JP2008065936A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To satisfactorily record or reproduce a plurality of optical recording media. <P>SOLUTION: When first to third optical recording media 1-3 are selectively recorded or reproduced, a first laser beam L1 having a wavelength λ1 of about 405 nm is condensed like a spot on the first optical recording medium (BD) 1 by a first objective lens 23. When the first laser beam L1 is condensed like the spot on the second optical recording medium (HD-DVD) 2 by a second objective lens 28, a first collimator lens 14 movably provided on an optical axis OA of the first laser beam L1 is moved by a prescribed amount along the optical axis OA of the first laser beam L1 according to respective substrate thicknesses of the first and second optical recording media 1, 2 to correct spherical aberration for the first and second optical recording media 1, 2. Further, a second laser beam L2 having a wavelength λ2 about 660 nm is condensed like a spot on the third optical recording medium (DVD) 3 by the second objective lens 28. Thus, the optical pickup device satisfactorily recording or reproducing the first to third optical recording media 1-3 is constituted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is an optical pickup device that records or reproduces a plurality of types of optical recording media, and includes a first collimator lens that is movably installed on the optical axis of a first laser beam having a wavelength λ1 of about 405 nm. The present invention relates to an optical pickup device capable of appropriately correcting spherical aberration with respect to the first and second optical recording media by moving each of the second optical recording media by a predetermined amount according to the thickness of each substrate.

  In general, an optical recording medium such as a disk-shaped optical disk or a card-shaped optical card has a high density on a track in which information signals such as video information, audio information, and computer data are spirally or concentrically formed on a transparent substrate. When a recorded track is recorded and a recorded track is reproduced, a desired track can be accessed at high speed.

  For example, CDs (Compact Discs) and DVDs (Digital Versatile Discs) have already been put on the market as optical discs to be used in this type of optical recording media. Recently, two types of high-density optical recording media with higher density have been distributed. is doing.

  That is, the two types of high-density optical recording media are BD (Blu-ray Disc) and HD-DVD (High Definition DVD).

  First, the above-described CD is irradiated with a laser beam obtained by narrowing a laser beam having a wavelength of about 785 nm with an objective lens having a numerical aperture (NA) of about 0.45 to 0.5, and 1 from the laser beam incident surface. An information signal is recorded on a recording layer (signal surface) located 2 mm apart, and the recorded information signal is reproduced.

  Further, the above-described DVD is irradiated with a laser beam obtained by narrowing a laser beam having a wavelength of about 660 nm with an objective lens having a numerical aperture (NA) of about 0.6 to 0.65, and the laser beam enters from the laser beam incident surface. An information signal is recorded on a recording layer (signal surface) located at a position 6 mm apart, and the recorded information signal is reproduced. At this time, the recording capacity of the DVD is 6 to 8 times higher than that of the CD, and when the diameter of the disk substrate is 12 cm, it is about 4.7 GB (gigabyte) on one side.

  The above BD was irradiated with a laser beam obtained by narrowing a laser beam having a wavelength of about 405 nm with an objective lens having a numerical aperture (NA) of about 0.85, and was separated from the laser beam incident surface by 0.1 mm. An information signal is recorded on the recording layer (signal surface) at the position, and the recorded information signal is reproduced. At this time, the recording capacity of the BD is about 25 GB (gigabytes) on one side when the disc substrate has a diameter of 12 cm and is 5 times higher than the DVD.

  Further, the above-mentioned HD-DVD is irradiated with a laser beam obtained by narrowing a laser beam having a wavelength of about 405 nm with an objective lens having a numerical aperture (NA) of about 0.65, and 0.6 mm from the laser beam incident surface. An information signal is recorded on a recording layer (signal surface) at a separated position, and the recorded information signal is reproduced. At this time, the recording capacity of the HD-DVD is three times higher than that of the DVD, and is about 15 GB (gigabytes) on one side when the diameter of the disk substrate is 12 cm.

  The recording capacities of the above-mentioned CD, DVD, BD, and HD-DVD are when the recording layer is a single layer, and the substrate thickness is also a single layer.

  On the other hand, the above-described Blu-ray Disc, HD-DVD, and DVD include a two-layer optical disc in which two recording layers are laminated, which will be described in detail later.

  In order to make it possible to utilize the BD and HD-DVDs according to the two standards as high-density optical recording media and to make use of the DVD or CD assets that are already on the market, BD and HD- It is desired to record or reproduce three types of optical recording media including DVD and DVD, or four types of optical recording media including BD, HD-DVD, DVD, and CD with one optical pickup device.

By the way, four types of optical recording media (BD, HD-DVD, DVD, CD) having different recording densities are recorded or reproduced by one optical pickup device, and BD and HD-DVD are recorded or corrected by correcting spherical aberration. There is an optical pickup device for reproduction (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2005-353261 (FIG. 5)

  FIG. 17 shows an example of a conventional optical pickup device.

  The conventional optical pickup device 100 shown in FIG. 17 is disclosed in the above-mentioned Patent Document 1 (Japanese Patent Laid-Open No. 2005-353261), and will be briefly described here with reference to Patent Document 1.

  As shown in FIG. 17, in the conventional optical pickup apparatus 100, the protective substrate thickness is 0.085 to 0.1 mm, the first optical disk having a large recording density ρ1, and the protective substrate thickness is 0.55. HD-DVD2 which is a second optical disk having a recording density ρ2 smaller than the above-mentioned recording density ρ1 at 0.65 mm and a recording density ρ3 smaller than the above-mentioned recording density ρ2 with a protective substrate thickness of 0.55 to 0.65 mm. 4 types of optical discs including DVD 3 to be 3 optical discs and CD4 to be a fourth optical disc having a protective substrate thickness of 1.2 mm and a recording density ρ 4 smaller than the recording density ρ 3 can be selectively recorded or reproduced. Has been.

  In this conventional optical pickup apparatus 100, a first laser light source 101 that emits a first laser beam L1 having a wavelength λ1 of about 400 nm to 420 nm for BD or HD-DVD, and a wavelength λ2 of 640 nm for DVD is used. The second laser light source 102 that emits the second laser light L2 of about 670 nm is mounted on the same substrate and is provided as a single unit with a so-called two laser 1 package 2L1P, and for CD use A third laser light source 103 that emits third laser light L3 having a wavelength λ3 of about 750 nm to 820 nm is provided.

  First, the case where BD1 or HD-DVD2 is selectively recorded or reproduced will be described.

  As described above, the light beam of the first laser light L1 emitted from the first laser light source 101 (wavelength 400 nm to 420 nm) is shared by the BD1 and the HD-DVD2. The light beam of the first laser light L1 emitted from the first laser light source 101 is corrected in beam shape by the beam shaper 104, passes through the dichroic prism 105 as a wavelength selection element, and is converted into a parallel light beam by the collimator 106. Then, the light passes through the polarization beam splitter 107 and enters a beam expander 108 having two optical elements 108A and 108B.

  At this time, the beam expander 108 in which at least one of the two optical elements 108A and 108B can move in the direction of the optical axis OA has a function of correcting the spherical aberration by changing the beam diameter of the parallel beam. In particular, a diffractive structure (diffraction ring zone) is formed on the optical surface of the optical element 108B in the beam expander 108, so that the chromatic aberration of the light flux of the first laser light L1 emitted from the first laser light source 101 is obtained. Correction is made.

  Further, the light beam of the first laser light L1 that has passed through the beam expander 108 passes through the quarter-wave plate 109 and the diaphragm 110.

  Here, when recording or reproducing BD1, the light beam of the first laser beam L1 that has passed through the diaphragm 110 is incident on the first objective lens 111 having a numerical aperture (NA) of 0.85, and the first laser beam is recorded. L1 is condensed in a spot shape on the information recording surface of BD1. On the other hand, when recording or reproducing the HD-DVD 2, the light beam of the first laser beam L1 that has passed through the diaphragm 110 is incident on the second objective lens 112 having a numerical aperture (NA) of 0.65 to 0.67. The first laser beam L1 is condensed in a spot shape on the information recording surface of the HD-DVD 2.

  At this time, the first objective lens 111 with NA of 0.85 and the second objective lens 112 with NA of 0.65 to 0.67 are rotated by rotating a lens holder (not shown) in the objective lens actuator mechanism 113. , Can selectively enter the optical path of the optical axis OA.

  Thereafter, the light flux of the first laser light L1 modulated and reflected by the information pits on each information recording surface of the BD1 or HD-DVD2 is again the first objective lens 111 or the second objective lens 112, the aperture 110, 1 / The light passes through the four-wave plate 109 and the beam expander 108 in order, is reflected by the polarization beam splitter 107, is given astigmatism by the cylindrical lens 114, passes through the sensor lens 115, and enters the light receiving surface of the photodetector 116. Therefore, the read signal of each information recorded on each information recording surface of BD1 or HD-DVD2 is obtained using the output signal.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 116. Based on this detection, a focusing actuator (not shown) and a tracking actuator (not shown) of the objective lens actuator mechanism 113 record the light beam of the first laser light L1 from the first laser light source 101 on the BD1 or HD-DVD 102. The first objective lens 111 or the second objective lens 112 is moved in the focus direction and the tracking direction so as to form an image on the surface.

  Next, the case where the DVD 3 is recorded or reproduced will be described. The light beam of the second laser light L2 emitted from the second laser light source 102 (wavelength 640 nm to 670 nm) is a beam as in the case of the first laser light L1. The beam shape is corrected by the shaper 104, passes through the dichroic prism 105, is converted into a parallel light beam by the collimator 106, passes through the polarization beam splitter 107, and enters the beam expander 108 having two optical elements 108 </ b> A and 108 </ b> B. . The light beam of the second laser light L2 that has passed through the beam expander 108 passes through the quarter-wave plate 109 and the diaphragm 110, and the second objective lens 112 having a numerical aperture (NA) of 0.65 to 0.67. Thus, the second laser beam L2 is focused in a spot shape on the information recording surface of the DVD 3.

  Thereafter, the light beam of the second laser light L2 modulated and reflected by the information pits on the information recording surface of the DVD 3 passes through the second objective lens 112, the diaphragm 110, the quarter wavelength plate 109, and the beam expander 108 again. Then, the light is reflected by the polarization beam splitter 107, given astigmatism by the cylindrical lens 114, passes through the sensor lens 115, and enters the light receiving surface of the photodetector 116. Therefore, the output signal of the DVD 3 is used. A read signal of information recorded on the information recording surface is obtained. Focus detection, track detection, and the method and operation of the objective lens actuator mechanism 113 based on this detection are the same as in the case of the above-described BD1 or HD-DVD2.

  Next, a case where CD4 is recorded or reproduced will be described. The light beam of the third laser light L3 emitted from the third laser light source 103 (wavelength = 750 nm to 820 nm) is reflected by the dichroic prism 105 and parallel by the collimator 106. It becomes a light beam, passes through the polarization beam splitter 107, and enters a beam expander 108 having two optical elements 108A and 108B. Then, the light beam that has passed through the beam expander 108 passes through the quarter-wave plate 109 and the diaphragm 110, and the second objective lens 112 condenses the third laser light L3 in a spot shape on the information recording surface of the CD4. I am letting.

  Thereafter, the light beam of the third laser light L3 modulated and reflected by the information pits on the information recording surface of the CD 4 passes through the second objective lens 112, the diaphragm 110, the quarter wavelength plate 109, and the beam expander 108. Then, it is reflected by the polarization beam splitter 107, given astigmatism by the cylindrical lens 114, passes through the sensor lens 115, and enters the light receiving surface of the photodetector 116. A read signal of information recorded on the recording surface is obtained. Focus detection, track detection, and the method and operation of the objective lens actuator mechanism 113 based on this detection are the same as in the case of the above-described BD1, HD-DVD2, or DVD3.

  By the way, according to the conventional optical pickup apparatus 100, the configuration is based on two lasers or three lasers, and the output of laser light is low for both two wavelengths or three wavelengths. Therefore, the BD1, HD-DVD2, DVD3, and CD4 are not all configured to be compatible with high speed.

  Further, according to the conventional optical pickup device 100, the BD1 or HD-DVD2 uses the same objective lens because the substrate thickness and the numerical aperture of the objective lens are different, although the wavelength used for the laser light is the same. It is extremely difficult to record or reproduce, and the two first and second objective lenses 111 and 112 are selectively used.

  At this time, it is most desirable to use the first objective lens 111 for BD1 and the second objective lens 112 for HD-DVD2, DVD3, or HD-DVD2, DVD3, CD4.

  Since the first objective lens 111 for BD requires a numerical aperture (NA) of 0.85, it needs to be made of a material having a high refractive index and high accuracy, and currently needs to be made of glass. In the case of glass, a diffractive surface cannot be formed. If BD1, HD-DVD2, DVD3, and CD4 are used as one objective lens, a diffractive element is required in combination with the glass lens, which increases the number of parts. is there. Furthermore, it is a glass having a high refractive index, and the chromatic aberration is large.

  On the other hand, the second objective lens 112 has a numerical aperture (NA) of 0.65 for the HD-DVD 2 and is almost equal to that of the DVD 3, so that resin molding is possible. Therefore, in the second objective lens 112, it is possible to correct the chromatic aberration by aligning the refracting surface with the diffractive surface, so that chromatic aberration can be corrected. However, due to the restrictions on the degree of freedom and the order used, It is difficult to correct chromatic aberration for three types of CD4 optical discs. Therefore, even if the collimator 106 configured by the conventional optical pickup device 100 and the expander lens 108 with the diffractive surface are shared by all three wavelengths, the chromatic aberration is corrected in any of the optical discs of HD-DVD2, DVD3, and CD4. If this is done, the chromatic aberration will worsen in other optical disks.

  Further, according to the conventional optical pickup device 100, since the plurality of lenses 108A and 108B are used for the expander lens 108, the aberration due to the eccentricity of the plurality of lenses and the shift of the optical axis caused by the movement of the expander lens 108. Since the diffractive surface is formed on the collimator 106 and the expander lens 108, there is a concern about the deterioration of the aberration during the optical axis shift (lens shift) of the first and second objective lenses 111 and 112. In addition, the lens shift characteristic, which is an important characteristic, is not taken into consideration, and the assembly of the optical pickup device 100 is extremely strict, the number of lenses is large, and the size of the optical pickup device 100 is large.

  Therefore, light that can be recorded or reproduced satisfactorily on three types of optical recording media including BD1, HD-DVD2, and DVD3, or on four types of optical recording media including BD1, HD-DVD2, DVD3, and CD4. A pickup device is desired.

The present invention has been made in view of the above problems, and the invention of claim 1 is an optical pickup for selectively recording or reproducing a plurality of optical recording media.
In order to selectively record or reproduce a first optical recording medium having a first substrate thickness and a second optical recording medium having a second substrate thickness larger than the first substrate thickness, the first optical recording medium having a wavelength λ1 is used. A first laser light source that emits one laser beam;
A second laser light source that emits a second laser beam having a wavelength λ2 longer than the wavelength λ1 in order to selectively record or reproduce a third optical recording medium having a substrate thickness substantially equal to the second substrate thickness. When,
A first separation optical element that separates the first laser light emitted from the first laser light source and each return light reflected by the first and second optical recording media;
A first collimator lens provided so as to be movable along the optical axis of the first laser beam that has passed through the first separation optical element, and correcting spherical aberration with respect to the first and second optical recording media; ,
A second separation optical element for separating the second laser light emitted from the second laser light source and the return light reflected from the third recording medium by the second laser light;
A second collimator lens fixedly installed along the optical axis of the second laser beam that has passed through the second separation optical element;
The first laser beam that has passed through the first collimator lens and the second laser beam that has passed through the second collimator lens are installed on an optical axis that intersects, and the first laser beam and the second laser beam, An optical member for branching the optical path;
A first objective lens that narrows down the first laser light that has passed through the optical path branching optical member and focuses the first laser light on the first optical recording medium in a spot shape;
The first laser light that has passed through the optical path branching optical member is narrowed down to focus the first laser light in a spot shape on the second optical recording medium, and the first laser light that has passed through the optical path branching optical member A second objective lens for focusing two laser beams and condensing the second laser beams in a spot shape on the third optical recording medium;
An optical pickup device comprising: an objective lens switching mechanism that selectively causes the first objective lens and the second objective lens to enter the optical path according to the first to third recording media. .

The invention according to claim 2 is an optical pickup for selectively recording or reproducing a plurality of optical recording media.
In order to selectively record or reproduce a first optical recording medium having a first substrate thickness and a second optical recording medium having a second substrate thickness larger than the first substrate thickness, the first optical recording medium having a wavelength λ1 is used. A first laser light source that emits one laser beam;
A second laser light source that emits a second laser beam having a wavelength λ2 longer than the wavelength λ1 in order to selectively record or reproduce a third optical recording medium having a substrate thickness substantially equal to the second substrate thickness. When,
A third laser that emits a third laser beam having a wavelength λ3 longer than the wavelength λ2 in order to selectively record or reproduce a fourth optical recording medium having a third substrate thickness greater than the second substrate thickness; A light source;
A first separation optical element that separates the first laser light emitted from the first laser light source and each return light reflected by the first and second optical recording media;
A first collimator lens provided so as to be movable along the optical axis of the first laser beam that has passed through the first separation optical element, and correcting spherical aberration with respect to the first and second optical recording media; ,
A second separation optical element that separates the second laser light emitted from the second laser light source and the return light reflected from the three recording media by the second laser light;
The second laser beam passing through the second separation optical element and the third laser beam emitted from the third laser light source are installed on an optical axis where the second laser beam and the third laser beam intersect. A first optical path branching optical member that branches light;
A second collimator lens fixedly installed along the optical axes of the second and third laser beams that have passed through the first optical path branching optical member;
The first laser beam that has passed through the first collimator lens and the second and third laser beams that have passed through the second collimator lens are disposed on an optical axis that intersects, and the first laser beam and the second laser beam , A second optical path branching optical member for branching the third laser light,
A first objective lens for focusing the first laser beam in a spot shape on the first optical recording medium by narrowing down the first laser beam that has passed through the second optical path branching optical member;
The first laser light that has passed through the second optical path branching optical member is narrowed down to focus the first laser light on the second optical recording medium, and the second optical path branching optical member The second laser beam that has passed through the aperture is narrowed down to focus the second laser beam on the third optical recording medium in a spot shape, and the third laser beam that has passed through the second optical path branching optical member is A second objective lens for focusing and condensing the third laser light in a spot shape on the fourth optical recording medium;
An optical pickup device comprising: an objective lens switching mechanism that selectively causes the first objective lens and the second objective lens to enter the optical path according to the first to fourth optical recording media. is there.

According to a third aspect of the present invention, in the optical pickup device according to the first or second aspect,
The first collimator lens is formed by bonding a positive lens and a negative lens, and when the wavelength of the first laser light is shifted in a long direction, axial chromatic aberration is shifted in a negative direction, while the first collimator lens is When the wavelength of the laser beam is shifted in a short direction, the axial chromatic aberration is shifted in a positive direction.

Furthermore, the invention according to claim 4 is the optical pickup device according to claim 2,
The second objective lens has a finite conjugate with respect to a case where the second optical recording medium is recorded or reproduced with the first laser light and a case where the fourth optical recording medium is recorded or reproduced with the third laser light. And is optimally designed with a substantially infinite conjugate to the second laser light,
The object distance of the second objective lens relative to the second optical recording medium is X (mm),
The object distance of the second objective lens relative to the fourth optical recording medium is X ′ (mm),
The focal length of the first collimator lens is fc (mm),
The focal length of the second objective lens with respect to the first laser light is f ₂ (mm),
3. The light according to claim 2, wherein when the distance from the first collimator lens to the first surface of the second objective lens is Y (mm), the following expression is satisfied. It is a pickup device.

  According to the optical pickup device of the first aspect, when selectively recording or reproducing the three types of the first to third optical recording media, the first laser beam having the wavelength λ1 of about 405 nm is first reflected by the first objective lens. When the first laser beam is condensed in a spot shape on the optical recording medium (BD), and the first laser beam is condensed in the spot shape on the second optical recording medium (HD-DVD) by the second objective lens, the first laser is used. A first collimator lens movably provided on the optical axis of the light is moved by a predetermined amount along the optical axis of the first laser light in accordance with the thickness of each substrate of the first and second optical recording media. First, spherical aberration is corrected for the second optical recording medium, and the second laser light having a wavelength λ2 of about 660 nm is condensed in a spot shape on the third optical recording medium (DVD) by the second objective lens. 3 types of first to third optical recording media Can be recorded or reproduced satisfactorily.

  According to the optical pickup device of the second aspect, when the first to fourth optical recording media are selectively recorded or reproduced, the first laser light having the wavelength λ1 of about 405 nm is transmitted by the first objective lens to the first light. When the first laser beam is condensed in a spot shape on the recording medium (BD) and the first laser beam is condensed in a spot shape on the second optical recording medium (HD-DVD) by the second objective lens, the first laser beam is collected. The first collimator lens movably provided on the optical axis of the first and second optical recording media is moved by a predetermined amount along the optical axis of the first laser light in accordance with the thickness of each substrate of the first and second optical recording media. , Correcting the spherical aberration with respect to the second optical recording medium, and condensing the second laser light having a wavelength λ2 of around 660 nm on the third optical recording medium (DVD) by the second objective lens, Further, the design wavelength λ3 is about 785 nm. The laser light that is focused into a spot shape by the second objective lens on the fourth optical recording medium (CD), can be favorably recorded or reproduced four of the first to fourth optical recording medium.

  According to the optical pickup device of the third aspect, the first collimator lens is formed by bonding a positive lens and a negative lens, and the axial chromatic aberration is negative when the wavelength of the first laser light is shifted in the long direction. On the other hand, when the wavelength of the first laser beam is shifted in the shorter direction, the axial chromatic aberration is shifted in the positive direction. Therefore, the first optical recording medium (BD) and the second optical recording medium (HD−) On-axis chromatic aberration can be satisfactorily corrected for DVD).

Furthermore, according to the optical pickup device of claim 4, the spherical aberration is corrected by the movement of the first collimator lens with respect to the second optical recording medium (HD-DVD), and the second optical recording medium (HD-DVD) is corrected. ), The third optical recording medium (DVD), and the fourth optical recording medium (CD) are selectively recorded or reproduced by the second objective lens, the object distance X (mm) of the second objective lens relative to the second optical recording medium. ), The object distance X ′ (mm) of the second objective lens relative to the fourth optical recording medium, the focal length fc (mm) of the first collimator lens, and the focal distance f _{2 of} the second objective lens relative to the first laser light. (Mm) and the distance Y (mm) from the first collimator lens to the first surface of the second objective lens, the three types of first 2 to 4 optical recording The body can be favorably recorded or reproduced.

  Hereinafter, an embodiment of an optical pickup device according to the present invention will be described in detail with reference to FIGS.

FIGS. 1A to 1D are diagrams schematically illustrating BD, HD-DVD, DVD, and CD as first to fourth optical recording media applied to an optical pickup device according to the present invention. ,
FIG. 2 is a diagram showing an overall configuration of an optical pickup device according to the present invention.
FIG. 3 shows the positional relationship of the first collimator lens when the first collimator lens is movably provided in the optical axis direction between the polarization beam splitter and the first dichroic prism in the optical pickup device according to the present invention. Figure,
4 (a) to 4 (c) are diagrams showing the state of the light flux depending on the position of the first collimator lens in the optical pickup device according to the present invention.
FIGS. 5A and 5B are diagrams showing longitudinal aberrations and sine conditions when a BD is recorded or reproduced using the first objective lens in the optical pickup device according to the present invention.
FIGS. 6A and 6B are diagrams showing longitudinal aberrations and sine conditions when an HD-DVD is recorded or reproduced using the second objective lens in the optical pickup device according to the present invention.
FIG. 7 is a view showing longitudinal aberration when a DVD is recorded or reproduced using the second objective lens in the optical pickup device according to the present invention;
FIG. 8 is a view showing longitudinal aberration when a CD is recorded or reproduced using the second objective lens in the optical pickup device according to the present invention.

  Before explaining the optical pickup device 10 according to the present invention shown in FIG. 2, four types of first to fourth optical recording media 1 to 4 selectively recorded or reproduced by the optical pickup device 10 will be described with reference to FIG. It demonstrates previously using (a)-(d).

  In the following FIGS. 1A to 1D, the case where each recording layer is a single layer and the case where the recording layers are two layers are separately provided for the four types of first to fourth optical recording media 1 to 4. They are shown together for convenience of illustration.

  First, the first optical recording medium 1 shown in FIG. 1A is one type of high-density optical recording medium called Blu-ray Disc (BD), and has a single recording layer 1r. And two first and second recording layers 1a and 1b. Here, the track pitch of each recording layer is set to 0.32 μm. The first optical recording medium (hereinafter referred to as BD) 1 can be recorded or reproduced by a laser beam obtained by focusing laser light having a wavelength of about 405 nm with an objective lens having a numerical aperture (NA) of about 0.85. Is to be done.

This BD1, when a single layer, when the substrate thickness 1t ₂ from the laser beam incident surface 1i is there is a single layer of the recording layer 1r located away 0.1 mm, also the two layers, the Since the interlayer distance between the first and second recording layers 1a and 1b is set to 25 μm, the design reference substrate thickness 1t ₀ from the laser beam incident surface 1i is a position of ± 12.5 μm centered on the position of 0.0875 mm. That is, the first recording layer 1a is at a position where the substrate thickness 1t ₁ is 0.075 mm from the laser beam incident surface 1i, and the second recording is performed at a position where the substrate thickness 1t ₂ is 0.1 mm from the laser beam incident surface 1i. The second recording layer 1b is located at the same position as the single-layer recording layer 1r, and includes the first at a position of 0.07 mm at the minimum and 0.105 mm at the maximum when the interlayer distance error range ± 5 μm is included. The second recording layers 1a and 1b are Get.

At this time, the design reference substrate thickness 1t ₀ of BD1 is the virtual design values, although the design criterion substrate optical disk having a thickness 1t ₀ is not present, the design reference substrate thickness 1t ₀ of BD1 at 0.0875mm When the recording layer 1r or the first and second recording layers 1a and 1b are recorded or reproduced using the optimized NA = 0.85 objective lens, spherical aberration of 100 mλ or more is generated. This is higher than the Marechal criterion and cannot be recorded or reproduced. Therefore, correction of spherical aberration is essential for BD1.

  Next, the second optical recording medium 2 shown in FIG. 1 (b) is a kind of high-density optical recording medium called High Definition Digital Versatile Disc (HD-DVD), and is a single-layer recording layer. There are those having 2r and those having two first and second recording layers 2a and 2b, and the track pitch of each recording layer is set to 0.40 μm. Unlike the BD1, the second optical recording medium (hereinafter referred to as HD-DVD) 2 has a numerical aperture (NA) of about 0.65, unlike the BD1. Recording or reproduction is performed by a laser beam obtained by squeezing with an objective lens.

When this HD-DVD 2 is a single layer, there is a single-layer recording layer 2r at a position where the design reference substrate thickness 2t ₀ is 0.6 mm away from the laser beam incident surface 2i, and there are two layers. Since the interlayer distance between the first and second recording layers 2a and 2b is set to 20 μm, ± 10 μm centered on the position where the design reference substrate thickness 2t ₀ is 0.6 mm from the laser beam incident surface 2i. position, i.e., the laser beam incident surface substrate from 2i thickness 2t ₁ is there is a first recording layer 2a in the position of 0.59 mm, the from the laser beam incident surface 2i on the position of the substrate thickness 2t ₂ is 0.61mm There are two recording layers 2b, and the first and second recording layers 1a and 1b can be at a position of 0.587 mm at the minimum and 0.613 mm at the maximum when the interlayer distance error range ± 3 μm is included.

  At this time, the recording layer 2r or the first and second recording layers 2a and 2b are respectively recorded using an objective lens with NA = 0.65 optimized with a design standard substrate thickness of HD-DVD 2 of 0.6 mm. When reproduced, spherical aberration of about 50 mλ occurs. This is not a level at which recording or reproduction is not possible, but it is desirable to correct the spherical aberration for the HD-DVD 2 in consideration of the margin.

  Next, the third optical recording medium 3 shown in FIG. 1 (c) is called a digital versatile disc (DVD), and has a single recording layer 3r and a two-layer first recording medium 3r. , Second recording layers 3a and 3b, and the track pitch of each recording layer is set to 0.74 μm. Unlike the BD1 and HD-DVD2, the third optical recording medium (hereinafter referred to as DVD) 3 focuses laser light having a wavelength of around 660 nm with an objective lens having a numerical aperture (NA) of about 0.65. Recording or reproduction is performed by the laser beam obtained in this way.

When this DVD 3 is a single layer, there is a single recording layer 3r at a position where the design reference substrate thickness 3t ₀ is 0.6 mm away from the laser beam incident surface 3i. Since the interlayer distance between the first and second recording layers 3a and 3b is set to 55 μm, ± 27.5 μm centered on the position where the design reference substrate thickness 3t ₀ is 0.6 mm from the laser beam incident surface 3i. position, i.e., the laser beam incident surface substrate from 3i thickness 3t ₁ is there is a first recording layer 3a to the position of 0.5725Mm, the position the laser beam incident surface substrate from 3i thickness 3t ₂ is placed apart 0.6275mm There is a second recording layer 3b. At this time, the recording layer 3r or the first and second recording layers 3a and 3b were recorded or reproduced using an objective lens with NA = 0.65 optimized with a design standard substrate thickness of DVD3 of 0.6 mm. ing.

  Next, the fourth optical recording medium 4 shown in FIG. 1D is called Compact Disc (CD), and the track pitch of the recording layer is set to 1.6 μm. This fourth optical recording medium (hereinafter referred to as CD) 4 is different from the BD1, HD-DVD2, and DVD3 in that the laser beam having a wavelength of about 785 nm is a numerical aperture (NA) of about 0.45 to 0.5. Recording or reproduction is performed by a laser beam obtained by focusing with the objective lens.

This CD 4 is a single layer, and the recording layer 4r is located at a position where the design reference substrate thickness 4t ₀ is 1.2 mm away from the laser beam incident surface 4i.

  The above-mentioned BD1, HD-DVD2, DVD3, and CD4 are formed in a disc shape with a total thickness of about 1.2 mm by bonding the substrate thickness up to each recording layer (signal surface) and a reinforcing plate. .

  Next, as shown in FIG. 2, the optical pickup device 10 according to the present invention includes an optical system for recording or reproducing BD1, an optical system for recording or reproducing HD-DVD2, and an optical system for recording or reproducing DVD3. And an optical system for recording or reproducing CD4, and in particular, a first collimator lens 14 to be described later for BD1 or HD-DVD2 recorded or reproduced using a laser beam having a wavelength of around 405 nm. The spherical aberration is corrected by moving the lens.

  At this time, the optical pickup device 10 is movable in the radial direction of each of the optical recording media 1 to 4 rotatably supported by a spindle motor (not shown).

  In the following embodiments, the case of recording or reproducing four types of BD1, HD-DVD2, DVD3, and CD4 will be described. However, the present invention is not limited to this, and three types of combinations of BD1, HD-DVD2, and DVD3 are also possible. Is possible.

  At this time, the optical system for BD and the optical system for HD-DVD have the same wavelength of the laser beam used as described above, but the objective lens has a different numerical aperture (NA). The optical system is shared until before.

  First, the BD optical system and the HD-DVD optical system will be described. The first laser light source 11 for BD and HD-DVD uses the first laser light L1 having a wavelength λ1 of about 405 nm as the first laser light L1. The light is emitted toward the grating 12 side.

  The first grating 12 described above uses a first laser beam L1 emitted from the first laser light source 11 as a pair with a main beam in order to detect a track position when selectively recording or reproducing BD1 and HD-DVD2. It has a function of branching into three beams consisting of sub-beams, and emits the three beams branched from the first laser light L1 toward the first separation optical element (hereinafter referred to as polarization beam splitter) 13 side.

  The polarization beam splitter 13 includes a polarization-selective transflective / reflective dielectric multilayer film 13a inside, and the first laser light source 11 emitted from the first laser light source 11 by the polarization-selective transflective / reflective dielectric multilayer film 13a. The laser beam L1 transmits the forward p-polarized light and reflects the return s-polarized light reflected by the BD1 or HD-DVD2, as will be described later, and is a polarization-selective transflective / reflective dielectric multilayer. Three beams of the first laser light L1 that has passed through the film 13a are emitted toward the first collimator lens 14 side.

  The first collimator lens 14 includes a collimator lens moving mechanism (not shown) such as a stepping motor or an ultrasonic motor, and is provided so as to be movable along the optical axis OA of the first laser light L1. -Depending on the thickness of each substrate of the DVD 2 and the wavelength of the first laser beam L1, the recording layer 1r or the first recording layer 1a or the second recording layer 1b of the BD 1 and the recording layer 2r or the first recording layer of the HD-DVD 2 It moves so as to optimize the spherical aberration with respect to the layer 2a or the second recording layer 2b, and the three beams of the first laser light L1 that has passed through the first collimator lens 14 are directed toward the first dichroic prism 15 side. The details of the movement of the first collimator lens 14 will be described later.

  The first dichroic prism 15 includes a wavelength-selective transflective / reflective dielectric multilayer film 15a therein, and the first laser beam having a wavelength λ1 of about 405 nm is provided by the wavelength-selective transflective / reflective dielectric multilayer film 15a. While transmitting L1, the second laser beam L2 having a wavelength λ2 of about 660 nm for DVD described later and the third laser beam L3 having a wavelength λ3 of about 785 nm for CD are reflected, and therefore the first laser beam L1 is reflected. And the second and third laser beams L2 and L3. The first dichroic prism 15 has the first laser beam L1 and the second and third laser beams L2 and L3. It is installed on the intersecting optical axis OA.

  Then, the first laser light L1 transmitted through the first dichroic prism 15, the second laser light L2 reflected by the first dichroic prism 15, or the third laser light L3 reflected by the first dichroic prism 15 is used. The light is emitted toward the rising mirror 16 side.

  The rising mirror 16 reflects both the first laser beam L1, the second laser beam L2, and the third laser beam L3, and bends the direction of each light beam by approximately 90 ° to the upper quarter wavelength plate 17 side. Guided.

  The quarter-wave plate 17 described above gives a phase difference of (λ1) / 4 to the first laser beam L1 having the wavelength λ1, and (λ2) / 4 to the second laser beam L2 having the wavelength λ2. And a phase difference of (λ3) / 4 with respect to the third laser beam L3 having the wavelength λ3, and the first to third laser beams L1 having passed through the quarter wavelength plate 17 ... L3 is selectively incident on the first objective lens assembly 20 or the second objective lens assembly 25 described below according to BD1, HD-DVD2, DVD3, and CD4.

  Here, the first objective lens assembly 20 includes a first aperture limiting element 22 accommodated in the lower part of the first lens holder 21 and a first objective lens 23 accommodated in the upper part. On the other hand, the second objective lens assembly 25 includes a second aperture limiting element 27 housed in the lower part of the second lens holder 26 and a second objective lens 28 housed in the upper part.

  The first and second objective lens assemblies 20 and 25 are configured to be able to selectively enter the optical path of the optical axis OA by an objective lens switching mechanism 29 using a driving force such as a motor. When recording or reproducing, the first objective lens assembly 20 is inserted in the optical path of the optical axis OA, and when recording or reproducing HD-DVD2, DVD3 and CD4, the second objective lens assembly 25 is aligned with the optical axis OA. It is designed to be inserted into the optical path.

  The objective lens switching mechanism 29 described above rotates the first objective lens assembly 20 and the second objective lens assembly 25 around a center axis (not shown) or slides left and right to thereby change the optical axis. It is possible to selectively enter the optical path of the OA.

At this time, the first aperture limiting element 22 in the first objective lens assembly 20 limits the numerical aperture (NA) of the first objective lens 23 to 0.85 relative to BD1. Further, the first objective lens 23 in the first objective lens assembly 20 causes the first laser beam L1 to be recorded on the recording layer 1r, the first recording layer 1a, or the second recording layer 1b of the BD1 when recording or reproducing the BD1. The first objective lens 23 is optimally designed with infinite conjugate when the design reference substrate thickness 1t ₀ {FIG. 1 (a)} of BD1 is 0.0875 mm. Details will be described later. The optimum design refers to a state that can be regarded as having no aberration.

  On the other hand, the second aperture limiting element 27 in the second objective lens assembly 25 limits the numerical aperture (NA) of the second objective lens 28 to the equivalent of 0.65 with respect to HD-DVD2 and DVD3, and to CD4. On the other hand, the numerical aperture (NA) of the second objective lens 28 is limited to be equivalent to 0.51. In addition, the second objective lens 28 in the second objective lens assembly 25 allows the first laser beam L1 to be recorded on the recording layer 2r of the HD-DVD2 or the HD-DVD2, when selectively recording or reproducing the HD-DVD2, DVD3, or CD4. The first recording layer 2a or the second recording layer 2b is condensed in a spot shape, and the second laser light L2 is condensed in a spot shape on the recording layer 3r of the DVD 3 or the first recording layer 3a or the second recording layer 3b. Further, the third laser beam L3 is condensed in a spot shape on the recording layer 4r of CD4. Although details of the second objective lens 28 will be described later, the focal length and the object distance of the second objective lens 28 are different from those of the HD-DVD2, DVD3, and CD4. Therefore, the second objective lens 28 and the second aperture limiting element 27 are arranged at an appropriate interval so that the numerical aperture (NA) is set to the above-described predetermined value with respect to HD-DVD2, DVD3, and CD4.

  Next, the first detection lens 18 for detecting each return light from the BD 1 or the HD-DVD 2 is formed with a cylindrical surface on the polarization beam splitter 13 side and a concave spherical surface on the opposite side. The first photodetector 19 receives each return light from the BD 1 or HD-DVD 2 and converts it into an electrical signal.

  Next, the second laser light source 31 for DVD emits the second laser light L2 having a wavelength λ2 of around 660 nm toward the second grating 32 side. The above-described second grating 32 has a function of branching the second laser light L2 emitted from the second laser light source 31 into three beams in order to detect the track position when recording or reproducing the DVD 3. Three beams branched from the two laser beams L2 are emitted toward the second separating optical element (hereinafter referred to as half mirror) 33 side.

  The half mirror 33 described above includes a semi-transmissive / reflective dielectric multilayer film 33a, and the semi-transmissive / reflective dielectric multilayer film 33a transmits 75% of the second laser light L2 having a wavelength λ2 of around 660 nm, and 20% The reflected second laser beam L2 is emitted toward the second dichroic prism 34 side.

  The second dichroic prism 34 includes a wavelength-selective transflective / reflective dielectric multilayer film 34a, transmits the second laser light L2 through the wavelength-selective transflective / reflective dielectric multilayer film 34a, and Since the third laser beam L3 is reflected, it is an optical element for branching the optical path for branching the second laser beam L2 and the third laser beam L3, and the second and third optical elements that have passed through the second dichroic prism 34. Laser beams L2 and L3 are emitted toward the second collimator lens 35 side.

  The second collimator lens 35 is fixed to convert the second laser light L2 having a wavelength λ2 of about 660 nm into substantially parallel light and to convert the third laser light L3 having a wavelength λ3 of about 785 nm into divergent light. The second and third laser beams L2 and L3 having passed through the second collimator lens 35 are emitted toward the first dichroic prism 15 described above.

  Next, the second detection lens 36 for detecting the return light from the DVD 3 is formed with a cylindrical surface on the half mirror 33 side and a concave spherical surface on the opposite side. The second photodetector 37 receives the return light from the DVD 3 and converts it into an electrical signal.

  Next, the hologram device assembly 40 is for recording or reproducing CD4, and includes a third laser light source 41, a third grating 42, a hologram 43, and a third photodetector 44 for CD. Integrated together. The third laser light source 41 emits a third laser light L3 having a design wavelength λ3 of around 785 nm. The third grating 42 branches the third laser light L3 emitted from the third laser light source 41 into three beams in order to detect the track position when recording or reproducing the CD4. The hologram 43 is an element for guiding the return light from the CD 4 to the third photodetector 44.

  In the case of three types of combinations of BD1, HD-DVD2, and DVD3, the hologram device assembly 40 for recording or reproducing CD4 and the second laser beam L2 and the third laser beam L3 are branched. The second dichroic prism 34 may be omitted.

  Next, FIG. 3 shows the first collimator when the first collimator lens 14 is provided so as to be movable in the optical axis direction between the polarization beam splitter 13 and the first dichroic prism 15 in the optical pickup device 10 having the above configuration. The positional relationship of the lens 14 is shown.

The first collimator lens 14 can be moved between the polarization beam splitter 13 and the first dichroic prism 15 along the optical axis OA of the first laser light L1 by a collimator lens moving mechanism (not shown). A design reference position P ₀ is set corresponding to the design reference substrate thickness 1t ₀ = 0.0875 mm of BD1, and a position P ₁ on the negative side of the design reference position P ₀ with respect to the design reference position P ₀ , or The position can be moved to positions P ₂ and P ₃ on the positive side from the design reference position P ₀ .

When the first collimator lens 14 is located at the design reference position P ₀ is adapted to convert the first laser beam L1 into parallel light.

Further, as illustrated in Fig. 4 (a), when recording or reproducing the second recording layer 1b substrate thickness 1t ₂ of BD1 is 0.1 mm, the first collimator lens 14 is polarized than the design reference position _{P 0} It moved to a position P ₁ of the beam splitter 13 side, by emitting a divergent light to the first laser light L1, recording or reproducing to correct the spherical aberration.

Further, as shown in FIG. 4 (b), when the substrate thickness 1t ₁ of BD1 is recording or reproducing the first recording layer 1a is 0.075 mm, the first collimator lens 14 is first than the design reference position _{P 0} Go to first dichroic prism 15 side position P _2, by emitting the converged light to the first laser light L1, recording or reproducing to correct the spherical aberration.

Furthermore, as shown in FIG. 4 (c), if the design standard substrate thickness 2t ₀ of HD-DVD 2 is for recording or reproducing the recording layer 2r is 0.6 mm, the first collimator lens 14 from the position _{P 2,} further moved to the first dichroic prism 15 side of the position P _3, by emitting the converged light to the first laser light L1, recording or reproducing to correct the spherical aberration.

Incidentally, slightly although not shown, when the substrate thickness 2t ₁ of HD-DVD 2 is recording or reproducing the first recording layer 2a is 0.59mm, the first collimator lens 14 than the position _{P 3} while moving to the first dichroic prism 15 side, when the substrate thickness 2t ₂ of HD-DVD 2 is recording or reproducing the second recording layer 2b is 0.61mm, from the position _{P 3} of the first collimator lens 14 However, it may be moved slightly to the design reference position P ₀ side.

Next, the 1st objective lens 23 used when recording or reproducing | regenerating BD1 is demonstrated. In the first objective lens 23, at least one of the first surface 23a on the first aperture limiting element 22 side and the second surface 23b on the BD1 side is formed as an aspheric surface. A single lens having a numerical aperture equivalent to 0.85 with respect to one laser beam L1 and a glass material having optical characteristics of, for example, S-LAL13 (trade name) manufactured by OHARA, Inc. The rate is 1.715588 when the design wavelength λ1 = 405 nm. In the first objective lens 23, the first surface 23a and the second surface 23b are both aspherical, and the design reference substrate thickness 1t ₀ of the first laser light L1 and the BD1 having the design wavelength λ1 = 405 nm With respect to 0.0875 mm, it is optimally designed with an infinite conjugate and designed to satisfy the sine condition.

Table 1 below shows the specifications of the first objective lens 23 optimally designed with infinite conjugate so as to record or reproduce BD1 with the first laser light L1.

Next, when the first surface 23a and the second surface 23b of the first objective lens 23 are formed to be aspherical surfaces, the aspherical surface is represented using the following polynomial expression 4. It is to be noted that the second objective lens 28 described later also represents an aspherical surface using the equation 4 in the same manner.

In this number 4,
Z is the distance from the apex of the first or second surface of the objective lens,
C is the curvature of each surface (curvature: 1 / radius),
h is the distance from the optical axis of the objective lens,
K is the conic constant,
N is the number of polynomial coefficients A _2i is an aspherical coefficient of degree 2i.

Table 2 below shows an example of the aspheric coefficients A _{4 to} A ₁₄ for forming the first surface 23a of the first objective lens 23 into an aspherical surface when the above-described equation 4 is used.

  At this time, the conic constant of the first surface 23a of the first objective lens 23 is −2.276512, and the radius is 1.672903 mm.

Table 3 below shows an example of the aspheric coefficients A _{4 to} A ₁₀ for forming the second surface 23b of the first objective lens 23 into an aspherical surface when the above-described equation 4 is used.

  At this time, the conic constant of the second surface 23b of the first objective lens 23 is −947.332404, the radius is −8.101843 mm, and the lens thickness is 2.98 mm.

  Next, FIG. 5A shows the case where the design wavelength λ1 = 405 nm when the BD1 is recorded or reproduced using the first objective lens 23 having the above specifications, and 1 nm before and after the design wavelength λ1 = 405 nm. FIG. 5 is a diagram showing longitudinal aberrations at shifted wavelengths λ1 = 404 nm and λ1 = 406 nm, and the horizontal axis indicates the distance (mm) from the image plane at the design wavelength λ1 = 405 nm until each light beam intersects the optical axis. The vertical axis represents the normalized entrance pupil radius of the first objective lens 23.

  At this time, on the image plane of the design wavelength λ1 = 405 nm, the axial aberration of the design wavelength λ1 = 405 nm is 0 mλ, and the axial aberration of the wavelength λ1 = 406 nm is 136 mλ, so the aberration on the image plane due to the wavelength shift is bad.

  FIG. 5B is a diagram showing a sine condition when BD1 is recorded or reproduced using the first objective lens 23 having the above specifications, and the horizontal axis shows the sine condition violation amount (mm). The vertical axis indicates the normalized entrance pupil radius of the first objective lens 23. As is apparent from FIG. 5B, the first objective lens 23 satisfies the sine condition.

  On the other hand, in the second objective lens 28, at least one of the first surface 28a on the second aperture limiting element 27 side and the second surface 28b on the HD-DVD2 side, DVD3 side or CD4 side is aspheric. In this embodiment, the numerical aperture (NA) is equivalent to 0.65 with respect to the first laser beam L1 and the second laser beam L2. A single lens having a numerical aperture (NA) of 0.51 with respect to the third laser light L3, and a glass material having optical characteristics of, for example, ZEONEX 330R (trade name) manufactured by Nippon Zeon Co., Ltd. is used. Both the first surface 28a and the second surface 28b are formed as aspherical surfaces, and a diffractive surface is formed at the first surface 28a.

  The refractive index of the ZEONEX 330R is 1.524707 for the first laser beam L1 having the design wavelength λ1 = 405 nm, and 1.506307 for the second laser beam L2 having the design wavelength λ2 = 660 nm. The refractive index for the third laser beam L3 having the design wavelength λ3 = 785 nm is 1.504388.

The second objective lens 28 is optimally designed in a finite conjugate with respect to the first laser light L1 having the design wavelength λ1 = 405 nm and the design reference substrate thickness 2t ₀ = 0.6 mm of the HD-DVD2, and the sine condition And an optimal design with an infinite conjugate with respect to the second laser beam L2 having the design wavelength λ2 = 660 nm and the design reference substrate thickness 3t ₀ = 0.6 mm of the DVD 3, and the design wavelength λ3 = 785 nm It is optimally designed in a finite conjugate with respect to the design reference substrate thickness 4t ₀ = 1.2 mm of the third laser beam L3 and CD4.

At this time, the diffractive structure of the first surface 28a of the second objective lens 28 represents a diffraction pattern by using the following polynomial expression 5. Then, a phase difference at a distance h from the optical axis of the first surface 28a of the diffraction pattern portion formed on the first surface 28a of the second objective lens 28 is obtained by the phase function Φ (x) shown in the following equation (5). The radial diffraction pattern is determined.

In this number 5,
N is the number of polynomial coefficients,
B _2i is a phase function coefficient of order 2i,
h is the distance from the optical axis of the second objective lens 28.

Table 4 below shows an optimal design with a finite conjugate (object distance is −160 mm) so that the HD-DVD 2 is recorded or reproduced by the first laser light L1 having the design wavelength λ1 = 405 nm, and the design wavelength λ2 = Optimum design with infinite conjugate (object distance is ∞) so that DVD3 is recorded or reproduced by the second laser beam L2 of 660 nm, and CD4 is recorded or reproduced by the third laser beam L3 of the design wavelength λ3 = 785 nm. The specifications of the second objective lens 28 when optimally designed with a finite conjugate (object distance is 57 mm) are shown in FIG.

Table 5 below shows an example of aspherical coefficients A _{4 to} A ₁₆ for forming the first surface 28a of the second objective lens 28 into an aspherical surface when the above-described polynomial of the number 4 is used. .

  At this time, the conic constant of the first surface 28a of the second objective lens 28 is −1.173642 and the radius is 1.912045 mm.

Table 6 below shows an example of aspherical coefficients A _{4 to} A ₁₂ for forming the second surface 28b of the second objective lens 28 into an aspherical surface when the above-described polynomial of number 4 is used. .

  At this time, the conic constant of the second surface 28b of the second objective lens 28 is 7.578232, the radius is −6.159406 mm, and the lens thickness is 2.3 mm.

Table 7 below shows an example of the phase function coefficients B _{4 to} B ₁₀ for forming the diffractive surface of the first surface 28 a of the second objective lens 28 when using the above-described polynomial of number 5. .

  The order of the diffractive surface of the first surface 28a of the second objective lens 28 is second order for the first laser light L1 having a wavelength λ1 of about 405 nm, and is second for the second laser light L2 having a wavelength λ2 of about 660 nm. The first order is used for the third laser light L3 having a wavelength λ3 of around 785 nm. Table 7 shows the diffraction orders when the first laser light L1 having the design wavelength λ1 = 405 nm is used. Indicates a quadratic value.

  Further, according to this combination of orders, for example, when the diffraction efficiency of 100% of the theoretical value is obtained for the first laser beam L1 having the wavelength λ1 of about 405 nm, the second laser beam having the wavelength λ2 of about 660 nm. Since a theoretical value of 84% is obtained for L2 and a theoretical value of 99% is obtained for the third laser beam L3 having a wavelength λ3 of around 785 nm, high-speed recording is possible for HD-DVD2, DVD3 and CD4. .

  Next, FIG. 6A shows the case where the design wavelength λ1 of the first laser beam L1 is 405 nm and the design wavelength λ1 when the HD-DVD 2 is recorded or reproduced using the second objective lens 28 having the above specifications. FIG. 4 is a diagram showing longitudinal aberrations at a wavelength λ1 = 404 nm and a wavelength λ1 = 406 nm that are shifted by 1 nm back and forth with respect to 405 nm. The difference between the wavelength λ1 = 406 nm and the design wavelength λ1 = 405 nm on the optical axis is 1. 89E-04 mm. On the image surface of the design wavelength λ1 = 405 nm, the axial aberration of the design wavelength λ1 = 405 nm is 0 mλ, and the axial aberration of the wavelength λ1 = 406 nm is 40 mλ. .

  FIG. 6B is a diagram showing a sine condition when the HD-DVD 2 is recorded or reproduced using the second objective lens 28 having the above specifications. As is apparent from FIG. 6B. The second objective lens 28 substantially satisfies the sine condition when recording or reproducing the HD-DVD 2.

  7 shows the case where the design wavelength λ2 = 660 nm of the second laser beam L2 and the design wavelength λ2 = 660 nm when the DVD 3 is recorded or reproduced using the second objective lens 28 having the above specifications. Is a diagram showing longitudinal aberration at a wavelength λ2 = 659 nm and a wavelength λ2 = 661 nm that are shifted by 1 nm, and the difference between the wavelength λ2 = 661 nm and the design wavelength λ2 = 660 nm on the optical axis is 4.91E−05 mm, There is almost no chromatic aberration. Since the axial aberration of the design wavelength λ2 = 660 nm is 0.5 mλ and the axial aberration of the wavelength λ2 = 661 nm is 4.4 mλ, there is no aberration on the image plane due to the wavelength shift. .

  Further, FIG. 8 shows the case where the design wavelength λ3 = 785 nm of the third laser beam L3 and the design wavelength λ3 = 785 nm when the CD4 is recorded or reproduced using the second objective lens 28 having the above specifications. FIG. 6 is a diagram showing longitudinal aberrations at a wavelength λ3 = 784 nm and a wavelength λ3 = 786 nm, which are shifted by 1 nm.

  Returning to FIG. 2 again, the case where BD1, HD-DVD2, DVD3, and CD4 are recorded or reproduced will be described.

First, when recording or reproducing the recording layer 1r or the second recording layer 1b in which the substrate thickness 1t ₂ {FIG. 1 (a)} of the BD 1 is 0.1 mm, the wavelength λ1 emitted from the first laser light source 11 is 405 nm. The front and rear first laser lights L1 are divergent light of linearly polarized light (p-polarized light), and pass through the first grating 12 and are divided into three beams at a predetermined branching ratio in order to detect a tracking signal. Then, the three beams of the first laser beam L1 that have passed through the first grating 12 are transmitted through the polarization-selective semi-transmissive / reflective dielectric multilayer film 13a of the polarization beam splitter 13, and the position P ₁ {FIG. 4 (a)} It passes through the first collimator lens 14 moved to, and becomes slightly divergent light.

  Thereafter, the divergent light of the first laser light L1 is transmitted through the wavelength selective semi-transmissive / reflective dielectric multilayer film 15 of the first dichroic prism 15, and the first laser light L1 is 90 ° by the rising mirror 16. The direction is changed, the linearly polarized light (p-polarized light) of the first laser light L1 passes through the quarter wavelength plate 17 and becomes circularly polarized light.

  Thereafter, the first laser light L1 is incident on a first aperture limiting element 22 housed in a lower part in the first lens holder 21, and the numerical aperture (NA) of the first objective lens 23 by the first aperture limiting element 22. The beam diameter is limited to be equivalent to 0.85, and three beams of the first laser light L1 obtained by focusing with the first objective lens 23 are incident from the laser beam incident surface 1i of the BD1, and the recording layer 1r or second Recording or reproducing is performed by condensing the recording layer 1b in a spot shape with good aberration.

Here, when recording or reproducing the recording layer 1r or the second recording layer 1b of the BD 1 having a substrate thickness of 0.1 mm, when the focal length of the first collimator lens 14 is 21.98 mm, the first collimator lens 14, as shown in FIG. 4 (a), when having reached the position _{P 1} is moved to the polarization beam splitter 13 side from the design reference position _{P 0} as -0.6Mm, aberration becomes best, on-axis The aberration is 5 mλ.

  Then, the return light by the first laser light L1 reflected by the recording layer 1r or the second recording layer 1b of the BD 1 becomes circularly polarized light opposite to the forward path and re-enters the first objective lens 23, and this first After the first aperture limiting element 22, the light is converged slightly by the objective lens 23, passes through the quarter-wave plate 17, and becomes linearly polarized light (s-polarized light) whose polarization direction is orthogonal to the forward path.

  Thereafter, the return light from the first laser beam L1 is turned 90 ° by the rising mirror 16 and is transmitted through the wavelength-selective semi-transmissive / reflective dielectric multilayer film 15a of the first dichroic prism 15, and the first collimator lens. 14, reflected by the polarization-selective transflective / reflective dielectric multilayer film 13 a of the polarization beam splitter 13, condensed by the first detection lens 18, and astigmatism on the cylindrical surface of the first detection lens 18. Is received by the first photodetector 19. The first photodetector 19 detects a tracking error signal, a focus error signal, and a main data signal when the recording layer 1r or the second recording layer 1b of the BD 1 is reproduced.

Next, a different point from the above will be described in the case of recording or reproducing the first recording layer 1a in which the substrate thickness 1t ₁ of the BD ₁ {FIG. 1 (a)} is 0.075 mm. The first laser light L1 transmitted through the polarization beam splitter 13 passes through the first collimator lens 14 moved to the position P ₂ {FIG. 4 (b)}, becomes slightly convergent light, and is a laser beam incident surface of the BD1. Recording or reproduction is performed by allowing the light to enter from 1i and condensing in a spot shape with good aberration on the first recording layer 1a.

Here, when recording or reproducing the first recording layer 1a of the BD 1 having a substrate thickness of 0.075 mm, when the focal length of the first collimator lens 14 is 21.98 mm, the first collimator lens 14 is As shown in FIG. 4 (b), when the position reaches the position P ₂ moved to the first dichroic prism 15 side by about +0.61 mm from the design reference position P ₀ , the aberration becomes the best, and the on-axis aberration is 4 mλ. Become.

Next, the case where the recording layer 2r having the design reference substrate thickness 2t ₀ {FIG. 1 (b)} of HD-DVD 2 of 0.6 mm is recorded or reproduced will be described. Wavelength λ1 emitted from the first laser light source 11 The first laser light L1 having a wavelength of about 405 nm is a divergent light of linearly polarized light (p-polarized light), and the three beams of the first laser light L1 obtained through the first grating 12 are polarized light selectivity of the polarization beam splitter 13. The light passes through the semi-transmissive / reflective dielectric multilayer film 13a, passes through the first collimator lens 14 moved to the position P ₃ {FIG. 4C}, and becomes convergent light whose object distance is equivalent to −160 mm.

  Thereafter, the convergent light of the first laser beam L1 is transmitted through the wavelength selective dielectric multilayer film 15 of the first dichroic prism 15, and the first laser beam L1 is turned 90 ° by the rising mirror 16, The p-polarized light passes through the quarter-wave plate 17 and becomes circularly polarized light.

  Thereafter, unlike the case of BD1, the first laser beam L1 is incident on a second aperture limiting element 27 housed in a lower portion in the second lens holder 26, and the second aperture limiting element 27 makes the second objective. The beam diameter is limited so that the numerical aperture (NA) of the lens 28 is equivalent to 0.65, and three beams of the first laser light L1 obtained by focusing with the second objective lens 28 are laser beam incident surfaces 2i of the HD-DVD2. The light is incident on the recording layer 2r and is condensed in a spot shape on the recording layer 2r with good aberration, and recording or reproduction is performed.

Here, when recording or reproducing the recording layer 2r of the HD-DVD 2 having a substrate thickness of 0.6 mm, when the focal length of the first collimator lens 14 is 21.98 mm, the first collimator lens 14 is 4 as shown in (c), when reaching the position P ₃ is moved from the design reference position P ₀ + 2.95 mm as the first dichroic prism 15 side, aberration becomes best, axial aberrations is 2. 3 mλ.

  Then, the return light from the first laser light L1 reflected by the recording layer 2r of the HD-DVD 2 becomes circularly polarized light opposite to the forward path and re-enters the second objective lens 28, and is reflected by the second objective lens 28. It becomes divergent light, passes through the second aperture limiting element 27, passes through the quarter-wave plate 17, and becomes linearly polarized light (s-polarized light) whose polarization direction is orthogonal to the forward path.

  Thereafter, the return light from the first laser beam L1 is turned 90 ° by the rising mirror 16 and is transmitted through the wavelength-selective semi-transmissive / reflective dielectric multilayer film 15a of the first dichroic prism 15, and the first collimator lens. 14, reflected by the polarization-selective transflective / reflective dielectric multilayer film 13 a of the polarization beam splitter 13, condensed by the first detection lens 18, and astigmatism on the cylindrical surface of the first detection lens 18. Is received by the first photodetector 19. The first photodetector 19 detects a tracking error signal, a focus error signal, and a main data signal when the recording layer 2r of the HD-DVD 2 is reproduced.

As described above, when recording or reproducing the first recording layer 2a in which the substrate thickness 2t ₁ of the HD-DVD 2 {FIG. 1 (b)} is 0.59 mm, the first collimator lens 14 is positioned. Second recording layer in which the substrate thickness 2t ₂ {FIG. 1 (b)} of the HD-DVD 2 is 0.61 mm while being moved slightly to the first dichroic prism 15 side than P ₃ {FIG. 4 (c)}. When recording or reproducing 2b, the first collimator lens 14 may be moved slightly to the design reference position P ₀ side from the position P ₃ {FIG. 4 (c)}.

Next, the case where the recording layer 3r having the design reference substrate thickness 3t ₀ {FIG. 1 (c)} of DVD3 of 0.6 mm is recorded or reproduced will be described. The wavelength λ2 emitted from the second laser light source 31 is 660 nm. The second laser beam L2 before and after is a divergent light of linearly polarized light (p-polarized light), and is split into three beams at a predetermined branching ratio in order to detect a tracking signal through the second grating 32. The three beams of the second laser light L2 that has passed through the second grating 32 are 75% light that has passed through the semi-transmissive / reflective dielectric multilayer film 33a of the half mirror 33, and the wavelength selectivity of the second dichroic prism 34. The translucent / reflective dielectric multilayer film 34a is transmitted.

  Thereafter, the light passes through the second collimator lens 35 to become parallel light and is reflected by the wavelength-selective semi-transmissive / reflective dielectric multilayer film 15a of the first dichroic prism 15, and the second laser light L2 is raised by the rising mirror 16 Thus, the 90 ° direction is turned, and the p-polarized light passes through the quarter-wave plate 17 and becomes circularly polarized light.

  Thereafter, the second laser beam L2 is incident on a second aperture limiting element 27 housed in a lower part of the second lens holder 26, and the second aperture limiting element 27 allows the numerical aperture (NA) of the second objective lens 28 to be increased. ) Is equivalent to NA 0.65, the diameter of the light beam is limited, and three beams of the second laser light L2 obtained by focusing with the second objective lens 28 are incident from the laser beam incident surface 3i of the DVD 3 on the recording layer 3r. Recording or reproduction is performed by condensing in a spot shape with good aberration.

  Then, the return light by the second laser light L2 reflected by the recording layer 3r of the DVD 3 becomes circularly polarized light opposite to the forward path and re-enters the second objective lens 28, and is reflected by the second objective lens 28 as parallel light. Then, after passing through the second aperture limiting element 27, it passes through the quarter-wave plate 17 and becomes linearly polarized light (s-polarized light) whose polarization direction is orthogonal to the forward path.

  Thereafter, the return light by the second laser light L2 is turned 90 ° by the rising mirror 16, reflected by the wavelength selective semi-transmissive / reflective dielectric multilayer film 15a of the first dichroic prism 15, and then reflected by the second collimator lens. 35, the wavelength selective semi-transmissive / reflective 34 a of the second dichroic prism 34 is transmitted, and 20% of the light is reflected by the semi-transmissive / reflective dielectric multilayer film 33 a of the half mirror 33, so that the second detection is performed. The light is condensed by the lens 36, given astigmatism on the cylindrical surface of the second detection lens 36, and received by the second photodetector 37. Then, the tracking error signal, the focus error signal, and the main data signal when the recording layer 3r of the DVD 3 is reproduced by the second photodetector 37 are detected.

The first recording layer 3a in which the substrate thickness 3t ₁ {FIG. 1 (c)} of the DVD 3 is 0.5725 mm or the substrate thickness 3t ₂ {FIG. 1 (c)} of the DVD 3 is 0.6275 mm. The second recording layer 3b may be recorded or reproduced in the same manner as described above.

Next, a case where the recording layer 4r having the design reference substrate thickness 4t ₀ {FIG. 1 (d)} of CD4 of 1.2 mm is recorded or reproduced will be described. The third laser light source 41 in the hologram device assembly 40 is described. The third laser light L3 having a wavelength λ3 emitted from the wavelength of about 785 nm is a divergent light of linearly polarized light (p-polarized light), passes through the third grating 42, and is branched into three beams for detecting the tracking signal. Divided by ratio. Then, the three beams of the third laser light L3 that has passed through the third grating 42 pass through the hologram 43 and are reflected by the wavelength-selective semi-transmissive / reflective 34a of the second dichroic prism 34.

  Thereafter, the third laser light L3 reflected by the second dichroic prism 34 is converted into predetermined divergent light by the second collimator lens 35, and the wavelength-selective transflective / reflective dielectric multilayer film 15a of the first dichroic prism 15 is used. After being reflected at, the up mirror 16 turns 90 ° and passes through the quarter-wave plate 17 so that the p-polarized light becomes circularly polarized light.

  Thereafter, the third laser beam L3 is incident on a second aperture limiting element 27 housed in a lower portion in the second lens holder 26, and the second aperture limiting element 27 allows the numerical aperture (NA) of the second objective lens 28 to be increased. ) Is equivalent to 0.51, the beam diameter of the third laser beam L3 obtained by focusing with the second objective lens 28 is made incident from the laser beam incident surface 4i of the CD4, and is incident on the recording layer 4r. Recording or reproduction is performed by condensing in a spot shape with good aberration.

  Then, the return light by the third laser light L3 reflected by the recording layer 4a of the CD4 becomes circularly polarized light opposite to the forward path and re-enters the second objective lens 28, and is converged by the second objective lens 28. Then, after passing through the second aperture limiting element 27, it passes through the quarter-wave plate 17 and becomes linearly polarized light (s-polarized light) whose polarization direction is orthogonal to the forward path.

  Thereafter, the return light by the third laser light L3 is turned by 90 ° by the rising mirror 16, reflected by the wavelength selective semi-transmissive / reflective dielectric multilayer film 15a of the first dichroic prism 15, and the second collimator lens. The third laser light L3 that passes through 35, is reflected by the wavelength-selective semi-transmissive / reflective 34a of the second dichroic prism 34, and is bent at a predetermined angle by the hologram 43 in the hologram device assembly 40 is the third laser light L3. Light is received by the photodetector 44. The third photodetector 44 detects the tracking error signal, the focus error signal, and the main data signal when the CD4 recording layer 4r is reproduced.

  Here, in the optical pickup device 10 according to the present invention, each relationship among the first collimator lens 14, the first objective lens 23, and the second objective lens 28, which is a main part of this embodiment, is illustrated in FIGS. 9 to 16. Will be described.

FIG. 9 is a diagram showing longitudinal aberration of the first collimator lens in the optical pickup device according to the present invention;
FIG. 10 is a diagram showing longitudinal aberrations of the optical system when a BD is recorded or reproduced by combining the first collimator lens and the first objective lens in the optical pickup device according to the present invention;
FIG. 11 is a diagram showing longitudinal aberrations of the optical system when an HD-DVD is recorded or reproduced by combining the first collimator lens and the second objective lens in the optical pickup device according to the present invention;
FIG. 12 is a diagram showing the relationship between the focal length f ₁ of the first objective lens and the focal length fc of the first collimator lens in the optical pickup device according to the present invention;
FIG. 13 is a diagram showing the object distance X of the second objective lens when the HD-DVD is recorded or reproduced with the first laser beam having the wavelength λ1 in the optical pickup device according to the present invention.
FIG. 14 shows an optical pickup device according to the present invention, in which the focal length fc of the first collimator lens, the object distance X of the second objective lens relative to the HD-DVD, and the first collimator lens to the first surface of the second objective lens. The figure which showed the relationship of the difference with the distance Y,
FIG. 15 is a diagram showing an object distance X ′ of the second objective lens when a CD is recorded or reproduced with a third laser beam having a wavelength λ3 in the optical pickup device according to the present invention.
FIG. 16 shows the focal length of the second objective lens with respect to the first laser beam when a lens shift of 0.1 mm occurs and the aberration becomes 15 mλ or less when a CD is recorded or reproduced in the optical pickup device according to the present invention. and f _2, is a diagram showing the relationship between the object distance X 'of the second objective lens with respect to the object distance X and the CD of the second objective lens for HD-DVD.

First, as described with reference to FIG. 2, the first collimator lens 14 which is a main part of this embodiment is a light beam of the first laser beam L1 in order to reduce chromatic aberration with respect to BD1 or HD-DVD2. The first collimator lens 14 is, for example, a negative lens (not shown) provided on the polarization beam splitter 13 side and a positive lens provided on the first dichroic prism 15 side. Table 8 below shows the specifications of the first collimator lens 14, which is a doublet in which two lenses (not shown) are bonded together.

  At this time, the first collimator lens 14 uses a negative lens glass material having optical characteristics of, for example, S-TIH1 (trade name) manufactured by OHARA. The first collimator lens 14 is used as the first laser light L1 having a design wavelength λ1 = 405 nm. On the other hand, the refractive index is 1.776299, and the Abbe number (reciprocal of dispersion) is 29.52. On the other hand, the positive lens glass material having optical characteristics of S-LAL18 (trade name) manufactured by OHARA, for example, is used, and the refractive index is 1.751656 with respect to the first laser light L1 having the design wavelength λ1 = 405 nm. And the Abbe number (reciprocal of variance) is 54.68.

  Conventionally, the doublet used for the first collimator lens 14 reduces chromatic aberration by itself using a glass material having a small dispersion and a large refractive index for the positive lens and a glass material having a large dispersion and a small refractive index for the negative lens. It is normal.

  On the other hand, in this embodiment, the doublet used for the first collimator lens 14 uses the glass material in which the refractive index of the positive lens and the negative lens are substantially the same as described above and the difference in dispersion is greatly different. When the wavelength of the light L1 is shifted in the long direction, the axial chromatic aberration is shifted in the negative direction. On the other hand, when the wavelength of the first laser light L1 is shifted in the short direction, the axial chromatic aberration is shifted in the positive direction. I understood that.

  At this time, the first objective lens 23 for BD is composed only of a refracting surface, and the material is glass. Therefore, when the wavelength of the first laser light L1 becomes longer regardless of the material and design, the axial chromatic aberration is in the positive direction. When the wavelength of the first laser beam L1 is shortened, axial chromatic aberration is greatly increased in the negative direction. For this reason, it is desirable that the first collimator lens 14 has substantially the same refractive index and a large dispersion difference as described above. Further, in the case of a combination of glass materials as in the past, a large difference in refractive index is necessary. For example, chromatic aberration can be corrected with a combination of S-TIH1 for a positive lens and BK7 for a negative lens. Compared with the above, the correction power of chromatic aberration in combination with the first objective lens 23 is low.

  FIG. 9 is a longitudinal aberration diagram of the first collimator lens 14 having the specifications shown in Table 8 above, in the case of the design wavelength λ1 = 405 nm of the first laser light L1 and before and after the design wavelength λ1 = 405 nm. Longitudinal aberrations at a wavelength λ1 = 404 nm and a wavelength λ1 = 406 nm shifted by 1 nm are shown. At this time, the difference between the design wavelength λ1 = 405 nm and the wavelength λ1 = 406 nm on the optical axis is −1.63E-02 mm, while the difference between the wavelength λ1 = 404 nm and the design wavelength λ1 = 405 nm is 1.66E−. The chromatic aberration is opposite to that of the first objective lens 23.

  FIG. 10 is a longitudinal aberration diagram of the optical system when the BD1 is recorded or reproduced by combining the first collimator lens 14 and the first objective lens 23 shown in Table 8 above, and the design wavelength of the first laser beam L1. Longitudinal aberrations are shown in the case of λ1 = 405 nm and in the case of wavelength λ1 = 404 nm and wavelength λ1 = 406 nm which are shifted by 1 nm back and forth with respect to the design wavelength λ1 = 405 nm. At this time, the difference between the design wavelength λ1 = 405 nm and the wavelength λ1 = 406 nm on the optical axis is 2.63E-02 mm, while the difference between the wavelength λ1 = 404 nm and the design wavelength λ1 = 405 nm is −2.65E−. The chromatic aberration is greatly improved as compared with the case of the first objective lens 23 alone shown in FIG. Since the axial aberration at the design wavelength λ1 = 405 nm is 2 mλ and the axial aberration at the wavelength λ1 = 406 nm is 107 mλ, the aberration on the image plane due to the wavelength shift is also improved.

  FIG. 11 is a longitudinal aberration diagram of the optical system when the HD-DVD 2 is recorded or reproduced by combining the first collimator lens 14 and the second objective lens 28 shown in Table 8 above, and the design of the first laser beam L1. Longitudinal aberrations are shown in the case of the wavelength λ1 = 405 nm and the wavelength λ1 = 404 nm and the wavelength λ1 = 406 nm which are shifted by 1 nm back and forth with respect to the design wavelength λ1 = 405 nm. At this time, the difference between the design wavelength λ1 = 405 nm and the wavelength λ1 = 406 nm on the optical axis is −2.19E-02 mm, while the difference between the wavelength λ1 = 404 nm and the design wavelength λ1 = 405 nm is 2.38E−. 02 mm, which is overcorrected as compared to the case of the second objective lens 28 alone shown in FIG. However, since the on-axis aberration of the design wavelength λ1 = 405 nm is 3 mλ and the on-axis aberration of the wavelength λ1 = 406 nm is 9 mλ, the deterioration of the aberration on the image surface due to the wavelength shift is small. . Since HD-DVD2 has a lower numerical aperture (NA) than BD1, there is no problem even if chromatic aberration is somewhat deteriorated.

  Further, in the triplet collimator lens bonded to each other, the chromatic aberration shifts in the negative direction when the wavelength of the first laser beam L1 becomes longer, and the chromatic aberration becomes shorter when the wavelength of the first laser beam L1 becomes shorter as in the doublet described above. May shift in the positive direction. Further, in a collimator lens having a diffractive surface and a refracting surface on both sides, the chromatic aberration is shifted in the negative direction when the wavelength of the first laser beam L1 is increased as in the doublet described above, and the wavelength of the first laser beam L1 is decreased. Then, a chromatic aberration that shifts in the positive direction may be used.

  In the case of DVD3, since the chromatic aberration is corrected only by the second objective lens 28, the second collimator lens 35 may be a single lens.

Next, consider the focal length f ₁ of the first objective lens 23 for BD. The effective diameter of the first objective lens 23 is preferably φ2 mm or more and φ4.25 mm or less in consideration of securing the working distance and miniaturization. In this case, the focal length f ₁ of the first objective lens 23 is in the range of 1.176 mm to 2.5 mm from the numerical aperture (NA) = 0.85. In this embodiment, it is shown in Table 1 above. Thus, it is set to 2.22 mm.

Figure 12 is a diagram showing the relationship between the focal length f ₁ of the first objective lens 23 in the case of recording or reproducing BD1 and the focal length fc of the first collimator lens 14. Although the focal length f ₁ of the first objective lens 23 coupling efficiency and the pupil edge strength determined by the relationship between the focal length fc of the first collimator lens 14, a standard radiation of the first laser light L1 having a wavelength λ1 is 405nm before and after Considering the angular distribution (for example, horizontal direction 8 °, vertical direction 22 °), as shown in FIG. 12, the range based on the focal length f ₁ of the first objective lens 23 and the focal length fc of the first collimator lens 14 By satisfying the above, it becomes an optical pickup device 10 suitable for recording or reproducing the BD1. Then, as shown in FIG. 12, when the focal length f ₁ of the first objective lens 23 and the focal length fc of the first collimator lens 14 are 1.176 ≦ f ₁ ≦ 2.5, It is the range by.

  However, a is a coefficient and 8 ≦ a ≦ 11. At this time, the coupling efficiency falls within the range of 0.25 to 0.4 at a standard radiation angle. If the standard radiation angle is about ± 1 °, the above-described range of Equation 6 is used. The coupling efficiency is sufficiently satisfied.

On the other hand, when sharing the first laser beam L1 having a wavelength .lambda.1, the focal length f ₁ with respect to the first laser beam L1 of the first objective lens 23, the focal length f ₂ with respect to the first laser beam L1 and the second objective lens 28 Is expressed by the following equation (7).

  However, b is a coefficient and 0.9 ≦ b ≦ 1.1. When Expression 7 is satisfied, it is possible to record or reproduce both the BD1 and HD-DVD2 recording / reproducing pupil edge intensity and the coupling efficiency substantially coincident with each other.

Next, the movement distance of the first collimator lens 14 corrects the spherical aberration caused by the error of the wavelength λ1 of the first laser beam L1 for selectively recording or reproducing BD1 and HD-DVD2, the interlayer distance error, the temperature, etc. However, if the estimated distance zmm (eg, z = 2.95 mm) from the design reference position P ₀ (parallel light emission) of the BD 1 to the position P ₃ of the HD-DVD 2 is estimated to be 2.3 times. good. For example, when a stepping motor or an ultrasonic motor is used as the moving mechanism of the first collimator lens 14, the movement of 10 mm is the limit in consideration of the aberration of the first collimator lens 14 due to the inclination and decentering, and the distance z is z ≦ 5. However, it is more preferable that z ≦ 4 in view of miniaturization.

  Next, FIG. 13 shows the object distance X of the second objective lens 28 when the HD-DVD 2 is recorded or reproduced with the first laser light L1 having the wavelength λ1. The object distance X of the second objective lens 28 with respect to the HD-DVD 2 represents the distance from the object point to the first surface 28a (on the first laser light source 11 side) of the second objective lens 28. Assuming that the image point is on the same side with respect to the second objective lens 28 as a negative value, in this embodiment, the object distance X of the second objective lens 28 relative to the HD-DVD 2 is as shown in Table 4 above. It is set to −160 mm.

Next, FIG. 14 shows the focal length fc of the first collimator lens 14, the object distance X of the second objective lens 28 relative to the HD-DVD 2, and the first surface 28 a (the first surface 28 a of the second objective lens 28 from the first collimator lens 14. FIG. 3 is a diagram showing a relationship of a difference between a distance Y (one laser light source 11 side) (corresponding to the sum of Y ₁ and Y ₂ in air conversion length shown in FIG. 2). When z ≦ 4, the second objective lens 28 may be XY that satisfies the following range of Eq.

At this time, the distance Y = Y ₁ + Y ₂ needs to be 10 mm or more.

  Next, characteristics of the second objective lens 28 will be described. In order to satisfy various characteristics such as diffraction efficiency and lens shift characteristics of HD-DVD2 and CD4, it is necessary to balance both HD-DVD2 and CD4. As shown in Table 4 above, it is necessary to set the object distances opposite to each other between HD-DVD 2 and CD 4.

  Next, FIG. 15 shows the object distance X ′ of the second objective lens 28 when CD4 is recorded or reproduced with the third laser beam L3 having the wavelength λ3. The object distance X ′ of the second objective lens 28 with respect to CD4 represents the distance from the object point to the first surface 28a (the third laser light source 41 side) of the second objective lens 28. This object distance X ′ is Assuming that the positive value is obtained when the image point is on the opposite side of the second objective lens 28, in this embodiment, the object distance X ′ of the second objective lens 28 with respect to CD4 is 57 mm as shown in Table 4 above. Is set.

  Here, the second objective lens 28 is mainly optimally designed for HD-DVD2 and DVD3, and CD4 obtains the object distance X ′ that minimizes the aberration, and the lens shift of CD4 is 0.1 mm and the aberration is 15 mλ or less. Make an optimal design.

Next, FIG. 16 is aberration when the lens shift occurs 0.1mm is when it becomes less 15Emuramuda, the focal length _f 2 with respect to the first laser beam L1 and the second objective lens 28 in the CD4, for HD-DVD 2 It is the figure which showed the relationship between the object distance X of the 2nd objective lens 28, and the body distance X 'of the 2nd objective lens 28 with respect to CD4. Regarding the lens shift characteristics in CD4, the maximum allowable value is 45 mλ or less when the lens shift is 0.3 mm, and the allowable range is 15 mλ or less when the lens shift is 0.1 mm.

In general, the lens shift characteristic is almost determined by the object distance. Object distance X satisfying the lens shift characteristics of the CD4 'is one may be at substantially constant at 45mm or more in the first range of 50 mm ± 5 mm regardless of the focal length _{f 2} for the laser beam L1 and the second objective lens 28 Dependence on the phase function coefficient, diffraction order, etc. is small. However, the object distance X of the second objective lens 28 for HD-DVD 2 was found to be smaller as the focal length _{f 2} with respect to the first laser beam L1 and the second objective lens 28 becomes long. The focal length _f 2 with respect to the first laser beam L1 and the second objective lens 28, the relationship between the object distance X of the second objective lens 28 for HD-DVD 2 is expressed by the number of below 9.

Further, by increasing the value of the object distance X ′ of the second objective lens 28 with respect to CD4, the lens shift characteristic with CD4 can be further improved, but in this case, the second objective lens 28 with respect to HD-DVD2 is improved. The value of the object distance X is also increased. For example, when the focal length f _{2 of} the second objective lens 28 with respect to the first laser beam L1 = 3 mm and the object distance X = −230 mm of the second objective lens 28 with respect to HD-DVD2, the object distance X ′ of the second objective lens 28 with respect to CD4. When 53 mm, the lens shift characteristic with CD4 is 15 mλ. Further, when the same focal length f ₂ = 3 mm, the object distance X of the second objective lens 28 with respect to HD-DVD 2 is −130 mm, and the object distance X ′ of the second objective lens 28 with respect to CD 4 is 60 mm, the lens shift characteristic with CD 4 Is 12 mλ. Therefore, the lens shift characteristic with CD4 can be satisfied by setting the value of the object distance X equal to or greater than that represented by the above formula (9).

  On the other hand, considering the lens shift characteristics in HD-DVD 2 in the same manner as in CD 4, when the lens shift is 0.1 mm, the object distance X of the second objective lens 28 relative to HD-DVD 2 is in the range of X = −65 mm ± 5 mm. 15 mλ. Since the wavelength of HD-DVD2 is shorter than that of CD4, the object distance condition is severe, and when X <-60 mm, the lens shift characteristic of HD-DVD2 does not hold.

The second objective lens 28 has an object distance X with respect to the HD-DVD 2 that satisfies X <−60, is a range obtained from the above equations 8 and 9, and an object distance X ′ with respect to the CD 4 satisfies 45 ≦ X ′. Satisfying the following formula 10 enables good recording or reproduction for HD-DVD2, DVD3, and CD4.

Here, the number 10 as described above, to represent the focal length _{f 2} with respect to the first laser beam L1 and the second objective lens 28 for HD-DVD 2 by the focal length fc of the first collimator lens 14, the number shown in the above 6 , When the coefficient a in the range of 8 ≦ a ≦ 11 is set to 8, for example, f ₁ = fc / 8 is obtained from the equation 6, and when this is substituted into the equation 7 shown above, f ₂ = 1. If the coefficient b in the range of 0.9 ≦ b ≦ 1.1 is set to 1, 1 for example, f ₂ = 0.18 fc. Substituting this f ₂ = 0.18fc into the above-described formula 10, the following formula 11 is obtained.

In the above formula 11, the range of the object distance X of the second objective lens 28 relative to the HD-DVD 2 can be obtained only by the focal length fc of the first collimator lens 14, and therefore can be calculated more simply than the above formula 10. Moreover, the focal length fc of the first collimator lens 14 is easy to measure the length of the focal length fc of the first collimator lens 14 because it is the first long focal than the focal length f ₂ for the laser beam L1 and the second objective lens 28 is there.

Therefore, the focal length fc of the first collimator lens 14, the focal length f _{2 of} the second objective lens 28 with respect to the first laser light L 1, and the _second with respect to the HD-DVD 2 are satisfied so as to satisfy the above formula 10 or formula 11. By appropriately setting the object distance X of the objective lens 28 and the object distance X ′ of the second objective lens 28 with respect to CD4, the HD-DVD2 and CD4 can be recorded or reproduced satisfactorily by the second objective lens 28. can do.

  As described above, when the optical pickup apparatus 10 according to the present invention is used to selectively record or reproduce the three types of first to third optical recording media 1 to 3, the wavelength λ1 is around 405 nm. The first laser light L1 is focused in a spot shape on the first optical recording medium (BD) 1 by the first objective lens 23, and the first laser light L1 is condensed by the second objective lens 28 to the second optical recording medium. The first collimator lens 14 movably provided on the optical axis OA of the first laser beam L1 when the light is condensed in a spot shape on the (HD-DVD) 2 is provided on the first and second optical recording media 1 and 2. A predetermined amount is moved along the optical axis OA of the first laser beam L1 in accordance with the thickness of each substrate to correct spherical aberration with respect to the first and second optical recording media 1 and 2, and further, the wavelength λ2 The second laser light L2 having a wavelength of around 660 nm is transmitted by the second objective lens 28. Thus, the three kinds of first to third optical recording media 1 to 3 can be recorded or reproduced satisfactorily by condensing them on the third optical recording medium (DVD) 3 in a spot shape.

  When the optical pickup device 10 according to the present invention is used to selectively record or reproduce four types of first to fourth optical recording media 1 to 4, the first laser having a wavelength λ1 of about 405 nm. The light L1 is condensed in a spot shape on the first optical recording medium (BD) 1 by the first objective lens 23, and the first laser light L1 is condensed by the second objective lens 28 on the second optical recording medium (HD-DVD). The first collimator lens 14 provided so as to be movable on the optical axis OA of the first laser beam L1 when condensing in a spot shape on the substrate 2 has a thickness of each substrate of the first and second optical recording media 1 and 2. Accordingly, the first and second optical recording media 1 and 2 are each moved by a predetermined amount along the optical axis OA of the first laser beam L1 to correct spherical aberration, and the wavelength λ2 is about 660 nm. The second laser beam L2 is transmitted through the second objective lens 28 to the third optical recording medium. The light is condensed in a spot shape on the body (DVD) 3, and the third laser light L3 having a wavelength λ3 of about 785 nm is condensed in a spot shape on the fourth optical recording medium (CD) 4 by the second objective lens 28. By doing so, the four types of first to fourth optical recording media 1 to 4 can be recorded or reproduced satisfactorily.

  At this time, the first collimator lens 14 is movably disposed between the polarization beam splitter 13 and the first dichroic prism 15 on the optical axis OA of the first laser beam L1, so that the first optical recording medium (BD) is provided. The collimator lens acts only on the first and second optical recording media (HD-DVD) 2, and the first collimator lens 14 is used as the first laser in accordance with the thicknesses of the first and second optical recording media 1 and 2. Spherical aberration can be corrected when the first and second optical recording media 1 and 2 are recorded or reproduced respectively by moving them by a predetermined amount along the optical axis OA of the light L1.

  Even when the first collimator lens 14 is moved by disposing the first collimator lens 14 closer to the first and second objective lenses 23 and 28 than the polarizing beam splitter 13, Since the conjugate relationship between the first collimator lens (outgoing system) 14 and the first detection lens (detection system) 18 and the first photodetector 19 can be kept constant, there is a risk of defocusing in the first photodetector 19. Absent. Further, the expander lens that is difficult to align the optical axis as described in the conventional example is not necessary, and the optical pickup device 10 can be downsized.

  In addition, since only the first laser light L1 emitted from the first laser light source 11 passes through the first collimator lens 14, the first objective lens 28 makes the first light only when the first laser light source 11 is used. The chromatic aberration between the chromatic aberration when recording or reproducing the recording medium (BD) 1 and the chromatic aberration when recording or reproducing the second optical recording medium (HD-DVD) 2 with the second objective lens 28 is corrected. For example, a collimator lens composed of two or three spherical lenses or a diffractive surface and a refracting surface can be obtained.

  Further, the light beam of the second laser light L2 emitted from the second laser light source 31 for recording or reproducing the third optical recording medium (DVD) 3 is installed in the vicinity of the first and second objective lenses 23 and 28. The light is branched by the first dichroic prism 15. Therefore, when the third optical recording medium (DVD) 3 is recorded or reproduced, since the emission system and the detection system are different from the first laser light source 11, the chromatic aberration is not deteriorated unnecessarily. Accordingly, the three types of first to third optical recording media 1 to 3 can achieve high speed.

  The same applies to the four types of optical recording media 1 to 4, and the light beams of the laser beams L 2 and L 3 from the second laser light source 31 and the third laser light source 41 are transmitted from the first and second objective lenses 23 and 28. The light is branched by a first dichroic prism 15 installed nearby. Therefore, when the third optical recording medium (DVD) 3 and the fourth optical recording medium (CD) 4 are selectively recorded or reproduced, an emission system and a detection system different from the first laser light source 11 are used. Therefore, chromatic aberration is not deteriorated unnecessarily. Accordingly, the four types of first to fourth optical recording media 1 to 4 can achieve high speed.

Further, the spherical aberration is corrected by moving the first collimator lens 14 with respect to the second optical recording medium (HD-DVD) 2, and the second optical recording medium (HD-DVD) 2 and the third optical recording medium ( DVD) 3 and the fourth optical recording medium (CD) 4 are selectively recorded or reproduced by the second objective lens 28, and the object distance X (mm) of the second objective lens 28 with respect to the second optical recording medium 2; The object distance X ′ (mm) of the second objective lens 28 with respect to the fourth optical recording medium 4, the focal length fc (mm) of the first collimator lens 14, and the focal length f of the second objective lens 28 with respect to the first laser light. ₂ (mm) and a distance Y (mm) from the first collimator lens 14 to the first surface 28a of the second objective lens 28, an appropriate relationship is maintained so as to satisfy the above-described Expression 10. 3 types It can be favorably recorded or reproduced through fourth optical recording medium 2-4.

(A)-(d) is the figure typically shown in order to demonstrate BD, HD-DVD, DVD, CD as the 1st-4th optical recording medium applied to the optical pick-up apparatus based on this invention. . It is the figure which showed the whole structure of the optical pick-up apparatus based on this invention. In the optical pick-up apparatus according to the present invention, when the first collimator lens is provided between the polarization beam splitter and the first dichroic prism so as to be movable in the optical axis direction, it is a diagram showing the positional relationship of the first collimator lens. is there. (A)-(c) is the figure which showed the state of the light beam by the position of the collimator lens of the optical pick-up apparatus which concerns on this invention. (A), (b) is the figure which showed the longitudinal aberration and sine condition when recording or reproducing | regenerating BD using the 1st objective lens in the optical pick-up apparatus based on this invention. (A), (b) is the figure which showed the longitudinal aberration and sine condition at the time of recording or reproducing | regenerating HD-DVD using the 2nd objective lens in the optical pick-up apparatus based on this invention. In the optical pick-up apparatus which concerns on this invention, it is the figure which showed the longitudinal aberration when recording or reproducing | regenerating DVD using the 2nd objective lens. In the optical pick-up apparatus which concerns on this invention, it is the figure which showed the longitudinal aberration when recording or reproducing | regenerating CD using the 2nd objective lens. In the optical pick-up apparatus which concerns on this invention, it is the figure which showed the longitudinal aberration of the 1st collimator lens. In the optical pick-up apparatus which concerns on this invention, it is the figure which showed the longitudinal aberration of the optical system when recording or reproducing | regenerating BD combining the 1st collimator lens and the 1st objective lens. In the optical pickup device according to the present invention, it is a diagram showing the longitudinal aberration of the optical system when HD-DVD is recorded or reproduced by combining the first collimator lens and the second objective lens. In the optical pickup apparatus according to the present invention, it is a diagram showing the relationship between the focal length fc of the focal length f ₁ and the first collimator lens of the first objective lens. FIG. 5 is a diagram showing an object distance X of a second objective lens when an HD-DVD is recorded or reproduced with a first laser beam having a wavelength λ1 in the optical pickup device according to the present invention. In the optical pickup device according to the present invention, the focal length fc of the first collimator lens, the object distance X of the second objective lens relative to the HD-DVD, and the distance Y from the first collimator lens to the first surface of the second objective lens, It is the figure which showed the relationship of the difference of. FIG. 5 is a diagram showing an object distance X ′ of a second objective lens when a CD is recorded or reproduced with a third laser beam having a wavelength λ3 in the optical pickup device according to the present invention. In the optical pickup device according to the present invention, when a CD is recorded or reproduced, when the lens shift is 0.1 mm and the aberration is 15 mλ or less, the focal length f _{2 of} the second objective lens with respect to the first laser beam is FIG. 5 is a diagram showing the relationship between the object distance X of the second objective lens for HD-DVD and the body distance X ′ of the second objective lens for CD. It is the figure which showed an example of the conventional optical pick-up apparatus.

Explanation of symbols

1 ... 1st optical recording medium (BD),
2 ... Second optical recording medium (HD-DVD),
3 ... Third optical recording medium (DVD),
4 ... Fourth optical recording medium (CD),
10: Optical pickup device,
11 ... 1st laser light source, 12 ... 1st grating,
13: First polarization separation optical element (polarization beam splitter),
13a: polarized light selective transflective / reflective dielectric multilayer film,
14 ... 1st collimator lens,
15 ... 1st dichroic prism, 15a ... Wavelength selective transflective / reflective dielectric multilayer film,
16 ... Raising mirror, 17 ... quarter wave plate,
18 ... 1st detection lens, 19 ... 1st photodetector,
20 ... first objective lens assembly, 21 ... first lens holder, 22 ... first aperture limiting element,
23 ... 1st objective lens, 23a ... 1st surface, 23b ... 2nd surface,
25 ... second objective lens assembly, 26 ... first lens holder, 27 ... second aperture limiting element,
28 ... first objective lens, 28a ... first surface, 28b ... second surface,
29 ... Objective lens switching mechanism,
31 ... Second laser light source, 32 ... Second grating,
33 ... second polarization separation optical element (half mirror),
33a ... Semi-transmissive / reflective dielectric multilayer film,
34 ... second dichroic prism, 34a ... wavelength selective semi-transmissive / reflective dielectric multilayer film,
35 ... 2nd collimator lens, 36 ... 2nd detection lens, 37 ... 2nd photodetector,
40. Hologram device assembly,
41 ... third laser light source, 42 ... third grating, 43 ... hologram,
44. Third photo detector,
fc: focal length of the first collimator lens,
f ₁ ... focal length of the first objective lens, f ₂ ... focal length of the second objective lens with respect to the first laser light,
L1 ... 1st laser beam, L2 ... 2nd laser beam, L3 ... 3rd laser beam, OA ... Optical axis,
P ₀ ... Design reference position of collimator lens for parallel light emission,
P ₁ ... Collimator lens position when recording or reproducing the recording layer 1r or the second recording layer 1b of BD1
P ₂ ... collimator lens position when recording or reproducing the first recording layer 1a of BD1,
P ₃ ... collimator lens position when recording or reproducing the recording layer 2r of the HD-DVD 2;
X: object distance, X ′: object distance.

Claims (4)

In an optical pickup for selectively recording or reproducing a plurality of optical recording media,
In order to selectively record or reproduce a first optical recording medium having a first substrate thickness and a second optical recording medium having a second substrate thickness larger than the first substrate thickness, the first optical recording medium having a wavelength λ1 is used. A first laser light source that emits one laser beam;
A second laser light source that emits a second laser beam having a wavelength λ2 longer than the wavelength λ1 in order to selectively record or reproduce a third optical recording medium having a substrate thickness substantially equal to the second substrate thickness. When,
A first separation optical element that separates the first laser light emitted from the first laser light source and each return light reflected by the first and second optical recording media;
A first collimator lens provided so as to be movable along the optical axis of the first laser beam that has passed through the first separation optical element, and correcting spherical aberration with respect to the first and second optical recording media; ,
A second separation optical element for separating the second laser light emitted from the second laser light source and the return light reflected from the third recording medium by the second laser light;
A second collimator lens fixedly installed along the optical axis of the second laser beam that has passed through the second separation optical element;
The first laser beam that has passed through the first collimator lens and the second laser beam that has passed through the second collimator lens are installed on an optical axis that intersects, and the first laser beam and the second laser beam, An optical member for branching the optical path;
A first objective lens that narrows down the first laser light that has passed through the optical path branching optical member and focuses the first laser light on the first optical recording medium in a spot shape;
The first laser light that has passed through the optical path branching optical member is narrowed down to focus the first laser light in a spot shape on the second optical recording medium, and the first laser light that has passed through the optical path branching optical member. A second objective lens for focusing two laser beams and condensing the second laser beams in a spot shape on the third optical recording medium;
An optical pickup device comprising: an objective lens switching mechanism that selectively causes the first objective lens and the second objective lens to enter the optical path according to the first to third recording media. In an optical pickup for selectively recording or reproducing a plurality of optical recording media,
In order to selectively record or reproduce a first optical recording medium having a first substrate thickness and a second optical recording medium having a second substrate thickness larger than the first substrate thickness, the first optical recording medium having a wavelength λ1 is used. A first laser light source that emits one laser beam;
A second laser light source that emits a second laser beam having a wavelength λ2 longer than the wavelength λ1 in order to selectively record or reproduce a third optical recording medium having a substrate thickness substantially equal to the second substrate thickness. When,
A third laser that emits a third laser beam having a wavelength λ3 longer than the wavelength λ2 in order to selectively record or reproduce a fourth optical recording medium having a third substrate thickness greater than the second substrate thickness; A light source;
A first separation optical element that separates the first laser light emitted from the first laser light source and each return light reflected by the first and second optical recording media;
A first collimator lens provided so as to be movable along the optical axis of the first laser beam that has passed through the first separation optical element, and correcting spherical aberration with respect to the first and second optical recording media; ,
A second separation optical element that separates the second laser light emitted from the second laser light source and the return light reflected from the three recording media by the second laser light;
The second laser beam passing through the second separation optical element and the third laser beam emitted from the third laser light source are installed on an optical axis where the second laser beam and the third laser beam intersect. A first optical path branching optical member that branches light;
A second collimator lens fixedly installed along the optical axes of the second and third laser beams that have passed through the first optical path branching optical member;
The first laser beam that has passed through the first collimator lens and the second and third laser beams that have passed through the second collimator lens are disposed on an optical axis that intersects, and the first laser beam and the second laser beam , A second optical path branching optical member for branching the third laser light,
A first objective lens for focusing the first laser beam in a spot shape on the first optical recording medium by narrowing down the first laser beam that has passed through the second optical path branching optical member;
The first laser light that has passed through the second optical path branching optical member is narrowed down to focus the first laser light on the second optical recording medium, and the second optical path branching optical member The second laser beam that has passed through the aperture is narrowed down to focus the second laser beam on the third optical recording medium in a spot shape, and the third laser beam that has passed through the second optical path branching optical member is A second objective lens for focusing and condensing the third laser light in a spot shape on the fourth optical recording medium;
An optical pickup device comprising: an objective lens switching mechanism that selectively causes the first objective lens and the second objective lens to enter the optical path according to the first to fourth optical recording media.   The first collimator lens is formed by bonding a positive lens and a negative lens, and when the wavelength of the first laser light is shifted in a long direction, axial chromatic aberration is shifted in a negative direction, while the first collimator lens is 3. The optical pickup device according to claim 1, wherein the axial chromatic aberration is shifted in a positive direction when the wavelength of the laser beam is shifted in a shorter direction. The second objective lens has a finite conjugate with respect to a case where the second optical recording medium is recorded or reproduced with the first laser light and a case where the fourth optical recording medium is recorded or reproduced with the third laser light. And is optimally designed with a substantially infinite conjugate to the second laser light,
The object distance of the second objective lens relative to the second optical recording medium is X (mm),
The object distance of the second objective lens relative to the fourth optical recording medium is X ′ (mm),
The focal length of the first collimator lens is fc (mm),
The focal length of the second objective lens with respect to the first laser light is f ₂ (mm),
3. The light according to claim 2, wherein when the distance from the first collimator lens to the first surface of the second objective lens is Y (mm), the following expression is satisfied. Pickup device.

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