JP4897405B2 - Optical pickup and optical information processing apparatus - Google Patents

Description

  The present invention relates to an optical pickup and an optical information processing apparatus, and in particular, records and reproduces information with respect to a plurality of types of optical recording media having different recording densities due to different wavelengths of light sources or transparent substrate thicknesses of optical recording media. When using a light source unit with two or more wavelengths of light sources in a single package as a light source, aberrations caused by different wavelengths or transparent substrate thickness with a single objective lens The present invention relates to an apparatus including an element to be corrected.

  Optical recording media such as CDs with a recording capacity of 0.65 GB and DVDs with a recording capacity of 4.7 GB are becoming popular as means for storing video information, audio information, or data on a computer. In recent years, there has been an increasing demand for further improvement in recording density and increase in capacity.

  As means for improving the recording density of such an optical recording medium, in an optical pickup for writing or reading information on the optical recording medium, the numerical aperture of the objective lens (hereinafter referred to as NA) is increased, or the light source It is effective to reduce the diameter of the beam spot that is collected by the objective lens and formed on the optical recording medium by shortening the wavelength.

  Therefore, for example, in the “CD optical recording medium”, the NA of the objective lens is 0.50 and the wavelength of the light source is 780 nm, whereas the recording density is higher than that of the “CD optical recording medium”. In the “DVD optical recording medium”, the NA of the objective lens is 0.65 and the wavelength of the light source is 660 nm. As described above, the optical recording medium is desired to further improve the recording density and increase the capacity. For this purpose, the NA of the objective lens is further larger than 0.65, or the wavelength of the light source is 660 nm. It is desired to make it even shorter.

  As such a large-capacity optical recording medium and optical information processing apparatus, a “Blu-ray Disc” standard that satisfies a capacity of 22 GB is achieved using a light source in the blue wavelength region and an objective lens with NA of 0.85 ( (Hereinafter referred to as BD) has been proposed.

  Even with an optical pickup capable of recording and / or reproducing high-density information such as BD, it is necessary to ensure information recording and / or reproduction even for a large amount of CDs and DVDs conventionally supplied. . Depending on the type of optical recording medium to be recorded and reproduced, a light source having an appropriate wavelength is selected, and an appropriate optical process is performed on the selected light flux, resulting from differences in the substrate thickness of each optical recording medium. It is desirable to correct spherical aberration. As means for correcting the aberration, an aberration correcting element having a diffractive structure has been proposed.

The aberration correction element is generally a flat element, but when such a flat element is mounted on an optical pickup, the aberration correction element is disposed at an angle. This is to avoid the problem that a part of the light beam traveling from the light source to the objective lens does not pass through the incident surface of the flat plate component and becomes specularly reflected light, and the specularly reflected light overlaps with the signal light and becomes noise light. It is.
JP 2006-99924 A

  However, when the aberration correction element having a diffractive structure is disposed obliquely, coma aberration occurs. Patent Document 1 proposes an assembly method for inclining an aberration correction element having a diffractive structure due to burrs of the diffractive structure. According to Patent Document 1, by shifting the center of the aberration correction element in which the diffractive structure is formed in a direction perpendicular to the optical axis, for example, coma aberration of the diffraction surface on the objective lens side which is one surface of the aberration correction element is reduced. It can be corrected. The other surface of the aberration correcting element needs to be separately corrected.

  In order to reduce the size of the optical pickup and reduce the number of assembling steps, a light source unit in which a plurality of light sources are placed in one package may be used. As such a two-wavelength light source unit, for example, in a two-wavelength light source unit corresponding to CD and DVD, the two light sources to be arranged have an interval of about several hundred microns. Patent Document 1 describes that the use of such an interval can reduce the other surface aberration of the aberration correction element that cannot be corrected, but the specific configuration is not clearly described.

  Therefore, the present invention actively uses an aberration correction element having a diffractive structure on an optical pickup capable of condensing on a plurality of types of optical recording media with a single objective lens in order to avoid the flare light. An object of the present invention is to provide an optical pickup and an optical information processing apparatus capable of suppressing a generated aberration and obtaining a good recording / reproducing signal for each of a plurality of types of optical recording media even when the optical recording medium is inclined. And

In order to achieve the above object, an optical pickup according to a first aspect of the present invention includes a first optical recording medium having a substrate thickness of 0.1 mm and a second substrate having a substrate thickness of 0.6 mm. In an optical pickup that performs one or more of recording, reproduction, and erasing on three types of optical recording media: an optical recording medium and a third optical recording medium having a substrate thickness of 1.2 mm.
A first light source that emits a first light beam having a first wavelength λ1 = 405 nm corresponding to the first optical recording medium, and a second wavelength λ2 = 660 nm corresponding to the second optical recording medium. A second light source that emits a second light beam having a third wavelength λ corresponding to the third optical recording medium
A third light source that emits a third light beam having 3 = 785 nm, an objective lens having an NA of 0.85 that is optimally designed for the first optical recording medium, and the second light source that is emitted from the second light source. Spherical aberration that occurs when a light beam is condensed on the second optical recording medium via the objective lens;
An aberration correction element for correcting spherical aberration generated when the third light beam emitted from the third light source is condensed on the third optical recording medium through the objective lens on one surface; Provided between the objective lens and the first to third light sources, the first, second, and third concentric circles on the optical axis center in the optical axis vertical plane on one surface of the aberration correction element A diffractive structure having a region is provided;
The first region corresponding to NA 0.45 of the diffractive structure is about the first light flux.
Most of the second light flux is transmitted as −1st order diffracted light, and most of the third light flux is transmitted as −2nd order diffracted light. The number of steps and the groove depth per step are selected, and the second region of NA0.45 to NA0.65 of the diffraction structure transmits most of the first light flux as 0th order light, For the second light flux, the majority of the second luminous flux is the first-order diffracted light, and for the third light flux, the number of steps of the diffractive structure and the groove depth per stage are such that most of the second light flux is transmitted by the zero-order light. Selected
The direction of the staircase of the diffraction structure in the first region is formed outward with respect to the optical axis of the objective lens, and the direction of the staircase of the diffraction structure in the second region is directed to the optical axis. The third region of NA 0.65 to NA 0.85 of the diffraction structure is a flat structure in which no diffraction structure is formed, and the second and third light sources are formed inward. In a direction in which the second light source is disposed on the optical axis of the objective lens and the coma aberration generated due to the optical axis deviation between the third light source and the objective lens is cancelled. Further, the aberration correction element is arranged so as to be inclined with respect to the optical axis and shifted in a direction perpendicular to the optical axis.

The optical pickup according to claim 2 is the optical pickup according to claim 1, serving as the second, third light source in the light source unit integrally constituting the third light source on the optical axis of said objective lens place manner, tilting the aberration correcting element in a direction to cancel the coma aberration caused by the optical axis deviation between the second light source and the objective lens to the optical axis, and the direction perpendicular to the optical axis It is characterized by being shifted .

An optical pickup according to a third aspect includes a first optical recording medium having a substrate thickness of 0.1 mm, a second optical recording medium having a substrate thickness of 0.6 mm, and a substrate thickness of 1.2 mm. In an optical pickup that performs one or more of recording, reproduction, and erasing with respect to three types of optical recording media of the third optical recording medium,
A first light source that emits a first light beam having a first wavelength λ1 = 405 nm corresponding to the first optical recording medium, and a second wavelength λ2 = 660 nm corresponding to the second optical recording medium. A second light source that emits a second light beam having a third wavelength λ corresponding to the third optical recording medium
A third light source that emits a third light beam having 3 = 785 nm, an objective lens having an NA of 0.85 that is optimally designed for the first optical recording medium, and the second light source that is emitted from the second light source. Spherical aberration that occurs when a light beam is condensed on the second optical recording medium via the objective lens;
An aberration correction element for correcting spherical aberration generated when the third light beam emitted from the third light source is condensed on the third optical recording medium through the objective lens on one surface; Provided between the objective lens and the first to third light sources, the first, second, and third concentric circles on the optical axis center in the optical axis vertical plane on one surface of the aberration correction element A diffractive structure having a region is provided;
The first region corresponding to NA 0.45 of the diffractive structure is about the first light flux.
Most of the second light flux is transmitted as −1st order diffracted light, and most of the third light flux is transmitted as −2nd order diffracted light. The number of steps and the groove depth per step are selected, and the second region of NA0.45 to NA0.65 of the diffraction structure transmits most of the first light flux as 0th order light, For the second light flux, the majority of the second luminous flux is the first-order diffracted light, and for the third light flux, the number of steps of the diffractive structure and the groove depth per stage are such that most of the second light flux is transmitted by the zero-order light. Selected, the direction of the step of the diffraction structure of the first region is formed outward with respect to the optical axis of the objective lens;
The direction of the staircase of the diffraction structure of the second region is formed inward with respect to the optical axis of the objective lens, and the third region of NA0.65 to NA0.85 of the diffraction structure. Is a flat structure in which no diffraction structure is formed, the first, second, and third light sources are integrated, and the first and third light sources are close to each other. A third light source is arranged so as to be on the optical axis of the objective lens, and the aberration correction element is arranged in the direction to cancel coma aberration caused by an optical axis shift between the second light source and the objective lens. It is characterized by being arranged to be inclined with respect to the axis and shifted in a direction perpendicular to the optical axis.

The light source optical pickup according to claim 4, in which the optical pickup of claim 3, wherein the first, second, and integrally constitutes the third light source, and is close to the first, second light source the first unit, the direction of the second light source are arranged such that the optical axis of the objective lens to cancel the coma aberration caused by the optical axis deviation between the third light source and the objective lens tilt the aberration correcting element to the optical axis, and wherein the placing is shifted to the optical axis and the vertical direction.

Further, the optical information processing apparatus according to claim 5, recorded for a plurality of types of optical recording media having different recording densities, reproducing, an optical information processing apparatus for performing one or more of the erase claim 1-4 The optical pickup according to any one of the above is provided.

  According to the above configuration, the aberration correction element having a diffractive structure suppresses the generated aberration even when the aberration correction element is tilted to avoid flare light, and can be applied to a plurality of types of optical recording media. And good recording / reproducing signals can be obtained.

  According to the present invention, the aberration correcting element having a diffractive structure can suppress the aberration generated by the aberration correcting element even if the aberration correcting element is inclined to avoid flare light. As a result, it is possible to obtain a good recording / reproducing signal.

FIG. 1 is a diagram showing a schematic configuration of an optical pickup in Reference Example 1 of the embodiment of the present invention. As shown in FIG. 1, three types of optical recording media (BD system, DVD system, CD system) are recorded or reproduced with different numerical apertures NA using a single objective lens 108 using different light source wavelengths. It is a compatible optical pickup.

  The substrate thicknesses of the BD, DVD, and CD optical recording media 109a, 109b, and 109c are 0.1 mm, 0.6 mm, and 1.2 mm, respectively, and the BD, DVD, and CD optical recording media. 109a, 109b, 109c. The numerical apertures (NA) are NA0.85, NA0.65, and NA0.50, respectively, and the wavelengths λ1, λ2, and λ3 of the first, second, and third light sources are λ1 = 395 to 415 nm and λ2 =, respectively. 650 to 670 nm, λ3 = 770 to 805 nm.

  The optical pickup shown in FIG. 1 has a semiconductor laser 101, a collimating lens 102, a polarization beam splitter 103, a wavelength selective beam splitter 104, a deflection prism 105, a quarter wavelength plate 106, an aberration with respect to the BD optical recording medium 109a. The correction element 107, the objective lens 108, the detection lens 110, and the light receiving element 112 are included. The center wavelength of the semiconductor laser 101 as the first light source is 405 nm, and the numerical aperture (NA) of the objective lens 108 is 0.85. The substrate thickness of the BD optical recording medium 109a is 0.1 mm.

  The light emitted from the semiconductor laser 101 is made into substantially parallel light by the collimator lens 102. The light that has passed through the collimator lens 102 enters the polarization beam splitter 103 and is deflected by the deflecting prism 105. Then, the light is converted into circularly polarized light by the quarter-wave plate 106 and condensed on the BD optical recording medium 109a via the aberration correction element 107 and the objective lens 108, whereby information is recorded and reproduced. The reflected light from the BD optical recording medium 109 a passes through the quarter-wave plate 106 and is then converted into linearly polarized light that is orthogonal to the polarization direction of the outgoing light. Separated and deflected, the light is guided onto the light receiving element 112 by the detection lens 110, and a reproduction signal, a focus error signal, and a track error signal are detected.

  This optical pickup has a two-wavelength laser unit 120 that generates laser light for the DVD optical recording medium 109b and laser light for the CD optical recording medium 109c, that is, the wavelengths are different from each other. Laser light can be emitted.

  Further, the light emitted from the DVD semiconductor laser 113 a having a center wavelength of 660 nm with respect to the DVD optical recording medium 109 b is deflected by the deflecting prism 105 through the collimating lens 115 and the wavelength selective beam splitter 104. Then, the light is condensed on the DVD optical recording medium 109b via the quarter-wave plate 106, the aberration correction element 107, and the objective lens 108. The DVD-type optical recording medium 109b has a substrate thickness of 0.6 mm and a numerical aperture (NA) of 0.65. Switching of NA is limited by the aberration correction element 107. Then, the reflected light from the DVD optical recording medium 109b passes through the objective lens 108 and the quarter wavelength plate 106, then is deflected by the wavelength selective beam splitter 104, separated from the incident light by the hologram element 114, and separated from the DVD system. Guided on the light receiving element 113c, a reproduction signal, a focus error signal, and a track error signal are detected.

  Further, the light emitted from the CD semiconductor laser 116 a having a central wavelength of 785 nm with respect to the CD optical recording medium 109 c is deflected by the deflecting prism 105 through the collimating lens 115 and the wavelength selective beam splitter 104. Then, the light is condensed on the CD optical recording medium 109 c via the quarter-wave plate 106, the aberration correction element 107, and the objective lens 108. The substrate thickness of the CD optical recording medium 109c is 1.2 mm, and the numerical aperture (NA) of the objective lens is 0.50. Switching of NA is limited by the aberration correction element 107. Then, the reflected light from the CD optical recording medium 109c passes through the objective lens 108 and the quarter wavelength plate 106, then is deflected by the wavelength selective beam splitter 104, and separated from the incident light by the hologram element 114 to be separated from the CD system. The light is guided onto the light receiving element 116c, and a reproduction signal, a focus error signal, and a track error signal are detected.

  The configuration of the optical pickup is not limited to this, and for example, a light receiving element housed in one package such as the two-wavelength laser unit 120 may be housed in another package. That is, in place of the two-wavelength laser unit 120 shown in FIG. 1, a two-wavelength laser unit excluding the DVD and CD light receiving elements 113c and 116c and the hologram element 114 is used, and the light receiving element and the hologram are arranged at different positions. May be. Further, instead of disposing the light receiving elements corresponding to the respective wavelengths as in the DVD and CD light receiving elements 113c and 116c, light having two wavelengths may be received by a common light receiving element.

  Here, the objective lens 108 is optimally designed so that a BD optical recording medium 109a having a thickness of 0.1 mm can be recorded / reproduced with high accuracy. The design wavelength is 405 nm, and the wavelength is designed to be sufficiently small at 0.01 λrms or less at the wavelength of 405 nm. The objective lens 108 is easily affected by manufacturing errors due to higher NA and shorter wavelengths. In other words, since the manufacturing margin is narrow, in the first embodiment, the objective lens 108 is one of the three types of optical recording media. The design corresponds to the BD optical recording medium 109a.

The objective lens 108 of the first reference example is optimally designed for the BD optical recording medium 109a having a thickness of 0.1 mm, but is not limited to this. For example, in a two-layer Blu-ray Disc optical recording medium having two information recording surfaces, the information recording surface is located at positions 0.075 mm and 0.100 mm from the light incident side. An objective lens having a design median of 0.0875 mm in thickness may be used.

FIG. 2 shows a specific configuration example of the objective lens 108. The objective lens 108 of Reference Example 1 has a double-sided aspherical shape, and in an orthogonal coordinate system with the vertex of the surface as the origin and the optical axis direction as the X-axis, r is the paraxial radius of curvature, κ is the number of cones, A , B, C, D, E, F, G, H, J,... Are aspherical coefficients, the aspherical shape is expressed by the relationship between the distance x in the optical axis direction of the surface and the radius R. 1)

で表される。各面および各領域の面データを（表１）に示す。

It is represented by The surface data of each surface and each region is shown in (Table 1).

ここで、ガラスの硝材は住田光学製のＫＶＣ８１、対物レンズ１０８の有効瞳半径は２．１５ｍｍである。なお、対物レンズ１０８の材料としては、ガラスに限らず、樹脂を用いてもよい。

Here, the glass material of the glass is KVC81 manufactured by Sumita Optical Co., Ltd., and the effective pupil radius of the objective lens 108 is 2.15 mm. The material of the objective lens 108 is not limited to glass, and a resin may be used.

  3 to 6 are diagrams for explaining the aberration correction element 107, FIG. 3 and FIG. 4 are enlarged sectional views, and FIG. 5 and FIG.

  As shown in FIG. 1, the aberration correction element 107 causes spherical aberration generated by the objective lens 108 due to the difference in substrate thickness with respect to the DVD optical recording medium 109 b. In addition to the function of correction and aperture restriction for switching the NA of the objective lens 108, the light emitted from the 785 nm CD semiconductor laser 116 a is applied to the CD optical recording medium 109 c by the objective lens 108. Have a function of limiting the aperture for correcting the spherical aberration caused by the difference and switching the NA of the objective lens 108.

3 and 4 are sectional views of the aberration correction element 107 of the first reference example . As a material of the aberration correction element 107, any material may be used as long as a UV resin layer is provided on glass, resin, or a glass substrate, and a diffraction structure is provided on the resin layer. Resin is desirable from the viewpoint of easy mass production. Since the aberration correction element 107 according to the first embodiment is mounted on the objective lens holder 108b and is movable for focusing and tracking, it is desirable that the aberration correction element 107 be light. As the resin, for example, PMMA (polymethyl methacrylate: refractive index at each wavelength of 405 nm, 660 nm, and 785 nm is 1.51, 1.49, 1.48), or an optical resin manufactured by Nippon Zeon Co., Ltd. having good moisture absorption characteristics. ZEONEX that is.

  As a method for manufacturing the diffractive structure, etching or molding may be performed when the material is glass, and imprinting or molding may be performed when the material is a resin material.

As shown in FIG. 5, the DVD-system correcting diffractive surface 53 has two first and second regions 53a and 53b that are concentrically divided within a range through which a light beam passes. The first area 53a corresponds to an area of NA 0.65 with respect to the DVD optical recording medium 109b. In the first reference example , the radius is set to 1.57 mm. The first region 53a is formed with a diffractive structure, and most of the first light flux with a wavelength of 405 nm is transmitted as 0th order light, and most of the second light flux with a wavelength of 660 nm is 1. Most of the third light flux having a wavelength of 785 nm is transmitted as zero-order light.

The second area 53b corresponds to an area from NA 0.65 for the DVD optical recording medium 109b to NA 0.85 for the BD optical recording medium 109c. In the first reference example , the radius is set to 1.57 mm to 2.2 mm. . The second region 53b has a flat structure where no diffractive structure is formed.

As shown in FIG. 6, the CD-system correcting diffractive surface 52 has two first and second regions 52a and 52b that are concentrically divided within a range through which a light beam passes. The first area 52a corresponds to an area of NA 0.50 with respect to the CD optical recording medium 109c, and in this reference example 1, the radius is set to 1.32 mm. The first region 52a is formed with a diffractive structure, and most of the first light flux having a wavelength of 405 nm and the second light flux having a wavelength of 660 nm are transmitted through zero-order light, and a third light flux having a wavelength of 785 nm is transmitted. Most of the light flux is first-order diffracted light.

The second area 52b corresponds to an area from NA 0.50 for the CD optical recording medium 109c to NA 0.85 for the BD optical recording medium 109a. In the first reference example , the radius is set to 1.32 mm to 2.2 mm. . The second region 52b has a flat structure where no diffractive structure is formed.

  In the first region 53a of the diffractive surface 53, a diffractive structure having a concentric pattern is formed at the optical axis center in the plane perpendicular to the optical axis, and + 1st order diffracted light is generated. The concentric diffraction pattern is a spherical aberration that occurs when light is focused on a DVD optical recording medium 109b having a wavelength of 660 nm and a substrate thickness of 0.6 mm by the objective lens 108 that is optimally designed for the BD optical recording medium 109a. It is designed to cancel out, and as a result, a spot that converges to the diffraction limit is formed on the DVD optical recording medium 109b.

  In the first region 52a of the diffractive surface 52, a diffractive structure having a concentric pattern is formed at the center of the optical axis in the plane perpendicular to the optical axis, and + 1st order diffracted light is generated. The concentric diffraction pattern is a spherical aberration that occurs when light is focused on a CD optical recording medium 109c having a wavelength of 785 nm and a substrate thickness of 1.2 mm by the objective lens 108 that is optimally designed for the BD optical recording medium 109a. As a result, a spot that converges to the diffraction limit is formed on the CD-based optical recording medium 109c.

  The second regions 52b and 53b outside the diffractive structure (ring zone region) on both surfaces of the diffractive surfaces 52 and 53 are flat portions where the diffractive structure is not formed, and transmit the second light beam and the third light beam as they are. For example, the light transmitted through the first region 53a is collected by the objective lens 108 with respect to the DVD optical recording medium 109b, and the light that has passed through the second region 53b is applied to the DVD optical recording medium 109b. The light is not condensed and becomes scattered light as shown in FIGS. 7A and 7B, and does not affect the light collection and does not affect the recording and reproduction. That is, it is possible to restrict NA 0.65 to the DVD optical recording medium 109b without performing a special structure or coating.

  Next, the height of each step of the diffraction surfaces 53 and 52 formed on the aberration correction element 107 will be described. First, the height of each step of the diffractive surface 53 will be described with reference to FIG. In a diffractive optical system, not all the incident light energy is converted into outgoing light, but is converted only with an efficiency called diffraction efficiency. When the serrated kinoform shape as shown by the dotted line in FIG. 8 is blazed at a certain wavelength, the diffraction efficiency at that wavelength is theoretically 100% in the case of thin approximation.

  The diffractive surface 53 is used as the first-order diffracted light only for the second light beam of 660 nm among the three wavelengths, and the diffractive surface 52 is 1 only for the third light beam of 785 nm among the three wavelengths. A shape approximated to a staircase as shown in FIG. 8 is used as the next diffracted light. In addition, the step shape is easier than manufacturing an ideal kinoform shape.

  FIGS. 9A and 9B show the relationship between the stepped groove depth D and the efficiency. FIG. 9A shows a case where a four-step staircase structure is selected as the first region 53a of the diffractive surface 53. For the BD_0 order light, the DVD_−1 order light, the DVD_0 order light, the DVD_ + 1 order light, and the CD_0 order light. It is a result. When PMMA is used as the material, a desired efficiency can be obtained for any wavelength when the groove depth D is 5.9 μm. The efficiency is 72%, 65%, and 63% for the 0th-order transmitted light of the first light flux, the 1st-order diffracted light of the second light flux, and the 0th-order transmitted light of the third light flux, respectively. The groove depth D of 5.9 μm becomes a groove depth of 0.196 μm when converted into one stage.

  FIG. 9B shows the results for the BD_0 order light, the DVD_0 order light, the CD_ + 1 order light, and the CD_0 order light when a two-step staircase structure is selected as the first region 52a of the diffractive surface 52. FIG. When PMMA is used as the material, a desired efficiency can be obtained for any wavelength when the groove depth D is 3.7 μm. The efficiency is 81%, 76%, and 39% for the 0th-order transmitted light of the first light flux, the 1st-order diffracted light of the second light flux, and the 0th-order transmitted light of the third light flux, respectively.

  Further, the cross section of the first region 53a on the diffraction surface 53 of the aberration correction element 107 is composed of a plurality of annular concavo-convex portions formed concentrically as shown in FIG. Each ring-shaped uneven portion is stepped and has four steps. The pitch of the ring-shaped uneven portions is gradually narrowed from the inside to the outside so that the diffractive structure has a lens effect.

The pitch of the zonal irregularities is set so that the aberration is corrected with the + 1st order diffracted light for the DVD optical recording medium 109b.
The optical path difference function of the diffractive surface is (Equation 2)

と定義される。

Is defined.

  However, in an orthogonal coordinate system in which the point intersecting the optical axis of the optical axis vertical plane is the origin and the optical axis direction is the X axis, φ: optical path difference function, R: radius (distance from the optical axis), C1, C2, ...: Optical path difference coefficient.

  The optical path difference coefficient of the first region 53a of the diffraction surface 53 for DVD system correction (Table 2 (a)), and similarly, the optical path difference coefficient of the first region 52a of the diffraction surface 52 for CD system correction ( Table 2 (b)) shows.

次に、本参考例１の収差補正素子１０７の外形形状について、詳細に説明する。図５，図６に示したように、収差補正素子１０７の外形の形状は、回折部（第１の領域）と平坦部（第２の領域）との境界と同様の円形状とする。なお、円形状とは、多角形を含み、図１０に示すような８角形においても、同様の効果が得られる。さらに、これらの円形状、多角形形状は外形形状が光束有効径の３０％増しの場合であり、それ以上に外形形状が大きい場合は四角の形状であってもよい。

Next, the outer shape of the aberration correction element 107 of Reference Example 1 will be described in detail. As shown in FIGS. 5 and 6, the outer shape of the aberration correction element 107 is the same circular shape as the boundary between the diffraction part (first region) and the flat part (second region). The circular shape includes a polygon, and the same effect can be obtained even in an octagon as shown in FIG. Furthermore, these circular and polygonal shapes are cases where the outer shape is 30% larger than the effective diameter of the light beam, and when the outer shape is larger than that, a square shape may be used.

Resin such as PMMA used in this Reference Example 1 has the advantage that it can be injection-molded, so it is most widely used for optical parts and is easy to mass-produce. However, it has a weak hygroscopicity. It is done. This not only fluctuates optical characteristics such as refractive index and transmittance, but also appears as deformation.

  FIGS. 11A to 11D show actual measurement results of the transmitted wavefront having a wavelength of 405 nm when the aberration correction element is square. FIG. 11A shows the result of transmission wavefront measurement in the first region 53a and the second region 53b within the effective beam diameter, and shows the wavefront shape. FIGS. 11B and 11C show the results of wavefront measurement by dividing the result of FIG. 11A into each region. FIG. 11B shows the transmitted wavefront shape 53g of only the diffractive portion, and FIG. 11C shows the transmitted wavefront shape 53f of only the flat portion. When wavefront aberration is calculated based on the wavefront shape, the wavefront shape in the effective ray diameter (first and second regions 53a and 53b) in FIG. 11A has a PV value of 0.5λ and wavefront aberration of 0. .1λrms and the wavefront accuracy is very poor. Usually, it is desirable that the wavefront aberration of the optical component is 0.02λrms or less.

  The wavefront aberration in the diffractive portion (first region 53a) in FIG. 11B is 0.02λ rms, which is good wavefront accuracy, whereas the flat portion (second region 53b) in FIG. ) Is as large as 0.13 λrms, and it can be seen that the cause of poor wavefront accuracy within the effective beam diameter is the flat portion. FIG. 11D is a plot of the wavefront shape of the flat portion along the circumferential direction. It is considered that the flat portion is wavy along the square shape of the aberration correction element 107 and causes wavefront deterioration.

  At the boundary between the diffraction part and the flat part of the aberration correcting element 107, there are 53d and 53e far from the square of the outer shape of the outline, and there is a difference in PMMA moisture absorption between the near 53d and the far 53e. This difference in moisture absorption becomes a difference in deformation, and undulation occurs.

  12A to 12D show actual measurement results of the transmitted wavefront having a wavelength of 405 nm when the aberration correction element is circular. FIG. 12A shows the result of transmission wavefront measurement in the first region 53a and the second region 53b within the effective beam diameter, and shows the wavefront shape. FIGS. 12B and 12C show the results of wavefront measurement by dividing the result of FIG. 12A into each region. FIG. 12B shows a transmitted wavefront shape 53g of only the diffractive portion, and FIG. 12C shows a transmitted wavefront shape 53f of only the flat portion. FIG. 12D is a plot of the wavefront shape of the flat portion along the circumferential direction. When the wavefront aberration is calculated from the wavefront shape in the effective beam diameter (first and second regions 53a and 53b) in FIG. 12A, the PV value is 0.1λ, the wavefront aberration is 0.02λrms, and FIG. The wavefront aberration in the diffraction portion (first region 53a) is 0.015λrms, and the wavefront aberration in the flat portion (second region 53b) in FIG. 12 (c) is 0.017λrms. Good wavefront accuracy.

  In this way, by making the outer shape of the aberration correction element 107 the same circular shape as the boundary between the diffractive portion and the flat portion, the change in shape due to moisture absorption by PMMA can be made uniform, and undulation can be reduced. A high-precision optical pickup can be provided.

  FIG. 13 is a diagram showing a schematic configuration of the actuator portion of the optical pickup. The optical pickup includes an objective lens 108 and an objective lens holder 108b that holds the objective lens 108. Further, a base portion 25 that supports the objective lens holding body 108b, and elastic support mechanisms 26 and 27 interposed between the base portion 25 and the objective lens holding body 108b are provided. The elastic support mechanisms 26 and 27 elastically support the objective lens holding body 108b with respect to the base portion 25 so that the objective lens holding body 108b can move in a total of two directions of the focus direction and the tracking direction. Here, the aforementioned focus direction refers to the Z-axis direction (optical axis direction of the objective lens 108) in FIG. 13, and the tracking direction refers to the X-axis direction (radial direction of the optical recording medium 109) in FIG.

  Further, driving means not shown in FIG. 13 is provided. The driving means includes, for example, a permanent magnet provided on the objective lens holding body 108b and a driving coil fixed relatively to the base portion 25. It is comprised by what is called a voice coil motor. The driving means drives the objective lens holding body 108b in the two directions according to the input current to the driving coil. Focus servo and tracking servo are performed to control a current input to the drive coil of the drive means to follow a predetermined laser beam spot on a recording track on the information recording surface of the optical recording medium 109.

The cross-sectional view shown in FIG. 3 is a diagram schematically showing the configuration of the aberration correction element 107 and the objective lens 108 in the first reference example . As shown in FIG. 3, the aberration correction element 107 and the objective lens 108 are integrated coaxially by an objective lens holding body 108b. Specifically, the aberration correction element 107 is fixed to one end, the objective lens 108 is fixed to the other end, and these are coaxially integrated along the optical axis.

  When recording / reproducing the optical recording medium, the objective lens 108 moves within a range of about ± 0.5 mm in the direction perpendicular to the optical axis by tracking control. However, since the DVD optical recording medium 109b and the CD optical recording medium 109c are diffracted by the aberration correction element 107, if the aberration correction element 107 does not move and only the objective lens 108 moves, the aberration is increased. This occurs and the focused spot deteriorates. In view of this, the aberration correction element 107 and the objective lens 108 are integrated and moved together during tracking control, thereby obtaining a good condensing spot.

  Further, as shown in FIG. 1, if the dual wavelength laser unit 120 for DVD / CD is used, the optical pickup can be downsized and the number of assembling steps can be reduced. However, in such a two-wavelength laser unit 120, the two light sources have an interval of about several hundred microns. Therefore, when the DVD semiconductor laser 113a (light source) is disposed on the optical axes of the objective lens 108 and the collimating lens 115, the light from the CD semiconductor laser 116a (light source) is as shown in FIG. As a result, the coma aberration as shown in FIG. 15 occurs. FIG. 15 shows wavefront aberrations on the image plane. The horizontal axis is the pupil radius position, the vertical axis is the wavefront aberration, and has an asymmetric shape called coma aberration.

By the way, when using a flat plate element such as the aberration correction element 107 of Reference Example 1, it is necessary to consider flare light. A part of the light traveling from the light source toward the objective lens 108 becomes specularly reflected light without passing through the incident surface of the optical component. When the aberration correction element 107 is arranged perpendicular to the incident light, the specularly reflected light overlaps with the reflected light from the optical recording medium 109, that is, the signal light, as shown in FIG. , May become noise light. Therefore, as a countermeasure, there is a method of slightly tilting the incident surface to the optical component. As shown in FIG. 16B, by arranging the aberration correction element 107 in an inclined manner, it is not necessary to superimpose the specularly reflected light on the signal light.

  However, when the aberration correction element 107 is tilted, the diffraction region is tilted with respect to the optical axis and the center thereof is shifted in a direction perpendicular to the optical axis. Such a tilt or shift does not particularly affect the condensing characteristic of the first light beam having a wavelength of 405 nm for BD that is not affected by the diffraction structure formed in the diffraction region. It affects the condensing characteristics of the received second light flux with a wavelength of 660 nm for DVD and the third light flux with a wavelength of 785 nm for CD, and aberrations occur during light collection.

Therefore, the aberration correction element of Reference Example 1 has the following layout. First, as shown in FIG. 4, a diffraction grating 53 for DVD system correction that requires mounting accuracy is arranged on the objective lens side, and the center of the diffraction pattern is made substantially coincident with the optical axis of the objective lens. A diffraction surface 53 for correcting the DVD system, which requires mounting accuracy, is arranged on the objective lens side because the aberration when the light having power by diffraction passes through a flat plate inclined with respect to the optical axis is larger. . The coma aberration is generally proportional to the third power of the NA value of the objective lens, the substrate thickness of the optical recording medium, and the reciprocal of the wavelength of the light source (laser light).

  Here, in the aberration correction element 107, the first region 53a of the diffractive surface 53 is for DVD, for example, NA 0.65, substrate thickness 0.6 mm, wavelength 660 nm, and the first region of the diffractive surface 52. 52a is for CD, for example, NA 0.50, substrate thickness 1.2mm, wavelength 785nm. Therefore, coma aberration caused by the positional deviation of the first area 53a for DVD is larger than the positional deviation of the first area 52a for CD.

With respect to the CD coma aberration, the light passing through the first region 52a of the CD diffraction surface 52 passes through the inclined flat plate, and the diffraction surface 52 is shifted with respect to the optical axis. Will occur. Here, in this first reference example , the coma for CD is reduced by the coma due to the angle of view generated by using the two-wavelength laser unit and the coma accompanying the tilt of the aberration correction element 107. The tilt direction of the aberration correction element 107 and the arrangement of the two-wavelength laser unit are devised.

  As shown in FIG. 17, the optical axis of the aberration correction element 107 is incident on the objective lens 108 obliquely with respect to the light emitted from the CD semiconductor laser 116a of the two-wavelength laser unit 120 and incident on the objective lens 108 obliquely. By tilting in the direction opposite to the light, as shown in FIG. 18, it is possible to cancel the coma due to the tilt of the aberration correction element 107 and the coma due to the angle of view of the two-wavelength laser unit 120.

  For example, in an optical system using an objective lens and an aberration correction element, when the aberration correction element is tilted by 2 ° with respect to the optical axis of the objective lens, the amount of coma generated in the CD system is about 0.03 λrms. On the other hand, the amount of generated coma aberration is set to 0.degree. By making the incident light of the objective lens tilted by about 0.05.degree. In the direction opposite to the direction of tilting the aberration correction element with respect to the optical axis of the objective lens. It can be about 01λrms.

  The angle of incident light on the objective lens: θ is the distance between the DVD and CD semiconductor lasers of the two-wavelength laser unit (deviation from the optical axis of the CD semiconductor laser): ΔX and the focal point of the collimating lens. Distance: Determined by f (θ = asin (Δx / f)). Therefore, an optimal focal length of the collimating lens or an inclination angle of the aberration correction element may be selected as the optical system.

In the first reference example , the configuration of the optical pickup for focusing on three types of optical recording media of BD, DVD, and CD has been described. However, “BD and DVD”, “BD and CD”, “DVD and It may be an optical pickup that collects light on two types of optical recording media “CD”.

That is, in the case of “BD and DVD”,
In an optical pickup comprising a light source unit comprising a BD objective lens, a DVD aberration correction element, and two light sources for BD and DVD, the light source for BD is arranged on the optical axis of the objective lens, Coma aberration that occurs when the light source for DVD is obliquely incident on the objective lens when the light source for DVD is disposed at a position shifted from the optical axis of the objective lens, It may be configured to cancel coma generated by obliquely arranging the aberration correction element.

In the case of “BD and CD”,
In an optical pickup comprising a light source unit having a BD objective lens, a CD aberration correction element, and two light sources for BD and CD, the light source for BD is arranged on the optical axis of the objective lens and is used for CD. Coma aberration generated when the light source for CD is arranged obliquely with respect to the optical axis, and the light source for CD is disposed at a position deviated from the optical axis of the objective lens, It may be configured to cancel coma generated by obliquely arranging the aberration correction element.

In the case of “DVD and CD”,
In an optical pickup including a DVD objective lens, a CD aberration correction element, and a light source unit including two light sources for DVD and CD, the light source for DVD is arranged on the optical axis of the objective lens, The aberration correction element is tilted with respect to the optical axis, and the CD light source is arranged at a position deviated from the optical axis of the objective lens. It may be configured to cancel coma generated by arranging the elements obliquely.

In the first reference example , the configuration in which the aberration correction element is disposed obliquely has been described. However, the aberration correction element has a flange portion 107b as shown in FIG. 19, and only the surface on which the diffraction structure is formed is an objective lens. The structure may be inclined with respect to the optical axis 108.

FIG. 20 is a diagram showing a schematic configuration of an optical pickup in Reference Example 2 of the embodiment of the present invention. This is an interchangeable optical pickup that records or reproduces three types of optical recording media with different NAs using different light source wavelengths with a single objective lens 108. The difference between the reference example 2 and the optical pickup described in the reference example 1 is that a three-wavelength laser unit is used. Thereby, the number of optical components can be reduced, and the assembly process can be reduced and the cost can be reduced.

Hereinafter, the optical pickup of the present Reference Example 2 will be described. Here, the components corresponding to the constituent elements described in FIG. 1 showing the reference example 1 and having equivalent functions are denoted by the same reference numerals.

In the three types of BD, DVD, and CD optical recording media in Reference Example 2, the substrate thicknesses are 0.1 mm, 0.6 mm, and 1.2 mm, respectively, and NA is NA 0.85. , NA0.65, NA0.50, and used wavelengths are λ1 = 395 to 415 nm, λ2 = 650 to 670 nm, and λ3 = 770 to 805 nm, respectively.

  The optical pickup shown in FIG. 20 has a BD semiconductor laser 201 for the BD optical recording medium 109a, a DVD semiconductor laser 213a for the DVD optical recording medium 109b, and a CD for the CD optical recording medium 109c. A three-wavelength laser unit 220 that generates light from the semiconductor laser 216a, that is, laser beams having different wavelengths can be emitted.

  For the BD optical recording medium 109a, the optical pickup includes a BD semiconductor laser 201, a collimating lens 215, a deflecting prism 105, a quarter wavelength plate 106, an aberration correcting element 107, and an objective lens 108. The center wavelength of the BD semiconductor laser 201 as the first light source is 405 nm, and the NA of the objective lens 108 is 0.85. The substrate thickness of the BD optical recording medium 109a is 0.1 mm.

  Light emitted from the BD semiconductor laser 201 is made into substantially parallel light by the collimator lens 215. The light that has passed through the collimating lens 215 is deflected by the deflecting prism 105. Information is recorded / reproduced by being converted into circularly polarized light by the quarter-wave plate 106 and condensed on the BD optical recording medium 109a via the aberration correction element 107 and the objective lens 108.

  The reflected light from the BD optical recording medium 109a passes through the quarter-wave plate 106, is converted into linearly polarized light that is orthogonal to the polarization direction of the forward light, is diffracted by the hologram element 214, and is incident on the incident light. Are separated and guided onto the BD and DVD light receiving elements 213c to detect a reproduction signal, a focus error signal, and a track error signal. Here, it is desirable to use the hologram element 214 having polarization selectivity. That is, a polarization-selective hologram element that diffracts the return light in the polarization direction orthogonal to the forward path that is transmitted as it is toward the optical path toward the optical recording medium and reflected by the optical recording medium is preferable.

  Further, the light emitted from the DVD semiconductor laser 213 a having a center wavelength of 660 nm with respect to the DVD optical recording medium 109 b passes through the collimator lens 215 and is deflected by the deflecting prism 105. Then, the light is condensed on the DVD optical recording medium 109b via the quarter-wave plate 106, the aberration correction element 107, and the objective lens 108. The substrate thickness of the DVD optical recording medium 109b is 0.6 mm, and the NA is 0.65. The NA is switched by the aberration correction element 107. Reflected light from the DVD optical recording medium 109b passes through the objective lens 108 and the quarter-wave plate 106, and is diffracted by the hologram element 214, separated from incident light, and guided onto the BD and DVD light receiving elements 213c. Thus, a reproduction signal, a focus error signal, and a track error signal are detected.

  Note that the BD-based and DVD-based light receiving elements 213c are shared here with BD signal detection, but separate light receiving elements may be provided. For example, a wavelength selective beam splitter 104, a detection lens 110, and a light receiving element 112 may be provided between the optical paths of the collimating lens 215 and the deflecting prism 105 shown in FIG.

  Further, the light emitted from the CD semiconductor laser 216 a having a central wavelength of 785 nm with respect to the CD optical recording medium 109 c is deflected by the deflecting prism 105 through the collimator lens 215. Then, the light is condensed on the CD optical recording medium 109 c via the quarter-wave plate 106, the aberration correction element 107, and the objective lens 108. The substrate thickness of the CD optical recording medium 109c is 1.2 mm, and the NA of the objective lens 108 is 0.50. Switching of NA is limited by the aberration correction element 107.

  The reflected light from the CD optical recording medium 109c passes through the objective lens 108 and the quarter wavelength plate 106, and is then deflected by the deflecting prism 105, separated from the incident light by the hologram element 214, and onto the CD light receiving element 216c. As a result, a reproduction signal, a focus error signal, and a track error signal are detected.

The light receiving element may be arranged outside the three-wavelength laser unit, or the light receiving element may be shared by three wavelengths as in the first reference example .

FIG. 21 is a view for explaining the longitudinal cross-sectional structure of each semiconductor laser in the three-wavelength laser unit 220 used in Reference Example 2. As is clear from FIG. 21, a BD semiconductor laser 201 and a DVD semiconductor laser 213a are arranged in a two-layer structure on the left side, and a single CD semiconductor laser 216a is formed on the right side. Yes.

As shown in FIG. 21, the BD semiconductor laser 201 and the DVD semiconductor laser 213a are arranged close to each other. Further, as described above, the amount of coma generated increases as the NA increases and the wavelength decreases. Therefore, in the present Reference Example 2, the portion where the two semiconductor lasers on the left side of FIG. 21 are disposed is disposed on the optical axis, and the CD-based semiconductor laser 216a is disposed offset from the optical axis and is the same as in the first embodiment. In addition, it is only necessary to select an optical system layout that cancels coma generated by obliquely arranging the aberration correction element 107.

FIG. 22 is a diagram showing a schematic configuration of the optical pickup according to the first embodiment of the present invention. This is an interchangeable optical pickup that records or reproduces three types of optical recording media with different NAs using different light source wavelengths with a single objective lens 108. The first embodiment has the same configuration as that of the reference example 1 shown in FIG. 1 except for the arrangement in the aberration correction element 207 and the two-wavelength laser unit 121 (light source).

Hereinafter, the optical pickup of the first embodiment will be described. Unlike the reference example 1, the aberration correction element 207 in the optical pickup according to the first embodiment corrects spherical aberration generated on two different optical recording media on one surface. Accordingly, optical elements having different functions such as a wave plate and chromatic aberration correction can be integrally formed on the other surface, so that the number of optical components can be reduced, and the assembly process can be reduced and the cost can be reduced.

  FIG. 23 is a diagram for explaining the aberration correction element 207, FIG. 24 is an enlarged sectional view, and FIG. 25 is a diagram showing each diffraction surface. The aberration correction element 207 corrects the spherical aberration that the light emitted from the DVD-based semiconductor laser 013a of 660 nm is generated by the objective lens 108 due to the difference in the substrate thickness with respect to the DVD-based optical recording medium 109b. In addition to having an aperture limiting function for switching the NA, the light emitted from the 785 nm CD semiconductor laser 116a with respect to the CD optical recording medium 109c causes spherical aberration caused by the difference in substrate thickness at the objective lens 108. It has functions of correction and aperture limitation for switching the NA of the objective lens 108.

FIG. 24 is a cross-sectional view of the aberration correction element 207 of the first embodiment. The material of the aberration correction element 207 may be glass, resin, or a UV resin layer provided on a glass substrate and a diffractive structure formed on the resin layer, but it is lighter and easier to mold than glass. Resin is desirable from the viewpoint of easy mass production. Since the aberration correction element 207 of the first embodiment is mounted on the objective lens holder 108b and is movable for focusing and tracking, a lighter one is desirable. Examples of the resin include PMMA (refractive indexes at wavelengths of 405 nm, 660 nm, and 785 nm are 1.51, 1.49, and 1.48) and ZEONEX, which is an optical resin made by Nippon Zeon Co., Ltd. having good moisture absorption characteristics. Can be mentioned.

As shown in FIG. 25, the diffractive surface 54 has three first, second, and third regions 54a, 54b, and 54c that are concentrically divided within a range through which a light beam passes. The first area 54a corresponds to an area of NA 0.45 with respect to the CD optical recording medium 109c, and is set to a radius of 1.25 mm in the first embodiment. The first region 54a has a diffractive structure, and most of the first light flux with a wavelength of 405 nm is transmitted as zero-order light, and most of the second light flux with a wavelength of 660 nm is − Most of the third light flux having a wavelength of 785 nm becomes -second order diffracted light.

The second area 54b corresponds to an area of NA 0.65 with respect to the DVD optical recording medium 109b. In the first embodiment, the radius is set to 1.715 mm. The diffractive structure is also formed in the second region 54b, and most of the first light flux with a wavelength of 405 nm is transmitted as zero-order light, and most of the second light flux with a wavelength of 660 nm is 1. Most of the third light flux having a wavelength of 785 nm is transmitted as zero-order light.

The third area 54c corresponds to an area from NA 0.65 for the DVD optical recording medium 109b to NA 0.85 for the BD optical recording medium 109a. In the first embodiment, the radius is set from 1.715 mm to 2.2 mm. . The third region 54c has a flat structure where no diffractive structure is formed.

  The first region 54a of the diffractive surface 54 is formed with a diffractive structure having a concentric pattern at the center of the optical axis in the plane perpendicular to the optical axis, and generates −1st order diffracted light for a wavelength of 660 nm. . The concentric diffraction pattern is a spherical aberration that occurs when light is focused on a DVD optical recording medium 109b having a wavelength of 660 nm and a substrate thickness of 0.6 mm by the objective lens 108 that is optimally designed for the BD optical recording medium 109a. It is designed to cancel out, and as a result, a spot that converges to the diffraction limit is formed on the DVD optical recording medium 109b.

  At the same time, the first region 54a of the diffractive surface 54 is formed with a diffractive structure having a concentric pattern at the center of the optical axis in the plane perpendicular to the optical axis, and generates -2nd order diffracted light for a wavelength of 785 nm. The concentric diffraction pattern is a spherical aberration that occurs when light is focused on a CD optical recording medium 109c having a wavelength of 785 nm and a substrate thickness of 1.2 mm by the objective lens 108 that is optimally designed for the BD optical recording medium 109a. As a result, a spot that converges to the diffraction limit is formed on the CD-based optical recording medium 109c.

  The third region 54c, which is outside the diffractive structure (ring zone region) of the diffractive surface 54, is a flat portion where no diffractive structure is formed, and transmits the second and third light beams as they are. For example, the light transmitted through the first and second areas 54a and 54b is collected by the objective lens 108 with respect to the DVD optical recording medium 109b, and the light transmitted through the third area 54c is the DVD optical recording medium. The light is not condensed with respect to 109b, becomes scattered light as shown in FIG. 7B, does not act on the condensed light, and does not affect recording and reproduction. That is, NA 0.65 is restricted for the DVD optical recording medium 109b without any special structure or coating.

  Next, the height of each step of the diffraction surface 54 formed on the aberration correction element 207 will be described. FIGS. 26 (a), (b), (c) and FIGS. 27 (a), (b), (c) show the relationship between the stepped groove depth D and the efficiency. 26A, 26B, and 26C show a case where a four-step staircase structure is selected as the first region 54a of the diffractive surface 54, and the BD_0 order light, the DVD_1 order light, and the CD_2 order. It is the result for light. When PMMA is used as the material, a desired efficiency can be obtained for any wavelength when the groove depth D is 7.2 μm. The efficiency is 86%, 67%, and 39% for the 0th-order transmitted light of the first light flux, the −1st-order diffracted light of the second light flux, and the −2nd-order diffracted light of the third light flux, respectively. The groove depth D of 7.2 μm is 2.4 μm when converted to one stage.

  FIGS. 27A, 27B, and 27C show the results for the BD_0 order light, the DVD_ + 1 order light, and the CD_0 order light when a five-step staircase structure is selected as the second region 54b of the diffraction surface 54. FIG. is there. When PMMA is used as a material, a desired efficiency can be obtained for any wavelength when the groove depth D is 6.4 μm. The efficiency is 84%, 73%, and 78% for the 0th-order transmitted light of the first light flux, the + 1st-order diffracted light of the second light flux, and the 0th-order diffracted light of the third light flux, respectively. The groove depth D of 6.4 μm is 1.6 μm when converted to one stage.

  Further, the cross section of the first region 54a of the diffractive surface 54 of the aberration correction element 207 is composed of a plurality of annular concavo-convex portions formed concentrically as shown in FIG. Each ring-shaped uneven portion is stepped and has four steps. The pitch of the ring-shaped uneven portions is gradually narrowed from the inside to the outside so that the diffractive structure has a lens effect.

  The optical path difference coefficient of the first region 54a of the diffractive surface 54 is shown in (Table 3 (a)), and similarly, the optical path difference coefficient of the second region 54b of the diffractive surface 54 is shown in (Table 3 (b)).

次に、本実施形態１における２波長レーザユニット１２１について説明する。参考例１で説明したように、ＤＶＤ／ＣＤ用の２波長レーザユニット１２１を用いれば、光ピックアップの小型化、組付工数の低減が図れる。しかしながら、このような２波長レーザユニット１２１では、光源に数百ミクロン程度の間隔を有している。本実施形態１において、参考例１とは異なる、ＣＤ系半導体レーザ１１６ａ（光源）を対物レンズ１０８およびコリメートレンズ１１５の光軸上に配置した場合について説明する。２波長レーザユニット１２１のＤＶＤ系半導体レーザ１１３ａ（光源）からの光は図２８に示す（実線の光束）ように像高をもってしまい、結果、前述した図１５に示すようなコマ収差が発生してしまう。

Next, the two-wavelength laser unit 121 in the first embodiment will be described. As described in Reference Example 1, if the dual wavelength laser unit 121 for DVD / CD is used, the optical pickup can be downsized and the number of assembling steps can be reduced. However, in such a two-wavelength laser unit 121, the light source has an interval of about several hundred microns. In the first embodiment, a case where a CD semiconductor laser 116a (light source) different from the reference example 1 is arranged on the optical axes of the objective lens 108 and the collimator lens 115 will be described. The light from the DVD semiconductor laser 113a (light source) of the two-wavelength laser unit 121 has an image height as shown in FIG. 28 (solid light beam), and as a result, coma aberration as shown in FIG. 15 is generated. End up.

In addition, when a flat plate element such as the aberration correction element 207 of the first embodiment is used, consideration for flare light is necessary. A part of the light traveling from the light source toward the objective lens 108 becomes specularly reflected light without passing through the incident surface of the optical component. When the aberration correction element 107 is arranged perpendicular to the incident light, the specularly reflected light overlaps with the reflected light from the optical recording medium 109, that is, the signal light, as shown in FIG. , May become noise light. Therefore, as a countermeasure, there is a method of slightly tilting the incident surface to the optical component. As shown in FIG. 16B, by arranging the aberration correction element 207 in an inclined manner, it is not necessary to superimpose the specularly reflected light on the signal light.

  However, when the aberration correction element 207 is tilted, the diffraction region is tilted with respect to the optical axis and the center thereof is shifted in a direction perpendicular to the optical axis. Such a tilt or shift does not particularly affect the condensing characteristic of the first light beam having a wavelength of 405 nm for BD that is not affected by the diffraction structure formed in the diffraction region. It affects the condensing characteristics of the received second light flux with a wavelength of 660 nm for DVD and the third light flux with a wavelength of 785 nm for CD, and aberrations occur during light collection.

Therefore, the aberration correction element according to the first embodiment has the following layout. As shown in FIG. 28, in the two-wavelength laser unit 121, the light beam is emitted from the DVD-based semiconductor laser 113a and incident on the objective lens 108 at an angle. For example, when incident at an angle of 0.35 deg, coma aberration of 0.04 λ rms occurs on a DVD.

  The inclination and shift direction of the aberration correction element 207 and the arrangement of the two-wavelength laser unit 121 are devised so as to reduce the coma aberration due to this angle of view by the inclination and shift coma aberration of the aberration correction element 207.

FIG. 29 shows coma aberration accompanying the shift of the aberration correction element. The aberration correction element of the first embodiment generates a large amount of coma in the DVD system with respect to the shift, whereas the amount of coma in the CD system is small. For this reason, the DVD system of the two-wavelength laser unit is used to correct the coma generated when entering the objective lens obliquely.

The present invention is not limited to the configuration described above, with respect to the shift of the aberration correcting element, if coma aberration occurs greatly in the CD system, 17, 20 of Reference Examples 1 and 2, the same light source arrangement as in FIG. 21 .

  As shown in FIG. 28, the optical axis of the aberration correction element 207 is obliquely incident on the objective lens 108 with respect to the light emitted from the DVD semiconductor laser 113a of the two-wavelength laser unit 121 and obliquely incident on the objective lens 108. By tilting and shifting in the same direction as the light, as shown in FIG. 18, it is possible to cancel the coma due to the tilt and shift of the aberration correction element and the coma due to the angle of view of the two-wavelength laser unit 121. .

  For example, when the light emitted from the DVD-based semiconductor laser 113a is incident obliquely by 0.35 deg, in the optical system using the above-described objective lens and aberration correction element, the aberration correction element is 2 ° with respect to the optical axis of the objective lens. When tilted and shifted by 0.035 mm, the amount of coma generated in the DVD system can be reduced to about 0.01 λrms.

  The angle of incident light on the objective lens: θ is the distance between the DVD and CD semiconductor lasers of the two-wavelength laser unit (deviation from the optical axis of the CD semiconductor laser): ΔX and the focal point of the collimating lens. Distance: Determined by f (θ = asin (Δx / f)). Therefore, an optimal focal length of the collimating lens or an inclination angle of the aberration correction element may be selected as the optical system.

FIG. 30 is a diagram showing a schematic configuration of an optical pickup according to the second embodiment of the present invention. This is an interchangeable optical pickup that records or reproduces three types of optical recording media with different NAs using a single objective lens 108 using different light source wavelengths. The second embodiment is different from the optical pickup described in the first embodiment in that a three-wavelength laser unit is used.

Hereinafter, the optical pickup according to the second embodiment will be described. The optical pickup shown in FIG. 30 has a BD semiconductor laser 201 for the BD optical recording medium 109a, a DVD semiconductor laser 216a for the DVD optical recording medium 109b, and a CD for the CD optical recording medium 109c. The three-wavelength laser unit 221 generated from the semiconductor laser 213a is provided, that is, laser beams having different wavelengths can be emitted.

  For the BD optical recording medium 109a, the optical pickup comprises a BD semiconductor laser 201, a collimating lens 215, a deflection prism 105, a quarter wavelength plate 106, an aberration correction element 207, and an objective lens 108. The center wavelength of the BD semiconductor laser 201 as the first light source is 405 nm, and the NA of the objective lens 108 is 0.85. The substrate thickness of the BD optical recording medium 109a is 0.1 mm.

  The light emitted from the BD semiconductor laser 201 is made into substantially parallel light by the collimator lens 215. The light that has passed through the collimating lens 215 is deflected by the deflecting prism 105. Information is recorded / reproduced by being converted into circularly polarized light by the quarter-wave plate 106 and condensed on the BD optical recording medium 109a via the aberration correction element 107 and the objective lens 108.

  The reflected light from the BD optical recording medium 109a passes through the quarter-wave plate 106, is converted into linearly polarized light that is orthogonal to the polarization direction of the forward light, is diffracted by the hologram element 214, and is incident on the incident light. Are separated and guided onto the BD and DVD light receiving elements 213c to detect a reproduction signal, a focus error signal, and a track error signal. Here, it is desirable to use the hologram element 214 having polarization selectivity. That is, a polarization-selective hologram element that diffracts the return light in the polarization direction orthogonal to the forward path that is transmitted as it is toward the optical path toward the optical recording medium and reflected by the optical recording medium is preferable.

  Further, the light emitted from the DVD semiconductor laser 213 a having a center wavelength of 660 nm with respect to the DVD optical recording medium 109 b passes through the collimator lens 215 and is deflected by the deflecting prism 105. Then, the light is condensed on the DVD optical recording medium 109b via the quarter-wave plate 106, the aberration correction element 107, and the objective lens 108. The substrate thickness of the DVD optical recording medium 109b is 0.6 mm, and the NA is 0.65. The NA is switched by the aberration correction element 207.

  Reflected light from the DVD optical recording medium 109b passes through the objective lens 108 and the quarter-wave plate 106, and is diffracted by the hologram element 214, separated from the incident light, and guided onto the BD and DVD light receiving elements 213c. Thus, a reproduction signal, a focus error signal, and a track error signal are detected.

  Note that the BD-based and DVD-based light receiving elements 213c are shared here with BD signal detection, but separate light receiving elements may be provided. For example, a wavelength selective beam splitter 104, a detection lens 110, and a light receiving element 112 may be provided between the optical paths of the collimating lens 215 and the deflecting prism 105 shown in FIG.

  Further, the light emitted from the CD semiconductor laser 216 a having a central wavelength of 785 nm with respect to the CD optical recording medium 109 c is deflected by the deflecting prism 105 through the collimator lens 215. Then, the light is condensed on the CD optical recording medium 109 c via the quarter-wave plate 106, the aberration correction element 107, and the objective lens 108. The substrate thickness of the CD optical recording medium 109c is 1.2 mm, and the NA of the objective lens 108 is 0.50. Switching of NA is limited by the aberration correction element 107.

  The reflected light from the CD optical recording medium 109c passes through the objective lens 108 and the quarter wavelength plate 106, and is then deflected by the deflecting prism 105, separated from the incident light by the hologram element 214, and onto the CD light receiving element 216c. As a result, a reproduction signal, a focus error signal, and a track error signal are detected.

The light receiving element may be arranged outside the three-wavelength laser unit, or the light receiving element may be shared by three wavelengths as in the first reference example .

FIG. 31 is a view for explaining the longitudinal sectional structure in the three-wavelength laser unit 221 used in the second embodiment. As is clear from FIG. 31, a BD semiconductor laser 201 and a CD semiconductor laser 216a are arranged in a two-layer structure on the left side, and a single DVD semiconductor laser 213a is formed on the right side. Yes. In addition, the light source arrangement as described with reference to FIG.

In the three-wavelength laser unit, as shown in FIG. 31, the BD semiconductor laser 201 and the CD semiconductor laser 216a are arranged close to each other. As described above, the amount of coma generated increases as the NA increases and the wavelength decreases. Therefore, in the second embodiment, a portion where the two semiconductor lasers on the left side of FIG. 31 are arranged is arranged on the optical axis, and the DVD-based semiconductor laser is arranged so as to be shifted from the optical axis, and similarly to the first embodiment. The layout of the optical system may be selected so as to cancel out coma generated by tilting and shifting the aberration correction element 207 obliquely.

  The light source arrangement of the DVD system and the CD system is reversed depending on the shift and tilt characteristics of the aberration correction element, not limited to the above-described configuration.

FIG. 32 is an enlarged cross-sectional view showing an aberration correction element according to Embodiment 3 of the present invention. As shown in FIG. 32, an aberration correction element 208 used for a compatible optical pickup that records or reproduces four types of optical recording media (to be described later) with different NAs using different light source wavelengths with a single objective lens 108. It is. Also in the aberration correction element 208 of the third embodiment, the coma aberration can be corrected by the shift and the tilt as in the above-described embodiments and reference examples . An aberration correction element 208 is used instead of the aberration correction element 207 of the optical pickup shown in FIGS.

  In addition to the BD system, DVD system, and CD system described above, the four types of optical recording media use a light source in the blue wavelength region and use an objective lens with an NA of 0.65, corresponding to 20 GB. This is an HD system of the “HD-DVD” standard (hereinafter referred to as HD) that satisfies the capacity securing.

  The substrate thicknesses of the BD, HD, DVD, and CD optical recording media 109a, 109d, 109b, and 109c are 0.1 mm, 0.6 mm, 0.6 mm, and 1.2 mm, respectively, and NA is NA0. .85, NA0.65, NA0.65, NA0.50, and used wavelengths are λ1 = 395 to 415 nm, λ1 = 395 to 415 nm, λ2 = 650 to 670 nm, and λ3 = 770 to 805 nm, respectively.

The aberration correction element 208 includes a diffractive surface 54 and a diffractive surface 55. The diffractive structure of the diffractive surface 54 is the same as that of the first and second embodiments. The diffractive surface 55 realizes a bifocal lens, and forms a good condensing spot on the BD optical recording medium 109a and the HD optical recording medium 109d. It is configured to transmit efficiently as the next diffracted light. Similar aberration correcting device of this embodiment 3 also the first embodiment, may be selected optical system layout for canceling the coma aberration generated by tilting and shifting obliquely arranged.

FIG. 33 is a diagram showing a schematic configuration of an optical information processing apparatus according to Embodiment 4 of the present invention. The fourth embodiment is one form of an optical information processing apparatus, and at least one of reproduction, recording, and erasing of information with respect to an optical recording medium using the optical pickup of any of the first to third embodiments described above. It is a device that performs.

  An optical pickup 91 corresponding to the optical pickup described above is provided. A spindle motor 98 that rotationally drives the optical recording medium 109, an optical pickup 91 that is used to record and reproduce information signals, and a feed motor 92 that moves the optical pickup 91 to the inner and outer circumferences of the optical recording medium 109. A modulation / demodulation circuit 94 that performs predetermined modulation and demodulation processing, a servo control circuit 93 that performs servo control of the optical pickup 91, and a system controller 96 that controls the entire optical information processing apparatus.

  The spindle motor 98 is driven and controlled by a servo control circuit 93 and is driven to rotate at a predetermined rotational speed. That is, the optical recording medium 109 to be recorded and reproduced is chucked on the drive shaft of the spindle motor 98 and is driven and controlled by the servo control circuit 93. The spindle motor 98 is rotationally driven at a predetermined rotational speed.

  When recording and reproducing information signals to and from the optical recording medium 109, the optical pickup 91 irradiates the optical recording medium 109 that is rotationally driven with laser light and detects the return light. The optical pickup 109 is connected to the modulation / demodulation circuit 94. When recording the information signal, a signal input from the external circuit 95 and subjected to a predetermined modulation process by the modulation / demodulation circuit 94 is supplied to the optical pickup 109. Based on the signal supplied from the modulation / demodulation circuit 94, the optical pickup 109 irradiates the optical recording medium 109 with laser light that has undergone light intensity modulation. Further, when reproducing the information signal, the optical pickup 91 irradiates the rotationally driven optical recording medium 109 with a laser beam having a constant output, and a reproduction signal is generated from the return light. The reproduction signal is supplied to the modem circuit 94.

  The optical pickup 91 is also connected to the servo control circuit 93. Then, as described above, the focus servo signal and the tracking servo signal are generated from the return light reflected and returned by the rotationally driven optical recording medium 109 at the time of recording / reproducing the information signal. It is supplied to the control circuit 93.

  The modem circuit 94 is connected to the system controller 96 and the external circuit 95. When the information signal is recorded on the optical recording medium 109, the modulation / demodulation circuit 94 receives a signal to be recorded on the optical recording medium 109 from the external circuit 95 under the control of the system controller 96. Apply modulation processing.

  The signal modulated by the modem circuit 94 is supplied to the optical pickup 91. Further, when reproducing the information signal from the optical recording medium 109, the modem circuit 94 receives the reproduction signal reproduced from the optical recording medium 109 from the optical pickup 91 under the control of the system controller 96, Predetermined demodulation processing. The signal demodulated by the modem circuit 94 is output from the modem circuit 94 to the external circuit 95.

  The feed motor 92 is for moving the optical pickup 91 to a predetermined position in the radial direction of the optical recording medium 109 when recording and reproducing information signals, and based on a control signal from the servo control circuit 93. Driven. That is, the feed motor 92 is connected to the servo control circuit 93 and is controlled by the servo control circuit 93.

  The servo control circuit 93 controls the feed motor 92 so that the optical pickup 91 is moved to a predetermined position facing the optical recording medium 109 under the control of the system controller 96. The servo control circuit 93 is also connected to the spindle motor 98 and controls the operation of the spindle motor 98 under the control of the system controller 96. That is, the servo control circuit 93 controls the spindle motor 98 so that the optical recording medium 109 is rotationally driven at a predetermined rotational speed when information signals are recorded on and reproduced from the optical recording medium 109.

  Further, as a method for determining the type of the optical recording medium 109, a tracking servo signal or a focus servo signal may be used. By providing the optical information processing apparatus for recording and reproducing on a plurality of types of optical recording media with the optical pickup of the present invention, the accuracy of the quality of recording and reproducing information on the optical recording media 109 having different substrate thicknesses is improved. Can do.

As described above, according to the optical information processing apparatus of the fourth embodiment, a plurality of types of optical recording media (for example, BD system, HD system, DVD system, CD system) having different substrate thicknesses by a single objective lens. ) Can be formed on the surface of the optical recording medium, and an optimum process for recording, reproducing or erasing information signals can be performed on the optical recording medium.

  An optical pickup and an optical information processing apparatus according to the present invention are capable of suppressing a plurality of types of aberrations generated by an aberration correction element having a diffractive structure even when the aberration correction element is tilted to avoid flare light. Optimal recording and reproduction processing with an optical pickup that can obtain good recording / reproducing signals for each optical recording medium and that can be focused on multiple types of optical recording media with a single objective lens It is useful as an apparatus that can operate and is compatible with different optical recording media.

The figure which shows schematic structure of the optical pick-up in the reference example 1 of embodiment of this invention. The figure which shows the specific structural example of an objective lens Sectional view enlarging the vicinity of the aberration correction element An enlarged cross-sectional view of the aberration correction element The figure which shows the diffraction surface for DVD system correction | amendment of an aberration correction element The figure which shows the diffraction surface for CD system correction | amendment of an aberration correction element (A) which shows the light beam of a DVD type optical recording medium, (a) is sectional drawing, (b) is a top view Diagram explaining the height (groove depth) of the diffraction surface (A) is the diffraction surface for DVD, (b) is the figure which shows the relationship between the step-like groove depth and efficiency of the diffraction surface for CD. Diagram showing the outer shape of the aberration correction element (A)-(d) is a figure which shows the wavefront shape of the transmitted light with a wavelength of 405 nm in which the aberration correction element is rectangular. (A)-(d) is a figure which shows the wavefront shape of the transmitted light with a wavelength of 405 nm when the aberration correction element is circular. The figure which shows schematic structure of the actuator part of an optical pick-up A diagram for explaining an optical path obliquely incident on the objective lens The figure which shows the coma aberration accompanying the oblique incident light of CD system (A) of flare light is incident on the light receiving element, and (b) is a diagram illustrating a state where the light receiving element is avoided. The figure which shows arrangement | positioning of an aberration correction element and a 2 wavelength laser unit The figure which shows the coma aberration accompanying arrangement | positioning of the diagonally incident light and aberration correction element of CD type | system | group The figure which shows the structural example of an aberration correction element The figure which shows schematic structure of the optical pick-up in the reference example 2 of embodiment of this invention. The figure which shows the longitudinal cross-section of each semiconductor laser in a 3 wavelength laser unit The figure which shows schematic structure of the optical pick-up in Embodiment 1 of this invention. Sectional view enlarging the vicinity of the aberration correction element An enlarged cross-sectional view of the aberration correction element The figure which shows the diffraction surface for DVD system and CD system correction of an aberration correction element (A) is a 1st light beam, (b) is a 2nd light beam, (c) is a figure which shows the relationship between the depth of 4 steps | paragraphs of step shapes with respect to a 3rd light beam, and efficiency. (A) is a 1st light beam, (b) is a 2nd light beam, (c) is a figure which shows the relationship between the depth and efficiency of five steps of step shapes with respect to a 3rd light beam. The figure which shows arrangement | positioning of an aberration correction element and a 2 wavelength laser unit The figure which shows the coma aberration accompanying the shift of the aberration correction element The figure which shows schematic structure of the optical pick-up in Embodiment 2 of this invention. The figure which shows the longitudinal cross-section of each semiconductor laser in a 3 wavelength laser unit Sectional drawing which expanded the vicinity of the aberration correction element in Embodiment 3 of this invention The figure which shows schematic structure of the optical information processing apparatus in Embodiment 4 of this invention.

Explanation of symbols

22 Pitch 25 Base portions 26, 27 Elastic support mechanisms 52, 53, 54, 55 Diffraction surfaces 52a, 53a, 54a First region 52b, 53b, 54b Second region 53d Near 53e Distant 53f, 53g Transmission wavefront shape 54c Third area 91 Optical pickup 92 Feed motor 93 Servo control circuit 94 Modulation / demodulation circuit 95 External circuit 96 System controller 98 Spindle motor 101 Semiconductor laser 102, 115, 215 Collimator lens 103 Polarization beam splitter 104 Wavelength selective beam splitter 105 Deflection prism 106 quarter-wave plate 107, 207, 208 aberration correction element 108 objective lens 108b objective lens holder 109 optical recording medium 109a BD optical recording medium 109b DVD optical recording medium 109c CD optical recording medium 1 0 detection lens 112 light receiving element 113a, 213a DVD semiconductor laser 113c, 213c DVD light receiving element 114, 214 hologram element 116a, 216a CD semiconductor laser 116c, 216c CD light receiving element 120, 121 two-wavelength laser unit 201 BD semiconductor Laser 220, 221 3-wavelength laser unit

Claims (5)

Three types of optical recording, a first optical recording medium having a substrate thickness of 0.1 mm, a second optical recording medium having a substrate thickness of 0.6 mm, and a third optical recording medium having a substrate thickness of 1.2 mm, having different recording densities. In an optical pickup that performs one or more of recording, reproduction, and erasing on a medium.
A first light source that emits a first light beam having a first wavelength λ1 = 405 nm corresponding to the first optical recording medium, and a second wavelength λ2 = 660 nm corresponding to the second optical recording medium. A second light source that emits a second light beam having a third wavelength λ corresponding to the third optical recording medium
A third light source that emits a third light beam having 3 = 785 nm, an objective lens having an NA of 0.85 that is optimally designed for the first optical recording medium, and the second light source that is emitted from the second light source. Spherical aberration that occurs when a light beam is condensed on the second optical recording medium via the objective lens;
An aberration correction element for correcting spherical aberration generated when the third light beam emitted from the third light source is condensed on the third optical recording medium through the objective lens on one surface; Provided between the objective lens and the first to third light sources, the first, second, and third concentric circles on the optical axis center in the optical axis vertical plane on one surface of the aberration correction element A diffractive structure having a region is provided;
The first region corresponding to NA 0.45 of the diffractive structure is about the first light flux.
Most of the second light flux is transmitted as −1st order diffracted light, and most of the third light flux is transmitted as −2nd order diffracted light. The number of steps and the groove depth per step are selected, and the second region of NA0.45 to NA0.65 of the diffraction structure transmits most of the first light flux as 0th order light, For the second light flux, the majority of the second luminous flux is the first-order diffracted light, and for the third light flux, the number of steps of the diffractive structure and the groove depth per stage are such that most of the second light flux is transmitted by the zero-order light. Selected
The direction of the staircase of the diffraction structure in the first region is formed outward with respect to the optical axis of the objective lens, and the direction of the staircase of the diffraction structure in the second region is directed to the optical axis. The third region of NA 0.65 to NA 0.85 of the diffraction structure is a flat structure in which no diffraction structure is formed, and the second and third light sources are formed inward. In a direction in which the second light source is disposed on the optical axis of the objective lens and the coma aberration generated due to the optical axis deviation between the third light source and the objective lens is cancelled. An optical pickup characterized in that the aberration correction element is disposed so as to be inclined with respect to the optical axis and shifted in a direction perpendicular to the optical axis. In the light source unit in which the second and third light sources are integrally configured, the third light source is disposed on the optical axis of the objective lens, and an optical axis shift between the second light source and the objective lens is achieved. 2. The optical pickup according to claim 1, wherein the aberration correction element is disposed so as to be tilted with respect to the optical axis and shifted in a direction perpendicular to the optical axis in a direction to cancel the coma generated. Three types of optical recording, a first optical recording medium having a substrate thickness of 0.1 mm, a second optical recording medium having a substrate thickness of 0.6 mm, and a third optical recording medium having a substrate thickness of 1.2 mm, having different recording densities. In an optical pickup that performs one or more of recording, reproduction, and erasing on a medium.
A first light source that emits a first light beam having a first wavelength λ1 = 405 nm corresponding to the first optical recording medium, and a second wavelength λ2 = 660 nm corresponding to the second optical recording medium. A second light source that emits a second light beam having a third wavelength λ corresponding to the third optical recording medium
A third light source that emits a third light beam having 3 = 785 nm, an objective lens having an NA of 0.85 that is optimally designed for the first optical recording medium, and the second light source that is emitted from the second light source. Spherical aberration that occurs when a light beam is condensed on the second optical recording medium via the objective lens;
An aberration correction element for correcting spherical aberration generated when the third light beam emitted from the third light source is condensed on the third optical recording medium through the objective lens on one surface; Provided between the objective lens and the first to third light sources, the first, second, and third concentric circles on the optical axis center in the optical axis vertical plane on one surface of the aberration correction element A diffractive structure having a region is provided;
The first region corresponding to NA 0.45 of the diffractive structure is about the first light flux.
Most of the second light flux is transmitted as −1st order diffracted light, and most of the third light flux is transmitted as −2nd order diffracted light. The number of steps and the groove depth per step are selected, and the second region of NA0.45 to NA0.65 of the diffraction structure transmits most of the first light flux as 0th order light, For the second light flux, the majority of the second luminous flux is the first-order diffracted light, and for the third light flux, the number of steps of the diffractive structure and the groove depth per stage are such that most of the second light flux is transmitted by the zero-order light. Selected, the direction of the step of the diffraction structure of the first region is formed outward with respect to the optical axis of the objective lens;
The direction of the staircase of the diffraction structure of the second region is formed inward with respect to the optical axis of the objective lens, and the third region of NA0.65 to NA0.85 of the diffraction structure. Is a flat structure in which no diffraction structure is formed, the first, second, and third light sources are integrated, and the first and third light sources are close to each other. A third light source is arranged so as to be on the optical axis of the objective lens, and the aberration correction element is arranged in the direction to cancel coma aberration caused by an optical axis shift between the second light source and the objective lens. An optical pickup characterized in that the optical pickup is disposed so as to be inclined with respect to an axis and shifted in a direction perpendicular to the optical axis. On the optical axis of the objective lens, the first and third light sources of the light source unit in which the first, second, and third light sources are integrally configured and the first, second, and second light sources are arranged close to each other. The aberration correction element is tilted with respect to the optical axis in a direction that cancels coma aberration caused by an optical axis shift between the second light source and the objective lens, and is perpendicular to the optical axis. The optical pickup according to claim 3, wherein the optical pickup is shifted in the direction. An optical information processing apparatus that performs one or more of recording, reproduction, and erasing on a plurality of types of optical recording media having different recording densities,
An optical information processing apparatus comprising the optical pickup according to claim 1.

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