JP2006252751A - Optical pickup optical system, objective lens, and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup optical system which forms a good spot by preventing decrease in diffraction efficiency, and suppresses the change of spherical aberration resulting from minute change of a laser beam, in order to establish compatibility to an existing optical disk or a new standard optical disk, when a diffraction structure is used. <P>SOLUTION: This optical pickup optical system 10 has compatibility at least in two kinds of optical disks of which the specification differs, and has at least an optical element 11 which has a phase shift surface on one surface. The phase shift surface 11a has a first region 11ai which focuses each laser beam on a recording surface of a corresponding optical disk. The region has at least one ring zone structure having a ring zone group of which the amount of optical path length addition to a first laser beam when a refraction surface located inside is made reference is almost that of two wave lengths, and a return level difference section of which the amount of optical path length addition to the first laser beam when the refraction surface located inside is made reference is that of almost three wave lengths in the opposite direction to a level difference of the ring zone group. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup device that records or reproduces data on a plurality of types of optical disks having different recording densities, and an objective lens used in the device.

  There are a plurality of standards with different recording densities for optical disks. For example, in recent years, new standard optical discs such as BD (Blu-ray Disc) and HD DVD, which are being put into practical use in order to further increase the capacity of information recording, are DVDs having a relatively high recording density among existing optical discs. Recording density is higher than Digital Versatile Disc). Therefore, in order to make an optical information recording / reproducing apparatus compatible with optical discs of different standards, the numerical aperture (NA) of light used for recording or reproducing information is changed in the apparatus, and the recording density difference is different. It is necessary to obtain a beam spot corresponding to.

  Specifically, in order to record or reproduce information on a new standard optical disk, it is necessary to narrow the beam spot using an optical system having a higher NA than that of an optical system dedicated to DVD. Since the spot diameter can be reduced as the wavelength becomes shorter, an optical system using a new standard optical disk needs to use a laser light source having an oscillation wavelength of about 405 nm, which is shorter than about 660 nm used in an optical system dedicated to DVD. . Therefore, in recent years, an optical pickup device having a light source unit capable of oscillating laser beams having different wavelengths is used as an optical information recording / reproducing device having compatibility with optical discs having different standards.

  In general, it is known that when an optical disk having a high recording density is used, tolerance for aberration is reduced. Therefore, in an optical information recording / reproducing apparatus that is compatible with a DVD or a new standard optical disk, how to suppress the spherical aberration becomes an even more important issue.

  In the text, the term “optical information recording / reproducing apparatus” includes all of the information recording apparatus, the information reproduction apparatus, and the information recording / reproducing apparatus. “Compatible” means that recording or reproduction of information is guaranteed without changing parts even if the optical disk to be used is switched.

  For a plurality of optical discs having different standards, it is proposed to arrange a diffractive structure in the optical path of the laser beam as one means for converging the laser beam on the recording surface of each optical disc in good condition. The proposal is disclosed in, for example, Patent Document 1 and Patent Document 2 below.

JP 2001-93179 A JP-A-9-54973

  Patent Document 1 has a diffractive optical element for recording or reproducing information on a new standard optical disk by using a laser beam of 400 nm level and recording or reproducing information on a DVD by using a laser beam of 650 nm level. An optical pickup is disclosed. In the optical pickup of Patent Document 1, the diffractive optical element is configured such that second-order diffracted light is used for recording or reproducing information on a new standard optical disc, and first-order diffracted light is used for recording or reproducing information on a DVD. The Alternatively, the diffractive optical element is configured to use third-order diffracted light for recording or reproducing information on a new standard optical disc and to use second-order diffracted light for recording or reproducing information on a DVD. With this configuration, while suppressing a decrease in the diffraction efficiency of each laser beam, the spherical aberration due to the different wavelength of each laser beam is corrected, and information is recorded or recorded on the recording surface of each optical disc. A spot suitable for reproduction is formed.

  However, in the configuration of the optical pickup disclosed in Patent Document 1, the spherical aberration caused by the laser light used when each optical disk is used slightly deviates from the wavelength that is suitable when each optical disk is used (hereinafter referred to as the design wavelength). No change is expected. In particular, when a diffractive optical element is used to obtain compatibility with multiple optical discs with protective layers of different thicknesses, the change in spherical aberration due to a slight change in the wavelength of the laser light actually used from the design wavelength Appears very large. The change in the spherical aberration may interfere with information recording or reproduction, in particular, information recording or reproduction on a new standard optical disc having a high recording density.

  Patent Document 2 discloses an optical head device that is compatible with two types of optical disks by utilizing the diffractive action of a diffractive optical element, as in Patent Document 1. In the optical head device, the diffractive optical element uses first-order diffracted light for recording or reproducing information on an optical disk having a high recording density, and transmitted light is used for recording or reproducing information on an optical disk having a low recording density. Configured.

Here, the optical head device of Patent Document 2 is designed to be compatible with a DVD (Compact Disc) whose recording density is relatively low. In other words, the optical head device of Patent Document 2 does not assume any information recording or reproduction with respect to the new standard optical disc. For this reason, when a 400 nm laser beam is used in the optical head device of Patent Document 2, various aberrations such as spherical aberration are generated on the recording surface of the new standard optical disc. A spot suitable for recording or reproduction cannot be formed. That is, information cannot be recorded or reproduced on the above-mentioned new standard optical disc. Further, even in the optical head device of Patent Document 2, it is difficult to control the spherical aberration due to the laser beam used when each optical disk is used being slightly deviated from the design wavelength. Therefore, it has the same problem as the above-mentioned Patent Document 1.

  Therefore, in view of the above circumstances, the present invention uses a diffractive structure in order to provide compatibility with an existing optical disc having a relatively high recording density and a new standard optical disc having a higher recording density than the existing optical disc. In addition, when any optical disk is used, the diffraction efficiency is effectively prevented from being lowered to form a good spot on the recording surface of each optical disk, and the laser beam used when using each optical disk is slightly changed from the design wavelength. However, it is an object of the present invention to provide an optical pickup optical system and an objective lens that can suppress a change in spherical aberration to be small, and an optical pickup device that includes the optical pickup optical system and the objective lens.

In order to solve the above-described problems, the optical pickup optical system of the present invention records information on each optical disc by selectively using the first and second laser beams having different wavelengths for at least two types of optical discs having different standards. Or an optical pickup optical system capable of reproduction, comprising: an objective lens; and an optical element that is disposed closer to the light source than the objective lens and has a phase shift surface on at least one surface, the first laser light being The thickness of the protective layer of the first optical disk on which information is recorded or reproduced is t1, and the information is recorded or reproduced using a second laser beam having a wavelength longer than that of the first laser beam. When the protective layer thickness of the optical disk is t2, t1 and t2 have the following relationship:
t1 ≦ t2
The filling,
When the numerical aperture of the objective lens required for recording or reproducing information on the first optical disk is NA1, and the numerical aperture required for recording or reproducing information on the second optical disk is NA2,
NA1 ≧ NA2
And
The phase shift surface, after passing through the optical element and the objective lens, converges the first laser beam on the recording surface of the first optical disc and converges the second laser beam on the recording surface of the second optical disc. The first region has an optical path length addition amount of about two wavelengths with respect to the first laser light when a reference is made to the inner refracting surface at the boundary between adjacent refracting surfaces. The amount of added optical path length to the first laser beam when the zonal group is formed with a level difference and the refractive surface is located outside and located outside the zonal group. It is characterized in that it has at least one annular zone structure including a return step portion having a length corresponding to approximately three wavelengths in a direction opposite to the step.

  According to the first aspect of the present invention, the laser beam used is changed slightly from the design wavelength particularly when recording or reproducing information on the new standard optical disc (first optical disc). Even in this case, the change in spherical aberration accompanying the change can be kept small. Also, with the above configuration, it is possible to satisfactorily suppress a decrease in diffraction efficiency during recording or reproduction of information on either the new standard optical disc or the existing optical disc (second optical disc). Therefore, according to the present invention, a spot suitable for recording or reproducing information can be formed on the recording surface of the target optical disc without being affected by a minute wavelength change.

  According to the optical pickup optical system of the second aspect, when the first laser beam is incident, on the incident side surface of the optical element for obtaining a desired spot diameter on the recording surface of the first optical disc. When the second laser beam is incident, the effective light beam diameter of the optical disk is larger than the effective light beam diameter on the incident side surface of the optical element for obtaining a desired spot diameter on the recording surface of the second optical disk. The phase shift surface contributes to the convergence of the first laser light transmitted through the optical element and the objective lens outside the first region, and the second laser transmitted through the optical element and the objective lens. It is desirable to have a second region that does not contribute to light convergence. In this case, when the second region is based on the inner refracting surface at the boundary between adjacent refracting surfaces, the optical path length addition amount for the first laser light is different from the first region. Different steps are formed.

  When the second region as described above is provided, it is preferable that the optical path length addition amount for the first laser light is approximately one wavelength or approximately −1 wavelength.

  According to the optical pickup optical system of the fourth aspect, when the second laser beam is incident, the incident side of the optical element for obtaining a desired spot diameter on the recording surface of the second optical disc is obtained. The effective light beam diameter at the surface is larger than the effective light beam diameter at the incident-side surface of the optical element for obtaining a desired spot diameter on the recording surface of the first optical disk when the first laser beam is incident. When set to be, the phase shift surface contributes to the convergence of the second laser light transmitted through the optical element and the objective lens outside the first region, and is transmitted through the optical element and the objective lens. It is desirable to have a second region that does not contribute to the convergence of the laser light. In this case, the second region is different from the first region in the amount of optical path length added to the second laser light when the inner surface is the reference surface at the boundary between adjacent refractive surfaces. Such a step is formed.

  When the second region as described above is provided, it is preferable that the step of the second region has an optical path length addition amount with respect to the second laser light of approximately one wavelength or approximately −1 wavelength (claim). Item 5).

  As described above, any laser beam can be used by providing a second region having a step that gives a predetermined optical path length difference outside the first region according to the size of the effective light beam diameter. A good spot can be formed on the recording surface of each optical disc.

  By holding the objective lens and the optical element constituting the optical pickup optical system by the same holding member, it is possible to effectively avoid the relative displacement between the two and prevent the performance deterioration. ).

The optical pickup optical system according to any one of claims 1 to 6, wherein the wavelength of the first laser light is λ1, the wavelength of the second laser light is λ2, and the refractive index of the objective lens with respect to the wavelength λ1 is Assuming that the refractive index of the objective lens for n1 and the second wavelength λ2 is n2, the following formula (1),
0.55 <(λ1 / (n1-1)) / (λ2 / (n2-1)) <0.65 (1)
It is mounted on an optical pickup device provided with a light source that irradiates at least two kinds of light fluxes that satisfy the above conditions. Such an optical pickup device can record or reproduce information on any of two types of optical discs having different standards. If the upper limit of conditional expression (1) is exceeded, the light utilization efficiency at the time of using the DVD is not preferable. If it is below the lower limit, the light utilization efficiency when using a BD or HD DVD decreases, which is not preferable.

Further, the objective lens according to the present invention is a light capable of recording or reproducing information with respect to each optical disc by selectively using the first and second laser beams having different wavelengths for at least two types of optical discs having different standards. An objective lens mounted on a pickup device, wherein a protective layer thickness of a first optical disk on which information is recorded or reproduced using a first laser beam is t1, and has a wavelength longer than that of the first laser beam. When the thickness of the protective layer of the second optical disk on which information is recorded or reproduced using the second laser beam is t2, t1 and t2 have the following relationship:
t1 ≦ t2
The filling,
When the numerical aperture of the objective lens required for recording or reproducing information on the first optical disk is NA1, and the numerical aperture required for recording or reproducing information on the second optical disk is NA2,
NA1 ≧ NA2
And
The objective lens has a phase shift structure on at least one surface, and the phase shift structure converges the first laser beam on the recording surface of the first optical disc and the second laser beam on the second optical disc. A first region that converges on the recording surface, and the first region includes an annular zone in which a step is formed such that an additional optical path length for the first laser beam is approximately two wavelengths; The optical path length addition amount for the first laser light when the refractive surface is located outside and located on the outside of the annular zone group is approximately three wavelengths in the direction opposite to the step constituting the annular zone group. It is characterized by having at least one annular zone structure comprising such a return step portion.

  According to the objective lens according to claim 9, the effective beam diameter on the incident-side surface of the objective lens when the first laser light is incident is the incidence of the objective lens when the second laser light is incident. When set to be larger than the effective light beam diameter on the side surface, the phase shift structure, like the phase shift surface in the optical pickup optical system, has only the first laser light outside the first region. It is desirable to have a second region that does not contribute to the convergence of the second laser beam. In the second region, when the refracting surface located on the inner side is used as a reference at the boundary between adjacent refracting surfaces, the optical path length addition amount for the first laser light is the same as the first region. Different steps are formed.

  In the second region of the phase shift structure, it is preferable that the optical path length addition amount with respect to the first laser beam is approximately one wavelength or approximately −1 wavelength.

  Further, the effective beam diameter on the incident side surface of the objective lens when the second laser beam is incident is larger than the effective beam diameter on the incident side surface of the objective lens when the first laser beam is incident. When set to be, it is desirable that the phase shift structure has a second region outside the first region that focuses only the second laser beam and does not contribute to the convergence of the first laser beam. In the second region, when the refracting surface located inside is used as a reference at the boundary between adjacent refracting surfaces, the optical path length addition amount for the second laser light is different from the first region. Is formed (claim 11).

  In the second region of the phase shift structure, the optical path length addition amount is preferably formed to be approximately one wavelength or approximately −1 wavelength (claim 12).

The objective lens according to any one of claims 8 to 12, wherein the wavelength of the first laser beam is λ1, the wavelength of the second laser beam is λ2, the refractive index of the objective lens with respect to the wavelength λ1 is n1, When the refractive index of the objective lens for the second wavelength λ2 is n2, the following equation (1),
0.55 <(λ1 / (n1-1)) / (λ2 / (n2-1)) <0.65 (1)
It is mounted on an optical pickup device provided with a light source that irradiates at least two types of light fluxes that satisfy the above conditions. Such an optical pickup device can record or reproduce information on any of at least two types of optical discs having different standards.

From another point of view, the optical pickup optical system according to the present invention uses the first and second laser beams having different wavelengths for at least two types of optical discs having different standards, so that information on each optical disc can be stored. An optical pickup optical system capable of recording or reproducing, comprising: an objective lens; and an optical element disposed on the light source side of the objective lens and having a phase shift surface on at least one surface, and a first laser beam The thickness of the protective layer of the first optical disc on which information is recorded or reproduced using t is t1, and the information is recorded or reproduced using a second laser beam having a wavelength longer than that of the first laser beam. When the protective layer thickness of the second optical disk is t2, t1 and t2 have the following relationship:
t1 ≦ t2
The filling,
When the numerical aperture of the objective lens required for recording or reproducing information on the first optical disk is NA1, and the numerical aperture required for recording or reproducing information on the second optical disk is NA2,
NA1 ≧ NA2
And
The phase shift surface, after passing through the optical element and the objective lens, converges the first laser beam onto the recording surface of the first optical disc, and converges the second laser beam onto the recording surface of the second optical disc. A first region that has a step that shifts the phase in the first direction for each incident laser beam, and a first region for each incident laser beam. In the i-th zone group having at least one annular zone structure including a return step portion that shifts the phase in a second direction opposite to the one direction, i-th position counted from the optical axis side The optical path length addition amount with respect to the first laser beam when the annular zone near the optical axis in the outermost annular zone is set as a reference is φie [λ], i-th position counted from the optical axis side. For the first stepped laser beam with reference to the annular zone near the optical axis at the return step. When the optical path length addition amount φim [λ] to be performed is as follows,
-5 <| φie-φ (i-1) m |-| φim-φie | <4 (2)
However, when i = 1, φ (i−1) = 0
(Claim 14).

According to the optical pickup optical system of claim 14, the optical system further includes the following condition (3):
2.7 <| φim-φie | <3.3 (3)
It is preferable to satisfy (claim 15).

Furthermore, from another point of view, the objective lens according to the present invention can record information on each optical disc by using different first and second laser beams having different wavelengths for at least two types of optical discs having different standards. An objective lens used in a reproducible optical pickup device, wherein the protective layer thickness of the first optical disk on which information is recorded or reproduced using the first laser light is t1, more than that of the first laser light When the thickness of the protective layer of the second optical disc on which information is recorded or reproduced using a second laser beam having a long wavelength is t2, t1 and t2 have the following relationship:
t1 ≦ t2
The filling,
When the numerical aperture of the objective lens required for recording or reproducing information on the first optical disk is NA1, and the numerical aperture required for recording or reproducing information on the second optical disk is NA2,
NA1 ≧ NA2
And
The objective lens has a phase shift structure on at least one surface, and the phase shift structure converges the first laser beam on the recording surface of the first optical disc and the second laser beam on the second optical disc. The first region converges on the recording surface of the first region, and the first region has a step that shifts the phase in the first direction with respect to each incident laser beam, and for each incident laser beam An annular zone structure comprising an annular zone that shifts the phase in the first direction and a return step portion that shifts the phase in the second direction opposite to the first direction for each incident laser beam. At least one of the i-th ring group located at the i-th position from the optical axis side, and the outermost annular zone with respect to the first laser beam when the annular zone near the optical axis is used as a reference The optical path length addition amount is φie [λ], which is the i th position from the optical axis side. When the optical path length addition amount φim [λ] with respect to the annular zone in the vicinity of the optical axis at the i-th return step portion to be placed is set as the following condition (2),
-5 <| φie-φ (i-1) m |-| φim-φie | <4 (2)
However, when i = 1, φ (i−1) = 0
(Claim 17).

According to the optical pickup optical system according to claim 17, the optical system further includes the following condition (3):
2.7 <| φim-φie | <3.3 (3)
It is preferable to satisfy (claim 18).

  As described above, according to the present invention, by designing one surface of the optical element or one surface of the objective lens as a step structure having the above-described characteristics, the design of the laser beam used when recording or reproducing information is performed. A change in spherical aberration due to a deviation from the wavelength can be suppressed to a small level. This is very effective especially when using a new standard optical disc with high recording density and low tolerance for aberration. At the same time, the step structure also has an effect of reducing a decrease in diffraction efficiency. Therefore, a good spot for recording or reproducing information can be formed on the recording surface of each optical disk, regardless of whether the first or second optical disk is used.

  Hereinafter, an embodiment of an optical pickup device 100 mounting the optical pickup optical system 10 according to the present invention and an optical pickup device 200 mounting the objective lens 20 according to the present invention will be described. The optical pickup devices 100 and 200 are mounted on an optical information recording / reproducing device having compatibility with the first and second optical discs D1 and D2 having different recording densities. All optical disks are placed on a turntable (not shown) and rotated when information is recorded or reproduced.

The optical disks D1 and D2 on which information is recorded or reproduced by each optical information recording / reproducing apparatus have the following relationship, where the thicknesses of the protective layers are t1 and t2.
t1 ≦ t2

Further, when information is recorded or reproduced on each of the optical discs D1 and D2, it is necessary to change the required NA value so that a beam spot corresponding to the difference in recording density can be obtained. Here, assuming that the optimum design numerical apertures required for recording or reproducing information on the optical discs D1 and D2 are NA1 and NA2, respectively, each NA has the following relationship.
NA1 ≧ NA2
That is, when recording or reproducing information on the first optical disc D1 having a higher recording density, formation of a spot having a smaller diameter is required, so that a necessary NA is increased.

  As a specific example, the first optical disc D1 is assumed to be a new standard optical disc capable of recording information with a capacity higher than that of a DVD, for example, BD or HD DVD. The second optical disk is assumed to be an optical disk having a relatively high recording density, such as a DVD, for example, an existing optical disk.

  When using the optical disks D1 and D2 having different recording densities as described above, laser beams having different wavelengths are used so as to obtain beam spot diameters corresponding to the recording densities. Specifically, when information is recorded on or reproduced from the first optical disc D1, in order to form a beam spot having a smaller diameter on the recording surface of the first optical disc D1, the shortest design wavelength ( A laser beam (hereinafter referred to as a first laser beam) that is a first wavelength) is irradiated from a light source. As the first wavelength, for example, a wavelength in the range of 400 nm is selected. When information is recorded on or reproduced from the second optical disc D2, a spot having a diameter larger than the spot formed on the recording surface of the first optical disc D1 appears on the recording surface of the second optical disc D2. The laser light (hereinafter referred to as the second laser light) having a design wavelength (second wavelength) longer than the first laser light is irradiated from the light source. As the second wavelength, for example, a wavelength in the range of 650 nm is selected.

  FIG. 1 is a diagram showing a schematic configuration of an optical pickup apparatus 100 on which an optical pickup optical system 10 is mounted and optical disks D1 and D2. The optical pickup device 100 includes a light source 1A that emits a first laser beam, a light source 2A that emits a second laser beam, collimating lenses 1B and 2B, a beam splitter 3, an optical pickup optical system 10, a half mirror 4, and a light receiving unit. 5 In FIG. 1, the first laser beam is indicated by a solid line, and the second laser beam is indicated by a dotted line.

  The first laser light emitted from the light source 1A when the first optical disc D1 is used is deflected by the half mirror 4 and converted into a parallel light beam via the collimator lens 1B, and then optical pickup optics via the beam splitter 3. Incident in system 10. Then, the first laser beam emitted from the optical pickup optical system 10 converges on the recording surface of the first optical disc D1 placed on the turntable.

  The second laser light emitted from the light source 2A when the second optical disc D2 is used is converted into a parallel light beam via the collimator lens 2B, and then enters the optical pickup optical system 10 via the beam splitter 3. Then, the second laser light emitted from the optical pickup optical system 10 converges on the recording surface of the second optical disk D2 placed on the turntable.

  As described above, each laser beam incident on the optical pickup optical system 10 is converted into a parallel light beam, thereby effectively preventing off-axis aberrations such as coma aberration when the optical pickup optical system 10 is tracking shifted. be able to.

  Each laser beam reflected by the recording surface of each optical disc D 1, D 2 passes through the half mirror 4 and is received by the light receiving unit 5.

  FIG. 2 is an enlarged view of the optical pickup optical system 10. The optical pickup optical system 10 includes a phase shift element 11 and an objective lens 12. The phase shift element 11 and the objective lens 12 are held by a lens holder 13. As described above, when the optical pickup optical system 10 is composed of a plurality of optical elements, each element is held by the same holding member like the lens holder 13, thereby degrading performance due to relative displacement of each element. This makes it easy to control the drive during focusing.

  The phase shift element 11 has a first surface 11a and a second surface 11b in order from the light source side. The first surface 11a is a phase shift surface having a phase shift structure in which steps as described in detail below are continuously formed. More specifically, the first surface 11a has an inner region (first region) 11ai around the optical axis AX and an outer region (second region) 11ao formed outside the inner region 11ai. The inner region 11ai and the outer region 11ao have different phase shift structures.

  In the present embodiment, the second surface 11b is formed as a flat surface. However, in the optical pickup optical system according to the present invention, the second surface 11b of the phase shift element 11 can also be configured as a phase shift surface like the first surface 11a.

  Hereinafter, the phase shift structure of the inner region 11ai of the first surface 11a will be described in detail. The phase shift structure of the inner region 11ai has a plurality of steps, and an annular group that shifts the phase in the first direction (for example, the direction from the optical pickup optical system 10 toward each optical disk) with respect to the incident light beam, It has an annular structure composed of a return step portion that shifts the phase in a second direction (for example, a direction from the optical pickup optical system 10 toward the light source) opposite to the one direction. FIG. 3 is a schematic diagram for explaining the annular zone structure. The optical path length addition amount used in the following description of the phase shift structure is based on the design wavelength (first wavelength) of the first laser beam.

As shown in FIG. 3, when attention is paid to the i-th ring zone structure (i-th ring zone structure) located from the optical axis AX, the optical path length addition amounts at the respective steps constituting the ring zone group are all formed to be the same. Is done. Further, an optical path length addition amount in the i-th zone group constituting the i-th zone structure is X (i), and an optical path length addition amount in the i-th return step portion constituting the i-th zone structure is Y (i). Then, the i-th zone structure is formed so as to satisfy the following condition (α).
-5 <| X (i) |-| Y (i) | <4 (α)

Here, when the annular zone near the optical axis is used as a reference, the optical path length addition amount at the outermost annular zone in the i-th annular zone is φie (unit: λ), and the optical path length addition at the i-th return step portion When the amount is φim (unit: λ), the condition (α) is expressed as the following condition (2).
-5 <| φie-φ (i-1) m |-| φim-φie | <4 (2)
However, when i = 1, φ (i−1) = 0.

  Condition (2) is a condition for minimizing the change in spherical aberration caused by the minute change of the wavelength of the first laser light from the first wavelength, particularly when recording or reproducing information on the first optical disc D1. is there. When the value of the condition (2) is below the lower limit, the correction for spherical aberration that changes due to the minute change of the wavelength of the laser beam used when recording or reproducing information on each optical disk from the design wavelength becomes excessive. If the value of condition (2) exceeds the upper limit, correction for the spherical aberration will be insufficient. Therefore, any state is not preferable for recording or reproducing information with high accuracy.

Further, when recording or reproducing information to or from the second optical disc D2, it is possible to prevent a decrease in the diffraction efficiency of the second laser beam and to form a good spot on the recording surface of the second optical disc D2. | Φim−φie | in 2), that is, the absolute value of the additional optical path length Y (i) is configured to satisfy the following condition (3).
2.7 <| φim-φie | <3.3 (3)

  Next, the phase shift structure of the outer region 11ao will be described. The outer region 11ao is provided when the effective light beam diameter required when using the first optical disc D1 and when using the second optical disc D2 is different.

  When the effective light beam diameter required when using the first optical disk D1 is larger than the effective light beam diameter required when using the second optical disk D2, the outer region 11ao transmits the first laser light transmitted through the region 11ao. Shifts well on the recording surface of the first optical disc D1, and does not contribute to the convergence on the recording surface of the second optical disc D2 with respect to the second laser light transmitted through the region 11ao. It is configured to have a structure.

  Specifically, the phase shift structure of the outer region 11ao is composed of a plurality of annular zones separated by at least one step. And the optical path length addition amount with respect to the 1st laser beam in each level | step difference is provided in inner area | region 11ai (more specifically, each level | step difference and return level | step-difference part in each ring zone group of inner side area | region 11ai). The optical path length is added differently from the laser beam.

  When the effective light beam diameter required when using the second optical disk D2 is larger than the effective light beam diameter required when using the first optical disk D1, the outer area 11ao passes through the area 11ao. The second laser beam converges satisfactorily on the recording surface of the second optical disc D2, and does not contribute to the convergence on the recording surface of the first optical disc D1 with respect to the first laser beam transmitted through the region 11ao. The phase shift structure is configured as described above. In this case, the phase shift structure of the outer region 11ao is configured such that the optical path length addition amount for the second laser light is different from the optical path length addition amount for the second laser light applied in the inner region 11ai.

  Next, the optical pickup device 200 will be described. FIG. 4 is a diagram showing a schematic configuration of the optical pickup device 200 on which the objective lens 20 is mounted and optical disks D1 and D2. 4, the same components as those of the optical pickup device 100 are denoted by the same reference numerals as those in FIG. 1, and the description thereof is omitted here.

  FIG. 5 is an enlarged view of the objective lens 20. The objective lens 20 has a first surface 20a and a second surface 20b in order from the light source side. The first surface 20a is configured as a phase shift surface similarly to the first surface 11a in the phase shift element 11 described above. The first surface 20a is divided into an inner region 20ai and an outer region 20ao having different phase shift structures. Since the phase shift structure of each of the regions 20ai and 20ao is the same as that of each of the regions 11ai and 11ao described above, description thereof is omitted here.

The optical pickup devices 100 and 200 on which the optical pickup optical system 10 and the objective lens 20 described above are mounted are optical elements of the optical pickup optical system 10 for the wavelengths of the first laser light and the second laser light. 11 and the objective lens 20 are designed so as to satisfy the following condition (1).
0.55 <(λ1 / (n1-1)) / (λ2 / (n2-1)) <0.65 (1)
Where λ1 is the first wavelength,
λ2 is the second wavelength,
n1 represents the refractive index of the optical element 11 or the objective lens 20 of the optical pickup optical system 10 for the first wavelength λ1,
n2 represents the refractive index of the optical element 11 or the objective lens 20 of the optical pickup optical system 10 for the second wavelength λ2, respectively.

  An optical pickup device that is equipped with the optical pickup optical system 10 and the objective lens 20 and is configured to satisfy the condition (1) increases the diffraction efficiency of laser light when using each optical disc, The effect of suppressing the change of the spherical aberration due to the minute change of the wavelength from the first wavelength when using the optical disc can be obtained more remarkably.

  Three specific examples based on the embodiment described above are presented. Example 1 is a specific example of the optical pickup device 100, and Examples 2 and 3 are specific examples of the optical pickup 200. Therefore, the schematic configuration of the optical pickup devices 100 and 200 of each embodiment is shown in FIG. 1 and FIG. In Example 1, the protective layer thickness t1 of the first optical disc D1 is 0.1 mm, and the protective layer thickness t2 of the second optical disc D2 is 0.6 mm. In Examples 2 and 3, the first optical disc D1 and the second optical disc D2 are used. In each of the optical discs D2, the protective layer thicknesses t1 and t2 are assumed to be 0.6 mm.

  Table 1 shows specific specifications of the optical pickup optical system 10 mounted on the optical pickup device 100 of the first embodiment.

  As shown by the magnification values in Table 1, in the optical pickup device 100 of the first embodiment, the laser light used is a parallel light beam even when the first and second optical disks D1 and D2 are used. The light enters the pickup optical system 10. Specific numerical configurations of the optical pickup device 100 including the optical pickup optical system 10 shown in Table 1 when the optical disks D1 and D2 are used are shown in Tables 2 and 3, respectively. However, in Tables 2 and 3, for convenience of explanation, the numerical configuration regarding the members disposed between the light source and the optical pickup optical system 10 and the label surface of each optical disk is omitted. In addition, the notation E in each table | surface represents the power which uses 10 as the radix and the number on the right of E is an exponent. The same applies to the tables shown in Examples 2 and 3 described later.

  In each table, r is the radius of curvature (unit: mm) of each lens surface, d is the lens thickness or lens interval (unit: mm) during information recording or reproduction, and n (Xnm) is the refractive index at wavelength Xnm. is there. Surface number 1 represents the first surface 11 a of the phase shift element 11, and surface number 2 represents the second surface 11 b of the element 11. Surface numbers 3 and 4 represent each surface of the objective lens 12, and surface numbers 5 and 6 represent a protective layer and a recording surface in each optical disc.

  According to Tables 1 to 3, in the optical pickup device 100 of Example 1, (λ1 / (n1-1)) / (λ2 / (n2-1)) = 0.592, and the condition (1) is satisfied. It is configured to meet.

The optical pickup device 100 according to the first embodiment is effective on the incident-side surface of the phase shift element 11 for obtaining a desired spot diameter on the recording surface of the first optical disc when the first laser beam is incident. When the second laser beam is incident, the beam diameter is designed to be larger than the effective beam diameter on the incident side surface for obtaining a desired spot diameter on the recording surface of the second optical disk. The Therefore, the first surface 11a (surface number 1) has an inner region 11ai and an outer region 11ao having different phase shift structures. In addition, when the range of each area | region in the 1st surface 11a is represented by the height h from the optical axis AX,
Inner region 11ai... H ≦ 1.35,
The outer region 11ao... 1.35 <h <1.70.

The first surface 11a of the phase shift element 11 and both surfaces of the objective lens 12 are aspheric. The shape of each aspherical surface is the distance (sag amount) from the tangential plane on the optical axis of the aspherical surface at the coordinate point on the aspherical surface where the height from the optical axis is h. The curvature (1 / r) on the axis is C, the conic coefficient is K, the fourth, sixth, eighth, tenth, twelfth, etc. aspheric coefficients are A ₄ , A ₆ , A ₈ , A ₁₀ , As A ₁₂ ,...

  Table 4 shows conical coefficients and aspheric coefficients that define the shape of each aspheric surface. As shown in Table 4, on the first surface 11a, the inner surface 11ai and the outer region 11ao have different aspheric shapes.

  The phase shift structure formed on the first surface 11a of the phase shift element 11 is specifically shown in Table 5. Table 5 is a table showing the range of the annular zone formed on the first surface 11a and the optical path length addition amount given by the first laser beam and the second laser beam passing through each annular zone. The range of each annular zone is represented by heights hmin to hmax from the optical axis AX.

  As shown in Table 5, the phase shift structure of the inner region 11ai has eight ring zones from the first to the eighth, and seven return steps from the first to the seventh provided between the ring zones. Consists of parts. In other words, the phase shift structure of the inner region 11ai has seven annular zone structures including an annular zone group and a return step portion from the first to the seventh. Each ring zone group is composed of three ring zones except for the first ring zone group. Each annular zone is formed so that the optical path length addition amount for the first laser light is two wavelengths (or -2 wavelengths). Further, each return step portion has an optical path length addition amount with respect to the first laser beam in a direction opposite to the optical path length addition amount of the immediately preceding annular zone (for example, the annular zone number 3 when focusing on the first return step portion). Are formed to have three wavelengths (or -3 wavelengths). Table 6 shows the values of condition (2) and condition (3) regarding each ring zone structure and the eighth ring zone group. As shown in Table 6, it can be seen that all of the first to seventh annular structures satisfy the conditions (2) and (3).

Moreover, as shown in Table 5, the phase shift structure of the outer region 11ao is composed of a plurality of annular zones. Each annular zone is formed such that the optical path length addition amount for the first laser beam is one wavelength.
By forming in this way, the phase shift structure of the outer region 11ao contributes only to the convergence of the first laser light transmitted through the optical element and the objective lens, and does not contribute to the convergence of the second laser light. An aperture limiting function for the second laser beam can be provided.

When the phase shift structure provided on the first surface 10a of the phase shift element 11 of the first embodiment described above is regarded as a diffraction structure, the diffraction structure can be represented by the following optical path difference function φ (h).

The optical path difference function φ (h) is diffracted by the imaginary ray and the diffractive structure when it is not diffracted by the diffractive structure at the height h from the optical axis on the diffractive surface (first surface 10a). The optical path length difference from the measured light is shown. P ₂ , P ₄ , P ₆ ,... Are secondary, quaternary, sixth order,. Table 7 shows optical path difference function coefficients P ₂ ,... That define the diffractive structure. m represents the diffraction order at which the diffraction efficiency of each laser beam is maximized in each of the regions 11ai and 11ao. As described above, the diffraction order m is set to a different value for each laser beam to be used and for each region in which the diffraction structure is provided. As shown in Table 8, the inner region 11ai has a diffractive structure that contributes to the convergence of the first laser beam and the second laser beam. On the other hand, the outer region 11ao contributes only to the convergence of the first laser beam transmitted through the optical element and the objective lens, that is, the aperture limiting function for the second laser beam having a small effective light beam diameter on the incident side surface. Has a diffractive structure.

  FIG. 6A shows the intensity and spot of the spot formed on the recording surface of the first optical disc D1 by the first laser beam changed by +5 nm from the design wavelength (405 nm) in the optical pickup device 100 of the first embodiment. It is a graph showing the relationship with the distance from a center. FIG. 6B shows the intensity of the spot formed by the second laser beam having the design wavelength (660 nm) on the recording surface of the second optical disc D2 and the distance from the center of the spot in the optical pickup device 100 of the first embodiment. It is a graph showing the relationship. FIG. 7A shows a conventional optical pickup device that does not have a return step portion, in other words, includes an optical pickup optical system having an annular structure constituted only by an annular group (hereinafter, an optical pickup of Comparative Example 1). FIG. 5 is a graph showing the relationship between the intensity of the spot formed on the recording surface of the first optical disc D1 and the distance from the center of the spot by the first laser beam changed by +5 nm from the design wavelength. FIG. 7B shows the relationship between the intensity of the spot formed by the second laser beam having the design wavelength on the recording surface of the second optical disc D2 and the distance from the center of the spot in the optical pickup device of Comparative Example 1. It is a graph to represent. In each graph, the vertical axis indicates the relative intensity when the intensity at the spot center is 100, and the horizontal axis indicates the distance (unit: mm) from the spot center. The graphs related to Examples 2 and 3 described below are the same.

  Comparing FIG. 6 (A) and FIG. 7 (A), the optical pickup device 100 according to the first embodiment can reduce the intensity of so-called side lobes generated around the spot and record or reproduce information. It turns out that the intensity | strength of this spot center part which contributes is raised. Here, in an optical information recording / reproducing apparatus including an optical pickup optical system that is substantially free of aberration when the first optical disk is used, a spot where a first laser beam having a design wavelength is formed on the recording surface of the first optical disk D1. The diameter (referring to the spot diameter when the intensity is 13.5%; the same applies hereinafter) is 0.397 (μm). The spot diameter shown in FIG. 7A is 0.359 (μm), whereas the spot diameter shown in FIG. 6A is 0.394 (μm), which is substantially the same as the spot diameter at the design wavelength. is there. Further, when it is assumed that the diffraction efficiency of light when the first laser beam having the design wavelength is non-aberrated and converges on the recording surface of the first optical disc D1, the spot shown in FIG. While the diffraction efficiency is 54.1%, the spot shown in FIG. 6A is considerably improved to 86.3%.

  Further, when FIG. 6B is compared with FIG. 7B, the optical pickup device 100 of Example 1 and the optical pickup device of Comparative Example 1 are approximately similar in spot shape and intensity including side lobes. I understand that. Here, in an optical information recording / reproducing apparatus including an optical pickup optical system that is substantially free of aberration when the second optical disk is used, a spot formed by the second laser beam having the design wavelength on the recording surface of the second optical disk D2 The diameter is 0.840 (μm). The spot diameter shown in FIG. 7B is 0.842 (μm), whereas the spot shown in FIG. 6B is 0.840 (μm), that is, the same diameter as the spot at the design wavelength. Further, when it is assumed that the diffraction efficiency of light when the second laser beam having the design wavelength is non-aberrated and converges on the recording surface of the second optical disc D2 is 100%, the spot shown in FIG. Although the diffraction efficiency is 86.9%, the spot shown in FIG. 6B falls slightly to 83.5%, but is in a sufficiently usable range.

  From the above comparison, the optical pickup device 100 of Example 1 suppresses a change in spherical aberration due to a minute change in wavelength when the first optical disc D1 is used, and has a high amount of light compared to the device of Comparative Example 1. It can be seen that a spot extremely close to the optimum diameter can be formed on the recording surface of the first optical disc D1. In addition, the optical pickup device 100 of the first embodiment has the same effect, but the spots formed on the recording surface of the optical disc D2 when using the second optical disc D2 are substantially the same as those of the device of the comparative example 1. It can also be seen that the state is maintained. That is, the optical pickup device 100 according to the first embodiment is capable of recording at high density while guaranteeing high-precision information recording or reproduction with respect to the existing second optical disc, and thus has a tolerance for aberration. Recording or reproduction of information with respect to the first optical disc D1 having a smaller can be realized with high accuracy regardless of whether or not there is a change in wavelength.

  Specific specifications of the objective lens 20 mounted on the optical pickup device 200 of Example 2 are shown in Table 9.

  As shown in Table 9, the magnification value indicates that the optical pickup device 200 of the second embodiment is also used in the same manner as in the first embodiment even when the first and second optical disks D1 and D2 are used. The light enters the objective lens 20 as a parallel light beam. Specific numerical configurations of the optical pickup device 200 including the objective lens 20 shown in Table 9 when the optical disks D1 and D2 are used are shown in Tables 10 and 11, respectively.

  In each table, surface numbers 1 and 2 represent the first surface 20a and the second surface 20b of the objective lens 20, respectively. Surface numbers 3 and 4 represent the protective layer and recording surface of each optical disc.

  According to Tables 9 to 11, the optical pickup device 200 of Example 2 is (λ1 / (n1-1)) / (λ2 / (n2-1)) = 0.592, which is the same as that of Example 1. In addition, it is configured to satisfy the condition (1).

In the optical pickup device 200 according to the second embodiment, the effective light beam diameter on the incident side surface of the objective lens 20 when the first laser beam is incident is the surface on the incident side when the second laser beam is incident. It is designed to be larger than the effective light beam diameter at. Therefore, the first surface 20a (surface number 1) has an inner region 20ai and an outer region 20ao having different phase shift structures. In addition, when the range of each area | region in the 1st surface 20a is represented by the height h from the optical axis AX,
Inner region 20ai... H ≦ 1.86,
The outer region 20ao... 1.86 <h <1.95.

  Both surfaces of the objective lens 20 are configured as aspherical surfaces. Table 12 shows conical coefficients and aspheric coefficients that define the shape of each aspheric surface. As shown in Table 12, the aspherical shapes of the inner region 20ai and the outer region 20ao are different on the first surface 20a.

  The phase shift structure formed on the first surface 20a of the objective lens 20 is specifically shown in Table 13. Table 13 is a table showing the range of the annular zone formed on the first surface 20a and the optical path length addition amount given by the first laser beam and the second laser beam passing through each annular zone. The range of each annular zone is represented by heights hmin to hmax from the optical axis AX.

  As shown in Table 13, the phase shift structure of the inner region 20ai has five ring zones from the first to the fifth and four return steps from the first to the fourth provided between the ring zones. Consists of parts. In other words, the phase shift structure of the inner region 20ai has four ring zone structures including a ring zone group and a return step portion, from the first to the fourth. Each ring zone group is composed of two ring zones except for the first ring zone group. Each annular zone is formed so that the additional optical path length for the first laser beam is two wavelengths. Further, each return step portion has an optical path length addition amount with respect to the first laser beam in a direction opposite to the optical path length addition amount of the immediately preceding annular zone (for example, the annular zone with the zone number 2 when focusing on the first return step portion). Are formed to have three wavelengths. Table 14 shows the values of condition (2) and condition (3) for each ring zone structure and the fifth ring zone group. As shown in Table 14, it can be seen that all of the first to fourth annular structures satisfy the conditions (2) and (3).

  Moreover, as shown in Table 13, the phase shift structure of the outer region 20ao is composed of a plurality of annular zones. Each annular zone is formed so that the additional optical path length is one wavelength with respect to the first laser beam.

Table 15 shows optical path difference function coefficients P ₂ ,... When the phase shift structure provided on the first surface 10a of the objective lens 20 described above is regarded as a diffraction structure. The diffraction order m is shown in Table 16. As shown in Table 16, the inner region 20ai has a diffractive structure that contributes to the convergence of the first laser beam and the second laser beam. On the other hand, the outer region 20ao has a diffractive structure that contributes only to the convergence of the first laser beam, that is, has an aperture limiting function for the second laser beam.

  FIG. 8A shows the intensity of the spot formed on the recording surface of the first optical disc D1 by the first laser beam changed by +5 nm from the design wavelength in the optical pickup device 200 of the second embodiment, and from the spot center. It is a graph showing the relationship with distance. FIG. 8B shows the relationship between the intensity of the spot formed by the second laser beam having the design wavelength on the recording surface of the second optical disc D2 and the distance from the center of the spot in the optical pickup device 200 of the second embodiment. It is a graph showing. FIG. 9A shows a conventional optical pickup device that does not have a return step portion, in other words, has the same configuration as that of the second embodiment except that it includes an objective lens having an annular zone structure that is constituted only by an annular zone group. (Hereinafter referred to as the optical pickup device of Comparative Example 2), the intensity of the spot formed on the recording surface of the first optical disc D1 by the first laser beam changed by +5 nm from the design wavelength and the distance from the center of the spot It is a graph showing a relationship. FIG. 9B shows the relationship between the intensity of the spot formed by the second laser beam having the design wavelength on the recording surface of the second optical disc D2 and the distance from the center of the spot in the optical pickup device of Comparative Example 2. It is a graph to represent.

  Comparing FIG. 8 (A) and FIG. 9 (A), the optical pickup device 200 of the second embodiment can reduce the intensity of the so-called side lobe generated around the spot and record or reproduce information. It turns out that the intensity | strength of this spot center part which contributes is raised. Here, in the optical information recording / reproducing apparatus dedicated to the first optical disc having the same configuration as that of the second embodiment, except that the objective lens is substantially free of aberration when the first optical disc is used, the first laser beam having the design wavelength is used. However, the diameter of the spot that will be formed on the recording surface of the first optical disc D1 is 0.520 (μm). The spot diameter shown in FIG. 9A is 0.522 (μm), and the spot diameter shown in FIG. 8A is 0.524 (μm), which is substantially the same as the spot at the design wavelength. Further, when it is assumed that the diffraction efficiency of light when the first laser beam having the design wavelength is non-aberrated and converges on the recording surface of the first optical disc D1, the spot shown in FIG. While the diffraction efficiency is 85.4%, the spot shown in FIG. 8A is improved to 94.3%.

  Further, comparing FIG. 8B and FIG. 9B, the optical pickup device 200 of Example 2 and the optical pickup device of Comparative Example 2 are approximately similar in spot shape and intensity including side lobes. I understand that. Here, a second laser beam having a design wavelength is used in the optical information recording / reproducing apparatus dedicated to the second optical disc having the same configuration as that of the second embodiment, except that an objective lens that has substantially no aberration is provided when the second optical disc is used. However, the diameter of the spot that will be formed on the recording surface of the second optical disc D2 is 0.918 (μm). The spot diameter shown in FIG. 9B is 0.917 (μm), and the spot diameter shown in FIG. 8A is 0.916 (μm), which is substantially the same as that at the design wavelength. Further, when it is assumed that the diffraction efficiency of light when the second laser light of the design wavelength is non-aberrated and converges on the recording surface of the second optical disc D2 is 100%, the spot shown in FIG. The diffraction efficiency is 91.7%, while the spot shown in FIG. 8B is slightly lowered to 88.7%, but is in a sufficiently usable range.

  From the above comparison, the optical pickup device 200 of Example 2 suppresses the change in spherical aberration due to a minute change in wavelength when the first optical disc D1 is used, and has a high amount of light compared to the device of Comparative Example 2. It can be seen that a spot extremely close to the optimum diameter can be formed on the recording surface of the first optical disc D1. Further, the optical pickup device 200 of the second embodiment has the same effect, but the spots formed on the recording surface of the optical disc D2 when using the second optical disc D2 are substantially the same as those of the device of the comparative example 2. It can also be seen that the state is maintained. That is, the optical pickup device 200 according to the second embodiment is capable of recording at high density while guaranteeing high-precision information recording or reproduction with respect to the existing second optical disk. Recording or reproduction of information with respect to the first optical disc D1 having a smaller can be realized with high accuracy regardless of whether or not there is a change in wavelength.

  Specific specifications of the objective lens 20 mounted on the optical pickup device 200 of Example 3 are shown in Table 17.

  As shown in Table 17, the magnification value indicates that the optical pickup device 200 according to the third embodiment is used even when the first and second optical disks D1 and D2 are used, as in the second embodiment. The laser light enters the objective lens 20 as a parallel light beam. Specific numerical configurations of the optical pickup device 200 including the objective lens 20 shown in Table 17 when the optical disks D1 and D2 are used are shown in Tables 18 and 19, respectively. The surface numbers 1 to 4 shown in Tables 18 and 19 represent the same surfaces as those described in Example 2 above.

  According to Tables 17 to 19, the optical pickup device 200 of Example 3 also has (λ1 / (n1-1)) / (λ2 / (n2-1)) = 0.582, which is the same as that of Example 1. In addition, it is configured to satisfy the condition (1).

The optical pickup device 200 according to the third embodiment is different from the above embodiments in that the effective light beam diameter on the incident-side surface of the objective lens 20 when the second laser light is incident is the first laser. It is designed to be larger than the effective light beam diameter on the incident side surface when light is incident. Therefore, the first surface 20a (surface number 1) has an inner region 20ai and an outer region 20ao having different phase shift structures. In addition, when the range of each area | region in the 1st surface 20a is represented by the height h from the optical axis AX,
Inner region 20ai... H ≦ 2.015,
The outer region 20ao... 2.015 <h <2.080.

  Both surfaces of the objective lens 20 are configured as aspherical surfaces. Table 20 shows conical coefficients and aspheric coefficients that define the shape of each aspheric surface. As shown in Table 20, on the first surface 20a, the aspheric shapes of the inner region 20ai and the outer region 20ao are different from each other.

  The phase shift structure formed on the first surface 20a of the objective lens 20 is specifically shown in Table 21. Table 21 is a table showing the range of the annular zone formed on the first surface 20a and the optical path length addition amount given by the first laser beam and the second laser beam passing through each annular zone. The range of each annular zone is represented by heights hmin to hmax from the optical axis AX.

  As shown in Table 21, the phase shift structure of the inner region 20ai has five ring zones from the first to the fifth and four return steps from the first to the fourth provided between the ring zones. Consists of parts. In other words, the phase shift structure of the inner region 20ai has four ring zone structures including a ring zone group and a return step portion, from the first to the fourth. Each ring zone group is composed of three ring zones except for the first ring zone group. Each annular zone is formed so that the additional optical path length for the first laser beam is two wavelengths. Further, each return step portion has an optical path length addition amount with respect to the first laser beam in a direction opposite to the optical path length addition amount of the immediately preceding annular zone (for example, the annular zone number 3 when focusing on the first return step portion). Are formed to have three wavelengths. Table 22 shows the values of condition (2) and condition (3) regarding each ring zone structure and the fifth ring zone group. As shown in Table 22, it can be seen that all the first to fourth annular zone structures satisfy the conditions (2) and (3).

  Moreover, as shown in Table 21, the phase shift structure of the outer region 20ao is composed of a plurality of annular zones. Each annular zone is formed so that the additional optical path length is equivalent to one wavelength with respect to the second laser beam.

Table 23 shows optical path difference function coefficients P ₂ ,... When the phase shift structure provided on the first surface 10a of the objective lens 20 described above is regarded as a diffraction structure. The diffraction order m is shown in Table 24. As shown in Table 24, the inner region 20ai has a diffractive structure that contributes to the convergence of the first laser beam and the second laser beam. On the other hand, the outer region 20ao has a diffractive structure that contributes only to the convergence of the second laser beam, that is, has an aperture limiting function for the first laser beam having a small effective beam diameter on the incident side surface. ing.

  FIG. 10A shows the intensity of the spot formed on the recording surface of the first optical disc D1 by the first laser beam changed by +5 nm from the design wavelength in the optical pickup device 200 of the third embodiment, and from the spot center. It is a graph showing the relationship with distance. FIG. 10B shows the relationship between the intensity of the spot formed by the second laser beam having the design wavelength on the recording surface of the second optical disc D2 and the distance from the center of the spot in the optical pickup device 200 of the third embodiment. It is a graph showing. FIG. 11A shows a conventional optical pickup device that does not have a return step portion, in other words, has the same configuration as that of the third embodiment except that it includes an objective lens having a ring zone structure that includes only a ring zone group. (Hereinafter referred to as the optical pickup device of Comparative Example 3), the intensity of the spot formed on the recording surface of the first optical disc D1 by the first laser beam changed by +5 nm from the design wavelength and the distance from the center of the spot It is a graph showing a relationship. FIG. 11B shows the relationship between the intensity of the spot formed by the second laser beam of the design wavelength on the recording surface of the second optical disc D2 and the distance from the center of the spot in the optical pickup device of Comparative Example 3. It is a graph to represent.

  Comparing FIG. 10A and FIG. 11A, the optical pickup device 200 according to the third embodiment can reduce the intensity of the so-called side lobe generated around the spot and record or reproduce information. It turns out that the intensity | strength of this spot center part which contributes is raised. Here, in the optical information recording / reproducing apparatus dedicated to the first optical disc having the same configuration as that of the third embodiment, except that the objective lens is substantially free of aberration when the first optical disc is used, the first laser beam having the design wavelength is used. However, the diameter of the spot that will be formed on the recording surface of the first optical disc D1 is 0.521 (μm). The spot diameter shown in FIG. 11 (A) is 0.534 (μm), whereas the spot diameter shown in FIG. 10 (A) is 0.530 (μm). It is closer to a more suitable spot shape. Further, when it is assumed that the diffraction efficiency of light when the first laser beam of the design wavelength is non-aberrated and converges on the recording surface of the first optical disk D1, the spot shown in FIG. The diffraction efficiency is 82.0%, whereas the spot shown in FIG. 10A is improved to 95.6%.

  Further, when FIG. 10B and FIG. 11B are compared, the optical pickup device 200 of Example 3 and the optical pickup device of Comparative Example 3 are approximately similar in spot shape and strength including side lobes. I understand that. Here, in the optical information recording / reproducing apparatus dedicated to the second optical disc having the same configuration as that of the third embodiment except that the objective lens is substantially free of aberration when the second optical disc is used, the second laser beam having the design wavelength is The diameter of the spot that will be formed on the recording surface of the second optical disc D2 is 0.851 (μm). The spot diameter shown in FIG. 11B is 0.861 (μm), whereas the spot diameter shown in FIG. 10B is 0.853 (μm), which is substantially the same as the spot diameter at the design wavelength. is there. Further, when it is assumed that the diffraction efficiency of light when the second laser beam having the design wavelength is non-aberrated and converges on the recording surface of the second optical disc D2 is 100%, the spot shown in FIG. The diffraction efficiency is 87.7%, while the spot shown in FIG. 10B is slightly reduced to 86.9%, but is in a sufficiently usable range.

  From the above comparison, the optical pickup device 200 of the third embodiment suppresses a change in spherical aberration due to a minute change in wavelength when the first optical disc D1 is used, and has a higher light quantity than the device of the third comparative example. It can be seen that a spot extremely close to the optimum diameter can be formed on the recording surface of the first optical disc D1. Further, the optical pickup device 200 of the third embodiment has the same effect, but the spots formed on the recording surface of the optical disc D2 when using the second optical disc D2 are substantially the same as those of the device of the comparative example 3. It can also be seen that the state is maintained. In other words, the optical pickup device 200 according to the third embodiment is capable of recording at high density while guaranteeing high-precision information recording or reproduction with respect to the existing second optical disk, and thus has tolerance for aberration. Recording or reproduction of information with respect to the first optical disc D1 having a smaller can be realized with high accuracy regardless of whether or not there is a change in wavelength.

  The above is the embodiment of the present invention. Each of the above-described embodiments is merely an example of an optical pickup device including the optical pickup optical system and the objective lens according to the present invention. That is, the present invention is not limited to the specific numerical configuration of each embodiment. For example, the surface on which the phase shift structure is provided may be the second surface instead of the first surface of the phase shift element or the objective lens. Moreover, you may provide a diffraction structure in both the 1st surface and the 2nd surface.

  In FIG. 3, a plurality of annular zones are shown. In each embodiment, it has been described that the inner regions 11ai and 20ai have a plurality of ring zones. However, according to the present invention, in the phase shift structure of each phase shift element and objective lens of the optical pickup optical system, if there is at least one ring zone structure, the change in aberration corresponding to a minute change in wavelength is suppressed. The effect to do is obtained. That is, it is not always necessary to form a plurality of the annular structures.

1 is a diagram illustrating a schematic configuration of an optical pickup device equipped with an optical pickup optical system according to an embodiment of the present invention and each optical disc. It is a figure which expands and shows the optical pick-up optical system of embodiment. It is a figure for demonstrating the ring zone structure of embodiment. 1 is a diagram showing a schematic configuration of an optical pickup device equipped with an objective lens according to an embodiment of the present invention and an optical disc. It is a figure which expands and shows the objective lens of embodiment. FIG. 6A shows the relationship between the intensity of the spot formed on the recording surface of the first optical disk by the first laser beam changed by +5 nm from the design wavelength and the distance from the center of the spot in the apparatus of the first embodiment. It is a graph showing. FIG. 6B is a graph showing the relationship between the intensity of the spot formed by the second laser beam having the design wavelength on the recording surface of the second optical disk and the distance from the center of the spot in the apparatus of the first embodiment. is there. FIG. 7A shows the relationship between the intensity of the spot formed on the recording surface of the first optical disk by the first laser beam changed by +5 nm from the design wavelength and the distance from the center of the spot in the apparatus of Comparative Example 1. It is a graph showing. FIG. 7B is a graph showing the relationship between the intensity of the spot formed by the second laser beam having the design wavelength on the recording surface of the second optical disc and the distance from the center of the spot in the apparatus of Comparative Example 1. is there. FIG. 8A shows the relationship between the intensity of the spot formed on the recording surface of the first optical disc by the first laser beam changed by +5 nm from the design wavelength and the distance from the center of the spot in the apparatus of Example 2. It is a graph showing. FIG. 8B is a graph showing the relationship between the intensity of the spot formed by the second laser beam having the design wavelength on the recording surface of the second optical disc and the distance from the center of the spot in the apparatus of the second embodiment. is there. FIG. 9A shows the relationship between the intensity of the spot formed on the recording surface of the first optical disc by the first laser beam changed by +5 nm from the design wavelength and the distance from the center of the spot in the apparatus of Comparative Example 2. It is a graph showing. FIG. 9B is a graph showing the relationship between the intensity of the spot formed by the second laser beam having the design wavelength on the recording surface of the second optical disc and the distance from the center of the spot in the apparatus of Comparative Example 2. is there. FIG. 10A shows the relationship between the intensity of the spot formed on the recording surface of the first optical disk by the first laser beam changed by +5 nm from the design wavelength and the distance from the center of the spot in the apparatus of Example 3. It is a graph showing. FIG. 10B is a graph showing the relationship between the intensity of the spot formed on the recording surface of the second optical disk by the second laser beam having the design wavelength and the distance from the center of the spot in the apparatus of Example 3. is there. FIG. 11A shows the relationship between the intensity of the spot formed on the recording surface of the first optical disk and the distance from the center of the spot by the first laser beam changed by +5 nm from the design wavelength in the apparatus of Comparative Example 3. It is a graph showing. FIG. 11B is a graph showing the relationship between the intensity of the spot formed by the second laser beam having the design wavelength on the recording surface of the second optical disk and the distance from the center of the spot in the apparatus of Comparative Example 3. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical pick-up optical system 11 Phase shift element 12 Objective lens 20 Objective lens D1, D2 Optical disk 100, 200 Optical pick-up apparatus

Claims (19)

An optical pickup optical system capable of recording or reproducing information with respect to each optical disc by selectively using the first and second laser beams having different wavelengths for at least two types of optical discs having different standards,
An objective lens;
An optical element disposed on the light source side of the objective lens and having a phase shift surface on at least one surface,
The thickness of the protective layer of the first optical disk on which information is recorded or reproduced using the first laser light is t1, and information is obtained using the second laser light having a wavelength longer than that of the first laser light. Where t2 is the thickness of the protective layer of the second optical disc on which recording or reproduction is performed, t1 and t2 have the following relationship:
t1 ≦ t2
The filling,
When the numerical aperture necessary for recording or reproducing information on the first optical disk of the objective lens is NA1, and the numerical aperture necessary for recording or reproducing information on the second optical disk is NA2,
NA1 ≧ NA2
And
The phase shift surface, after passing through the optical element and the objective lens, converges the first laser beam onto the recording surface of the first optical disc, and causes the second laser beam to converge to the second laser beam. Having a first region that converges on the recording surface of the optical disc;
The first region is a step at the boundary between adjacent refracting surfaces such that the additional amount of optical path length for the first laser light is about two wavelengths when the inner refracting surface is used as a reference. The optical path length addition amount with respect to the first laser beam in a case where the annular zone group is formed on the outer side of the annular zone group and the refractive surface located on the inner side is a reference. An optical pickup optical system having at least one annular zone structure including a return step portion having approximately three wavelengths in a direction opposite to the optical path length addition amount. The optical pickup optical system according to claim 1,
When the first laser light is incident, the effective light beam diameter on the incident-side surface of the optical element for obtaining a desired spot diameter on the recording surface of the first optical disc is the second laser. When light is incident, it is larger than the effective light beam diameter on the incident side surface of the optical element for obtaining a desired spot diameter on the recording surface of the second optical disc,
The phase shift surface contributes to convergence of the first laser light that has passed through the optical element and the objective lens outside the first region, and the first phase that has passed through the optical element and the objective lens. A second region that does not contribute to the convergence of the second laser beam,
The second region is different from the first region in the optical path length addition amount with respect to the first laser light when the inner refractive surface is used as a reference at the boundary between adjacent refractive surfaces. An optical pickup optical system characterized in that such a step is formed. The optical pickup optical system according to claim 2,
In the second region, the optical path length addition amount for the first laser light is about one wavelength or about −1 wavelength. The optical pickup optical system according to claim 1,
When the second laser beam is incident, the effective light beam diameter on the incident side surface of the optical element for obtaining a desired spot diameter on the recording surface of the second optical disc is the first laser beam. When light is incident, it is larger than the effective light beam diameter on the incident-side surface of the optical element to obtain a desired spot diameter on the recording surface of the first optical disc,
The phase shift surface contributes to convergence of the second laser light that has passed through the optical element and the objective lens outside the first region, and the first phase that has passed through the optical element and the objective lens. Having a second region that does not contribute to the convergence of one laser beam,
The second region is different from the first region in the optical path length addition amount with respect to the second laser light when a reference is made to the inner refracting surface at the boundary between adjacent refracting surfaces. An optical pickup optical system characterized in that such a step is formed. The optical pickup optical system according to claim 4, wherein
The step of the second region is formed so that the optical path length addition amount for the second laser light is about one wavelength or about −1 wavelength. In the optical pickup optical system according to any one of claims 1 to 5,
The optical pickup optical system, wherein the objective lens and the optical element are held by the same holding member. An optical pickup device capable of recording or reproducing information by selectively using first and second laser beams having different wavelengths for at least two types of optical discs having different standards,
An optical pickup optical system according to any one of claims 1 to 6,
A light source for irradiating the first and second laser beams,
The wavelength of the first laser light is λ1, the wavelength of the second laser light is λ2, the refractive index of the optical element for the wavelength λ1 is n1, and the refractive index of the optical element for the second wavelength λ2 is n2. Then, the following formula (1),
0.55 <(λ1 / (n1-1)) / (λ2 / (n2-1)) <0.65 (1)
An optical pickup device satisfying the requirements. It is an objective lens mounted on an optical pickup device capable of recording or reproducing information on each optical disc by properly using the first and second laser beams having different wavelengths for at least two types of optical discs having different standards. And
The thickness of the protective layer of the first optical disk on which information is recorded or reproduced using the first laser light is t1, and information is obtained using the second laser light having a wavelength longer than that of the first laser light. Where t2 is the thickness of the protective layer of the second optical disc on which recording or reproduction is performed, t1 and t2 have the following relationship:
t1 ≦ t2
The filling,
When the numerical aperture necessary for recording or reproducing information on the first optical disk of the objective lens is NA1, and the numerical aperture necessary for recording or reproducing information on the second optical disk is NA2,
NA1 ≧ NA2
And
The objective lens has a phase shift structure on at least one surface;
The phase shift structure has a first region for converging the first laser beam on the recording surface of the first optical disc and converging the second laser beam on the recording surface of the second optical disc. Have
The first region is located on the outer side of the annular zone group in which a step is formed so that the optical path length addition amount for the first laser beam is approximately two wavelengths, and is located on the inner side. A return step portion in which the optical path length addition amount for the first laser light with respect to the refracting surface is approximately three wavelengths in the direction opposite to the optical path length addition amount in the step constituting the annular zone group. And an objective lens having at least one annular zone structure. The objective lens according to claim 8, wherein
The effective beam diameter on the incident side surface of the objective lens when the first laser beam is incident is the effective beam diameter on the incident side surface of the objective lens when the second laser beam is incident. Bigger,
The phase shift structure has a second region outside the first region that does not contribute to the convergence of the second laser beam by focusing only the first laser beam,
The second region is different from the first region in the optical path length addition amount with respect to the first laser light when the inner refractive surface is used as a reference at the boundary between adjacent refractive surfaces. An objective lens having such a level difference. The objective lens according to claim 9, wherein
In the second region, the optical path length addition amount for the first laser light is about one wavelength or about −1 wavelength. The objective lens according to claim 8, wherein
The effective beam diameter on the incident side surface of the objective lens when the second laser beam is incident is the effective beam diameter on the incident side surface of the objective lens when the first laser beam is incident. Bigger,
The phase shift structure has a second region that does not contribute to the convergence of the first laser beam by focusing only the second laser beam outside the first region,
The second region is different from the first region in the optical path length addition amount with respect to the second laser light when a reference is made to the inner refracting surface at the boundary between adjacent refracting surfaces. An objective lens having a step. The objective lens according to claim 11, wherein
The objective lens, wherein in the second region of the phase shift structure, an optical path length addition amount with respect to the second laser light is formed to be approximately one wavelength or approximately −1 wavelength. An optical pickup device capable of recording or reproducing information with respect to each optical disc by selectively using the first and second laser beams having different wavelengths for two types of optical discs having different standards,
The objective lens according to any one of claims 8 to 12,
A light source for irradiating the first and second laser beams,
The wavelength of the first laser light is λ1, the wavelength of the second laser light is λ2, the refractive index of the objective lens for the wavelength λ1 is n1, and the refractive index of the objective lens for the second wavelength λ2 is n2. Then, the following formula (1),
0.55 <(λ1 / (n1-1)) / (λ2 / (n2-1)) <0.65 (1)
An optical pickup device satisfying the requirements. An optical pickup optical system capable of recording or reproducing information with respect to each optical disc by selectively using the first and second laser beams having different wavelengths for at least two types of optical discs having different standards,
An objective lens;
An optical element disposed on the light source side of the objective lens and having a phase shift surface on at least one surface,
The thickness of the protective layer of the first optical disk on which information is recorded or reproduced using the first laser light is t1, and information is obtained using the second laser light having a wavelength longer than that of the first laser light. Where t2 is the thickness of the protective layer of the second optical disc on which recording or reproduction is performed, t1 and t2 have the following relationship:
t1 ≦ t2
The filling,
When the numerical aperture necessary for recording or reproducing information on the first optical disk of the objective lens is NA1, and the numerical aperture necessary for recording or reproducing information on the second optical disk is NA2,
NA1 ≧ NA2
And
The phase shift surface, after passing through the optical element and the objective lens, converges the first laser beam onto the recording surface of the first optical disc, and causes the second laser beam to converge on the second optical disc. A first region that converges on the recording surface of
The first region is an annular group having a plurality of steps whose phase is shifted in the first direction with respect to each incident laser beam, and the first direction with respect to each incident laser beam. Having at least one annular zone structure including a return step portion that shifts the phase in the opposite second direction,
An optical path length addition amount with respect to the first laser light in the outermost annular zone in the i-th annular zone that is counted from the optical axis side when the annular zone near the optical axis is used as a reference. φie [λ], an optical path length addition amount φim [with respect to the first laser light when the annular zone near the optical axis is used as a reference at the i-th return step portion positioned i-th counting from the optical axis side λ], the following condition (2),
-5 <| φie-φ (i-1) m |-| φim-φie | <4 (2)
However, when i = 1, φ (i−1) = 0
An optical pickup optical system characterized by satisfying Furthermore, the following condition (3),
2.7 <| φim-φie | <3.3 (3)
The optical pickup optical system according to claim 14, wherein: An optical pickup device capable of recording or reproducing information with respect to each optical disc by selectively using the first and second laser beams having different wavelengths for at least two types of optical discs having different standards,
An optical pickup optical system according to claim 14 or 15,
A light source for irradiating the first and second laser beams,
The wavelength of the first laser light is λ1, the wavelength of the second laser light is λ2, the refractive index of the optical element for the wavelength λ1 is n1, and the refractive index of the optical element for the second wavelength λ2 is n2. Then, the following formula (1),
0.55 <(λ1 / (n1-1)) / (λ2 / (n2-1)) <0.65 (1)
An optical pickup device satisfying the requirements. An objective lens used in an optical pickup device capable of recording or reproducing information with respect to each optical disc by selectively using first and second laser beams having different wavelengths for at least two types of optical discs having different standards. ,
The thickness of the protective layer of the first optical disk on which information is recorded or reproduced using the first laser light is t1, and information is obtained using the second laser light having a wavelength longer than that of the first laser light. Where t2 is the thickness of the protective layer of the second optical disc on which recording or reproduction is performed, t1 and t2 have the following relationship:
t1 ≦ t2
The filling,
When the numerical aperture necessary for recording or reproducing information on the first optical disk of the objective lens is NA1, and the numerical aperture necessary for recording or reproducing information on the second optical disk is NA2,
NA1 ≧ NA2
And
The objective lens has a phase shift structure on at least one surface;
The phase shift structure has a first region for converging the first laser beam on the recording surface of the first optical disc and converging the second laser beam on the recording surface of the second optical disc. Have
The first region has a step that shifts the phase in the first direction for each incident laser beam, and the annular zone group that shifts the phase in the first direction for each incident laser beam; And at least one annular zone structure including a return step portion that shifts the phase in a second direction opposite to the first direction with respect to each incident laser beam,
An optical path length addition amount with respect to the first laser light in the outermost annular zone in the i-th annular zone that is counted from the optical axis side when the annular zone near the optical axis is used as a reference. When φie [λ] is the optical path length addition amount φim [λ] with respect to the annular zone in the vicinity of the optical axis at the i-th return step located at the i-th position counted from the optical axis side, Condition (2),
-5 <| φie-φ (i-1) m |-| φim-φie | <4 (2)
However, when i = 1, φ (i−1) = 0
Objective lens characterized by satisfying Furthermore, the following condition (3),
2.7 <| φim-φie | <3.3 (3)
The objective lens according to claim 17, wherein: An optical pickup device capable of recording or reproducing information with respect to each optical disc by properly using the first and second laser beams having different wavelengths for two types of optical discs having different standards,
The objective lens according to claim 17 or claim 18,
A light source for irradiating each of the luminous fluxes,
The wavelength of the first laser light is λ1, the wavelength of the second laser light is λ2, the refractive index of the objective lens for the wavelength λ1 is n1, and the refractive index of the objective lens for the second wavelength λ2 is n2. Then, the following formula (1),
0.55 <(λ1 / (n1-1)) / (λ2 / (n2-1)) <0.65 (1)
An optical pickup device satisfying the requirements.

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