction structure HOE1 formed in the first area AREA1, the depth D of the staircase structure formed in each annular zone is
D · (N1-1) / λ1 = 2 · q (10)
The number of divisions P in each annular zone is set to 5. However, λ1 represents the wavelength of the laser beam emitted from the first emission point EP1 in units of micron (here, λ1 = 0.408 μm), and N1 is the medium refractive index of the L1 lens with respect to the wavelength λ1, q is a natural number.

  When the first light flux having the first wavelength λ1 is incident on the step structure in which the depth D in the optical axis direction is set in this way, an optical path difference of 2 × λ1 (μm) is generated between the adjacent step structures. The first light beam is transmitted as it is as the 0th-order diffracted light without being diffracted because the phase difference is not substantially given.

  In addition, when a third light flux having a third wavelength λ3 (here, λ3 = 0.785 μm) is incident on the staircase structure, (2 × λ1 / (N1-1) · ( An optical path difference of (N3-1) / λ3) × λ3 (μm) occurs. N3 is the medium refractive index of the L1 lens with respect to the wavelength λ3. Since (N3-1) / λ3 is approximately twice (N1-1) / λ1 in the third wavelength λ3, an optical path difference of approximately 1 × λ3 (μm) occurs between adjacent staircase structures. Similarly to the first light beam, the light beam is not diffracted and is transmitted as zero-order diffracted light because no phase difference is substantially given.

  On the other hand, when a second light flux having a second wavelength λ2 (here, λ2 = 0.658 μm) is incident on the staircase structure, {2 × λ1 / (N1-1) × ( N2-1) / λ2} × λ2 = {2 × 0.408 / (1.52422-1) × (1.5064-1) /0.658} × λ2 = 1.199 · λ2 (μm) A difference occurs. Since the number of divisions P in each annular zone is set to 5, an optical path difference corresponding to one wavelength of the second wavelength λ2 occurs between adjacent annular zones ((1.199-1) × 5≈ 1) The second light beam is diffracted in the + 1st order direction (+ 1st order diffracted light). At this time, the diffraction efficiency of the + 1st order diffracted light of the second light flux is 87.5%, but the amount of light is sufficient for recording / reproducing information with respect to the DVD.

  As shown in FIG. 8, the optical surface S2 on the optical disk side of the L1 lens has a third area AREA3 including the optical axis corresponding to the area in NA3, and a fourth area AREA4 corresponding to the area from NA3 to NA1. In the third area AREA3, as shown in FIGS. 3C and 3D, a plurality of annular zones having a staircase structure formed therein are arranged around the optical axis. A diffraction structure HOE2 is formed.

In the diffraction structure HOE2 formed in the third region AREA3, the depth D of the staircase structure formed in each annular zone is
D · (N1-1) / λ1 = 5 · q (11)
The number of divisions P in each annular zone is set to 2. However, λ1 represents the wavelength of the laser beam emitted from the third light emitting point EP1 in units of micron (here, λ1 = 0.408 μm), N1 is the medium refractive index of the L1 lens with respect to the wavelength λ1, q is a natural number.

  When the first light flux having the first wavelength λ1 is incident on the staircase structure in which the depth D in the optical axis direction is set in this way, an optical path difference of 5 × λ1 (μm) is generated between the adjacent staircase structures. However, since the first light beam is not substantially given a phase difference, the first light beam is transmitted without being diffracted as zero-order diffracted light.

  In addition, when a second light beam having the second wavelength λ2 (here, λ2 = 0.658 μm) is incident on the staircase structure, (5 × λ1 / (N1-1) · ( An optical path difference of (N2-1) / λ2) × λ2 (μm) occurs. N2 is the medium refractive index of the L1 lens with respect to the wavelength λ2. Since the ratio of λ2 / (N2-1) and λ1 / (N1-1) is approximately 5: 3 for the second wavelength λ2, there is an optical path difference of approximately 3 × λ2 (μm) between adjacent staircase structures. Similarly to the first light beam, the second light beam is transmitted without being diffracted and transmitted as the 0th-order diffracted light similarly to the first light beam.

  On the other hand, when a third light beam having a third wavelength λ3 (here, λ3 = 0.785 μm) is incident on the staircase structure, {5 × λ1 / (N1-1) × ( N3-1) / λ3} × λ3 = {5 × 0.408 / (1.52422-1) × (1.5050-1) /0.785} × λ3 = 2.5 · λ3 (μm) A difference occurs. Since the number P of divisions in each annular zone is set to 2, the third light beam is diffracted in the ± 1st order direction with substantially the same diffraction efficiency (+ 1st order diffracted light and −1st order diffracted light). In this embodiment, information is recorded / reproduced with respect to the CD using the + 1st order diffracted light, and the diffraction efficiency of the + 1st order diffracted light of the second light flux at this time is slightly over 40%. Further, the −1st order diffracted light becomes flare light.

  Here, in order to increase the diffraction efficiency of the + 1st order diffracted light, for example, the inclination of the surface parallel to the staircase-shaped optical axis and the surface not parallel to the optical axis is optimized, or the surface of the surface not parallel to the optical axis is It can be improved by slightly changing the shape from that which is desirable in terms of wavefront aberration. It is also possible to increase the efficiency by changing the medium dispersion of the material constituting the L1 lens and changing the number of divisions P of the staircase shape.

  The L2 lens is designed so that the spherical aberration is minimized with respect to a combination of the first wavelength λ1, a certain finite magnification, and the protective substrate of the BD. Therefore, when the first magnification M1 with respect to the first light beam, the third magnification M3 with respect to the second light beam, and the fourth magnification M4 with respect to the third light beam are set to the same 0 as in the present embodiment, the protective substrate of the BD And the spherical aberration of the second light flux transmitted through the L2 lens and the DVD protective substrate due to the difference in thickness of the DVD protective substrate and the CD protective substrate, and the third transmitted through the L2 lens and the CD protective substrate. The spherical aberration of the light beam will be overcorrected.

  The width of each annular zone of the diffractive structure HOE1 provided on the optical surface S1 on the semiconductor laser light source side of the L1 lens and the diffractive structure HOE2 provided on the optical surface S2 on the optical disk side of the L1 lens is respectively the second luminous flux and the second luminous flux. It is set so that spherical aberration in the direction of insufficient correction is added to the + 1st order diffracted light by the diffraction action when three light beams are incident. The amount of spherical aberration added by the diffractive structures HOE1 and HOE2 and the spherical aberration in the overcorrected direction caused by the difference in thickness between the BD protective substrate, the DVD protective substrate, and the CD protective substrate cancel each other. The second light beam transmitted through the diffractive structure HOE1 and the DVD protective substrate forms a good spot on the information recording surface of the DVD, and the third light beam transmitted through the diffractive structure HOE2 and the CD protective substrate is used to record the information on the CD. Forms a good spot on the surface.

  By using two diffractive structures HOE in this way, the magnifications M1, M3, and M4 of the respective light beams can be reduced to zero while corresponding to three types of optical disks with one objective optical system. By setting all the imaging magnifications to 0, the problem of coma aberration caused by lens shift due to tracking when recording / reproducing information on all optical discs from the first optical disc to the third optical disc is solved. Therefore, this is a very preferable configuration.

  In this embodiment, both surfaces of the L1 lens have the diffractive structure HOE. However, at least one diffractive structure HOE may be provided on the L2 lens. If two diffractive structures HOE are used, the same effect as the above double-sided diffractive structure HOE is obtained. Can be obtained.

  Further, in the second area AREA2 of the semiconductor laser light source side optical surface S1 of the L1 lens or the fourth area AREA4 of the optical surface S2 of the optical disc, a cross-sectional shape including the optical axis is composed of a plurality of annular zones having a sawtooth shape. A diffractive structure DOE1 and a diffractive structure DOE2 that are diffractive structures (hereinafter, this diffractive structure is referred to as “diffractive structure DOE”) may be formed.

  The diffractive structure DOE1 is a diffractive structure DOE2 for suppressing the chromatic aberration of the objective optical system OBJ in the blue-violet region and the change of spherical aberration due to the temperature change, which are particularly problematic when the L2 lens is formed of a plastic lens, for example. This is a structure for suppressing the chromatic aberration of the objective optical system OBJ in both the blue-purple and red colors, and the spherical aberration change due to the temperature change, which are particularly problematic when the L2 lens is formed of a plastic lens.

  In the diffractive structure DOE1, the height d1 of the step closest to the optical axis is designed so that the diffraction efficiency of a desired order of diffracted light is 100% with respect to a wavelength of 400 nm to 420 nm. When the first light beam enters the diffractive structure DOE1 in which the depth of the step is set in this way, diffracted light is generated with a diffraction efficiency of 95% or more, and sufficient diffraction efficiency is obtained. Thus, chromatic aberration can be corrected.

  In the diffractive structure DOE2, the height d1 of the step closest to the optical axis is, for example, that the diffraction efficiency of diffracted light of a desired order is 100 with respect to a wavelength of 400 nm (the refractive index of the L1 lens with respect to the wavelength of 400 nm is 1.5273). It is designed to be%. When the first light beam enters the diffractive structure DOE1 in which the step depth is set as described above, + 2nd order diffracted light is generated with a diffraction efficiency of 96.8%, and when the second light beam enters, the + 1st order diffracted light is generated. Occurs at a diffraction efficiency of 93.9%, so that sufficient diffraction efficiency is obtained in any wavelength region, and even when chromatic aberration is corrected in the blue-violet region, chromatic aberration correction in the wavelength region of the second light flux is excessive. Not too much. Here, the diffraction efficiency is distributed to the first light flux and the second light flux. However, by optimizing the first wavelength λ1, the diffraction efficiency of the first light flux may be emphasized.

  In the objective optical element in this embodiment, such a diffractive structure DOE is not provided, but these diffractive structures DOE may be provided on the optical surface of the L2 lens in addition to the second area AREA2 and the fourth area AREA4. In this case, the diffractive structure DOE may be a single diffractive structure DOE with the entire optical surface in which the diffractive structure DOE is provided by the L2 lens as one region, or the optical surface in which the diffractive structure DOE is provided by the L2 lens As two or three concentric regions centering on the axis, different diffractive structures DOE may be provided in each region. The diffraction efficiencies in the respective regions at this time may be set such that the diffraction efficiencies are distributed to the first light flux and the third light flux in the region where the first light flux and the third light flux are transmitted in common (for example, the height of the step). Is designed so that the diffraction efficiency is 100% with respect to the wavelength of 400 nm (the refractive index of the L1 lens with respect to the wavelength of 400 nm is 1.5273), the second-order diffracted light becomes 96. When the second light beam is incident at a diffraction efficiency of 8%, the + 1st order diffracted light is generated at a diffraction efficiency of 93.9%, and when the third light beam is incident, the + 1st order diffracted light is at a diffraction efficiency of 99.2%. It is possible to distribute the diffraction efficiency to the first light beam and the second light beam in a region where the first light beam and the second light beam are transmitted in common. Further, by optimizing with respect to the first wavelength λ1, a configuration in which the diffraction efficiency of the first light flux is emphasized may be adopted.

  Furthermore, in the diffractive structures DOE1 and DOE2, in the blue-violet region, when the wavelength of the incident light beam becomes longer, the spherical aberration changes in the direction of insufficient correction, and when the wavelength of the incident light beam becomes shorter, the spherical aberration is corrected. It has the wavelength dependence of spherical aberration that changes in the excess direction. Accordingly, the usable temperature range of the objective optical element, which is a high NA plastic lens, is expanded by canceling out the spherical aberration change generated in the light condensing element in accordance with the environmental temperature change.

  In the L1 lens of the present embodiment, the diffractive structure HOE is formed on the optical surface S1 on the semiconductor laser light source side, and the diffractive structure DOE is formed on the optical surface S2 on the optical disk side. The diffraction structure DOE may be formed on the surface S1, and the diffraction structure HOE may be formed on the optical surface S2.

It is a figure which shows the example of a diffraction structure. It is a figure which shows the example of a diffraction structure. It is a figure which shows the example of a diffraction structure. It is a figure which shows the example of a phase difference provision structure. It is a figure which shows schematically the structure of optical pick-up apparatus PU1 concerning 1st Embodiment. It is a perspective view of the objective lens actuator apparatus used for the optical pick-up apparatus of this Embodiment. It is a figure which shows schematically the structure of optical pick-up apparatus PU2 concerning 2nd Embodiment. It is the front view (a) of an objective optical element, a side view (b), and a rear view (c). It is a figure which shows the structural example of the optical pick-up apparatus which divides | segments an optical path with a half mirror and guides an optical path to an objective optical element. It is a figure which shows the structural example of the optical pick-up apparatus which separates an optical path by moving a mirror, and guides an optical path to an objective optical element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Objective lens actuator mechanism 20 Tracking actuator AP Aperture BS Beam shaper COL Collimator CY1 Cylindrical lens DOE Diffraction structure DP Dichroic prism EXP Beam expander HOE Diffraction structure L1, L2 Optical element (lens)
LD1 Semiconductor laser LD2 Semiconductor laser LD3 Semiconductor lasers OBJ1 and OBJ2 Objective optical elements OD1 to 4 Optical disc PBS Polarizing beam splitter PD Photodetector PU1 Optical pickup device PU2 Optical pickup device QWP 1/4 wavelength plate SL1 Sensor lens

Claims (26)

Reproduction of information from the first optical information recording medium having the first protective substrate thickness t1 and the second optical information recording medium having the second protective substrate thickness t2 (t2 ≠ t1) using the light flux having the wavelength λ1 and In an optical pickup device that only records information
A first light source that emits a first light flux of wavelength λ1,
A first objective optical element and a second objective optical element provided separately from each other;
When reproducing information from the first optical information recording medium and / or recording information, a first protective substrate is formed by using one of the first and second objective optical elements as the first light flux. By condensing on the information recording surface via
When reproducing information from the second optical information recording medium and / or recording information, a second protective substrate is used by using the first luminous flux as the other of the first and second objective optical elements. Configured to be focused on the information recording surface via
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1 (1)
An optical pickup device satisfying the requirements. A first optical information recording medium having a first protective substrate thickness t1 and a second protective substrate thickness t2 (t2 ≠ t1) using at least a first luminous flux having a wavelength λ1 and a second luminous flux having a wavelength λ2 (λ1 ≠ λ2). Information recording and information recording of a third optical information recording medium having a third protective substrate thickness t3, which has a recording density different from that of the second optical information recording medium having the above and the first and second information recording media In an optical pickup device that performs
A first light source that emits a first luminous flux;
A second light source that emits a second light flux;
A first objective optical element and a second objective optical element provided separately from each other;
An optical path through which the first light beam emitted from the first light source enters the first or second objective optical element, and a second light beam emitted from the second light source is the first or second objective. At least partly in common with the optical path that passes through before entering the optical element,
When reproducing information from the first optical information recording medium and / or recording information, the first protective substrate is formed by using one of the first and second objective optical elements as the first light flux. By condensing on the information recording surface via
When reproducing information from the second optical information recording medium and / or recording information recording, the second light beam is used as the second light beam by using the other one of the first and second objective optical elements. It is performed by condensing on the information recording surface through a protective substrate,
When reproducing information from and / or recording information from the third optical information recording medium, the third light beam is used as the third light beam by using one of the first and second objective optical elements. Configured to be focused on the information recording surface through a protective substrate,
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1 (1)
An optical pickup device satisfying the requirements. A first optical information recording medium having a first protective substrate thickness t1 and a second protective substrate thickness t2 (t2 ≠ t1) using at least a first luminous flux having a wavelength λ1 and a second luminous flux having a wavelength λ2 (λ1 ≠ λ2). Information recording and information recording of a third optical information recording medium having a third protective substrate thickness t3, which has a recording density different from that of the second optical information recording medium having the above and the first and second information recording media In an optical pickup device that performs
A first light source that emits a first luminous flux;
A second light source that emits a second light flux;
A first objective optical element and a second objective optical element provided separately from each other;
When reproducing information from the first optical information recording medium and / or recording information, the first protective substrate is formed by using one of the first and second objective optical elements as the first light flux. By condensing on the information recording surface via
When reproducing information from the second optical information recording medium and / or recording information recording, the second light beam is used as the second light beam by using the other one of the first and second objective optical elements. It is performed by condensing on the information recording surface through a protective substrate,
When reproducing information from and / or recording information from the third optical information recording medium, the third light beam is used as the third light beam by using one of the first and second objective optical elements. Configured to be focused on the information recording surface through a protective substrate,
Either one of the first objective optical element and the second objective optical element has a phase structure on at least one optical surface and is made of plastic,
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1 (1)
An optical pickup device satisfying the requirements. First optical information recording having a first protective substrate thickness t1 using at least a first light flux of wavelength λ1, a second light flux of λ2 (λ1 ≠ λ2), and a third light flux of λ3 (λ1 ≠ λ3 and λ2 ≠ λ3). The recording density is different from that of the medium, the second optical information recording medium having the second protective substrate thickness t2 (t2 ≠ t1), and the first and second optical information recording media, and the second optical information recording medium having the third protective substrate thickness t3. In an optical pickup device for reproducing information and / or recording information on a third optical information recording medium and a fourth optical information recording medium having a fourth protective substrate thickness t4 (t4 ≠ t1 and t4 ≠ t2),
A first light source that emits a first light flux having the wavelength λ1;
A second light source that emits a second light flux having the wavelength λ2.
A third light source that emits a third light flux having the wavelength λ3;
A first objective optical element and a second objective optical element provided separately from each other;
An optical path through which the first light beam emitted from the first light source enters the first or second objective optical element, and a second light beam emitted from the second light source is the first or second objective. At least partly in common with the optical path that passes through before entering the optical element,
When reproducing information from the first optical information recording medium and / or recording information, the first protective substrate is formed using one of the first and second objective elements with the first light flux. Through the condensing on the information recording surface,
When reproducing information from the second optical information recording medium and / or recording information, a second protective substrate is used by using the first luminous flux as the other of the first and second objective optical elements. By condensing on the information recording surface via
When reproducing information and / or recording information from the third optical information recording medium, the second light beam is used as the third light beam by using one of the first and second objective optical elements. By condensing on the information recording surface through a protective substrate,
When reproducing information and / or recording information from the fourth optical information recording medium, the third light beam is used as the fourth light beam by using one of the first and second objective optical elements. Constructed by focusing on the information recording surface through a protective substrate,
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1
An optical pickup device satisfying the requirements. First optical information recording having a first protective substrate thickness t1 using at least a first light flux of wavelength λ1, a second light flux of λ2 (λ1 ≠ λ2), and a third light flux of λ3 (λ1 ≠ λ3 and λ2 ≠ λ3). The recording density is different from that of the medium, the second optical information recording medium having the second protective substrate thickness t2 (t2 ≠ t1), and the first and second optical information recording media, and the second optical information recording medium having the third protective substrate thickness t3. In an optical pickup device for reproducing information and / or recording information on a third optical information recording medium and a fourth optical information recording medium having a fourth protective substrate thickness t4 (t4 ≠ t1 and t4 ≠ t2),
A first light source that emits a first light flux having the wavelength λ1;
A second light source that emits a second light flux having the wavelength λ2.
A third light source that emits a third light flux having the wavelength λ3;
In the case of having a first objective optical element and a second objective optical element which are provided separately from each other and performing information reproduction and / or information recording from the first optical information recording medium, One light beam is condensed on the information recording surface via the first protective substrate using one of the first and second objective elements,
When reproducing information from and / or recording information from the second optical information recording medium, a second protective substrate is used by using the first light beam as the other of the first and second objective optical elements. By condensing on the information recording surface via
When reproducing information from the third optical information recording medium and / or recording information, the second light beam is used as the third light beam by using one of the first and second objective optical elements. It is performed by condensing on the information recording surface through a protective substrate,
In the case of reproducing information from the fourth optical information recording medium and / or recording information, the third light beam is used as the fourth light beam by using one of the first and second objective optical elements. Constructed by focusing on the information recording surface through a protective substrate,
Either one of the first objective optical element and the second objective optical element has a phase structure on at least one optical surface and is made of plastic,
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1
An optical pickup device satisfying the requirements.   One of the first and second objective optical elements is used for reproducing information from the first optical information recording medium and / or recording information, and the other is from the second to fourth optical information recording media. 6. The optical pickup device according to claim 4, wherein the optical pickup device is used for reproducing information and / or recording information.   When reproducing information from the first or second optical information recording medium and / or recording information, the first light beam emitted from the first light source is in an optical path toward the first or second optical information recording medium. 7. The optical pickup device according to claim 1, further comprising objective optical element driving means for movably arranging the first or second objective optical element. The objective optical element driving means includes a lens holder that holds the first and second objective optical elements and is rotatable with respect to a central axis that holds the optical axes so as to be positioned on the same circumference, and the lens Drive means for rotationally driving a support shaft provided on the central axis of the lens holder at the edge of the holder;
When reproducing information from the first optical information recording medium and / or recording information, the first objective optical element held by the first rotating operation of the lens holder by the driving means is placed in the optical path. Placed in
When reproducing information from the second optical information recording medium and / or recording information, the second objective optical element held by the second rotating operation of the lens holder by the driving means is placed in the optical path. The optical pickup device according to claim 7, wherein the optical pickup device is arranged in a position. When reproducing information and / or recording information from the first and second optical information recording media, the first and second objective optical elements are fixedly arranged and the first light emitted from the first light source is emitted. A beam splitter disposed in an optical path through which the light beam passes and separating the incident first light beam in first and second directions different from each other;
The beam splitter is configured to cause a part of the first light beam emitted from the separated first light source to be incident on the first objective optical element, and to allow a part of the first light beam to be incident on the second objective optical element. The optical pickup device according to claim 1, wherein the optical pickup device is an optical pickup device.   The optical pickup device according to claim 9, wherein the beam splitter is a polarization beam splitter that separates a beam according to a polarization direction component of an incident light beam.   The optical pickup device according to claim 9, wherein the beam splitter is a half mirror that separates an incident light beam into transmitted light and reflected light.   12. The optical pickup device according to claim 9, wherein a λ / 4 wavelength plate is disposed in an optical path between the first light source and the beam splitter.   13. The optical pickup device according to claim 4, wherein the first to third light sources are configured as a single packaged light source unit.   13. The optical pickup device according to claim 4, wherein the second and third light sources are configured as a single packaged light source unit. When reproducing information from the first to fourth optical information recording media and / or recording information, the first and second objective optical elements are respectively fixedly arranged,
The first light flux emitted from the first light source and the second and third light fluxes emitted from the packaged second and third light sources are disposed at the incident positions, and the incident first light flux, A wavelength selection element that selectively transmits or reflects the second to third light fluxes;
A collimator that is disposed at a position where the first to third light fluxes that have passed or reflected through the wavelength selection element are incident, and that makes the incident light flux parallel light;
A beam expander that changes a light beam system of at least one of the first to third light beams that has passed through the collimator;
A quarter-wave plate disposed at a position where the first to third light beams that have passed through the beam expander are incident together;
The half light beam is disposed at a position where the first to third light beams are incident, and has a characteristic of transmitting or reflecting a part of the first light beam and transmitting or reflecting the second and third light beams. A mirror, and
While a part of the first light beam transmitted through the half mirror is incident on the first objective optical element, a part of the reflected first light beam is incident on the second objective optical element,
14. The light according to claim 12 or 13, wherein the second and third light beams transmitted or reflected by the half mirror are incident on the first objective optical element or the second objective optical element. Pickup device.   The at least one of the first and second objective optical elements is made of plastic and is a single optical element having a phase structure, according to any one of claims 1 to 15. Optical pickup device.   At least one of the first and second objective optical elements includes a first optical element and a second optical element, and one of the first and second optical elements is an optical element made of plastic, and the other 16. The optical pickup device according to claim 1, wherein is an optical element having a phase structure.   At least one of the first and second objective optical elements includes a first optical element and a second optical element, and at least one of the first and second optical elements has a phase structure made of plastic. The optical pickup device according to claim 1, wherein the optical pickup device is an element.   The optical pickup device according to any one of claims 1 to 18, wherein one of the first and second objective optical elements is formed of a glass lens. A first protective substrate thickness t1 using a first light flux of wavelength λ1 (400 nm ≦ λ1 ≦ 420 nm), a second light flux of λ2 (640 nm ≦ λ2 ≦ 670 nm) and a third light flux of λ3 (780 nm ≦ λ3 ≦ 800 nm). Recording density is different from the first optical information recording medium having the second protective information, the second optical information recording medium having the second protective substrate thickness t2 (t2 ≠ t1), and the first and second optical information recording media. Light for reproducing information and / or recording information on a third optical information recording medium having a protective substrate thickness t3 and a fourth optical information recording medium having a fourth protective substrate thickness t4 (t4 ≠ t1 and t4 ≠ t2) In the pickup device,
A first light source that emits a first light flux having the wavelength λ1;
A second light source that emits a second light flux having the wavelength λ2.
A third light source that emits a third light flux having the wavelength λ3;
A first objective optical element and a second objective optical element provided separately from each other;
In the case of reproducing information from the first optical information recording medium and / or recording information, the first light beam is used as the first objective optical element among the first and second objective elements. By condensing on the information recording surface through the protective substrate of
In the case of reproducing information from the second optical information recording medium and / or recording information, the first luminous flux is used as the second objective optical element out of the first and second objective optical elements. By condensing on the information recording surface through the protective substrate of 2,
In the case of reproducing information from the third optical information recording medium and / or recording information, the second light beam is used as the third light beam by using a second objective optical element among the first and second objective optical elements. By condensing on the information recording surface through the protective substrate of
When reproducing information from the fourth optical information recording medium and / or recording information, the third light beam is used as the fourth light beam by using the second objective optical element among the first and second objective optical elements. By condensing on the information recording surface through the protective substrate of
The first protective substrate thickness t1 and the second protective substrate thickness t2 are:
2.5 <t2 / t1 (1)
While satisfying
The second objective optical element is a part of the first to third light beams, and a first region through which a central light beam portion including an optical axis passes, and an intermediate light beam portion outside the central light beam portion pass through. A second region to
When reproducing information from the second optical information recording medium and / or recording information, the first light flux passing through the first and second areas is placed on the information recording surface of the second optical information recording medium. Focused,
When reproducing information from the third optical information recording medium and / or recording information, the second light flux passing through the first area and the second area is used as the information recording surface of the third optical information recording medium. Focused on the top,
When reproducing information from the fourth optical information recording medium and / or recording information, the third light beam passing through the first area is condensed on the information recording surface of the fourth optical information recording medium. An optical pickup device characterized by that. The second objective optical element has a first diffractive structure formed in the first region, and the second diffractive structure is formed in the second region. 21. The optical pickup device according to claim 20, wherein the light beam is incident as convergent light, and the third light beam is incident as divergent light. The second objective optical element diffracts the first to third light beams incident on the first diffractive structure as 10th order light, 6th order light, and 5th order light, and enters the second diffractive structure. The optical pickup device according to claim 21, wherein the first and second light beams are diffracted as fifth-order light and third-order light, respectively. The second objective optical element diffracts the first to third light beams incident on the first diffractive structure as secondary light, primary light, and primary light, respectively, and enters the second diffractive structure. The optical pickup device according to claim 21, wherein the first and second light beams are diffracted as secondary light and primary light, respectively.   24. The light according to claim 20, wherein at least one of the first and second objective optical elements is a single optical element having a diffractive structure made of a plastic material. Pickup device.   At least one of the first and second objective optical elements includes a first optical element and a second optical element, and at least one of the first and second optical elements has a diffractive structure made of plastic. The optical pickup device according to claim 20, wherein the optical pickup device is an element. 26. The optical pickup device according to claim 20, wherein one of the first and second objective optical elements is constituted by a glass lens.

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