JP2009037719A - Optical pickup device and objective optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low cost optical pickup which is compatible with BD and HD using the same light flux with one objective optical element without using a complicated mechanism and to provide an objective optical element. <P>SOLUTION: The objective optical element has an optical plane divided into a plurality of concentric areas, and the plurality of areas have at least a first area for optical disk and at least second area for optical disk. The first light beam passing the first area for optical disk is condensed on an information recording surface of the first optical disk but not on an information recording surface of the second optical disk while the first light beam passing the second area for optical disk is condensed on the information recording surface of the second optical disk but not on the information recording surface of the first optical disk. The total area A of the first area for optical disk is larger than the total area B of the second area for optical disk (A>B). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup device and an objective optical element capable of recording and / or reproducing information interchangeably with respect to different types of optical disks using light beams having the same wavelength.

  In recent years, research and development of high-density optical disc systems that can record and / or reproduce information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm. Development is progressing rapidly. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4, 7 GB) Can record information of 23 to 27 GB per layer on an optical disk with a diameter of 12 cm, which is the same size as the above, and an optical disk that records and reproduces information with specifications of NA 0.65 and light source wavelength 405 nm, so-called With HD DVD (hereinafter referred to as HD), information of 15 to 20 GB per layer can be recorded on an optical disk having a diameter of 12 cm. These optical disks are referred to herein as high density optical disks.

  By the way, it can be said that the value of an optical disc player / recorder (optical information recording / reproducing device) as a product is sufficient simply by saying that information can be appropriately recorded / reproduced only on one of these types of high-density optical discs. It is desirable to have a performance capable of appropriately recording / reproducing information while maintaining compatibility with both BD and HD.

  However, BD and HD are generated based on the difference in the thickness of the protective substrate using the wavelength difference because the thickness of each protective substrate is different although the wavelength of the light beam used is the same. It is difficult to correct spherical aberration. Therefore, it is more difficult to provide compatibility between BD and HD using a single objective optical element, as compared with compatibility with other optical disks.

  Under such circumstances, Patent Document 1 describes an objective optical element and an optical pickup device that use liquid crystal to give different aberrations during recording / reproduction of BD and HD, and enable compatibility with one objective optical element. Has been.

Patent Document 2 describes a pickup device that enables compatibility between BD and HD with a single objective optical element by sorting light beams having the same wavelength using a diffraction effect.
JP 2007-26540 A JP 2006-147069 A

  However, since the optical pickup device described in Patent Document 1 requires a liquid crystal, power supply and electrical control are necessary, which complicates the mechanism and increases the cost. It was.

  In addition, as in the optical pickup device described in Patent Document 2 above, when realizing the compatibility between BD and HD using a diffraction effect, for example, use of light passing from a light source to one optical disk through a diffraction structure Efficiency (the utilization efficiency here is the ratio of the amount of light that contributes to the spot on the optical disk to the amount of light incident on the optical surface on the light source side of the objective optical element) is 40% (in the case of diffraction distribution using a diffraction structure) (Theoretically does not exceed 50%), the light utilization efficiency from the optical disk to the photodetector through the same diffraction structure (the utilization efficiency here is the optical surface on the optical disk side of the objective optical element) Since the ratio of the amount of light that contributes to the spot on the photodetector with respect to the amount of incident light is 40%, the total utilization efficiency (here, the utilization efficiency is the optical surface on the light source side of the objective optical element) The ratio of the amount of light that contributes to the spot on the photodetector with respect to the amount of incident light is only squared to 40%, and only 16% of the light can be used. You can say that.

  Therefore, there is a demand for a configuration that does not use much of the diffraction effect and that enables compatibility between BD and HD with a common objective lens. In addition, when the amount of light is distributed between the BD and the HD, the desired performance cannot be obtained when the BD is used or when the HD is used.

  The present invention considers the above-mentioned problems, and collects a light beam having the same wavelength, for example, on a BD and HD information recording surface using a common objective lens without using a complicated mechanism. Enables the recording or reproduction of information, works well for both BD and HD, and / or works well during recording and reproduction, and has a high light utilization efficiency and An object is to provide an objective optical element.

The optical pickup device according to claim 1 includes a first light source that emits a first light beam having a wavelength λ1 (380 nm <λ1 <450 nm), and an objective for condensing the first light beam on an information recording surface of an optical disc. A condensing optical system having an optical element;
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an optical pickup device that records and / or reproduces information by focusing on a surface,
The objective optical element has its optical surface divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
The total area A of the first optical disk area is larger than the total area B of the second optical disk area (A> B).

  The present inventors have divided the optical surface of the objective optical element into at least one first optical disk area and at least one second optical disk area, and have passed through the first optical disk area. Is condensed on the information recording surface of the first optical disc, is not condensed on the information recording surface of the second optical disc, and the first light flux that has passed through the second optical disc region is the second optical disc. Both of the first optical disc and the second optical disc using the first light flux having the same wavelength by condensing on the information recording surface of the first optical disc and not condensing on the information recording surface of the first optical disc. It was found that information can be recorded / reproduced. Further, by using such a configuration, it is possible to increase the light utilization efficiency as compared with an objective optical element that uses the diffraction effect to make the first optical disk and the second optical disk compatible.

  However, according to such a technique, the sum of the amount of the light beam passing through the first optical disk region and the amount of the light beam passing through the second optical disk region does not exceed the amount of the light beam emitted from the light source. Therefore, it is desirable to effectively use the luminous flux as much as possible. Here, the inventors paid attention to the reflection characteristics of BD and HD. Generally, the reflectivity of the HD information recording surface is higher than the reflectivity of the BD information recording surface. Therefore, for example, if the reflectance of the second optical disk is higher than that of the first optical disk, there is no problem even if a small amount of light is condensed on the information recording surface of the second optical disk accordingly. Information can be recorded / reproduced, and the surplus can be condensed on the information recording surface of the first optical disc. It can be carried out.

  According to a second aspect of the present invention, there is provided the optical pickup device according to the first aspect, wherein the first optical disc is a BD, the second optical disc is an HD, and includes the optical axis of the objective optical element. A region close to is the second optical disc region, and the maximum image-side numerical aperture of the first optical disc region is smaller than 0.85.

    According to a third aspect of the present invention, in the optical pickup device of the first or second aspect, the first optical disc is a BD, the second optical disc is an HD, and includes the optical axis of the objective optical element. The area closest to the center is the second optical disk area, and the maximum effective diameter of the first optical disk area is smaller than 2 · f1 · NA1. However, f1 represents the focal length of the first optical disk area of the objective optical element in the first light flux, and NA1 is 0.85.

    According to a fourth aspect of the present invention, there is provided the optical pickup device according to the first aspect, wherein the first optical disc is a BD, the second optical disc is an HD, and includes the optical axis of the objective optical element. The area close to is the first optical disk area, and the maximum image-side numerical aperture of the second optical disk area is smaller than 0.65.

    According to a fifth aspect of the present invention, in the optical pickup device of the first or fourth aspect, the first optical disk is a BD, the second optical disk is an HD, and includes the optical axis of the objective optical element. The region closest to the center is the first optical disc region, and the maximum effective diameter of the second optical disc region is smaller than 2 · f 2 · NA 2. Here, f2 represents the focal length of the second optical disk area of the objective optical element in the first light flux, and NA2 is 0.65.

    According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the objective optical element is a single lens.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to fifth aspects, the objective optical element includes a first optical element and a second optical element. The optical surface is divided into the plurality of concentric regions.

  An optical pickup device according to an eighth aspect of the present invention is the optical pickup device according to any one of the first to seventh aspects, wherein the objective optical element includes three or more areas including the first optical disk area and the second optical disk area. It has 10 or less ring-shaped areas.

  The optical pickup device according to a ninth aspect is the invention according to any one of the first to eighth aspects, wherein a working distance of the objective optical element during recording and / or reproduction of the first optical disc and the second optical disc. The working distance of the objective optical element during recording and / or reproduction is different.

According to a tenth aspect of the present invention, in the invention according to the ninth aspect, the working distance WD1 of the objective optical element at the time of recording and / or reproduction of the first optical disk, and the recording and / or recording of the second optical disk. Alternatively, the working distance WD2 of the objective optical element during reproduction satisfies the following conditional expression.
-0.36mm ≤ WD1-WD2 ≤ 0.17mm

An optical pickup device according to an eleventh aspect of the invention is the optical pickup apparatus according to the tenth aspect of the invention, wherein the working distance WD1 of the objective optical element during recording and / or reproduction of the first optical disc and the recording and / or recording of the second optical disc. Alternatively, the working distance WD2 of the objective optical element during reproduction satisfies the following conditional expression.
| WD1-WD2 | ≧ 0.1mm

The objective optical element according to claim 12 is a first light source that emits a first light flux having a wavelength λ1 (380 nm <λ1 <450 nm), and an objective for condensing the first light flux on an information recording surface of an optical disc. A condensing optical system having an optical element;
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an objective optical element used in an optical pickup device that records and / or reproduces information by focusing on a surface,
The objective optical element has its optical surface divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
The total area A of the first optical disk area is larger than the total area B of the second optical disk area (A> B).

    The objective optical element according to claim 13 is the center of the invention according to claim 12, wherein the first optical disc is a BD, the second optical disc is an HD, and includes the optical axis of the objective optical element. A region close to is the second optical disc region, and the maximum image-side numerical aperture of the first optical disc region is smaller than 0.85.

    The objective optical element according to claim 14 is the invention according to claim 12 or 13, wherein the first optical disc is a BD, the second optical disc is an HD, and includes the optical axis of the objective optical element. The area closest to the center is the second optical disk area, and the maximum effective diameter of the first optical disk area is smaller than 2 · f1 · NA1. However, f1 represents the focal length of the first optical disk area of the objective optical element in the first light flux, and NA1 is 0.85.

    The objective optical element according to claim 15 is the center of the invention according to claim 12, wherein the first optical disc is a BD, the second optical disc is an HD, and includes the optical axis of the objective optical element. The area close to is the first optical disk area, and the maximum image-side numerical aperture of the second optical disk area is smaller than 0.65.

    The objective optical element according to claim 16 is the center of the invention according to claim 15, wherein the first optical disc is a BD, the second optical disc is an HD, and includes the optical axis of the objective optical element. An area close to is the first optical disk area, and the maximum effective diameter of the second optical disk area is smaller than 2 · f2 · NA2. Here, f2 represents the focal length of the second optical disk area of the objective optical element in the first light flux, and NA2 is 0.65.

  The objective optical element according to claim 17 is the invention according to any one of claims 12 to 16, wherein the objective optical element is composed of a single lens.

    The objective optical element according to claim 18 is the invention according to any one of claims 12 to 16, wherein the objective optical element includes a first optical element and a second optical element. The optical surface is divided into the plurality of concentric regions.

  The objective optical element according to claim 19 is the invention according to any one of claims 12 to 18, wherein the objective optical element includes three or more areas including the first optical disk area and the second optical disk area. It has 10 or less ring-shaped areas.

  The objective optical element according to claim 20 is the invention according to any one of claims 12 to 19, wherein a working distance of the objective optical element during recording and / or reproduction of the first optical disk and the second optical disk The working distance of the objective optical element during recording and / or reproduction is different.

    The objective optical element according to claim 21 is the objective optical element according to claim 20, wherein a working distance of the objective optical element during recording and / or reproduction of the first optical disc, and recording and / or recording of the second optical disc. The working distance of the objective optical element during reproduction is different.

The objective optical element according to a twenty-second aspect is the invention according to the twenty-first aspect, wherein a working distance WD1 of the objective optical element at the time of recording and / or reproduction of the first optical disk, and a recording and / or recording of the second optical disk. Alternatively, the working distance WD2 of the objective optical element during reproduction satisfies the following conditional expression.
| WD1-WD2 | ≧ 0.1mm

  The optical pickup apparatus of the present invention records / reproduces information with respect to at least the first optical disc and the second optical disc. The optical pickup device has at least one first light source. Furthermore, the optical pickup device has a condensing optical system for condensing the first light flux on the information recording surface of the first optical disc and condensing the first light flux on the information recording surface of the second optical disc. The optical pickup device also includes a light receiving element that receives a reflected light beam from the information recording surface of the first optical disc or the second optical disc.

  When the optical pickup device is a device for recording / reproducing the third optical disc and / or the fourth optical disc in addition to the first optical disc and the second optical disc, in addition to the first light source, the second light source and / or You may have a 3rd light source. When the optical pickup device is a device that records / reproduces the third optical disc and / or the fourth optical disc in addition to the first optical disc and the second optical disc, the condensing optical system receives the second light from the second light source. The light beam is condensed on the information recording surface of the third optical disk, and the third light beam from the third light source is condensed on the information recording surface of the fourth optical disk. Further, when the optical pickup device is a device for recording / reproducing the third optical disc and / or the fourth optical disc in addition to the first optical disc and the second optical disc, the information recording surface of the third optical disc or the fourth optical disc A light receiving element that receives the reflected light beam from the light source may be included.

  The first optical disc has a protective substrate having a thickness t1 and an information recording surface. The second optical disc has a protective substrate having a thickness t2 (t1 <t2) and an information recording surface. The first optical disc and the second optical disc have the same wavelength of light flux used for recording / reproduction. The first optical disk is preferably a BD and the second optical disk is preferably an HD, but the present invention is not limited to this. When the third optical disk or the fourth optical disk is used, the third optical disk has a protective substrate having a thickness t3 (t2 ≦ t3) and an information recording surface. The fourth optical disc has a protective substrate having a thickness t4 (t3 <t4) and an information recording surface. The third optical disk is preferably a DVD and the fourth optical disk is preferably a CD, but is not limited thereto. The first optical disc, the second optical disc, the third optical disc, or the fourth optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.

  In the BD, information is recorded / reproduced by an objective optical element having an NA of 0.85, and the thickness of the protective substrate is about 0.1 mm. In the HD, information is recorded / reproduced by an objective optical element having an NA of 0.65 to 0.67, and the thickness of the protective substrate is about 0.6 mm. Furthermore, DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective optical element having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm. ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like are included. Further, in this specification, a CD is a CD series optical disc in which information is recorded / reproduced by an objective optical element having an NA of about 0.45 to 0.51 and the protective substrate has a thickness of about 1.2 mm. It is a generic name and includes CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW, and the like. As for the recording density, the recording density of BD is the highest, followed by HD, DVD, and CD in that order.

  In addition, regarding the thicknesses t1, t2, t3, and t4 of the protective substrate, it is preferable to satisfy the following conditional expressions (1), (2), (3), and (4), but is not limited thereto.

0.0750 mm ≦ t1 ≦ 0.1125 mm (1)
0.5mm ≦ t2 ≦ 0.7mm (2)
0.5mm ≦ t3 ≦ 0.7mm (3)
1.0mm ≦ t4 ≦ 1.3mm (4)

  In the present specification, the light source such as the first light source, the second light source or the third light source is preferably a laser light source. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used.

  When BD is used as the first optical disc and HD is used as the second optical disc, the wavelength λ1 of the first light beam emitted from the first light source is preferably 380 nm or more and 450 nm or less. When a DVD is used as the third optical disk and a CD is used as the fourth optical disk, the wavelength λ2 of the second light beam emitted from the second light source is preferably 630 nm or more and 670 nm or less, and is emitted from the third light source. The wavelength λ3 of the third light flux is preferably 760 nm or more and 820 nm or less.

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

  The condensing optical system has an objective optical element. The objective optical element focuses the first light flux on the information recording surface of the first optical disc so that information can be recorded / reproduced, and the first light flux is recorded / reproduced on the information recording surface of the second optical disc. Concentrate as much as possible. The condensing optical system may include only the objective optical element, but may include a coupling lens such as a collimator lens and a beam expander in addition to the objective optical element. The coupling lens is a single lens or a lens group that is disposed between the objective optical element and the light source and changes the divergence angle of the light beam. The beam expander is a lens group that is disposed between the objective optical element and the light source and changes the diameter of the light beam without changing the divergence angle of the light beam. The collimating lens is a kind of coupling lens, and is a lens that changes a light beam incident on the collimating lens into parallel light. Further, the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like. May be. The condensing optical system may have an objective optical element for the third optical disk and an objective optical element for the fourth optical disk in addition to the objective optical elements for the first optical disk and the second optical disk. The objective optical element for the first optical disk and the second optical disk may also serve as the objective optical element for the third optical disk and / or the fourth optical disk.

  In this specification, the objective optical element is disposed at a position facing the optical disk in a state where the optical disk is loaded in the optical pickup device, and has a function of condensing the light beam emitted from the light source on the information recording surface of the optical disk. An optical system having Preferably, the objective optical element is an optical system that is disposed at a position facing the optical disc in the optical pickup device and has a function of condensing a light beam emitted from the light source on the information recording surface of the optical disc, An optical system that can be integrally displaced at least in the optical axis direction by an actuator. The objective optical element may be composed of two or more lenses and optical elements, or may be only a single lens. The objective optical element may be a glass lens, a plastic lens, or a hybrid lens in which an optical path difference providing structure or the like is provided on a glass lens with a photocurable resin or the like. When the objective optical element has a plurality of lenses, a glass lens and a plastic lens may be mixed and used. When the objective optical element has a plurality of lenses, it may be a combination of a flat plate optical element having an optical path difference providing structure and an aspheric lens, or a combination of an optical element having a flat plate portion and a swash plate portion and an aspheric lens. There may be. The objective optical element may have an optical path difference providing structure. The objective optical element preferably has an aspheric refractive surface.

When the objective optical element is a plastic lens, it is preferable to use a cyclic olefin-based resin material. Among the cyclic olefin-based materials, the refractive index at a temperature of 25 ° C. with respect to a wavelength of 405 nm is 1.54 to 1.60. The refractive index change rate dN / 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 −20 × 10 ^{−5 to} −5 × 10 ^It is more preferable to use a resin material in the range of ⁻⁵ (more preferably −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ). When the objective optical element is a plastic lens, the coupling lens is preferably a plastic lens.

  The standard image side numerical aperture necessary for reproducing / recording information on the first optical disc is NA1, and the standard image side numerical aperture necessary for reproducing / recording information on the second optical disc is used. NA2 (NA1> NA2), NA3 (NA2 ≧ NA3) as the image-side numerical aperture required for reproducing / recording information on the third optical disc, and reproducing information on the fourth optical disc / NA4 (NA3> NA4) is the image-side numerical aperture required for recording. NA1 is preferably 0.8 or more and 0.9 or less. More preferably, NA1 is 0.85. NA2 and NA3 are preferably 0.55 or more and 0.7 or less. More preferably, NA2 is 0.65 and NA3 is 0.65. NA4 is preferably 0.4 or more and 0.55 or less. More preferably, NA4 is 0.45.

  The objective optical element is divided into a first region including at least the optical axis and a second region around the first region. The first region and the second region may have a clear structural difference between the first region and the second region on the optical surface of the objective optical element. On the other hand, the objective optical element may be a convenient area without providing a clear area in terms of configuration.

  The first light beam that has passed through the first area of the objective optical element is used for recording / reproduction of the first optical disk and the second optical disk, and the first light beam that has passed through the second area is used for recording / reproduction of the first optical disk. However, it is not used for recording / reproduction of the second optical disc. That is, the first area is a so-called shared area (first optical disk area + second optical disk area) used for both the first optical disk and the second optical disk, and the second area is used only for the first optical disk. It can be said that this is a so-called dedicated area (first optical disk area). The first area is preferably an area of NA2 or less, and the second area is preferably an area larger than NA2 and NA1 or less. For example, when the first optical disk is a BD and the second optical disk is an HD, the first area is preferably an area having an image-side numerical aperture (NA) of 0.65 or less, and the second area is an image. It is preferable that the side numerical aperture is greater than 0.65 and 0.85 or less.

  When the objective optical element is viewed from another viewpoint, the optical surface of the objective optical element is divided into a plurality of concentric areas, and the plurality of areas are at least one first optical disk area and at least one second optical disk area. It can be said that it has. The first light flux that has passed through the first optical disk area is condensed so that information can be recorded / reproduced on the information recording surface of the first optical disk, and is not condensed on the information recording surface of the second optical disk. The first light flux that has passed through the second optical disc area is condensed so that information can be recorded / reproduced on the information recording surface of the second optical disc, and is not condensed on the information recording surface of the first optical disc.

Further, the total area A of the first optical disk area is larger than the total area B of the second optical disk area (A> B). Here, the “total area of the optical disk area” means the total area of the areas projected onto the optical axis orthogonal plane when each optical disk area is projected in the optical axis direction. With such a configuration, it is possible to appropriately record and reproduce information by distributing the light flux in a balanced manner to both optical disks. Even in the area within NA2, it is preferable that the total area A of the first optical disk area is larger than the total area B of the second optical disk area (A> B). In other words, the total area A of the first optical disk area is the total area B of the second optical disk area in the remaining area excluding the outermost ring-shaped area farthest from the optical axis of the objective optical element. Is larger than (A> B). Further, when the values of A and B are different between the plurality of regions on the optical surface on the light source side of the objective optical element and the plurality of regions on the optical surface on the optical disc side, the plurality of regions on the optical surface on the light source side of the objective optical element It is preferable that the above is satisfied.

  The objective optical element may have a compatible optical path difference providing structure that enables use of the third optical disk and / or the fourth optical disk. Further, the objective optical element may have an optical path difference providing structure for correcting the aberration change at the time of temperature change or wavelength change. In addition, the optical path difference providing structure in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.

  The first optical disk area and the second optical disk area are preferably provided alternately, but the present invention is not limited to this. The most central area including the optical axis may be the first optical disk area or the second optical disk area.

  That is, the first light flux that has passed through the first optical disk area has a very small aberration on the information recording surface of the first optical disk, so that information cannot be recorded / reproduced on the information recording surface of the second optical disk. The aberration is large. On the other hand, the first light flux that has passed through the second optical disk area has a large aberration on the information recording surface of the first optical disk so that information cannot be recorded / reproduced. On the information recording surface of the second optical disk, Aberration is very small.

  Both the first optical disk area and the second optical disk area are preferably refracting surfaces. In this case, the light beam that has passed through the first optical disk area is reflected on the information recording surface of the first optical disk by using the refraction action. And condensing the light beam that has passed through the second optical disk area onto the information recording surface of the second optical disk. Such a configuration is preferable because a loss of light amount can be reduced when reflected light on the information recording surface of the optical disc passes through the correction surface. In this case, a light receiving element having a relatively low sensitivity can be used as the light receiving element, so that the cost of the optical pickup device can be reduced.

  When the objective optical element has a first optical element and a second optical element, and the optical surface of the first optical element is divided into a plurality of concentric areas, the first optical disk area and the second optical disk One of the use areas transmits the first light beam (has no power with respect to the first light beam), and the other records / reproduces information on the information recording surface of the optical disc with respect to the first light beam that has passed. However, it is also possible to adopt a configuration in which the aberration is corrected so that the light can be condensed (having power with respect to the first light flux). In particular, the objective optical element has a first optical element that is a correction element and a second optical element that is an aspheric lens, and only the aspheric lens protects the first optical disk or the second optical disk. In the case where the aspherical lens has an optical performance capable of condensing the first light beam on the information recording surface via the substrate, it is preferable to adopt the above-described configuration. For example, when the aspherical lens is designed so that the first light beam can be condensed on the information recording surface with respect to the BD with only the aspherical lens, the first optical element (BD) area of the first optical element is The second optical disc (HD) region transmits the first light flux, and has a structure that corrects aberrations so that the first light flux is condensed on the information recording surface of the HD. Is preferred.

  On the other hand, the first optical disc area corrects the aberration so that the first light beam that has passed through is focused on the information recording surface of the first optical disc so that information can be recorded / reproduced. The use area may be configured to correct aberration so that information can be recorded / reproduced on the information recording surface of the second optical disk that has passed. In particular, the objective optical element includes a first optical element that is a correction element and a second optical element that is an aspheric lens, and the aspheric lens alone protects both the first optical disc and the second optical disc. In the case where the first light beam cannot be condensed on the information recording surface via the substrate, the above-described configuration is preferable. For example, when the aspherical lens is designed so that the first light beam cannot be condensed with respect to both BD and HD with only the aspherical lens, the area for the first optical disk (BD) of the first optical element is The aberration is corrected so that the first light flux is condensed on the BD information recording surface, and the second optical disc (HD) area is collected on the HD information recording surface with respect to the first light flux. It is preferable to have a structure that corrects aberration so as to emit light.

  When the objective optical element is composed of a single lens, a step may be provided on the aspherical optical surface of the single objective lens, thereby dividing it into a plurality of concentric regions. It is preferable that the first optical disc region has the same aspherical shape, and the second optical disc region has a different aspherical shape. When the objective optical element has a plurality of first optical disk areas, it is preferable that these first optical disk areas have the same aspherical shape, and when the objective optical element has a plurality of second optical disk areas, It is preferable that the second optical disc regions have the same aspherical shape.

  Further, from the viewpoint of facilitating manufacture of the objective optical element, it is preferable that the number of ring-shaped areas including the first optical disk area and the second optical disk area is 3 or more and 10 or less. When the number of ring-shaped areas is 3, for example, as shown in FIG. 9, the center area including the optical axis is the first optical disk area BA1, the surrounding area is the second optical disk area HA, and the surrounding area. An example in which the outermost peripheral area is the first optical disk area BA2 can be considered. As a result of diligent research, the present inventor combined the first optical disk area and the second optical disk area from the viewpoint of reducing the side rope of the spot and facilitating the manufacture of the objective optical element. It was found that the number of ring-shaped regions is preferably 5 or more and 10 or less. More preferably, the number of annular zones is 6 or more and 10 or less. Even when the objective optical element includes the first optical element on the light source side and the second optical element on the optical disc side, the above-described range of the preferable number of annular zones can be applied.

Next, when performing recording / reproduction of the second optical disc, in order to prevent the light flux that has passed through the first optical disc area from falling on the defocus area, the light flux that has passed through the first optical disc area is 2 It is preferable that the objective optical element has a flare on the information recording surface of the optical disc. Specifically, “to flare” means that light that has passed through the first optical disk area on the information recording surface of the second optical disk is distributed in the donut-shaped area. In particular, when the first optical disc is a BD and the second optical disc is an HD, it is preferable that the inner diameter of the donut-shaped region be Φ0.030 mm or more. In the case of a plurality of donut-shaped regions, it is preferable that the smallest diameter among the inner diameters of each donut-shaped region is Φ0.030 mm or more. In order to generate a good flare when the first optical disc is a BD and the second optical disc is an HD, the working distance (WD _BD ) of the objective optical element in the first optical disc (BD); the value of the difference between the working distance of the objective optical element (WD _HD) in the second optical disk _{(HD) (WD BD -WD HD} ), - 0.36 (mm) or more, to 0.17 (mm) or less Is preferred. More preferably, it is -0.10 (mm) or more and 0.15 (mm) or less. From another viewpoint, it is preferable that the following conditional expression (5) is satisfied.
2 ・ f1 ・ NA1 '> 2 ・ f2 ・ NA2' (5)
F1 is the focal length of the first optical disk area of the objective optical element in the first light flux, f2 is the focal distance of the second optical disk area of the objective optical element in the first light flux, and NA1 'is the first optical disk of the objective optical element. The numerical aperture according to the standard of the area for use and the numerical aperture according to the standard of the area for the second optical disc of the NA2 ′ object optical element are shown. It should be noted that even when the objective optical element has the first optical element on the light source side and the second optical element on the optical disk side, the preferable conditions for generating the flare can be applied.

  In order to obtain an appropriate spot diameter, the following conditions are preferably satisfied. The following conditions are not limited to the case where the objective optical element is a single lens, but also when the objective optical element includes the first optical element on the light source side and the second optical element on the optical disk side, Conditions are applicable.

  First, when the region closest to the center including the optical axis is the second optical disc region, it is preferable that the maximum image-side numerical aperture of the first optical disc region is smaller than NA1. The maximum effective diameter of the first optical disk area is preferably smaller than 2 · f1 · NA1. Note that f1 is the focal length of the first optical disk area of the objective optical element in the first light flux, and NA1 indicates the image-side numerical aperture defined by the standard required for recording / reproduction of the first optical disk. . For example, when the first optical disk is a BD and the second optical disk is an HD, the maximum image-side numerical aperture of the first optical disk area is preferably smaller than 0.85. In addition, it is preferable that the maximum effective diameter of the first optical disk area is smaller than 2 · f1 · 0.85.

  Next, when the area closest to the center including the optical axis is the first optical disk area, the maximum image-side numerical aperture of the second optical disk area is preferably smaller than NA2. Further, it is preferable that the maximum effective diameter of the second optical disk area is smaller than 2 · f2 · NA2. Note that f2 is the focal length of the second optical disk area of the objective optical element in the first light flux, and NA2 is the image-side numerical aperture defined by the standard required for recording / reproduction of the second optical disk. . For example, when the first optical disk is a BD and the second optical disk is an HD, the maximum image-side numerical aperture of the second optical disk area is preferably smaller than 0.65. The maximum effective diameter of the second optical disk area is preferably smaller than 2 · f2 · 0.65.

  Next, as a configuration for improving the off-axis characteristics of the objective optical element that is a single lens, 1) change the aspherical shape of the first optical disk area and the second optical disk area, or 2) For example, as shown in FIG. 10, a configuration in which an optical path difference providing structure is provided in the second optical disc area is conceivable. Here, to improve the off-axis characteristics means that the wavefront aberration becomes 0.1 RMS or less when the light beam enters the objective optical element at an oblique incidence of 0.5 °.

In the case of the configuration in which the first optical disk area and the second optical disk area have different aspherical shapes in ₁ ), the working distance (WD ₁ ) of the objective optical element during recording / reproduction of the first optical disk and the second optical disk It is preferable that the working distance (WD ₂ ) of the objective optical element at the time of recording / reproducing is different, and more preferably, the absolute value (| WD ₁ −WD ₂ |) of the difference between WD ₁ and WD ₂ is set to 0. It is preferable to design to be 1 (mm) or more.

  On the other hand, in order not to cause a large step on the optical surface, it is preferable to provide an off-axis characteristic by providing an optical path difference providing structure in the second optical disc area as in 2). Depending on other design conditions, the above method 1) or 2) may be used properly.

  Incidentally, on the optical surface on the optical disc side of the single objective optical element, there are a region through which the light beam used for recording / reproduction of the first optical disc passes and a region through which the light beam used for recording / reproduction of the second optical disc passes. An objective optical element that does not overlap is preferable because the loss of light quantity can be reduced. When this viewpoint is emphasized, it is preferable that the number of annular zones of the objective optical element is small. For example, a three-band objective optical element is preferable.

  Further, from the viewpoint of reducing the thickness of a single objective optical element, a step is provided on the surface of the optical surface of the objective optical element, and the step is a region on the far side of the region closer to the optical axis with the step as a boundary. It is desirable that the level difference be shorter than the optical path. For example, the example shown in FIG. 13 is an example in which a step for thinning the objective optical element is further provided in the first optical disk area, which is the central area, with respect to the objective optical element shown in FIG. Even when such a step is provided, it is desirable that the spherical aberration and the sine condition are corrected to a necessary level.

  The step between the first optical disc region and the second optical disc region is not limited to the example shown in FIG. When the objective optical element is made of plastic, it may be a step that produces a diffractive action that compensates for the spherical aberration change caused by the temperature change of the plastic by the change of the laser oscillation wavelength accompanying the temperature change. When the objective optical element is made of glass, the influence of temperature change is small, so that it is easy to obtain a deep step without degrading temperature characteristics.

The sum Δ of the lengths of coding in the optical axis direction of all the steps provided on the optical surface of the objective optical element (sign is a region where the optical path of each step is closer to the optical axis than the region on the far side It is desirable that the following conditional expression (6) is satisfied in the case where it is shortened:
0.1 mm ≦ Δ ≦ 1.0 mm (6)
If it is above the lower limit, the effect of thinning is great, and if it is below the upper limit, the sine condition can be corrected to the required level while reducing the thickness. Note that “the sum of the coding lengths” means that when both a positive length value and a negative length value exist, they are added as they are. For example, if the positive length value is +1 and the negative length value is −0.5, (+1) + (− 0.5) = + 0.5, ie, +0. 5 is “the sum of the lengths of encoding”.

  As shown in FIG. 9, when the first optical disk area and the second optical disk area are provided in a single objective optical element, a large level difference (for example, a level difference of 50 μm or more in the optical axis direction) is provided at the boundary between the areas. ) May occur. Such a large step, when the objective optical element is molded using a mold, may become a hindrance when the optical element is removed from the mold, making the objective optical element more difficult to manufacture. Therefore, when a large step (for example, a step of 50 μm or more in the optical axis direction) occurs at the boundary of each region, the inclined surface is inclined with respect to the optical axis at the step portion so that it can be easily removed from the mold. (Taper) is preferably provided. For example, as shown in FIG. 9, in the case where the middle region is recessed in the optical axis direction, as shown in FIG. 14, only the surface SS1 with the step surface facing the optical axis is inclined. The surface SS2 in which the step surface faces in the direction opposite to the optical axis is not inclined, so that the influence on the optical performance can be minimized, and the loss of light amount due to the taper can be reduced. It is preferable because it can be easily removed from.

  Furthermore, the optical surface of the objective optical element has an optical path difference providing structure for the purpose of compatibility with the third optical disc and the fourth optical disc, and the purpose is to correct the change in aberration that occurs at the time of temperature change or wavelength change. The optical path difference providing structure may be overlapped. One of the preferred examples is an optical path difference providing structure for correcting an aberration change occurring when the temperature or wavelength changes only in the first optical disk area or only in the second area of the objective optical element. Is provided. In the above description, the example in which the optical path difference providing structure is provided on the optical surface on the light source side is described. However, the optical path difference providing structure for the above-described purpose may be provided on the optical surface on the optical disc side. .

  When the objective optical element has a first optical element and a second optical element, and the first optical element is divided into a plurality of concentric areas, the plurality of areas do not give aberration and an area that gives aberration. It is preferable to have a transparent region (for example, a flat plate region and an aspherical region), but is not limited thereto. The plurality of regions provided in the first optical element may be all regions that give aberration.

  When the first optical element has a region that does not give aberration (for example, a region of a flat plate portion) and a region that gives aberration (for example, a region on an aspherical surface or a swash plate), a region that does not give aberration is It is preferable that one of the first optical disk area and the second optical disk area, and the other area to be given aberration.

  A preferred example in the case where the correction surface is provided on the flat plate-like first optical element will be described with reference to FIG. As shown in FIG. 1, in this example, the objective optical element OE includes a flat plate-like first optical element L1, a second optical element L2 that is an aspheric lens, a first optical element L1, and a second optical element. It has a frame HE to hold and fix. The second optical element L2 is designed so as to be able to focus the first light beam on the information recording surface of the BD by itself. A correction surface CS is provided in a region of NA 0.65 or less that is the first region A1 of the first surface S1 of the first optical element L1. A region (first optical disc region) larger than NA 0.65, which is the second region A2 of the first surface S1 of the first optical element L1, and NA 0.85 or less is a flat surface.

  The correction surface CS is divided into a plurality of regions having a region BA on a plane and a region HA having an aspherical surface by steps. The area BA on the plane and the area HA having the aspherical surface are alternately provided. The area BA on the plane is a first optical disk (BD) area, and the area HA having an aspherical surface is a second optical disk (HD) area. Since the second optical element is designed to be optimized for BD, the first light beam that has passed through the first optical element, that is, the first light beam that has passed through the BD area BA, which is an area on the plane, It is condensed on the information recording surface of the BD by the element. On the other hand, since the first light beam is not condensed on the HD information recording surface only by the second optical element, the first light beam passes through the HD area HA of the first optical element, thereby giving an aberration due to the aspherical shape. Is done. As a result, the first optical element and the second optical element jointly give aberration, so that the first light flux that has passed through the HD region is condensed on the HD information recording surface. Note that the HD region having an aspherical shape has a structure in which the step is directed opposite to the optical axis near the optical axis, and the step is directed toward the optical axis in a region away from the optical axis. . In addition, an aspherical surface having no step is provided in the transition region therebetween.

  That is, when BD recording / reproduction is performed, the light beam that has passed through the BD area BA and the second area A2 in the first area A1 of the first optical element L1 is reflected on the BD information recording surface by the second optical element. The light flux that has been focused on and passed through the HD area HA of the first area A1 of the first optical element L1 is not collected on the information recording surface of the BD. On the other hand, when recording / reproducing HD, the first light flux that has passed through the HD area HA of the first area A1 of the first optical element L1 is condensed on the information recording surface of the HD by the second optical element. Thus, the first light flux that has passed through the BD area BA and the second area of the first area A1 of the first optical element is not condensed on the HD information recording surface.

  Next, the step amount of the step provided in the first optical element will be described. Examples of the level difference are roughly divided into three types.

The first example is a case where the step amount of the step on the correction surface is a step amount that gives an optical path difference of a times the wavelength λ1 to the first light flux. Note that a is an arbitrary positive integer other than 0. In this case, the step amount d1 can be expressed by the following equation (7).
d1 = a · λ1 / (n−1) (7)
Here, n is the refractive index of the optical element having a correction surface for the light flux with wavelength λ1.

  For example, when the second optical element is a single lens optimized for BD, when the first light beam is condensed on the information recording surface of the BD, almost no aberration occurs as shown in FIG. . Next, when the first light beam is condensed on the HD information recording surface using only the second optical element, a large aberration occurs as shown in FIG. The aberration diagram shown in FIG. 3 is an aberration diagram of only the first region.

  Therefore, as the objective optical element, an objective optical element having a flat plate-like first optical element having a correction surface as shown in FIG. 1 and a second optical element which is a lens optimized for BD is used, and the amount of the step is set. 4 satisfies the expression (7), the aberration in the first region is as shown in FIG. FIG. 4A shows the aberration in BD, and FIG. 4B shows the aberration in HD. In this case, a = 1.

  Note that the step amount need not be equal for all steps on the correction surface. For example, the step in the region near the optical axis of the correction surface may be increased, and the step in the region far from the optical axis of the correction surface may be decreased. Or the reverse may be sufficient. For example, while the amount of the step satisfies the expression (7), a = 2 is set for the step in the region near the optical axis of the correction surface, and a = 1 is set for the step in the region far from the optical axis of the correction surface. In this case, the aberration in the first region is as shown in FIG. FIG. 7A shows the aberration in BD, and FIG. 7B shows the aberration in HD.

The second example is a case where the amount of step difference on the correction surface is a step amount that gives an optical path difference b times the wavelength λ1 to the first light flux. Note that b is 0 or the sum of any positive integer and x. x is an arbitrary value between 0.4 and 0.6. In this case, the step amount d2 can be expressed by the following equation (8).
d1 = b · λ1 / (n−1) (8)

  As the objective optical element, an objective optical element having a flat plate-like first optical element having a correction surface as shown in FIG. 1 and a second optical element which is a lens optimized for BD is used. When the expression (8) is satisfied, the aberration in the first region is as shown in FIG. FIG. 5A shows the aberration in BD, and FIG. 5B shows the aberration in HD. In this case, b = 1 + 0.5.

A third example is a case where the step amount of the step on the correction surface is a step amount that gives an optical path difference c times the wavelength λ1 to the first light flux. Note that c is 0 or the sum of any positive integer and y. y is an arbitrary value greater than 0 and less than 0.4 or greater than 0.6 and less than 1. In this case, the step amount d3 can be expressed by the following equation (9).
d1 = c · λ1 / (n−1) (9)

  As the objective optical element, an objective optical element having a flat plate-like first optical element having a correction surface as shown in FIG. 1 and a second optical element which is a lens optimized for BD is used. When the expression (9) is satisfied, the aberration in the first region is as shown in FIG. FIG. 6A shows the aberration in BD, and FIG. 6B shows the aberration in HD. In this case, c = 1 + 0.8.

  In addition, the correction surface is not of a type having a first optical disk (BD) dedicated area and a second optical disk (HD) dedicated area. 1. Condensed light on the information recording surface of one optical disc (although some aberrations remain) so that it can be recorded / reproduced, and the first light flux that has passed through also on the information recording surface of the second optical disc (some aberrations remain) However, when the light is collected so as to be recorded / reproduced, the aberration in the first region is as shown in FIG. FIG. 8A shows the aberration in BD, and FIG. 8B shows the aberration in HD. In this case, since the same amount of aberration occurs in both BD and HD, the first optical disk priority area and the second optical disk priority area do not exist in this example.

  Note that the following modes can be considered when compatibility with other optical discs as well as the first optical disc and the second optical disc is performed with one objective optical element.

As a first example, for example, a third light beam having a wavelength λ3 emitted from a third light source is condensed on the information recording surface of the fourth optical disk by the objective optical element, and the wavelength λ3 is a wavelength λ1. If it is an approximate integer multiple of 1 and an attempt is made to enable compatibility with the fourth optical disk by the diffraction structure, 1) it becomes difficult to make the diffraction angles different between the first light flux of λ1 and the third light flux of λ3, 2) When a special diffraction structure that can make the diffraction angles of the first light flux and the third light flux different is used, there is a problem that the light use efficiency is lowered. Therefore, a fourth optical disk area may be provided in the second area in addition to the first optical disk area and the second optical disk area. For example, as shown in FIG. 11, the fourth optical disk area CD, the first optical disk area BD, the second optical disk area HD, and the second area outside the fourth optical disk area CD in order from the inner area including the optical axis. An example in which the first optical disk area BD is provided can be considered. Note that the fact that the wavelength λ3 is a substantially integer multiple of the wavelength λ1 means that the following conditional expression (10) is satisfied.
(M−0.2) · λ1 ≦ λ3 ≦ (m + 0.2) · λ1 (10)
Note that m represents an arbitrary positive integer of 2 or more.

  Further, when the fourth optical disk area as described above is provided, the maximum image-side numerical aperture of the fourth optical disk area is made smaller than the numerical aperture that is used as a standard for recording / reproducing of the fourth optical disk. Is preferred. Therefore, it is preferable that the maximum effective diameter of the fourth optical disk area is smaller than 2 · f4 · NA4. Note that f4 represents the focal length of the fourth optical disk area of the objective optical element in the third light flux, and NA4 represents the image-side numerical aperture defined by the standard required for recording / reproducing of the fourth optical disk. For example, when the fourth optical disk is a CD, the maximum image-side numerical aperture of the fourth optical disk area is preferably smaller than 0.45. More preferably, it is 0.43 or less. When the fourth optical disk is a CD, the maximum effective diameter of the fourth optical disk area is preferably smaller than 2 · fCD · 0.45, and more preferably 2 · fCD · 0.43 or less. Note that fCD represents the focal length of the CD-dedicated region of the objective optical element in the CD light flux.

  Further, by providing an optical path difference providing structure in at least one of the fourth optical disk area, the first optical disk area, and the second optical disk area in the second area, the recording of the third optical disk (for example, DVD) is performed. / Reproduction may be enabled. For example, as shown in FIG. 12, the fourth optical disk area CD, the first optical disk area BD, the second optical disk area HD, and the second area outside of the fourth optical disk area CD in order from the inner area including the optical axis. An optical path difference providing structure DVD that enables recording / reproduction of the third optical disk is provided in the fourth optical disk area CD, the inner first optical disk area BD, and the second optical disk area HD as the first optical disk area BD. Examples are possible.

When the objective optical element of the present invention is applied to a hybrid optical disk in which recording layers of a plurality of types of optical disks including the first optical disk and the second optical disk are laminated on one optical disk, the objective optical element of the first optical disk It is preferable that the working distance (WD ₁ ) and the working distance (WD ₂ ) of the objective optical element in the second optical disc are different. When the first optical disc is BD and the second optical disc is HD, that is, when a hybrid optical disc in which BD and HD are laminated is used, it is more preferable to set the value of the difference between these working distances to (WD ₁ −WD ₂ ), preferably 50 μm or more and 250 μm or less. More preferably, it is 100 μm or more and 250 μm or less. An example in which recording layers of a plurality of types of optical disks are stacked on a single optical disk is a hybrid disk in which recording layers of BD / HD / DVDs are stacked on one side as disclosed in JP-A-2007-42254. Can be mentioned.

  As shown in FIG. 18, the single objective optical element OL1 of the present invention for the first optical disk and the second optical disk and the objective optical element OL2 for other optical disks (for example, the third optical disk / fourth optical disk). Alternatively, a lens unit that is integrally formed may be used. As shown in FIG. 18, the integrally formed lens unit is a case where the first objective optical element OL1 and the second objective optical element OL2 are fused (for example, the first objective optical element). And a second objective optical element as shown in FIG. 19 or FIG. 20 as well as a lens unit having a second objective optical element and a second objective optical element. The optical elements may be integrated by molding separately, and then fitting, adhering or engaging with each other.

  FIG. 19 shows an example of a lens unit in which the first objective optical element and the second objective optical element are engaged and integrally formed. The second objective optical element OL2 made of plastic forms an opening HL having a stepped portion ST in the rectangular plate-shaped flange portion FL2, and the flange portion FL1 is held by the stepped portion ST in the opening HL. In this way, the first objective optical element OL1 made of glass or plastic of the present invention is assembled from the optical axis direction and integrated by adhesion or the like, and the first objective optical element OL1 and the second objective optical element are integrated. A lens unit OE in which OL2 is arranged in parallel is formed.

  FIG. 20 shows another example of a lens unit in which a first objective optical element and a second objective optical element are engaged and integrally formed. The second objective optical element OL2 made of plastic forms a notch CT having a stepped portion ST in the rectangular plate-like flange portion FL2, and the flange portion FL1 is held by the stepped portion ST in the notch CT. In this way, the first objective optical element OL1 made of glass or plastic of the present invention is assembled from the direction orthogonal to the optical axis and integrated by adhesion or the like, and the first objective optical element OL1 and the second objective optical are integrated. A lens unit OE in which the elements OL2 are arranged in parallel is formed.

  As shown in FIG. 21, the flange portion FL1 of the first objective optical element OL1 may be supported on the upper surface of the flange portion FL2 without forming the step ST in the opening HL or the notch CT. Alternatively, although not shown, the first objective optical element OL1 made of glass or plastic and the second objective optical element OL2 made of plastic may be integrated by assembling to a holding member which is a separate member. good. In any case, it is preferable that the holding member has an opening, and the objective lens unit is fitted therein.

  The first light beam may be incident on the objective optical element as parallel light, or may be incident on the objective optical element as divergent light or convergent light. Preferably, the magnification m1 of the first light beam incident on the objective optical element satisfies the following formula (11).

−0.02 <m1 <0.02 (11)

  On the other hand, when the first light flux is incident on the objective optical element as diverging light, the magnification m1 of the first light flux incident on the objective optical element preferably satisfies the following formula (12).

  -0.10 <m1 <0.00 (12)

In order to make the sine condition compatible during both recording / reproduction of the first optical disk and recording / reproduction of the second optical disk, it is preferable to satisfy the following conditional expression (13).
m11 <m12 (13)
M11 represents the magnification of the first light beam incident on the objective optical element at the time of recording / reproduction of the first optical disk, and m12 represents the objective optical of the first light beam at the time of recording / reproduction of the second optical disk. The magnification of the incident light beam to the element is shown.

  For example, when recording / reproducing the first optical disk, the first light beam is incident on the objective optical element as infinite parallel light, and when recording / reproducing the second optical disk, the first light beam is incident on the objective optical element as finite convergent light. Is a preferred example.

  The optical information recording / reproducing apparatus has an optical disc drive apparatus having the optical pickup device described above.

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

  An optical information recording / reproducing apparatus using each of the above-described methods is generally equipped with the following components, but is not limited thereto. An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc These include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.

  In addition to these components, the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.

  According to the present invention, with a simple and low-cost configuration, without using a complicated mechanism for BD and HD, it is compatible with one objective optical element of BD and HD that uses the same light beam at low cost. In addition, it is possible to provide an optical pickup device and an objective optical element with high light utilization efficiency.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a diagram schematically showing a configuration of the optical pickup apparatus PU1 of the present embodiment that can appropriately record / reproduce information with respect to the BD as the first optical disc and the HD as the second optical disc. is there. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. The present invention is not limited to the present embodiment.

  The optical pickup device PU1 includes an objective optical element OE, a λ / 4 wavelength plate QWP, a collimating lens CL, a polarizing prism PBS, a semiconductor laser LD (first light source) that emits a 405 nm laser beam (first beam), and a sensor. And a light receiving element PD that receives a reflected light beam from the information recording surface RL1 of the lenses SL and BD and the information recording surface RL2 of the HD. In this drawing, an example having the first optical element and the second optical element is shown as the objective optical element OE, but instead of this objective optical element, a single objective optical as shown in FIG. An element may be used.

  The objective optical element OE is an optical element having the flat plate-like first optical element L1 which is the correction element shown in FIG. 1 and the second optical element L2 of the aspherical lens.

  A case of recording / reproducing BD will be described. First, the divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD is transmitted through the polarizing prism PBS, converted into a parallel light beam by the collimator lens CL, and then linearly generated by the quarter-wave plate QWP. Polarized light is converted into circularly polarized light, its beam diameter is regulated by a diaphragm (not shown), and a spot formed on the information recording surface RL1 of the BD via the protective substrate PL1 having a thickness of 0.0875 mm by the objective optical element OE. Become.

  At this time, the light beam that has passed through the BD area (first optical disk area) BA and the second area (first optical disk area) A2 of the first area A1 of the first optical element L1 is BD by the second optical element. Are condensed on the information recording surface to form a spot, and the light flux that has passed through the HD region (second optical disc region) HA of the first region A1 of the first optical element L1 is condensed on the information recording surface of the BD. Does not form a spot. If a single objective optical element as shown in FIG. 9 is used as the objective optical element, the light beam that has passed through the BD area BA1 and the second area BA2 in the first area is reflected on the information recording surface of the BD. A light beam that has been condensed to form a spot and has passed through the HD area HA does not form a condensed spot on the information recording surface of the BD.

  The reflected light beam modulated by the information pits on the information recording surface RL1 passes through the objective optical element OE and the aperture again, and then is converted from circularly polarized light to linearly polarized light by the quarter wave plate QWP, and converged by the collimating lens CL. After being reflected by the polarizing prism PBS, the light is converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, the information recorded on the BD can be read by using the output signal of the light receiving element PD to focus or track the objective optical element OE by the biaxial actuator AC.

  Next, a case where HD recording / reproduction is performed will be described. First, the divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD is transmitted through the polarizing prism PBS, converted into a parallel light beam by the collimator lens CL, and then linearly generated by the quarter-wave plate QWP. Polarized light is converted into circularly polarized light, its beam diameter is regulated by a diaphragm (not shown), and a spot formed on the information recording surface RL2 of the HD via the protective substrate PL2 having a thickness of 0.6 mm by the objective optical element OE Become.

  At this time, the first light beam that has passed through the HD area HA of the first area A1 of the first optical element L1 is condensed on the information recording surface of the HD by the second optical element to form a spot. The first light flux that has passed through the BD area BA and the second area of the first area A1 of the element does not form a condensed spot on the HD information recording surface. If a single objective optical element as shown in FIG. 9 is used as the objective optical element, the light beam that has passed through the HD area HA is condensed on the information recording surface of the HD to form a spot. The light beam that has passed through the BD area BA1 and the second area BA2 in one area does not form a condensed spot on the HD information recording surface.

  The reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective optical element OE and the aperture, and then converted from circularly polarized light to linearly polarized light by the quarter wave plate QWP, and converged by the collimating lens CL. After being reflected by the polarizing prism PBS, the light is converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, by using the output signal of the light receiving element PD, the objective optical element OE is focused or tracked by the biaxial actuator AC, whereby the information recorded on the HD can be read.

(Example)
Next, examples that can be used in the above-described embodiment will be described. Example 1 is an objective optical element of a single lens. The first embodiment is an example in which the working distance of BD is different from the working distance of HD. Example 1 is an example of three regions. Examples 2 and 3 are examples having a first optical element on the light source side and a second optical element on the optical disk side. In the following embodiments, the first optical disc is BD and the second optical disc is HD. In all the embodiments, the total area A of the first optical disk area is larger than the total area B of the second optical disk area.

In the following tables, ri is the radius of curvature, di is the position in the optical axis direction from the i-th surface to the (i + 1) -th surface, and ni is the refractive index of each surface. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented using E (for example, 2.5 × E−3). In addition, the optical surface of the objective optical element is formed as an aspherical surface that is symmetric about the optical axis and is defined by mathematical formulas obtained by substituting the coefficients shown in Table 1 into Formula 1.

  Here, X (h) is an axis in the optical axis direction (with the light traveling direction being positive), κ is a conical coefficient, Ai is an aspherical coefficient, h is a height from the optical axis, and r is a paraxial radius of curvature. It is.

Example 1
In the first embodiment, the central area including the optical axis is the first optical disk area, and from there, the second optical disk area and the second area are sequentially arranged outward in the direction orthogonal to the optical axis. It is a structure of a three-ring zone in which a region is provided. All the regions have an aspheric shape, and the two first optical disc regions have the same aspheric shape. In addition, the working distance in BD is different from the working distance in HD. FIG. 15 shows the lens shape and the light collection state for each of BD and HD. FIG. 15A shows a condensing state for BD, and FIG. 15B shows a condensing state for HD. In this embodiment, the total area A of the first optical disk region is 0.728π, and the total area B of the second optical disk region is 0.712π, which satisfies A> B.

  Table 1 shows lens data of Example 1.

  In Example 1 in which the working distance when using BD is different from the working distance when using HD, a simulation was performed at an incident angle of 0.5 degree of light flux when using HD, and the value of wavefront aberration was 0.0908 λrms. It has become. Therefore, it can be seen that the difference in the working distance when using BD and the working distance when using HD makes the wavefront aberration value of the obliquely incident light beam small, and the off-axis characteristics are good.

(Example 2)
The second embodiment includes a first optical element that is a correction element and a second optical element that is an aspheric lens. In the correction element, the central area including the optical axis is the second optical disk area (inner second optical disk area), and the first optical disk area (inner first optical disk area) is sequentially formed from the correction element toward the outer side in the direction orthogonal to the optical axis. An optical disk area), a second optical disk area (outer second optical disk area), and a first optical disk area (outer first optical disk area) as a second area. The first optical disk area has an aspherical afocal design for both the inner first optical disk area and the outer first optical disk area, and the second optical disk area has an inner second optical disk area and an outer second optical disk. Both regions have an aspheric shape. Further, the optical surface on the light source side is provided with an inclined surface between the inner first optical disc region and the outer second optical disc region. On the other hand, on the optical surface on the optical disc side, an inclined surface is provided between the inner second optical disc region and the inner first optical disc region.

  Table 2 shows lens data of Example 2. On the optical surface on the light source side of the correction element, the 2-1 surface is the inner second optical disc region, the 2-2 surface is the inner first optical disc region, the 2-3 surface is the inclined surface, and the 4-2 surface is the outer second optical disc region. , 2-5 is the outer first optical disc area. On the other hand, on the optical surface of the correction element on the optical disc side, the 3-1 surface is the inner second optical disc region, the 2-2 surface is the inclined surface, the 3-3 surface is the inner first optical disc region, and the 3-4 surface is the outer second surface. The optical disc area, surface 3-5 is the outer first optical disc area. In this embodiment, the total area A of the first optical disk region is 1.4804π, and the total area B of the second optical disk region is 0.7696π, which satisfies A> B.

(Example 3)
The third embodiment includes a first optical element that is a correction element and a second optical element that is an aspheric lens. In the correction element, the central area including the optical axis is the second optical disk area (inner second optical disk area), and the first optical disk area (inner first optical disk area) is sequentially formed from the correction element toward the outer side in the optical axis orthogonal direction. An optical disk area), a second optical disk area (outer second optical disk area), and a first optical disk area (outer second optical disk area) as a second area. The first optical disk area has an aspherical afocal design for both the inner first optical disk area and the outer first optical disk area, and the second optical disk area has an inner second optical disk area and an outer second optical disk. Both regions have an aspheric shape. Further, an inclined surface is provided on the optical surface on the light source side between the inner first optical disc region and the outer second optical disc region. On the other hand, on the optical surface on the optical disc side, an inclined surface is provided between the inner second optical disc region and the inner first optical disc region. Schematic diagrams of this objective optical element are shown in FIGS. FIG. 16 is a diagram showing a condensing state when a BD is used as the first optical disc, and FIG. 17 is a diagram showing a condensing state when an HD is used as the second optical disc.

  Table 3 shows lens data of Example 3. On the optical surface on the light source side of the correction element, the 2-1 surface is the inner second optical disc region, the 2-2 surface is the inner first optical disc region, the 2-3 surface is the inclined surface, and the 4-2 surface is the outer second optical disc region. , 2-5 is the outer first optical disc area. On the other hand, on the optical surface of the correction element on the optical disc side, the 3-1 surface is the inner second optical disc region, the 2-2 surface is the inclined surface, the 3-3 surface is the inner first optical disc region, and the 3-4 surface is the outer second surface. The optical disc area, surface 3-5, is the outer first optical disc area. In this embodiment, the total area A of the first optical disk region is 1.4227π, and the total area B of the second optical disk region is 0.7696π, which satisfies A> B.

Table 4 summarizes data such as focal lengths of the second and third embodiments.

It is sectional drawing of an example of the objective optical element OE which concerns on this invention. It is a figure which shows schematically the structure of the optical pick-up apparatus which concerns on this invention. FIG. 5A is an aberration diagram when an objective optical element optimized for BD is used. It is an aberration diagram (a)-(b) at the time of using an example of the objective optical element which concerns on this invention. FIG. 6 is aberration diagrams (a) to (b) when another example of the objective optical element according to the present invention is used. FIG. 6 is aberration diagrams (a) to (b) when another example of the objective optical element according to the present invention is used. FIG. 6 is aberration diagrams (a) to (b) when another example of the objective optical element according to the present invention is used. FIG. 6 is aberration diagrams (a) to (b) when another example of the objective optical element according to the present invention is used. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is the schematic at the time of seeing an example of the objective optical element which concerns on this invention from an optical axis direction. It is the schematic at the time of seeing an example of the objective optical element which concerns on this invention from an optical axis direction. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is a part of sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the lens unit which concerns on this invention. It is a schematic perspective view of an example of the lens unit which concerns on this invention. It is a schematic perspective view of an example of the lens unit which concerns on this invention. It is a part of sectional drawing of an example of the lens unit which concerns on this invention.

Explanation of symbols

A1 1st area A2 2nd area L1 1st optical element L2 2nd optical element BA BD exclusive area HA HD exclusive area OA Optical axis CS Correction surface HE Frame body OE Objective optical element S1 1st optical surface S2 2nd optical surface PU1 Optical pickup device LD Blue-violet semiconductor laser AC Biaxial actuator PBS Polarizing prism CL Collimating lens PL1 Protective substrate PL2 Protective substrate RL1 Information recording surface RL2 Information recording surface QWP λ / 4 wavelength plate

Claims (22)

A condensing optical system having a first light source that emits a first light flux having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the first light flux on an information recording surface of an optical disc; ,
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an optical pickup device that records and / or reproduces information by focusing on a surface,
The objective optical element has its optical surface divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
The total area A of the first optical disc region is larger than the total area B of the second optical disc region (A> B), The first optical disc is a BD and the second optical disc is an HD;
The region closest to the center including the optical axis of the objective optical element is the second optical disc region,
2. The optical pickup device according to claim 1, wherein a maximum image-side numerical aperture of the first optical disc area is smaller than 0.85. The first optical disc is a BD and the second optical disc is an HD;
The region closest to the center including the optical axis of the objective optical element is the second optical disc region,
3. The optical pickup device according to claim 1, wherein a maximum effective diameter of the first optical disk area is smaller than 2 · f1 · NA1. However, f1 represents the focal length of the first optical disk area of the objective optical element in the first light flux, and NA1 is 0.85. The first optical disc is a BD and the second optical disc is an HD;
The region closest to the center including the optical axis of the objective optical element is the first optical disc region,
2. The optical pickup device according to claim 1, wherein a maximum image-side numerical aperture of the second optical disc area is smaller than 0.65. The first optical disc is a BD and the second optical disc is an HD;
The region closest to the center including the optical axis of the objective optical element is the first optical disc region,
5. The optical pickup device according to claim 1, wherein a maximum effective diameter of the second optical disc area is smaller than 2 · f 2 · NA 2. Here, f2 represents the focal length of the second optical disk area of the objective optical element in the first light flux, and NA2 is 0.65.   The optical pickup device according to claim 1, wherein the objective optical element is a single lens. The objective optical element has a first optical element and a second optical element,
The optical pickup device according to claim 1, wherein an optical surface of the first optical element is divided into the plurality of concentric regions.   8. The objective optical element according to claim 1, wherein the first optical disk area and the second optical disk area are combined to have a ring-shaped area of 3 to 10 in total. Optical pickup device.   The working distance of the objective optical element during recording and / or reproduction of the first optical disc is different from the working distance of the objective optical element during recording and / or reproduction of the second optical disc. The optical pick-up apparatus in any one of 1-8. The working distance WD1 of the objective optical element at the time of recording and / or reproduction of the first optical disc and the working distance WD2 of the objective optical element at the time of recording and / or reproduction of the second optical disc satisfy the following conditional expressions: The optical pickup device according to claim 9, wherein the optical pickup device is satisfied.
-0.36mm ≤ WD1-WD2 ≤ 0.17mm The working distance WD1 of the objective optical element at the time of recording and / or reproduction of the first optical disc and the working distance WD2 of the objective optical element at the time of recording and / or reproduction of the second optical disc satisfy the following conditional expressions: The optical pickup device according to claim 10, wherein the optical pickup device is satisfied.
| WD1-WD2 | ≧ 0.1mm A condensing optical system having a first light source that emits a first light flux having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the first light flux on an information recording surface of an optical disc; ,
The first light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the first light beam is recorded on the information record of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an objective optical element used in an optical pickup device that records and / or reproduces information by focusing on a surface,
The objective optical element has its optical surface divided into a plurality of concentric regions,
The plurality of areas have at least one first optical disk area and at least one second optical disk area,
The first light flux that has passed through the area for the first optical disc is condensed on the information recording surface of the first optical disc, not condensed on the information recording surface of the second optical disc,
The first light flux that has passed through the area for the second optical disc is condensed on the information recording surface of the second optical disc, not condensed on the information recording surface of the first optical disc,
The objective optical element, wherein a total area A of the first optical disk region is larger than a total area B of the second optical disk region (A> B). The first optical disc is a BD and the second optical disc is an HD;
The region closest to the center including the optical axis of the objective optical element is the second optical disc region,
The objective optical element according to claim 12, wherein a maximum image-side numerical aperture of the first optical disk area is smaller than 0.85. The first optical disc is a BD and the second optical disc is an HD;
The region closest to the center including the optical axis of the objective optical element is the second optical disc region,
14. The objective optical element according to claim 12, wherein a maximum effective diameter of the first optical disk area is smaller than 2 · f 1 · NA 1. However, f1 represents the focal length of the first optical disk area of the objective optical element in the first light flux, and NA1 is 0.85. The first optical disc is a BD, the second optical disc is an HD,
The region closest to the center including the optical axis of the objective optical element is the first optical disc region,
The objective optical element according to claim 12, wherein a maximum image-side numerical aperture of the second optical disc area is smaller than 0.65. The first optical disc is a BD and the second optical disc is an HD;
The region closest to the center including the optical axis of the objective optical element is the first optical disc region,
The objective optical element according to claim 15, wherein a maximum effective diameter of the second optical disc area is smaller than 2 · f 2 · NA 2. Here, f2 represents the focal length of the second optical disk area of the objective optical element in the first light flux, and NA2 is 0.65.   The objective optical element according to claim 12, wherein the objective optical element is a single lens. The objective optical element has a first optical element and a second optical element,
The objective optical element according to claim 12, wherein an optical surface of the first optical element is divided into the plurality of concentric regions.   19. The objective optical element according to claim 12, wherein the first optical disk area and the second optical disk area together have a ring-shaped area of 3 to 10 in total. Objective optical element.   The working distance of the objective optical element during recording and / or reproduction of the first optical disc is different from the working distance of the objective optical element during recording and / or reproduction of the second optical disc. The objective optical element in any one of 12-19. The working distance WD1 of the objective optical element at the time of recording and / or reproduction of the first optical disc and the working distance WD2 of the objective optical element at the time of recording and / or reproduction of the second optical disc satisfy the following conditional expressions: The objective optical element according to claim 20, wherein the objective optical element is satisfied.
-0.36mm ≤ WD1-WD2 ≤ 0.17mm The working distance WD1 of the objective optical element at the time of recording and / or reproduction of the first optical disc and the working distance WD2 of the objective optical element at the time of recording and / or reproduction of the second optical disc satisfy the following conditional expressions: The objective optical element according to claim 21, wherein the objective optical element is satisfied.
| WD1-WD2 | ≧ 0.1mm